WO2015114074A1

WO2015114074A1 - Electric battery cell, especially rechargeable lithium-sulfur battery cell, comprising a volume compensating element

Info

Publication number: WO2015114074A1
Application number: PCT/EP2015/051890
Authority: WO
Inventors: Thomas Wöhrle; Thomas Kretschmar
Original assignee: Robert Bosch Gmbh
Priority date: 2014-02-03
Filing date: 2015-01-30
Publication date: 2015-08-06
Also published as: DE102014201836A1

Abstract

The invention relates to an electric battery cell, in particular a lithium-sulfur battery cell, comprising a housing (1), at least one anode (2), at least one sulfur cathode (3), a separator element (4) between the anode (2) and the cathode (3), and at least one elastic volume-compensating element (5) for compensating variations in the volume of the anode (2) and/or the cathode (3). The invention further relates to a rechargeable lithium-sulfur battery comprising at least two lithium-sulfur battery cells of said type.

Description

Description title

Galvanic battery cell, in particular rechargeable lithium-sulfur battery cell, with volume compensation element

State of the art

The present invention relates to a galvanic battery cell having at least one volume compensation element, wherein the galvanic battery cell is in particular a rechargeable lithium-sulfur battery cell. Furthermore, the present invention relates to a rechargeable lithium-sulfur battery having at least two of the lithium-sulfur battery cells according to the invention. By the term battery is meant here that at least two battery cells are interconnected. The terms

Battery cell and cell are used synonymously in the present specification.

Recently, highly sophisticated rechargeable batteries, also referred to as secondary batteries or accumulators, are being used in various technology fields, ie a parallel or serial combination of a plurality of individual electrically connected rechargeable battery cells to form a battery pack or a so-called battery module.

Applications for such batteries are for example in

To find motor vehicle area for driving an electric motor or an additional electric motor, which may be provided in addition to a conventional internal combustion engine, for example in a hybrid vehicle or the like, as well as in other technical areas, such as stationary equipment, mobile phones, smartphones, portable computers, Video cameras or MP3 players. Already known for a wide range of applications is the lithium-ion battery technology, which stands out for its high energy density and extremely low self-discharge. Known rechargeable lithium-ion batteries consist of at least one, usually two and more lithium-ion battery cells, which have at least one positive and one negative electrode, which lithium ions can reversibly on or off again. An example of such a known lithium-ion battery cell can be found in DE 10 201 1015 830 A1, which contains an electrode stack which has a plurality of electrode sheets and separator sheets arranged therebetween. Furthermore, the lithium-ion battery cell described therein comprises one or more

Volume compensation devices which serve to compensate for changes in the volume of the electrochemical cell, which are caused in particular by charging and discharging of the cell, in relation to a cell holding device, so that the cell is uniformly frictionally or frictionally operatively connected to the cell holding device.

However, lithium-ion battery cells have the disadvantage that their energy density in relation to their weight is not high enough, for example, to provide sufficient electric vehicles, in particular to achieve, for example, a satisfactory range of the electric vehicle. Consequently, the research is on

Automotive Engineering seeks to develop new concepts for secondary battery cells. The currently most promising future concept for

Secondary batteries based on a lithium-sulfur base, which should overcome the known limitations in terms of energy density and thus also in terms of the highly limited range of electric vehicles. Extensive research activities are currently attempting to solve the technical challenges of lithium-sulfur batteries. An important aspect in this case are the strong volume changes or the significant volume increases in volume that occur during a charging or discharging process of the respective battery cell. Thus, during the discharging process of the battery cell, the metallic lithium of the cell anode is successively reduced. It combines in a first large discharge section with sulfur to form so-called polysulfides (Li ₂ S _x with x> 4), which are soluble in the electrolyte. At the maximum achievable concentration of dissolved polysulfides in the electrolyte while the inner volume of the battery cell is taken the least. As the discharge progresses, however, the polysulfides are further reduced and finally deposit as LiS ₂ and Li ₂ S in or at the porous cathode. Here, the volume of the electrodes and thus the total cell volume change again. These processes take place when charging the battery cell in accordance with the reverse order again. Depending on the exact construction the respective battery cell, in particular depending on the case

Applying layer thicknesses, it can be assumed that a relative volume change of the total cell volume in the range of> 12%, this value could increase further in proportion to the specific energy density actually achieved.

In order to deposit the lithium in a dense, uniform and homogeneous manner on the anode, in particular when the cell is being charged, there is a corresponding pressure on the cell

or on the respective electrode from the outside necessary. Desired values may be in the range of 100 N / cm ² . If this pressure is not guaranteed, the return of lithium tends to be undesirable in one

spongy, irregular and inhomogeneous deposit instead. This leads to greatly reduced lifetimes and cycle strengths and to the constant swelling of the cells, in particular in so-called bag battery cells, also known as pouch cells or soft packs, which have a soft outer packaging, for example based on aluminum composite foil. Consequently, it seems questionable whether such a volume change in lithium-sulfur battery cells can ever be completely prevented or in principle must be tolerated. It can therefore be assumed that a uniform pressure load on the battery cell or its electrodes is required, which can be achieved, for example, by a constant force introduction or pressurization independent of the volume of the battery cell or of its cell dimension.

As a solution to the previously described problem has been to

Cyclizing appropriate prototypes of novel lithium-sulfur battery cells used inter alia, a spring-loaded metal jig. A carryover of such an experimental tensioning device to a real end product, in particular a battery module or battery pack design designed for use in the vehicle does not appear to make sense, especially for weight reasons, or would at least be the technological advantages of the lithium-sulfur technique, such as the high energy density ratio for the low weight of

Battery cell, again by the additional weight for the clamping device,

Relating the spring mechanism and the introduction of force. A useful realistic and particularly weight-saving concept for the solution of the previous one described problem is not present so far. A direct transfer of the known from the above prior art, that is, for example, from DE 10 201 1 015 830 A1 known approach is not possible in this respect, since the basic structure and operation of a lithium-ion battery cell fundamentally different from the structure and the operation of a lithium-sulfur battery cell, in particular with respect to the potentially toxic lithium sulfides produced by the discharge, which are to be kept under any circumstances under lock and key.

Disclosure of the invention

In order to solve the problems of the prior art described above, the present invention provides a galvanic battery cell, in particular a lithium-sulfur battery cell. The inventive

Battery cell has a housing and electrodes, that is at least one

Anode, which is preferably a lithium metal anode or an anode made of a lithium alloy, a carbon or a silicon-carbon composite material, and at least one sulfur cathode.

Furthermore, the battery cell according to the invention on a Separatorelement, between the electrodes, ie between the anode, that is, the negative

Electrode, and the cathode, that is, the positive electrode is arranged to separate them from each other, as well as at least one elastic reversible volume compensation element, which compensates for a potential

Volume change or the volume thrusts of the anode and / or the cathode is used. Accordingly, according to the invention is such

Volume compensating element, preferably in the form of a volume-compressible layer, between the known necessary

Battery elements such as the electrodes, in particular between the anode or cathode and separator elements introduced, or the

Volume compensation element is provided as part of the separator or as a current collector or part of a current collector of one of the electrodes of the battery cell. The volume compensation element can therefore be considered more elastic

Separator may be provided as Abieiter at the cathode and anode or as an additional element outside of the anode, separator or cathode. Depending on The design of the housing of the battery cell according to the invention, the battery cell according to the invention a hard shell battery cell, ie a so-called hardcase cell with a hard shell housing, for example made of deep-drawn aluminum, or a bag battery cell with a bag-like housing or a soft packaging, for example

Aluminum composite foil, also known as a pouch cell or soft pack.

Alternatively or in addition to the previously described embodiment, a plurality of volume compensation elements may be provided in the battery cell according to the invention, at least one of which as part of the

Separator element, at least one as a collector or part of the collector of one of the electrodes and at least one is formed as a separate component.

At least one or even each volume compensation element comprises an elastic, network-like or porous structure, which the

Volume thrusts of the electrodes when charging or discharging the

rechargeable battery cell absorbs and thus an undesirable

Total volume change of the cell can balance. The

Volume compensation element in addition to its elasticity preferably has a porosity of 5 to 95% by volume, more preferably from 20 to 80% by volume, most preferably from 30 to 70% by volume. The porous according to the invention

Volume compensation element may also receive, store and / or release a liquid electrolyte or a gel electrolyte of the battery cell. In addition, the volume compensation element can be used to dissipate heat through the housing to the outside, so perceive additional cooling functions in the form of a derivative of heat over existing metals. The

Volume compensation element may be a nonwoven, a volume nonwoven a porous membrane or a foam element. There are, inter alia, on polyimide, on polyester aramid but also on cellulose based nonwoven separators. One example is a polyimide-based separator sold under the trade name Energain® by DuPont (USA).

In a preferred embodiment of the battery cell according to the invention, the volume compensation element comprises a metal-based material, in particular aluminum, nickel, copper or stainless steel, a carbon-based material or a cellulosic, plastic or glass based material, wherein the

Volume compensation element can also consist entirely of this material. Alternatively, the volume compensation element may also comprise a composite of two or more of these materials or even consist entirely of this. In the event that the volume compensation element as

Collector or part of a collector of an electrode is provided, the glass or plastic-based materials are preferably coated over the entire surface with metal or carbon to ensure their conductivity.

The volume compensation element of the battery cell according to the invention has on at least one side surface on a conductive layer, which preferably comprises aluminum, copper, nickel, stainless steel, carbon black, graphite or graphene, or may consist entirely of this material. The by the

Volume compensating element formed volume compensating layer may further be provided on both sides with a thin, electrically conductive layer. With "side" is thereby one of the two sides of the

Volume compensation element meant, the surface of which is large compared to the surface of the remaining side surfaces of the volume compensation element. This layer is applied to the back of an electrode and could additionally serve as a current collector (synonym for collector), referred to in English in this form as "current collector foil".

The battery cell according to the invention is preferably in the form of a

Stack assembly formed, which is composed of at least the sulfur cathode, the separator element, the anode and the volume compensation element in this order. The housing preferably surrounds the

Stack assembly. One direction of the volume change is this

Arrangement in the stacking direction. The volume change therefore runs in a direction substantially perpendicular to the main surface of the individual

Battery cell elements, that is, in a so-called thickness direction of the battery cell, wherein the volume compensation element can at least partially compensate for the change in volume, preferably completely compensate. The volume change can in such an arrangement as Thickness change of the cell will be described. The necessary thickness of all volume compensation elements is in particular by the

Compressibility determined. The total compressible length of all volume compensation elements must be at least on the order of the total transferred lithium anode layer thickness.

Alternatively, the battery cell according to the invention may comprise a stacked arrangement, which is constructed at least from the sulfur cathode, the separator element and the anode in this order, wherein the compensation element is formed as part of the separator and at least partially compensates for the change in volume. The housing preferably surrounds the

Stack assembly. This will provide a functional integration of the

Volume equalization achieved directly in the separator, for which in particular separators based on polyester or preferably polyimide are suitable. Both mentioned separators are preferably nonwovens, which consist of a phase-shaped network.

In addition, could in the battery cell according to the invention another

Volume compensation element also outside the battery cell, ie outside the arrangement of anode, sulfur cathode, separator and

Volume compensation element may be arranged, preferably wherein the additional volume compensation element acts as electrical insulation. In a composite of a plurality of such battery cells, that is, a battery having a plurality of such battery cells, a corresponding additional or additional volume compensation element can also be arranged between the individual cells. In such a case, an additional function of the electrical insulation could be integrated by the volume compensation element.

According to another aspect of the invention is further a

Rechargeable lithium-sulfur battery with at least two of the

Provided previously described lithium-sulfur battery cells, wherein preferably an additional volume compensation element between the individual battery cells is arranged, which here further preferably acts as electrical insulation. Advantages of the invention

The battery cell according to the invention, in particular the volume compensation element of the battery cell according to the invention achieves a volume balance within each battery cell when charging and / or discharging the respective cell, while constant force application or pressurization in particular to the individual lithium-sulfur battery cell elements, without a significant increase in weight with it bring. It represents a significant improvement to a complex battery cell design with necessary

mechanical spring function by a corresponding metal structure or other mechanically resilient structures that initiates counteracting forces or pressure from the outside into a cell or a cell network.

Due to the low density of the volume compensation elements and the relatively low material thickness required is only a small, negligible

To expect weight gain in the total battery module. The total specific energy, ie the quotient of stored energy and mass of the total module is not significantly reduced.

The battery cell according to the invention achieved by means of the volume compensation element can in principle be used both in hardcase cells and in pouch cells, wherein in both cases the desired volume compensation is made possible inside the cell. Due to the full-surface conditioning of the volume compensation element a very constant and homogeneous distribution of force is achieved. This in turn is very advantageous for the life and cycle stability of the respective battery cell.

Short description of the drawing

Figure 1 of the present invention shows a schematic layer structure of a lithium-sulfur battery cell according to a preferred embodiment of the invention. Preferred embodiment of the invention

Figure 1 shows a preferred embodiment of the battery cell according to the invention, and more precisely the layer structure of a battery cell according to the preferred embodiment in partial cross-section.

The layer structure shown extends from the center starting on both sides in a similar structure, which is arranged overall in a housing 1, of which in the figure in the sectional view, only the two outer walls are shown, which limit the layer structure from the outside. Outwardly from the middle of the layer structure, the illustrated battery cell has a current collector 6, which discharges the current from a cathode 3, then the cathode 3 itself, a separator 4, an anode protection layer 7, an anode 2, and a volume compensation element 5 with respective ones optional current arrester coatings 51. All components of the layer structure are present in layer form, which are stacked accordingly. In the present preferred embodiment of the battery cell according to the invention, the cathode 3 has sulfur, which is preferably present in an electrically conductive mixture, for example in a carbon structure. The separator 4 is used in the layer structure as insulation and separation between the sulfur cathode 3 and the anode 2, which includes lithium here. Between the separator element 4 and the lithium anode 2, the anode protective layer 7 is arranged, which inter alia serves to protect the lithium anode 2 from the usually aggressive electrolyte and the dissolved lithium sulfides, which are further contained in the battery cell. The anode protective layer 7 can be constructed of a solid organic, inorganic or ceramic lithium-ion conductor. The volume compensation element 5 is in the present

Embodiment as a separate component and includes a cross-linked flexible aluminum structure with high porosity, for example, 80% by volume. As an alternative to the aluminum structure, the compensation element 5 also from a Carbon web be constructed, or alternatively, from polymeric materials. The porosity of the volume compensation element 5 gives it, inter alia, its desired flexibility, by which a potential

Volume change of the electrodes 2, 3 can be compensated. Further, electrolyte (not shown) contained in the battery cell can thereby be contained in the battery cell

Volume compensation element 5 is added or stored, which can be dispensed again as needed. The current conductor coatings 51 of the volume compensation element 5, which are provided as an optional component of the volume compensation element 5, in the present embodiment comprise copper or nickel layers, which conduct the current of the lithium anode 2. The housing 1 of the battery cell shown in Figure 1 is in the preferred embodiment, a part of a hard shell housing 1, in which the described layer structure is completely absorbed.

During operation of the battery cell according to the invention, volume changes of the electrodes 2, 3 may occur during their charging or discharging, as already described above. For example, during the discharge process, the metallic lithium of the anode 2 is gradually reduced and combines with the sulfur of the cathode 3 to polysulfides dissolved in the electrolyte. As the discharge progresses, the polysulfides finally precipitate as LiS ₂ and Li ₂ S in or on the porous cathode 3, resulting in a change in the volume of the electrodes 2, 3 and thus of the total cell volume. These

Operations take place when charging the battery cell in accordance with the reverse order again. In order to deposit the lithium in a dense, uniform and homogeneous manner on the anode 2, in particular when the cell is charged, a corresponding pressure on the cell or the respective electrode 2, 3 from the outside is necessary, which can be exerted by the housing 1. These volume changes of the electrodes 2, 3, which are shown in FIG. 1 in the region 91 with arrows which extend from the cathode 3 outward in the thickness direction of the battery cell, can lead to unwanted damage, inter alia, of the housing 1, for example to a regular battery cell Damage or bursting of the housing 1 and thus to an increase in pressure up to an unwanted escape of dangerous ingredients of the battery cell. Order now the occurring

To be able to compensate volume changes in the region 91, which usually meet the inclusion forces acting from the housing 1 from the outside to inside, which are represented in the region 93 by inwardly directed arrows are the volume compensation elements 5 in the battery cell according to the invention

Region 92 of the battery cell provided on the outside of the respective anode 2, which absorb the externally acting pressure forces in the range 93 and acting from the inside out expansion forces of the electrodes 2, 3 in the region 91 and thereby compensate, as shown in the region 92 by arrows is. As a result, the volume compensation element 5 can damage the

Housing 1 by occurring during charging or discharging of the battery cell expansion forces of the expanding electrodes 2, 3 prevent and thereby provide a significant safety factor for the use of lithium-sulfur battery cells.

Claims

claims

1. Galvanic battery cell, in particular lithium-sulfur battery cell, with

a housing (1),

at least one anode (2),

at least one sulfur cathode (3),

a separator element (4) arranged between the anode (2) and the cathode (3), and

at least one elastic volume compensation element (5) to compensate for a change in volume of the anode (2) and / or the cathode (3).

2. Battery cell according to claim 1, wherein the volume compensation element (5) has a porosity of 5 to 95% by volume.

3. Battery cell according to claim 1 or 2, wherein the

Volume compensation element (5) is a nonwoven, a volume fleece is a porous membrane or a foam element.

4. Battery cell according to one of the preceding claims, wherein the volume compensation element (5) is a metal-based material,

in particular aluminum, copper, nickel or stainless steel, a carbon-based material or a plastic-based or glass-based material, or a composite of two or more of these

Materials.

5. Battery cell according to one of the preceding claims, wherein the volume compensation element (5) on at least one side surface has a conductive layer (51), which preferably comprises copper, nickel, stainless steel, aluminum, carbon black, graphite or graphene. Battery cell according to one of the preceding claims, wherein the anode (2) is a lithium anode, or a lithium alloy,

Having carbon or a silicon-carbon composite material.

Battery cell according to one of the preceding claims,

wherein the battery cell has a stacked configuration composed of at least the sulfur cathode (3), the separator element (4), the anode (2) and the volume balance element (5) in this order, wherein a volume change occurs in the stacking direction and the volume compensation element (5) at least partially compensates for the volume change, or

wherein the battery cell has a stacked arrangement composed of at least the sulfur cathode (3), the separator element (4) and the anode (2) in this order, wherein a

Volume change occurs in the stacking direction, the

Volume compensation element (5) is formed as part of the separator element (4) and at least partially compensates the change in volume.

Battery cell according to one of the preceding claims, wherein the battery cell has an additional volume compensation element which is arranged outside the arrangement of anode (2), sulfur cathode (3), separator element (4) and volume compensation element (5), preferably wherein the additional volume compensation element as electrical insulation works.

Battery cell according to one of the preceding claims, wherein at least one volume compensation element (5) receive, store and / or can discharge electrolyte, and / or at least one volume compensation element (5) for dissipating heat via the housing (1) to the outside.

Battery cell according to one of the preceding claims, wherein the battery cell is a hard-shell battery cell or a bag battery cell. Rechargeable lithium-sulfur battery with at least two of the lithium-sulfur battery cells according to any one of the preceding claims, wherein preferably an additional

Volume compensation element is disposed between the individual battery cells, wherein the additional volume compensation element further preferably acts as electrical insulation.