A non-aqueous electrolyte and a lithium-ion battery

Abstract

To overcome the problems of low high-temperature cycling performance and low high-temperature storage performance of existing lithium-ion batteries at high voltages, the present invention provides a non-aqueous electrolyte and a lithium-ion battery. The present invention provides a non-aqueous electrolyte, comprising a lithium salt, a solvent, and an additive. The additive comprises additive A and additive B, and the additive B is a boron-containing compound; additive A is as shown in formula I, wherein R1 is selected from C1-C4 alkylene groups, and R2, R3, and R4 are each independently selected from hydrogen, C1-C6 alkyl groups, C1-C6 fluoroalkyl groups, C2-C6 alkenyl groups, C2-C6 fluoroalkenyl groups, or C2-C6 alkynyl groups. The electrolyte provided by the present invention can significantly improve the high-temperature cycling performance and high-temperature storage performance of the electrolyte.

Description

Technical Field

[0001] The present invention belongs to the technical field of secondary batteries, and particularly relates to a non-aqueous electrolyte and a lithium ion battery. Background Art

[0002] Lithium ion batteries are widely used in consumer electronic products and power batteries due to their advantages such as high specific energy, good fast charge and discharge capabilities, and low self-discharge. The operating conditions of electronic products and power batteries are becoming more and more complex, and the requirements for lithium ion batteries are also getting higher and higher, especially the demand for battery capacity and life.

[0003] The performance of lithium ion batteries is a key factor related to whether they are popular in the market. The main indicators for evaluating the performance of lithium ion batteries include cycle performance, safety performance, low temperature performance, high temperature storage performance, etc. In the existing lithium ion batteries, the SEI film formed at the negative electrode interface during charge and discharge has poor toughness, low mechanical strength, and poor stability. As the number of battery cycles increases, the capacity retention rate of the battery decreases, the high temperature cycle performance of the battery decreases, and the high temperature storage performance of the battery is low. Summary of the Invention

[0004] Aiming at the problems of low high temperature cycle performance and high temperature storage performance of existing lithium ion batteries under high voltage, the present invention provides a non-aqueous electrolyte and a lithium ion battery.

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

[0006] The present invention provides a non-aqueous electrolyte, which includes a lithium salt, a solvent, and an additive. The additive includes additive A and additive B, and the additive B is a boron-containing compound; additive A is as shown in formula I,

[0007]

[0008] wherein, R1 is selected from C1-C4 alkylene groups, and R2, R3, and R4 are each independently selected from hydrogen, C1-C6 alkyl groups, C1-C6 fluoroalkyl groups, C2-C6 alkenyl groups, C2-C6 fluoroalkenyl groups, or C2-C6 alkynyl groups.

[0009] Preferably, the boron-containing compound is selected from one or more of the following compounds,

[0010]

[0011] wherein, X1, X2, X3, and X4 are each independently selected from H, O, F, halogen-substituted or unsubstituted C1-C6 alkane groups, C1-C6 alkylsilyl groups with carbon atoms, C1-C6 alkenyl groups with carbon atoms, C1-C6 alkynyl groups with carbon atoms, halogen-substituted or unsubstituted aromatic hydrocarbon groups.

[0012] Preferably, based on the total mass of the electrolyte being 100%, the mass ratio of additive A in the electrolyte is 0.01% - 5%.

[0013] Preferably, based on the total mass of the electrolyte being 100%, the mass ratio of additive B in the electrolyte is 0.01 - 5%.

[0014] Preferably, additive A is 3 - isocyanatopropyltrimethoxysilane, and additive B is tris(trimethylsilyl) borate.

[0015] Preferably, the concentration of the lithium salt in the electrolyte is 0.5M - 2M.

[0016] Preferably, the concentration of the lithium salt in the electrolyte is 0.9M - 1.3M.

[0017] Preferably, the electrolyte further includes an auxiliary additive, and the auxiliary additive is selected from one or more of vinylene carbonate, ethylene vinylene carbonate, methylene vinylene carbonate, fluoroethylene carbonate, trifluoromethyl carbonate, and difluoroethylene carbonate;

[0018] Based on the total mass of the electrolyte being 100%, the mass content of the auxiliary additive is 0.01% - 20%.

[0019] On the other hand, the present application provides a lithium - ion battery, including a positive electrode sheet, a negative electrode sheet, a separator, and the non - aqueous electrolyte described in any one of the above.

[0020] Preferably, in the positive electrode sheet and the negative electrode sheet, the mass ratio of B element derived from additive B is not less than 100 ppm.

[0021] Beneficial effects

[0022] In the non - aqueous electrolyte provided by the present application, the compound additive A contains - N = C = O bond functional groups and - Si - O bonds. The - N = C = O unsaturated bond group can form a stable interface film on the surface of the negative electrode. At the same time, the - Si - O bond contained can bind hydrogen and metal ions, protecting the positive electrode active material while optimizing the positive electrode / non - aqueous electrolyte interface. The boron - containing compound additive B in the present application can be preferentially reduced on the surface of the negative electrode to participate in the formation of the negative electrode SEI film. The formed SEI film is rich in B - O and B - F bonds with stronger mechanical properties and better toughness, improving the continuous repair ability of the SEI film during the cycling process and effectively enhancing the cycling performance of the battery. Additive A and additive B act synergistically to generate a passivation film on the surface of the battery electrode, and this passivation film has good thermal stability in extreme environments, can effectively stabilize the battery system, and improve the high - temperature storage performance and high - temperature cycling performance. Detailed Embodiments

[0023] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention more clear and understandable, the present invention will be further described in detail below in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0024] An embodiment of the present invention provides a non-aqueous electrolyte, which includes a lithium salt, a solvent and an additive. The additive includes additive A and additive B, and the additive B is a boron-containing compound; the additive A is as shown in formula I,

[0025]

[0026] wherein, R1 is selected from C1-C4 alkylene groups, and R2, R3 and R4 are each independently selected from hydrogen, C1-C6 alkyl groups, C1-C6 fluoroalkyl groups, C2-C6 alkenyl groups, C2-C6 fluoroalkenyl groups or C2-C6 alkynyl groups.

[0027] Specifically, C1-C4 alkyl groups include methylene, ethylene, propylene, butylene, etc. C1-C6 alkyl groups include straight-chain or branched-chain alkyl groups with 1-6 carbon atoms, such as methyl, ethyl, isopropyl, isobutyl, etc. C2-C6 alkenyl groups include straight-chain or branched-chain alkenyl groups with 2-6 carbon atoms. Similarly, C2-C6 alkynyl groups include straight-chain or branched-chain alkynyl groups with 2-6 carbon atoms.

[0028] The compound additive A in the non-aqueous electrolyte contains -N=C=O bond functional groups and -Si-O bonds. The -N=C=O unsaturated bond group can form a stable interface film on the negative electrode surface. At the same time, the -Si-O bonds contained can combine hydrogen and metal ions, protecting the positive electrode active material while optimizing the positive electrode / non-aqueous electrolyte interface. The boron-containing compound additive B in this application can be preferentially reduced on the negative electrode surface to participate in the formation of the negative electrode SEI film. The formed SEI film is rich in B-O and B-F bonds with stronger mechanical properties and better toughness, improving the continuous repair ability of the SEI film during the cycle and effectively enhancing the cycle performance of the battery. Additive A and additive B act synergistically to generate a passivation film on the battery electrode surface, and this passivation film has good thermal stability in extreme environments, can effectively stabilize the battery system, and improve the high-temperature storage performance and high-temperature cycle performance.

[0029] In some embodiments, the boron-containing compound is selected from one or more of the following compounds,

[0030]

[0031] Among them, X1, X2, X3, and X4 are each independently selected from H, O, F, halogen-substituted or unsubstituted C1-C6 alkyl groups, C1-C6 alkylsilyl groups having a carbon atom number of C1-C6, C1-C6 alkenyl groups having a carbon atom number of C1-C6, C1-C6 alkynyl groups having a carbon atom number of C1-C6, and halogen-substituted or unsubstituted aromatic hydrocarbon groups.

[0032] Specifically, the C1-C6 alkyl group may include a straight-chain alkyl group or a branched-chain alkyl group having 1 to 6 carbon atoms, such as methyl, ethyl, pentyl, isobutyl, etc.; the C1-C6 alkenyl group may include a straight-chain alkenyl group or a branched-chain alkenyl group having 1 to 6 carbon atoms, such as ethylene, butene, propylene, etc. Halogen elements include fluorine, chlorine, bromine, iodine and other elements. The boron-containing compound additive B in the present application can be preferentially reduced on the negative electrode surface to participate in the formation of the negative electrode SEI film. The formed SEI film is rich in B-O and B-F bonds with stronger mechanical properties and better toughness, improving the continuous repair ability of the SEI film during the cycling process and effectively enhancing the cycling performance and high-temperature storage performance of the battery.

[0033] In some embodiments, based on the total mass of the electrolyte being 100%, the mass ratio of the additive A in the electrolyte is 0.01% to 5%.

[0034] When the mass content of the additive A added to the electrolyte is in the range of 0.01% to 5%, the group containing -N=C=O unsaturated bonds can form a stable interfacial film on the negative electrode surface. At the same time, the contained -Si-O bond can combine hydrogen and metal ions, protecting the positive electrode active material while optimizing the positive electrode / non-aqueous electrolyte interface and improving the high-temperature cycling performance and high-temperature storage performance of the battery.

[0035] When the mass content of the additive A added to the non-aqueous electrolyte is less than 0.01%, an SEI film cannot be formed at the negative electrode interface; if the mass content of the additive A is higher than 5%, although the battery has a high capacity retention rate and good high-temperature storage performance, the amount of additive added increases, and the cost of the electrolyte increases.

[0036] Specifically, the mass ratio of the additive A in the non-aqueous electrolyte is 0.01%, 0.05%, 0.08%, 0.1%, 0.13%, 0.17%, 2%, 2.6%, 3%, 3.4%, 4%, 4.7%, 5%. As long as the mass ratio of the additive A in the electrolyte is in the range of 0.01% to 5%.

[0037] In some embodiments, based on the total mass of the electrolyte being 100%, the mass ratio of the additive B in the electrolyte is 0.01 to 5%.

[0038] The mass ratio of additive B added to the non-aqueous electrolyte ranges from 0.01% to 5%. Additive B can be preferentially reduced on the surface of the negative electrode to participate in the formation of the electrode interface film. The formed SEI film is rich in B-O bonds and B-F bonds with stronger mechanical properties and better toughness, improving the continuous repair ability of the SEI film during the cycling process and effectively enhancing the cycling performance and high-temperature storage performance of the battery.

[0039] If the mass of additive B added to the aqueous electrolyte is less than 0.01%, an SEI film cannot be formed. If the mass content of additive B is higher than 5%, although the battery has a high capacity retention rate and good high-temperature storage performance, the addition amount of the additive increases, and the cost of the electrolyte increases.

[0040] Specifically, the mass ratio of additive B in the non-aqueous electrolyte is 0.01%, 0.05%, 0.08%, 0.1%, 0.13%, 0.17%, 2%, 2.6%, 3%, 3.4%, 4%, 4.5%, 4.7%, 5%. As long as the mass ratio of additive B in the electrolyte ranges from 0.01% to 5%.

[0041] In some preferred embodiments, the additive A is 3-isocyanatopropyltrimethoxysilane. The additive B is tris(trimethylsilyl) borate.

[0042] In some preferred embodiments, based on the total mass of the electrolyte being 100%, the mass ratio of 3-isocyanatopropyltrimethoxysilane in the electrolyte is 3%; the mass ratio of tris(trimethylsilyl) borate in the electrolyte is 2%.

[0043] It should be noted that the above are only optional types of the present invention and do not represent a limitation to the present invention.

[0044] In some embodiments, the concentration of the lithium salt in the non-aqueous electrolyte is 0.5M to 2M. When the lithium salt concentration is too low, the conductivity of the non-aqueous electrolyte is low, which will affect the rate and cycling performance of the entire battery system. When the lithium salt concentration is too high, the viscosity of the non-aqueous electrolyte is too large, which is also not conducive to the improvement of the rate of the entire battery system. Specifically, the lithium salt concentration can be 0.5M, 0.7M, 1.0M, 1.2M, 1.3M, 1.5M, 1.6M, 1.7M, 1.8M, 1.9M, 2.0M, etc. As long as the concentration of the lithium salt ranges from 0.5M to 2M.

[0045] In some embodiments, the lithium salt is selected from one or more of organic electrolyte salts and inorganic electrolyte salts. Inorganic lithium salts include but are not limited to LiPF6, LiBF4, LiSbF6, LiAsF6, LiTaF6, LiAlCl4, Li2B 10 Cl 10 、Li2B10 F 10 、 one or more of lithium salts of LiClO4, LiCF3SO3, chelated orthoborate and chelated orthophosphate, and the organic lithium salts include but are not limited to lithium bis(oxalato)borate [LiB(C2O4)2], lithium bis(malonato)borate [LiB(O2CCH2CO2)2], lithium bis(difluoromalonato)borate [LiB(O2CCF2CO2)2], lithium (malonatooxalato)borate [LiB(C2O4)(O2CCH2CO2)], lithium (difluoromalonatooxalato)borate [LiB(C2O4)(O2CCF2CO2)], lithium tris(oxalato)phosphate [LiP(C2O4)3] and lithium tris(difluoromalonato)phosphate [LiP(O2CCF2CO2)3].

[0046] Specifically, in some other embodiments, the lithium salt is selected from fluorine-containing lithium salts, including but not limited to one or more of hexafluorophosphate, hexafluoroarsenate, perchlorate, lithium trifluoromethanesulfonate, lithium difluoro(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium tris(trifluoromethylsulfonyl)methide.

[0047] In some preferred embodiments, the concentration of the lithium salt in the non-aqueous electrolyte is 0.9 M to 1.3 M.

[0048] In some embodiments, the solvent is selected from non-aqueous organic solvents.

[0049] In preferred embodiments, the non-aqueous organic solvents include but are not limited to ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl formate, ethyl formate, ethyl propionate, propyl propionate, methyl butyrate, tetrahydrofuran.

[0050] In some embodiments, the non-aqueous electrolyte further includes an auxiliary additive, and the auxiliary additive includes but is not limited to vinylene carbonate and its derivatives, ethylene carbonate derivatives having non-conjugated unsaturated bonds in their side chains, halogen-substituted cyclic carbonates, and salts of chelated orthoborate and chelated orthophosphate.

[0051] Based on the total mass of the electrolyte being 100%, the mass content of the auxiliary additive is 0.01% to 20%.

[0052] Adding an auxiliary additive to the electrolyte, in cooperation with additive A and additive B, forms a SEI film with high mechanical strength, good toughness and strong stability at the negative electrode interface, thereby improving the high-temperature cycling performance of the battery.

[0053] In some embodiments, the auxiliary additive is selected from one or more of vinylene carbonate, ethylene vinylene carbonate, methylene ethylene carbonate, fluoroethylene carbonate, trifluoromethyl ethylene carbonate and difluoroethylene carbonate.

[0054] On the other hand, an embodiment of the present invention further provides a lithium-ion battery, which includes a positive electrode sheet, a negative electrode sheet, a separator, and the non-aqueous electrolyte described in any one of the above embodiments.

[0055] The lithium-ion battery provided by this application can generate an SEI film with high mechanical strength, good toughness, and strong stability at the electrode interface during the charge and discharge process, improving the high-temperature cycle performance and high-temperature performance of the battery.

[0056] In some embodiments, in the positive electrode sheet and the negative electrode sheet, the mass ratio of element B derived from additive B is not less than 100 ppm.

[0057] After the battery is injected with the electrolyte, the electrolyte needs to infiltrate the positive electrode sheet and the negative electrode sheet. This application stipulates that in the electrolyte infiltrating the positive electrode sheet and the negative electrode sheet, the mass ratio of element B in additive B is not less than 100 ppm, which can enable the electrolyte to better infiltrate the positive electrode sheet and the negative electrode sheet. The SEI film formed at the negative electrode interface is rich in B-O and B-F bonds with stronger mechanical properties and better toughness, improving the continuous repair ability of the SEI film during the cycling process and effectively enhancing the cycling performance of the battery.

[0058] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode material. The positive electrode material includes a positive electrode active material, a first conductive agent, and a first binder. The negative electrode sheet includes a negative electrode current collector and a negative electrode material. The negative electrode material includes a negative electrode active material, a second conductive agent, and a second binder.

[0059] In some embodiments, the positive electrode active material includes one or more of lithium iron phosphate, lithium manganese iron phosphate, lithium cobaltate, ternary LiNi a Co b Mn c O2 materials (where a + b + c = 1 and a ≥ b), and the negative electrode active material is selected from graphite and / or silicon.

[0060] In a preferred embodiment, the negative electrode active material includes, but is not limited to, natural graphite, artificial graphite, mesocarbon microbeads (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel-structured lithiated TiO2-Li4Ti5O 12 , Li-Al alloy.

[0061] The present invention is further described below through examples.

[0062] The types and contents of additive A and additive B added in the following examples and comparative examples are shown in Table 1.

[0063] Table 1

[0064]

[0065]

[0066]

[0067] Example 1

[0068] This example is used to illustrate the non-aqueous electrolyte disclosed in the present invention. The preparation method of the non-aqueous electrolyte includes the following operating steps:

[0069] Preparation of non-aqueous electrolyte: Mix ethylene carbonate (EC), diethyl carbonate (DEC), and propylene carbonate (PC) in a mass ratio of 1:1:1 as the organic solvent. Add additive A and additive B with the mass percentage contents shown in Example 1 of Table 1 to the organic solvent. After mixing evenly, add LiPF6 to obtain a non-aqueous electrolyte with a LiPF6 concentration of 1.1 mol / L.

[0070] Fabrication of the positive electrode sheet: Mix the positive electrode active material lithium cobalt oxide (LiCoO2), the conductive agent CNT (Carbon Nanotube), and the binder PVDF (polyvinylidene fluoride) in a mass ratio of 95:1.5:1.5. Stir and mix well in N-methylpyrrolidone solvent to form a uniform positive electrode paste. Coat this paste on the positive electrode current collector aluminum foil, dry it, and cold press it to obtain the positive electrode sheet.

[0071] Fabrication of the negative electrode sheet: Mix the negative electrode active material graphite, the conductive agent acetylene black, the binder styrene-butadiene rubber, and the thickener sodium carboxymethyl cellulose in a mass ratio of 96:1.2:1.5:1.3 in deionized water solvent. Stir and mix well to form a uniform negative electrode paste. Coat this paste on the negative electrode current collector copper foil, dry it, and cold press it to obtain the negative electrode sheet.

[0072] Fabrication of non-aqueous electrolyte: Use a PE porous polymer film as the separator.

[0073] Stack the positive electrode sheet, the separator, and the negative electrode sheet in sequence, with the separator in the middle of the positive and negative electrodes to play an isolation role. Then wind the stacked electrode sheets and the separator to obtain a wound core. Place the wound core in an aluminum-plastic film bag that has been formed by punching the shell. Inject the above-prepared non-aqueous electrolyte into the baked and dried battery cell respectively. After processes such as vacuum packaging, standing, and formation, a lithium-ion battery is obtained.

[0074] Examples 2 - 16

[0075] Examples 2 - 16 are used to illustrate the non-aqueous electrolyte and lithium-ion battery disclosed in the present invention, including most of the operating steps in Example 1. The differences are as follows:

[0076] In the preparation of the non-aqueous electrolyte of Example 2-16, the contents and types of Additive A and Additive B are different, as shown in Table 1.

[0077] Comparative Examples 1-8

[0078] Comparative Examples 1-8 are used to compare and illustrate the non-aqueous electrolyte and battery disclosed in the present invention, including most of the operation steps in Example 1. The differences are as follows:

[0079] In the preparation of the non-aqueous electrolyte, the types and contents of Additive A and Additive B are different, as shown in Table 1.

[0080] Performance Test

[0081] The following performance tests were carried out on the lithium-ion batteries prepared in Examples 1-16 and Comparative Examples 1-8:

[0082] 45°C Cycle Test

[0083] The test method is as follows: In an incubator at 45±2°C, the lithium-ion battery is charged at a constant current and voltage of 1C to 4.45V, with a cut-off current of 0.05C, and then discharged at 1C to 3V. Multiple charge and discharge cycles are carried out under the above conditions. Calculate the capacity retention rate of the battery after 800 cycles, with 5 batteries in each group.

[0084] Capacity retention rate (%) = Discharge capacity (mAh) in the 800th cycle / Discharge capacity (mAh) in the third cycle × 100%

[0085] The average value of the capacity retention rates of 5 batteries in each group after cycling through different weeks is recorded in Table 2.

[0086] 60°C High Temperature Storage Test

[0087] After the lithium-ion battery is left standing at 25±2°C for 2 hours, it is charged and discharged at 1C / 0.5C, and the charge and discharge voltage is 3.0-4.45V. The discharge capacity of this time is the first discharge capacity, and then the battery is fully charged. Subsequently, the battery is placed in storage at 60°C for 30 days, and the remaining capacity retention rate and thickness expansion rate of the battery after storage are calculated.

[0088] The calculation formula is: Remaining capacity retention rate on the 30th day (%) = (Remaining discharge capacity on the 30th day) / (First cycle discharge capacity) × 100%;

[0089] Calculate the thickness expansion rate of the battery after storage. Thickness expansion rate on the 30th day (%) = (Battery thickness after 30 days of storage) / (Initial battery thickness) × 100%;

[0090] The test results obtained from Examples 1-16 and Comparative Examples 1-8 are filled into Table 2.

[0091] Table 2 Performance test data table of each example and comparative example

[0092]

[0093]

[0094] According to the test data in Table 2, compared with Comparative Example 1, in Comparative Example 2, additive A was added to the electrolyte alone, and the high-temperature cycle capacity retention rate of the battery was significantly improved, and the high-temperature storage expansion rate of the battery was slightly reduced. In Comparative Example 3, additive B was added alone, and both the high-temperature cycle performance and high-temperature storage performance of the battery were significantly improved. In Comparative Example 4, the content of additive A was continuously increased, and the improvement of the high-temperature cycle capacity retention rate and high-temperature storage thickness expansion rate of the battery was not obvious, indicating that when there is only additive A in the electrolyte, increasing the content of additive A has no obvious improvement on the high-temperature cycle and high-temperature storage performance of the battery. In Comparative Example 5, the content of additive B was continuously increased, and the high-temperature storage thickness expansion rate of the battery was significantly reduced, but the cycle performance was not significantly improved, indicating that the increase in the content of additive B in the electrolyte helps to form the SEI film at the negative electrode interface, but the stability of the SEI film is low and there is no obvious improvement in the battery cycle performance. Comparing Comparative Examples 1-5 with Example 1, in Example 1, additive A and additive B were added simultaneously, which can significantly improve the high-temperature cycle performance and high-temperature storage performance. It shows that when additive B and additive A are added simultaneously to the electrolyte, additive A contains -N=C=O bond functional groups and -Si-O bonds. The -N=C=O unsaturated bond group can form a stable interfacial film on the negative electrode surface. At the same time, the contained -Si-O bond can combine hydrogen and metal ions, protecting the positive active material while optimizing the positive electrode / non-aqueous electrolyte interface. The boron-containing compound additive B can be preferentially reduced on the negative electrode surface to participate in the formation of the negative electrode SEI film. The formed SEI film is rich in B-O and B-F bonds with stronger mechanical properties and better toughness, improving the continuous repair ability of the SEI film during the cycle process and effectively enhancing the cycle performance of the battery. The two work together to improve the high-temperature cycle performance and high-temperature storage performance of the battery.

[0095] Compared with Example 1, in Examples 2 to 10, the contents of Additive A and Additive B were adjusted. As the contents of Additive A and Additive B increased, the cycle performance and high-temperature storage performance improved. Among them, when the content of Additive A in the electrolyte was 3% and the content of Additive B was 2%, the battery had a higher high-temperature cycle capacity retention rate and a lower battery expansion rate. Comparing Example 5 with Example 11 and Example 12 with Example 2, when the content of Additive B or Additive A in the electrolyte was higher than 5%, the battery still had good high-temperature storage performance and high-temperature cycle performance. However, as the contents of Additive A and Additive B increased, the cost of the electrolyte increased. Comparing Example 10 with Examples 13 to 16, additives A and B with the same structure added to the electrolyte both had the effect of significantly improving the high-temperature cycle performance and high-temperature storage performance of the battery.

[0096] From the test results of Example 7, Comparative Example 6 to Comparative Example 8, it can be seen that when the existing isocyanate additives and siloxane additives were added separately to the electrolyte, the battery had a low high-temperature cycle capacity retention rate and a high thickness expansion rate. When the isocyanate additives and siloxane additives were added to the electrolyte, there was no obvious improvement in the high-temperature cycle capacity retention rate and thickness expansion rate of the battery. It is speculated that the isocyanate additives and siloxane additives added to the electrolyte have no synergistic effect with Additive B and have no obvious improvement on the high-temperature cycle and high-temperature storage performance of the battery. It shows that only when Additive A shown in Structural Formula I of the present application is added to the electrolyte and synergizes with Additive B, can it have the effect of significantly improving the high-temperature cycle performance and high-temperature storage performance of the battery.

[0097] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A non-aqueous electrolyte, characterized in that, It includes a lithium salt, a solvent and an additive. The additive includes additive A and additive B, and the additive B is a boron-containing compound; the additive A is selected from 3-isocyanatopropyltrimethoxysilane or ; The boron-containing compound is selected from one or more of tris(trimethylsilyl) borate, , ; Based on the total mass of the electrolyte being 100%, the mass percentage of additive A in the electrolyte is 0.01% to 5%; Based on the total mass of the electrolyte being 100%, the mass percentage of additive B in the electrolyte is 0.01% to 5%.

2. The non-aqueous electrolyte according to claim 1, wherein Additive A is 3-isocyanatopropyltrimethoxysilane, and additive B is tris(trimethylsilyl) borate.

3. The non-aqueous electrolyte according to claim 1, characterized in that, The concentration of the lithium salt in the electrolyte is 0.5 M to 2 M.

4. The non-aqueous electrolyte according to claim 3, characterized in that, The concentration of the lithium salt in the electrolyte is 0.9 M to 1.3 M.

5. The non-aqueous electrolyte according to claim 1, characterized in that, The electrolyte further includes an auxiliary additive, and the auxiliary additive is selected from one or more of vinylene carbonate, ethylene vinylene carbonate, methylene vinylene carbonate, fluoroethylene carbonate, trifluoromethyl carbonate, and difluoroethylene carbonate; Based on the total mass of the electrolyte being 100%, the mass percentage of the auxiliary additive is 0.01% to 20%.

6. A lithium-ion battery, characterized in that, It includes a positive electrode sheet, a negative electrode sheet, a separator, and the non-aqueous electrolyte according to any one of claims 1-5.

7. The lithium-ion battery according to claim 6, characterized in that, In the positive electrode sheet and the negative electrode sheet, the mass percentage of boron element derived from additive B is not less than 100 ppm.

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