Electrolyte additive, electrolyte and lithium ion battery

Abstract

The invention discloses an electrolyte additive, an electrolyte and a lithium ion battery, and relates to the technical field of batteries. The electrolyte additive comprises a compound shown in the formula I and 2, 2-difluoroethyl alkyl sulfonate, the mass ratio of the compound shown in the formula I to the 2, 2-difluoroethyl alkyl sulfonate is (1-5): (1-5), the structure of the compound shown in the formula I is as follows: # imgabs0 #, in the formula I, R1 is selected from fluorine atoms, R2 is selected from fluorine atoms, R3 is selected from fluorine atoms, R4 is selected from fluorine atoms, and R4 is selected from fluorine atoms; r2, R3, R4 and R5 are independently selected from a hydrogen atom, a fluorine atom, trifluoromethyl, a cyano group, an amino group, a nitro group, a carboxyl group, an ether group, a C1-C6 alkyl group, a C2-C6 alkenyl group and a C2-C6 alkynyl group. According to the invention, the compound shown in the formula I and the 2, 2-difluoroethyl alkyl sulfonate are added into the electrolyte and can play a synergistic role, so that the overcharge problem of the battery can be improved, and the electrical property and the safety performance of the battery can be improved.

Description

Technical Field

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

[0002] Overcharging of batteries is a common problem faced by many types of batteries (especially lithium-ion batteries), which may lead to a decline in battery performance, a shortening of battery life, and even safety risks. To address the issue of battery overcharging, the overcharging resistance of the battery can be improved through material modification. For example, a positive temperature coefficient (PTC) coating is coated on the surface of the positive active material. When the temperature rises, the resistance of the PTC coating increases significantly, thereby cutting off the circuit. However, modifying the positive active material itself has a complex process, high cost, and increases the positive impedance, thereby deteriorating the battery performance. It is also possible to introduce overcharging-resistant additives into the electrolyte, such as biphenyl (BP), cumene (CHB), and terphenyl (TP). However, these additives are unstable themselves and have a large film-forming impedance, which may increase the battery impedance and thereby deteriorate the battery electrical performance, and cannot well balance the electrical performance and safety performance. Currently, there is no efficient and feasible solution. Summary of the Invention

[0003] The purpose of the present invention is to overcome the deficiencies of the prior art and provide an electrolyte additive, an electrolyte, and a lithium-ion battery. The present invention adds the compound shown in Formula I and 2,2-difluoroethyl alkyl sulfonate to the electrolyte, and they can play a synergistic role, which is beneficial to improving the problem of battery overcharging. Moreover, it can also improve the electrical performance and safety performance of the battery.

[0004] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0005] In the first aspect, the present invention provides an electrolyte additive, which includes the compound shown in Formula I and 2,2-difluoroethyl alkyl sulfonate. The mass ratio of the compound shown in Formula I to 2,2-difluoroethyl alkyl sulfonate is (1 - 5):(1 - 5). The structure of the compound shown in Formula I is as follows:

[0006]

[0007] Among them, in Formula I, R1 is a fluorine atom, and R2, R3, R4, and R5 are independently selected from a hydrogen atom, a fluorine atom, a trifluoromethyl group, a cyano group, an amino group, a nitro group, a carboxyl group, an ether group, a C1 - C6 alkyl group, a C2 - C6 alkenyl group, and a C2 - C6 alkynyl group.

[0008] Preferably, the mass ratio of the compound shown in Formula I to 2,2-difluoroethyl alkyl sulfonate is (1 - 3):(1 - 3).

[0009] More preferably, the mass ratio of the compound represented by Formula I to the 2,2-difluoroethyl alkyl sulfonate is any one of 1:1, 1:2, 1:3, 2:1, 2:2, 2:3, 3:1, 3:2, 3:3 or a range value between the two.

[0010] Preferably, the 2,2-difluoroethyl alkyl sulfonate includes but is not limited to 2,2-difluoroethyl methyl sulfonate and 2,2-difluoroethyl trifluoromethanesulfonate, and their structures are respectively shown as follows:

[0011]

[0012] Preferably, the structure of Formula I includes at least one of Formula I-(1) to I-(12):

[0013]

[0014]

[0015] In a second aspect, the present invention also provides an electrolyte, comprising a solvent, a lithium salt, and an electrolyte additive.

[0016] Preferably, the mass percentage of the lithium salt in the electrolyte is 10-18%.

[0017] Preferably, the mass percentage of the electrolyte additive in the electrolyte is 2-6%.

[0018] Preferably, the solvent includes cyclic carbonates and / or linear esters. The cyclic carbonates include at least one of ethylene carbonate (EC), propylene carbonate (PC), and fluoroethylene carbonate (FEC); the linear esters include at least one of ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl acetate (EA), ethyl propionate (EP), and propyl propionate (PP).

[0019] Preferably, the lithium salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium bis(trifluoromethyl)imide (LiTFSI), and lithium bis(fluorosulfonyl)imide (LiFSI).

[0020] Preferably, the electrolyte further includes a negative electrode film-forming additive and a positive electrode film-forming additive.

[0021] More preferably, the negative electrode film-forming additive includes at least one of vinylene carbonate (VC), fluoroethylene carbonate (FEC), divinyl sulfone (DTD), methylene methanedisulfonate (MMDS), 1,3-propane sultone (PS), and propylene sulfonic acid lactone (PST).

[0022] More preferably, the positive electrode film-forming additive includes at least one of lithium difluorophosphate (LiPO2F2), lithium tetrafluoroborate (LiBF4), lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)phosphate (LiODFP), lithium difluoro(oxalato)borate (LiODFB), tris(trimethylsilyl) phosphate (TMSP), and tris(trimethylsilyl) borate (TMSB).

[0023] In a third aspect, the present invention also provides a lithium-ion battery, including a positive electrode plate, a separator, a negative electrode plate, and an electrolyte. The positive electrode plate includes a positive electrode current collector and a positive electrode active material layer. The positive electrode active material layer includes a positive electrode active material, and the positive electrode active material includes a non-high-voltage positive electrode active material and a high-voltage positive electrode active material.

[0024] Preferably, the non-high-voltage positive electrode active material includes at least one of lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium manganese iron phosphate, and lithium cobalt oxide.

[0025] Preferably, the high-voltage positive electrode active material includes at least one of lithium nickel manganese oxide and lithium-rich manganese-based materials.

[0026] By introducing a high-voltage positive electrode active material into the positive electrode active material of the present invention, lithium can be preferentially deintercalated during overcharging of the battery, maintaining the stability of the positive electrode, and thus improving the safety of the battery.

[0027] Preferably, the mass percentage of the high-voltage positive electrode active material in the positive electrode active material is 5-20%.

[0028] Preferably, the D50 particle size of the high-voltage positive electrode active material is 5-15 μm.

[0029] Preferably, the negative electrode plate includes a negative electrode current collector and a negative electrode active material layer. The negative electrode active material layer includes a negative electrode active material, and the negative electrode active material includes graphite and / or silicon-carbon material.

[0030] Preferably, the positive electrode current collector is any one of aluminum foil and carbon-coated aluminum foil, and the negative electrode current collector is any one of copper foil and carbon-coated copper foil.

[0031] Preferably, the positive electrode active material layer further includes a conductive agent, a binder, and a dispersant. The conductive agent in the positive electrode active material layer is at least one of carbon black (SP), carbon nanotubes (CNT), and graphene. The binder is polyvinylidene fluoride (PVDF), and the dispersant is polyvinylpyrrolidone (PVP).

[0032] Preferably, the negative electrode active material layer further comprises a conductive agent and a binder. The conductive agent in the negative electrode active material layer is at least one of carbon black and single-walled carbon nanotubes, and the binder is at least one of carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), and polyacrylic acid (PAA).

[0033] Preferably, the separator is a coated polypropylene (PP) and / or polyethylene (PE) based film, and the coating is a ceramic (CCS) layer and a binder (PCS) layer.

[0034] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0035] (1) By adding the compound shown in Formula I to the electrolyte, the present invention is beneficial to improving the wettability of the electrolyte, promoting lithium ion transport, and thus improving the kinetic performance of the battery. Specifically, the compound shown in Formula I contains a fluorobenzene structure and a borane structure. The presence of the fluorobenzene structure is not only beneficial to the formation of the solid electrolyte interface (SEI) film on the anode, but also due to the influence of the ortho-substitution of the fluorine atom and the borane structure, the high electronegativity of the fluorine atom and the large steric hindrance effect of the benzene ring structure can also inhibit the decomposition of the borane at the negative electrode, thereby protecting the negative electrode. In addition, due to the high reactivity of the fluorobenzene structure at ultra-high voltages, a large amount of gas is generated when the battery is significantly overcharged, thus timely opening the explosion-proof valve and activating the current interruption device (CID), which has an obvious improvement effect on the overcharging of the battery. On the other hand, the introduction of the borane structure is beneficial to the formation of a film on the surface of the high-voltage positive electrode active material at high voltages, which is beneficial to improving the stability of the interface of the high-voltage positive electrode active material. At the same time, due to the electron-deficient effect of the borane, it has a good inhibitory effect on the deterioration of the electrolyte caused by the oxygen evolution of the high-voltage positive electrode active material at high voltages.

[0036] (2) By adding 2,2-difluoroethyl alkyl sulfonate to the electrolyte, on the one hand, 2,2-difluoroethyl alkyl sulfonate can selectively adsorb on the manganese / nickel transition metal sites of the high-voltage positive electrode active material to form an antioxidant "buffer layer", and can push the free solvent molecules away from the positive electrode / electrolyte interface, thereby reducing the oxidative decomposition of the solvent molecules at the cathode under high voltages. On the other hand, when 2,2-difluoroethyl alkyl sulfonate adsorbs on the high-voltage positive electrode active material, the carbon-carbon bond in 2,2-difluoroethyl alkyl sulfonate shows a relatively weak strength, which helps the cleavage of the semi-fluorinated -CF2H group and helps to form a LiF-rich and firm positive electrode passivation layer, thereby effectively inhibiting the cracking and transition metal dissolution of the high-voltage positive electrode active material particles. At the same time, on the negative electrode side, 2,2-difluoroethyl alkyl sulfonate is induced to form beneficial SEI components such as LiF and lithium alkyl sulfonate, which is beneficial to improving the stability of the negative electrode and inhibiting the decomposition of the solvent at the anode.

[0037] (3) In the present invention, a compound shown by Formula I and 2,2-difluoroethyl alkyl sulfonate are simultaneously added into the electrolyte. The 2,2-difluoroethyl alkyl sulfonate can be adsorbed on the surface of the high-voltage positive electrode active material and synergistically oxidize with the compound shown by Formula I to form an inorganic cathode electrolyte interface film (CEI) rich in multiple components of B, F, and S, which is beneficial to further improving the antioxidant property of the high-voltage positive electrode active material, and then inhibiting the decomposition of the electrolyte during overcharge. At the same time, the 2,2-difluoroethyl alkyl sulfonate and the compound shown by Formula I can synergistically promote the formation of the inorganic component LiF in the negative electrode SEI film, improve the stability of the negative electrode SEI film, and also inhibit the dissolution of the negative electrode SEI film during overcharge, protect the negative electrode, and then reduce side reactions. Detailed Embodiments

[0038] To better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments, but the protection scope and implementation manners of the present invention are not limited thereto.

[0039] The materials, reagents, etc. used in the following embodiments are, unless otherwise specified, reagents and materials that can be obtained from commercial channels.

[0040]

[0041]

[0042] Example 1

[0043] A lithium-ion battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer coated on the positive electrode current collector; the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer coated on the negative electrode current collector. The positive electrode current collector is a carbon-coated aluminum foil, and the negative electrode current collector is a copper foil.

[0044] The positive electrode active material layer includes a positive electrode active material, a conductive agent, a binder, and a dispersant. The positive electrode active material includes a non-high-voltage positive electrode active material and a high-voltage positive electrode active material. The non-high-voltage positive electrode active material is lithium iron phosphate, and the high-voltage positive electrode active material is lithium nickel manganate. The negative electrode active material layer includes a negative electrode active material, a conductive agent, and a binder. The negative electrode active material includes graphite.

[0045] Preparation method of positive electrode sheet: Based on the total mass of the positive electrode active material layer being 100%, the positive electrode active material layer includes 91.77% by mass of lithium iron phosphate non-high-voltage positive electrode active material, 4.83% of lithium nickel manganate high-voltage positive electrode active material (purchased from Nantong Xiangrui New Materials Co., Ltd.), 1.0% of Super P conductive agent, 0.5% of carbon nanotube conductive agent, 0.2% of polyvinylpyrrolidone dispersant, and 1.7% of polyvinylidene fluoride binder. Mix the above components according to the formula amount, and then add N-methylpyrrolidone solvent and mix evenly to obtain the positive electrode slurry. The solid content of the positive electrode slurry is 76.1%. Then, coat the positive electrode slurry on the surface of carbon-coated aluminum foil, roll and dry it, and then slice it to obtain the positive electrode sheet.

[0046] The mass percentage of the high-voltage positive electrode active material lithium nickel manganate in the positive electrode active material is 5%, and the D50 particle size of the high-voltage positive electrode active material lithium nickel manganate is 9.36 um.

[0047] Preparation method of negative electrode sheet: Mix artificial graphite, Super P conductive agent, CMC binder, and SBR binder according to a mass ratio of 95.8:1:1.3:1.9, and then add deionized water and stir evenly to obtain the negative electrode slurry. The solid content of the negative electrode slurry is 51.3%. Coat the negative electrode slurry on the surface of copper foil, roll and dry it, and then slice it to obtain the negative electrode sheet;

[0048] The separator is a composite separator of 9PE + 0.5CCS + 2PCS (um).

[0049] The electrolyte includes a solvent, a lithium salt, an electrolyte additive, a negative electrode film-forming additive, and a positive electrode film-forming additive. Among them, the solvent is 27% ethylene carbonate (EC), 25% ethyl methyl carbonate (EMC), 26.9% dimethyl carbonate (DMC); the lithium salt is 13.5% lithium hexafluorophosphate (LiPF6); the negative electrode film-forming additive is 3.5% vinylene carbonate (VC), 0.5% fluoroethylene carbonate (FEC), 0.8% divinyl sulfone (DTD); the positive electrode film-forming additive is 0.5% lithium difluorophosphate (LiPO2F2), 0.3% tris(trimethylsilyl) phosphate (TMSP).

[0050] The electrolyte additive includes the compound shown in formula I-(1) and 2,2-difluoroethyl methanesulfonate, and the mass ratio of the two is 1:1. And the mass percentage of the electrolyte additive in the electrolyte is 2%; the structure of the compound shown in formula I-(1) is as follows:

[0051]

[0052] Preparation method of lithium-ion battery: Assemble the above-mentioned positive electrode sheet, negative electrode sheet, electrolyte and separator to form a battery, and then perform formation on the battery at 45°C (the steps of formation are: first charge at 0.05C to 3.1V, charge at 0.1C to 3.5V, charge at 0.3C to 3.7V, charge at 0.05C to 4.3V, and finally discharge at 0.2C to 3.4V). After the formation is completed, perform aging and grading to obtain a lithium-ion battery.

[0053] Example 2

[0054] A lithium-ion battery, different from Example 1, wherein the mass percentage of the high-voltage positive electrode active material lithium nickel manganate in the positive electrode active material is 20%, the electrolyte additive includes the compound shown in Formula I-(1) and 2,2-difluoroethyl methyl sulfonate, and the mass ratio of the two is 2:3, and the mass percentage of the electrolyte additive in the electrolyte is 5%, and the solvent is 27% ethylene carbonate (EC), 25% ethyl methyl carbonate (EMC), 23.9% dimethyl carbonate (DMC).

[0055] Example 3

[0056] A lithium-ion battery, different from Example 2, wherein the electrolyte additive includes the compound shown in Formula I-(1) and 2,2-difluoroethyl methyl sulfonate, and the mass ratio of the two is 1:5, and the mass percentage of the electrolyte additive in the electrolyte is 6%, and the solvent is 27% ethylene carbonate (EC), 25% ethyl methyl carbonate (EMC), 22.9% dimethyl carbonate (DMC).

[0057] Example 4

[0058] A lithium-ion battery, different from Example 2, wherein the electrolyte additive includes the compound shown in Formula I-(1) and 2,2-difluoroethyl methyl sulfonate, and the mass ratio of the two is 5:1, and the mass percentage of the electrolyte additive in the electrolyte is 6%, and the solvent is 27% ethylene carbonate (EC), 25% ethyl methyl carbonate (EMC), 22.9% dimethyl carbonate (DMC).

[0059] Example 5

[0060] A lithium-ion battery, different from Example 2, wherein the electrolyte additive includes the compound shown in Formula I-(1) and 2,2-difluoroethyl trifluoromethanesulfonate, and the mass ratio of the two is 2:3, and the mass percentage of the electrolyte additive in the electrolyte is 5%.

[0061] Example 6

[0062] A lithium-ion battery, which is different from that of Example 2 in that the electrolyte additive comprises the compound shown in Formula I-(2) and 2,2-difluoroethyl methyl sulfonate, and the mass ratio of the two is 2:3, and the mass percentage of the electrolyte additive in the electrolyte is 5%.

[0063] The structure of the compound shown in Formula I-(2) is as follows:

[0064]

[0065] Example 7

[0066] A lithium-ion battery, which is different from that of Example 2 in that the electrolyte additive comprises the compound shown in Formula I-(3) and 2,2-difluoroethyl methyl sulfonate, and the mass ratio of the two is 2:3, and the mass percentage of the electrolyte additive in the electrolyte is 5%.

[0067] The structure of the compound shown in Formula I-(3) is as follows:

[0068]

[0069] Example 8

[0070] A lithium-ion battery, which is different from that of Example 2 in that the electrolyte additive comprises the compound shown in Formula I-(4) and 2,2-difluoroethyl methyl sulfonate, and the mass ratio of the two is 2:3, and the mass percentage of the electrolyte additive in the electrolyte is 5%.

[0071] The structure of the compound shown in Formula I-(4) is as follows:

[0072]

[0073] Example 9

[0074] A lithium-ion battery, which is different from that of Example 2 in that the electrolyte additive comprises the compound shown in Formula I-(5) and 2,2-difluoroethyl methyl sulfonate, and the mass ratio of the two is 2:3, and the mass percentage of the electrolyte additive in the electrolyte is 5%.

[0075] The structure of the compound shown in Formula I-(5) is as follows:

[0076]

[0077] Example 10

[0078] A lithium-ion battery, which is different from that of Example 2 in that the electrolyte additive includes the compound shown in Formula I-(6) and 2,2-difluoroethyl methyl sulfonate, the mass ratio of the two is 2:3, and the mass percentage of the electrolyte additive in the electrolyte is 5%.

[0079] The structure of the compound shown in Formula I-(6) is as follows:

[0080]

[0081] Example 11

[0082] A lithium-ion battery, which is different from that of Example 2 in that the electrolyte additive includes the compound shown in Formula I-(7) and 2,2-difluoroethyl methyl sulfonate, the mass ratio of the two is 2:3, and the mass percentage of the electrolyte additive in the electrolyte is 5%.

[0083] The structure of the compound shown in Formula I-(7) is as follows:

[0084]

[0085] Example 12

[0086] A lithium-ion battery, which is different from that of Example 2 in that the electrolyte additive includes the compound shown in Formula I-(8) and 2,2-difluoroethyl methyl sulfonate, the mass ratio of the two is 2:3, and the mass percentage of the electrolyte additive in the electrolyte is 5%.

[0087] The structure of the compound shown in Formula I-(8) is as follows:

[0088]

[0089] Example 13

[0090] A lithium-ion battery, which is different from that of Example 2 in that the electrolyte additive includes the compound shown in Formula I-(9) and 2,2-difluoroethyl methyl sulfonate, the mass ratio of the two is 2:3, and the mass percentage of the electrolyte additive in the electrolyte is 5%.

[0091] The structure of the compound shown in Formula I-(9) is as follows:

[0092]

[0093] Example 14

[0094] A lithium-ion battery, which is different from that of Example 2 in that the electrolyte additive includes the compound shown in Formula I-(10) and 2,2-difluoroethyl methyl sulfonate, the mass ratio of the two is 2:3, and the mass percentage of the electrolyte additive in the electrolyte is 5%.

[0095] The structure of the compound shown in Formula I-(10) is as follows:

[0096]

[0097] Example 15

[0098] A lithium-ion battery, which is different from that of Example 2 in that the electrolyte additive includes the compound shown in Formula I-(11) and 2,2-difluoroethyl methyl sulfonate, the mass ratio of the two is 2:3, and the mass percentage of the electrolyte additive in the electrolyte is 5%.

[0099] The structure of the compound shown in Formula I-(11) is as follows:

[0100]

[0101] Example 16

[0102] A lithium-ion battery, which is different from that of Example 2 in that the electrolyte additive includes the compound shown in Formula I-(12) and 2,2-difluoroethyl methyl sulfonate, the mass ratio of the two is 2:3, and the mass percentage of the electrolyte additive in the electrolyte is 5%.

[0103] The structure of the compound shown in Formula I-(12) is as follows:

[0104]

[0105] Comparative Example 1

[0106] A lithium-ion battery, which is different from that of Example 2 in that the compound shown in Formula I-(1) is not added to the electrolyte additive, and the solvent is 27% ethylene carbonate (EC), 25% ethyl methyl carbonate (EMC), 25.9% dimethyl carbonate (DMC).

[0107] Comparative Example 2

[0108] A lithium-ion battery, which is different from that of Example 2 in that 2,2-difluoroethyl trifluoromethanesulfonate is not added to the electrolyte additive, and the solvent is 27% ethylene carbonate (EC), 25% ethyl methyl carbonate (EMC), 26.9% dimethyl carbonate (DMC).

[0109] Comparative Example 3

[0110] A lithium-ion battery, which is different from that of Example 2 in that the fluorobenzene structure and the borane structure in the compound shown in Formula I are not ortho positions, and the structure of the compound shown in Formula I is as follows:

[0111]

[0112] Comparative Example 4

[0113] A lithium-ion battery, which is different from that of Example 2 in that the electrolyte additive includes the compound shown in Formula I-(1) and 2,2-difluoroethyl methyl sulfonate, and the mass ratio of the two is 1:10, and the mass percentage of the electrolyte additive in the electrolyte is 11%, and the solvent is 27% ethylene carbonate (EC), 25% ethyl methyl carbonate (EMC), and 17.9% dimethyl carbonate (DMC).

[0114] Comparative Example 5

[0115] A lithium-ion battery, which is different from that of Example 2 in that the electrolyte additive includes the compound shown in Formula I-(1) and 2,2-difluoroethyl methyl sulfonate, and the mass ratio of the two is 10:1, and the mass percentage of the electrolyte additive in the electrolyte is 11%, and the solvent is 27% ethylene carbonate (EC), 25% ethyl methyl carbonate (EMC), and 17.9% dimethyl carbonate (DMC).

[0116] Performance testing

[0117] Capacity test:

[0118] Charge the lithium-ion batteries in the examples and comparative examples at a constant current of 1C to 3.65V at 25°C, then charge at a constant voltage of 3.65V to 0.05C, and then discharge at a constant current of 1C to 2.5V. This is recorded as one charge-discharge cycle process, and the initial discharge capacity is recorded as the capacity.

[0119] High-temperature cycle test:

[0120] Place the lithium-ion batteries in the examples and comparative examples in an incubator at 45°C, charge at a constant current of 1C to 3.65V, then charge at a constant voltage of 3.65V to 0.05C, and then discharge at a constant current of 1C to 2.5V. This is recorded as one charge-discharge cycle process, and the initial discharge capacity is recorded; the capacity retention rate = (remaining discharge capacity / initial discharge capacity) × 100%, and the number of cycles when the capacity retention rate of the lithium-ion battery is 80% is recorded as the high-temperature cycle number.

[0121] High-temperature storage test:

[0122] The lithium-ion batteries in the examples and comparative examples were charged at a constant current of 1C to 3.65V at 25°C, then charged at a constant voltage of 3.65V to 0.05C, and then discharged at a constant current of 1C to 2.5V. This was recorded as one charge-discharge cycle process. The initial discharge capacity was recorded. After being fully charged again, the lithium-ion batteries were placed in an oven at 45°C for 60 days. After the storage ended, the lithium-ion batteries were left standing at room temperature for 2h and then discharged at 1C to 2.5V. The remaining discharge capacity of the lithium-ion batteries at this time was recorded and the final battery capacity retention rate was calculated. The battery capacity retention rate = (remaining discharge capacity / initial discharge capacity) × 100% was the high-temperature storage retention rate;

[0123] Overcharge test:

[0124] The lithium-ion batteries in the examples and comparative examples were charged at a constant current of 1C to 3.65V at 25°C, then charged at a constant voltage of 3.65V to 0.05C, and then discharged at a constant current of 1C to 2.5V. This was recorded as one charge-discharge cycle process. The initial discharge capacity was recorded. After being fully charged again, they were charged at a constant current of 1C to 10V. If the battery did not catch fire or explode, the test was considered passed. The overcharge test pass rate was N / 10 pass, indicating that the total number of parallel samples of the test batteries was 10, and the number of batteries that passed the overcharge performance test was N.

[0125] The above test results are shown in Table 1.

[0126] Table 1

[0127]

[0128] Comparing Comparative Examples 1-2 with Example 2 respectively, it can be seen that when only the compound shown in Formula I-(1) or 2,2-difluoroethyl trifluoromethanesulfonate is added to the electrolyte, the high-temperature cycle life and high-temperature storage retention rate of the lithium-ion battery both decrease. This is because if the compound shown in Formula I and 2,2-difluoroethyl alkylsulfonate are not added to the electrolyte simultaneously, they cannot produce a synergistic effect, the stability of the positive and negative electrode interfaces decreases, especially the stability of the positive electrode interface decreases. When overcharged, oxygen is easily released from the positive electrode, resulting in the oxidation and decomposition of the electrolyte, increasing the risk of thermal runaway during overcharge of the battery, and further affecting the electrical performance and safety performance of the lithium-ion battery.

[0129] Comparing Comparative Example 3 with Example 2, in the compound shown in Formula I in Comparative Example 3, the fluorobenzene structure and the borane structure are not ortho-substituted, resulting in a decrease in electron cloud density and steric hindrance effect, making the borane easily decompose at the negative electrode, and further affecting the electrical performance of the lithium-ion battery.

[0130] Comparing Comparative Examples 4-5 with Example 2 respectively, it can be seen that when the mass ratio of the compound shown in Formula I-(1) to 2,2-difluoroethyl methanesulfonate is too large or too small, the synergistic effect between the compound shown in Formula I and 2,2-difluoroethyl alkylsulfonate decreases, which cannot effectively inhibit the decomposition of the electrolyte during overcharge, and will also reduce the stability of the negative electrode SEI film, thereby affecting the electrical performance of the lithium-ion battery.

[0131] In summary, the present invention generates a synergistic effect by adding the compound shown in Formula I-(1) and 2,2-difluoroethyl methanesulfonate to the electrolyte simultaneously, and controlling the mass ratio of the two within the range defined in the present invention is beneficial to improving the problem of overcharge of lithium-ion batteries. At the same time, it can also improve the safety performance and electrical performance of lithium-ion batteries.

[0132] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. An electrolyte additive, characterized in that, Comprising a compound represented by Formula I and 2,2-difluoroethyl alkyl sulfonate, the mass ratio of the compound represented by Formula I to 2,2-difluoroethyl alkyl sulfonate is (1 - 5):(1 - 5), and the structure of the compound represented by Formula I is as follows: Wherein, in Formula I, R1 is a fluorine atom, and R2, R3, R4, and R5 are independently selected from a hydrogen atom, a fluorine atom, a trifluoromethyl group, a cyano group, an amino group, a nitro group, a carboxyl group, an ether group, a C1 - C6 alkyl group, a C2 - C6 alkenyl group, and a C2 - C6 alkynyl group.

2. The electrolyte additive according to claim 1, characterized in that, The 2,2-difluoroethyl alkyl sulfonate includes at least one of 2,2-difluoroethyl methyl sulfonate and 2,2-difluoroethyl trifluoromethanesulfonate.

3. The electrolyte additive according to claim 1, wherein The structure of Formula I includes at least one of Formula I-(1) to I-(12):

4. An electrolyte, characterized in that, Comprising a solvent, a lithium salt, and an electrolyte additive as described in any one of claims 1 - 3.

5. The electrolyte according to claim 4, wherein, The mass percentage of the lithium salt in the electrolyte is 10 - 18%; and / or, The mass percentage of the electrolyte additive in the electrolyte is 2 - 6%; and / or, The solvent includes a cyclic carbonate and / or a linear ester. The cyclic carbonate includes at least one of ethylene carbonate, propylene carbonate, and fluorinated ethylene carbonate; the linear ester includes at least one of ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, ethyl acetate, ethyl propionate, and propyl propionate; and / or, The lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(trifluoromethyl)imide, and lithium bis(fluorosulfonyl)imide.

6. The electrolyte according to claim 4, wherein, The electrolyte further includes a negative electrode film-forming additive and a positive electrode film-forming additive.

7. The electrolyte according to claim 6, wherein The negative electrode film-forming additive includes at least one of vinylene carbonate, fluorinated ethylene carbonate, ethylene sulfate, methylene methanedisulfonate, 1,3-propane sulfonate, and propylene sulfonate; and / or, The positive electrode film-forming additive includes at least one of lithium difluorophosphate, lithium tetrafluoroborate, lithium bis(oxalato)borate, lithium difluoro bis(oxalato)phosphate, lithium difluorooxalato borate, tris(trimethylsilyl) phosphate, and tris(trimethylsilyl) borate.

8. A lithium-ion battery, characterized in that, Comprising a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte as described in any one of claims 4 - 7. The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer. The positive electrode active material layer includes a positive electrode active material, and the positive electrode active material includes a non-high-voltage positive electrode active material and a high-voltage positive electrode active material.

9. The lithium-ion battery according to claim 8, wherein, The non-high-voltage positive electrode active material includes at least one of lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium manganese iron phosphate, and lithium cobalt oxide; and / or, The high-voltage positive electrode active material includes at least one of lithium nickel manganese oxide and lithium-rich manganese-based materials.

10. The lithium-ion battery according to claim 8, characterized in that, The mass percentage of the high-voltage positive electrode active material in the positive electrode active material is 5 - 20%; and / or, The D50 particle size of the high-voltage positive electrode active material is 5 - 15 μm.

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