Preparation method and application of single ion conductor composite binder

Abstract

The invention discloses a preparation method and application of a single ion conductor composite binder. The binding agent is prepared by carrying out compound modification on a copolymer of butyl acrylate and 2-acrylamido-2-lithium methylpropanesulfonate and polyisobutene. The binder is mainly characterized in that firstly, the binder can be completely dissolved in a toluene non-polar solvent, and the problem that a traditional binder is incompatible with sulfide electrolyte is solved; and secondly, due to the unique molecular structure design, the adhesive has excellent adhesive property and ionic conductivity, and the interface impedance can be remarkably reduced. A butyl acrylate flexible chain segment provides elastic support, and a sulfonate group of 2-acrylamido-2-lithium methylpropanesulfonate and the surfaces of sulfide particles form strong chemical bonding, so that the binding force with electrolyte is enhanced. The binder is simple in preparation process, controllable in cost and suitable for large-scale production, and an important material solution is provided for promoting 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 specifically relates to a preparation method and application of a single-ion conductor composite binder, and in particular to an application of a composite binder soluble in a non-strongly polar solvent for wet film formation of a sulfide solid electrolyte and in a sulfide all-solid-state battery. Background Art

[0002] With the growing demand for high-safety, 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 risk of electrolyte leakage and combustion. Sulfide electrolytes have become the most promising technology 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. The binder systems such as PVDF and CMC commonly used in existing lithium-ion batteries cannot be dissolved in these solvents, resulting in poor contact at the electrode-electrolyte interface, which seriously affects battery performance.

[0003] At present, the research on binders for sulfide electrolytes is mainly focused on non-polar materials such as butadiene rubber, but these materials generally have problems such as insufficient adhesion and lack of functional groups. More importantly, almost all existing binders have ion conductivity, forming an ion transport barrier at the electrode-electrolyte interface, greatly increasing the interface impedance. Therefore, the development of a new binder that has both non-polar solvent solubility, excellent bonding properties and ion conductivity characteristics has become a key technical bottleneck in promoting the industrialization of sulfide all-solid-state batteries. Summary of the invention

[0004] The purpose of the present invention is to provide a method for preparing a single ion conductor composite binder soluble in a non-strongly polar solvent. The present invention innovatively combines the flexibility of acrylic polymers, the ion conductivity of lithium sulfonate groups and the high viscosity of polyisobutylene (which is conducive to the film formation of sulfide solid electrolytes) through molecular design, thereby achieving a binder with both adhesion, ion conductivity and high viscosity, providing key technical support for the industrialization of sulfide all-solid-state batteries.

[0005] To achieve the above object, the present invention provides the following technical solutions: A method for preparing a single ion conductor composite binder soluble in a non-strongly polar solvent comprises the following steps: S1, butyl acrylate monomer, the terminal group is lithium sulfonate group (-SO 3 The single ion conductor monomer, initiator and surfactant of Li are added into phosphate buffer, and the obtained polymerization solution is subjected to emulsion polymerization under an inert atmosphere to obtain a copolymer binder; S2. Dissolve polyisobutylene and copolymer binders in a non-strongly polar solvent and blend them to obtain a single ion conductor composite binder.

[0006] As an embodiment of the present invention, in step S1, the terminal group is a lithium sulfonate group (-SO 3 The single ion conductor monomer of Li) is 2-acrylamide-2-methylpropanesulfonate lithium.

[0007] Preferably, the lithium 2-acrylamide-2-methylpropanesulfonate is obtained by lithiation of the sulfonic acid group on 2-acrylamide-2-methylpropanesulfonic acid.

[0008] Lithiation step: neutralize the 2-acrylamide-2-methylpropanesulfonic acid aqueous solution (concentration 10-20wt%) with a lithium hydroxide aqueous solution (concentration 5-10wt%) to pH=7-8 to obtain lithium 2-acrylamide-2-methylpropanesulfonate.

[0009] Preferably, 2-acrylamide-2-methylpropanesulfonic acid is obtained by subjecting sodium 2-acrylamide-2-methylpropanesulfonate to a cation exchange treatment.

[0010] Cation exchange treatment step: Pass an aqueous solution of sodium 2-acrylamide-2-methylpropanesulfonate (concentration of 10-20 wt%) through a column filled with a hydrogen-type strongly acidic cation exchange resin to obtain the sulfonic acid of 2-acrylamide-2-methylpropanesulfonic acid.

[0011] As an embodiment of the present invention, in step S1, the butyl acrylate monomer and the terminal group are lithium sulfonate groups (-SO 3 The molar ratio of the single ion conductor monomer of Li is 5-8:1.

[0012] Sulfide electrolytes react and decompose with polar solvents, and the choice of film-forming solvents is limited, so it is important to prepare a non-strong polar solvent binder that can be dissolved in toluene. The present invention adjusts the molar ratio of two monomers (butyl acrylate monomer and single ion conductor monomer) to prepare a single ion conductor binder that can be dissolved in non-strong polar solvents such as toluene and is used for film formation of sulfide electrolytes in sulfide all-solid-state batteries. Butyl acrylate monomer, end group is lithium sulfonate group (-SO 3 When the molar ratio of the single ion conductor monomer of Li is lower than 5:1, the solubility in non-strong polar solvents such as toluene will deteriorate.

[0013] Through molecular design, the present invention innovatively combines the flexibility of acrylic polymers, the ion conductivity properties of lithium sulfonate groups and the high viscosity of polyisobutylene (which is conducive to the film formation of sulfide solid electrolytes), thereby achieving a bond that combines adhesion, ion conductivity and high viscosity.

[0014] As an embodiment of the present invention, in the polymerization solution of step S1, the terminal group is a lithium sulfonate group (-SO 3 The content of the single ion conductor monomer of Li) is 3-5wt%.

[0015] As an embodiment of the present invention, in step S1, the initiator is ammonium persulfate, the surfactant is sodium dodecyl sulfate, the initiator concentration is 0.5-0.8wt%, and the surfactant concentration is 0.2-0.4wt% in the polymerization solution.

[0016] As an embodiment of the present invention, in step S1, the concentration of the phosphate buffer is 0.1 mol / L.

[0017] As an embodiment of the present invention, in step S1, the inert atmosphere includes nitrogen. After the emulsion polymerization reaction, a saturated sodium chloride aqueous solution is added dropwise to break the emulsion, and the obtained product is washed to obtain a copolymer binder.

[0018] As an embodiment of the present invention, in step S2, the non-strongly polar solvent includes one or more of toluene, p-xylene, and o-xylene.

[0019] As an embodiment of the present invention, in step S2, the mass ratio of the copolymer binder to the polyisobutylene is 1:3-6, and the blending time is 20-30 h.

[0020] As an embodiment of the present invention, in step S2, the solid content (composite formed by polyisobutylene and 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.

[0021] The carboxyl group in the butyl acrylate monomer and the amide group in the 2-acrylamide-2-methylpropanesulfonic acid lithium monomer in the present invention will form chemical bonds with the functional groups on the surface of the sulfide electrolyte to improve ion conduction. Although the copolymer binder has good ion conduction properties, it is not viscous enough and cannot be used as a binder for sulfide electrolyte film formation. It cannot form a film alone. Polyisobutylene has high viscosity and good film formation for sulfide electrolytes. It can be dissolved in non-strong polar solvents such as toluene that have little effect on sulfides, but it cannot conduct lithium ions.

[0022] The polyisobutylene and copolymer binders of the present invention form an adhesive composite. When the polyisobutylene and copolymer binders are mixed, the functional groups and chemical bonds on their molecular chains interact with each other, thereby enhancing the stability of the composite binder and forming a composite. The obtained composite binder has a better film-forming effect, is more stable during the charge and discharge process, and is not easy to decompose.

[0023] The present invention also provides an application of the single ion conductor composite binder in preparing a sulfide electrolyte membrane.

[0024] The present invention also provides a method for preparing a sulfide electrolyte membrane, comprising the following steps: A1. Mixing and ball-milling a sulfide solid electrolyte, a single ion conductor composite binder and a non-strongly polar solvent to form a uniform sulfide electrolyte slurry; A2. Forming a sulfide electrolyte slurry into a film by wet coating, and drying the film to obtain a sulfide electrolyte membrane.

[0025] As an embodiment of the present invention, in step A1, the sulfide solid electrolyte is Li 6 PS 5 Cl type solid electrolyte.

[0026] As an embodiment of the present invention, in step A1, the non-strong polar solvent includes one or more of toluene, p-xylene, and o-xylene. The non-strong polar solvent in step A1 is preferably the same as the non-strong polar solvent in the single ion conductor composite binder.

[0027] As an embodiment of the present invention, in step A1, the mass fraction of the adhesive composite (composite adhesive) formed by polyisobutylene and copolymer adhesive in the sulfide electrolyte is 1-2%. The mass ratio of the sulfide solid electrolyte to the non-strongly polar solvent is 10:5-8.

[0028] As an embodiment of the present invention, in step A1, the ball milling time is 1-2 h, the rotation speed is 200-300 rpm, and the ball milling is carried out in a sealed argon atmosphere.

[0029] As an embodiment of the present invention, in step A2, the drying treatment is performed by constant temperature drying in a vacuum oven, the constant temperature drying temperature is 40-80°C, the time is 10-15 h, and the vacuum degree is 0.03-0.08 MPa.

[0030] As an embodiment of the present invention, in step A2, the thickness of the obtained sulfide electrolyte membrane is 30-60 μm.

[0031] The present invention also provides an application of the single ion conductor composite binder in preparing a sulfide all-solid-state battery.

[0032] Compared with the prior art, the present invention has the following beneficial effects: The binder provided by the present invention has non-polar solvent solubility, excellent bonding performance and ion conduction characteristics through innovative molecular structure design, which can solve the technical difficulties of wet film formation of sulfide solid electrolyte. It can not only improve the bonding force between electrolyte and binder, but also effectively reduce the interface impedance through single ion conduction characteristics, while showing excellent electrochemical stability. Its simple preparation process is highly compatible with existing production lines, greatly reducing production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings: Figure 1 A flow chart of a method for preparing a single ion conductor composite binder soluble in a non-strongly polar solvent provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0034] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. The examples are only used to explain the present invention, not to limit the scope of the present invention.

[0035] The present invention adopts butyl acrylate and 2-acrylamide-2-methylpropanesulfonic acid lithium copolymer and polyisobutylene to be compositely modified, which can achieve solubility in non-polar solvents and have both adhesiveness and single ion conduction functions. The butyl acrylate flexible segment provides elastic support, and the sulfonate group of 2-acrylamide-2-methylpropanesulfonic acid lithium forms a strong chemical bond with the surface of the sulfide particles, thereby enhancing the binding force with the electrolyte. In addition, the dissociated lithium ions of the single ion conductor unit can migrate directionally along the polymer chain, giving the electrolyte membrane a higher ionic conductivity. At the same time, the highly viscous polyisobutylene can improve the film-forming property of the sulfide electrolyte. This composite binder has good solubility in the non-strongly polar solvent toluene and is perfectly matched with the sulfide electrolyte.

[0036] Example 1 A method for preparing a single ion conductor composite binder soluble in a non-strongly polar solvent, such as Figure 1 As shown, the steps are as follows: (1) Lithiated single ion conductor monomer: 15 g of sodium 2-acrylamido-2-methylpropanesulfonate was dissolved in 85 g of deionized water. The solution was passed through a column filled with a hydrogen-type strongly acidic cation exchange resin to convert the terminal group of the monomer from -SO 3 Na is exchanged for -SO 3 H, and then neutralized with a 7wt% lithium hydroxide aqueous solution to pH = 7 to obtain a terminal group of -SO 3 Lithium single ion conductor monomer 2-acrylamido-2-methylpropanesulfonate.

[0037] (2) Preparation of copolymer binder: 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 were weighed and added to 25 g of 0.1 mol / L phosphate buffer (mixed with 1 mol / L sodium dihydrogen phosphate and 1 mol / L sodium hydrogen phosphate to obtain a phosphate buffer with a pH of 7). After evacuating the air and replacing the nitrogen three times, the temperature was raised to 60°C and polymerized for 2 h to obtain an emulsion. A saturated sodium chloride aqueous solution was then added dropwise to break the emulsion, and the polymer was washed. The mixture was then dried at 80°C in a vacuum oven for 10 h to obtain a copolymer binder.

[0038] (3) Preparing a composite binder solution in a non-strongly polar solvent: 1.0 g of polyisobutylene and 0.25 g of the copolymer obtained in (2) were dissolved in 30 g of toluene solvent and magnetically stirred at room temperature for 24 hours until a uniform composite binder solution was formed with a solid content of 4.0 wt%.

[0039] (4) Preparation of sulfide electrolyte slurry: In a glove box filled with argon, 10 g of sulfide electrolyte (Li 6 PS 5 Cl), added to a ball mill, and then added 2.5 g of the composite binder solution and 6 g of toluene solvent to evenly disperse the electrolyte. After sealing, ball milling was performed at room temperature for 2 h at a ball milling speed of 300 rpm to obtain a uniform electrolyte slurry. The mass fraction of the composite binder (polyisobutylene and copolymer binder forming a binder composite) in the sulfide electrolyte was 1%.

[0040] (5) Sulfide electrolyte wet film formation: The operation is carried out in a glove box filled with argon gas, and the electrolyte slurry is coated on the copper foil substrate with a thickness of 60 μm, and then directly blow-dried for 2 h. After that, it is dried in a vacuum oven at a temperature of 50 ° C and a vacuum degree of 0.05 MPa. The constant temperature drying time is 12 h.

[0041] Example 2 A method for preparing a single ion conductor composite binder soluble in a non-strongly polar solvent comprises the following steps: (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 convert the terminal group of the monomer from -SO 3 Na is exchanged for -SO 3 H, and then neutralized with a 7wt% lithium hydroxide aqueous solution to pH = 7 to obtain a terminal group of -SO3 Lithium single ion conductor monomer 2-acrylamido-2-methylpropanesulfonate.

[0042] (2) Preparation of copolymer binder: 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 were weighed and added to 25 g of 0.1 mol / L phosphate buffer (mixed with 1 mol / L sodium dihydrogen phosphate and 1 mol / L sodium hydrogen phosphate to obtain a phosphate buffer with a pH of 7). After evacuating the air and replacing the nitrogen three times, the temperature was raised to 60°C and polymerized for 2 h to obtain an emulsion. A saturated sodium chloride aqueous solution was then added dropwise to break the emulsion, and the polymer was washed. The mixture was dried at 80°C in a vacuum oven for 10 h to obtain a copolymer binder.

[0043] (3) Preparing a composite binder solution in a non-strongly polar solvent: 1.0 g of polyisobutylene and 0.20 g of the copolymer obtained in (2) were dissolved in 30 g of toluene solvent and magnetically stirred at room temperature for 24 hours until a uniform composite binder solution was formed with a solid content of 3.8 wt%.

[0044] (4) Preparation of sulfide electrolyte slurry: In a glove box filled with argon, 10 g of sulfide electrolyte (Li 6 PS 5 Cl), added to a ball mill, and then added 5.2 g of the composite binder solution and 5 g of toluene solvent to evenly disperse the electrolyte. After sealing, ball milling was performed at room temperature for 2 h at a ball milling speed of 300 rpm to obtain a uniform electrolyte slurry. The mass fraction of the composite binder (polyisobutylene and copolymer binder forming a binder composite) in the sulfide electrolyte was 2%.

[0045] (5) Sulfide electrolyte wet film formation: The operation is carried out in a glove box filled with argon gas, and the electrolyte slurry is coated on the copper foil substrate with a thickness of 60 μm, and then directly blow-dried for 2 h. After that, it is dried in a vacuum oven at a temperature of 50 ° C and a vacuum degree of 0.05 MPa. The constant temperature drying time is 12 h.

[0046] Comparative Example 1 The step (1) in Example 1 is eliminated, and the lithiated single ion conductor monomer 2-acrylamide-2-methylpropanesulfonate is not added. Only polybutyl acrylate polymer is prepared, and then blended with polyisobutylene to prepare a composite binder, which is then used for wet film formation of sulfide electrolyte.

[0047] Comparative Example 2 Step (3) in Example 1 was eliminated, and the composite binder was not prepared by blending with polyisobutylene. The poly(butyl acrylate / 2-acrylamide-2-methylpropanesulfonic acid lithium) copolymer was directly used as a binder, and then used for wet film formation of sulfide electrolyte. Since the viscosity of the copolymer is lower than that of polyisobutylene, the final film formation effect is not very good.

[0048] Comparative Example 3 Only the amount of the composite binder in step (4) of Example 1 was changed, and the mass fraction of the composite binder (adhesive composite formed by polyisobutylene and copolymer binder) in the sulfide electrolyte was 3%.

[0049] Comparative Example 4 This comparative example is basically the same as Example 1, except that the single-ion conductor monomer 2-acrylamide-2-methylpropanesulfonate lithium is replaced by an equal amount of styrenesulfonyl (trifluoromethanesulfonyl) imide lithium. Since its molecular chain contains benzene rings and is too rigid, the copolymer finally prepared cannot be dissolved in toluene and can only form a dispersion. The composite after blending with polyisobutylene cannot be completely dissolved in toluene. The surface of the electrolyte membrane finally formed by coating is rough and unevenly dispersed.

[0050] Comparative Example 5 This comparative example is basically the same as Example 1, except that polyisobutylene is replaced by an equal amount of nitrile rubber, the surface flatness of the electrolyte membrane finally formed by coating is lower than that of polyisobutylene, and the measured ionic conductivity is significantly lower than that of Example 1.

[0051] Comparative Example 6 This comparative example is basically the same as Example 1, except that the preparation of the composite binder solution is eliminated, polyisobutylene, copolymer binder and sulfide electrolyte are added to a ball mill at the same time for ball milling (the amount of solvent is the same as that in Example 1) to prepare a slurry, and the ionic conductivity of the final film is lower than that in Example 1.

[0052] The embodiments and comparative examples were tested as follows: Test of ionic conductivity: The prepared electrolyte membrane was cut into small discs, which were then loaded into a pressure battery mold and pressed at a pressure of 1 ton for 1 minute. An electrochemical workstation with specification model CHI660E was used to perform an AC impedance test at room temperature in a normal atmospheric atmosphere, and the ionic conductivity was calculated. The results are shown in Table 1.

[0053] Table 1. Electrochemical performance data of sulfide electrolyte membrane

[0054] As can be seen from the table, the impedance of the sulfide electrolyte membrane of Examples 1 and 2 is less than that of the comparative example, and its ionic conductivity is higher than that of the comparative example. This is mainly because the flexible segment of butyl acrylate provides elastic support, and the sulfonate group of 2-acrylamide-2-methylpropanesulfonic acid lithium forms a strong chemical bond with the surface of the sulfide particles, enhancing the binding force with the electrolyte. In addition, the dissociated lithium ions of the single ion conductor unit can migrate directionally along the polymer chain, giving the electrolyte membrane a higher ionic conductivity. At the same time, polyisobutylene with high viscosity can improve the film-forming property of the sulfide electrolyte. This composite binder has good solubility in the non-strong polar solvent toluene, and is perfectly matched with the sulfide electrolyte. It can solve the key problem that traditional polar solvent binders cannot be used in sulfide systems, and realizes the uniform dispersion and stable slurry preparation of sulfide electrolytes, providing key technical support for the industrialization of sulfide all-solid-state batteries.

[0055] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that these are merely examples, and any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a single ion conductor composite binder, characterized in that: The following steps are involved: S1, adding butyl acrylate monomer, single ion conductor monomer with terminal group as lithium sulfonate group, initiator and surfactant into phosphate buffer, and subjecting the obtained polymerization solution to emulsion polymerization under inert atmosphere to obtain copolymer binder; S2. Dissolve polyisobutylene and copolymer binders in a non-strongly polar solvent and blend them to obtain a single ion conductor composite binder.

2. The method for preparing the single ion conductor composite binder according to claim 1, characterized in that: In step S1, the single ion conductor monomer whose terminal group is a lithium sulfonate group is 2-acrylamide-2-methylpropanesulfonate lithium.

3. The method for preparing the single ion conductor composite binder according to claim 1, characterized in that: In step S1, the molar ratio of the butyl acrylate monomer to the single ion conductor monomer having a lithium sulfonate group as the terminal group is 5-8:

1.

4. The method for preparing the single ion conductor composite binder according to claim 1, characterized in that: In step S2, the non-strongly polar solvent includes one or more of toluene, p-xylene, and o-xylene.

5. The method for preparing the single ion conductor composite binder according to claim 1, characterized in that: In step S2, the mass ratio of the copolymer binder to the polyisobutylene is 1:3-6; And / or, in step S2, the solid content of the obtained single ion conductor composite binder is 1-4 wt %.

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

7. A method for preparing a sulfide electrolyte membrane, comprising the following steps: A1, mixing a sulfide solid electrolyte, a single ion conductor composite binder obtained by the preparation method according to claim 1 and a non-strong polar solvent, and ball milling them to form a uniform sulfide electrolyte slurry; A2. Forming a sulfide electrolyte slurry into a film by wet coating, and drying the film to obtain a sulfide electrolyte membrane.

8. The method for preparing a sulfide electrolyte membrane according to claim 7, characterized in that: In step A1, the mass fraction of the adhesive composite formed by the polyisobutylene and copolymer adhesives in the sulfide electrolyte is 1-2%.

9. The method for preparing a sulfide electrolyte membrane according to claim 7, characterized in that: In step A2, the thickness of the obtained sulfide electrolyte membrane is 30-60 μm.

10. Use of the single ion conductor composite binder obtained by the preparation method according to claim 1 in the preparation of sulfide all-solid-state batteries.

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