Lithium ion battery

Abstract

The application relates to a lithium ion battery. The lithium ion battery comprises an electrolyte, a negative electrode sheet and a positive electrode sheet, the electrolyte comprises a first additive and a second additive, the first additive is fluoroethylene carbonate, the second additive is a sulfonyl fluoride compound, and A+lambda*B >= alpha / P+beta is met; A represents the mass percentage of fluoroethylene carbonate in the electrolyte, the unit is %, B represents the mass percentage of the second additive in the electrolyte, the unit is %, P represents the porosity of the negative electrode sheet, the unit is %, and the value range is 25-40; lambda represents a replacement equivalent coefficient, the value range is 0.1-0.5; alpha represents a porosity requirement coefficient of the negative electrode sheet, the value range is 80-120; and beta represents a reference film forming requirement coefficient, the value range is 3-7. In the scheme provided by the application, a stable and dense composite SEI film can be constructed, the cycle stability of the battery is improved, gas production is inhibited, and the long cycle life and high-temperature storage performance of the lithium ion battery are improved.

Description

Technical Field

[0001] This application relates to the field of electrochemical energy storage device technology, and in particular to a lithium-ion battery. Background Technology

[0002] With the rapid development of electric vehicles, large-scale energy storage, and other fields, the market has placed higher demands on the energy density of lithium-ion batteries. Silicon, due to its extremely high theoretical specific capacity (approximately 3579 mAh / g, far exceeding graphite's 372 mAh / g), is considered the preferred anode material for next-generation high-energy-density lithium-ion batteries. However, silicon undergoes volume expansion / contraction of over 300% during charging and discharging. This drastic volume change causes the electrode material particles to break and pulverize, leading to repeated rupture and regeneration of the solid electrolyte interphase (SEI) film on its surface. This process continuously consumes electrolyte and active lithium, resulting in a continuous increase in battery internal resistance and rapid capacity decay, severely limiting the practical application of silicon anodes.

[0003] To stabilize the silicon anode interface, fluoroethylene carbonate (FEC) is often added to the electrolyte as a film-forming additive, allowing it to preferentially decompose on the silicon surface to form a lithium fluoride (LiF)-rich SEI film. LiF has a high mechanical modulus and a wide electrochemical stability window, effectively buffering the volumetric stress of silicon and inhibiting excessive growth and cracking of the SEI film. However, during long-term cycling, FEC is continuously consumed to repair the SEI film damaged by volume changes, leading to a continuous decrease in the concentration of FEC in the electrolyte. Once it falls below the critical level required to maintain a stable interface, the repair capacity of the SEI film significantly deteriorates, the battery interface impedance rises sharply, and the capacity drops drastically, severely limiting the battery's cycle life. To alleviate this problem, the amount of electrolyte injected is often increased to maintain sufficient FEC reserves. However, this directly limits further improvement in battery energy density. Furthermore, simply increasing the initial concentration of FEC can easily lead to oxidative decomposition of FEC on the positive electrode side, causing increased gas production and swelling of the battery, and deteriorating the battery's high-temperature performance and safety performance.

[0004] Therefore, it is necessary to develop an electrolyte that can slow down electrolyte consumption and form a more stable and robust SEI film, thereby effectively extending the cycle life of lithium-ion batteries. Summary of the Invention

[0005] To address or partially address the problems existing in related technologies, this application provides a lithium-ion battery capable of constructing a stable and dense composite SEI film, improving battery cycle stability and suppressing gas generation, thereby enhancing the long cycle life and high-temperature storage performance of the lithium-ion battery.

[0006] This application provides a lithium-ion battery, including an electrolyte, a negative electrode, and a positive electrode. The electrolyte contains a lithium salt, a solvent, and an additive. The additive includes a first additive and a second additive. The first additive is fluoroethylene carbonate, and the second additive is a compound having the following structural formula. ; The fluoroethylene carbonate in the electrolyte, the second additive, and the negative electrode sheet satisfy the following relationship: A+λ×B≥α / P+β; Wherein, A represents the mass percentage content of fluoroethylene carbonate in the electrolyte, in %; B represents the mass percentage content of the second additive in the electrolyte, in %; P represents the porosity of the negative electrode sheet, in % and ranging from 25 to 40; λ represents the substitution equivalent coefficient, ranging from 0.1 to 0.5; α represents the porosity requirement coefficient of the negative electrode sheet, ranging from 80 to 120; and β represents the baseline film formation requirement coefficient, ranging from 3 to 7.

[0007] In some implementations, 5 ≤ A ≤ 25, and preferably, 8 ≤ A ≤ 18.

[0008] In some implementations, 0.1 ≤ B ≤ 15, and preferably, 0.5 ≤ B ≤ 8.

[0009] In some embodiments, the additive further includes a third additive, which includes at least one selected from vinylene carbonate, 1,3-propanesulfonate lactone, vinyl sulfate, succinate, adiponitrile, 1,3,6-hexanetrionitrile, propylene sulfonate lactone, methanedisulfonate, ethylene glycol bis(propionitrile) ether, pentafluoroethoxyphosphazene, dicyclohexylcarbonyl, trimethyl imide phosphate, and hexamethylene diisocyanate.

[0010] In some embodiments, the third additive is present in the electrolyte at a mass percentage of 5% to 15%.

[0011] In some embodiments, the third additive is selected from succinic anhydride, 1,3,6-hexanetrionitrile, and 1,3-propanesulfonate lactone.

[0012] In some embodiments, the lithium salt includes at least one of lithium hexafluorophosphate, lithium difluorooxalate borate, lithium difluorodioxalate phosphate, lithium tetrafluoroborate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, and lithium bis(oxalate borate).

[0013] In some embodiments, the lithium salt has a mass percentage content of 10% to 25% in the electrolyte.

[0014] In some embodiments, the solvent includes at least one selected from ethylene carbonate, propylene carbonate, diethyl carbonate, methyl ethyl carbonate, dimethyl carbonate, ethyl propionate, propyl propionate, ethyl fluorocarbonate, methyl ethyl fluorocarbonate, dimethyl fluorocarbonate, propylene fluorocarbonate, γ-butyrolactone, sulfolane, methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, n-butyl acetate, isobutyl acetate, n-amyl acetate, isoamyl acetate, methyl propionate, methyl butyrate, ethyl butyrate, methyl acrylate, and ethyl acrylate.

[0015] In some embodiments, the total content of the solvent accounts for 55% to 75% of the total mass of the electrolyte.

[0016] In some embodiments, the negative electrode sheet contains a negative electrode active material, which includes at least one of graphite, hard carbon, silicon, silicon oxide, and silicon carbide.

[0017] In some embodiments, the negative electrode active material includes silicon-based materials.

[0018] In some embodiments, the silicon content in the negative electrode active material is 5% to 25%.

[0019] In some embodiments, the positive electrode sheet contains a positive electrode active material, which includes at least one of lithium cobalt oxide, nickel-cobalt-manganese ternary materials, lithium iron phosphate, and lithium manganese oxide.

[0020] The technical solution provided in this application can include the following beneficial results: by introducing a second additive, a fluorosulfonamide compound, into the electrolyte, it works synergistically with the first additive, fluoroethylene carbonate (FEC). The fluoroethylene carbonate primarily provides lithium fluoride (LiF), forming a LiF-rich SEI film. The second additive, due to its higher reducing activity, can serve as a supplementary source of LiF. It also introduces nitrogen and sulfur components, which, in the early stages of film formation, participate in the construction of the SEI film together with FEC. This results in a more stable composite SEI film with a high ionic conductivity transport network, possessing both excellent mechanical strength and interfacial ionic conductivity. This allows it to better adapt to the significant volume changes of the silicon anode, fundamentally delaying the concentration decay of FEC and the sharp increase in interfacial impedance. This enables the battery to maintain effective interfacial repair capabilities during long cycles even with low initial FEC content and low electrolyte retention, significantly delaying or even eliminating capacity "drops," improving battery cycle life, and reducing the risk of gas generation caused by excessively high FEC content, thus enhancing the battery's high-temperature storage safety and cycle stability.

[0021] By establishing a quantitative relationship between electrolyte formulation and negative electrode porosity, the required additive content can be calculated scientifically, accurately, and quickly for negative electrode sheets with different porosities. This achieves optimal matching between electrolyte formulation and electrode structure, avoiding the blindness of traditional "trial and error" methods and providing design guidance for high-energy-density batteries.

[0022] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and do not limit this application. Detailed Implementation

[0023] The embodiments of this application will now be described in more detail. It should be understood that this application may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to make this application more thorough and complete, and to fully convey the scope of this application to those skilled in the art.

[0024] The terminology used in this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. Unless otherwise defined, all terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. While the methods and materials described herein, or any equivalent methods and materials, may also be used in the implementation or testing of the invention, preferred methods and materials are now described.

[0025] It should be understood that although the terms “first,” “second,” “third,” etc., may be used in this application to describe various information, such information should not be limited to these terms. These terms are only used to distinguish information of the same type from one another. Features defined as “first” or “second” may explicitly or implicitly include one or more of that feature. The singular forms “a,” “the,” and “the” used in this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any or all possible combinations of one or more of the associated listed items.

[0026] Where numerical ranges are provided, it should be understood that every intermediate value between the upper and lower limits of the range and any other specified or intermediate value within the specified range is covered within the present invention. The upper and lower limits of these smaller ranges may be independently included in the smaller range and are also covered within the present invention, subject to any explicitly excluded limits within the specified range. Where a specified range includes one or two limits, the range excluding any or both of those included limits is also included within the present invention. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0027] This application provides an electrolyte comprising lithium salt, solvent, and additives.

[0028] The additives include a first additive and a second additive. The first additive is fluoroethylene carbonate (FEC), and the second additive is a compound having the following structural formula; .

[0029] The first additive, fluoroethylene carbonate, serves as the primary source of LiF, enabling the formation of a high-mechanical-strength SEI film on the negative electrode surface—a LiF-reinforced framework with high mechanical strength. The second additive, a fluorosulfonamide with the aforementioned structure, namely dimethylaminosulfonyl fluoride, possesses an extremely high reduction potential. It preferentially undergoes a reduction reaction on the negative electrode surface during the initial film formation phase, overcoming the solvent and some FECs. Its decomposition products also provide LiF, as well as sulfur- and nitrogen-containing inorganic components and organic sulfides. LiF enhances the mechanical strength of the SEI film, while the sulfur- and nitrogen-containing components form a high-ionic-conductivity transport network, contributing to improved ionic conductivity. Therefore, when the first and second additives are used together, they form a composite SEI film combining a "LiF-reinforced framework + ion-conducting network," exhibiting excellent toughness, adaptability, and rapid ion transport capabilities. This allows it to better withstand volume changes in silicon materials, reducing SEI breakage and regeneration, and comprehensively improving the cycle stability of lithium-ion batteries. Furthermore, the high reducing activity of the second additive allows it to decompose preferentially over FEC, sharing the burden of FEC as a source of LiF and reducing FEC film consumption during long-term cycling. This fundamentally slows down the decay rate of FEC in the electrolyte, enabling the battery to maintain effective interfacial repair capabilities during long cycles even with lower initial FEC content and lower electrolyte retention, thus significantly delaying or even eliminating capacity "plummeting." Simultaneously, by reducing dependence on high-concentration FEC, it also significantly reduces gas generation caused by FEC oxidation and decomposition on the positive electrode side, improving the battery's high-temperature storage safety and cycle stability.

[0030] Based on the electrolyte's mass percentage of 100%, the mass percentage of fluoroethylene carbonate in the electrolyte is 5% to 25%, preferably 8% to 18%. Specifically, the amount of fluoroethylene carbonate added can be 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, or any range between the above values. Within this range, fluoroethylene carbonate exhibits good solubility and compatibility in commonly used organic solvents, ensuring the homogeneity and stability of the electrolyte system. Furthermore, during the initial charge-discharge process of the battery, it can reduce and form a LiF-rich SEI film on the negative electrode surface. Simultaneously, it can serve as a continuous LiF replenishment source during subsequent long-term cycling, participating in the dynamic repair and reinforcement of the SEI film, ensuring the lithium-ion battery maintains excellent long-term cycle life. If the content of fluoroethylene carbonate is too low (<5%), it is difficult to sustain long-term consumption cycles; if the content is too high (>25%), it will not only increase costs, but also lead to an increased risk of swelling during high-temperature storage.

[0031] Based on the electrolyte's mass percentage of 100%, the second additive's mass percentage in the electrolyte is 0.1% to 15%, preferably 0.5% to 8%. Specifically, the amount of the second additive can be 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, or any range between the above values. Within this range, the second additive can fully utilize its high reduction potential characteristic, effectively participating in SEI formation in the early stages of film formation. Its decomposed LiF can strengthen the mechanical framework of the SEI film, while the introduced sulfur and nitrogen-containing components construct a transport network with high ionic conductivity, synergistically forming a composite SEI structure with FEC, improving the interface's tolerance to volumetric stress and ion transport efficiency. If the content of the second additive is too high, it may cause its decomposition products to accumulate excessively at the interface, increase interfacial resistance, or trigger other side reactions; if the content is too low, it will not be able to fully exert its synergistic film-forming and consumption-sharing effects with FEC.

[0032] In the embodiments of this application, the additive may further include a third additive. The third additive includes at least one selected from the following: vinylene carbonate, 1,3-propanesulfonate lactone, vinyl sulfate, succinate, adiponitrile, 1,3,6-hexanetrionitrile, propenesulfonate lactone, methylene disulfonate, ethylene glycol bis(propionitrile) ether, pentafluoroethoxyphosphazene, dicyclohexylcarbonyl, trimethyl imide phosphate, and hexamethylene diisocyanate. The introduction of these third additives can further optimize the performance of the electrolyte, such as improving SEI film toughness, enhancing high-temperature stability, and increasing the electrolyte's antioxidant properties. Combined with the first additive FEC and the second additive, they can further optimize the overall performance of the electrolyte.

[0033] The third additive has a mass percentage of 5% to 15% in the electrolyte. Specifically, the amount of the third additive can be 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, or any range between these values. Within this range, the third additive can effectively perform its auxiliary function, providing a beneficial supplement to the main additive system. Excessive amounts of the third additive can complicate the electrolyte system, potentially introducing uncontrollable side reactions, increasing costs, and possibly affecting the synergistic effect of the main additive system.

[0034] Preferably, the third additive can be selected from succinic anhydride, 1,3,6-hexanetrionitrile, and 1,3-propanesulfonate lactone; more preferably, the mass ratio of succinic anhydride, 1,3,6-hexanetrionitrile, and 1,3-propanesulfonate lactone is 1:1:2. By using the above-mentioned third additive, the sulfur- and nitrogen-containing components further introduced can synergistically optimize the performance of the electrolyte with the first and second additives, improve the SEI film's tolerance to volumetric stress and ion transport performance, and enhance the overall performance of the silicon anode lithium-ion battery.

[0035] In the embodiments of this application, the lithium salt includes at least one selected from lithium hexafluorophosphate (LiPF6), lithium difluorooxalate borate (LiODFB), lithium difluorodioxalate phosphate (LiDFOP), lithium tetrafluoroborate (LiBF4), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium difluorophosphate (LiPO2F2), and lithium bis(oxalate borate) borate (LiBOB). These lithium salts have comprehensive advantages such as high ionic conductivity, good passivation effect on electrode materials, and relatively low cost.

[0036] The lithium salt content in the electrolyte is 10% to 25% by mass. Specifically, the amount of lithium salt added can be 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, or any range between these values. Lithium salts within this range ensure that the electrolyte has suitable ion concentration and conductivity, meeting the normal charge and discharge requirements of the battery.

[0037] In the embodiments of this application, the solvent is an organic solvent, including at least one of ethylene carbonate, propylene carbonate, diethyl carbonate, methyl ethyl carbonate, dimethyl carbonate, ethyl propionate, propyl propionate, ethyl fluorocarbonate, methyl ethyl fluorocarbonate, dimethyl fluorocarbonate, propylene fluorocarbonate, γ-butyrolactone, sulfolane, methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, n-butyl acetate, isobutyl acetate, n-amyl acetate, isoamyl acetate, methyl propionate, methyl butyrate, ethyl butyrate, methyl acrylate, and ethyl acrylate.

[0038] In one specific embodiment of this application, a combination of high dielectric constant solvents (such as ethylene carbonate (EC) and propylene carbonate (PC)) and low viscosity solvents (such as ethyl propionate (EP) and propyl propionate (PP)) can be used to balance the dissociation of lithium salts and the rapid migration of ions.

[0039] The total solvent content accounts for 55% to 75% of the total electrolyte mass. Specifically, the total solvent content can be 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, or any range between these values. This range ensures that the lithium salt and various additives can be fully dissolved to form a homogeneous and stable solution system, while providing a sufficient medium for lithium ion migration.

[0040] The electrolyte described in this application is suitable for lithium-ion batteries, and especially for silicon-based negative electrode lithium-ion batteries.

[0041] The lithium-ion battery of this application embodiment includes the electrolyte described above, as well as main materials such as positive electrode, negative electrode and separator.

[0042] In this embodiment of the application, the negative electrode sheet includes a negative current collector and a negative electrode material layer coated on at least one surface of the negative current collector. The negative electrode material layer is formed by coating the surface of the negative current collector with a negative electrode slurry.

[0043] The negative electrode current collector mentioned in the embodiments of this application is not particularly limited, as long as it is conductive and will not cause adverse chemical changes in the battery. Typical negative electrode current collectors can be copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or composite current collectors, etc.; copper foil is preferred.

[0044] The negative electrode slurry comprises a negative electrode active material, a conductive agent, and a binder. The negative electrode active material is primarily a compound capable of reversibly inserting / deintercalating lithium ions. The negative electrode active material mentioned in the embodiments of this application includes at least one of graphite, hard carbon, silicon, silicon oxide compounds, and silicon carbide compounds; preferably, it is a silicon-based material, such as a silicon carbide compound; more preferably, it is a silicon carbide compound with a silicon doping content of 5% to 25%. The silicon doping content refers to the mass percentage of silicon in the silicon carbide compound, which can specifically be 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, etc., or any range between the above values. In some embodiments of this application, the conductive agent can be one or more of superconducting carbon black, acetylene black, Ketjen black, natural graphite, artificial graphite, graphene, carbon fiber, carbon nanotubes, etc. The adhesive can be one or more of carboxymethyl cellulose, styrene-butadiene rubber, styrene-acrylic emulsion, lithium polyacrylate, polyacrylic acid, and sodium alginate.

[0045] In the embodiments of this application, the first additive fluoroethylene carbonate, the second additive, and the negative electrode sheet in the electrolyte satisfy the following relationship: A+λ×B≥α / P+β; Where A represents the mass percentage of fluoroethylene carbonate in the electrolyte, in %; B represents the mass percentage of the second additive in the electrolyte, in %; P represents the porosity of the negative electrode sheet, in % and ranging from 25 to 40; λ represents the substitution equivalent coefficient, ranging from 0.1 to 0.5; α represents the porosity requirement coefficient of the negative electrode sheet, ranging from 80 to 120; and β represents the baseline film formation requirement coefficient, ranging from 3 to 7.

[0046] Specifically, (A+λ×B) represents the total effective film-forming dose, which signifies the total capacity of the electrolyte to form an effective SEI film. Since the first and second additives have similar functions but different efficiencies, a substitution equivalence factor λ is introduced to convert the contribution of the second additive into an equivalent amount of the first additive (FEC). The λ value was obtained through extensive comparative experiments, ranging from 0.1 to 0.5, reflecting the substitution efficiency of the second additive per unit mass for the film-forming function of FEC. For example, λ=0.3 means that 1% of the second additive is approximately equivalent to 0.3% of the FEC in terms of film formation contribution.

[0047] (α / P+β) represents the minimum dosage required to form a stable SEI film, signifying the "minimum film-forming agent equivalent" necessary to form a sufficiently stable SEI film on a specific negative electrode. (α / P) reflects the significant impact of negative electrode porosity on film formation difficulty. The smaller the porosity (P) of the negative electrode, the denser the electrode, making electrolyte wetting more difficult. This increases the difficulty for the electrolyte to contact the effective reaction sites on the surface of the negative electrode active material (especially silicon), thus requiring a higher concentration of film-forming agent to ensure coverage. α is the porosity requirement coefficient for the negative electrode; a larger value indicates a more sensitive negative electrode to the amount of film-forming agent required. β is the baseline film formation requirement, i.e., without considering the influence of negative electrode porosity (theoretically, when porosity is infinitely large), representing the minimum basic film-forming agent dosage required to form a fundamentally stable SEI film on the silicon surface. This includes the consumption required to overcome the inherent properties of the silicon surface and to initiate the initial reaction with silicon.

[0048] This relationship allows for precise and quantitative design of electrolyte formulations for negative electrode sheets with different porosities, ensuring the formation of a sufficiently stable SEI film even with low electrolyte levels, avoiding interfacial failure, and thus extending cycle life.

[0049] The porosity P% of the negative electrode sheet satisfies the condition: 25 ≤ P ≤ 40. Specifically, it can be 25%, 28%, 30%, 32%, 35%, 38%, 40%, or any range between these values. Within this range, the electrode structure achieves an optimal balance between electrolyte wettability, ion transport kinetics, and electrode mechanical strength / energy density, ensuring the electrolyte system can fully perform its function and improving battery cycle life and safety. If the porosity of the negative electrode sheet is below 25%, the electrode is too dense, resulting in poor wettability and uneven electrolyte distribution; if it is above 40%, the electrode compaction density is low, affecting the volumetric energy density, and the electrode structure strength may be insufficient, making it prone to structural degradation during cycling and affecting the long-term reliability of the battery.

[0050] Understandably, the porosity of the negative electrode can be measured using mercury intrusion porosimetry or gas adsorption.

[0051] Lithium-ion batteries using the electrolyte of this application, particularly in silicon-based anode systems, achieve a composite SEI film with excellent mechanical strength and ionic conductivity through the synergistic effect of the first and second additives. This significantly improves the cycle life of silicon-based anode batteries under low electrolyte retention conditions and effectively delays capacity drop. Furthermore, the application of this electrolyte reduces the battery's reliance on FEC during long-term cycling, fundamentally avoiding the risks of gas generation and swelling caused by excessively high initial FEC concentrations, thus improving the battery's high-temperature storage and safety performance. By establishing a defined quantitative relationship, the electrolyte formulation is correlated with the anode pore structure, providing a precise and reliable guiding method for electrolyte design in high-energy-density batteries.

[0052] The lithium-ion battery of this application embodiment includes the electrolyte described above, as well as main materials such as positive electrode, negative electrode and separator.

[0053] In this embodiment, the positive electrode sheet includes a positive current collector and a positive electrode material layer coated on at least one surface of the positive current collector. The positive electrode material layer is formed by coating the surface of the positive current collector with a positive electrode slurry.

[0054] The positive electrode current collector mentioned in the embodiments of this application is not particularly limited, as long as it is conductive and will not cause adverse chemical changes in the battery, it can be any known material suitable for use as a positive electrode current collector. In one embodiment, the positive electrode current collector can be a metal material such as aluminum, stainless steel, nickel plating, titanium, tantalum, or carbon material such as carbon cloth or carbon paper; preferably, it is aluminum foil.

[0055] The positive electrode slurry may contain a positive electrode active material, a conductive agent, and a binder. The positive electrode active material primarily provides the source of lithium ions. The positive electrode active material mentioned in the embodiments of this application may be selected from at least one of lithium cobalt oxide, nickel-cobalt-manganese ternary materials, lithium iron phosphate, and lithium manganese oxide; preferably, it is a high-voltage positive electrode material such as lithium cobalt oxide or nickel-cobalt-manganese ternary materials, which have high theoretical capacity and voltage plateau under high voltage. The conductive agent mentioned in the embodiments of this application can improve the conductivity of the electrode and may be selected from superconducting carbon black, acetylene black, Ketjen black, natural graphite, artificial graphite, graphene, carbon fiber, carbon nanotubes, etc. The binder may be at least one of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene ternary copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene ternary copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0056] In some embodiments of this application, the battery separator can be a porous polymer membrane made of polyolefin polymers (such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer and ethylene / methacrylate copolymer).

[0057] In the lithium-ion battery mentioned in this application, a separator is disposed between the positive and negative electrodes to prevent short circuits. The battery manufacturing process may include the following steps: overlapping the positive and negative electrode sheets via the separator, and then, as needed, winding, folding, or performing other operations, placing them into a casing; injecting electrolyte into the casing and sealing it; and then performing processes such as settling, formation, capacity testing, and inspection to complete the battery manufacturing. Furthermore, overcurrent protection components, conductive plates, etc., may be placed in the casing as needed to prevent pressure rise and overcharging / discharging within the electrochemical device.

[0058] This application also provides an electronic device including the aforementioned lithium-ion battery. This electronic device can be a consumer electronics product, or a product used in fields such as new energy vehicles and energy storage. This lithium-ion battery, while ensuring high energy density (low liquid retention), achieves superior cycle life, lower thickness expansion rate, and better high-temperature storage performance, possessing significant practical value and commercial prospects.

[0059] To make the present invention easier to understand, the present application will be further described in detail below with reference to embodiments. These embodiments are for illustrative purposes only and are not limited to the scope of application of the present application. Unless otherwise specified, the raw materials or components used in the present application can be obtained commercially or by conventional methods.

[0060] Example 1 (1) Preparation of positive electrode sheet Lithium cobalt oxide (LCO), carbon nanotubes (CNTs), and polyvinylidene fluoride (PVDF) binder were thoroughly mixed in N-methylpyrrolidone (NMP) solvent at a mass ratio of 97:1.5:1.5 to obtain a homogeneous positive electrode slurry. This slurry was uniformly coated on both sides of an aluminum foil with a safety primer as the positive electrode current collector. After drying, cold pressing, slitting, sheet forming, welding of tabs, and adhesive bonding, a positive electrode sheet meeting the winding requirements was produced.

[0061] (2) Preparation of negative electrode sheet The negative electrode active material (graphite and silicon carbide compounds (10% silicon content)) is thoroughly mixed with a binder (styrene-butadiene rubber-sodium carboxymethyl cellulose composite binder SBR-CMC) and a conductive agent (carbon black) at a mass ratio of 95:3.5:1.5 in deionized water to obtain a homogeneous negative electrode slurry. This negative electrode slurry is then uniformly coated on both sides of the negative electrode current collector copper foil. After drying, cold pressing, slitting, sheet forming, welding of tabs, and adhesive application, a negative electrode sheet that meets the winding requirements is produced.

[0062] (3) Preparation of electrolyte The organic solvents ethylene carbonate (EC), propylene carbonate (PC), ethyl propionate (EP), and propyl propionate (PP) were mixed and stirred evenly in a mass ratio of 1:1:2.5:5.5 to prepare a mixed solvent. Subsequently, based on the total mass of the electrolyte, 15% of the first additive fluoroethylene carbonate (FEC), 2% of succinate (SN), 2% of 1,3,6-hexanetrionitrile (HTCN), 4% of 1,3-propanesulfonyl lactone (PS), 13.5% of LiPF6, and 10% of the second additive dimethylaminosulfonyl fluoride were added and mixed evenly to obtain the electrolyte.

[0063] (4) Preparation of lithium-ion batteries PE porous polymer film is used as the separator.

[0064] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes. After winding and tab welding, a bare cell is obtained. The bare cell is then placed in a pre-formed aluminum-plastic film to complete the top and side sealing. After high-temperature baking, the prepared electrolyte is injected, followed by processes such as settling, formation, aging, capacity testing, and inspection to obtain a lithium-ion battery.

[0065] Examples 2-23, Comparative Examples 1 and 2 use the same method as Example 1, the difference being the amount of the first additive and the second additive added, or the porosity of the negative electrode sheet, as shown in Table 1.

[0066] The batteries prepared in the above-described examples and comparative examples were subjected to the same lithium-ion battery performance tests, and the test results were recorded in Table 1.

[0067] (1) 25℃ cycle test The lithium-ion battery was left to stand at 25°C for 2 hours, then charged to 4.55V at a constant current of 0.5C, with a cutoff current of 0.05C. After standing for 10 minutes, the full-charge thickness D0 was measured. Subsequently, it was discharged at 0.5C to 3.0V, and the discharge capacity C0 was recorded as the initial capacity. This cycle was repeated 600 times to obtain the capacity C after 600 cycles. 600 Thickness D 600 Then the capacity retention rate = C 600 / C0, thickness growth rate = [(D 600 / D0)-1]×100%.

[0068] (2) Storage test at 60℃ The lithium-ion battery was charged at a constant current of 0.5C for 32 minutes and then left to stand for 10 minutes. The cell thickness T0 was measured. The lithium-ion battery was then charged to 4.53V at a constant current and voltage of 0.5C in a constant temperature chamber at (25±2)℃, with a cutoff current of 0.05C. The fully charged battery was then left to stand open-circuit at (60±2)℃ for 21 days. After storage for 28 days, the thermal thickness T0 after storage was measured. 28 Calculate the thickness expansion rate of the lithium-ion battery (T) 28 -T0) / T0.

[0069] Table 1

[0070] Note: In the relationship A+λ×B≥α / P+β, A represents the amount (%) of the first additive fluoroethylene carbonate FEC, B represents the amount (%) of the second additive dimethylaminosulfonyl fluoride, and P represents the porosity (%) of the negative electrode sheet; λ= 0.25; α= 100; β= 5.

[0071] According to the comparison between Example 5 and Comparative Example 1, when the electrolyte contains only the first additive fluoroethylene carbonate (FEC) and does not contain the second additive dimethylaminosulfonyl fluoride (Comparative Example 1), the capacity retention rate of the lithium-ion battery after 600 cycles at 25°C is 82%, and the thickness expansion rate after storage at 60°C for 28 days is 9.2%. However, when the electrolyte contains both FEC and the second additive dimethylaminosulfonyl fluoride (Example 5), under the same test conditions, the battery's cycle capacity retention rate increases to 87%, and the thickness expansion rate is significantly reduced to 6.5%. This comparative result fully demonstrates that the introduction of the second additive, dimethylaminosulfonyl fluoride, has a significant synergistic effect with FEC. With its higher reduction potential and ability to provide sulfur and nitrogen-containing components, the second additive, dimethylaminosulfonyl fluoride, together with the LiF framework provided by FEC, constructs a more stable composite SEI film with better ion conductivity, effectively improving the stability of the electrode interface and thus improving cycle performance. At the same time, by sharing the consumption of FEC and reducing its effective required concentration, it significantly suppresses gas generation and swelling caused by FEC oxidation and decomposition during high-temperature storage, thereby simultaneously improving the high-temperature storage performance and safety performance of the battery, resulting in a better overall performance of the lithium-ion battery.

[0072] A comparison of Example 13 and Comparative Example 2 shows that when the electrolyte contains no FEC but only the second additive dimethylaminosulfonyl fluoride (Comparative Example 2), the battery's cycle and storage performance deteriorates significantly. After 600 cycles at 25°C, the capacity retention rate is only 68%, and after 28 days of storage at 60°C, the thickness expansion rate reaches as high as 14%. In contrast, when the electrolyte contains both FEC and the second additive dimethylaminosulfonyl fluoride (Example 13), the capacity retention rate reaches 82%, and the thickness expansion rate drops to 9.1%. This comparative result fully demonstrates that although the second additive dimethylaminosulfonyl fluoride has unique film-forming functions, it cannot completely replace the core role of FEC as the main LiF source and basic film-forming agent. FEC is the foundation for building a high-strength SEI framework, while the second additive dimethylaminosulfonyl fluoride serves as a key functional supplement and synergist. Both are indispensable and must be used together to achieve functional complementarity and synergy, thereby improving cycle performance while effectively suppressing high-temperature gas generation and achieving an overall improvement in battery performance.

[0073] A comparison of Examples 1 to 7 shows that when the electrolyte contains both FEC and the second additive dimethylaminosulfonyl fluoride, the cycle performance and high-temperature storage performance of the lithium-ion battery do not increase monotonically with increasing FEC content, but rather show a trend of first improving and then decreasing. The main reason for this is that when the FEC content is too low (e.g., below 5%), a complete and mechanically strong initial SEI protective layer cannot be formed on the negative electrode surface, leading to interface instability in the early stages of cycling, thus limiting the improvement in long-term cycle and storage performance. As the FEC content increases (e.g., reaching 8%–18%), the sufficient LiF source it provides ensures the density and stability of the SEI film, significantly improving cycle performance. However, when the FEC content exceeds a certain threshold, excessive FEC not only increases cost but also causes significant oxidative decomposition reactions on the high-voltage positive electrode side, leading to a sharp increase in battery gas production and an increased risk of swelling during high-temperature storage, thereby deteriorating storage safety performance. Simultaneously, an excessively thick SEI film may also increase interfacial impedance, negatively impacting long-term cycle stability.

[0074] A comparison of Examples 8 to 13 shows that, with a fixed FEC content, the cycle life and high-temperature storage performance of the battery initially increase and then decreases as the content of the second additive, dimethylaminosulfonyl fluoride, increases. This is because adding an appropriate amount of the second additive, dimethylaminosulfonyl fluoride, allows it to leverage its high reducing activity and multifunctional film-forming properties, effectively improving the ionic conductivity and structural stability of the SEI film, thereby simultaneously improving cycle life and suppressing gas generation. However, when the content of the second additive, dimethylaminosulfonyl fluoride, is too high, its limited solubility in the electrolyte or excessive accumulation of decomposition products may lead to heterogeneity of the interfacial film, increasing interfacial impedance. Furthermore, excessive dimethylaminosulfonyl fluoride may also alter the viscosity and conductivity of the electrolyte system, affecting lithium-ion migration kinetics and potentially interfering with the initial film-forming process, thus adversely affecting the battery's long-term cycle stability and high-temperature storage performance.

[0075] A comparison of Examples 14 to 16 shows that lithium-ion batteries exhibit optimal cycle and high-temperature storage performance when the porosity of the negative electrode is in a moderate range (e.g., 30%–35%). This is because a moderate porosity of the negative electrode ensures that the electrolyte fully wets the electrode active material, guaranteeing uniform film formation and unobstructed lithium-ion transport pathways, while also maintaining sufficient mechanical strength and high volumetric energy density. Too low a porosity (e.g., <25%) leads to difficulty in electrolyte wetting, uneven interfacial reactions, and increased local impedance; while too high a porosity (e.g., >40%) reduces electrode compaction density, sacrifices volumetric energy density, and may affect the structural integrity of the electrode.

[0076] A comparison of Examples 17 to 23 shows that when the amounts of the first additive, fluoroethylene carbonate (FEC), and the second additive, dimethylaminosulfonyl fluoride, satisfy the critical condition defined by the relationship "A + λ × B ≥ α / P + β", that is, when the total effective film-forming dose provided by the electrolyte formulation is greater than or equal to the minimum film-forming dose determined by the pore structure of the negative electrode, the prepared electrolyte can most effectively meet the continuous needs of lithium-ion batteries for interface repair and protection during long-term cycling. Especially for silicon-based negative electrodes, electrolyte systems satisfying this relationship can form an SEI film with excellent strength and ionic conductivity, effectively suppressing the destructive effects of the huge volume expansion of silicon particles during cycling, avoiding pulverization of active materials and contact failure with the current collector, thereby fundamentally ensuring the long lifespan and high safety of the battery.

[0077] The various embodiments of this application have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or improvement of the technology in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A lithium-ion battery, comprising an electrolyte, a negative electrode, and a positive electrode, wherein the electrolyte comprises a lithium salt, a solvent, and additives, characterized in that: The additives include a first additive and a second additive, wherein the first additive is fluoroethylene carbonate and the second additive is a compound having the following structural formula; ； The fluoroethylene carbonate in the electrolyte, the second additive, and the negative electrode sheet satisfy the following relationship: A+λ×B≥α / P+β; Wherein, A represents the mass percentage content of fluoroethylene carbonate in the electrolyte, in %; B represents the mass percentage content of the second additive in the electrolyte, in %; P represents the porosity of the negative electrode sheet, in % and ranging from 25 to 40; λ represents the substitution equivalent coefficient, ranging from 0.1 to 0.5; α represents the porosity requirement coefficient of the negative electrode sheet, ranging from 80 to 120; and β represents the baseline film formation requirement coefficient, ranging from 3 to 7.

2. The lithium-ion battery according to claim 1, characterized in that, 5≤A≤25, preferably, 8≤A≤18.

3. The lithium-ion battery according to claim 1, characterized in that, 0.1≤B≤15, preferably 0.5≤B≤8.

4. The lithium-ion battery according to claim 1, characterized in that, The additive further includes a third additive, which comprises at least one of vinylene carbonate, 1,3-propanesulfonate lactone, vinyl sulfate, succinate, adiponitrile, 1,3,6-hexanetrionitrile, propylene sulfonate lactone, methanedisulfonate, ethylene glycol bis(propionitrile) ether, pentafluoroethoxyphosphazene, dicyclohexylcarbonyl, trimethyl imide phosphate, and hexamethylene diisocyanate. Preferably, the third additive has a mass percentage content of 5% to 15% in the electrolyte.

5. The lithium-ion battery according to claim 4, characterized in that, The third additive is selected from succinic anhydride, 1,3,6-hexanetrionitrile and 1,3-propanesulfonate lactone.

6. The lithium-ion battery according to claim 1, characterized in that, The lithium salt includes at least one of lithium hexafluorophosphate, lithium difluorooxalate borate, lithium difluorodioxalate phosphate, lithium tetrafluoroborate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, and lithium bis(oxalate borate). Preferably, the lithium salt has a mass percentage content of 10% to 25% in the electrolyte.

7. The lithium-ion battery according to claim 1, characterized in that, The solvent includes at least one of ethylene carbonate, propylene carbonate, diethyl carbonate, methyl ethyl carbonate, dimethyl carbonate, ethyl propionate, propyl propionate, ethyl fluorocarbonate, methyl ethyl fluorocarbonate, dimethyl fluorocarbonate, propylene fluorocarbonate, γ-butyrolactone, sulfolane, methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, n-butyl acetate, isobutyl acetate, n-amyl acetate, isoamyl acetate, methyl propionate, methyl butyrate, ethyl butyrate, methyl acrylate, and ethyl acrylate. Preferably, the total content of the solvent accounts for 55% to 75% of the total mass of the electrolyte.

8. The lithium-ion battery according to any one of claims 1 to 7, characterized in that, The negative electrode sheet contains a negative electrode active material, which includes at least one of graphite, hard carbon, silicon, silicon oxide, and silicon carbide.

9. The lithium-ion battery according to claim 8, characterized in that, The negative electrode active material includes silicon-based materials; Preferably, the silicon content in the negative electrode active material is 5% to 25%.

10. The lithium-ion battery according to any one of claims 1 to 7, characterized in that, The positive electrode sheet contains a positive electrode active material, which includes at least one of lithium cobalt oxide, nickel-cobalt-manganese ternary materials, lithium iron phosphate, and lithium manganese oxide.

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