Low-temperature high-power lithium ion battery

Abstract

The application relates to the technical field of lithium ion batteries, in particular to a low-temperature high-power lithium ion battery. In the scheme, the negative electrode material adopts forged needle-shaped coke secondary particle graphite liquid-phase carbon coating design, an coating layer capable of making Li+ rapidly diffuse is introduced on the surface of the graphite, rapid transmission from the surface to the interior is realized, the enrichment of Li+ in a local part can be avoided, the content of impurities and foreign matters is controlled through strict control of the coating material of the fast ion channel, the transmission channel of Li+ is avoided from being blocked, the rate and low-temperature high-rate discharge performance of the battery are improved, the rapid charge-discharge capacity of the battery is enhanced, and the demand of high-power application in a low-temperature environment is met. Through optimization of an electrolyte formula and an additive and modification of the coating design of the negative electrode material, a stable solid electrolyte interface (SEI) film can be formed, the unstable growth of the SEI film is inhibited, and the cycle life and safety of the battery are prolonged.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of lithium ion batteries, in particular to a low-temperature high-power lithium ion battery. BACKGROUND

[0002] The low-temperature battery can be applied to polar unmanned reconnaissance machines, intercoms, electronic atomizers, intelligent devices in low-temperature regions and the like, and the development of low-temperature lithium ion batteries is also urgently needed in the military and aerospace fields.

[0003] The traditional lithium ion battery cannot meet the working requirements under extreme temperature. The service life and performance are greatly affected under the working environment temperature below 0 DEG C or above 40 DEG C. The main reasons for the performance degradation of the lithium ion battery under low temperature include:

[0004] (1) the mass transfer process of lithium ions in the electrode and the electrode / liquid interface is slowed down;

[0005] (2) the ionic conductivity of the electrolyte is reduced;

[0006] (3) anode plating lithium, lithium dendrite growth and SEI film thickening;

[0007] (4) the desolvation process of lithium ions is difficult.

[0008] Under low temperature, the kinetic rate of lithium ions is slowed down, which is the most important factor affecting the electrochemical performance, the capacity of the battery is attenuated under low temperature, the cycle rate performance is poor, and the lithium precipitation phenomenon is obvious. The development of domestic low-temperature lithium ion batteries is mainly for electronic digital products, and the realization of low temperature is generally in the environment of-20-30 DEG C, supporting 0.2C discharge, and the minimum of military products is-40 DEG C, supporting 0.1-0.2C discharge. In order to meet the market demand of low-temperature high-rate discharge lithium ion batteries, it is urgent to develop lithium ion battery products suitable for low-temperature environment and having high-rate performance. SUMMARY

[0009] In order to solve the above technical problems, the application provides a low-temperature high-power lithium ion battery, which comprises a positive electrode sheet, a negative electrode sheet, a diaphragm and an electrolyte, the positive electrode sheet is coated with a modified positive electrode material, and the negative electrode sheet is coated with a modified negative electrode material.

[0010] The modified positive electrode material is coated with a composite material on the positive electrode material, and the composite material is boron-doped titanium dioxide nanotube array solid-supported molybdenum disulfide;

[0011] The modified negative electrode material is designed as forged needle-shaped coke secondary particles, inorganic carbon is introduced on the surface of the forged needle-shaped coke secondary particles, and a liquid-phase carbon coating layer is formed after carbonization of pitch;

[0012] The electrolyte composition comprises 10-15% lithium salt, 70%-80% solvent system and 10-15% additives.

[0013] Preferably, the preparation step of the negative electrode sheet comprises:

[0014] S101, modified negative electrode material preparation: mix graphite and inorganic carbon at a certain temperature to make inorganic carbon uniformly coated on the surface of graphite, then perform pitch carbonization treatment on the coated graphite to obtain a modified negative electrode material;

[0015] S102, mix the modified negative electrode material, conductive agent and binder according to the mass ratio (93-96):(1-4):(1-3), prepare a slurry through high-speed dispersion equipment, coat, roll compact, and cut to prepare negative electrode sheets of corresponding lengths, weld copper-plated composite nickel tabs at the middle position of the negative electrode sheets and paste glue to obtain negative electrode sheets.

[0016] Preferably, in step S101, the preparation step of the modified negative electrode material preparation comprises:

[0017] A1, mix graphite and inorganic carbon according to the mass ratio (3-4):(1-2) at a temperature of 80-90℃ to make inorganic carbon uniformly coated on the surface of graphite, then perform solidification, pyrolysis and pitch carbonization treatment on the coated graphite;

[0018] A2, place the product of step A1 in an ethylene atmosphere at a temperature of 150-200℃ for 1-2h by using chemical vapor deposition method;

[0019] A3, place the product of step A2 in a reaction kettle, mix ethylene tar and effective components of catalytic oil slurry according to the ratio (1-2):(1-2) and add them to the reaction kettle, add catalyst and crosslinking agent to the reaction kettle, heat to 240-330℃, control the reaction pressure to be 0.5-2.5MPa, the stirring speed of the reactor is 150-450r / min, and the reaction time is 3-4h;

[0020] A4, slowly release the pressure to normal pressure, introduce air into the bottom of the reaction kettle at an air inlet amount of 0.5-2L / min, the stirring speed of the reactor is 200-350r / min, the reaction temperature is 240-300℃, the reaction time is 2-6h, stop introducing air and stirring, and then remove the light components to obtain the modified negative electrode material.

[0021] Preferably, the catalyst is p-toluenesulfonic acid, and the content is 3%-8% of the total mass of raw materials; the crosslinking agent is one of trioxane and polyoxymethylene, and the content is 7%-12% of the total mass of raw materials.

[0022] Preferably, the conductive agent is a mixture of superconducting carbon black and SWCNT single-walled carbon nanotubes, and the binder is PAA polyacrylonitrile multi-copolymer emulsion.

[0023] Preferably, the preparation step of the positive electrode sheet comprises:

[0024] S201, composite material preparation, titanium sheet is subjected to electrochemical anodic boronization treatment in an organic solution of 0.5wt% NH4BF4, 5wt% deionized water and ethylene glycol, then subjected to anodic oxidation in an organic solution containing fluoride ions, and the oxidized sample is subjected to heat treatment in a 200-450℃ electric resistance furnace for 2h, then cooled to room temperature in the furnace; the boron-doped titanium oxide nanometer array after heat treatment is used as a substrate, vacuumized and heated, then a molybdenum disulfide target is sputtered by using a radio frequency power source, cooled to 45℃ and taken out, to obtain a composite material;

[0025] S202, the composite material and the positive electrode active material are mixed at a certain temperature, so that the composite material is uniformly coated on the surface of the positive electrode active material, then the positive electrode active material coated with the composite material is solidified, to obtain a modified positive electrode material;

[0026] S203, the modified positive electrode material, the conductive agent and the binder are mixed in a mass ratio of (96-98):(1-2):(1-2), and a slurry is prepared by using a high-speed dispersion device, then coated, roll-pressed and cut, to obtain positive electrode sheets with corresponding lengths, and copper-plated composite nickel tabs are attached to the middle positions of the positive electrode sheets.

[0027] Preferably, in step S202, the composite material and the positive electrode active material are mixed in a mass ratio of (3-4):(1-2) at a temperature of 80-90℃.

[0028] Preferably, the positive electrode active material is obtained by adding lithium cobaltate, ternary material and lithium manganate into a stirring cylinder in a ratio of (1-2):(5-7):(2-3) and mixing.

[0029] Preferably, the solvent component of the electrolyte solution comprises ethyl acetate, methyl propionate and methyl acetate; the lithium salt comprises lithium bisfluorosulfonylimide, and the additive comprises vinyl sulfate and triphosphite.

[0030] Preferably, the mass ratio of the ethyl acetate, methyl propionate and methyl acetate is (1-2):(1.5-2):(1-3), and the mass ratio of the vinyl sulfate and triphosphite is (1-2):(1-2).

[0031] As can be seen from the above, the following beneficial effects can be obtained by applying the application:

[0032] 1. The negative material adopts forged needle-shaped coke secondary particle graphite liquid carbon coating design, which introduces a coating layer that can make Li+ rapidly diffuse on the surface of graphite, which not only plays a role in rapid transmission from the surface to the inside, but also can avoid the enrichment of Li+ in the local area, and the strict control of the fast ion channel with the coating material can control the content of impurities and foreign matter, avoid blocking the transmission channel of Li+, improve the rate and low-temperature high-rate discharge performance of the battery, enhance the rapid charge and discharge capacity of the battery, and meet the demand of high-power application in low-temperature environment.

[0033] 2. By optimizing the electrolyte formula and additives, and modifying the coating design of the negative material, a stable solid electrolyte interface layer (SEI) film can be formed, the unstable growth of the SEI film is inhibited, the cycle life of the battery is prolonged, and the safety is improved.

[0034] 3. Boron-doped titanium dioxide nanotubes are used as coating materials, which can establish a fast ion channel network on the surface of the positive material and accelerate the transmission rate of lithium ions in the positive material, thereby improving the high-rate discharge performance and low-temperature performance of the battery. Boron-doped titanium dioxide nanotubes have an ordered arrangement structure and can effectively transmit electrons, improving the electronic conductivity of the positive material and helping to improve the rate discharge capacity and cycle stability of the battery. DETAILED DESCRIPTION

[0035] The technical solutions in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor are within the scope of protection of the present application.

[0036] EMBODIMENTS

[0037] To solve the above technical problems, the embodiment provides a low-temperature high-power lithium ion battery, which comprises a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, the positive electrode sheet is coated with a modified positive electrode material, and the negative electrode sheet is coated with a modified negative electrode material; wherein the modified positive electrode material is coated with a composite material on the positive electrode material, and the composite material is boron-doped titanium dioxide nanotube array solid-supported molybdenum disulfide, so as to improve the conductivity and ion transmission rate of the battery. The modified negative electrode material is prepared by designing graphite into forged needle-shaped coke secondary particles, introducing inorganic carbon on the surface of the forged needle-shaped coke secondary particles, and forming a liquid-phase carbon coating layer after bitumen carbonization; the electrolyte composition comprises 10-15% lithium salt, 70%-80% solvent system and 10-15% additive. The graphite negative electrode adopts the forged needle-shaped coke secondary particles, which can reduce the aggregate particle size, shorten the diffusion distance, make the battery have high rate performance and low-temperature kinetic performance, then the diffusion rate and stability of lithium ions in the negative electrode material are improved by innovating the coating material, and the high-rate discharge performance and low-temperature performance of the battery are improved.

[0038] Specifically, the preparation steps of the negative electrode sheet include:

[0039] S101, modified negative electrode material preparation: mix graphite and inorganic carbon at a certain temperature to uniformly coat the inorganic carbon on the surface of the graphite, then perform bitumen carbonization treatment on the coated graphite to obtain a modified negative electrode material;

[0040] Specifically, in the step S101, the preparation steps of the modified negative electrode material preparation include:

[0041] A1, mix the forged needle-shaped coke secondary particle graphite and inorganic carbon according to the mass ratio (3-4):(1-2) at a temperature of 80-90 DEG C, so that the inorganic carbon is uniformly coated on the surface of the graphite, and then perform solidification, pyrolysis and bitumen carbonization treatment on the coated graphite;

[0042] A2, using chemical vapor deposition method, the product of step A1 is placed in an ethylene atmosphere at a temperature of 150-200 DEG C, and the reaction time is 1-2h;

[0043] A3, the product of step A2 is placed in a reaction kettle, ethylene tar and effective components of catalytic oil slurry are mixed according to the ratio of (1-2):(1-2) and then added into the reaction kettle, catalyst and crosslinking agent are added into the reaction kettle, the temperature is raised to 240-330 DEG C, the reaction pressure is controlled at 0.5-2.5 MPa, the stirring speed of the reactor is 150-450 r / min, and the reaction time is 3-4h;

[0044] In the above scheme, the catalyst is p-toluenesulfonic acid, and the content is 3%-8% of the total mass of the raw materials; the crosslinking agent is one of trioxane and polyoxymethylene, and the content is 7%-12% of the total mass of the raw materials.

[0045] A4, slowly unloading pressure to normal pressure, air inlet amount is selected to be 0.5-2 L / min, the stirring speed of the reactor is 200-350 r / min, the reaction temperature is 240-300 DEG C, the reaction time is 2-6 h, the air inlet and the stirring are stopped, and then the light component is removed to obtain the liquid-phase carbon-coated modified negative electrode material. The inorganic carbon introduced on the surface of the forged needle coke secondary particle can effectively improve the diffusion rate of lithium ions, reduce the internal resistance of the battery, and improve the low-temperature rate discharge efficiency of the battery. The coating layer formed after the carbonization of pitch can also protect the negative electrode material from the corrosion of the electrolyte and prolong the service life of the battery.

[0046] S102, the modified negative electrode material, the conductive agent and the binder are mixed according to the mass ratio (93-96):(1-4):(1-3), and a slurry is prepared by a high-speed dispersion device. After coating, roll compaction and slitting, the substrate is cut into negative electrode sheets of corresponding lengths, and copper-plated composite nickel tabs are welded at the middle position of the negative electrode sheets and then glued, to obtain the negative electrode sheets. By selecting the carbon-coated design of the forged needle coke secondary particles, the fast ion channel can be ensured to be unobstructed, the existence of impurities and foreign matters can be avoided to hinder the transmission of lithium ions, the Li+ transmission rate of the negative electrode material can be improved, and the fast charging and discharging and low-temperature performance of the battery can be improved. This design can effectively improve the electrical conductivity of the negative electrode material, thereby improving the power and low-temperature discharge performance of the battery.

[0047] The substrate of the negative electrode sheet adopts a carbon-coated copper foil structure, and a copper-plated composite nickel strip is used as the tab, which can improve the current transmission capacity and thermal conductivity of the electrode sheet, reduce the contact resistance between the electrode sheet and the battery cell, and further improve the power and low-temperature discharge performance of the battery.

[0048] Further, the conductive agent adopts a mixture of superconducting carbon black and SWCNT single-walled carbon nanotubes, which can improve the conductivity of the negative electrode, reduce the internal resistance of the battery, and further improve the rate performance and low-temperature performance of the battery. The binder is PAA polyacrylonitrile multi-copolymer emulsion. Using PAA polyacrylonitrile multi-copolymer emulsion as the binder can improve the structural stability of the electrode sheet, improve the mechanical strength and corrosion resistance of the electrode sheet, reduce the impedance of the battery cell, and improve the rate and low-temperature rate performance of the battery.

[0049] Further, the preparation steps of the positive electrode sheet include:

[0050] S201, the composite material is prepared, the titanium sheet is subjected to electrochemical anodic boronization treatment in an organic solution of 0.5wt% NH4BF4, 5wt% deionized water and ethylene glycol as a solvent, then subjected to anodic oxidation in an organic solution containing fluoride ions, the oxidized sample is subjected to heat treatment in a 200-450℃ electric resistance furnace, heat preservation for 2h, then furnace cooling to room temperature; the boron-doped titanium dioxide nanotube array after heat treatment is used as a substrate, vacuumizing, heating, then sputtering a molybdenum disulfide target by using a radio frequency power source, cooling to 45℃ and taking out, to obtain a composite material; the boron-doped titanium dioxide nanotube has an ordered arrangement structure and can effectively transmit electrons, improving the electron conductivity of the positive electrode material and helping to improve the rate discharge capacity and cycle stability of the battery. By applying this coated modified material to the lithium ion battery electrode sheet, the performance of the battery can be improved as a whole in terms of power, capacity and cycle life.

[0051] S202, the composite material and the positive electrode active material are mixed at a certain temperature to make the composite material uniformly coated on the surface of the positive electrode active material, then the coated positive electrode active material is solidified to obtain a modified positive electrode material, the positive electrode active material is lithium cobaltate; in this step, the composite material and the positive electrode active material are mixed at a temperature of 80-90℃ according to a mass ratio of (3-4):(1-2).

[0052] S203, the modified positive electrode material, the conductive agent and the binder are mixed according to a mass ratio of (96-98):(1-2):(1-2), prepared into a slurry by a high-speed dispersion device, the substrate is coated, roll-pressed and cut to prepare a positive electrode sheet with a corresponding length, and a copper-plated composite nickel tab is plated at the middle position of the positive electrode sheet and glued. The substrate of the positive electrode sheet is carbon-coated aluminum foil, which can reduce the polarization resistance of the battery, improve the ionic conductivity, and improve the rate performance and low-temperature high-power discharge performance of the battery.

[0053] By immobilizing molybdenum disulfide on the boron-doped titanium dioxide nanotube, a composite material with good electrochemical performance is formed, which is used as a coated modified material of the positive electrode material. Since the boron-doped titanium dioxide nanotube is used as a coating material, a fast ion channel network can be established on the surface of the positive electrode material, accelerating the transmission rate of lithium ions inside the positive electrode material, thereby improving the high-rate discharge performance and low-temperature performance of the battery. Moreover, the boron-doped titanium dioxide nanotube has high high-temperature resistance and chemical stability, which can maintain the stability of the material structure during the operation of the battery, reduce the aging speed of the battery and prolong the service life of the battery. Moreover, the above positive electrode sheet modification method does not need to use toxic or environmentally polluting solvents and additives, has high environmental friendliness and sustainability, and meets the development trend of green manufacturing. This not only helps to improve the competitiveness of the product, but also contributes to environmental protection.

[0054] In the above scheme, the positive active material is obtained by mixing lithium cobaltate, ternary material and lithium manganate in a stirring cylinder in a ratio of (1-2):(5-7):(2-3). The positive active material is mixed by mixing and doping the raw materials in a suitable ratio to improve the stability of the positive electrode under overcharge conditions, while taking into account the energy density and providing the cycle life of the battery.

[0055] The solvent component of the electrolyte includes ethyl acetate, methyl propionate and methyl acetate; the lithium salt includes lithium bisfluorosulfonylimide, and the additives include vinyl sulfate and triphosphite. Low-viscosity solvents such as ethyl acetate, methyl propionate and methyl acetate have good solubility and low viscosity, which helps to improve the ion transport rate of the electrolyte, reduce the internal resistance of the battery, and improve the rate discharge and low-temperature discharge performance. It can also provide higher solubility, ensure the complete dissolution of lithium salt, increase the concentration of lithium ions in the electrolyte, and thus improve the energy density of the battery. Using lithium bisfluorosulfonylimide as a high-dissociation lithium salt can increase the concentration of lithium ions in the electrolyte, thereby reducing the concentration polarization impedance and improving the rate performance and low-temperature performance of the battery. As electrolyte additives, vinyl sulfate and triphosphite can form a solid electrolyte interface (SEI) film with high Li+ conductivity, inhibit the growth of harmful SEI film, thereby reducing the impedance of ions passing through the solid electrolyte and reducing the polarization loss of the battery. These additives can also form a loose and porous solid electrolyte interface on the positive and negative electrodes of the battery, reducing the interface resistance and improving the power and low-temperature rate performance of the battery. Through these optimization schemes, the rate performance and low-temperature high-rate discharge performance of the battery are significantly improved, providing more reliable energy for military, aerospace, unmanned aerial vehicles, electronic atomizers, energy storage and other fields.

[0056] wherein the mass ratio of ethyl acetate, methyl propionate and methyl acetate is (1-2):(1.5-2):(1-3); the mass ratio of vinyl sulfate and triphosphite is (1-2):(1-2). Preferably, the mass ratio of ethyl acetate, methyl propionate and methyl acetate is 1:1.5:2, and the mass ratio of vinyl sulfate and triphosphite is 1:1.

[0057] The low-temperature high-power discharge polymer lithium ion battery product supports rate discharge at -20℃ low-temperature environment, and the technical indicators are as follows: capacity: 2.5Ah (9.25wh), rated voltage: 4.2V, working temperature: -20℃-60℃, charging cutoff voltage: 4.2V, charging current: 600mA, discharge cutoff voltage: 3.0V, maximum continuous discharge current: 20C capacity retention rate >90%, minimum discharge temperature: -20℃, low-temperature discharge performance: -20℃ storage for 4h at 10C discharge, discharge capacity retention rate >85%.

[0058] Temperature °C Initial voltage V Discharge rate C Discharge current mA Discharge capacity mAh Capacity retention rate % 25 4.198 0.2 500 2558 100％ -20 4.193 10.0 25000 2250 88.0％

[0059] Table 1

[0060] Table 1 is a data table of the low-temperature high-power lithium ion battery of the present embodiment at -20℃ low-temperature storage for 4h and 10C discharge.

[0061] The low-temperature high-power discharge polymer lithium ion battery product supports rate discharge under a -30℃ low-temperature environment, and the product technical indexes are as follows: capacity: 0.6Ah (2.22wh), rated voltage: 4.2V, working temperature: -30℃-60℃, charging cutoff voltage: 4.2V, charging current: 600mA, discharge cutoff voltage: 3.0V, maximum continuous discharge current: 20C capacity retention rate >90%, minimum discharge temperature: -30℃, low-temperature discharge performance: -30℃ storage for 4h and 5C discharge, discharge capacity retention rate >90%.

[0062] Temperature °C Initial voltage V Discharge rate C Discharge current mA Discharge capacity mAh Capacity retention rate % 25 4.201 0.2 120 608 100％ -30 4.192 5.0 3000 556 91.4％

[0063] Table 2

[0064] Table 2 is a data table of the low-temperature high-power lithium ion battery of the present embodiment at -30℃ low-temperature storage for 4h and 5C discharge.

[0065] The low-temperature high-power discharge polymer lithium ion battery product supports rate discharge under a -30℃ low-temperature environment, and the product technical indexes are as follows: capacity: 10Ah (37wh), rated voltage: 4.2V, working temperature: -40℃-60℃, charging cutoff voltage: 4.2V, charging current: 20A, discharge cutoff voltage: 3.0V, maximum continuous discharge: 300A, minimum discharge temperature: -40℃, low-temperature discharge performance: -30℃ storage for 4h and 5C discharge, discharge capacity retention rate >80%.

[0066] Temperature °C Initial voltage V Discharge rate C Discharge current mA Discharge capacity mAh Capacity retention rate % Temperature °C Initial voltage V Discharge rate C Discharge current mA Discharge capacity mAh Capacity retention rate % 25 4.198 0.2 2000 10128 100％ -40 4.189 3.0 30000 8765 86.5％

[0067] Table 3

[0068] Table 3 is a data table of the low-temperature high-power lithium ion battery of the present embodiment at -40℃ low-temperature storage for 4h and 3C discharge.

[0069] As can be seen from the above, the low-temperature high-power lithium ion battery of the present embodiment has relatively significant advancement at -40℃. The specific manifestations are as follows:

[0070] 1) Extreme low-temperature working ability: the battery product can work normally under an extreme low-temperature environment of -40℃, and has good discharge performance, which belongs to a relatively advanced and advanced technical level in the field of lithium ion batteries.

[0071] 2) High power discharge capability: The battery product has a high discharge power, with a maximum continuous discharge of up to 300A, which is an advanced level of high power discharge in the field of lithium ion batteries, and can meet the application scenarios with high requirements for high power discharge.

[0072] 3) Wide temperature range operation: The battery product operates in a temperature range from -40℃ to 60℃, which is an extremely wide temperature range, and can meet the use requirements in various extreme environments, reflecting the advanced adaptability of the product in extreme conditions.

[0073] 4) Excellent low-temperature discharge performance: Even at -40℃ low-temperature environment, it can still maintain 80% discharge capacity when discharging at 3C, which shows that the battery product has excellent performance in extremely cold conditions, providing reliable energy support for applications in extremely cold environments.

[0074] The above-described embodiments do not constitute a limitation on the protection scope of the technical solutions. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the above-described embodiments shall be included in the protection scope of the technical solutions.

Claims

1. A low-temperature, high-power lithium-ion battery, characterized in that: It includes a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the positive electrode is coated with a modified positive electrode material, and the negative electrode is coated with a modified negative electrode material; The modified cathode material is made by coating the cathode material with a composite material, and the composite material is a boron-doped titanium dioxide nanotube array supported on molybdenum disulfide. The modified negative electrode material is made by designing graphite into secondary needle-shaped coke particles after forging, introducing inorganic carbon on the surface of the secondary needle-shaped coke particles, and forming a liquid phase carbon coating layer after pitch carbonization. The preparation steps of the modified negative electrode material include: A1. The graphite and inorganic carbon of the forged needle-shaped coke secondary particles are mixed at a mass ratio of (3-4):(1-2) at a temperature of 80-90℃ so that the inorganic carbon is uniformly coated on the graphite surface. Then the coated graphite is cured, pyrolyzed and carbonized with pitch. A2. Using chemical vapor deposition, the product from step A1 is placed in an ethylene atmosphere at a temperature of 150-200℃ for 1-2 hours. A3. Place the product of step A2 into a reactor, mix the effective components of ethylene tar and catalytic oil slurry in a ratio of (1-2):(1-2) and add them to the reactor. Add the catalyst and crosslinking agent to the reactor, heat to 240-330℃, control the reaction pressure at 0.5-2.5MPa, stir the reactor at 150-450r / min, and react for 3-4h. A4. Slowly release the pressure to atmospheric pressure, introduce air into the bottom of the reactor at a rate of 0.5-2 L / min, stir the reactor at a speed of 200-350 r / min, maintain the reaction temperature at 240-300℃, and react for 2-6 hours. Stop introducing air and stirring, and then remove the light components to obtain the modified negative electrode material. The electrolyte comprises 10-15% lithium salt, 70%-80% solvent, and 10-15% additives.

2. The low-temperature high-power lithium-ion battery according to claim 1, characterized in that: The preparation steps of the negative electrode sheet include: mixing modified negative electrode material, conductive agent and binder in a mass ratio of (93-96):(1-4):(1-3), preparing a slurry through a high-speed dispersion device, coating, compacting with rollers and cutting to make a negative electrode sheet of corresponding length, welding copper-plated composite nickel electrode tabs at the middle position of the negative electrode sheet and attaching adhesive to obtain the negative electrode sheet.

3. The low-temperature high-power lithium-ion battery according to claim 2, characterized in that: The catalyst is p-toluenesulfonic acid, with a content of 3%-8% of the total mass of the raw materials; the crosslinking agent is one of paraformaldehyde and paraformaldehyde, with a content of 7%-12% of the total mass of the raw materials.

4. The low-temperature high-power lithium-ion battery according to claim 2, characterized in that: The conductive agent is a mixture of superconducting carbon black and SWCNT single-walled carbon nanotubes, and the binder is a PAA polyacrylonitrile multi-element copolymer emulsion.

5. The low-temperature high-power lithium-ion battery according to claim 1, characterized in that: The preparation steps of the positive electrode sheet include: S201. Preparation of composite material: Titanium sheets were electrochemically anolylated in an organic solution containing 0.5 wt% NH4BF4, 5 wt% deionized water, and ethylene glycol. Then, they were anodized in an organic solution containing fluoride ions. The oxidized sample was heat-treated in a resistance furnace at 200-450℃ for 2 hours and then cooled to room temperature with the furnace. The heat-treated boron-doped titanium oxide nanoarray was used as a matrix. After vacuuming and heating, molybdenum disulfide target material was sputtered using an RF power supply. The sample was then cooled to 45℃ and removed to obtain the composite material. S202. The composite material and the positive electrode active material are mixed at a certain temperature, and then the positive electrode active material coated with the composite material is cured to obtain the modified positive electrode material. S203. The modified positive electrode material, conductive agent and binder are mixed in a mass ratio of (96-98):(1-2):(1-2), and a slurry is prepared by high-speed dispersion equipment. After coating, roller compaction and slitting, a positive electrode sheet of corresponding length is made. Copper-plated composite nickel tabs are attached to the middle position of the positive electrode sheet.

6. The low-temperature high-power lithium-ion battery according to claim 5, characterized in that: In the steps In S202, the composite material and the positive electrode active material are mixed at a mass ratio of (3-4):(1-2) at a temperature of 80-90℃.

7. The low-temperature high-power lithium-ion battery according to claim 6, characterized in that: The positive electrode active material is obtained by mixing lithium cobalt oxide, ternary materials, and lithium manganese oxide in a mixing tank at a ratio of (1-2):(5-7):(2-3).

8. The low-temperature high-power lithium-ion battery according to claim 1, characterized in that: The electrolyte solvent includes ethyl acetate, methyl propionate, and methyl acetate; the lithium salt includes lithium difluorosulfonylimide, and the additives include vinyl sulfate and triphosphite.

9. The low-temperature high-power lithium-ion battery according to claim 8, characterized in that: The mass ratio of ethyl acetate, methyl propionate and methyl acetate is (1-2):(1.5-2):(1-3); the mass ratio of vinyl sulfate and triphosphite is (1-2):(1-2).