Electrolyte additive composition, electrolyte and battery

Abstract

This application provides an electrolyte additive composition, an electrolyte, and a battery, relating to the field of secondary battery technology. The electrolyte additive composition includes a lithium salt additive and an electrolyte functional additive. The electrolyte functional additive has the following structural formula: applying an electrolyte functional additive with a specific structural formula as an electrolyte additive in a battery can effectively improve the problem of severe capacity decay during high-voltage cycling and extend the battery's cycle life.

Description

Technical Field

[0001] This application relates to the field of secondary battery technology, and more specifically, to an electrolyte additive composition, an electrolyte, and a battery. Background Technology

[0002] The continued boom in computer, communication, and consumer electronics has led to the rapid development of the lithium-ion battery industry. In particular, the rise of new energy vehicles in recent years has spurred the development of power lithium-ion batteries, placing higher demands on their energy density and safety performance. Electric vehicle range has become one of the most important performance indicators for consumers, and battery energy density determines the range of an electric vehicle on a single charge. Improving battery energy density within limited space and weight has become a hot research topic. Increasing the operating voltage of the cathode material is currently one of the mainstream methods to improve the energy density of lithium-ion batteries. High-voltage cathode materials, such as high-voltage binary, high-voltage ternary, high-voltage lithium cobalt oxide, and layered lithium-rich oxide (LLO), have become research hotspots. However, as the voltage of lithium-ion batteries continues to increase, the cathode material will have a higher electrode potential, leading to more intense oxidative decomposition of the electrolyte at the cathode and more vigorous reactions at the cathode interface. As the battery undergoes charge-discharge cycles, the internal resistance of the battery gradually increases, resulting in a decline in battery performance or even battery failure. Summary of the Invention

[0003] The main objective of this application is to provide an electrolyte additive composition, an electrolyte, and a battery to solve the problem that the electrolyte has poor stability at high voltage, which leads to severe capacity decay of the battery during high voltage cycling.

[0004] To achieve the above objectives, according to a first aspect of this application, an electrolyte additive composition is provided, comprising a lithium salt additive and an electrolyte functional additive, wherein the electrolyte functional additive has CB number CB62437455 and its structural formula is shown in Formula 1:

[0005]

[0006] Furthermore, in the electrolyte additive composition, the mass ratio of lithium salt additive to electrolyte functional additive is (0.5-1):(0.3-1).

[0007] Furthermore, the lithium salt additive includes at least one of lithium bis(fluorosulfonyl)imide (LiFSI), lithium difluorophosphate (LiPO2F2), lithium borate, lithium difluorophosphate, and lithium hexafluorophosphate.

[0008] Furthermore, the electrolyte additive composition also includes carbonate additives; the mass ratio of the carbonate additives to the electrolyte functional additives is (0.1-1):(0.3-1).

[0009] Furthermore, carbonate additives include at least one of vinylene carbonate (VC) and fluoroethylene carbonate.

[0010] Furthermore, the electrolyte additive composition also includes a sulfur-containing additive; the mass ratio of the sulfur-containing additive to the electrolyte functional additive is (0.5-3):(0.3-1).

[0011] Furthermore, the sulfur-containing additives include at least one of 1,3-propanesulfonate lactone (PS), 1,3-propenesulfonate lactone (PST), and vinyl sulfate (DTD).

[0012] According to a third aspect of this application, an electrolyte is provided, comprising a lithium salt, an organic solvent, and an electrolyte additive composition according to a second aspect of this application.

[0013] Furthermore, the mass fraction of lithium salt in the electrolyte is 9% to 15%.

[0014] Furthermore, the mass fraction of the electrolyte additive composition in the electrolyte is greater than 0 and less than or equal to 5%.

[0015] Furthermore, the organic solvent accounts for 80% to 90% of the mass fraction in the electrolyte.

[0016] Furthermore, the electrolyte functional additive has a mass fraction of 0.3% to 1% in the electrolyte.

[0017] Furthermore, the organic solvent includes at least one of cyclic carbonates, linear carbonates, and linear carboxylic esters.

[0018] Furthermore, the organic solvent includes cyclic carbonates, chain carbonates and chain carboxylic esters, wherein the mass ratio of cyclic carbonates, chain carbonates and chain carboxylic esters is (1-15):(20-70):(5-20).

[0019] Furthermore, the cyclic carbonates include fluoroethylene carbonate and ethylene carbonate, wherein the mass ratio of fluoroethylene carbonate to ethylene carbonate is 1:(0.8 to 1.2).

[0020] Furthermore, the electrolyte additive composition includes lithium salt additives, carbonate additives, sulfur-containing additives, and electrolyte functional additives, wherein the mass ratio of lithium salt additives, carbonate additives, sulfur-containing additives, and electrolyte functional additives is (0.2-0.8):(0.2-0.8):(1-3):(0.3-1).

[0021] According to a fourth aspect of this application, a battery is provided that includes the electrolyte of the third aspect of this application.

[0022] Furthermore, the battery also includes a negative electrode sheet containing negative electrode active material.

[0023] Furthermore, the anode active material includes carbon-based anode materials.

[0024] Furthermore, the battery also includes a positive electrode sheet containing positive electrode active material.

[0025] Furthermore, the positive electrode active materials include Li2MnO3 and LiMn 0.375 Ni 0.375 Co 0.25 At least one of O2.

[0026] Furthermore, the positive electrode active material is Li2MnO3 or LiMn 0.375 Ni 0.375 Co 0.25 A mixture of O2, including Li2MnO3 and LiMn 0.375 Ni 0.375 Co 0.25 The molar ratio of O2 is 1:3.

[0027] By applying the technical solution of this application, lithium salt additives are added to the electrolyte additive composition. The lithium salts can participate in the formation of a solid electrolyte interphase (SEI) film. Electrolyte functional additives with specific structural formulas are used as electrolyte additives in batteries. On the one hand, these functional additives can form a uniform and dense SEI film at the negative electrode, inhibiting the reduction of the electrolyte on the negative electrode surface, thereby reducing interfacial side reactions and lowering the negative electrode interfacial impedance. On the other hand, the O-Si bonds and carbon-nitrogen triple bonds in these functional additives can eliminate H2O and HF, reducing proton impurities in the electrolyte and improving the stability of the electrolyte. Furthermore, the cyclopentadiene in these functional additives can inhibit the oxidative decomposition of the electrolyte under high voltage, improving the high-voltage stability of the electrolyte. Moreover, cyclopentadiene containing 4 F substituents has stronger oxidation resistance than cyclopentadiene containing 1 to 3 F substituents, thus more effectively improving the problem of severe capacity decay during high-voltage cycling and extending the battery's cycle life. Detailed Implementation

[0028] As described in the background section of this application, the prior art suffers from the problem that the electrolyte has poor stability under high voltage and is prone to oxidation and decomposition, resulting in poor cycle performance of the battery.

[0029] To address the aforementioned technical problems, in a typical embodiment of this application, an electrolyte additive composition is provided. This electrolyte additive composition includes a lithium salt additive and an electrolyte functional additive, the structural formula of which is shown in Formula 1:

[0030]

[0031] Adding an electrolyte functional additive with the above-mentioned structure to the electrolyte can, on the one hand, form a uniform and dense SEI film at the negative electrode, inhibiting the reduction of the electrolyte on the negative electrode surface, thereby reducing interfacial side reactions and lowering the negative electrode interfacial impedance; on the other hand, the O-Si bonds and carbon-nitrogen triple bonds in the electrolyte functional additive can eliminate H2O and HF, reducing proton impurities in the electrolyte; furthermore, the cyclopentadiene in the electrolyte functional additive can inhibit the oxidative decomposition of the electrolyte under high voltage, improving the high-voltage stability of the electrolyte, and the cyclopentadiene containing 4 F substituents has stronger oxidation resistance than the cyclopentadiene containing 1 to 3 F substituents. The electrolyte functional additive simultaneously contains O-Si bonds, carbon-nitrogen triple bonds, and cyclopentadiene containing 4 fluorine substituents, and the three can synergistically improve the stability of the electrolyte, which is beneficial to significantly improving the high-voltage cycle performance of the battery.

[0032] In some embodiments, the mass ratio of lithium salt additive to electrolyte functional additive is (0.5-1):(0.3-1).

[0033] Lithium salt additives exhibit high oxidation stability and can participate in electrochemical reactions, maintaining electrolyte stability under high voltage and reducing electrolyte decomposition. Simultaneously, the chemical bonds in electrolyte functional additives can eliminate H₂O and HF in the electrolyte. Therefore, the synergistic effect of lithium salt additives and electrolyte functional additives can significantly improve the stability of the electrolyte under high voltage conditions.

[0034] Electrolyte functional additives form a uniform and dense SEI film on the negative electrode surface. At the same time, lithium salt additives can participate in the formation of the SEI film. Under the combined action of electrolyte functional additives and lithium salt additives, the stability and density of the film can be promoted, thereby reducing interfacial impedance and side reactions. By reducing side reactions inside the battery, the discharge capacity and average voltage of the battery can be maintained, thereby improving the cycle life of the battery.

[0035] In addition to improving cycle life, the introduction of lithium salt additives can also improve battery performance at high and low temperatures, reduce the generation of harmful gases (such as H2, CO, CO2, etc.) inside the battery, reduce internal pressure and the risk of thermal runaway, thereby improving battery safety performance.

[0036] In summary, by combining lithium salt additives and electrolyte functional additives, the battery can maintain more stable performance and longer service life under high voltage conditions, thus meeting the high performance requirements of modern electronic devices and new energy vehicles. This approach improves electrolyte stability, optimizes the formation of SEI / CEI films, extends battery cycle life, enhances battery performance at high and low temperatures, and improves battery safety.

[0037] The mass ratio of lithium salt additive to electrolyte functional additive is (0.5–1):(0.3–1), for example, it can be a range of 0.5:1, 0.8:1, 1:1, 0.5:0.3, or any combination thereof. By limiting this mass ratio of lithium salt additive to electrolyte functional additive, the chemical properties of the electrolyte and the physical structure of the protective film can be optimized to ensure the conductivity, chemical stability, and electrochemical window of the electrolyte, thereby improving the battery performance at different temperatures. This is particularly suitable for operating environments with large temperature fluctuations, such as outdoor energy storage devices.

[0038] This application does not limit the specific type of lithium salt additive, and it can be a conventional lithium salt additive in the art. For example, in some embodiments, the lithium salt additive includes at least one of lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, lithium borate, lithium difluorophosphate, and lithium hexafluorophosphate.

[0039] In some embodiments, the electrolyte additive composition further includes a carbonate additive; the mass ratio of the carbonate additive to the electrolyte functional additive is (0.1-1):(0.3-1).

[0040] Carbonate additives can promote the formation of SEI film on the negative electrode surface. The formation of SEI film can reduce the formation of lithium dendrites and the direct oxidation of negative electrode materials, thereby reducing the risk of battery short circuit and further improving the cycle life and safety of the battery.

[0041] Carbonate additives possess high oxidation potential, good chemical stability, and thermal stability. Adding carbonate additives can improve the conductivity of the electrolyte, further widening its electrochemical window and allowing it to remain stable over a wider voltage range, thus helping the battery maintain performance under high voltage operation. Secondly, the addition of carbonate solvents can optimize electrolyte volatility, reducing evaporation during high temperatures or charge / discharge processes, enhancing the battery's thermal stability, making it particularly suitable for devices requiring high power output and improving overall battery safety. Furthermore, carbonate additives have low freezing points, improving the fluidity and conductivity of the electrolyte at low temperatures, thereby enhancing battery performance and reliability in cold environments.

[0042] In summary, by introducing carbonate additives, the composition of the electrolyte can be optimized through the combined effects of lithium salt additives, electrolyte functional additives, and carbonate additives. This not only further improves the battery's cycle stability and voltage drop under high voltage, but also significantly improves the battery's safety and low-temperature performance.

[0043] The mass ratio of carbonate additives to electrolyte functional additives is (0.1–1):(0.3–1), for example, it can be a range of 0.1:1, 0.5:1, 1:1, 1:0.5, 1:0.3, or any combination thereof. By limiting the ratio of carbonate additives to electrolyte functional additives, the physicochemical properties of the entire electrolyte, including viscosity, conductivity, and chemical stability, can be optimized, thereby improving the overall performance of the battery.

[0044] This application does not limit the specific type of carbonate additive, and it can be any conventional carbonate additive in the art. For example, in some embodiments, the carbonate additive includes at least one of vinylene carbonate and fluoroethylene carbonate.

[0045] In some embodiments, the electrolyte additive composition further includes a sulfur-containing additive; the mass ratio of the sulfur-containing additive to the electrolyte functional additive is (0.5-3):(0.3-1).

[0046] Sulfur-containing additives can promote the formation of SEI and CEI films, optimize the physical properties of the SEI / CEI films, and thus further reduce the interfacial impedance of the battery. Sulfur-containing additives exhibit good thermal and electrochemical stability, not only improving the stability and hydrolysis resistance of the electrolyte at high voltages but also maintaining the integrity of the SEI / CEI films at higher temperatures, reducing the negative impact of high-temperature charge-discharge cycles on battery performance, and enabling the battery to maintain good performance even in high-temperature environments. Sulfur-containing additives typically possess good solvent compatibility and conductivity, improving the overall conductivity of the electrolyte and optimizing the charge-discharge efficiency of the battery.

[0047] In summary, the addition of sulfur-containing additives can not only further reduce the capacity decay and voltage drop of the battery during cycling, but also enhance the stability of the electrolyte and the high-temperature performance of the battery, optimize the conductivity, enhance the interface stability of the battery, and further improve the overall performance of the battery.

[0048] The mass ratio of sulfur-containing additives to electrolyte functional additives is (0.5–3):(0.3–1), for example, it can be a range of 0.5:1, 0.8:1, 1:1, 2:1, 3:1, 3:0.5, 3:0.3, or any combination thereof. By limiting the mass ratio of sulfur-containing additives to electrolyte functional additives within the above range, the formation of the SEI / CEI film inside the battery can be optimized through synergistic effects. In addition to further reducing capacity decay and voltage drop during battery cycling, it can also improve the thermal stability and low-temperature performance of the battery.

[0049] This application does not limit the specific type of sulfur-containing additive, and it can be a conventional sulfur-containing additive in the art. For example, in some embodiments, the sulfur-containing additive includes at least one of 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, and vinyl sulfate.

[0050] In another typical embodiment of this application, an electrolyte is provided, which includes a lithium salt, an organic solvent, and the electrolyte additive composition described in the above embodiments of this application.

[0051] Because it includes the above-mentioned electrolyte additive composition, the electrolyte can form a more stable electrochemical environment inside the battery, effectively improving the problems of severe capacity decay and voltage drop during battery cycling at high voltage, and extending the cycle life of the battery. This electrolyte is suitable for lithium-ion batteries.

[0052] Lithium salts are the primary source of conductive ions in the electrolyte. In some embodiments, the mass fraction of lithium salts in the electrolyte is 9% to 15%, for example, 10%, 11%, 12%, 13%, 14%, 15%, or any combination thereof. By limiting the amount of lithium salt added within the above range, sufficient conductivity of the electrolyte can be ensured, guaranteeing efficient ion transport during battery charging and discharging, while also ensuring sufficient lithium salt participates in the formation of the SEI / CEI film.

[0053] In some embodiments, the electrolyte additive composition has a mass fraction in the electrolyte that is greater than 0 and less than or equal to 5%.

[0054] By limiting the amount of electrolyte additive composition added within the above range, it is ensured that the electrolyte additive composition can exert its effective function to the maximum extent in the electrolyte.

[0055] The electrolyte additive composition has a mass fraction in the electrolyte greater than 0 and less than or equal to 5%, for example, a range of 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, or any two of these.

[0056] Organic solvents are a major component of the electrolyte, responsible for transporting lithium ions. In some embodiments, the mass fraction of the organic solvent in the electrolyte is 80% to 90%, for example, a range of 80%, 82%, 84%, 86%, 88%, 90%, or any combination thereof. By limiting the amount of organic solvent added within the above range, sufficient fluidity can be provided to ensure rapid transport of lithium ions between electrodes, thereby maintaining the high conductivity of the battery. Secondly, a suitable solvent ratio is beneficial for the formation of a stable and dense interfacial film, promoting the formation of the SEI / CEI film and reducing side reactions. In addition, it helps to ensure that the electrolyte has suitable viscosity, conductivity, and chemical stability, maintaining stable lithium ion transport even under low or high temperature conditions, thereby improving the charge-discharge efficiency, stability, and safety of lithium-ion batteries.

[0057] The synergistic effect of lithium salt, electrolyte additive composition and organic solvent can optimize the viscosity and conductivity of the electrolyte, maintain its good stability, and thus improve the charge and discharge performance and energy efficiency of the battery under high and low temperature environments.

[0058] This application does not limit the proportion of each additive in the electrolyte, as long as the above requirements are met. For example, in some embodiments, the mass fraction of the electrolyte functional additive in the electrolyte is 0.3% to 1%, such as 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, or any combination thereof. By limiting the amount of electrolyte functional additive added, its effectiveness in improving severe capacity decay and voltage drop can be achieved, while avoiding changes in electrolyte viscosity or increased costs, thus contributing to electrolyte formulation optimization and improved lithium-ion battery performance.

[0059] In some embodiments, the organic solvent includes at least one of cyclic carbonates, linear carbonates, and linear carboxylic esters. This combines the advantages of cyclic carbonates, linear carbonates, and linear carboxylic esters, improving the overall performance of the battery. Specifically, cyclic carbonates maintain good conductivity at low temperatures, promoting the formation of a stable SEI film at low temperatures, while linear carbonates and linear carboxylic esters help reduce viscosity and have better stability at high temperatures. Thus, by limiting the specific type of organic solvent, the stability of the electrolyte at high and low temperatures can be improved, while also enhancing the capacity retention rate of the battery during high and low temperature cycling, meeting the needs of the battery in different application scenarios.

[0060] When the organic solvent includes cyclic carbonates, linear carbonates, and linear carboxylic esters, the mass ratio of cyclic carbonates, linear carbonates, and linear carboxylic esters is (1–15):(20–70):(5–20). By limiting the ratio of cyclic carbonates, linear carbonates, and linear carboxylic esters, the electrolyte formulation can be optimized, balancing lithium-ion transport rate, SEI / CEI film formation, high and low temperature performance, cost-effectiveness, internal resistance reduction, chemical stability, and battery safety.

[0061] In some embodiments, cyclic carbonates include at least one selected from propylene carbonate, ethylene carbonate, fluoroethylene carbonate, butylene carbonate, and γ-butyrolactone; chain carbonates include at least one selected from dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate; and chain carboxylic acid esters include at least one selected from methyl formate, ethyl formate, propyl formate, butyl formate, methyl acetate, ethyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, butyl butyrate, ethyl fluoroacetate, fluoropropyl acetate, and fluoropropyl propionate. By selecting the above components as organic solvents in the electrolyte, on the one hand, the electrolyte can have good fluidity, improving the electrochemical reaction rate; on the other hand, the electrolyte can have good electrochemical stability, improving the cycle performance of the battery at high voltages.

[0062] In some embodiments, the cyclic carbonate includes fluoroethylene carbonate and ethylene carbonate, wherein the mass ratio of fluoroethylene carbonate to ethylene carbonate is 1:(0.8 to 1.2).

[0063] By selecting fluoroethylene carbonate and ethylene carbonate as cyclic carbonates, 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.

[0064] In some embodiments, the electrolyte additive composition includes lithium salt additives, carbonate additives, sulfur-containing additives, and electrolyte functional additives, wherein the mass ratio of lithium salt additives, carbonate additives, sulfur-containing additives, and electrolyte functional additives is (0.2-0.8):(0.2-0.8):(1-3):(0.3-1).

[0065] By selecting the components of the electrolyte additive composition, the electrolyte exhibits higher electrochemical stability at high voltages, which is beneficial for further improving the battery's cycle performance at high voltages and reducing capacity decay.

[0066] This application does not limit the specific preparation method of the electrolyte, as long as it contains the above-mentioned components. For example, a specific preparation method of the electrolyte includes the following steps: under a protective atmosphere, adding an electrolyte additive composition to an organic solvent, then adding a lithium salt, and stirring and mixing at a first temperature to obtain the electrolyte; wherein, the protective atmosphere can be argon, and the first temperature can be 5-15°C.

[0067] In yet another typical embodiment of this application, a battery is provided that includes the electrolyte described in the above embodiments.

[0068] Thanks to the inclusion of the electrolyte described above, this battery exhibits excellent cycle stability, especially with high capacity retention and low voltage drop during cycling under high voltage conditions. Furthermore, this battery can meet the requirements of different temperature scenarios.

[0069] 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.

[0070] The negative electrode sheet includes a negative electrode current collector and a negative electrode active layer containing negative electrode active material disposed on the surface of the negative electrode current collector.

[0071] In the specific preparation of 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 thoroughly stirred to form a uniform negative electrode slurry. The negative electrode slurry is then uniformly coated onto the negative electrode current collector, and after drying, rolling, and slitting, the negative electrode sheet is obtained. In one specific embodiment, the negative electrode active layer comprises, by mass percentage, 70%–99% graphite negative electrode material, 0.5%–15% conductive agent, and 0.5%–15% binder.

[0072] The negative electrode current collector can be made of 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, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyvinyl alcohol, and sodium polyacrylate.

[0073] This application does not limit the specific type of negative electrode active material in the negative electrode sheet, and it can be at least one of commonly used negative electrode active materials, such as 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.

[0074] The positive electrode sheet includes a positive current collector and a positive active layer containing positive active material disposed on the surface of the positive current collector.

[0075] In the specific preparation of 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 thoroughly stirred to form a uniform positive electrode slurry. The positive electrode slurry is then uniformly coated onto the positive electrode current collector, and after drying, rolling, and slitting, the positive electrode sheet is obtained. In one specific embodiment, the positive electrode active layer comprises, by mass percentage, 70%–99% positive electrode active material, 0.5%–15% conductive agent, and 0.5%–15% binder.

[0076] The positive current collector can be made of 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, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polyethylene, polypropylene, polyvinyl alcohol, and sodium polyacrylate.

[0077] This application does not limit the specific type of positive electrode active material in the positive electrode sheet, and it can be a commonly used positive electrode active material, such as a composite oxide of lithium with at least one of cobalt, nickel, manganese, or combinations thereof. Specifically, it can be at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, nickel-cobalt-manganese ternary materials, nickel-cobalt-aluminum ternary materials, lithium iron phosphate, lithium nickel manganese oxide, and lithium-rich manganese-based materials. In some embodiments, the positive electrode active material is Li₂MnO₃ or LiMn 0.375 Ni 0.375 Co 0.25 A mixture of O2, including Li2MnO3 and LiMn 0.375 Ni 0.375 Co 0.25 The molar ratio of O2 is 1:3.

[0078] The battery also includes a separator. This application does not limit the specific choice of separator material, and it can be separator materials commonly used in batteries, such as polypropylene separators, polyethylene separators, polypropylene / polyethylene double-layer composite separators, polypropylene / polyethylene / polypropylene (PP / PE / PP) triple-layer composite separators, etc.

[0079] In battery manufacturing, positive electrode sheets, separators, and negative electrode sheets are wound or stacked to obtain battery cells. The battery cells are then encapsulated in pre-stamped aluminum-plastic films. After the encapsulated batteries are dried, electrolyte is injected into the dried batteries. The batteries are then aged, formed, and resealed to complete the battery manufacturing process.

[0080] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0081] Example 1

[0082] The electrolyte in this embodiment is composed of an organic solvent, a lithium salt, and additives; the additives include vinylene carbonate, lithium difluorophosphate, 1,3-propanesulfonate lactone, and functional additives as shown in Formula 1.

[0083] The electrolyte contains 0.5% vinylene carbonate, 0.5% lithium difluorophosphate, 2% 1,3-propanesulfonyl lactone, and 0.5% functional additives.

[0084]

[0085] The lithium salt is lithium hexafluorophosphate, which has a mass fraction of 15% in the electrolyte. The organic solvent has a mass fraction of 81.5% in the electrolyte and is composed of fluoroethylene carbonate, ethylene carbonate, ethyl difluoroacetate, and diethyl carbonate. Based on the total mass of the organic solvent as 100%, the mass fractions of fluoroethylene carbonate, ethylene carbonate, ethyl difluoroacetate, and diethyl carbonate are 10%, 15%, and 65%, respectively.

[0086] The preparation method of the electrolyte in this embodiment includes: under an argon atmosphere, adding the formulated amounts of vinylene carbonate, lithium difluorophosphate, 1,3-propanesulfonic acid lactone, and functional additives to an organic solvent according to the above mass fractions, then adding lithium hexafluorophosphate, and stirring and mixing at 10°C to obtain the electrolyte.

[0087] Example 2

[0088] The only difference between the electrolyte in this embodiment and that in Example 1 is that the mass fraction of vinylene carbonate in the electrolyte is 0.2%, and the mass fraction of the organic solvent is 81.8%.

[0089] Example 3

[0090] The only difference between the electrolyte in this embodiment and that in Example 1 is that the mass fraction of vinylene carbonate in the electrolyte is 0.8%, and the mass fraction of the organic solvent is 81.2%.

[0091] Example 4

[0092] The only difference between the electrolyte in this embodiment and that in Example 1 is that the mass fraction of lithium difluorophosphate in the electrolyte is 0.2%, and the mass fraction of the organic solvent is 81.8%.

[0093] Example 5

[0094] The only difference between the electrolyte in this embodiment and that in Example 1 is that the mass fraction of lithium difluorophosphate in the electrolyte is 0.8%, and the mass fraction of the organic solvent is 81.2%.

[0095] Example 6

[0096] The only difference between the electrolyte in this embodiment and that in Example 1 is that the mass fraction of 1,3-propanesulfonic acid lactone in the electrolyte is 1%, and the mass fraction of the organic solvent is 82.5%.

[0097] Example 7

[0098] The only difference between the electrolyte in this embodiment and that in Example 1 is that the mass fraction of 1,3-propanesulfonic acid lactone in the electrolyte is 3%, and the mass fraction of the organic solvent is 80.5%.

[0099] Example 8

[0100] The only difference between the electrolyte in this embodiment and that in Example 1 is that the mass fraction of the electrolyte functional additive is 0.3% and the mass fraction of the organic solvent is 81.7%.

[0101] Example 9

[0102] The only difference between the electrolyte in this embodiment and that in Example 1 is that the mass fraction of the electrolyte functional additive is 1%, and the mass fraction of the organic solvent is 81%.

[0103] Example 10

[0104] The only difference between the electrolyte in this embodiment and that in Example 1 is that the mass fraction of the electrolyte functional additive is 1.5% and the mass fraction of the organic solvent is 80.5%.

[0105] Example 11

[0106] The difference between the electrolyte in this embodiment and that in Example 1 is that the mass fraction of the electrolyte functional additive in the electrolyte is 0.2%, and the mass fraction of the organic solvent is 81.8%.

[0107] Example 12

[0108] The difference between the electrolyte in this embodiment and that in Example 1 is that vinylene carbonate and 1,3-propanesulfonic acid lactone are not added, and the mass fraction of the organic solvent is 84%.

[0109] Comparative Example 1

[0110] An electrolyte that differs from that of Example 1 in that no electrolyte functional additives are added and the mass fraction of the organic solvent is 82%.

[0111] Comparative Example 2

[0112] An electrolyte that differs from Example 1 in that the electrolyte functional additive is replaced with an additive as shown in Formula 2:

[0113]

[0114] Comparative Example 3

[0115] An electrolyte that differs from Example 1 in that the electrolyte functional additive is replaced with an additive shown in Formula 3:

[0116]

[0117] Comparative Example 4

[0118] An electrolyte that differs from Example 1 in that the electrolyte functional additive is replaced with an additive shown in Formula 4:

[0119]

[0120] Test example

[0121] The electrolytes of the examples and comparative examples 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 onto a copper foil current collector, vacuum drying, and obtaining a negative electrode sheet;

[0122] The cathode 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;

[0123] A battery cell is obtained by winding or stacking a positive electrode sheet, a Celgard 2400 separator, and a negative electrode sheet. The battery cell is then packaged into a pre-stamped aluminum-plastic film. After the packaged battery is dried, the electrolytes from the examples and comparative examples are injected into the dried battery. After aging, formation, and secondary sealing, a lithium-ion battery is obtained.

[0124] The following electrochemical tests were performed using the Xinwei charge-discharge test cabinet.

[0125] (1) Room temperature cycling performance test:

[0126] 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 until the current is ≤0.05C. After resting for 10 minutes, it is discharged at a constant current of 1C to a cutoff voltage of 2.5V. This constitutes one charge-discharge cycle. The lithium-ion battery is subjected to 1000 charge-discharge cycles under the above conditions.

[0127] The capacity retention rate (%) of a lithium-ion battery after 1000 cycles = (discharge capacity of the 1000th cycle / initial discharge capacity) × 100%.

[0128] The average voltage (V) of a lithium-ion battery after 1000 cycles = discharge energy of the 1000th cycle / discharge capacity of the 1000th cycle.

[0129] (2) High-temperature cycling performance test

[0130] 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 until the current ≤0.05C. After resting for 10 minutes, it was discharged at a constant current of 1C to a cutoff voltage of 2.5V. This constitutes one charge-discharge cycle. The lithium-ion battery was subjected to 800 charge-discharge cycles under the above conditions.

[0131] The capacity retention rate (%) of a lithium-ion battery after 800 cycles = (discharge capacity of the 800th cycle / initial discharge capacity) × 100%.

[0132] The average voltage (V) of a lithium-ion battery after 800 cycles = discharge energy of the 800th cycle / discharge capacity of the 800th cycle.

[0133] The test results are shown in Table 1.

[0134] Table 1

[0135]

[0136] Comparing the performance test results of Examples 1-12 and Comparative Example 1, it can be found that by introducing functional additives with the structure shown in Formula 1, the capacity retention rate after 1000 cycles at room temperature and 800 cycles at high temperature can be significantly improved and the voltage drop can be reduced, thus solving the problem of rapid capacity decay and voltage decay in high-voltage material system batteries.

[0137] Comparing the performance test results of Examples 1-12 and Comparative Examples 2-4, it can be found that only when the structure of the electrolyte functional additive contains O-Si bonds, carbon-nitrogen triple bonds, and fluorocyclopentadiene, can the resulting electrolyte have good cycle performance at both room temperature and high temperature, making it suitable for high-voltage environments.

[0138] Comparing the performance test results of Examples 1-9, it can be found that when the mass ratio of lithium salt additive to electrolyte functional additive is (0.5-1):(0.3-1), the cycle stability of the electrolyte is higher. Comparing the performance test results of Examples 8-11, it can be found that when the mass fraction of electrolyte functional additive in the electrolyte is 0.3%-1%, the battery made from this electrolyte has better cycle performance. Comparing the performance test results of Examples 1 and 12, it can be found that by selecting the components of the electrolyte additive composition, this application can effectively improve the stability of the electrolyte, thereby improving the cycle performance of the battery.

[0139] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. An electrolyte additive composition, characterized in that, It includes lithium salt additives and electrolyte functional additives; the structural formula of the electrolyte functional additive is shown in Formula 1: Formula 1.

2. The electrolyte additive composition according to claim 1, characterized in that, The mass ratio of the lithium salt additive to the electrolyte functional additive is (0.5~1):(0.3~1).

3. The electrolyte additive composition according to claim 2, characterized in that, The lithium salt additive includes at least one of lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, lithium borate, lithium bis(fluoro)borate, and lithium hexafluorophosphate.

4. The electrolyte additive composition according to claim 2, characterized in that, The electrolyte additive composition further includes carbonate additives; the mass ratio of the carbonate additives to the electrolyte functional additives is (0.1~1):(0.3~1).

5. The electrolyte additive composition according to claim 4, characterized in that, The carbonate additives include at least one of vinylene carbonate and fluoroethylene carbonate.

6. The electrolyte additive composition according to any one of claims 2 to 5, characterized in that, The electrolyte additive composition further includes a sulfur-containing additive; the mass ratio of the sulfur-containing additive to the electrolyte functional additive is (0.5~3):(0.3~1).

7. The electrolyte additive composition according to claim 6, characterized in that, The sulfur-containing additive includes at least one of 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, and vinyl sulfate.

8. An electrolyte, characterized in that, The electrolyte comprises lithium salt, organic solvent, and electrolyte additive composition according to any one of claims 1 to 7.

9. The electrolyte according to claim 8, characterized in that, The lithium salt has a mass fraction of 9% to 15% in the electrolyte; and / or, The electrolyte additive composition has a mass fraction in the electrolyte that is greater than 0 and less than or equal to 5%; and / or, The organic solvent has a mass fraction of 80% to 90% in the electrolyte.

10. The electrolyte according to claim 8, characterized in that, The electrolyte functional additive has a mass fraction of 0.3% to 1% in the electrolyte.

11. The electrolyte according to claim 8 or 9, characterized in that, The organic solvent includes at least one of cyclic carbonates, chain carbonates, and chain carboxylic esters.

12. The electrolyte according to claim 11, characterized in that, The organic solvent includes cyclic carbonates, linear carbonates, and linear carboxylic esters, wherein the mass ratio of the cyclic carbonates, the linear carbonates, and the linear carboxylic esters is (1~15):(20~70):(5~20); and / or, The cyclic carbonate comprises fluoroethylene carbonate and ethylene carbonate, wherein the mass ratio of the fluoroethylene carbonate to the ethylene carbonate is 1:(0.8~1.2); and / or, The electrolyte additive composition includes lithium salt additives, carbonate additives, sulfur-containing additives, and electrolyte functional additives, wherein the mass ratio of the lithium salt additives, carbonate additives, sulfur-containing additives, and electrolyte functional additives is (0.2~0.8):(0.2~0.8):(1~3):(0.3~1).

13. A battery, characterized in that, The battery comprises the electrolyte according to any one of claims 8 to 12.

14. The battery according to claim 13, characterized in that, The battery further includes a negative electrode sheet containing a negative electrode active material; and / or, The battery also includes a positive electrode sheet containing positive electrode active material.

15. The battery according to claim 14, characterized in that, 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, wherein the negative electrode active material includes a carbon-based negative electrode material; and the positive electrode active material includes Li2MnO3 and LiMn. 0.375 Ni 0.375 Co 0.25 At least one of O2.

16. The battery according to claim 15, characterized in that, The positive electrode active material is Li2MnO3 or LiMn 0.375 Ni 0.375 Co 0.25 A mixture of O2, including Li2MnO3 and LiMn 0.375 Ni 0.375 Co 0.25 The molar ratio of O2 is 1:(2~4).

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