Asymmetric polymer solid electrolyte, preparation method and application

Abstract

The invention relates to the technical field of lithium ion batteries, and discloses an asymmetric polymer solid electrolyte, and a preparation method and application thereof, and the preparation method comprises the following steps: step 1, adding a polymer into a PVDF-HFP suspension, and fully mixing to obtain a mixed solution A; preparing a first electrolyte film by adopting the mixed solution A; 2, adding a polyether ionic conductor polymer into the PVDF-HFP suspension, fully mixing to obtain a mixed solution B, and preparing a second electrolyte film on the surface of the first electrolyte film by adopting the mixed solution B to obtain a composite electrolyte film; and step 3, drying the composite electrolyte film to obtain the required solid electrolyte. The battery prepared from the asymmetric solid electrolyte shows excellent wide temperature cycle performance, and the range is-30 DEG C to 70 DEG C. The performance of the lithium metal battery obtained by adopting the polymer electrolyte is greatly improved.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to an asymmetric polymer solid electrolyte, its preparation method, and its application. Background Technology

[0002] Solid-state lithium-ion batteries, with their high safety, high energy density, and long cycle stability, have become a new core energy storage device suitable for new energy vehicles, energy storage power stations, and other fields. Polymer solid electrolytes, as the core medium for lithium-ion transport in batteries, directly determine the battery's ion transport efficiency, mechanical support capabilities, and interface compatibility, making them a key breakthrough for the industrialization of solid-state batteries.

[0003] Currently, mainstream polymer solid electrolytes primarily use polyethylene oxide (PEO) or polyacrylonitrile (PAN) as a single matrix, but both have unavoidable performance shortcomings. PEO's molecular chain is too flexible, resulting in a solid film with poor mechanical strength and weak puncture resistance. During battery cycling, it cannot withstand the penetration of lithium dendrites growing on the lithium metal anode surface, easily leading to short circuit risks. Furthermore, it is difficult to adapt to the deformation of expanding anodes such as silicon-based electrodes, resulting in film structure damage and interface failure. PAN's molecular chain lacks sites specifically for lithium ion coordination, failing to effectively dissociate lithium salts and guide lithium ion migration, resulting in consistently low room-temperature ionic conductivity. Simultaneously, PAN's strong polarity leads to poor interfacial compatibility with the lithium metal anode, easily forming a heterogeneous, high-impedance solid electrolyte interphase (SEI) film. During battery cycling, the interfacial impedance continuously increases, and after 100 cycles, the capacity retention is often below 70%, failing to meet the requirements for long-life batteries. To balance high ionic conductivity and excellent mechanical properties, existing technologies often attempt to modify PEO and PAN by blending. However, the two molecules have significantly different polarities (PEO is weakly polar and PAN is strongly polar), resulting in poor compatibility and easy phase separation in the blended system. Summary of the Invention

[0004] This invention addresses the technical problems existing in the prior art by providing an asymmetric polymer solid electrolyte, its preparation method, and its application.

[0005] The technical solution adopted in this invention is: a method for preparing an asymmetric polymer solid electrolyte, comprising the following steps: Step 1: Add the polymer to the PVDF-HFP suspension and mix thoroughly to obtain mixed solution A. The mass ratio of PVDF-HFP to polymer in mixed solution A is 50-100:1-2. Use mixed solution A to prepare the first electrolyte film. The polymer is one of polyacrylonitrile (PAN), polymethyl methacrylate (PMMA), polyethyl methacrylate (PEMA), and polyimide (PI). Step 2: Add a polyether-based ion conductor polymer to the PVDF-HFP suspension and mix thoroughly to obtain mixed solution B. The mass ratio of PVDF-HFP to the polyether-based ion conductor polymer in mixed solution B is 500-1000:1-10. Use mixed solution B to prepare a second electrolyte film on the surface of the first electrolyte film to obtain a composite electrolyte film. The polyether-based ion conductor polymer is one of polyethylene oxide (PEO), polypropylene glycol (PPG), polyethylene glycol dimethyl ether (PEGDME), and polyethylene glycol methacrylate (PEGMA). Step 3: After the composite electrolyte film is dried, the desired solid electrolyte can be obtained.

[0006] Furthermore, in step 1, the dispersion medium of the PVDF-HFP suspension is a mixed solution composed of N,N-dimethylformamide and acetone in a mass ratio of 1:1.

[0007] Furthermore, in step 1, the mixed solution A is mixed under magnetic stirring at 80 °C for 8 hours, and the first electrolyte film is prepared by electrospinning.

[0008] Furthermore, in step 2, the mixed solution B is mixed by magnetic stirring at 80 °C for 8 hours, and the third electrolyte film is prepared by electrospinning.

[0009] Furthermore, the preparation parameters for the electrospinning are as follows: The voltage is 18 kV and the feed rate is 0.8 mL·h. -1 The preparation temperature was 30 ℃, and the distance between the anode and the cathode was 24 cm.

[0010] Furthermore, step 3, after drying the composite electrolyte, also includes vacuum impregnation, wherein the impregnation solution is a tantalum-doped lithium lanthanum zirconium oxide solution.

[0011] An asymmetric polymer solid electrolyte comprises a first electrolyte film and a second electrolyte film stacked from top to bottom; the first electrolyte film is composed of a polymer composite PVDF-HFP-based ion gel electrolyte as the matrix and tantalum-doped lithium lanthanum zirconium oxide as the filler; the second electrolyte film is composed of a polyether-based ion conductor polymer composite PVDF-HFP-based ion gel electrolyte as the matrix and tantalum-doped lithium lanthanum zirconium oxide as the filler.

[0012] Furthermore, the thickness of the first electrolyte film is 10–20 μm, and the thickness of the second electrolyte film is 10–20 μm.

[0013] Application of an asymmetric polymer solid electrolyte, wherein the solid electrolyte is used in the preparation of lithium metal batteries.

[0014] The beneficial effects of this invention are: The asymmetric solid electrolyte obtained in this invention uses a polyether-based ion-conducting polymer composite PVDF-HFP-based ion gel electrolyte as the positive electrode electrolyte and a polymer (polyacrylonitrile PAN, polymethyl methacrylate PMMA, polyethyl methacrylate PEMA, polyimide PI) composite PVDF-HFP-based ion gel electrolyte as the negative electrode electrolyte. This electrolyte can achieve high compatibility with lithium negative electrodes and high-voltage positive electrodes over a wide temperature range. The polyether-based ion-conducting polymer / polyvinylidene fluoride cohexafluoropropylene (PVDF-HFP) matrix adjacent to the lithium negative electrode can enable Li... + Ion flux homogenization and the promotion of stable solid electrolyte interphase (SEI) formation through dynamic interface remodeling; excellent high voltage withstand capability on the positive electrode side, effectively suppressing transition metal dissolution and electrolyte decomposition. The addition of LLZTO enhances LiPF6 dissociation through selective adsorption. The highly porous asymmetric polymer framework structure helps eliminate macroscopic interfaces between different materials, thereby enabling rapid Li… + Ion transport.

[0015] The battery obtained using the asymmetric solid-state electrolyte of this invention exhibits excellent wide-temperature cycling performance, ranging from -30 °C to 70 °C. This asymmetric structural design of the asymmetric polymer electrolyte enhances its performance in lithium metal batteries. Detailed Implementation

[0016] The present invention will be further described below with reference to specific embodiments.

[0017] A method for preparing an asymmetric polymer solid electrolyte includes the following steps: Step 1: Add the polymer to the PVDF-HFP suspension and mix thoroughly to obtain mixed solution A. The mass ratio of PVDF-HFP to polymer in mixed solution A is 50-100:1-2. Use mixed solution A to prepare the first electrolyte film. The polymer is one of polyacrylonitrile (PAN), polymethyl methacrylate (PMMA), polyethyl methacrylate (PEMA), and polyimide (PI).

[0018] The dispersion medium for the PVDF-HFP suspension is a mixed solution of N,N-dimethylformamide and acetone in a mass ratio of 1:1; the mixed solution A is mixed under magnetic stirring at 80 °C for 8 hours, and the first electrolyte film is prepared by electrospinning.

[0019] Step 2: Add a polyether-based ion-conducting polymer to the PVDF-HFP suspension and mix thoroughly to obtain mixed solution B. The mass ratio of PVDF-HFP to the polyether-based ion-conducting polymer in mixed solution B is 500–1000:1–10. Use mixed solution B to prepare a second electrolyte film on the surface of the first electrolyte film to obtain a composite electrolyte film. Mixed solution B is magnetically stirred at 80°C for 8 hours. The second electrolyte film is prepared by electrospinning. The polyether-based ion-conducting polymer is one of polyethylene oxide (PEO), polypropylene glycol (PPG), polyethylene glycol dimethyl ether (PEGDME), or polyethylene glycol methacrylate (PEGMA).

[0020] The electrospinning preparation parameters in steps 1 and 2 are as follows: The voltage is 18 kV and the feed rate is 0.8 mL·h. -1 The preparation temperature was 30 ℃, and the distance between the anode and the cathode was 24 cm.

[0021] Step 3: After drying the composite electrolyte film, it is vacuum impregnated to obtain the desired solid electrolyte; the impregnation solution is a tantalum-doped lithium lanthanum zirconium oxide (LLZTO) solution (the concentration of the impregnation solution and the impregnation time are adjusted according to actual needs). The composite electrolyte film is dried at 80 °C for 12 h.

[0022] The solid electrolyte comprises a first electrolyte film and a third electrolyte film stacked from top to bottom. The first electrolyte film is composed of a polymer (polyacrylonitrile PAN, polymethyl methacrylate PMMA, polyethyl methacrylate PEMA, polyimide PI) composite PVDF-HFP-based ionogel electrolyte as the matrix and tantalum-doped lithium lanthanum zirconium oxide as the filler. The second electrolyte film is composed of a polyether-based ion conductor polymer (polyethylene oxide PEO, polypropylene glycol PPG, polyethylene glycol dimethyl ether PEGDME, polyethylene glycol methacrylate PEGMA) composite PVDF-HFP-based ionogel electrolyte as the matrix and tantalum-doped lithium lanthanum zirconium oxide as the filler. The thickness of the first electrolyte film is 10–20 μm, and the thickness of the third electrolyte film is 10–20 μm.

[0023] A lithium metal battery is prepared using an asymmetric electrolyte, with the first electrolyte film facing the positive electrode side and the second electrolyte film facing the negative electrode side.

[0024] Example 1 A method for preparing an asymmetric polymer solid electrolyte includes the following steps: Step 1: Disperse 0.16 g of PAN and 0.624 g of PVDF-HFP in a dispersion medium (composed of 2.8 mL LDF and 1.2 mL acetone); mix at 80 °C with magnetic stirring at 400 r / min for 8 hours to obtain mixed solution A; take 1.5 mL of mixed solution A and insert it into a syringe through a stainless steel nozzle connected to a high-voltage power supply. Electrospinning is performed, with the applied voltage, feed rate, temperature, and distance between the anode and cathode fixed at 18 kV, 0.8 mL / h, and 0.8 mL / h, respectively. -1 The first electrolyte film was prepared at 30°C and 24 cm.

[0025] Step 2: Disperse 0.064 g of PEO and 0.624 g of PVDF-HFP in a dispersion medium (composed of 2.8 mL of DMF and 1.2 mL of acetone); mix at 80 °C and 400 r / min using magnetic stirring for 8 hours to obtain mixed solution B; take 1.5 mL of mixed solution B and insert it into a syringe through a stainless steel nozzle connected to a high-voltage power supply. Electrospinning is performed, with the applied voltage, feed rate, temperature, and distance between the anode and cathode fixed at 18 kV, 0.8 mL / h, and 0.8 mL / h, respectively. -1 The second electrolyte film was prepared at 30°C and 24 cm.

[0026] Step 3: Dry the composite electrolyte film obtained in Step 2 at 80 °C for 12 h, and then cut the asymmetric film into circular pieces with a diameter of 16 mm to obtain the desired solid electrolyte.

[0027] Example 2 A method for preparing an asymmetric polymer solid electrolyte includes the following steps: Step 1: Disperse 0.36 g of PMMA and 0.624 g of PVDF-HFP in a dispersion medium (composed of 2.8 mL LDMF and 1.2 mL acetone); mix at 80 °C with magnetic stirring at 400 r / min for 8 hours to obtain mixed solution A; take 1.5 mL of mixed solution A and insert it into a syringe through a stainless steel nozzle connected to a high-voltage power supply. Electrospinning is performed, with the applied voltage, feed rate, temperature, and distance between the anode and cathode fixed at 18 kV, 0.8 mL / h, and 0.8 mL / h, respectively. -1 The first electrolyte film was prepared at 30°C and 24 cm.

[0028] Step 2: Disperse 0.064 g of PPG and 0.624 g of PVDF-HFP in a dispersion medium (composed of 2.8 mL of DMF and 1.2 mL of acetone); mix at 80 °C and 400 r / min using magnetic stirring for 8 hours to obtain mixed solution B; take 1.5 mL of mixed solution B and insert it into a syringe through a stainless steel nozzle connected to a high-voltage power supply. Electrospinning is performed, with the applied voltage, feed rate, temperature, and distance between the anode and cathode fixed at 18 kV, 0.8 mL / h, and 0.8 mL / h, respectively. -1 The second electrolyte film was prepared at 30°C and 24 cm.

[0029] Step 3: Dry the composite electrolyte film obtained in Step 2 at 80 °C for 12 h, and then cut the asymmetric film into circular pieces with a diameter of 16 mm to obtain the desired solid electrolyte.

[0030] Example 3 A method for preparing an asymmetric polymer solid electrolyte includes the following steps: Step 1: Disperse 0.16 g of PEMA and 0.624 g of PVDF-HFP in a dispersion medium (composed of 2.8 mL LDMF and 1.2 mL acetone); mix at 80 °C with magnetic stirring at 400 r / min for 8 hours to obtain mixed solution A; take 1.5 mL of mixed solution A and insert it into a syringe through a stainless steel nozzle connected to a high-voltage power supply. Electrospinning is performed, with the applied voltage, feed rate, temperature, and distance between the anode and cathode fixed at 18 kV, 0.8 mL / h, and 0.8 mL / h, respectively. -1 The first electrolyte film was prepared at 30°C and 24 cm.

[0031] Step 2: Disperse 0.16 g of PEGDME and 0.624 g of PVDF-HFP in a dispersion medium (composed of 2.8 mL of DMF and 1.2 mL of acetone); mix at 80 °C and 400 r / min using magnetic stirring for 8 hours to obtain mixed solution B; take 1.5 mL of mixed solution B and insert it into a syringe through a stainless steel nozzle connected to a high-voltage power supply. Electrospinning is used, with the applied voltage, feed rate, temperature, and distance between the anode and cathode fixed at 18 kV, 0.8 mL / h, and 0.8 mL / h, respectively. -1 The second electrolyte film was prepared at 30°C and 24 cm.

[0032] Step 3: Dry the composite electrolyte film obtained in Step 2 at 80 °C for 12 h, and then cut the asymmetric film into circular pieces with a diameter of 16 mm to obtain the desired solid electrolyte.

[0033] Example 4 A method for preparing an asymmetric polymer solid electrolyte includes the following steps: Step 1: Disperse 0.16 g of PI and 0.624 g of PVDF-HFP in a dispersion medium (composed of 2.8 mL LDMF and 1.2 mL acetone); mix at 80 °C with magnetic stirring at 400 r / min for 8 hours to obtain mixed solution A; take 1.5 mL of mixed solution A and insert it into a syringe through a stainless steel nozzle connected to a high-voltage power supply. Electrospinning is performed, with the applied voltage, feed rate, temperature, and distance between the anode and cathode fixed at 18 kV, 0.8 mL / h, and 0.8 mL / h, respectively. -1 The first electrolyte film was prepared at 30°C and 24 cm.

[0034] Step 2: Disperse 0.064 g of PEGMA and 0.624 g of PVDF-HFP in a dispersion medium (composed of 2.8 mL of DMF and 1.2 mL of acetone); mix at 80 °C and 400 r / min using magnetic stirring for 8 hours to obtain mixed solution B; take 1.5 mL of mixed solution B and insert it into a syringe through a stainless steel nozzle connected to a high-voltage power supply. Electrospinning is performed, with the applied voltage, feed rate, temperature, and distance between the anode and cathode fixed at 18 kV, 0.8 mL / h, and 0.8 mL / h, respectively. -1 The second electrolyte film was prepared at 30°C and 24 cm.

[0035] Step 3: Dry the composite electrolyte membrane obtained in Step 2 at 80 °C for 12 h, and then cut the asymmetric membrane into circular pieces with a diameter of 16 mm; vacuum impregnate the cut circular pieces with an LLZTO concentration of 10 mg / mL in the impregnation solution for 20 h.

[0036] Comparative Example 1 The other steps in this comparative example are the same as in Example 1, except that step 2 is not included, resulting in a solid electrolyte including the first electrolyte film as in Example 1.

[0037] Comparative Example 2 The other steps in this comparative example are the same as in Example 1, except that step 1 is not included, resulting in a solid electrolyte including the third electrolyte film as in Example 1.

[0038] The solid electrolytes obtained in the above embodiments and comparative examples were subjected to performance tests, including ionic conductivity, electrochemical window, and mechanical performance tests.

[0039] Ionic conductivity: The polymer solid electrolyte membranes (SPEs) prepared above were assembled with two stainless steel electrodes (SS) into SS / SPEs / SS coin cells for testing. The cell assembly process was carried out in a glove box with water and oxygen content both below 0.1 ppm. Electrochemical impedance spectroscopy (EIS) was performed at a frequency range of 0.1 Hz to 2 MHz at room temperature (25 ± 5 °C) to measure the electrochemical impedance of the polymer solid electrolyte, and the ionic conductivity was calculated from the impedance data obtained from the EIS test.

[0040] Electrochemical window: Assembled lithium-to-stainless steel sheet batteries with a polymer solid electrolyte in the middle, and tested using linear sweep voltammetry (LSV).

[0041] Mechanical property testing: The mechanical elongation of the sample is determined on a tensile testing machine.

[0042] The performance test results are shown in Table 1. Table 1: Performance test results of Examples 1-4 and comparative examples

[0043] As can be seen from the table above, the battery obtained by using the solid electrolyte of this invention can effectively improve the ionic conductivity and electrochemical window.

[0044] The asymmetric solid-state electrolyte obtained in this invention uses a PVDF-HFP-based ion gel electrolyte composed of polyether-based ion conductor polymers (ethylene oxide PEO, polypropylene glycol PPG, polyethylene glycol dimethyl ether PEGDME, and polyethylene glycol methacrylate PEGMA) as the positive electrode electrolyte and a PVDF-HFP-based ion gel electrolyte composed of polymers (polyacrylonitrile PAN, polymethyl methacrylate PMMA, polyethyl methacrylate PEMA, and polyimide PI) as the negative electrode electrolyte. This electrolyte can achieve high compatibility with lithium negative electrodes and high-voltage positive electrodes over a wide temperature range. The polyether-based ion conductor polymer / polyvinylidene fluoride cohexafluoropropylene (PVDF-HFP) matrix adjacent to the lithium negative electrode can enable Li... + Ion flux homogenization and the promotion of stable solid electrolyte interphase (SEI) formation through dynamic interface remodeling; on the positive electrode side, the polymer (polyacrylonitrile PAN, polymethyl methacrylate PMMA, polyethyl methacrylate PEMA, polyimide PI) / PVDF-HFP matrix exhibits excellent high voltage withstand capability, effectively suppressing transition metal dissolution and electrolyte decomposition. The addition of LLZTO enhances LiPF6 dissociation through selective adsorption. The highly porous asymmetric polymer framework structure helps eliminate macroscopic interfaces between different materials, thereby enabling rapid Li… + Ion transport.

[0045] The battery obtained using the asymmetric solid-state electrolyte of this invention exhibits excellent wide-temperature cycling performance, ranging from -30 °C to 70 °C. This asymmetric structural design of the asymmetric polymer electrolyte enhances its performance in lithium metal batteries.

Claims

1. A method for preparing an asymmetric polymer solid electrolyte, characterized in that, Includes the following steps: Step 1: Add the polymer to the PVDF-HFP suspension and mix thoroughly to obtain mixed solution A. The mass ratio of PVDF-HFP to polymer in mixed solution A is 50-100:1-2. Use mixed solution A to prepare the first electrolyte film. The polymer is one of polyacrylonitrile (PAN), polymethyl methacrylate (PMMA), polyethyl methacrylate (PEMA), and polyimide (PI). Step 2: Add a polyether-based ion conductor polymer to the PVDF-HFP suspension and mix thoroughly to obtain mixed solution B. The mass ratio of PVDF-HFP to the polyether-based ion conductor polymer in mixed solution B is 500-1000:1-10. Use mixed solution B to prepare a second electrolyte film on the surface of the first electrolyte film to obtain a composite electrolyte film. The polyether-based ion conductor polymer is one of polyethylene oxide (PEO), polypropylene glycol (PPG), polyethylene glycol dimethyl ether (PEGDME), and polyethylene glycol methacrylate (PEGMA). Step 3: After the composite electrolyte film is dried, the desired solid electrolyte can be obtained.

2. The method for preparing a solid electrolyte based on a PEO / PAN asymmetric polymer according to claim 1, characterized in that, In step 1, the dispersion medium for the PVDF-HFP suspension is a mixed solution composed of N,N-dimethylformamide and acetone in a mass ratio of 1:

1.

3. The method for preparing a solid electrolyte based on a PEO / PAN asymmetric polymer according to claim 1, characterized in that, In step 1, the mixed solution A is mixed under magnetic stirring at 80 °C for 8 hours, and the first electrolyte film is prepared by electrospinning.

4. The preparation method of a solid electrolyte based on PEO / PAN asymmetric polymer according to claim 1, characterized in that, In step 2, the mixed solution B is mixed by magnetic stirring at 80 °C for 8 hours, and the third electrolyte film is prepared by electrospinning.

5. The preparation method of a solid electrolyte based on a PEO / PAN asymmetric polymer according to claim 4, characterized in that, The preparation parameters for the electrospinning are as follows: The voltage is 18 kV and the feed rate is 0.8 mL·h. -1 The preparation temperature was 30 ℃, and the distance between the anode and the cathode was 24 cm.

6. The method for preparing a solid electrolyte based on a PEO / PAN asymmetric polymer according to claim 1, characterized in that, Step 3, after the composite electrolyte film is dried, also includes vacuum impregnation, wherein the impregnation solution is a tantalum-doped lithium lanthanum zirconium oxide solution.

7. The solid electrolyte based on the PEO / PAN asymmetric polymer obtained by any one of the preparation methods described in claims 1 to 6, characterized in that, The solid electrolyte includes a first electrolyte film and a second electrolyte film stacked from top to bottom; the first electrolyte film is composed of a polymer composite PVDF-HFP-based ion gel electrolyte as the matrix and tantalum-doped lithium lanthanum zirconium oxide as the filler, and the second electrolyte film is composed of a polyether-based ion conductor polymer composite PVDF-HFP-based ion gel electrolyte as the matrix and tantalum-doped lithium lanthanum zirconium oxide as the filler.

8. The solid electrolyte based on PEO / PAN asymmetric polymer according to claim 7, characterized in that, The thickness of the first electrolyte film is 10–20 μm, and the thickness of the second electrolyte film is 10–20 μm.

9. The application of the PEO / PAN asymmetric polymer solid electrolyte as described in any one of claims 7-8, characterized in that, The solid electrolyte is used in the preparation of lithium metal batteries.

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