Binder for sulfide solid electrolyte and application thereof

Abstract

The invention provides a binder for sulfide solid electrolyte and application of the binder, and the binder for sulfide solid electrolyte comprises the following components in parts by mass: 0.2-0.6 part of PEG12-PMAA-Li and 12-20 parts of polyvinylidene fluoride. The preparation method of the PEG12-PMAA-Li comprises the following steps: (1) carrying out a Michael addition reaction on amino-dodecapolyethylene glycol and methacrylic acid in the presence of a catalyst to form a PEG12-PMAA block copolymer; and (2) uniformly mixing the PEG12-PMAA block copolymer with lithium hydroxide, so that carboxyl of a PMAA chain segment in the PEG12-PMAA block copolymer is completely converted into lithium carboxylate. According to the invention, through a synergistic system of PEG12-PMAA-Li and polyvinylidene fluoride, dual effects of ion conduction promotion and mechanical property enhancement are exerted in the sulfide solid electrolyte.

Description

Technical Field

[0001] This invention belongs to the field of solid-state lithium battery technology, specifically relating to a binder for sulfide solid electrolytes and its application. Background Technology

[0002] In all-solid-state lithium batteries, sulfide solid electrolytes have a room-temperature ionic conductivity of 10⁻⁶. -3 ~10 -2 With its excellent S / cm and compatibility with lithium metal, it has become a core electrolyte candidate material. Wet film deposition processes, due to their suitability for roll-to-roll mass production, have become the mainstream route for preparing sulfide electrolyte membranes, while the selection of solvents and binders directly determines the film quality and electrochemical performance.

[0003] Current binders for sulfide solid electrolytes often exhibit poor solubility and uneven dispersion in solvents. Furthermore, the weak interfacial bonding between a single binder and the electrolyte can lead to grain boundary impedance, resulting in low ionic conductivity and insufficient mechanical strength of the electrolyte membrane. Additionally, some binders suffer from chemical compatibility issues with sulfide solid electrolytes, potentially triggering side reactions and affecting stability, thus failing to meet the performance requirements of all-solid-state batteries. Therefore, developing composite binders that are solvent-compatible, synergistically regulate interfacial stability through multiple components, and balance ionic conductivity and mechanical strength is crucial for overcoming the application bottlenecks of sulfide electrolyte membranes.

[0004] Patent application CN119752365A discloses a composite binder for sulfide solid-state batteries, comprising a polar binder A, a non-polar binder B, and a solvent. The mass ratio of binder A to binder B is 1~10:5~1, and the mass ratio of the total mass of binder A and binder B to the mass of the solvent is 1:10~100.

[0005] Patent application CN120041113A discloses a polymer binder for sulfide solid-state batteries, its preparation method, and its application. The binder is copolymerized from vinyltriethoxysilane, lithium 4-vinylphenylborate, and styrene. By introducing silane groups, the interfacial adhesion with the sulfide electrolyte is enhanced through their coupling effect. Simultaneously, the condensation reaction consumes water in the system, reducing the water content of the electrolyte membrane. Lithium 4-vinylphenylborate provides dissociated lithium ions, improving the ionic conductivity of the binder and reducing its negative impact on the conductivity of the sulfide electrolyte. The styrene groups improve the solubility of the binder in non-polar solvents.

[0006] Developing a composite binder that is highly soluble in solvents, has excellent compatibility with sulfide solid electrolytes, and can improve the ionic conductivity, mechanical strength, and stability of electrolyte membranes remains of great significance. Summary of the Invention

[0007] To address the aforementioned technical problems in the prior art, this invention provides a binder for sulfide solid electrolytes and its application.

[0008] This invention provides a binder for sulfide solid electrolytes, comprising, by weight, 0.2-0.6 parts PEG12-PMAA-Li and 12-20 parts polyvinylidene fluoride; the preparation method of the PEG12-PMAA-Li includes the following steps: (1) Amino-dodecyl polyethylene glycol (CAS: 933789-97-0) and methacrylic acid form a PEG12-PMAA block copolymer by Michael addition reaction under a catalyst; (2) Mix the PEG12-PMAA block copolymer and lithium hydroxide evenly so that the carboxyl groups of the PMAA segments in the PEG12-PMAA block copolymer are completely converted into lithium carboxylate salts to obtain the PEG12-PMAA-Li.

[0009] Reaction principle: In the amino-propylene Michael addition reaction, the amino group (-NH2) in amino-dodecyl polyethylene glycol acts as a nucleophile. The lone pair of electrons on its nitrogen atom has strong nucleophilicity and attacks the β-carbon atom of the carbon-carbon double bond (CH2=CH-) conjugated with the carboxyl group (-COOH) in the methacrylic acid molecule (the β-carbon carries a partial positive charge due to the electron-withdrawing effect of the carboxyl group). Subsequently, the π bond of the carbon-carbon double bond breaks, and the electron is transferred to the α-carbon atom to form a carbocation intermediate. This intermediate quickly binds to the proton in the system. Finally, the amino-dodecyl polyethylene glycol segment and the methacrylic acid segment are connected through the newly formed CN bond to generate PEG12-PMAA block copolymer. After treatment with lithium hydroxide, lithium carboxylate salt groups are introduced to obtain PEG12-PMAA-Li.

[0010] Preferably, in step (1), the mass ratio of amino-dodecyl polyethylene glycol to methacrylic acid is 1:0.5-3.

[0011] Preferably, in step (1), the catalyst used for the Michael addition reaction is an organic base.

[0012] More preferably, in step (1), the organic base is trimethylamine, triethylamine, tripropylamine, tributylamine, N-methyltetrahydropyrrole, or pyridine.

[0013] Preferably, in step (1), the mass ratio of amino-dodecyl polyethylene glycol to catalyst is 1:0.06-0.1.

[0014] Preferably, in step (1), the solvent used for the Michael addition reaction is at least one of toluene and xylene.

[0015] Preferably, in step (1), the Michael addition reaction is carried out at a temperature of 65-70°C for 8-10 hours.

[0016] Preferably, the mass ratio of lithium hydroxide in step (2) to amino-dodecyl polyethylene glycol in step (1) is 1:4-10.

[0017] This invention also provides a method for preparing a sulfide solid electrolyte membrane, comprising the following steps: S1. Dissolve the binder used for the above-mentioned sulfide solid electrolyte to obtain a binder solution; S2. After mixing the sulfide electrolyte with the binder solution, the mixture is thoroughly ground. The resulting slurry is then coated and dried at low temperature and under vacuum to obtain the sulfide solid electrolyte membrane.

[0018] Preferably, the mass ratio of the binder used for the sulfide solid electrolyte in step S1 to the sulfide electrolyte in step S2 is 1:1.8-4.

[0019] Preferably, in step S1, the solvent used for dissolution is at least one selected from toluene, chlorobenzene, p-xylene, tetrahydrofuran, dimethyl carbonate, dimethylformamide, glycol dimethyl ether, dibutyl ether, triethyl phosphate, dimethyl sulfoxide, butyl butyrate, ethyl acetate, benzyl acetate, butyl isobutyrate, and acetonitrile.

[0020] Compared with the prior art, the present invention has the following beneficial effects: In this invention, the binder used in the sulfide solid electrolyte plays a dual role in promoting ion conduction and enhancing mechanical properties through a synergistic system of PEG12-PMAA-Li and polyvinylidene fluoride.

[0021] (1) Enhanced ion transport performance: The lithium carboxylate salt groups in PEG12-PMAA-Li can act as ion sources to promote the dissociation of lithium salts in the system; the fluorocarbon chains of PVDF have strong polarity and can construct continuous ion transport channels to reduce ion migration resistance; at the same time, the flexible mobility of PEG12 chain segments can drive the Li + Rapid migration and the synergistic effect of these three factors significantly improve the ion conduction efficiency of the sulfide electrolyte membrane.

[0022] (2) Enhanced mechanical properties: PVDF itself has excellent toughness, providing a flexible substrate for the binder; the polar groups of PEG12-PMAA-Li can form a strong interaction with the surface of sulfide electrolyte powder, enhancing the interfacial bonding force; the composite system formed by the two has both rigidity and toughness, effectively improving the defects of traditional sulfide electrolyte membranes that are prone to brittleness. Attached Figure Description

[0023] Figure 1The figures show the AC impedance spectra of the electrolyte films in Examples 1-4 and Comparative Examples 1-2, where AF represents the examples and B represents the comparative examples. Detailed Implementation

[0024] The equipment used in the following experiments and their models are shown in Table 1.

[0025] Table 1

[0026] Example 1 The sulfide solid electrolyte film based on the composite binder in this embodiment was prepared by the following method: In an argon-filled glove box, 5g of composite binder was dispersed into 8g of dimethyl sulfoxide. The mixture was then magnetically stirred at 800rpm in a sealed container for 2 hours to obtain a uniform slurry. 15g of sulfide solid electrolyte LiPSCl4 and 20g of xylene were added to a ball mill jar, followed by the above slurry. The ball loading was 50g, the milling speed was 500rpm, and the milling time was 20min. The above steps were repeated twice. The two dispersed slurries were then coated onto a current collector and release paper respectively at a speed of 1cm / s and a thickness of 100μm using a scraper coater. The slurries were then dried at low temperature and under vacuum for testing.

[0027] The above-mentioned composite binder was prepared by uniformly mixing 0.2g PEG12-PMAA-Li and 12g PVDF in a high-speed mixer.

[0028] The preparation method of PEG12-PMAA-Li is as follows: 5g of amino-dodecyl polyethylene glycol and 2.5g of methacrylic acid were added to a reaction vessel, along with 50g of solvent and 0.3g of organic base. Nitrogen gas was introduced, and the reaction was carried out at 65°C for 8 hours to generate a PEG12-PMAA block copolymer. Then, 0.5g of lithium hydroxide was added and stirred for 30 minutes. Toluene was removed by distillation to obtain the PEG12-PMAA-Li. The organic base used was trimethylamine; the solvent used was toluene.

[0029] Example 2 The sulfide solid electrolyte film based on the composite binder in this embodiment was prepared by the following method: In an argon-filled glove box, 8g of composite binder was dispersed in 10g of dimethyl sulfoxide. The mixture was magnetically stirred at 1000rpm in a sealed container for 4 hours to obtain a uniform slurry. 15g of sulfide solid electrolyte LiPSCl4 and 20g of xylene were added to a ball mill jar, followed by the above slurry. The ball loading was 50g, the cylinder rotation speed was 600rpm, and the ball milling time was 25min. The above steps were repeated twice. The two dispersed slurries were coated onto the current collector and release paper respectively at a speed of 1cm / s and a thickness of 100μm using a scraper coater. The slurries were then dried at low temperature and under vacuum for testing.

[0030] The above-mentioned composite binder was prepared by uniformly mixing 0.3g PEG12-PMAA-Li and 14g PVDF in a high-speed mixer.

[0031] The preparation method of PEG12-PMAA-Li is as follows: 10g of amino-dodecyl polyethylene glycol and 10g of methacrylic acid were added to a reaction vessel, along with 100g of solvent and 0.65g of organic base. Nitrogen gas was introduced, and the reaction was carried out at 67°C for 9 hours to generate a PEG12-PMAA block copolymer. Then, 2.2g of lithium hydroxide was added and stirred for 50 minutes. Toluene was removed by distillation to obtain the PEG12-PMAA-Li. The organic base used was triethylamine, and the solvent used was xylene.

[0032] Example 3 The sulfide solid electrolyte film based on the composite binder in this embodiment was prepared by the following method: In an argon-filled glove box, 5g of composite binder was dispersed in 8g of N,N-dimethylformamide. The mixture was magnetically stirred at 800rpm in a sealed container for 2 hours to obtain a uniform slurry. 15g of sulfide solid electrolyte LiPSCl4 and 20g of dimethyl carbonate were added to a ball mill jar, followed by the above slurry. The ball loading was 50g, the milling speed was 500rpm, and the milling time was 20min. The above steps were repeated twice. The two dispersed slurries were coated onto a current collector and release paper respectively at a speed of 1cm / s and a thickness of 100μm using a scraper coater. The slurries were then dried at low temperature and under vacuum for testing.

[0033] The above-mentioned composite binder was prepared by uniformly mixing 0.5g PEG12-PMAA-Li and 16g PVDF in a high-speed mixer.

[0034] The preparation method of PEG12-PMAA-Li is as follows: 50g of amino-dodecyl polyethylene glycol and 80g of methacrylic acid were added to a reaction vessel, along with 500g of solvent and 4.4g of organic base. Nitrogen gas was introduced, and the reaction was carried out at 69°C for 9.5 hours to generate a PEG12-PMAA block copolymer. Then, 11.76g of lithium hydroxide was added and stirred for 55 minutes. Toluene was removed by distillation to obtain the PEG12-PMAA-Li. The organic base used was N-methyltetrahydropyrrole, and the solvent used was toluene.

[0035] Example 4 The sulfide solid electrolyte film based on the composite binder in this embodiment was prepared by the following method: In an argon-filled glove box, 5g of composite binder was dispersed in 8g of dimethyl sulfoxide. The mixture was magnetically stirred at 800rpm in a sealed container for 2 hours to obtain a uniform slurry. 20g of sulfide solid electrolyte LiPSCl4 and 20g of xylene were added to a ball mill jar, followed by the above slurry. The ball loading was 50g, the cylinder rotation speed was 600rpm, and the ball milling time was 20min. The above steps were repeated twice. The two dispersed slurries were coated onto the current collector and release paper respectively at a speed of 1cm / s and a thickness of 100μm using a scraper coater. The slurries were then dried at low temperature and under vacuum for testing.

[0036] The above-mentioned composite binder was prepared by uniformly mixing 0.6g of PEG12-PMAA-Li and 20g of PVDF in a high-speed mixer.

[0037] The preparation method of PEG12-PMAA-Li is as follows: 20g of amino-dodecyl polyethylene glycol and 60g of methacrylic acid were added to a reaction vessel, along with 200g of solvent and 2g of organic base. Nitrogen gas was introduced, and the reaction was carried out at 70°C for 10 hours to generate a PEG12-PMAA block copolymer. Then, 5g of lithium hydroxide was added and stirred for 60 minutes. Toluene was removed by distillation to obtain the PEG12-PMAA-Li. The organic base used was pyridine, and the solvent used was xylene.

[0038] Comparative Example 1 The binder used in this comparative example is PIB, and the remaining preparation steps are the same as in Example 1.

[0039] Comparative Example 2 The binder used in this comparative example is SBS, and the remaining preparation steps are the same as in Example 1.

[0040] Test Example 1 (1) Ionic conductivity testing method The ionic conductivity was determined using the AC impedance method. The electrolyte membrane was ground into powder using a mortar and pestle, and 100 mg was placed in a pressure cell mold. The pressure was then increased to 10 MPa. The electrochemical workstation was set to AC impedance testing with a frequency range of 1 MHz to 1 Hz. After the test, the thickness of the sulfide electrolyte sheet was measured, and the calculation formula is as follows: σ Li+ =L / RS, where R is the AC impedance value, L is the thickness of the solid electrolyte sheet, and S is the area of ​​the solid electrolyte sheet.

[0041] Mechanical performance testing methods The mechanical properties of the composite adhesive were determined based on the peel strength of the sulfide solid electrolyte membrane. Bending tests were performed on the sulfide solid electrolyte membrane using an electrode flexibility tester: the Flex 10 was used to test the fracture angle of the electrolyte membrane. A sample coated on release paper was cut to a length of 50 mm and a width of 10 mm, and a peel thickness of 0.1 mm was applied. The bending angular velocity was set to 2° / s, and the angle measurement range was 0~90°. The two ends of the sample were fixed to the clamps, and the membrane was bent at a uniform speed along the MD / TD direction. The bending angle at which the first through-crack appeared was recorded as the fracture angle. Peel strength tests were performed on the sulfide solid electrolyte membrane using a peel strength tester 5: a WDW-5 was used to test the peel strength of the electrolyte membrane. A sample coated on the current collector was cut to a length of 200 mm and a width of 15 mm. A 180° peel mode was used, with a tensile speed of 50 mm / min and a load range of 0~5 N. The upper and lower clamps held the pre-peeled ends of the substrate and the membrane respectively, ensuring the force direction was consistent. The equipment was started for peeling, and the peel strength (average peel force / sample width) was recorded.

[0042] The electrolyte films prepared in Examples 1-4 and Comparative Examples 1-2 were subjected to the above tests, and the test results are shown in Table 2 and... Figure 1 .

[0043] Table 2

[0044] As can be seen, the ionic conductivity and mechanical properties of the electrolyte films in Examples 1-4 are superior to those in Comparative Examples 1-2, indicating that the room temperature ionic conductivity of the sulfide electrolyte film prepared by the composite binder of the present invention is significantly higher than that of the electrolyte film prepared using traditional PIB and SBS binders, with a significant increase in conductivity. The peel strength of the sulfide electrolyte film prepared by the composite binder of the present invention is much higher than that of the traditional PIB and SBS binder system, and the fracture point angle can meet the bending requirements of flexible batteries.

Claims

1. A binder for sulfide solid electrolytes, characterized in that, The PEG12-PMAA-Li comprises 0.2-0.6 parts by weight of PEG12-PMAA-Li and 12-20 parts by weight of polyvinylidene fluoride; the preparation method of the PEG12-PMAA-Li includes the following steps: (1) Amino-dodecyl polyethylene glycol and methacrylic acid form a PEG12-PMAA block copolymer by Michael addition reaction under a catalyst; (2) Mix the PEG12-PMAA block copolymer and lithium hydroxide evenly so that the carboxyl groups of the PMAA segments in the PEG12-PMAA block copolymer are completely converted into lithium carboxylate salts to obtain the PEG12-PMAA-Li.

2. The binder for sulfide solid electrolytes according to claim 1, characterized in that, In step (1), the mass ratio of amino-dodecyl polyethylene glycol to methacrylic acid is 1:0.5-3.

3. The binder for sulfide solid electrolytes according to claim 1, characterized in that, In step (1), the catalyst used in the Michael addition reaction is an organic base.

4. The binder for sulfide solid electrolytes according to claim 3, characterized in that, The organic base is trimethylamine, triethylamine, tripropylamine, tributylamine, N-methyltetrahydropyrrole, or pyridine.

5. The binder for sulfide solid electrolytes according to claim 1, characterized in that, In step (1), the mass ratio of amino-dodecyl polyethylene glycol to catalyst is 1:0.06-0.

1.

6. The binder for sulfide solid electrolytes according to claim 1, characterized in that, In step (1), the solvent used in the Michael addition reaction is at least one of toluene and xylene.

7. The binder for sulfide solid electrolytes according to claim 1, characterized in that, In step (1), the Michael addition reaction is carried out at a temperature of 65-70°C for 8-10 hours.

8. The binder for sulfide solid electrolytes according to claim 1, characterized in that, In step (2), the mass ratio of lithium hydroxide to amino-dodecyl polyethylene glycol in step (1) is 1:4-10.

9. A method for preparing a sulfide solid electrolyte membrane, characterized in that, Includes the following steps: S1. Dissolve the binder for the sulfide solid electrolyte according to any one of claims 1-8 to obtain a binder solution; S2. After mixing the sulfide electrolyte with the binder solution, the mixture is thoroughly ground. The resulting slurry is then coated and dried at low temperature and under vacuum to obtain the sulfide solid electrolyte membrane.

10. The method for preparing a sulfide solid electrolyte membrane according to claim 9, characterized in that, The mass ratio of the binder used in step S1 to the sulfide solid electrolyte in step S2 is 1:1.8-4.

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