Lithium ion battery and electronic device

Abstract

The invention relates to a lithium ion battery and an electronic device. Specifically, the lithium ion battery comprises 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 side or two sides of the positive electrode current collector, the positive electrode material layer comprises a ternary material and polysiloxane, and the ternary material comprises a nickel element, a cobalt element and a manganese element; the molar content of the nickel element is greater than or equal to 50%, and the electrolyte comprises a trinitrile compound; based on the mass of the positive electrode material layer, the mass content of polysiloxane is a%, and a is more than or equal to 0.05 and less than or equal to 3. The rate capability and the storage characteristic of the battery at high temperature are improved, and particularly the thermal safety performance is improved.

Description

[0001] This application is a divisional application with application number 202410114561.8, application date January 26, 2024, and invention name “Lithium-ion battery and electronic device”. Technical Field

[0002] The present application relates to the field of energy storage, and in particular to a lithium-ion battery and an electronic device. Background Art

[0003] With the development of mobile device technology, people's demand for secondary batteries has increased significantly, especially lithium-ion batteries with high energy density, high voltage, long cycle storage and low self-discharge. However, with repeated charge and discharge, the storage performance of lithium-ion batteries decreases, which is more serious at high temperatures. The reason is that the moisture or other effects in the battery cause the electrolyte to decompose or the active material to deteriorate, resulting in an increase in the internal resistance of the battery.

[0004] Lithium cobalt oxide, the cathode material, has excellent storage characteristics and charge-discharge efficiency and is the most widely used, but 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, but the surface of the material is damaged under high temperature or high voltage, affecting the rate performance and storage characteristics of the battery.

[0005] In order to solve the above problems, people have tried various methods to coat the surface of the positive electrode active material or remove surface impurities, but none of them satisfactorily solve the above constraints. Therefore, it is urgent to develop a chemical system that solves the above problems while improving the high temperature safety performance of lithium-ion batteries. Summary of the invention

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

[0007] The present application provides a lithium-ion battery, which includes a positive electrode, a negative electrode and an electrolyte, wherein the positive electrode includes a positive electrode material layer, and the positive electrode material layer includes a ternary material and polysiloxane; the ternary material includes: nickel element, cobalt element and manganese element, and the molar content of the nickel element is greater than or equal to 50%, and the electrolyte includes a trinitrile compound, and the molar content of the nickel element is the ratio of the molar amount of the nickel element to the molar amount of the metal element other than the lithium element in the ternary material. The present application improves the rate performance and storage characteristics of the battery at high temperature, and especially improves the thermal safety performance.

[0008] According to some embodiments of the present application, the polysiloxane includes at least one of cyclopentasiloxane, cyclotrimethylsiloxane, bis-polyethylenedimethylsiloxane, polydimethylsiloxane, polymethylsiloxane or polyimidesiloxane. Preferably, cyclopentasiloxane with a macrocyclic structure can obtain better effects and the passivation film structure is stable at high temperatures.

[0009] According to some embodiments of the present application, based on the mass of the positive electrode material layer, the mass content of the polysiloxane is a%, 0.05≤a≤3, preferably 0.1≤a≤2. When the mass content of the 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 temperature.

[0010] According to some embodiments of the present application, the trinitrile compound includes: 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 at least one of 1,2,5-tris(cyanoethoxy)pentane, preferably the trinitrile compound includes: 1,3,6-hexanetricarbonitrile and 1,2,3-tris(2-cyanoethoxy)propane, thereby improving lithium ion charge transfer, improving rate, reducing gas production and improving safety performance.

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

[0012] According to some embodiments of the present 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 an embodiment of the present application, the ternary material includes lithium nickel cobalt manganese oxide. This is conducive to improving the capacity of the battery.

[0013] According to some embodiments of the present application, the electrolyte further includes a PO additive, and the PO additive includes at least one of the following compounds of Formula 1 to Formula 4:

[0014]

[0015] The above-mentioned PO additive further enhances the stability of the passivation film, thereby inhibiting the occurrence of phase change accompanying the redox process and significantly improving storage at high temperatures.

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

[0017] According to some embodiments of the present application, based on the mass of the positive electrode material layer, the mass content of the polysiloxane is a%, 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, thereby further improving the rate performance and safety performance at high temperature.

[0018] In another aspect of the present application, the present application provides an electronic device, which includes any lithium-ion battery provided in the present application.

[0019] The present application uses a combination of a specific positive electrode material layer and an electrolyte, and the design improves the rate performance and storage characteristics at high temperatures, and especially improves the thermal safety performance.

[0020] Additional aspects and advantages of the embodiments of the present application will be described, shown, or explained in part in the subsequent description through implementation of the embodiments of the present application. DETAILED DESCRIPTION

[0021] The embodiments of the present application will be described in detail below. The embodiments of the present application should not be interpreted as limiting the present application.

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

[0023] The present application uses a combination of a specific positive electrode material layer and an electrolyte, and the design significantly improves the rate performance and storage characteristics at high temperatures, especially improves the thermal safety performance.

[0024] In some embodiments, the present 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 collector and a positive electrode material layer disposed on a surface of the positive electrode collector.

[0027] The positive electrode material layer comprises a positive electrode material, and the positive electrode material layer may be one layer or multiple layers. The positive electrode material is any substance that can reversibly insert and remove lithium ions.

[0028] The present application relates to a lithium-ion battery and an electronic device. Specifically, the present application provides a lithium-ion battery, which includes: 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 side or both sides of the positive electrode current collector, the positive electrode material layer includes a ternary material and polysiloxane, the electrolyte includes a trinitrile compound, in some embodiments, the ternary material includes: nickel element, cobalt element and manganese element, the chemical composition of the ternary material in the present application contains nickel element, the molar content of nickel element is the ratio of the molar amount of nickel element to the molar amount of metal elements other than lithium element in the ternary material, and the molar content of nickel element is greater than or equal to 50%. This design improves the rate performance and storage characteristics at high temperature, especially improves the thermal safety performance.

[0029] On the one hand, due to the cation mixing effect and the changes in the surface microstructure of the material during the first charge, the first charge and discharge efficiency of the ternary material is not high, and the gas generation is serious, which makes the safety more prominent. On the other hand, the ternary material is a secondary spherical particle formed by the agglomeration of primary particles. Since the secondary particles will break under high compaction, the lithium ion diffusion coefficient and electronic conductivity are low, making the rate performance of the material unsatisfactory. In particular, for high-nickel ternary materials, as the nickel content increases, the cycle performance and thermal stability deteriorate.

[0030] The inventors of the present application found in experiments that the addition of polysiloxane during the slurry 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 the surface microstructure during the charge and discharge process, but also can increase the compaction density and reduce particle breakage. However, the stability of the passivation film decreases at high temperatures. The inventors further found that when the positive electrode is in an electrolyte system containing a trinitrile compound, the trinitrile compound 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 obtains excellent safety performance.

[0031] In some embodiments, the polysiloxane in the positive electrode may be present in the positive electrode material layer in the form of particles, and the polysiloxane may be mixed with the particles of the ternary material. In other embodiments, the polysiloxane may also be present on the surface of the ternary material in the form of a coating layer. Regardless of the form in which the polysiloxane exists in the positive electrode material layer, as the lithium-ion battery is charged and discharged, the part of the polysiloxane in contact with the ternary material can form a passivation film on the surface of the ternary material, and because the presence of the trinitrile compound can inhibit the high-temperature decomposition of the passivation film, the synergistic effect of the ternary material, polysiloxane and the trinitrile compound is achieved to obtain excellent rate performance, storage characteristics and safety performance.

[0032] In some embodiments, the polysiloxane includes at least one of cyclopentasiloxane (Formula 5), ​​cyclotrimethylsiloxane, bis-polyethylenedimethylsiloxane, polydimethylsiloxane, polymethylsiloxane or polyimidesiloxane. Preferably, cyclopentasiloxane having a macrocyclic structure, such as the structure of Formula 5 shown below, can obtain better effects, and the passivation film structure is stable at high temperature and is not easy to decompose.

[0033]

[0034] In some embodiments, based on the mass of the positive electrode material layer, the mass content of polysiloxane in the positive electrode material layer is a%, wherein 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 consisting 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 the present application, the molar content of nickel in the ternary material is greater than or equal to 60%. Optionally, the molar content of nickel in the ternary material is greater than or equal to 80%.

[0036] According to some embodiments of the present 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. The type of positive electrode conductive material is not limited, and 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 positive electrode conductive materials may be used alone or in any combination.

[0038] The positive electrode material layer also includes a positive electrode binder. The type of the positive electrode binder is not particularly limited, as long as it is a material that can be dissolved or dispersed in the liquid medium used in electrode manufacturing. Examples of positive electrode binders 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, 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; fluorine-based polymers such as polyvinylidene fluoride, polytetrafluoroethylene, fluorinated polyvinylidene fluoride, and polytetrafluoroethylene-ethylene copolymers; polymer compositions having ion conductivity of alkali metal ions (especially lithium ions), etc. The above positive electrode binders may 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 that can dissolve or disperse the positive electrode material, the conductive material, the positive electrode binder, and the thickener used as needed. Examples of solvents used to form positive electrode slurries may include any of aqueous solvents and organic solvents. Examples of aqueous media may include, but are not limited to, water and mixed media 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, 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; non-protonic polar solvents such as hexamethylphosphoramide and dimethyl sulfoxide, etc.

[0040] In some embodiments, the positive electrode material layer further includes a thickener. The thickener is generally used to adjust the viscosity of the slurry. In the case of using an aqueous medium, a thickener and a styrene-butadiene rubber emulsion can be used for slurrying. The type of thickener is not particularly limited, and examples thereof may include, but are not limited to, carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein, and salts thereof. The above thickeners may 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, metal materials such as aluminum, stainless steel, nickel plating, titanium, tantalum, and carbon materials such as carbon cloth and carbon paper. In some embodiments, the positive electrode current collector is a metal material. In some embodiments, the positive electrode current collector is aluminum.

[0042] In some embodiments, in order to reduce the electronic contact resistance between the positive electrode current collector and the positive electrode material layer, the surface of the positive electrode 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 an inorganic oxide, a conductive agent, and a binder.

[0043] In some embodiments, the positive electrode can be made 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 a conventional method, that is, the positive electrode material and the binder, as well as the conductive material and the thickener as needed, are dry mixed to form a sheet, and the obtained sheet is pressed onto the positive electrode current collector; or these materials are dissolved or dispersed in a liquid medium to form a slurry, and the slurry is applied to the positive electrode current collector and dried to form a positive electrode material layer on the current collector, thereby obtaining a positive electrode.

[0044] II. Electrolyte

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

[0046] The passivation film formed by polysiloxane on the surface of ternary materials has the problem of being not resistant to high temperatures. The present application finds that when the electrolyte contains trinitrile compounds, the stability of the passivation film formed by polysiloxane on the surface of high-nickel ternary materials at high temperatures can be enhanced, and the reaction at the interface between the electrolyte and the positive electrode material can be inhibited, which not only improves lithium ion charge transfer and improves the rate, but also reduces gas production and improves safety performance.

[0047] According to an embodiment of the present application, the trinitrile compound includes: at least one of 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, based on the mass of the electrolyte, the mass content of the trinitrile compound in the electrolyte is b%, 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 the 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 the rate and safety performance.

[0049] According to some embodiments of the present 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 in a range consisting of any two of the above values. When a / b meets the above ratio, the rate performance and safety performance at high temperature can be further improved.

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

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

[0053]

[0054] The above-mentioned PO additive further enhances the stability of the passivation film, thereby inhibiting the occurrence of phase change accompanying the redox process and significantly improving storage at high temperatures.

[0055] In some embodiments, the mass content of the PO additive is c%, based on the mass of the electrolyte, wherein 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 the 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 consisting of any two of the above values. When a / c satisfies the above ratio, the rate performance and safety performance at high temperature can be further improved.

[0057] In some embodiments, the electrolyte further comprises any non-aqueous solvent known in the prior art that can be used as a solvent for the 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 carboxylates, chain carboxylates, cyclic ethers, chain ethers, phosphorus-containing organic solvents, and sulfur-containing organic solvents.

[0059] In some embodiments, the solvent used in the electrolyte of the present application includes cyclic carbonates, chain carbonates, cyclic carboxylates, chain carboxylates, and combinations thereof. In some embodiments, the solvent used in the electrolyte of the present application includes an organic solvent selected from the group consisting of the following substances: 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 the present application includes: 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 arbitrarily. The quality of the electrolyte is not particularly limited as long as it does not impair the effects of the present 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 sides of the negative electrode current collector, wherein the negative electrode material layer contains a negative electrode material. In some embodiments, the chargeable capacity of the negative electrode material is greater than the discharge capacity of the positive electrode material to prevent lithium metal from being accidentally precipitated on the negative electrode during charging.

[0063] In some embodiments, as the negative electrode current collector for holding the negative electrode material, any known current collector may be used. Examples of the negative electrode current collector include, but are not limited to, metal materials such as copper, nickel, stainless steel, and nickel-plated steel. In some embodiments, the negative electrode 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. Negative electrode materials may 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 can improve the bonding between the negative electrode material particles and the bonding between the negative electrode material and the current collector. The type of negative electrode binder is not particularly limited, as long as it is a material that is stable to the solvent used in the manufacture of the electrolyte or electrode. In some embodiments, the negative electrode binder includes a resin binder. Examples of resin binders include, but are not limited to, fluororesins, polyacrylonitrile (PAN), polyimide resins, acrylic resins, polyolefin resins, and the like. When an aqueous solvent is used to prepare the negative electrode mixture slurry, the negative electrode binder includes, but is not limited to, carboxymethyl cellulose (CMC) or its salt, styrene-butadiene rubber (SBR), polyacrylic acid (PAA) or its salt, polyvinyl alcohol, and the like.

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

[0067] IV. Isolation membrane

[0068] In some embodiments, in order to prevent short circuit, a separator may be provided between the positive electrode and the negative electrode. In this case, the electrolyte of the present application may generally be used by permeating the separator.

[0069] In some embodiments, there is no particular restriction on the material and shape of the isolation membrane, as long as the effect of the present application is not significantly impaired. The isolation membrane may be a resin, glass fiber, inorganic substance, etc. formed of a material that is stable to the electrolyte of the present application. In some embodiments, the isolation membrane includes a porous sheet or a non-woven fabric-like material with excellent liquid retention. Examples of materials for resin or glass fiber isolation membranes may include, but are not limited to, polyolefins, aromatic polyamides, polytetrafluoroethylene, polyether sulfone, etc. In some embodiments, the polyolefin is polyethylene or polypropylene. In some embodiments, the polyolefin is polypropylene. The materials of the above isolation membranes may be used alone or in any combination.

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

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

[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 films, etc. In the thin film form, the separator has a pore size of 0.01 μm to 1 μm and a thickness of 5 μm to 50 μm. In addition to the above-mentioned independent thin film separators, the following separators can also be used: a separator formed by forming a composite porous layer containing the above-mentioned inorganic particles on the surface of the positive electrode and / or the negative electrode using a resin-based adhesive, for example, a separator formed by using fluororesin as an adhesive to form a porous layer on both sides of the positive electrode with 90% of the aluminum oxide particles having a particle size less than 1 μm.

[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 range, insulation and mechanical strength can be ensured, and the rate characteristics and energy density of the lithium-ion battery can be ensured.

[0074] The present application further provides an electronic device, which includes a lithium-ion battery according to any one of the present applications.

[0075] The use of the lithium-ion battery of the present 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 the present application can be used for, but not limited to, laptop computers, pen-input computers, mobile computers, e-book players, portable phones, portable fax machines, portable copiers, portable printers, head-mounted stereo headphones, video recorders, LCD televisions, portable cleaners, portable CD players, mini-discs, transceivers, electronic notepads, calculators, memory cards, portable recorders, radios, backup power supplies, motors, cars, motorcycles, power-assisted bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries and lithium-ion capacitors, etc.

[0076] The preparation of lithium-ion batteries is described below in conjunction with specific embodiments. Those skilled in the art will understand that the preparation method described in this application is only an example, and any other suitable preparation method is within the scope of this application.

[0077] 1. Preparation of lithium-ion batteries

[0078] 1. Preparation of 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 evenly to obtain a slurry. The slurry was coated on a 9μm thick copper foil. After drying and cold pressing, the negative electrode was obtained by cutting and welding the tabs.

[0080] 2. Preparation of positive electrode

[0081] The ternary material, 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 stirred evenly to obtain a positive electrode slurry. The positive electrode slurry was coated on a 12μm thick aluminum foil, dried, cold pressed, and then cut and welded to obtain a positive electrode. The specific ternary materials used refer to the embodiment table.

[0082] 3. Preparation of electrolyte

[0083] In a dry argon environment, 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%. 4.3% by mass of fluoroethylene carbonate, 3.2% by mass of adiponitrile, trinitrile compound and PO additive were added to the basic electrolyte to obtain electrolytes of different embodiments and comparative examples.

[0084] 4. Preparation of isolation membrane

[0085] A 7-micron thick polyethylene porous 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 order and placed in an outer packaging foil, leaving a liquid injection port. The electrolyte is poured from the liquid injection port, packaged, and then subjected to conventional processes such as formation to obtain a lithium-ion battery.

[0088] 2. Test Method

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

[0090] At 65°C, the lithium-ion battery is charged to 4.3V at 1C constant current, then charged to 0.05C at 4.3V constant voltage, and then discharged to 2.0V at 1C constant current. This is the first cycle. The lithium-ion battery is cycled 1000 times under the above conditions. "1C" is the current value that completely discharges the battery capacity within 1 hour.

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

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

[0093] 2. Rate performance test of lithium-ion batteries at high temperature

[0094] At 60°C, 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 perform discharge tests at 0.2C and 5.0C to obtain discharge capacity 1 and discharge capacity 2 respectively.

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

[0096] 3. Test of thickness expansion rate of lithium-ion battery due to thermal abuse

[0097] At 25°C, let the lithium-ion battery stand for 30 minutes, measure the thickness H1 of the lithium-ion battery, and then start heating at a heating rate of 5°C / min. When the temperature rises to 130°C, keep it for 30 minutes, and measure the thickness H2 of the lithium-ion battery. The thermal abuse thickness expansion rate of the lithium-ion battery is calculated by the following formula:

[0098] Expansion ratio = [(H2-H1) / H1] x 100%.

[0099] 3. 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 positive electrode material layer, the mass content of polysiloxane is a%. The polysiloxanes used in Table 1 are as follows: cyclopentapolydimethylsiloxane (S1), cyclotripolydimethylsiloxane (S2), bisethylenepolydimethylsiloxane (S3), polydimethylsiloxane (S4), polymethylsiloxane (S5), polyimidesiloxane (S6). The positive electrode active materials used are commercially available NCM532, NCM622, and NCM811 (NCM532 means that the metal elements other than lithium in the ternary material are basically Ni, Co, and Mn, and the molar ratio of Ni, Co, and Mn is 5:3:2, and 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 brackets are mass content.

[0107] When the positive electrode material layer includes polysiloxane and the electrolyte includes a trinitrile compound, the ternary material and the polysiloxane are first evenly dispersed in the preparation of the positive electrode, which not only forms a passivation film rich in Si-O bonds on the surface of the ternary material to inhibit the destruction of the surface microstructure during the charge and discharge process, but also can increase the compaction density and reduce particle breakage. However, the stability of the passivation film decreases at high temperatures. The inventors also found that when the positive electrode is in an electrolyte system containing a trinitrile compound, the trinitrile compound inhibits the high-temperature decomposition of the passivation film, which not only improves the rate performance and storage characteristics at high temperatures, but also obtains satisfactory safety performance.

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

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

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

[0111] When the nickel content in the ternary material is higher, especially when the molar content of nickel is greater than or equal to 60%, the polysiloxane and trinitrile compounds are more beneficial to its protection. The trinitrile compound significantly improves the stability of the protective film formed by polysiloxane on the surface of the ternary material at high temperature, inhibits phase change, improves the thermal stability of the ternary material, and can further improve battery performance.

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

[0113] Table 2

[0114]

[0115]

[0116] The results show that when the positive electrode material layer includes polysiloxane and the electrolyte includes trinitrile compounds and PO additives, unexpected thermal safety performance is obtained. This may be because the PO additive can delay the inward transfer of heat generated by side reactions on the surface of the material, 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, thereby further improving the thermal safety performance of lithium-ion batteries.

[0117] When the mass content of the PO additive is 0.1% to 5%, the battery performance can be further improved. In particular, when the mass content of the trinitrile compound and the PO additive simultaneously satisfies 0.5≤c≤4 and 0.1≤a / c≤1, further improvement is achieved, and the improvement in thermal safety performance is particularly obvious.

[0118] References to "embodiments", "partial embodiments", "one embodiment", "another example", "example", "specific example" or "partial example" throughout the specification mean that at least one embodiment or example in the present application includes the specific features, structures, materials or characteristics described in the embodiment or example. Therefore, descriptions appearing in various places throughout the specification, such as: "in some embodiments", "in an embodiment", "in one embodiment", "in another example", "in an example", "in a specific example" or "example", do not necessarily refer to the same embodiment or example in the present application. In addition, the specific features, structures, materials or characteristics in the present application may be combined in one or more embodiments or examples in any suitable manner.

[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 limitations on the present application, and that changes, substitutions and modifications may 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 comprises a positive electrode material layer, and the positive electrode material layer comprises: a ternary material and polysiloxane; The ternary material comprises: nickel, cobalt and manganese; the molar content of the nickel is greater than or equal to 50%; the electrolyte comprises a trinitrile compound; the molar content of the nickel is the ratio of the molar amount of the nickel element to the molar amount of the metal element other than lithium in the ternary material; The polysiloxane comprises at least one of cyclopentasiloxane, cyclotrimethylsiloxane, bis-ethylenedimethylsiloxane, polydimethylsiloxane, polymethylsiloxane or polyimidesiloxane; based on the mass of the positive electrode material layer, the mass content of the polysiloxane is a%, 0.05≤a≤3; The trinitrile compound includes at least one of 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%, wherein 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 compound includes: 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 includes at least one of the compounds of Formula 1 to Formula 4 below:

7. The lithium-ion battery according to claim 6, characterized in that: Satisfy 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 the nickel element is greater than or equal to 80%.

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

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