Lithium ion battery

Abstract

The invention relates to a lithium ion battery. The lithium ion battery comprises a positive pole piece, a negative pole piece, a diaphragm and an electrolyte, the electrolyte comprises a lithium salt, a solvent and an additive, the additive comprises a first additive selected from benzamide compounds, the positive pole piece comprises a positive current collector and a positive material layer coated on the surface of the positive current collector, and the negative pole piece comprises a negative material layer coated on the surface of the negative current collector. The positive electrode material layer contains a positive electrode active material; wherein A represents the mass percentage content of the first additive in the electrolyte; b represents the specific surface area of the positive electrode active material; c represents the median particle size of the positive electrode active material; and D represents the porosity of the positive pole piece. In the scheme provided by the invention, the electrolyte can construct a complete and compact composite CEI layer with high ionic conductivity on a positive electrode interface, electrolyte decomposition and cobalt dissolution are effectively inhibited, the high-temperature storage performance of the battery can be effectively improved while the cycle life is prolonged, and the electrolyte is particularly suitable for a high-voltage lithium ion battery system.

Description

Technical Field

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

[0002] With the rapid development of the new energy industry, lithium-ion batteries are increasingly widely used in consumer electronics, electric vehicles, energy storage devices, and other fields. The market is placing higher demands on batteries' energy density, cycle life, safety performance, and high-temperature storage stability. Among these, increasing the battery's operating voltage is one of the key ways to improve energy density.

[0003] In high-voltage lithium-ion battery systems (≥4.5V), organic solvents in the electrolyte readily undergo oxidative decomposition at the positive electrode interface, forming a thick and unstable CEI film. This process continuously consumes active lithium within the system and increases interfacial impedance, leading to battery capacity decay. Simultaneously, high-voltage conditions exacerbate structural distortions in the positive electrode material itself (such as irreversible phase transitions in layered materials) and the dissolution of transition metals. These transition metals further catalyze the oxidative decomposition of the electrolyte, further deteriorating the battery's cycle performance. Therefore, developing a high-voltage resistant electrolyte that remains stable under high voltage conditions is crucial for improving the battery's long-term cycle life. Summary of the Invention

[0004] To address or partially address the problems existing in related technologies, this application provides a lithium-ion battery that can construct a complete, dense composite CEI layer with high ionic conductivity at the positive electrode interface, effectively suppressing electrolyte decomposition and cobalt dissolution, improving cycle life, and effectively enhancing the battery's high-temperature storage performance, making it particularly suitable for high-voltage lithium-ion battery systems.

[0005] This application provides a lithium-ion battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the electrolyte comprises a lithium salt, a solvent, and an additive; the additive comprises a first additive, wherein the first additive is selected from benzamide compounds represented by the following general structural formula:

[0006] R1 and R2 are each independently selected from hydrogen and C1 to C6 alkyl groups; R3 is selected from hydrogen, fluorine or cyano; R4 is selected from C1 to C6 alkyl groups substituted with at least one fluorine atom. The positive electrode sheet includes a positive current collector and a positive electrode material layer coated on the surface of the positive current collector, wherein the positive electrode material layer contains a positive electrode active material, satisfying the following: ; Wherein, A represents the mass percentage content of the first additive in the electrolyte, in units of %; and B represents the specific surface area of ​​the positive electrode active material, in units of m².2 / g; C represents the median particle size of the positive electrode active material, in μm; D represents the porosity of the positive electrode sheet, in μm.

[0007] In some implementations... .

[0008] In some embodiments, the first additive is selected from at least one compound with the following structural formulas: .

[0009] In some embodiments, the electrolyte contains 0.1 ≤ A ≤ 3; preferably 0.5 ≤ A ≤ 1.

[0010] In some embodiments, in the positive electrode, 0.3 ≤ B ≤ 1.5, 5 ≤ C ≤ 15, and 0.1 ≤ D ≤ 0.3.

[0011] In some embodiments, the additive further includes a second additive selected from at least one of fluoroethylene carbonate, 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.

[0012] In some embodiments, the second additive has a mass percentage content of 5% to 25% in the electrolyte.

[0013] In some embodiments, the lithium salt is selected from 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).

[0014] In some embodiments, the lithium salt has a mass percentage content of 10% to 25% in the electrolyte.

[0015] In some embodiments, the solvent is selected from 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.

[0016] In some embodiments, the solvent has a mass percentage content of 70% to 85% in the electrolyte.

[0017] In some embodiments, the positive electrode active material is selected from at least one of lithium cobalt oxide, nickel-cobalt-manganese ternary materials, lithium iron phosphate, and lithium manganese oxide; preferably lithium cobalt oxide or nickel-cobalt-manganese ternary materials.

[0018] In some embodiments, the negative electrode sheet includes a negative current collector and a negative electrode material layer coated on the surface of the negative current collector, wherein the negative electrode material layer contains a negative electrode active material; the negative electrode active material is selected from at least one of graphite, hard carbon, silicon, silicon oxide and silicon carbide; preferably silicon or silicon carbide composite.

[0019] In some embodiments, the upper limit cutoff voltage of the lithium-ion battery is greater than or equal to 4.5V.

[0020] The technical solution provided in this application can include the following beneficial results: By introducing benzamide compounds as additives to the electrolyte, and by controlling the relationship between the content of benzamide compounds in the electrolyte and the parameters of the positive electrode, it is possible not only to utilize the synergistic effect of the bifunctional groups within the benzamide compound molecules and the interface self-assembly effect to overcome the limitations of single-functional additives, but also to construct a complete, dense composite CEI layer with high ionic conductivity on the positive electrode surface, effectively inhibiting electrolyte decomposition and the dissolution of the positive electrode transition metal cobalt, while improving the structural stability of the positive electrode and the stability of the electrolyte, enhancing cycle life and high-temperature storage performance, and making it suitable for high-voltage scenarios; moreover, it can avoid the compatibility problem of fixed concentrations of benzamide compound additives in different positive electrode structures, ensuring the integrity and density of the CEI film layer, avoiding the problem of excessive additive leading to an overly thick CEI film layer and increased impedance, and also avoiding the problem of insufficient additive leading to incomplete coverage of the CEI film layer at the positive electrode interface and continuous interface decomposition, thereby reducing gas production while maintaining low impedance, and simultaneously obtaining excellent interface stability and excellent interface ion transport capability.

[0021] In this benzamide compound, the benzene ring acts as an electron bridging platform, enabling a synergistic effect between the amide group and the fluoroalkyl group. The conjugated system of the benzene ring also enhances the polarity of the CF bond in -CF3, making it easier to break and generate LiF. The amide group (-CONR1R2) has a strong lithium-ion coordination ability and can be inserted into Li through its strong coordination. + The solvation sheath enables the directional enrichment of active molecules at the electrode interface; fluoroalkyl groups (-R4) preferentially undergo electrochemical decomposition under high pressure to generate LiF nanoparticles, constructing a substrate with high ionic conductivity. In addition, the amide group is also believed to be able to cleave and provide a nitrogen source, forming Li3N / LiN. x O yHigh-speed ion channels can synergistically construct a composite CEI layer with the aforementioned LiF nanoparticles. Furthermore, when this benzamide compound is used in conjunction with other additives such as FEC in the electrolyte, the two can synergistically form a stable and dense CEI layer and SEI layer at the electrode interface, thereby synergistically improving the cycle life and storage performance of the battery.

[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] To adapt to high-voltage cathode materials, novel single-function additives have been developed in related technologies, such as nitrile compounds that enhance antioxidant properties and sulfonyl lactone compounds that enhance interfacial stability. However, the use of these functional additives cannot simultaneously solve the problems of interfacial stability, cathode structure protection, and ion transport efficiency, and still has obvious shortcomings.

[0028] This application provides a lithium-ion battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte. The electrolyte contains a lithium salt, a solvent, and an additive. The additive includes a first additive selected from benzamide compounds represented by the following general structural formula:

[0029] R1 and R2 are each independently selected from hydrogen and C1 to C6 alkyl groups; R3 is selected from hydrogen, fluorine or cyano; R4 is selected from C1 to C6 alkyl groups substituted with at least one fluorine atom.

[0030] In this embodiment, benzamide compounds are introduced as additives to the electrolyte. The benzene ring in these additives acts as an electron bridging platform, enabling a synergistic effect between the amide group and the fluoroalkyl group. Specifically, the fluoroalkyl group (-R4) preferentially undergoes electrochemical decomposition under high voltage to generate LiF nanoparticles, constructing a substrate with high ionic conductivity; the amide group (-CONR1R2) possesses strong lithium-ion coordination ability and can intercalate into LiF nanoparticles through its strong coordination. + The solvation sheath enables the directional enrichment of active molecules at the electrode interface. The amide group is also believed to be able to cleave and provide a nitrogen source, forming Li3N / LiN. x O y High-speed ion channels synergistically construct a composite CEI layer with LiF generated from the decomposition of fluorinated alkyl groups. Furthermore, the conjugated system of the benzene ring enhances the polarity of the CF bond in -CF3, making it easier to break and generate LiF, which is beneficial for the formation of the CEI film at the cathode interface. Therefore, by introducing benzamide-based additives, utilizing their intramolecular bifunctional group synergistic effect and interfacial self-assembly effect, the limitations of single-functional additives can be overcome, constructing a complete, dense composite CEI layer with high ionic conductivity on the cathode surface. This effectively inhibits electrolyte decomposition and cobalt dissolution, improves cycle life and high-temperature storage performance, and is suitable for high-voltage applications.

[0031] The inventors of this application further discovered through experiments that the effective concentration of benzamide-based compound additives introduced into the electrolyte is not a fixed value, but needs to be precisely matched with the microscopic interface structure of the positive electrode sheet. To quantify this matching relationship, this application defines the optimal performance range using the following formula. That is, the positive electrode sheet includes a positive current collector and a positive electrode material layer coated on the surface of the positive current collector, the positive electrode material layer containing a positive electrode active material, satisfying: ; Where A represents the mass percentage of the first additive in the electrolyte, in %; and B represents the specific surface area of ​​the positive electrode active material, in m². 2 / g; C represents the median particle size of the positive electrode active material, in μm; D represents the porosity of the positive electrode sheet, in μm.

[0032] Further preferred .

[0033] In this formula, the exponents for each parameter are weighted based on experimental data analysis to balance the influence of various factors. This provides comprehensive and quantifiable guidance for electrolyte and electrode material parameters in lithium-ion battery design. Specifically: Among them The effect of the first additive, benzamide compounds, may exhibit saturation characteristics. The square root function reflects the diminishing marginal utility principle, meaning that once the content (A%) of the first additive exceeds a certain threshold, the performance improvement gradually decreases. Furthermore, the mass percentage of the first additive, benzamide compounds, in the electrolyte, as analyzed above, is maintained within the range of 0.1 ≤ A ≤ 3, preferably within the range of 0.5 ≤ A ≤ 1. Specific examples include 0.1%, 0.25%, 0.4%, 0.5%, 0.6%, 0.85%, 1%, 1.5%, 2%, 2.5%, 3%, or any value within the above range. Within this range, the benzamide compounds ensure complete interfacial coverage while avoiding excessive CEI film thickness and increased impedance due to overdose. When the benzamide compound content is below 0.1%, interfacial coverage is insufficient; above 3%, not only does cost increase, but it may also lead to increased side reactions, higher electrolyte viscosity, and aggravated interfacial impedance.

[0034] For positive electrode sheets, parameters such as the particle size, specific surface area, and porosity of the positive electrode active material all play a crucial role in the consumption of the first additive.

[0035] Among them, in the formula The specific surface area (B) of the cathode active material is given the highest weight to emphasize that it is the most crucial factor determining the reaction interface size and influencing the consumption of the first additive. A larger B value means a larger reaction area per unit mass, requiring more first additive molecules to cover and modify these interfaces. Furthermore, maintaining the specific surface area of ​​the cathode active material within 0.3 ≤ B ≤ 1.5 allows the cathode active particles to remain within a relatively fine range, generally exhibiting nanoscale, primary particle, or porous structures. This improves the lithium-ion diffusion kinetics of cathode active materials such as lithium cobalt oxide, meeting the requirements of high-rate batteries. However, a high specific surface area leads to higher side reactions, which is detrimental to cycle stability under high voltage. Therefore, this embodiment limits it to 1.5 μm. 2 A weight of / g can cover the needs of high-rate application scenarios while meeting the requirements of high-voltage battery systems.

[0036] In the formula The median particle size of the reactive cathode active material has a mild positive correlation with the interface protection requirement, and is a minor but significant factor affecting the amount of the first additive added. Smaller particle sizes result in more active sites on the particle surface, increasing the demand (consumption) of the first additive. Therefore, considering the relationship between the specific surface area and particle size of the cathode active material and the consumption of the first additive, using smaller particles can shorten the diffusion path, improve the lithium-ion insertion / extraction rate, and meet the application requirements of high-power batteries. Furthermore, controlling the median particle size D50 of the cathode active material within the range of 5 ≤ C ≤ 15 can balance the material's processing performance and electrochemical performance.

[0037] In the formula As a regulatory factor, porosity is an important factor affecting structural stability. Lower porosity results in higher electrode density, which means difficulty in electrolyte wetting and narrower ion transport channels. The first additive needs to pass through these narrow channels to reach the reaction interface, leading to low utilization efficiency. Therefore, a higher initial concentration is required to ensure sufficient molecules reach the interface. Conversely, higher porosity allows for stronger electrolyte penetration within the electrode, improving the contact efficiency between the first additive and the electrode interface, thus allowing for a moderate reduction in the first additive concentration. Furthermore, controlling the porosity of the positive electrode within the range of 0.1 ≤ D ≤ 0.3 ensures sufficient electrolyte wetting while improving the electrode's mechanical strength.

[0038] In this embodiment, by controlling the relationship between the content of benzamide compounds as additives in the electrolyte and various parameters of the positive electrode, the compatibility problem of benzamide compound additives with a fixed concentration in different positive electrode structures can be avoided, ensuring the integrity and density of the CEI film layer. This avoids the problem of excessive CEI film layer and increased impedance caused by excessive additives, and also avoids the problem of incomplete CEI film layer coverage and continuous interface decomposition caused by insufficient additives. Thus, while reducing gas production, low impedance is maintained, and excellent interface stability and excellent interface ion transport capability are obtained simultaneously.

[0039] In some embodiments of this application, the first additive is selected from at least one compound with the following structural formulas: .

[0040] Formula 1 is 2-(trifluoromethyl)benzamide, with CAS number 360-64-5. The amide group in this compound provides strong coordination ability, allowing the molecule to preferentially enter Li. + The solvent sheath, thus precisely delivered to the electrode interface, has a structure in which the benzene ring is linked to a trifluoromethyl group, which is considered to be advantageous for preferential electrochemical decomposition under high voltage, effectively generating LiF; at the same time, its amide group (-CONH2) decomposes during the cycle, providing a nitrogen source to form components with high ionic conductivity such as Li3N.

[0041] Formula 2 is N-methyl-2-(trifluoromethyl)benzamide, with CAS number 171426-41-8. This compound inherits the high ionic coordination ability of the amide through N-alkylation (-CONHCH3), while retaining the function of the -CF3 group to promote LiF generation. The N-alkylation modification in this structure may help improve the chemical stability of the molecule and have better overall performance.

[0042] Formula 3 is 4-fluoro-2-(trifluoromethyl)benzamide, with CAS number 207919-06-0. This compound has both a trifluoromethyl group and a para-fluorine atom on the benzene ring, forming a dual fluorine source structure. The fluorine atom substitution, acting as an electron-withdrawing group, is expected to enhance the polarity of CF and increase the likelihood of CF cleavage. This unique structure is believed to promote the formation of more LiF, constructing a CEI substrate with high ionic conductivity and more effectively suppressing the dissolution of cobalt ions from the cathode. Through this synergistic and enhanced interfacial stabilization effect of dual fluorine, the formed CEI layer has better density and can effectively block subsequent side reactions caused by cobalt dissolution, making it particularly suitable for applications with stringent high-temperature storage requirements.

[0043] Formula 4, with CAS number 1203952-60-6, is a combination of the aforementioned advantageous structures. Its N-alkylation (-CONHCH3) enhances molecular stability, while possessing a para-fluorine atom and a -CF3 group, forming a dual-site fluorine substitution structure. This design is believed to synergistically promote LiF formation and maintain good coordination and film-forming ability, thereby constructing a denser CEI layer, effectively suppressing cobalt dissolution and related side reactions, ultimately resulting in improved cycle life and structural stability under high voltage.

[0044] Formula 5 has a CAS number of 1203956-49-3. The cyano substitution at the para position of the amide group will improve the overall antioxidant properties of the molecule, which may be more advantageous in applications under high temperature storage and higher pressure scenarios.

[0045] In some embodiments of this application, the additive in the electrolyte further includes a second additive. The second additive is selected from at least one of fluoroethylene carbonate (FEC), vinylene carbonate (VC), 1,3-propanesulfonate lactone (PS), vinyl sulfate (DTD), succinic anionyl nitrile (SN), adiponitrile (ADN), 1,3,6-hexanetrionitrile (HTCN), propenesulfonate lactone (PST), methylene disulfonate (MMDS), ethylene glycol bis(propionitrile) ether (EGBE), pentafluoroethoxyphosphazene, dicyclohexylcarbonyl, trimethyl imide phosphate, and hexamethylene diisocyanate.

[0046] Introducing other functional additives into benzamide compounds can synergistically enhance the interfacial film, suppress gas generation, and improve low-temperature performance. For example, FEC can functionally participate in the formation of the CEI layer with the first additive, effectively improving the flexibility and stability of the CEI film. Nitrile compounds such as SN and ADN can improve the antioxidant properties of the electrolyte, suppress solvent decomposition under high pressure, suppress gas generation, and improve cycle stability. PS can improve the thermal stability of the CEI film, improve gas generation during high-temperature storage, and enhance high-temperature cycling performance.

[0047] Furthermore, the total mass percentage of the second additive in the electrolyte is 5% to 25%, which is the total content of all the second additives in the electrolyte. Specifically, it can be 5%, 10%, 12%, 15%, 18%, 20%, 22%, 25%, or any value within the above range. By limiting the amount of the second additive to the above range, it is possible to avoid excessive additives leading to increased side reactions and affecting battery performance.

[0048] In some preferred embodiments of this application, the second additive comprises fluoroethylene carbonate, and the mass percentage of fluoroethylene carbonate in the electrolyte is 5% to 25%, preferably 5% to 20%.

[0049] In some embodiments of this application, the lithium salt is selected from at least one of 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 (LiPOF2), and lithium bis(oxalate borate) (LiBOB).

[0050] Lithium salts can be used in high-voltage battery systems, maintaining stability and ionic conductivity under high voltage. For example, LiPF6 has high ionic conductivity but strong hydrolysis sensitivity, while boron / phosphorus salts such as LiODFB and LiDFOP have good hydrolysis stability and interface formation ability, and imide salts such as LiTFSI and LiFSI also have good high-temperature stability.

[0051] Furthermore, the mass percentage of lithium salt in the electrolyte is 10% to 25%. Specifically, it can be 10%, 12%, 15%, 18%, 20%, 22%, 25%, or any value within the above range. Limiting the amount of lithium salt added within the above range can balance the effects of ion conduction and viscosity.

[0052] In some embodiments of this application, the solvent of the electrolyte is selected from at least one of ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), dimethyl carbonate (DMC), ethyl propionate (EP), propyl propionate (PP), ethyl fluorocarbonate (DFEA), methyl ethyl fluorocarbonate (FEMC), dimethyl fluorocarbonate (FDMC), propylene fluorocarbonate (FPC), 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 (MP), methyl butyrate, ethyl butyrate, methyl acrylate, and ethyl acrylate.

[0053] In the embodiments of this application, the organic solvent in the electrolyte can be a combination of carbonate and carboxylic acid ester solvents, such as a compound combination of EC, PC, EP, PP, etc., which can ensure the solubility of lithium salt and ion migration rate. Among them, carbonates have a larger dielectric constant, which can effectively dissociate lithium salt, and also play an important role in forming the interfacial film. However, carbonates such as EC are not resistant to oxidation when used alone, and are prone to oxidation under high voltage cathode, resulting in gas generation. Carboxylic acid esters have lower viscosity, which can improve battery kinetics. The combination of the two is suitable for high voltage battery systems.

[0054] Furthermore, the solvent's mass percentage in the electrolyte is 70%–85%. Specifically, it can be 70%, 72%, 75%, 78%, 80%, 82%, 85%, or any value within the above range. Maintaining the organic solvent's addition within this range ensures the solubility and compatibility of all components.

[0055] 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.

[0056] The positive electrode material layer is formed by coating the surface of the positive electrode current collector with a positive electrode slurry. The positive electrode slurry may contain a positive electrode active material, a conductive agent, and a binder. The positive electrode active material mainly 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 a high theoretical capacity and voltage plateau under high voltage.

[0057] The conductive agent mentioned in the embodiments of this application can improve the conductivity of the electrode and can be selected from superconducting carbon black, acetylene black, Ketjen black, natural graphite, artificial graphite, graphene, carbon fiber, carbon nanotubes (CNTs), etc. The binder can be at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0058] In some embodiments of this 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.

[0059] 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.

[0060] 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-carbon compounds; preferably silicon or silicon-carbon composites. In some embodiments of this application, the conductive agent may be one or more of superconducting carbon black (SP), acetylene black, Ketjen black, natural graphite, artificial graphite, graphene, carbon fiber, and carbon nanotubes (CNTs). The binder may be one or more of carboxymethyl cellulose, styrene-butadiene rubber, styrene-acrylic emulsion, lithium polyacrylate, polyacrylic acid, and sodium alginate.

[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] The lithium-ion battery provided in this application embodiment is suitable for high-voltage systems. The upper limit cutoff voltage of the lithium-ion battery is greater than or equal to 4.5V.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] Example 1 (1) Preparation of positive electrode sheet Lithium cobalt oxide (LCO), a positive electrode active material, CNT (conductive agent), and PVDF (adhesive agent) were thoroughly mixed in 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 for 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.

[0067] (2) Preparation of negative electrode sheet The negative electrode active material (graphite and silicon, with silicon content at 15% by weight) is mixed with an adhesive (styrene-butadiene rubber-sodium carboxymethyl cellulose composite adhesive SBR-CMC) and a conductive agent (carbon black) at a mass ratio of 95:3.5:1.5 in a deionized water solvent and stirred thoroughly to obtain a homogeneous negative electrode slurry. This negative electrode slurry is then uniformly coated onto 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 meeting the winding requirements is produced.

[0068] (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, 2% succinate (SN), 2% 1,3,6-hexanetrionitrile (HTCN), 4% 1,3-propanesulfonyl lactone (PS), 13.5% LiPF6, 0.3% ODFB, 15% FEC, and 0.5% of the first additive (benzamide compound) were added and mixed evenly to obtain the electrolyte.

[0069] (4) Preparation of lithium-ion batteries PE porous polymer film is used as the separator.

[0070] 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.

[0071] Examples 2-18 and Comparative Examples 1-4 use the same method as Example 1, the difference being that the composition or amount of the additives are different, or the parameters of the positive electrode are different, as shown in Table 1.

[0072] 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 are recorded in Table 1.

[0073] (1) Storage test at 80℃ The lithium-ion battery was charged to 4.55V at a constant current of 0.5C, with a cutoff current of 0.05C, and left to stand for 10 minutes. It was then discharged to 3.0V at 0.2C for activation, followed by constant current charging at 0.5C for 36 minutes (30% SOC), and the cell thickness T0 was measured. Subsequently, it was charged to 4.55V at a constant current of 0.5C, with a cutoff current of 0.05C, and left to stand for 10 minutes. The fully charged cell was then transferred to an 80℃ oven and stored for 12 hours. After that, the hot appearance of the cell was observed, and the hot thickness T1 of the cell was measured. The hot thickness expansion rate (%) was defined as (T1-T0) / T0.

[0074] (2) 45℃ cycle test The lithium-ion battery was charged at room temperature with a constant current of 0.5C to 4.55V, with a cutoff current of 0.05C. After resting for 10 minutes, it was discharged at 0.2C to 3.0V for activation, followed by constant current charging at 0.5C for 36 minutes (30% SOC). It was then placed at 45℃ for 2 hours, charged at a constant current of 0.5C to 4.55V, with a cutoff current of 0.05C, and the hot-state fully charged 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 for 300 cycles (cls) to obtain the capacity C after 300 cycles. 300 Then the capacity retention rate = C 300 / C0.

[0075] Table 1

[0076] Notes: " / " indicates non-existent; "A" indicates the mass percentage of the first additive in the electrolyte; "B" indicates the specific surface area of ​​the positive electrode active material; "C" indicates the median particle size of the positive electrode active material; "D" indicates the porosity of the positive electrode sheet; "Calculated value" indicates... The calculated value.

[0077] A comparison between Comparative Example 1 and Example 1 revealed that adding benzamide compounds as additives to the lithium-ion battery electrolyte, along with the solvent, lithium salt, and other additives in the electrolyte, and in conjunction with the positive electrode active material, can solve the interfacial instability problem of the high-voltage positive electrode. This results in the formation of a dense and stable CEI film at the positive electrode interface, effectively suppressing electrolyte decomposition and gas generation, preventing rapid impedance growth, and improving the battery's high-temperature storage stability and cycle capacity retention. Specifically, the thickness expansion rate measured at 80°C for 12 hours directly measures the electrolyte's oxidation resistance on the positive electrode side, reflecting the effectiveness of the CEI film formation; a lower thickness expansion rate indicates higher oxidation resistance on the positive electrode side. The capacity retention rate after 300 cycles at 45°C comprehensively measures the stability of the positive electrode interface; a higher capacity retention rate likely indicates higher positive electrode interface stability.

[0078] A comparison of Examples 1-5 revealed that the cyano group in Formula 5 exhibits the best antioxidant properties among the benzamide compounds, with its thermal thickness expansion rate decreasing to below 10% after 12 hours of storage at 80°C. However, it also shows slightly poorer anode compatibility, with its capacity retention decreasing to 74.60% after 300 cycles at 45°C. Overall, the benzamide compounds in Formula 4 containing difluorinated groups and N-alkylated (-CONHCH3) show the best synergistic performance, with a thermal thickness expansion rate of 10.50% after 12 hours of storage at 80°C and a capacity retention rate of 80.60% after 300 cycles at 45°C. This significantly improves the high-temperature storage stability of the battery while maintaining good cycle stability, resulting in better balance between the positive and negative electrode interfaces.

[0079] Through comparison of Examples 4, 6-9, and Comparative Example 1, it was found that when the parameters of the positive electrode active material and the porosity of the positive electrode are fixed, the addition amount of the first additive, benzamide compound, in the electrolyte is 0.1% to 3%, preferably 0.5% to 1%, which can effectively solve the interfacial instability problem of the high-voltage positive electrode, form a stable CEI film, and effectively improve the stability of the positive electrode interface. However, when the first additive is absent or its content is too low, the coverage effect on the positive electrode interface is poor. When the content of the first additive is too high, the CEI film layer is too thick, which will repeatedly consume active lithium, which is not conducive to maintaining a good cycle life.

[0080] Through comparisons of Examples 10-16 and Comparative Examples 2 and 3, it was found that, theoretically, positive electrode active materials with large specific surface area and small particle size require the addition of more benzamide compounds as the first additive to form a stable CEI film layer on the positive electrode side, thereby improving the stability of the positive electrode interface and enhancing battery storage and cycle performance under high voltage systems. Conversely, positive electrode active materials with small specific surface area and large particle size theoretically require less first additive to maintain good cycle life. The smaller the porosity of the positive electrode sheet, the more theoretically the amount of first additive needed should be increased. Therefore, when the first additive and the positive electrode sheet meet the requirements... When the conditions of 0.1 ≤ A ≤ 3, 0.3 ≤ B ≤ 1.5, 5 ≤ C ≤ 15, and 0.1 ≤ D ≤ 0.3 are met, the integrity and compactness of the CEI film can be guaranteed. This avoids the problems of excessive additives leading to an overly thick CEI film and increased impedance, as well as insufficient additives leading to incomplete CEI film coverage and continuous interface decomposition. Thus, while reducing gas production, low impedance can be maintained, and excellent interface stability and excellent interface ion transport capabilities can be obtained simultaneously.

[0081] A comparison of Examples 17 and 18 with Comparative Example 4 revealed that without the addition of FEC additive, an effective protective SEI layer could not be formed at the negative electrode interface, which was detrimental to the battery's high-temperature storage and cycle life. While a lower FEC content resulted in less electrolyte oxidation and gas generation, which improved the battery's high-temperature storage performance, it also led to poor long-cycle interface protection, hindering cycle life improvement. Conversely, a higher FEC content resulted in more electrolyte oxidation and gas generation, which was detrimental to high-temperature storage performance and increased side reactions at the electrode interface, further hindering cycle life improvement. Therefore, limiting the FEC content in the electrolyte to 5%–25% is preferable.

[0082] 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, a negative electrode, a separator, and an electrolyte, characterized in that; The electrolyte comprises a lithium salt, a solvent, and an additive; the additive comprises a first additive selected from benzamide compounds represented by the following general structural formula: R1 and R2 are each independently selected from hydrogen and C1 to C6 alkyl groups; R3 is selected from hydrogen, fluorine or cyano; R4 is selected from C1 to C6 alkyl groups substituted with at least one fluorine atom. The positive electrode sheet includes a positive current collector and a positive electrode material layer coated on the surface of the positive current collector, wherein the positive electrode material layer contains a positive electrode active material, satisfying the following: ； Wherein, A represents the mass percentage content of the first additive in the electrolyte, in units of %; and B represents the specific surface area of ​​the positive electrode active material, in units of m². 2 / g; C represents the median particle size of the positive electrode active material, in μm; D represents the porosity of the positive electrode sheet, in μm.

2. The lithium-ion battery according to claim 1, characterized in that, 。 3. The lithium-ion battery according to claim 1, characterized in that, The first additive is selected from at least one compound with the following structural formulas: 。 4. The lithium-ion battery according to claim 1, characterized in that, In the electrolyte, 0.1 ≤ A ≤ 3; preferably 0.5 ≤ A ≤ 1; And / or, in the positive electrode, 0.3 ≤ B ≤ 1.5, 5 ≤ C ≤ 15, 0.1 ≤ D ≤ 0.

3.

5. The lithium-ion battery according to claim 1, characterized in that, The additive further includes a second additive selected from at least one of fluoroethylene carbonate, 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 second additive has a mass percentage content of 5% to 25% in the electrolyte.

6. The lithium-ion battery according to claim 1, characterized in that, The lithium salt is selected from 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 is selected from 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 solvent in the electrolyte has a mass percentage content of 70% to 85%.

8. The lithium-ion battery according to claim 1, characterized in that, The positive electrode active material is selected from at least one of lithium cobalt oxide, nickel-cobalt-manganese ternary materials, lithium iron phosphate, and lithium manganese oxide; preferably lithium cobalt oxide or nickel-cobalt-manganese ternary materials.

9. The lithium-ion battery according to claim 1, characterized in that, The negative electrode sheet includes a negative current collector and a negative electrode material layer coated on the surface of the negative current collector. The negative electrode material layer contains a negative electrode active material. The negative electrode active material is selected from at least one of graphite, hard carbon, silicon, silicon oxide, and silicon-carbon compound. Preferably, it is silicon or silicon-carbon composite.

10. The lithium-ion battery according to any one of claims 1-9, characterized in that, The upper limit cutoff voltage of the lithium-ion battery is greater than or equal to 4.5V.

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