High-temperature-resistant fast-charging PVDF-HFP-based all-solid-state electrolyte membrane as well as preparation method and application thereof

Abstract

The invention provides a high-temperature-resistant fast-charging PVDF-HFP-based all-solid-state electrolyte membrane as well as a preparation method and application thereof, and relates to the technical field of power batteries. The preparation method comprises the following steps: uniformly mixing a polyvinylidene fluoride-hexafluoropropylene copolymer, a lithium salt and a polar solvent to obtain a PVDF-HFP solution; then uniformly mixing the PVDF-HFP solution with a cross-linking agent and a 2, 2-bis (4-allyloxy-3, 5-dibromophenyl) propane monomer, so as to obtain a precursor solution; uniformly mixing an initiator with the precursor solution to obtain a reaction solution; and finally, coating a substrate with the reaction solution, and heating at 70-80 DEG C for 12-16 hours to obtain the high-temperature-resistant fast-charging PVDF-HFP-based all-solid-state electrolyte membrane. When the high-temperature-resistant and fast-charging PVDF-HFP-based all-solid-state electrolyte membrane is applied to a lithium metal battery, the thermal safety and the high-temperature-resistant and fast-charging performance can be remarkably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of power batteries, and particularly relates to a high-temperature-resistant fast-charging PVDF-HFP-based all-solid-state electrolyte membrane, a preparation method thereof, and an application thereof. Background Art

[0002] With the increasing demand for high-energy and high-power-density energy storage devices, lithium-ion batteries can no longer meet the current research in the battery field. Lithium metal batteries have been widely used in the battery field due to their high theoretical capacity (3860 mAh g -1 ). Among them, the electrolyte, as a key component, is crucial for the development of efficient battery configurations. However, the organic liquid electrolytes used in traditional lithium metal batteries have safety hazards, and their instability and flammability limit their development. Solid-state electrolytes (SSEs) have received extensive attention due to their good adaptability to lithium metal anodes and high safety.

[0003] Among them, polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP) stands out due to its excellent room-temperature ionic conductivity (10 - 4 mS cm -2 ), good thermal stability, and relatively high electrochemical window. Compared with PVDF, its rich fluorinated alkyl groups are more conducive to the dissociation of Li ions. While having a well-continuous film-forming crystalline region of vinylidene fluoride units, the amorphous region composed of hexafluoropropylene (HFP) units can additionally capture a large amount of Li + , providing favorable conditions for the conduction of Li + . However, to achieve efficient ion transport and long-term cycle stability of SSEs, a stable internal structure is crucial. However, the PVDF-HFP electrolyte membrane always results in a porous structure during the preparation process, leading to uneven distribution of Li + during the transport process, and then causing uneven Li deposition, and ultimately leading to the growth of lithium dendrites piercing the thin film and causing a short circuit, affecting the battery cycle life.

[0004] Chinese Patent CN111009686A discloses an all-solid-state polymer electrolyte containing a high concentration of lithium salt, aiming to improve the room-temperature ionic conductivity of the all-solid-state polymer electrolyte. The all-solid-state polymer electrolyte is composed of a lithium salt and a polyvinylidene fluoride-hexafluoropropylene copolymer, wherein the content of the lithium salt is greater than 50 wt.%. The thickness of the all-solid-state polymer electrolyte of this patent is 100 μm, and the room-temperature ionic conductivity is only in the range of 1.2×10 -4 ~2.1×10 -4 S / cm, and it does not optimize the internal structure of the electrolyte membrane. Summary of the Invention

[0005] To solve the above technical problems, the present invention provides a high-temperature resistant and fast-charging PVDF-HFP-based all-solid electrolyte membrane, its preparation method and application. The high-temperature resistant and fast-charging PVDF-HFP-based all-solid electrolyte membrane prepared by the present invention has high thermal stability and high-temperature resistant fast-charging performance.

[0006] The technical solution of the present invention is as follows:

[0007] The present invention provides a preparation method of a high-temperature resistant and fast-charging PVDF-HFP-based all-solid electrolyte membrane, comprising the following steps:

[0008] (1) Mix a polyvinylidene fluoride-hexafluoropropylene copolymer, a lithium salt and a polar solvent to obtain a PVDF-HFP solution;

[0009] (2) Mix the PVDF-HFP solution with a cross-linking agent and 2,2-bis(4-allyloxy-3,5-dibromophenyl)propane monomer to obtain a precursor solution;

[0010] (3) Mix an initiator with the precursor solution to obtain a reaction solution;

[0011] (4) Coat the reaction solution on a substrate and heat it at 70°C to 80°C for 12 to 16 hours to obtain a high-temperature resistant and fast-charging PVDF-HFP-based all-solid electrolyte membrane.

[0012] Preferably, in step (4), the reaction solution is coated on the substrate with a doctor blade.

[0013] Preferably, the substrate is a glass plate.

[0014] In the present invention, if 2,2-bis(4-allyloxy-3,5-dibromophenyl)propane monomer is not added, the performance of the prepared electrolyte membrane compared with that of the pure PVDF-HFP electrolyte membrane: the thickness has no obvious change, and the difference range does not exceed 5 μm. The tensile strength also has no change, and the difference range does not exceed 1 MPa. Moreover, due to the large steric hindrance of cross-linking agents such as pentaerythritol tetraacrylate (PETEA), it is not conducive to the transport of lithium ions, and the electrochemical data is even worse than that of the pure PVDF-HFP electrolyte membrane.

[0015] When 2,2-bis(4-allyloxy-3,5-dibromophenyl)propane monomer is replaced with other monomers (such as material 91-77-0), the thickness of the prepared electrolyte membrane is close to that of the pure PVDF-HFP electrolyte membrane. However, when this electrolyte membrane is applied to a cyclic Li symmetric battery, the overpotential is large and the cycle time is short.

[0016] In a specific embodiment, the lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, lithium bis(trifluoromethanesulfonyl)imide, lithium perchlorate, lithium fluoride, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, and lithium bis(pentafluoroethylsulfonyl)imide; preferably, the lithium salt is lithium bis(trifluoromethanesulfonyl)imide.

[0017] In a specific embodiment, the polar solvent includes at least one of N-methylpyrrolidone, N,N-dimethylformamide, acetone, and tetrahydrofuran; preferably, the polar solvent is N,N-dimethylformamide.

[0018] In the present invention, any solvent that can easily dissolve PVDF-HFP can be selected.

[0019] In a specific embodiment, the crosslinking agent includes at least one of pentaerythritol triacrylate, pentaerythritol tetraacrylate, ethylene glycol dimethacrylate, trimethylolpropane trimethacrylate, and N,N'-methylenebisacrylamide; preferably, the crosslinking agent is pentaerythritol tetraacrylate.

[0020] In a specific embodiment, the initiator includes azobisisoheptonitrile and / or azobisisobutyronitrile; preferably, the initiator is azobisisobutyronitrile.

[0021] In a specific embodiment, in step (1), the concentration of lithium bis(trifluoromethanesulfonyl)imide in the PVDF-HFP solution is 1 to 1.5 M; the mass ratio of the poly(vinylidene fluoride-hexafluoropropylene) copolymer to the polar solvent is (1 to 1.5):(5 to 7.5).

[0022] In the present invention, if there is too much poly(vinylidene fluoride-hexafluoropropylene) copolymer, the viscosity of the electrolyte membrane will be too high and it will not dissolve; if there is too little, the film-forming property will be poor. If there is too much lithium salt, it is not easy to dissolve; if there is too little, the ionic conductivity will be low. If there is too much polar solvent, the drying will be incomplete and side reactions with lithium metal will occur; if there is too little, PVDF-HFP will not dissolve.

[0023] In a specific embodiment, in step (2), the 2,2-bis(4-allyloxy-3,5-dibromophenyl)propane monomer accounts for 5 to 6 wt% of the precursor solution; the molar ratio of the 2,2-bis(4-allyloxy-3,5-dibromophenyl)propane monomer to the crosslinking agent is 3 to 3.2:2.8 to 3.

[0024] In the present invention, if there is too much crosslinking agent, the viscosity of the electrolyte membrane will increase and the mechanical rigidity will be poor; if there is too little crosslinking agent, the polymerization will be affected and the crosslinking with BADP will be incomplete.

[0025] In a specific embodiment, in step (3), the addition amount of the initiator is 0.1 to 0.2 wt% of the precursor solution.

[0026] The present invention also provides a high-temperature resistant and fast-charging PVDF-HFP-based all-solid-state electrolyte membrane, which is prepared by the above-mentioned preparation method.

[0027] The present invention also provides the application of the above-mentioned high-temperature resistant and fast-charging PVDF-HFP-based all-solid-state electrolyte membrane in a lithium metal battery or a lithium-ion battery. Preferably, the lithium metal battery is a Li||NCM811 battery.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] 1. In the preparation method of the electrolyte membrane of the present invention, the 2,2-bis(4-allyloxy-3,5-dibromophenyl) propane monomer and the cross-linking agent act synergistically, reducing the thickness of the electrolyte membrane while also improving its tensile strength and ionic conductivity. Applying the electrolyte membrane of the present invention to a lithium battery has better high-temperature resistant and fast-charging performance compared with a pure PVDF-HF electrolyte membrane.

[0030] 2. Compared with a pure PVDF-HFP membrane, the high-temperature resistant and fast-charging PVDF-HFP-based all-solid-state electrolyte membrane prepared by the present invention is more uniform, smoother, thinner, less volatile, and has better tensile strength and ionic conductivity. Applying it to a lithium metal battery can significantly improve the thermal safety and electrochemical performance. Description of the Drawings

[0031] Figure 1 are the scanning electron microscope pictures and thickness gauge test charts of two electrolyte membranes;

[0032] Figure 2 are the tensile strength test charts of two electrolytes;

[0033] Figure 3 are the thermogravimetric analysis charts of two electrolytes;

[0034] Figure 4 is the Fourier transform infrared spectroscopy (FTIR) chart of the electrolyte membrane prepared in Example 1;

[0035] Figure 5 are the ion conductivity comparison charts of two electrolytes;

[0036] Figure 6 are the long-cycle test comparison charts of assembling two electrolyte membranes with NCM811 and Li negative electrodes into a Li||NCM811 battery under the conditions of 1C charge and discharge and 60°C high temperature;

[0037] Figure 7To match two electrolyte membranes with NCM811 and Li anode and assemble them into a Li||NCM811 battery for long-cycle test comparison diagrams under fast charging conditions of 5C charge and discharge at 250°C. Detailed implementation mode

[0038] The following uses specific examples to further illustrate the present invention, but the implementation mode of the invention is not limited thereto.

[0039] Example 1

[0040] Pentaerythritol tetraacrylate PETEA; 2,2-bis(4-allyloxy-3,5-dibromophenyl)propane BADP; azobisisobutyronitrile AIBN; polyvinylidene fluoride-hexafluoropropylene copolymer PVDF-HFP; lithium bis(trifluoromethanesulfonyl)imide LiTFSI; N,N-dimethylformamide DMF.

[0041] Provide a preparation method of a high-temperature resistant and fast-charging PVDF-HFP-based all-solid-state electrolyte membrane, including the following steps:

[0042] Step 1: Mix 0.948 g of PVDF-HFP, 1.185 g of LiTFSI and 5 mL (4.72 g) of DMF evenly to obtain a PVDF-HFP solution with a LiTFSI concentration of 1 mol / L.

[0043] Step 2: Mix 5 ml of the PVDF-HFP solution, 5.3 wt% (0.4 g) of BADP monomer and 2.6 wt% (0.2 g) of PETEA cross-linking agent (the molar ratio of BADP:PETEA is 3.2:2.9) evenly, and stir for 2 h to obtain a precursor solution (precursor mass = 0.948 g + 1.185 g + 4.72 g + 0.6 g = 7.453 g, and the percentage of BADP monomer in the precursor mass is 0.4 / 7.453 = 5.3 wt%).

[0044] Step 3: Add 0.1 wt% of AIBN thermal polymerization initiator to the precursor solution and stir evenly to obtain a reaction solution;

[0045] Step 4: Use a scraper to apply the solution on a glass plate, and then heat the reaction solution at 70°C for 12 h to obtain a high-temperature resistant and fast-charging PVDF-HFP-based all-solid-state electrolyte membrane.

[0046] Example 2

[0047] Prepare a high-temperature resistant and fast-charging PVDF-HFP-based all-solid-state electrolyte membrane according to the steps of Example 1, with the only difference being: adjusting "0.948 g of PVDF-HFP" in Step 1 to "0.958 g of PVDF-HFP"; other steps remain unchanged.

[0048] Example 3

[0049] Prepare a high-temperature resistant and fast-charging PVDF-HFP-based all-solid-state electrolyte membrane according to the steps of Example 1, with the only difference being that "0.948 g of PVDF-HFP" in Step 1 is adjusted to "0.938 g of PVDF-HFP"; other steps remain unchanged.

[0050] Example 4

[0051] Prepare a high-temperature resistant and fast-charging PVDF-HFP-based all-solid-state electrolyte membrane according to the steps of Example 1, with the only difference being that "heating the reaction solution at 70 °C for 12 h" in Step 4 is adjusted to "heating the reaction solution at 75 °C for 12 h"; other steps remain unchanged.

[0052] Example 5

[0053] Prepare a high-temperature resistant and fast-charging PVDF-HFP-based all-solid-state electrolyte membrane according to the steps of Example 1, with the only difference being that "heating the reaction solution at 70 °C for 12 h" in Step 4 is adjusted to "heating the reaction solution at 80 °C for 12 h"; other steps remain unchanged.

[0054] Comparative Example 1

[0055] Provide a preparation method of a pure PVDF-HFP membrane, including the following steps:

[0056] 0.948 g of PVDF-HFP, 1.185 g of LiTFSI and 5 mL (4.72 g) of DMF are mixed evenly to obtain a PVDF-HFP solution with a LiTFSI concentration of 1 mol / L. The solution is coated on a glass plate and then dried at 70 °C for 12 h to obtain a pure PVDF-HFP membrane.

[0057] Performance test

[0058] Next, characterize the modified PVDF-HFP membrane prepared in Example 1 and the pure PVDF-HFP membrane prepared in Comparative Example 1:

[0059] From Figure 1 As shown, from the SEM pictures scanned of the two electrolyte thin films, namely the prepared high-temperature resistant and fast-charging PVDF-HFP-based all-solid-state electrolyte membrane and the pure PVDF-HFP membrane, it can be seen that the surface of the prepared all-solid-state electrolyte membrane is more uniform and smooth. At the same time, the test by a thickness gauge also shows that the prepared high-temperature resistant and fast-charging PVDF-HFP-based all-solid-state electrolyte membrane is thinner. Figure 1 The unit for testing the thickness in

[0060] From Figure 2From the tensile strength, it can be seen that among the two electrolyte films, the prepared all-solid-state electrolyte film has a higher tensile strength, up to 13.4 MPa, which is much greater than 7.5 MPa of the pure PVDF-HFP film, proving that the introduced monomer BADP can significantly improve the mechanical properties of the electrolyte film after polymerization with the cross-linking agent PETEA.

[0061] From Figure 3 From the thermogravimetric analysis, it can be seen that during the pyrolysis process of the high-temperature fast-charging PVDF-HFP-based all-solid-state electrolyte film and the pure PVDF-HFP film, when the temperature rises from room temperature to 300 °C, the total weight loss rates of the high-temperature fast-charging PVDF-HFP-based all-solid-state electrolyte film and the pure PVDF-HFP film are 20.8% and 26.8% respectively. This indicates that the introduction of the thermally stable copolymer matrix significantly delays the volatilization of the electrolyte film.

[0062] From Figure 4 The polymerization of the precursor solution was verified by Fourier transform infrared spectroscopy (FTIR). In the range of 1650 - 1600 cm -1 , the C=C bending vibration and stretching vibration of the acrylic acid group in the BADP and PETEA monomers were respectively observed. The characteristic C=C peak was not observed in the polymerized high-temperature fast-charging PVDF-HFP-based all-solid-state electrolyte film, indicating the successful cross-linking and curing of BADP and PETEA.

[0063] From Figure 5 From the ion conductivity comparison chart, it can be seen that at room temperature of 25 °C, the ion conductivity of the high-temperature fast-charging PVDF-HFP-based all-solid-state electrolyte film is as high as 0.35 mS / cm, while the ion conductivity of the pure PVDF-HFP film is only 0.27 mS / cm. Even as the temperature increases, the ion conductivity of the all-solid-state electrolyte film is always greater than that of the pure PVDF-HFP film. This indicates that the high-temperature fast-charging PVDF-HFP-based all-solid-state electrolyte film has excellent ion conductivity.

[0064] From Figure 6It can be seen that the high-temperature fast-charging PVDF-HFP-based all-solid-state electrolyte membrane prepared in Example 1 is used as the separator (electrolyte) of a lithium-metal battery, which is matched with NCM811 and a Li anode to assemble a Li||NCM811 battery. At the same time, a Li||NCM811 battery with a pure PVDF-HFP membrane is used as a comparison. The two batteries are subjected to long-cycle tests under the conditions of 1C charge and discharge and a high temperature of 60°C. It can be seen that the Li||NCM811 battery with the high-temperature fast-charging PVDF-HFP-based all-solid-state electrolyte membrane can stably cycle more than 150 times, and the capacity retention rate is 96%. On the contrary, the cycling performance of the Li||NCM811 battery with a pure PVDF-HFP membrane-based rapidly decays, and the capacity retention rate after only 100 cycles is lower than 80%, and it decays rapidly. The above results prove the remarkable effect of the high-temperature fast-charging PVDF-HFP-based all-solid-state electrolyte membrane in improving the thermal safety and electrochemical performance in actual lithium-metal batteries.

[0065] It can be seen from Figure 7 It can be seen that the high-temperature fast-charging PVDF-HFP-based all-solid-state electrolyte membrane prepared in Example 1 is used as the separator (electrolyte) of a lithium-metal battery, which is matched with NCM811 and a Li anode to assemble a Li||NCM811 battery. At the same time, a Li||NCM811 battery with a pure PVDF-HFP membrane is used as a comparison. The two batteries are subjected to long-cycle tests under the conditions of 5C charge and discharge and a fast-charging condition of a high temperature of 250°C. It can be seen that the Li||NCM811 battery with the high-temperature fast-charging PVDF-HFP-based all-solid-state electrolyte membrane can stably cycle 200 times, and the capacity retention rate is 70.3%. On the contrary, the cycling performance of the Li||NCM811 battery with a pure PVDF-HFP membrane-based rapidly decays, and the capacity retention rate after 100 cycles is 54.6%, and it decays rapidly. The above results prove the remarkable effect of the high-temperature fast-charging PVDF-HFP-based all-solid-state electrolyte membrane in the fast-charging performance in actual lithium-metal batteries.

[0066] The above-disclosed are only the preferred embodiments of the present invention. Of course, the scope of the rights of the present invention cannot be limited thereby. Therefore, equivalent changes made according to the claims of the present invention still fall within the scope covered by the present invention.

Claims

1. Preparation method of high-temperature fast-charging PVDF-HFP-based all-solid-state electrolyte membrane, characterized in that, It includes the following steps: (1) Mix polyvinylidene fluoride - hexafluoropropylene copolymer, lithium salt and polar solvent to obtain a PVDF - HFP solution; (2) Mix the PVDF - HFP solution with a cross - linker and 2,2 - bis(4 - allyloxy - 3,5 - dibromophenyl) propane monomer to obtain a precursor solution; (3) Mix an initiator with the precursor solution to obtain a reaction solution; (4) Coat the reaction solution on a substrate and heat it at 70 °C - 80 °C for 12 - 16 h to obtain a high - temperature resistant fast - charging PVDF - HFP - based all - solid - state electrolyte membrane.

2. The preparation method of the high-temperature resistant and fast-charging PVDF-HFP-based all-solid-state electrolyte membrane according to claim 1, characterized in that, The lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, lithium bis(trifluoromethanesulfonyl)imide, lithium perchlorate, lithium fluoride, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, and lithium bis(pentafluoroethylsulfonyl)imide; preferably, the lithium salt is lithium bis(trifluoromethanesulfonyl)imide.

3. The preparation method of the high-temperature resistant and fast-charging PVDF-HFP-based all-solid-state electrolyte membrane according to claim 1, characterized in that, The polar solvent includes at least one of N - methylpyrrolidone, N,N - dimethylformamide, acetone, and tetrahydrofuran; preferably, the polar solvent is N,N - dimethylformamide.

4. The preparation method of the high-temperature resistant and fast-charging PVDF-HFP-based all-solid-state electrolyte membrane according to claim 1, wherein The cross - linker includes at least one of pentaerythritol triacrylate, pentaerythritol tetraacrylate, ethylene glycol dimethacrylate, trimethylolpropane trimethacrylate, and N,N'-methylenebisacrylamide; preferably, the cross - linker is pentaerythritol tetraacrylate.

5. The preparation method of the high-temperature resistant and fast-charging PVDF-HFP-based all-solid-state electrolyte membrane according to claim 1, wherein, The initiator includes azobisisoheptonitrile and / or azobisisobutyronitrile; preferably, the initiator is azobisisobutyronitrile.

6. The preparation method of the high-temperature resistant and fast-charging PVDF-HFP based all-solid-state electrolyte membrane according to claim 1, characterized in that, In step (1), the concentration of the lithium salt in the PVDF - HFP solution is 1 - 1.5 M; the mass ratio of the polyvinylidene fluoride - hexafluoropropylene copolymer to the polar solvent is (1 - 1.5):(5 - 7.5).

7. The preparation method of the high-temperature resistant and fast-charging PVDF-HFP-based all-solid-state electrolyte membrane according to claim 1, wherein In step (2), the 2,2 - bis(4 - allyloxy - 3,5 - dibromophenyl) propane monomer accounts for 5 - 6 wt% of the precursor solution; the molar ratio of the 2,2 - bis(4 - allyloxy - 3,5 - dibromophenyl) propane monomer to the cross - linker is 3 - 3.2:2.8 - 3.

8. The preparation method of the high-temperature resistant and fast-charging PVDF-HFP-based all-solid-state electrolyte membrane according to claim 1, wherein In step (3), the addition amount of the initiator is 0.1 - 0.2 wt% of the precursor solution.

9. A high-temperature fast-charging PVDF-HFP-based all-solid-state electrolyte membrane, characterized in that, Prepared by the preparation method according to any one of claims 1 - 8.

10. Application of the high - temperature resistant fast - charging PVDF - HFP - based all - solid - state electrolyte membrane according to claim 9 in a lithium - metal battery or a lithium - ion battery; preferably, the lithium - metal battery is a Li||NCM811 battery.

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