Lithium ion battery

Abstract

The invention relates to a lithium ion battery, which comprises a positive plate, a negative plate and an electrolyte, the electrolyte comprises a first additive anhydride additive, a second additive mannitol carbonate sulfate and ethyl propionate; a negative active material in the negative plate comprises silicon carbon; the lithium ion battery meets the following relational expression: S1 / 0.2 < 150A1 + 120A2 + 13A3 < S1 / 0.06; wherein S1 is the mass percentage of ethyl propionate in the solvent, A1 is the mass percentage of the first additive in the electrolyte, A2 is the mass percentage of the second additive in the electrolyte, and A3 is the mass percentage of silicon carbon in the negative electrode active material, and the lithium ion battery has good high-temperature cycle performance and good storage performance.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, specifically relating to a lithium-ion battery. Background Technology

[0002] With societal development, consumers have increasingly higher demands for electronic products, primarily driven by the pursuit of longer battery life. Currently, increasing the charging cut-off voltage of battery cells is an effective way to address this issue. However, battery cells can experience short battery life under different operating conditions. 304 stainless steel-cased batteries exhibit deteriorating high-temperature cycle performance, leading to lithium plating on the negative electrode; high-temperature storage causes severe corrosion of the steel casing, resulting in leakage and safety hazards. High-temperature environments also bring a series of new problems. On one hand, the positive electrode material itself is prone to irreversible phase transitions at high temperatures, and the layered structure of lithium cobalt oxide becomes unstable, causing reversible capacity loss. On the other hand, high temperatures result in severe continuous electrolyte consumption, increasing the cell polarization level, and the generated free acid directly corrodes the positive electrode material and internal battery components, causing direct capacity loss and increased cell internal resistance. These problems are more pronounced when batteries are used in high-temperature environments.

[0003] Currently, mannitol carbonate sulfate additive is a commonly used and effective high-temperature additive in power batteries. It can control the continuous growth of free acid and suppress side reactions on the negative electrode during film formation. However, when applied to lithium cobalt oxide systems in consumer batteries, although it can improve high-temperature cycling, it corrodes the steel casing, posing a safety hazard. Therefore, there is an urgent need to improve the existing technology. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a lithium-ion battery with good high-temperature cycle performance and good storage performance.

[0005] The technical solution adopted by the present invention to solve the above problems is as follows:

[0006] A lithium-ion battery includes a positive electrode, a negative electrode, and an electrolyte. The electrolyte includes a first additive (an acid anhydride additive), a second additive (mannitol carbonate sulfate), and ethyl propionate. The negative electrode active material in the negative electrode includes silicon-carbon. The lithium-ion battery satisfies the following relationship:

[0007] S1 / 0.2<150A1+120A2+13A3<S1 / 0.06;

[0008] Wherein, S1 is the mass percentage of ethyl propionate in the solvent, A1 is the mass percentage of the first additive in the electrolyte, A2 is the mass percentage of the second additive in the electrolyte, and A3 is the mass percentage of silicon carbon in the negative electrode active material.

[0009] In the above technical solution, the first additive in the electrolyte mainly functions as an electrolyte stabilizer, inhibiting lithium salt decomposition, controlling the increase of free acid levels, and reacting with oxygen free radicals released from the positive electrode material. It also improves high-temperature corrosion. The second additive in the electrolyte preferentially forms a low-resistance passivation layer at both the positive and negative electrodes, reducing the components of the first additive that form a high-resistance film at the positive electrode. This allows the first additive to primarily function as an electrolyte stabilizer, improving the low-temperature discharge performance of the battery cell and suppressing side reactions between the electrolyte and the positive electrode in high-temperature environments. Ethyl propionate in the electrolyte, as a solvent, has extremely low viscosity and melting point, and extremely high conductivity, which can mitigate the high viscosity of the second additive.

[0010] The lithium-ion battery of the present invention, through the setting of ethyl propionate, the first additive, the second additive, and the silicon-carbon content in the negative electrode active material, makes the lithium-ion battery relationship: S1 / 0.2 < 150A1 + 120A2 + 13A3 < S1 / 0.06, which can effectively improve the high-temperature cycle performance of high-voltage lithium cobalt oxide batteries and have good storage performance.

[0011] Further, the first additive is at least one of succinic anhydride, 2-sulfobenzoic anhydride, butylene anhydride, biphenyl anhydride, NA-anhydride, acrylic anhydride, acetic propionic anhydride, and maleic anhydride.

[0012] Furthermore, based on the total mass of the electrolyte as 100%, the mass percentage of the first additive is 0.75-5.4%.

[0013] Furthermore, based on the total mass of the electrolyte as 100%, the mass percentage of the second additive is 0.5-6.0%.

[0014] Furthermore, the electrolyte also includes lithium salt and organic solvent; based on the total mass of the electrolyte (100%), the mass percentage of lithium salt does not exceed 18%, and the mass percentage of organic solvent is not less than 65%.

[0015] Further, the lithium salt is at least one selected from lithium hexafluorophosphate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorosulfonyl imide, lithium difluoromethyl imide, lithium difluorodioxalate phosphate, and lithium nitrate.

[0016] Further, the organic solvent is two or more of the following: ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl formate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, and ethyl difluoroacetate.

[0017] Furthermore, the electrolyte also includes a third additive, fluoroethylene carbonate; the mass percentage of the third additive is not less than 10% based on the total mass of the electrolyte (100%).

[0018] In the above technical solution, the third additive in the electrolyte is a conventional additive that can form films at the negative and positive electrodes to suppress side reactions between the electrodes and the electrolyte.

[0019] The present invention has the following beneficial effects:

[0020] The lithium-ion battery of the present invention, through the setting of ethyl propionate, the first additive, the second additive, and the silicon-carbon content in the negative electrode active material, makes the lithium-ion battery relationship: S1 / 0.2 < 150A1 + 120A2 + 13A3 < S1 / 0.06, which can effectively improve the high-temperature cycle performance of high-voltage lithium cobalt oxide batteries and have good storage performance. Detailed Implementation

[0021] To make the technical problems, solutions, and advantages of this invention clearer, a detailed description will be provided below with reference to specific examples. However, the scope of protection of this invention is not limited to the following specific embodiments. The described embodiments are merely some, not all, of the embodiments of this invention, and are not intended to limit the invention. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0022] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0023] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0024] This invention is designed for lithium-ion batteries, and includes Examples 1-11 and Comparative Examples 1-3. Some relevant parameters in the formulation are shown in Table 1. All contents in the formulation are mass percentages.

[0025] Table 1. Some relevant parameters in the examples and comparative examples.

[0026]

[0027] The preparation method of the lithium-ion battery in Example 1 specifically includes the following steps:

[0028] Preparation of the positive electrode sheet: The positive electrode active material lithium cobalt oxide (LiCoO2), conductive agent carbon black, binder polyvinylidene fluoride PVDF, and carbon nanotubes (CNT) are mixed in a mass ratio of 98:0.5:1.1:0.4 to obtain a mixture. The mixture is weighed at a mass ratio of 0.2% to N-methylpyrrolidone solvent and added to the N-methylpyrrolidone solvent. The mixture is stirred and mixed thoroughly to form a uniform positive electrode slurry. The positive electrode slurry is coated on the positive electrode current collector Al foil, dried, and then rolled to obtain the positive electrode sheet.

[0029] Preparation of negative electrode sheet: Weigh out the negative electrode active materials graphite, silicon carbide, binder styrene-butadiene rubber, polyacrylic acid, thickener lithium carboxymethyl cellulose, and conductive agent carbon nanotubes (CNT) in a mass ratio of 86.5:10:1.5:1.5:0.25:0.25, and mix them thoroughly in an appropriate amount of deionized water solvent to form a uniform negative electrode slurry; coat the negative electrode slurry onto the negative electrode current collector copper foil, dry it, and roll it to obtain the negative electrode sheet.

[0030] The diaphragm is made of 9μm thick polyethylene (PE) membrane with an aluminum oxide coating.

[0031] Preparation of electrolyte: Lithium salt: lithium hexafluorophosphate (LiPF6) 12.5%; First additive: succinic anhydride 1%; Second additive: mannitol sulfate 0.5%; Third additive: fluoroethylene carbonate 10%; Solvent equals 100% minus the mass percentage of lithium salt and all additives, with ethylene carbonate: propylene carbonate: ethyl propionate = 1:3:6; Mix the above electrolyte raw materials to obtain the electrolyte.

[0032] After welding the tabs to the positive and negative electrodes, the positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as an insulator between the positive and negative electrodes. Then, they are wound to obtain a bare cell. The bare cell is placed in a stainless steel shell, and the prepared electrolyte is injected into the dried bare cell. After vacuum sealing, settling, formation, capacity testing, and aging, a steel-shell lithium-ion battery is obtained.

[0033] The lithium-ion batteries of Examples 2-11 and Comparative Examples 1-3 differ from the lithium-ion battery of Example 1 only in the amount of the first additive and the second additive added. The reduced portions of the first additive and the second additive are replaced by solvents. The preparation methods are similar.

[0034] The lithium-ion batteries of the above embodiments and comparative examples were subjected to performance tests. The test methods are as follows, and the test results are shown in Table 1.

[0035] 1.45℃ Cyclic Experiment:

[0036] The batteries obtained in the examples and comparative examples were placed in an environment of 45±2℃ and left to stand for 2 hours. When the battery body reached 45±2℃, the battery was charged at a constant current of 5C to 4.55V with a cutoff current of 0.05C. After the battery was fully charged, it was left to stand for 5 minutes, and then discharged at a constant current of 0.5C to the cutoff voltage of 3.0V. After the battery was discharged, it was left to stand for 5 minutes. This was recorded as one cycle. The discharge capacity of the third cycle was recorded as the initial capacity Q. When the cycle reached 250 cycles, the discharge capacity Q1 of the last cycle was recorded. The capacity retention rate was Q1 / Q*100%. A capacity retention rate of ≥80% after 250 cycles was considered a pass. At the same time, the lithium plating at the interface was recorded after disassembly. The recorded results are shown in Table 2.

[0037] 2. Storage Experiment:

[0038] The batteries obtained in the examples and comparative examples were placed in an environment of 25±2℃ and left to stand for 2 hours. The batteries were then charged to 4.55V using a constant current and constant voltage method according to standard charging (0.2C), with a cutoff current of 0.05C. They were then discharged to 3V using a constant current method according to standard discharging (0.2C), and the initial discharge capacity Cap0 was recorded. According to storage requirements, the fully charged batteries were placed in different temperature environments for the required time. The batteries were then removed and left to stand at room temperature for 2 hours. They were then discharged to 3V using a constant current method according to standard discharging (0.2C), and the discharge capacity was recorded as the remaining capacity Cap1. A Cap1 / Cap0 ratio ≥ 80% was considered a pass. The battery was charged to 4.55V using a constant current and constant voltage method according to standard charging (0.2C), with a cutoff current of 0.05C. It was then discharged to 3V using a constant current method according to standard discharging (0.2C), and the discharge capacity was recorded as the recovery capacity Cap2. After the test, the battery was observed for leakage. (Note: For the above storage, the Cap2 test was cycled 3 times, and the maximum capacity value was taken; Cap2 / Cap0 ≥ 90%, and the battery showed no leakage on the outside, indicating a pass). The storage conditions for the 70℃-48h storage experiment were: 70℃ for 48 hours; the storage conditions for the 85℃-6h storage experiment were: 85℃ for 6 hours. The calculation formula is as follows:

[0039] Battery capacity retention rate (%) = Cap1 / Cap0 * 100%;

[0040] Battery capacity recovery rate (%) = Cap2 / Cap0 * 100%;

[0041] The test results are recorded in Table 2.

[0042] Table 2 Performance test results of the examples and comparative examples

[0043]

[0044]

[0045] According to the test results in Table 2, the lithium-ion batteries of the present invention have significantly better capacity retention rates at 45°C, 70°C-48h, and 85°C-6h than the lithium-ion batteries of the comparative example. Furthermore, none of the lithium-ion batteries in the examples showed leakage. This indicates that the design of the present invention can effectively improve the high-temperature cycle performance of high-voltage lithium cobalt oxide batteries and has good storage performance.

[0046] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0047] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0048] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A lithium-ion battery, characterized in that, The battery comprises a positive electrode, a negative electrode, and an electrolyte. The electrolyte includes a first additive (an acid anhydride additive), a second additive (mannitol carbonate sulfate), and ethyl propionate. The negative electrode active material in the negative electrode comprises silicon-carbon. The lithium-ion battery satisfies the following relationship: S1 / 0.2<150A1+120A2+13A3<S1 / 0.06; Wherein, S1 is the mass percentage of ethyl propionate in the solvent, A1 is the mass percentage of the first additive in the electrolyte, A2 is the mass percentage of the second additive in the electrolyte, and A3 is the mass percentage of silicon carbon in the negative electrode active material.

2. The lithium-ion battery according to claim 1, characterized in that, The first additive is at least one of succinic anhydride, 2-sulfobenzoic anhydride, butenoic anhydride, biphenyl anhydride, NA-anhydride, acrylic anhydride, acetic propionic anhydride, and maleic anhydride.

3. The lithium-ion battery according to claim 1, characterized in that, Based on the total mass of the electrolyte as 100%, the mass percentage of the first additive is 0.75-5.4%.

4. The lithium-ion battery according to claim 1, characterized in that, Based on the total mass of the electrolyte (100%), the mass percentage of the second additive is 0.5-6.0%.

5. The lithium-ion battery according to claim 1, characterized in that, The electrolyte also includes lithium salt and organic solvent; based on the total mass of the electrolyte (100%), the mass percentage of lithium salt is no more than 18%, and the mass percentage of organic solvent is no less than 65%.

6. The lithium-ion battery according to claim 5, characterized in that, The lithium salt is at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorosulfonyl imide, lithium difluoromethyl imide, lithium difluorodioxalate phosphate, and lithium nitrate.

7. The lithium-ion battery according to claim 5, characterized in that, The organic solvent is two or more of the following: ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl formate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, and ethyl difluoroacetate.

8. The lithium-ion battery according to any one of claims 1-7, characterized in that, The electrolyte also includes a third additive, fluoroethylene carbonate; the mass percentage of the third additive is not less than 10% based on the total mass of the electrolyte (100%).

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