A wide-temperature-range high-power start-up lithium ion battery capable of low-temperature charging and discharging cycles

Abstract

This invention relates to a wide-temperature-range, high-power, low-temperature charge-discharge-cycle-capable starting lithium-ion battery. The invention comprises a positive electrode, a negative electrode, and an electrolyte, characterized in that: the positive electrode is composed of a lithium iron phosphate material body, a conductive agent, carbon nanotubes, a binder, and aluminum foil; the lithium iron phosphate material body is composed of lithium iron phosphate, titanium, and highly conductive carbon; the content of highly conductive carbon is 1.3–2.0%; the negative electrode is composed of artificial graphite, a conductive agent, sodium carboxymethyl cellulose, a binder, and copper foil, with 91–93 parts of artificial graphite, 2–5 parts of conductive agent, 0.5–1.5 parts of sodium carboxymethyl cellulose, and 2–3 parts of binder; the electrolyte is composed of lithium hexafluorophosphate, lithium salt additives, film-forming additives, and a low-melting-point solvent, with the concentration of lithium hexafluorophosphate being above 1.3 mol / L, lithium salt additives being 0.5–9 parts, and film-forming additives being 0.2–3 parts. This invention expands the operating temperature range of lithium-ion batteries to -40℃ to 65℃.

Description

Technical Field

[0001] This invention relates to a wide-temperature-range, high-power, low-temperature charge-discharge-cycle-capable starting lithium-ion battery, belonging to the field of lithium-ion batteries. Background Technology

[0002] The typical charging temperature range for high-power starting lithium-ion batteries is 0℃ to 40℃, and the discharging temperature range is -20℃ to 60℃. Charging at low temperatures can cause lithium plating on the negative electrode surface, posing a safety hazard. Therefore, the battery needs to be heated before charging at 0℃, requiring an internal heating system, which increases battery cost and structural complexity. Normally, batteries can only discharge at low rates (0.1 to 1C) at -20℃, which is insufficient for high-rate discharge at -20℃ or even ultra-low temperatures (-40℃). This means that currently used batteries often fail to start vehicles properly at low temperatures. Based on the application requirements of starting lithium-ion batteries, the cells need to have a wide temperature range of -40℃ to 65℃, as well as the ability to discharge at ultra-high rates and charge at low temperatures, and to function normally at 65℃. Currently, there are no such wide-temperature-range, high-power starting lithium-ion batteries capable of low-temperature charge-discharge cycles. Summary of the Invention

[0003] The purpose of this invention is to overcome the above-mentioned shortcomings in the prior art and to provide a reliable, wide-temperature-range, high-power, low-temperature charge-discharge-cycle starting lithium-ion battery.

[0004] The technical solution adopted by this invention to solve the above problems is as follows: This wide-temperature-range, high-power, low-temperature charge-discharge cycle-capable starting lithium-ion battery includes a positive electrode, a negative electrode, and an electrolyte. Its characteristics are: the positive electrode is composed of a lithium iron phosphate material body, a conductive agent, carbon nanotubes, a binder, and aluminum foil; the lithium iron phosphate material body is composed of lithium iron phosphate, titanium, and highly conductive carbon, wherein the titanium content is 1900–3600 mg / kg, increasing the specific capacity of the lithium iron phosphate material body, improving cycle performance, increasing low-temperature release rate, and improving rate performance; the highly conductive carbon has a mass percentage of 1.3–2.0%, which effectively enhances the starting lithium-ion battery's performance. The performance of a battery depends on its carbon content. Low carbon content results in insufficient conductivity, while high carbon content leads to processing difficulties, low specific capacity, and decreased performance. High-conductivity carbon has a D50 of 4–12 µm, resulting in more uniform particle size and more stable performance. High-conductivity carbon coating improves the conductivity of the material, reduces the internal resistance of the cell, and improves rate performance. In the positive electrode, the weight percentage of lithium iron phosphate material is 90–95 parts, the weight percentage of conductive agent is 3–6 parts, the weight percentage of carbon nanotubes is 0.5–1.5 parts, and the weight percentage of binder is 2–4.3 parts, which increases the conductivity of the positive electrode, reduces the internal resistance of the cell, and allows the cell performance to be effectively utilized. The negative electrode sheet is composed of artificial graphite, a conductive agent, sodium carboxymethyl cellulose (CMC), a binder, and copper foil. The artificial graphite comprises 91-93 parts by weight, the conductive agent comprises 2-5 parts by weight, the sodium carboxymethyl cellulose (CMC) comprises 0.5-1.5 parts by weight, and the binder comprises 2-3 parts by weight. This increases the conductivity of the negative electrode sheet, reduces the internal resistance of the battery cell, and allows the battery cell performance to be effectively utilized. The sodium carboxymethyl cellulose (CMC) acts as a dispersant, ensuring that the artificial graphite in the negative electrode sheet is evenly dispersed in water and does not settle. The electrolyte is composed of lithium hexafluorophosphate, lithium salt additives, film-forming additives and low-melting-point solvents, wherein the concentration of lithium hexafluorophosphate is above 1.3 mol / L, the weight percentage of lithium salt additives is 0.5 to 9 parts, and the weight percentage of film-forming additives is 0.2 to 3 parts.

[0005] Preferably, the artificial graphite in the negative electrode sheet of the present invention is made from pitch coke, which undergoes grinding and shaping, pre-carbonization, graphitization, liquid-phase pitch coating, and carbonization to finally form graphite particles coated with amorphous carbon.

[0006] Preferably, the artificial graphite in the negative electrode sheet of the present invention has a D50 of 4–9 µm, resulting in more uniform particle size, more stable performance, and a specific surface area ≤ 3.0 m². 2 / g, low specific surface area, high degree of graphitization, can significantly improve lithium-ion channels and reduce contact interface impedance, which can ensure the rapid and orderly insertion of lithium ions into the negative electrode lattice structure under low temperature charging.

[0007] Preferably, the lithium salt additive in the electrolyte of the present invention is lithium difluorophosphate, lithium difluorooxalate borate, lithium bis(fluorosulfonyl)imide, or lithium tetrafluoroborate, wherein the weight percentages of lithium difluorophosphate are 0.5–3 parts, lithium difluorooxalate borate are 0.5–3 parts, lithium bis(fluorosulfonyl)imide are 1–9 parts, and lithium tetrafluoroborate are 0.5–3 parts. This facilitates rapid ion migration, improves low-temperature high-rate discharge, and enhances high-temperature cycle life.

[0008] Preferably, the film-forming additive in the electrolyte of the present invention is vinyl sulfate or ethylene carbonate, wherein the weight percentage of vinyl sulfate is 0.2 to 3 parts, and the weight percentage of ethylene carbonate is 1 to 3 parts. This reduces the interfacial impedance of the SEI film while maintaining high and low temperature stability.

[0009] Preferably, the low-melting-point solvent in the electrolyte of this invention is ethylene carbonate, diethyl carbonate, methyl ethyl carbonate, dimethyl carbonate, ethyl propionate, or fluoroethylene carbonate; wherein the weight percentages of ethylene carbonate, diethyl carbonate, methyl ethyl carbonate, dimethyl carbonate, ethyl propionate, and fluoroethylene carbonate are 5-25 parts, 5-25 parts, 35 parts, 35 parts, 40 parts, and 3 parts. This facilitates lithium salt dissociation, reduces electrolyte viscosity, increases ion migration rate, improves electrode wetting, enhances battery capacity and low-temperature performance, ensures reliable charge-discharge cycle performance at -20 to -40°C, and reliable high-rate discharge performance at -20 to -40°C.

[0010] Compared with the prior art, the present invention has the following advantages and effects: it effectively solves the problems of lithium ion migration being hindered and lithium plating during charging at low temperature and high current, realizes rapid lithium ion migration, increases effective ion channels, and provides a stable SEI film.

[0011] This invention enables trucks to achieve the required starting current and voltage at an extremely low ambient temperature of -40°C and a 5C discharge rate; it can withstand 100 charge-discharge cycles without heating at -20°C to -30°C, with a capacity recovery of over 90% at room temperature; the cell exhibits reliable safety performance, passing thermal shock and needle penetration tests; and it achieves a capacity recovery rate of over 90% after 10 days of storage at a high temperature of 65°C. This invention effectively expands the operating temperature range of lithium-ion batteries to -40°C to 65°C, improves low-temperature cycle life, and enhances low-temperature starting capability. Detailed Implementation

[0012] The present invention will be further described in detail below through embodiments. The following embodiments are explanations of the present invention, and the present invention is not limited to the following embodiments. Example

[0013] The wide-temperature-range, high-power, low-temperature charge-discharge-cycle starting lithium-ion battery of the present invention includes a positive electrode, a negative electrode, and an electrolyte. The positive electrode is composed of a lithium iron phosphate material substrate, a conductive agent, carbon nanotubes, a binder, and aluminum foil. The lithium iron phosphate material substrate is composed of lithium iron phosphate, titanium, and highly conductive carbon, wherein the titanium content is 1900–3600 mg / kg, the highly conductive carbon mass percentage is 1.3–2.0%, and the D50 of the highly conductive carbon is 4–12 µm. In the positive electrode, the lithium iron phosphate material substrate comprises 90–95 parts by weight, the conductive agent comprises 3–6 parts by weight, the carbon nanotubes comprise 0.5–1.5 parts by weight, and the binder comprises 2–4.3 parts by weight.

[0014] The negative electrode sheet is composed of artificial graphite, a conductive agent, sodium carboxymethyl cellulose, a binder, and copper foil. The artificial graphite comprises 91–93 parts by weight, the conductive agent 2–5 parts by weight, the sodium carboxymethyl cellulose 0.5–1.5 parts by weight, and the binder 2–3 parts by weight. The artificial graphite has a D50 of 4–9 µm and a specific surface area ≤3.0 m². 2 / g. Artificial graphite is made from pitch coke as raw material. It is produced through grinding and shaping, pre-carbonization, graphitization, liquid-phase pitch coating, and carbonization to finally form graphite particles coated with amorphous carbon.

[0015] The electrolyte is composed of lithium hexafluorophosphate, lithium salt additives, film-forming additives and low-melting-point solvents. The concentration of lithium hexafluorophosphate is above 1.3 mol / L, the weight of lithium salt additives is 0.5 to 9 parts, and the weight of film-forming additives is 0.2 to 3 parts.

[0016] The lithium salt additive in the electrolyte is lithium difluorophosphate, lithium difluorooxalate borate, lithium bis(fluorosulfonyl)imide, or lithium tetrafluoroborate, wherein the weight percentage of lithium difluorophosphate is 0.5 to 3 parts, the weight percentage of lithium difluorooxalate borate is 0.5 to 3 parts, the weight percentage of lithium bis(fluorosulfonyl)imide is 1 to 9 parts, and the weight percentage of lithium tetrafluoroborate is 0.5 to 3 parts.

[0017] The film-forming additive in the electrolyte is vinyl sulfate or ethylene carbonate, wherein the weight parts of vinyl sulfate are 0.2 to 3 parts and the weight parts of ethylene carbonate are 1 to 3 parts.

[0018] The low-melting-point solvent in the electrolyte is ethylene carbonate, diethyl carbonate, methyl ethyl carbonate, dimethyl carbonate, ethyl propionate, or fluoroethylene carbonate; wherein the weight percentages of ethylene carbonate, diethyl carbonate, methyl ethyl carbonate, dimethyl carbonate, ethyl propionate, and fluoroethylene carbonate are 5 to 25 parts, 5 to 25 parts, less than 35 parts, less than 35 parts, less than 40 parts, and less than 3 parts.

[0019] The composition and performance of the starting lithium-ion battery in this application are described in a table below.

[0020] Table 1: Composition of the positive electrode sheets in Examples 1-8

[0021] Table 2: Composition of the lithium iron phosphate material matrix in Examples 1-8

[0022] Table 3: Composition of the negative electrode sheets in Examples 1-8

[0023] Table 4: Composition of the electrolytes in Examples 1-8

[0024] Table 5: Current and voltage of the starting lithium-ion batteries in Examples 1-8 during discharge at -40°C and 5C rate.

[0025] Table 6: Performance of the starting lithium-ion batteries from Examples 1-8 after 100 charge-discharge cycles at -20℃ to -30℃ without heating.

[0026] Table 7: Capacity recovery rate of the starting lithium-ion batteries from Examples 1-8 after storage at 65°C for 10 days.

[0027] As can be seen, the present invention can effectively expand the operating temperature range of lithium-ion batteries to -40℃~65℃, improve low-temperature cycle life, and enhance low-temperature start-up capability.

[0028] Furthermore, it should be noted that the specific embodiments described in this specification may differ in the shape and name of their components, etc. The above description is merely illustrative of the structure of the present invention. All equivalent or simple variations made based on the structure, features, and principles described in this patent concept are included within the protection scope of this patent. Those skilled in the art can make various modifications or additions to the described specific embodiments or use similar methods to substitute them, as long as they do not deviate from the structure of the present invention or exceed the scope defined by the claims, all of which should fall within the protection scope of this invention.

Claims

1. A wide-temperature-range, high-power, low-temperature charge-discharge-cycle-capable starting lithium-ion battery, comprising a positive electrode, a negative electrode, and an electrolyte, characterized in that: The positive electrode sheet is composed of a lithium iron phosphate material body, a conductive agent, carbon nanotubes, a binder, and aluminum foil. The lithium iron phosphate material body is composed of lithium iron phosphate, titanium, and highly conductive carbon, wherein the titanium content is 1900–3600 mg / kg, the highly conductive carbon mass percentage is 1.3–2.0%, and the D50 of the highly conductive carbon is 4–12 µm. In the positive electrode sheet, the weight percentage of the lithium iron phosphate material body is 90–95 parts, the weight percentage of the conductive agent is 3–6 parts, the weight percentage of the carbon nanotubes is 0.5–1.5 parts, and the weight percentage of the binder is 2–4.3 parts. The negative electrode sheet is composed of artificial graphite, a conductive agent, sodium carboxymethyl cellulose, a binder, and copper foil. The artificial graphite in the negative electrode sheet is made from pitch coke, which undergoes grinding and shaping, pre-carbonization, graphitization, liquid-phase pitch coating, and carbonization to ultimately form graphite particles coated with amorphous carbon. The artificial graphite in the negative electrode sheet has a D50 of 4–9 µm and a specific surface area ≤3.0 m². 2 / g; the weight parts of artificial graphite are 91 to 93 parts, the weight parts of conductive agent are 2 to 5 parts, the weight parts of sodium carboxymethyl cellulose are 0.5 to 1.5 parts, and the weight parts of binder are 2 to 3 parts. The electrolyte is composed of lithium hexafluorophosphate, lithium salt additives, film-forming additives, and low-melting-point solvents. The lithium salt additives are lithium difluorophosphate, lithium difluorooxalate borate, lithium difluorosulfonyl imide, or lithium tetrafluoroborate. The film-forming additives are vinyl sulfate or ethylene carbonate. The low-melting-point solvents are ethylene carbonate, diethyl carbonate, methyl ethyl carbonate, dimethyl carbonate, ethyl propionate, or fluoroethylene carbonate. The concentration of lithium hexafluorophosphate is above 1.3 mol / L, the weight percentage of lithium salt additives is 0.5 to 9 parts, and the weight percentage of film-forming additives is 0.2 to 3 parts.

2. The starting lithium-ion battery with wide temperature range, high power, and low-temperature charge / discharge cycle capability according to claim 1, characterized in that: The lithium difluorophosphate is present in parts by weight of 0.5 to 3, the lithium difluorooxalate borate is present in parts by weight of 0.5 to 3, the lithium difluorosulfonyl imide is present in parts by weight of 1 to 9, and the lithium tetrafluoroborate is present in parts by weight of 0.5 to 3.

3. The starting lithium-ion battery with wide temperature range, high power, and low-temperature charge / discharge cycle capability according to claim 1, characterized in that: The weight percentages of vinyl sulfate are 0.2 to 3 parts, and the weight percentages of ethylene carbonate are 1 to 3 parts.

4. The starting lithium-ion battery with wide temperature range, high power, and low-temperature charge / discharge cycle capability according to claim 1, characterized in that: The weight percentages of ethylene carbonate are 5 to 25 parts, diethyl carbonate are 5 to 25 parts, methyl ethyl carbonate are less than 35 parts, dimethyl carbonate are less than 35 parts, ethyl propionate are less than 40 parts, and fluoroethylene carbonate are less than 3 parts.

Images