Electrolyte and battery
By using additives with fully conjugated structures in the electrolyte to generate free radical cations that participate in SEI film formation, the high cost and stability issues of existing non-in-situ SEI preparation methods are solved, and the high-efficiency cycle performance of the battery is improved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- BYD CO LTD
- Filing Date
- 2021-09-27
- Publication Date
- 2026-06-09
Smart Images
Figure QLYQS_1 
Figure BDA0003282541420000021 
Figure BDA0003282541420000031
Abstract
Description
Technical Field
[0001] This application relates to the field of electrolyte technology, specifically to an electrolyte and a battery. Background Technology
[0002] In lithium-ion batteries, after the negative electrode and electrolyte come into contact, a passivation layer (SEI film) forms on the surface of the negative electrode. This passivation film hinders further reactions between the negative electrode and the electrolyte, giving lithium batteries low self-discharge rates and long storage life. Currently, SEI preparation mainly includes two categories: in-situ SEI and non-in-situ SEI. In-situ SEI is generally formed on the negative electrode surface in situ using electrolyte components through electrochemical reactions. Non-in-situ SEI is generally formed by coating the negative electrode surface with materials through physical contact or chemical reactions.
[0003] Existing methods for preparing artificial SEIs (Sediment-In-Situ) utilize low-temperature atomic layer deposition (ALD) to deposit amorphous LiF onto the anode, forming an artificial SEI. Amorphous LiF is both an electronic insulator and an ionic conductor, and as an artificial SEI, it can suppress dendritic and filamentary growth. However, ALD is costly and inefficient, hindering large-scale fabrication. Furthermore, the interaction between this artificially generated SEI and the anode is weak, making it prone to defects in later stages of cycling, leading to rapid performance degradation.
[0004] Existing in-situ SEI preparation methods utilize functional polyurethane-conductive polymer cross-linked network polymers as artificial SEI films to coat silicon and graphite particles. These artificial SEI films possess high modulus and high toughness, effectively suppressing the cyclic expansion of silicon or graphite, and also exhibit high ionic conductivity. However, the polyurethane-conductive polymer cross-linked network polymers are prone to swelling in the electrolyte, and long-term cycling can lead to detachment from the negative electrode, resulting in the loss of the protective function of the artificial SEI. Summary of the Invention
[0005] To address the problem of unstable performance of the SEI film formed in existing electrolytes, this application provides an electrolyte and a battery.
[0006] The technical solution adopted in this application to solve the above-mentioned technical problems is as follows:
[0007] This application provides an electrolyte comprising an electrolyte salt, a solvent, and an additive, wherein the additive comprises a first additive having a structural formula as shown in formula (1):
[0008]
[0009] In formula (1), m is 0, 1 or 2; n is 1 or 2; g is an integer from 1 to 8; R is selected from one of a single bond, a substituted or unsubstituted C1 to C10 alkyl group, or a substituted or unsubstituted C6 to C12 aromatic group; R1 and R2 are each independently selected from one of a substituted or unsubstituted C1 to C10 alkyl group or a substituted or unsubstituted C6 to C10 aromatic group; X is an anion.
[0010] Optionally, in formula (1), m is 1 or 2; n is 1 or 2; g is an integer from 1 to 8; R is selected from one of substituted or unsubstituted C1 to C10 alkyl groups or substituted or unsubstituted C6 to C12 aryl groups; R1 and R2 are each independently selected from one of substituted or unsubstituted C1 to C10 alkyl groups or substituted or unsubstituted C6 to C10 aromatic groups; X is an anion.
[0011] Optionally, R1 and R2 are each independently selected from one of the following: a C1-C10 alkyl group, a C6-C10 aromatic group, a C1-C10 alkyl group containing hydroxyl, halogen, carbonyl or carboxyl substituents, or a C6-C10 aromatic group containing hydroxyl, halogen, carbonyl or carboxyl substituents.
[0012] Optionally, substituted or unsubstituted aromatic groups include benzene, biphenyl, and trialkyl-substituted benzene.
[0013] Optionally, X is selected from PF6 - ClO4 - and BF4 - One or more of the following.
[0014] Optionally, the first additive is selected from one or more of methyl viologen hexafluorophosphate, p-phenylenedimethyl viologen hexafluorophosphate, biphenylenedimethyl viologen hexafluorophosphate, and 1,3,5-trimethyl viologen benzene hexafluorophosphate.
[0015] Optionally, the mass percentage of the first additive is 0.1% to 5% based on the total mass of the electrolyte (100%).
[0016] Optionally, the additive further includes a second additive selected from one or more of fluoroethylene carbonate, vinylene carbonate, and 1,3-propanesulfonate lactone.
[0017] Optionally, the second additive has a mass percentage content of 0.1% to 15%.
[0018] Optionally, the second additive includes fluoroethylene carbonate, vinylene carbonate and 1,3-propanesulfonate lactone, wherein the mass ratio of fluoroethylene carbonate, vinylene carbonate and 1,3-propanesulfonate lactone is 10:(0-1):(0-4).
[0019] Optionally, the solvent is selected from one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, and ethyl butyrate.
[0020] Optionally, the electrolyte salt is selected from one or more of lithium hexafluorophosphate, lithium bis(oxalato)borate, lithium bis(trifluoromethanesulfonyl)imide, and lithium bis(difluorosulfonyl)imide.
[0021] On the other hand, this application also provides a battery, including a positive electrode, a negative electrode, and the electrolyte.
[0022] Optionally, the negative electrode includes a negative electrode active material, a conductive agent, and a binder. The negative electrode active material is selected from one or more of carbon-based, silicon-based, silicon suboxide-based, tin-based, and phosphorus-based materials. The conductive agent is selected from one or more of acetylene black, super P, and Ketjen black. The binder is selected from one or more of polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene-butadiene rubber, and polyacrylic acid.
[0023] According to the electrolyte provided in this application, the viologen unit contained in the first additive of the structural formula shown in formula (1) has a fully conjugated structure and is electron-deficient, making it easy to gain electrons and be reduced. It can be electrochemically reduced to generate free radical cations, and its reduction potential is higher than that of commonly used solvents and additives, so it can be preferentially reduced. The conjugated structure is beneficial to improving the stability and lifetime of free radical cations. Free radical cations polymerize to form oligomers, which participate in the formation of the SEI film. At the same time, the conjugated structure is beneficial to improving the interfacial stability between the oligomers and the negative electrode through π-π interactions. The SEI film formed in situ has a stronger interaction with the negative electrode, which improves the mechanical strength, ion conduction performance and stability of the SEI film, thereby improving the cycle stability of the battery. Detailed Implementation
[0024] To make the technical problems, technical solutions, and beneficial effects solved by this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.
[0025] This application provides an electrolyte comprising an electrolyte salt, a solvent, and an additive, wherein the additive comprises a first additive having a structural formula as shown in formula (1):
[0026]
[0027] In formula (1), m is 0, 1 or 2; n is 1 or 2; g is an integer from 1 to 8; R is selected from one of a single bond, a substituted or unsubstituted C1 to C10 alkyl group, or a substituted or unsubstituted C6 to C12 aromatic group; R1 and R2 are each independently selected from one of a substituted or unsubstituted C1 to C10 alkyl group or a substituted or unsubstituted C6 to C10 aromatic group; X is an anion.
[0028] In this embodiment, as shown in formula (2), the first additive in the structure shown in formula (1) contains viologen units, which are fully conjugated and have electron-deficient characteristics, making them easy to gain electrons and be reduced. They can be electrochemically reduced to generate free radical cations, and their reduction potential is higher than that of commonly used solvents and additives, so they can be preferentially reduced. The conjugated structure is beneficial to improving the stability and lifetime of free radical cations. As shown in formula (3), free radical cations polymerize to form oligomers, which participate in the formation of the SEI film. At the same time, the conjugated structure is beneficial to the oligomers and the negative electrode through π-π interactions to improve interfacial stability. The SEI film formed in situ interacts more strongly with the negative electrode, improving the mechanical strength, ion conduction performance and stability of the SEI film, thereby improving the cycle stability of the battery.
[0029]
[0030] In some embodiments, in formula (1), m is 1 or 2; n is 1 or 2; g is an integer from 1 to 8; R is selected from one of substituted or unsubstituted C1 to C10 alkyl groups or substituted or unsubstituted C6 to C12 aryl groups; R1 and R2 are each independently selected from one of substituted or unsubstituted C1 to C10 alkyl groups or substituted or unsubstituted C6 to C10 aromatic groups; X is an anion.
[0031] In some embodiments, R1 and R2 are each independently selected from one of the following: a C1-C10 alkyl group, a C6-C10 aromatic group, a C1-C10 alkyl group containing a hydroxyl, halogen, carbonyl, or carboxyl substituent, or a C6-C10 aromatic group containing a hydroxyl, halogen, carbonyl, or carboxyl substituent.
[0032] In some embodiments, the substituted or unsubstituted aromatic groups include benzene, biphenyl, and trialkyl-substituted benzene. The selected aromatic groups are all conjugated structures, which is beneficial for improving the stability and lifetime of the free radical cation.
[0033] In some embodiments, X is selected from PF6. - ClO4 - and BF4 - One or more of the following. The selected anion is consistent with the commonly used lithium salt anion, which is conducive to the formation of an inorganic-rich SEI.
[0034] In some embodiments, the first additive is selected from one or more of methyl viologen hexafluorophosphate, p-phenylenedimethyl viologen hexafluorophosphate, biphenylenedimethyl viologen hexafluorophosphate, and 1,3,5-trimethyl viologenbenzene hexafluorophosphate. The structural formula of methyl viologen hexafluorophosphate is shown in formula (4), the structural formula of p-phenylenedimethyl viologen hexafluorophosphate is shown in formula (5), the structural formula of biphenylenedimethyl viologen hexafluorophosphate is shown in formula (6), and the structural formula of 1,3,5-trimethyl viologenbenzene hexafluorophosphate is shown in formula (7). The selected substances have conjugated structures, which is beneficial for improving the stability and lifetime of free radical cations and does not introduce adverse side reactions.
[0035]
[0036] The synthesis process of methyl viologen hexafluorophosphate (MV(PF6)2) is as follows: methyl viologen chloride dihydrate (MVCl2·2H2O) and ammonium hexafluorophosphate (NH4PF6) are dissolved in water at a molar ratio of 1:2, stirred and refluxed to obtain a clear solution, cooled and filtered to obtain a solid powder, and vacuum dried to obtain methyl viologen hexafluorophosphate.
[0037] The synthesis process of hexafluorophosphate p-phenylenediol (BMV(PF6)2) is as follows: 2,4-dinitrochlorobenzene and 4,4'-bipyridine are added to acetone solvent, and the mixture is heated to reflux to produce a solid. The solid is cooled and filtered, washed with acetone, and the solid is then heated to reflux with acetone, filtered while hot, and dried to obtain Zincke salt.
[0038] Zincke salt and p-phenylenediamine were heated under reflux in ethanol, cooled, and filtered. The filter cake was dissolved in methanol and added dropwise to acetone, causing a precipitate to form. The precipitate was filtered, washed, and dried. The dried precipitate was then heated under reflux in acetonitrile with iodomethane to produce a solid intermediate. This intermediate was cooled to room temperature, filtered, washed with acetone, and dried. The intermediate was dissolved in water, and ion exchange was performed with NH4PF6. After stirring, filtration, washing with water, and drying, the target product, p-phenylenediamine hexafluorophosphate, was obtained.
[0039] The synthesis of biphenyl dimethyl viologen hexafluorophosphate is as follows: Zincke salt and 4,4'-biphenyldiamine are heated to reflux in ethanol, cooled to room temperature, filtered, washed with acetone, and the filter cake is dissolved in anhydrous methanol. NH4PF6 is added, stirred, filtered, and the filter cake is washed with acetone and dried. The resulting filter cake is heated to reflux in acetonitrile with iodomethane, cooled, filtered, and the solid intermediate is washed with acetone and dried. The intermediate is dissolved in water, and NH4PF6 is added for ion exchange. The mixture is stirred, filtered, washed with water, and dried to obtain the target product, biphenyl dimethyl viologen hexafluorophosphate.
[0040] The synthesis of 1,3,5-trimethylviolinbenzene hexafluorophosphate is as follows: 4,4'-bipyridine and 1,3,5-tribromomethylbenzene are heated under reflux in acetonitrile, cooled, filtered, washed with acetonitrile, and the resulting solid is dissolved in water. NH4PF6 is added, stirred, filtered, and the filter cake is dried. The resulting filter cake is heated under reflux in acetonitrile with iodomethane, cooled to room temperature, filtered, and the solid intermediate is washed with acetone and dried. The intermediate is dissolved in water, and NH4PF6 is added for ion exchange. The mixture is stirred, filtered, washed with water, and dried to obtain the target product, 1,3,5-trimethylviolinbenzene hexafluorophosphate.
[0041] In some embodiments, the mass percentage of the first additive is 0.1% to 5% based on the total mass of the electrolyte (100%).
[0042] If the content of the first additive is too low, its effect on improving battery performance will be insignificant. If the content of the first additive is too high, it will lead to a decrease in battery cycle performance and increase costs.
[0043] In some embodiments, the additive further includes a second additive selected from one or more of fluoroethylene carbonate (FEC), vinylene carbonate (VC), and 1,3-propanesulfonate lactone (PS). Adding the second additive improves the oxidative stability of the battery, protects the negative and positive electrodes, and also has a synergistic effect with the first additive, improving the battery's cycle stability and enhancing the protection effect.
[0044] In some embodiments, the mass percentage of the second additive is 0.1% to 15%. It should be noted that, unless otherwise specified, the amount of the second additive added to the electrolyte is generally less than 10%, preferably 0.1-5%, to avoid deterioration of battery performance due to the second additive. When the second additive is selected from additives that improve electrolyte stability, such as fluoroethylene carbonate, its content can be more than 10%. In some embodiments, the second additive includes fluoroethylene carbonate, vinylene carbonate, and 1,3-propanesulfonate lactone, with a mass ratio of fluoroethylene carbonate, vinylene carbonate, and 1,3-propanesulfonate lactone of 10:(0-1):(0-4).
[0045] In some embodiments, the solvent is selected from one or more of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate, diethyl carbonate (DEC), methyl ethyl carbonate, methyl propionate, ethyl propionate, propyl propionate (PP), methyl butyrate, and ethyl butyrate.
[0046] In some embodiments, the electrolyte salt is selected from one or more of lithium hexafluorophosphate, lithium bis(oxalato)borate, lithium bis(trifluoromethanesulfonyl)imide, and lithium bis(difluorosulfonyl)imide.
[0047] On the other hand, embodiments of this application also provide a battery, including a positive electrode, a negative electrode, and an electrolyte.
[0048] In some embodiments, the negative electrode includes a negative electrode active material, a conductive agent, and a binder. The negative electrode active material is selected from one or more of carbon-based, silicon-based, silicon suboxide-based, tin-based, and phosphorus-based materials. The conductive agent is selected from one or more of acetylene black, super P, and Ketjen black. The binder is selected from one or more of polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene-butadiene rubber, and polyacrylic acid.
[0049] The present application will be further illustrated by the following examples.
[0050] Example 1
[0051] In this embodiment, EC, PC, DEC and PP are mixed in a mass ratio of 2:1:1:6 to obtain an organic solvent. The organic solvent is mixed with LiPF6 to make the lithium salt concentration 1M. Based on 100 parts by weight of electrolyte, the first additive is 0.5% by mass of methyl viologen hexafluorophosphate and the second additive is 10% by mass of FEC, as shown in formula (2).
[0052] Battery fabrication: A slurry was prepared by mixing SiO / C, acetylene black, and sodium carboxymethyl cellulose in a mass ratio of 90:5:5. This slurry was coated onto copper foil and dried to obtain the negative electrode. A full cell was assembled and tested using a LiCoO2 positive electrode, a negative electrode, and an electrolyte.
[0053] Example 2
[0054] In this embodiment, unlike in Embodiment 1, the electrolyte contains 1% methyl viologen hexafluorophosphate per 100 parts by weight of electrolyte.
[0055] Example 3
[0056] In this embodiment, unlike in Embodiment 1, the electrolyte contains 2% methyl viologen hexafluorophosphate per 100 parts by weight of electrolyte.
[0057] Example 4
[0058] In this embodiment, unlike in Embodiment 1, the electrolyte contains 3% methyl viologen hexafluorophosphate per 100 parts by weight of electrolyte.
[0059] Example 5
[0060] In this embodiment, EC, PC, DEC and PP are mixed in a mass ratio of 2:1:1:6 to obtain an organic solvent. The organic solvent is mixed with LiPF6 to make the lithium salt concentration 1M. Based on 100 parts by weight of electrolyte, the second additive is 10% FEC, 4% PS and 1% VC by mass percentage, and the first additive is 0.5% p-phenylenediamine hexafluorophosphate by mass percentage, with the structure shown in formula (3).
[0061] Battery fabrication: A slurry was prepared by mixing graphite, acetylene black, and sodium carboxymethyl cellulose in a mass ratio of 90:5:5. This slurry was coated onto copper foil and dried to obtain the negative electrode. A full cell was assembled and tested using a LiCoO2 positive electrode, a negative electrode, and an electrolyte.
[0062] Example 6
[0063] In this embodiment, unlike in Example 5, the electrolyte contains 1% p-phenylenediamine hexafluorophosphate by weight relative to 100 parts by weight of the electrolyte.
[0064] Example 7
[0065] In this embodiment, unlike in Example 5, the electrolyte contains 2% p-phenylenediamine hexafluorophosphate by weight relative to 100 parts by weight of the electrolyte.
[0066] Example 8
[0067] In this embodiment, unlike in Example 5, the electrolyte contains 3% p-phenylenediamine hexafluorophosphate by weight relative to 100 parts by weight of the electrolyte.
[0068] Example 9
[0069] In this embodiment, unlike in Example 5, the first additive in the electrolyte is 0.5% methyl violetine hexafluorophosphate, relative to 100 parts by weight of the electrolyte.
[0070] Example 10
[0071] In this embodiment, unlike in Example 5, the first additive in the electrolyte is 0.5% by weight of biphenyl dimethyl violetine hexafluorophosphate, relative to 100 parts by weight of the electrolyte.
[0072] Example 11
[0073] In this embodiment, unlike in Example 5, the first additive in the electrolyte is 1,3,5-trimethylviolinbenzene hexafluorophosphate at a mass percentage of 0.5% relative to 100 parts by weight of the electrolyte.
[0074] Comparative Example 1
[0075] In this comparative example, unlike Example 1, the second additive in the electrolyte of this example is FEC with a mass percentage of 10% relative to 100 parts by weight of electrolyte, and the first additive is not added.
[0076] Comparative Example 2
[0077] In this comparative example, unlike Example 5, the second additive in the electrolyte of this example is 10% FEC, 4% PS and 1% VC by mass percentage, relative to 100 parts by weight of electrolyte, and the first additive is not added.
[0078] The batteries prepared in Examples 1-11 and Comparative Examples 1 and 2 were subjected to cycle performance tests at 25°C and 45°C. The test results are shown in Table 1.
[0079] Cyclic performance test: The battery was charged at 25℃ and 45℃ at a rate of 1.3C to 4.1V, then constant at 1.0C, then charged at a rate of 1.0C to 4.2V, constant at 0.7C, then charged at a rate of 0.7C to 4.3V, constant at 0.4C; then charged at a rate of 0.4C to 4.45V, constant at 0.025C; and finally discharged at a rate of 0.2C to 3.0V. The initial charge capacity and discharge capacity were recorded. After 500 cycles of this charge-discharge cycle, the discharge capacity of the 500th cycle was recorded, and the capacity retention rate after 500 cycles was calculated. The capacity retention rate (%) after 500 cycles = discharge capacity of the 500th cycle / initial discharge capacity × 100%; the cutoff voltage was 4.45V. The test results are shown in Table 1.
[0080] Table 1
[0081]
[0082] As shown in Table 1, based on the test results of Examples 1-4 and Comparative Example 1, the battery cycle performance at 25°C and 45°C was improved after adding the first additive, methyl viologen hexafluorophosphate. Based on the test results of Examples 5-8 and Comparative Example 2, it can be seen that by changing the composition and components of the first additive, replacing it with terephthalic acid dimethyl viologen hexafluorophosphate, the battery cycle performance was significantly improved. Based on the test results of Examples 5 and 9-11, compared to methyl viologen hexafluorophosphate, the conjugated structure formed by multiple methyl viologens provides a greater improvement in the battery's cycle performance at both room temperature and high temperature.
[0083] The above are merely preferred embodiments of this application and are not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.
Claims
1. An electrolyte, characterized in that, It includes an electrolyte salt, a solvent, and an additive, wherein the additive includes a first additive and a second additive, the first additive having a structural formula as shown in formula (1): （1） In formula (1), m is 1 or 2; n is 1 or 2; g is an integer from 1 to 8; R is selected from a single bond, a substituted or unsubstituted C1 to C10 alkyl group, or a substituted or unsubstituted C6 to C12 aromatic group; R1 and R2 are each independently selected from a substituted or unsubstituted C1 to C10 alkyl group or a substituted or unsubstituted C6 to C10 aromatic group; X is an anion, and X is selected from PF6. - ClO4 - and BF4 - One or more; The second additive is selected from one or more of fluoroethylene carbonate, vinylene carbonate, and 1,3-propanesulfonate lactone.
2. The electrolyte according to claim 1, characterized in that, In formula (1), m is 1 or 2; n is 1 or 2; g is an integer from 1 to 8; R is selected from one of substituted or unsubstituted C1 to C10 alkyl groups or substituted or unsubstituted C6 to C12 aryl groups; R1 and R2 are each independently selected from one of substituted or unsubstituted C1 to C10 alkyl groups or substituted or unsubstituted C6 to C10 aromatic groups; X is an anion.
3. The electrolyte according to claim 1 or 2, characterized in that, R1 and R2 are each independently selected from one of the following: a C1-C10 alkyl group, a C6-C10 aromatic group, a C1-C10 alkyl group containing a hydroxyl, halogen, carbonyl or carboxyl substituent, or a C6-C10 aromatic group containing a hydroxyl, halogen, carbonyl or carboxyl substituent.
4. The electrolyte according to claim 1 or 2, characterized in that, Substituted or unsubstituted aromatic groups include benzene, biphenyl, and trialkyl-substituted benzene.
5. The electrolyte according to claim 1, characterized in that, The first additive is selected from one or more of p-phenylenediamine hexafluorophosphate, biphenylenediamine hexafluorophosphate, and 1,3,5-trimethylviolenene hexafluorophosphate.
6. The electrolyte according to claim 1, characterized in that, Based on the total mass of the electrolyte as 100%, the mass percentage of the first additive is 0.1-5%.
7. The electrolyte according to claim 1, characterized in that, The second additive has a mass percentage content of 0.1-15%.
8. The electrolyte according to claim 1, characterized in that, The second additive comprises fluoroethylene carbonate, vinylene carbonate and 1,3-propanesulfonate lactone, wherein the mass ratio of fluoroethylene carbonate, vinylene carbonate and 1,3-propanesulfonate lactone is 10:(0~1):(0~4).
9. The electrolyte according to claim 1, characterized in that, The solvent is selected from one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, and ethyl butyrate.
10. The electrolyte according to claim 1, characterized in that, The electrolyte salt is selected from one or more of lithium hexafluorophosphate, lithium bis(oxalato)borate, lithium bis(trifluoromethanesulfonyl)imide, and lithium bis(difluorosulfonyl)imide.
11. A battery, characterized in that, It includes a positive electrode, a negative electrode, and an electrolyte as described in any one of claims 1 to 10.
12. The battery according to claim 11, characterized in that, The negative electrode comprises a negative electrode active material, a conductive agent, and a binder. The negative electrode active material is selected from one or more of carbon-based, silicon-based, silicon suboxide-based, tin-based, and phosphorus-based materials. The conductive agent is selected from one or more of acetylene black, super P, and Ketjen black. The binder is selected from one or more of polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene-butadiene rubber, and polyacrylic acid.