A polymer-based composite solid electrolyte and its preparation method

Abstract

This invention discloses a polymer-based composite solid electrolyte and its preparation method. The solid electrolyte comprises a polymer matrix, a lithium salt, and strontium titanate. Strontium titanate is dispersed in the polymer matrix and enriched at the polymer matrix phase interface and pore regions, forming a chain-like bridging structure along the interface direction for continuous ion transport. The preparation method includes the following steps: dissolving the polymer matrix and lithium salt in an organic solvent and stirring to form a homogeneous solution; adding strontium titanate and stirring to disperse it, forming a precursor solution; forming a film from the precursor solution; and removing residual solvent through drying and vacuum drying. This invention can control the spatial distribution of the high-dielectric inorganic nanofiller strontium titanate in the polymer matrix, causing it to be distributed in a chain-like manner at the interface and pore regions, thus constructing a quasi-continuous ion transport channel. This can reduce ion transport impedance and improve overall ion transport efficiency, which is of great significance for the development of high-performance solid-state lithium metal batteries.

Description

Technical Field

[0001] This invention pertains to battery materials and their preparation methods, specifically a polymer-based composite solid electrolyte and its preparation method. Background Technology

[0002] Lithium metal batteries are known for their extremely high theoretical specific capacity (3860 mAh g). -1 With the lowest possible electrochemical potential, lithium metal is considered an important development direction for achieving high-energy-density energy storage systems, and it has broad application prospects in fields such as electric vehicles and large-scale energy storage. However, traditional liquid electrolytes have safety hazards such as volatility, flammability, and leakage, and they are prone to inducing dendrite growth on the surface of lithium metal anodes, leading to a decrease in battery cycle life and even causing safety problems.

[0003] To address the aforementioned issues, solid-state electrolytes are considered an effective alternative. Among them, polymer solid-state electrolytes have attracted widespread attention due to their good flexibility, excellent processability, and ability to form good interfacial contact with electrodes. However, traditional polymer solid-state electrolytes still suffer from problems such as limited lithium salt dissociation, low room-temperature ionic conductivity, and discontinuous ion transport pathways, which limit their application in high-performance solid-state lithium metal batteries.

[0004] To address these issues, existing technologies have proposed various modification strategies. For example, Chinese patent CN117613376A improves ionic conductivity by constructing a cross-linked polymer network; Chinese patent CN118955776A enhances lithium-ion migration by introducing functional groups onto the polymer backbone through chemical grafting; and Chinese patent CN120784435A improves electrolyte stability by constructing a polymer network structure through in-situ polymerization. However, these methods often rely on complex chemical reaction processes or specific reaction conditions, resulting in complex preparation processes. Furthermore, they primarily focus on regulating the polymer molecular structure, limiting their ability to control the spatial construction of ion transport pathways.

[0005] In addition, existing technologies have extensively studied methods to improve the performance of polymer electrolytes by introducing inorganic nanofillers. However, inorganic nanofillers are usually randomly dispersed or locally aggregated in the polymer matrix, lacking effective control over their spatial distribution behavior. This makes it difficult to form continuous or quasi-continuous ion transport channels, and the ion transport process is still constrained by interfacial impedance and path discontinuity.

[0006] In summary, existing polymer composite solid electrolyte systems still suffer from limitations in ion transport efficiency, discontinuous ion transport pathways, and insufficient interface control. There is an urgent need to develop a composite electrolyte system capable of constructing ordered ion transport pathways within a polymer matrix, achieving a significant improvement in ion transport performance while ensuring a simple and controllable preparation process. Summary of the Invention

[0007] Purpose of the invention: In order to overcome the shortcomings of the prior art, the purpose of this invention is to provide a polymer-based composite solid electrolyte with ordered interface structure and high ion transport efficiency. Another purpose of this invention is to provide a simple and convenient method for preparing a polymer-based composite solid electrolyte with good uniformity, good stability.

[0008] Technical solution: The present invention provides a polymer-based composite solid electrolyte comprising a polymer matrix, a lithium salt, and strontium titanate; strontium titanate is dispersed in the polymer matrix and enriched at the polymer matrix phase interface and pore region, forming a chain-bridged structure for continuous ion transport by being chain-connected along the interface direction.

[0009] Further, the mass ratio of the polymer matrix, lithium salt, and strontium titanate (SrTiO3) is 1:0.8~1.8:0.2~1.2. Preferably, the mass ratio of the polymer matrix, lithium salt, and SrTiO3 is 1:1.5:0.3~0.7.

[0010] Furthermore, the polymer matrix is ​​polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP) with an average molecular weight of 455,000.

[0011] Furthermore, the lithium salt is lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium hexafluorophosphate, or lithium fluorosulfonate.

[0012] Furthermore, the particle size of strontium titanate is 50~300 nm. Preferably, the average particle size of the strontium titanate nanoparticles is 200 nm.

[0013] Furthermore, the spacing between strontium titanate elements in the chain-bridged structure is 10~500 nm.

[0014] Furthermore, the thickness of the solid electrolyte membrane is 100~520 μm.

[0015] The present invention discloses a method for preparing a polymer-based composite solid electrolyte, comprising the following steps:

[0016] Step 1: Dissolve the polymer matrix and lithium salt in an organic solvent and stir to form a homogeneous solution;

[0017] Step 2: Add strontium titanate and stir to disperse, forming a precursor solution;

[0018] Step 3: Form the precursor solution into a film;

[0019] Step four: After drying and vacuum drying, the residual solvent is removed to obtain the polymer-based composite solid electrolyte.

[0020] Furthermore, the stirring temperature is 30~60℃.

[0021] Furthermore, in step four, the drying temperature is 30~60℃, and the vacuum drying temperature is 50~120℃.

[0022] Furthermore, in step one, the organic solvent is N,N-dimethylformamide (DMF).

[0023] Preparation Principle: This invention introduces strontium titanate (SrTiO3) filler to form a chain-bridged structure within a polymer matrix. This structure, achieved through the physical interaction between the filler and the polymer matrix, results in the filler particles forming chains at the microscale, thereby creating continuous ion channels in the electrolyte. Unlike traditional techniques, this invention does not rely on simple material blending or interfacial chemical modification. Instead, it optimizes the continuity of ion transport paths and effectively suppresses the accumulation of space charge by controlling the spatial distribution of the filler and the resulting polarization effect.

[0024] Beneficial effects: Compared with the prior art, the present invention has the following significant features:

[0025] 1. It can regulate the spatial distribution of high dielectric inorganic nanofiller strontium titanate in polymer matrix, so that it is distributed in a chain-like manner in the interface and pore region, and forms a chain-like structure along the interface direction, thereby constructing a quasi-continuous ion transport channel. It can reduce ion transport impedance and improve overall ion transport efficiency from the structural level, which is of great significance for the development of high-performance solid-state lithium metal batteries.

[0026] 2. It can improve the microstructure of materials and enhance the uniformity of the system. Strontium titanate is distributed relatively uniformly in the polymer matrix and forms a specific structure in the interface region, which helps to regulate the microstructure state of the polymer matrix, improve the overall uniformity and stability of the material, and provide a more favorable environment for ion migration.

[0027] 3. The composite solid electrolyte constructed in this invention has good interfacial contact characteristics with the lithium metal anode, exhibiting stable interfacial behavior during battery operation, which helps to reduce interfacial polarization and maintain a stable cycle state, improve the stability of the electrode / electrolyte interface, and thus improve the overall operational stability of the battery.

[0028] 4. The LiFePO4|Li solid-state battery assembled with the prepared composite solid electrolyte exhibited good cycle stability in long-term cycle tests and could still maintain a high capacity retention rate after long-term cycling, indicating that the electrolyte system has excellent performance in practical battery applications and significantly improves the cycle performance of the whole battery.

[0029] 5. The method of preparing composite solid electrolytes by combining solution blending and film formation is simple, mild and highly controllable, suitable for large-scale preparation and has good prospects for engineering applications. Attached Figure Description

[0030] Figure 1 This is a scanning electron microscope image of the composite solid electrolyte of Embodiment 1 of the present invention;

[0031] Figure 2 These are long-cycle performance curves of the LiFePO4|Li solid-state batteries assembled in Examples 1, 2 and Comparative Example 1 of this invention.

[0032] Figure 3 These are the electrochemical AC impedance spectra of the composite solid electrolytes of Examples 1, 2 and Comparative Example 1 of the present invention, where a is Example 1, b is Example 2 and c is Comparative Example 1.

[0033] Figure 4 The graph shows the lithium-ion transference number test results of the composite solid electrolytes of Examples 1, 2 and Comparative Example 1 of the present invention, where a is Example 1, b is Example 2 and c is Comparative Example 1. Detailed Implementation

[0034] Unless otherwise specified, all materials and reagents used in the following examples are commercially available. Experimental methods not specifically described in the examples are generally performed under standard conditions or as recommended by the manufacturer. Polyvinylidene fluoride-hexafluoropropylene copolymer was purchased from Maclean's reagents and has an average molecular weight of 455,000.

[0035] Example 1

[0036] A method for preparing a polymer composite solid electrolyte for solid-state lithium metal batteries includes the following steps:

[0037] (1) Preparation of electrolyte solution: In a glove box filled with argon gas, H2O < 0.1 ppm, O2 < 0.1 ppm, weigh 0.6 g PVDF-HFP and 0.9 g LiTFSI and add them to 6 mL DMF solvent. Stir magnetically for 3 hours at 50 °C to fully dissolve them and obtain a homogeneous and transparent polymer lithium salt solution.

[0038] (2) Introduction of nanofiller: Add 0.39g of nano-strontium titanate (SrTiO3) particles with an average particle size of about 200nm to the solution obtained in step (1), and continue to stir magnetically at 50℃ for 12 hours to make the nano-strontium titanate uniformly dispersed in the solution to obtain the composite electrolyte precursor solution.

[0039] (3) Preparation of solid electrolyte membranes:

[0040] The precursor solution obtained in step (2) was poured into a polytetrafluoroethylene mold and film-forming treatment was performed by sol-gel method. The film was then dried in a hydrothermal oven at 50°C for 3 hours. Subsequently, the resulting film was transferred to a vacuum oven and dried at 120°C for 12 hours to remove residual solvent, resulting in a composite solid electrolyte membrane with a thickness of 210 μm.

[0041] Application Example 1

[0042] (1) Preparation of positive electrode:

[0043] Lithium iron phosphate (LFP) active material, SuperP conductive agent, and polyvinylidene fluoride (PVDF) binder were mixed in N-methylpyrrolidone (NMP) solvent at a mass ratio of 8:1:1. The mixture was ground and stirred to form a uniform slurry, which was then coated onto an aluminum foil current collector and vacuum dried at 80°C for 12 hours. The resulting material was then punched to obtain a positive electrode sheet with a diameter of 10 mm and an areal loading of approximately 2.5 mg / cm². -2 .

[0044] (2) Battery assembly:

[0045] Using the positive electrode obtained in step (1) as the positive electrode, a lithium metal sheet with a thickness of 0.5 mm as the negative electrode, and the composite solid electrolyte membrane of Example 1 as the electrolyte, a CR2032 coin cell was assembled in a glove box filled with argon (H2O < 0.1 ppm, O2 < 0.1 ppm).

[0046] Electrochemical testing:

[0047] After the assembled battery was left to stand at 25°C for 24 hours, its electrochemical performance was tested on the testing system.

[0048] Test Results: Performance tests were conducted on the composite solid-state electrolyte prepared in this embodiment and the assembled solid-state battery. The results are as follows: Figure 1 and Figure 2 As shown, the SrTiO3 nanoparticles exhibit a chain-bridged distribution characteristic at the polymer interface and in the porous region, with the spacing between the strontium titanate nanoparticles in the chain-bridged structure ranging from 10 to 500 nm. The AC impedance and lithium-ion transference number of the composite solid electrolyte membranes obtained in Examples 1, 2, and Comparative Example 1 were tested, and the results are as follows: Figure 3 and Figure 4 As shown. The room temperature ionic conductivity of Examples 1, 2, and Comparative Example 1 is 1.16 mS / cm. -1 0.76 mS cm -1 and 0.36 mS cm -1The lithium-ion transference numbers were 0.57, 0.52, and 0.24, respectively. It can be seen that Example 1 exhibits the highest ionic conductivity and lithium-ion transference number, indicating lower internal ion transport resistance, and that Li... + Its contribution to total ion transport is higher. Analysis suggests that the SrTiO3 nanoparticles in Example 1 form more fully developed chain-like bridging structures at the polymer matrix interface and in the porous region, enabling the construction of more continuous quasi-continuous ion transport channels. Simultaneously, the high dielectric properties of SrTiO3 help promote lithium salt dissociation and weaken the Li... + The electrostatic interaction between the electrolyte and anions increases the concentration of migratable lithium ions. Furthermore, the chain-bridged structure induces a more favorable local polarization environment for ion migration at the interface, reducing space charge accumulation and interface polarization. Therefore, Example 1 exhibits superior ion transport kinetics. In addition, the battery based on the electrolyte obtained in Example 1 demonstrates good cycle stability, especially in long-cycle testing, where the capacity retention rate is 71% after 400 cycles, exhibiting superior performance. This performance advantage is attributed to the high dielectric effect of the SrTiO3 filler and the formation of the chain-bridged structure, which greatly enhances the battery's stability.

[0049] Example 2

[0050] A method for preparing a polymer composite solid electrolyte for solid-state lithium metal batteries includes the following steps:

[0051] (1) Preparation of electrolyte solution: In a glove box filled with argon gas, H2O < 0.1 ppm, O2 < 0.1 ppm, weigh 0.6 g PVDF-HFP and 0.9 g LiTFSI and add them to 6 mL DMF solvent. Stir magnetically for 3 hours at 50 °C to fully dissolve them and obtain a homogeneous and transparent polymer lithium salt solution.

[0052] (2) Introduction of nanofiller: Add 0.21g of nano-strontium titanate (SrTiO3) particles with an average particle size of about 200nm to the solution obtained in step (1), and continue to stir magnetically at 50℃ for 12 hours to make the nano-strontium titanate uniformly dispersed in the solution to obtain a composite electrolyte precursor solution.

[0053] (3) Preparation of solid electrolyte membranes:

[0054] The precursor solution obtained in step (2) was poured into a polytetrafluoroethylene mold and film-forming treatment was performed by sol-gel method. The film was then dried in a hydrothermal oven at 50°C for 3 hours. Subsequently, the resulting film was transferred to a vacuum oven and dried at 120°C for 12 hours to remove residual solvent, resulting in a composite solid electrolyte membrane with a thickness of 210 μm.

[0055] Application Example 2

[0056] (1) Preparation of positive electrode:

[0057] LFP active material, SuperP conductive agent, and PVDF binder were mixed in NMP solvent at a mass ratio of 8:1:1, ground and stirred to form a uniform slurry, which was then coated onto an aluminum foil current collector and vacuum dried at 80°C for 12 hours. The resulting material was then punched to obtain a positive electrode sheet with a diameter of 10 mm and an areal loading of approximately 2.5 mg / cm². -2 .

[0058] (2) Battery assembly:

[0059] Using the positive electrode obtained in step (1) as the positive electrode, a lithium metal sheet with a thickness of 0.5 mm as the negative electrode, and the composite solid electrolyte membrane of Example 2 as the electrolyte, a CR2032 coin cell was assembled in a glove box filled with argon (H2O<0.1ppm, O2<0.1ppm).

[0060] The assembled battery was subjected to the same electrochemical performance test as in Example 1, and the results are as follows: Figures 2-4 As shown, the battery exhibits good cycle stability, retaining 67% of its capacity after 400 cycles, a slight decrease compared to Example 1. Meanwhile, Example 2 shows a room-temperature ionic conductivity of 0.76 mS / cm. -1 The lithium-ion transference number was 0.52, which was lower than that of Example 1 but significantly higher than that of Comparative Example 1. Analysis suggests that the SrTiO3 filler in Example 2 also improved the ion transport environment in the polymer matrix and promoted lithium salt dissociation. However, due to the relatively low filler content, the degree of chain bridging structure construction and interface enrichment effect were weaker than in Example 1, resulting in a decrease in the connectivity of the quasi-continuous ion channels. Therefore, its ion transport capacity and cycle stability were slightly lower than those of Example 1.

[0061] Example 3

[0062] A method for preparing a polymer composite solid electrolyte for solid-state lithium metal batteries includes the following steps:

[0063] (1) Preparation of electrolyte solution: In a glove box filled with argon, H2O<0.1ppm, O2<0.1ppm, weigh 0.3g PVDF-HFP and 0.54g LiTFSI and add them to 6mL DMF solvent. Stir magnetically for 3 hours at 30℃ to fully dissolve them and obtain a uniform and transparent polymer lithium salt solution.

[0064] (2) Introduction of nanofiller: Add 0.36g of nano strontium titanate (SrTiO3) particles with an average particle size of about 50nm to the solution obtained in step (1), and continue to stir magnetically at 30℃ for 12 hours to make the nano strontium titanate uniformly dispersed in the solution to obtain a composite electrolyte precursor solution.

[0065] (3) Preparation of solid electrolyte membranes:

[0066] The precursor solution obtained in step (2) was poured into a polytetrafluoroethylene mold and film-forming treatment was performed by sol-gel method. The film was then dried in a hydrothermal oven at 30°C for 3 hours. Subsequently, the resulting film was transferred to a vacuum oven and dried at 50°C for 12 hours to remove residual solvent, resulting in a composite solid electrolyte membrane with a thickness of 100 μm.

[0067] Example 4

[0068] A method for preparing a polymer composite solid electrolyte for solid-state lithium metal batteries includes the following steps:

[0069] (1) Preparation of electrolyte solution: In a glove box filled with argon gas, H2O<0.1ppm, O2<0.1ppm, weigh 1.5g PVDF-HFP and 1.2g LiTFSI and add them to 6mL DMF solvent. Stir magnetically for 3 hours at 60℃ to fully dissolve them and obtain a homogeneous and transparent polymer lithium salt solution.

[0070] (2) Introduction of nanofiller: Add 0.3g of nano-strontium titanate (SrTiO3) particles with an average particle size of about 300nm to the solution obtained in step (1), and continue to stir magnetically at 60℃ for 12 hours to make the nano-strontium titanate uniformly dispersed in the solution to obtain a composite electrolyte precursor solution.

[0071] (3) Preparation of solid electrolyte membranes:

[0072] The precursor solution obtained in step (2) was poured into a polytetrafluoroethylene mold and film-forming treatment was performed by sol-gel method. The film was then dried in a hydrothermal oven at 60°C for 3 hours. Subsequently, the resulting film was transferred to a vacuum oven and dried at 70°C for 12 hours to remove residual solvent, resulting in a composite solid electrolyte membrane with a thickness of 520 μm.

[0073] Example 5

[0074] A method for preparing a polymer composite solid electrolyte for solid-state lithium metal batteries includes the following steps:

[0075] (1) Preparation of electrolyte solution: In a glove box filled with argon, H2O<0.1ppm, O2<0.1ppm, weigh 0.5g PVDF-HFP and 0.75g LiTFSI and add them to 6mL DMF solvent. Stir magnetically for 3 hours at 40℃ to fully dissolve them and obtain a uniform and transparent polymer lithium salt solution.

[0076] (2) Introduction of nanofiller: Add 0.35g of nano-strontium titanate (SrTiO3) particles with an average particle size of about 100nm to the solution obtained in step (1), and continue to stir magnetically at 40℃ for 12 hours to make the nano-strontium titanate uniformly dispersed in the solution to obtain a composite electrolyte precursor solution.

[0077] (3) Preparation of solid electrolyte membranes:

[0078] The precursor solution obtained in step (2) was poured into a polytetrafluoroethylene mold and film-forming treatment was performed by sol-gel method. The film was then dried in a hydrothermal oven at 50°C for 3 hours. Subsequently, the resulting film was transferred to a vacuum oven and dried at 90°C for 12 hours to remove residual solvent, resulting in a composite solid electrolyte membrane with a thickness of 170 μm.

[0079] Example 6

[0080] A method for preparing a polymer composite solid electrolyte for solid-state lithium metal batteries includes the following steps:

[0081] (1) Preparation of electrolyte solution: In a glove box filled with argon gas, H2O<0.1ppm, O2<0.1ppm, weigh 1.0g PVDF-HFP and 1.5g LiTFSI and add them to 6mL DMF solvent. Stir magnetically for 3 hours at 45℃ to fully dissolve them and obtain a uniform and transparent polymer lithium salt solution.

[0082] (2) Introduction of nanofiller: Add 0.3g of nano-strontium titanate (SrTiO3) particles with an average particle size of about 250nm to the solution obtained in step (1), and continue to stir magnetically at 50℃ for 12 hours to make the nano-strontium titanate uniformly dispersed in the solution to obtain a composite electrolyte precursor solution.

[0083] (3) Preparation of solid electrolyte membranes:

[0084] The precursor solution obtained in step (2) was poured into a polytetrafluoroethylene mold and film-forming treatment was performed by sol-gel method. The film was then dried in a hydrothermal oven at 40°C for 3 hours. Subsequently, the resulting film was transferred to a vacuum oven and dried at 100°C for 12 hours to remove residual solvent, resulting in a composite solid electrolyte membrane with a thickness of 350 μm.

[0085] Comparative Example 1

[0086] The comparative example is identical to Example 1 in all other steps, except that nano-strontium titanate filler is not added. The specific steps are as follows:

[0087] (1) Preparation of electrolyte solution: In a glove box filled with argon (H2O < 0.1 ppm, O2 < 0.1 ppm), weigh 0.6 g of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP) and 0.9 g of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and add them to 6 mL of N,N-dimethylformamide (DMF) solvent. Stir magnetically for 3 hours at 50 °C to fully dissolve the polymer lithium salt solution.

[0088] (2) Preparation of solid electrolyte membranes:

[0089] The polymer lithium salt solution obtained in step (1) was poured into a polytetrafluoroethylene mold and film-forming treatment was performed by sol-gel method. The film was then dried in a hydrothermal oven at 50°C for 3 hours. Subsequently, the resulting film was transferred to a vacuum oven and dried at 120°C for 12 hours to remove residual solvent, thus obtaining a composite solid electrolyte membrane.

[0090] (3) Preparation of positive electrode:

[0091] Lithium iron phosphate (LFP) active material, Super P conductive agent, and polyvinylidene fluoride (PVDF) binder were mixed in N-methylpyrrolidone (NMP) solvent at a mass ratio of 8:1:1. The mixture was ground and stirred to form a uniform slurry, which was then coated onto an aluminum foil current collector and vacuum dried at 80 °C for 12 hours. The resulting positive electrode sheet had a diameter of 10 mm and an areal loading of approximately 2.5 mg / cm². -2 .

[0092] (4) Battery assembly:

[0093] Using the positive electrode obtained in step (3) as the positive electrode, a lithium metal sheet with a thickness of 0.5 mm as the negative electrode, and the composite solid electrolyte membrane prepared in step (2) as the electrolyte, a CR2032 coin cell was assembled in a glove box filled with argon gas (H2O < 0.1 ppm, O2 < 0.1 ppm).

[0094] The obtained solid-state battery was subjected to the same performance test as in Application Example 1, and the results showed that: Figure 2 The assembled solid-state battery performed poorly, especially in cycle testing, where the capacity retention was only 21% after 400 cycles. Furthermore, as... Figures 3-4 The room temperature ionic conductivity of Comparative Example 1 was only 0.36 mS / cm. -1The lithium-ion transference number was only 0.24, significantly lower than that in Examples 1 and 2. This result indicates that without the introduction of SrTiO3 filler, the polymer matrix lacks effective interfacial polarization regulation and chain bridging structures, resulting in limited lithium salt dissociation, discontinuous ion transport paths, and low lithium ion transference. + Migration is susceptible to the cooperative motion of anions and the accumulation of space charge, resulting in high overall ion transport impedance, severe interfacial polarization, and ultimately manifested as low conductivity, low lithium-ion transference number, and poor cycle stability. (Comparative Example 2)

[0095] The comparative example is the same as Example 1 in all other steps, except that the amount of SrTiO3 added is 0.8g.

[0096] The resulting membrane was too brittle to be completely peeled off, and a usable composite solid electrolyte membrane with a uniform structure could not be obtained.

[0097] Test results: This comparative example shows that when the content of nano-strontium titanate filler is too high, the nanoparticles in the precursor solution are difficult to disperse uniformly, and problems such as cracking and embrittlement occur during film formation, making it impossible to obtain a usable composite solid electrolyte membrane. Combining Examples 1-2 and Comparative Example 1, it can be seen that there is an optimal range for the amount of nano-strontium titanate added; too high or too low a content is detrimental to the improvement of electrolyte performance or its formation.

[0098] Comparative Example 3

[0099] The comparative example follows the same steps as Example 1, except that SrTiO3 is replaced with BaTiO3. The results showed that while the battery functioned normally, its cycle stability was lower than that of Application Example 1. Analysis suggests that the interfacial interaction between BaTiO3 and the polymer matrix in this system is weak, making it difficult to form a similar chain-like bridging distribution structure. This results in insufficient continuity of the ion transport path, thus affecting the overall cycle performance.

[0100] Comparative Example 4

[0101] The comparative example followed the same steps as Example 1, except that the amount of SrTiO3 added was 0.1g. The results showed that the battery's cycle performance was inferior to that of Application Example 1. Analysis suggests that when the amount of SrTiO3 added is too low, it is difficult to form an effective chain-like network in the system, and continuous bridging relationships cannot be established between the fillers, resulting in insufficient ion transport channel construction and thus affecting the battery's cycle stability.

Claims

1. A polymer-based composite solid electrolyte, characterized in that: It includes a polymer matrix, a lithium salt, and strontium titanate; the strontium titanate is dispersed in the polymer matrix and enriched at the polymer matrix phase interface and pore region, forming a chain-bridged structure for continuous ion transport along the interface direction.

2. The polymer-based composite solid electrolyte according to claim 1, characterized in that: The mass ratio of the polymer matrix, lithium salt, and strontium titanate is 1:0.8~1.8:0.2~1.

2.

3. The polymer-based composite solid electrolyte according to claim 1, characterized in that: The polymer matrix is ​​a polyvinylidene fluoride-hexafluoropropylene copolymer with an average molecular weight of 455,000.

4. The polymer-based composite solid electrolyte according to claim 1, characterized in that: The lithium salt is lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluorophosphate, or lithium fluorosulfonate.

5. The polymer-based composite solid electrolyte according to claim 1, characterized in that: The strontium titanate has a particle size of 50~300 nm.

6. The polymer-based composite solid electrolyte according to claim 1, characterized in that: The spacing between the strontium titanate elements in the chain-bridged structure is 10~500 nm.

7. The polymer-based composite solid electrolyte according to claim 1, characterized in that: The thickness of the solid electrolyte membrane is 100~520 μm.

8. A method for preparing a polymer-based composite solid electrolyte according to any one of claims 1 to 7, characterized in that, Includes the following steps: Step 1: Dissolve the polymer matrix and lithium salt in an organic solvent and stir to form a homogeneous solution; Step 2: Add strontium titanate and stir to disperse, forming a precursor solution; Step 3: Form the precursor solution into a film; Step four: After drying and vacuum drying, the residual solvent is removed to obtain the polymer-based composite solid electrolyte.

9. The method for preparing the polymer-based composite solid electrolyte according to claim 8, characterized in that: The stirring temperature is 30~60℃.

10. The method for preparing the polymer-based composite solid electrolyte according to claim 8, characterized in that: In step four, the drying temperature is 30~60℃, and the vacuum drying temperature is 50~120℃.

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