Preparation Method and Application of a Single-Ion Conductor Composite Binder

Abstract

The present invention discloses a preparation method and application of a single-ion conductor composite binder. The binder is prepared by compounding and modifying a copolymer of butyl acrylate and lithium 2-acrylamido-2-methylpropanesulfonate with polyisobutylene. Its main features are as follows: First, the binder can be completely dissolved in the non-polar solvent toluene, solving the problem of incompatibility between traditional binders and sulfide electrolytes; Second, the unique molecular structure design endows it with excellent adhesion performance and ion conduction ability at the same time, which can significantly reduce the interfacial impedance. The flexible chain segment of butyl acrylate provides elastic support, and the sulfonic acid groups of lithium 2-acrylamido-2-methylpropanesulfonate form strong chemical bonds with the surface of sulfide particles, enhancing the binding force with the electrolyte. The preparation process of the binder of the present invention is simple, the cost is controllable, and it is suitable for large-scale production, providing an important material solution for promoting the industrialization of sulfide all-solid-state batteries.

Description

Technical Field

[0001] The present invention belongs to the technical field of all-solid-state batteries, and particularly relates to a preparation method and application of a single-ion conductor composite binder, and more particularly to the application of a composite binder soluble in non-strongly polar solvents in the wet film formation of sulfide solid electrolytes and sulfide all-solid-state batteries. Background Art

[0002] With the increasing demand for high-safety and high-energy-density batteries in electric vehicles and energy storage systems, all-solid-state batteries have attracted much attention due to their characteristics of completely eliminating the risks of electrolyte leakage and combustion. Sulfide electrolytes have become the most promising technical route for industrialization due to their excellent room-temperature ionic conductivity and good mechanical processing properties. However, sulfide electrolytes still face major challenges in practical applications: in traditional wet coating processes, sulfide electrolytes are extremely sensitive to polar solvents and must be processed using non-polar solvents such as toluene and hexane, while common binder systems such as PVDF and CMC in existing lithium-ion batteries cannot dissolve in these solvents, resulting in poor contact at the electrode-electrolyte interface and seriously affecting battery performance.

[0003] Currently, the research on binders for sulfide electrolytes mainly focuses on non-polar materials such as cis-butadiene rubber, but these materials generally have problems such as insufficient adhesion and lack of functional groups. More importantly, existing binders almost all do not have ion conduction ability, forming an ion transport barrier at the electrode-electrolyte interface and significantly increasing the interface impedance. Therefore, developing a new type of binder with solubility in non-strongly polar solvents, excellent adhesion performance, and ion conduction characteristics has become the key technical bottleneck for promoting the industrialization of sulfide all-solid-state batteries. Summary of the Invention

[0004] The purpose of the present invention is to provide a preparation method of a single-ion conductor composite binder soluble in non-strongly polar solvents. Through molecular design, the present invention innovatively combines the flexibility of acrylate polymers, the ion conduction characteristics of lithium sulfonate groups, and the high viscosity of polyisobutylene (which is beneficial to the film formation of sulfide solid electrolytes), realizing a binder with adhesiveness, ion conductivity, and high viscosity, providing key technical support for the industrialization of sulfide all-solid-state batteries.

[0005] To achieve the above purpose, the present invention provides the following technical solutions:

[0006] A preparation method of a single-ion conductor composite binder soluble in non-strongly polar solvents, comprising the following steps:

[0007] S1. Add butyl acrylate monomer, a single-ion conductor monomer with a sulfonate lithium group (-SO3Li) at the end group, an initiator, and a surfactant into a phosphate buffer solution. The resulting polymerization solution is subjected to emulsion polymerization under an inert atmosphere to obtain a copolymer binder.

[0008] S2. Dissolve polyisobutene and the copolymer binder in a non-strongly polar solvent for blending to obtain a single-ion conductor composite binder.

[0009] As an embodiment of the present invention, in step S1, the single-ion conductor monomer with a sulfonate lithium group (-SO3Li) at the end group is lithium 2-acrylamido-2-methylpropanesulfonate.

[0010] Preferably, lithium 2-acrylamido-2-methylpropanesulfonate is obtained by lithiating the sulfonic acid group on 2-acrylamido-2-methylpropanesulfonic acid.

[0011] Lithiation step: Neutralize an aqueous solution of 2-acrylamido-2-methylpropanesulfonic acid (concentration: 10 - 20 wt%) to pH = 7 - 8 with an aqueous solution of lithium hydroxide (concentration: 5 - 10 wt%) to obtain lithium 2-acrylamido-2-methylpropanesulfonate.

[0012] Preferably, 2-acrylamido-2-methylpropanesulfonic acid is obtained by subjecting sodium 2-acrylamido-2-methylpropanesulfonate to cation exchange treatment.

[0013] Cation exchange treatment step: Pass an aqueous solution of sodium 2-acrylamido-2-methylpropanesulfonate (concentration: 10 - 20 wt%) through a column filled with a hydrogen-form strongly acidic cation exchange resin to obtain the sulfonic acid of 2-acrylamido-2-methylpropanesulfonic acid.

[0014] As an embodiment of the present invention, in step S1, the molar ratio of the butyl acrylate monomer to the single-ion conductor monomer with a sulfonate lithium group (-SO3Li) at the end group is 5 - 8:1.

[0015] Sulfide electrolytes will react and decompose with polar solvents, and the selection of their film-forming solvents is restricted. Therefore, it is important to prepare a non-strongly polar solvent binder that can dissolve in toluene, etc. In the present invention, by regulating the molar ratio of two monomers (butyl acrylate monomer and single-ion conductor monomer), the prepared single-ion conductor binder can dissolve in non-strongly polar solvents such as toluene and is used for film formation of sulfide electrolytes in sulfide all-solid-state batteries. When the molar ratio of the butyl acrylate monomer to the single-ion conductor monomer with a sulfonate lithium group (-SO3Li) at the end group is lower than 5:1, the solubility in non-strongly polar solvents such as toluene will deteriorate.

[0016] Through molecular design, the present invention innovatively combines the flexibility of acrylate polymers, the ionic conduction characteristics of lithium sulfonate groups, and the high viscosity of polyisobutene (which is beneficial for the film formation of sulfide solid electrolytes), achieving adhesion with both adhesiveness, ionic conductivity, and high viscosity.

[0017] As an embodiment of the present invention, in the polymerization solution of step S1, the content of the single-ion conductor monomer with a lithium sulfonate group (-SO3Li) at the end is 3-5 wt%.

[0018] As an embodiment of the present invention, in step S1, the initiator is ammonium persulfate, and the surfactant is sodium dodecyl sulfate. In the polymerization solution, the initiator concentration is 0.5-0.8 wt%, and the surfactant concentration is 0.2-0.4 wt%.

[0019] As an embodiment of the present invention, in step S1, the concentration of the phosphate buffer solution is 0.1 mol / L.

[0020] As an embodiment of the present invention, in step S1, the inert atmosphere includes nitrogen. After the emulsion polymerization reaction, saturated aqueous sodium chloride solution is dropped in for demulsification, and the obtained product is washed to obtain the copolymer binder.

[0021] As an embodiment of the present invention, in step S2, the non-polar solvent includes one or more of toluene, p-xylene, and o-xylene.

[0022] As an embodiment of the present invention, in step S2, the mass ratio of the copolymer binder to polyisobutene is 1:3-6. The blending time is 20-30 h.

[0023] As an embodiment of the present invention, in step S2, the solid content (the complex formed by polyisobutene and the copolymer binder) in the obtained single-ion conductor composite binder is 1-4 wt%. The single-ion conductor composite binder is a solution system containing the composite binder.

[0024] In the present invention, the carboxyl group in the butyl acrylate monomer and the amide group in the 2-acrylamido-2-methylpropanesulfonic acid lithium monomer will form a chemical bond interaction with the functional groups on the surface of the sulfide electrolyte, improving ionic conduction. Although the copolymer binder has good ionic conduction characteristics, its viscosity is insufficient and it cannot be used as a binder for the sulfide electrolyte to form a film. Alone, it cannot form a film. Polyisobutene has high viscosity and has good film-forming properties for sulfide electrolytes. It can be dissolved in non-polar solvents such as toluene that have little effect on sulfides, but it cannot conduct lithium ions.

[0025] The polyisobutylene and copolymer binder of the present invention form an adhesive composite. The polyisobutylene and copolymer binder are mixed, and the functional groups and chemical bonds on their molecular chains interact with each other, enhancing the stability of the composite binder to form a composite. The resulting composite binder has a better film-forming effect, is more stable during the charge and discharge process, and is not easily decomposed.

[0026] The present invention also provides an application of the single-ion conductor composite binder in the preparation of a sulfide electrolyte membrane.

[0027] The present invention also provides a method for preparing a sulfide electrolyte membrane, comprising the following steps:

[0028] A1. Mix and ball-mill a sulfide solid electrolyte, a single-ion conductor composite binder, and a non-polar solvent to form a uniform sulfide electrolyte slurry;

[0029] A2. Form a film from the sulfide electrolyte slurry by wet coating and perform a drying treatment to obtain a sulfide electrolyte membrane.

[0030] As an embodiment of the present invention, in step A1, the sulfide solid electrolyte is a Li6PS5Cl type solid electrolyte.

[0031] As an embodiment of the present invention, in step A1, the non-polar solvent includes one or more of toluene, p-xylene, and o-xylene. The non-polar solvent in step A1 is preferably the same as the non-polar solvent in the single-ion conductor composite binder.

[0032] As an embodiment of the present invention, in step A1, the adhesive composite (composite binder) formed by polyisobutylene and copolymer binder accounts for 1-2% by mass of the sulfide electrolyte. The mass ratio of the sulfide solid electrolyte to the non-polar solvent is 10:5-8.

[0033] As an embodiment of the present invention, in step A1, the ball-milling time is 1-2 h and the rotation speed is 200-300 rpm. The ball-milling is carried out in a sealed argon atmosphere.

[0034] As an embodiment of the present invention, in step A2, the drying treatment is carried out by constant-temperature drying in a vacuum oven. The temperature of the constant-temperature drying is 40-80 °C, the time is 10-15 h, and the vacuum degree is 0.03-0.08 MPa.

[0035] As an embodiment of the present invention, in step A2, the thickness of the obtained sulfide electrolyte membrane is 30-60 μm.

[0036] The present invention also provides an application of the single-ion conductor composite binder in the preparation of a sulfide all-solid-state battery.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] The binder provided by the present invention, through innovative molecular structure design, has both non-polar solvent solubility, excellent adhesion performance and ion conduction characteristics, and can solve the technical difficulties of wet film formation of sulfide solid electrolytes. It can not only improve the binding force between the electrolyte and the binder, but also effectively reduce the interfacial impedance through single-ion conduction characteristics, and at the same time exhibit excellent electrochemical stability. Its simple preparation process is highly compatible with existing production lines, greatly reducing production costs. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0040] Figure 1 It is a flowchart of a preparation method of a single-ion conductor composite binder soluble in non-strongly polar solvents provided by an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0041] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. The examples given are only for explaining the present invention, and are not intended to limit the scope of the present invention.

[0042] The present invention is made by compounding and modifying butyl acrylate and lithium 2-acrylamido-2-methylpropanesulfonate copolymer with polyisobutylene, and can achieve solubility in non-polar solvents and have both adhesion and single-ion conduction functions. The flexible chain segment of butyl acrylate provides elastic support, and the sulfonic acid groups of lithium 2-acrylamido-2-methylpropanesulfonate form strong chemical bonds with the surface of sulfide particles, enhancing the binding force with the electrolyte. And the dissociated lithium ions of the single-ion conductor unit can migrate directionally along the polymer chain, endowing the electrolyte membrane with higher ionic conductivity. At the same time, polyisobutylene with high viscosity can improve the film-forming property of the sulfide electrolyte, and this composite binder has good solubility in the non-strongly polar solvent toluene and is perfectly matched with the sulfide electrolyte.

[0043] Example 1

[0044] A preparation method of a single-ion conductor composite binder soluble in non-strongly polar solvents, as Figure 1 shown, the steps are as follows:

[0045] (1) Lithiated single-ion conductor monomer: Dissolve 15 g of sodium 2-acrylamido-2-methylpropanesulfonate in 85 g of deionized water. Pass the solution through a column filled with hydrogen-type strongly acidic cation exchange resin to exchange the terminal group of the monomer from -SO3Na to -SO3H. Then, neutralize it with a 7 wt% aqueous lithium hydroxide solution to pH = 7 to obtain the single-ion conductor monomer lithium 2-acrylamido-2-methylpropanesulfonate with a terminal group of -SO3Li.

[0046] (2) Preparation of copolymer binder: Weigh 5 g of butyl acrylate monomer, 1.38 g of lithium 2-acrylamido-2-methylpropanesulfonate, 0.25 g of ammonium persulfate, and 0.12 g of sodium dodecyl sulfate. Add them to 25 g of a 0.1 mol / L phosphate buffer solution (mix 1 mol / L of sodium dihydrogen phosphate and 1 mol / L of disodium hydrogen phosphate to obtain a phosphate buffer solution with pH = 7). After evacuating and replacing nitrogen three times, raise the temperature to 60 °C and polymerize for 2 h to obtain an emulsion. Then, drop in a saturated sodium chloride aqueous solution for demulsification, and wash the polymer. Dry it in a constant-temperature vacuum dryer at 80 °C for 10 h to obtain the copolymer binder.

[0047] (3) Preparation of composite binder solution in a non-strongly polar solvent: Take 1.0 g of polyisobutene and 0.25 g of the copolymer obtained in (2), and dissolve them in 30 g of toluene solvent. Stir magnetically at room temperature for 24 h until a uniform composite binder solution with a solid content of 4.0 wt% is formed.

[0048] (4) Preparation of sulfide electrolyte slurry: Operate in a glove box filled with argon. Take 10 g of sulfide electrolyte (Li6PS5Cl), add it to a ball mill jar, then add 2.5 g of the composite binder solution and 6 g of toluene solvent to disperse the electrolyte evenly. After sealing, perform ball milling at room temperature for 2 h with a ball milling speed of 300 rpm to obtain a uniform electrolyte slurry. The mass fraction of the composite binder (polyisobutene, copolymer binder forms an adhesive complex) in the sulfide electrolyte is 1%.

[0049] (5) Wet film formation of sulfide electrolyte: Operate in a glove box filled with argon. Coat the electrolyte slurry on a copper foil substrate with a thickness controlled at 60 μm, and then directly dry it by blowing air for 2 h. Then, perform drying treatment using a vacuum oven at a temperature of 50 °C, a vacuum degree of 0.05 MPa, and a constant-temperature drying time of 12 h.

[0050] Example 2

[0051] A preparation method of a single-ion conductor composite binder soluble in a non-strongly polar solvent, the steps are as follows:

[0052] (1) Lithiated single-ion conductor monomer: Dissolve 15 g of sodium 2-acrylamido-2-methylpropanesulfonate in 85 g of deionized water. Pass the solution through a column filled with hydrogen-type strongly acidic cation exchange resin to exchange the terminal group of the monomer from -SO3Na to -SO3H. Then, neutralize it to pH = 7 with a 7 wt% aqueous lithium hydroxide solution to obtain the single-ion conductor monomer lithium 2-acrylamido-2-methylpropanesulfonate with a terminal group of -SO3Li.

[0053] (2) Preparation of copolymer binder: Weigh 6 g of butyl acrylate monomer, 1.2 g of lithium 2-acrylamido-2-methylpropanesulfonate, 0.20 g of ammonium persulfate, and 0.10 g of sodium dodecyl sulfate. Add them to 25 g of a 0.1 mol / L phosphate buffer solution (mix 1 mol / L sodium dihydrogen phosphate and 1 mol / L disodium hydrogen phosphate to obtain a phosphate buffer solution with pH = 7). After evacuating and replacing nitrogen three times, raise the temperature to 60 °C and polymerize for 2 h to obtain an emulsion. Then, drop in a saturated sodium chloride aqueous solution for demulsification, and wash the polymer. Dry it in a constant-temperature vacuum oven at 80 °C for 10 h to obtain the copolymer binder.

[0054] (3) Preparation of composite binder solution in a non-strongly polar solvent: Take 1.0 g of polyisobutene and 0.20 g of the copolymer obtained in (2), and dissolve them in 30 g of toluene solvent. Stir magnetically at room temperature for 24 h until a uniform composite binder solution is formed, with a solid content of 3.8 wt%.

[0055] (4) Preparation of sulfide electrolyte slurry: Operate in a glove box filled with argon. Take 10 g of sulfide electrolyte (Li6PS5Cl), add it to a ball milling jar, then add 5.2 g of the composite binder solution and 5 g of toluene solvent to disperse the electrolyte evenly. After sealing, perform ball milling treatment at room temperature for 2 h with a ball milling speed of 300 rpm to obtain a uniform electrolyte slurry. The mass fraction of the composite binder (polyisobutene, copolymer binder forms an adhesive complex) in the sulfide electrolyte is 2%.

[0056] (5) Wet film formation of sulfide electrolyte: Operate in a glove box filled with argon. Coat the electrolyte slurry on a copper foil substrate with a thickness controlled at 60 μm, and then directly dry it by blowing air for 2 h. Then, perform drying treatment using a vacuum oven at a temperature of 50 °C, a vacuum degree of 0.05 MPa, and a constant-temperature drying time of 12 h.

[0057] Comparative Example 1

[0058] Cancel step (1) in Example 1, do not add lithiated single-ion conductor monomer lithium 2-acrylamido-2-methylpropanesulfonate, only prepare poly(butyl acrylate) polymer, and then blend it with polyisobutylene to prepare a composite binder, and then use it for wet film formation of sulfide electrolyte.

[0059] Comparative Example 2

[0060] Cancel step (3) in Example 1, do not blend with polyisobutylene to prepare a composite binder, directly use poly(butyl acrylate / lithium 2-acrylamido-2-methylpropanesulfonate) copolymer as a binder, and then use it for wet film formation of sulfide electrolyte. Since the viscosity of the copolymer is lower than that of polyisobutylene, the final film-forming effect is not very good.

[0061] Comparative Example 3

[0062] Only change the amount of the composite binder in step (4) of Example 1. The mass fraction of the composite binder (polyisobutylene, copolymer binder forms an adhesive complex) in the sulfide electrolyte is 3%.

[0063] Comparative Example 4

[0064] This comparative example is basically the same as Example 1, except that: lithium 2-acrylamido-2-methylpropanesulfonate is replaced with an equal amount of lithium phenylsulfonyl(trifluoromethanesulfonyl)imide. Since its molecular chain contains a benzene ring and has too high rigidity, the finally prepared copolymer cannot be dissolved in toluene and can only form a dispersion. The composite after blending with polyisobutylene also cannot be completely dissolved in toluene, and the surface of the finally coated electrolyte membrane is rough and unevenly dispersed.

[0065] Comparative Example 5

[0066] This comparative example is basically the same as Example 1, except that: polyisobutylene is replaced with an equal amount of nitrile rubber. The flatness of the surface of the finally coated electrolyte membrane is lower than that of polyisobutylene, and the measured ionic conductivity is significantly lower than that of Example 1.

[0067] Comparative Example 6

[0068] This comparative example is basically the same as Example 1, except that: cancel the preparation of the composite binder solution, add polyisobutylene, copolymer binder and sulfide electrolyte into the ball mill tank for ball milling treatment (the solvent dosage is the same as that in Example 1) to prepare a slurry, and the ionic conductivity of the finally formed film is lower than that of Example 1.

[0069] Test the examples and comparative examples, and the method is as follows:

[0070] Measurement of ionic conductivity: The prepared electrolyte membrane was cut into small round pieces, and then loaded into a pressure cell mold. It was stamped under a pressure of 1 ton, and the pressure was maintained for 1 minute. An electrochemical workstation with the model CHI660E was used to conduct AC impedance testing in a normal atmospheric atmosphere at room temperature, and the ionic conductivity was calculated. The results are shown in Table 1.

[0071] Table 1. Electrochemical performance data of sulfide electrolyte membranes

[0072]

[0073] It can be seen from the table that the impedance of the sulfide electrolyte membranes in Examples 1 and 2 is less than that of the comparative example, and their ionic conductivity is higher than that of the comparative example. This is mainly because the flexible chain segment of butyl acrylate provides elastic support, and the sulfonate groups of lithium 2-acrylamido-2-methylpropanesulfonate form strong chemical bonds with the surface of sulfide particles, enhancing the binding force with the electrolyte. Moreover, the dissociated lithium ions of the single-ion conductor unit can migrate directionally along the polymer chain, endowing the electrolyte membrane with higher ionic conductivity. At the same time, polyisobutene with high viscosity can improve the film-forming property of the sulfide electrolyte. This composite binder has good solubility in the non-polar solvent toluene and is perfectly matched with the sulfide electrolyte, which can solve the key problem that traditional polar solvent binders cannot be used in the sulfide system, realizing the uniform dispersion of the sulfide electrolyte and the preparation of stable slurries, providing key technical support for the industrialization of sulfide all-solid-state batteries.

[0074] The specific embodiments described above further elaborate on the purpose, technical solutions, and beneficial effects of the present invention. It should be understood that these are only examples. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation method of a single-ion conductor composite binder, characterized in that It includes the following steps: S1. Add butyl acrylate monomer, a single-ion conductor monomer with a sulfonate lithium group at the end group, an initiator, and a surfactant into a phosphate buffer solution. The obtained polymerization solution is subjected to emulsion polymerization under an inert atmosphere to obtain a copolymer binder; S2. Blend polyisobutylene and the copolymer binder in a non-strongly polar solvent to obtain a single-ion conductor composite binder; In step S1, the molar ratio of the butyl acrylate monomer to the single-ion conductor monomer with a sulfonate lithium group at the end group is 5-8:1; In step S2, the mass ratio of the copolymer binder to polyisobutylene is 1:3-6.

2. The preparation method of the single-ion conductor composite binder according to claim 1, wherein In step S1, the single-ion conductor monomer with a sulfonate lithium group at the end group is lithium 2-acrylamido-2-methylpropane sulfonate.

3. The preparation method of the single-ion conductor composite binder according to claim 1, wherein, In step S2, the non-strongly polar solvent includes one or more of toluene, p-xylene, and o-xylene.

4. The preparation method of the single-ion conductor composite binder according to claim 1, characterized in that, In step S2, the solid content in the obtained single-ion conductor composite binder is 1-4 wt%.

5. Application of a single-ion conductor composite binder obtained by the preparation method as claimed in claim 1 in the preparation of a sulfide electrolyte membrane.

6. A preparation method of a sulfide electrolyte membrane, which includes the following steps: A1. Mix a sulfide solid electrolyte, the single-ion conductor composite binder obtained by the preparation method as claimed in claim 1, and a non-strongly polar solvent and ball-mill them to form a uniform sulfide electrolyte slurry; A2. Form a film from the sulfide electrolyte slurry by wet coating and perform a drying treatment to obtain a sulfide electrolyte membrane; In step A1, the mass fraction of the single-ion conductor composite binder in the sulfide electrolyte is 1-2%.

7. The method for preparing a sulfide electrolyte membrane according to claim 6, wherein, In step A2, the thickness of the obtained sulfide electrolyte membrane is 30-60 μm.

8. Application of a single-ion conductor composite binder obtained by the preparation method as claimed in claim 1 in the preparation of a sulfide all-solid-state battery.

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