Electrolyte additive composition, electrolyte and battery

Abstract

This application provides an electrolyte additive composition, an electrolyte, and a battery, relating to the field of lithium-ion 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 lithium-ion battery technology, and more specifically, to an electrolyte additive composition, an electrolyte, and a battery. Background Technology

[0002] With the development of portable electronic devices and electric vehicles, consumers' demands for battery life are increasing. Battery energy density directly determines the duration of a single use; higher energy density provides longer usage time. Currently, energy density is mostly increased by raising the operating voltage of lithium-ion batteries. However, as the operating voltage continues to increase, the electrode potential of the positive electrode material also rises, which brings a series of negative effects. These include: at high voltages, solvent molecules and lithium salts in the electrolyte are more prone to oxidative decomposition on the positive electrode surface, generating harmful substances such as water and HF. These substances not only consume active lithium but also react with the positive electrode material, leading to structural damage and the dissolution of transition metals. After the transition metals dissolve, they may be reduced on the negative electrode surface, damaging the solid electrolyte interphase (SEI) film, further increasing the battery's internal resistance and causing severe capacity decay during cycling. 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 of capacity decay in batteries during high-voltage cycling in related technologies.

[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, the structural formula of which is shown in Formula 1:

[0005]

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

[0007] Furthermore, the electrolyte additive composition also includes carbonate additives; the mass ratio of carbonate additives to electrolyte functional additives is (0-1):(0.3-1).

[0008] Furthermore, carbonate additives include at least one of vinylene carbonate and fluoroethylene carbonate.

[0009] Furthermore, the lithium salt additive includes at least one of lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, lithium borate, lithium bis(fluoro)borate, and lithium hexafluorophosphate.

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

[0011] Furthermore, the sulfur-containing additives include at least one of propylene sulfite, 1,3-propanesulfonate lactone, and ethylene sulfate.

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

[0013] Furthermore, the lithium salt has a mass fraction of 10%–15% in the electrolyte; and / or,

[0014] The organic solvent in the electrolyte has a mass fraction of 80%–90%; and / or,

[0015] The electrolyte additive composition has a mass fraction in the electrolyte that is greater than 0 and less than or equal to 5%.

[0016] Furthermore, the electrolyte functional additive has a mass fraction of 0.3% to 1% in the electrolyte; and / or,

[0017] The lithium salt additive has a mass fraction of 0.5% to 1% in the electrolyte; and / or,

[0018] The mass fraction of carbonate additives in the electrolyte is 0–1%; and / or,

[0019] The sulfur-containing additive has a mass fraction of 0.5% to 3% in the electrolyte.

[0020] Furthermore, the organic solvent includes at least one of cyclic carbonates, linear carbonates, and linear carboxylic esters.

[0021] 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).

[0022] According to a fourth aspect of this application, a battery is provided, the battery comprising the electrolyte provided in the third aspect.

[0023] Furthermore, the battery also includes a negative electrode sheet containing a negative electrode active material; and / or,

[0024] The battery also includes a positive electrode sheet containing positive electrode active material;

[0025] Preferably, the negative electrode active material includes a carbon-based negative electrode material; the positive electrode active material includes Li₂MnO₃ and LiMnO₂. 0.375 Ni 0.375 Co0.25 At least one of O2;

[0026] More preferably, the positive electrode active material is Li2MnO3 or LiMn 0.375 Ni 0.375 Co 0.25 A mixture of O2, including Li2MnO and LiMn 0.375 Ni 0.375 Co 0.25 The molar ratio of O2 is (0-25):(75-100).

[0027] By applying the technical solution of this application, an electrolyte functional additive with a specific structural formula is used as an electrolyte additive in a battery. On the one hand, this electrolyte functional additive can form a uniform and dense protective film (i.e., CEI film) on the positive electrode surface, effectively inhibiting the oxidative decomposition of the electrolyte under high voltage, reducing the dissolution of transition metals on the positive electrode surface, preventing the reduction and destruction of the SEI film by transition metals on the negative electrode surface, reducing interfacial side reactions, lowering the negative electrode interfacial impedance, and thus reducing the battery's internal resistance. On the other hand, the N-Si bonds in the structure of this electrolyte functional additive can eliminate harmful substances such as water and HF. Through the reaction of the N-Si bonds with these harmful substances, the proton concentration can be effectively reduced, preventing these proton impurities from damaging the SEI film and CEI film, while improving the chemical stability of the electrolyte. This effectively improves the problem of severe capacity decay during battery cycling under high voltage and extends the battery's cycle life. Detailed Implementation

[0028] As described in the background section of this application, existing batteries suffer from capacity decay during high-voltage cycling. To address this problem, a first aspect of this application provides an electrolyte additive composition, comprising a lithium salt additive and an electrolyte functional additive, the structural formula of which is shown in Formula 1:

[0029]

[0030] During battery charging and discharging, especially the first charge and discharge, electrolyte functional additives undergo oxidation on the positive electrode surface, forming a thin protective film (CEI film). These additives contain specific chemical bonds, such as N-Si bonds. These functional groups are active and react with the surface of the positive electrode material or the decomposition products of the electrolyte functional additives, participating in the formation of the CEI film through chemical bonding during electrochemical processes. For example, the Si element can form stable compounds with O or F elements, thus constituting part of the CEI film. This film can prevent or slow down subsequent electrolyte decomposition reactions, suppress side reactions, protect the structural stability of the positive electrode material, and reduce the dissolution of transition metals. Thus, by forming a stable and dense film on the positive electrode surface, the interfacial impedance of the electrode surface can be reduced. This means that the electron and ion conduction pathways inside the battery are smoother, reducing energy loss during charge-discharge cycles.

[0031] Trace amounts of water in the electrolyte can undergo hydrolysis, producing hydrogen gas and harmful protons (H+). + These protons can further trigger side reactions in the electrolyte and positive and negative electrode materials, accelerating battery capacity decay. Chemical bonds in electrolyte functional additives, such as N-Si bonds, can form stable complexes with protons in water molecules, thereby eliminating water, reducing hydrogen generation and proton concentration, and improving electrolyte stability. Simultaneously, they can also form stable chemical bonds with fluorine atoms in HF, thereby neutralizing HF, reducing its concentration in the electrolyte, and improving electrolyte stability. Thus, by reducing water and HF in the electrolyte, the chemical stability of the electrolyte can be significantly improved, reducing its decomposition under high voltage. Furthermore, chemical bonds in electrolyte functional additives, such as N-Si bonds, can react with proton impurities (H+) generated by the decomposition of water and HF in the electrolyte. + The reaction can effectively reduce the proton concentration and decrease the impact of the proton concentration on the SEI and CEI membranes.

[0032] In summary, electrolyte functional additives improve the chemical properties of the electrolyte and the physicochemical characteristics of the electrode surface, thereby effectively addressing the severe capacity decay problem during battery cycling by protecting the battery interface, reducing side reactions, lowering internal resistance, eliminating water and HF in the electrolyte, and improving electrolyte stability. In particular, they can improve the electrolyte's tolerance to high voltage conditions, enabling the battery to remain stable over a wider operating voltage range. This allows the battery to operate more effectively at high voltages without rapid capacity decay, thus extending the battery's cycle life.

[0033] Furthermore, by introducing electrolyte functional additives, the formation of a protective film can be promoted, the loss of active materials and the decline in electrochemical activity can be reduced, and the voltage drop of the battery during cycling can also be reduced, thereby promoting the improvement of the overall cycle performance of the battery. In addition, by reducing the side reactions of electrolyte and electrode materials, especially suppressing the generation of harmful gases, the risk of internal pressure and thermal runaway of the battery is reduced, thereby improving the safety of the battery.

[0034] In some embodiments, the mass ratio of lithium salt additive to electrolyte functional additive is (0.5-1):(0.3-1).

[0035] 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.

[0036] Electrolyte functional additives form a uniform and dense CEI film on the positive electrode surface, reducing side reactions of the electrolyte on the positive electrode surface and the dissolution of transition metals. At the same time, lithium salt additives can participate in the formation of SEI and CEI films. Under the combined action of electrolyte functional additives and lithium salt additives, the stability and density of the films 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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 preferred embodiments, the lithium salt additive includes at least one of lithium bis(fluorosulfonyl)imide (LiFSI), lithium difluorophosphate (LiPO2F2), lithium borate, lithium difluorophosphate, and lithium hexafluorophosphate.

[0041] In some embodiments, the electrolyte additive composition further includes carbonate additives; the mass ratio of carbonate additives to electrolyte functional additives is (0-1):(0.3-1).

[0042] Carbonate additives can form an SEI film on the surface of the negative electrode. The formation of the SEI film can reduce the formation of lithium dendrites and the direct oxidation of the negative electrode material, thereby reducing the risk of battery short circuit and further improving the cycle life and safety of the battery.

[0043] 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.

[0044] 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.

[0045] The mass ratio of carbonate additives to electrolyte functional additives is (0–1):(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.

[0046] 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 (VC) and fluoroethylene carbonate.

[0047] 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).

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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 propylene sulfite (PS), 1,3-propanesulfonate lactone (PST), and ethylene sulfate (DTD).

[0052] A third aspect of this application provides an electrolyte comprising a lithium salt, an organic solvent, and the electrolyte additive composition provided in the second aspect.

[0053] 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.

[0054] Lithium salts are the main source of conductive ions in the electrolyte. In some embodiments, the mass fraction of lithium salts in the electrolyte is 10% to 15%. By limiting the amount of lithium salt added within the above range, it is possible to ensure that the electrolyte has sufficient conductivity, guaranteeing efficient ion transport during the battery's charge and discharge process, while also ensuring that sufficient lithium salt participates in the formation of the SEI / CEI film.

[0055] The mass fraction of lithium salt in the electrolyte is 10% to 15%, for example, 10%, 11%, 12%, 13%, 14%, 15%, or any combination thereof.

[0056] In some embodiments, the mass fraction of the electrolyte additive composition in the electrolyte is greater than 0 and less than or equal to 5%. By limiting the amount of electrolyte additive composition added to the above range, it is ensured that the electrolyte additive composition can exert its effective function in the electrolyte to the maximum extent.

[0057] 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.

[0058] Organic solvents are a major component of the electrolyte, responsible for transporting lithium ions. In some embodiments, the organic solvent accounts for 80% to 90% of the electrolyte by mass. By limiting the amount of organic solvent added within this range, sufficient fluidity can be provided to ensure rapid lithium ion transport 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 ensure that the electrolyte has suitable viscosity, conductivity, and chemical stability, maintaining stable lithium ion transport even under low or high temperature conditions, thus improving the charge-discharge efficiency, stability, and safety of lithium-ion batteries.

[0059] The organic solvent has a mass fraction of 80% to 90% in the electrolyte, for example, a range of 80%, 82%, 84%, 86%, 88%, 90%, or any combination thereof.

[0060] 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.

[0061] 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%. 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, which helps to optimize the electrolyte formulation and improve the performance of lithium-ion batteries.

[0062] In some embodiments, the electrolyte functional additive has a mass fraction of 0.3% to 1% in the electrolyte, for example, a range of 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 role can be maximized, effectively improving the battery's capacity retention and reducing voltage drop during high-voltage cycling, thereby optimizing the electrolyte formulation and enhancing the battery's electrochemical performance.

[0063] In some embodiments, the lithium salt additive is present in the electrolyte at a mass fraction of 0.5% to 1%, for example, a range consisting of 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, or any combination thereof. The lithium salt additive can participate in electrochemical reactions, and by limiting the amount of lithium salt additive added, in addition to maintaining stable battery output under high-voltage cycling and effectively reducing voltage drop, the energy density of the battery can also be improved.

[0064] In some embodiments, the carbonate additive is present in the electrolyte at a mass fraction of 0–1%, for example, a range of 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, or any combination thereof. By limiting the amount of carbonate additive added, a uniform and dense SEI film can be formed, maximizing its multiple functions.

[0065] In some embodiments, the sulfur-containing additive is present in the electrolyte at a mass fraction of 0.5% to 3%, for example, a range consisting of 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, or any combination thereof. By limiting the amount of sulfur-containing additive added, both the effectiveness of the additive and cost can be considered.

[0066] This application does not limit the specific type of organic solvent; it can be any organic solvent conventional in the art. In some embodiments, the organic solvent includes at least one of cyclic carbonates, linear carbonates, and linear carboxylic esters. In some preferred embodiments, the organic solvent includes cyclic carbonates, linear carbonates, and linear carboxylic esters, thus combining the advantages of cyclic carbonates, linear carbonates, and linear carboxylic esters to improve the overall performance of the battery. Specifically, cyclic carbonates can 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 improving the capacity retention rate of the battery during high and low temperature cycling, meeting the needs of the battery in different application scenarios.

[0067] 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.

[0068] 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.

[0069] A fourth aspect of this application provides a battery comprising the electrolyte provided in the third aspect.

[0070] 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.

[0071] 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.

[0072] The negative electrode sheet includes a negative electrode current collector and a negative electrode active layer formed of negative electrode active material disposed on the surface of the negative electrode current collector.

[0073] 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.

[0074] 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.

[0075] 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 the negative electrode active materials commonly used in batteries, 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.

[0076] The positive electrode includes a positive current collector and a positive active layer formed of positive active material disposed on the surface of the positive current collector.

[0077] 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.

[0078] 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.

[0079] This application does not limit the specific type of positive electrode active material in the positive electrode sheet. It can be a positive electrode active material commonly used in batteries, 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 preferred embodiments, the positive electrode active material is Li₂MnO₃ or LiMnO₂. 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 (0-25):(75-100).

[0080] 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.

[0081] 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.

[0082] The present application will be further described in detail below with reference to specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in this application. Unless otherwise specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products.

[0083] Example 1

[0084] 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 a functional additive as shown in Formula 1, with CAS number 3442-82-8.

[0085] The electrolyte contains 0.5% vinylene carbonate, 0.5% lithium difluorophosphate, 2% 1,3-propanesulfonate lactone, and 0.5% functional additives.

[0086]

[0087] 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.

[0088] 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, followed by adding lithium hexafluorophosphate, and stirring and mixing at 10°C to obtain the electrolyte.

[0089] Example 2

[0090] The difference from 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%.

[0091] Example 3

[0092] The difference from 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%.

[0093] Example 4

[0094] The difference from 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%.

[0095] Example 5

[0096] The difference from 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%.

[0097] Example 6

[0098] The difference from Example 1 is that the mass fraction of 1,3-propanesulfonic acid lactone in the electrolyte is 0.5%, and the mass fraction of the organic solvent is 83%.

[0099] Example 7

[0100] The difference from 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%.

[0101] Example 8

[0102] The difference from Example 1 is that the functional additive has a mass fraction of 0.2% in the electrolyte and the organic solvent has a mass fraction of 81.8%.

[0103] Example 9

[0104] The difference from Example 1 is that the functional additive has a mass fraction of 0.8% in the electrolyte and the organic solvent has a mass fraction of 81.2%.

[0105] Example 10

[0106] The difference from Example 1 is that the functional additive has a mass fraction of 1% in the electrolyte and the organic solvent has a mass fraction of 81%.

[0107] Example 11

[0108] The difference from Example 1 is that the functional additive has a mass fraction of 1.5% in the electrolyte and the organic solvent has a mass fraction of 80.5%.

[0109] Example 12

[0110] The difference from Example 1 is that vinylene carbonate, lithium difluorophosphate, and 1,3-propanesulfonic acid lactone are not added, and the mass fraction of the organic solvent is 84.5%.

[0111] Example 13

[0112] The difference from Example 1 is that lithium difluorophosphate and 1,3-propanesulfonic acid lactone are not added, and the mass fraction of the organic solvent is 84%.

[0113] Example 14

[0114] The difference from 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%.

[0115] Example 15

[0116] The difference from Example 1 is that vinylene carbonate and lithium difluorophosphate are not added, and the mass fraction of the organic solvent is 82.5%.

[0117] Comparative Example 1

[0118] The difference from Example 1 is that no functional additives are added, and the mass fraction of the organic solvent is 82%.

[0119] Comparative Example 2

[0120] The difference from Example 1 is that the functional additive is replaced with an additive as shown in Formula 2:

[0121]

[0122] Comparative Example 3

[0123] The difference from Example 1 is that the functional additive is replaced with an additive as shown in Formula 3:

[0124]

[0125] Test example

[0126] 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;

[0127] 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;

[0128] 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.

[0129] The following electrochemical tests were performed using the Xinwei charge-discharge test cabinet.

[0130] (1) Room temperature cycling performance test:

[0131] 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.

[0132] The capacity retention rate (%) of a lithium-ion battery after 1000 cycles = (discharge capacity of the 1000th cycle / initial discharge capacity) × 100%.

[0133] The average voltage (V) of a lithium-ion battery after 1000 cycles = discharge energy of the 1000th cycle / discharge capacity of the 1000th cycle.

[0134] (2) High-temperature cycling performance test

[0135] 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.

[0136] The capacity retention rate (%) of a lithium-ion battery after 800 cycles = (discharge capacity of the 800th cycle / initial discharge capacity) × 100%.

[0137] The average voltage (V) of a lithium-ion battery after 800 cycles = discharge energy of the 800th cycle / discharge capacity of the 800th cycle.

[0138] The test results are shown in Table 1.

[0139] Table 1

[0140]

[0141] Comparing Examples 1-15 with Comparative Example 1, it can be seen 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.

[0142] Comparing Examples 1-15 with Comparative Examples 2 and 3, it can be seen that although the functional additive in Comparative Example 2 also contains N-Si bonds, and the functional additive in Comparative Example 3 contains C=O bonds and a cyclic structure, the improvement in cycle performance and voltage drop is limited. Specifically, Examples 1-7 and 9 show greater capacity retention and voltage drop reduction after 1000 cycles at room temperature and 800 cycles at high temperature than Comparative Example 2. Example 8 shows significantly greater capacity retention and voltage drop reduction after 1000 cycles at room temperature and 800 cycles at high temperature than Comparative Example 2. However, due to the lower amount of functional additive in Example 8, its capacity retention and voltage drop reduction after 800 cycles at high temperature are not as good as Comparative Example 2. Examples 1-15 show greater capacity retention and voltage drop reduction after 1000 cycles at room temperature and 800 cycles at high temperature than Comparative Example 3. Therefore, it can be seen that the functional additive with the structure shown in Formula 1 in this application is not an independent action of a single functional group, but rather the whole structure produces a multi-faceted synergistic effect in the electrolyte. This synergistic effect is the key to improving battery performance and stability.

[0143] Comparing Examples 1-15, it can be seen that Example 4 did not meet the requirement of a mass ratio of lithium salt additive to electrolyte functional additive of (0.5-1):(0.3-1), Example 8 had a lower dosage of functional additive, and Example 11 had a higher dosage of functional additive, resulting in less improvement than Examples 1-3, 5-7, and Example 10. By limiting the mass fraction of each component within a specific range, the battery's cycle capacity retention rate under high voltage and voltage drop can be further improved.

[0144] 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, The electrolyte additive composition includes a lithium salt additive and an electrolyte functional additive, the structural formula of which 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 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). The carbonate additives include at least one of vinylene carbonate and fluoroethylene carbonate; 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 or 3, 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). The sulfur-containing additives include at least one of propylene sulfite, 1,3-propanesulfonate lactone, and ethylene sulfate.

5. An electrolyte, characterized in that, The electrolyte comprises lithium salt, organic solvent, and electrolyte additive composition according to any one of claims 1 to 4.

6. The electrolyte according to claim 5, characterized in that, The lithium salt has a mass fraction of 10% to 15% in the electrolyte; and / or, The organic solvent in the electrolyte has a mass fraction of 80% to 90%; 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%.

7. The electrolyte according to claim 5 or 6, characterized in that, The electrolyte functional additive has a mass fraction of 0.3% to 1% in the electrolyte; and / or, The lithium salt additive has a mass fraction of 0.5% to 1% in the electrolyte; and / or, The mass fraction of carbonate additives in the electrolyte is 0.1% to 1%; and / or, The sulfur-containing additive has a mass fraction of 0.5% to 3% in the electrolyte.

8. The electrolyte according to claim 5 or 6, characterized in that, The organic solvent includes at least one of cyclic carbonates, chain carbonates, and chain carboxylic esters.

9. The electrolyte according to claim 5 or 6, characterized in that, The organic solvent includes cyclic carbonates, chain carbonates and chain carboxylic esters, wherein the mass ratio of the cyclic carbonates, the chain carbonates and the chain carboxylic esters is (1~15):(20~70):(5~20).

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

11. The battery according to claim 10, characterized in that, The battery also includes a negative electrode sheet containing a negative electrode active material; The battery also includes a positive electrode sheet containing a positive electrode active material; The negative electrode active material includes a carbon-based negative electrode material; the positive electrode active material includes Li2MnO3 and LiMn. 0.375 Ni 0.375 Co 0.25 At least one of O2.

12. The battery according to claim 11, 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 (0~25):(75~100).

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