Electrolyte and lithium ion battery

Abstract

The application provides an electrolyte and a lithium ion battery. The electrolyte comprises an organic solvent, a lithium salt electrolyte and an additive. The additive comprises a nitrile compound containing a benzene ring structure and a carbon-carbon double bond, and a nitrile compound containing triphenylamine and a sulfonyl fluoride group. In the electrolyte, the content of the nitrile compound containing the benzene ring structure and the carbon-carbon double bond is 0.3-1.2% by weight, and the content of the nitrile compound containing the triphenylamine and the sulfonyl fluoride group is 0.3-1.2% by weight. The electrolyte solves the problem of poor high-temperature cycle performance and high-temperature storage performance of the lithium ion battery in the prior art.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of lithium ion batteries, in particular to an electrolyte and a lithium ion battery. BACKGROUND

[0002] Lithium ion batteries are widely used in digital, energy storage, power, military aerospace and communication equipment fields due to their high energy density, high output power and high charging efficiency. However, in lithium ion batteries, the oxidation decomposition of the electrolyte, especially the increased reaction rate of the oxidation decomposition of the electrolyte under high temperature conditions, causes the capacity of the battery to quickly decay under high temperature, and is often accompanied by the dissolution of metal ions during high temperature cycling and high temperature storage, resulting in poor high temperature cycling performance and high temperature storage performance, and serious decline in battery performance. With the increasing demand for lithium ion batteries in the market, higher demands are placed on the comprehensive performance of the battery, so it is of great significance to provide an electrolyte that can improve the high temperature cycling and high temperature storage performance. SUMMARY

[0003] The main purpose of the present application is to provide an electrolyte and a lithium ion battery to solve the problem of poor high temperature cycling performance and high temperature storage performance of lithium ion batteries in the prior art.

[0004] To achieve the above-mentioned purpose, the present application provides an electrolyte, comprising an organic solvent, a lithium salt electrolyte and an additive, the additive comprising a nitrile compound containing a benzene ring structure and a carbon-carbon double bond, and a nitrile compound containing triphenylamine and a sulfonyl fluoride group.

[0005] In the electrolyte, the content of the nitrile compound containing a benzene ring structure and a carbon-carbon double bond is 0.3% to 1.2% by weight, and the content of the nitrile compound containing triphenylamine and a sulfonyl fluoride group is 0.3% to 1.2% by weight.

[0006] The structure of the nitrile compound containing triphenylamine and a sulfonyl fluoride group is shown in formula I

[0007]

[0008] Further, the nitrile compound containing a benzene ring structure and a carbon-carbon double bond is selected from at least one of cyanostilbene, 1,4-bis(4-cyanostyryl)benzene and 4,4'-dicyanostilbene.

[0009] Further, the content of the nitrile compound containing triphenylamine and a sulfonyl fluoride group is 0.3% to 0.5%.

[0010] Further, the content of the nitrile compound containing a benzene ring structure and a carbon-carbon double bond is 0.3% to 0.5%.

[0011] Further, the organic solvent includes at least one of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate.

[0012] Further, the organic solvent is obtained by mixing ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate in a volume ratio of (20-40):(0-15):(0-20):(0-20):(30-60).

[0013] Further, the lithium salt electrolyte is selected from at least one of lithium hexafluorophosphate (LiPF6), lithium perchlorate, lithium tetrafluoroborate, lithium bisfluorooxalate borate, lithium bis(trifluoromethylsulfonyl)imide, and lithium bisfluorosulfonylimide.

[0014] Further, in the electrolyte, the concentration of the lithium salt electrolyte is 0.8-1.5 mol / L.

[0015] Further, the electrolyte further includes a carbonate-based additive, and the carbonate-based additive is selected from at least one of vinylene carbonate (VC) and fluoroethylene carbonate (FEC).

[0016] Further, in the electrolyte, the content of the carbonate-based additive is 0.2%-1.5% by weight.

[0017] Further, the electrolyte further includes a lithium salt additive, and the lithium salt additive is selected from at least one of lithium bisfluorosulfonylimide (LiFSI), lithium difluorophosphate (LiPO2F2), lithium bisoxalate borate (LiBOB), and lithium difluorobisoxalate phosphate (LiODFP).

[0018] Further, in the electrolyte, the content of the lithium salt additive is 0.3%-1.5% by weight.

[0019] Further, the electrolyte further includes a sulfur-containing additive, and the sulfur-containing additive is selected from at least one of 1,3-propane sultone (PS), 1,3-propene sultone (PST), vinylene sulfide-containing acid (DTD), and methylene methylene disulfonate (MMDS).

[0020] Further, in the electrolyte, the content of the sulfur-containing additive is 0.5%-1.5% by weight.

[0021] According to another aspect of the present application, a lithium ion battery is provided, which includes the electrolyte as above.

[0022] Further, the lithium ion battery comprises a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator, the positive electrode sheet comprises a positive electrode active material, the positive electrode active material is a ternary material, the negative electrode sheet comprises a negative electrode active material, and the negative electrode active material is graphite and / or silicon carbon.

[0023] By using the technical solution of the present application, on the one hand, the unsaturated functional group C=C in the nitrile compound containing a benzene ring structure and a carbon-carbon double bond can be oxidized and reduced, and participate in the formation of positive and negative electrodes, thereby improving the stability of the positive and negative electrode interfaces of the lithium ion battery, so that the high-temperature cycle performance and the high-temperature storage performance of the lithium ion battery can be improved; on the other hand, the sulfonyl fluoride group in the nitrile compound containing triphenylamine and a sulfonyl fluoride group as shown in formula I can participate in the formation of the positive electrode, has a protective effect on the positive electrode, reduces the dissolution of transition metal ions in the positive electrode, improves the stability of the positive electrode interface of the lithium ion battery, and the nitrile compound containing triphenylamine and a sulfonyl fluoride group has high-temperature stability; in addition, more HF is easily generated by the decomposition of LiPF6 and other lithium salts in the electrolyte at high temperature, the CN groups in the two additives have strong electronegativity, can effectively combine the HF generated by the electrolyte, effectively reduce the acidity of the electrolyte, reduce the corrosion of the positive electrode to avoid the destruction of the structure of the positive electrode material, reduce the dissolution of transition metal ions in the positive electrode, and avoid the dissolved metal ions from passing through the solid electrolyte interface film (SEI film) to reach the negative electrode to obtain electrons and be reduced to metal elements, thereby destroying the structure of the SEI film, thereby stabilizing the positive and negative electrode interfaces of the lithium ion battery, improving the high-temperature storage and high-temperature cycle performance of the lithium ion battery, and delaying the capacity decay of the battery at high temperature.

[0024] The electrolyte of the present application can improve the stability of the positive and negative electrode interfaces of the lithium ion battery, improve the high-temperature cycle performance and the high-temperature storage performance of the lithium ion battery, and delay the capacity decay of the battery at high temperature. DETAILED DESCRIPTION

[0025] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict.

[0026] As described in the background, the prior art has the problem of poor high-temperature cycle performance and high-temperature storage performance of the lithium ion battery. In order to solve the above problem, the present application provides an electrolyte, which comprises an organic solvent, a lithium salt electrolyte and an additive, the additive comprises a nitrile compound containing a benzene ring structure and a carbon-carbon double bond, and a nitrile compound containing triphenylamine and a sulfonyl fluoride group;

[0027] In the electrolyte, the content of the nitrile compound containing a benzene ring structure and a carbon-carbon double bond is 0.3% to 1.2% by weight, and the content of the nitrile compound containing triphenylamine and a sulfonyl fluoride group is 0.3% to 1.2% by weight;

[0028] The structure of the nitrile compound containing triphenylamine and a sulfonyl fluoride group is shown as formula I

[0029]

[0030] In order to improve the high-temperature storage and high-temperature cycle performance of the lithium ion battery, the application provides an electrolyte. On the one hand, the unsaturated functional group C=C in the nitrile compound containing a benzene ring structure and a carbon-carbon double bond can be oxidized and reduced, participate in the film formation of the positive and negative electrodes, and improve the stability of the positive and negative electrode interfaces of the lithium ion battery, thereby improving the high-temperature cycle performance and high-temperature storage performance of the lithium ion battery. On the other hand, the sulfuryl fluoride group in the nitrile compound containing triphenylamine and a sulfuryl fluoride group shown in formula I participates in the film formation of the positive electrode and forms a dense film layer, has a good protective effect on the positive electrode, reduces the dissolution of the transition metal of the positive electrode, improves the stability of the positive electrode interface of the lithium ion battery, reduces the capacity attenuation and volume expansion of the battery in the high-temperature storage of the lithium ion battery, and the nitrile compound containing triphenylamine and a sulfuryl fluoride group has high-temperature stability. In addition, more HF is easily decomposed from LiPF6 and other lithium salts in the electrolyte at high temperature, the CN groups in the two additives have strong electronegativity, can effectively combine the HF generated in the electrolyte, effectively reduce the acidity of the electrolyte, reduce the corrosion of the positive electrode to avoid the structure damage of the positive electrode material, reduce the dissolution of the transition metal ion of the positive electrode, and avoid the dissolved metal ion from passing through the solid electrolyte interface film (SEI film) to reach the negative electrode to obtain electrons and be reduced into metal elements, thereby destroying the structure of the SEI film, thereby stabilizing the positive and negative electrode interfaces of the lithium ion battery, improving the high-temperature storage and high-temperature cycle performance of the lithium ion battery, and delaying the capacity attenuation of the battery at high temperature. The electrolyte of the application can improve the stability of the positive and negative electrode interfaces of the lithium ion battery, improve the high-temperature cycle performance and high-temperature storage performance of the lithium ion battery, and delay the capacity attenuation of the battery at high temperature.

[0031] In some embodiments, the nitrile compound containing a benzene ring structure and a carbon-carbon double bond is selected from at least one of cyano styrene, 1,4-bis(4-cyanostyryl)benzene, and 4,4'-dicyano-stilbene.

[0032] The nitrile compound containing a benzene ring structure and a carbon-carbon double bond is used to participate in the film formation of the positive and negative electrodes, thereby improving the stability of the positive and negative electrode interfaces of the lithium ion battery, and the formed film layer has good conductivity to lithium ions, thereby reducing the impedance of the battery.

[0033] In some embodiments, the content of the nitrile compound containing triphenylamine and a sulfuryl fluoride group is 0.3% to 0.5%.

[0034] Under the above content, the lithium ion battery has a low DCR growth rate, can reduce the heat generation level of the battery, improve the safety performance of the battery, and reduce the capacity attenuation of the battery.

[0035] In some embodiments, the content of the nitrile compound containing benzene ring structure and carbon-carbon double bond is 0.3% to 0.5%. The lithium ion battery has a low DCR growth rate, reduces the battery impedance and heat production, improves the safety performance of the battery, and reduces the capacity attenuation of the battery.

[0036] In some embodiments, the organic solvent includes at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate. The above organic solvents not only can effectively dissolve the lithium salt electrolyte, but also can provide good ion transmission performance, thereby improving the energy density and power density of the battery.

[0037] In an embodiment, the organic solvent is obtained by mixing ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate according to a volume ratio of (20-40):(0-15):(0-20):(0-20):(30-60). The above solvent ratio has good fast-charging performance of the power battery and high electrolyte wettability, which is beneficial to prevent lithium precipitation during overcharging.

[0038] In some embodiments, the lithium salt electrolyte is selected from at least one of lithium hexafluorophosphate (LiPF6), lithium perchlorate, lithium tetrafluoroborate, lithium bisfluorooxalate borate, lithium bis(trifluoromethylsulfonyl)imide, and lithium bisfluorosulfonylimide. The above lithium salt electrolyte can provide conductive ions to achieve charge transmission, while ensuring the electrochemical stability and high conductivity of the electrolyte.

[0039] In an embodiment, the concentration of the lithium salt electrolyte in the electrolyte is 0.8 mol / L to 1.5 mol / L. The lithium salt electrolyte in the concentration range has a low internal resistance, high safety performance, and high cycle life.

[0040] In some embodiments, the electrolyte further includes a carbonate additive, and the carbonate additive is selected from at least one of vinylene carbonate (VC) and fluoroethylene carbonate (FEC).

[0041] The reaction of the above carbonate additive VC, FEC, and lithium salt electrolyte is beneficial to the formation of a negative electrode film of the lithium ion battery, and improves the cycle performance and life of the lithium ion battery.

[0042] In an embodiment, the content of the carbonate additive in the electrolyte is 0.2% to 1.5% by weight.

[0043] The above additive amount is beneficial to the formation of a dense SEI film and ion conduction in the negative electrode, thereby reducing the battery impedance and reducing the high-temperature gas production.

[0044] In some embodiments, the electrolyte further comprises a lithium salt additive selected from at least one of lithium bisfluorosulfonylimide (LiFSI), lithium difluorophosphate (LiPO2F2), lithium bis(oxalato)borate (LiBOB), lithium difluorobis(oxalato)phosphate (LiODFP).

[0045] The use of the above lithium salt additive is conducive to the formation of a dense SEI film on the positive and negative electrodes respectively, inhibits the dissolution of metal ions from the positive electrode, weakens the damage of metal ions to the SEI film of the negative electrode, improves the thermal stability of the formed film, and improves the high-temperature cycle performance and life of the lithium ion battery.

[0046] In one embodiment, the content of the lithium salt additive in the electrolyte is 0.3% to 1.5% by weight.

[0047] The above addition amount is conducive to the formation of a more dense SEI film on the positive and negative electrodes respectively and the ion conduction, reduces the initial DCR and the DCR growth rate at high temperature, and reduces the high-temperature gas production.

[0048] In some embodiments, the electrolyte further comprises a sulfur-containing additive selected from at least one of 1,3-propane sulfite (PS), 1,3-propylene sulfite (PST), sulfur-containing acid ethylene ester (DTD), methylene disulfonic acid methylene ester (MMDS).

[0049] The above sulfur-containing additive assists the film formation on the positive and negative electrodes, and further improves the high-temperature cycle performance of the lithium ion battery.

[0050] In one embodiment, the content of the sulfur-containing additive in the electrolyte is 0.5% to 1.5% by weight.

[0051] The above addition amount is conducive to the formation of a dense SEI film on the negative electrode and reduces the risk of excessive film formation, and improves the cycle performance of the lithium ion battery.

[0052] According to another aspect of the present application, a lithium ion battery is provided, comprising the electrolyte as above.

[0053] In an embodiment, the lithium ion battery comprises a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator, the positive electrode sheet comprises a positive electrode active material, the positive electrode active material is a ternary material, the negative electrode sheet comprises a negative electrode active material, the negative electrode active material is graphite and / or silicon-carbon. The ternary material refers to a composite material composed of lithium, nickel, cobalt, manganese and aluminum elements, has high electrochemical activity and stability, and can obtain high-voltage and high-energy-density batteries. Then in the ternary high-voltage system lithium ion battery, the side reaction rate of the positive electrode material with high oxidation activity and the electrolyte increases, and the side reaction between the electrolyte and the positive electrode material intensifies, which can cause more metal ions of the positive electrode active material to be reduced. Therefore, there is a more serious problem of deterioration of high-temperature cycle performance and high-temperature storage performance. The electrolyte of the present application is beneficial to stabilizing the positive and negative electrode interface in the ternary high-voltage system lithium ion battery, improving the high-temperature storage and high-temperature cycle performance of the lithium ion battery, and delaying the capacity decay of the battery at high temperature. The positive electrode active material can be specifically lithium nickel cobalt manganese oxide ternary material, and the structure is Li(Ni x Co y Mn z )O2, wherein 0.6≤x<0.9, 0<y≤0.2, 0<z≤0.2, and x+y+z=1.

[0054] The present application will be further described in detail below in combination with specific embodiments, which cannot be understood as limiting the scope of the present application.

[0055] Embodiment 1

[0056] An electrolyte comprises an organic solvent, a lithium salt electrolyte lithium hexafluorophosphate (LiPF6) and an additive, the additive comprises a nitrile compound containing a benzene ring structure and a carbon-carbon double bond, 4,4'-dicyanostilbene, a nitrile compound containing triphenylamine and sulfonyl fluoride groups shown in formula I, a carbonate additive vinylene carbonate (VC), a lithium salt additive lithium difluorophosphate (LiPO2F2), a sulfur-containing additive 1,3-propylene sulfite (PST), the content of 4,4'-dicyanostilbene is 0.5%, the content of the nitrile compound containing triphenylamine and sulfonyl fluoride groups shown in formula I is 0.5%, the content of the carbonate additive is 0.5%, the content of the lithium salt additive is 1%, and the content of the sulfur-containing additive is 1%, the rest is the lithium salt electrolyte and the organic solvent; wherein the concentration of the lithium salt electrolyte in the electrolyte is 1.0 mol / L, and the organic solvent is obtained by mixing ethylene carbonate (EC), diethyl carbonate, methyl ethyl carbonate and propylene carbonate (PC) in a volume ratio of 30:20:45:5.

[0057] The preparation steps of the electrolyte are as follows:

[0058] Under argon atmosphere, formula amount of nitrile compound containing benzene ring structure and carbon-carbon double bond 4,4'-dicyanostilbene, nitrile compound containing triphenylamine and sulfonyl fluoride group shown in formula I, carbonate additive, lithium salt additive, sulfur-containing additive, and then lithium salt electrolyte is added into organic solvent, and the mixture is stirred at 12℃ to obtain electrolyte.

[0059]

[0060] Example 2

[0061] An electrolyte includes an organic solvent, a lithium salt electrolyte lithium perchlorate, and an additive, the additive including a nitrile compound containing benzene ring structure and carbon-carbon double bond 4-cyanostyrene, a nitrile compound containing triphenylamine and sulfonyl fluoride group shown in formula I, a carbonate additive fluoroethylene carbonate (FEC), a lithium salt additive lithium bisfluorosulfonylimide (LiFSI), and a sulfur-containing additive 1,3-propane sultone (PS). The content of 4,4'-dicyanostilbene is 0.3%, the content of the nitrile compound containing triphenylamine and sulfonyl fluoride group shown in formula I is 0.3%, the content of the carbonate additive is 0.2%, the content of the lithium salt additive is 0.3%, and the content of the sulfur-containing additive is 0.5%, with the balance being the lithium salt electrolyte and the organic solvent. The concentration of the lithium salt electrolyte in the electrolyte is 0.8 mol / L, and the organic solvent is obtained by mixing ethylene carbonate and methyl ethyl carbonate in a volume ratio of 20:60.

[0062] The preparation steps of the electrolyte are the same as those in Example 1.

[0063] Example 3

[0064] An electrolyte includes an organic solvent, a lithium salt electrolyte lithium tetrafluoroborate, and an additive, the additive including a nitrile compound containing benzene ring structure and carbon-carbon double bond 1,4-bis(4-cyanostyryl)benzene, a nitrile compound containing triphenylamine and sulfonyl fluoride group shown in formula I, a carbonate additive vinylene carbonate (VC), a lithium salt additive lithium bis(oxalato)borate (LiBOB), and a sulfur-containing additive vinylene sulfate (DTD). The content of 4,4'-dicyanostilbene is 1.2%, the content of the nitrile compound containing triphenylamine and sulfonyl fluoride group shown in formula I is 1.2%, the content of the carbonate additive is 1.5%, the content of the lithium salt additive is 1.5%, and the content of the sulfur-containing additive is 1.5%, with the balance being the lithium salt electrolyte and the organic solvent. The concentration of the lithium salt electrolyte in the electrolyte is 1.5 mol / L, and the organic solvent is obtained by mixing ethylene carbonate and methyl ethyl carbonate in a volume ratio of 40:30.

[0065] The preparation steps of the electrolyte are the same as those in Example 1.

[0066] Example 4

[0067] The difference from Example 1 is only that the content of 4,4'-dicyanostilbene in the electrolyte is 0.3% by weight.

[0068] Example 5

[0069] The difference from Example 1 is only that the content of 4,4'-dicyanostilbene in the electrolyte is 1% by weight.

[0070] Example 6

[0071] The difference from Example 1 is only that the content of the nitrile compound containing triphenylamine and sulfonyl fluoride groups represented by Formula I in the electrolyte is 0.3% by weight.

[0072] Example 7

[0073] The difference from Example 1 is only that the content of the nitrile compound containing triphenylamine and sulfonyl fluoride groups represented by Formula I in the electrolyte is 1% by weight.

[0074] Comparative Example 1

[0075] The difference from Example 1 is only that 4,4'-dicyanostilbene is not added.

[0076] Comparative Example 2

[0077] The difference from Example 1 is only that the nitrile compound containing triphenylamine and sulfonyl fluoride groups represented by Formula I is not added.

[0078] Comparative Example 3

[0079] The difference from Example 1 is only that 4,4'-dicyanostilbene and the nitrile compound containing triphenylamine and sulfonyl fluoride groups represented by Formula I are not added.

[0080] Battery performance test

[0081] (1) The electrolyte in each example and comparative example is used to prepare a lithium ion battery, and the lithium ion battery preparation steps are as follows:

[0082] A slurry of graphite as a negative electrode material, acetylene black as a conductive agent, and CMC and SBR as binders in a mass ratio of 94:1:2:3 is coated on a copper foil current collector, vacuum dried, and a negative electrode sheet is obtained; a slurry of NCM811 as a positive electrode material, acetylene black as a conductive agent, and PVDF as a binder in a mass ratio of 94:3:3 is coated on an aluminum foil current collector, vacuum dried, and a positive electrode sheet is obtained; the positive electrode sheet, the negative electrode sheet, a Celgard2400 separator, and the electrolyte are assembled into a soft package battery.

[0083] (2) High temperature cycle performance test: the high temperature cycle performance test was carried out by using a blue electric battery charge-discharge test cabinet, and the steps were as follows:

[0084] At 45℃, the lithium ion battery was charged to a voltage of 4.3V at 0.5C (nominal capacity) constant current, then charged to a current of 0.05C at 4.3V constant voltage, and then discharged to a cut-off voltage of 2.8V at 1C constant current after 10min of standing. The above was one charge-discharge cycle; the lithium ion battery was subjected to 800 cycles of charge-discharge at 45℃ according to the above conditions, and the capacity retention rate and volume expansion rate of the lithium ion battery after 800 cycles were calculated.

[0085] The calculation formula of the capacity retention rate of the lithium ion battery after 800 cycles was as follows: the capacity retention rate after 800 cycles (%) = (discharge capacity after 800 cycles / first discharge capacity) x 100%;

[0086] The calculation formula of the volume expansion rate of the lithium ion battery after 800 cycles was as follows: the volume expansion rate (%) = (the volume of the battery after 800 cycle discharge - the initial volume of the battery) / the initial volume of the battery x 100%.

[0087] The capacity retention rate and volume expansion rate after 800 cycles at 45℃ were shown in Table 1.

[0088] (3) High temperature storage performance test of lithium ion battery: the high temperature storage performance test was carried out by using a blue electric battery charge-discharge test cabinet, and the specific steps were as follows:

[0089] At 25℃, the lithium ion battery was charged to a voltage of 4.3V at 0.5C constant current, then charged to a current of 0.05C at 4.3V constant voltage, and then the initial volume V0 and initial discharge capacity C0 of the battery were measured, and the initial DCR R0 was measured; then the lithium ion battery was stored in a constant temperature oven at 60℃ for 90 days, and the DCR (R1) of the battery at this time, the recovery capacity C1 and the retention capacity C2, and the volume V1 of the battery after storage were measured, and the capacity recovery rate, the capacity retention rate and the volume expansion rate of the battery were calculated, and the calculation formula was as follows:

[0090] The volume expansion rate of the lithium ion battery after 60℃ storage for 90 days (%) = (V1-V0) / V0x100%.

[0091] The capacity recovery rate of the lithium ion battery after 60℃ storage for 90 days (%) = (C1 / C0) x 100%;

[0092] The capacity retention rate of the lithium ion battery after 60℃ storage for 90 days (%) = (C2 / C0) x 100%;

[0093] The DCR growth rate (%) of the lithium ion battery after 90 days of storage at 60°C = (R1-R0) / R0x100%.

[0094] The initial volume of the lithium ion battery is V0, the initial discharge capacity is C0, the initial DCR is R0, and the volume expansion rate, capacity recovery rate, capacity retention rate, and DCR growth rate of the lithium ion battery after 90 days of storage at 60°C are shown in Table 1.

[0095] (4) Metal dissolution test of the lithium ion battery after 90 days of storage at 60°C, the specific steps are as follows:

[0096] The lithium ion battery after 90 days of storage at 60°C in (3) was discharged at 0.5C constant current to a voltage of 2.8V, then the cell was disassembled, the negative electrode powder on the copper current collector was scraped with a ceramic knife, and the metal dissolution test was performed using an inductively coupled plasma optical emission spectrometer (ICP OES). The total content of Ni, Co, and Mn in the negative electrode powder is shown in Table 1.

[0097] Table 1

[0098]

[0099]

[0100] As can be seen from Table 1, the lithium ion battery prepared based on the electrolyte of Examples 1-7 and Comparative Examples 1-3 has a lower total amount of metal dissolution, a higher high-temperature cycle capacity retention rate, a higher high-temperature storage capacity retention rate, and a higher high-temperature storage capacity recovery rate. The lithium ion battery prepared based on the electrolyte of the present application can protect the positive electrode transition metal dissolution, while having a lower volume expansion rate and a lower high-temperature gas production, as well as excellent high-temperature cycle performance and high-temperature storage performance.

[0101] As can be seen from Examples 1, 4, and 5, when the content of additive 4,4'-dicyanostilbene is 0.3% to 0.5%, the lithium ion battery has a lower DCR growth rate, which can reduce its heat generation, improve its safety performance, and has excellent high-temperature cycle performance, high-temperature storage capacity retention rate, and high-temperature storage capacity recovery rate.

[0102] As can be seen from Examples 1, 6, and 7, when the content of the nitrile compound containing triphenylamine and sulfonyl fluoride groups represented by Formula I is 0.3% to 0.5%, the lithium ion battery has a lower DCR growth rate, which can reduce its heat generation, improve its safety performance, and has excellent high-temperature cycle performance, high-temperature storage capacity retention rate, and high-temperature storage capacity recovery rate.

[0103] It can be seen from the comparison of the comparative example 2 and the comparative example 3 that the addition of the additive 4,4'-dicyanostilbene can significantly reduce the volume expansion rate of the lithium ion battery during the high-temperature cycle process, has an inhibitory effect on metal dissolution, and significantly improves the high-temperature cycle performance of the battery system.

[0104] It can be seen from the comparison of the comparative example 1 and the comparative example 3 that the addition of the additive, the nitrile compound containing triphenylamine and sulfonyl fluoride groups represented by formula I, can significantly reduce the volume expansion rate of the lithium ion battery during the high-temperature storage process, has an inhibitory effect on the positive electrode metal dissolution, and the inhibitory effect is better than that of the additive 4,4'-dicyanostilbene, thereby significantly improving the high-temperature storage performance of the battery system.

[0105] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Various modifications and changes can be made by those skilled in the art based on the spirit and principles of the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. An electrolyte, characterized in that, It includes organic solvents, lithium salt electrolytes, and additives, wherein the additives include nitrile compounds containing benzene ring structures and carbon-carbon double bonds, and nitrile compounds containing triphenylamine and sulfonyl fluoride groups; By weight percentage, the electrolyte contains 0.3% to 1.2% of the nitrile compounds with benzene ring structures and carbon-carbon double bonds, and 0.3% to 1.2% of the nitrile compounds with triphenylamine and sulfonyl fluoride groups. The structure of the nitrile compound containing triphenylamine and sulfonyl fluoride groups is shown in Formula I. 。 2. The electrolyte according to claim 1, characterized in that, The nitrile compound containing a benzene ring structure and a carbon-carbon double bond is selected from at least one of 4-cyanostylenide, 1,4-bis(4-cyanostylenyl)benzene, and 4,4'-dicyanostylenide.

3. The electrolyte according to claim 1, characterized in that, The content of the nitrile compound containing triphenylamine and sulfonyl fluoride groups is 0.3% to 0.5%.

4. The electrolyte according to claim 1, characterized in that, The content of the nitrile compound containing a benzene ring structure and a carbon-carbon double bond is 0.3% to 0.5%.

5. The electrolyte according to any one of claims 1 to 4, characterized in that, Organic solvents include at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate.

6. The electrolyte according to any one of claims 1 to 4, characterized in that, The organic solvent is obtained by mixing ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate and methyl ethyl carbonate in a volume ratio of (20~40):(0~15):(0~20):(0~20):(30~60).

7. The electrolyte according to any one of claims 1 to 4, characterized in that, The lithium salt electrolyte is selected from at least one of lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium difluorooxalate borate, lithium bis(trifluoromethanesulfonyl)imide, and lithium difluorosulfonylimide. In the electrolyte, the concentration of the lithium salt electrolyte is 0.8 mol / L to 1.5 mol / L.

8. The electrolyte according to any one of claims 1 to 4, characterized in that, The electrolyte also includes carbonate additives, which are selected from at least one of vinylene carbonate and fluoroethylene carbonate; The content of the carbonate additive in the electrolyte is 0.2% to 1.5% by weight.

9. The electrolyte according to any one of claims 1 to 4, characterized in that, The electrolyte also includes lithium salt additives, which are selected from at least one of lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, lithium bis(oxalate)borate, and lithium difluorobis(oxalate)phosphate. The content of the lithium salt additive in the electrolyte is 0.3% to 1.5% by weight.

10. The electrolyte according to any one of claims 1 to 4, characterized in that, The electrolyte also includes a sulfur-containing additive, which is selected from at least one of 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, vinyl sulfate, and methylene disulfonate. The content of the sulfur-containing additive in the electrolyte is 0.5% to 1.5% by weight.

11. A lithium-ion battery, characterized in that, Includes the electrolyte according to any one of claims 1 to 10; The lithium-ion battery includes a positive electrode, a negative electrode, an electrolyte, and a separator. The positive electrode includes a positive active material, which is a ternary material. The negative electrode includes a negative active material, which is graphite and / or silicon-carbon.

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