Lithium-ion batteries and electronic devices

Abstract

This application relates to a lithium-ion battery and an electronic device. Specifically, this application provides a lithium-ion battery comprising: a positive electrode, a negative electrode, and an electrolyte. The positive electrode comprises: a positive electrode current collector and a positive electrode material layer located on one or both sides of the positive electrode current collector. The positive electrode material layer comprises: a ternary material and a polysiloxane. The ternary material comprises: nickel, cobalt, and manganese; the molar content of nickel is greater than or equal to 50%. The electrolyte comprises a trinitrile compound. Based on the mass of the positive electrode material layer, the mass content of the polysiloxane is a%, 0.05 ≤ a ≤ 3%. This application improves the rate performance and storage characteristics of the battery at high temperatures, especially enhancing thermal safety performance.

Description

[0001] This application is a divisional application of application number 202410114561.8, filed on January 26, 2024, entitled "Lithium-ion Battery and Electronic Device". Technical Field

[0002] This application relates to the field of energy storage, specifically to a lithium-ion battery and electronic device. Background Technology

[0003] With the technological advancements in mobile devices, the demand for rechargeable batteries has increased significantly, especially for lithium-ion batteries with high energy density, high voltage, long cycle life, and low self-discharge. However, with repeated charge and discharge cycles, the storage performance of lithium-ion batteries deteriorates, becoming more severe at high temperatures. This is because moisture or other effects within the battery cause electrolyte decomposition or active material degradation, leading to increased internal resistance.

[0004] Lithium cobalt oxide, the cathode material, has excellent storage characteristics and charge / discharge efficiency, making it the most widely used. However, its structural stability deteriorates under high voltage. Ternary materials are cheaper than lithium cobalt oxide and can be used for high voltage and high capacity applications, but surface damage occurs at high temperatures or voltages, affecting the battery's rate performance and storage characteristics.

[0005] To address these issues, various methods have been attempted, including coating and protecting the surface of the positive electrode active material or removing surface impurities. However, none of these methods have satisfactorily resolved the limitations. Therefore, there is an urgent need to develop chemical systems that can solve these problems while improving the high-temperature safety performance of lithium-ion batteries. Summary of the Invention

[0006] The embodiments of this application address, to some extent, the problems existing in the prior art by adjusting the composition of the positive electrode and the components of the electrolyte used in lithium-ion batteries.

[0007] This application provides a lithium-ion battery comprising a positive electrode, a negative electrode, and an electrolyte. The positive electrode includes a positive electrode material layer comprising a ternary material and a polysiloxane. The ternary material comprises nickel, cobalt, and manganese, with a nickel molar content greater than or equal to 50%. The electrolyte comprises a trinitrile compound, wherein the nickel molar content is the ratio of the molar amount of nickel to the molar amount of the metal elements other than lithium in the ternary material. This application improves the rate performance and storage characteristics of the battery at high temperatures, and particularly enhances its thermal safety performance.

[0008] According to some embodiments of this application, the polysiloxane includes at least one of cyclopentapolydimethylsiloxane, cyclotripolydimethylsiloxane, dipolyethylenedimethylsiloxane, polydimethylsiloxane, polymethylsiloxane, or polyimidesiloxane. Cyclopentapolydimethylsiloxane with a macrocyclic structure is preferred, as it provides better performance and a stable passivation film structure at high temperatures.

[0009] According to some embodiments of this application, the mass content of the polysiloxane is a%, 0.05 ≤ a ≤ 3, preferably 0.1 ≤ a ≤ 2, based on the mass of the cathode material layer. When the mass content of polysiloxane in the cathode material layer is within the above range, it helps to further improve the rate performance and safety performance at high temperatures.

[0010] According to some embodiments of this application, the trinitrile compounds include: 1,3,5-pentanetricarbonitrile, 1,2,3-propanetricarbonitrile, 1,3,6-hexanetricarbonitrile, 1,2,6-hexanetricarbonitrile, 1,2,3-tris(2-cyanoethoxy)propane, 1,2,4-tris(2-cyanoethoxy)butane, 1,1,1-tris(cyanoethoxymethylene)ethane, 1,1,1-tris(cyanoethoxymethylene)propane, 3-methyl At least one of -1,3,5-tris(cyanoethoxy)pentane, 1,2,7-tris(cyanoethoxy)heptane, 1,2,6-tris(cyanoethoxy)hexane or 1,2,5-tris(cyanoethoxy)pentane, preferably the trinitrile compound comprising: 1,3,6-hexanetricarbonitrile and 1,2,3-tris(2-cyanoethoxy)propane, thereby improving lithium-ion charge transport, improving rate capability, reducing gas production, and enhancing safety performance.

[0011] According to some embodiments of this application, the mass content of the trinitrile compound is b% based on the mass of the electrolyte, with 0.05 ≤ b ≤ 8, preferably 0.1 ≤ b ≤ 5, which helps to further improve rate performance and safety performance. According to some embodiments of this application, the mass content of the polysiloxane is a% based on the mass of the positive electrode material layer, and the mass content of the trinitrile compound is b% based on the mass of the electrolyte, where a and b satisfy the relationship: 0.03 ≤ a / b ≤ 1, thereby improving rate performance and safety performance at high temperatures.

[0012] According to some embodiments of this application, the molar content of nickel in the ternary material is greater than or equal to 60%, preferably greater than or equal to 80%. According to embodiments of this application, the ternary material includes lithium nickel cobalt manganese oxide. This is beneficial for improving battery capacity.

[0013] According to some embodiments of this application, the electrolyte further includes a PO additive, the PO additive comprising at least one compound of formula 1 to formula 4.

[0014]

[0015] The aforementioned PO additives further enhance the stability of the passivation film, thereby inhibiting the occurrence of phase transitions during redox processes and significantly improving storage at high temperatures.

[0016] According to some embodiments of this application, the mass content of the PO additive is c%, 0.1≤c≤5, based on the mass of the electrolyte; preferably 0.1≤c≤3. When the mass content of the PO additive is within the above range, it helps to further improve performance.

[0017] According to some embodiments of this application, the mass content of the polysiloxane is a% based on the mass of the positive electrode material layer, and the mass content of the PO additive is c% based on the mass of the electrolyte, wherein a and c satisfy the relationship: 0.03≤a / c≤2, thereby further improving the rate performance and safety performance at high temperatures.

[0018] In another aspect of this application, this application provides an electronic device comprising any of the lithium-ion batteries described in this application.

[0019] This application improves rate performance and storage characteristics at high temperatures by using a specific combination of positive electrode material layer and electrolyte, and in particular enhances thermal safety performance.

[0020] Additional aspects and advantages of the embodiments of this application will be described, shown, or illustrated in part by way of implementation of the embodiments of this application in the following description. Detailed Implementation

[0021] The embodiments of this application will be described in detail below. These embodiments should not be construed as limiting the scope of this application.

[0022] Unless otherwise expressly stated, the terms used in this application shall have the meanings indicated below.

[0023] By using a specific combination of positive electrode material layer and electrolyte, this application significantly improves the rate performance and storage characteristics at high temperatures, and in particular enhances thermal safety performance.

[0024] In some embodiments, this application provides a lithium-ion battery comprising a positive electrode, a negative electrode, and an electrolyte as described below.

[0025] I. Positive electrode

[0026] The positive electrode includes a positive electrode current collector and a positive electrode material layer disposed on the surface of the positive electrode current collector.

[0027] The positive electrode material layer contains a positive electrode material, and the positive electrode material layer may be one or more layers. The positive electrode material is any substance capable of reversibly inserting and de-intercalating lithium ions.

[0028] This application relates to a lithium-ion battery and an electronic device. Specifically, this application provides a lithium-ion battery comprising: a positive electrode, a negative electrode, and an electrolyte. The positive electrode includes a positive electrode current collector and a positive electrode material layer located on one or both sides of the positive electrode current collector. The positive electrode material layer comprises a ternary material and a polysiloxane. The electrolyte comprises a trinitrile compound. In some embodiments, the ternary material includes nickel, cobalt, and manganese. The ternary material in this application contains nickel in its chemical composition. The molar content of nickel is the ratio of the molar amount of nickel to the molar amount of the metal elements other than lithium in the ternary material, and the molar content of nickel is greater than or equal to 50%. This design improves rate performance and storage characteristics at high temperatures, and particularly enhances thermal safety performance.

[0029] On the one hand, ternary materials suffer from low initial charge-discharge efficiency and significant gas generation due to cation mixing effects and changes in the surface microstructure during the first charge. On the other hand, ternary materials are secondary spherical particles formed by primary particle agglomeration. These secondary particles break down under high compaction, resulting in low lithium-ion diffusion coefficients and electronic conductivity, leading to unsatisfactory rate performance. This is particularly true for high-nickel ternary materials, where cycle performance and thermal stability deteriorate with increasing nickel content.

[0030] In their experiments, the inventors of this application discovered that adding polysiloxane during the mixing process of the positive electrode not only forms a passivation film rich in Si-O bonds on the surface of the ternary material, inhibiting the destruction of surface microstructures during charging and discharging, but also increases compaction density and reduces particle breakage. However, the stability of the passivation film decreases at high temperatures. The inventors further discovered that in an electrolyte system containing trinitrile compounds, the trinitrile compounds can inhibit the high-temperature decomposition of the passivation film, which not only improves the rate performance and storage characteristics at high temperatures, but also achieves excellent safety performance.

[0031] In some embodiments, the polysiloxane in the positive electrode may exist in the form of particles within the positive electrode material layer, and the polysiloxane may be mixed with the particles of the ternary material. In other embodiments, the polysiloxane may also exist as a coating layer on the surface of the ternary material. Regardless of the form in which the polysiloxane exists in the positive electrode material layer, as the lithium-ion battery is charged and discharged, a passivation film can be formed on the surface of the ternary material at the portion where the polysiloxane contacts it. Furthermore, the presence of the trinitrile compound can suppress the high-temperature decomposition of this passivation film. Through the synergistic effect of the ternary material, the polysiloxane, and the trinitrile compound, excellent rate performance, storage characteristics, and safety performance are achieved.

[0032] In some embodiments, the polysiloxane includes at least one of cyclopentadimethylsiloxane (Formula 5), ​​cyclotridimethylsiloxane, dipolyethylenedimethylsiloxane, polydimethylsiloxane, polymethylsiloxane, or polyimidesiloxane. Cyclopentadimethylsiloxane with a macrocyclic structure, as shown in Figure 5 below, is preferred, as it provides better performance; the passivation film structure is stable at high temperatures and is not easily decomposed.

[0033]

[0034] In some embodiments, the mass content of polysiloxane in the positive electrode material layer is a%, based on the mass of the positive electrode material layer, where 0.05 ≤ a ≤ 3. In some embodiments, 0.1 ≤ a ≤ 2. In some embodiments, a is 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 1, 1.5, 2, 2.5, 3, or within a range of any two of the above values. When the mass content of polysiloxane in the positive electrode material layer is within the above range, it helps to further improve the rate performance and safety performance at high temperatures.

[0035] According to some embodiments of this application, the molar content of nickel in the ternary material is greater than or equal to 60%, and optionally, the molar content of nickel in the ternary material is greater than or equal to 80%.

[0036] According to some embodiments of this application, the ternary material includes lithium nickel cobalt manganese oxide.

[0037] In some embodiments, the positive electrode material layer further includes a positive electrode conductive material. There is no limitation on the type of positive electrode conductive material; any known conductive material can be used. Examples of positive electrode conductive materials may include, but are not limited to, carbon black such as acetylene black; carbon materials such as amorphous carbon such as needle coke; carbon nanotubes; graphene, etc. The above-mentioned positive electrode conductive materials can be used alone or in any combination.

[0038] The positive electrode material layer also includes a positive electrode binder. There are no particular restrictions on the type of positive electrode binder, as long as it is a material that can be dissolved or dispersed in the liquid medium used during electrode manufacturing. Examples of positive electrode adhesives may include, but are not limited to, one or more of the following: resin-based polymers such as polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, and nitrocellulose; rubber-like polymers such as styrene-butadiene rubber, nitrile rubber, fluororubber, isoprene rubber, polybutadiene rubber, and ethylene-propylene rubber; thermoplastic elastomer-like polymers such as styrene-butadiene-styrene block copolymers or their hydrides, ethylene-propylene-diene terpolymers, styrene-ethylene-butadiene-ethylene copolymers, and styrene-isoprene-styrene block copolymers or their hydrides; soft resin-like polymers such as syndiotactic-1,2-polybutadiene, polyvinyl acetate, ethylene-vinyl acetate copolymers, and propylene-α-olefin copolymers; fluorinated polymers such as polyvinylidene fluoride, polytetrafluoroethylene, fluorinated polyvinylidene fluoride, and polytetrafluoroethylene-ethylene copolymers; and polymer compositions with ion conductivity of alkali metal ions (especially lithium ions). The above-mentioned positive electrode adhesive can be used alone or in any combination.

[0039] In some embodiments, the type of solvent used to form the positive electrode slurry is not limited, as long as it is a solvent capable of dissolving or dispersing the positive electrode material, conductive material, positive electrode binder, and thickener used as needed. Examples of solvents used to form the positive electrode slurry may include any of aqueous solvents and organic solvents. Examples of aqueous media may include, but are not limited to, water and mixtures of alcohol and water. Examples of organic media may include, but are not limited to, aliphatic hydrocarbons such as hexane; aromatic hydrocarbons such as benzene, toluene, xylene, and methylnaphthalene; heterocyclic compounds such as quinoline and pyridine; ketones such as acetone, methyl ethyl ketone, and cyclohexanone; esters such as methyl acetate and methyl acrylate; amines such as diethylenetriamine and N,N-dimethylaminopropylamine; ethers such as diethyl ether, propylene oxide, and tetrahydrofuran; amides such as N-methylpyrrolidone, dimethylformamide, and dimethylacetamide; and aprotic polar solvents such as hexamethylphosphoramide and dimethyl sulfoxide.

[0040] In some embodiments, the positive electrode material layer further includes a thickener. Thickeners are typically used to adjust the viscosity of the slurry. In the case of using an aqueous medium, a thickener and styrene-butadiene rubber latex can be used for slurry preparation. There are no particular limitations on the type of thickener; examples may include, but are not limited to, carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein, and their salts. The aforementioned thickeners can be used alone or in any combination.

[0041] In some embodiments, the type of positive electrode current collector is not particularly limited, and it can be any material known to be suitable for use as a positive electrode current collector. Examples of positive electrode current collectors may include, but are not limited to, metallic materials such as aluminum, stainless steel, nickel plating, titanium, and tantalum; and carbon materials such as carbon cloth and carbon paper. In some embodiments, the positive electrode current collector is a metallic material. In some embodiments, the positive electrode current collector is aluminum.

[0042] In some embodiments, to reduce the electronic contact resistance between the positive current collector and the positive electrode material layer, the surface of the positive current collector may include a conductive additive or a conductive coating. Examples of conductive additives may include, but are not limited to, carbon and precious metals such as gold, platinum, and silver. Examples of conductive coatings may include a mixture layer containing inorganic oxides, conductive agents, and binders.

[0043] In some embodiments, the positive electrode can be fabricated by forming a positive electrode material layer containing a positive electrode material and a binder on a positive electrode current collector. The manufacture of a positive electrode using a positive electrode material can be carried out by conventional methods, namely, dry mixing the positive electrode material and binder, as well as conductive materials and thickeners as needed, to form a sheet, and pressing the resulting sheet onto the positive electrode current collector; or dissolving or dispersing these materials in a liquid medium to form a slurry, coating the slurry onto the positive electrode current collector and drying it to form a positive electrode material layer on the current collector, thereby obtaining the positive electrode.

[0044] II. Electrolyte

[0045] In some embodiments, the electrolyte used in the lithium-ion battery of this application includes an electrolyte and a solvent for dissolving the electrolyte. In some embodiments, the electrolyte of this application includes a trinitrile compound.

[0046] The passivation film formed by polysiloxane on the surface of ternary materials has the problem of not being resistant to high temperatures. This application found that when the electrolyte contains trinitrile compounds, it can enhance the stability of the passivation film formed by polysiloxane on the surface of high-nickel ternary materials at high temperatures, suppress the reaction at the interface between the electrolyte and the cathode material, not only improve lithium-ion charge transport and improve rate capability, but also reduce gas production and improve safety performance.

[0047] According to embodiments of this application, the trinitrile compound includes at least one selected from: 1,3,5-pentanetricarbonitrile, 1,2,3-propanetricarbonitrile, 1,3,6-hexanetricarbonitrile, 1,2,6-hexanetricarbonitrile, 1,2,3-tris(2-cyanoethoxy)propane, 1,2,4-tris(2-cyanoethoxy)butane, 1,1,1-tris(cyanoethoxymethylene)ethane, 1,1,1-tris(cyanoethoxymethylene)propane, 3-methyl-1,3,5-tris(cyanoethoxy)pentane, 1,2,7-tris(cyanoethoxy)heptane, 1,2,6-tris(cyanoethoxy)hexane, or 1,2,5-tris(cyanoethoxy)pentane.

[0048] In some embodiments, the mass content of the trinitrile compound in the electrolyte is b%, based on the electrolyte mass, wherein 0.05 ≤ b ≤ 8. In some embodiments, 0.5 ≤ b ≤ 6. In some embodiments, 1 ≤ b ≤ 5. In some embodiments, 1 ≤ b ≤ 3. In some embodiments, b is 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 1, 1.5, 2, 2.5, 3, 4, 5, 6, 7, 8, or within a range consisting of any two of the above values. When the mass content of the trinitrile compound is within the above range, it helps to further improve rate capability and safety performance.

[0049] According to some embodiments of this application, the lithium-ion battery satisfies the relationship: 0.03≤a / b≤1.

[0050] In some embodiments, 0.05 ≤ a / b ≤ 1. In some embodiments, 0.1 ≤ a / b ≤ 1. In some embodiments, a / b is 0.03, 0.05, 0.1, 0.2, 0.5, 1, or within a range of any two of the above values. When a / b meets the above ratio, the rate performance and safety performance at high temperatures can be further improved.

[0051] In some embodiments, the electrolyte further includes a PO additive, the PO additive comprising the following:

[0052] At least one of the compounds of formulas 1 to 4,

[0053]

[0054] The aforementioned PO additives further enhance the stability of the passivation film, thereby inhibiting the occurrence of phase transitions during redox processes and significantly improving storage at high temperatures.

[0055] In some embodiments, the mass content of the PO additive is c%, based on the electrolyte mass, where 0.1 ≤ c ≤ 5. In some embodiments, 0.1 ≤ c ≤ 4. In some embodiments, 0.3 ≤ c ≤ 3. In some embodiments, 0.5 ≤ c ≤ 3. In some embodiments, c is 0.1, 0.2, 0.3, 0.4, 0.5, 1, 1.5, 2, 2.5, 3, 4, 5, or within a range consisting of any two of the above values. When the mass content of the PO additive is within the above range, it helps to further improve performance.

[0056] In some embodiments, 0.03 ≤ a / c ≤ 2. In some embodiments, 0.05 ≤ a / c ≤ 1. In some embodiments, a / c is 0.03, 0.05, 0.1, 0.2, 0.5, 1, 1.5, 2, or within a range of any two of the above values. When a / c meets the above ratios, rate performance and safety performance at high temperatures can be further improved.

[0057] In some embodiments, the electrolyte further comprises any non-aqueous solvent known in the art that can be used as a solvent for an electrolyte.

[0058] In some embodiments, the non-aqueous solvent includes, but is not limited to, one or more of the following: cyclic carbonates, chain carbonates, cyclic carboxylic acid esters, chain carboxylic acid esters, cyclic ethers, chain ethers, phosphorus-containing organic solvents, and sulfur-containing organic solvents.

[0059] In some embodiments, the solvent used in the electrolyte of this application includes cyclic carbonates, linear carbonates, cyclic carboxylic acid esters, linear carboxylic acid esters, and combinations thereof. In some embodiments, the solvent used in the electrolyte of this application comprises an organic solvent selected from the group consisting of: ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl propionate, propyl propionate, n-propyl acetate, ethyl acetate, and combinations thereof. In some embodiments, the solvent used in the electrolyte of this application comprises: ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl propionate, propyl propionate, and combinations thereof.

[0060] In some embodiments, the electrolyte is not particularly limited, and any substance known as an electrolyte can be used. The mass of the electrolyte is not particularly limited, as long as it does not impair the effectiveness of this application.

[0061] III. Negative electrode

[0062] The negative electrode includes a negative electrode current collector and a negative electrode material layer located on one or both surfaces of the negative electrode current collector, the negative electrode material layer containing negative electrode material. In some embodiments, the rechargeable capacity of the negative electrode material is greater than the discharge capacity of the positive electrode material to prevent unintentional deposition of lithium metal on the negative electrode during charging.

[0063] In some embodiments, any known current collector can be used as the negative current collector to retain the negative electrode material. Examples of negative current collectors include, but are not limited to, metallic materials such as copper, nickel, stainless steel, and nickel-plated steel. In some embodiments, the negative current collector is copper.

[0064] In some embodiments, the negative electrode material is not particularly limited, as long as it can reversibly absorb and release lithium ions. Examples of negative electrode materials may include, but are not limited to, carbon materials such as natural graphite and artificial graphite; metals such as silicon (Si) and tin (Sn); or oxides of metal elements such as Si and Sn. The negative electrode material can be used alone or in combination.

[0065] In some embodiments, the negative electrode material layer may further include a negative electrode binder. The negative electrode binder improves the bonding between negative electrode material particles and the bonding between the negative electrode material and the current collector. There are no particular limitations on the type of negative electrode binder, as long as it is a material stable to the electrolyte or the solvent used in electrode manufacturing. In some embodiments, the negative electrode binder includes a resin binder. Examples of resin binders include, but are not limited to, fluoropolymers, polyacrylonitrile (PAN), polyimide resins, acrylic resins, polyolefin resins, etc. When preparing the negative electrode slurry using an aqueous solvent, the negative electrode binder includes, but is not limited to, carboxymethyl cellulose (CMC) or its salts, styrene-butadiene rubber (SBR), polyacrylic acid (PAA) or its salts, polyvinyl alcohol, etc.

[0066] In some embodiments, the negative electrode can be prepared by coating a negative electrode slurry containing a negative electrode material, a resin binder, etc. onto a negative electrode current collector, drying it, and then calendering it to form a negative electrode material layer on both sides of the negative electrode current collector, thereby obtaining the negative electrode.

[0067] IV. Separating membrane

[0068] In some embodiments, a separator may be provided between the positive and negative electrodes to prevent short circuits. In this case, the electrolyte of this application can typically penetrate the separator and be used.

[0069] In some embodiments, there are no particular limitations on the material and shape of the separator, as long as it does not significantly impair the effectiveness of this application. The separator may be a resin, glass fiber, inorganic material, etc., formed from a material stable to the electrolyte of this application. In some embodiments, the separator includes a porous sheet or non-woven fabric-like material with excellent liquid retention properties. Examples of materials for resin or glass fiber separators may include, but are not limited to, polyolefins, aromatic polyamides, polytetrafluoroethylene, polyethersulfone, etc. In some embodiments, the polyolefin is polyethylene or polypropylene. In some embodiments, the polyolefin is polypropylene. The above-mentioned separator materials can be used alone or in any combination.

[0070] In some embodiments, the separator may also be a material formed by laminating the above-mentioned materials, examples of which include, but are not limited to, a three-layer separator formed by laminating polypropylene, polyethylene, and polypropylene in that order.

[0071] In some embodiments, examples of inorganic materials may include, but are not limited to, oxides such as alumina and silicon dioxide, nitrides such as aluminum nitride and silicon nitride, and sulfates (e.g., barium sulfate, calcium sulfate, etc.). The inorganic material may be in, but is not limited to, particulate or fibrous form.

[0072] In some embodiments, the separator may be in the form of a thin film, examples of which include, but are not limited to, nonwoven fabrics, woven fabrics, microporous membranes, etc. In the thin film form, the pore size of the separator is 0.01 μm to 1 μm, and the thickness is 5 μm to 50 μm. In addition to the above-mentioned independent thin film separator, the following separator may also be used: a separator formed by using a resin-based adhesive to form a composite porous layer containing the above-mentioned inorganic particles on the surface of the positive and / or negative electrodes, for example, a separator formed by using fluororesin as an adhesive to form a porous layer of alumina particles with a particle size of less than 1 μm on both sides of the positive electrode.

[0073] In some embodiments, the thickness of the separator is arbitrary. In some embodiments, the thickness of the separator is greater than 1 μm, greater than 5 μm, or greater than 8 μm. In some embodiments, the thickness of the separator is less than 50 μm, less than 40 μm, or less than 30 μm. When the thickness of the separator is within the above ranges, insulation and mechanical strength can be ensured, and the rate performance and energy density of the lithium-ion battery can be guaranteed.

[0074] This application also provides an electronic device comprising a lithium-ion battery according to any of the claims in this application.

[0075] The application of the lithium-ion battery in this application is not particularly limited, and it can be used in any electronic device known in the prior art. In some embodiments, the lithium-ion battery of this application can be used in, but is not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, headsets, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, household large-capacity batteries, and lithium-ion capacitors, etc.

[0076] The preparation of lithium-ion batteries is described below with reference to specific embodiments. Those skilled in the art will understand that the preparation methods described in this application are merely examples, and any other suitable preparation methods are within the scope of this application.

[0077] I. Preparation of Lithium-ion Batteries

[0078] 1. Preparation of the negative electrode

[0079] Artificial graphite, styrene-butadiene rubber, and lithium carboxymethyl cellulose were mixed with deionized water in a mass ratio of 96.5%:2.5%:1% and stirred until homogeneous to obtain a slurry. The slurry was then coated onto a 9μm thick copper foil. After drying and cold pressing, the foil was cut and tabs were welded to obtain the negative electrode.

[0080] 2. Preparation of the positive electrode

[0081] Ternary materials, carbon nanotubes, carbon black, and polyvinylidene fluoride were mixed with N-methylpyrrolidone (NMP) in a mass ratio of 97:0.5:0.5:2. Polysiloxane was added, and the mixture was stirred until homogeneous to obtain a positive electrode slurry. This positive electrode slurry was coated onto a 12 μm thick aluminum foil, dried, cold-pressed, and then cut and welded to obtain the positive electrode. The specific ternary materials used are shown in the example table.

[0082] 3. Preparation of electrolyte

[0083] In a dry argon atmosphere, ethylene carbonate (EC), polycarbonate (PC), dimethyl carbonate (DMC), and polypropylene (PP) were mixed in a mass ratio of 1:1:1:2, and LiPF6 was added to form a basic electrolyte, wherein the mass content of LiPF6 in the basic electrolyte was 12%. Electrolytes of different embodiments and comparative examples were obtained by adding 4.3% by mass of fluoroethylene carbonate, 3.2% by mass of adiponitrile, trionitrile compounds, and PO additives to the basic electrolyte.

[0084] 4. Preparation of the separating membrane

[0085] A 7-micrometer-thick porous polyethylene polymer film was used as the separator.

[0086] 5. Preparation of lithium-ion batteries

[0087] The obtained positive electrode, separator, and negative electrode are wound in sequence and placed in an outer packaging foil, leaving an injection port. Electrolyte is poured in through the injection port, the battery is sealed, and then processed through conventional processes such as formation to produce a lithium-ion battery.

[0088] II. Testing Methods

[0089] 1. Testing the capacity retention of lithium-ion batteries after high-temperature cycling.

[0090] At 65°C, the lithium-ion battery is charged at a constant current of 1C to 4.3V, then charged at a constant voltage of 4.3V to a current of 0.05C, and finally discharged at a constant current of 1C to 2.0V. This constitutes the first cycle. The lithium-ion battery is subjected to 1000 cycles under these conditions. "1C" refers to the current value at which the battery capacity is completely discharged within one hour.

[0091] The capacity retention rate of a lithium-ion battery after 1000 cycles is calculated using the following formula:

[0092] Capacity retention rate = (Discharge capacity of the 1000th cycle / Discharge capacity of the first cycle) × 100%.

[0093] 2. High-Temperature Rate Performance Testing of Lithium-ion Batteries

[0094] At 60℃, discharge at 0.2C to 2.0V, let stand for 5 minutes, charge at 0.5C to 4.3V, charge at constant voltage to 0.05C and let stand for 5 minutes. Adjust the discharge rate and conduct discharge tests at 0.2C and 5.0C respectively to obtain discharge capacity 1 and discharge capacity 2.

[0095] Rate performance = (discharge capacity 2 / discharge capacity 1) × 100%.

[0096] 3. Test of thermal abuse thickness expansion rate of lithium-ion batteries

[0097] At 25°C, the lithium-ion battery was left to stand for 30 minutes, and its thickness H1 was measured. Then, the temperature was increased at a rate of 5°C / min until it reached 130°C, which was maintained for 30 minutes, and the thickness H2 was measured again. The thermal abuse thickness expansion rate of the lithium-ion battery was calculated using the following formula:

[0098] Expansion rate = [(H2-H1) / H1]×100%.

[0099] III. Test Results

[0100] Table 1 shows the effects of the positive electrode material layer polysiloxane and the electrolyte trinitrile compound on the rate performance, storage characteristics and thermal safety performance of lithium-ion batteries at high temperatures.

[0101] Based on the mass of the cathode material layer, the mass content of polysiloxane is a%. Table 1 shows the following polysiloxanes used: cyclopentadimethylsiloxane (S1), cyclotridimethylsiloxane (S2), diethylenedimethylsiloxane (S3), polydimethylsiloxane (S4), polymethylsiloxane (S5), and polyimidesiloxane (S6). The cathode active materials used are commercially available NCM532, NCM622, and NCM811 (NCM532 indicates that the metal elements other than lithium in the ternary material are mainly Ni, Co, and Mn, and the molar ratio of Ni, Co, and Mn is 5:3:2; NCM622 and NCM811 are similar).

[0102] Based on the mass of the electrolyte, the mass content of the trinitrile compound is b%, and the trinitrile compounds used are as follows: 1,3,6-hexanetricarbonitrile (T1), 1,2,6-hexanetricarbonitrile (T2), and 1,2,3-tris(2-cyanoethoxy)propane (T3).

[0103] Table 1

[0104]

[0105]

[0106] Note: The numbers in parentheses represent mass content.

[0107] When the cathode material layer includes polysiloxane and the electrolyte includes trinitrile compounds, the ternary material and polysiloxane are uniformly dispersed during cathode preparation. This not only forms a passivation film rich in Si-O bonds on the surface of the ternary material, suppressing the destruction of surface microstructure during charging and discharging, but also increases the compaction density and reduces particle breakage. However, the stability of the passivation film decreases at high temperatures. The inventors also found that when the cathode is in an electrolyte system containing trinitrile compounds, the trinitrile compounds inhibit the high-temperature decomposition of the passivation film, which not only improves the rate performance and storage characteristics at high temperatures, but also achieves satisfactory safety performance.

[0108] When the mass content of polysiloxane is 0.1% to 2%, battery performance can be further improved.

[0109] When the mass content of trinitrile compounds is 1% to 5%, battery performance can be further improved.

[0110] When the mass content of polysiloxane a% and the mass content of trinitrile compound b% satisfy 0.03≤a / b≤1, the battery performance can be further improved.

[0111] The higher the nickel content in ternary materials, especially when the molar content of nickel is greater than or equal to 60%, the more beneficial the protection provided by polysiloxanes and trinitrile compounds. Trinitrile compounds significantly improve the stability of the protective film formed by polysiloxanes on the surface of ternary materials at high temperatures, suppress phase transitions, and enhance the thermal stability of ternary materials, which can further improve battery performance.

[0112] Table 2 shows the effect of the electrolyte containing PO additive on the rate performance, storage characteristics, and thermal safety performance of lithium-ion batteries at high temperatures. Except for the parameters listed in Table 2, the settings of Examples 2-1 to 2-19 are the same as those of Examples 1-3. In Examples 2-20 to 2-21, T1(1) + T3(1) is used as a trinitrile compound to replace T1(2) in Examples 1-3.

[0113] Table 2

[0114]

[0115]

[0116] The results show that when the cathode material layer includes polysiloxane and the electrolyte includes trinitrile compounds and PO additives, unexpected thermal safety performance is achieved. This may be because the PO additives can delay the inward transfer of heat generated by side reactions on the material surface, effectively improve the stability of the internal structure of the material and inhibit the occurrence of internal side reactions, thereby improving the stability of the material and further improving the thermal safety performance of lithium-ion batteries.

[0117] Battery performance can be further improved when the mass content of PO additive is between 0.1% and 5%. In particular, when the mass content of trinitrile compound and PO additive simultaneously meets the conditions of 0.5≤c≤4 and 0.1≤a / c≤1, further improvement is achieved, with a particularly significant improvement in thermal safety performance.

[0118] Throughout this specification, references to "embodiment," "partial embodiment," "one embodiment," "another example," "example," "specific example," or "partial example" mean that at least one embodiment or example in this application includes a specific feature, structure, material, or characteristic described in that embodiment or example. Therefore, descriptions appearing throughout this specification, such as "in some embodiments," "in an embodiment," "in one embodiment," "in another example," "in one example," "in a specific example," or "example," do not necessarily refer to the same embodiments or examples in this application. Furthermore, specific features, structures, materials, or characteristics in this application can be combined in any suitable manner in one or more embodiments or examples.

[0119] Although illustrative embodiments have been demonstrated and described, those skilled in the art should understand that the above embodiments should not be construed as limiting the present application, and that changes, substitutions and modifications can be made to the embodiments without departing from the spirit, principles and scope of the present application.

Claims

1. A lithium-ion battery, characterized in that, include: Positive electrode, negative electrode, and electrolyte; The positive electrode includes a positive electrode material layer, which includes: a ternary material and a polysiloxane; The ternary material comprises nickel, cobalt, and manganese; the molar content of nickel is greater than or equal to 50%; the electrolyte comprises a trinitrile compound; and the molar content of nickel is the ratio of the molar amount of nickel to the molar amount of the metal elements other than lithium in the ternary material. The polysiloxane includes at least one of cyclopentadimethylsiloxane, cyclotridimethylsiloxane, dipolyethylenedimethylsiloxane, polydimethylsiloxane, polymethylsiloxane, or polyimidesiloxane; the mass content of the polysiloxane is a%, 0.05≤a≤3, based on the mass of the cathode material layer; The trinitrile compound includes at least one of the following: 1,3,5-pentanetricarbonitrile, 1,2,3-propanetricarbonitrile, 1,3,6-hexanetricarbonitrile, 1,2,6-hexanetricarbonitrile, 1,2,3-tris(2-cyanoethoxy)propane, 1,2,4-tris(2-cyanoethoxy)butane, 1,1,1-tris(cyanoethoxymethylene)ethane, 1,1,1-tris(cyanoethoxymethylene)propane, 3-methyl-1,3,5-tris(cyanoethoxy)pentane, 1,2,7-tris(cyanoethoxy)heptane, 1,2,6-tris(cyanoethoxy)hexane, or 1,2,5-tris(cyanoethoxy)pentane; Based on the mass of the electrolyte, the mass content of the trinitrile compound is b%, where a and b satisfy the relationship: 0.03≤a / b≤1.

2. The lithium-ion battery according to claim 1, characterized in that, 0.1≤a≤2。 3. The lithium-ion battery according to claim 1, characterized in that, The trinitrile compounds include: 1,3,6-hexanetricarbonitrile and 1,2,3-tris(2-cyanoethoxy)propane.

4. The lithium-ion battery according to any one of claims 1 to 3, characterized in that, Based on the mass of the electrolyte, the mass content of the trinitrile compound is b%, and 0.05 ≤ b ≤ 8%.

5. The lithium-ion battery according to any one of claims 1 to 3, characterized in that, Based on the mass of the electrolyte, the mass content of the trinitrile compound is b%, and 0.1 ≤ b ≤ 5.

6. The lithium-ion battery according to any one of claims 1 to 3, characterized in that, The electrolyte further includes a PO additive, wherein the PO additive comprises at least one compound of formula 1 to formula 4.

7. The lithium-ion battery according to claim 6, characterized in that, It satisfies at least one of the following: (a) Based on the mass of the electrolyte, the mass content of the PO additive is c%, 0.1≤c≤5; (b) Based on the mass of the positive electrode material layer, the mass content of the polysiloxane is a%, and based on the mass of the electrolyte, the mass content of the PO additive is c%, wherein a and c satisfy the relationship: 0.03≤a / c≤2.

8. The lithium-ion battery according to any one of claims 1 to 3, characterized in that, The molar content of nickel is greater than or equal to 80%.

9. An electronic device, characterized in that, include: The lithium-ion battery according to any one of claims 1 to 8.

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