High-temperature lithium ion battery electrolyte and lithium ion battery containing same

Abstract

According to the high-temperature lithium ion battery electrolyte and the lithium ion battery containing the high-temperature lithium ion battery electrolyte, tris (trimethylsilane) phosphate, 2-(3-(trifluoromethyl)-1H-pyrazol-1-yl) acetonitrile and 1, 2, 3-trifluorobenzene are selected as additives in the electrolyte, and the three components can synergistically improve the high-temperature stability of the electrolyte, so that the high-temperature stability of the electrolyte is improved; and gas generated by thermal decomposition and side reaction is reduced, so that the risk that the internal pressure of the battery is abnormally increased or the battery swells due to the gas generated by the electrolyte in the high-temperature long-term storage process is reduced. Meanwhile, the influence of impurities in the electrolyte can be reduced, an electrochemical window is improved, the stability of the electrolyte can be kept at high temperature, and the service life of the battery can be prolonged.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and in particular to a high-temperature lithium-ion battery electrolyte and a lithium-ion battery containing the same. Background Art

[0002] Lithium-ion batteries have been widely used in consumer electronics and power batteries due to their excellent specific energy, fast charging and discharging capabilities, and extremely low self-discharge rate. With the popularity of lithium-ion batteries in diversified scenarios, various electronic devices have increasingly stringent requirements on battery performance, among which high-temperature cycle life and safety performance have become key indicators for measuring battery quality.

[0003] In high temperature environments, the high temperature cycle life and safety of lithium-ion batteries are solid guarantees for their normal operation. Conventional electrolytes will undergo irreversible oxidative decomposition on the surface of the positive electrode under high voltage, leading to a series of side reactions such as gas generation, battery swelling, electrode structure damage, transition metal dissolution, and increased polarization voltage, which will lead to the attenuation of the cycle performance of high-voltage positive electrode materials. Limited additive selection: Although some additives such as VC, PS, FEC and DTD can improve the high temperature storage performance of batteries, they each have some disadvantages. For example, DTD produces a large amount of gas during formation, which affects the later battery performance; FEC has poor high temperature performance. Positive electrode materials may release reactive oxygen at high temperatures, which will oxidize the solvent in the electrolyte, further affecting the stability of the battery.

[0004] During storage at high temperature (≥45°C), the capacity retention and recovery rates of the battery will be significantly lower than those at room temperature. For example, after a conventional battery without high-temperature additives was stored at 45°C for 3 months, the capacity retention and capacity recovery rates at 30%SOC / 100%SOC were lower. Therefore, while we are committed to improving the high-temperature cycle performance of lithium-ion batteries, we must also pay attention to their resistance to thermal shock after cycling. However, the current lithium-ion batteries still need to be improved in terms of high-temperature cycle performance and thermal shock resistance, and we urgently need to work together to overcome these challenges. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a high-temperature lithium-ion battery electrolyte having the advantages of high temperature resistance and thermal shock resistance and a lithium-ion battery containing the electrolyte.

[0006] To achieve the above object, the technical solution adopted by the present invention is: In a first aspect, the present invention provides a high-temperature lithium-ion battery electrolyte, which is composed of a lithium salt, an additive and an organic solvent, wherein the additive includes tris(trimethylsilane)phosphate, 2-(3-(trifluoromethyl)-1H-pyrazol-1-yl)acetonitrile and 1,2,3-trifluorobenzene, and the mass ratio of the tris(trimethylsilane)phosphate, 2-(3-(trifluoromethyl)-1H-pyrazol-1-yl)acetonitrile and 1,2,3-trifluorobenzene is 1:1:(1.5-3), and the content of the additive accounts for 0.1-1wt% of the total mass of the lithium-ion battery electrolyte.

[0007] The main components of the additives in the electrolyte of the present invention are tris(trimethylsilyl)phosphate, 2-(3-(trifluoromethyl)-1H-pyrazol-1-yl)acetonitrile and 1,2,3-trifluorobenzene. Among them, tris(trimethylsilyl)phosphate, as a substitute for halogenated alkane carbonate, has higher thermal stability and chemical stability, can maintain the structure and performance stability of the electrolyte under high temperature conditions, and reduce the gas generated by thermal decomposition. 2-(3-(trifluoromethyl)-1H-pyrazol-1-yl)acetonitrile can promote oxidation at the positive electrode interface to form a passivation film and a dense solid electrolyte interface (SEI) film, which can protect the positive electrode material from erosion by the electrolyte, reduce the side reaction between the electrolyte and the positive electrode, and thus reduce the risk of gas generation and battery bulging. 1,2,3-Trifluorobenzene has stable thermodynamic properties, which can alleviate the decomposition of electrolyte at high temperature and reduce the generation of acidic substances. These acidic substances usually accelerate the decomposition of electrolyte and the dissolution of positive electrode ions, thus causing the battery performance to decline. 1,2,3-Trifluorobenzene helps maintain the stability of electrolyte and reduce gas generation by reducing the generation of these harmful substances. The synergistic effect of these three components can not only improve the stability of the electrolyte itself, but also reduce the impact of impurities in the electrolyte on the stability of the electrolyte.

[0008] Preferably, the lithium salt is at least one of lithium perchlorate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium bis(oxalatoborate), lithium difluoro(oxalatoborate), lithium bis(fluorosulfonyl)amide, and lithium bis(fluorosulfonyl)imide. The lithium salt of the present invention does not contain lithium hexafluorophosphate (LiPF6) because LiPF6 decomposes to produce gases such as hydrogen fluoride under high temperature. Hydrogen fluoride is not only corrosive, but also further reacts with other components in the electrolyte to generate more gases, exacerbating the increase in gas pressure inside the battery.

[0009] More preferably, the lithium salt is a composition of lithium difluorooxalatoborate and lithium bis(fluorosulfonyl)amide in a mass ratio of 1:(1-1.2). Lithium difluorooxalatoborate and lithium bis(fluorosulfonyl)amide have high thermal stability and can synergistically improve the high temperature performance of the electrolyte.

[0010] Preferably, the concentration of the lithium salt in the lithium ion battery electrolyte is 0.5-2 mol / L.

[0011] Preferably, the organic solvent is at least one of propylene carbonate, N-methyl-N-butylpiperidinium diimide and ethylene glycol dimethyl ether.

[0012] More preferably, the organic solvent is a composition of propylene carbonate, N-methyl-N-butylpiperidinium diimide and ethylene glycol dimethyl ether in a mass ratio of 1:1:(0.5-1). The boiling point of propylene carbonate is about 240°C, which is a high boiling point solvent; N-butyl-N-methylpiperidinium bis(trifluoromethanesulfonyl)imide salt is an ionic liquid with good thermal stability; ethylene glycol dimethyl ether has a boiling point of 82-83°C, which is a low boiling point solvent. High boiling point solvents ensure high temperature stability, slow down the volatilization of the electrolyte, and maintain component stability; low boiling point solvents improve ion conduction and reduce viscosity. The three solvents are proportioned to synergistically improve the high temperature stability of the electrolyte.

[0013] In a second aspect, the present invention provides a lithium-ion battery, comprising a positive electrode sheet, a separator, a negative electrode sheet and the high-temperature lithium-ion battery electrolyte described in the first aspect.

[0014] Compared with the prior art, the present invention has the following beneficial effects: The invention enhances the high temperature stability of the electrolyte and optimizes the use performance of the battery by adding additives of specific composition into the electrolyte of the lithium ion battery. Specifically, the present invention uses tris(trimethylsilyl)phosphate, 2-(3-(trifluoromethyl)-1H-pyrazol-1-yl)acetonitrile and 1,2,3-trifluorobenzene as additives, wherein tris(trimethylsilyl)phosphate replaces halogenated alkane carbonate, which can enhance the stability of the electrolyte and optimize the performance of the battery liquid at high temperature; 2-(3-(trifluoromethyl)-1H-pyrazol-1-yl)acetonitrile can promote oxidation at the positive electrode interface to form a passivation film and a dense SEI film, thereby improving thermal stability and high temperature tolerance; 1,2,3-trifluorobenzene, as a polyfluorinated benzene compound, has stable thermodynamic properties, alleviates the decomposition of acidic substances in the electrolyte, reduces the dissolution of positive electrode ions, improves high-temperature cycle and storage stability, forms a stable SEI film, extends the battery life, and has cost advantages; these three components synergistically enhance the high-temperature stability of the electrolyte, reduce the gas generated by thermal decomposition and side reactions, thereby reducing the risk of abnormal increase in battery internal pressure or battery bulging caused by gas production during long-term storage at high temperature. At the same time, they can also reduce the impact of impurities in the electrolyte, improve the electrochemical window, help maintain the stability of the electrolyte at high temperatures, and extend battery life. DETAILED DESCRIPTION

[0015] In order to better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0016] The sources of the raw materials used in the following examples and comparative examples are as follows: Tris(trimethylsilyl)phosphate: manufacturer is Shanghai Yien Chemical Technology Co., Ltd., model number is R013415; 2-(3-(Trifluoromethyl)-1H-pyrazol-1-yl)acetonitrile: manufacturer: Shanghai Chuangyan Chemical Technology Co., Ltd.; 1,2,3-Trifluorobenzene: manufacturer is Shanghai Haohong Biopharmaceutical Technology Co., Ltd., model number is 1199476; Lithium difluorooxalate borate: manufacturer is Shanghai Haohong Biopharmaceutical Technology Co., Ltd., model number is 1228572; Lithium bis(fluorosulfonyl)amide: manufacturer is Shanghai Yuanye Biotechnology Co., Ltd., model number is Y28522; Propylene carbonate: manufacturer is Shanghai Haohong Biopharmaceutical Technology Co., Ltd., model number is 1147013; N-Methyl-N-butylpiperidinium diimide: the manufacturer is Wuhan Haishan Technology Co., Ltd.; Ethylene glycol dimethyl ether: The manufacturer is Shanghai Jizhi Biochemical Technology Co., Ltd., model number is E11800.

[0017] Unless otherwise specified, other materials, reagents, etc. used in the examples can be obtained from commercial sources.

[0018] Example 1 A high-temperature lithium-ion battery electrolyte consists of a lithium salt, an additive and an organic solvent, wherein the additive comprises tris(trimethylsilyl)phosphate, 2-(3-(trifluoromethyl)-1H-pyrazol-1-yl)acetonitrile and 1,2,3-trifluorobenzene, wherein the mass ratio of the tris(trimethylsilyl)phosphate, 2-(3-(trifluoromethyl)-1H-pyrazol-1-yl)acetonitrile and 1,2,3-trifluorobenzene is 1:1:2, and the content of the additive accounts for 0.5wt% of the total mass of the electrolyte; the lithium salt is a composition of lithium difluorooxalatoborate and lithium bis(fluorosulfonyl)amide in a mass ratio of 1:1.3, and the concentration of the lithium salt in the lithium-ion battery electrolyte is 1 mol / L; and the organic solvent is a composition of propylene carbonate, N-methyl-N-butylpiperidinium diimide and ethylene glycol dimethyl ether in a mass ratio of 1:1:0.7.

[0019] Example 2 A high-temperature lithium-ion battery electrolyte is composed of a lithium salt, an additive and an organic solvent. The additive comprises tris(trimethylsilyl)phosphate, 2-(3-(trifluoromethyl)-1H-pyrazol-1-yl)acetonitrile and 1,2,3-trifluorobenzene. The mass ratio of tris(trimethylsilyl)phosphate, 2-(3-(trifluoromethyl)-1H-pyrazol-1-yl)acetonitrile and 1,2,3-trifluorobenzene is 1:1:1.5, and the content of the additive accounts for 1wt% of the total mass of the electrolyte. The lithium salt is a composition of lithium difluorooxalatoborate and lithium bis(fluorosulfonyl)amide in a mass ratio of 1:1, and the concentration of the lithium salt in the lithium-ion battery electrolyte is 0.5 mol / L. The organic solvent is a composition of propylene carbonate, N-methyl-N-butylpiperidinium diimide and ethylene glycol dimethyl ether in a mass ratio of 1:1:0.5.

[0020] Example 3 A high-temperature lithium-ion battery electrolyte consists of a lithium salt, an additive and an organic solvent, wherein the additive comprises tris(trimethylsilyl)phosphate, 2-(3-(trifluoromethyl)-1H-pyrazol-1-yl)acetonitrile and 1,2,3-trifluorobenzene, wherein the mass ratio of the tris(trimethylsilyl)phosphate, 2-(3-(trifluoromethyl)-1H-pyrazol-1-yl)acetonitrile and 1,2,3-trifluorobenzene is 1:1:3, and the content of the additive accounts for 0.1wt% of the total mass of the electrolyte; the lithium salt is a composition of lithium difluorooxalatoborate and lithium bis(fluorosulfonyl)amide in a mass ratio of 1:1.2, and the concentration of the lithium salt in the lithium-ion battery electrolyte is 2 mol / L; and the organic solvent is a composition of propylene carbonate, N-methyl-N-butylpiperidinium diimide and ethylene glycol dimethyl ether in a mass ratio of 1:1:1.

[0021] Example 4 The difference between Example 4 and Example 1 is that propylene carbonate is not added, and N-methyl-N-butylpiperidinium diimide and ethylene glycol dimethyl ether in a mass ratio of 1:0.7 are used as the organic solvent.

[0022] Example 5 The difference between Example 5 and Example 1 is that: N-methyl-N-butylpiperidinium diimide is not added, and propylene carbonate and ethylene glycol dimethyl ether with a mass ratio of 1:0.7 are used as the organic solvent.

[0023] Example 6 The difference between Example 5 and Example 1 is that ethylene glycol dimethyl ether is not added, and propylene carbonate and N-methyl-N-butylpiperidinium diimide in a mass ratio of 1:1 are used as the organic solvent.

[0024] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that tris(trimethylsilyl)phosphate is not added, and 2-(3-(trifluoromethyl)-1H-pyrazol-1-yl)acetonitrile and 1,2,3-trifluorobenzene in a mass ratio of 1:2 are used as additives.

[0025] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that: 2-(3-(trifluoromethyl)-1H-pyrazol-1-yl)acetonitrile is not added, and tris(trimethylsilyl)phosphate and 1,2,3-trifluorobenzene in a mass ratio of 1:2 are used as additives.

[0026] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that 1,2,3-trifluorobenzene is not added, tris(trimethylsilyl)phosphate with a mass ratio of 1:1 is used, and 2-(3-(trifluoromethyl)-1H-pyrazol-1-yl)acetonitrile is not added as an additive.

[0027] Comparative Example 4 The difference between Comparative Example 4 and Example 1 is that tris(trimethylsilyl)phosphate, 2-(3-(trifluoromethyl)-1H-pyrazol-1-yl)acetonitrile and 1,2,3-trifluorobenzene in a mass ratio of 2:1:1 are used as additives.

[0028] Comparative Example 5 The difference between Comparative Example 5 and Example 1 is that tris(trimethylsilyl)phosphate, 2-(3-(trifluoromethyl)-1H-pyrazol-1-yl)acetonitrile and 1,2,3-trifluorobenzene in a mass ratio of 1:2:1 are used as additives.

[0029] Application Example 1-6 and Comparative Application Example 1-5 Preparation of electrolyte: Add additives according to the formula amount into the organic solvent and mix evenly, then add lithium salt and mix evenly to obtain the electrolytes of Examples 1-6 and Comparative Examples 1-5, respectively.

[0030] Preparation of positive electrode sheet: The positive electrode active material lithium cobalt oxide (LiCoO2), the conductive agent CNT (Carbon Nanotube), and the binder PVDF (polyvinylidene fluoride) are fully stirred and mixed in N-methylpyrrolidone solvent at a mass ratio of 97:1.5:1.5 to form a uniform positive electrode slurry. The slurry is coated on the positive electrode current collector Al foil, dried, and cold pressed to obtain a positive electrode sheet.

[0031] Preparation of negative electrode sheet: The negative electrode active material graphite, the conductive agent acetylene black, the binder styrene butadiene rubber, and the thickener sodium carboxymethyl cellulose are fully stirred and mixed in a proper amount of deionized water solvent at a mass ratio of 95:2:2:1 to form a uniform negative electrode slurry. The slurry is coated on the negative electrode current collector Cu foil, dried, and cold pressed to obtain a negative electrode sheet.

[0032] Production of lithium-ion batteries: PE porous polymer film is used as the separator.

[0033] The positive electrode sheet, the separator and the negative electrode sheet are stacked in order, so that the separator is located between the positive and negative electrodes to play a role of isolation, and then the stacked electrode sheet and the separator are wound to obtain a winding core. The winding core is placed in an aluminum-plastic film bag that has been punched and formed, and the electrolytes prepared in Examples 1-6 and Comparative Examples 1-5 are respectively injected into the baked and dried batteries, and after vacuum packaging, standing, formation and other processes, the lithium-ion batteries of Application Examples 1-6 and Comparative Application Examples 1-5 are obtained.

[0034] Performance Testing (1) Battery rate performance test Under a constant temperature environment of 25℃, discharge to 3.0V at 0.2C, stand for 10min, charge to 4.2V at 0.2C, then charge at constant voltage at 4.2V to a current of 0.02C, stand for 15min, and then discharge to 3.0V at 0.2C. The discharge capacity at this time is recorded as C0; stand for 30min, charge to 4.2V at 0.5C, then charge at constant voltage at 4.2V to a current of 0.02C, stand for 15min, and then discharge to 3.0V at 2C. The discharge capacity at this time is recorded as C1. Rate performance = C0 / C1×100%. The test results are shown in Table 1.

[0035] (2) Battery cycle performance test at 45°C At 45°C, the lithium battery is first charged to 4.2V at a constant current of 1C, then further charged to a current of 0.02C at a constant voltage of 4.2V, and then discharged to 3.0V at a constant current of 1C. This is a charge and discharge cycle process, and the discharge capacity this time is the discharge capacity of the first cycle. The battery is subjected to multiple cycle charge and discharge tests in the above manner, and the discharge capacity of the 300th cycle is detected, and the capacity retention rate of the battery after the cycle is calculated by the following formula. The test results are shown in Table 1.

[0036] ; (3) Battery storage performance test at 60°C (high temperature) Capacity test: At 25°C, the lithium battery was first charged to 4.2V at a constant current of 1C, and then further charged to a current of 0.02C at a constant voltage of 4.5V, and then discharged to 3.0V at a constant current of 0.2C. This was a charge and discharge cycle, and the discharge capacity was recorded; then charged to 4.2V at a current of 1C, constant current and constant voltage, and then transferred to a high temperature box at 60°C for storage; a capacity test was performed every 20 days, and the 100-day capacity retention rate was calculated. The test results are shown in Table 1.

[0037] Table 1 Battery performance of application examples 1-6 and comparative application examples 1-5 Group / Performance Capacity retention rate after 2C discharge / % Capacity retention rate after 300 cycles at 45℃ / % Capacity retention after 100 days storage at 60℃ / % Application Example 1 97.60 93.72 92.53 Application Example 2 97.27 93.12 92.13 Application Example 3 97.35 93.19 92.30 Application Example 4 93.39 90.16 88.32 Application Example 5 93.48 90.03 88.39 Application Example 6 93.62 90.32 88.86 Comparative application example 1 50.85 46.33 45.44 Comparative Application Example 2 50.81 46.28 45.26 Comparative Application Example 3 51.21 46.65 45.93 Comparative Application Example 4 66.47 62.87 64.10 Comparative Application Example 5 66.59 63.34 64.43 It can be seen from Table 1 that, combined with the data of Application Example 1 and Application Examples 4-6, the organic solvent of Example 1 is a compound of three solvents: propylene carbonate, N-methyl-N-butylpiperidinyl diimide and ethylene glycol dimethyl ether, and its battery performance at high temperature is higher than that of Examples 4-5. This may be because the combination of low boiling point solvent, high boiling point solvent and ionic liquid can synergistically improve the high temperature stability of the electrolyte.

[0038] Combining the data of Application Example 1 and Comparative Application Examples 1-3, it can be seen that the type of additive has a great influence on the high temperature performance of the battery. When tris(trimethylsilyl) phosphate, 1,2,3-trifluorobenzene and 2-(3-(trifluoromethyl)-1H-pyrazol-1-yl)acetonitrile are used in combination, the battery performs better at high temperatures. When any one of tris(trimethylsilyl) phosphate, 1,2,3-trifluorobenzene and 2-(3-(trifluoromethyl)-1H-pyrazol-1-yl)acetonitrile is missing, the battery performance is significantly reduced.

[0039] Combining the data of Application Examples 1-3 and Comparative Application Examples 4-5, it can be seen that when the mass ratio of tris(trimethylsilyl) phosphate, 2-(3-(trifluoromethyl)-1H-pyrazol-1-yl)acetonitrile, and 1,2,3-trifluorobenzene is 1:1:(1.5-3), the high temperature performance of the battery reaches a better level.

[0040] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A high temperature lithium ion battery electrolyte, comprising a lithium salt, an additive and an organic solvent, characterized in that: The additive includes tris(trimethylsilyl)phosphate, 2-(3-(trifluoromethyl)-1H-pyrazol-1-yl)acetonitrile and 1,2,3-trifluorobenzene, the mass ratio of tris(trimethylsilyl)phosphate, 2-(3-(trifluoromethyl)-1H-pyrazol-1-yl)acetonitrile and 1,2,3-trifluorobenzene is 1:1:(1.5-3), and the content of the additive accounts for 0.1-1wt% of the total mass of the electrolyte.

2. The high temperature lithium ion battery electrolyte according to claim 1, characterized in that: The lithium salt is at least one of lithium perchlorate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium bis(oxalatoborate), lithium difluoro(oxalatoborate), lithium bis(fluorosulfonyl)amide, and lithium bis(fluorosulfonyl)imide.

3. The high temperature lithium ion battery electrolyte according to claim 1 or 2, characterized in that: The lithium salt is a composition of lithium difluorooxalatoborate and lithium bis(fluorosulfonyl)amide in a mass ratio of 1:(1-1.2).

4. The high temperature lithium ion battery electrolyte according to claim 1, characterized in that: The concentration of the lithium salt in the lithium ion battery electrolyte is 0.5-2 mol / L.

5. The high temperature lithium ion battery electrolyte according to claim 1, characterized in that: The organic solvent is at least one of propylene carbonate, N-methyl-N-butylpiperidinium diimide and ethylene glycol dimethyl ether.

6. The high temperature lithium ion battery electrolyte according to claim 1 or 5, characterized in that: The organic solvent is a composition of propylene carbonate, N-methyl-N-butylpiperidinium diimide and ethylene glycol dimethyl ether in a mass ratio of 1:1:(0.5-1).

7. A lithium ion battery, characterized in that: The lithium-ion battery comprises a positive electrode sheet, a separator, a negative electrode sheet and a high-temperature lithium-ion battery electrolyte according to any one of claims 1 to 6.