A low-temperature polymer lithium battery and its preparation method

Abstract

The present invention belongs to the field of battery technology, specifically relating to a low-temperature polymer lithium battery and its preparation method. The low-temperature polymer lithium battery comprises a positive electrode, a negative electrode, a polymer electrolyte membrane, and a battery case. By preparing the polymer electrolyte membrane and optimizing the solid-state electrolyte formulation, the present invention produces a low-temperature polymer lithium battery with high ionic conductivity, good discharge performance in extremely low-temperature environments, excellent cycle stability, and high safety. This battery is of great significance for promoting the development of related industries in cold regions.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries, and in particular relates to a low-temperature polymer lithium battery and a preparation method thereof. Background Art

[0002] With the rapid development of modern science and technology, lithium batteries, as key components for energy storage and power supply, have been widely used in many fields such as consumer electronics, electric vehicles, and aerospace. However, the performance of traditional lithium batteries decreases significantly in low-temperature environments, which limits their application in cold regions. As the temperature decreases, the viscosity of the electrolyte increases significantly, resulting in a decrease in conductivity and a slowdown in the migration rate of ions in the electrolyte, which in turn affects the discharge performance of the battery. In low-temperature environments, the auxiliary materials in the positive and negative electrode materials inside the battery may undergo vitrification, which hinders the conduction of lithium ions, resulting in an increase in the internal resistance of the battery and a decrease in performance. At low temperatures, the number of ion channels inside the battery decreases, and the diffusion rate of ions in the material decreases, further affecting the discharge efficiency and cycle stability of the battery.

[0003] Therefore, developing a low-temperature polymer lithium battery with high ionic conductivity, good discharge performance in extremely low temperature environments, excellent cycle stability and high safety is of great significance for promoting the development of related industries in cold regions. Summary of the Invention

[0004] The purpose of the present invention is to provide a low-temperature polymer lithium battery and a preparation method thereof, wherein the low-temperature polymer lithium battery has high ion conductivity, can maintain good discharge performance in an extreme low temperature environment, has excellent cycle stability and high safety.

[0005] A low-temperature polymer lithium battery comprises a positive electrode sheet, a negative electrode sheet, a polymer electrolyte membrane and a battery shell.

[0006] The raw materials for preparing the positive electrode sheet include positive electrode active material, conductive agent, adhesive and N-methylpyrrolidone.

[0007] Preferably, the mass ratio of the positive electrode active material, the conductive agent, and the binder is 8:1:1.

[0008] Preferably, the positive electrode active material includes one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium cobaltate, and lithium iron phosphate; more preferably, it is lithium iron phosphate.

[0009] Preferably, the conductive agent includes one or more of conductive graphite, acetylene black, superconducting carbon, and conductive carbon black; further preferably, it is conductive carbon black.

[0010] Preferably, the conductive carbon black has a particle size of 25-35 nm and an ash content of ≤0.01%.

[0011] In some preferred embodiments, the conductive carbon black is purchased from Tianjin Baochi Chemical Technology Co., Ltd.

[0012] Preferably, the binder comprises polyvinylidene fluoride.

[0013] The polyvinylidene fluoride has a melt index of 0.5-2.0 g / 10 min at 230° C., a melting point of 156-165° C., and a moisture content of ≤0.1%.

[0014] In some preferred embodiments, the polyvinylidene fluoride is purchased from Arkema, France, PNDF 760.

[0015] Preferably, the negative electrode sheet is a lithium sheet.

[0016] Preferably, the battery shell is a button battery shell, CR2025 type.

[0017] The preparation method of the polymer electrolyte membrane comprises the following steps: uniformly mixing polyethylene oxide, lithium salt and plasticizer, adding inorganic nanoparticles and performing ball milling, spreading the ball-milled slurry on a glass plate, and drying it under argon at 100-120° C. for 2-5 hours to obtain the polymer electrolyte membrane.

[0018] Preferably, the thickness of the polymer electrolyte membrane is 30-40 μm.

[0019] Preferably, the average relative molecular mass of the polyethylene oxide is 100,000, and the viscosity of a 5% polyethylene oxide aqueous solution at 25° C. is 15-50 cp.

[0020] In some preferred embodiments, the polyethylene oxide is purchased from Sigma-Aldrich (Shanghai) Co., Ltd.

[0021] Using polyethylene oxide as a monomer to prepare polymer electrolyte membranes through self-polymerization not only improves the safety of lithium batteries but also enhances their low-temperature resistance. This is likely because, on the one hand, the polyethylene oxide electrolyte has a stable crystal structure, which makes it difficult for lithium ions to form dendritic structures (lithium dendrites) during migration, thereby effectively avoiding the risk of battery short circuits and explosions. Furthermore, solid electrolytes themselves are safer than liquid electrolytes. Furthermore, polyethylene oxide electrolytes maintain good performance over a wide temperature range, and even at low temperatures, the migration rate of lithium ions is not significantly affected, thus ensuring the battery's low-temperature performance. Polyethylene oxide electrolytes are also highly compatible with lithium metal anodes, which helps improve the battery's electrochemical performance. However, polyethylene oxide has a high degree of crystallinity at room temperature, which interferes with the movement of polymer chains and lithium ions. This results in poor conductivity of polyethylene oxide-based polymer electrolytes at the operating temperature of lithium metal batteries, affecting the overall battery performance. Furthermore, polyethylene oxide has relatively low mechanical strength and poor resistance to puncture short circuits, which may affect the battery's safety and stability.

[0022] Preferably, the lithium salt includes one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluorophosphate, lithium perchlorate, and lithium tetrafluoroborate.

[0023] Preferably, the plasticizer includes one or more of butyronitrile, dimethyl carbonate, ethylene carbonate, N,N-dimethylformamide, propylene carbonate, fluoroethylene carbonate, and triethylene glycol dimethyl ether; more preferably, triethylene glycol dimethyl ether.

[0024] Nitrile is a commonly used plasticizer, but its unstable interfacial contact with lithium anodes limits its application. By selecting triethylene glycol dimethyl ether as a plasticizer and controlling its addition amount, not only can the ionic conductivity of polyethylene oxide polymer electrolyte membranes be improved, but also the electrochemical performance and cycle life of lithium-ion batteries can be enhanced. This may be because triethylene glycol dimethyl ether not only reduces the crystallinity of polyethylene oxide, making the polymer segments more flexible and facilitating the migration of lithium ions, thereby improving ionic conductivity, but also improves the compatibility between polyethylene oxide polymer electrolyte membranes and electrode materials, helping to form a stable electrolyte / electrode interface, thereby improving the battery's cycle performance.

[0025] Preferably, the mass ratio of the polyethylene oxide to the inorganic nanoparticles is (1-3):1.

[0026] By adding inorganic nanoparticles, especially LLZO, not only can more ion channels be formed in the polymer electrolyte membrane, which helps the migration of lithium ions and thus improves the ionic conductivity of the PEO polymer electrolyte membrane, but it can also enhance the mechanical strength of the PEO polymer electrolyte membrane and improve its ability to resist puncture short circuits, thereby enhancing the safety and stability of the battery. In addition, LLZO particles can form good interfacial contact with the electrode material, which helps to reduce the interfacial resistance and improve the electrochemical performance of the battery. However, the ionic conductivity of traditional LLZO inorganic nanoparticles is also low, which has limited improvement on the overall electrochemical performance of the battery and poor stability in air.

[0027] Preferably, the added amount of the lithium salt is 2%-5% of the mass of the polyethylene oxide.

[0028] Preferably, the added amount of the plasticizer is 15%-20% of the total mass of the polyethylene oxide and the inorganic nanoparticles.

[0029] Preferably, the ball milling speed is 200-300 rpm, and the ball milling time is 5-8 h.

[0030] The method for preparing the inorganic nanoparticles comprises the following steps:

[0031] S1. Lithium hydroxide, lanthanum nitrate, zirconium acetate, aluminum nitrate, gallium oxide, tantalum pentoxide, niobium pentoxide, and a weak acid are mixed, and dilute nitric acid is added dropwise until no precipitation occurs. The mixture is stirred at 70-80° C. for 10-15 hours to form a uniform gel. The mixture is heated to 150-200° C. and dried for 1-2 hours. The mixture is sintered in steps and then crushed and ground to a particle size of <100 nm to obtain substance 1.

[0032] S2. Dissolve the silane coupling agent in an ethanol aqueous solution and adjust the pH value of the system to 4-5, add substance 1, stir at 50-60°C for 6-8h, centrifuge, wash with anhydrous ethanol 2-3 times, and vacuum dry at 50-60°C to constant weight to obtain.

[0033] Preferably, the weak acid includes one or more of citric acid, tartaric acid, and acetic acid; more preferably, it is citric acid.

[0034] Adding an appropriate amount of citric acid before adding dilute nitric acid to dissolve the metal salt not only improves the stability of the gel, thereby improving the quality of the prepared inorganic nanoparticles, but also increases the battery's cycle life. This may be because, on the one hand, citric acid not only adjusts the pH value of the reactants, thereby adjusting the stability of the sol, but also forms coordination complexes with metal ions, which helps to stabilize the dispersion of metal ions in the sol and prevents the hydrolysis and precipitation of metal ions that hinder the reaction. On the other hand, the appropriate addition of citric acid can form a dispersed coating on the material surface, slowing the diffusion rate of lithium ions, thereby reducing the degradation rate of the battery material and improving the battery's cycle life.

[0035] Preferably, the molar ratio of the lithium hydroxide, lanthanum nitrate, zirconium acetate, aluminum nitrate, gallium oxide, tantalum pentoxide, niobium pentoxide, and weak acid is (7.5-8.5): (2.8-3.2): (1.3-1.6): (0.1-0.3): (0.1-0.3): (0.2-0.3): (0.2-0.3): (4.5-5.5); further preferably, it is 8:3:1.5:0.2:0.2:0.25:0.25:5.

[0036] Doping LLZO with aluminum, gallium, tantalum, and niobium not only improves its electrochemical performance but also enhances the density and stability of inorganic nanoparticles. This is likely because Al doping affects the LLZO lattice structure by creating lithium ion vacancies, facilitating lithium ion migration and stabilizing the cubic phase of LLZO, which typically has higher conductivity. Ga doping improves lithium ion migration efficiency by regulating the lithium ion occupancy rate in octahedral vacancies and optimizing grain size and bottleneck dimensions. Co-doping with Al and Ga further enhances the ionic conductivity of LLZO. Ta doping not only improves the ionic conductivity of LLZO by altering the lattice structure and lithium ion migration pathways, but also changes the Al occupancy in LLZO, providing more space for lithium ion migration. Furthermore, co-doping with Al and Ta can stabilize the cubic phase of LLZO and reduce the formation of the tetragonal phase. Nb doping can also improve the ionic conductivity of LLZO by affecting the lattice structure and ion occupancy. The four elements work synergistically to further enhance the performance of LLZO by stabilizing the cubic phase, optimizing lithium-ion migration channels, and improving ionic conductivity, thereby improving the stability and electrochemical performance of polymer electrolytes and lithium-ion batteries. Furthermore, Al doping can lower the densification temperature of LLZO, while Ga doping can achieve higher density and ionic conductivity at lower sintering temperatures, thereby achieving high-performance LLZO at lower sintering temperatures and saving energy. However, the poor interfacial compatibility between the inorganic nanoparticles and the polymer matrix affects the performance of the polymer electrolyte and lithium-ion battery.

[0037] Preferably, the concentration of the dilute nitric acid is 3-5 mol / L.

[0038] The specific steps of the step-by-step sintering are: heating to 250-300°C at a rate of 5°C / min and keeping warm for 1.5-2.5h; heating to 750-800°C at a rate of 5°C / min and keeping warm for 8-12h; heating to 1100-1150°C at a rate of 5°C / min and keeping warm for 1-2h, and cooling to room temperature at a rate of 10°C / min.

[0039] Through three-stage sintering, LLZO crystal defects can be reduced and the overall quality and performance of the sample can be improved. The first calcination at a lower temperature helps to remove adsorbed water, crystallization water and possible volatile impurities in the raw materials. The second calcination at a medium temperature can further promote the formation of LLZTO crystal nuclei and initial crystal growth. The calcination time at this stage is relatively long, which helps to stabilize and uniformly distribute the crystal structure. At the same time, this step can continue to remove residual impurities and improve the purity of the sample. The third calcination at a higher temperature accelerates the crystal growth and densification process to form an LLZTO sample with excellent performance. In addition, high-temperature calcination can also eliminate pores and defects in the sample and improve the overall quality and performance of the sample.

[0040] Preferably, the silane coupling agent includes one or more of glycidyltrimethoxysilane, 3-(2,3-glycidyloxy)propyltrimethoxysilane, and γ-aminopropyltriethoxysilane; further preferably, 3-(2,3-glycidyloxy)propyltrimethoxysilane and γ-aminopropyltriethoxysilane.

[0041] Preferably, the mass ratio of the 3-(2,3-epoxypropoxy)propyltrimethoxysilane to γ-aminopropyltriethoxysilane is (1-3):1; more preferably, it is 2:1.

[0042] The use of specific silane coupling agents to strengthen the surface of element-doped LLZO can further enhance the electrochemical performance and stability of lithium-ion batteries. This is likely due to the synergistic effect of the two silane coupling agents. On the one hand, they chemically bond to the doped LLZO surface, forming a strong interfacial layer that not only improves the mechanical strength of the polymer electrolyte membrane but also reduces charge transfer resistance at the interface. On the other hand, the epoxy groups of 3-(2,3-epoxypropoxy)propyltrimethoxysilane and the amino groups of γ-aminopropyltriethoxysilane, respectively, have excellent compatibility with organic polymers such as polyethylene oxide. Through chemical reactions or physical entanglement, they can tightly bind inorganic and organic polymers together, forming a continuous, dense interfacial layer that facilitates lithium ion transport and electrolyte stability. By optimizing the interfacial structure, the two silane coupling agents can significantly enhance the electrochemical performance of lithium-ion batteries, reduce the degree of polarization, and increase the lithium ion migration rate and cycling stability. Furthermore, they can also reduce side reactions at the interface, extending the battery's service life.

[0043] Preferably, the volume concentration of ethanol in the ethanol aqueous solution is 60% to 70%.

[0044] Preferably, the mass ratio of the silane coupling agent to the ethanol aqueous solution is 1:40-50.

[0045] Preferably, the mass ratio of the silane coupling agent to substance one is (1.5-2.5):1.

[0046] The method for preparing the low-temperature polymer lithium battery comprises the following steps:

[0047] A1. Mix the positive electrode active material and the conductive agent in a ball mill and mill at a speed of 200-300 rpm for 30-50 minutes. Then, add a binder and dropwise add N-methylpyrrolidone. Continue milling for 50-60 minutes. Then, apply the mixture on the current collector and dry it in a vacuum oven at 85°C for 24 hours to obtain the positive electrode sheet.

[0048] A2. Place the positive electrode sheet and polymer electrolyte membrane in the bottom of the battery case in turn, then place the lithium sheet, cover with the top cover and seal. The battery assembly pressure is 1kPa, and the pressure holding time is 10s. After assembly, let it stand for 2-3h.

[0049] Preferably, the added amount of N-methylpyrrolidone is 4-5 times the mass of the positive electrode active material.

[0050] Preferably, the purpose of drying in a vacuum oven at 85° C. for 24 h (reduced pressure drying) is to remove N-methylpyrrolidone.

[0051] Compared with the prior art, the advantages and beneficial effects of the present invention are:

[0052] 1. The present invention provides a low-temperature polymer lithium battery. By preparing a polymer electrolyte membrane and optimizing the solid electrolyte formula, a low-temperature polymer lithium battery with high ionic conductivity, good discharge performance in extremely low-temperature environments, excellent cycle stability and high safety is prepared. This is of great significance for promoting the development of related industries in cold regions.

[0053] 2. The present invention uses polyethylene oxide as a monomer and prepares a polymer electrolyte membrane through self-polymerization, which can not only improve the safety of the lithium battery, but also improve its low-temperature resistance.

[0054] 3. By adding inorganic nanoparticles, especially LLZO, the present invention can not only form more ion channels in the polymer electrolyte membrane, which helps the migration of lithium ions and thus improves the ionic conductivity of the PEO polymer electrolyte membrane, but also enhances the mechanical strength of the PEO polymer electrolyte membrane and improves its ability to resist puncture short circuits, thereby enhancing the safety and stability of the battery.

[0055] 4. The present invention adopts aluminum, gallium, tantalum and niobium to dope LLZO, which can not only improve its electrochemical performance, but also improve the density and stability of inorganic nanoparticles.

[0056] 5. The present invention uses a specific silane coupling agent to strengthen the surface of the element-doped LLZO, which can further improve the electrochemical performance and stability of the lithium-ion battery.

[0057] 6. The present invention selects triethylene glycol dimethyl ether as a plasticizer and controls its addition amount, thereby not only improving the ionic conductivity of the polyethylene oxide polymer electrolyte membrane, but also improving the electrochemical performance and cycle life of the lithium ion battery. DETAILED DESCRIPTION

[0058] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0059] The raw materials used in the present invention are all commercially available, specifically:

[0060] The conductive carbon black had a particle size of 25-35 nm and an ash content of ≤0.01%, and was purchased from Tianjin Baochi Chemical Technology Co., Ltd.

[0061] Polyvinylidene fluoride, with a melt index of 0.5-2.0 g / 10 min at 230° C., a melting point of 156-165° C., and a moisture content of ≤0.1%, was purchased from Arkema, France, PNDF 760.

[0062] The average relative molecular mass of polyethylene oxide is 100,000, and the viscosity of a 5% polyethylene oxide aqueous solution at 25° C. is 15-50 cp. The polyethylene oxide was purchased from Sigma-Aldrich (Shanghai) Co., Ltd.

[0063] Example 1

[0064] This embodiment provides a low-temperature polymer lithium battery, including a positive electrode sheet, a negative electrode sheet, and a polymer electrolyte membrane.

[0065] The raw materials for preparing the positive electrode sheet are positive electrode active material, conductive agent, adhesive and N-methylpyrrolidone.

[0066] The mass ratio of the positive electrode active material, the conductive agent and the binder is 8:1:1.

[0067] The positive electrode active material is lithium iron phosphate.

[0068] The conductive agent is conductive carbon black.

[0069] The negative electrode sheet is a lithium sheet.

[0070] The battery case is a button battery case, CR2025 type.

[0071] The preparation method of the polymer electrolyte membrane comprises the following steps: uniformly mixing polyethylene oxide, lithium salt and plasticizer, adding inorganic nanoparticles and performing ball milling, spreading the ball-milled slurry on a glass plate, and drying it under argon at 110° C. for 4 hours to obtain the polymer electrolyte membrane.

[0072] The thickness of the polymer electrolyte membrane is 35 μm.

[0073] The lithium salt is lithium bis(trifluoromethanesulfonyl)imide, and the added amount is 4% of the mass of the polyethylene oxide.

[0074] The plasticizer is triethylene glycol dimethyl ether, and the added amount is 18% of the total mass of polyethylene oxide and inorganic nanoparticles.

[0075] The mass ratio of the polyethylene oxide to the inorganic nanoparticles is 2:1.

[0076] The ball milling speed is 250 rpm, and the ball milling time is 6 h.

[0077] The preparation method of the inorganic nanoparticles comprises the following steps:

[0078] S1. Lithium hydroxide, lanthanum nitrate, zirconium acetate, aluminum nitrate, gallium oxide, tantalum pentoxide, niobium pentoxide, and a weak acid were mixed, and dilute nitric acid was added dropwise until no precipitation occurred. The mixture was stirred at 75°C for 12 hours to form a uniform gel. The mixture was heated to 180°C and dried for 1.5 hours. After step-by-step sintering, the mixture was crushed and ground to a particle size of <100 nm to obtain substance 1.

[0079] S2. Dissolve the silane coupling agent in an ethanol aqueous solution and adjust the pH value of the system to 4. Add substance 1, stir at 55°C for 7 hours, centrifuge, wash with anhydrous ethanol three times, and vacuum dry at 55°C to constant weight to obtain.

[0080] The weak acid is citric acid.

[0081] The molar ratio of the lithium hydroxide, lanthanum nitrate, zirconium acetate, aluminum nitrate, gallium oxide, tantalum pentoxide, niobium pentoxide and weak acid is 8:3:1.5:0.2:0.2:0.25:0.25:5.

[0082] The concentration of the dilute nitric acid is 4 mol / L.

[0083] The specific steps of the step-by-step sintering are: heating to 280°C at a rate of 5°C / min and keeping warm for 2 hours; heating to 780°C at a rate of 5°C / min and keeping warm for 10 hours; heating to 1120°C at a rate of 5°C / min and keeping warm for 1.5 hours, and cooling to room temperature at a rate of 10°C / min.

[0084] The silane coupling agent is 3-(2,3-epoxypropoxy)propyltrimethoxysilane and γ-aminopropyltriethoxysilane, with a mass ratio of 2:1.

[0085] The volume concentration of ethanol in the ethanol aqueous solution is 65%.

[0086] The mass ratio of the silane coupling agent to the ethanol aqueous solution is 1:45.

[0087] The mass ratio of the silane coupling agent to substance one is 2:1.

[0088] The method for preparing the low-temperature polymer lithium battery comprises the following steps:

[0089] A1. Mix the positive electrode active material and conductive agent in a ball mill and mill at 250 rpm for 40 min. Then, add a binder and dropwise add N-methylpyrrolidone. Continue milling for 55 min. Then, apply the mixture on a current collector and dry it in a vacuum oven at 85°C for 24 h to obtain a positive electrode sheet.

[0090] A2. Place the positive electrode sheet and polymer electrolyte membrane in the bottom of the battery case in turn, then place the lithium sheet, cover with the top cover and seal. The battery assembly pressure is 1kPa, and the pressure holding time is 10s. After assembly, let it stand for 3h.

[0091] The added amount of N-methylpyrrolidone is 5 times the mass of the positive electrode active material.

[0092] Example 2

[0093] The difference between this embodiment and embodiment 1 is that the mass ratio of the polyethylene oxide to the inorganic nanoparticles is 5:2.

[0094] Comparative Example 1

[0095] The difference between this comparative example and Example 1 is that the preparation method of the polymer electrolyte membrane comprises the following steps: uniformly mixing polyethylene oxide and lithium salt, adding inorganic nanoparticles and performing ball milling, spreading the ball-milled slurry on a glass plate, and drying it under argon at 110° C. for 4 hours.

[0096] Comparative Example 2

[0097] The difference between this comparative example and Example 1 is that the plasticizer is acetonitrile, and the added amount is 18% of the total mass of polyethylene oxide and inorganic nanoparticles.

[0098] Comparative Example 3

[0099] The difference between this comparative example and Example 1 is that the preparation method of the inorganic nanoparticles comprises the following steps:

[0100] S1. Lithium hydroxide, lanthanum nitrate, zirconium acetate, gallium oxide, tantalum pentoxide, niobium pentoxide, and a weak acid were mixed, and dilute nitric acid was added dropwise until no precipitation occurred. The mixture was stirred at 75°C for 12 hours to form a uniform gel. The mixture was heated to 180°C and dried for 1.5 hours. After step-by-step sintering, the mixture was crushed and ground to a particle size of <100 nm to obtain substance 1.

[0101] S2. Dissolve the silane coupling agent in an ethanol aqueous solution and adjust the pH value of the system to 4. Add substance 1, stir at 55°C for 7 hours, centrifuge, wash with anhydrous ethanol three times, and vacuum dry at 55°C to constant weight to obtain.

[0102] The molar ratio of the lithium hydroxide, lanthanum nitrate, zirconium acetate, gallium oxide, tantalum pentoxide, niobium pentoxide and weak acid is 8:3:1.5:0.2:0.25:0.25:5.

[0103] Comparative Example 4

[0104] The difference between this comparative example and Example 1 is that the preparation method of the inorganic nanoparticles comprises the following steps:

[0105] S1. Lithium hydroxide, lanthanum nitrate, zirconium acetate, aluminum nitrate, gallium oxide, niobium pentoxide, and a weak acid were mixed, and dilute nitric acid was added dropwise until no precipitation occurred. The mixture was stirred at 75°C for 12 hours to form a uniform gel. The mixture was heated to 180°C and dried for 1.5 hours. After step-by-step sintering, the mixture was crushed and ground to a particle size of <100 nm to obtain substance 1.

[0106] S2. Dissolve the silane coupling agent in an ethanol aqueous solution and adjust the pH value of the system to 4. Add substance 1, stir at 55°C for 7 hours, centrifuge, wash with anhydrous ethanol three times, and vacuum dry at 55°C to constant weight to obtain.

[0107] The molar ratio of the lithium hydroxide, lanthanum nitrate, zirconium acetate, aluminum nitrate, gallium oxide, niobium pentoxide and weak acid is 8:3:1.5:0.2:0.2:0.25:5.

[0108] Comparative Example 5

[0109] The difference between this comparative example and Example 1 is that the preparation method of the inorganic nanoparticles comprises the following steps:

[0110] S1. Lithium hydroxide, lanthanum nitrate, zirconium acetate, aluminum nitrate, gallium oxide, tantalum pentoxide, and niobium pentoxide were mixed, and dilute nitric acid was added dropwise until no precipitation occurred. The mixture was stirred at 75°C for 12 hours to form a uniform gel. The mixture was heated to 180°C and dried for 1.5 hours. After step-by-step sintering, the mixture was crushed and ground to a particle size of <100 nm to obtain substance 1.

[0111] S2. Dissolve the silane coupling agent in an ethanol aqueous solution and adjust the pH value of the system to 4. Add substance 1, stir at 55°C for 7 hours, centrifuge, wash with anhydrous ethanol three times, and vacuum dry at 55°C to constant weight to obtain.

[0112] Comparative Example 6

[0113] The difference between this comparative example and Example 1 is that the specific steps of the step-by-step sintering are: heating to 280°C at a rate of 5°C / min and keeping warm for 2h; heating to 780°C at a rate of 5°C / min and keeping warm for 10h, and cooling to room temperature at a rate of 10°C / min.

[0114] Comparative Example 7

[0115] The difference between this comparative example and Example 1 is that the preparation method of the inorganic nanoparticles comprises the following steps: mixing lithium hydroxide, lanthanum nitrate, zirconium acetate, aluminum nitrate, gallium oxide, tantalum pentoxide, niobium pentoxide, and a weak acid, adding dilute nitric acid dropwise until no precipitate is formed, stirring at 75°C for 12 hours to form a uniform gel, heating to 180°C and drying for 1.5 hours, sintering in steps, and then crushing and grinding to a particle size of <100 nm.

[0116] Comparative Example 8

[0117] The difference between this comparative example and Example 1 is that the silane coupling agent is 3-(2,3-epoxypropoxy)propyltrimethoxysilane.

[0118] Performance Testing

[0119] Electrochemical impedance spectroscopy was used to measure the battery impedance and calculate its ionic conductivity. The voltage amplitude was 15 mV, the frequency range was 0.5 to 1.5 MHz, and the test temperature was -20°C. Cyclic performance was tested at 25°C and -20°C: The battery was charged to 4.5 V at a constant current and voltage of 0.5 C, with a cutoff current of 0.05 C. It was then discharged to 3.0 V at a constant current of 0.1 C. This cycle was repeated for 500 cycles. The capacity retention at the 500th cycle was calculated as (initial capacity - capacity after 500 cycles) / initial capacity × 100%. The capacity retention at 25°C and -20°C was calculated. The results are shown in Table 1.

[0120] Table 1 Measurement results

[0121]

[0122] According to statistics, the low-temperature polymer lithium batteries prepared in Examples 1 and 2 of the present invention have high ionic conductivity and good cycling stability at both room and low temperatures. Comparative Example 1 did not add a plasticizer, Comparative Example 2 used acetonitrile as the plasticizer, Comparative Example 3 did not use aluminum for doping, Comparative Example 4 did not use tantalum for doping, Comparative Example 5 did not add a weak acid, Comparative Example 6 did not perform high-temperature sintering, Comparative Example 7 did not modify the doped LLZO, and Comparative Example 8 did not add γ-aminopropyltriethoxysilane to modify the doped LLZO. The low-temperature polymer lithium batteries prepared had poor performance. Therefore, the low-temperature polymer lithium batteries prepared using the raw materials and methods described in this application have high ionic conductivity, can maintain good discharge performance in extreme low-temperature environments, and have excellent cycling stability and high safety.

[0123] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A low-temperature polymer lithium battery, characterized in that: Including positive electrode sheet, negative electrode sheet, polymer electrolyte membrane and battery shell; The raw materials for preparing the positive electrode sheet include positive electrode active material, conductive agent, adhesive, and N-methylpyrrolidone; The preparation method of the polymer electrolyte membrane comprises the following steps: uniformly mixing polyethylene oxide, lithium salt and plasticizer, adding inorganic nanoparticles and performing ball milling, spreading the ball-milled slurry on a glass plate, and drying it under argon at 100-120° C. for 2-5 hours to obtain the polymer electrolyte membrane; The method for preparing the inorganic nanoparticles comprises the following steps: S1. Lithium hydroxide, lanthanum nitrate, zirconium acetate, aluminum nitrate, gallium oxide, tantalum pentoxide, niobium pentoxide, and a weak acid are mixed, and dilute nitric acid is added dropwise until no precipitation occurs. The mixture is stirred at 70-80° C. for 10-15 hours to form a uniform gel. The mixture is heated to 150-200° C. and dried for 1-2 hours. The mixture is sintered in steps and then crushed and ground to a particle size of <100 nm to obtain substance 1. S2. Dissolve the silane coupling agent in an ethanol aqueous solution and adjust the pH value of the system to 4-5, add substance 1, stir at 50-60°C for 6-8h, centrifuge, wash with anhydrous ethanol 2-3 times, and vacuum dry at 50-60°C to constant weight to obtain.

2. The low-temperature polymer lithium battery according to claim 1, characterized in that: The raw materials for preparing the positive electrode sheet include positive electrode active material, conductive agent and adhesive.

3. The low-temperature polymer lithium battery according to claim 1, characterized in that: The average relative molecular mass of the polyethylene oxide is 100,000, and the viscosity of a 5% polyethylene oxide aqueous solution at 25° C. is 15-50 cp.

4. The low-temperature polymer lithium battery according to claim 1, characterized in that: The plasticizer includes one or more of butyronitrile, dimethyl carbonate, ethylene carbonate, N,N-dimethylformamide, propylene carbonate, fluoroethylene carbonate, and triethylene glycol dimethyl ether.

5. The low-temperature polymer lithium battery according to claim 1, characterized in that: The molar ratio of the lithium hydroxide, lanthanum nitrate, zirconium acetate, aluminum nitrate, gallium oxide, tantalum pentoxide, niobium pentoxide and weak acid is (7.5-8.5): (2.8-3.2): (1.3-1.6): (0.1-0.3): (0.1-0.3): (0.2-0.3): (0.2-0.3): (4.5-5.5).

6. The low-temperature polymer lithium battery according to claim 1, characterized in that: The specific steps of the step-by-step sintering are: heating to 250-300°C at a rate of 5°C / min and keeping warm for 1.5-2.5h; heating to 750-800°C at a rate of 5°C / min and keeping warm for 8-12h; heating to 1100-1150°C at a rate of 5°C / min and keeping warm for 1-2h, and cooling to room temperature at a rate of 10°C / min.

7. The low-temperature polymer lithium battery according to claim 1, characterized in that: The silane coupling agent includes one or more of glycidyltrimethoxysilane, 3-(2,3-glycidoxy)propyltrimethoxysilane, and γ-aminopropyltriethoxysilane.

8. The low-temperature polymer lithium battery according to claim 1, characterized in that: The silane coupling agent includes 3-(2,3-epoxypropoxy)propyltrimethoxysilane and γ-aminopropyltriethoxysilane.

9. The low-temperature polymer lithium battery according to claim 1, characterized in that: The weak acid includes one or more of citric acid, tartaric acid, and acetic acid.

10. The low-temperature polymer lithium battery according to claim 1, characterized in that: The lithium salt includes one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluorophosphate, lithium perchlorate, and lithium tetrafluoroborate.

11. A method for preparing a low-temperature polymer lithium battery according to any one of claims 1 to 10, characterized in that: The following steps are involved: A1. Mix the positive electrode active material and the conductive agent in a ball mill and mill at a speed of 200-300 rpm for 30-50 minutes. Then, add a binder and dropwise add N-methylpyrrolidone. Continue milling for 50-60 minutes. Then, apply the mixture on the current collector and dry it in a vacuum oven at 85°C for 24 hours to obtain the positive electrode sheet. A2. Place the positive electrode sheet and polymer electrolyte membrane in the bottom of the battery case in turn, then place the lithium sheet, cover with the top cover and seal. The battery assembly pressure is 1kPa, and the pressure holding time is 10s. After assembly, let it stand for 2-3h.

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