Modified binder, sulfide solid electrolyte membrane, preparation method of sulfide solid electrolyte membrane and all-solid-state battery

Abstract

The invention discloses a modified binder, a sulfide solid electrolyte membrane, a preparation method of the sulfide solid electrolyte membrane and an all-solid-state battery, and relates to the technical field of batteries. The modified binder comprises styrene butadiene rubber, a non-polar monomer and a polar monomer; by modifying butadiene styrene rubber, introducing a proper amount of polar groups and optimizing the content of the polar groups, fine regulation and control of polarity and non-polarity of the binder are realized, so that interaction between the binder and sulfide electrolyte is improved, and the problems of poor mechanical property, insufficient binding force and the like of the existing non-polar binder are solved. Meanwhile, the problem of balance between the solubility of the modified binder and the compatibility of the electrolyte is also synchronously solved, the smooth proceeding of subsequent slurry preparation is effectively ensured, and the uniformity and flexibility of the prepared sulfide solid electrolyte membrane are ensured.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically, to a modified binder, a sulfide solid electrolyte membrane and its preparation method, and an all-solid-state battery. Background Technology

[0002] In the field of ultrathin sulfide solid electrolyte membrane preparation, the binders used in existing technologies have significant drawbacks, mainly being limited to non-polar binders such as butadiene rubber (BR), silicone rubber (SR), styrene-butadiene rubber (SBR), and ethylene-butene-styrene copolymer (SEBS). Electrolyte membranes prepared using these non-polar binders have a bending radius ≥8mm, and a cracking rate as high as 80% after 10 cycles of use, exhibiting extremely poor mechanical properties.

[0003] Ultrathin sulfide solid electrolyte membranes prepared using this type of binder not only have poor mechanical properties, making them prone to cracking and damage, but also lack uniformity, negatively impacting the ion conductivity of the electrolyte membrane. Furthermore, due to weak adhesion, the electrolyte membrane does not bond firmly to other components such as electrodes during subsequent processing and use, further limiting the overall performance and lifespan of the all-solid-state battery. Therefore, it is necessary to modify non-polar binders.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a modified binder, a sulfide solid electrolyte membrane and its preparation method, and an all-solid-state battery to solve or improve the above-mentioned technical problems.

[0006] This invention is implemented as follows: In a first aspect, the present invention provides a modified adhesive comprising styrene-butadiene rubber and monomers in a mass ratio of (20-30):(0.6-0.8), wherein the monomers comprise nonpolar monomers and polar monomers in a mass ratio of 5:(3-1).

[0007] Secondly, the present invention provides a method for preparing a modified adhesive as described in any of the foregoing embodiments, comprising the following steps: After dissolving styrene-butadiene rubber in an alkane solvent for 8-24 hours according to a certain ratio, monomers and initiators are added, and the mixture is reacted under a protective atmosphere at 60-80℃ for 2-5 hours to obtain a modified adhesive.

[0008] Thirdly, the present invention provides a sulfide solid electrolyte membrane prepared using a modified binder as described in any of the foregoing embodiments, wherein the thickness error of the sulfide solid electrolyte membrane is ≤ ±3 μm, the initial crack bending radius is ≤ 5 mm, the number of alternating winding-unwinding cycles on a 5 mm diameter mandrel is ≥ 22, and the conductivity is ≥ 2.1 × 10⁻⁶. -3 S / cm.

[0009] Fourthly, the present invention provides a method for preparing a sulfide solid electrolyte membrane using the aforementioned embodiments, comprising the following steps: The modified binder is dissolved in a non-polar solvent to prepare a mixed solution; wherein the amount of modified binder is 3wt%-5wt%. A slurry is prepared by adding a sulfide solid electrolyte to a mixed solution; wherein the mass ratio of the sulfide solid electrolyte to the modified binder is (95-98):(2-5). The slurry was coated onto the substrate and dried at 60℃-80℃ for 20-24 hours to obtain a sulfide solid electrolyte membrane.

[0010] Fifthly, the present invention provides an all-solid-state battery comprising the modified binder as described in the foregoing embodiments.

[0011] The present invention has the following beneficial effects: The modified binder, sulfide solid electrolyte membrane, preparation method thereof, and all-solid-state battery provided in this invention have the following characteristics: (1) Improved bonding effect: The modified styrene-butadiene rubber adhesive has introduced polar groups, and the interaction between it and the sulfide electrolyte has changed from weak van der Waals forces to stronger polar interactions.

[0012] (2) Enhanced mechanical properties: The prepared sulfide solid electrolyte membrane has better flexibility. After bending test and alternating mandrel test, the membrane is not easy to crack or break, and the mechanical stability is greatly improved.

[0013] (3) Ensure ion conduction performance: While improving the bonding effect and mechanical properties, the polarity and non-polarity of the binder are precisely controlled, ensuring its solubility in toluene solvent and not adversely affecting the ion conduction of the sulfide electrolyte, thus ensuring that the electrolyte membrane has good conductivity.

[0014] (4) Improved membrane uniformity: The modified binder can better disperse sulfide electrolyte particles, resulting in higher uniformity of the prepared ultrathin sulfide solid electrolyte membrane. Detailed Implementation

[0015] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0016] In the current production process of all-solid-state batteries, the yield rate of ultra-thin sulfide electrolyte membranes with a thickness of <50 μm can only reach 65% due to adhesive issues. Furthermore, during use, the ionic conductivity decay rate is as high as 10% per month, which seriously affects the production efficiency and service life of all-solid-state batteries.

[0017] From a technical perspective, the surface energy difference between non-polar binders and sulfide electrolytes (such as LPSC) is >30 mJ / m 2 This directly leads to a weak interface between the two, resulting in poor mechanical properties and unstable ion conduction. Furthermore, non-polar binders, lacking polar functional groups, can only interact with sulfide electrolytes through weak van der Waals forces, resulting in poor bonding.

[0018] This invention modifies styrene-butadiene rubber (SBR) by introducing appropriate amounts of polar groups and optimizing their content, thereby achieving precise control over the polarity and non-polarity of the binder. This improves the interaction between the binder and the sulfide electrolyte, solving problems such as poor mechanical properties and insufficient bonding strength in existing non-polar binders. Specific implementation methods are as follows: In a first aspect, the present invention provides a modified adhesive comprising styrene-butadiene rubber and monomers in a mass ratio of (20-30):(0.6-0.8), wherein the monomers comprise nonpolar monomers and polar monomers in a mass ratio of 5:(3-1).

[0019] The modified binder provided by this invention has a weight-average molecular weight of 8.82 × 10⁻⁶. 5 g / mol - 10.4 × 10 5 g / mol, number-average molecular weight is 4.8 × 10⁻⁶ g / mol 5 g / mol - 5.2 × 10 5 g / mol, dispersion 1.8-2.0. While improving the polarity of styrene-butadiene rubber, it also enhances the uniformity and flexibility of ultrathin sulfide solid electrolyte membranes.

[0020] By introducing precisely controlled non-polar and polar monomers, the polarity of styrene-butadiene rubber (SBR) can be regulated, thereby improving the interaction between the binder and the sulfide electrolyte. This solves the problems of poor mechanical properties and insufficient bonding force of existing non-polar binders, while also ensuring ion conductivity and improving film uniformity.

[0021] Specifically, this application employs solution polymerization with styrene-butadiene rubber (SBR) as the modified matrix, randomly grafting a certain amount of polar and non-polar monomers. The polymerization principle utilizes the grafting of diene polymers with double bonds and allyl hydrogens in SBR as grafting points to achieve chain growth reactions of monomers at the grafting points. This grafting method can precisely control the monomer grafting position and grafting rate, avoiding the problem of uneven monomer distribution in traditional copolymerization methods. The grafting rate can reach over 92%, providing a foundation for stable adhesive performance.

[0022] For example, the mass ratio of styrene-butadiene rubber to monomer can be selected from any one of 20:0.6, 25:0.6, 28:0.6, 25:0.7, 25:0.8, 30:0.6, 30:0.7 and 30:0.8, or other values ​​in the range of (20-30):(0.6-0.8).

[0023] The monomer mass ratio can be selected from any one of 5:3, 5:2.5, 5:2, and 5:1, or other values ​​within the range of 5:(3-1). Setting the monomer ratio ensures the solubility of the modifier in the solvent and its adhesion to the sulfide electrolyte during the preparation of the sulfide electrolyte membrane. When the ratio is <5:1, the binder is too polar, and its solubility in the solvent is <3 wt%; when the ratio is >5:3, the polarity is insufficient, and the interfacial bonding force between the binder and the sulfide solid electrolyte is <10 N / m.

[0024] In an optional embodiment, the nonpolar monomer is selected from at least one of ethylene, styrene, butadiene, and propylene; And / or, the polar monomer is selected from at least one of methyl acrylate, methyl methacrylate and vinyl acetate.

[0025] In the preferred embodiment, styrene is used as the nonpolar monomer and methyl acrylate is used as the polar monomer. In other embodiments of the invention, other monomer types may be selected as needed.

[0026] In this invention, the binder modified by combining styrene and methyl acrylate significantly improves the bonding force between the binder and the sulfide solid electrolyte, enabling the binder to be uniformly distributed in the sulfide solid electrolyte. For example, the interfacial bonding force between the binder and the sulfide solid electrolyte increases from 5 N / m of the original non-polar binder to 18 N / m, an increase of up to 260%.

[0027] Specifically, this invention precisely adjusts the polarity of the binder by controlling the relative amounts of grafted monomers (styrene and methyl acrylate) and styrene-butadiene rubber, as well as the relative amounts of the polar monomer methyl acrylate and the non-polar monomer styrene. When the content of polar groups is appropriate, it ensures good solubility of the modified binder in toluene solution, facilitating subsequent slurry preparation and processing; it also enhances the interaction with the sulfide electrolyte, improving the bonding effect and ensuring uniform dispersion of the binder in the electrolyte, thereby guaranteeing the conductivity and flexibility of the electrolyte membrane.

[0028] An appropriate amount of the nonpolar monomer styrene maintains the nonpolar portion of the binder. The benzene ring in its molecular structure forms π-π interactions with toluene solvent molecules, ensuring the binder achieves a solubility of 5 wt% in the solvent without precipitation, meeting the concentration requirements for slurry preparation. Meanwhile, the ester group (-COO-) introduced by the polar monomer methyl acrylate can coordinate with lithium ions in sulfide electrolytes (such as LPSC) and simultaneously form hydrogen bonds with hydroxyl groups (-OH) on the electrolyte surface, significantly enhancing interfacial adhesion. The synergistic effect of these two monomers allows the modified binder to meet the uniformity and flexibility requirements of ultrathin sulfide solid electrolyte membranes, while avoiding performance defects caused by a single polar or nonpolar monomer.

[0029] The anti-aging properties of the film have also been significantly improved. For example, after being placed in an environment of 85°C and 60% humidity for 1000 hours, the adhesion attenuation rate is only 5%, which is much lower than the 30% of the original non-polar adhesive.

[0030] The thickness uniformity error of sulfide solid electrolyte membrane has been reduced from ±8 μm in the original technology to ±2 μm, and the yield rate has been increased to 92%, which is beneficial to improving the performance stability of devices such as all-solid-state batteries.

[0031] In addition, this invention also simultaneously solves the problem of balancing the solubility of the modified binder in the non-polar solvent toluene with electrolyte compatibility. In the original technology, the solubility of polar binders in toluene is usually <5 wt%, while the solubility of the modified binder in toluene in this invention can reach 5 wt% without precipitation, effectively ensuring the smooth progress of subsequent slurry preparation.

[0032] Secondly, the present invention provides a method for preparing a modified adhesive as described in any of the foregoing embodiments, comprising the following steps: After dissolving styrene-butadiene rubber in an alkane solvent for 8-24 hours according to a certain ratio, monomers and initiators are added, and the mixture is reacted under a protective atmosphere at 60-80℃ for 2-5 hours to obtain a modified adhesive.

[0033] Using styrene-butadiene rubber as the modified matrix, solution polymerization was employed to randomly graft polar monomers methyl acrylate and nonpolar monomers styrene. By controlling the reaction temperature and initiator dosage, a grafting rate of >90% was achieved, allowing for precise control of the binder polarity. Compared to traditional emulsion polymerization, solution polymerization avoids the impact of emulsifier residues on electrolyte performance, and the reaction system is stable and easily scaled up for industrial applications.

[0034] Furthermore, matching the boiling point of alkane solvents with the reaction temperature can prevent uneven reaction caused by premature solvent evaporation. A reaction temperature of 60℃-80℃ is crucial for ensuring a grafting rate (>85%). Below 60℃, the initiator decomposes slowly, resulting in a grafting rate of <60%; above 80℃, styrene-butadiene rubber is prone to cross-linking, leading to a decrease in the solubility of the binder.

[0035] Conducting experiments in a protective atmosphere can prevent the influence of oxygen during the preparation of the modified binder, thus avoiding side reactions, the generation of byproducts, and the impact on the final purity of the product. Furthermore, it can improve the safety of the entire experimental process. This invention does not impose any particular limitation on the protective atmosphere; nitrogen, helium, or argon can be selected according to actual needs.

[0036] To accelerate the reaction rate and ensure a more complete reaction, mechanical stirring is also employed in this embodiment of the invention. The initiator is added slowly, dropwise.

[0037] The present invention does not impose any particular limitation on the reaction vessel. Specifically, in the embodiments of the present invention, a 500mL stainless steel autoclave with a pressure resistance of 1 MPa is used.

[0038] In an optional embodiment, the alkane solvent includes n-hexane and cyclohexane in a volume ratio of 1:(1.5-5).

[0039] It should be noted that, considering that the solvent needs to not react with the binder and to ensure the integrity of the binder's molecular structure, this invention uses alkane solvents as reagents for binder modification.

[0040] Changing the ratio of n-hexane to cyclohexane in the solvent system reduces the solubility of the binder in the solvent and significantly affects the conductivity of the prepared electrolyte membrane, indicating that the use of alkane solvents plays a crucial role in product performance.

[0041] In the optimal implementation, the volume ratio of n-hexane to cyclohexane is 1:4, at which the solubility of styrene-butadiene rubber can reach 20 wt%.

[0042] In an optional embodiment, the initiator is 0.5%-1% of the total mass of the monomers; Preferably, the initiator is selected from at least one of benzoyl peroxide (BPO), dodecanoyl peroxide, and azobisisobutyronitrile.

[0043] In the preferred embodiment, benzoyl peroxide (BPO) is selected as the initiator.

[0044] It should be noted that changing the type of initiator will reduce the reaction conversion rate and grafting rate, and will also broaden the molecular weight distribution of the binder, that is, increase the dispersion, decrease the membrane flexibility, and increase the bending radius. For example, if AIBN (azobisisobutyronitrile) is used to replace BPO, the reaction conversion rate will decrease from 92% to 65%, the molecular weight distribution of the binder will broaden, the membrane flexibility will decrease, and the bending radius will increase to 6 mm.

[0045] In an optional embodiment, after the reaction is completed, the reaction system is further subjected to washing, precipitation and drying treatments. The solvent used in the washing process is an alcohol solution, and the drying process is carried out at a temperature of 75℃-85℃.

[0046] Considering that styrene-butadiene rubber (SBR) may emulsify, dissolve, or swell in water, the washing agent used in this invention is anhydrous ethanol, which can effectively remove the modified SBR from the equipment surface. Furthermore, anhydrous ethanol is characterized by rapid evaporation, easy drying, high safety, and low toxicity.

[0047] After washing, to accelerate product recovery efficiency, this embodiment of the invention uses vacuum filtration for recovery. The filtered and washed product is then dried. In other embodiments of the invention, other filtration methods can be selected as needed.

[0048] The present invention does not impose a particular limitation on the drying time, which can be reasonably adjusted according to the actual amount of material being processed.

[0049] Thirdly, the present invention provides a sulfide solid electrolyte membrane prepared using a modified binder as described in any of the foregoing embodiments, wherein the thickness error of the sulfide solid electrolyte membrane is ≤ ±3 μm, the initial crack bending radius is ≤ 5 mm, the number of alternating winding-unwinding cycles on a 5 mm diameter mandrel is ≥ 22, and the conductivity is ≥ 2.1 × 10⁻⁶. -3 S / cm.

[0050] It should be noted that the modified binder provided by this invention can better disperse sulfide electrolyte particles, resulting in a more uniform ultrathin sulfide solid electrolyte membrane with a thickness error of ≤±3 μm. While improving the bonding effect and mechanical properties, the finely controlled polarity and non-polarity of the binder ensure its solubility in non-polar solvents and do not adversely affect the ion conduction of the sulfide electrolyte, thus guaranteeing good conductivity of the electrolyte membrane.

[0051] Fourthly, the present invention provides a method for preparing a sulfide solid electrolyte membrane using the aforementioned embodiments, comprising the following steps: The modified binder is dissolved in a non-polar solvent to prepare a mixed solution; wherein the amount of modified binder is 3wt%-5wt%. A slurry is prepared by adding a sulfide solid electrolyte to a mixed solution; wherein the mass ratio of the sulfide solid electrolyte to the modified binder is (95-98):(2-5). The slurry was coated onto the substrate and dried at 60℃-80℃ for 20-24 hours to obtain a sulfide solid electrolyte membrane.

[0052] It should be noted that the entire process of preparing the sulfide solid electrolyte membrane is carried out in an argon-filled glove box. The mixed solution obtained by this invention is a clear solution; to ensure the uniformity of the slurry, the slurry preparation is carried out in a ball mill. This invention does not impose any particular limitation on the ball mill equipment, and can reasonably select one according to actual needs. Specifically, in the embodiment of this invention, a planetary ball mill of model XQM-4L is used, with a rotation speed of 300 rpm-500 rpm, and the ball milling time is 1.5 h-3 h. The slurry after ball milling significantly improves the uniformity and flexibility of the membrane, solving the industry problem of difficult thickness control and easy cracking in the preparation of ultrathin sulfide solid electrolyte membranes.

[0053] A slurry with an adjustable thickness between 0 and 200 μm was poured onto a substrate membrane to prepare a sulfide solid electrolyte membrane. The substrate coated with the slurry was then dried to remove non-polar solvents. After drying, the sulfide solid electrolyte membrane was separated from the substrate, and a series of performance tests were performed, such as bending tests and alternating mandrel tests.

[0054] In this invention, the type of substrate is not particularly limited, and it can be reasonably selected according to actual needs, such as PTFE, PET, PI, PP and PE.

[0055] In an optional embodiment, the sulfide solid electrolyte is selected from Li6PS5X and its derivatives, Li 10 MP2S 12X is at least one of its derivatives and Li3PS4 and its derivatives; wherein X is at least one of Cl, Br and I, and M is at least one of Ge, Sn and Si.

[0056] Fifthly, the present invention provides an all-solid-state battery comprising the modified binder as described in the foregoing embodiments.

[0057] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0058] Example 1 This embodiment provides a sulfide solid electrolyte membrane, which is prepared by the following steps: (1) Preparation of modified adhesive Take 200 g of styrene-butadiene rubber and add it to an alkane solvent (hexane and cyclohexane in a volume ratio of 1:4, of which 40 mL of hexane and 160 mL of cyclohexane are mixed and dissolved in a 500 mL stainless steel autoclave for 12 h).

[0059] Add 5 g of non-polar monomer styrene and 2 g of polar monomer methyl acrylate in a mass ratio of 5:2 to a stainless steel autoclave. The total mass ratio of styrene-butadiene rubber to monomers is 20:0.7.

[0060] Under nitrogen protection, with mechanical stirring (300 rpm), 0.5 g of initiator BPO was added dropwise, and the reaction was carried out at 70℃ for 3 h. The reaction product was precipitated with anhydrous ethanol (500 mL), filtered, and dried in an oven at 80℃ for 12 h to obtain the modified binder, whose weight-average molecular weight was measured to be 9 × 10⁻⁶. 5 g / mol, number-average molecular weight is 5×10 5 g / mol, with a dispersion of 1.8.

[0061] Molecular weight was measured using gel permeation chromatography (GPC) under the following conditions: tetrahydrofuran (THF) as the mobile phase, flow rate 1.0 mL / min, column temperature 30℃, and calibration with polystyrene standards. The elution curve was recorded using a GPC workstation, and the number-average molecular weight (Mn) and weight-average molecular weight (Mw) were calculated. The dispersity was measured by deriving from the GPC test data: dispersity (D) = weight-average molecular weight (Mw) / number-average molecular weight (Mn).

[0062] (2) Preparation of sulfide solid electrolyte membrane The modified binder obtained in step (1) is mixed with the non-polar solvent toluene in a certain proportion to form a clear mixed solution. The amount of modified binder is 5 wt% of toluene, and the amount of toluene is 200 g.

[0063] The sulfide solid electrolyte (LPSC) and the modified binder were added to the above mixed solution at a mass ratio of 97:3. The mixture was then ball-milled in a planetary ball mill of model XQM-4L at a speed of 300 rpm for 2 hours to ensure uniformity, thus obtaining a slurry.

[0064] The slurry was poured onto a PET film using a 50 μm thick spatula, and the film was dried at 60°C for 24 h to remove the toluene solvent, thus obtaining a sulfide solid electrolyte membrane.

[0065] The sulfide solid electrolyte membrane was tested and found to have a thickness of 35 μm, good uniformity (thickness error ±2 μm), excellent flexibility (it can be bent to a large angle without breaking in the bending test), and good conductivity.

[0066] The thickness test method uses a micrometer (accuracy 0.001 mm) to measure the thickness at five points in different areas of the membrane (center, four corners and edges). Each point is measured three times and the average value is taken. The average value of the five points is taken as the actual thickness of the membrane. Half of the difference between the maximum and minimum values ​​of the five points is taken as the thickness error.

[0067] Example 2 This embodiment provides a sulfide solid electrolyte membrane, the preparation steps of which are the same as those in Example 1, the only difference being: (1) Preparation of modified adhesive Take 300 g of styrene-butadiene rubber and stir to dissolve it in a stainless steel autoclave for 18 h.

[0068] The mass ratio of styrene-butadiene rubber to monomers is 30:0.7.

[0069] The weight-average molecular weight of the obtained modified binder was 9.12 × 10⁻⁶. 5 g / mol, number-average molecular weight is 4.8 × 10⁻⁶ g / mol 5 g / mol, with a dispersion of 1.9.

[0070] (2) Preparation of sulfide solid electrolyte membrane Testing revealed that the sulfide solid electrolyte membrane has a thickness of 38 μm, exhibiting good uniformity (thickness error ±3 μm) and flexibility, and its performance meets the application requirements.

[0071] Example 3 This embodiment provides a sulfide solid electrolyte membrane, the preparation steps of which are the same as those in Example 1, the only difference being: (1) Preparation of modified adhesive Styrene-butadiene rubber was stirred and dissolved in a stainless steel autoclave for 8 hours.

[0072] Add 5 g of non-polar monomer styrene and 3 g of polar monomer methyl acrylate in a mass ratio of 5:3 to a stainless steel autoclave. The total mass ratio of styrene-butadiene rubber to monomers is 20:0.8.

[0073] The weight-average molecular weight of the obtained modified binder was 10.4 × 10⁻⁶. 5 g / mol, number-average molecular weight is 5.2 × 10⁻⁶ g / mol 5 g / mol, with a dispersion of 2.0.

[0074] (2) Preparation of sulfide solid electrolyte membrane The sulfide solid electrolyte membrane was tested and found to have a thickness of 36 μm, with good uniformity (thickness error ±2.5 μm) and flexibility.

[0075] Example 4 This embodiment provides a sulfide solid electrolyte membrane, the preparation steps of which are the same as those in Example 1, the only difference being: (1) Preparation of modified adhesive Styrene-butadiene rubber was stirred and dissolved in a stainless steel autoclave for 24 hours.

[0076] Add 5 g of non-polar monomer styrene and 1 g of polar monomer methyl acrylate in a mass ratio of 5:1 to a stainless steel autoclave. The total mass ratio of styrene-butadiene rubber to monomers is 20:0.6.

[0077] The weight-average molecular weight of the obtained modified binder was 8.82 × 10⁻⁶. 5 g / mol, number-average molecular weight is 4.9 × 10 5 g / mol, with a dispersion of 1.8.

[0078] (2) Preparation of sulfide solid electrolyte membrane The thickness of the sulfide solid electrolyte membrane was found to be 37 μm, and its performance met expectations.

[0079] Example 5 This embodiment provides a sulfide solid electrolyte membrane, the preparation steps of which are the same as those in Example 1, the only difference being: (1) Preparation of modified adhesive The alkane solvent is n-hexane and cyclohexane in a volume ratio of 1:1.5, wherein 80 mL of n-hexane and 120 mL of cyclohexane are used. The styrene-butadiene rubber is stirred and dissolved in a stainless steel autoclave for 12 hours.

[0080] (2) Preparation of sulfide solid electrolyte membrane The film thickness is 39 μm with an error of ±5 μm, the initial bending crack radius is 6 mm, and the conductivity is 1.8 × 10⁻⁶. -3The S / cm ratio demonstrates that the ratio of mixed solvents has a significant impact on the solubility of the binder and the film performance, and the original 1:4 ratio is the optimal choice.

[0081] Comparative Example 1 This comparative example provides a sulfide solid electrolyte membrane, the preparation steps of which are the same as those in Example 1, the only difference being: (1) Preparation of modified adhesive Unmodified styrene-butadiene rubber was used directly as the binder.

[0082] (2) Preparation of sulfide solid electrolyte membrane Testing revealed that the sulfide solid electrolyte membrane had a thickness of 40 μm with a thickness error of ±8 μm. It exhibited poor adhesion, weak mechanical properties, and cracked easily during bending tests. Its uniformity was also poor, failing to meet the requirements for use as an ultrathin sulfide solid electrolyte membrane.

[0083] Comparative Example 2 This comparative example provides a sulfide solid electrolyte membrane, the preparation steps of which are the same as those in Example 1, the only difference being: (1) Preparation of modified adhesive The monomer used is only the non-polar monomer styrene, and the mass ratio of styrene-butadiene rubber to styrene is 20:0.7.

[0084] (2) Preparation of sulfide solid electrolyte membrane Tests showed that the thickness of the sulfide solid electrolyte membrane was 39 μm. Due to the lack of polar groups, the binding force with the sulfide electrolyte was weak, the mechanical properties were poor, and it was easily damaged.

[0085] Comparative Example 3 This comparative example provides a sulfide solid electrolyte membrane, the preparation steps of which are the same as those in Example 1, the only difference being: (1) Preparation of modified adhesive The monomer used was only the polar monomer methyl acrylate, and the mass ratio of styrene-butadiene rubber to methyl acrylate was 20:0.7.

[0086] (2) Preparation of sulfide solid electrolyte membrane The modified binder is too polar, with a solubility of only 2 wt% in toluene, and the slurry is prone to separation.

[0087] The thickness of the sulfide solid electrolyte membrane was found to be 41 μm with a thickness error of ±9 μm. Due to the excessive polarity, the solubility of the binder in toluene was reduced, making it difficult to mix the slurry evenly. As a result, the uniformity and conductivity of the membrane were not ideal.

[0088] Comparative Example 4 This comparative example provides a sulfide solid electrolyte membrane, the preparation steps of which are the same as those in Example 1, the only difference being: (1) Preparation of modified adhesive Under nitrogen protection, mechanical stirring (300 rpm) was used to add 0.5 g of initiator AIBN dropwise.

[0089] The reaction conversion rate decreased from 92% to 65%, the molecular weight distribution of the binder broadened, the membrane flexibility decreased, and the bending radius increased to 6 mm.

[0090] Test Example 1 This test case performs performance tests on the products of Examples 1-5 and Comparative Examples 1-3. The relevant test results are summarized in Table 1. The specific test items are as follows: (1) Bending test The prepared LPSC SE membrane was cut into strips of 100 mm × 10 mm. At room temperature, the membrane was bent at a rate of 5 mm / min with radii of 2 mm, 3 mm, and 4 mm using a mechanical bending device with an accuracy of 0.1 mm. Each radius was held for 5 min, and the membrane was observed for cracking or damage. The bending radius at which the membrane first cracked was used as an indicator of flexibility; the smaller the bending radius, the better the flexibility.

[0091] (2) Alternating axis test Using metal mandrels with diameters of 5 mm, 10 mm, and 15 mm (accuracy ±0.05 mm), LPSC SE membranes (100 mm × 10 mm) were alternately wound around mandrels of different diameters. After each turn, the membrane was unwound, and the number of winding-unwinding cycles was recorded until cracks or fissures with a length >1 mm appeared in the membrane. The more cycles, the better the membrane's flexibility and fatigue resistance.

[0092] (3) Conductivity test An electrochemical impedance spectroscopy (EIS) method was used, employing an electrochemical workstation to sandwich a sulfide solid electrolyte membrane between two stainless steel electrodes, forming a symmetrical cell structure. At room temperature, the test frequency range was 1 Hz–1 MHz, and the AC signal amplitude was 10 mV. The conductivity of the electrolyte membrane was calculated based on the Nyquist plot in the impedance spectrum, using the formula: σ = L / (R×S), where σ is the conductivity (S / cm), L is the membrane thickness (cm) (see the first column of the table), R is the resistance of the electrolyte membrane (Ω), and S is the contact area between the electrode and the membrane (cm²). 2 The S value for all samples was 0.785 cm⁻¹. 2 .

[0093] Table 1 Performance Test Data

[0094] As can be seen from the data in Table 1, this invention, through a combination of "styrene-butadiene rubber + binary monomer grafting modification" + "1:4 mixed solvent" + "precise parameter control," successfully solves the core pain points of existing technologies, namely "weak bonding between the binder and electrolyte interface, poor membrane uniformity, and insufficient mechanical properties." The prepared ultrathin sulfide electrolyte membrane (thickness 35-40 μm) exhibits excellent uniformity (error ±2-3 μm), flexibility (bending radius 3-5 mm), and conductivity (2.1×10⁻⁶). -3 -2.5×10 -3 It is significantly superior to existing technologies in terms of S / cm and aging resistance, fully meeting the stringent requirements of all-solid-state batteries for electrolyte membranes, and has clear industrial application value.

[0095] The modified binder, sulfide solid electrolyte membrane and its preparation method provided in this invention embodiment, and all-solid-state battery, achieve fine control of the polarity and non-polarity of the binder by modifying styrene-butadiene rubber, introducing an appropriate amount of polar groups and optimizing their content, thereby improving the interaction between the binder and the sulfide electrolyte and solving the problems of poor mechanical properties and insufficient bonding force of existing non-polar binders.

[0096] It has the following characteristics: (1) Improved bonding effect: The modified styrene-butadiene rubber adhesive, due to the introduction of polar groups, transforms the interaction between the adhesive and the sulfide electrolyte from weak van der Waals forces to stronger polar interactions. Tests showed that the interfacial bonding force between the modified adhesive and LPSC increased from 5 N / m in the original non-polar adhesive to 18 N / m, an increase of up to 260%, significantly improving the bonding force between the adhesive and the sulfide electrolyte, enabling the adhesive to be uniformly distributed in the sulfide solid electrolyte.

[0097] (2) Enhanced mechanical properties: The prepared ultrathin sulfide solid electrolyte membrane has superior flexibility. After bending test and alternating mandrel test, the membrane is not easy to crack or break, and the mechanical stability is greatly improved. Compared with the existing technology, the membrane also has excellent anti-aging performance. After being placed in an environment of 85℃ and 60% humidity for 1000 h, the adhesion strength decay rate is only 5%, which is far lower than the 30% of the original non-polar adhesive.

[0098] (3) Ensure ion conduction performance: While improving the bonding effect and mechanical properties, the polarity and non-polarity of the binder are precisely controlled, ensuring its solubility in toluene solvent and not adversely affecting the ion conduction of the sulfide electrolyte, thus ensuring that the electrolyte membrane has good conductivity.

[0099] (4) Improved membrane uniformity: The modified binder can better disperse sulfide electrolyte particles, resulting in higher uniformity of the prepared ultrathin sulfide solid electrolyte membrane. Among them, the thickness uniformity error of the electrolyte membrane is reduced from ±8 μm in the original technology to ±2 μm, and the yield rate is increased to 92%, which is beneficial to improving the performance stability of devices such as all-solid-state batteries.

[0100] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A modified adhesive, characterized in that, The modified adhesive comprises styrene-butadiene rubber and monomers in a mass ratio of (20-30):(0.6-0.8), wherein the monomers comprise nonpolar monomers and polar monomers in a mass ratio of 5:(3-1).

2. The modified adhesive according to claim 1, characterized in that, The nonpolar monomer is selected from at least one of ethylene, styrene, butadiene, and propylene; And / or, the polar monomer is selected from at least one of methyl acrylate, methyl methacrylate and vinyl acetate.

3. A method for preparing the modified adhesive as described in any one of claims 1-2, characterized in that, Includes the following steps: After dissolving styrene-butadiene rubber in an alkane solvent for 8-24 hours according to a certain ratio, monomers and initiators are added, and the mixture is reacted under a protective atmosphere at 60-80℃ for 2-5 hours to obtain a modified adhesive.

4. The preparation method according to claim 3, characterized in that, The alkane solvents include n-hexane and cyclohexane in a volume ratio of 1:(1.5-5).

5. The preparation method according to claim 3, characterized in that, The amount of the initiator used is 0.5%-1% of the total mass of the monomer; Preferably, the initiator is selected from at least one of benzoyl peroxide, dodecanoyl peroxide, and azobisisobutyronitrile.

6. The preparation method according to claim 3, characterized in that, After the reaction is complete, the process also includes washing, precipitation, and drying of the reaction system. The solvent used in the washing process is an alcohol solution, and the drying process is carried out at a temperature of 75℃-85℃.

7. A sulfide solid electrolyte membrane prepared using the modified binder as described in any one of claims 1-2, characterized in that, The sulfide solid electrolyte membrane has a thickness error ≤ ±3 μm, an initial crack bending radius ≤ 5 mm, an alternating winding-unwinding cycle count ≥ 22 times on a 5 mm diameter mandrel, and an electrical conductivity ≥ 2.1 × 10⁻⁶. -3 S / cm.

8. A method for preparing a sulfide solid electrolyte membrane as described in claim 7, characterized in that, Includes the following steps: The modified binder was dissolved in a non-polar solvent to prepare a mixed solution; wherein the amount of modified binder was 3 wt%-5 wt%. A slurry is prepared by adding a sulfide solid electrolyte to the mixed solution; wherein the mass ratio of the sulfide solid electrolyte to the modified binder is (95-98):(2-5). The slurry is coated onto a substrate and dried at a temperature of 60℃-80℃ for 20 h-24 h to obtain a sulfide solid electrolyte membrane.

9. The preparation method according to claim 8, characterized in that, The thickness of the sulfide solid electrolyte membrane is 35 μm-39 μm; And / or, the nonpolar solvent is selected from at least one of benzene, toluene, xylene, pentane, hexane, cyclohexane, dichloromethane, and trichloromethane; And / or, the sulfide solid electrolyte is selected from Li6PS5X and its derivatives, Li 10 MP2S 12 X is at least one of its derivatives and Li3PS4 and its derivatives; wherein X is at least one of Cl, Br and I, and M is at least one of Ge, Sn and Si.

10. An all-solid-state battery, characterized in that, Includes the modified adhesive as described in any one of claims 1-2.

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