Electrolyte additive composition, electrolyte and battery

Abstract

The invention provides an electrolyte additive composition, an electrolyte and a battery, and relates to the technical field of secondary batteries. The electrolyte additive composition comprises a lithium salt additive, a carbonic ester additive, a sulfur-containing additive and an O-Si bond-containing additive, wherein the mass ratio of the lithium salt additive to the carbonic ester additive to the sulfur-containing additive to the additive containing the O-Si bond is (0.2-1): (0.2-1): (1-3): (0.3-1); the additive containing the O-Si bond is at least one of 2, 4-bis (trimethylsiloxy) pyrimidine and trimethylsilyl 2-(fluorosulfonyl) difluoroacetate. By selecting the components of the electrolyte additive composition and the ratio of the components, the physical structure and chemical components of the CEI membrane can be regulated and controlled, the SEI membrane is stabilized, and the cycle performance of the battery under high voltage is improved.

Description

Technical Field

[0001] The present application relates to the technical field of secondary batteries, and in particular to an electrolyte additive composition, an electrolyte and a battery. Background Art

[0002] The continued prosperity of computers, communications and consumer electronics has brought about the rapid development of the lithium-ion battery industry. In particular, the rise of new energy vehicles in recent years has promoted the development of power lithium-ion batteries and put forward higher energy density and safety performance requirements for them. The endurance of electric vehicles has become one of the performance indicators that consumers pay most attention to, and the energy density of the battery determines the single mileage of electric vehicles. Improving the energy density of the battery under limited space and weight has become a hot topic of research by all parties. Increasing the working voltage of the positive electrode material is one of the current mainstream ways to improve the energy density of lithium-ion batteries. At present, high-voltage positive electrode materials, such as high-voltage binary, high-voltage ternary, high-voltage lithium cobalt oxide, layered lithium-rich oxide (LLO), etc. have become research hotspots. As the voltage of lithium-ion batteries continues to increase, the positive electrode material will have a higher electrode potential, the oxidation decomposition of the electrolyte at the positive electrode and the positive electrode interface reaction will be more intense, and as the battery charge and discharge cycle proceeds, the internal resistance of the battery gradually increases, which in turn causes the battery performance to decline or even fail. Summary of the invention

[0003] The main purpose of the present application is to provide an electrolyte additive composition, an electrolyte and a battery to solve the problem that the electrolyte has poor stability under high voltage, resulting in serious capacity decay of the battery during the cycle process under high voltage.

[0004] In order to achieve the above-mentioned purpose, according to the first aspect of the present application, there is provided an electrolyte additive composition, which includes a lithium salt additive, a carbonate additive, a sulfur-containing additive and an additive containing an O-Si bond; wherein the mass ratio of the lithium salt additive, the carbonate additive, the sulfur-containing additive and the additive containing an O-Si bond is (0.2-1): (0.2-1): (1-3): (0.3-1); the additive containing an O-Si bond is at least one of 2,4-bis(trimethylsilyloxy)pyrimidine and trimethylsilyl 2-(fluorosulfonyl)difluoroacetate.

[0005] Furthermore, the lithium salt additive includes at least one of lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, lithium borate, lithium difluoroborate, and lithium hexafluorophosphate; the carbonate additive includes at least one of vinylene carbonate and fluoroethylene carbonate; and the sulfur-containing additive includes at least one of propylene sulfite, 1,3-propylene sulfonate, and vinyl sulfate.

[0006] Furthermore, the additive containing an O-Si bond is at least one of 2,4-bis(trimethylsilyloxy)pyrimidine and trimethylsilyl 2-(fluorosulfonyl)difluoroacetate, the lithium salt additive is lithium difluorophosphate, the carbonate additive is vinylene carbonate, and the sulfur-containing additive is 1,3-propylene sulfonate.

[0007] Furthermore, the mass ratio of the lithium salt additive, the carbonate additive, the sulfur-containing additive and the additive containing an O-Si bond is (0.5-0.8): (0.5-0.8): (2-3): (0.3-1).

[0008] According to a second aspect of the present application, an electrolyte is provided, which includes a lithium salt, an organic solvent and the electrolyte additive composition of the first aspect of the present application.

[0009] Furthermore, the mass fraction of lithium salt in the electrolyte is 9% to 15%.

[0010] Furthermore, the mass fraction of the electrolyte additive composition in the electrolyte is greater than 1.2% and less than or equal to 5%.

[0011] Furthermore, the mass fraction of the organic solvent in the electrolyte is 80% to 90%.

[0012] Furthermore, the lithium salt includes at least one of lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, lithium borate, lithium difluoroborate, and lithium hexafluorophosphate; the organic solvent includes cyclic carbonates, chain carbonates, and chain carboxylates; wherein the mass ratio of cyclic carbonates, chain carbonates, and chain carboxylates is (10-30):(50-70):(10-20).

[0013] Furthermore, in the organic solvent, the cyclic carbonate is a compound of fluoroethylene carbonate and ethylene carbonate, and in the compound, the mass ratio of fluoroethylene carbonate to ethylene carbonate is 1:(0.5-1.5).

[0014] Furthermore, the chain carbonate is diethyl carbonate.

[0015] Furthermore, the chain carboxylic acid ester is ethyl difluoroacetate.

[0016] Furthermore, the lithium salt is lithium hexafluorophosphate.

[0017] According to a third aspect of the present application, a battery is provided, the battery comprising the electrolyte according to the second aspect of the present application.

[0018] Furthermore, the battery also includes a negative electrode sheet containing a negative electrode active material.

[0019] Furthermore, the negative electrode active material includes a carbon-based negative electrode material.

[0020] Furthermore, the battery also includes a positive electrode sheet containing positive electrode active material.

[0021] Furthermore, the positive electrode active material includes Li2MnO3, LiMn 0.375 Ni 0.375 Co 0.25 At least one of O2.

[0022] Furthermore, the positive electrode active material is Li2MnO3, LiMn 0.375 Ni 0.375 Co 0.25 O2 mixture, including Li2MnO3, LiMn 0.375 Ni 0.375 Co 0.25 The molar ratio of O2 is 1:3.

[0023] By applying the technical solution of the present application, the electrolyte additives are composed of lithium salt additives, carbonate additives, sulfur-containing additives and O-Si bond-containing additives. The four ingredients can synergistically improve the stability of SEI film and CEI film, improve the stability of the electrolyte under high voltage, and thus improve the cycle performance of the battery. DETAILED DESCRIPTION

[0024] The technical solutions in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present application and its application or use. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application.

[0025] As described in the background technology of this application, there is a problem in the prior art that the electrolyte has poor stability at high voltage, resulting in decreased battery cycle performance. In order to solve the above technical problems, in a typical embodiment of the present application, an electrolyte additive composition is provided, which includes a lithium salt additive, a carbonate additive, a sulfur-containing additive and an additive containing an O-Si bond; wherein the mass ratio of the lithium salt additive, the carbonate additive, the sulfur-containing additive and the additive containing an O-Si bond is (0.2-1): (0.2-1): (1-3): (0.3-1), specifically, the ratio can be 0.2:0.2:2:1, 0.2:0.5:1:1, 0.5:1:3:0.5, etc., or other values ​​within this range, which are not specifically limited here; the additive containing an O-Si bond is at least one of 2,4-bis(trimethylsilyloxy)pyrimidine and trimethylsilyl 2-(fluorosulfonyl)difluoroacetate.

[0026] Lithium salt additives help to form the SEI film, thereby limiting the passage of solvent molecules through the SEI film, slowing down the decomposition of the electrolyte and improving the interfacial stability of the electrolyte. Carbonate additives can form a stable SEI film on the surface of the negative electrode during the first charge and discharge process of the battery, which can effectively prevent direct contact between the electrolyte and the negative electrode material, reduce side reactions, and improve the cycle stability of the battery; in addition, carbonate additives can also help remove water and HF from the electrolyte, improving the safety and stability of the battery. Sulfur-containing additives can inhibit the decomposition of the electrolyte at high voltages, forming a protective SEI film, thereby preventing the collapse of the electrode material structure and improving the electrochemical stability of the battery. The additive 2,4-bis(trimethylsilyloxy)pyrimidine containing an O-Si bond can cooperate with the above-mentioned additives to eliminate water and hydrofluoric acid in the electrolyte, and can reduce the damage of transition metal ions to the negative electrode SEI film, further enhancing the stability of the electrolyte; the additive trimethylsilyl 2-(fluorosulfonyl)difluoroacetate containing an O-Si bond can cooperate with the above-mentioned additives to form a uniform and dense CEI film and SEI film on the positive and negative electrode surfaces, inhibit the dissolution of transition metal ions and the release of oxygen, reduce interfacial side reactions, and reduce the positive and negative electrode interface impedance. In addition, it can also eliminate water and hydrofluoric acid in the electrolyte, reduce proton impurities in the electrolyte, improve the stability of the electrolyte, and help to further improve the cycle performance of the battery at high voltage.

[0027] In some embodiments, the lithium salt additive includes at least one of lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, lithium borate, lithium difluoroborate, and lithium hexafluorophosphate; the carbonate additive includes at least one of vinylene carbonate and fluoroethylene carbonate; the sulfur-containing additive includes at least one of propylene sulfite, 1,3-propylene sulfonate, and vinyl sulfate.

[0028] The above-mentioned lithium salt additive and the additive containing O-Si bond 2,4-bis(trimethylsilyloxy)pyrimidine or trimethylsilyl 2-(fluorosulfonyl)difluoroacetate disclosed in the present application can cooperate with each other to promote the formation of SEI and CEI films, improve the stability and compactness of SEI and CEI films, thereby reducing interfacial impedance, reducing side reactions, and enabling the battery to maintain more stable performance and longer service life at high voltage. The above-mentioned carbonate additives have high oxidation potential, good chemical stability and thermal stability. By adding carbonate additives, the conductivity of the electrolyte can be increased, the electrochemical window of the electrolyte can be further broadened, and the electrolyte can be kept stable in a wider voltage range, which helps the battery to maintain performance when running at high voltage. Secondly, the addition of carbonate solvents can optimize the volatility of the electrolyte, reduce the volatilization of the electrolyte at high temperature or during charging and discharging, enhance the thermal stability of the battery, and is particularly suitable for equipment requiring high power output, thereby improving the overall safety of the battery. In addition, carbonate additives have a lower freezing point, which can improve the fluidity and conductivity of the electrolyte under low temperature conditions, thereby improving the performance and reliability of the battery under low temperature conditions. The above-mentioned sulfur-containing additives can promote the formation of SEI film and CEI film, optimize the physical properties of SEI / CEI film, and further reduce the interfacial impedance of the battery. Sulfur-containing additives have good thermal stability and electrochemical stability, which can not only improve the stability and hydrolysis resistance of the electrolyte under high voltage, but also maintain the integrity of SEI / CEI film at higher temperatures, reduce the negative impact of high temperature charge and discharge cycles on battery performance, and enable the battery to maintain good performance in high temperature environments. Sulfur-containing additives usually have good solvent compatibility and conductivity, which can improve the overall conductivity of the electrolyte and optimize the charge and discharge efficiency of the battery. By controlling the types of lithium salt additives, carbonate additives, and sulfur-containing additives, the components can work together to significantly improve the stability of the electrolyte under high voltage.

[0029] In some embodiments, the additive containing an O-Si bond is at least one of 2,4-bis(trimethylsilyloxy)pyrimidine and trimethylsilyl 2-(fluorosulfonyl)difluoroacetate, the lithium salt additive is lithium difluorophosphate, the carbonate additive is vinylene carbonate, and the sulfur-containing additive is 1,3-propylene sulfonate.

[0030] By selecting specific lithium salt additives, carbonate additives, and sulfur-containing additives, they can work together with the above-mentioned O-Si bond-containing additives to optimize the composition of the electrolyte, form stable SEI film and CEI film on the surface of the positive and negative electrodes, enhance the overall performance of the battery, and further improve the cycle stability of the battery at high voltage.

[0031] In some embodiments, the mass ratio of lithium salt additives, carbonate additives, sulfur-containing additives and additives containing O-Si bonds is (0.5-0.8): (0.5-0.8): (2-3): (0.3-1). Specifically, it can be 0.5:0.5:2:0.3, 0.5:0.8:2:0.3, 0.8:0.5:3:0.5, etc., or other values ​​within this range, which are not particularly limited herein.

[0032] The proportion of different additives also has a great influence on the performance of the electrolyte. Controlling the mass ratio of lithium salt additives, carbonate additives, sulfur-containing additives and additives containing O-Si bonds within the above range can balance the performance of the battery and have good cycle stability under high voltage and high temperature.

[0033] In another typical embodiment of the present invention, an electrolyte is provided. The electrolyte includes a lithium salt, an organic solvent and the electrolyte additive composition of the above embodiment.

[0034] By adding the above electrolyte additive composition to the electrolyte, the stability of the electrolyte at high voltage can be significantly improved, thereby improving the cycle performance of the battery at high voltage. In addition, the charge and discharge efficiency of the battery can be improved and the energy density of the battery can be increased.

[0035] In some embodiments, the mass fraction of lithium salt in the electrolyte is 9% to 15%, specifically, it can be 10%, 11%, 12%, 13%, 14%, 15%, etc., or other values ​​within the range, which are not specifically limited here. By limiting the amount of lithium salt added to the above range, it can be ensured that the electrolyte has sufficient conductivity and ensures efficient ion transmission during the charge and discharge process of the battery.

[0036] In some embodiments, the mass fraction of the electrolyte additive composition in the electrolyte is greater than 1.2% and less than or equal to 5%, specifically, it can be 1.5%, 2%, 3%, 4%, 5%, etc., or other values ​​within the range, which are not specifically limited here. By limiting the addition amount of the electrolyte additive composition to the above range, it is ensured that the electrolyte additive composition can play an effective role in the electrolyte to the maximum extent.

[0037] In some embodiments, the mass fraction of the organic solvent in the electrolyte is 80% to 90%, specifically, it can be 80%, 82%, 84%, 88%, 90%, etc., or other values ​​within the range, which are not specifically limited here. By limiting the amount of organic solvent added to the above range, sufficient fluidity can be provided to ensure the rapid transmission of lithium ions between electrodes, thereby maintaining the high conductivity of the battery; secondly, the appropriate solvent ratio is conducive to the formation of a stable and dense interface film, promotes the formation of SEI and CEI films, and reduces side reactions; in addition, it also helps to ensure that the electrolyte has a suitable viscosity, conductivity and chemical stability, and can maintain stable lithium ion transmission even under low or high temperature conditions, thereby improving the charging and discharging efficiency, stability and safety of lithium-ion batteries.

[0038] Through the synergistic effect of lithium salt, electrolyte additive composition and organic solvent, the viscosity and conductivity of the electrolyte can be optimized to maintain good stability, thereby improving the charge and discharge performance and energy efficiency of the battery in high and low temperature environments.

[0039] In some embodiments, the lithium salt includes at least one of lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, lithium borate, lithium difluoroborate, and lithium hexafluorophosphate.

[0040] The above-mentioned lithium salt has good thermal stability, can maintain the stability of the electrolyte under high temperature conditions, reduce side reactions, and improve the safety and cycle performance of the battery at high temperatures. In addition, the above-mentioned lithium salt has good electrical conductivity, can accelerate the migration rate of lithium ions, and improve the charge and discharge efficiency and power density of the battery.

[0041] In some embodiments, the organic solvent includes cyclic carbonates, chain carbonates and chain carboxylates; wherein the mass ratio of cyclic carbonates, chain carbonates and chain carboxylates is (10-30):(50-70):(10-20), specifically, it can be 30:50:20, 20:70:10, 10:70:20, etc., or other values ​​within this range, which are not particularly limited herein.

[0042] By limiting the ratio of cyclic carbonates, chain carbonates and chain carboxylates, the electrolyte formulation can be optimized, taking into account the balance of lithium ion transmission rate, SEI film and CEI film formation, high and low temperature performance, chemical stability and battery safety.

[0043] In some embodiments, the cyclic carbonate includes at least one of propylene carbonate, ethylene carbonate, fluoroethylene carbonate, butylene carbonate, and γ-butyrolactone; the chain carbonate includes at least one of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate; the chain carboxylic acid ester includes at least one of methyl formate, ethyl formate, propyl formate, butyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, butyl butyrate, ethyl fluoroacetate, propyl fluoroacetate, and propyl fluoropropionate. By selecting the above components as the organic solvent in the electrolyte, on the one hand, the electrolyte can have good fluidity and improve the electrochemical reaction rate, and on the other hand, the electrolyte can have good electrochemical stability and improve the cycle performance of the battery under high voltage.

[0044] In some embodiments, in the organic solvent, the cyclic carbonate is a compound of fluoroethylene carbonate and vinyl carbonate, in which the mass ratio of fluoroethylene carbonate to vinyl carbonate is 1:(0.5-1.5), specifically, it can be 1:0.5, 1:0.8, 1:1, 1:1.2, 1:1.5, etc., or other values ​​within this range, which are not particularly limited herein; the chain carbonate is diethyl carbonate; the chain carboxylic acid ester is ethyl difluoroacetate; and the lithium salt is lithium hexafluorophosphate.

[0045] By selecting fluoroethylene carbonate and ethylene carbonate as cyclic carbonates, on the one hand, the stability of the electrolyte can be improved, thereby improving the cycle performance of the battery; on the other hand, the electrolyte can have a suitable viscosity, which is beneficial to improving the rate performance of the battery. By limiting the types of cyclic carbonates, chain carbonates, chain carboxylates, and lithium salts, it is possible to synergize with electrolyte additives to improve the stability of the electrolyte at high voltage and high temperature, improve the cycle performance of the battery at high voltage and high temperature, and expand the application range of the battery.

[0046] The present application does not limit the specific preparation method of the electrolyte, as long as it contains the above components. For example, the specific preparation method of the electrolyte includes the following steps: adding the electrolyte additive composition to the organic solvent under a protective atmosphere, then adding the lithium salt, stirring and mixing at a first temperature to obtain the electrolyte; wherein the protective atmosphere can be argon, and the first temperature can be 5 to 15°C, specifically, 5°C, 8°C, 10°C, 12°C, 15°C, etc., or other values ​​within this range, which are not specifically limited here.

[0047] In another typical embodiment of the present application, a battery is provided. The battery includes the electrolyte in the above embodiment.

[0048] Due to the inclusion of the above-mentioned electrolyte, the battery has excellent cycle stability, especially high capacity retention and low voltage drop when cycled under high voltage conditions. In addition, the battery can meet the needs of different temperature scenarios.

[0049] In some embodiments, the battery further includes a negative electrode sheet containing a negative electrode active material and a positive electrode sheet containing a positive electrode active material.

[0050] The negative electrode sheet includes a negative electrode current collector and a negative electrode active layer including a negative electrode active material disposed on the surface of the negative electrode current collector.

[0051] When preparing the negative electrode sheet, the negative electrode active material, the first conductive agent, and the first binder can be dispersed in an appropriate amount of solvent, and fully stirred and mixed to form a uniform negative electrode slurry; the negative electrode slurry is evenly coated on the negative electrode current collector, and the negative electrode sheet is obtained after drying, rolling and cutting. In a specific embodiment, the negative electrode active layer includes 70% to 99% of graphite negative electrode material, 0.5% to 15% of conductive agent, and 0.5% to 15% of binder in terms of mass percentage.

[0052] Among them, the material of the negative electrode current collector can be at least one of copper foil, nickel foam, and copper foam; the first conductive agent can be selected from at least one of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, and graphene; the first binder can be selected from at least one of carboxymethyl cellulose, styrene-butadiene rubber, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyvinyl alcohol, and sodium polyacrylate.

[0053] The present application does not limit the specific type of the negative electrode active material in the negative electrode sheet, and it can be a currently commonly used negative electrode active material, such as at least one of graphite, hard carbon, soft carbon, mesophase carbon microspheres, and silicon-based negative electrode materials. In some preferred embodiments, the negative electrode active material includes a carbon-based negative electrode material.

[0054] The positive electrode sheet includes a positive electrode current collector and a positive electrode active layer including a positive electrode active material disposed on the surface of the positive electrode current collector.

[0055] When preparing the positive electrode sheet, the positive electrode active material, the second conductive agent, and the second binder can be dispersed in an appropriate amount of solvent, and fully stirred and mixed to form a uniform positive electrode slurry; the positive electrode slurry is evenly coated on the positive electrode current collector, and the positive electrode sheet is obtained after drying, rolling and slitting. In a specific embodiment, the positive electrode active layer includes 70% to 99% of the positive electrode active material, 0.5% to 15% of the conductive agent, and 0.5% to 15% of the binder in terms of mass percentage.

[0056] Among them, the material of the positive electrode current collector can be at least one of aluminum foil and nickel foil; the second conductive agent can be selected from at least one of carbon black, acetylene black, graphene, Ketjen black, and carbon fiber; the second binder can be selected from at least one of polytetrafluoroethylene, polyvinylidene fluoride, carboxymethyl cellulose, styrene-butadiene rubber, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polyethylene, polypropylene, polyvinyl alcohol, and sodium polyacrylate.

[0057] The present application does not limit the specific type of positive electrode active material in the positive electrode sheet, which can be a currently commonly used positive electrode active material, such as at least one composite oxide of lithium and metals of cobalt, nickel, manganese and combinations thereof. Specifically, it can be at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, nickel cobalt manganese ternary material, nickel cobalt aluminum ternary material, lithium iron phosphate, lithium nickel manganese oxide, and lithium-rich manganese-based materials. In some embodiments, the positive electrode active material is Li2MnO3, LiMn 0.375 Ni 0.375 Co 0.25 O2 mixture, including Li2MnO3, LiMn 0.375 Ni 0.375 Co 0.25 The molar ratio of O2 is 1:3.

[0058] The battery also includes a diaphragm. The present application does not limit the specific selection of the diaphragm material, and it can be a diaphragm material commonly used in batteries, such as a polypropylene diaphragm, a polyethylene diaphragm, a polypropylene / polyethylene double-layer composite diaphragm, a polypropylene / polyethylene / polypropylene (PP / PE / PP) three-layer composite diaphragm, etc.

[0059] When preparing the battery, the positive electrode sheet, the separator and the negative electrode sheet are wound or stacked to obtain the battery cell, and the battery cell is encapsulated in a pre-stamped aluminum-plastic film. After the encapsulated battery is dried to remove moisture, the electrolyte is injected into the dry battery. After the battery is aged, formed and sealed for the second time, the battery preparation is completed.

[0060] The present application is further described in detail below in conjunction with specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in the present application.

[0061] Example 1

[0062] The electrolyte of this embodiment is composed of an organic solvent, a lithium salt and an electrolyte additive composition; the electrolyte additive composition includes vinylene carbonate, lithium difluorophosphate, 1,3-propane sultone and 2,4-bis(trimethylsilyloxy)pyrimidine;

[0063] The mass fraction of vinylene carbonate in the electrolyte is 0.5%, the mass fraction of lithium difluorophosphate in the electrolyte is 0.5%, the mass fraction of 1,3-propane sultone in the electrolyte is 2%, and the mass fraction of 2,4-bis(trimethylsilyloxy)pyrimidine in the electrolyte is 0.5%;

[0064] The lithium salt is lithium hexafluorophosphate, and its mass fraction in the electrolyte is 15%; the mass fraction of the organic solvent in the electrolyte is 81.5%, and it is composed of fluoroethylene carbonate, ethylene carbonate, ethyl difluoroacetate, and diethyl carbonate. Based on the total mass of the organic solvent being 100%, the mass fraction of fluoroethylene carbonate is 10%, the mass fraction of ethylene carbonate is 10%, the mass fraction of ethyl difluoroacetate is 15%, and the mass fraction of diethyl carbonate is 65%.

[0065] The preparation method of the electrolyte of this embodiment includes: under an argon atmosphere, adding a formulated amount of vinylene carbonate, lithium difluorophosphate, 1,3-propane sultone and 2,4-bis(trimethylsilyloxy)pyrimidine to an organic solvent according to the above mass fractions, then adding lithium hexafluorophosphate, stirring and mixing at a temperature of 10° C. to obtain the electrolyte.

[0066] Example 2

[0067] The electrolyte of this embodiment is different from that of Embodiment 1 only in that the mass fraction of vinylene carbonate in the electrolyte is 0.2%, and the mass fraction of the organic solvent is 81.8%.

[0068] Example 3

[0069] The electrolyte of this embodiment is different from that of Embodiment 1 only in that the mass fraction of vinylene carbonate in the electrolyte is 0.8%, and the mass fraction of the organic solvent is 81.2%.

[0070] Example 4

[0071] The electrolyte of this embodiment is different from that of Embodiment 1 only in that the mass fraction of lithium difluorophosphate in the electrolyte is 0.2%, and the mass fraction of the organic solvent is 81.8%.

[0072] Example 5

[0073] The electrolyte of this embodiment is different from that of Embodiment 1 only in that the mass fraction of lithium difluorophosphate in the electrolyte is 0.8%, and the mass fraction of the organic solvent is 81.2%.

[0074] Example 6

[0075] The electrolyte of this embodiment is different from that of Embodiment 1 only in that the mass fraction of 1,3-propane sultone in the electrolyte is 1%, and the mass fraction of the organic solvent is 82.5%.

[0076] Example 7

[0077] The electrolyte of this embodiment is different from that of Embodiment 1 only in that the mass fraction of 1,3-propane sultone in the electrolyte is 3%, and the mass fraction of the organic solvent is 80.5%.

[0078] Example 8

[0079] The electrolyte of this embodiment is different from that of Embodiment 1 only in that the mass fraction of 2,4-bis(trimethylsilyloxy)pyrimidine in the electrolyte is 0.3%, and the mass fraction of the organic solvent is 81.7%.

[0080] Example 9

[0081] The electrolyte of this embodiment is different from that of Embodiment 1 only in that the mass fraction of 2,4-bis(trimethylsilyloxy)pyrimidine in the electrolyte is 1%, and the mass fraction of the organic solvent is 81%.

[0082] Example 10

[0083] The electrolyte of this embodiment is different from that of Embodiment 1 only in that the composition of the organic solvent is different. The organic solvent consists of fluoroethylene carbonate, ethyl difluoroacetate and diethyl carbonate. Taking the total mass fraction of the organic solvent as 100%, the mass fraction of fluoroethylene carbonate is 20%, the mass fraction of ethyl difluoroacetate is 15%, and the mass fraction of diethyl carbonate is 65%.

[0084] Embodiment 11

[0085] The electrolyte of this embodiment is different from that of Embodiment 1 only in that the composition of the organic solvent is different. The organic solvent is composed of ethylene carbonate, ethyl acetate and diethyl carbonate. Taking the total mass fraction of the organic solvent as 100%, the mass fraction of ethylene carbonate is 20%, the mass fraction of ethyl acetate is 15%, and the mass fraction of diethyl carbonate is 65%.

[0086] Example 12

[0087] The electrolyte of this embodiment is different from that of embodiment 1 only in that ethyl methyl carbonate is used instead of diethyl carbonate.

[0088] Embodiment 13

[0089] The electrolyte of this embodiment is different from that of Embodiment 1 only in that the composition of the organic solvent is different, and the electrolyte is composed of fluoroethylene carbonate, ethylene carbonate, and diethyl carbonate. Taking the total mass of the organic solvent as 100%, the mass fraction of fluoroethylene carbonate is 20%, the mass fraction of ethylene carbonate is 15%, and the mass fraction of diethyl carbonate is 65%.

[0090] Embodiment 14

[0091] The electrolyte of this embodiment is different from that of embodiment 1 only in that the mass fractions of the components in the organic solvent are different, wherein the mass fraction of fluoroethylene carbonate is 15%, the mass fraction of ethylene carbonate is 15%, the mass fraction of ethyl difluoroacetate is 10%, and the mass fraction of diethyl carbonate is 60%.

[0092] Embodiment 15

[0093] The electrolyte of this embodiment is different from that of embodiment 1 only in that the mass fractions of the components in the organic solvent are different, wherein the mass fraction of fluoroethylene carbonate is 5%, the mass fraction of ethylene carbonate is 5%, the mass fraction of ethyl difluoroacetate is 20%, and the mass fraction of diethyl carbonate is 70%.

[0094] Embodiments 16 to 30

[0095] The electrolytes described in Examples 16 to 30 correspond to the electrolytes described in Examples 1 to 15, respectively, except that trimethylsilyl 2-(fluorosulfonyl)difluoroacetate is used to replace 2,4-bis(trimethylsilyloxy)pyrimidine in the electrolytes described in Examples 1 to 15.

[0096] Comparative Example 1

[0097] An electrolyte solution, which is different from Example 1 only in that 2,4-bis(trimethylsilyloxy)pyrimidine is not added.

[0098] Comparative Example 2

[0099] An electrolyte, which differs from Example 1 only in that the additive containing O-Si bonds is different, and its structural formula is

[0100] Comparative Example 3

[0101] An electrolyte, which differs from Example 1 only in that the additive containing O-Si bonds is different, and its structural formula is

[0102] Comparative Example 4

[0103] An electrolyte solution, which is different from Example 1 only in that the mass fraction of vinylene carbonate is 1.5% and the mass fraction of the organic solvent is 80.5%.

[0104] Comparative Example 5

[0105] An electrolyte solution, which is different from Example 1 only in that the mass fraction of 1,3-propane sultone is 0.8% and the mass fraction of the organic solvent is 82.7%.

[0106] Test example

[0107] The electrolytes of the embodiment and the comparative example were applied to lithium-ion batteries, and the performance of the lithium-ion batteries was tested. The specific preparation method of the lithium-ion battery includes: mixing graphite, acetylene black, carboxymethyl cellulose and styrene-butadiene rubber in a mass ratio of 94:1:2:3 to form a negative electrode slurry; coating the negative electrode slurry on a copper foil current collector, vacuum drying, and preparing a negative electrode sheet;

[0108] The positive electrode material (0.25Li2MnO3 · 0.75LiMn 0.375 Ni 0.375 Co 0.25 O2), acetylene black and polyvinylidene fluoride are mixed in a mass ratio of 94:3:3 to form a positive electrode slurry; the positive electrode slurry is coated on an aluminum foil current collector, and vacuum dried to obtain a positive electrode sheet;

[0109] The positive electrode sheet, Celgard2400 separator and negative electrode sheet are wound or stacked to obtain a battery cell, and the battery cell is encapsulated in a pre-stamped aluminum-plastic film. After the encapsulated battery is dried to remove moisture, the electrolyte of the embodiment and the comparative example is injected into the dried battery. After the battery is aged, formed and sealed for a second time, a lithium ion battery is obtained.

[0110] The following electrochemical tests were performed using a Xinwei charge and discharge test cabinet.

[0111] (1) Normal temperature cycle performance test:

[0112] At 25°C, the lithium-ion battery is charged at a constant current of 0.5C (nominal capacity) to a voltage of 4.6V, then charged at a constant voltage of 4.6V to a current ≤ 0.05C, left for 10 minutes, and then discharged at a constant current of 1C to a cut-off voltage of 2.5V. The above is one charge and discharge cycle. The lithium-ion battery is charged and discharged 1000 times under the above conditions.

[0113] Capacity retention rate (%) of a lithium-ion battery after 1000 cycles = (discharge capacity at the 1000th cycle / initial discharge capacity) × 100%.

[0114] The average voltage (V) of a lithium-ion battery after 1000 cycles = discharge energy at the 1000th cycle / discharge capacity at the 1000th cycle.

[0115] (2) High temperature cycle performance test

[0116] At 45°C, the lithium-ion battery was charged at a constant current of 1.0C (nominal capacity) to a voltage of 4.6V, then charged at a constant voltage of 4.6V to a current of ≤0.05C, left for 10 minutes, and then discharged at a constant current of 1C to a cut-off voltage of 2.5V. The above is one charge and discharge cycle. The lithium-ion battery was charged and discharged 800 times under the above conditions.

[0117] Capacity retention rate (%) of the lithium-ion battery after 800 cycles = (discharge capacity at the 800th cycle / initial discharge capacity) × 100%.

[0118] The average voltage (V) of the lithium-ion battery after 800 cycles = the discharge energy at the 800th cycle / the discharge capacity at the 800th cycle.

[0119] The test results are shown in Table 1.

[0120] Table 1

[0121]

[0122]

[0123]

[0124] It can be seen from the above test results that the room temperature cycle performance and high temperature cycle performance of the electrolyte in the embodiment of the present application are significantly better, and its high voltage resistance is excellent and has a wide range of applications. The above is only a preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various changes and variations. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. An electrolyte additive composition, characterized in that: It includes lithium salt additives, carbonate additives, sulfur-containing additives and additives containing O-Si bonds; the mass ratio of the lithium salt additives, the carbonate additives, the sulfur-containing additives and the additives containing O-Si bonds is (0.2-1): (0.2-1): (1-3): (0.3-1); the additive containing O-Si bonds is at least one of 2,4-bis(trimethylsilyloxy)pyrimidine and trimethylsilyl 2-(fluorosulfonyl)difluoroacetate.

2. The electrolyte additive composition according to claim 1, characterized in that: The lithium salt additive includes at least one of lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, lithium borate, lithium difluoroborate, and lithium hexafluorophosphate; the carbonate additive includes at least one of vinylene carbonate and fluoroethylene carbonate; the sulfur-containing additive includes at least one of propylene sulfite, 1,3-propylene sulfonate, and vinyl sulfate.

3. The electrolyte additive composition according to claim 1, characterized in that: The additive containing an O-Si bond is at least one of 2,4-bis(trimethylsilyloxy)pyrimidine and trimethylsilyl 2-(fluorosulfonyl)difluoroacetate, the lithium salt additive is lithium difluorophosphate, the carbonate additive is vinylene carbonate, and the sulfur-containing additive is 1,3-propylene sulfonate.

4. The electrolyte additive composition according to any one of claims 1 to 3, characterized in that: The mass ratio of the lithium salt additive, the carbonate additive, the sulfur-containing additive and the additive containing an O-Si bond is (0.5-0.8): (0.5-0.8): (2～3)：(0.3～1)。 5. An electrolyte, characterized in that: The electrolyte comprises a lithium salt, an organic solvent and the electrolyte additive composition according to any one of claims 1 to 4.

6. The electrolyte according to claim 5, characterized in that The mass fraction of the lithium salt in the electrolyte is 9% to 15%; and / or, The mass fraction of the electrolyte additive composition in the electrolyte is greater than 1.2% and less than or equal to 5%; and / or, The mass fraction of the organic solvent in the electrolyte is 80% to 90%.

7. The electrolyte according to claim 5 or 6, characterized in that The lithium salt includes at least one of lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, lithium borate, lithium difluoroborate, and lithium hexafluorophosphate; the organic solvent includes cyclic carbonate, chain carbonate, and chain carboxylate; wherein the mass ratio of the cyclic carbonate, the chain carbonate, and the chain carboxylate is (10-30):(50-70):(10-20).

8. The electrolyte according to claim 7, characterized in that In the organic solvent, the cyclic carbonate is a compound of fluoroethylene carbonate and ethylene carbonate, and in the compound, the mass ratio of the fluoroethylene carbonate to the ethylene carbonate is 1: (0.5~1.5); and / or, the chain carbonate is diethyl carbonate; and / or, the chain carboxylic acid ester is ethyl difluoroacetate; and / or, the lithium salt is lithium hexafluorophosphate.

9. A battery, characterized in that: The battery comprises the electrolyte according to any one of claims 5 to 8.

10. The battery according to claim 9, characterized in that The battery further comprises a negative electrode sheet containing a negative electrode active material; and / or, The battery also includes a positive electrode sheet containing a positive electrode active material; Preferably, the negative electrode active material includes a carbon-based negative electrode material; the positive electrode active material includes Li2MnO3, LiMn 0.375 Ni 0.375 Co 0.25 At least one of O2; More preferably, the positive electrode active material is Li2MnO3, LiMn 0.375 Ni 0.375 Co 0.25 O2 mixture, including Li2MnO3, LiMn 0.375 Ni 0.375 Co 0.25 The molar ratio of O2 is 1:(2~4).

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