ION-EXCHANGE BATTERY WITH A PLATE CONFIGURATION CROSS REFERENCE TO RELATED APPLICATIONS [0001] The present application claims priority under the Paris Convention to US Application Number 61/434,959, filed January 21 , 201 1 , the entire contents of which are incorporated herein by reference. FIELD OF THE INVENTION [0002] The present invention relates to a secondary battery. In particular, the invention relates to an ion exchange secondary battery having a plate configuration. BACKGROUND OF THE INVENTION [0003] Since the invention of lead-acid batteries, the energy storage and conversion industry has entered the "secondary battery times". As known in the art, a "secondary battery", also referred to as a rechargeable battery, is a battery wherein the internal electrochemical reactions are reversible. Various kinds of secondary batteries are applied in different fields depending on their specific requirements. For example, portable electronic devices require a battery with a high energy density as in lithium ion (Li-ion) batteries, electric tools require a high power output as in Li-ion, Ni-MH, and Ni-Cd batteries, and large energy storage applications (such as a UPS), motor start-up batteries, wind power/solar energy storage devices all require batteries with low cost and long service life. [0004] Lead-acid batteries have been occupying the majority of the battery market share, especially among energy storage fields for several decades. But this fact should not conceal many disadvantages of the lead-acid batteries, in particular, the lead pollution problem associated with its manufacture, battery recall and recycle after use, short service life (typically 2 years), and low energy density. It is necessary to find a new battery, which comes with low cost, long service life, environment friendly and good safety characteristics, to replace the present lead-acid batteries. Although the current Li-ion and Ni-MH batteries have better performance than lead-acid batteries in energy density, power density, service life and environment aspects, they still cannot replace the lead-acid batteries mainly because of the cost.
[0005] To solve this problem, many researchers turned to aqueous Li-ion battery, hoping to use water based electrolytes in place of organic electrolytes and drastically reduce the cost of Li-ion batteries, and also to solve the safety problem with Li-ion batteries. In 1994, Jeff Dahn et al. presented an aqueous battery with LiMn204 as the cathode material, vanadium oxide such as V02 as the anode material, and a water solution of lithium salts as the electrolyte [LI W., DAHN J.R., WAINWRIGHT D.S., Science, 264 (1994), 1 1 15]. Up to now, all reported aqueous Li-ion batteries used the same principle as the Li-ion battery, based on an embedded type structure on both positive and negative electrodes, such as LiMn204/V02, LiNi0 8iCoo i902/LiV308, LiM^O^TiP^, LiMn204/LiTi2(P04)3, and
LiCo02/LiV308. A further example of such batteries is provided in US Patent Number 7, 189,475. However, all these batteries have a low energy density and poor cycle life, because of the decomposition of the intercalation anode materials during charging and discharging in the aqueous solution (i.e. water). [0006] A need exists for an improved aqueous secondary battery that can replace current lead-acid batteries. SUMMARY OF THE INVENTION [0007] Accordingly to one aspect, the invention provides a rechargeable battery consisting of a cathode electrode, an anode electrode and an electrolyte. [0008] In one aspect, the invention provides a rechargeable battery comprising a shell and a cover, the shell containing: [0009] - at least one cathode plate, comprising a current collector, a cathode active material, a binder and a conductive agent; [0010] - at least one anode plate comprising an electrically conductive and electrochemically inert material; [0011] - an electrolyte comprising a solution of at least one metal salt, wherein the metal is capable of being reduced and deposited onto the surface of the anode during charging of the battery and oxidized and dissolved into the electrolyte during discharging of the battery.
BRIEF DESCRIPTION OF THE DRAWINGS [0012] The features of the invention will become more apparent in the following detailed description in which reference is made to the appended drawings wherein: [0013] Figure 1 shows a schematic of a cathode electrode according to one aspect of the invention. [0014] Figure 2 shows a schematic of an anode electrode according to one aspect of the invention. [0015] Figure 3 shows a schematic of a cover of the battery according to one aspect of the invention. [0016] Figure 4 shows a schematic of a cathode electrode according to the embodiment illustrated in Example 1 . [0017] Figure 5 shows a schematic of the anode electrode according to the embodiment illustrated in Example 1 . [0018] Figure 6 shows a schematic of the battery structure according to the embodiment illustrated in Example 1 . [0019] Figure 7 shows the charge and discharge curve of the battery of Example 1 . [0020] Figure 8 shows the cyclability curve of the battery in Example 1 . DETAILED DESCRIPTION OF THE INVENTION [0021] The terms "comprise", "comprises", "comprised" or "comprising" may be used in the present description. As used herein (including the specification and/or the claims), these terms are to be interpreted as specifying the presence of the stated features, integers, steps or components, but not as precluding the presence of one or more other feature, integer, step, component or a group thereof as would be apparent to persons having ordinary skill in the relevant art. [0022] In one aspect, the present invention relates to a structure design of a novel secondary battery, based on the principle of ion-exchange in the electrolyte. Such battery is referred to herein as an Ion-Exchange Battery (IEB).
[0023] In one aspect of the present invention, as illustrated in the accompanying figures, there is provided a battery 300 having a plate structure comprising a positive electrode or cathode 310, a negative electrode or anode 320, an electrolyte 340 and separator 330. [0024] As shown in Figure 1 , the positive electrode 310 comprises a current collector 31 1 , cathode active materials 312, at least one binder 313 and at least one conductive agent or material 314. In a preferred embodiment of the invention, the cathode active materials 312 comprise lithium (Li) and/or sodium (Na) intercalation cathode materials. [0025] A negative electrode 320 according to an aspect of the invention is illustrated in Figure 2. As shown, the negative electrode 320 generally comprises an electrically conductive and electrochemically inert plate 321 with a plating or coating layer 322. [0026] The electrolyte according to one aspect of the invention comprises a solution, preferably an aqueous solution, of metal salts. The solvent may comprise water, ethanol, methanol or mixtures thereof. The metal salts comprise at least one sort of metal ion, which can be reduced and deposited onto the surface of the anode plate 322 during charging, and oxidized and dissolved into the electrolyte during discharging. [0027] As illustrated in Figure 6, the electrodes 310, 320 of the invention preferably have a generally plate shape, and are preferably electrically separated from each other by a separator 330. In a preferred embodiment of the invention, the separator 330 comprises a generally porous membrane. The electrodes 310, 320 and separator 330 are packed in a shell 380, casing or other such container as will be known to persons skilled in the art. The shell 380 may, for example, be formed of a plastic or metal material. A cover 360 is preferably provided on the shell 380, in order to separate the internal components of the battery from the external environment. In a preferred embodiment, the cover 360 may be insulative. The cathode current collector 31 1 and the negative (anode) electrode 320 are connected through the cover 360 with the output circuit, 316 and 326. [0028] In another aspect, as shown in Figure 3, the cathode current collector 31 1 may penetrate through the cover 360. In such case, a cap 31 16 may be provided over the exposed ends of the collectors 31 1 . Various materials may be used to form the cap 31 16. For example, the cap 31 16 may be formed from graphite, conductive plastics, Pb, Sn or an alloy of such metals. [0029] In one preferred embodiment, as shown in Figure 6, the battery may be provided with a pressure limiting, or pressure relief means, as known in the art, which serves to
prevent a pressure buildup inside the battery 300. In one aspect, the pressure relief means comprises a pressure relief valve 370. The valve 370 may be provided at any location on the battery as would be apparent to persons skilled in the art. In one aspect, the valve 370 may be located on the cover 360 as shown in Figure 6. [0030] The lithium ion intercalation compounds of the cathode active material may comprise layered structure compounds, spinel structure compounds or olivine structure compounds. The layered structure compounds may be represented by the compositional formula Li1+xMyM'zM"c02+n, where each of M, M', M" represents an element selected from Ni, Mn, Co, Mg, Ti, Cr, V, Zn, Zr, Si, Al, and where x, y, z, c, n individually satisfy the following relationships: 0< x <0.5, 0< y <1 , 0< z <1 , 0 <c <1 , and -0.2< n <0.2. The spinel structure compounds may be represented by the compositional formula Li1+xMnyMzOk, where M is at least one element selected from Na, Li, Co, Mg, Ti, Cr, V, Zn, Zr, Si, Al, and where x, y, z, k individually satisfy the following relationships: 0< x <0.5, 1 < y <2.5, 0< z <0.5, and 3< k <6. The olivine structure compounds may be represented by the compositional formula LixM-|. yM'y(XO4)n, where: M is an element selected from Fe, Mn, V, Co; M' is at least one element selected from Mg, Ti, Cr, V, Al, Co; X' is selected from S, P and Si; and, x, y and n individually satisfy the following relationships: 0< x <2, 0< y <0.6, 1 < n <1.5. [0031 ] According to one embodiment, the invention comprises a LiMn204/Zn battery with LiMn204 as the cathode active material, tin plated copper film/foil as the anode, and 5 mol/L ZnCI2 as the electrolyte. In such example, during charging, Li+ ions deintercalate from the spinel crystal lattice of LiMn204, while trivalent manganese is oxidized to tetravalent manganese with an accompanying electron output. In this example of the invention, LiMn204 turns to Li-|.x Mn204 and Zn2 + ions in the electrolyte are reduced to a metallic state and are deposited on the anode surface. When the battery is charging (as shown in Figure 2), the reaction at the cathode is LiMn204-xe~→ Li+ + Li-|.xMn204, and the reaction at the anode is Zn2 + + xe"→ (x / 2) Zn. The discharging process reverses these reactions. [0032] In the current lithium battery industry, almost all cathode materials are doped, coated, or modified by various methods. For example, LiMn204 is no longer able to represent the general formula of a "lithium manganese oxide" that is widely used. Strictly, the general formula of the material should be according to the general formula of the spinel structure compound that the present invention involves. However, doping, coating and other modifications cause the chemical formula of the material to be more complex, so the formula LiMn204 should include the cathode materials of a variety of modifications, and be consistent
with the general formula of the spinel structure compounds, as described in the present invention. The chemical formula of LiFeP04, and other materials described herein, will be understood to include the materials of a variety of modifications and to be consistent with the general formulae of layered structure, spinel structure or olivine structure compounds. [0033] In one aspect of the invention, the cathode active material comprises a material that can reversibly intercalate-deintercalate. Such compounds include those that are able to intercalate-deintercalate lithium, sodium and other ions. When the cathode active material is a lithium ion intercalation-deintercalation compound, it can preferably be selected from, for example, LiMn204, LiFeP04, LiCo02, LiMxP04, LiMxSiOy (where M is a metal with a variable valence, x) and other compounds. When the cathode active material is a sodium ion intercalation-deintercalation compounds, it can be, for example, NaVP04F. [0034] The cathode current collector of the invention may be selected from a stainless steel mesh or foil, graphite plate or foil, carbon fiber or a combination thereof. The thickness of the collector is between 0.01 mm and 50 mm. [0035] The anode electrode 320 of the invention may comprise a flat or porous plate with a thickness between 0.001 mm and 5 mm. The plate may comprise a material selected from carbon based materials, stainless steel, and metals or metal combinations, alloys etc., and combinations thereof. The plate forming the anode is preferably electroplated or coated by one of C, Sn, In, Ag, Pb, Co, and Zn. [0036] In one embodiment, the separator 330 is preferably a porous membrane having a pore size between 0.01 and 1000 microns and a porosity of 20 - 95%. [0037] In one aspect, the electrolyte of the present ion-exchange battery contains at least one sort of metal ion chosen from: Zn, Ni, Fe, Cr, Cu and Mn and combinations thereof. In operation of the battery of the invention, the metal ion of the electrolyte is reduced and deposited onto the surface of the anode during the charging phase. During the discharge phase, the above reaction/process is reversed. That is, during discharge, the metal deposited on the surface of the anode is oxidized and returned to its ionic state in the electrolyte solution. The solvent of the electrolyte is preferably water or an aqueous solution. For example, the solvent may comprise water, ethanol, methanol, or any mixture thereof. In one aspect, the concentration of the metal dissolved in the solvent may be 0.5-15 mol/L. [0038] According to one embodiment of the invention, the electrolyte comprises an aqueous solution comprising LiCI, Li2S04, LiN03, ZnCI2, ZnS04, Zn(N03)2 or any
combination thereof. In one aspect, the electrolyte comprises a solution containing 1 mol/L LiCI, or Li2S04, LiN03, and 4 mol/L ZnCI2, or ZnS04, or Zn(N03)2. [0039] To accelerate the rate of ion exchange, additional Li or Na salts may be added to the electrolyte. In such case, these salts may be added to any desired concentration, such as 1 -15 mol/L. [0040] Without being restricted to any particular theory, the working principle of the present ion-exchange battery is described below: during the charging process, Li/Na ions within the cathode deintercalate into the electrolyte while, simultaneously, the metal ions contained in the electrolyte are reduced and deposited onto the surface of the anode. The discharging process reverses these reactions. Thus, according to the invention, an ion exchange process takes place in the electrolyte. For this reason, the battery is termed an ion-exchange battery (IEB). [0041] Again, without limiting the invention in any way, the principle of the battery of the invention is: when charging, the cathode active material reacts, where Li (HOST)- e"→ Li + + (HOST), and the anode presents Mx+ + xe"→ M. Li (HOST) is a lithium ion intercalation compound; M is a metal; Mx+ is the ionic state of M. If the cathode active material is a sodium ion intercalation compound, the cathode active material reacts with Na (HOST)-e"→ Na + + (HOST), and the anode presents Mx + + xe~→ M when charging. [0042] As shown in Figure 6, the present invention also provides a battery pack, comprising a number of plate ion-exchange battery units 300 connected in parallel. For example, 2 to 10 such units may be connected. However, the invention is not intended to be limited to any specific number of units. [0043] According to the present description, the invention provides plate shaped ion- exchange batteries having a number of suitable combinations of the cathodes, anodes and electrolytes. [0044] As described herein, the present invention comprises new battery system, wherein the cathode active material comprises ion intercalation/deintercalation compounds. The electrochemical reversibility of the cathode relies on the intercalation (during charging of the battery) and deintercalation (during discharging of the battery) of ions to/from the cathode active material. The electrochemical reversibility of the anode relies on a metal ion being reduced (during charging of the battery) and oxidized (during discharging of the battery) on the surface of the anode plate.
[0045] In a preferred embodiment, the electrolyte of the invention contains both the deintercalated ions of the cathode active material and the ion that deposits/dissolves to/from the anode surface. [0046] As discussed above, the cathode of the invention comprises at least a cathode current collector, one or more cathode active materials, one or more binders, and one or more conductive agents. The cathode current collector preferably comprises a composite material that may use carbon based conductive materials. Different carbon or carbon composite materials have different electrical properties. For example, graphite and conductive carbon fibre are both good electronic conductors, and also have excellent structural strength. As such, these materials can be used as a cathode current collector in the present invention. In addition, by mixing the conductive carbon black and a binder, such as PVDF (polyvinylidene fluoride), polyethylene, polypropylene, uniformly and heat treating, the conductive material can be made with both good electronic conductivity and flexibility. Such a conductive material is found to have suitable properties for use as a cathode collector for the invention. [0047] In a preferred embodiment, the cathode active material are mixed with the cathode conductive agent and binder uniformly, and are then coated onto the current collector. To obtain a desired energy density, the current collector should not be too thick; the preferred range of the thickness is between 0.01 mm - 5 mm. To facilitate electrolyte infiltration and to ensure good mobility of intercalation ions, the coating of the cathode active material should not be thick, and the preferred range of such thickness is between 0.1 mm - 10 mm. As mentioned above, a cathode structure according to the invention is shown in Figure 1 . [0048] The anode structure consists mainly of an anode plate. In principle, any material that has good conductivity and sufficient chemical stability can be used as the anode plate. For example, Al, Fe, Ni, Cu, Ag, Cd, W, Au, Pb, Sn, stainless steel and graphite, and combinations of same, can be used for making an anode plate according to the invention. Considering conductive resistance, structural strength and weight, the preferred thickness of the anode plate should be between 0.005 - 1 mm. [0049] To protect the anode plate, improve the overpotential of hydrogen evolution on the surface of the plate, and enhance the current efficiency of the anode, the anode surface is preferably covered with a layer of metal or metal oxide by a process such as plating, coating, etc. The material for the plating or coating is selected from at least one of Sn, Ag,
Pb, Co, Zn, and their oxide powders. The thickness of the plating or coating is preferably between 0 - 0.1 mm. As mentioned above, an anode structure according to the invention is shown in Figure 2. [0050] The cathode of the battery is preferably porous, made of powder, and has a high- current discharge capability. But the anode, which comprises a plate or foil of carbon or of the aforementioned metals, is flat, and its specific area may be limited. For example, if the surface of the anode is porous, the specific area will be high and, as such, the anode would have better electrochemical properties and a higher current discharge capability. [0051] The present inventor has found that using metal foam as the anode substrate, and further plating suitable material thereon, can improve the discharge performance of the anode. For example, an anode comprised of a nickel foam material with silver plated thereon was found to have better discharge performance than nickel foam itself. [0052] The electrolyte of the invention preferably includes at least one kind of metal ion that proceeds with reduction-oxidation reactions on the surface of the anode during charge and discharge, respectively. For example, with LiMn204 as the cathode active material, the electrolyte preferably contains Zn2+ ions, and the zinc salt may be chosen from the sulfate or chloride. In such case, the preferred concentration of Zn2+ in the electrolyte is about 4 - 6 mol/L. [0053] The cathode, anode, separator membrane and electrolyte can be placed in a special container, such as discussed above and as shown in the appended figures. As will be understood, the cathode and anode need to be connected to an external circuit, to provide an electron conducting channel. [0054] In one embodiment of the invention, as illustrated in Figure 3, the current collectors 31 1 of the cathodes extend externally of the shell 380 and run across the battery cover 360. It will be understood that the apertures in the cover 360 through with the current collectors 31 1 extend are preferably sealed in a suitable manner. In the illustrated embodiment, the anodes 320 also extend through the cover 360 and run across same to connect with the external circuit. As shown in Figure 3, the anode plate can be connected to the external circuit wires by welding or other methods inside or outside the battery. [0055] As shown in Figure 3 and as discussed above, the portions of the cathode current collectors 31 1 extending through the battery cover 360 are preferably sealed with a protective cover or cap 31 16 that has good electrical conductivity and is chemically stable.
The role of the protective cap 31 16 is to prevent water in the electrolyte of the battery from evaporating out through the opening through which the cathode current collectors extend. In the result, the caps 3116 aid in preventing the corrosion of the external circuit wires and the cathode current collectors. The preferred materials of the protective caps 31 16 are impermeable graphite, conductive plastics, lead alloy, etc. Various materials having the aforementioned properties will be apparent to persons skilled in the art. [0056] As will be understood by persons skilled in the art, all features described herein can be replaced by features that can provide the same, equal or similar purposes.
Therefore, unless otherwise stated, the features disclosed herein are only the general features of equal or similar examples. [0057] As will be understood by persons skilled in the art after having reviewed the present description, the main advantages offered by the present invention include one or more of: 1) desirable qualitative characteristics such a battery providing good
electrochemical performance, environmental safety, and/or low-cost; 2) a battery having a simple structure, which facilitates manufacturing time/cost and provides high reliability; and 3) a battery that can be widely used, including replacing the current lead-acid batteries. [0058] Examples [0059] Aspects of the present invention are described below by means of various illustrative examples. The examples contained herein are not intended to limit the invention in any way but to illustrate same in more detail. It should be understood that the experiments in the following examples, unless otherwise indicated, are in accordance with conditions as would be known to persons skilled in the art or the conditions recommended by manufacturers. Unless indicated otherwise, all percentages, ratios, proportions referred to in the examples are calculated by weight. [0060] Example 1 [0061] The cathode active material LiMn204, conductive carbon black and SBR (styrene butadiene rubber milk) were mixed uniformly in accordance with the proportion of 85:10:5, and then the mixture was added into water to make slurry. The cathode current collector comprised a graphite plate with a thickness of 1 mm; the slurry was coated onto the graphite plate and dried at 105 °C for 10 hours. The active material coated on each graphite plate was 5 g, and the total amount of the cathode active material was 20 g, with a theoretical capacity of 2000 mAh. The configuration of the cathode is shown in figure 4.
[0062] The anode of the battery comprised a copper foil with a thickness of 0.1 mm, and had the configuration as shown in Figure 5. The size of the anode substrate was slightly larger than that of the cathode, so that the full capacity of the cathode could be used and the current distribution at the edge of the anode would be uniform. The copper foil was covered by a certain thickness of plating/coating to enhance the adhesion properties of metal reduced from metal ions in the electrolyte. In this example, the surface of the copper foil was coated with a layer of tin by plating, and the thickness of the tin plating was about 0.01 mm. [0063] The separator membrane of the battery was a non-woven material with a thickness of 0.1 mm. [0064] The battery was formed with five anode plates and four cathode plates in alternating fashion. The adjacent anode and cathode electrodes were separated by a layer of the non-woven membrane. The assembled electrodes were placed in a plastic battery shell, and then 20 ml of electrolyte was injected. The cathode current collector and anode plate was allowed to extend through the battery cover, and were sealed by a binder. [0065] The electrolyte comprised a water solution containing 4 mol/L LiCI and 4.5 mol/L ZnCI. When charging, Li+ ions deintercalated from the cathode and dissolved into the electrolyte with electron output through the current collector; meanwhile Zn2+ ions in the electrolyte were reduced and electrodeposited on the surface of the anode. For maintaining the concentration of Zn2+ in the electrolyte after charging, the amount of Zn2+ in the electrolyte was chosen to be more than the amount of Zn on the anode plate after charging. In this example, 0.09 mol Zn2+ was provided in the electrolyte. This amount was based on a calculation that, at 2 Ah, there would be 0.035 mol Zn2+ consumed during charging. The concentration of Zn2+ in the electrolyte after charging is 2.75 mol/L. [0066] Small amounts of gas would be expected to be generated during charging. Such gas is due to decomposition of water to hydrogen and oxygen. Some of this gas can be expected to diffuse to the opposite electrode and be converted back to water. Nevertheless, an anti-explosion valve (pressure valve) would be provided on the battery cover to prevent the explosion caused by the inner pressure of the battery. It is also expected that the gas generation resulted in the charge-discharge current efficiency of the battery to be less than 100%. The voltage-capacity curve of the first charge and discharge is shown in Figure 7, wherein the y axis shows voltage and the x axis shows time. As shown in Figure 7, the
charge voltage of this battery is about 2V on average and the discharge voltage is about 1 .8V. As shown in Table 1 , the first charge-discharge current efficiency is 93%.
[0067] As shown in Figure 8, the discharge capacity of the above battery shows no decay after 100 cycles. [0068] Example 2 [0069] A battery was made according to a method similar to that of Example 1 .
However, in this case, the anode plate comprised a tin plated nickel foam, of the same size as the anode plate of Example 1 . Using nickel foam as the skeleton for the anode provides an increased specific area than a metal plate/foil, and the tin plating provides a better interface for the electrodeposition of Zn. The performance of the battery according to this example is shown in Table 1 . [0070] Example 3 [0071] A battery was made according to a method similar to that of Example 1 .
However, in this case, the anode plate comprised 316L stainless steel. The thickness of the stainless steel plate was 0.5 mm. The surface of the stainless steel was passivated with concentrated sulfuric acid and then sanded rough with abrasive paper. The performance of the battery according to this example is shown in Table 1 .
[0072] Table 1
[0073] Although the invention has been described with reference to certain specific embodiments, various modifications thereof will be apparent to those skilled in the art without departing from the purpose and scope of the invention as outlined in the claims
appended hereto. Any examples provided herein are included solely for the purpose of illustrating the invention and are not intended to limit the invention in any way. Any drawings provided herein are solely for the purpose of illustrating various aspects of the invention and are not intended to be drawn to scale or to limit the invention in any way. The disclosures of all prior art recited herein are incorporated herein by reference in their entirety.