Lithium ion battery and electronic equipment
By using additives such as triisocyanate compounds and fluoroethylene carbonate to form a stable SEI film in lithium-ion batteries, the instability problem in the overhang region caused by volume changes in silicon-based anode materials is solved, thereby improving the cycle performance and safety of the battery.
Patent Information
- Application Number
- CN202511544408.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-10-27
- Publication Date
- 2026-01-16
AI Technical Summary
In existing lithium-ion batteries, the instability of the overhang region caused by volume changes in silicon-based anode materials during charge and discharge leads to frequent side reactions, affecting battery cycle performance and safety.
By adding additives such as triisocyanate compounds and fluoroethylene carbonate to the electrolyte, a stable SEI film is formed, optimizing the overhang area ratio and silicon-carbon material content of the negative electrode, thereby synergistically suppressing side reactions.
It significantly improves the cycle performance and safety of lithium-ion batteries, reduces electrolyte consumption and internal resistance, and extends battery life.
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Abstract
Description
Technical Field
[0001] This application relates to the field of lithium-ion battery technology, and in particular to a lithium-ion battery and electronic device. Background Technology
[0002] Lithium-ion batteries have been widely used in consumer electronics, new energy vehicles, and energy storage due to their advantages such as high energy density, no memory effect, and environmental friendliness. With technological advancements, users are placing higher demands on the cycle life, energy density, and safety of lithium-ion batteries.
[0003] Silicon boasts a theoretical lithium intercalation capacity of up to 4200 mAh / g, more than 10 times that of traditional graphite anodes (372 mAh / g). Therefore, silicon-based materials are considered ideal anode materials for next-generation high-energy-density lithium-ion batteries. However, silicon undergoes significant volume changes during charge and discharge, with a volume expansion rate as high as 300-400%. This leads to cracking and detachment of the anode active material layer, damaging the solid electrolyte interphase (SEI) film and severely impacting battery cycle performance. To further improve battery safety, the projected area of the anode active material layer is typically designed to be larger than that of the cathode active material layer, forming an "overhang" region—a region extending beyond the cathode in the anode electrode. This design prevents excessive lithium ion aggregation and dendrite formation at the anode edge during charging, reducing the risk of short circuits. However, the anode active material in the overhang region lacks lithium ions for intercalation / deintercalation reactions from the cathode, making it difficult to form a stable SEI film. Simultaneously, the high reactivity of silicon-based anodes makes the overhang region more susceptible to side reactions with the electrolyte, leading to rapid electrolyte consumption, increased battery impedance, and ultimately further deterioration of cycle performance.
[0004] Therefore, there is a need to find a solution that can effectively stabilize the chemical interface of the overhang region, suppress its side reactions with the electrolyte, and improve 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 and electronic device that can form a stable and robust SEI film at the negative electrode interface, reduce side reactions between the overhang region of the negative electrode sheet and the electrolyte, and significantly improve the cycle performance of the battery.
[0006] This application provides a lithium-ion battery comprising a positive electrode, a negative electrode, and an electrolyte. The negative electrode includes a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector. The positive electrode includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector. The projected area of the negative active material layer is larger than the projected area of the positive active material layer. The negative active material layer has an overhang region located outside the edge of the positive active material layer, and the ratio of the area of the overhang region to the total area of the negative active material layer is a%. The negative active material layer contains silicon-carbon material, and the mass percentage of the silicon-carbon material in the negative active material layer is m%. The electrolyte contains an organic solvent, a lithium salt, and an additive. The additive contains a triisocyanate compound, and the mass percentage of the triisocyanate compound in the electrolyte is b%. Wherein, 0.0004 ≤ b / (m×a) ≤ 1.
[0007] In some embodiments, the relationship between the negative electrode and the electrolyte satisfies: 0.0005≤b / (m×a)≤0.05.
[0008] In some implementations, 'a' satisfies: 1 ≤ a ≤ 30.
[0009] In some implementations, m satisfies: 0.01 ≤ m ≤ 30.
[0010] In some implementations, b satisfies: 0.01 ≤ b ≤ 1.
[0011] In some embodiments, the triisocyanate compound is at least one compound with the structure shown by the following general chemical formula: ; Wherein, Y is selected from straight-chain or branched alkane groups having 1 to 10 carbon atoms, or fluoroalkane groups having 1 to 10 carbon atoms that are partially or completely replaced by fluorine atoms.
[0012] In some embodiments, the triisocyanate compound is selected from at least one of the following compounds: .
[0013] In some embodiments, the additive further comprises fluoroethylene carbonate and nitrile compounds; the fluoroethylene carbonate is present in the electrolyte at a mass percentage of 5% to 25%; and the nitrile compounds are present in the electrolyte at a mass percentage of 1% to 10%.
[0014] In some embodiments, the nitrile compound is selected from at least one of dioxonitrile and 1,3,6-hexanetrionitrile.
[0015] In some embodiments, the lithium salt in the electrolyte is selected from at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium difluorooxalateborate, and lithium tetrafluoroborate.
[0016] In some embodiments, the organic solvent in the electrolyte is selected from at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, fluoroethylene carbonate, ethyl acetate, and propyl propionate.
[0017] In some embodiments, the positive electrode active material is selected from at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, and lithium iron phosphate.
[0018] A second aspect of this application provides an electronic device including the aforementioned lithium-ion battery.
[0019] The technical solution provided in this application can include the following beneficial results: By using triisocyanate compound additives to form a stable SEI film on the surface of the negative electrode during charge and discharge, the volume expansion effect of the silicon-carbon negative electrode is suppressed, the pulverization of the active material is reduced, and the structural stability of the electrode is improved. Simultaneously, it can react with trace amounts of water, HF, and other byproducts in the electrolyte, playing a role in dehydration and acid suppression, reducing electrolyte decomposition, lowering battery internal resistance, and improving battery cycle stability. Furthermore, by optimizing the relationship between the overhang area ratio of the negative electrode, the silicon content in the silicon-carbon negative electrode material, and the mass percentage of triisocyanate additives in the electrolyte, side reactions between the overhang area of the negative electrode and the electrolyte can be effectively reduced, achieving precise and effective protection of the overhang interface of the negative electrode, thereby improving battery energy density and further enhancing battery cycle performance.
[0020] When the combination of the second additive, fluoroethylene carbonate, and the third additive, nitrile compounds, especially adiponitrile and 1,3,6-hexanetrionitrile, is used in conjunction with the first additive, triisocyanate compounds, the fluoroethylene carbonate and triisocyanate compounds preferentially reduce and form a tough, dense, and elastic SEI film on the negative electrode, especially on the silicon surface, using their multifunctional groups. This film can effectively cover and stabilize the electrochemically inert overhang region, which is traditionally difficult to form a film, and precisely block the sites where side reactions occur. At the same time, the nitrile compounds can oxidize and form a film on the positive electrode, inhibiting positive electrode degradation and metal ion dissolution. They can also effectively complex dissolved metal ions, thereby greatly suppressing interfacial side reactions and capacity decay, and synergistically improving the long cycle life of lithium-ion batteries.
[0021] 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
[0022] 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.
[0023] 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.
[0024] 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.
[0025] 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.
[0026] One important way to improve battery energy density is to use electrode materials with higher theoretical specific capacity. In terms of anode materials, the theoretical specific capacity of silicon-based materials (up to 4200 mAh / g) is much higher than that of commercially available graphite anodes (372 mAh / g), so it is considered one of the ideal anode materials for the next generation of high-energy-density lithium-ion batteries. However, silicon-based materials experience severe volume expansion and contraction during the insertion and extraction of lithium ions. This huge volume effect brings a series of problems: (1) it causes the active material particles to pulverize and fall off the current collector, resulting in irreversible capacity decay; (2) it destroys the solid electrolyte interphase (SEI) film formed on the surface of the anode, and the exposed fresh silicon surface will continuously react with the electrolyte, consuming active lithium and electrolyte, increasing the internal resistance of the battery, and causing the capacity to continuously decrease; (3) repeated volume changes cause the SEI film to continuously break and regenerate, becoming thick and unstable, which is not conducive to the conduction of lithium ions.
[0027] Besides the inherent problems with silicon-based materials, the battery's structural design also significantly impacts cycle life. In wound or stacked batteries, the negative electrode area is typically required to be slightly larger than the positive electrode area, and the area of the negative active material layer is larger than that of the positive active material layer. This results in the edge of the negative active material layer being located outside the edge of the positive active material layer, creating an "overhang" or "redundant" region in the negative electrode. This design is primarily intended to prevent lithium ions from depositing and forming lithium dendrites in the negative electrode region corresponding to the positive electrode edge during charging, thus preventing safety hazards. However, during normal charging and discharging, this overhang region, lacking a corresponding positive electrode, maintains a relatively stable potential close to the potential for lithium metal deposition. While an initial SEI film can form in this region during the initial formation process, the lack of continuous lithium-ion insertion / extraction reactions for "dynamic maintenance," coupled with the relatively poor electronic conductivity of silicon-carbon materials, results in an SEI film that is typically not dense or stable enough. During long-term cycling, especially under high-temperature conditions, the unstable SEI film in the overhang region will continuously decompose and react with the electrolyte, generating gas and consuming limited lithium salt and solvent. This not only directly leads to battery capacity decay and increased internal resistance, but may also cause battery swelling due to gas production, and even trigger more serious safety issues.
[0028] Therefore, effectively stabilizing the chemical interface of the overhang region, suppressing its side reactions with the electrolyte, and improving the cycle life of lithium-ion batteries are currently key technical challenges.
[0029] To address the aforementioned problems, this application provides a lithium-ion battery that overcomes the deficiencies of existing high-energy-density lithium-ion batteries by forming a stable and robust SEI film in the electrochemically sensitive overhang region, suppressing side reactions in this region, and improving the cycle performance of the high-energy-density battery.
[0030] The lithium-ion battery provided in this application includes a positive electrode, a separator, a negative electrode, and an electrolyte that wets the positive electrode, the separator, and the negative electrode.
[0031] The electrolyte contains organic solvents, lithium salts, and additives.
[0032] The organic solvent may be selected from at least one of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), fluoroethylene carbonate (FEC), ethyl acetate, and propyl propionate. In some embodiments of this application, the organic solvent is preferably a mixture of ethylene carbonate, propylene carbonate, and propyl propionate.
[0033] The organic solvent in the electrolyte is 30% to 85% by mass, for example, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, etc., or any value within the above range.
[0034] The lithium salt may be selected from at least one of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium difluorooxalate borate (LiDFOB), and lithium tetrafluoroborate (LiBF4). In some embodiments of this application, the lithium salt is a mixture of lithium hexafluorophosphate and lithium difluorooxalate borate; preferably, it is a mixture of lithium hexafluorophosphate and lithium difluorooxalate borate in a mass ratio of (10~35):1.
[0035] The mass percentage of lithium salt in the electrolyte is 5% to 25%, for example, 5%, 8%, 10%, 12%, 15%, 18%, 20%, 23%, 25%, or any value within the above range.
[0036] The additive may include a first additive, which is a triisocyanate compound. Specifically, the triisocyanate compound is at least one compound with the structure shown in the following general chemical formula: ; Wherein, Y is selected from straight-chain or branched alkane groups having 1 to 10 carbon atoms, or fluoroalkane groups having 1 to 10 carbon atoms that are partially or completely replaced by fluorine atoms.
[0037] Furthermore, the triisocyanate compound is selected from at least one of the following compounds: .
[0038] Triisocyanate compounds, as the primary additive, possess three isocyanate groups (-NCO) with strong reducing properties. These groups preferentially reduce the negative electrode surface to form a highly elastic and high-impedance SEI film, effectively mitigating volume expansion of the negative electrode, inhibiting electrolyte solvent penetration, reducing pulverization of electrode active materials, and improving the structural stability of the electrode, especially the negative electrode. Furthermore, the three isocyanate groups (-NCO) can react with trace amounts of water, HF, and other byproducts in the electrolyte, acting as a dehydrator and acid suppressant, reducing electrolyte decomposition, lowering battery internal resistance, and improving battery cycle stability.
[0039] The triisocyanate compound in the electrolyte has a mass percentage of b%, 0.01 ≤ b ≤ 1, preferably 0.1 ≤ b ≤ 0.5%. Specific examples include 0.01%, 0.05%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, etc., or any value within the above range. If the triisocyanate compound additive content is too low, it is difficult to form a robust and stable SEI film containing carbamate and urea groups; if the content is too high, it easily reacts with transition metal ions on the positive electrode, deteriorating the battery's kinetic performance and cycle stability.
[0040] The additive may also include a second additive and a third additive, wherein the second additive is fluoroethylene carbonate and the third additive is a nitrile compound. Specifically, the nitrile compound may be selected from at least one of adiponitrile (AND) and 1,3,6-hexanetrionitrile (HTCN); preferably, a combination of adiponitrile and 1,3,6-hexanetrionitrile.
[0041] In the embodiments of this application, fluoroethylene carbonate can synergistically form a stable and robust SEI film with triisocyanate compounds, while nitrile compounds can react with byproducts and synergistically inhibit electrolyte decomposition with triisocyanate compounds, thereby improving high-voltage stability. Through the synergy of the first additive, the second additive, and the third additive, the long-term cycle stability and high-temperature storage stability of the battery can be significantly improved.
[0042] In some embodiments of this application, the mass percentage of fluoroethylene carbonate in the electrolyte is 5% to 25%, specifically, for example, 5%, 8%, 10%, 12%, 15%, 18%, 20%, 23%, 25%, or any value within the above range.
[0043] In some embodiments of this application, the mass percentage of nitrile compounds in the electrolyte is 1% to 10%, specifically, for example, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any value within the above range.
[0044] The negative electrode includes a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector, the negative active material layer being formed by coating the surface of the negative current collector with a negative electrode slurry. The positive electrode includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, the positive active material layer being formed by coating the surface of the positive current collector with a positive electrode slurry.
[0045] 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 enriched 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.
[0046] 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.
[0047] The projected area of the negative electrode active material layer mentioned in the embodiments of this application is larger than the projected area of the positive electrode active material layer, resulting in an overhang region in the negative electrode active material layer located outside the edge of the positive electrode active material layer. This means that when the positive and negative electrode sheets are aligned and assembled, the edge of the negative electrode sheet will extend beyond the edge of the positive electrode sheet, forming a region around the edge of the negative electrode sheet where there is no directly corresponding positive electrode active material. This region is called the overhang region, also known as the redundant region.
[0048] The ratio of the area of the overhang region to the total area of the entire negative electrode active material layer is a%, where 1 ≤ a ≤ 30, preferably 5 ≤ a ≤ 20. The area percentage of the overhang region can be, for example, 1%, 3%, 5%, 8%, 10%, 12%, 15%, 18%, 20%, 25%, 30%, or any value within the above range. A sufficiently large overhang region can effectively prevent edge lithium plating, but an excessively large overhang region will reduce the battery's energy density and increase the risk of side reactions.
[0049] In some embodiments of the present application, through the size design of the negative electrode sheet die-cutting process, the length of the negative electrode active material layer of the negative electrode sheet can be made greater than the length of the positive electrode sheet, and / or the width of the negative electrode active material layer can be made greater than the width of the positive electrode sheet, so as to ensure that the area ratio of the overhang area of the negative electrode sheet is between 1% and 30%, avoiding the risk of lithium dendrites caused by too low area and increasing the side reaction area caused by too high area. The specific size can be determined according to the actual use process of the positive and negative electrode sheets.
[0050] The negative electrode active material layer contains a negative electrode active substance, a conductive agent, and a binder. The negative electrode active substance therein is mainly a compound capable of reversibly intercalating / deintercalating lithium ions. The negative electrode active substance mentioned in the embodiments of the present application is a silicon-carbon material, that is, a mixture or composite of a silicon material and a carbon material. While utilizing the high capacity advantage of silicon to improve the energy density, this negative electrode active substance partially inhibits the volume expansion of silicon through the buffering effect of the carbon material and maintains the basic conductive network of the electrode.
[0051] In some embodiments of the present application, the silicon material in the silicon-carbon material can be selected from one or more of elemental silicon, silicon oxide (SiO x , 0 < x < 2), silicon-metal alloy, etc. The carbon material can be selected from one or more of artificial graphite, natural graphite, hard carbon, soft carbon, etc. The silicon doping amount in the silicon-carbon material is 5% - 25%, such as 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, etc., or any value within the above range. When the silicon doping amount is within this range, the balance between the high energy density of the battery and the acceptable cycle life can be achieved.
[0052] The mass percentage content of the silicon-carbon material in the entire negative electrode active material layer is m%, 0.01 ≤ m ≤ 30, preferably 1 ≤ m ≤ 25, and further preferably 5 ≤ m ≤ 20%. The mass ratio of the silicon-carbon material can be, for example, 0.01%, 0.05%, 0.1%, 0.5%, 0.8%, 1%, 3%, 5%, 8%, 10%, 12%, 15%, 18%, 20%, 25%, 30%, etc., or any value within the above range. An appropriate amount of silicon can significantly improve the capacity, and controlling its content helps to balance the capacity and the cycle life.
[0053] In some embodiments of the present application, the conductive agent can be one or more of superconducting carbon black SP, acetylene black, Ketjen black, natural graphite, artificial graphite, graphene, carbon fiber, carbon nanotube CNT, etc. The binder can be one or more of carboxymethyl cellulose, styrene-butadiene rubber, styrene-acrylic emulsion, lithium polyacrylate, polyacrylic acid, sodium alginate.
[0054] The negative electrode slurry may also include a solvent, such as N2. Methylpyrrolidone (NMP) or an aqueous solvent is used to mix the negative electrode active material with optional binders and conductive agents to obtain the desired viscosity.
[0055] In the embodiments of this application, the area ratio of the overhang region of the negative electrode sheet, the mass ratio of silicon-carbon material in the negative electrode active material, and the mass ratio of triisocyanate compounds in the electrolyte satisfy the following: 0.0004≤b / (m×a)≤1; preferably 0.0005≤b / (m×a)≤0.05.
[0056] In this embodiment, by co-designing the relationship between the overhang region structure of the negative electrode, the content of silicon-carbon material, and the content of triisocyanate compound additives, the battery design can be guided. This allows the triisocyanate compound additives in the electrolyte to preferentially and at the most suitable dosage form a dense, stable, and elastic SEI film in the electrochemically sensitive overhang region of the negative electrode. This effectively blocks the continuous side reactions between the electrolyte and this region, significantly reduces the consumption of active lithium and electrolyte, suppresses side reactions in this region, and enables the battery to maintain a long cycle life and high-temperature cycling and storage performance, while reducing gas generation and swelling at high temperatures.
[0057] Furthermore, the embodiments of this application optimize the overhang area ratio of the negative electrode, the silicon-carbon negative electrode content, and the triisocyanate compound additives. Under the premise of ensuring that the overhang area can prevent edge lithium plating, a stable SEI film can be formed in this area through the synergy of triisocyanate compounds, fluoroethylene carbonate, and nitrile compounds in the electrolyte. This avoids excessively increasing the overhang area or overusing additives in pursuit of cycle life, and avoids increased internal resistance and decreased low-temperature performance. It can achieve the best balance between safety performance and cycle life without sacrificing energy density.
[0058] Moreover, by limiting the parameter relationships, the optimal addition range of triisocyanate compound additives can be quickly determined based on the target silicon-carbon material content and overhang region design, or the amount of silicon-carbon material and overhang region design can be optimized based on the existing additive dosage, greatly improving R&D efficiency and product designability.
[0059] The positive electrode active material layer includes 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 can be selected from at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, and lithium iron phosphate. The conductive agent mentioned in the embodiments of this application improves the conductivity of the electrode and can be selected from superconducting carbon black SP, acetylene black, Ketjen black, natural graphite, artificial graphite, graphene, carbon fiber, carbon nanotubes (CNTs), etc. The binder can be at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.
[0060] The positive electrode slurry may also include a solvent, such as N2. Methylpyrrolidone (NMP) or an aqueous solvent is used to mix the positive electrode active material with optional binders and conductive agents to obtain the desired viscosity.
[0061] 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).
[0062] 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. 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.
[0063] This application also provides an electronic device that includes 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.
[0064] 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.
[0065] Example 1 (1) Preparation of negative electrode sheet Artificial graphite (anode active material), silicon-carbon material (20% silicon doping), conductive agent Super P, and binder sodium carboxymethyl cellulose were mixed in a mass ratio of (96-X):X:1.5:2.5. Deionized water was added and stirred until homogeneous to obtain a negative electrode slurry with a solid content of 45wt%. This negative electrode slurry was uniformly coated onto one surface of the copper foil of the negative electrode current collector and dried at 110℃. The above steps were repeated on the other surface of the negative electrode current collector. After cold pressing, the negative electrode sheet was die-cut into a negative electrode sheet with two or more negative electrode tabs on one side of the negative electrode current collector and a size of 75mm×865mm.
[0066] (2) Preparation of positive electrode sheet LiNi, the positive electrode active material 0.5 Co 0.3 Mn 0.2 Conductive agent acetylene black and binder polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 96:2:2, and N-methylpyrrolidone (NMP) solvent is added. The mixture is stirred under vacuum until a homogeneous positive electrode slurry with a solid content of 75 wt% is formed. This slurry is uniformly coated onto the positive electrode current collector aluminum foil and dried at 85°C. The above steps are repeated on the other surface of the positive electrode current collector. After cold pressing, the positive electrode sheet is die-cut into a positive electrode sheet with two or more positive electrode tabs on one side of the positive electrode current collector, and the specifications are 74 mm × 867 mm.
[0067] (3) Preparation of electrolyte In an argon-atmospheric glove box with a water content of <10ppm, ethylene carbonate (EC), propylene carbonate (PC), and propyl propionate (PP) were mixed uniformly at a mass ratio of 2:1:7 to obtain the base solvent. Based on the total mass of the electrolyte (100%), 12.5% LiPF6 and 0.5% lithium difluorooxalate borate (LiODFB) were added as lithium salts, respectively. The first additive (triisocyanate compound), the second additive (fluoroethylene carbonate (FEC), and the third additive (nitrile compound) as shown in Table 1 were also added, and the mixture was thoroughly mixed to obtain the electrolyte.
[0068] (4) Preparation of lithium-ion batteries PE porous polymer film is used as the separator.
[0069] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes for isolation. The stacked electrodes and separator are then wound together to form a core. The core is placed in a pre-formed aluminum-plastic film bag, and the top and sides are sealed. It is then dried in an 85°C vacuum oven for 12 hours to remove moisture. The prepared electrolyte is then injected, and the battery undergoes vacuum sealing, settling, formation, shaping, capacity testing, and secondary sealing to obtain a lithium-ion battery.
[0070] Examples 2-26 and Comparative Examples 1-3 use the same method as Example 1, but differ in the type or content of electrolyte additives, the area of the overhang region of the negative electrode sheet, and the mass ratio of silicon-carbon material, the active material of the negative electrode sheet, as shown in Table 1.
[0071] The batteries prepared in the above-described examples and comparative examples were subjected to the same lithium-ion battery performance tests. 45℃ Cyclic Test The lithium-ion batteries were left to stand at (45±2)℃ for 30 minutes to reach a constant temperature. The batteries were then charged at a constant current of 1C to a voltage of 4.53V, followed by constant voltage charging at 4.53V until the current was less than or equal to 0.05C. Finally, they were discharged at a constant current of 1C to a voltage of 2.8V. This constitutes one charge-discharge cycle, and the discharge capacity obtained at this point is recorded as the initial discharge capacity C0. Using the initial discharge capacity as 100%, the charge-discharge cycles were repeated. After 700 cycles, the test was stopped, and the discharge capacity of the lithium-ion batteries at this point was recorded as the discharge capacity after 700 cycles, C1. Five batteries were used in each group, and the cycle capacity retention rate was calculated. The test results are shown in Table 1.
[0072] Capacity retention rate = C1 / C0; Table 1
[0073] Comparative test data from Examples 1-26 and Comparative Examples 1-3 show that adding triisocyanate compounds as additives to the lithium-ion battery electrolyte, in conjunction with the second additive fluoroethylene carbonate and the third additive nitrile compounds, can synergistically form a stable and elastic SEI film. Furthermore, by controlling the content of triisocyanate compounds, the area ratio of the overhang region of the negative electrode sheet in the negative electrode active material layer, and the proportion of silicon-carbon materials mixed in the negative electrode sheet within the range of 0.0004≤b / (m×a)≤1, especially within the range of 0.0005≤b / (m×a)≤0.05, the synergistic effect of these three factors can effectively reduce the side reactions between the overhang region and the electrolyte, thereby effectively improving the cycle performance of the lithium-ion battery.
[0074] A comparison of Examples 1-8 shows that controlling the proportion of silicon-carbon material mixed in the negative electrode sheet within the range of 1% to 20%, and ensuring that it meets the condition of 0.0004≤b / (m×a)≤1, can improve the battery's energy density while balancing the battery's cycle capacity retention rate. When the silicon content is extremely low, almost pure graphite, the improvement effect on battery energy density is not good. If the silicon content is too high, the volume expansion rate of the electrode will increase significantly during charge and discharge, which is still detrimental to the long-term cycle stability of lithium-ion batteries.
[0075] A comparison of Examples 2 and 9-13 shows that when the overhang region in the negative electrode sheet accounts for 5% to 20% of the total area of the negative electrode active material layer, and the condition of 0.0004 ≤ b / (m×a) ≤ 1 is met, the cycle capacity retention rate of the battery can be effectively improved. Within this range, the overhang region can reduce the risk of lithium dendrite formation in the battery and prevent an increase in the area of side reactions in the negative electrode sheet, thereby effectively improving the cycle performance of the battery.
[0076] A comparison of Examples 10 and 14-19 shows that a triisocyanate compound additive content in the electrolyte within the range of 0.1% to 0.5%, while ensuring that it meets the condition of 0.0004 ≤ b / (m×a) ≤ 1, can effectively improve the battery's cycle capacity retention. If the triisocyanate compound additive content is too low, it cannot effectively cover the overhang region of the negative electrode and the surface of the silicon-carbon material, resulting in poor protection for the negative electrode. If the content is too high, it is prone to side reactions with the transition metal ions of the positive electrode, which can worsen the battery's energy density and long-cycle stability.
[0077] A comparison of Examples 10, 20, and 21 with Comparative Examples 1-3 shows that the first additive containing three isocyanate groups (-NCO) described in this application has higher functionality. It can preferentially and rapidly reduce the overhang region of the negative electrode to a more stable and elastic SEI film, and effectively passivate the silicon-carbon negative electrode material, effectively reducing side reactions between the overhang region and the electrolyte. This simultaneously improves the stability of both the negative electrode and the electrolyte, effectively enhancing the cycle performance of the lithium-ion battery. Other isocyanate compounds do not show the same improvement effect on silicon-carbon negative electrode batteries as the triisocyanate compound additive described in this application.
[0078] A comparison of Examples 10 and 22-26 shows that when the combination of the second additive FEC, the third additive nitrile compound, especially adiponitrile and 1,3,6-hexanetrionitrile, described in the examples of this application, and the first additive triisocyanate compound are used in combination, the synergistic effect on improving battery cycle performance is better.
[0079] 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 a positive electrode sheet, a negative electrode sheet, and an electrolyte, characterized by, The negative electrode tab comprises a negative current collector and a negative active material layer arranged on at least one surface of the negative current collector; and the positive electrode tab comprises a positive current collector and a positive active material layer arranged on at least one surface of the positive current collector. The projected area of the negative active material layer is greater than that of the positive active material layer, the negative active material layer has an overhang region outside the edge of the positive active material layer, the ratio of the area of the overhang region to the total area of the negative active material layer is a%, the negative active material layer comprises a silicon-carbon material, the mass percentage of the silicon-carbon material in the negative active material layer is m%, the electrolyte comprises an organic solvent, a lithium salt and an additive, the additive comprises a triisocyanate compound, and the mass percentage of the triisocyanate compound in the electrolyte is b%. 0.0004≤b / (m×a)≤1.
2. The lithium-ion battery of claim 1, wherein, The relationship between the negative electrode tab and the electrolyte satisfies 0.0005≤b / (m×a)≤0.
05.
3. The lithium-ion battery of claim 1, wherein, The a satisfies 1≤a≤30. The m satisfies 0.01≤m≤30. The b satisfies 0.01≤b≤1.
4. The lithium-ion battery of claim 1, wherein, The triisocyanate compound is at least one compound represented by the following general chemical formula: ； Y is selected from a linear or branched alkyl group having 1-10 carbon atoms or a fluoroalkyl group having 1-10 carbon atoms partially or completely substituted by fluorine atoms.
5. The lithium-ion battery of claim 4, wherein, The triisocyanate compound is selected from at least one of the following compounds: 。 6. The lithium-ion battery of claim 1, wherein, The additive further comprises fluoroethylene carbonate and a nitrile compound. The mass percentage of the fluoroethylene carbonate in the electrolyte is 5%-25%, and the mass percentage of the nitrile compound in the electrolyte is 1%-10%.
7. The lithium-ion battery of claim 6, wherein, The nitrile compound is selected from at least one of adiponitrile and 1,3,6-hexanetricarbonitrile.
8. The lithium-ion battery of claim 1, wherein: The lithium salt in the electrolyte is selected from at least one of lithium hexafluorophosphate, lithium bisfluorosulfonylimide, lithium bis(trifluoromethanesulfonyl)imide, lithium difluoro(oxalato)borate and lithium tetrafluoroborate. The organic solvent in the electrolyte is selected from at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, fluoroethylene carbonate, ethyl acetate and propyl propionate.
9. The lithium-ion battery of claim 1, wherein, The positive active material is selected from at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium cobaltate, lithium manganate, lithium nickelate and lithium iron phosphate.
10. An electronic device, comprising: The lithium ion battery comprises the lithium ion battery according to any one of claims 1-9.