A polymer binder for sulfide solid-state batteries, a preparation method thereof, and applications

Abstract

The present invention relates to a polymer binder for a sulfide solid-state battery, a preparation method thereof, and an application. The binder is copolymerized from vinyltriethoxysilane, lithium 4-vinylbenzeneborate, and styrene. By introducing a silyl group, its coupling effect is utilized to enhance the interfacial adhesion with the sulfide electrolyte, and at the same time, the water in the system is consumed through a condensation reaction to reduce the water content of the electrolyte membrane; lithium 4-vinylbenzeneborate provides dissociated lithium ions to improve the ionic conductivity of the binder and reduce the negative impact on the conductivity of the sulfide electrolyte; the styrene group improves the solubility of the binder in non-polar solvents. The binder can be dissolved in solvents such as toluene and xylene, and is mixed with the sulfide electrolyte into a film through a wet coating process, with strong process compatibility. The binder of the present invention has the characteristics of high adhesiveness, ionic conductivity, and low water content, and can significantly improve the interfacial stability and electrochemical performance of the sulfide solid-state battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries, and particularly relates to a polymer binder for sulfide solid-state batteries, a preparation method thereof, and an application thereof. Background Art

[0002] Existing lithium-ion batteries that have been widely used in the energy storage field have safety hazards of flammability and leakage due to the presence of organic liquid electrolytes in themselves, especially when the size of lithium-ion batteries is getting larger and larger. In contrast, all-solid-state lithium-ion batteries using non-flammable inorganic sulfide solid electrolytes have received increasing attention due to their safety, long cycle life, and high power density.

[0003] However, the sulfide electrolyte itself has high reactivity. During the wet coating process, the only solvents that can be selected to interact weakly with it are non-polar solvents, such as alkanes, some benzenes, and some ether solvents. Existing binders, such as polyvinylidene fluoride, carboxymethyl cellulose, polyacrylic acid, polyvinyl alcohol, sodium alginate, etc., need to be dissolved in polar solvents, while polar solvents have poor compatibility with sulfide electrolytes and are basically unusable. Moreover, most of the existing binders rely on hydrogen bonds or intermolecular forces for adhesion, and the interaction force is weak. Limited by this, the organic-inorganic interface between the sulfide electrolyte and the electrode material (such as the positive active material) in the sulfide solid battery is prone to peeling due to the volume change during charge and discharge, resulting in a decrease in the battery cycle life. Another point is that most of the existing conventional binders are ionic insulators. For example, PVDF is an insulator, which will hinder the transmission of lithium ions and increase the interfacial impedance.

[0004] Therefore, synthesizing a binder with strong adhesion, soluble in non-polar solvents, and having ionic conductivity has become an urgent problem to be solved for the application of sulfide electrolytes in film formation. Summary of the Invention

[0005] The purpose of the present invention is to solve the problems existing in the prior art, and provide a polymer binder for sulfide solid-state batteries, a preparation method thereof, and an application thereof. Silane is introduced into the polymer main chain, and the coupling effect is used to enhance the adhesion of the inorganic and organic interfaces. Moreover, water will be consumed during coupling, which is beneficial to reducing the internal water content and enhancing the stability of the sulfide electrolyte. Lithium borate groups that are easily dissociated are introduced to enhance ionic conductivity. Moreover, the polymer obtained by polymerizing 4-vinylphenyl lithium borate matches or has a synergistic effect with the sulfide electrolyte. Therefore, the addition of the polymer binder will not cause too much reduction in the sulfide electrolyte after film formation. Introducing a benzene ring structure can enhance the solubility in non-polar solvents.

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] The present invention provides a polymer binder for a sulfide solid-state battery, which is obtained by emulsion polymerization. The emulsion polymerization method is to directly polymerize emulsion polymerization monomer 1, or to polymerize emulsion polymerization monomer 2 and then lithiate the acid group.

[0008] Emulsion polymerization monomer 1 includes vinyltriethoxysilane, styrene, and lithium 4-vinylphenylborate.

[0009] Emulsion polymerization monomer 2 includes vinyltriethoxysilane, styrene, and 4-vinylphenylboric acid.

[0010] As an embodiment of the present invention, the mass fractions of the components in the emulsion polymerization monomer are as follows: for emulsion polymerization monomer 1: vinyltriethoxysilane 10-30%, styrene 40-70%, lithium 4-vinylphenylborate 10-30%; for emulsion polymerization monomer 2: vinyltriethoxysilane 10-30%, styrene 40-70%, 4-vinylphenylboric acid 10-30%.

[0011] Preferably, for emulsion polymerization monomer 1: vinyltriethoxysilane 12-20%, styrene 50-63%, lithium 4-vinylphenylborate 25-30%; for emulsion polymerization monomer 2: vinyltriethoxysilane 12-20%, styrene 50-63%, 4-vinylphenylboric acid 25-30%.

[0012] As an embodiment of the present invention, the lithiation of the acid group is to immerse the polymer obtained by polymerizing emulsion polymerization monomer 2 in a lithium hydroxide solution.

[0013] The present invention needs to achieve a balance of various properties, such as lithium conduction, enhanced adhesion, and enhanced solubility on average. If the content of a certain component is too high and it is too biased towards a certain property, other properties will decline. The mass ratio of each component is: lithium 4-vinylphenylborate 10-30%, vinyltriethoxysilane 10-30%, styrene 40-70%. The polymerization method of the binder is generally an emulsion polymerization method.

[0014] The chemical structural formula of the polymer binder of the present invention is as follows:

[0015] ,

[0016] Among them, a, b, and c are the mass ratios of the monomer components in the polymer, a is 10-30%, b is 10-30%, and c is 40-70%.

[0017] The present invention also provides a preparation method of the polymer binder, and the preparation method is method one or method two;

[0018] Method one includes the following steps:

[0019] Weigh the initiator, vinyltriethoxysilane, styrene, lithium 4-vinylbenzeneborate, emulsifier and water, mix them, heat for polymerization, and obtain the polymer binder after demulsification, washing with water and drying.

[0020] Method 2 includes the following steps:

[0021] Weigh the initiator, vinyltriethoxysilane, styrene, 4-vinylbenzeneboric acid, emulsifier and water, mix them, heat for polymerization, and obtain the polymer after demulsification, washing with water and drying. Then soak the polymer in lithium hydroxide solution to obtain the polymer binder.

[0022] In the emulsion polymerization process of the present invention, in Method 1, 4-vinylbenzeneboric acid is first converted into lithium 4-vinylbenzeneborate and then polymerized, while in Method 2, the acid group is lithiated after polymerization.

[0023] As an embodiment of the present invention, in Method 1, 4-vinylbenzeneboric acid reacts with lithium hydroxide to obtain lithium 4-vinylbenzeneborate. Preparation steps: Mix 4-vinylbenzeneboric acid with water and then dropwise add an aqueous lithium hydroxide solution with a mass concentration of 4-6 wt% until the pH value is greater than 7 to obtain lithium 4-vinylbenzeneborate. The mass ratio of 4-vinylbenzeneboric acid to water is 5-10:100.

[0024] As an embodiment of the present invention, in Method 1 and Method 2, the initiator is a high-temperature initiator or a low-temperature initiator; the high-temperature initiator is ammonium persulfate; the low-temperature initiator is a mixture of sodium bisulfite and ammonium persulfate (mass ratio 10-15:2-15); the emulsifier is sodium hexadecylsulfonate.

[0025] As an embodiment of the present invention, in Method 1 and Method 2, the dosage of the high-temperature initiator is 0.3-0.4% of the total mass of the emulsion polymerization monomers. The dosage of the low-temperature initiator is 0.1-0.5% of the total mass of the emulsion polymerization monomers. The dosage of the emulsifier is 1.4-2% of the total mass of the emulsion polymerization monomers. The dosage of water is 1.5-4 times the total mass of the emulsion polymerization monomers.

[0026] As an embodiment of the present invention, in Method 1 and Method 2, when using the high-temperature initiator, the temperature for heating polymerization is 55-65 °C and the time is 1-2 h; when using the low-temperature initiator, the temperature for heating polymerization is 30-40 °C and the time is 2-3 h.

[0027] As an embodiment of the present invention, in Method 2, the concentration of the lithium hydroxide solution is 1-10 wt%.

[0028] As an embodiment of the present invention, in Method 1 and Method 2, the heating polymerization is carried out in an inert atmosphere (such as nitrogen, argon, etc.).

[0029] The present invention also provides an application of the polymer binder in a sulfide solid-state battery.

[0030] The present invention also provides a method for preparing a sulfide electrolyte membrane, comprising the following steps:

[0031] S1. Dissolve the polymer binder to obtain a binder solution;

[0032] S2. Mix the sulfide electrolyte with the binder solution and then grind thoroughly. After coating the obtained slurry, perform low-temperature drying and vacuum drying to obtain the sulfide electrolyte membrane.

[0033] In step S1, the solvent used for dissolution includes one or more of toluene, xylene, butyl butyrate, and dichloromethane. The solvent is a non-polar or weakly polar single or mixed solvent. The content of the binder in the binder solution is 1-10 wt%.

[0034] In step S2, the mass of the binder is 1-5 wt% of the sulfide electrolyte.

[0035] For the use of the binder of the present invention, generally, the sulfide electrolyte is mixed with a binder solution and then subjected to wet coating. The sulfide electrolyte and the binder solution are mixed in a certain proportion and then ground thoroughly. The slurry is coated on a substrate, followed by low-temperature drying and then vacuum drying. The dried electrolyte membrane is peeled off from the substrate.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] (1) The silyl groups introduced on the polymer main chain can greatly enhance the interaction effect between the binder and the sulfide electrolyte. Moreover, water is consumed during coupling, which is beneficial to reducing the internal water content and enhancing the stability of the sulfide electrolyte.

[0038] (2) The lithium borate groups introduced on the polymer main chain can improve the ionic conductivity of the polymer body. Compared with general binders with ionic insulation, the reduction in the conductivity of the sulfide electrolyte after film formation is not obvious. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] By reading the detailed description of the non-limiting embodiments with reference to the following drawings, other features, objects, and advantages of the present invention will become more apparent:

[0040] Figure 1 It is a schematic SEM diagram of the electrode after P-1 film formation;

[0041] Figure 2 It is a schematic diagram of the charge-discharge performance of P-1;

[0042] Figure 3 It is an infrared spectrum diagram of P-1 polymer. Detailed implementation mode

[0043] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. The following examples are implemented on the premise of the technical solution of the present invention, providing detailed implementation modes and specific operation processes, which will help those skilled in the art to further understand the present invention. It should be noted that the protection scope of the present invention is not limited to the following embodiments. Several adjustments and improvements made on the premise of the concept of the present invention all belong to the protection scope of the present invention.

[0044] Example 1

[0045] 20 g of 4-vinylphenylboronic acid was mixed with 100 g of water, and then an aqueous lithium hydroxide solution with a mass concentration of 5 wt% was added dropwise until the pH value was greater than 7. After drying at 60 °C, lithium 4-vinylphenylborate was obtained.

[0046] 0.15 g of ammonium persulfate, 10 g of vinyltriethoxysilane, 30 g of styrene, 15 g of lithium 4-vinylphenylborate, 0.9 g of sodium hexadecylsulfonate, and 100 g of water were weighed and added to a flask. The flask was evacuated and replaced with nitrogen, heated to 60 °C, and polymerized for 1 h. Then, it was demulsified, washed with water, and dried to obtain a polymer.

[0047] 1 g of the polymer was dissolved in a mixed solvent of 24 g of toluene and dichloromethane (volume ratio 6:1) to obtain a polymer solution. The polymer solution was mixed with a lithium phosphorus sulfur chlorine electrolyte (the polymer was 4 wt% of the electrolyte) to obtain an electrolyte slurry, which was coated to obtain sample P-1. The SEM schematic diagram is as shown in Figure 1 shown, and the charge-discharge performance schematic diagram is as shown in Figure 2 shown, and the infrared spectrum diagram is as shown in Figure 3 shown.

[0048] Example 2

[0049] 0.13 g of ammonium persulfate, 0.05 g of sodium bisulfite, 7 g of vinyltriethoxysilane, 32 g of styrene, 13 g of 4-vinylphenylboronic acid, 0.6 g of sodium hexadecylsulfonate, and 100 g of water were weighed and added to a flask. The flask was evacuated and replaced with nitrogen, heated to 35 °C, and polymerized for 2 h. Then, it was demulsified, washed with water, and dried to obtain a polymer. The polymer was soaked in a 10 wt% lithium hydroxide solution for 24 h to obtain a polymer.

[0050] 1 g of the polymer was dissolved in 24 g of butyl butyrate solvent to obtain a polymer solution. The polymer solution was mixed with a lithium phosphorus sulfur chlorine electrolyte (the polymer was 4 wt% of the electrolyte) to obtain an electrolyte slurry, which was coated to obtain sample P-2.

[0051] Example 3

[0052] Weigh 0.13 g of sodium persulfate, 0.13 g of sodium bisulfite, 6 g of vinyltriethoxysilane, 36 g of styrene, 11 g of 4-vinylphenylboronic acid, 0.45 g of sodium hexadecylbenzenesulfonate, and 100 g of water, add them to a flask, evacuate and replace with nitrogen, heat to 30 °C and polymerize for 2 h. Then, demulsify, wash with water and dry to obtain a polymer. Put the polymer into a 10 wt% lithium hydroxide solution, update the solution every 12 hours, and change it a total of 7 times to perform the operation of replacing sodium ions with lithium ions. After completion, a polymer is obtained.

[0053] Dissolve 1 g of the polymer in 24 g of xylene to obtain a polymer solution, mix it with a lithium phosphorus sulfur chlorine electrolyte (the polymer is 4 wt% of the electrolyte) to obtain an electrolyte slurry, and perform coating to obtain sample P-3.

[0054] Example 4

[0055] Weigh 0.1 g of sodium persulfate, 0.05 g of sodium bisulfite, 5 g of vinyltriethoxysilane, 32 g of styrene, 9 g of lithium 4-vinylphenylborate, 0.5 g of sodium hexadecylbenzenesulfonate, and 100 g of water, add them to a flask, evacuate and replace with nitrogen, heat to 32 °C and polymerize for 1 h. Then, demulsify, wash with water and dry to obtain a polymer.

[0056] Subsequently, dissolve 1 g of the polymer in 24 g of toluene to obtain a polymer solution, mix it with a lithium phosphorus sulfur chlorine electrolyte (the polymer is 4 wt% of the electrolyte) to obtain an electrolyte slurry, and perform coating to obtain sample P-4.

[0057] Example 5

[0058] Weigh 0.12 g of ammonium persulfate, 0.02 g of sodium bisulfite, 5 g of vinyltriethoxysilane, 39 g of styrene, 8 g of 4-vinylphenylboronic acid, 0.7 g of sodium hexadecylsulfonate, and 100 g of water, add them to a flask, evacuate and replace with nitrogen, heat to 35 °C and polymerize for 2 h. Then, demulsify, wash with water and dry to obtain a polymer. Immerse the polymer in a 10 wt% lithium hydroxide solution for 24 h to obtain a polymer.

[0059] Dissolve 1 g of the polymer in 24 g of butyl butyrate solvent to obtain a polymer solution, mix it with a lithium phosphorus sulfur chlorine electrolyte (the polymer is 4 wt% of the electrolyte) to obtain an electrolyte slurry, and perform coating to obtain sample P-5.

[0060] Comparative Example 1

[0061] The preparation steps of this comparative example are basically the same as those of Example 1, except that: vinyltriethoxysilane is not added during the preparation of the polymer to obtain sample D-1.

[0062] Comparative Example 2

[0063] The preparation steps of this comparative example are basically the same as those of Example 1, except that: styrene is not added during the preparation of the polymer, and sample D-2 is obtained. The polymer binder obtained in this comparative example is shown to be a polar polymer and is insoluble in non-polar solvents.

[0064] Comparative Example 3

[0065] The preparation steps of this comparative example are basically the same as those of Example 1, except that: during the preparation of the polymer, lithium 4-vinylbenzeneborate is replaced with an equal mass of lithium vinylsulfonate to obtain the polymer. The polymer obtained in this comparative example is insoluble in non-polar solvents and is a hard monomer, making it difficult to form a film alone.

[0066] Performance test:

[0067] The water content and ionic conductivity of the electrolyte membranes prepared in the examples and comparative examples were tested, and the test methods are as follows:

[0068] Water content test method The water content test method uses the Karl Fischer method. Take 3 g of the sample and place it in a sample bottle. Use nitrogen as the carrier gas to blow the water in the sample into the anode solution of the Karl Fischer reagent. The iodide ions in the anode solution start to electrolyze to produce iodine, which reacts quantitatively with water. The water content is calculated based on the electricity consumed by the electrolysis.

[0069] (2) Ionic conductivity test method

[0070] The ionic conductivity measurement method uses the AC impedance method. After grinding the electrolyte membrane with a mortar, take 100 mg and place it in a pressure cell mold. Subsequently, apply pressure up to 10 MPa. The test parameters of the electrochemical workstation are set as the AC impedance test frequency range of 1 MHz to 1 Hz for testing. After the test is completed, measure the thickness of the sulfide electrolyte sheet. The calculation formula is as follows: σ Li+ =L / RS, where R is the AC impedance value, L is the thickness of the solid electrolyte sheet, and S is the area of the solid electrolyte sheet.

[0071] The changes in the water content of the polymer binders obtained by polymerizing the present invention in different proportions before and after film coating are shown in Table 1.

[0072] Table 1 Changes in water content

[0073]

[0074] The changes in the ionic conductivity of the polymer binders obtained by polymerizing the present invention in different proportions after film coating are shown in Table 2.

[0075] Table 2 Ionic conductivity

[0076]

[0077] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various deformations or modifications within the scope of the claims, which does not affect the essence of the present invention.

Claims

1. A polymer binder for sulfide solid-state batteries, characterized in that: The polymer binder is obtained by emulsion polymerization, wherein the emulsion polymerization is performed by directly polymerizing the emulsion polymerization monomer 1, or by polymerizing the emulsion polymerization monomer 2 and then lithiation of the acid group; Emulsion polymerization monomer 1 includes vinyl triethoxysilane, styrene and lithium 4-vinyl phenyl borate; Emulsion polymerized monomers 2 include vinyltriethoxysilane, styrene and 4-vinylbenzeneboronic acid.

2. The polymer binder according to claim 1, characterized in that The mass fractions of the components in the emulsion polymerization monomer 1 are: 10-30% vinyl triethoxysilane, 40-70% styrene, and 10-30% lithium 4-vinylbenzene borate; The mass fractions of the components in the emulsion polymerization monomer 2 are: 10-30% of vinyltriethoxysilane, 40-70% of styrene, and 10-30% of 4-vinylbenzeneboric acid.

3. A method for preparing a polymer binder as claimed in claim 1, characterized in that: The preparation method is method one or method two; Method 1 includes the following steps: Weigh an initiator, vinyl triethoxysilane, styrene, 4-vinyl phenyl lithium borate, an emulsifier and water, mix them, heat and polymerize them, demulsify them, wash them with water and dry them to obtain a polymer binder; Method 2 includes the following steps: An initiator, vinyl triethoxysilane, styrene, 4-vinyl benzene boronic acid, an emulsifier and water are weighed and mixed, and the mixture is heated for polymerization, demulsified, washed with water and dried to obtain a polymer, and then the polymer is immersed in a lithium hydroxide solution to obtain a polymer binder.

4. The method for preparing a polymer binder according to claim 3, characterized in that: In method 1, 4-vinylbenzeneboronic acid is reacted with lithium hydroxide to obtain lithium 4-vinylbenzeneborate.

5. The method for preparing a polymer binder according to claim 3, characterized in that: In method 1 and method 2, the initiator is a high-temperature initiator or a low-temperature initiator; the high-temperature initiator is ammonium persulfate; the low-temperature initiator is a mixture of sodium bisulfite and ammonium persulfate; and the emulsifier is sodium hexadecyl sulfonate.

6. The method for preparing a polymer binder according to claim 5, characterized in that: In method 1 and method 2, when a high temperature initiator is used, the temperature of the heating polymerization is 55-65°C and the time is 1-2 h; when a low temperature initiator is used, the temperature of the heating polymerization is 30-40°C and the time is 2-3 h.

7. Use of the polymer binder as claimed in claim 1 in a sulfide solid-state battery.

8. A method for preparing a sulfide electrolyte membrane, characterized in that: The steps include: S1. dissolving the polymer binder as claimed in claim 1 to obtain a binder solution; S2. The sulfide electrolyte and the binder solution are mixed and then fully ground. The obtained slurry is coated and then low-temperature dried and vacuum dried to obtain a sulfide electrolyte membrane.

9. The method for preparing a sulfide electrolyte membrane according to claim 8, characterized in that: In step S1, the solvent used for dissolution includes one or more of toluene, xylene, butyl butyrate, and dichloromethane.

10. The method for preparing a sulfide electrolyte membrane according to claim 8, characterized in that: In step S2, the mass of the binder is 1-5wt% of the sulfide electrolyte.

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