Patent Application
20240304822
The present disclosure generally relates to a technical field of energy storage electronics, and more particularly to a positive electrode sheet and a lithium-ion battery.
Lithium-ion batteries have been widely used as power sources in life due to their irreplaceable advantages of a low self-discharge rate, a long cycle life, a high operating voltage, a low pollution and so on. The lithium-ion batteries have broad prospects in mobile communications, notebook computers, new energy vehicles and so on. At the same time, users also make requirements for the lithium-ion batteries, such as a high energy density, a fast charging and so on.
In the lithium-ion battery system, in order to improve the energy density of the battery, the industry continues to improve the operating voltage of the battery. When the voltage of the lithium battery is greater than or equal to 4.25 V, the decomposition of an electrolyte is aggravated and by-products are increased. Therefore, after being cycled or stored at a high temperature, the battery will suffer from problems of a gas generation, a capacity degradation and a continuous increase in a direct current impedance, resulting in a decrease in power performance of the battery. The existing methods to improve the cycling performance of the battery are mainly to add an electrolyte additive to a non-aqueous electrolyte. The existing electrolyte additive can improve the high-temperature cycling of a high-voltage battery, the problem of the gas expansion after storage and the problem of capacity degradation to a certain extent, but the problem of excessive increase in the direct current impedance still needs to be solved.
In a first aspect, the present disclosure provides a positive electrode sheet, including: a positive electrode current collector and a positive electrode material layer formed on the positive electrode current collector. The positive electrode sheet has a potential range of greater than or equal to 4.25 V with respect to metal lithium, and the positive electrode material layer includes a positive electrode active material doped or coated with metal elements and a compound represented by formula I:
In some embodiments, the positive electrode sheet satisfies a following condition:
In some embodiments, the positive electrode active material is selected from a compound represented by formula (1) and/or formula (2):
Li1+xNiaCobM1cM21−a−b−cO2−yAy Formula (1)
Li1+zMneL2−eO4−dBd Formula (2)
In some embodiments, the content m of the compound represented by the formula I in the positive electrode material layer is from 50 ppm to 5000 ppm.
In some embodiments, the total content n of the metal elements doped and coated in the positive electrode material layer is from 100 ppm to 3000 ppm.
In some embodiments, the compacted density k of the positive electrode material layer is from 3.0 to 3.6 g/cm3.
In some embodiments, a thickness of the positive electrode material layer on one side of the positive electrode current collector is from 80 to 200 μm, and a one-side areal density of the positive electrode material layer is from 15 to 30 mg/cm2.
In some embodiments, the alkyl group of 1 to 5 carbon atoms is selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, sec-pentyl, or neopentyl; the fluoroalkyl group of 1 to 5 carbon atoms is selected from a group obtained by substituting one or more hydrogen elements in the alkyl group of 1 to 5 carbon atoms with fluorine elements. The unsaturated hydrocarbonyl group of 2 to 5 carbon atoms is selected from vinyl, propenyl, allyl, butenyl, pentenyl, methyl vinyl, methyl allyl, ethynyl, propynyl, propargyl, butynyl, or pentynyl. The ether group of 1 to 5 carbon atoms is selected from methyl ether, ethyl ether, methyl ethyl ether, propyl ether, methyl propyl ether, or ethyl propyl ether. The fluoroether group of 1 to 5 carbon atoms is selected from fluoromethyl ether, fluoroethyl ether, fluoromethyl ethyl ether, fluoropropyl ether, fluoromethyl propyl ether, and fluoroethyl propyl ether.
In some embodiments, the compound represented by the formula I is selected from at least one of tripropargyl phosphate, dipropargyl methyl phosphate, dipropargyl fluoromethyl phosphate, dipropargyl methoxymethyl phosphate, dipropargyl ethyl phosphate, dipropargyl propyl phosphate, trifluoromethyl dipropargyl phosphate, dipropargyl 2,2,2-trifluoroethyl phosphate, dipropargyl 3,3,3-trifluoropropyl phosphate, hexafluoroisopropyl dipropargyl phosphate, triallyl phosphate, diallyl methyl phosphate, diallyl ethyl phosphate, diallyl propyl phosphate, trifluoromethyl diallyl phosphate, dipropargyl methyl ether phosphate, dipropargyl fluoromethyl ether phosphate, diallyl 2,2,2-trifluoroethyl phosphate, diallyl 3,3,3-trifluoropropyl phosphate, or diallyl hexafluoroisopropyl phosphate.
In a second aspect, the present disclosure provides a lithium-ion battery, including: a negative electrode sheet, a non-aqueous electrolyte, and the above-mentioned positive electrode sheet.
In order that the technical problems, technical solutions and advantageous effects to be solved by the present disclosure can be more clearly understood, the present disclosure will be described in further detail with reference to the accompanying drawings and the embodiments. It should be understood that the particular embodiments described herein are only used to explain the present disclosure, but are not intended to limit the present disclosure.
The embodiments of the present disclosure provide a positive electrode sheet including a positive electrode current collector and a positive electrode material layer formed on the positive electrode current collector, in which the positive electrode sheet has a potential range of greater than or equal to 4.25 V with respect to metal lithium, and the positive electrode material layer includes a positive electrode active material doped or coated with metal elements and a compound represented by formula I:
The method of performing the liquid chromatography-mass spectrometer chromatographic analysis on the positive electrode sheet is as follows: the battery is disassembled in a glove box and the positive electrode sheet is taken out. Then, the cut positive electrode sheet is immersed in a suitable solvent (such as DMC, or acetonitrile), and subjected to ultrasonic vibration for a suitable time to dissolve the substance in the positive electrode material layer of the positive electrode sheet into the solvent. Then, the solution is detected by the liquid chromatography-mass spectrometer (LC-MS), and has a characteristic peak in a region of a retention time of 6.5 min to 7.5 min, as shown in
In some embodiments, the duration of ultrasonic vibration of the positive electrode sheet in the solvent is 2 hours or more.
In the present disclosure, the alkyl group of 1 to 5 carbon atoms can be selected from, for example, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, sec-pentyl, or neopentyl. The fluoroalkyl group of 1 to 5 carbon atoms is selected from a group obtained by substituting one or more hydrogen elements in the alkyl group of 1 to 5 carbon atoms (such as the above-mentioned groups) with fluorine elements.
The unsaturated hydrocarbonyl group of 2 to 5 carbon atoms can be selected from, for example, vinyl, propenyl, allyl, butenyl, pentenyl, methyl vinyl, methyl allyl, ethynyl, propynyl, propargyl, butynyl, or pentynyl.
The ether group of 1 to 5 carbon atoms can be selected from, for example, methyl ether, ethyl ether, methyl ethyl ether, propyl ether, methyl propyl ether, or ethyl propyl ether.
The fluoroether group of 1 to 5 carbon atoms can be selected from, for example, fluoromethyl ether, fluoroethyl ether, fluoromethyl ethyl ether, fluoropropyl ether, fluoromethyl propyl ether, or fluoroethyl propyl ether.
The compound represented by the formula I is added into the positive electrode material layer. At the same time, the relationship between the mass percent content m of the compound represented by the formula I in the positive electrode material layer, the total content n of metal elements doped in and/or coated on the positive electrode material in the positive electrode active layer, and the compacted density k of the positive electrode material layer is rationally designed. When the positive electrode material layer satisfies the condition
the synergistic effect of the compound represented by the formula I with the doped elements of the positive electrode active material and the positive electrode compacted density can be exerted sufficiently, so that the positive electrode active material has a high structural stability. Therefore, side reactions between the surface of the positive electrode material layer and the non-aqueous electrolyte are significantly reduced in the battery, and the increase in the positive electrode impedance during the high-temperature cycling/storage is reduced, in particular, the high-temperature performance of the battery is greatly improved.
In preferred embodiments, the positive electrode sheet satisfies a following condition:
When the content m of the compound represented by the formula I in the positive electrode material layer, the total content n of the doped and coated metal elements in the positive electrode material layer, and the compacted density k of the positive electrode material layer satisfy the above condition, it is beneficial to further reduction in the impedance increase of the battery and improve the high-temperature cycling performance of the battery.
In some embodiments, the positive electrode active material is selected from a compound represented by formula (1) and/or formula (2):
Li1+xNiaCobM1cM21−a−b−cO2−yAy Formula (1)
Li1+zMneL2−eO4−dBa Formula (2)
In specific embodiments, the positive electrode active material includes a positive electrode active material matrix and doped and/or coated metal elements, in which the positive electrode active material matrix includes at least one of LiNi0.5Co0.2Mn0.3O2, LiNi0.6Co0.2Mn0.2O2, LiNi0.7Co0.1Mn0.2O2, LiNi0.5Co0.1Mn0.1O2, and LiMn2O4, and the doped and/or coated metal elements include one or more of W, Mg, Ti, Ca, Zr, Zn, Si, Fe, and Ce.
In specific embodiments, the positive electrode active material matrix is LiNi0.5Co0.2Mn0.3O2, and the potential range of the positive electrode sheet relative to metal lithium is greater than or equal to 4.35 V.
In specific embodiments, the positive electrode active material matrix is LiNi0.6Co0.2Mn0.2O2, and the potential range of the positive electrode sheet relative to metal lithium is greater than or equal to 4.35 V.
In specific embodiments, the positive electrode active material matrix is LiNi0.7Co0.1Mn0.2O2, and the potential range of the positive electrode sheet relative to metal lithium is greater than or equal to 4.30 V.
In specific embodiments, the positive electrode active material matrix is LiNi0.5Co0.1Mn0.1O2, and the potential range of the positive electrode sheet relative to metal lithium is greater than or equal to 4.25 V. In specific embodiments, the positive electrode active material matrix is LiMn2O4, and the potential range of the positive electrode sheet relative to metal lithium is greater than or equal to 4.35 V.
In embodiments of the present disclosure, the content m of the compound represented by the formula I in the positive electrode material layer is in a range of 50 ppm to 10000 ppm. In specific embodiments, the content m of the compound represented by the formula I in the positive electrode material layer can be 50 ppm, 60 ppm, 80 ppm, 90 ppm, 100 ppm, 150 ppm, 200 ppm, 300 ppm, 400 ppm, 500 ppm, 700 ppm, 900 ppm, 1000 ppm, 1500 ppm, 2000 ppm, 3000 ppm, 4000 ppm, 5000 ppm, 6000 ppm, 7000 ppm, 8000 ppm, 9000 ppm or 10000 ppm.
In preferred embodiments, the content m of the compound represented by the formula I in the positive electrode material layer is from 50 ppm to 5000 ppm.
The compound represented by the formula I participates in the formation of a passivation film on the surface of the positive electrode active material, which is beneficial to avoidance of a direct contact between the positive electrode material layer and the non-aqueous electrolyte, reduction in a decomposition reaction of the non-aqueous electrolyte on the positive electrode material layer, and improvement of the stability of the positive electrode active material and the stability of the battery at a high temperature. In the positive electrode material layer, if the content of the compound represented by the formula I is too small, then its passivation effect on the positive electrode material is limited, so that the effect of improving the high-temperature performance of the battery is not apparent; otherwise, if the content of the compound represented by the formula I is too large, then the film formed on the surface of the positive electrode active material is thicker, and the internal resistance of the battery is greater.
In embodiments of the present disclosure, the total content n of the metal elements doped and coated in the positive electrode material layer is from 50 ppm to 10000 ppm. In specific embodiments, the total content n of the metal elements doped and coated in the positive electrode material layer can be 50 ppm, 60 ppm, 80 ppm, 90 ppm, 100 ppm, 150 ppm, 200 ppm, 300 ppm, 400 ppm, 500 ppm, 700 ppm, 900 ppm, 1000 ppm, 1500 ppm, 2000 ppm, 3000 ppm, 4000 ppm, 5000 ppm, 6000 ppm, 7000 ppm, 8000 ppm, 9000 ppm or 10000 ppm.
In preferred embodiments, the total content n of the metal elements doped and coated in the positive electrode material layer is from 100 ppm to 3000 ppm.
By doping or coating metal elements in the positive electrode material layer, it is beneficial to improvement of the stability of the positive electrode active material. Specifically, a nickel-cobalt-manganese ternary material, a nickel-cobalt-aluminum ternary material or lithium manganate can be used as the positive electrode active material matrix. The positive electrode active material matrix is doped or coated to obtain the positive electrode active material. When the doping process is performed, the metal elements are embedded in a lattice of the positive electrode active material matrix to replace part of cobalt, nickel, manganese or aluminum position to form a stable doped state and suppress the dissolution of metal ions. When the coating process is performed, the metal elements are coated on the outer surface of the positive electrode active material in the form of an oxide or a metal salt, to avoid direct contact between the positive electrode active material and the non-aqueous electrolyte. The higher the content of doped or coated metal elements in the positive electrode material, the better the structural stability of the positive electrode material and the better the high-temperature storage performance. However, when the content of the doped or coated metal elements is too large, the impedance of the material will increase.
In embodiments of the present disclosure, the compacted density k of the positive electrode material layer is from 2.8 to 3.8 g/cm3. In specific embodiments, the compacted density k of the positive electrode material layer is 2.8 g/cm3, 2.9 g/cm3, 3.0 g/cm3, 3.1 g/cm3, 3.2 g/cm3, 3.3 g/cm3, 3.4 g/cm3, 3.5 g/cm3, 3.6 g/cm3, 3.7 g/cm3 or 3.8 g/cm3.
In preferred embodiments, the compacted density k of the positive electrode material layer is from 3.0 to 3.6 g/cm3.
The compacted density of the positive electrode material layer is related to its porosity. Within a certain range, the smaller the compacted density, the more developed its pore structure, the more benefited the liquid phase conduction of active ions, and the better the high-temperature performance. However, if the compacted density of the positive electrode material layer is too small, it will cause electrode powders to fall off, and if the compacted density is too high, it will lead to poor electrolyte infiltration and poor high-temperature performance.
In some embodiments, a thickness of the positive electrode material layer on one side of the positive electrode current collector is from 80 to 200 μm.
In preferred embodiments, the thickness of the positive electrode material layer on one side of the positive electrode current collector is from 100 to 150 μm.
The thickness of the positive electrode material layer on one side of the positive electrode current collector is also a key technical parameter in the design and manufacture of the lithium-ion battery. Under the same electrode size, the greater the thickness of the positive electrode material layer on one side of the positive electrode current collector, the higher the energy density of the battery, but the internal resistance will further increase. While the thickness of the positive electrode material layer on one side of the positive electrode current collector decreases, the energy density of the battery decreases, which is not conducive to commercial applications.
In some embodiments, a one-side areal density of the positive electrode material layer is from 15 to 30 mg/cm2.
In some embodiments, the particle diameter D50 of the positive electrode active material is from 1 to 30 μm.
In some embodiments, the compound represented by the formula I is selected from at least one of tripropargyl phosphate, dipropargyl methyl phosphate, dipropargyl fluoromethyl phosphate, dipropargyl methoxymethyl phosphate, dipropargyl ethyl phosphate, dipropargyl propyl phosphate, trifluoromethyl dipropargyl phosphate, dipropargyl 2,2,2-trifluoroethyl phosphate, dipropargyl 3,3,3-trifluoropropyl phosphate, hexafluoroisopropyl dipropargyl phosphate, triallyl phosphate, diallyl methyl phosphate, diallyl ethyl phosphate, diallyl propyl phosphate, trifluoromethyl diallyl phosphate, dipropargyl methyl ether phosphate, dipropargyl fluoromethyl ether phosphate, 2,2,2-trifluoroethyl diallyl phosphate, diallyl 3,3,3-trifluoropropyl phosphate, or diallyl hexafluoroisopropyl phosphate.
In preferred embodiments, the compound represented by the formula I is selected from one or more of following compounds:
In some embodiments, the positive electrode material layer further includes a positive electrode binder and a positive electrode conductive agent. The positive electrode active material, the compound represented by the formula I, the positive electrode binder and the positive electrode conductive agent are blended to obtain the positive electrode material layer.
With a total mass of the positive electrode material layer being 100%, a mass percent content of the positive electrode binder is from 1 to 2%, and a mass percent content of the positive electrode conductive agent is from 0.5 to 2%.
The positive electrode binder includes one or more of thermoplastic resins such as polyvinylidene fluoride, vinylidene fluoride copolymers, polytetrafluoroethylene, vinylidene fluoride-hexafluoropropylene copolymers, tetrafluoroethylene-hexafluoropropylene copolymers, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymers, ethylene-tetrafluoroethylene copolymers, vinylidene fluoride-tetrafluoroethylene copolymers, vinylidene fluoride-trifluoroethylene copolymers, vinylidene fluoride-trichloroethylene copolymers, vinylidene fluoride-fluoroethylene copolymers, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymers, thermoplastic polyimides, polyethylene and polypropylene and so on; acrylic resins; sodium carboxymethyl cellulose; polyvinyl butyral; ethylene-vinyl acetate copolymers; polyvinyl alcohol; and styrene butadiene rubbers.
The positive electrode conductive agent includes one or more of conductive carbon black, conductive carbon spheres, conductive graphite, conductive carbon fibers, carbon nanotubes, graphene or reduced graphene oxide.
In some embodiments, the compound represented by the formula I is formed on the surface of the positive electrode material layer, or the compound represented by the formula I is mixed in the interior of the positive electrode material layer.
When the compound represented by the formula I is formed on the surface of the positive electrode material layer, its preparation method can be a method as follows:
A coating containing the compound represented by the formula I is formed on a surface of the positive electrode material layer by means of surface coating. Specifically, the positive electrode active material, the positive electrode conductive agent and the positive electrode binder can be dispersed in an organic solvent firstly, preparing a positive electrode slurry. The positive electrode slurry is coated and dried to form the positive electrode material layer. Then, the compound represented by the formula I is dispersed in an organic solvent, and the obtained solution of the compound represented by the formula I is sprayed on the surface of the positive electrode material layer. After drying it to remove the solvent, the positive electrode material layer including the compound represented by the formula I is obtained.
When the compound represented by the formula I is mixed in the interior of the positive electrode material layer, its preparation method can be a method as follows:
In some embodiments, the positive electrode current collector is selected from metal materials that can conduct electrons. Preferably, the positive electrode current collector includes one or more of Al, Ni, tin, copper, and stainless steel. In more preferred embodiments, the positive current collector is selected from aluminum foil.
Another embodiment of the present disclosure provides a lithium-ion battery including a negative electrode sheet, a non-aqueous electrolyte, and the above-mentioned positive electrode sheet.
In some embodiments, the non-aqueous electrolyte includes anon-aqueous organic solvent, and the non-aqueous organic solvent includes one or more of an ether solvent, a nitrile solvent, a carbonate solvent, and a carboxylate solvent.
In some embodiments, the ether solvent includes cyclic ethers or linear ethers, preferably linear ethers with 3 to 10 carbon atoms and cyclic ethers with 3 to 6 carbon atoms. The cyclic ethers can specifically be, but are not limited to, one or more of 1,3-dioxolane (DOL), 1,4-dioxane (DX), crown ethers, tetrahydrofuran (THF), 2-methyl tetrahydrofuran (2-CH3-THF), and 2-trifluoromethyl tetrahydrofuran (2-CF3-THF); and the linear ethers can specifically be, but are not limited to, dimethoxymethane, diethoxymethane, ethoxymethoxymethane, ethylene glycol di-n-propyl ether, ethylene glycol di-n-butyl ether, and diethylene glycol dimethyl ether. Dimethoxymethane, diethoxymethane, and ethoxymethoxymethane, which are low in viscosity and impart high ion conductivity, are particularly preferred because the solvation ability of linear ethers with lithium ions is high and ion dissociation can be improved. One kind of ether compound may be used alone, or two or more kinds of ether compounds may be used in any combination and ratio. The addition amount of the ether compounds is not particularly limited, and it is arbitrary within a range of not significantly destroying the effect of the high-compacted lithium-ion battery in the present disclosure. The addition amount of the ether compounds is usually 1% or more by volume, preferably 2% or more by volume, more preferably 3% or more by volume, in addition, usually 30% or less by volume, preferably 25% or less by volume, more preferably 20% or less by volume of the ether compounds in the non-aqueous solvent of 100% by volume. When two or more ether compounds are used in combination, the total amount of the ether compounds needs to satisfy the above ranges. When the addition amount of the ether compounds is within the above-mentioned preferred ranges, it is easy to ensure the effect of improving the ion conductivity by increasing the lithium-ion dissociation degree of the chain ethers and reducing the viscosity. In addition, when the negative electrode active material is a carbon material, co-intercalation of the chain ethers and lithium ions can be suppressed, so that input-output characteristics and charge-discharge rate characteristics can be brought into appropriate ranges.
In some embodiments, the nitrile solvent may specifically be, but is not limited to, one or more of acetonitrile, glutaronitrile, and malononitrile.
In some embodiments, the carbonate solvent includes cyclic carbonates or linear carbonates, the cyclic carbonates can specifically be, but are not limited to, one or more of ethylene carbonate (EC), propylene carbonate (PC), γ-butyrolactone (GBL), and butylene carbonate (BC); and the linear carbonates can specifically be, but are not limited to, one or more of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and dipropyl carbonate (DPC). The content of the cyclic carbonates is not particularly limited, and it is arbitrary within a range of not significantly destroying the effect of the lithium-ion battery in the present disclosure. However, in the case of using one kind of cyclic carbonate alone, the lower limit of the content of the cyclic carbonates is usually 3% or more by volume, and preferably 5% or more by volume, relative to the total amount of the solvent in the non-aqueous electrolyte. By setting this range, it is possible to avoid a decrease in conductivity due to a decrease in the dielectric constant of the non-aqueous electrolyte, and it is easy to make the large-current discharge characteristics, stability with respect to the negative electrode, and cycle characteristics of the non-aqueous electrolyte battery reach good ranges. In addition, the upper limit is usually 90% or less by volume, preferably 85% or less by volume, and more preferably 80% or less by volume. By setting this range, the oxidation/reduction resistance of the non-aqueous electrolyte can be improved, thereby contributing to the improvement of the stability during high-temperature storage. The content of the linear carbonates is not particularly limited, but is usually 15% or more by volume, preferably 20% or more by volume, and more preferably 25% or more by volume relative to the total amount of the solvent in the non-aqueous electrolyte. In addition, the volume percent is usually 90% or less, preferably 85% or less, and more preferably 80% or less. By making the content of the linear carbonates within the above ranges, it is easy to make the viscosity of the non-aqueous electrolyte in an appropriate range, suppress the decrease in ion conductivity, and thus contribute to making the output characteristics of the non-aqueous electrolyte battery reach a good range. When two or more linear carbonates are used in combination, the total amount of the linear carbonates needs to satisfy the above ranges.
In some embodiments, linear carbonates having fluorine atoms (hereinafter simply referred to as “fluorinated linear carbonates”) may further be preferably used. The number of fluorine atoms in the fluorinated linear carbonates is not particularly limited as long as it is 1 or more, but is usually 6 or less, and preferably 4 or less. When the fluorinated linear carbonates have a plurality of fluorine atoms, the fluorine atoms may be bonded to the same carbon or to different carbons. Examples of the fluorinated linear carbonates include fluorinated dimethyl carbonate derivatives, fluorinated ethyl methyl carbonate derivatives, and fluorinated diethyl carbonate derivatives.
The carboxylate solvent includes cyclic carboxylates and/or linear carbonates. Examples of the cyclic carboxylates include one or more of γ-butyrolactone, γ-valerolactone, and δ-valerolactone. Examples of the linear carbonates include one or more of methyl acetate (MA), ethyl acetate (EA), propyl acetate (EP), butyl acetate, propyl propionate (PP), and butyl propionate.
In some embodiments, the sulfone solvent includes cyclic sulfones and linear sulfones. Preferably, in the case of the cyclic sulfones, they usually have 3 to 6 carbon atoms, and preferably 3 to 5 carbon atoms. In the case of the linear sulfones, they are usually a compound having 2 to 6 carbon atoms, and preferably a compound having 2 to 5 carbon atoms. The addition amount of the sulfone solvent is not particularly limited, and it is arbitrary within a range of not significantly destroying the effect of the lithium-ion battery in the present disclosure. With respect to the total amount of the solvent in the non-aqueous electrolyte, the volume percent of the sulfone solvent is usually 0.3% or more, preferably 0.5% or more, more preferably 1% or more, in addition, usually 40% or less, preferably 35% or less, and more preferably 30% or less. When using two or more sulfone solvents in combination, the total amount of the sulfone solvents needs to satisfy the above ranges. When the addition amount of the sulfone solvent is within the above ranges, an electrolyte having excellent high-temperature storage stability tends to be obtained.
In preferred embodiments, the non-aqueous organic solvent is a mixture of cyclic carbonates and linear carbonates.
In some embodiments, the non-aqueous electrolyte further includes lithium salts including one or more of LiPF6, LiBOB, LiDFOB, LiPO2F2, LiBF4, LiSbF6, LiAsF6, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiC(SO2CF3)3, LiN(SO2F)2, LiClO4, LiAlCl4, LiCF3SO3, Li2B10Cl10, and lithium salts of lower aliphatic carboxylates.
In preferred embodiments, the lithium salts include LiPF6 and auxiliary lithium salts, and the auxiliary lithium salts include one or more of LiBOB, LiDFOB, LiPO2F2, LiBF4, LiSbF6, LiAsF6, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiC(SO2CF3)3, LiN(SO2F)2, LiClO4, LiAlCl4, LiCF3SO3, Li2B10Cl10, and lithium salts of lower aliphatic carboxylates.
Under the above conditions, adding LiPF6 as the main lithium salt in the non-aqueous electrolyte in combination with the above-mentioned auxiliary lithium salts can further improve the thermal shock resistance of the battery. It is presumed that the compound represented by the formula I contained in the positive electrode is dissolved in a small amount in the non-aqueous electrolyte, and the combination with the above lithium salts has the effect of improving the stability of the non-aqueous electrolyte and avoiding the decomposition of the non-aqueous electrolyte to produce a gas.
In some embodiments, in the non-aqueous electrolyte, a mass percent content of the LiPF6 is from 5% to 20%, and a mass percent content of the auxiliary lithium salts is from 0.05% to 5%.
In some embodiments, the non-aqueous electrolyte further includes an additive including at least one of a cyclic sulfate ester compound, a sultone ester compound, a cyclic carbonate ester compound, an unsaturated phosphate ester compound, and a nitrile compound.
Preferably, the cyclic sulfate ester compound is selected from at least one of vinyl sulfate, propylene sulfate, or methyl vinyl sulfate. The sultone ester compound is selected from at least one of 1,3-propane sultone, 1,4-butane sultone or 1,3-propene sultone. The cyclic carbonate ester compound is selected from at least one of vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate or a compound represented by formula 2,
The unsaturated phosphate ester compound is selected from at least one of compounds represented by formula 3:
In preferred embodiments, the unsaturated phosphate ester compound may be at least one of tripropargyl phosphate, dipropargyl methyl phosphate, dipropargyl ethyl phosphate, dipropargyl propyl phosphate, dipropargyl trifluoromethyl phosphate, dipropargyl 2,2,2-trifluoroethyl phosphate, dipropargyl 3,3,3-trifluoropropyl phosphate, dipropargyl hexafluoroisopropyl phosphate, triallyl phosphate, diallyl methyl phosphate, diallyl ethyl phosphate, diallyl propyl phosphate, diallyl trifluoromethyl phosphate, diallyl 2,2,2-trifluoroethyl phosphate, diallyl 3,3,3-trifluoropropyl phosphate, and diallyl hexafluoroisopropyl phosphate.
The nitrile compound includes one or more of succinonitrile, glutaronitrile, ethylene glycol bis(propionitrile) ether, hexanetrinitrile, adiponitrile, pimelonitrile, suberonitrile, azelanitrile, and sebaconitrile.
In some other embodiments, the additive may further include other additives that can improve battery performance: for example, additives that improve battery safety performance, such as fluorophosphate esters, cyclophosphazene, and other flame retardant additives; or tert-amylbenzene, tert-butylbenzene and other anti-overcharge additives.
It should be noted that, unless otherwise specified, in general, the addition amount of any optional substance in the additive in the non-aqueous electrolyte is 10% or less, for example, the additive is added in an amount ranging from 0.05 to 10% in the non-aqueous electrolyte. Preferably, the addition amount is from 0.1 to 5%, and more preferably, the addition amount is from 0.1% to 2%. Specifically, the addition amount of any optional substance in the additive can be 0.05%, 0.08%, 0.1%, 0.5%, 0.8%, 1, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7% 7.5%, 7.8%, 8%, 8.5%, 9%, 9.5%, or 10%.
In some embodiments, when the additive is selected from fluoroethylene carbonate, with a total mass of the non-aqueous electrolyte being 100%, the addition amount of fluoroethylene carbonate is from 0.05% to 30%.
In some embodiments, the negative electrode sheet includes a negative electrode material layer including a negative electrode active material. The negative electrode active material is selected from at least one of a silicon-based negative electrode, a carbon-based negative electrode, a lithium-based negative electrode, and a tin-based negative electrode.
The silicon-based negative electrode includes one or more of silicon materials, silicon oxides, silicon-carbon composite materials, and silicon alloy materials. The carbon-based negative electrode includes one or more of graphite, hard carbon, soft carbon, graphene, and intermediate phase carbon microspheres. The lithium-based negative electrode includes one or more of metal lithium or a lithium alloy. The lithium alloy may specifically be at least one of a lithium-silicon alloy, a lithium-sodium alloy, a lithium-potassium alloy, a lithium-aluminum alloy, a lithium-tin alloy and a lithium-indium alloy. The tin-based negative electrode includes one or more of tin, tin carbon, tin oxide, and tin metal compounds.
In some embodiments, the negative electrode material layer further includes a negative electrode binder and a negative electrode conductive agent. The negative electrode active material, the negative electrode binder and the negative electrode conductive agent are blended to obtain the negative electrode material layer.
The selectable compounds of the negative electrode binder and the negative electrode conductive agent are the same as those of the positive electrode binder and the positive electrode conductive agent respectively, and will not be repeated here.
In some embodiments, the negative electrode sheet further includes a negative electrode current collector, and the negative electrode material layer covers a surface of the negative electrode current collector.
The negative electrode current collector is selected from metal materials that can conduct electrons. Preferably, the negative electrode current collector includes one or more of Al, Ni, tin, copper, and stainless steel. In more preferred embodiments, the negative electrode current collector is selected from copper foil.
In some embodiments, the lithium-ion battery further includes a separator, and the separator is located between the positive electrode sheet and the negative electrode sheet.
The separator can be an existing conventional separator, and can be a polymer separator, non-woven fabric and so on, including but not limited to single-layer PP (polypropylene), single-layer PE (polyethylene), double-layer PP/PE, double-layer PP/PP and three-layer PP/PE/PP separators, and the like.
The present disclosure is further illustrated by way of examples below.
The compounds involved in the following Examples and Comparative Examples are shown in Table 1 below.
This example is used to illustrate the lithium-ion battery disclosed in the present disclosure and its preparation method, including the steps as follows:
The mass percent content m of the compound represented by the formula I in the positive electrode material layer, the total content n of metal elements doped in and/or coated on the positive electrode material in the positive electrode active layer, and the compacted density k of the positive electrode active material layer are shown in Table 2.
Ethylene carbonate (EC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) were mixed according to a mass ratio of EC:DEC:EMC=1:1:1. Then, lithium hexafluorophosphate (LiPF6) was added to a molar concentration of 1 mol/L, and then 1% LiPO2F2 was added.
The above-mentioned prepared positive electrode sheet and the above-mentioned negative electrode sheet were assembled into a laminated soft-packed battery cell.
In a glove box with a dew point controlled at −40° C. or less, the above-prepared electrolyte was injected into the battery cell, sealed under vacuum, and subjected to standing for 24 hours. Then, the normal formation of a first charging is performed according to the following steps: charging at a constant current of 0.05 C for 180 min, charging at a constant current of 0.2 C to 3.95 V, second sealing under vacuum, and then further charging at a constant current of 0.2 C to the cut-off voltage 4.35 V of the battery. At this time, the negative electrode graphite was in a state of completely intercalating lithium, and the potential relative to lithium was about 0.05 V. At this time, the potential of the positive electrode sheet relative to metal lithium is 4.40 V. After standing at room temperature for 24 hours, it was discharged to 3.0 V at a constant current of 0.2 C.
Examples 2 to 56 are used to illustrate the lithium-ion battery disclosed in the present disclosure and its preparation method, including most of the operation steps in Example 1, with the exceptions as follows: the positive electrode sheet components and electrolyte additive components shown in Table 2 are used.
Comparative Examples 1 to 23 are used to comparatively illustrate the lithium-ion battery disclosed in the present disclosure and its preparation method, including most of the operating steps in Example 1, with the exceptions as follows: the positive electrode sheet components and electrolyte additive components shown in Table 2 are used.
A plurality of identical lithium-ion batteries were prepared for each Example and Comparative Example to facilitate testing of the battery performance.
The performance of the lithium-ion batteries prepared above is tested as follows:
The capacity retention rate and DCIR increase rate of the high-temperature cycle were calculated according to the following formula:
battery cycle capacity retention rate=discharge capacity for the 1500th cycle/discharge capacity for the first cycle×100%;
battery cycle DCIR increase rate (%)=(discharge DCIR for the 1500th cycle−discharge DCIR for the first cycle)/discharge DCIR for the first cycle×10000.
battery storage capacity retention rate (%)=battery discharge capacity after storage for 90 days/battery discharge capacity before storage×100%;
battery storage DCIR increase rate (%)=(discharge DCIR after storage for 90 days−discharge DCIR before storage)/discharge DCIR before storage×100%.
Test results obtained in Examples 1 to 43, Comparative Examples from 1 to 3, and Comparative Examples 12 to 23 are shown in Table 3.
As can be seen from the test results of Examples 1 to 43, Comparative Examples 1 to 3, and Comparative Examples 12 to 17, when the content m of the compound represented by the formula I in the positive electrode material layer, the total content n of the doped and coated metal elements in the positive electrode material layer, and the compacted density k of the positive electrode material layer satisfy the limitative condition
the lithium-ion battery has higher high-temperature cycling and high-temperature storage capacity retention rates and a lower impedance increase rate. It is speculated that due to the synergistic effect of the compound represented by the formula I with the doped element of the positive electrode active material and the positive electrode compacted density, so that the positive electrode active material has a high structural stability. Therefore, side reactions between the surface of the positive electrode material layer and the non-aqueous electrolyte are significantly reduced in the battery, and the increase in the positive electrode impedance during the high-temperature cycling/storage is reduced. In particular, the high-temperature stability of lithium salts and solvents in the non-aqueous electrolyte is improved, and the high-temperature capacity retention performance of the battery can be greatly improved.
As can be seen from the test results of Examples 1 to 19, Examples 23 to 29 and Examples 36 to 41, in the positive electrode material layer, if the content of the compound represented by the formula I is too small, then its passivation effect on the positive electrode material is limited, so that the effect of improving the high-temperature performance of the battery is not apparent. Otherwise, if the content of the compound represented by the formula I is too large, then the film formed on the surface of the positive electrode active material is thicker, and the internal resistance of the battery is greater. The higher the content of doped and coated metal elements in the positive electrode material, the better the structural stability of the positive electrode material, and the better the high-temperature storage performance. However, too much coating will cause the impedance of the material to increase.
As can be seen from the test results of Comparative Examples 18 to 23, even if the content m of the compound represented by the formula I in the positive electrode material layer, the total content n of the doped and coated metal elements in the positive electrode material layer, and the compacted density k of the positive electrode material layer satisfy the condition
when the m value, the n value and the k value do not satisfy their range limits, the lithium-ion battery still does not have good electrochemical performance.
As can be seen from the test results of Examples 44 to 48, for different compounds represented by the formula I, when the content m of the compound represented by the formula I in the positive electrode material layer, the total content n of the doped and coated metal elements in the positive electrode material layer, and the compacted density k of the positive electrode material layer satisfy the preset relationship
they have a similar promotion effect on the lithium-ion battery, and all have a certain improvement effect on the high-temperature cycle performance and high-temperature storage performance of the lithium-ion battery, illustrating that the relationship provided in the present disclosure are applicable to various compounds represented by the Formula I.
As can be seen from the test results of Examples 49 to 56 and Comparative Examples 4 to 11, when different positive electrode active materials are used, when the content m of the compound represented by the formula I in the positive electrode material layer, the total content n of the doped and coated metal elements in the positive electrode material layer, and the compacted density k of the positive electrode material layer satisfy the preset relationship
the battery also has good high-temperature cycle performance and initial capacity, which shows that the relationship provided in the present disclosure is universal for the improvement of the high-temperature performance of lithium-ion batteries using different positive electrode active materials.
The above descriptions are only preferred embodiments of the present disclosure, and are not intended to limit the present disclosure. Any modifications, equivalent replacements and improvements made within the range of spirit and principles of the present disclosure should be included in the protection scope of the present disclosure.
| Number | Date | Country | Kind |
|---|---|---|---|
| 202210284289.9 | Mar 2022 | CN | national |
The present application is a national phase entry under 35 U.S.C. § 371 of International Application PCT/CN2023/080935, filed Mar. 10, 2023, which claims priority to Chinese Patent Application No. 202210284289.9, filed Mar. 22, 2022, the entire disclosures of which are incorporated herein by reference.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/CN2023/080935 | 3/10/2023 | WO |
