WO2019104365A1

WO2019104365A1 - Current collector

Info

Publication number: WO2019104365A1
Application number: PCT/AU2017/051322
Authority: WO
Inventors: Manuel WIESER
Original assignee: Nano-Nouvelle Pty Ltd
Priority date: 2017-11-30
Filing date: 2017-11-30
Publication date: 2019-06-06

Abstract

A current collector for an electrochemical cell or a battery, the current collector comprising a porous polymeric substrate coated with a conductive material, characterised in that the current collector has anisotropic properties.

Description

TITLE

Current Collector TECHNICAL FIELD

[0001] The present invention relates to a current collector for use in electrochemical cells of batteries.

BACKGROUND ART

[0002] Batteries, such as lithium ion batteries, typically comprise a number of

electrochemical cells, each of which comprises an anode, a separator and a cathode. Reactions take place during discharge of the battery at the anode and cathode that cause positive ions to be generated at the anode, with those ions travelling through an electrolyte, through the separator and through an electrolyte on the cathode side to the cathode. The positive ions are reduced at the cathode. This results in generation of an electric current, which can be collected through an external circuit. Charging of the batteries involves applying an external voltage to cause the reactions that occur during discharge to be reversed.

[0003] In order to extract or recover the electrons generated during the chemical reactions that take place during discharge of the battery, the anode active material and the cathode active material are normally placed into contact with current collectors. A current collector is a highly conductive material which serves the purpose of collecting electrons in electrode type applications, such as lithium ion batteries, capacitors, fuel cells and the like.

[0004] In lithium ion battery electrodes, the anodes (negative electrodes) and cathodes (positive electrodes) typically include respective active material substances that are responsible for storing charge carriers, with the active material substances being applied to flat metal foils. The flat metal foils normally serve as the current collector. The material chosen for the current collector on the anode is commonly copper, whereas aluminium is commonly used as the cathode collector material on the cathode.

[0005] The current industry standard for current collectors for anodes is a copper foil having a thickness of 9 to 10μm. However, the required thickness is dependent upon the type of application. In particular, high-energy applications tend to use anode current collectors in the form of copper foil having thicknesses between 9 and 1 m m whilst high power applications tend to use copper foils as current collectors with a thickness between 10 to 25μm. [0006] To further improve the energy density of commercial lithium ion batteries, the size and volume of the battery components has to be reduced. For current collector foils, this translates into a reduction in thickness, which strongly impacts the weight of the battery cell and also has a minor impact on its volume.

[0007] Although these copper foils are effective at collecting current generated in the battery, the thickness of the copper foil is relatively large. This results in the battery having increased weight and increased volume. Attempts have been made to reduce the thickness of the copper for current collectors to 8 μm or less, with many manufacturers being of the view that copper foil current collectors having a thickness of 6 μm or less would be desirable. However, such thin copper foils are difficult to manufacture and handle and frequently suffer from tearing or breakage during the electrode production process or during the assembly of the battery cell. Commercial application of such thin copper foils as current collectors in batteries has proven to be problematic.

[0008] Metal foams with a thickness in the millimetre range are commonly used as current collectors in nickel battery systems. In practice, it is difficult to create metal foams that have a very thin thickness whilst maintaining a high percentage of porosity. Further, metal foams typically have pore structures that may best be described as interconnected pores that are randomly distributed in space with no particular directionality or anisotropy.

[0009] The current industry standard for cathode current collectors in lithium ion batteries is to use an aluminium foil having a thickness of from 10 to 25μm, with the lower thickness being applied to energy type applications and the larger thickness being applied in power type applications.

[0010] Another challenging factor associated with the use of metal foil current collectors resides in delamination of active material particles/films from the flat current collector surfaces during the course of long term cycling or the cycling at high current rates.

[0011] An alternative approach to providing a current collector for an electrode for a lithium ion battery is described in US patent publication number 2008/0318125 in the name of

Sakamoto. This patent application is now abandoned. Sakamoto described a positive electrode for an alkaline storage battery. The electrode comprises a polymeric material that is formed as a foamed resin, a non- woven fabric or a woven fabric, that has a three dimensional network stmcture and has a void portion in which a plurality of pores are coupled in three dimensions. The resin skeleton is coated with a nickel coating layer. The thickness of the nickel coating layer ranges from 0.5 to 5μm. The average pore diameter of the pores forming the void portion of the positive electrode substrate falls in the range of from not less than 15μm to not more than 450μm. By adjusting the average pore diameter to within this range, the current collectivity is improved.

[0012] The nickel coated porous resin material of Sakamoto is filled with a positive electrode active material containing nickel hydroxide particles wherein the filling amount of the positive electrode active material is not less than 3 times and not more than 10 times of weight of the positive electrode substrate. Further, a proportion of the nickel coating layer to the positive electrode substrate is not less than 30wt% and not more than 80wt%.

[0013] The present applicant has also described conductive porous materials that can be used in batteries in its international patent application publication number PCT/AU2010/001511, the entire contents of which I herein incorporated by cross-reference. The contents of the applicant’s earlier international patent application numbers PCT/AU2012/000266 and

PCT/AU2013/000088 are also incorporated herein by cross-reference.

[0014] It will be clearly understood that, if a prior art publication is referred to herein, this reference does not constitute an admission that the publication forms part of the common general knowledge in the art in Australia or in any other country.

SUMMARY OF INVENTION

[0015] The present invention is directed to a current collector, which may at least partially overcome at least one of the abovementioned disadvantages or provide the consumer with a useful or commercial choice.

[0016] With the foregoing in view, the present invention in one form, resides broadly in a current collector for an electrochemical cell or a battery, the current collector comprising a porous polymeric substrate coated with a conductive material, characterised in that the current collector has anisotropic properties.

[0017] By“the current collector having anisotropic properties”, it is meant that one or more properties of the current collector when measured along one direction differ from the one or more properties measured in a different direction.

[0018] In one embodiment, the current collector has one or more properties measured in a longitudinal direction or a machine direction (MD) that is different to the one or more properties measured in a transverse direction (TD) or a cross-machine direction.

[0019] In one embodiment, the anisotropic property of the current collector is mechanical strength. In another embodiment, the anisotropic property of the current collector is electrical conductivity.

[0020] In one embodiment, the current collector has a mechanical strength in one direction that is at least 10% higher than a mechanical strength when measured in a transverse direction to the one direction.

[0021] In other embodiments, the current collector has a mechanical strength in one direction that is at least 20% higher than a mechanical strength when measured in a transverse direction, or has a mechanical strength in one direction that is at least 30% higher than a mechanical strength when measured in a transverse direction, or has a mechanical strength in one direction that is at least 40% higher than a mechanical strength when measured in a transverse direction, or has a mechanical strength in one direction that is at least 50% higher than a mechanical strength when measured in a transverse direction, or has a mechanical strength in one direction that is at least 60% higher than a mechanical strength when measured in a transverse direction, or has a mechanical strength in one direction that is at least 70% higher than a mechanical strength when measured in a transverse direction, or has a mechanical strength in one direction that is at least 80% higher than a mechanical strength when measured in a transverse direction, or has a mechanical strength in one direction that is at least 90% higher than a mechanical strength when measured in a transverse direction, or has a mechanical strength in one direction that is at least 2 times higher than a mechanical strength when measured in a transverse direction, or has a mechanical strength in one direction that is at least 3 times higher than a mechanical strength when measured in a transverse direction, or has a mechanical strength in one direction that is at least 4 times higher than a mechanical strength when measured in a transverse direction, or has a mechanical strength in one direction that is at least 5 times higher than a mechanical strength when measured in a transverse direction, or has a mechanical strength in one direction that is at least 10 times higher than a mechanical strength when measured in a transverse direction, or has a mechanical strength in one direction that is at least 20 times higher than a mechanical strength when measured in a transverse direction, or has a mechanical strength in one direction that is from 10% higher to 20 times higher than a mechanical strength when measured in a transverse direction.

[0022] In one embodiment, the current collector has an electrical conductivity in one direction that is at least 10% higher than an electrical conductivity when measured in a transverse direction to the one direction.

[0023] In other embodiments, the current collector has an electrical conductivity in one direction that is at least 20% higher than an electrical conductivity when measured in a transverse direction, or has an electrical conductivity in one direction that is at least 30% higher than an electrical conductivity when measured in a transverse direction, or has an electrical conductivity in one direction that is at least 40% higher than an electrical conductivity when measured in a transverse direction, or has an electrical conductivity in one direction that is at least 50% higher than an electrical conductivity when measured in a transverse direction, or has an electrical conductivity in one direction that is at least 60% higher than an electrical conductivity when measured in a transverse direction, or has an electrical conductivity in one direction that is at least 70% higher than an electrical conductivity when measured in a transverse direction, or has an electrical conductivity in one direction that is at least 80% higher than an electrical conductivity when measured in a transverse direction, or has an electrical conductivity in one direction that is at least 90% higher than an electrical conductivity when measured in a transverse direction, or has an electrical conductivity in one direction that is at least 2 times higher than an electrical conductivity when measured in a transverse direction, or has an electrical conductivity in one direction that is at least 3 times higher than an electrical conductivity when measured in a transverse direction, or has an electrical conductivity in one direction that is at least 4 times higher than an electrical conductivity when measured in a transverse direction, or has an electrical conductivity in one direction that is at least 5 times higher than an electrical conductivity when measured in a transverse direction, or has an electrical conductivity in one direction that is at least 10 times higher than an electrical conductivity when measured in a transverse direction, or has an electrical conductivity in one direction that is at least 20 times higher than an electrical conductivity when measured in a transverse direction, or has an electrical conductivity in one direction that is at from 10% higher to 20 times higher than an electrical conductivity when measured in a transverse direction.

[0024] In one embodiment, the current collector has a mechanical strength in the machine direction that is from 18% to 307% higher than compared to the mechanical strength in the transverse direction. In one embodiment, the current collector has a mechanical strength in the machine direction that is from 1.2 to 4.1 times higher than the mechanical strength in the transverse direction.

[0025] In one embodiment, the current collector has an electrical conductivity that is from 25% to 346% higher in the machine direction when compared to the transverse direction. In one embodiment, the current collector has an electrical conductivity that is from 1.2 to 4.5 times higher than the electrical conductivity in the transverse direction.

[0026] In one embodiment, the current collector exhibits higher mechanical strength in a machine direction when compared to mechanical strength in a transverse machine direction.

[0027] In one embodiment, the current collector exhibits higher mechanical strength in a transvers machine direction when compared to mechanical strength in a machine direction.

[0028] In one embodiment, the current collector exhibits higher electrical conductivity in a machine direction when compared to electrical conductivity in a transverse machine direction.

[0029] In one embodiment, the current collector exhibits higher electrical conductivity in a transverse machine direction when compared to electrical conductivity in a machine direction.

[0030] In one embodiment, the porous polymeric substrate comprises an electrically non- conductive polymeric substrate.

[0031] The porous polymeric substrate may be selected from materials including cellulose and its derivatives including cellulose acetate, cellulose nitrate, mixed cellulose esters, polyolefins including polyethylene, polypropylene, polybutene, polyisobutylene, ethylene propylene rubber and variations thereof, polyethylene terephthalate (PET), polyacrylonitrile (PAN), polyvinylchloride (PVC), polyether sulfone (PES), polyamides including Nylon and variations thereof, polyimides and variations thereof, polyurethanes and variations thereof, polytetrafluoroethylene (PTFE), polyvinylidene fluoride PVDF, polycarbonate, and or a mixture of those. In other embodiments, the porous substrate may comprise a porous carbon substrate or a graphene substrate or a carbon nanofiber substrate or a carbon nanotube substrate.

[0032] The substrate may comprise fibres of single polymer or several different polymer fibres mixed together. The substrate may constitute a woven or non-woven substrate. The substrate may comprise a continuous structure containing a single polymer or the substrate may comprise a layered or laminated structure where individual layers may be comprised of different polymers.

[0033] The substrate may be produced by means of a wet-laying, melt-blowing, wet stretching electro spinning, knitting, variations of these methods or any other method deemed suitable to create a substrate with the desired structure-property relationships. The porous polymeric substrate or the electrically conductive porous material may have an overall thickness that ranges from 1 m m to 5000mm or higher. A more preferred thickness of the porous polymeric substrate would be from lμm to 5000μm, or from lμm to lOOOμm, or from lμm to 500μm, or from lμm to 400μm, or from lμm to 250 μm, or from 1 μm to 150 μm, or from lμm to 100μm, or from lμm to 50μm or from lμm to 20μm.

[0034] In one embodiment, the porous polymeric substrate comprises a porous polyethylene terephthalate (PET) substrate. PET is suitable for use in this application due to its good temperature stability and no known toxicity.

[0035] In one embodiment, the PET substrate is made from PET fibres having a circular cross-section with small diameter. This substrate can be used for the creation of the current collectors. In other embodiments, the substrate is made from PET fibres having a large diameter, which can be used to create thicker current collectors. It will also be appreciated that current collectors made from substrates having smaller diameter fibres will tend to have smaller pores than current collectors made from substrates having larger diameter fibres.

[0036] In one embodiment, the porous polymeric substrate comprises a plurality of fibres, with a greater proportion of the fibres extending in the one direction and a lesser proportion of the fibres extending in the other direction.

[0037] In one embodiment, the porous polymeric material is coated with an electrically conductive material. In one embodiment, the electrically conductive material comprises a metal. The metal may be selected from copper, nickel, aluminium, iron, titanium, gold, platinum or mixtures or alloys of two or more thereof. Other metals may also be used.

[0038] The electrically conductive porous material may have pore sizes that range from 0.1μm to 3000μm. The electrically conductive porous material may have a porosity of 30% to 95% (by volume).

[0039] The electrically conductive porous material may have a specific surface area that ranges from 0.005m²/cm³ to 100m²/cm³, 0.005m²/cm³ to 50m²/cm³, or from 0.005m²/cm³ to 20m²/cm³, or from 0.005m²/cm³ to 10m²/cm³, or from 0.005m²/cm³ to 2m²/cm³, or from 0.005m²/cm³ to 0.2m²/cm³.

[0040] In some embodiments, at least part of the porosity in the substrate is interconnected and open to the surface.

[0041] It will be appreciated that the pore sizes, porosity and surface area of the unit conductive porous material may be varied or selected to accord with the specific requirements of the application of use.

[0042] One way of describing conductivity in porous solids is to use an‘equivalent solid’ conductivity. For example, if the material has a volume fraction of solid of only 20%, and the measured conductivity is x, the‘equivalent solid’ conductivity would be 5 times x. Similarly, if the material has a volume fraction of solid of 50%, and the measured conductivity is y, the ‘equivalent solid’ conductivity would be 2 times y. This way of comparison is useful for comparing the quality of solids in stmctures with different volume fraction of solids.

[0043] The electrically conductive porous material may have an electrical equivalent solid conductivity in the range of from 0.01 S/cm to 500,000S/cm. A more preferred electrical equivalent solid conductivity would be in the range of 10,000S/cm and 500,000S/cm, or 30,000S/cm and 500,000S/cm, or 500,000S/cm and 500,000S/cm, or l00,000S/cm and

500,000S/cm, or 200,000S/cm and 500,000S/cm, or 300,000S/cm and 500,000S/cm or

30,000S/cm and 350,000S/cm. One possible range of electrical equivalent solid conductivity is from 30,000 to 350,000S/cm.

[0044] In one embodiment, the electrically conductive porous material comprises a porous polymeric material having a thin coating of a metal applied thereto. The metal may be applied to the porous polymeric materials such that the metal coating has a thickness that is less than 8000nm, or less than 5000nm, or less than 3000nm, or less than 2000nm or less than lOOOnm, or less 500nm, or less than 300nm, or less than 200nm, or less than lOOnm, or less than 50nm, or less than 30nm. The metal coating may have a thickness that is at least lnm thick, or at least 2nm thick, or at least 5nm thick, or at least lOnm thick or at least 20nm thick.

[0045] In embodiments, where the current collector is a thin current collector, the current collector may have total weight values that fall in the range of from 2.5mg/cm to 8.0mg/cm , or from 3.0mg/cm to 8.0mg/cm , or from 3.5mg/cm to 8.0mg/cm , or from 4.0mg/cm to 8.0mg/cm², or from 4.5mg/cm² to 8.0mg/cm², or from 5.0mg/cm² to 8.0mg/cm², or from 5.5mg/cm² to 8.0mg/cm², or from 7.0mg/cm²to 8.0mg/cm², or from 3.0mg/cm² to

5.5mg/cm .These weight values have been demonstrated and are commercially useful. These weight values would correspond to a reduction in weight of 75%, 70%, 65%, 60%, 55%, 50%, 45%, 30% and 16% respectively, relative to a lOμm solid copper foil

[0046] Advantageously, the pores/openings created by the fibres and their spatial orientation establishes a certain directionality of pores/openings, extending into the current collector’s structure in a largely downwardly facing pattern (in other words, generally perpendicular to the surface of the current collector). This results in the current collector having an open surface with the pores extending generally downwardly from the surface. This allows the openings to be easily filled with active material particles. However, there are also sufficient fibres in the substrate to effectively prevent particles of active material from easily passing through the current collector. It is postulated that certain percentage of fibres being aligned in the transverse direction effectively aids in keeping the current collector structure open enough so that it can be filled with active material while at the same time preventing particles from falling through the stmcture due to fibres in the transverse direction acting as a barrier. In this manner, the particles of active material can be retained on and in the current collector. It has been demonstrated by the present inventors that the particles of active material can nestle into the pores but not fall straight through the pores.

[0047] The current collector of the present invention may be manufactured by selecting an appropriate substrate that has anisotropic properties and then applying an electrically conductive coating to the substrate. Any of the methods disclosed in our international patent applications mentioned in the introductory part of the specification, or in our US patent application number 15/295647, the entire contents of which are herein incorporated by cross-reference, may be used to produce the current collector in accordance with the present invention.

[0048] In some embodiments, the current collector may have a porosity that falls in the range of from 60% to 95%, or from 70% to 95%.

[0049] In some embodiments, the current collector has a weight percentage of metal (calculated by dividing the weight of metal by the combined weight of metal plus substrate) of from 80 to 95%.

[0050] In some embodiments, the substrate has a volume fraction of metal of from 2 to 30%, or from 2 to 20%.

[0051] The current collector may have a thickness that falls in the range of from 5 μm to 1 mm or even higher, or from 5μm to 400μm, or from 5μm to lOμm, or from 25μm to 400μm. The thickness of the current collector in accordance with the present invention can vary quite greatly, depending upon the desired thickness in the end application.

[0052] In a second aspect, the present invention provides a current collector for an electrochemical cell or a battery, the current collector comprising a porous polymeric substrate coated with a conductive material, characterised in that the porous polymeric substrate comprises a woven or nonwoven substrate comprising a plurality of fibres that have a width that is greater than a height of the fibres.

[0053] In this aspect, the fibres that are used in the porous polymeric substrate may be described as flat or flattened fibres.

[0054] In one embodiment, the fibres may have a width that is at least 1.2 times the height of the fibres, or at least 1.4 times the height of the fibres, or at least 1.5 times the height of the fibres, or at least 1.75 times the height of the fibres, or at least 2 times the height of the fibres, or at least 3 times the height of the fibres, or at least 4 times the height of the fibres, or at least 5 times the fibres, or at least 6 times the height of the fibres, or at least 7 times the height of the fibres, or at least 8 times the height of the fibres, or at least 9 times the height of the fibres, or at least 10 times the height of the fibres, or up to 20 times the height of the fibres.

[0055] In some embodiments, the porous polymeric substrate used in the second aspect of the invention may have anisotropic properties.

[0056] Embodiments of the second aspect of the present invention may advantageously combine the requirement for low thickness (because even if 2 or 3 fibres are stacked on top of each other in the substrate, the thickness of the substrate will be relatively low due to the flattened nature of the fibres) with high-strength in the machine and/or transverse direction due to the geometry of the fibres.

[0057] Other features of the second aspect of the present invention may as be described with reference to the first aspect of the present invention.

[0058] In a third aspect, the present invention provides a current collector for an electrochemical cell or a battery, the current collector comprising a porous polymeric substrate coated with a conductive material, characterised in that the porous polymeric substrate coated with the conductive material is reduced in thickness after application of the conductive material.

[0059] In a fourth aspect, the present invention provides a method for producing a current collector for an electrochemical cell or a battery, the method comprising coating a porous polymeric substrate with a conductive material and subsequently reducing a thickness of the porous polymeric substrate coated with the conductive material.

[0060] In one embodiment, the thickness of the porous polymeric substrate coated with the conductive material is reduced by subjecting it to rolling or calendaring or stamping. [0061] In one embodiment, the thickness of the porous polymeric substrate coated with the conductive material is reduced by at least 10%, or reduced by at least 20%, or reduced by at least 30%, or reduced by at least 40%, or reduced by at least 50%. In one embodiment, the thickness of the porous polymeric substrate coated with a conductive material is reduced by 10 to 60%, or by 20 to 55%, all by 30 to 50%, or by 40 to 50%, or by about 50%, or by about 60%.

[0062] The step of reducing the thickness of the porous polymeric substrate coated with the conductive material also reduces the porosity of the current collector. The reduction in porosity closely follows the reduction in thickness.

[0063] In one embodiment, the porous polymeric substrate coated with the conductive material is subjected to rolling or calendaring at a temperature ranging from 10°C to 300°C, or from 10°C to 250°C, or from 10°C to 200°C, or from 10°C to 150°C, or from 10°C to 100°C, or from 10°C to 70°C, or from 10°C to 50°C. In some embodiments, the rolling or calendaring step is carried out at room temperature.

[0064] Some of the experimental work conducted by the present inventors has shown that decreasing the thickness of the current collector, in combination with the use of specific polymer substrates, can surprisingly lead to an increase in the specific electrical conductivity of the current collector.

[0065] It has also been found that reducing the thickness of the current collector after the metal coating has been applied to the porous polymer substrate is advantageous in that the metal coating typically increases the strength of the substrate, thereby lowering the likelihood that the current collector will tear or break during further processing on electrode coating or cell assembly lines.

[0066] In a fifth aspect, the present invention provides a method for assembling a battery comprising, producing a current collector for an electrochemical cell or a battery by coating a porous polymeric substrate with a conductive material and subsequently applying a layer of active material to the current collector.

[0067] In a sixth aspect, the present invention provides a method for assembling a battery comprising, producing a current collector for an electrochemical cell or a battery by coating a porous polymeric substrate with a conductive material and subsequently reducing a thickness of the porous polymeric substrate coated with the conductive material, followed by applying a slurry comprising active material particles to the current collector. [0068] In one embodiment, the layer of active material comprises a film of active material.

In another embodiment, the layer of active material comprises active material particles. In one embodiment, a slurry of active material particles is applied to the current collector.

[0069] In one aspect, the slurry is applied to only a single side of the current collector. In another aspect, the slurry is applied to both sides of the current collector. In another embodiment, the layer of active material is applied to only one side of the current collector. In another embodiment, the layer of active material is applied to both sides of the current collector.

[0070] Further features of the third, fourth and fifth aspect of the present invention may be as described with reference to the first aspect of the present invention. Embodiments of the third, fourth and fifth aspect of the present invention may use the porous substrate coated with the conductive material of the first and/or second aspects of the present invention.

[0071] In all aspects of the present invention, the coating may be applied by any suitable technique. In some embodiments, the coating may be applied to the surface by various means. For example, an initial layer may be applied by atomic layer deposition, electrodeposition, electroless deposition, hydrothermal methods, electrophoresis, photocatalytic methods, sol-gel methods, other vapour phase methods such as chemical vapour deposition, physical vapour deposition and close-spaced sublimation. Further layers of the same coating or of a different coating or coatings using one or more of these methods may also be applied. It may be useful to coat the material such that the composition of the material is not uniform throughout. For example, a coating method may be used that only penetrates partway into the porous material. The coating may also be applied by sequential use of different coating methods. Any of the methods disclosed in our international patent applications mentioned in the introductory part of the specification, or in our US patent application number 15/295647, the entire contents of which are herein incorporated by cross-reference, may be used to produce the current collector in accordance with the present invention.

[0072] In embodiments of all aspects of the present invention, the current collector may be heated to an elevated temperature, such as up to 300°C, without any noticeable loss of functionality as a current collector being observed. In some embodiments, the current collector may be heated to an elevated temperature of up to 300°C without changing its dimension or suffering from shrinkage. The current collector may be heated to the elevated temperature for a period of up to 12 hours or longer without any loss of functionality or without changing dimensions. [0073] Any of the features described herein can be combined in any combination with any one or more of the other features described herein within the scope of the invention.

[0074] The reference to any prior art in this specification is not, and should not be taken as an acknowledgement or any form of suggestion that the prior art forms part of the common general knowledge.

BRIEF DESCRIPTION OF DRAWINGS

[0075] Various embodiments of the invention will be described with reference to the following drawings, in which:

[0076] Figure 1 shows a plan-view SEM photomicrograph of an uncoated substrate suitable for the use in fabricating current collectors in accordance with example 8;

[0077] Figure 2 shows a cross-section photomicrograph of the obtained electrode, with active material particles being integrated into the void spaces of the current collector in accordance with example 8;

[0078] Figure 3 shows a cross-section photomicrograph of the obtained electrode, with active material particles being coated on one side of a 6μm solid copper current collector foil in accordance with example 9;

[0079] Figure 4 shows a cross-section SEM photomicrograph of the obtained electrode, with active material particles being coated on the current collector in accordance with example 10; and

[0080] Figures 5A and 5B show plan-view SEM photomicrographs of the obtained current collector in its original state and after being calendared at calendaring condition number 3 in accordance with example 11.

DESCRIPTION OF EMBODIMENTS

In the examples given hereunder, the following substrates were used:

PET substrate made from circular PET fibres (fibre diameter < 10μm )

• Membrane 1: 10μm thickness

• Membrane 2: 15μm thickness

• Membrane 3: 30μm thickness

PET substrate made from circular PET fibres (fibre diameter > 10μm ) • Membrane 4: 105μm thickness

• Membrane 5: 160μm thickness

Non-woven composite membrane

• Membrane 6: 30μm thickness; basis weight: 18.0 g/m²²; non-woven fibrous composite structure consisting out of three different types of polymer fibres

PET substrate made from flat PET fibres

• Membrane 7:

o 140μm thickness; 42g/m²² basis weight; Fibre type: 20μm in width, 3μm in

thickness

• Membrane 8:

o 100μm thickness; 41g/m²² basis weight; Fibre type: 18μm in width, 2.5μm in thickness

• Membrane 9:

o 30μm thickness; l8g/m²² basis weight; Membrane type: non-woven fibrous

composite structure including flat PET fibres and a second polymeric fibre.

Example 1 : Membrane 1

[0081] An electroless copper coating was applied to a porous polymeric, non-woven substrate consisting of polyethylene terephthalate fibres (PET). The thickness of the substrate before the application of the copper coating was 10μm. The substrate was pretreated with an activator comprising Macuplex D34C with 12M HC1. Macuplex D34C is a proprietary commercially available activator that contains palladium chloride and tin chloride. The activation step took place at 26.5°C for a period of three minutes. A copper layer was then applied by contacting the substrate with Enthone Envision copper plating chemistry at a temperature of 46°C for a period of 70 minutes.

[0082] A copper loading of 2.87mg/cm² was applied to the polymeric substrate. The copper coating was estimated to be 980 nm in thickness on average. The current collector had the following properties:

Example 2: Membrane 2

[0083] In this example, an electroless copper coating was applied to a porous polymeric, non-woven substrate consisting of polyethylene terephthalate fibres (PET). The thickness of the substrate before the application of the copper coating was 15μm. The substrate was pretreated with an activator comprising Macuplex D34C with 12M HC1. Macuplex D34C is a proprietary commercially available activator that contains palladium chloride and tin chloride. The activation step took place at 26.5°C for a period of three minutes. A copper layer was then applied by contacting the substrate with Enthone Envision copper plating chemistry at a temperature of 46°C for a period of 45 minutes.

[0084] A copper loading of 4.25mg/cm was applied to the polymeric substrate. The copper coating was estimated to be 936 nm in thickness on average. The current collector had the following properties:

Example 2.1: Membrane 2

[0085] An electroless copper coating was applied to a porous polymeric, non-woven substrate as described in example 2. The substrate was pretreated with an activator comprising Macuplex D34C with 12M HC1. Macuplex D34C is a proprietary commercially available activator that contains palladium chloride and tin chloride. The activation step took place at 26.5°C for a period of three minutes. The substrate was then contacted with an accelerator comprising Macuplex 9338 with 12M HC1. Contact between the accelerator and the substrate took place at 48.5°C for a period of one minute. A copper layer was then applied by contacting the substrate with MacDermid Copper 85 at a temperature of 46.5°C for a period of 120 minutes.

[0086] A copper loading of 2.5 lmg/cm was applied to the polymeric substrate. The cross- section SEM photomicrograph was used to estimate the coating thickness of the applied copper coating. The copper coating was estimated to be 900 nm to 1200 nm in thickness.

Example 3 : Membrane 4 [0087] In this example, an electroless copper coating was applied to a porous polymeric, non-woven substrate consisting out of polyethylene terephthalate fibres (PET). The thickness of the substrate before the application of the copper coating was 104μm. The substrate was pretreated with an activator comprising Macuplex D34C with 12M HC1. Macuplex D34C is a proprietary commercially available activator that contains palladium chloride and tin chloride. The activation step took place at 26.5°C for a period of three minutes. A copper layer was then applied by contacting the substrate with MacDermid Copper 85 at a temperature of 46°C for a period of 60 minutes. The current collector had the following properties:

Example 4: Membrane 5

[0088] In this example, an electroless copper coating was applied to a porous polymeric, non-woven substrate consisting out of polyethylene terephthalate fibres (PET). The thickness of the substrate before the application of the copper coating was 160μm. The substrate was pretreated with an activator comprising Macuplex D34C with 12M HC1. Macuplex D34C is a proprietary commercially available activator that contains palladium chloride and tin chloride. The activation step took place at 26.5°C for a period of three minutes. A copper layer was then applied by contacting the substrate with MacDermid Copper 85 at a temperature of 46°C for a period of 60 minutes. The current collector had the following properties:

Example 5 : Membrane 6

[0089] A porous polymeric membrane with a non-woven fibrous composite structure and a thickness of 30μm was coated with copper using electroless deposition. The substrate was pretreated with an activator comprising Macuplex D34C with 12M HC1. Macuplex D34C is a proprietary commercially available activator that contains palladium chloride and tin chloride. The activation step took place at 26.5°C for a period of three minutes. The substrate was then contacted with an accelerator comprising Macuplex 9338 with 12M HC1. Contact between the accelerator and the substrate took place at 48.5°C for a period of one minute. A copper layer was then applied by contacting the substrate with MacDermid Copper 85 at a temperature of 46.5°C for a period of 30 minutes.

[0090] A copper loading of 4.30 mg/cm was applied to the polymeric substrate. The copper coating was estimated to be 59nm in thickness on average. The current collector had the following properties:

Example 6: Membrane 6 coated with Nickel

[0091] A porous polymeric membrane with a non- woven fibrous composite structure and a thickness of 30μm was coated with nickel using electroless deposition. The substrate was pretreated with an activator comprising Macuplex D34C with 12M HC1. Macuplex D34C is a proprietary commercially available activator that contains palladium chloride and tin chloride. The activation step took place at 26.5°C for a period of three minutes. The substrate was then contacted with an accelerator comprising Macuplex 9338 with 12M HC1. Contact between the accellerator and the substrate took place at 48.5°C for a period of one minute. A nickel layer was then applied by contacting the substrate with a solution containing, 28.3g/L nickel(II)sulfate hexahydrate, 42g/L citric acid, 3.5g/L DMAB and 26g/L sodium hydroxide for a period of 10 minutes at a temperature of 50°C.

[0092] A nickel loading of 0.57mg/cm² was applied to the polymeric substrate. The current collector had the following properties:

Example 7 : Membrane 6 coated with copper and then nickel

[0093] A porous polymeric membrane with a non-woven fibrous composite structure and a thickness of 30m m was coated with copper using electroless deposition. The substrate was pretreated with an activator comprising Macuplex D34C with 12M HC1. Macuplex D34C is a proprietary commercially available activator that contains palladium chloride and tin chloride. The activation step took place at 26.5°C for a period of three minutes. The substrate was then contacted with an accelerator comprising Macuplex 9338 with 12M HC1. Contact between the accellerator and the substrate took place at 48.5°C for a period of one minute. A copper layer was then applied by contacting the substrate with MacDermid Copper 85 at a temperature of 46.5°C for a period of 47.5 minutes.

[0094] A copper loading of 3.78mg/cm² was applied to the polymeric substrate. This material had the following properties:

[0095] Following the application of a copper layer, a nickel layer was applied to the initial copper layer by contacting the substrate with an electroless nickel solution containing, 28.3g/L nickel(II)sulfate hexahydrate, 42g/L citric acid, 3.5g/L DMAB and 26g/L sodium hydroxide for a period of lOmin at a temperature of 50°C. A nickel loading of 0.06mg/cm² was applied. The following properties were obtained:

[0096] A number of alternative porous polymeric substrates made from flat or flattened fibres can be used to make current collectors in accordance with the present invention, including the following:

[0097] Membrane 7, a PET substrate made from flat PET fibres. The membrane was of 140m m thickness; Fibre type: 20μm in width and 3μm in thickness.

[0098] Figure 1 shows a plan-view SEM photomicrograph of the alternative uncoated substrate suitable for the use in fabricating current collectors by the invention described in this patent.

[0099] Membrane 8 is a PET membrane made from flattened fibres. The membrane was of 100μm thickness; Fibre type: 18μm in width and 2.5 μm in thickness.

[00100] Membrane 9 is a PET membrane made from flattened fibres. The membrane was of 30μm thickness; non-woven fibrous composite structure including flat PET fibres and a second polymeric fibre.

Example 8: Membrane 2

[00101] In this example, an electroless copper coating was applied to a porous polymeric, non-woven substrate consisting out of polyethylene terephthalate fibres (PET). The thickness of the substrate before the application of the copper coating was 15μm. The substrate was pretreated with an activator comprising Macuplex D34C with 12M HC1. Macuplex D34C is a proprietary commercially available activator that contains palladium chloride and tin chloride. The activation step took place at 26.5°C for a period of three minutes. A copper layer was then applied by contacting the substrate with Enthone Envision copper plating chemistry at a temperature of 46°C for a period of 50 minutes.

[00102] A copper loading of 2.71mg/cm² was applied to the polymeric substrate. The copper coating was estimated to be 822 nm in thickness on average. The current collector had the following properties:

[00103] An anode slurry mixture was prepared for the purpose of applying an active material coating to the current collector. The slurry mixture contained 94.5% of the graphite active material by weight, 2.5% SBR binder by weight and 1.5% CMC binder by weight and 1.5% Super P Carbon Black by weight as the conductive additive. Water was used as the solvent and the active material slurry was applied to the current collector by a blade-type coating mechanism.

[00104] The graphite active material used in this example was artificial MCMB (Meso- porous Carbon Microbeads) sourced from Gelon LIB Co., Limited. The active material has a particle size distribution of d₁₀≥ Sμm; d₅₀= 16.5-1 9μm; d₉₀≤ 32μm and the specific capacity of the graphite active material is≥320mAh/g.

[00105] A total coating weight of 13.88mg/cm was applied to the current collector. It has to be noted that for a substrate where the coating forms an integrated electrode structure meaning that the active material occupies the void space within the volume of the current collector, the notion of a coating per side is not applicable. The total electrode thickness obtained after the coating process was measured to be 124μm with a calculated porosity of 54%. The coated electrode was then calendered at a pressure of 100bar which reduced the total electrode thickness tol09μm and a calculated porosity of 37%.

[00106] The total calculated capacity based on active material loading weight and specific active material capacity of the obtained electrode was 4.40mAh/cm² (which would correspond to a capacity of 2.20mAh/cm per side for a conventional foil based electrode.

[00107] The so calculated capacity per volume of the entire electrode amounted to

404mAh/cm³. The calculated capacity per weight of the entire electrode (including the weight of the current collector) amounted to 258mAh/g.

[00108] Total electrode capacity per area: 4.40mAh/cm²

[00109] Total electrode capacity per volume 404mAh/cm³

[00110] Total electrode capacity per weight 258mAh/g.

[00111] Figure 2 shows a cross-section photomicrograph of the obtained electrode, with active material particles being integrated into the void spaces of the current collector.

Example 9 - Comparative Example - 6μm copper foil electrode [00112] Electrodeposited battery grade solid copper foil with a thickness of 6 μm was sourced form Targray Technology International Inc.

[00113] An anode slurry mixture was prepared for the purpose of applying an active material coating to the current collector. The slurry mixture contained 94.5% of the graphite active material by weight, 2.5% SBR binder by weight and 1.5% CMC binder by weight and 1.5% Super P Carbon Black by weight as the conductive additive. Water was used as the solvent and the active material slurry was applied to the current collector by a blade-type coating mechanism.

[00114] A total coating weight of 7.8mg/cm² was applied to one side of the 6μm thick solid copper foil. This would correspond to an active material coating weight of 15.60mg/cm for the weight of a two sided coating on the current collector. The total electrode thickness obtained after the coating process was measured to be 75μm with a calculated porosity of 47%. The coated electrode was then calendered at a pressure of lOObar which reduced the total electrode thickness to 68μm and a calculated porosity of 41 %.

[00115] The total calculated capacity based on active material loading weight and specific active material capacity of the obtained electrode was 2.48mAh/cm² for the one-sided coating on the current collector. This would correspond to a total capacity of 4.96mAh/cm for a two sided coating on the current collector.

[00116] The calculated capacity per volume of the entire electrode amounted to

384mAh/cm³. The calculated capacity per weight of the entire electrode (including the weight of the current collector) amounted to 238mAh/g.

[00117] Figure 3 shows a cross-section photomicrograph of the obtained electrode, with active material particles being integrated into the void spaces of the current collector.

Example 10 - Membrane 6

[00118] A porous polymeric membrane with a non- woven fibrous composite structure and a thickness of 30μm was coated with copper using electroless deposition. The substrate was pretreated with an activator comprising Macuplex D34C with 12M HC1. Macuplex D34C is a proprietary commercially available activator that contains palladium chloride and tin chloride. The activation step took place at 27.5°C for a period of three minutes. The substrate was then contacted with an accelerator comprising Macuplex 9338 with 12M HC1. Contact between the accellerator and the substrate took place at 48.5°C for a period of one minute. A copper layer was then applied by contacting the substrate with MacDermid Copper 85 at a temperature of 46.5°C for a period of 60 minutes.

[00119] A copper loading of 4.95 mg/cm² was applied to the polymeric substrate. The copper coating was estimated to be 61nm in thickness on average.

[00120] The copper coated current collector was calendered to reduce its thickness before coating the current collector with graphite active material. The calendering process reduced the thickness of the current collector from 59μm and a porosity of 66% before calendering to a thickness of 30μm and a porosity of 34% after calendering. The solid equivalent conductivity of the current collector remained unchanged.

[00121] An anode slurry mixture was prepared for the purpose of applying an active material coating to the current collector. The slurry mixture contained 96.5 % of the graphite active material by weight, 2.5% PVDF binder by weight and 1.0% Super P C-65 Carbon Black by weight as the conductive additive. NMP was used as the solvent and the active material slurry was applied to the current collector by a blade-type coating mechanism.

[00122] The graphite active material used in this example was BTR 918S, a natural graphite, sourced from Tianjin BTR New Energy Technology Co., Ltd. The active material has a particle size distribution of d₁₀: 9- 13μm; d₅₀: 17-23μm; d₉₀: 27-36μm and the specific capacity of the graphite active material is 338mAh/g.

[00123] A total coating weight of 24.72mg/cm² was applied to the current collector. This corresponds to a coating weight of 12.36mg/cm per side of the current collector. The electrode was then calendered to adjust the porosity of the active material coating. The total electrode thickness after calendering was measured to be 1 88m m and the active material coating had an average calculated coating porosity of 34%.

[00124] The total calculated capacity based on active material loading weight and specific active material capacity of the obtained electrode was 8.08mAh/cm². This corresponds to a capacity of 4.04mAh/cm² per side of the electrode.

[00125] The calculated capacity per volume of the entire electrode amounted to

404m Ah/cm³. The calculated capacity per weight of the entire electrode (including the weight of the current collector) amounted to 258mAh/g

[00126] Figure 4 shows a plan-view and a cross-section SEM photomicrograph of the obtained current collector.

[00127] Examples 11 and 12 show examples that involved calendering of the current collector before the application of an active material coating.

Example 11 - Membrane 2

[00128] In this example, an electroless copper coating was applied to a porous polymeric, non-woven substrate consisting out of polyethylene terephthalate fibres (PET). The thickness of the substrate before the application of the copper coating was 15μm. The substrate was pretreated with an activator comprising Macuplex D34C with 12M HCh Macuplex D34C is a proprietary commercially available activator that contains palladium chloride and tin chloride. The activation step took place at 26.5°C for a period of three minutes. A copper layer was then applied by contacting the substrate with Enthone Envision copper plating chemistry at a temperature of 46°C for a period of 45 minutes. A copper loading of 1.12mg/cm² was applied to the polymeric substrate.

[00129] The obtained current collector was then calendered using three different calendering conditions to achieve the desired reduction in thickness. The letter A denotes the properties of the uncalendered current collector and the letter B, C and D denote the properties of the current collector after the calendering at condition 1, 2, and 3.

[00130] Calendering condition 1 : Pressure: 50bar; Temperature: 50°C; Number of passes: 2

[00131] Calendering condition 2: Pressure: 100bar; Temperature: RT; Number of passes: 1 [00132] Calendering condition 3: Pressure: lOObar; Temperature: 70°C; Number of passes: 1

[00133] Calendaring condition 3 obtained a compacted current collector with a thickness of 6m m and good levels of conductivity. A reduction in thickness from 19μm to 6μm corresponds to a 68% thickness reduction through the calendaring process.

[00134] Figures 5 A to 5D show plan-view SEM photomicrographs of the obtained current collector in its original state and after being calendared at calendaring conditions number 3.

Example 12 - Membrane 6

[00135] A porous polymeric membrane with a non-woven fibrous composite structure and a thickness of 30 μm was coated with copper using electroless deposition. The substrate was pretreated with an activator comprising Macuplex D34C with 12M HC1. Macuplex D34C is a proprietary commercially available activator that contains palladium chloride and tin chloride. The activation step took place at 26.5°C for a period of three minutes. The substrate was then contacted with an accelerator comprising Macuplex 9338 with 12M HC1. Contact between the accellerator and the substrate took place at 48.5°C for a period of one minute. A copper layer was then applied by contacting the substrate with MacDermid Copper 85 at a temperature of 46.5°C for a period of 30 minutes. A copper loading of 4.30mg/cm was applied to the polymeric substrate.

[00136] A second substrate was prepared in the same way but the substrate was contacted with MacDermid Copper 85 at a temperature of 46.5°C for a period of 27 minutes. A copper loading of 3.71mg/cm was applied to the polymeric substrate.

[00137] Each of the obtained current collector substrates was then calendered using either force or a combination of force and temperature.

[00138] The first current collector with a copper loading of 4.30mg/cm was calendered using the following conditions: [00139] Calendaring condition: Force: 240 Tons; Temperature: RT; Number of passes: 1

[00140] Calendaring at such conditions yielded a reduction in thickness of the current collector from 53μm to 28μm which corresponds to a reduction of current collector thickness of 47%. It also has to be noted that the conductivity of the current collector improved with the calendaring process. The letter A denotes the properties of the uncalendared current collector and the letter B denotes the current collector after the calendaring process.

[00141] The second current collector with a copper loading of 3.71mg/cm² was calendered using the following conditions:

[00142] Calendering condition: Force: 270 Tons; Temperature: 120°C; Number of passes: 1

[00143] Calendering at such conditions yielded a reduction in thickness of the current collector from 52μm to 26μm which corresponds to a reduction of current collector thickness of 50%. It also has to be noted that the conductivity of the current collector improved with the calendering process. The letter A denotes the properties of the uncalendered current collector and the letter B denotes the properties of the current collector after the calendering process.

[00144] A number of other examples we conducted in which porous polymer substrates were coated with copper coatings. The results of the examples are shown in table 1:

[00145] Further tests were carried out to measure the tensile strength of some of the copper coated current collector samples. The results are shown in the table below:

[00146] Further testing on the tensile strength of current collectors in accordance with the present invention demonstrate that the tensile strength of the polymer substrate is improved by the metal coating the following table sets out the percentage increase in tensile strength of the substrate to current collector for machine direction (MD) and transverse direction (TD). The subscript U denotes uncoated and the subscript C denotes coated.

[00147] Metals useful as the conductive material for current collector applications can be selected from the following: copper, nickel, aluminium, iron, titanium, gold, platinum or mixtures or alloys of two or more thereof.

[00148] The directional characteristics for some of the membranes are imparted by the fact that a higher percentage of the fibres in the substrate are aligned and are running in the machine direction. A lower percentage of the fibres is running into the transverse direction. The fibre distribution imparts a certain degree of anisotropy to the current collector leading to three unique aspects described below.

• Mechanical strength - Higher mechanical strength into the machine direction as opposed to the transverse direction.

• Electrical conductivity - Higher electrical conductivity into the machine direction as opposed to the transverse direction

• Spatial orientation and directionality of openings and pores - In addition, the openings and pores created by the fibres and their spatial orientation establishes a certain directionality of pores/openings, extending into current collector's structure in a largely downwardly facing pattern (perpendicular to the surface of the current collector). This allows the openings to be easily filled with active material particles.

[00149] A range of membrane thicknesses and corresponding basis weights are possible. Examples include:

Base membrane: 8 - 10μm thickness and a weight of 2- 4g/m²

Base membrane: 12 - 20μm thickness and a weight of 5 - 8g/m²

Base membrane: 20 -30μm thickness and a weight of 8 - 12g/m² [00150] Other thicknesses and weights can also be used.

[00151] The amount of fibres running into the machine direction and the transverse direction, stated as a percentage may fall within the following ranges:

90% fibres MD vs. 10% fibres in TD

80% fibres MD vs. 20% fibres in TD

70% fibres MD vs. 30% fibres in TD

60% fibres MD vs. 40% fibres in TD

55% fibres MD vs. 45% fibres in TD

[00152] The calculated porosity of these membranes before a metal coating is applied will typically lie in the range of 50 to 98%, or from 60 to 95%, or from 70 to 95%, or from 70-80%. The fibres of the substrate give a gross thickness with larger“pores” without taking space from the active materials. The aim is to maximise the active material content in the given current collector volume without sacrificing on the performance of the current collector.

[00153] The metal content with the current collector can be expressed in several ways. In one embodiment, the metal content of the current collector can be expressed as a weight percentage of metal, determined as a weight of metal as a fraction of the total current collector weight (polymer + metal). In this case the thin micro-porous membranes may possess a weight percentage of metal of 80-95%.

[00154] Alternatively, the metal content could be described as the volume fraction of metal contained within the structure. For the thin micro-porous current collector the volume fraction of metal such as copper usually ranges between 2% and 20%. Of course higher levels between 20% and 40% may also be useful in certain applications.

[00155] The size, shape and spatial orientation of the openings/pores within the current collector will impact on how easily the volume of the current collector can be filled with active material.

[00156] The openings ideally have a size that allows the active material particle to infiltrate the volume of the current collector but do not allow the active material paste to simply fall through the structure due to its low thickness, as this can cause difficulties during electrode manufacture or assembly of the cells. For example, it is typical to apply the active material to the current collector by blade coating techniques, slot-die coating, screening or rolling. If the active material (which is typically applied in the form of a paste or slurry containing graphite, binders and other components) can easily pass through the current collector, this can lead to the active material passing through the current collector and causing a build-up of material on the supporting surface underneath the current collector, which can cause difficulty in obtaining and even coating of the active material on the current collector and can also form sites for potential breakage of the current collector during electrode coating or cell assembly.

[00157] Examples for openings/pore size ranges are:

5-10μm

10-20μm

20-50μm

50-100μm

[00158] Standard graphite active material particles have an average diameter of 15 -23μm with some particles being only 10μm in diameter and the largest ones being up to 50μm in diameter. Various graphites with a smaller average particle diameter size of 5-15 μm may also be used. [00159] Electrodes need to be calendered after graphite coating to provide the optimal density of the active material. This process applies high forces on the current collector structure and an open current collector will allow the particles to nestle in the structure whilst minimising damaging the structure.

[00160] Other particulate active materials such as silicon, tin, carbons in various forms, and composite particles such as graphite/silicon, graphite/lithium, or carbon/silicon and

carbon/lithium and core shell particle structures incorporating one or more of the aforementioned materials of graphite, carbon, silicon, lithium, copper or composites thereof may only have an average diameter of l- 10μm or less than lμm.

[00161] The openings in the micro-porous current collector may be designed to match the active material in use.

[00162] In other embodiments, a thick microporous current collector having a thickness in the range of from 25 to 400μm can be used. In embodiments where the current collector comprises a thick current collector, examples of total weight values that fall in the range of from 4.0mg/cm to 30mg/cm², or from 6.0mg/cm² to 30mg/cm², or from 8.0mg/cm²to 30mg/cm², or from 10.0mg/cm² to 30mg/cm², or from 12.0mg/cm² to 30mg/cm², or from 15.0mg/cm² to 30mg/cm², or from 18.0mg/cm to 30mg/cm , or from 20.0mg/cm to 30mg/cm , or from 6.0mg/cm to 15.0mg/cm². These values correspond to a 55% reduction in weight relative to 10μm copper foil to a 234% increase in weight relative to 10μm copper foil. It has to be pointed out that although the weight for some of these examples is increased relative to the weight of lOμm copper foil, the resulting current collector possess a much desired mass to volume ratio (density).

Embodiments where the current collector is a thick current collector, the current collector has a very low weight per volume/thickness of these thicker current collectors.

[00163] The thick porous polymeric substrate can comprise a substrate made from PET fibres having a circular cross-section with diameter of 10-15 μm (alternatively fibres with a larger diameter of up to 30 μm or a fibre diameter as little as 5 μm could be used). It is expected that this“thicker current collector” is likely to be predominantly used in combination with lithium metal batteries where lithium metal is plated into the void space of the 3D porous structure. However, filling the current collector with active material particles of a given shape and dimension may also be feasible. Active material particles with a smaller diameter such as 1- 10μm may be preferred in combination with this thicker structure.

[00164] The thicker micro-porous current collector structure also possesses a certain degree of anisotropy through the plane of the current collector as opposed to the in-plane anisotropic features of strength and conductivity.

[00165] The spatial orientation/directionality of openings/pores in this thicker membrane may also be important. This current collector provides an alternative to the structure of copper foams while being able to achieve thicknesses and porosities at such thicknesses that are unattainable for copper foams. In particular, this current collector allows for the creation of thicker current collector structures with thicknesses thin enough to be out of reach of metal foams (<400μm), while maintaining high levels of porosity (>70%) of up to 95%, while being able to create pores/openings in the 50-100μm range or larger. This is not something that can be achieved with metal foams, while creating a structure of sufficient strength for commercial processing and while creating a structure where the directionality of pores/opening is such that they are extending into current collector's structure in a largely downwardly facing pattern.

[00166] A range of membrane thicknesses and corresponding basis weights are possible. Examples include:

Base membrane: 80- 120μm thickness and a weight of 8 - 14g/m²²

Base membrane: 140 - 180μm thickness and a weight of 18 - 25g/m²²

Production of a current collector with a thicknesses of at least 400μm is possible.

[00167] The calculated porosity of these membranes before a metal coating is applied lies in the range of 85-95%. Porosity ranges of 70% to 95% are useful.

[00168] The openings of the pores ideally have a size and orientation that in the case of a lithium metal battery allows the lithium ions supplied by the opposing electrode (cathode) to migrate into the porous structure and deposit as metallic lithium. In the case of active material particles the openings should allow the particles to easily infiltrate the volume of the current collector but do not allow the active material paste to simply fall through the structure.

[00169] Examples for openings/pore size ranges are

10-20μm

20- 50μm

50- 100μm 100-200μm

200-500μm

[00170] Standard graphite active material particles have an average diameter of 15-23μm with some particles being only 10μm in diameter and the largest ones being up to 50μm in diameter. Various graphite’s with a smaller average particle diameter size of 5-15μm may also be used.

[00171] Other particulate active materials such as silicon, tin, carbons in various forms, and composite particles such graphite/silicon, graphite/lithium, or carbon/silicon and carbon/lithium and core shell particle structures incorporating one or more of the aforementioned materials of graphite, carbon, silicon, lithium, copper or composites thereof may only have an average diameter of 1-10μm or less than 1μm.

[00172] The openings in the micro-porous current collector may be designed to match the active material in use.

[00173] Further, the shape of the openings could be varied by the anisotropy of the fibre structure to maximise the capacity, particularly with a large pore to particle ratio. It is expected that the average pore size required will decrease with a decrease in active material particle size.

[00174] In the present specification and claims (if any), the word‘comprising’ and its derivatives including‘comprises’ and‘comprise’ include each of the stated integers but does not exclude the inclusion of one or more further integers.

[00175] Reference throughout this specification to‘one embodiment’ or‘an embodiment’ means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearance of the phrases‘in one embodiment’ or‘in an embodiment’ in various places throughout this specification are not necessarily all referring to the same embodiment.

Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more combinations.

[00176] In compliance with the statute, the invention has been described in language more or le specific to structural or methodical features. It is to be understood that the invention is not limited to specific features shown or described since the means herein described comprises preferred forms of putting the invention into effect. The invention is, therefore, claimed in any of its forms or modifications within the proper scope of the appended claims (if any) appropriately interpreted by those skilled in the art.

Claims

1. A current collector for an electrochemical cell or a battery, the current collector comprising a porous polymeric substrate coated with a conductive material, characterised in that the current collector has anisotropic properties.

2. A current collector for an electrochemical cell or a battery, the current collector comprising a porous polymeric substrate coated with a conductive material, characterised in that the porous polymeric substrate comprises a woven or nonwoven substrate comprising a plurality of fibres that have a width that is greater than a height of the fibres.

3. A current collector as claimed in claim 1 wherein the fibres that are used in the porous polymeric substrate comprise flat or flattened fibres.

4. A current collector as claimed in claim 2 or claim 3 wherein , the fibres have a width that is at least 1.2 times the height of the fibres, or at least 1.4 times the height of the fibres, or at least 1.5 times the height of the fibres, or at least 1.75 times the height of the fibres, or at least 2 times the height of the fibres, or at least 3 times the height of the fibres, or at least 4 times the height of the fibres, or at least 5 times the fibres, or at least 6 times the height of the fibres, or at least 7 times the height of the fibres, or at least 8 times the height of the fibres, or at least 9 times the height of the fibres, or at least 10 times the height of the fibres, or up to 20 times the height of the fibres.

5. A current collector for an electrochemical cell or a battery, the current collector comprising a porous polymeric substrate coated with a conductive material, characterised in that the porous polymeric substrate coated with the conductive material is reduced in thickness after application of the conductive material.

6. A current collector as claimed in claim 5 wherein the thickness of the porous polymeric substrate coated with the conductive material is reduced by at least 10%, or reduced by at least 20%, or reduced by at least 30%, or reduced by at least 40%, or reduced by at least 50%. In one embodiment, the thickness of the porous polymeric substrate coated with a conductive material is reduced by 10 to 60%, or by 20 to 55%, all by 30 to 50%, or by 40 to 50%, or by about 50%, or by about 60%.

7. A current collector as claimed in any one of the preceding claims wherein the current collector has one or more properties measured in a longitudinal direction or a machine direction (MD) that is different to the one or more properties measured in a transverse direction (TD) or a cross-machine direction.

8. A current collector as claimed in claim 7 wherein the anisotropic property of the current collector is mechanical strength or the anisotropic property of the current collector is electrical conductivity.

9. A current collector as claimed in claim 8 wherein the current collector has a mechanical strength in one direction that is at least 10% higher than a mechanical strength when measured in a transverse direction to the one direction.

10. A current collector as claimed in claim 9 wherein the current collector has a mechanical strength in one direction that is at least 20% higher than a mechanical strength when measured in a transverse direction, or has a mechanical strength in one direction that is at least 30% higher than a mechanical strength when measured in a transverse direction, or has a mechanical strength in one direction that is at least 40% higher than a mechanical strength when measured in a transverse direction, or has a mechanical strength in one direction that is at least 50% higher than a mechanical strength when measured in a transverse direction, or has a mechanical strength in one direction that is at least 60% higher than a mechanical strength when measured in a transverse direction, or has a mechanical strength in one direction that is at least 70% higher than a mechanical strength when measured in a transverse direction, or has a mechanical strength in one direction that is at least 80% higher than a mechanical strength when measured in a transverse direction, or has a mechanical strength in one direction that is at least 90% higher than a mechanical strength when measured in a transverse direction, or has a mechanical strength in one direction that is at least 2 times higher than a mechanical strength when measured in a transverse direction, or has a mechanical strength in one direction that is at least 3 times higher than a mechanical strength when measured in a transverse direction, or has a mechanical strength in one direction that is at least 4 times higher than a mechanical strength when measured in a transverse direction, or has a mechanical strength in one direction that is at least 5 times higher than a mechanical strength when measured in a transverse direction, or has a mechanical strength in one direction that is at least 10 times higher than a mechanical strength when measured in a transverse direction, or has a mechanical strength in one direction that is at least 20 times higher than a mechanical strength when measured in a transverse direction, or has a mechanical strength in one direction that is from 10% higher to 20 times higher than a mechanical strength when measured in a transverse direction.

11. A current collector as claimed in claim 8 wherein the current collector has an electrical conductivity in one direction that is at least 10% higher than an electrical conductivity when measured in a transverse direction to the one direction, or the current collector has an electrical conductivity in one direction that is at least 20% higher than an electrical conductivity when measured in a transverse direction, or has an electrical conductivity in one direction that is at least 30% higher than an electrical conductivity when measured in a transverse direction, or has an electrical conductivity in one direction that is at least 40% higher than an electrical conductivity when measured in a transverse direction, or has an electrical conductivity in one direction that is at least 50% higher than an electrical conductivity when measured in a transverse direction, or has an electrical conductivity in one direction that is at least 60% higher than an electrical conductivity when measured in a transverse direction, or has an electrical conductivity in one direction that is at least 70% higher than an electrical conductivity when measured in a transverse direction, or has an electrical conductivity in one direction that is at least 80% higher than an electrical conductivity when measured in a transverse direction, or has an electrical conductivity in one direction that is at least 90% higher than an electrical conductivity when measured in a transverse direction, or has an electrical conductivity in one direction that is at least 2 times higher than an electrical conductivity when measured in a transverse direction, or has an electrical conductivity in one direction that is at least 3 times higher than an electrical conductivity when measured in a transverse direction, or has an electrical conductivity in one direction that is at least 4 times higher than an electrical conductivity when measured in a transverse direction, or has an electrical conductivity in one direction that is at least 5 times higher than an electrical conductivity when measured in a transverse direction, or has an electrical conductivity in one direction that is at least 10 times higher than an electrical conductivity when measured in a transverse direction, or has an electrical conductivity in one direction that is at least 20 times higher than an electrical conductivity when measured in a transverse direction, or has an electrical conductivity in one direction that is at from 10% higher to 20 times higher than an electrical conductivity when measured in a transverse direction.

12. A current collector as claimed in claim 8 wherein the current collector has a mechanical strength in the machine direction that is from 18% to 307% higher than compared to the mechanical strength in the transverse direction, or the current collector has a mechanical strength in the machine direction that is from 1.2 to 4.1 times higher than the mechanical strength in the transverse direction.

13. A current collector as claimed in claim 7 wherein the current collector has an electrical conductivity that is from 25% to 346% higher in the machine direction when compared to the transverse direction, or the current collector has an electrical conductivity that is from 1.2 to 4.5 times higher than the electrical conductivity in the transverse direction.

14. A current collector as claimed in any one of the preceding claims wherein the porous polymeric substrate comprises an electrically non-conductive polymeric substrate.

15. A current collector as claimed in any one of the preceding claims wherein the substrate comprises fibres of a single polymer or several different polymer fibres mixed together, or a woven or non-woven substrate, or a continuous structure containing a single polymer or a layered or laminated structure where individual layers comprise different polymers.

16. A current collector as claimed in any one of the preceding claims wherein the porous polymeric substrate or the electrically conductive porous material has an overall thickness that ranges from lμm to 5000μm or from lμm to 5000μm, or from 1μm to 1000μm, or from 1μm to 500μm, or from lμm to 450μm, or from lμm to 250μm, or from lμm to 150μm, or from lμm to 100μm, or from lμm to 50μm or from 1 μm to 20μm.

17. A current collector as claimed in any one of the preceding claims wherein the porous polymeric substrate comprises a porous polyethylene terephthalate (PET) substrate.

18. A current collector as claimed in any one of the preceding claims wherein the porous polymeric substrate comprises a plurality of fibres, with a greater proportion of the fibres extending in the one direction and a lesser proportion of the fibres extending in the other direction.

19. A current collector as claimed in any one of the preceding claims wherein a porous polymeric material is coated with an electrically conductive material comprising a metal.

20. A current collector as claimed in claim 19 wherein the metal is selected from copper, nickel, aluminium, iron, titanium, gold, platinum or mixtures or alloys of two or more thereof.

21. A current collector as claimed in any one of the preceding claims wherein the electrically conductive porous material has pore sizes that range from 0.1 μm to 3000μm and/or a porosity of 30% to 95% (by volume).

22. A current collector as claimed in any one of the preceding claims wherein the electrically conductive porous material has a specific surface area that ranges from 0.005m²/cm³ to

100m²/cm³, 0.005m²/cm³ to 50m²/cm³, or from 0.005m²/cm³ to 20m²/cm³, or from 0.005m²/cm³ to 10m²/cm³, or from 0.005m²/cm³ to 2m²/cm³, or from 0.005m²/cm³ to 0.2m²/cm³.

23. A current collector as claimed in any one of the preceding claims wherein at least part of the porosity in the substrate is interconnected and open to the surface.

24. A current collector as claimed in any one of the preceding claims wherein the electrically conductive porous material has an electrical equivalent solid conductivity in the range of from 0.01S/cm to 500,000S/cm, or in the range of 10,000S/cm and 500,000S/cm, or 30,000S/cm and 500,00S/cm, or 500,00S/cm and 500,000S/cm, or 100,000S/cm and 500,000S/cm, or

200,000S/cm and 500,000S/cm, or 300,000S/cm and 500,000S/cm or 30,000S/cm and

350,000S/cm. One possible range of electrical equivalent solid conductivity is from 30,000S/cm to 350,000S/cm.

25. A current collector as claimed in any one of the preceding claims wherein the electrically conductive porous material comprises a porous polymeric material having a thin coating of a metal applied thereto, the metal being applied to the porous polymeric materials such that the metal coating has a thickness that is less than 8000nm, or less than 5000nm, or less than 3000nm, or less than 2000nm or less than 1000nm, or less 500nm, or less than 300nm, or less than 200nm, or less than lOOnm, or less than 50nm, or less than 30nm, with the metal coating having a thickness that is at least lnm thick, or at least 2nm thick, or at least 5nm thick, or at least lOnm thick or at least 20nm thick.

26. A current collector as claimed in any one of the preceding claims wherein the current collector has a porosity that falls in the range of from 60% to 95%, or from 70% to 95%.

27. A current collector as claimed in any one of the preceding claims wherein the current collector has a weight percentage of metal, calculated by dividing the weight of metal by the combined weight of metal plus substrate, of from 80 to 95%.

28. A current collector as claimed in any one of the preceding claims wherein the substrate has a volume fraction of metal of from 2 to 30%, or from 2 to 20%.

29. A current collector as claimed in any one of the preceding claims wherein the current collector has a thickness that falls in the range of from 5 μm to 1 mm, or from 5 μm to 400 μm, or from 5 μm to 10 μm, or from 25 μm to 400 μm.

30. A current collector as claimed in any one of the preceding claims wherein the current collector is a thin current collector having a thickness of from 5 to 30 μm, the current collector having total weight values that fall in the range of from 2.5mg/cm² to 8.0mg/cm², or from 3.0mg/cm to 8.0mg/cm , or from 3.5mg/cm to 8.0mg/cm , or from 4.0mg/cm to 8.0mg/cm , or from 4.5mg/cm² to 8.0mg/cm² , or from 5.0mg/cm² to 8.0mg/cm² , or from 5.5mg/cm² to 8.0mg/cm² , or from 7.0mg/cm² to 8.0mg/cm² , or from 3.0mg/cm² to 5.5mg/cm².

31. A current collector as claimed in any one of claims 1 to 29 wherein the current collector has a thickness in the range of from 25 to 400m m and the current collector has a total weight values that fall in the range of from 4.0mg/cm² to 30mg/cm², or from 6.0mg/cm² to 30mg/cm², or from 8.0mg/cm to 30mg/cm , or from 10.0mg/cm to 30mg/cm , or from 12.0mg/cm to 30mg/cm² , or from 15.0mg/cm² to 30mg/cm² , or from 18.0mg/cm² to 30mg/cm² , or from

20.0mg/cm² to 30mg/cm², or from 6.0mg/cm² to 15.0mg/cm².

32. A method for producing a current collector for an electrochemical cell or a battery, the method comprising coating a porous polymeric substrate with a conductive material and subsequently reducing a thickness of the porous polymeric substrate coated with the conductive material.

33. A current collector as claimed in claim 32 wherein the thickness of the porous polymeric substrate coated with the conductive material is reduced by subjecting it to rolling or calendaring or stamping.

34. A method as claimed in claim 32 or claim 33 wherein the thickness of the porous polymeric substrate coated with the conductive material is reduced by at least 10%, or reduced by at least 20%, or reduced by at least 30%, or reduced by at least 40%, or reduced by at least 50%. In one embodiment, the thickness of the porous polymeric substrate coated with a conductive material is reduced by 10 to 60%, or by 20 to 55%, all by 30 to 50%, or by 40 to 50%, or by about 50%, or by about 60%.

35. A method as claimed in any one of claims 32 to 34 wherein the porous polymeric substrate coated with the conductive material is subjected to rolling or calendaring at a temperature ranging from 10°C to 300°C, or from 10°C to 250°C, or from 10°C to 200°C, or from 10°C to 150°C, or from 10°C to 100°C, or from 10°C to 70°C, or from 10°C to 50°C. In some embodiments, the rolling or calendaring step is carried out at room temperature.

36. A method for assembling a battery comprising, producing a current collector for an electrochemical cell or a battery by coating a porous polymeric substrate with a conductive material and subsequently applying a layer of active material to the current collector.

37. A method for assembling a battery comprising, producing a current collector for an electrochemical cell or a battery by coating a porous polymeric substrate with a conductive material and subsequently reducing a thickness of the porous polymeric substrate coated with the conductive material, followed by applying a layer of active material to the current collector.

38. A method as claimed in claim 36 or claim 37 wherein the layer of active material is applied to only a single side of the current collector.

39. A method as claimed in claim 36 or claim 37 wherein the layer of active material is applied to both sides of the current collector.

40. A method as claimed in claim 38 or claim 39 in which the layer of active material comprises active material particles.

41. A method as claimed in claim 40 wherein the layer of active material is formed by applying a slurry containing particles of the active material to the current collector.

42. A current collector as claimed in any one of claims 1 to 32 wherein the current collector can be heated to up to 300°C without any noticeable loss of functionality as a current collector being observed or without changing its dimension or suffering from shrinkage.

43. A current collector as claimed in any one of claims 1 to 31 or 42 wherein openings and pores created by fibres in the substrate results in a plurality of pores or openings extending into the current collector in a largely downwardly facing pattern, essentially perpendicular to the surface of the current collector.

44. A method as claimed in any one of claims 36 to 41 wherein openings and pores created by fibres in the substrate results in a plurality of pores or openings extending into the current collector in a largely downwardly facing pattern, essentially perpendicular to the surface of the current collector.

45. A method as claimed in claim 44 wherein the plurality of pores or openings are filled with particles of active material.