A high-temperature lithium-ion battery electrolyte and a lithium-ion battery containing the same

Abstract

The present invention relates to a high-temperature lithium-ion battery electrolyte and a lithium-ion battery containing the same. The present invention selects tris(trimethylsilyl) phosphate, 2-(3-(trifluoromethyl)-1H-pyrazol-1-yl)acetonitrile, and 1,2,3-trifluorobenzene as additives in the electrolyte. These three components can synergistically improve the high-temperature stability of the electrolyte, reduce the gases generated due to thermal decomposition and side reactions, thereby reducing the risk of abnormal increase in the internal pressure of the battery or battery swelling caused by gas generation during long-term storage at high temperature. At the same time, they can also reduce the influence of impurities in the electrolyte, improve the electrochemical window, help maintain the stability of the electrolyte at high temperature, and extend the battery life.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and specifically relates 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 the fields of consumer electronics and power batteries due to their excellent specific energy, outstanding fast charge and discharge capabilities, and extremely low self-discharge rate. With the popularization of lithium-ion batteries in diverse scenarios, the requirements for battery performance by various electronic devices have become increasingly stringent. Among them, high-temperature cycle life and safety performance have become key indicators for measuring battery quality.

[0003] In a high-temperature environment, the high-temperature cycle life and usage safety of lithium-ion batteries are the solid guarantees for their normal operation. Traditional electrolytes will undergo irreversible oxidative decomposition on the surface of the positive electrode under high voltage, resulting in a series of side reactions such as gas generation, battery swelling, electrode structure damage, transition metal dissolution, and increased polarization voltage, thereby leading to the attenuation of the cycle performance of high-voltage positive electrode materials. Limited choice of additives: Although some additives such as VC, PS, FEC, and DTD can improve the high-temperature storage performance of batteries, they each have some drawbacks. For example, DTD generates a large amount of gas during formation, affecting the subsequent battery performance; FEC has poor high-temperature performance. The positive electrode material may release active oxygen at high temperatures, and these active oxygen 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 rate and recovery rate of the battery will decrease significantly compared to storage at room temperature. For example, for a conventional battery without high-temperature additives, after storing at 45°C for 3 months, the capacity retention rate and capacity recovery rate at 30% SOC / 100% SOC are relatively low. Therefore, while working on improving the high-temperature cycle performance of lithium-ion batteries, we must also pay attention to their thermal shock resistance after cycling. However, current lithium-ion batteries still need to be improved in terms of high-temperature cycle performance and thermal shock resistance, and it is urgent for us to work together to overcome these challenges. Summary of the Invention

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

[0006] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0007] 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. 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 - 1 wt% of the total mass of the lithium-ion battery electrolyte.

[0008] The main components of the additive 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 an alternative component to halogenated alkane carbonates, has higher thermal stability and chemical stability, and can maintain the structure and performance stability of the electrolyte under high-temperature conditions, reducing the generation of gases due to 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 being eroded by the electrolyte, reduce side reactions between the electrolyte and the positive electrode, thereby reducing the risk of gas generation and battery swelling. 1,2,3-Trifluorobenzene has stable thermodynamic properties, can alleviate the decomposition of the electrolyte at high temperature, and reduce the generation of acidic substances, which usually accelerate the decomposition of the electrolyte and the dissolution of positive ions, resulting in a decline in battery performance. 1,2,3-Trifluorobenzene helps to maintain the stability of the 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 electrolyte stability.

[0009] Preferably, the lithium salt is at least one of lithium perchlorate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium bis(fluorosulfonyl)amide, and lithium bis(fluorosulfonyl)imide. The lithium salt of the present invention does not add lithium hexafluorophosphate (LiPF6) because LiPF6 will decompose to produce gases such as hydrogen fluoride in a high-temperature environment. Hydrogen fluoride is not only corrosive but also reacts with other components in the electrolyte to generate more gases, exacerbating the increase in the internal pressure of the battery.

[0010] More preferably, the lithium salt is a composition of lithium difluoro(oxalato)borate and lithium bis(fluorosulfonyl)amide with a mass ratio of 1:(1 - 1.2). Lithium difluoro(oxalato)borate and lithium bis(fluorosulfonyl)amide have high thermal stability and can synergistically improve the high-temperature performance of the electrolyte.

[0011] Preferably, the concentration of the lithium salt in the lithium-ion battery electrolyte is 0.5 - 2 mol / L.

[0012] Preferably, the organic solvent is at least one of propylene carbonate, N-methyl-N-butylpiperidinium bisimide, and ethylene glycol dimethyl ether.

[0013] More preferably, the organic solvent is a composition of propylene carbonate, N-methyl-N-butylpiperidinium bisimide, and ethylene glycol dimethyl ether with a mass ratio of 1:1:(0.5 - 1). The boiling point of propylene carbonate is about 240 °C, which belongs to a high-boiling solvent; N-butyl-N-methylpiperidinium bis(trifluoromethanesulfonyl)imide salt belongs to an ionic liquid and has good thermal stability; the boiling point of ethylene glycol dimethyl ether is 82 - 83 °C, which belongs to a low-boiling solvent. The high-boiling solvent ensures high-temperature stability, slows down the volatilization of the electrolyte, and maintains the stability of the components; the low-boiling solvent improves ion conduction and reduces viscosity. Through the ratio of the three solvents, the high-temperature stability of the electrolyte is synergistically improved.

[0014] In a second aspect, the present invention provides a lithium-ion battery, which includes a positive electrode sheet, a separator, a negative electrode sheet, and the high-temperature type lithium-ion battery electrolyte according to the first aspect.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0016] By adding additives with a specific composition to the lithium-ion battery electrolyte, the present invention enhances the high-temperature stability of the electrolyte and optimizes the use performance of the battery. Specifically, the present invention uses tris(trimethylsilyl) phosphate, 2-(3-(trifluoromethyl)-1H-pyrazol-1-yl)acetonitrile, and 1,2,3-trifluorobenzene as additives. Among them, tris(trimethylsilyl) phosphate replaces haloalkane carbonate, which can enhance the stability of the electrolyte and optimize the use performance of the battery liquid at high temperatures; 2-(3-(trifluoromethyl)-1H-pyrazol-1-yl)acetonitrile can promote the formation of a passivation film and a dense SEI film by oxidation at the positive electrode interface, 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 ions, improves high-temperature cycle and storage stability, forms a stable SEI film, extends the battery life, and has a cost advantage at the same time; these three components synergistically enhance the high-temperature stability of the electrolyte, reduce the gases generated by thermal decomposition and side reactions, thereby reducing the risk of abnormal increase in the internal pressure of the battery or battery swelling caused by gas generation during long-term high-temperature storage of the electrolyte. At the same time, they can also reduce the influence of impurities in the electrolyte, improve the electrochemical window, contribute to maintaining the stability of the electrolyte at high temperatures, and extend the battery life. Specific Embodiments

[0017] To better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0018] The sources of the raw materials used in the following examples and comparative examples are as follows:

[0019] Tris(trimethylsilyl)phosphate: manufacturer is Shanghai Yien Chemical Technology Co., Ltd., model number is R013415;

[0020] 2-(3-(Trifluoromethyl)-1H-pyrazol-1-yl)acetonitrile: manufacturer: Shanghai Chuangyan Chemical Technology Co., Ltd.;

[0021] 1,2,3-Trifluorobenzene: manufacturer is Shanghai Haohong Biopharmaceutical Technology Co., Ltd., model number is 1199476;

[0022] Lithium difluorooxalate borate: manufacturer is Shanghai Haohong Biopharmaceutical Technology Co., Ltd., model number is 1228572;

[0023] Lithium bis(fluorosulfonyl)amide: manufacturer is Shanghai Yuanye Biotechnology Co., Ltd., model number is Y28522;

[0024] Propylene carbonate: manufacturer is Shanghai Haohong Biopharmaceutical Technology Co., Ltd., model number is 1147013;

[0025] N-Methyl-N-butylpiperidinium diimide: the manufacturer is Wuhan Haishan Technology Co., Ltd.;

[0026] Ethylene glycol dimethyl ether: The manufacturer is Shanghai Jizhi Biochemical Technology Co., Ltd., model number is E11800.

[0027] Unless otherwise specified, other materials, reagents, etc. used in the examples can be obtained from commercial sources.

[0028] Example 1

[0029] 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.

[0030] Example 2

[0031] A high-temperature lithium-ion battery electrolyte is composed of a lithium salt, an additive, and an organic solvent. 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, and the content of the additive accounts for 1 wt% of the total mass of the electrolyte; the lithium salt is a composition of lithium difluorooxalate borate and bis(fluorosulfonyl)aminolithium with 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 bisimide, and ethylene glycol dimethyl ether with a mass ratio of 1:1:0.5.

[0032] Example 3

[0033] A high-temperature lithium-ion battery electrolyte is composed of a lithium salt, an additive, and an organic solvent. 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 1:1:3, and the content of the additive accounts for 0.1 wt% of the total mass of the electrolyte; the lithium salt is a composition of lithium difluorooxalate borate and bis(fluorosulfonyl)aminolithium with a mass ratio of 1:1.2, and the concentration of the lithium salt in the lithium-ion battery electrolyte is 2 mol / L; the organic solvent is a composition of propylene carbonate, N-methyl-N-butylpiperidinium bisimide, and ethylene glycol dimethyl ether with a mass ratio of 1:1:1.

[0034] Example 4

[0035] The difference between Example 4 and Example 1 is that propylene carbonate is not added, and N-methyl-N-butylpiperidinium bisimide and ethylene glycol dimethyl ether with a mass ratio of 1:0.7 are used as the organic solvent.

[0036] Example 5

[0037] The difference between Example 5 and Example 1 is that N-methyl-N-butylpiperidinium bisimide 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.

[0038] Example 6

[0039] 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 bisimide with a mass ratio of 1:1 are used as the organic solvent.

[0040] Comparative Example 1

[0041] The difference between Comparative Example 1 and Example 1 lies in that tris(trimethylsilyl) phosphate is not added, and 2-(3-(trifluoromethyl)-1H-pyrazol-1-yl)acetonitrile and 1,2,3-trifluorobenzene with a mass ratio of 1:2 are used as additives.

[0042] Comparative Example 2

[0043] The difference between Comparative Example 2 and Example 1 lies in that 2-(3-(trifluoromethyl)-1H-pyrazol-1-yl)acetonitrile is not added, and tris(trimethylsilyl) phosphate and 1,2,3-trifluorobenzene with a mass ratio of 1:2 are used as additives.

[0044] Comparative Example 3

[0045] The difference between Comparative Example 3 and Example 1 lies in that 1,2,3-trifluorobenzene is not added, and tris(trimethylsilyl) phosphate with a mass ratio of 1:1 and 2-(3-(trifluoromethyl)-1H-pyrazol-1-yl)acetonitrile not added are used as additives.

[0046] Comparative Example 4

[0047] The difference between Comparative Example 4 and Example 1 lies in that tris(trimethylsilyl) phosphate, 2-(3-(trifluoromethyl)-1H-pyrazol-1-yl)acetonitrile, and 1,2,3-trifluorobenzene with a mass ratio of 2:1:1 are used as additives.

[0048] Comparative Example 5

[0049] The difference between Comparative Example 5 and Example 1 lies in that tris(trimethylsilyl) phosphate, 2-(3-(trifluoromethyl)-1H-pyrazol-1-yl)acetonitrile, and 1,2,3-trifluorobenzene with a mass ratio of 1:2:1 are used as additives.

[0050] Application Examples 1-6 and Comparative Application Examples 1-5

[0051] Preparation of the electrolyte: The additives were added to the organic solvent according to the formulation amounts and mixed evenly, and then the lithium salt was added and mixed evenly to obtain the electrolytes of Examples 1-6 and Comparative Examples 1-5 respectively.

[0052] Fabrication of the positive electrode sheet: The positive electrode active material lithium cobaltate (LiCoO2), the conductive agent CNT (Carbon Nanotube), and the binder PVDF (polyvinylidene fluoride) were fully stirred and mixed in an N-methylpyrrolidone solvent at a mass ratio of 97:1.5:1.5 to form a uniform positive electrode paste. This paste was coated on the positive electrode current collector Al foil, dried, and cold-pressed to obtain the positive electrode sheet.

[0053] Fabrication of the negative electrode sheet: Graphite as the negative active material, acetylene black as the conductive agent, styrene-butadiene rubber as the binder, and sodium carboxymethyl cellulose as the thickening agent were thoroughly stirred and mixed in an appropriate amount of deionized water solvent at a mass ratio of 95:2:2:1 to form a uniform negative electrode slurry. This slurry was coated on a negative current collector Cu foil, dried, and cold-pressed to obtain the negative electrode sheet.

[0054] Fabrication of the lithium-ion battery: A PE porous polymer film was used as the separator.

[0055] The positive electrode sheet, the separator, and the negative electrode sheet were stacked in sequence, with the separator placed in the middle of the positive and negative electrodes to play an isolation role. Then, the stacked electrode sheets and the separator were wound to obtain a wound core. The wound core was placed in a formed aluminum-plastic film bag. The electrolytes prepared in Examples 1-6 and Comparative Examples 1-5 were respectively injected into the baked and dried battery. After processes such as vacuum packaging, standing, and formation, the lithium-ion batteries of Application Examples 1-6 and Comparative Application Examples 1-5 were obtained.

[0056] Performance testing

[0057] (1) Battery rate performance testing

[0058] In a constant temperature environment of 25 °C, discharge at 0.2C to 3.0V, stand for 10 min, charge at 0.2C to 4.2V, then charge at a constant voltage of 4.2V until the current is 0.02C, stand for 15 min, and then discharge at 0.2C to 3.0V. The discharge capacity at this time was recorded as C0; stand for 30 min, charge at 0.5C to 4.2V, then charge at a constant voltage of 4.2V until the current is 0.02C, stand for 15 min, and then discharge at 2C to 3.0V. The discharge capacity at this time was recorded as C1. The rate performance = C0 / C1 × 100%. The test results are shown in Table 1.

[0059] (2) 45 °C cycle performance testing of the battery

[0060] At 45 °C, first charge the lithium battery at a constant current of 1C to 4.2V, further charge at a constant voltage of 4.2V until the current is 0.02C, and then discharge the battery at a constant current of 1C to 3.0V. This is a charge-discharge cycle process, and the discharge capacity at this time is the discharge capacity of the first cycle. The battery was subjected to multiple cycle charge-discharge tests in the above manner, and the discharge capacity of the 300th cycle was detected. The capacity retention rate of the battery after cycling was calculated by the following formula. The test results are shown in Table 1.

[0061] ;

[0062] (3) 60 °C (high temperature) storage performance testing of the battery

[0063] Capacity test: At 25 °C, first charge the lithium battery at a constant current of 1C to 4.2V, then charge it at a constant voltage of 4.5V until the current reaches 0.02C, and then discharge the battery at a constant current of 0.2C to 3.0V. This is a charge-discharge cycle process, and record the discharge capacity. Then charge it at a constant current of 1C until 4.2V under constant current and constant voltage, and then transfer it to a high-temperature oven at 60 °C for storage. Conduct a capacity test every 20 days and calculate the capacity retention rate after 100 days. The test results are shown in Table 1.

[0064] Table 1 Battery performance of Application Examples 1-6 and Comparative Application Examples 1-5

[0065] Group / Performance Capacity retention rate after 2C discharge / % Capacity retention rate after 300 cycles at 45°C / % Capacity retention rate after 100 days of storage at 60°C / % 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

[0066] As can be seen from Table 1, combining the data of Application Example 1 and Application Examples 4-6, it can be known that in Example 1, the organic solvents selected are a compound of propylene carbonate, N-methyl-N-butylpiperidine bisimide and ethylene glycol dimethyl ether. The performance of its battery at high temperature is higher than that of Examples 4-5. This may be because the combination of a low-boiling-point solvent, a high-boiling-point solvent and an ionic liquid can synergistically improve the high-temperature stability of the electrolyte.

[0067] Combining the data of Application Example 1 and Comparative Application Examples 1-3, it can be known 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 performance of the battery at high temperature is better. When any one of tris(trimethylsilyl) phosphate, 1,2,3-trifluorobenzene and 2-(3-(trifluoromethyl)-1H-pyrazol-1-yl)acetonitrile is missing, the performance of the battery drops significantly.

[0068] Combining the data of Application Examples 1-3 and Comparative Application Examples 4-5, it can be known 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 an excellent level.

[0069] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions 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(trimethylsilane)phosphate, 2-(3-(trifluoromethyl)-1H-pyrazol-1-yl)acetonitrile and 1,2,3-trifluorobenzene, the mass ratio of 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 electrolyte; 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).

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. 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 4.