Composite solid electrolyte membrane and preparation method and application thereof

Abstract

The application relates to the technical field of batteries, in particular to a composite solid electrolyte membrane and a preparation method and application thereof. The composite solid electrolyte membrane comprises the following layers which are sequentially stacked: a first membrane layer comprising a polymer, a solid electrolyte and a lithium salt; a second membrane layer comprising a polymer, a solid electrolyte and a lithium salt; and a third membrane layer which is an interface layer; wherein the solid electrolyte and the lithium salt content of the second membrane layer are higher than those of the first membrane layer, and the polymer is formed by polymerization of raw materials comprising triacetyl cellulose (TCA) and polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP). The composite solid electrolyte membrane has improved high-temperature resistance and good ion transmission performance.

Description

Technical Field

[0001] This invention relates to the field of battery technology, specifically to a composite solid electrolyte membrane, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries need to meet the requirements of being leak-proof, non-flammable, and non-explosive. Using solid-state electrolytes is one of the effective ways to improve battery safety. Solid-state electrolytes can be mainly classified into inorganic solid-state electrolytes and polymer solid-state electrolyte systems based on their materials. Among them, polymer solid-state electrolytes have good processing properties, interfacial contact, flexibility, and mechanical strength, making them the most promising solid-state electrolyte system for application.

[0003] With the development of applications such as automotive power batteries and drones, lithium batteries are required not only to have high energy density but also to have better fast charging and discharging performance, while ensuring that battery safety is not compromised. Under high-rate charging and discharging environments, even higher requirements are placed on the battery's high-temperature resistance.

[0004] Currently, polymer solid-state electrolyte systems typically employ polymers such as polyethylene oxide (PEO), polyacrylonitrile (PAN), polymethyl methacrylate (PMMA), polyvinylidene fluoride (PVDF), and polydimethylsiloxane (PDMS). However, these materials lack sufficient high-temperature strength. Therefore, it is necessary to increase the high-temperature deformation and expansion temperature of polymer solid-state electrolytes to reduce the probability of thermal runaway in batteries and improve the safety performance of lithium batteries. Summary of the Invention

[0005] Based on this, the present invention provides a composite solid electrolyte membrane, its preparation method and application, which solves at least one problem in the prior art.

[0006] In a first aspect, the present invention provides a composite solid electrolyte membrane comprising the following layers stacked sequentially:

[0007] The first membrane layer comprises a polymer, a solid electrolyte, and a lithium salt;

[0008] The second membrane layer comprises a polymer, a solid electrolyte, and a lithium salt;

[0009] The third film layer is the interface layer;

[0010] The solid electrolyte and lithium salt content of the second membrane layer are higher than those of the first membrane layer. The polymer is formed by polymerization of raw materials including cellulose triacetate (TCA) and polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP).

[0011] Secondly, the present invention provides a method for preparing the above-mentioned composite solid electrolyte membrane, which includes the following steps:

[0012] Cellulose triacetate, polyvinylidene fluoride-hexafluoropropylene, solid electrolyte, lithium salt and solvent are mixed into a slurry and formed into a planar membrane layer, which is then dried to obtain the first membrane layer.

[0013] Cellulose triacetate, polyvinylidene fluoride-hexafluoropropylene, solid electrolyte, lithium salt and solvent are mixed into a slurry and formed into a planar membrane layer, which is then dried to obtain a second membrane layer.

[0014] The first and second film layers are hot-pressed together, and then dried and annealed to obtain a composite film layer.

[0015] The prepolymer solution used to prepare the interface layer was applied to the surface of the above composite film layer, cured under ultraviolet light, and dried to obtain the third film layer.

[0016] Thirdly, the present invention provides the application of the above-mentioned composite solid electrolyte membrane in solid-state batteries.

[0017] Fourthly, the present invention provides a solid-state battery comprising the above-described composite solid-state electrolyte membrane.

[0018] Due to the adoption of the above technical solutions, the embodiments of the present invention have at least the following beneficial effects:

[0019] (1) The polymer triacetate cellulose (TCA) in the composite solid electrolyte membrane is resistant to high temperature and has strong flexibility, providing mechanical support and high temperature resistance. TCA has a melting point of up to 300℃, which can improve the high temperature safety of the battery.

[0020] (2) The polymer formed by TCA and PVDF-HFP allows the composite solid electrolyte membrane to melt and block micropores when the temperature reaches 160℃, forming closed pores; the TCA component in the polymer acts as a skeleton, resulting in small deformation of the composite solid electrolyte membrane, which further improves the safety of the battery; as a flexible matrix, PVDF-HFP can enhance interfacial contact, provide some ion transport channels, and the polymer matrix can alleviate the brittleness of oxide solid electrolytes and improve electrode / electrolyte interface contact.

[0021] (3) Solid-state batteries assembled with composite solid electrolyte membranes, positive electrode plates, and negative electrode plates have simple manufacturing processes, superior battery electrical performance, long cycle life, small expansion coefficient, and improved battery safety performance. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the composite solid electrolyte membrane in an embodiment of the present invention. Detailed Implementation

[0023] The following will provide a clear and complete description of the concept and technical effects of the present invention, so as to fully explain the purpose, solution and effects of the present invention.

[0024] The present invention aims to provide a safe composite solid electrolyte membrane that does not deform at high temperatures and has good ion transport performance, and to use it in solid-state batteries with high-energy-density high-nickel materials as positive electrodes and silicon-carbon, metallic lithium or inactive materials as negative electrodes (or self-generated negative electrodes).

[0025] In a first aspect, the present invention provides a composite solid electrolyte membrane, such as... Figure 1 As shown, it comprises the following layers stacked sequentially:

[0026] The first film layer 1 includes a polymer, a solid electrolyte, and a lithium salt;

[0027] The second membrane layer 2 comprises a polymer, a solid electrolyte, and a lithium salt;

[0028] The third film layer 3 is the interface layer;

[0029] The solid electrolyte and lithium salt content of the second membrane layer 2 are higher than those of the first membrane layer 1. The polymer is formed by polymerization of raw materials including cellulose triacetate (TCA) and polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP).

[0030] The above technical solution effectively improves the high-temperature performance of the composite solid electrolyte membrane, reduces expansion, extends battery cycle life, and enhances battery safety. The polymer raw material includes TCA, which gives the first and second membrane layers high-temperature resistance, contributing to improved high-temperature battery safety. The second membrane layer has higher solid electrolyte and lithium salt contents than the first membrane layer, allowing for concentration gradient-guided ion transport, particularly utilizing the lithium salt concentration gradient. The third membrane layer, also known as the surface layer, can be formed by UV curing of a prepolymerized liquid coated on the second membrane layer, which is beneficial for the stability of the electrolyte-electrode interface. Located on the outermost layer of the composite solid electrolyte membrane, the third membrane layer can directly contact the negative electrode lithium metal of the battery.

[0031] In some optional embodiments, the solid electrolyte can be one or more of lithium aluminum phosphide (LiALP), lithium aluminum titanium phosphide (LiALTiP), lithium lanthanum zirconium oxide (LLZO), lithium lanthanum zirconium tantalum oxide (LLZTO), lithium phosphorus oxynitrogen (LiPON), lithium zirconium oxychloride (Li2ZrCl6O), high-entropy garnet electrolyte (LLNSZTO), garnet inorganic electrolyte (LLZT), lithium titanium aluminum phosphate (LATP), etc.

[0032] In some optional embodiments, the lithium salt may include lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and may also include one or more of lithium hexafluorophosphate, lithium perchlorate (LiCIO4), lithium bis(oxalateborate), lithium tetrafluoroborate (LiBF4), lithium nitrate (LiNO3), lithium difluorooxalateborate, lithium difluorooxalate phosphate, lithium tetrafluorooxalate phosphate, lithium bis(fluorosulfonyl)imide, lithium difluorobis(malonate) phosphate, lithium hexafluoroarsenate, etc.

[0033] In some optional embodiments, the solid electrolyte and lithium salt contents of the second membrane layer 2 are both 10% or more higher than those of the first membrane layer 1. Preferably, based on the total mass of the first and second membrane layers, the solid electrolyte in the first membrane layer accounts for 8%-16% of the total mass, and the solid electrolyte in the second membrane layer accounts for 18%-30% of the total mass. Based on the total mass of the first and second membrane layers, the lithium salt content in the first membrane layer is 8%-20%, and the lithium salt content in the second membrane layer is 28%-50%. More preferably, based on the total mass of the first and second membrane layers, the solid electrolyte in the first membrane layer accounts for 10%-16% of the total mass, and the solid electrolyte in the second membrane layer accounts for 20%-30% of the total mass. The total mass of the first and second membrane layers is 100% each. The lithium salt content in the first membrane layer is 10%-20%, and the lithium salt content in the second membrane layer is 30%-50%.

[0034] In some alternative embodiments, the polymer is polymerized from raw materials including cellulose triacetate (TCA), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), and a crosslinking agent.

[0035] The total mass of the first and second membrane layers is 100% each, with TCA accounting for 3%-12% of the total mass of the first membrane layer and PVDF-HFP accounting for 12%-26% of the total mass of the second membrane layer. Preferably, the total mass of the first and second membrane layers is 100% each, with TCA accounting for 5%-10% of the total mass of the first membrane layer and PVDF-HFP accounting for 14%-25% of the total mass of the second membrane layer. The crosslinking agent can be dicumyl peroxide (DCP), accounting for 0.5% of the total mass of the first or second membrane layer.

[0036] In some optional embodiments, the first membrane layer 1 comprises a polymer, a solid electrolyte, a lithium salt, additives, and a plasticizer, and the second membrane layer 2 comprises a polymer, a solid electrolyte, a lithium salt, additives, and a plasticizer.

[0037] The aforementioned additives include one or more of the following: ethylene carbonate (EC), sulfolane (TMS), dimethyl sulfoxide, succinate (SN), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), ethyl fluorocarbonate, difluoroethylene carbonate, 1,2-dimethoxypropane (DMP), dimethoxymethane (DMM), ethylene glycol dimethyl ether (DME), acetonitrile (ACN), trimethyl phosphate (TMP), triethyl phosphate (TEP), fluoroethylene carbonate (FEC), vinylene carbonate (VC), vinyl sulfate (DTD), propylene-1,3-sulfonyl lactone (PST), and 1,3-propanesulfonyl lactone (PS). The total mass of the first and second membrane layers is 100% each, and the additives account for 3%-8% of the total mass of either the first or second membrane layer. Preferably, the total mass of the first and second films is 100%, and the additives account for 3%-5% of the total mass of the first or second film. These high dielectric constant aprotic organic solvents, as additives, can effectively suppress crystallization in solid electrolytes and promote lithium ion transport in the electrolyte, thereby improving the ionic conductivity of solid electrolytes at room temperature.

[0038] In some alternative embodiments, the third film layer 3 is formed by UV curing of a prepolymer liquid comprising a solid electrolyte, polyethylene oxide (PEO) and an initiator.

[0039] In the aforementioned third film layer, the solid electrolyte accounts for 15%-25% of the total mass of the prepolymer solution, preferably 16%-23%. PEO accounts for 15%-25% of the total mass of the prepolymer solution, preferably 15%-22%. The solvent of the prepolymer solution is one or more of anhydrous acetonitrile, diethyl ether, chloroform, benzene, toluene, dichloromethane, and dimethylformamide, accounting for 50%-75% of the total mass of the prepolymer solution, preferably 60%-70%. The initiator can be benzophenone (Bp), accounting for 0.5%-3% of the total mass of the prepolymer solution. The coating thickness of the third film layer is generally 1-4 μm, preferably 2-4 μm. The third film layer containing inorganic solid electrolyte (such as LLNSZTO) can mitigate the violent contact reaction between polymer electrolyte and other components and lithium metal, ensuring the formation of a thin and dense composite SEI between the electrolyte and the negative electrode. The formation of the composite SEI layer further promotes the chemical-electrochemical balance at the interface, ultimately achieving stable stripping / electroplating of lithium metal.

[0040] Secondly, the present invention provides a method for preparing the above-mentioned composite solid electrolyte membrane, which includes the following steps:

[0041] Cellulose triacetate, polyvinylidene fluoride-hexafluoropropylene, solid electrolyte, lithium salt and solvent are mixed into a slurry and formed into a planar membrane layer, which is then dried to obtain the first membrane layer 1;

[0042] Cellulose triacetate, polyvinylidene fluoride-hexafluoropropylene, solid electrolyte, lithium salt and solvent are mixed into a slurry and formed into a planar membrane layer, which is then dried to obtain the second membrane layer 2.

[0043] The first and second film layers are hot-pressed together, and then dried and annealed to obtain a composite film layer.

[0044] The prepolymer solution used to prepare the interface layer is applied to the surface of the above composite film layer (i.e., the second film layer), cured under ultraviolet light, and dried to obtain the third film layer 3.

[0045] In some optional embodiments, the above-mentioned mixing of cellulose triacetate, polyvinylidene fluoride-hexafluoropropylene, solid electrolyte, lithium salt, and solvent into a slurry includes: mixing cellulose triacetate, polyvinylidene fluoride-hexafluoropropylene, and solvent in a closed mixing tank, stirring at 80°C for 6 hours or more, adding the solid electrolyte, dispersing at high speed (10,000 rpm, 1 hour), adding the lithium salt, and stirring to form a slurry. The solvent accounts for 30%-75% of the total mass of the slurry, preferably 35%-75% of the total mass of the slurry; the solvent can be one or more of N-methylpyrrolidone (NMP) and dimethyl sulfoxide (DMSO). The slurry is cast into a polytetrafluoroethylene template (or coated onto a PET release film) to a set thickness, and then dried (it can be dried at 80°C for 2 hours).

[0046] In some optional embodiments, the hot-pressing temperature is 115-125°C, the hot-pressing pressure is 9-11 MPa, and the hot-pressing time is 3-7 minutes. Preferably, the hot-pressing temperature is 120°C, the hot-pressing pressure is 10 MPa, and the hot-pressing time is 5 minutes. Hot pressing can be achieved using a hot press machine, stacking the first film layer and the second film layer in sequence, followed by hot rolling to densify them. After drying, the residual solvent is <100 ppm, indicating that the solvent is essentially completely removed. Drying can be vacuum drying, with a drying temperature of 80-100°C and a drying time of 2-24 hours.

[0047] In some optional embodiments, the annealing temperature is 150°C and the annealing time is 1 hour. Annealing at 150°C for 1 hour improves the crystallinity and mechanical strength of the polymer, ultimately obtaining an electrolyte membrane of the required thickness.

[0048] Thirdly, the present invention provides the application of the above-mentioned composite solid electrolyte membrane in solid-state batteries.

[0049] Fourthly, the present invention provides a solid-state battery comprising the above-described composite solid-state electrolyte membrane.

[0050] The following describes a typical implementation.

[0051] Example 1

[0052] The composite solid electrolyte membrane was prepared according to the following steps:

[0053] (1) Add 0.7g TCA, 2g PVDF-HFP, 0.06g DCP, and 0.5g DMSO to 4.7g NMP and stir at 80℃ for 6 hours until completely dissolved; add 1.4g LLNSZTO powder and disperse at high speed (10000 rpm, 1 hour) to avoid agglomeration; add 1.5g LiTFSI and continue stirring for 2 hours to form a uniform slurry; degas under vacuum (-0.1 MPa, 30 minutes) to obtain a mixed slurry for forming the first film layer; cast the mixed slurry into a polytetrafluoroethylene template with a wet film thickness of 30 μm; pre-dry at 80℃ for 2 hours to evaporate some of the solvent and obtain the first film layer (labeled as sample 1);

[0054] (2) Add 0.7g TCA, 2g PVDF-HFP, 0.075g DCP, and 0.6g PC to 2.4g NMP and stir at 80℃ for 6 hours until completely dissolved; add 2.5g LLNSZTO powder and disperse at high speed (10000 rpm, 1 hour) to avoid agglomeration; add 4g LiTFSI and continue stirring for 2 hours to form a uniform slurry; degas under vacuum (-0.1 MPa, 30 minutes) to obtain a mixed slurry for forming the second film layer; cast the mixed slurry into a polytetrafluoroethylene template with a wet film thickness of 30μm; pre-dry at 80℃ for 2 hours to evaporate some of the solvent and obtain the second film layer (labeled as sample 2).

[0055] (3) The first and second film layers were stacked and placed under a hot press. They were continuously hot-pressed at 120°C and 10 MPa for 5 minutes to eliminate pores and achieve complete composite. The composite was then vacuum dried (100°C for 24 hours) to reduce the residual solvent to <100 ppm, resulting in a composite of the first and second film layers with a thickness of 55 μm. The second film layer had a 20% higher lithium salt content than the first film layer. The composite of the first and second film layers was annealed at 150°C for 1 hour to improve the crystallinity and mechanical strength of the polymer, resulting in a composite film layer (marked as sample 3).

[0056] (4) 1g LLNSZTO was dispersed in anhydrous acetonitrile by ultrasonication, and 0.9g PEO and 0.01g Bp photoinitiator were added under magnetic stirring at room temperature to obtain a prepolymer solution. The obtained prepolymer solution was coated onto the surface of the second layer of the composite membrane and cured under ultraviolet light. The flexible interface layer with a thickness of 3-4μm was obtained by vacuum drying. The membrane was volatilized at room temperature for 4h and then vacuum dried at 60℃ for 6h to finally obtain a composite solid electrolyte membrane with a thickness of 58μm (marked as sample 4).

[0057] Comparative Example 1

[0058] The preparation steps of this comparative example are basically the same as those of sample 4 in Example 1, except that TCA is replaced with the same mass of PVDF-HFP, and the resulting composite solid electrolyte membrane is labeled as sample 5.

[0059] Samples 1 and 2 were vacuum dried (100℃, 24 hours) to reduce residual solvent to <100 ppm, and then annealed at 150℃ for 1 hour before use.

[0060] In a glove box with a dew point of -40°C, the prepared NCM811 positive electrode, composite solid electrolyte membrane (sample 4), and lithium negative electrode were stacked sequentially, with the third layer of the composite solid electrolyte membrane facing the lithium negative electrode, to encapsulate an NCM811 / Li pouch battery. Similarly, samples 1, 2, 3, and 5 were encapsulated into NCM811 / Li pouch batteries. The NCM811 / Li pouch batteries assembled from samples 1 to 5 were subjected to room temperature cycling performance tests, high-temperature storage performance tests, and thermal shock performance tests.

[0061] Room temperature cycle performance test: At 25℃, the formed battery was charged to 4.2V using a constant current and constant voltage of 0.5C (cutoff current of 0.01C), and then discharged to 3.0V using a constant current of 0.5C. The capacity retention rate after 300 charge / discharge cycles was calculated using the following formula:

[0062] Capacity retention rate after 300 cycles (%) = Discharge capacity at cycle 300 / Discharge capacity at cycle 1 × 100%

[0063] High-temperature storage performance test: The thickness of the battery after formation was measured. The battery was charged to 4.2V at 25℃ using a constant current and constant voltage of 0.5C (cutoff current 0.01C), and then stored at 85℃ for 4 hours. After high-temperature storage, the thickness of the cell or battery was measured in an oven, and the increase rate of battery thickness before and after high-temperature storage was calculated. The calculation formula is as follows:

[0064] Battery thickness increase rate (%) = (Battery thickness after high temperature - Battery thickness before high temperature) / Battery thickness before high temperature × 100%

[0065] Thermal shock performance test: Charge the battery to 4.2V at a constant current and constant voltage of 0.5C at 25℃ (cutoff current is 0.01C), place the battery in an oven, and heat the oven to 150℃±2℃ at a rate of 5℃±2℃ / minute. After the oven reaches 150℃±2℃, maintain it for 10 minutes. If the battery is observed not to catch fire or explode, it passes the test.

[0066] As shown in Table 1, the composite solid electrolyte membrane (sample 4) of Example 1 maintains high cycle capacity, excellent high-temperature storage performance, strong thermal shock resistance, and high safety.

[0067] Table 1 Performance test results of NCM811 / Li pouch cells assembled from various samples

[0068]

[0069] Samples 1-4 use solid electrolyte membranes made of TCA, which are porous support layers composed of high-temperature resistant TCA and PVDF-HFP composites, providing mechanical support, high-temperature resistance, and safety performance. Sample 5, however, is made of pure PVDF-HFP composite and performs worse in high-temperature resistance and thermal shock tests.

[0070] By comparing samples 1 to 3, it can be seen that samples 1 and 2 use a single electrolyte membrane, which results in the battery's cycle performance being inferior to that of sample 3.

[0071] By comparing samples 3 and 4, it can be seen that sample 4, which contains a surface layer (third film layer), has a more favorable interface for the stability of the electrolyte-electrode interface, thus benefiting the battery's cycle performance.

[0072] By comparing samples 4 and 5, it can be seen that the battery made with the composite solid electrolyte membrane without TCA expands and deforms significantly at high temperatures. At the same time, under the influence of heat generated over a long period of time during long-term cycling, the interface deforms, which affects the cycle life of the battery.

[0073] The above description is merely a preferred embodiment of the present invention. The present invention is not limited to the above-described embodiments. Any embodiment that achieves the technical effects of the present invention by the same or equivalent means should fall within the protection scope of the present invention. Within the protection scope of the present invention, various modifications and variations can be made to the technical solutions and / or implementation methods.

Claims

1. A composite solid-state electrolyte membrane, characterized by, The composite solid-state electrolyte film comprises the following layers in sequence: a first film layer comprising a polymer, a solid-state electrolyte and a lithium salt; a second film layer comprising a polymer, a solid-state electrolyte and a lithium salt; a third film layer being an interface layer; wherein the solid-state electrolyte and the lithium salt in the second film layer are both higher than those in the first film layer, and the polymer is formed by polymerization of raw materials comprising cellulose triacetate and polyvinylidene hexafluoropropylene.

2. The composite solid-state electrolyte film of claim 1, wherein The solid-state electrolyte and the lithium salt in the second film layer are both 10% or more higher than those in the first film layer.

3. The composite solid-state electrolyte film of claim 1, wherein The polymer is formed by polymerization of raw materials comprising cellulose triacetate, polyvinylidene hexafluoropropylene and a cross-linking agent.

4. The composite solid-state electrolyte film of claim 1, wherein The first film layer comprises a polymer, a solid-state electrolyte, a lithium salt, an additive and a plasticizer, and the second film layer comprises a polymer, a solid-state electrolyte, a lithium salt, an additive and a plasticizer.

5. The composite solid-state electrolyte film of claim 1, wherein The third film layer is formed by UV curing of a prepolymer solution comprising a solid-state electrolyte, polyethylene oxide and an initiator.

6. The method of claim 1-5, wherein the composite solid-state electrolyte film is prepared by a method comprising: The method comprises the following steps: mixing cellulose triacetate, polyvinylidene hexafluoropropylene, a solid-state electrolyte, a lithium salt and a solvent into a slurry, and making a planar film layer, and drying to obtain the first film layer; mixing cellulose triacetate, polyvinylidene hexafluoropropylene, a solid-state electrolyte, a lithium salt and a solvent into a slurry, and making a planar film layer, and drying to obtain the second film layer; compositing the first film layer and the second film layer by hot pressing, and drying and annealing to obtain a composite film layer; coating a prepolymer solution for preparing an interface layer on the surface of the composite film layer, curing under ultraviolet light, and drying to obtain the third film layer.

7. The method of claim 6, wherein, The temperature of the hot pressing is 115-125℃, the pressure of the hot pressing is 9-11 Mpa, and the time of the hot pressing is 3-7 minutes.

8. The method of claim 6, wherein, The temperature of the annealing is 150℃, and the time of the annealing is 1 hour.

9. Use of the composite solid-state electrolyte film according to any one of claims 1-5 in a solid-state battery.

10. A solid state battery, characterized by The composite solid-state electrolyte film according to any one of claims 1-5.

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