Non-aqueous electrolyte and lithium-ion battery

Abstract

A non-aqueous electrolyte and a lithium-ion battery, the non-aqueous electrolyte comprising a lithium salt, an additive, and a solvent, and the additive comprising an o-phenylene trimethyl silicon oxyborate compound. According to the provided non-aqueous electrolyte, not only can the technical problem in the prior art of the service life of a lithium-ion battery being shortened when cycling and storage are carried out under high-temperature conditions be solved, but also the non-aqueous electrolyte can also have good overcharge prevention capabilities, so as to protect a battery cell.

Description

Non-aqueous electrolyte and lithium ion battery

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on December 27, 2023, with application number 202311821608.6, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application belongs to the technical field of electrolyte materials, and specifically relates to a non-aqueous electrolyte and a lithium-ion battery. Background Art

[0003] With the continuous advancement of science and technology in recent years, the lithium-ion power batteries used in new energy vehicles have placed higher demands on the overall performance of batteries. To meet the needs of electric vehicles for long driving range and wide temperature range, it is necessary to develop lithium-ion secondary batteries with higher energy density, better high-temperature cycle performance, and better storage performance, so as to achieve the goal of achieving a lifespan of more than 10 years for automotive power batteries.

[0004] However, high-energy-density lithium-ion secondary batteries typically use transition metal oxides with a high nickel content (e.g., lithium nickel cobalt manganese oxide materials) as positive electrode materials. The operating voltage of the above-mentioned positive electrode materials is relatively high, typically 4.2-4.4V, so they are prone to problems such as interface degradation, particle breakage, and electrolyte oxidation under high temperature and high pressure, resulting in a rapid decrease in the cycle life of the battery at high temperatures. Therefore, it is necessary to develop electrolyte additive materials that can stably form films at high temperatures. At the same time, in order to improve the safety performance of the battery, the electrolyte additives should also have a certain anti-overcharge capability.

[0005] In recent years, from the perspective of improving the battery's charge and discharge capacity and cyclability, storage durability, and overcharge safety, the existing technology has disclosed many practical application studies of electrolyte additives in lithium secondary batteries. However, there are still some problems in the application process, so it is necessary to develop an electrolyte that can have good high-temperature cycle performance, storage performance and safety performance.

[0006] Summary of the Invention

[0007] The present application provides a non-aqueous electrolyte and a lithium-ion battery. The non-aqueous electrolyte provided in the present application not only solves the technical problem of lithium-ion batteries' lifespan degradation during cycling and storage under high-temperature conditions, which exists in the prior art, but also provides excellent overcharge protection, thereby protecting the battery cell.

[0008] In a first aspect, the present application provides a non-aqueous electrolyte, comprising a lithium salt, an additive, and a solvent, wherein the additive comprises an o-phenylene trimethylsiloxyborate compound having a structure shown in Formula 1:

[0009] Wherein, R1 is selected from at least one of hydrogen, halogen, substituted or unsubstituted C1-C4 alkyl, substituted or unsubstituted C2-C3 alkenyl or substituted or unsubstituted C2-C3 alkynyl.

[0010] The o-phenylene trimethylsiloxyborate compound having the structure shown in Formula 1 in the present application contains two different functional groups in its structure. On the one hand, the trimethylsilyl group has the function of absorbing residual moisture and hydrofluoric acid in the electrolyte, reducing the dissolution of positive electrode metal atoms and the self-discharge of the battery, thereby improving the cycle and storage performance of the battery; on the other hand, the phenyl group in the o-phenylene trimethylsiloxyborate compound forms a viscous substance when it is oxidatively polymerized, which can block the diaphragm, causing the battery to lose power, thereby playing a protective role, preventing the battery from further overcharging and causing safety hazards.

[0011] In summary, the o-phenylene trimethylsiloxyborate compound additive provided in this application can not only passivate the positive electrode interface, form a stable SEI protective film, and reduce the self-discharge of the battery, but also has a good ability to protect the battery from overcharge, thereby improving the high-temperature storage performance, cycle performance and safety performance of the battery.

[0012] In the present application, the substituted or unsubstituted C1-C4 alkyl group refers to an alkyl group having 1-4 carbon atoms in the main chain, for example, 1, 2, 3, or 4.

[0013] In the present application, the substituted or unsubstituted C2-C3 alkenyl group refers to an alkenyl group having 2-3 carbon atoms in the main chain, for example, 2 or 3.

[0014] In the present application, the substituted or unsubstituted C2-C3 alkynyl group refers to an alkynyl group having 2-3 carbon atoms in the main chain, for example, 2 or 3.

[0015] In the present application, the present application also provides a method for preparing an o-phenylene trimethylsiloxy borate compound having a structure shown in Formula 1, which comprises the following steps:

[0016] Specifically, a 500mL dry flask connected to a mercury-sealed bubbler (with the tail pipe vented into a fume hood) is charged with borane and tetrahydrofuran solutions under nitrogen. A solution of catechol (also known as pyrocatechol) containing the substituent R1 in 50mL of tetrahydrofuran is added dropwise over 30 minutes at 0°C with thorough stirring. After stirring for 30 minutes at 25°C, the product intermediate, catechol borane containing the substituent R1, is obtained by distillation.

[0017] The catechol borane containing the substituent R1 is reacted with C 14 H 23OPSi and methanol solvent are mixed, heated for reaction, and then the solvent methanol is evaporated using a rotary evaporator to obtain an o-phenylene trimethylsiloxyborate compound having a structure shown in Formula 1.

[0018] Preferably, the additive includes an o-phenylene trimethylsiloxy borate compound having a structure shown in Formula 1:

[0019] Wherein, R1 is selected from hydrogen, fluorine atom or isobutyl group.

[0020] Preferably, based on the total mass of the non-aqueous electrolyte as 100%, the mass percentage of the o-phenylene trimethylsiloxyborate compound having the structure shown in Formula 1 is 0.01-5%, preferably 0.1-2%, for example, it can be 0.01%, 0.05%, 0.1%, 0.5%, 1.0%, 1.5%, 2.0%, 3%, 4%, 5%, etc.

[0021] Preferably, the additives may further include high temperature additives and film-forming additives.

[0022] Preferably, the high-temperature additive includes any one or a combination of at least two of a cyclic carbonate compound containing an unsaturated bond, a halogen-substituted cyclic carbonate compound, a sulfate compound, a sulfite compound, a sultone compound, a nitrile compound, an aromatic compound, an isocyanate compound, a phosphazene compound, a cyclic anhydride compound, a phosphite compound, a phosphate compound or a borate compound.

[0023] Preferably, the cyclic carbonate compound containing an unsaturated bond includes vinylene carbonate and / or vinyl ethylene carbonate.

[0024] Preferably, the halogen-substituted cyclic carbonate compound includes fluoroethylene carbonate.

[0025] Preferably, the sulfate ester compound comprises vinyl sulfate.

[0026] Preferably, the sulfite compound comprises vinyl sulfite.

[0027] Preferably, the sultone compound includes 1,3-propane sultone.

[0028] Preferably, the nitrile compound includes succinonitrile and / or adiponitrile.

[0029] Preferably, the aromatic compound comprises biphenyl and / or cyclohexylbenzene.

[0030] Preferably, the isocyanate compound includes 1,4-butanediisocyanate.

[0031] Preferably, the phosphazene compound includes ethoxypentafluorocyclotriphosphazene.

[0032] Preferably, the cyclic anhydride compound includes succinic anhydride and / or maleic anhydride.

[0033] Preferably, the phosphite compound includes tris(trimethylsilyl)phosphite.

[0034] Preferably, the phosphate compound includes tris(trimethylsilyl)phosphate.

[0035] Preferably, the borate compound comprises tris(trimethylsilyl)borate.

[0036] Preferably, based on the total mass of the non-aqueous electrolyte as 100%, the mass percentage of the high-temperature additive is 0.01-2%, preferably 0.1% to 1.5%, for example, it can be 0.01%, 0.02%, 0.05%, 0.08%, 0.1%, 0.2%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, etc.

[0037] Preferably, the film-forming additive comprises fluoroethylene carbonate and / or vinyl sulfate.

[0038] Preferably, based on the total mass of the non-aqueous electrolyte as 100%, the mass percentage of the fluoroethylene carbonate is 0-2%, preferably 0.2-0.8%, for example, it can be 0%, 0.02%, 0.05%, 0.08%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, etc.

[0039] Preferably, based on the total mass of the non-aqueous electrolyte as 100%, the mass percentage of the vinyl sulfate is 0-2%, preferably 0.5-1.5%, for example, it can be 0%, 0.02%, 0.05%, 0.08%, 0.1%, 0.2%, 0.5%, 0.7%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, etc.

[0040] Preferably, the lithium salt includes a main salt and a auxiliary salt.

[0041] Preferably, the main salt comprises lithium hexafluorophosphate.

[0042] Preferably, based on the total mass of the non-aqueous electrolyte as 100%, the mass percentage of the main salt is 10-20%, preferably 10-15%, for example, it can be 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, etc.

[0043] Preferably, the auxiliary salt comprises lithium difluorophosphate.

[0044] Preferably, based on the total mass of the non-aqueous electrolyte as 100%, the mass percentage of the auxiliary salt is 0.1-1.5%, preferably 0.1-1%, for example, it can be 0.1%, 0.2%, 0.5%, 0.7%, 0.8%, 1%, 1.2%, 1.5%, etc.

[0045] In the present application, the types and contents of the main salt and the auxiliary salt are regulated to reduce the film formation resistance of the battery, thereby improving the performance of the battery.

[0046] Preferably, the solvent includes cyclic carbonate and chain ester compounds.

[0047] Preferably, the chain ester compound includes chain carbonate ester and chain carboxylic acid ester.

[0048] Preferably, the chain ester compound includes any one or a combination of at least two of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate or propyl acetate.

[0049] Preferably, the cyclic carbonate includes any one of ethylene carbonate, propylene carbonate or butylene carbonate, or a combination of at least two of them.

[0050] Preferably, the volume ratio of the cyclic carbonate to the chain ester compound is (5-40):(60-95), for example, it can be 5:95, 8:92, 10:90, 15:85, 20:80, 25:75, 30:70, 35:65, 40:60, etc.

[0051] In the present application, by regulating the volume ratio of cyclic carbonate and chain ester compounds, the viscosity and dielectric constant of the electrolyte can be regulated so that the conductivity value of the electrolyte is the highest. If the volume ratio is too low, the dielectric constant of the electrolyte will be small and the dissociation of the lithium salt will be weak. Conversely, the viscosity of the electrolyte will be too high and the transfer of lithium ions will be difficult.

[0052] Preferably, based on the total mass of the non-aqueous electrolyte as 100%, the mass percentage of the solvent is 70-90%, for example, it can be 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, etc.

[0053] In a second aspect, the present application provides a lithium-ion battery, comprising a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator, wherein the electrolyte comprises the non-aqueous electrolyte according to the first aspect.

[0054] Preferably, the material of the positive electrode plate includes lithium transition metal oxide and / or lithium transition metal phosphate.

[0055] Preferably, the lithium transition metal oxide includes the lithium transition metal oxide includes LiCoO2, LiNi x Co y Mn z O2、LiNi x Mn y Any one of O2, LiMn2O4, LiMnO2 or Li2MnO4, or a combination of at least two thereof, wherein 0≤x≤1, 0≤y≤1, and 0≤z≤1; wherein the value of x may be 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1, the value of y may be 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1, and the value of z may be 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1, etc., but are not limited to the listed values, and other values ​​not listed within the above numerical ranges are equally applicable.

[0056] Preferably, the lithium transition metal phosphate compound mainly includes any one of LiFePO 4 , LiMnPO 4 or LiCoPO 4 or a combination of at least two of them.

[0057] Preferably, the material of the negative electrode plate includes any one of carbonaceous materials, alloy materials or lithium metal oxide materials, or a combination of at least two of them.

[0058] Preferably, the material of the negative electrode plate includes any one of natural graphite, artificial graphite, soft carbon, hard carbon or lithium titanate, or a combination of at least two of them.

[0059] Compared with the prior art, this application has the following beneficial effects:

[0060] The present application provides a non-aqueous electrolyte, wherein the o-phenylene trimethylsiloxy borate compound having the structure shown in Formula 1 contains two different functional groups in its structure. On the one hand, the trimethylsilyl group has the function of absorbing residual water and hydrofluoric acid in the electrolyte, reducing the dissolution of positive electrode metal atoms and the self-discharge of the battery, thereby improving the cycle and storage performance of the battery; on the other hand, the phenyl group in the o-phenylene trimethylsiloxy borate compound forms a viscous substance when it is oxidatively polymerized, which can block the diaphragm, causing the battery to be powered off, thereby playing a protective role, preventing the battery from further overcharging, and causing safety hazards. In summary, the o-phenylene trimethylsiloxy borate compound additive provided by the present application can not only passivate the positive electrode interface, form a stable SEI protective film, reduce the self-discharge of the battery, but also have a good ability to protect the battery from overcharging, thereby improving the high-temperature storage performance, cycle performance and safety performance of the battery. DETAILED DESCRIPTION

[0061] The technical solution of the present application is further described below through specific implementation methods. Those skilled in the art should understand that the embodiments are only used to help understand the present application and should not be regarded as specific limitations of the present application.

[0062] Example 1

[0063] This embodiment provides a non-aqueous electrolyte, which includes lithium hexafluorophosphate, additives and solvents, wherein the additives include an o-phenylene trimethylsiloxyborate compound having a structure shown in Formula 1-1, fluorovinylene carbonate, vinyl sulfate and lithium difluorophosphate.

[0064] This embodiment provides a synthesis route for the o-phenylene trimethylsiloxy borate compound having the structure shown in Formula 1-1, which comprises the following steps:

[0065] Specifically, in a round-bottom flask, add equal amounts of C 14 H 23 OPSi, C6H5BO2 and methanol solvent are mixed, and the temperature is heated to 55°C and stirred for 2 hours. The solvent methanol is then evaporated using a rotary evaporator to obtain an o-phenylene trimethylsiloxyborate compound having the structure shown in Formula 1-1.

[0066] Based on the total mass of the non-aqueous electrolyte being 100%, the mass percentage of lithium hexafluorophosphate is 12.5%; the mass percentage of the o-phenylene trimethylsiloxyborate compound having the structure shown in Formula 1-1 is 0.5%, the mass percentage of fluorovinylene carbonate is 0.5%, the mass percentage of vinyl sulfate is 1%, and the mass percentage of lithium difluorophosphate is 1%; the mass percentage of the solvent is 84.5%, and the specific composition includes ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate in a mass ratio of 30:50:20.

[0067] This embodiment also provides a method for preparing the non-aqueous electrolyte, which comprises the following steps:

[0068] When the oxygen content is less than 0.1 ppm and the water content is less than 0.1 ppm, the above components are mixed according to the formula amount and stirred evenly to obtain the non-aqueous electrolyte.

[0069] Example 2

[0070] This embodiment provides a non-aqueous electrolyte, which includes lithium hexafluorophosphate, additives and solvents. The additives include o-phenylene trimethylsiloxyborate compounds having the structure shown in Formula 1-2, fluorovinylene carbonate, vinyl sulfate and lithium difluorophosphate.

[0071] This embodiment provides a synthesis route for the o-phenylene trimethylsiloxyboronic acid ester compound having the structure shown in Formula 1-2, which comprises the following steps:

[0072] Specifically, in a round-bottom flask, add equal amounts of C 14 H 23 OPSi and C 10 H 13 BO2 and methanol solvent are mixed, and the temperature is heated to 55°C, and stirring is continued for 2 hours. Then, the solvent methanol is evaporated using a rotary evaporator to obtain an o-phenylene trimethylsiloxyborate compound having the structure shown in Formula 1-2.

[0073] Based on the total mass of the non-aqueous electrolyte being 100%, the mass percentage of lithium hexafluorophosphate is 12.5%; the mass percentage of the o-phenylene trimethylsiloxyborate compound having the structure shown in Formula 1-2 is 0.5%, the mass percentage of fluorovinylene carbonate is 0.5%, the mass percentage of vinyl sulfate is 1%, and the mass percentage of lithium difluorophosphate is 1%; the mass percentage of the solvent is 84.5%, and the specific composition includes ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate in a mass ratio of 30:50:20.

[0074] The preparation method of the non-aqueous electrolyte in this embodiment is the same as that in Example 1.

[0075] Example 3

[0076] The difference between this embodiment and Example 1 is that, based on the total mass of the non-aqueous electrolyte being 100%, the mass percentage of lithium hexafluorophosphate is 15%; the mass percentage of the o-phenylene trimethylsiloxyborate compound having the structure shown in Formula 1-1 is 0.5%, the mass percentage of fluorovinylene carbonate is 1%, the mass percentage of vinyl sulfate is 0.1%, and the mass percentage of lithium difluorophosphate is 0.4%; the mass percentage of the solvent is 83%, and the specific composition includes ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate in a mass ratio of 30:50:20. Other contents are the same as in Example 1.

[0077] Example 4

[0078] The difference between this embodiment and Example 1 is that, based on the total mass of the non-aqueous electrolyte being 100%, the mass percentage of lithium hexafluorophosphate is 10%; the mass percentage of the o-phenylene trimethylsiloxyborate compound having the structure shown in Formula 1-1 is 0.5%, the mass percentage of fluorovinylene carbonate is 1%, the mass percentage of vinyl sulfate is 1%, and the mass percentage of lithium difluorophosphate is 1%; the mass percentage of the solvent is 86.5%, and the specific composition includes ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate in a mass ratio of 30:50:20. Other contents are the same as in Example 1.

[0079] Example 5

[0080] The difference between this embodiment and embodiment 1 is that fluoroethylene carbonate is replaced by vinylene carbonate in an equal amount, and the rest is the same as embodiment 1.

[0081] Example 6

[0082] The difference between this embodiment and embodiment 1 is that the composition of the solvent includes ethylene carbonate and diethyl carbonate in a volume ratio of 1:9, and the rest is the same as embodiment 1.

[0083] Example 7

[0084] The difference between this embodiment and embodiment 1 is that the o-phenylene trimethylsiloxyborate compound with the structure shown in formula 1-1 is replaced with an equal amount of the o-phenylene trimethylsiloxyborate compound with the structure shown in formula 1-3, and the rest is the same as embodiment 1.

[0085] Example 8

[0086] The difference between this embodiment and embodiment 1 is that lithium difluorophosphate is replaced by lithium hexafluorophosphate of the same content, and the rest is the same as embodiment 1.

[0087] Example 9

[0088] The difference between this embodiment and embodiment 1 is that fluorovinylene carbonate, vinyl sulfate and lithium difluorophosphate are replaced by equal amounts of o-phenylene trimethylsiloxyborate compounds having the structure shown in Formula 1-1, and the rest are the same as in embodiment 1.

[0089] Comparative Example 1

[0090] The difference between this comparative example and Example 1 is that the o-phenylene trimethylsiloxyborate compound having the structure shown in Formula 1-1 is not added, and the content of the solvent is adjusted so that the mass percentage of the total system is 100%. The other aspects are the same as Example 1.

[0091] Comparative Example 2

[0092] The difference between this comparative example and Example 1 is that the o-phenylene trimethylsiloxyborate compound having the structure shown in Formula 1-1 is replaced with an equal amount of fluoroethylene carbonate, and the rest is the same as Example 1.

[0093] Comparative Example 3

[0094] The difference between this comparative example and Example 1 is that the o-phenylene trimethylsiloxyborate compound having the structure shown in Formula 1-1 is replaced with an equal amount of tris(trimethylsilyl)borate, and the rest is the same as Example 1.

[0095] Application Examples 1 to 9 and Comparative Application Examples 1 to 3

[0096] The non-aqueous electrolytes provided in Examples 1 to 9 and Comparative Examples 1 to 3 were used to prepare lithium-ion batteries. The preparation method is as follows:

[0097] Preparation of positive electrode sheet: The positive electrode active material lithium nickel cobalt manganese oxide (LiNi 0.8 Co 0.1 Mn 0.1 O2), conductive agent Super-P, and adhesive PVDF were dissolved in solvent N-methylpyrrolidone at a mass ratio of 95.8:2.2:2.0 and mixed evenly to prepare positive electrode slurry. The positive electrode slurry was evenly coated on the current collector aluminum foil with a coating amount of 18 mg / cm 2 , then dried at 90°C, cold pressed, trimmed, cut and slit, dried at 90°C under vacuum conditions for 4 hours, and welded to the tabs to produce a positive electrode sheet for a lithium-ion secondary battery that meets the requirements;

[0098] Preparation of negative electrode sheet: Dissolve the negative electrode active material artificial graphite, conductive agent Super-P, thickener CMC, and binder SBR in the solvent deionized water at a mass ratio of 96.5:1.0:1.0:1.5 and mix them evenly to make negative electrode slurry. Then, evenly coat the negative electrode slurry on the current collector copper foil with a coating amount of 8.9 mg / cm 2 , then dried at 90°C, cold pressed, trimmed, cut and slit, dried at 110°C under vacuum conditions for 4 hours, and welded to the tabs to produce a negative electrode sheet for a lithium-ion secondary battery that meets the requirements;

[0099] Preparation of lithium-ion battery: The positive electrode sheet, negative electrode sheet and polyethylene separator of the lithium-ion secondary battery prepared according to the above process are laminated into a battery with a thickness of 8 mm, a width of 60 mm and a length of 130 mm, and vacuum baked at 90°C for 10 h, injected with the non-aqueous electrolyte in the embodiment and the comparative example, and allowed to stand for 24 h. Then, it is charged to 4.4 V with a constant current of 0.1C (200 mA), and then charged at a constant voltage of 4.4 V until the current drops to 0.05C (100 mA), and then discharged to 2.8 V with a constant current of 0.1C (200 mA). The charge and discharge are repeated twice, and finally charged to 3.8 V with a constant current of 0.1C (200 mA). The preparation of the lithium-ion battery is completed.

[0100] Test conditions

[0101] The lithium-ion batteries provided in Application Examples 1 to 9 and Comparative Application Examples 1 to 3 were tested using the following test methods:

[0102] High temperature storage performance test of lithium-ion secondary batteries:

[0103] At 25°C, the lithium ion secondary batteries prepared in Example 1 to Example 9 and Comparative Example 1 to Comparative Example 3 were first charged to 4.35V at a constant current of 0.05C, and then charged to a current of 0.05C at a constant voltage of 4.35V, and then discharged to 2.8V at a constant current of 0.5C. The discharge capacity of this discharge is the discharge capacity of the lithium ion secondary battery before high temperature storage; then the lithium ion secondary battery was charged to 4.35V at a constant current of 0.5C, and the lithium ion secondary battery was discharged to 2.8V. The secondary battery is stored at 60°C for 30 days. After the storage period, the lithium-ion secondary battery is placed in a 25°C environment and then discharged to 2.8V at a constant current of 0.5C. The lithium-ion secondary battery is then charged to 4.35V at a constant current of 0.5C. The battery is further charged at a constant voltage of 4.35V until the current reaches 0.05C. The lithium-ion secondary battery is then discharged to 2.8V at a constant current of 0.5C. The last discharge capacity is the discharge capacity of the lithium-ion secondary battery after high-temperature storage. The capacity retention rate (%) of the lithium-ion secondary battery after high-temperature storage = [discharge capacity of the lithium-ion secondary battery after high-temperature storage / discharge capacity of the lithium-ion secondary battery before high-temperature storage] × 100%.

[0104] High temperature cycle performance test of lithium-ion secondary batteries:

[0105] The high-temperature cycle performance of the lithium-ion secondary batteries prepared in Example 1 to Example 9 and Comparative Example 1 to Comparative Example 3 was tested. The specific method is as follows: at 45°C, the lithium-ion secondary batteries were first charged to 4.35V at a constant current of 0.5C, then charged at a constant voltage of 4.35V until the current was cut off at 0.05C, and then discharged to 2.8V at a constant current of 0.5C. This is a charge and discharge cycle process, and the discharge capacity this time is the discharge capacity of the first cycle. The lithium-ion secondary battery was subjected to a cyclic charge and discharge test in the above manner, and the discharge capacity of the 800th cycle was taken. The capacity retention rate (%) of the lithium-ion secondary battery after 800 cycles = [discharge capacity of the 800th cycle / discharge capacity of the first cycle] × 100%.

[0106] High temperature storage gas generation performance test of lithium-ion secondary batteries:

[0107] At 25°C, the lithium-ion secondary batteries prepared in Examples 1 to 9 and Comparative Examples 1 to 3 were first charged to 4.35V at a constant current of 0.5C. They were then charged at a constant voltage of 4.35V until the current reached 0.05C, and then discharged at a constant current of 0.5C to 2.8V. This discharge capacity represents the discharge capacity of the lithium-ion secondary battery before high-temperature storage. The lithium-ion secondary batteries were then charged to 4.35V at a constant current of 0.5C, and then charged at a constant voltage of 4.35V until the current reached 0.05C, fully charging the batteries. The volume of the batteries was measured using the water displacement method, and the thickness of the batteries was measured using a micrometer.

[0108] The lithium-ion battery was then stored at 60°C for 30 days. After storage, the lithium-ion secondary battery was placed in a 25°C environment and the battery volume was tested using the water displacement method. Specifically, a beaker of pure water was placed on a balance and weighed, recording it as reading 1. The battery before storage (fresh battery) or after storage was then immersed in the water in the beaker and weighed, recording it as reading 2. The volume of the battery before storage (fresh battery) or after storage was subtracted from reading 1. The density of water is 1 mg / mL, and a reading of 1 mL corresponds to a volume of 1 mL for the battery before storage (fresh battery) or after storage. Therefore, if the battery immersed in water is before storage, then reading 2 minus reading 1 is the volume of the battery before storage, and if the battery immersed in water is after storage, then reading 2 minus reading 1 is the volume of the battery after storage. The volume after storage / volume before storage is the ratio of the volume of the battery after storage to the volume of the battery before storage. The thickness of the battery was measured with a micrometer. The lithium-ion secondary battery was then discharged at a constant current of 0.5C to 2.8V. It was then charged at a constant current of 0.5C to 4.35V. It was further charged at a constant voltage of 4.35V until the current dropped to 0.05C. The battery was then discharged at a constant current of 0.5C to 2.8V. The final discharge capacity was the discharge capacity of the lithium-ion secondary battery after high-temperature storage. Battery volume expansion (%) = (volume after storage / volume before storage - 1) × 100%.

[0109] The test results are shown in Table 1:

[0110] Table 1

[0111] It can be seen from Table 1 that the battery provided in Application Example 1 of this application has the best high-temperature cycle performance and high-temperature storage performance.

[0112] It can be seen from Application Examples 1, 5 and 6 that by regulating the volume ratio of the solvent and the types and contents of the high-temperature additives and film-forming additives, the lithium-ion secondary battery has better high-temperature performance.

[0113] It can be seen from Application Examples 1 and 8 that by regulating the types and contents of the main salt and auxiliary salt, the film formation resistance of the battery can be reduced, thereby improving the performance of the battery.

[0114] From the comparison between Application Example 1 and Comparative Application Example 1 and Comparative Application Example 2, it can be seen that compared with the battery without adding o-phenylene trimethylsiloxyborate compounds, with the addition of o-phenylene trimethylsiloxyborate compounds, the capacity retention rate of the lithium-ion secondary battery stored at 55°C increases, and the gas production during storage decreases, and the cycle capacity retention rate increases accordingly.

[0115] It can be seen from Application Example 1 and Comparative Application Example 3 that conventional tris(trimethylsilyl)borate cannot achieve the technical effects of the o-phenylene trimethylsiloxyborate compounds in this application.

[0116] The applicant declares that while the above-mentioned embodiments are used to illustrate the process of the present application, the present application is not limited to the above-mentioned process steps, which does not mean that the present application must rely on the above-mentioned process steps in order to be implemented. Those skilled in the art should understand that any improvements to the present application, equivalent replacements for the raw materials used in the present application, addition of auxiliary components, and selection of specific methods, etc., fall within the scope of protection and disclosure of the present application.

Claims

1. A non-aqueous electrolyte, which comprises a lithium salt, an additive and a solvent, and the additive comprises an o-phenylene trimethylsilyl borate compound having the structure shown in Formula 1: Among them, R1 is selected from at least one of hydrogen, halogen, substituted or unsubstituted C1-C4 alkyl, substituted or unsubstituted C2-C3 alkenyl, or substituted or unsubstituted C2-C3 alkynyl.

2. The non-aqueous electrolyte according to claim 1, wherein The additive includes an o-phenylene trimethylsilyl borate compound having the structure shown in Formula 1: Among them, R1 is selected from hydrogen, a fluorine atom, or isobutyl.

3. The non-aqueous electrolyte according to claim 1 or 2, wherein Based on the total mass of the non-aqueous electrolyte being 100%, the mass percentage content of the o-phenylene trimethylsilyloxy borate compound having the structure shown in Formula 1 is 0.01-5%, preferably 0.1-2%.

4. The non-aqueous electrolyte according to any one of claims 1-3, wherein The additive may further include a high-temperature additive and a film-forming additive; Preferably, the high-temperature additive includes any one or a combination of at least two of a cyclic carbonate compound containing an unsaturated bond, a halogen-substituted cyclic carbonate compound, a sulfate compound, a sulfite compound, a sultone compound, a nitrile compound, an aromatic compound, an isocyanate compound, a phosphazene compound, a cyclic anhydride compound, a phosphite compound, a phosphate compound, or a borate compound; Preferably, the cyclic carbonate compound containing an unsaturated bond includes vinylene carbonate and / or ethylene vinyl carbonate; Preferably, the halogen-substituted cyclic carbonate compound includes fluoroethylene carbonate; Preferably, the sulfate compound includes ethylene sulfate; Preferably, the sulfite compound includes ethylene sulfite; Preferably, the sultone compound includes 1,3-propane sultone; Preferably, the nitrile compound includes succinonitrile and / or adiponitrile; Preferably, the aromatic compound includes biphenyl and / or cyclohexylbenzene; Preferably, the isocyanate compound includes 1,4-butane diisocyanate; Preferably, the phosphazene compound includes ethoxy pentafluorocyclotriphosphazene; Preferably, the cyclic anhydride compound includes succinic anhydride and / or maleic anhydride; Preferably, the phosphite compound includes tris(trimethylsilyl) phosphite; Preferably, the phosphate compound includes tris(trimethylsilyl) phosphate; Preferably, the borate compound includes tris(trimethylsilyl) borate; Preferably, based on the total mass of the non-aqueous electrolyte being 100%, the mass percentage content of the high-temperature additive is 0.01-2%, preferably 0.1% to 1.5%.

5. The non-aqueous electrolyte according to claim 4, wherein, The film-forming additive includes fluoroethylene carbonate and / or ethylene sulfate; Preferably, based on the total mass of the non-aqueous electrolyte being 100%, the mass percentage content of fluoroethylene carbonate is 0-2%, preferably 0.2-0.8%; Preferably, based on the total mass of the non-aqueous electrolyte being 100%, the mass percentage content of ethylene sulfate is 0-2%, preferably 0.5-1.5%.

6. The non-aqueous electrolyte according to any one of claims 1-5, wherein, The lithium salt includes a main salt and a co-salt; Preferably, the main salt includes lithium hexafluorophosphate; Preferably, based on the total mass of the non-aqueous electrolyte being 100%, the mass percentage content of the main salt is 10-20%, preferably 10-15%; Preferably, the co-salt includes lithium difluorophosphate; Preferably, based on the total mass of the non-aqueous electrolyte being 100%, the mass percentage content of the co-salt is 0.1-1.5%, preferably 0.1-1%.

7. The non-aqueous electrolyte according to any one of claims 1-6, wherein, The solvent includes cyclic carbonates and chain ester compounds; Preferably, the chain ester compounds include chain carbonates and / or chain carboxylates; Preferably, the chain ester compounds include any one or a combination of at least two of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, or propyl acetate; Preferably, the cyclic carbonate includes any one or a combination of at least two of ethylene carbonate, propylene carbonate, or butylene carbonate; Preferably, the volume ratio of the cyclic carbonate to the chain ester compounds is (5 - 40):(60 - 95); Preferably, based on the total mass of the non-aqueous electrolyte being 100%, the mass percentage content of the solvent is 70 - 90%.

8. A lithium-ion battery, which includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator, and the electrolyte includes the non-aqueous electrolyte according to any one of claims 1 - 7. The material of the positive electrode sheet includes lithium transition metal oxides and / or lithium transition metal phosphate compounds; 9. The lithium ion battery according to claim 8, wherein, Preferably, the lithium transition metal phosphate compounds mainly include any one or a combination of at least two of LiFePO4, LiMnPO4, or LiCoPO4. Preferably, the lithium transition metal oxide includes LiCoO2, LiNi x Co y Mn z O2, LiNi x Mn y O2, LiMn2O4, LiMnO2 or Li2MnO4, or a combination of any one or at least two thereof, where 0 ≤ x ≤ 1, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1; The material of the negative electrode sheet includes any one or a combination of at least two of carbonaceous materials, alloy materials, or lithium metal oxide materials; 10. The lithium ion battery according to claim 8 or 9, wherein, Preferably, the material of the negative electrode sheet includes any one or a combination of at least two of natural graphite, artificial graphite, soft carbon, hard carbon, or lithium titanate. ​

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