Preparation method of high-safety soft package lithium battery

Abstract

According to the preparation method of the high-safety soft package lithium battery provided by the invention, through the synergistic effect of a sodium alginate-polyethylene oxide dual-network polymer electrolyte system and a carbon nanotube enhanced composite electrode system, the ionic conductivity and the interface stability are remarkably improved while the structural strength is ensured; and the flame-retardant plasticizing component and three-dimensional conductive network optimization are combined, so that the prepared lithium ion battery has high energy density, excellent rate capability, good safety and long cycle life, and is particularly suitable for high-end application of electric automobiles, energy storage systems and the like.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, specifically relating to a method for preparing a high-safety soft-pack lithium battery. Background Technology

[0002] In the field of lithium-ion battery technology, traditional polyethylene oxide (PEO)-based polymer electrolytes, while possessing good ionic conductivity and compatibility with lithium metal, generally exhibit low mechanical strength and limited ionic conductivity due to high crystallinity at room temperature, making it difficult to simultaneously meet the requirements of high safety, high energy density, and long cycle life. Existing technologies often employ cross-linking, adding inorganic fillers, or blending with rigid polymers to improve mechanical properties; however, these methods often sacrifice ionic conductivity or increase interfacial impedance. Furthermore, most traditional liquid or gel electrolytes are flammable, posing a risk of thermal runaway, making them unsuitable for direct application in electric vehicles and large-scale energy storage applications where safety requirements are extremely high. Therefore, developing a solid or quasi-solid polymer electrolyte system that combines high ionic conductivity, excellent mechanical strength, and intrinsic flame-retardant properties has become a crucial issue urgently needing breakthroughs in this field.

[0003] In electrode manufacturing, traditional electrodes typically rely on a mixed conductive network composed of binders such as polyvinylidene fluoride (PVDF) and conductive carbon black. This network has limited electronic conductivity, and the binders are often electrochemically inert, reducing the overall energy density of the electrode. Simultaneously, ion transport within the electrode largely depends on channels formed by electrolyte wetting. However, the pore structures created by traditional coating processes are often unevenly distributed and poorly connected, especially in thick electrodes where ion transport impedance increases significantly, limiting the battery's rate performance. Furthermore, the stress generated by the volume changes of the active material during cycling can easily lead to structural pulverization and conductive network breakage, affecting cycle stability. Therefore, constructing an electrode structure that balances high electronic conductivity, efficient ion transport pathways, and strong mechanical stability is of great significance for improving the overall performance of batteries.

[0004] In battery assembly processes, challenges often arise such as poor electrode-electrolyte interface contact, lithium dendrite growth, and instability of the solid electrolyte interphase (SEI) film. Conventional electrolyte injection methods struggle to ensure uniform electrolyte distribution within multilayer stacked structures, easily leading to localized dry areas and increased interfacial impedance. Furthermore, improperly controlled formation processes can result in a porous or unevenly distributed SEI film, failing to effectively suppress continuous electrolyte decomposition and lithium dendrite penetration. This is particularly pronounced when using high-capacity negative electrodes or high-voltage positive electrodes, where interfacial side reactions are more severe, directly impacting battery cycle life and safety. Therefore, developing precise stacking, electrolyte injection, and formation processes to achieve stable construction and dynamic maintenance of the electrode-electrolyte interface is crucial for ensuring long-term reliable battery operation.

[0005] In summary, current lithium-ion battery technology still faces a series of challenges in achieving synergistic improvements in high energy density and high safety, optimizing multi-scale transport efficiency within the electrode, and maintaining interface stability during long-term cycling. Solving these problems will not only help advance the driving range and safety performance of electric vehicles to new heights, but is also crucial for cost control and long-term reliability of large-scale energy storage systems. The fabrication method described in this paper addresses these bottlenecks by innovating material systems and finely controlling processes, aiming to develop a novel lithium-ion battery with superior overall performance and providing an effective solution for the development of next-generation energy storage technologies. Summary of the Invention

[0006] This invention discloses a method for preparing a high-safety soft-pack lithium battery to solve any of the above-mentioned and potential problems in the prior art.

[0007] To solve the above-mentioned technical problems, the specific solution of the present invention is as follows: A method for preparing a high-safety soft-pack lithium battery includes the following steps: 1) Preparation of electrolyte membrane: Dissolve 1.5-3 parts of sodium alginate in 50 parts of deionized water and stir at 60℃ for 1 h to obtain a sodium alginate solution; dissolve 2-4 parts of triblock copolymer PEO-PPO-PEO in 30 parts of deionized water and stir magnetically at 20-30℃ for 1-1.5 h to obtain a triblock copolymer solution; mix the above two solutions, add 0.8-1.5 parts of lithium salt and 0.8-1.3 parts of filler, and emulsify in a high-speed shear emulsifier at 5000 rpm. Stir for 1-1.5 hours to form a uniform slurry; then add 0.8-1.2 parts of flame retardant and continue stirring for 30 minutes; finally add 0.1-0.3 parts of crosslinking agent genipin, stir at 100 rpm for 5-10 minutes and then stop stirring. React at 40℃ for 1.5-2.5 hours to form a double network gel; spread the slurry evenly on a polyethylene terephthalate substrate with a thickness controlled at 50±5 μm, and dry in a vacuum drying oven at 50℃ for 12 hours to obtain a flexible polymer electrolyte membrane; 2) Preparation of positive electrode sheet: Mix 8.0 parts of lithium nickel manganese cobalt oxide, 0.2-0.5 parts of sodium alginate, 0.2-0.3 parts of lithium polyacrylate and 0.8-1 parts of pore-forming agent, add 20 parts of 90% ethanol as solvent, stir at 200 rpm for 2 h, add 1.0 part of carbon nanotube pre-dispersed slurry, and then disperse at 1000 rpm for 30-45 min to form a uniform slurry; coat the slurry on aluminum foil current collector, the wet film thickness is 150±5 μm, dry in an oven at 60℃ for 1 h, then vacuum dry at 70℃ for 10-12 h to remove moisture and solvent, and then heat to below 250℃ for vacuum drying for 2-4 h; 3) Preparation of negative electrode sheet: Mix 8.0 parts graphite, 0.2-0.5 parts sodium alginate, 0.2-0.3 parts lithium polyacrylate and 0.6-0.8 parts pore-forming agent, add 15 parts of 90% ethanol as solvent, stir at 150 rpm for 2 h, add 0.8 parts carbon nanotube pre-dispersion slurry, and disperse at 2000 rpm for 20-30 min to form a uniform slurry; coat the slurry onto copper foil current collector, the wet film thickness is 120±5 μm, dry in an oven at 60℃ for 1 h, then vacuum dry at 70℃ for 10-12 h to remove moisture and solvent, and then heat to below 250℃ for vacuum drying for 2-4 h; 4) Assembly and packaging: including cutting, tab welding, stacking, thermoforming, housing and packaging, final sealing, formation and aging.

[0008] Preferably, the flame retardant is tris(2,2,2-trifluoroethyl) phosphate.

[0009] Preferably, the filler is nano-sized lithium lanthanum zirconium oxide.

[0010] Preferably, the lithium salt is lithium bis(trifluoromethanesulfonyl)imide.

[0011] Specifically, the carbon nanotube pre-dispersed slurry is prepared by dissolving 0.2-0.3 parts of sodium carboxymethyl cellulose in 1 part of a 20% ethanol solution, and then uniformly adding 1 part of carbon nanotubes into the solution over 10-15 minutes. During the addition process, the mixture is continuously stirred at 500 rpm to prevent local over-concentration and the formation of unopenable "dry powder clumps" caused by adding the mixture all at once. At the same time, low-speed stirring prevents the mixture from floating on the surface and avoids splashing or entraining too many air bubbles, ensuring that the carbon nanotube powder can be quickly wetted and encapsulated when it enters the liquid phase. After the addition is completed, the mixture is then subjected to indirect stirring and homogenization at 3500 rpm for 10-15 minutes to prevent local overheating of the slurry and solvent evaporation. Each stirring session lasts 2-3 minutes, followed by a 1-minute stop.

[0012] Preferably, the pore-forming agent is tributyl acetyl citrate. After vacuum drying at 70°C in steps 2) and 3), the temperature is raised to 180-220°C and vacuum dried for 2-4 hours.

[0013] Preferably, the positive electrode, electrolyte membrane, and negative electrode are designed with a size gradient during stacking. The positive electrode is 50mm×50mm, the polymer electrolyte membrane is 54mm×54mm, and the negative electrode is 52mm×52mm. The polymer electrolyte membrane is covered on the positive electrode, and then the negative electrode is covered to form a stacked structure. 8 to 10 layers are stacked in parallel.

[0014] The advantages and beneficial effects of this invention are as follows: 1. In the preparation of polymer electrolyte membranes, sodium alginate, as a natural polymer, has carboxyl groups on its molecular chain that can coordinate with lithium ions. The PEO segments in the triblock copolymer PEO-PPO-PEO provide excellent lithium-ion transport channels, while the PPO segments enhance the mechanical stability of the system. The interpenetrating network structure formed by the crosslinking of these two polymers with genipin maintains the rigid framework of sodium alginate while utilizing the ionic conductivity of the PEO segments. The specially introduced tris(2,2,2-trifluoroethyl) phosphate flame retardant utilizes phosphorus to form a phosphate protective layer at high temperatures, while fluorine captures free radicals through strong electronegativity, achieving a dual flame retardant mechanism in both the gas and condensed phases. Simultaneously, the lithium lanthanum zirconium oxide filler not only acts as a rigid reinforcing phase to improve the mechanical strength of the membrane, but its inherent ionic conductivity also provides an additional fast channel for lithium-ion transport. This composite structure of rigid filler and flexible polymer effectively resolves the contradiction between ionic conductivity and mechanical strength in traditional polymer electrolytes.

[0015] 2. In electrode fabrication, the synergistic use of carbon nanotubes and bifunctional binders allows multi-walled carbon nanotubes to construct a continuous three-dimensional conductive network within the electrode. This network structure not only provides an efficient electron transport path, but its abundant surface functional groups also enable strong physicochemical interactions with the active material, enhancing the electrode's structural stability. The composite binder system of sodium alginate and lithium polyacrylate exhibits a synergistic effect. Sodium alginate, through its linear molecular chains, forms a strong bond with the current collector, while the branched structure of lithium polyacrylate better encapsulates the active material particles. The combination of these two components ensures effective bonding from the current collector to the active material. As a pore-forming agent, tributyl acetylacetate decomposes and volatilizes during heat treatment, leaving a uniformly distributed pore size gradient structure inside the electrode. These interconnected channels not only provide sufficient wetting space for the electrolyte, but also further construct a rapid lithium-ion transport channel, enabling lithium ions to quickly and uniformly reach the active sites deep within the electrode during high-rate charging and discharging. This effectively suppresses electrode polarization and capacity decay caused by ion diffusion lag, thereby fundamentally and synergistically improving the electrode's ionic conductivity, active material utilization rate, and structural stability.

[0016] 3. The positive electrode-electrolyte-negative electrode size gradient design used in the battery assembly process effectively eliminates the electric field concentration phenomenon at the electrode edge and suppresses the formation of lithium dendrites.

[0017] 4. The lithium-ion battery ultimately obtained by this invention achieves significant improvements in multiple performance indicators. The dual-network polymer electrolyte not only provides a high level of ionic conductivity, but its unique flame-retardant properties further enhance battery safety. The multi-level porous structure constructed in the electrodes ensures rapid ion and electron transport, giving the battery excellent rate performance. The stable interface structure and robust electrode system guarantee the battery's capacity retention during long-term cycling. This comprehensive improvement in overall performance makes the battery particularly suitable for applications with stringent requirements for safety, energy density, and cycle life, such as power batteries for electric vehicles and large-scale energy storage systems, providing crucial technical support for the development of next-generation lithium-ion battery technology. Detailed Implementation

[0018] The present invention will be further described in detail below with reference to the embodiments. PEO-PPO-PEO is Pluronic F127, sodium alginate is 300-600 mPa·s, lithium nickel manganese cobalt oxide is NMC111; carbon nanotubes are multi-walled with an outer diameter of 6-13 nm and a length of 15-25 μm, and other reagents are all conventional types unless otherwise specified.

[0019] Carbon nanotube pre-dispersed slurry: Dissolve 30g of sodium carboxymethyl cellulose in 100g of 20% ethanol solution, then add 100g of carbon nanotubes uniformly to the solution over 15min. During the addition process, stir continuously at 500rpm. After the addition is complete, perform indirect stirring homogenization at 3500rpm for 12min, stirring for 3min each time and stopping for 1min. The slurry is ready for use.

[0020] Each group of electrolyte membranes was prepared using the following methods: A1: Dissolve 200g of sodium alginate in 5000g of deionized water and stir at 60℃ for 1h to obtain a sodium alginate solution; dissolve 300g of triblock copolymer PEO-PPO-PEO in 3000g of deionized water and stir magnetically at 25±1℃ for 1h to obtain a triblock copolymer solution; mix the above two solutions, add 100g of lithium bis(trifluoromethanesulfonyl)imide and 100g of nano-sized lithium lanthanum zirconium oxide, and emulsify in a high-speed shear emulsifier at 5000... Stir at rpm for 1.5 h to form a uniform slurry; then add 100 g of tris(2,2,2-trifluoroethyl) phosphate and continue stirring for 30 min; finally add 20 g of crosslinking agent genipin, stir at 100 rpm for 5 min and then stop stirring, react at 40 °C for 2 h to form a double network gel; spread the slurry evenly on a polyethylene terephthalate substrate with a thickness controlled at 50 ± 5 μm, and dry in a vacuum drying oven at 50 °C for 12 h to obtain a flexible polymer electrolyte membrane; A2: Dissolve 150g of sodium alginate in 5000g of deionized water and stir at 60℃ for 1h to obtain a sodium alginate solution; dissolve 200g of triblock copolymer PEO-PPO-PEO in 3000g of deionized water and stir magnetically at 28±1℃ for 1.5h to obtain a triblock copolymer solution; mix the above two solutions, add 150g of lithium bis(trifluoromethanesulfonyl)imide and 80g of nano-sized lithium lanthanum zirconium oxide, and emulsify in a high-speed shear emulsifier at 5000r. Stir for 1.5 h to form a uniform slurry; then add 80 g of tris(2,2,2-trifluoroethyl) phosphate and continue stirring for 30 min; finally add 30 g of crosslinking agent genipin, stir at 100 rpm for 10 min and then stop stirring, react at 40 °C for 2.5 h to form a double network gel; spread the slurry evenly on a polyethylene terephthalate substrate with a thickness controlled at 50 ± 5 μm, and dry in a vacuum drying oven at 50 °C for 12 h to obtain a flexible polymer electrolyte membrane; A3: Dissolve 300g of sodium alginate in 5000g of deionized water and stir at 60℃ for 1h to obtain a sodium alginate solution; dissolve 400g of triblock copolymer PEO-PPO-PEO in 3000g of deionized water and stir magnetically at 22±1℃ for 1h to obtain a triblock copolymer solution; mix the two solutions, add 80g of lithium bis(trifluoromethanesulfonyl)imide and 130g of nano-sized lithium lanthanum zirconium oxide, and emulsify in a high-speed shear emulsifier at 5000r. Stir for 1 hour to form a uniform slurry; then add 120g of tris(2,2,2-trifluoroethyl) phosphate and continue stirring for 30 minutes; finally add 10g of crosslinking agent genipin, stir at 100 rpm for 10 minutes and then stop stirring, react at 40℃ for 1.5 hours to form a double network gel; spread the slurry evenly on a polyethylene terephthalate substrate with a thickness controlled at 50±5μm, and dry in a vacuum drying oven at 50℃ for 12 hours to obtain a flexible polymer electrolyte membrane; A4: Dissolve 100g PVDF in 6000g NMP, stir at 60℃ for 4 hours, add 50g LiPF6 and 100g LLZO, stir and cast into a film with a thickness controlled at 50±5μm, and vacuum dry at 60℃ for 12 hours. A5: Dissolve 200g of sodium alginate in 5000g of deionized water and stir at 60℃ for 1h to obtain a sodium alginate solution; dissolve 300g of polyvinyl alcohol in 3000g of deionized water and stir magnetically at 25±1℃ for 1h; mix the two solutions, add 100g of lithium bis(trifluoromethanesulfonyl)imide and 100g of nano-sized lithium lanthanum zirconium oxide, and stir at 5000rpm for 1.5h in a high-speed shear emulsifier to form a uniform slurry; then add 100g of tri(2,2,2-trifluoroethyl) phosphate and continue stirring for 30min; finally add 20g of crosslinking agent genipin, stir at 100rpm for 5min and then stop stirring, react at 40℃ for 2h to form a double network gel; spread the slurry evenly on a polyethylene terephthalate substrate with a thickness controlled at 50±5μm, and dry in a vacuum drying oven at 50℃ for 12h to obtain a flexible polymer electrolyte membrane; A6: Dissolve 200g of sodium alginate in 5000g of deionized water and stir at 60℃ for 1h to obtain a sodium alginate solution; dissolve 300g of triblock copolymer PEO-PPO-PEO in 3000g of deionized water and stir magnetically at 25±1℃ for 1h to obtain a triblock copolymer solution; mix the two solutions, add 100g of lithium bis(trifluoromethanesulfonyl)imide and 100g of nano-sized lithium lanthanum zirconium oxide, and emulsify in a high-speed shear emulsifier. Stir at 5000 rpm for 1.5 h to form a uniform slurry; then add 100 g of triethyl phosphate and continue stirring for 30 min; finally add 20 g of crosslinking agent genipin, stir at 100 rpm for 5 min and then stop stirring, react at 40 °C for 2 h to form a double network gel; spread the slurry evenly on a polyethylene terephthalate substrate with a thickness controlled at 50 ± 5 μm, and dry in a vacuum drying oven at 50 °C for 12 h to obtain a flexible polymer electrolyte membrane; A7: Dissolve 200g of sodium alginate in 5000g of deionized water and stir at 60℃ for 1h to obtain a sodium alginate solution; dissolve 150g of triblock copolymer PEO-PPO-PEO in 3000g of deionized water and stir magnetically at 25±1℃ for 1h to obtain a triblock copolymer solution; mix the two solutions, add 100g of lithium bis(trifluoromethanesulfonyl)imide and 100g of nano-grade lithium lanthanum zirconium oxide, and emulsify in a high-speed shear emulsifier at 5000... Stir at rpm for 1.5 h to form a uniform slurry; then add 100 g of tris(2,2,2-trifluoroethyl) phosphate and continue stirring for 30 min; finally add 20 g of crosslinking agent genipin, stir at 100 rpm for 5 min and then stop stirring, react at 40 °C for 2 h to form a double network gel; spread the slurry evenly on a polyethylene terephthalate substrate with a thickness controlled at 50 ± 5 μm, and dry in a vacuum drying oven at 50 °C for 12 h to obtain a flexible polymer electrolyte membrane; A8: Dissolve 150g of sodium alginate in 5000g of deionized water and stir at 60℃ for 1h to obtain a sodium alginate solution; dissolve 200g of triblock copolymer PEO-PPO-PEO in 3000g of deionized water and stir magnetically at 28±1℃ for 1.5h to obtain a triblock copolymer solution; mix the above two solutions, add 150g of lithium bis(trifluoromethanesulfonyl)imide and 70g of nano-sized lithium lanthanum zirconium oxide, and emulsify in a high-speed shear emulsifier at 5000r. Stir for 1.5 h to form a uniform slurry; then add 80 g of tris(2,2,2-trifluoroethyl) phosphate and continue stirring for 30 min; finally add 30 g of crosslinking agent genipin, stir at 100 rpm for 10 min and then stop stirring, react at 40 °C for 2.5 h to form a double network gel; spread the slurry evenly on a polyethylene terephthalate substrate with a thickness controlled at 50 ± 5 μm, and dry in a vacuum drying oven at 50 °C for 12 h to obtain a flexible polymer electrolyte membrane; Prepare each group of positive and negative electrodes using the following methods: B1: Preparation of positive electrode sheet: 80g NMC111, 3g sodium alginate, 2g lithium polyacrylate and 8g tributyl acetylacetate were mixed, and 200g of 90% ethanol was added as solvent. The mixture was stirred at 200rpm for 2h, and 10g carbon nanotube pre-dispersed slurry was added. The mixture was then dispersed at 1000rpm for 40min to form a uniform slurry. The slurry was coated on an aluminum foil current collector with a wet film thickness of 150±5μm. The film was dried in an oven at 60℃ for 1h, then vacuum dried at 70℃ for 10h, and then vacuum dried at 200℃ for 3h. Preparation of negative electrode sheet: 80g graphite, 3g sodium alginate, 2g lithium polyacrylate and 7g tributyl acetylacetic acid were mixed, and 150g of 90% ethanol was added as solvent. The mixture was stirred at 150rpm for 2h, and 8g carbon nanotube pre-dispersed slurry was added. The mixture was then dispersed at 2000rpm for 25min to form a uniform slurry. The slurry was coated on a copper foil current collector with a wet film thickness of 120±5μm. The film was dried in an oven at 60℃ for 1h, then vacuum dried at 70℃ for 10h, and then vacuum dried at 200℃ for 3h. B2: Preparation of positive electrode sheet: 80g NMC111, 2g sodium alginate, 3g lithium polyacrylate and 10g tributyl acetylacetate were mixed, and 200g of 90% ethanol was added as solvent. The mixture was stirred at 200rpm for 2h, and 10g carbon nanotube pre-dispersed slurry was added. The mixture was then dispersed at 1000rpm for 45min to form a uniform slurry. The slurry was coated on an aluminum foil current collector with a wet film thickness of 150±5μm. The film was dried in an oven at 60℃ for 1h, then vacuum dried at 70℃ for 12h, and then vacuum dried at 180℃ for 4h. Preparation of negative electrode sheet: 80g graphite, 2g sodium alginate, 2g lithium polyacrylate and 6g tributyl acetylacetic acid were mixed and 150g 90% ethanol was added as solvent. The mixture was stirred at 150rpm for 2h. 8g carbon nanotube pre-dispersed slurry was added and dispersed at 2000rpm for 30min to form a uniform slurry. The slurry was coated on copper foil current collector with a wet film thickness of 120±5μm. It was dried in an oven at 60℃ for 1h, then vacuum dried at 70℃ for 12h, and then vacuum dried at 220℃ for 2h.

[0021] B3: Preparation of positive electrode sheet: 80g NMC111, 5g sodium alginate, 2g lithium polyacrylate and 8g tributyl acetylacetate were mixed, and 200g of 90% ethanol was added as solvent. The mixture was stirred at 200rpm for 2h, and 10g carbon nanotube pre-dispersed slurry was added. The mixture was then dispersed at 1000rpm for 30min to form a uniform slurry. The slurry was coated on an aluminum foil current collector with a wet film thickness of 150±5μm. The film was dried in an oven at 60℃ for 1h, then vacuum dried at 70℃ for 12h, and then vacuum dried at 220℃ for 2h. Preparation of negative electrode sheet: 80g graphite, 5g sodium alginate, 3g lithium polyacrylate and 8g tributyl acetylacetic acid were mixed and 150g 90% ethanol was added as solvent. The mixture was stirred at 150rpm for 2h. 8g carbon nanotube pre-dispersed slurry was added and dispersed at 2000rpm for 20min to form a uniform slurry. The slurry was coated on a copper foil current collector with a wet film thickness of 120±5μm. It was dried in an oven at 60℃ for 1h, then vacuum dried at 70℃ for 10h, and then vacuum dried at 180℃ for 4h.

[0022] B4: Preparation of positive electrode sheet: 80g NMC111, 5g sodium alginate, 2g lithium polyacrylate and 8g ammonium bicarbonate were mixed, and 200g of 90% ethanol was added as solvent. The mixture was stirred at 200rpm for 2h, and 10g carbon nanotube pre-dispersed slurry was added. The mixture was then dispersed at 1000rpm for 30min to form a uniform slurry. The slurry was coated on an aluminum foil current collector with a wet film thickness of 150±5μm. The film was dried in an oven at 60℃ for 1h, then vacuum dried at 70℃ for 12h, and then vacuum dried at 240℃ for 2h. Preparation of negative electrode sheet: 80g graphite, 5g sodium alginate, 3g lithium polyacrylate and 8g ammonium bicarbonate were mixed, and 150g of 90% ethanol was added as solvent. The mixture was stirred at 150rpm for 2h, and 8g carbon nanotube pre-dispersed slurry was added. The mixture was then dispersed at 2000rpm for 20min to form a uniform slurry. The slurry was coated on a copper foil current collector with a wet film thickness of 120±5μm. The film was dried in an oven at 60℃ for 1h, then vacuum dried at 70℃ for 10h, and then vacuum dried at 240℃ for 4h.

[0023] Experiment 1: The electrolyte membrane, positive electrode, and negative electrode were cut and assembled according to the following dimensions: positive electrode 50mm×50mm, polymer electrolyte membrane 54mm×54mm, and negative electrode 52mm×52mm. The aluminum positive electrode tab and nickel negative electrode tab were welded to the blank area of ​​the current collector using ultrasonic welding. The polymer electrolyte membrane was then covered on the positive electrode, followed by the negative electrode, forming a stacked structure with 8 to 10 layers stacked in parallel. During stacking, the electrode pores were fully wetted with a lithium salt liquid electrolyte. The stacked cells were held at 70℃ and 10 MPa for 5 minutes, and then subjected to conventional casing and packaging, final sealing, formation, and aging to produce lithium batteries. Ten cells were used in each group. Cycle performance tests were conducted at 0.1C rate. The average specific capacity of the first cycle and the average number of cycles when the specific capacity decayed to 80% were recorded, as well as the average ionic conductivity of each group. When calculating the average, groups with a deviation of 5% from the average were excluded. The results are shown in Table 1.

[0024] Table 1

Claims

1. A method for preparing a high-safety soft-pack lithium battery, comprising preparing an electrolyte membrane, preparing a positive electrode sheet, preparing a negative electrode sheet, and assembling and packaging; characterized in that: The preparation of the electrolyte membrane includes: dissolving 1.5-3 parts of sodium alginate in 50 parts of deionized water and stirring at 60°C for 1 hour to obtain a sodium alginate solution; dissolving 2-4 parts of the triblock copolymer PEO-PPO-PEO in 30 parts of deionized water and magnetically stirring at 20-30°C for 1-1.5 hours to obtain a triblock copolymer solution; mixing the two solutions, adding 0.8-1.5 parts of lithium salt and 0.8-1.3 parts of filler, and emulsifying in a high-speed shear emulsifier... Stir at 5000 rpm for 1-1.5 h to form a uniform slurry; then add 0.8-1.2 parts of flame retardant and continue stirring for 30 min; finally add 0.1-0.3 parts of crosslinking agent genipin, stir at 100 rpm for 5-10 min and then stop stirring, react at 40℃ for 1.5-2.5 h to form a double network gel; spread the slurry evenly on a polyethylene terephthalate substrate with a thickness controlled at 50±5 μm, and dry in a vacuum drying oven at 50℃ for 12 h to obtain the final product.

2. The preparation method according to claim 1, characterized in that: The flame retardant is tris(2,2,2-trifluoroethyl) phosphate.

3. The preparation method according to claim 1, characterized in that: The filler is a nano-sized lithium lanthanum zirconium oxide.

4. The preparation method according to claim 1, characterized in that: The lithium salt is lithium bis(trifluoromethanesulfonyl)imide.

5. The preparation method according to claim 1, characterized in that: The preparation of the positive electrode includes: Mix 8.0 parts of lithium nickel manganese cobalt oxide, 0.2-0.5 parts of sodium alginate, 0.2-0.3 parts of lithium polyacrylate, and 0.8-1 parts of pore-forming agent. Add 20 parts of 90% ethanol as a solvent and stir at 200 rpm for 2 hours. Add 1.0 part of carbon nanotube pre-dispersed slurry and disperse at 1000 rpm for 30-45 minutes to form a uniform slurry. Coat the slurry onto an aluminum foil current collector with a wet film thickness of 150±5 μm. Dry in an oven at 60℃ for 1 hour, then vacuum dry at 70℃ for 10-12 hours to remove moisture and solvent. Finally, raise the temperature to below 250℃ and vacuum dry for 2-4 hours.

6. The preparation method according to claim 1, characterized in that: The preparation of the negative electrode includes: Mix 8.0 parts graphite, 0.2-0.5 parts sodium alginate, 0.2-0.3 parts lithium polyacrylate and 0.6-0.8 parts pore-forming agent, add 15 parts of 90% ethanol as solvent, stir at 150 rpm for 2 hours, add 0.8 parts carbon nanotube pre-dispersed slurry, and disperse at 2000 rpm for 20-30 minutes to form a uniform slurry; coat the slurry onto a copper foil current collector with a wet film thickness of 120±5 μm, dry in an oven at 60℃ for 1 hour, then vacuum dry at 70℃ for 10-12 hours to remove moisture and solvent, and then heat to below 250℃ for vacuum drying for 2-4 hours.

7. The preparation method according to claim 5 or 6, characterized in that: The carbon nanotube pre-dispersed slurry is prepared by dissolving 0.2-0.3 parts of sodium carboxymethyl cellulose in 1 part of a 20% ethanol solution, and then uniformly adding 1 part of carbon nanotubes into the solution over 10-15 minutes. During the addition process, the mixture is continuously stirred at 500 rpm. After the addition is completed, the mixture is then homogenized by indirect stirring at 3500 rpm for 10-15 minutes, with each stirring session lasting 2-3 minutes and followed by a 1-minute stop.

8. The preparation method according to claim 5 or 6, characterized in that: The pore-forming agent is tributyl acetyl citrate, which is dried under vacuum at 70°C and then heated to 180-220°C for 2-4 hours under vacuum.

Images