A low-temperature resistant lithium battery

Abstract

The present invention discloses a low-temperature resistant lithium battery, which comprises a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte. The positive electrode sheet includes a positive current collector and a positive mixture layer coated on the positive current collector. The negative electrode sheet includes a negative current collector and a negative mixture layer coated on the negative current collector. The negative mixture layer includes a negative active material and a negative additive. The negative additive includes a nitride, glass fiber and an apatite-type lithium ion conductor. The mass ratio of the nitride, glass fiber and apatite-type lithium ion conductor is (60-80):(10-20):(10-20). The electrolyte includes a lithium salt, an organic solvent and an electrolyte additive. The electrolyte additive includes potassium bromide, a ferrocene derivative and a buffer. Compared with the prior art, the low-temperature resistant lithium battery provided by the present invention has excellent charge and discharge performance at -45 °C through double improvements on the negative electrode material and the electrolyte.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and particularly to a low-temperature resistant lithium battery. Background Art

[0002] In recent years, with the wide application of new energy electric vehicles, lithium batteries, as important power sources, have attracted more and more attention. The performance of lithium batteries is directly related to aspects such as the endurance, charging speed, and safety of electric vehicles. However, the performance of lithium batteries in low-temperature environments is relatively poor, which is one of the key factors restricting their use in polar regions and cold regions in the north.

[0003] The electrolyte of a lithium battery is the carrier for ion transport in the battery, generally composed of a lithium salt and an organic solvent. The electrolyte plays a role in conducting ions between the positive and negative electrodes of the lithium battery. Since the charge and discharge reactions in the battery are closely related to the ambient temperature, the temperature in the environment has the greatest impact on the battery performance. In a low-temperature environment, the viscosity of the lithium battery electrolyte decreases, the conductivity drops, and the activity of the active substances also decreases. This will cause the concentration difference of the electrolyte to become larger and the polarization phenomenon to intensify, thereby causing the charging process to terminate prematurely.

[0004] In addition, at low temperatures, the diffusion rate of lithium ions in the carbon negative electrode will slow down, increasing the risk of battery polarization. The decrease in temperature will also lead to a decrease in the reaction rate of the electrode. Assuming the battery voltage remains constant, the discharge current decreases, and the power output of the battery will also decrease. Therefore, the performance of lithium batteries in extremely low-temperature environments is not as good as that at other temperatures.

[0005] In the current technical system, lithium iron phosphate batteries are the most widely used batteries in electric vehicles. This type of battery has the advantages of high safety and long single-cell life, but its performance at low temperatures is relatively poor. Low temperature has an impact on the positive and negative electrodes, electrolyte, and binder of lithium iron phosphate, thus greatly limiting the application of lithium iron phosphate batteries at low temperatures of 0°C.

[0006] In view of this, a technical solution to solve the problem of the low-temperature performance of lithium batteries is needed. Summary of the Invention

[0007] The purpose of the present invention is to provide a low-temperature resistant lithium battery to solve the problem of poor charge and discharge performance of current lithium iron phosphate batteries in low-temperature environments. By double improvement of the electrode materials and electrolyte of the lithium battery, the application of lithium iron phosphate batteries at low temperatures is greatly improved.

[0008] To achieve the above purpose, the present invention adopts the following technical solutions:

[0009] A low-temperature resistant lithium battery, comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte. The positive electrode sheet includes a positive electrode current collector and a positive electrode mixture layer coated on the positive electrode current collector. The negative electrode sheet includes a negative electrode current collector and a negative electrode mixture layer coated on the negative electrode current collector;

[0010] The negative electrode mixture layer includes a negative electrode active material and a negative electrode additive. The negative electrode additive includes a nitride, glass fiber and an apatite-type lithium ion conductor. The mass ratio of the nitride, the glass fiber and the apatite-type lithium ion conductor is (60-80):(10-20):(10-20). The electrolyte includes a lithium salt, an organic solvent and an electrolyte additive. The electrolyte additive includes potassium bromide, a ferrocene derivative and a buffer.

[0011] Preferably, the electrolyte additive accounts for 0.5-2% of the total mass of the electrolyte. Potassium bromide accounts for 40-50% of the total mass of the electrolyte additive, the ferrocene derivative accounts for 10-20% of the total mass of the electrolyte additive, and the buffer accounts for 30-40% of the total mass of the electrolyte additive.

[0012] Preferably, the buffer is a mixture of polyvinylidene fluoride and nano-aluminum oxide, and the mass ratio of polyvinylidene fluoride to nano-aluminum oxide is 1:1. The buffer used in the present invention can effectively improve the interfacial properties between different objects, reduce the interfacial impedance, and further increase the migration rate of lithium ions at low temperature, so as to further improve the charge and discharge performance of the lithium battery at low temperature.

[0013] Preferably, the negative electrode additive accounts for 1-5% of the total mass of the negative electrode mixture layer.

[0014] Preferably, the nitride is a mixture of nano-boron nitride and nano-aluminum nitride, and the mass ratio of nano-boron nitride to nano-aluminum nitride is 2:1. Among them, the use of a mixture of nano-boron nitride and nano-aluminum nitride as the nitride of the negative electrode additive has the following advantages: 1) It can effectively improve the low-temperature performance of the battery: Research shows that the mixture of nano-boron nitride and nano-aluminum nitride can improve the low-temperature performance of the battery, so that the battery still has a high discharge capacity and cycle stability in a low-temperature environment; 2) It can improve the conductivity of the material: The mixture of nano-boron nitride and nano-aluminum nitride as a negative electrode additive can improve the conductivity of the negative electrode material, accelerate the electron transfer rate, shorten the charge and discharge time of the electrode, and thus improve the power density of the battery; 3) It can increase the cycle life of the battery: Adding a mixture of nano-boron nitride and nano-aluminum nitride can inhibit the growth rate of the SEI film on the negative electrode, slow down the attenuation of the electrode capacity, and increase the cycle life of the battery.

[0015] Preferably, the negative electrode additive further includes one of vanadium oxide nanoparticles and iron oxide nanoparticles. Among them, adding vanadium oxide nanoparticles to the negative electrode material can improve the conductivity of the negative electrode, thereby improving the performance of the battery at low temperatures; in addition, vanadium oxide nanoparticles can also serve as a lithium ion insertion material, improving its charge-discharge rate and cycle life. Iron oxide nanoparticles have a special surface area and chemical activity, can increase the contact area between the electrode material and the electrolyte, and can block micropores by inserting lithium ions, reducing the volume change at low temperatures, and improving the performance and cycle life of the battery.

[0016] Preferably, the negative electrode additive further includes molybdenum carbide (Mo2C); among them, molybdenum carbide can serve as a lithium storage medium, can slow down the diffusion rate of lithium ions at low temperatures, and improve the low-temperature performance of the battery; in addition, molybdenum carbide can also increase the electronic conduction performance of the battery and improve the output power of the battery.

[0017] Preferably, the negative electrode additive further includes a urushiol compound, and the urushiol compound is one of catechol, ciprofloxacin, and cyproterone. The urushiol compound can improve the electronic conduction performance and electrolyte conductivity of the battery, thereby improving the performance of the battery at low temperatures. Specifically: 1) Catechol can promote the insertion and extraction reactions of lithium ions in the electrode by forming a complex with lithium ions, thereby improving the discharge capacity and cycle performance of the battery; in a low-temperature environment, catechol can improve the electronic conduction performance of the negative electrode, reduce the polarization phenomenon of the battery, and improve the low-temperature performance of the battery. 2) Ciprofloxacin can improve the ionization degree and ion transferability of the electrolyte, and improve the output power and charge-discharge efficiency of the battery; as a negative electrode additive, ciprofloxacin forms a composite electrode with the active material, improves the discharge capacity and cycle performance of the battery, and improves the performance of the battery at low temperatures. 3) Cyproterone has good polarity and can be used as a negative electrode additive to improve the insertion and extraction rate of lithium ions in the negative electrode, thereby improving the energy density and cycle performance of the battery; cyproterone can also form a chemical bond with the negative electrode material, enhance the affinity between the negative electrode material and the electrolyte, and improve the low-temperature resistance performance of the battery.

[0018] Preferably, the negative electrode additive further includes a metal-organic framework (MOF); MOF has porosity and a high surface area, and as a negative electrode additive, it can improve the insertion and extraction kinetics of lithium ions in the negative electrode and improve the low-temperature performance of the battery.

[0019] Preferably, the negative electrode additive further includes graphite fluoride and nano metal powder, and the mass ratio of graphite fluoride to nano metal powder is 1:2. Among them, graphite fluoride can improve the reversible capacity of the negative electrode material and lithium ions, and reduce the polarization potential of lithium ions on the surface of the negative electrode, which can improve the conductivity of the battery and overcome the polarization problem of the electrode at low temperature. Nano metal powder can provide an additional conduction path, which helps to improve the performance of the battery; in addition, nano metal powder interacts with the ammonium salt in the battery electrolyte, thereby increasing the conductivity of the electrolyte, which is beneficial to the operation of the battery at low temperature.

[0020] Preferably, the negative electrode additive further includes multi-walled carbon nanotubes and graphene nanoribbons, and the mass ratio of multi-walled carbon nanotubes to graphene nanoribbons is 1:1. Among them, adding multi-walled carbon nanotubes can improve the strength and stability of the electrode and increase the specific surface area of the electrode; in addition, multi-walled carbon nanotubes can also promote the conduction between electrode rods, thereby improving the performance of the battery; at low temperature, multi-walled carbon nanotubes also help to maintain the active mass of the electrode and avoid the freezing and stretching of materials. Graphene nanoribbons are a kind of slender one-dimensional nanomaterial, which can be used to promote the conduction between electrode rods and improve the capacitance and electrochemical activity of the negative electrode; at low temperature, graphene nanoribbons can increase the diffusion rate of lithium ions, thereby improving the performance of the battery at low temperature.

[0021] Preferably, the ferrocene derivative is one of bis(2-carbazolyl)ferrocene, ferrocene-benzimidazole derivative and ferrocene-acetylene derivative. By adding ferrocene derivatives, firstly, it can effectively inhibit the precipitation of electrolytes in the electrolyte because there are many isolation spaces inside its molecules, and it has strong selectivity for the dissolution of macromolecules. Secondly, this type of additive can form a layer similar to a protective film on the electrode surface and reduce the activity of the electrochemical reaction at extremely low temperatures, thereby improving the stability of the battery and extending its life. In addition, ferrocene derivatives can also improve the conductivity and kinetic response speed of the battery at extremely low temperatures, further improving its energy density and power density.

[0022] Preferably, the ferrocene derivative is a ferrocene-benzimidazole derivative; compared with the other two additives, the ferrocene-benzimidazole derivative has better chemical stability and polarization resistance. Specifically: 1) Good electrochemical stability: This additive has good electrochemical stability and the ability to prevent lithium aggregation, and can resist the weakening of the electrolyte and the evaporation of the electrolyte at low temperature. 2) Good polarization resistance performance: This additive has excellent polarization resistance performance, which can reduce the granulation on the surface of the carbon negative electrode, thereby improving the efficiency and stability of the battery.

[0023] Preferably, the ferrocene derivative is a carbonyl ferrocene derivative; the carbonyl ferrocene derivative improves the electrochemical performance of the battery at low temperatures by forming a stable complex with lithium ions. In a low-temperature environment, the activity of lithium ions in the battery decreases, and the formation of solid-phase nucleation and lithium dendrites will affect the battery performance. However, carbonyl ferrocene can encapsulate lithium ions in its structure, reducing the dendritization and nucleation of lithium ions, thereby improving the cycle life and energy density of the battery. In addition, carbonyl ferrocene can also improve the electrochemical stability of the battery, prevent the volatilization and decomposition of the electrolyte, and will not have a negative impact on the safety of the battery.

[0024] Preferably, the preparation method of the apatite-type lithium ion conductor includes the following steps:

[0025] 1) Raw material preparation: Lithium carbonate, nano-aluminum oxide and trisodium phosphate are mixed in a molar ratio of 1:1:1 and mixed evenly by a ball mill;

[0026] 2) Reaction: The mixed powder sample is placed in a high-temperature furnace and subjected to a solid-phase reaction under atmosphere protection;

[0027] 3) Heating: Heat from room temperature to 800 °C at a heating rate of 10 °C / min and hold for 1-2 h to ensure sufficient reaction;

[0028] 4) Cooling: After high-temperature treatment, turn off the high-temperature furnace and wait for it to cool naturally to room temperature;

[0029] 5) Heat treatment: The obtained apatite-type lithium ion conductor sample is placed in a vacuum heat treatment furnace and held at 400 °C for 24 h to remove residual gases and moisture in the sample, thus obtaining the apatite-type lithium ion conductor.

[0030] Preferably, the electrolyte additive further includes trifluoromethylphenylthioamide. Trifluoromethylphenylthioamide is an organic ionic liquid; firstly, trifluoromethylphenylthioamide can form a stable electrolyte layer and inhibit the precipitation of substances on the electrode surface and the increase in impedance of the battery at low temperatures; secondly, the high polarity and strong ion interaction ability of trifluoromethylphenylthioamide can improve the ionic conductivity of the electrolyte and maintain excellent performance such as high efficiency and high energy density of the battery. In addition, trifluoromethylphenylthioamide also has excellent chemical corrosion resistance and stability, and can maintain the stability of the electrolyte at extremely low temperatures.

[0031] Preferably, the electrolyte additive further includes polyphosphate. In a low-temperature environment, the conduction rate of lithium ions decreases, but polyphosphate can form a complex with lithium salt to improve the lithium ion conductivity. In addition, polyphosphate can also form a protective layer on the surface of the electrolyte to prevent battery polarization and shorten the battery life.

[0032] Preferably, the electrolyte additive further includes N-sulfonyl benzoimide derivatives; the N-sulfonyl benzoimide derivatives can be prepared by using thionyl chloride to catalyze the reaction of dipropyl phosphate and benzoic acid; the preparation method of the N-sulfonyl benzoimide derivatives includes the following steps:

[0033] 1) Add thionyl chloride to a container containing dipropyl phosphate, mix evenly with a magnetic stirrer, and react at room temperature for 2-4 hours;

[0034] 2) Under heating conditions, slowly add benzoic acid to the above reaction mixture, keep the reaction temperature at 60-80 °C, and the reaction time is 4-6 hours;

[0035] 3) Sieve out the generated HCl and inorganic compounds, and remove the remaining solvent by rotary evaporation concentration to obtain N-sulfonyl benzoimide derivatives.

[0036] First of all, N-sulfonyl benzoimide derivatives can be used as a good chelating agent to form stable complexes with metal cations, thereby reducing dendritization and impedance increase of the electrolyte at low temperatures. Secondly, due to its good solubility and ionic conductivity at extremely low temperatures, it can improve the energy density and cycle life of the battery. In addition, N-sulfonyl benzoimide derivatives also have good chemical stability and the ability to prevent lithium accumulation, which can reduce capacity loss and conductivity decline during the charge and discharge process of the battery.

[0037] Preferably, the electrolyte additive further includes one of 4-dimethyl-1H-imidazole (DMI), 2,2,6,6-tetramethyl-1-piperidone (TMP), and 1,3-dimethyl-2-phenylimidazole (DMBI). By adding the above-mentioned nitrogen-containing heterocyclic compounds to the electrolyte, the conductivity of the electrolyte at low temperatures can be improved by enhancing ion transport, suppressing electrolyte polarization, and enhancing the stability of the electrolyte interface, thus solving the problem of insufficient electrolyte performance at low temperatures. Specifically: 1) Enhance ion transport: At low temperatures, the mobility of the electrolyte deteriorates, resulting in a decrease in conductivity. After adding this type of additive to the electrolyte, the nitrogen atom therein can form a complex with lithium cations or other ions, thereby promoting ion transport and improving the mobility and conductivity of the electrolyte. 2) Suppress electrolyte polarization: At low temperatures, the solubility in the electrolyte decreases, resulting in electrolyte polarization. Adding this type of additive can suppress the occurrence of electrolyte polarization through ways such as forming hydrogen bonds and charge transfer, which is of great significance for improving the stability and conductivity of the electrolyte at low temperatures. 3) Enhance the stability of the electrolyte interface: At low temperatures, the interface between the electrolyte film and the electrolyte is prone to instability, hindering ion transport and causing electrolyte polarization. This type of additive can enhance the stability of the electrolyte interface through ways such as forming hydrogen bonds and ion complexes, thereby promoting ion transport and increasing the conductivity of the electrolyte.

[0038] Preferably, the electrolyte additive further includes 4-dimethyl-1H-imidazole. Compared with the other two additives, 4-dimethyl-1H-imidazole has higher ionic conductivity, a lower melting point, and better solubility. Specifically: 1) Higher ionic conductivity: At low temperatures, the ionic conductivity of the electrolyte decreases, resulting in a decline in battery performance. After adding 4-dimethyl-1H-imidazole to the electrolyte, it can significantly increase the ionic conductivity of the electrolyte, thereby improving the performance of the battery at low temperatures. 2) Lower melting point: The melting point refers to the temperature at which a substance changes from a solid state to a liquid state under normal pressure. The melting point of 4-dimethyl-1H-imidazole is -20°C, which is lower than that of the other three additives. Therefore, at low temperatures, the 4-dimethyl-1H-imidazole additive can turn into a liquid state faster, which helps to improve the reaction rate and efficiency of the battery. 3) Better solubility: In the electrolyte, the additive must be able to dissolve completely; otherwise, it will affect its stability and reliability in the battery. 4-dimethyl-1H-imidazole has better solubility, so it is not easy to form precipitates, crystals, or other attachments and can maintain good stability at low temperatures.

[0039] Preferably, the electrolyte additive further includes an indigoimide compound; wherein, the indigoimide compound is one of indigo, nicotinic phthalocyanine, alkannin, and bromoindigo. As an electrolyte additive, the indigoimide compound can form a stable complex with lithium ions, and at the same time, its structure has the potential to exceed the local minimum energy, and can maintain sufficient activity in a low-temperature environment, thereby effectively improving the performance and stability of the battery at low temperatures.

[0040] Preferably, the electrolyte additive further includes a fatty acid amide compound; wherein, the fatty acid amide compound is one of methyl amino stearate, n-octanamide, procainamide, and oleamide: The fatty acid amide compound can form a chelate with lithium ions, improve the conductivity of the battery, and at the same time can also be used as a solvent, which can reduce problems such as the viscosity and dendrification of the electrolyte, thereby improving the energy density and lifespan of the battery at low temperatures.

[0041] Preferably, the positive electrode mixture layer includes a positive electrode active material, a positive electrode binder, a positive electrode conductive agent, and a positive electrode dispersant, and the positive electrode active material is a lithium iron phosphate material.

[0042] Preferably, the organic solvent includes at least one of ethyl acetate, methyl formate, methyl acetate, and ethyl propionate. The ethyl acetate, methyl formate, methyl acetate, and ethyl propionate are all linear carboxylic acid esters, which still have high conductivity under low-temperature conditions. The improved electrolyte can better adapt to working under low-temperature conditions, thereby further improving the charge and discharge performance of the lithium battery at low temperatures.

[0043] In addition, the electrolyte additive further includes a low-temperature aid, and the low-temperature aid accounts for 3-6% of the total mass of the electrolyte additive. The low-temperature aid includes a nanoporous activator and an alkyl-modified alcohol ester. The specific preparation method includes the following steps:

[0044] (1) Weigh 3.4-3.6 grams of nano-aluminum oxide powder and add it to 25-30 milliliters of saturated sodium chloride solution, heat it to boiling, keep it for 30-35 minutes, filter it while it is hot, disperse the filtrate and 0.45-0.55 grams of europium nitrate in 10-12 milliliters of sodium dodecyl sulfate aqueous solution, slowly add sodium hydroxide aqueous solution to the dispersion at 25-30 °C while stirring, stop adding alkali when the pH value of the system reaches between 9.2-9.3, let it stand and age for 6-8 hours, filter, wash, and dry it, obtain solid particles, place them in a muffle furnace and calcine for 2.5-3.0 hours, the calcination temperature is 470-480 °C, and grind them into powder after cooling naturally with the furnace to obtain the nanoporous activator;

[0045] (2) Weigh 14.5 - 14.8 grams of trimethylsilane, 7.4 - 7.6 grams of ethanolamine, and 45 - 50 milliliters of ethylene glycol and add them to a three-necked flask equipped with a thermometer, a dropping funnel, and a condenser. Heat and stir to raise the temperature to 70 - 72 °C. Weigh 0.04 - 0.05 grams of the nanoporous activator prepared in step (1) and disperse it in the prepared triethylamine-ethanol mixed solvent according to a mass ratio of 1:14 - 16. Ultrasonically treat for 10 - 15 minutes, and add the obtained dispersion to a four-necked flask. Continuously stir for 50 - 60 minutes;

[0046] (3) Pass nitrogen into the three-necked flask. Under a nitrogen atmosphere, add 18 - 20 milliliters of dimethylaminoethyl methacrylate and 10 - 12 milliliters of oleic acid. Continue to raise the temperature to 90 - 95 °C and keep it warm for preheating reaction for 1.5 - 2.0 hours. Then add 1.3 - 1.5 grams of azobisisobutyronitrile to the three-necked flask, raise the temperature to 110 - 115 °C, and continuously react for 3 - 4 hours. The obtained reaction product is rotary evaporated to remove the remaining solvent, cooled, allowed to stand, crystallized, and dried to obtain this low-temperature additive.

[0047] The low-temperature additive added in the present invention is obtained by synergistically combining the prepared nanoporous activator with an alkyl-modified alcohol ester to obtain an additive with significantly improved low-temperature resistance. It can maintain the stability of other additives in the electrolyte, and can maintain the persistent state of the microscopic molecular structure even under long-term low-temperature use conditions, inhibit the occurrence of side reactions, and further improve the low-temperature resistance of the battery.

[0048] Compared with the prior art, the beneficial effects of the present invention are as follows: The low-temperature resistant lithium battery provided by the present invention, through the dual improvement of the negative electrode material and the electrolyte, enables the battery of the present invention to still have excellent charge and discharge performance at -45°C. Especially when combined with the application of lithium iron phosphate as the positive electrode active material, the charge and discharge performance at low temperature is even more excellent. The electrolyte used in the lithium battery of the present invention is added with potassium bromide, ferrocene derivatives and a buffer. Among them, potassium bromide can lower the freezing point of the entire electrolyte, and jointly with the buffer, optimize the composition of the electrolyte, so that the electrolyte still has a high conductivity below -10°C, improving the electrocyclic activity of the electrolyte, and thus improving the charge and discharge performance of the lithium battery in a low-temperature environment. And the addition of ferrocene derivatives, first of all, it can effectively inhibit the precipitation of electrolytes in the electrolyte because there are many isolated spaces inside its molecules, and it has a strong selectivity for the dissolution of macromolecules. Secondly, this additive can form a layer similar to a protective film on the electrode surface and reduce the activity of the electrochemical reaction at extremely low temperatures, thereby improving the stability of the battery and extending its life. In addition, ferrocene derivatives can also improve the conductivity and kinetic response speed of the battery at extremely low temperatures, further improving its energy density and power density. In addition, the present invention also improves the negative electrode material. The negative electrode additive in the negative electrode material adopts a mixture of nitride, glass fiber and apatite-type lithium ion conductor. Among them, glass fiber is used as a heat insulation material, but due to its certain electrical insulation, when mixed with nitride, on the one hand, it uses the superconductivity of nitride at low temperature to relieve its electrical insulation, and on the other hand, its good heat insulation performance combined with nitride can further improve the charge and discharge performance of the lithium battery at low temperature; in addition, the added apatite-type lithium ion conductor, through its good lithium ion conductivity, improves the conductivity of the lithium ion battery and the diffusion rate of lithium ions at low temperature; in addition, the apatite-type lithium ion conductor can also absorb the moisture in the battery to form a hydrate, improving the low-temperature performance of the battery. Therefore, the improved electrolyte and negative electrode material of the present invention act together, enabling the lithium battery of the present invention to still have excellent charge and discharge performance at ultra-low temperature. Detailed implementation manners

[0049] To make the technical solutions and advantages of the present invention clearer, the present invention and its beneficial effects will be further described in detail below in combination with specific implementation manners, but the implementation manners of the present invention are not limited thereto.

[0050] Example 1

[0051] A low-temperature resistant lithium ion battery in this example includes a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte. The positive electrode sheet includes a positive electrode current collector and a positive electrode mixture layer coated on the positive electrode current collector. The negative electrode sheet includes a negative electrode current collector and a negative electrode mixture layer coated on the negative electrode current collector;

[0052] The positive electrode mixture layer includes a positive electrode active material, a positive electrode binder, a positive electrode conductive agent, and a positive electrode dispersant. The positive electrode active material is 90 wt% of lithium iron phosphate material, the positive electrode binder is 3.5 wt% of polyvinylidene fluoride, the positive electrode conductive agent is 6.3 wt% of conductive carbon black, and the positive electrode dispersant is 0.2 wt% of polyvinylpyrrolidone;

[0053] The negative electrode mixture layer includes a negative electrode active material, a negative electrode additive, a negative electrode binder, a negative electrode conductive agent, and a negative electrode dispersant; the negative electrode active material is 90 wt% of artificial graphite, the negative electrode additive is a mixture of 3.5 wt% of an apatite-type lithium ion conductor, glass fiber, nano boron nitride, and nano aluminum nitride, wherein the mass ratio of the apatite-type lithium ion conductor, glass fiber, nano boron nitride, and nano aluminum nitride is 20:20:40:20, the negative electrode binder is a mixture of 4 wt% of sodium carboxymethyl cellulose and styrene-butadiene rubber, the negative electrode conductive agent is 2.3 wt% of conductive carbon black, and the negative electrode dispersant is 0.2 wt% of polyvinylpyrrolidone;

[0054] The separator is a PE membrane;

[0055] The electrolyte includes a lithium salt, an organic solvent, and an electrolyte additive. The lithium salt is 15% of LiPF6, the organic solvents are ethylene carbonate (EC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and ethyl acetate (EA), and the mass ratio of EC, EMC, DMC, and EA is 30:25:20:25. The electrolyte additive is a mixture of 2% of potassium bromide, a ferrocene-benzimidazole derivative, polyvinylidene fluoride, and nano aluminum oxide, and the mass ratio of potassium bromide, the ferrocene-benzimidazole derivative, polyvinylidene fluoride, and nano aluminum oxide is 3:1:1:1.

[0056] The preparation method of the low-temperature resistant lithium battery includes the following steps:

[0057] Positive electrode sheet: The positive electrode active material lithium iron phosphate, the conductive agent conductive carbon black, the binder polyvinylidene difluoride (PVDF), and the dispersant polyvinylpyrrolidone are fully stirred and mixed evenly in an N-methylpyrrolidone solvent system, and then coated on an aluminum foil, dried, and cold-pressed to obtain a positive electrode sheet.

[0058] Negative electrode sheet: The negative electrode active material artificial graphite, the conductive agent conductive carbon black, styrene-butadiene rubber (SBR), sodium carboxymethyl cellulose (CMC), polyvinylpyrrolidone, the additive apatite-type lithium ion conductor, glass fiber, nano boron nitride, and nano aluminum nitride are fully stirred and mixed evenly in a deionized water solvent system, and then coated on a copper foil, dried, and cold-pressed to obtain a negative electrode sheet.

[0059] Separator: Using polyethylene (PE) as the base film and coating a nano aluminum oxide coating on the base film as the separator membrane.

[0060] Electrolyte: In a glove box filled with argon (moisture < 10 ppm, oxygen content < 1 ppm), EC, EMC, DMC, and EA were mixed evenly at a mass ratio of 30:25:20:25. A mixture of potassium bromide, ferrocene-benzimidazole derivative, polyvinylidene fluoride, and nano-aluminum oxide with a mass ratio of 3:1:1:1 was added to the mixed solution, and then 15% by mass of LiPF6 was slowly added and stirred until it was completely dissolved to obtain the electrolyte in this example.

[0061] The positive electrode sheet, separator, and negative electrode sheet were stacked in sequence and wound in the same direction to obtain a bare battery cell, which was then packaged with an aluminum-plastic film. The battery after injecting the electrolyte was subjected to conventional processes such as encapsulation, shelving, formation, aging, secondary encapsulation, and grading to obtain a lithium-ion battery.

[0062] Example 2

[0063] The difference from Example 1 lies in the composition of the negative electrode mixture layer. The negative electrode mixture layer in this example includes a negative electrode active material, a negative electrode additive, a negative electrode binder, a negative electrode conductive agent, and a negative electrode dispersant; the negative electrode active material is 90 wt% artificial graphite, the negative electrode additive is a mixture of 3.5 wt% apatite-type lithium ion conductor, glass fiber, and nano-aluminum nitride, wherein the mass ratio of the apatite-type lithium ion conductor, glass fiber, and nano-aluminum nitride is 20:20:60, the negative electrode binder is a mixture of 4 wt% sodium carboxymethyl cellulose and styrene-butadiene rubber, the negative electrode conductive agent is 2.3 wt% conductive carbon black, and the negative electrode dispersant is 0.2 wt% polyvinylpyrrolidone.

[0064] The rest is the same as in Example 1 and will not be elaborated here.

[0065] Example 3

[0066] The difference from Example 1 lies in the composition of the negative electrode mixture layer. The negative electrode mixture layer in this example includes a negative electrode active material, a negative electrode additive, a negative electrode binder, a negative electrode conductive agent, and a negative electrode dispersant; the negative electrode active material is 90 wt% artificial graphite, the negative electrode additive is a mixture of 3.5 wt% apatite-type lithium ion conductor, glass fiber, and nano-boron nitride, wherein the mass ratio of the apatite-type lithium ion conductor, glass fiber, and nano-boron nitride is 20:20:60, the negative electrode binder is a mixture of 4 wt% sodium carboxymethyl cellulose and styrene-butadiene rubber, the negative electrode conductive agent is 2.3 wt% conductive carbon black, and the negative electrode dispersant is 0.2 wt% polyvinylpyrrolidone.

[0067] The rest is the same as in Example 1 and will not be elaborated here.

[0068] Example 4

[0069] The difference from Example 1 lies in the composition of the negative electrode mixture layer. The negative electrode mixture layer of this example includes a negative electrode active material, a negative electrode additive, a negative electrode binder, a negative electrode conductive agent, and a negative electrode dispersant; the negative electrode active material is artificial graphite at 90 wt%, the negative electrode additive is a mixture of 3.5 wt% of nano boron nitride and nano aluminum nitride, wherein the mass ratio of nano boron nitride to nano aluminum nitride is 2:1, the negative electrode binder is a mixture of 4 wt% of sodium carboxymethyl cellulose and styrene-butadiene rubber, the negative electrode conductive agent is 2.3 wt% of conductive carbon black, and the negative electrode dispersant is 0.2 wt% of polyvinylpyrrolidone.

[0070] The rest is the same as in Example 1 and will not be elaborated here.

[0071] Example 5

[0072] The difference from Example 1 lies in the composition of the negative electrode mixture layer. The negative electrode mixture layer of this example includes a negative electrode active material, a negative electrode additive, a negative electrode binder, a negative electrode conductive agent, and a negative electrode dispersant; the negative electrode active material is artificial graphite at 90 wt%, the negative electrode additive is 3.5 wt% of glass fiber, the negative electrode binder is a mixture of 4 wt% of sodium carboxymethyl cellulose and styrene-butadiene rubber, the negative electrode conductive agent is 2.3 wt% of conductive carbon black, and the negative electrode dispersant is 0.2 wt% of polyvinylpyrrolidone.

[0073] The rest is the same as in Example 1 and will not be elaborated here.

[0074] Example 6

[0075] The difference from Example 1 lies in the composition of the negative electrode mixture layer. The negative electrode mixture layer of this example includes a negative electrode active material, a negative electrode additive, a negative electrode binder, a negative electrode conductive agent, and a negative electrode dispersant; the negative electrode active material is artificial graphite at 90 wt%, the negative electrode additive is 3.5 wt% of an apatite-type lithium ion conductor, the negative electrode binder is a mixture of 4 wt% of sodium carboxymethyl cellulose and styrene-butadiene rubber, the negative electrode conductive agent is 2.3 wt% of conductive carbon black, and the negative electrode dispersant is 0.2 wt% of polyvinylpyrrolidone.

[0076] The rest is the same as in Example 1 and will not be elaborated here.

[0077] Example 7

[0078] Differing from Example 1 is the composition of the electrolyte. The electrolyte of this example includes a lithium salt, an organic solvent, and an electrolyte additive. The lithium salt is 15% LiPF6, the organic solvent is ethylene carbonate (EC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and ethyl acetate (EA), and the mass ratio of EC, EMC, DMC, and EA is 30:25:20:25. The electrolyte additive is a mixture of potassium bromide, ferrocene-benzimidazole derivative, and nano-aluminum oxide, and the mass ratio of potassium bromide, ferrocene-benzimidazole derivative, and nano-aluminum oxide is 3:1:2.

[0079] The rest is the same as in Example 1 and will not be elaborated here.

[0080] Example 8

[0081] Differing from Example 1 is the composition of the electrolyte. The electrolyte of this example includes a lithium salt, an organic solvent, and an electrolyte additive. The lithium salt is 15% LiPF6, the organic solvent is ethylene carbonate (EC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and ethyl acetate (EA), and the mass ratio of EC, EMC, DMC, and EA is 30:25:20:25. The electrolyte additive is a mixture of potassium bromide, ferrocene-benzimidazole derivative, and polyvinylidene fluoride, and the mass ratio of potassium bromide, ferrocene-benzimidazole derivative, and polyvinylidene fluoride is 3:1:2.

[0082] The rest is the same as in Example 1 and will not be elaborated here.

[0083] Example 9

[0084] Differing from Example 1 is the composition of the electrolyte. The electrolyte of this example includes a lithium salt, an organic solvent, and an electrolyte additive. The lithium salt is 15% LiPF6, the organic solvent is ethylene carbonate (EC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and ethyl acetate (EA), and the mass ratio of EC, EMC, DMC, and EA is 30:25:20:25. The electrolyte additive is 2% potassium bromide.

[0085] The rest is the same as in Example 1 and will not be elaborated here.

[0086] Example 10

[0087] Differing from Example 1 is the composition of the electrolyte. The electrolyte of this example further includes a low-temperature additive, and the low-temperature additive accounts for 5% of the total mass of the electrolyte additive. The specific preparation method of this low-temperature additive includes the following steps:

[0088] (1) Weigh 3.5 g of nano-aluminum oxide powder and add it to 25 mL of saturated sodium chloride solution. Heat it to boiling and maintain for 30 minutes. Filter while it is hot. The filtrate and 0.50 g of europium nitrate are dispersed in 11 mL of aqueous sodium dodecyl sulfate solution. Slowly add aqueous sodium hydroxide solution to the dispersion at 25 °C while stirring. Stop adding alkali when the pH value of the system reaches between 9.2 - 9.3. Let it stand for aging for 7 hours, then filter, wash, and dry. Place the obtained solid particles in a muffle furnace and calcine for 2.8 hours at a calcination temperature of 470 °C. After natural cooling with the furnace, grind it into powder to obtain the nano-porous activator;

[0089] (2) Measure 14.5 g of trimethylsilane, 7.5 g of ethanolamine, and 48 mL of ethylene glycol and add them to a three-necked flask equipped with a thermometer, a dropping funnel, and a condenser. Heat and stir to raise the temperature to 70 °C. Weigh 0.04 g of the nano-porous activator prepared in step (1) and disperse it in the prepared triethylamine-ethanol mixed solvent according to a mass ratio of 1:14. Ultrasonically treat for 10 minutes, and add the obtained dispersion to a four-necked flask and continuously stir for 55 minutes;

[0090] (3) Pass nitrogen into the three-necked flask. Under a nitrogen atmosphere, add 18 mL of dimethylaminoethyl methacrylate and 10 mL of oleic acid, continue to raise the temperature to 90 °C, and keep it warm and pre-react for 1.8 hours. Then add 1.4 g of azobisisobutyronitrile to the three-necked flask and raise the temperature to 110 °C and continuously react for 3 hours. The obtained reaction product is rotary evaporated to remove the remaining solvent, cooled, allowed to stand, crystallized, and dried to obtain this low-temperature auxiliary agent.

[0091] The rest is the same as in Example 1 and will not be elaborated here.

[0092] Example 11

[0093] The difference from Example 2 is the composition of the electrolyte. The electrolyte in this example includes a lithium salt, an organic solvent, and an electrolyte additive. The lithium salt is 15% LiPF6, the organic solvents are ethylene carbonate (EC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and ethyl acetate (EA), and the mass ratio of EC, EMC, DMC, and EA is 30:25:20:25. The electrolyte additive is a mixture of potassium bromide, ferrocene-benzimidazole derivative, and nano-aluminum oxide, and the mass ratio of potassium bromide, ferrocene-benzimidazole derivative, and nano-aluminum oxide is 3:1:2.

[0094] The rest is the same as in Example 2 and will not be elaborated here.

[0095] Example 12

[0096] Differing from Example 2 is the composition of the electrolyte. The electrolyte of this example includes a lithium salt, an organic solvent, and an electrolyte additive. The lithium salt is 15% LiPF6, the organic solvent is ethylene carbonate (EC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and ethyl acetate (EA), and the mass ratio of EC, EMC, DMC, and EA is 30:25:20:25. The electrolyte additive is a mixture of potassium bromide, ferrocene-benzimidazole derivative, and polyvinylidene fluoride, and the mass ratio of potassium bromide, ferrocene-benzimidazole derivative, and polyvinylidene fluoride is 3:1:2.

[0097] The rest is the same as in Example 2 and will not be elaborated here.

[0098] Example 13

[0099] Differing from Example 2 is the composition of the electrolyte. The electrolyte of this example includes a lithium salt, an organic solvent, and an electrolyte additive. The lithium salt is 15% LiPF6, the organic solvent is ethylene carbonate (EC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and ethyl acetate (EA), and the mass ratio of EC, EMC, DMC, and EA is 30:25:20:25. The electrolyte additive is 2% potassium bromide.

[0100] The rest is the same as in Example 2 and will not be elaborated here.

[0101] Example 14

[0102] Differing from Example 2 is the composition of the electrolyte. The electrolyte of this example further includes a low-temperature additive, and the low-temperature additive accounts for 5% of the total mass of the electrolyte additive. The specific preparation method of the low-temperature additive includes the following steps:

[0103] (1) Weigh 3.5 grams of nano-aluminum oxide powder and add it to 25 milliliters of saturated sodium chloride solution. Heat it to boiling and keep it for 30 minutes. Filter it while it is hot. Disperse the filtrate and 0.50 grams of europium nitrate in 11 milliliters of sodium dodecyl sulfate aqueous solution. Slowly add sodium hydroxide aqueous solution to the dispersion at 25°C while stirring. When the pH value of the system reaches between 9.2 and 9.3, stop adding alkali, let it stand and age for 7 hours, filter, wash, and dry. Place the obtained solid particles in a muffle furnace and calcine for 2.8 hours at a calcination temperature of 470°C. After natural cooling with the furnace, grind it into powder to obtain a nano-porous activator;

[0104] (2) Measure 14.5 g of trimethylsilane, 7.5 g of ethanolamine, and 48 mL of ethylene glycol and add them to a three-necked flask equipped with a thermometer, a dropping funnel, and a condenser. Heat and stir to raise the temperature to 70 °C. Weigh 0.04 g of the nanoporous activator prepared in step (1) and disperse it in the prepared triethylamine-ethanol mixed solvent at a mass ratio of 1:14. Sonicate for 10 minutes, add the resulting dispersion to a four-necked flask, and continuously stir for 55 minutes;

[0105] (3) Introduce nitrogen into the three-necked flask. Under a nitrogen atmosphere, add 18 mL of dimethylaminoethyl methacrylate and 10 mL of oleic acid. Continue to raise the temperature to 90 °C and keep it warm for preheating and reacting for 1.8 hours. Then add 1.4 g of azobisisobutyronitrile to the three-necked flask, raise the temperature to 110 °C, and continuously react for 3 hours. The resulting reaction product is rotary-evaporated to remove the remaining solvent, cooled, allowed to stand, crystallized, and dried to obtain this low-temperature auxiliary agent.

[0106] The rest is the same as in Example 2 and will not be elaborated here.

[0107] Example 15

[0108] Different from Example 4 is the composition of the electrolyte. The electrolyte in this example includes a lithium salt, an organic solvent, and an electrolyte additive. The lithium salt is 15% LiPF6, the organic solvents are ethylene carbonate (EC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and ethyl acetate (EA), and the mass ratio of EC, EMC, DMC, and EA is 30:25:20:25. The electrolyte additive is a mixture of potassium bromide, ferrocene-benzimidazole derivative, and nano-aluminum oxide, and the mass ratio of potassium bromide, ferrocene-benzimidazole derivative, and nano-aluminum oxide is 3:1:2.

[0109] The rest is the same as in Example 4 and will not be elaborated here.

[0110] Example 16

[0111] Different from Example 4 is the composition of the electrolyte. The electrolyte in this example includes a lithium salt, an organic solvent, and an electrolyte additive. The lithium salt is 15% LiPF6, the organic solvents are ethylene carbonate (EC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and ethyl acetate (EA), and the mass ratio of EC, EMC, DMC, and EA is 30:25:20:25. The electrolyte additive is a mixture of ferrocene-benzimidazole derivative, polyvinylidene fluoride, and nano-aluminum oxide, and the mass ratio of ferrocene-benzimidazole derivative, polyvinylidene fluoride, and nano-aluminum oxide is 1:1:1.

[0112] The rest is the same as in Example 4 and will not be elaborated here.

[0113] Example 17

[0114] Differing from Example 5 is the composition of the electrolyte. The electrolyte of this example includes a lithium salt, an organic solvent, and an electrolyte additive. The lithium salt is 15% LiPF6, the organic solvent is ethylene carbonate (EC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and ethyl acetate (EA), and the mass ratio of EC, EMC, DMC, and EA is 30:25:20:25. The electrolyte additive is a mixture of potassium bromide, ferrocene-benzimidazole derivative, and nano-aluminum oxide, and the mass ratio of potassium bromide, ferrocene-benzimidazole derivative, and nano-aluminum oxide is 3:1:2.

[0115] The rest is the same as in Example 5 and will not be elaborated here.

[0116] Example 18

[0117] Differing from Example 5 is the composition of the electrolyte. The electrolyte of this example includes a lithium salt, an organic solvent, and an electrolyte additive. The lithium salt is 15% LiPF6, the organic solvent is ethylene carbonate (EC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and ethyl acetate (EA), and the mass ratio of EC, EMC, DMC, and EA is 30:25:20:25. The electrolyte additive is a mixture of ferrocene-benzimidazole derivative, polyvinylidene fluoride, and nano-aluminum oxide, and the mass ratio of ferrocene-benzimidazole derivative, polyvinylidene fluoride, and nano-aluminum oxide is 1:1:1.

[0118] The rest is the same as in Example 5 and will not be elaborated here.

[0119] Example 19

[0120] Differing from Example 6 is the composition of the electrolyte. The electrolyte of this example includes a lithium salt, an organic solvent, and an electrolyte additive. The lithium salt is 15% LiPF6, the organic solvent is ethylene carbonate (EC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and ethyl acetate (EA), and the mass ratio of EC, EMC, DMC, and EA is 30:25:20:25. The electrolyte additive is a mixture of potassium bromide, ferrocene-benzimidazole derivative, and nano-aluminum oxide, and the mass ratio of potassium bromide, ferrocene-benzimidazole derivative, and nano-aluminum oxide is 3:1:2.

[0121] The rest is the same as in Example 6 and will not be elaborated here.

[0122] Example 20

[0123] Differing from Example 6 is the composition of the electrolyte. The electrolyte of this example includes a lithium salt, an organic solvent, and an electrolyte additive. The lithium salt is 15% LiPF6, the organic solvent is ethylene carbonate (EC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and ethyl acetate (EA), and the mass ratio of EC, EMC, DMC, and EA is 30:25:20:25. The electrolyte additive is 2% potassium bromide.

[0124] The rest is the same as in Example 6 and will not be elaborated here.

[0125] Example 21

[0126] Differing from Example 1 is the composition of the electrolyte. The electrolyte additive of this example further includes the addition of trifluoromethylphenylthioamide, and trifluoromethylphenylthioamide accounts for 5% of the total mass of the electrolyte additive.

[0127] The rest is the same as in Example 1 and will not be elaborated here.

[0128] Example 22

[0129] Differing from Example 1 is the composition of the electrolyte. The electrolyte additive of this example further includes an N-sulfonylbenzimide derivative, and the N-sulfonylbenzimide derivative accounts for 5% of the total mass of the electrolyte additive; the preparation method of the N-sulfonylbenzimide derivative is as follows:

[0130] 1) Add thionyl chloride to a container containing dipropyl phosphate, mix evenly with a magnetic stirrer, and react at room temperature for 2 - 4 hours;

[0131] 2) Under heating conditions, slowly add benzoic acid to the above reaction mixture, maintain the reaction temperature at 60 - 80 °C, and the reaction time is 4 - 6 hours;

[0132] 3) Sieve out the generated HCl and inorganic compounds, and remove the remaining solvent by rotary evaporation concentration to obtain the N-sulfonylbenzimide derivative.

[0133] The rest is the same as in Example 1 and will not be elaborated here.

[0134] Example 23

[0135] Differing from Example 1 is the composition of the electrolyte. The electrolyte additive of this example further includes 4-dimethyl-1H-imidazole, and 4-dimethyl-1H-imidazole accounts for 5% of the total mass of the electrolyte additive.

[0136] The rest is the same as in Example 1 and will not be elaborated here.

[0137] Example 24

[0138] Different from Example 1 is the composition of the negative electrode mixture layer. The negative electrode additive in this example further includes vanadium oxide nanoparticles, and the vanadium oxide nanoparticles account for 5% of the total mass of the negative electrode additive.

[0139] The rest is the same as in Example 1 and will not be elaborated here.

[0140] Example 25

[0141] Different from Example 1 is the composition of the negative electrode mixture layer. The negative electrode additive in this example further includes molybdenum carbide, and the molybdenum carbide accounts for 5% of the total mass of the negative electrode additive.

[0142] The rest is the same as in Example 1 and will not be elaborated here.

[0143] Example 26

[0144] Different from Example 1 is the composition of the negative electrode mixture layer. The negative electrode additive in this example further includes catechol, and the catechol accounts for 5% of the total mass of the negative electrode additive.

[0145] The rest is the same as in Example 1 and will not be elaborated here.

[0146] Example 27

[0147] Different from Example 1 is the composition of the negative electrode mixture layer. The negative electrode additive in this example further includes cyproterone, and the cyproterone accounts for 5% of the total mass of the negative electrode additive.

[0148] The rest is the same as in Example 1 and will not be elaborated here.

[0149] Example 28

[0150] Different from Example 1 is the composition of the negative electrode mixture layer. The negative electrode additive in this example further includes metal-organic framework (MOF), and the metal-organic framework accounts for 5% of the total mass of the negative electrode additive.

[0151] The rest is the same as in Example 1 and will not be elaborated here.

[0152] Example 29

[0153] Different from Example 1 is the active material used in the positive electrode sheet. The positive electrode active material in this Example 1 is lithium cobalt oxide.

[0154] The rest is the same as in Example 1 and will not be elaborated here.

[0155] Example 30

[0156] Different from Example 1 is the active material used in the positive electrode sheet. The positive electrode active material in this Example 1 is LiNi 1 / 3Co 1 / 3 Mn 1 / 3 O2.

[0157] The rest is the same as in Example 1 and will not be elaborated here.

[0158] The lithium batteries prepared in Examples 1 to 30 were subjected to electrochemical performance tests, and the test results are shown in Table 1.

[0159] Table 1

[0160]

[0161]

[0162] It can be seen from the above Examples 1 to 6 that the best charge-discharge performance of the battery is achieved when the additives of the negative electrode material of the present invention use a mixture of apatite-type lithium ion conductor, glass fiber, nano boron nitride and nano aluminum nitride. If only nitrides or apatite-type lithium ion conductors are used, lacking the heat insulation effect of glass fiber, although the capacity retention rate of the lithium battery at 0 °C is similar, the capacity retention at low temperature is greatly reduced, and as the temperature gets lower, the performance drops faster. See the comparison between Example 4, Example 6 and Example 1. If only glass fiber is added, although glass fiber has good heat insulation effect, lacking the auxiliary effect of nitrides and apatite-type lithium ion conductors, the ionic conductivity decreases, and a dendritic network for conduction and heat conduction and nitrogen-doped sites cannot be formed in the negative electrode, which cannot increase the migration ability of lithium ions inside and on the surface of the negative electrode, nor can it assist glass fiber to further exert its heat insulation function. Therefore, the negative electrode material with only glass fiber added cannot well adapt to working at low temperature. In addition, if apatite-type lithium ion conductor, glass fiber and a single nitride are added, although it still has certain low-temperature resistance at -20 °C, it cannot adapt to the working environment at -45 °C. Thus, it can be seen that the best charge-discharge performance of the battery is achieved when the additives of the negative electrode material of the present invention use a mixture of apatite-type lithium ion conductor, glass fiber, nano boron nitride and nano aluminum nitride.

[0163] In addition, from the comparison between Examples 7 to 20 and Examples 1 to 6, it can be seen that when improving the electrolyte and the negative electrode material simultaneously, if the added substances are different, it will also have a great impact on the low-temperature performance of the lithium battery. The synergistic effect of using a mixture of potassium bromide, ferrocene derivatives, polyvinylidene fluoride, and nano-aluminum oxide as the electrolyte additive and the improved negative electrode can achieve better charge-discharge performance for the lithium battery of the present invention. From the comparison between Examples 7 to 9 and Example 1, and between Examples 11 to 13 and Example 2, it can be seen that if the composition of the electrolyte buffer is changed, the added buffer has no obvious improvement on the interfacial characteristics between substances, and it is impossible to improve the charge-discharge performance of the lithium battery at low temperatures by effectively reducing the impedance. If potassium bromide is missing, the ionic conductivity of the lithium battery decreases, and it is also impossible to effectively improve the charge-discharge performance of the lithium battery at low temperatures. However, even if a mixture of potassium bromide, ferrocene derivatives, polyvinylidene fluoride, and nano-aluminum oxide is used as the electrolyte additive, without the cooperation of the negative electrode additive, it is also impossible to effectively improve the charge-discharge performance of the lithium battery at low temperatures. In the present invention, on the one hand, the ionic conductivity of the system is enhanced through the negative electrode additive, and the influence of temperature is reduced through the heat-insulating material; on the other hand, the electrolyte additive can further enhance the ionic conductivity, and at the same time, the buffer improves the interfacial characteristics between substances, enabling the lithium battery of the present invention to better adapt to the working state at low temperatures, so as to have excellent charge-discharge performance even below -20°C. In addition, from the comparison between Example 10 and Example 1, and between Example 14 and Example 2, it can be seen that the electrolyte added with low-temperature additives can further ensure the stability of each substance in the electrolyte, enabling the battery to still have a good capacity retention rate at -20°C and -45°C.

[0164] In addition, from the comparison between Example 1 and Examples 21 to 23, it can be seen that adding electrolyte additives such as trifluoromethylphenylthioamide, N-sulfonylbenzimide derivatives, and 4-dimethyl-1H-imidazole to the electrolyte can further improve the ionic conductivity and the capacity retention rate at low temperatures.

[0165] In addition, from the comparison between Example 1 and Examples 24 to 28, it can be seen that adding additives such as vanadium oxide nanoparticles, molybdenum carbide, catechol, cyproterone, and metal-organic frameworks to the negative electrode mixture layer can further improve the ionic conductivity and the capacity retention rate at low temperatures.

[0166] In addition, it can be seen from the comparison between Example 1 and Examples 29 to 30 that the lithium battery of the present invention has more excellent performance at low temperatures with lithium iron phosphate material as the positive electrode active material layer. Thus, using lithium iron phosphate material as the positive electrode active material, graphite as the negative electrode, and adding negative electrode additives such as apatite-type lithium ion conductor, glass fiber, nano boron nitride, and nano aluminum nitride to the negative electrode mixture layer, and then combining with an electrolyte added with potassium bromide, ferrocene derivative, polyvinylidene fluoride, and nano alumina, can enable this lithium battery to have good ionic conductivity and still have excellent charge and discharge performance at -45°C.

[0167] According to the disclosure and teachings of the above specification, those skilled in the art to which the present invention pertains can also make changes and modifications to the above embodiments. Therefore, the present invention is not limited to the above specific embodiments, and any obvious improvements, substitutions, or variations made by those skilled in the art based on the present invention all fall within the protection scope of the present invention. In addition, although some specific terms are used in this specification, these terms are only for convenience of description and do not constitute any limitation to the present invention.

Claims

1. A low-temperature resistant lithium battery, comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte. The positive electrode sheet includes a positive electrode current collector and a positive electrode mixture layer coated on the positive electrode current collector. The negative electrode sheet includes a negative electrode current collector and a negative electrode mixture layer coated on the negative electrode current collector; characterized in that: The negative electrode mixture layer includes a negative electrode active material and a negative electrode additive. The negative electrode additive includes a nitride, glass fiber and an apatite-type lithium ion conductor; the mass ratio of the nitride, the glass fiber and the apatite-type lithium ion conductor is (60~80):(10~20):(10~20); the negative electrode additive accounts for 1~5% of the total mass of the negative electrode mixture layer; The electrolyte includes a lithium salt, an organic solvent and an electrolyte additive. The electrolyte additive includes potassium bromide, a ferrocene derivative and a buffer; The electrolyte additive accounts for 0.5~2% of the total mass of the electrolyte; potassium bromide accounts for 40~50% of the total mass of the electrolyte additive, the ferrocene derivative accounts for 10~20% of the total mass of the electrolyte additive; the buffer accounts for 30~40% of the total mass of the electrolyte additive; The buffer is a mixture of polyvinylidene fluoride and nano-aluminum oxide; the mass ratio of polyvinylidene fluoride and nano-aluminum oxide is 1:1; The nitride is a mixture of nano-boron nitride and nano-aluminum nitride, and the mass ratio of nano-boron nitride to nano-aluminum nitride is 2:1; The ferrocene derivative is one of bis(2-carbazolyl)ferrocene, ferrocene-benzimidazole derivative and ferrocene-acetylene derivative.

2. The low-temperature resistant lithium battery according to claim 1, wherein The preparation method of the apatite-type lithium ion conductor includes the following steps: 1) Raw material preparation: Lithium carbonate, nano-aluminum oxide and trisodium phosphate are mixed according to a molar ratio of 1:1:1 and mixed evenly by a ball mill; 2) Reaction: The mixed powder sample is placed in a high-temperature furnace and subjected to a solid-phase reaction under atmosphere protection; 3) Heating: The temperature is raised from room temperature to 800 °C at a heating rate of 10 °C / min and held for 1-2 h to make the reaction sufficient; 4) Cooling: After high-temperature treatment, the high-temperature furnace is closed and allowed to cool naturally to room temperature; 5) Heat treatment: The obtained apatite-type lithium ion conductor sample is put into a vacuum heat treatment furnace and held at 400 °C for 24 h to remove residual gas and moisture in the sample, and the apatite-type lithium ion conductor is obtained.

3. The low-temperature resistant lithium battery according to claim 1, wherein The electrolyte additive further includes trifluoromethylphenylthioamide.

4. The low-temperature resistant lithium battery according to claim 1, characterized in that, The positive electrode mixture layer includes a positive electrode active material, a positive electrode binder, a positive electrode conductive agent and a positive electrode dispersant, and the positive electrode active material is a lithium iron phosphate material.

5. The low-temperature resistant lithium battery according to claim 1, characterized in that The electrolyte additive further includes an N-sulfonylbenzimide derivative; the preparation method of the N-sulfonylbenzimide derivative includes the following steps: 1) Sulfuryl chloride is added to a container containing dipropyl phosphate, and evenly mixed with a magnetic stirrer and reacted at room temperature for 2-4 hours; 2) Under heating conditions, benzoic acid is slowly added to the above reaction mixture, maintaining the reaction temperature at 60 - 80 °C for a reaction time of 4 - 6 hours; 3) The generated HCl and inorganic compounds are sieved out, and the remaining solvent is removed by rotary evaporation concentration to obtain the N-thiobenzoylbenzimide derivative.

6. The low-temperature resistant lithium battery according to claim 1, wherein The electrolyte additive further includes one of 4-dimethyl-1H-imidazole, 2,2,6,6-tetramethyl-1-piperidone, and 1,3-dimethyl-2-phenylimidazole.

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