Electrolyte and lithium ion battery

Abstract

The invention 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; the electrolyte comprises the following components in percentage by weight: 0.3%-1.2% of nitrile compounds containing benzene ring structures and carbon-carbon double bonds, and 0.3%-1.2% of nitrile compounds containing triphenylamine and sulfonyl fluoride groups. Based on the electrolyte provided by the invention, the problems of poor high-temperature cycle performance and high-temperature storage performance of the lithium ion battery in the prior art are solved.

Description

Technical Field

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

[0002] Lithium-ion batteries are widely used in digital, energy storage, power, military aerospace, and communication equipment due to their advantages such as high energy density, high output power, and high charging efficiency. However, in lithium-ion batteries, the oxidation and decomposition of electrolytes, especially the oxidation and decomposition reaction rate of electrolytes under high temperature conditions, will increase more, causing the battery capacity to decay rapidly at high temperatures, and the high-temperature cycle and high-temperature storage process is often accompanied by the dissolution of metal ions, resulting in poor high-temperature cycle performance and high-temperature storage performance, and serious degradation of battery performance. As the market demand for lithium-ion batteries continues to grow, higher requirements are placed on the comprehensive performance of batteries. Therefore, it is of great significance to provide electrolytes that can improve high-temperature cycle and high-temperature storage performance. Summary of the invention

[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 cycle performance and high-temperature storage performance of lithium-ion batteries in the prior art.

[0004] In order to achieve the above-mentioned object, the present application provides an electrolyte, comprising an organic solvent, a lithium salt electrolyte and an additive, wherein 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;

[0005] In terms of weight percentage, the content of the nitrile compound containing a benzene ring structure and a carbon-carbon double bond in the electrolyte is 0.3% to 1.2%, and the content of the nitrile compound containing triphenylamine and sulfonyl fluoride groups is 0.3% to 1.2%;

[0006] The structure of the nitrile compound containing triphenylamine and sulfonyl fluoride groups is shown in Formula I

[0007]

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

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

[0010] Furthermore, 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 ethyl methyl carbonate.

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

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

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

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

[0016] Furthermore, in terms of weight percentage, the content of carbonate additives in the electrolyte is 0.2% to 1.5%.

[0017] Furthermore, the electrolyte also includes a lithium salt additive, and the lithium salt additive is selected from at least one of lithium bis(fluorosulfonyl)imide (LiFSI), lithium difluorophosphate (LiPO2F2), lithium bis(oxalatoborate) (LiBOB), and lithium difluorobis(oxalatophosphate) (LiODFP).

[0018] Furthermore, in terms of weight percentage, the content of the lithium salt additive in the electrolyte is 0.3% to 1.5%.

[0019] Furthermore, the electrolyte also includes a sulfur-containing additive, and the sulfur-containing additive is selected from at least one of 1,3-propane sultone (PS), 1,3-propylene sultone (PST), dithiodisulfate (DTD), and methylene disulfonate (MMDS).

[0020] Furthermore, in terms of weight percentage, the content of the sulfur-containing additive in the electrolyte is 0.5% to 1.5%.

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

[0022] Furthermore, the lithium-ion battery includes a positive electrode plate, a negative electrode plate, an electrolyte and a separator, the positive electrode plate includes a positive electrode active material, the positive electrode active material is a ternary material, the negative electrode plate includes a negative electrode active material, the negative electrode active material is graphite and / or silicon carbon.

[0023] By applying 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 as an additive can be oxidized and reduced, participates in the film formation of the positive and negative electrodes, and improves 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 sulfonyl fluoride group in the nitrile compound containing triphenylamine and sulfonyl fluoride groups as shown in the added formula I can participate in the positive electrode film formation, has a protective effect on the positive electrode, reduces the dissolution of the positive electrode transition metal, and improves the stability of the positive electrode interface of the lithium-ion battery, and the nitrile compound containing triphenylamine and sulfonyl fluoride groups has high temperature stability. Qualitative; In addition, lithium salts such as LiPF6 in the electrolyte can easily decompose more HF at high temperatures. The CN groups in the two additives have strong electronegativity and can effectively combine with the HF generated by the electrolyte, effectively reducing the acidity of the electrolyte, reducing positive electrode corrosion to avoid structural damage to the positive electrode material, reducing the dissolution of positive electrode transition metal ions, and preventing the dissolved metal ions from passing through the solid electrolyte interface membrane (SEI membrane) to reach the negative electrode to obtain electrons and be reduced to metal elements, destroying the structure of the SEI membrane, thereby stabilizing the positive and negative electrode interfaces of lithium-ion batteries, improving the high-temperature storage and high-temperature cycle performance of lithium-ion batteries, and delaying the battery capacity decay at high temperatures.

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

[0025] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application may be combined with each other.

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

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

[0028] The structure of the nitrile compound containing triphenylamine and sulfonyl fluoride groups is shown in Formula I

[0029]

[0030] In order to improve the high-temperature storage and high-temperature cycle performance of lithium-ion batteries, the present 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 as an additive can be oxidized and reduced, and participates 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, thereby improving the high-temperature cycle performance and high-temperature storage performance of the lithium-ion battery; on the other hand, the sulfonyl fluoride group in the nitrile compound containing triphenylamine and sulfonyl fluoride groups shown in the added formula I participates in the positive electrode film formation and forms a dense film layer, which has a good protective effect on the positive electrode, reduces the dissolution of the positive electrode transition metal, improves the stability of the positive electrode interface of the lithium-ion battery, and reduces the battery capacity attenuation during high-temperature storage of the lithium-ion battery. And volume expansion, and the nitrile compound containing triphenylamine and sulfonyl fluoride groups has high temperature stability; in addition, lithium salts such as LiPF6 in the electrolyte at high temperature are easy to decompose more HF, and the groups CN in the two additives have strong electronegativity, which can effectively combine the HF generated by the electrolyte, effectively reduce the acidity of the electrolyte, reduce positive electrode corrosion to avoid structural damage to the positive electrode material, reduce the dissolution of positive electrode transition metal ions, and prevent the dissolved metal ions from passing through the solid electrolyte interface membrane (SEI membrane) to reach the negative electrode to obtain electrons and be reduced to metal elements, destroying the structure of the SEI membrane, thereby stabilizing the positive and negative electrode interfaces of lithium-ion batteries, improving the high temperature storage and high temperature cycle performance of lithium-ion batteries, and delaying the battery capacity decay at high temperatures. The electrolyte of the present application can improve the stability of the positive and negative electrode interfaces of lithium-ion batteries, improve the high temperature cycle performance and high temperature storage performance of lithium-ion batteries, and delay the battery capacity decay at high temperatures.

[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 cyanostyrene, 1,4-bis(4-cyanostyryl)benzene, and 4,4'-dicyanodiphenylethylene.

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

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

[0034] At the above content, lithium-ion batteries have a lower DCR growth rate, which can reduce battery heat generation, improve battery safety performance and reduce battery capacity attenuation.

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

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

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

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

[0039] In one 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 this concentration range has lower internal resistance, higher safety performance and higher 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 carbonate additives VC and FEC react with the lithium salt electrolyte, which is beneficial to the negative electrode film formation of the lithium ion battery and improves the cycle performance and life of the lithium ion battery.

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

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

[0044] In some embodiments, the electrolyte further includes a lithium salt additive, and the lithium salt additive is selected from at least one of lithium bis(fluorosulfonyl)imide (LiFSI), lithium difluorophosphate (LiPO2F2), lithium bis(oxalatoborate) (LiBOB), and lithium difluorobis(oxalatophosphate) (LiODFP).

[0045] The use of the above-mentioned lithium salt additives is conducive to forming a dense SEI film at the positive and negative electrodes respectively, inhibiting the dissolution of positive electrode metal ions, reducing the damage of metal ions to the negative electrode SEI film, improving the thermal stability of the film, and improving the high-temperature cycle performance and life of lithium-ion batteries.

[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 forming a denser SEI film and ion conduction at the positive and negative electrodes, respectively, reducing the initial DCR and the DCR growth rate at high temperature, and reducing high-temperature gas production.

[0048] In some embodiments, 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-propylene sultone (PST), dithiodisulfate (DTD), and methylene disulfonate (MMDS).

[0049] The above-mentioned sulfur-containing additives assist in the film formation of the positive and negative electrodes, thereby improving the high-temperature cycle performance of lithium-ion batteries.

[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-mentioned addition amount is conducive to forming a dense SEI film at the negative electrode and reducing the risk of excessive film formation, thereby improving the cycle performance of lithium-ion batteries.

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

[0053] In one embodiment, a lithium-ion battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte solution, and a separator. The positive electrode sheet includes a positive electrode active material, which is a ternary material. The negative electrode sheet includes a negative electrode active material, which is graphite and / or silicon carbide. The ternary material refers to a composite material composed of elements such as lithium, nickel, cobalt, manganese, and aluminum, and has high electrochemical activity and stability, and a high-voltage and high-energy-density battery can be obtained. However, in a ternary high-voltage system lithium-ion battery, the side reaction rate between the positive electrode material with high oxidation activity and the electrolyte solution increases, and the intensification of the side reaction between the electrolyte solution and the positive electrode material will 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. Using the electrolyte of the present application is beneficial to stabilizing the interfaces of the positive and negative electrodes 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 attenuation of the battery capacity at high temperatures. The positive electrode active material may specifically be a lithium nickel cobalt manganese oxide ternary material, and the structure is Li(Ni x Co y Mn z )O2, where 0.6 ≤ x < 0.9, 0 < y ≤ 0.2, 0 < z ≤ 0.2, and x + y + z = 1.

[0054] The following further describes the present application in detail with specific embodiments, and these embodiments should not be construed as limiting the scope claimed by the present application.

[0055] Example 1

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

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

[0058] Under an argon atmosphere, a formulated amount of a nitrile compound containing a benzene ring structure and a carbon-carbon double bond, 4,4'-dicyanodiphenylethylene, a nitrile compound containing triphenylamine and sulfonyl fluoride groups as shown in Formula I, a carbonate additive, a lithium salt additive, and a sulfur-containing additive are added to an organic solvent, and then a lithium salt electrolyte is added, and the mixture is stirred and mixed at a temperature of 12° C. to obtain an electrolyte.

[0059]

[0060] Example 2

[0061] An electrolyte comprises an organic solvent, a lithium salt electrolyte lithium perchlorate and an additive, wherein the additive comprises a nitrile compound 4-cyanostyrene containing a benzene ring structure and a carbon-carbon double bond, a nitrile compound containing triphenylamine and sulfonyl fluoride groups as shown in Formula I, a carbonate additive fluoroethylene carbonate (FEC), a lithium salt additive lithium bis(fluorosulfonyl)imide (LiFSI), and a sulfur-containing additive 1,3-propane sultone (PS). In terms of weight percentage, the content of 4,4'-dicyanodistilbene is 0.3%, the content of the nitrile compound containing triphenylamine and sulfonyl fluoride groups as 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%, the content of the sulfur-containing additive is 0.5%, and the balance is the lithium salt electrolyte and the organic solvent; wherein 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 ethyl methyl 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 comprises an organic solvent, a lithium salt electrolyte lithium tetrafluoroborate and an additive, wherein the additive comprises a nitrile compound 1,4-bis(4-cyanostyryl)benzene containing a benzene ring structure and a carbon-carbon double bond, a nitrile compound containing triphenylamine and sulfonyl fluoride groups as shown in Formula I, a carbonate additive vinylene carbonate (VC), a lithium salt additive lithium bis(oxalatoborate) (LiBOB), and a sulfur-containing additive vinyl sulfate (DTD). In terms of weight percentage, the content of 4,4'-dicyanodiphenylethylene is 1.2%, the content of the nitrile compound containing triphenylamine and sulfonyl fluoride groups as 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%, the content of the sulfur-containing additive is 1.5%, and the balance is the lithium salt electrolyte and the organic solvent; wherein the concentration of the lithium salt electrolyte in the electrolyte is 1.5 mol / L, and the organic solvent is obtained by mixing vinyl carbonate and ethyl methyl 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 only difference from Example 1 is that, in terms of weight percentage, the content of 4,4'-dicyanodiphenylethylene in the electrolyte is 0.3%.

[0068] Example 5

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

[0070] Example 6

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

[0072] Example 7

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

[0074] Comparative Example 1

[0075] The only difference from Example 1 is that no 4,4'-dicyanophenylethylene is added.

[0076] Comparative Example 2

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

[0078] Comparative Example 3

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

[0080] Battery performance test

[0081] (1) The electrolytes in the embodiments and comparative examples were used to prepare lithium ion batteries. The steps for preparing the lithium ion batteries were as follows:

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

[0083] (2) High temperature cycle performance test: Use the Blue Power battery charge and discharge test cabinet to perform high temperature cycle performance test. The steps are as follows:

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

[0085] The calculation formula of the capacity retention rate of the lithium-ion battery after the 800th cycle is as follows: Capacity retention rate after the 800th cycle (%) = (discharge capacity of the 800th cycle / first discharge capacity) × 100%;

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

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

[0088] (3) High temperature storage performance test of lithium-ion batteries: The high temperature storage performance test is carried out using a Blue Power battery charge and discharge test cabinet. The specific steps are as follows:

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

[0090] The volume expansion ratio (%) of a lithium-ion battery after storage at 60°C for 90 days = (V1-V0) / V0×100%.

[0091] Capacity recovery rate of lithium-ion battery after storage at 60°C for 90 days (%) = (C1 / C0) × 100%;

[0092] Capacity retention rate of lithium-ion battery after storage at 60°C for 90 days (%) = (C2 / C0) × 100%;

[0093] DCR growth rate (%) of lithium-ion battery after storage at 60°C for 90 days = (R1-R0) / R0×100%.

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

[0095] (4) Metal dissolution test of lithium-ion batteries stored at 60°C for 90 days. The specific steps are as follows:

[0096] The lithium-ion battery stored at 60°C for 90 days in (3) was discharged at a constant current of 0.5C to a voltage of 2.8V, and then the battery 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 shown in Table 1, by comparing Examples 1-7 and Comparative Examples 1-3, it can be seen that the lithium-ion batteries prepared based on the electrolytes of Examples 1-7 of the present application have 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 from dissolution, and at the same time has a lower volume expansion rate and lower high-temperature gas production, as well as excellent high-temperature cycle performance and high-temperature storage performance.

[0101] From the comparison of Example 1, Example 4 and Example 5, it can be seen that when the content of the additive 4,4'-dicyanodiphenylethylene is 0.3% to 0.5%, the lithium-ion battery has a lower DCR growth rate, 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] By comparing Example 1, Example 6 and Example 7, it can be seen that the content of the nitrile compound containing triphenylamine and sulfonyl fluoride groups shown in Formula I is 0.3% to 0.5%, and 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] From the comparison between Comparative Example 2 and Comparative Example 3, it can be seen that the addition of the additive 4,4'-dicyanostilbene can significantly reduce the volume expansion rate of the lithium-ion battery during high-temperature cycling, inhibit metal dissolution, and significantly improve the high-temperature cycling performance of the battery system.

[0104] From the comparison between Comparative Example 1 and Comparative Example 3, it can be seen that the addition of the nitrile compound containing triphenylamine and sulfonyl fluoride groups shown in the additive formula I can significantly reduce the volume expansion rate of the lithium-ion battery during high-temperature storage, and has an inhibitory effect on the dissolution of the positive electrode metal, 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 description is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. An electrolyte, characterized in that: The invention comprises an organic solvent, a lithium salt electrolyte and an additive, wherein 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 terms of weight percentage, 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%, and the content of the nitrile compound containing triphenylamine and sulfonyl fluoride groups is 0.3% to 1.2%; 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-cyanostyrene, 1,4-bis(4-cyanostyryl)benzene and 4,4'-dicyanodiphenylethylene.

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 The organic solvent includes at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate; Preferably, the organic solvent is ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate in a volume ratio of (20-40): (0-15): (0~20):(0~20):(30~60) are mixed.

6. 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 bis(trifluoromethylsulfonyl)imide and lithium bis(fluorosulfonyl)imide; Preferably, in the electrolyte, the concentration of the lithium salt electrolyte is 0.8 mol / L to 1.5 mol / L.

7. The electrolyte according to any one of claims 1 to 4, characterized in that The electrolyte further includes a carbonate additive, wherein the carbonate additive is selected from at least one of vinylene carbonate and fluoroethylene carbonate; Preferably, in the electrolyte, the content of the carbonate additive is 0.2% to 1.5% by weight.

8. The electrolyte according to any one of claims 1 to 4, characterized in that The electrolyte further comprises a lithium salt additive, wherein the lithium salt additive is selected from at least one of lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, lithium bis(oxalatoborate), and lithium difluorobis(oxalatophosphate); Preferably, in the electrolyte, the content of the lithium salt additive is 0.3% to 1.5% by weight.

9. The electrolyte according to any one of claims 1 to 4, characterized in that The electrolyte further comprises a sulfur-containing additive, wherein the sulfur-containing additive is selected from at least one of 1,3-propane sultone, 1,3-propylene sultone, vinyl sulfate, and methylene disulfonate; Preferably, in terms of weight percentage, the content of the sulfur-containing additive in the electrolyte is 0.5% to 1.5%.

10. A lithium ion battery, characterized in that: An electrolyte comprising any one of claims 1 to 9; Preferably, the lithium-ion battery comprises a positive electrode plate, a negative electrode plate, the electrolyte and a separator, the positive electrode plate comprises a positive electrode active material, the positive electrode active material is a ternary material, the negative electrode plate comprises a negative electrode active material, the negative electrode active material is graphite and / or silicon carbon.

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