A lithium-ion battery

Abstract

To overcome the problems of insufficient positive electrode stability and electrolyte decomposition and gas generation in existing high-voltage lithium-ion batteries, this invention provides a lithium-ion battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte. The positive electrode includes a positive electrode material layer containing a positive electrode active material, the surface of which has a lithium phosphate coating layer. The non-aqueous electrolyte comprises a non-aqueous organic solvent, a lithium salt, and additives. The non-aqueous organic solvent includes a cyclic carbonate containing fluoroethylene carbonate. The additives include compounds shown in structural formula 1 and structural formula 2. The lithium-ion battery according to structural formulas 1 and 2 satisfies the following conditions: 0.2≤P×(A+B) / (100-C)≤2.25, and 30≤P≤150, 10≤C≤20, 0.05≤A≤0.5, 0.3≤B≤1. The lithium-ion battery provided by this invention can maintain the intrinsic material stability of the positive electrode active material under high operating voltage conditions, while significantly reducing gas generation at high temperatures.

Description

Technical Field

[0001] This invention belongs to the field of energy storage device technology, specifically relating to a lithium-ion battery. Background Technology

[0002] Lithium-ion batteries, with their advantages of high operating voltage, wide operating temperature range, high energy density, high output power, no memory effect, and long cycle life, are widely used not only in 3C digital products such as mobile phones and laptops, but also have a broad application market in new energy vehicles and large-scale energy storage. With the rapid development of new energy, the application of non-aqueous electrolyte lithium-ion batteries has also seen explosive growth. However, with end-users' urgent demand for improved driving range in new energy vehicles, there is a need to further increase the energy density of power batteries.

[0003] Compared to commonly used battery systems (lithium iron phosphate system, ternary system), spinel-structured lithium nickel manganese oxide (LiNi) is a better choice. 0.5 Mn 1.5 Lithium-ion battery materials (LiNiO4) and lithium-rich materials possess higher energy and power densities, and due to their cobalt-free nature, they offer a low-cost advantage, making them suitable for power batteries and large-scale energy storage applications. They are two of the most promising and attractive cathode materials for the future development of lithium-ion batteries. Among them, spinel-structured lithium nickel manganese oxide (LiNiO4) is particularly promising. 0.5 Mn 1.5 O4 has a three-dimensional diffusion channel, and its theoretical discharge specific capacity can reach 147 mAh g. -1 The voltage platform is as high as 4.7V; while lithium-rich materials have a higher specific capacity (≥250mAh / g) and their application voltage is also higher than 4.5V.

[0004] In practical applications, it has been found that under high-voltage systems, the intrinsic stability of materials decreases, and lattice destruction and ion dissolution lead to performance degradation. Simultaneously, the electrolyte is prone to decomposition at high potentials, and gas generation and interfacial film loss further exacerbate performance degradation. While cathode coating and oxidation-resistant electrolyte design can mitigate electrolyte performance degradation under high voltage to some extent, gas generation and capacity loss remain significant and difficult-to-solve problems under high-temperature conditions. To meet the performance requirements of electric vehicles, it is necessary to provide a targeted electrolyte and high-voltage lithium-ion battery with excellent high-temperature performance. Summary of the Invention

[0005] To address the problems of insufficient positive electrode stability and electrolyte decomposition and gas generation in existing high-voltage lithium-ion batteries, this invention provides a lithium-ion battery.

[0006] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows:

[0007] This invention provides a lithium-ion battery, comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte. The positive electrode comprises a positive electrode material layer containing a positive electrode active material, and the surface of the positive electrode active material has a lithium phosphate coating layer. The non-aqueous electrolyte comprises a non-aqueous organic solvent, a lithium salt, and additives. The non-aqueous organic solvent comprises a cyclic carbonate containing fluoroethylene carbonate, and the additives comprise compounds shown in structural formula 1 and compounds shown in structural formula 2.

[0008]

[0009] Structural Formula 1

[0010] R1, R2, and R3 are each independently selected from C1-C5 alkyl or haloalkyl groups, C2-C5 unsaturated hydrocarbon groups or unsaturated haloalkyl groups, and at least one of R1, R2, and R3 is the unsaturated hydrocarbon group or unsaturated haloalkyl group.

[0011]

[0012] Structural Formula 2

[0013] Among them, R4, R5, R6, R7, R8, and R9 are each independently selected from one of hydrogen atoms, halogen atoms, or C1-C5 groups;

[0014] The lithium-ion battery meets the following conditions:

[0015] 0.2≤P×(A+B) / (100-C)≤2.25, and 30≤P≤150, 10≤C≤20, 0.05≤A≤0.5, 0.3≤B≤1;

[0016] Where P is the thickness of the lithium phosphate coating layer, in nm;

[0017] C represents the mass percentage of cyclic carbonates in the non-aqueous electrolyte, expressed as % .

[0018] A represents the mass percentage of the compound shown in structural formula 1 in the non-aqueous electrolyte, in percentages (%).

[0019] B represents the mass percentage of the compound shown in structural formula 2 in the non-aqueous electrolyte, in units of .

[0020] Optionally, the lithium-ion battery meets the following conditions:

[0021] 0.32≤P×(A+B) / (100-C)≤1.2, and / or

[0022] The thickness P of the lithium phosphate coating layer is 50~100 nm, and / or

[0023] The non-aqueous electrolyte contains 12% to 17% cyclic carbonate by mass (C), and / or

[0024] The mass percentage A of the compound shown in structural formula 1 in the non-aqueous electrolyte is 0.05%~0.3%, and / or

[0025] The mass percentage B of the compound shown in structural formula 2 in the non-aqueous electrolyte is 0.5%~0.8%.

[0026] Optionally, the cyclic carbonate further includes at least one of ethylene carbonate, propylene carbonate, and butene carbonate.

[0027] Optionally, in structural formula 1, the alkyl groups of C1-C5 are selected from methyl, ethyl, propyl, isopropyl, or butyl; the haloalkyl groups of C1-C5 are selected from monofluoromethyl, difluoromethyl, trifluoromethyl, 2-fluoroethyl, 2,2-difluoroethyl, 2,2,2-trifluoroethyl, 3,3-difluoropropyl, 3,3,3-trifluoropropyl, or hexafluoroisopropyl; the unsaturated hydrocarbon groups of C2-C5 are selected from vinyl, allyl, 3-butenyl, isobutenyl, 4-pentenyl, ethynyl, propynyl, 3-butynyl, or 1-methyl-2-propynyl.

[0028] Preferably, the compound represented by structural formula 1 includes one or more of the following: triargyl 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, diallyl 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.

[0029] Optionally, in structural formula 2, R4, R5, R6, R7, R8, and R9 are each independently selected from one of hydrogen atoms, fluorine atoms, or C1-C5 groups, and the C1-C5 groups include one or more of trifluoromethyl, C1-C5 hydrocarbon groups, oxygen-containing hydrocarbon groups, silicon-containing hydrocarbon groups, and cyano-substituted hydrocarbon groups.

[0030] Optionally, the compound represented by structural formula 2 includes one or more of the following compounds:

[0031]

[0032] Optionally, the mass percentage F% of fluoroethylene carbonate in the non-aqueous electrolyte satisfies: 0.3 ≤ F ≤ 4.

[0033] Optionally, the non-aqueous electrolyte satisfies the following condition: 0.05 ≤ (F + B) / C ≤ 0.5.

[0034] Optionally, the additive further includes at least one of cyclic sulfate compounds, sultone compounds, unsaturated cyclic carbonate compounds, silane phosphate compounds, and nitrile compounds;

[0035] The cyclic sulfate compounds include at least one of propylene sulfate and vinyl methyl sulfate; and / or

[0036] The sultone compounds include at least one of 1,3-propane sultone, 1,4-butane sultone, and 1,3-propene sultone; and / or

[0037] The unsaturated cyclic carbonate compounds include at least one of vinylene carbonate, ethylene vinylene carbonate, and ethylene methylene carbonate: and / or

[0038] The silane phosphate compounds include at least one of tris(trimethylsilyl) phosphate and tris(triethylsilyl) phosphate: and / or

[0039] The nitrile compounds include at least one of succinonitrile, glutaronitrile, hexane trinitrile, adiponitrile, pimelonitrile, suberonitrile, azelaonitrile, and sebaconitrile.

[0040] Optionally, the non-aqueous organic solvent further includes one or more of chain carbonates, carboxylic ester solvents, and ether solvents.

[0041] Optionally, the positive electrode active material includes at least one of the compounds represented by formula (A) or formula (B):

[0042] LiNi x M 2-x A y O r B p Formula (A)

[0043] nLi2MnO3·(1 - n)LiMO2 Formula (B)

[0044] In formula (A), 0 ≤ x ≤ 1, 0 ≤ 2 - x ≤ 2, 0 ≤ y ≤ 0.05, 1 ≤ r ≤ 4, 0 ≤ p ≤ 4, r + p ≤ 4, M is selected from at least one of Mn or Al, A is selected from at least one of Mg, Cu, Zn, Sn, B, Ga, Cr, Sr, V, Nb, Ce, Zr, W, Ti, and B is selected from at least one of F, Cl, Br;

[0045] In formula (B), 0 < n < 1, and M is selected from at least one of Ni, Mn, or Al.

[0046] According to the lithium-ion battery provided by the present invention, a cyclic carbonate containing fluoroethylene carbonate, a compound shown in structural formula 1, and a compound shown in structural formula 2 are added to the non-aqueous electrolyte. Simultaneously, a lithium phosphate coating layer is applied to the surface of the positive electrode active material. The lithium phosphate coating layer provides a certain degree of protection for the positive electrode active material, inhibiting the dissolution of transition metals (such as Mn) in the positive electrode active material. During the battery formation stage, the cyclic carbonate, the compound shown in structural formula 1, and the compound shown in structural formula 2 decompose on the positive electrode surface and participate in the formation of the positive electrode surface interface film. The positive electrode surface interface film provides good barrier protection against the non-aqueous electrolyte. To reduce the decomposition and gas production of non-aqueous electrolytes under high voltage, an organic-inorganic protective layer is formed by the interlocking of the lithium phosphate coating layer and the positive electrode surface interface film on the surface of the positive electrode active material. Through extensive research, the inventors discovered that when the thickness P of the lithium phosphate coating layer, the mass percentage C of the cyclic carbonate in the non-aqueous electrolyte, the mass percentage A of the compound shown in structural formula 1 in the non-aqueous electrolyte, and the mass percentage B of the compound shown in structural formula 2 in the non-aqueous electrolyte satisfy the conditions 0.2≤P×(A+B) / (100-C)≤2.25, and 30≤P≤150, 10≤C≤20, 0.05≤A≤0, the desired effect is achieved. When 0.5 ≤ B ≤ 1, the resulting lithium-ion battery can maintain the intrinsic material stability of the positive electrode active material under high operating voltage conditions. Simultaneously, the gas production of the lithium-ion battery at high temperatures is significantly reduced. This is presumably because the cyclic carbonate, the compound shown in structural formula 1, and the compound shown in structural formula 2 compete with each other in forming the positive electrode surface interface film. By adjusting the content of these three compounds, the composition of the positive electrode surface interface film can be controlled, thereby obtaining a positive electrode surface interface film with higher bonding strength to the lithium phosphate coating layer. Furthermore, the thickness of the lithium phosphate coating layer affects the formation density of the positive electrode surface interface film. Generally, the lithium phosphate coating layer... The higher the thickness of the coating, the lower the thickness of the interface film formed on the positive electrode surface, which in turn affects the isolation and protection effect of the organic-inorganic protective layer between the positive electrode and the non-aqueous electrolyte. When the thickness P of the lithium phosphate coating layer, the mass percentage C of the cyclic carbonate in the non-aqueous electrolyte, the mass percentage A of the compound shown in structural formula 1 in the non-aqueous electrolyte, and the mass percentage B of the compound shown in structural formula 2 in the non-aqueous electrolyte are under synergistic conditions, the resulting organic-inorganic protective layer is stable under high voltage, which can effectively improve the stability of the positive electrode active material and the non-aqueous electrolyte under high working voltage and improve the electrochemical performance of high-voltage lithium-ion batteries. Detailed Implementation

[0047] To make the technical problems solved, the technical solutions, and the beneficial effects of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0048] This invention provides a lithium-ion battery, including a positive electrode, a negative electrode, and a non-aqueous electrolyte. The positive electrode includes a positive electrode material layer containing a positive electrode active material, and the surface of the positive electrode active material has a lithium phosphate coating layer. The non-aqueous electrolyte includes a non-aqueous organic solvent, a lithium salt, and additives. The non-aqueous organic solvent includes a cyclic carbonate containing fluoroethylene carbonate, and the additives include compounds shown in structural formula 1 and compounds shown in structural formula 2.

[0049]

[0050] Structural Formula 1

[0051] R1, R2, and R3 are each independently selected from C1-C5 alkyl or haloalkyl groups, C2-C5 unsaturated hydrocarbon groups or unsaturated haloalkyl groups, and at least one of R1, R2, and R3 is the unsaturated hydrocarbon group or unsaturated haloalkyl group.

[0052]

[0053] Structural Formula 2

[0054] Among them, R4, R5, R6, R7, R8, and R9 are each independently selected from one of hydrogen atoms, halogen atoms, or C1-C5 groups;

[0055] The lithium-ion battery meets the following conditions:

[0056] 0.2≤P×(A+B) / (100-C)≤2.25, and 30≤P≤150, 10≤C≤20, 0.05≤A≤0.5, 0.3≤B≤1;

[0057] Where P is the thickness of the lithium phosphate coating layer, in nm;

[0058] C represents the mass percentage of cyclic carbonates in the non-aqueous electrolyte, expressed as % .

[0059] A represents the mass percentage of the compound shown in structural formula 1 in the non-aqueous electrolyte, in percentages (%).

[0060] B represents the mass percentage of the compound shown in structural formula 2 in the non-aqueous electrolyte, in units of .

[0061] The lithium phosphate coating provides some protection for the positive electrode active material, inhibiting the dissolution of transition metals (such as Mn) in the positive electrode active material. During the battery formation stage, cyclic carbonates, compounds shown in structural formula 1, and compounds shown in structural formula 2 decompose on the positive electrode surface and participate in the formation of the positive electrode surface interface film. The positive electrode surface interface film has a good barrier protection effect on the non-aqueous electrolyte, reducing the decomposition and gas production of the non-aqueous electrolyte under high voltage. The lithium phosphate coating and the positive electrode surface interface film are interlocked on the surface of the positive electrode active material to form an organic-inorganic protective layer. Through extensive research, the inventors discovered that when the thickness P of the lithium phosphate coating and the cyclic carbonates in the non-aqueous electrolyte are... When the mass percentages of the ester (C), the compound represented by structural formula 1 in the non-aqueous electrolyte (A), and the compound represented by structural formula 2 in the non-aqueous electrolyte (B) satisfy the conditions 0.2≤P×(A+B) / (100-C)≤2.25, 30≤P≤150, 10≤C≤20, 0.05≤A≤0.5, and 0.3≤B≤1, the resulting lithium-ion battery can maintain the intrinsic material stability of the positive electrode active material under high operating voltage conditions. Simultaneously, the gas production of the lithium-ion battery at high temperatures is significantly reduced. The low content of the compound is presumably due to the competitive relationship between the cyclic carbonate, the compound shown in Structural Formula 1, and the compound shown in Structural Formula 2 in forming the positive electrode surface interface film. By adjusting the content of these three compounds, the composition of the positive electrode surface interface film can be controlled, thereby obtaining a positive electrode surface interface film with higher bonding strength to the lithium phosphate coating layer. At the same time, the thickness of the lithium phosphate coating layer affects the formation density of the positive electrode surface interface film. Generally, the higher the thickness of the lithium phosphate coating layer, the lower the thickness of the formed positive electrode surface interface film, which in turn affects the isolation and protection effect of the organic-inorganic protective layer between the positive electrode and the non-aqueous electrolyte. When the thickness P of the lithium phosphate coating layer, the mass percentage C of the cyclic carbonate in the non-aqueous electrolyte, the mass percentage A of the compound shown in Structural Formula 1 in the non-aqueous electrolyte, and the mass percentage B of the compound shown in Structural Formula 2 in the non-aqueous electrolyte are under synergistic conditions, the resulting organic-inorganic protective layer is stable under high voltage, which can effectively improve the stability of the positive electrode active material and the non-aqueous electrolyte under high operating voltage and improve the electrochemical performance of high-voltage lithium-ion batteries.

[0062] In a preferred embodiment, the lithium-ion battery satisfies the following conditions:

[0063] 0.32≤P×(A+B) / (100-C)≤1.2.

[0064] When the thickness P of the lithium phosphate coating, the mass percentage C of the cyclic carbonate in the non-aqueous electrolyte, the mass percentage A of the compound shown in structural formula 1 in the non-aqueous electrolyte, and the mass percentage B of the compound shown in structural formula 2 in the non-aqueous electrolyte further meet the above conditions, it is beneficial to further suppress the dissolution of transition metal ions of the positive electrode active material under high voltage, and at the same time suppress the decomposition and gas generation of the non-aqueous electrolyte at high temperature.

[0065] In a specific embodiment, the thickness P of the lithium phosphate coating layer can be any two values ​​between 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, 110nm, 120nm, 130nm, 140nm, 150nm, or more.

[0066] In a preferred embodiment, the thickness P of the lithium phosphate coating layer is 50~100 nm.

[0067] By applying a lithium phosphate coating of appropriate thickness to the surface of the positive electrode active material, the corrosive effect of non-aqueous electrolytes on the surface of the positive electrode active material can be reduced, ensuring the stability of the positive electrode-electrolyte interface under high voltage, preventing crystal structure collapse, and resulting in superior cycle performance. However, the coating thickness affects the specific capacity of the material; a thicker coating leads to a lower specific capacity, causing low capacity phenomena. It also affects the formation of the positive electrode surface interface film. The design of non-aqueous electrolytes under high-voltage conditions must consider the decomposition and gas generation caused by contact between the positive electrode active material and the non-aqueous electrolyte. The positive electrode coating, to a certain extent, blocks the contact between the non-aqueous electrolyte and the material itself. A thicker lithium phosphate coating reduces the amount of additives required for the formation of the positive electrode surface interface film during the non-aqueous electrolyte formation stage. Within the above-mentioned lithium phosphate coating thickness range, it is beneficial for protecting the positive electrode active material without significant capacity loss and for ensuring synergistic cooperation with the positive electrode surface interface film.

[0068] The thickness of the lithium phosphate coating on the surface of the positive electrode active material can be detected by XPS etching or TEM. The test method is as follows: the battery is discharged to 0% SOC, the positive electrode is cleaned with DMC after disassembly, and then the electrode is ion polished (CP) or FIB cut. The coating thickness can be preliminarily confirmed by combining the P element distribution of SEM-mapping. In some embodiments, in order to achieve more accurate thickness detection, electron probe microanalysis (EPMA) can be used to perform line scan or area scan analysis on individual particles, and the thickness of the lithium phosphate coating can be confirmed by combining the element distribution curve.

[0069] In a specific embodiment, the mass percentage C of the cyclic carbonate in the non-aqueous electrolyte can be any two values ​​between 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, or more.

[0070] In a preferred embodiment, the mass percentage C of the cyclic carbonate in the non-aqueous electrolyte is 12% to 17%.

[0071] Cyclic carbonates have superior film-forming properties. However, if the mass percentage (C) of cyclic carbonates is too low, it is difficult to form a stable positive electrode surface interface film on the surface of the positive electrode active material. If the mass percentage (C) of cyclic carbonates is too high, it will lead to an increase in the viscosity of the non-aqueous electrolyte, affecting the wetting efficiency of the non-aqueous electrolyte on the positive electrode material layer and the ion conduction efficiency. Furthermore, under high voltage conditions (≥4.5V), especially in high-temperature environments, the decomposition of cyclic carbonates is intensified, easily combining electrons to decompose and produce carbon-based gases (CO, CO2, alkane / olefin). They are also easily catalyzed by transition metal ions to produce solvated hydrogen structures, inducing hydrogen production and leading to increased electrolyte gas production.

[0072] In a specific embodiment, the mass percentage A of the compound represented by structural formula 1 in the non-aqueous electrolyte can be any two values ​​between 0.05%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, or more.

[0073] In a preferred embodiment, the mass percentage A of the compound represented by structural formula 1 in the non-aqueous electrolyte is 0.05% to 0.3%.

[0074] The compound shown in Structural Formula 1 tends to form a film on the positive electrode surface during the battery formation stage, and the phosphorus-containing component in its decomposition products has a good affinity with the lithium phosphate coating layer, which can improve the bonding strength between the positive electrode surface interface film and the lithium phosphate coating layer. If the amount of the compound shown in Structural Formula 1 added is too low, it will affect the bonding strength between the positive electrode surface interface film and the lithium phosphate coating layer; if the amount of the compound shown in Structural Formula 1 added is too high, it will affect the content of the components derived from the compound shown in Structural Formula 2 and the cyclic carbonate in the positive electrode surface interface film, which will have an adverse effect on the film formation quality of the positive electrode surface interface film.

[0075] In a specific embodiment, the mass percentage B of the compound shown in structural formula 2 in the non-aqueous electrolyte can be any two values ​​between 0.3%, 0.4%, 0.6%, 0.65%, 0.7%, 0.75%, 0.8%, 0.85%, 0.9%, 0.95%, 1%, or more.

[0076] In a preferred embodiment, the mass percentage B of the compound represented by structural formula 2 in the non-aqueous electrolyte is 0.5% to 0.8%.

[0077] The compound shown in Structural Formula 2 participates in the formation of both the positive and negative electrode surface interface films, effectively improving the thermal stability of both films and inhibiting hydrogen generation caused by solvated hydrogen migration. If the amount of the compound shown in Structural Formula 2 added is too low, it will affect the thermal stability of both films. If the amount of the compound shown in Structural Formula 2 added is too high, it will affect the synergistic effect with the compound shown in Structural Formula 1 and the cyclic carbonate, which is also detrimental to improving the film quality.

[0078] In some embodiments, the cyclic carbonate further includes at least one of ethylene carbonate, propylene carbonate, and butene carbonate.

[0079] In some embodiments, in structural formula 1, the alkyl groups of C1-C5 are selected from methyl, ethyl, propyl, isopropyl, or butyl; the haloalkyl groups of C1-C5 are selected from monofluoromethyl, difluoromethyl, trifluoromethyl, 2-fluoroethyl, 2,2-difluoroethyl, 2,2,2-trifluoroethyl, 3,3-difluoropropyl, 3,3,3-trifluoropropyl, or hexafluoroisopropyl; the unsaturated hydrocarbon groups of C2-C5 are selected from vinyl, allyl, 3-butenyl, isobutenyl, 4-pentenyl, ethynyl, propynyl, 3-butynyl, or 1-methyl-2-propynyl.

[0080] In a preferred embodiment, the compound represented by structural formula 1 includes one or more of the following: triargyl 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, diallyl 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.

[0081] In some embodiments, in structural formula 2, R4, R5, R6, R7, R8, and R9 are each independently selected from one of hydrogen atoms, fluorine atoms, or C1-C5 groups, and the C1-C5 groups include one or more of trifluoromethyl, C1-C5 hydrocarbon groups, oxygen-containing hydrocarbon groups, silicon-containing hydrocarbon groups, and cyano-substituted hydrocarbon groups.

[0082] In a preferred embodiment, the compound represented by structural formula 2 includes one or more of the following compounds:

[0083]

[0084] In some embodiments, the mass percentage F% of fluoroethylene carbonate in the non-aqueous electrolyte satisfies: 0.3 ≤ F ≤ 4.

[0085] In some embodiments, the non-aqueous electrolyte satisfies the following condition: 0.05 ≤ (F+B) / C ≤ 0.5.

[0086] In this embodiment, fluoroethylene carbonate is not used as the main solvent, but only as an auxiliary solvent to improve the intrinsic voltage withstand capability of the electrolyte, thus balancing system stability and gas generation suppression. The inventors discovered through extensive research that when a lithium phosphate coating layer is applied to the surface of the high-voltage cathode material crystal, and the cyclic carbonate contains a certain amount of fluoroethylene carbonate, the amount of non-fluorinated carbonate in the electrolyte can be reduced to 20% or less. Furthermore, as the thickness of the lithium phosphate coating layer increases, the content of non-fluorinated carbonate can be further reduced. This is presumably because: the lithium phosphate coating layer improves the structural stability of the cathode active material, suppressing ion dissolution and lattice breakage, thus weakening the catalytic effect of the electrolyte; simultaneously, the fluorine atoms of the fluoroethylene carbonate in the cyclic carbonate have strong electronegativity and weak polarity, which can effectively increase the oxidative decomposition voltage of the solvent, making it easier to obtain a solvent that meets the requirements for high-voltage electrolyte use. However, because fluoroethylene carbonate induces more gas generation at high voltages compared to other non-fluorinated carbonates (such as EC),... This is related to the carbon-oxygen bond breaking and free radical generation of linear esters under high pressure: EC is more easily decomposed, and the decomposition of linear esters is incomplete. More solvated hydrogen produced by the decomposition of non-fluorinated carbonates migrates to the negative electrode to react, while fluoroethylene carbonate decomposes later. The free radicals produced by linear esters combine with solvated hydrogen to generate more carbon gases (such as CO, CO2, or alkane / olefin). At the same time, the compound shown in structural formula 2 has similar chemical properties to non-fluorinated carbonates. Therefore, by controlling the cyclic carbonate, fluoroethylene carbonate, and the compound shown in structural formula 2 to meet the conditions 0.05≤(F+B) / C≤0.5, 10≤C≤20, 0.3≤F≤4, and 0.3≤B≤1, it is beneficial to synergistically affect the stability of non-aqueous electrolytes and reduce gas generation in lithium-ion batteries at high temperatures.

[0087] In a preferred embodiment, the non-aqueous electrolyte satisfies the following conditions:

[0088] 0.06≤(F+B) / C≤0.3; preferred values ​​are 12≤C≤17, 0.5≤F≤3, and 0.5≤B≤0.8.

[0089] In some embodiments, the additive further includes at least one of cyclic sulfate compounds, sulfonyl lactone compounds, unsaturated cyclic carbonate compounds, silane phosphate compounds, and nitrile compounds.

[0090] In some embodiments, the cyclic sulfate compound includes at least one of propylene sulfate and vinyl methyl sulfate.

[0091] In some embodiments, the sulfonyl lactone compound includes at least one of 1,3-propanesulfonyl lactone, 1,4-butanesulfonyl lactone, and 1,3-propenesulfonyl lactone.

[0092] In some embodiments, the unsaturated cyclic carbonate compound includes at least one of vinylene carbonate, ethylene ethylene carbonate, and ethylene methylene carbonate.

[0093] In some embodiments, the silane phosphate compound includes at least one of tris(trimethylsilane) phosphate and tris(triethylsilane) phosphate.

[0094] In some embodiments, the nitrile compound includes at least one selected from succinic acid, glutaronitrile, hexanetrionitrile, adiponitrile, heptacyanide, octadionitrile, nonadionitrile, and sebaconitrile.

[0095] In some embodiments, the lithium salt includes LiPF6, LiTFSI, LiBOB, LiDFOB, LiDFOP, LiBF4, LiSbF6, LiAsF6, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiC(SO2CF3)3, LiClO4, LiAlCl4, LiCF3SO3, LiSO3F, and Li2B. 10 Cl 10 At least one of lithium chloroborane, lithium tetrafluorooxalate phosphate, lithium trioxalate phosphate, lithium lower aliphatic carboxylic acids having four or fewer carbon atoms, or lithium tetraphenylborate.

[0096] In some embodiments, the concentration of the lithium salt in the non-aqueous electrolyte is 0.1 mol / L to 4 mol / L. In a preferred embodiment, the concentration of the lithium salt in the non-aqueous electrolyte is 0.5 mol / L to 2.5 mol / L. Specifically, in the non-aqueous electrolyte, the concentration of the lithium salt can be 0.5 mol / L, 0.55 mol / L, 0.6 mol / L, 0.65 mol / L, 0.7 mol / L, 0.8 mol / L, 0.85 mol / L, 0.9 mol / L, 0.95 mol / L, 1.0 mol / L, 1.1 mol / L, 1.15 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.45 mol / L, 1.5 mol / L, 1.6 mol / L, 1.7 mol / L, 1.8 mol / L, 1.9 mol / L, 2.0 mol / L, 2.1 mol / L, 2.2 mol / L, 2.3 mol / L, 2.4 mol / L, or 2.5 mol / L.

[0097] In some embodiments, the mass content of the non-aqueous organic solvent is 65% to 90% based on the total mass of the non-aqueous electrolyte being 100%.

[0098] Specifically, based on the total mass of the non-aqueous electrolyte as 100%, the mass content of the non-aqueous organic solvent can be 65%, 68%, 71%, 74%, 76%, 78%, 79%, 80%, 81.5%, 82%, 84%, 85%, 86%, 87%, 89%, or 90%.

[0099] In some embodiments, the non-aqueous organic solvent further includes one or more of chain carbonates, carboxylic acid ester solvents, and ether solvents.

[0100] In some embodiments, the chain carbonate may specifically be, but is not limited to, at least one of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and dipropyl carbonate (DPC). The content of the cyclic carbonate is not particularly limited and is arbitrary within a range that does not significantly impair the performance of the lithium-ion battery of this invention. However, when using a single type, its content is typically 3% or more, preferably 5% or more, by volume relative to the total amount of solvent in the non-aqueous electrolyte. By setting this range, a decrease in conductivity due to a decrease in the dielectric constant of the non-aqueous electrolyte can be avoided, making it easier to achieve good high-current discharge characteristics, stability relative to the negative electrode, and cycle characteristics of the non-aqueous electrolyte battery. Furthermore, the upper limit is typically 90% or less by volume, preferably 85% or less, and more preferably 80% or less. By setting this range, the oxidation / reduction resistance of the non-aqueous electrolyte can be improved, thereby contributing to improved stability during high-temperature storage. The content of the chain carbonate is not particularly limited, but relative to the total amount of solvent in the non-aqueous electrolyte, it is typically 15% or more by volume, preferably 20% or more, and more preferably 25% or more. Furthermore, it is typically 90% or less by volume, preferably 85% or less, and more preferably 80% or less. By keeping the content of the chain carbonate within the above range, it is easy to achieve an appropriate viscosity for the non-aqueous electrolyte, suppressing the decrease in ionic conductivity, and thus helping to achieve a good range of output characteristics for the non-aqueous electrolyte battery. When using two or more chain carbonates in combination, it is sufficient to ensure that the total amount of the chain carbonate meets the above range.

[0101] In some embodiments, fluorine-containing chain carbonates (hereinafter referred to as "fluorinated chain carbonates") are also preferably used. There is no particular limitation on the number of fluorine atoms in a fluorinated chain carbonate as long as it is 1 or more, but it is generally 6 or less, preferably 4 or less. When a fluorinated chain carbonate has multiple fluorine atoms, these fluorine atoms can be bonded to the same carbon atom or to different carbon atoms. Examples of fluorinated chain carbonates include dimethyl fluorinated carbonate derivatives, methyl ethyl fluorinated carbonate derivatives, and diethyl fluorinated carbonate derivatives.

[0102] In some embodiments, the carboxylic acid ester solvent includes cyclic carboxylic acid esters and / or chain carbonates. Examples of cyclic carboxylic acid esters include at least one of γ-butyrolactone, γ-valerolactone, and δ-valerolactone. Examples of chain carbonates include at least one of methyl acetate (MA), ethyl acetate (EA), propyl acetate (EP), butyl acetate, propyl propionate (PP), and butyl propionate.

[0103] In some embodiments, the ether solvent includes cyclic ethers or chain ethers, preferably chain ethers with 3 to 10 carbon atoms and cyclic ethers with 3 to 6 carbon atoms. The cyclic ethers can specifically but not limited to be at least one of 1,3-dioxolane (DOL), 1,4-dioxane (DX), crown ether, tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-CH3-THF), 2-trifluoromethyltetrahydrofuran (2-CF3-THF); the chain ethers can specifically but not limited to be dimethoxymethane, diethoxymethane, ethoxymethoxymethane, ethylene glycol di-n-propyl ether, ethylene glycol di-n-butyl ether, diethylene glycol dimethyl ether. Since the chain ethers have a high solvation ability with lithium ions and can improve ion dissociation, dimethoxymethane, diethoxymethane, and ethoxymethoxymethane with low viscosity and high ionic conductivity are particularly preferred. The ether compounds can be used alone or in combination of two or more in any combination and ratio. The addition amount of the ether compounds is not particularly limited and is arbitrary within the range that does not significantly damage the effect of the high-compaction lithium-ion battery of the present invention. In a non-aqueous solvent with a volume ratio of 100%, it is usually 1% or more, preferably 2% or more, more preferably 3% or more in volume ratio, and usually 30% or less, preferably 25% or less, more preferably 20% or less in volume ratio.

[0104] In some embodiments, the positive electrode active material includes at least one of the compounds represented by formula (A) or formula (B):

[0105] LiNi x M 2-x A y O r B p Formula (A)

[0106] nLi2MnO3·(1-n)LiMO2 Formula (B)

[0107] In formula (A), 0≤x≤1, 0≤2-x≤2, 0≤y≤0.05, 1≤r≤4, 0≤p≤4, r + p≤4, M is selected from at least one of Mn or Al, A is selected from at least one of Mg, Cu, Zn, Sn, B, Ga, Cr, Sr, V, Nb, Ce, Zr, W, Ti, and B is selected from at least one of F, Cl, Br;

[0108] In formula (B), 0 < n < 1, and M is selected from at least one of Ni, Mn, or Al.

[0109] In some specific embodiments of the present invention, when the positive electrode active material of the lithium-ion battery of the present invention includes the compound represented by formula (A), the positive electrode active material includes LiNi 0.5 Mn 1.5 O4.

[0110] In some specific embodiments of the present invention, when the positive electrode active material of the lithium-ion battery of the present invention includes the compound shown in formula (B), the positive electrode active material may include 0.1Li2MnO3·0.9LiNi 0.5 Mn 0.5 O2, 0.3Li2MnO3·0.7LiNi 0.5 Mn 0.5 O2, 0.5Li2MnO3·0.5LiNi 0.5 Mn 0.5 O2, 0.5Li2MnO3·0.5LiNi 0.4 Mn 0.6 O2, 0.6Li2MnO3·0.4LiNi 0.5 Mn 0.5 O2, 0.7Li2MnO3·0.3LiNi 0.5 Mn 0.5 O2, 0.8Li2MnO3·0.2LiNi 0.4 Mn 0.6 O2, 0.9Li2MnO3·0.1LiNi 0.4 Mn 0.6 O2, 0.7Li2MnO3·0.3LiNi 0.5 Con 0.2 Mn 0.3 At least one of O2.

[0111] When the positive electrode active material of the lithium-ion battery is selected from the above materials, the lithium-ion battery has higher energy density and power density, and at the same time, it has the advantage of low cost because it does not contain cobalt.

[0112] In some embodiments, the positive electrode material layer further includes a positive electrode binder and a positive electrode conductive agent, and the positive electrode active material, the positive electrode binder and the positive electrode conductive agent are blended to obtain the positive electrode material layer.

[0113] The positive electrode binder includes at least one of the following: polyvinylidene fluoride (PVDF), copolymers of PVDF, polytetrafluoroethylene (PTFE), copolymers of PVDF-hexafluoropropylene, copolymers of tetrafluoroethylene-hexafluoropropylene, copolymers of tetrafluoroethylene-perfluoroalkyl vinyl ethers, copolymers of ethylene-tetrafluoroethylene, copolymers of PVDF-tetrafluoroethylene, copolymers of PVDF-trifluoroethylene, copolymers of PVDF-trichloroethylene, copolymers of PVDF-fluorinated vinylidene, copolymers of PVDF-hexafluoropropylene-tetrafluoroethylene, thermoplastic polyimide, polyethylene, and polypropylene; acrylic resins; and styrene-butadiene rubber.

[0114] The positive electrode conductive agent includes at least one of conductive carbon black, conductive carbon spheres, conductive graphite, conductive carbon fiber, carbon nanotubes, graphene, or reduced graphene oxide.

[0115] In some embodiments, the positive current collector comprises a metallic material capable of conducting electrons. Preferably, the positive current collector comprises at least one of Al, Ni, tin, copper, and stainless steel. In a more preferred embodiment, the positive current collector is selected from aluminum foil.

[0116] In some embodiments, the negative electrode includes a negative electrode material layer, the negative electrode material layer includes a negative electrode active material, and the negative electrode active material includes at least one of carbon-based negative electrode, silicon-based negative electrode, tin-based negative electrode, and lithium negative electrode. The carbon-based negative electrode may include graphite, hard carbon, soft carbon, graphene, mesophase carbon microspheres, etc.; the silicon-based negative electrode may include silicon materials, silicon oxides, silicon-carbon composite materials, and silicon alloy materials, etc.; the tin-based negative electrode may include tin, tin-carbon, tin oxide, and tin metal compounds; the lithium negative electrode may include metallic lithium or lithium alloys. Specifically, the lithium alloy may be at least one of lithium-silicon alloy, lithium-sodium alloy, lithium-potassium alloy, lithium-aluminum alloy, lithium-tin alloy, and lithium-indium alloy.

[0117] In a more preferred embodiment, the negative electrode active material includes at least one of graphite, hard carbon, soft carbon, graphene, and silicon-carbon composite materials.

[0118] In some embodiments, the silicon material is one or more of silicon nanoparticles, silicon nanowires, silicon nanotubes, silicon thin films, 3D porous silicon, and hollow porous silicon.

[0119] In some embodiments, the negative electrode further includes a negative electrode current collector, and the negative electrode material layer covers the surface of the negative electrode current collector. The negative electrode current collector includes a metallic material capable of conducting electrons. Preferably, the negative electrode current collector includes at least one of Al, Ni, tin, copper, and stainless steel. In a more preferred embodiment, the negative electrode current collector is selected from copper foil.

[0120] In some embodiments, the negative electrode material layer further includes a negative electrode binder and a negative electrode conductive agent, and the negative electrode active material, the negative electrode binder and the negative electrode conductive agent are blended to obtain the negative electrode material layer.

[0121] The negative electrode binder includes at least one of the following: polyvinylidene fluoride (PVDF), copolymers of PVDF, polytetrafluoroethylene (PTFE), copolymers of PVDF-hexafluoropropylene, copolymers of tetrafluoroethylene-hexafluoropropylene, copolymers of tetrafluoroethylene-perfluoroalkyl vinyl ethers, copolymers of ethylene-tetrafluoroethylene, copolymers of PVDF-tetrafluoroethylene, copolymers of PVDF-trifluoroethylene, copolymers of PVDF-trichloroethylene, copolymers of PVDF-fluorinated vinylidene, copolymers of PVDF-hexafluoropropylene-tetrafluoroethylene, thermoplastic polyimide, polyethylene, and polypropylene; acrylic resins; and styrene-butadiene rubber.

[0122] The negative electrode conductive agent includes at least one of conductive carbon black, conductive carbon spheres, conductive graphite, conductive carbon fiber, carbon nanotubes, graphene, or reduced graphene oxide.

[0123] In some embodiments, the lithium-ion battery further includes a separator located between the positive electrode and the negative electrode.

[0124] The diaphragm can be a conventional diaphragm, such as a ceramic diaphragm, a polymer diaphragm, a non-woven fabric, or an inorganic-organic composite diaphragm, including but not limited to single-layer PP (polypropylene), single-layer PE (polyethylene), double-layer PP / PE, double-layer PP / PP, and triple-layer PP / PE / PP diaphragms.

[0125] The present invention will be further illustrated by the following examples.

[0126] Table 1

[0127]

[0128]

[0129]

[0130] Example 1

[0131] This embodiment illustrates the lithium-ion battery and its preparation method disclosed in this invention, and includes the following steps:

[0132] The positive electrode preparation steps are as follows: Lithium nickel manganese oxide (LNMO) active material with a lithium phosphate coating, conductive carbon black, and polyvinylidene fluoride binder are mixed in a mass ratio of 94.5:3.0:2.5 and dispersed in N-methyl-2-pyrrolidone to obtain a positive electrode slurry. The positive electrode slurry is uniformly coated on both sides of an aluminum foil, and after drying, rolling, and vacuum drying, aluminum leads are welded on using an ultrasonic welder to obtain the positive electrode plate. The thickness of the electrode plate is between 120-150 μm. The compaction density of the positive electrode material is controlled to be 3.1 g / cm³ by the areal density and rolling thickness of the positive electrode material. 3The thickness of the lithium phosphate coating is shown in Table 1.

[0133] The negative electrode preparation steps are as follows: Graphite material, conductive carbon black, styrene-butadiene rubber (SBR) binder, and carboxymethyl cellulose are mixed in a mass ratio of 95.2:1.0:2.4:1.4 and dispersed in deionized water to obtain a negative electrode slurry. The negative electrode slurry is coated on both sides of a copper foil, dried, rolled, and vacuum dried, and then nickel leads are welded on using an ultrasonic welding machine to obtain the negative electrode plate. The thickness of the electrode plate is between 120-150 μm. The compaction density of the negative electrode material is controlled to be 1.6 g / cm³ by the areal density and rolling thickness of the negative electrode material. 3 .

[0134] The electrolyte preparation steps are as follows: The non-aqueous solvent is a mixture of EC (ethylene carbonate), FEC (fluoroethylene carbonate), EMC (methyl ethyl carbonate), and DEC (diethyl carbonate). The amounts of EC and FEC added are shown in Table 1. EMC and DEC are used to make up the remaining solvent, and the mass ratio of EMC to DEC is 42:40. After mixing, LiPF6 with a concentration of 1 mol / L is added, and the additives are added according to the weight percentage shown in Table 1.

[0135] The membrane preparation steps are as follows: a three-layer membrane of polypropylene, polyethylene and polypropylene with a thickness of 20μm is used;

[0136] The battery assembly steps are as follows: a three-layer separator with a thickness of 20μm is placed between the positive plate and the negative plate. Then, the sandwich structure composed of the positive plate, the negative plate and the separator is wound up. The wound body is flattened and placed in an aluminum-plastic shell. After welding the tabs, the aluminum-plastic shell is sealed to obtain the cell to be injected with electrolyte. The electrolyte prepared above is cut and injected into the cell. After standing for 1 hour, it is sealed. After sealing, the battery is aged at 45℃ for 48 hours.

[0137] Then perform the initial charging formation as follows: charge at a constant current of 0.05C for 3 hours, charge at a constant current of 0.1C for 2 hours, charge at a constant current of 0.2C for 2 hours, rest for 1 hour, age at 45°C for 48 hours, and then further charge at a constant current of 0.2C to 4.85V, and discharge at a constant current of 0.2C to 3.4V.

[0138] Examples 2-26

[0139] Examples 2-26 illustrate the preparation method of the lithium-ion battery disclosed in this invention, including most of the operation steps in Example 1, with the following differences:

[0140] The thickness of the lithium phosphate coating, the composition of the non-aqueous organic solvent, the additives and their amounts are shown in Examples 2-26 of Table 1.

[0141] Comparative Examples 1-17

[0142] Comparative Examples 1-17 are used to illustrate the preparation method of the lithium-ion battery disclosed in this invention, including most of the operation steps in Example 1, the difference being:

[0143] The thickness of the lithium phosphate coating, the composition of the non-aqueous organic solvent, the additives and their amounts are shown in Comparative Examples 1 to 17 in Table 1.

[0144] Performance testing

[0145] The lithium-ion batteries prepared above were subjected to the following performance tests:

[0146] The formed battery was charged to 4.85V at room temperature using a 1C constant current and constant voltage method, then discharged to 3.4V using a 1C constant current method. The initial discharge capacity was recorded. The battery was then charged to 4.85V again using a 1C constant current and constant voltage method, and the initial volume was determined by the water displacement method. The battery was then stored at 60℃ for 30 days. After cooling to room temperature, the volume after storage was measured. The battery's retention capacity was measured by discharging to 3.4V using a 1C method. The calculation formula is as follows:

[0147] First-cycle discharge capacity (mAh / g) = Initial discharge capacity / Mass of active material × 100%;

[0148] Battery capacity retention rate (%) = Retained capacity / Initial capacity × 100%;

[0149] Battery volume expansion rate (%) = (volume after storage - initial volume) / initial volume × 100%;

[0150] (1) The test results obtained from Examples 1-17 and Comparative Examples 1-17 are filled in Table 2.

[0151] Table 2

[0152]

[0153] The test results of Examples 1-17 and Comparative Examples 1-17 show that in a battery system using compounds shown in Structural Formula 1 and Structural Formula 2 as additives, cyclic carbonates containing fluoroethylene carbonate as non-aqueous organic solvents, and a lithium phosphate coating layer on the surface of the positive electrode active material, by controlling the thickness P of the lithium phosphate coating layer, the mass percentage C of the cyclic carbonate in the non-aqueous electrolyte, the mass percentage A of the compound shown in Structural Formula 1 in the non-aqueous electrolyte, and the mass percentage B of the compound shown in Structural Formula 2 in the non-aqueous electrolyte, the following conditions are met: 0.2≤P×(A+B) / (100-C)≤2.25, 30≤P≤150, 10≤C≤20, 0.05≤A≤0.5, 0.3≤B≤1. The resulting lithium-ion battery exhibits high capacity retention and low expansion rate under high-temperature storage. The hypothesis is that the cyclic carbonate, the compound shown in Structural Formula 1, and the compound shown in Structural Formula 2 compete with each other when constructing the cathode surface interface film. By adjusting the proportions of these three components, the composition of the cathode surface interface film can be controlled, thereby obtaining a cathode surface interface film that bonds more tightly with the lithium phosphate coating layer. Furthermore, the thickness of the lithium phosphate coating layer affects the density of the cathode surface interface film, thus influencing the effectiveness of the organic-inorganic protective layer in isolating and protecting the cathode from the non-aqueous electrolyte. When the thickness of the lithium phosphate coating layer (P), the mass percentage of the cyclic carbonate in the non-aqueous electrolyte (C), the mass percentage of the compound shown in Structural Formula 1 in the non-aqueous electrolyte (A), and the mass percentage of the compound shown in Structural Formula 2 in the non-aqueous electrolyte (B) are in a synergistic state, the formed organic-inorganic protective layer can remain stable under high voltage conditions. In this case, not only can the stability of the cathode active material and the non-aqueous electrolyte be effectively improved under high operating voltage, but the electrochemical performance of the high-voltage lithium-ion battery can also be significantly enhanced.

[0154] A comparison of the test results from Examples 1-5 and Examples 6-17 shows that when the thickness P of the lithium phosphate coating layer, the mass percentage C of the cyclic carbonate in the non-aqueous electrolyte, the mass percentage A of the compound shown in structural formula 1 in the non-aqueous electrolyte, and the mass percentage B of the compound shown in structural formula 2 in the non-aqueous electrolyte further satisfy the conditions 0.32≤P×(A+B) / (100-C)≤1.2, and 50≤P≤100, 12≤C≤17, 0.05≤A≤0.3, and 0.5≤B≤0.8, the adverse effects of the silicon-containing decomposition products of the second additive on the battery can be further suppressed, the battery impedance can be reduced, and the electrochemical performance stability of the battery at high temperatures can be improved.

[0155] The test results of Comparative Examples 1-10 show that when the P, C, A, and B values ​​do not meet their respective range limits, even if the limit of 0.2 ≤ P × (A + B) / (100 - C) ≤ 2.25 is met, the resulting lithium-ion battery does not have good high-temperature storage performance. This indicates that excessively high or low P, C, A, and B values ​​are not conducive to improving the high-temperature performance of lithium-ion batteries. The test results of Comparative Examples 10-17 show that when the P, C, A, and B values ​​do not meet the limit of 0.2 ≤ P × (A + B) / (100 - C) ≤ 2.25, even if their respective content range limits are met, it will still lead to the deterioration of the high-temperature performance of lithium-ion batteries and the increase of gas production. This indicates that there is an interaction between the compound shown in Structural Formula 1, the compound shown in Structural Formula 2, the cyclic carbonate with fluorinated ethylene carbonate, and the lithium phosphate coating layer. Only when the four reach a good balance can they have a significant effect on improving the performance of the battery.

[0156] (2) The test results obtained from Examples 1-4 and Examples 18-21 are filled in Table 3.

[0157] Table 3

[0158]

[0159] A comparison of the test results from Examples 1-4 and Examples 18-21 shows that in the battery system provided by this invention, when the non-aqueous electrolyte further satisfies the conditions 0.05≤(F+B) / C≤0.5, 10≤C≤20, 0.3≤F≤4, and 0.3≤B≤1, the high-temperature storage performance and first-cycle discharge capacity of the battery can be further improved. Under these conditions, the lithium phosphate coating layer improves the structural stability of the positive electrode active material, inhibits ion dissolution and lattice breakage, and weakens the catalytic effect of the electrolyte. Fluoroethylene carbonate (FEC) in cyclic carbonates, due to the strong electronegativity and weak polarity of fluorine atoms, increases the oxidative decomposition voltage of the solvent, making it suitable for high-voltage electrolytes. However, at high voltages, FEC produces more gas than other non-fluorinated carbonates (such as EC). This is because linear esters undergo carbon-oxygen bond breakage under high voltage to generate free radicals: EC decomposes more easily, while FEC decomposes later, resulting in the generation of more carbonaceous gases (such as CO, CO2, or alkanes / olefins). The compound shown in Structural Formula 2 has similar chemical properties to non-fluorinated carbonates, serving as a substitute for them. Therefore, by controlling the ratio of cyclic carbonates, fluoroethylene carbonates, and the compound shown in Structural Formula 2, the stability of the non-aqueous electrolyte can be synergistically enhanced, reducing gas production in lithium-ion batteries at high temperatures.

[0160] (3) The test results obtained in Examples 1, 22-26 are filled in Table 4.

[0161] Table 4

[0162]

[0163] As can be seen from the test results of Examples 1 and 22-26, in the battery system of the present invention, under the conditions that 0.2≤P×(A+B) / (100-C)≤2.25, 30≤P≤150, 10≤C≤20, 0.05≤A≤0.5, and 0.3≤B≤1, the use of different compounds shown in structural formula 1 and structural formula 2 can improve the high-temperature storage performance and first-cycle discharge capacity of lithium-ion batteries. This indicates that the different compounds shown in structural formula 1 and the different compounds shown in structural formula 2 have common performance characteristics and produce similar effects in the electrolyte system.

[0164] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A lithium-ion battery, characterized in that, The electrolyte includes a positive electrode, a negative electrode, and a non-aqueous electrolyte. The positive electrode includes a positive electrode material layer containing a positive electrode active material. The surface of the positive electrode active material has a lithium phosphate coating layer. The non-aqueous electrolyte includes a non-aqueous organic solvent, a lithium salt, and additives. The non-aqueous organic solvent includes a cyclic carbonate containing fluoroethylene carbonate. The additives include compounds shown in structural formula 1 and compounds shown in structural formula 2. Structural Formula 1 R1, R2, and R3 are each independently selected from C1-C5 alkyl groups or C1-C5 haloalkyl groups, C2-C5 unsaturated hydrocarbon groups or unsaturated haloalkyl groups, and at least one of R1, R2, and R3 is the unsaturated hydrocarbon group or unsaturated haloalkyl group. Structural Formula 2 Among them, R4, R5, R6, R7, R8, and R9 are each independently selected from one of hydrogen atoms, halogen atoms, or C1-C5 groups; The lithium-ion battery meets the following conditions: 0.2≤P×(A+B) / (100-C)≤2.25, and 30≤P≤150, 10≤C≤20, 0.05≤A≤0.5, 0.3≤B≤1; Where P is the thickness of the lithium phosphate coating layer, in nm; C represents the mass percentage of cyclic carbonates in the non-aqueous electrolyte, expressed as % . A represents the mass percentage of the compound shown in structural formula 1 in the non-aqueous electrolyte, in percentages (%). B represents the mass percentage of the compound shown in structural formula 2 in the non-aqueous electrolyte, in units of .

2. The lithium-ion battery according to claim 1, characterized in that, The lithium-ion battery meets the following conditions: 0.32≤P×(A+B) / (100-C)≤1.2, and / or The thickness P of the lithium phosphate coating layer is 50~100 nm, and / or The non-aqueous electrolyte contains 12% to 17% cyclic carbonate by mass (C), and / or The mass percentage A of the compound shown in structural formula 1 in the non-aqueous electrolyte is 0.05%~0.3%, and / or The mass percentage B of the compound shown in structural formula 2 in the non-aqueous electrolyte is 0.5%~0.8%.

3. The lithium-ion battery according to claim 1, characterized in that, The cyclic carbonates also include at least one of ethylene carbonate, propylene carbonate, and butene carbonate.

4. The lithium-ion battery according to claim 1, characterized in that, In structural formula 1, the alkyl groups of C1-C5 are selected from methyl, ethyl, propyl, isopropyl, or butyl; the haloalkyl groups of C1-C5 are selected from monofluoromethyl, difluoromethyl, trifluoromethyl, 2-fluoroethyl, 2,2-difluoroethyl, 2,2,2-trifluoroethyl, 3,3-difluoropropyl, 3,3,3-trifluoropropyl, or hexafluoroisopropyl; the unsaturated hydrocarbon groups of C2-C5 are selected from vinyl, allyl, 3-butenyl, isobutenyl, 4-pentenyl, ethynyl, propynyl, 3-butynyl, or 1-methyl-2-propynyl.

5. The lithium-ion battery according to claim 1, characterized in that, The compound shown in Structural Formula 1 includes one or more of triallyl phosphate, diallylmethyl phosphate, diallylethyl phosphate, diallylpropyl phosphate, diallyl(trifluoromethyl)phosphate, diallyl(2,2,2-trifluoroethyl)phosphate, diallyl(3,3,3-trifluoropropyl)phosphate, diallyl(hexafluoroisopropyl)phosphate, tripropargyl phosphate, dipropargylmethyl phosphate, dipropargylethyl phosphate, dipropargylpropyl phosphate, dipropargyl(trifluoromethyl)phosphate, dipropargyl(2,2,2-trifluoroethyl)phosphate, dipropargyl(3,3,3-trifluoropropyl)phosphate, dipropargyl(hexafluoroisopropyl)phosphate.

6. The lithium-ion battery according to claim 1, characterized in that, In Structural Formula 2, R4, R5, R6, R7, R8, and R9 are each independently selected from one of a hydrogen atom, a fluorine atom, or a C1-C5 group, and the C1-C5 group includes one or more of a trifluoromethyl group, a C1-C5 hydrocarbon group, an oxygen-containing hydrocarbon group, a silicon-containing hydrocarbon group, and a cyano-substituted hydrocarbon group.

7. The lithium-ion battery according to claim 6, characterized in that, The compound shown in Structural Formula 2 includes one or more of the following compounds: 。 8. The lithium-ion battery according to claim 1, characterized in that, The mass percentage content F% of fluoroethylene carbonate in the non-aqueous electrolyte satisfies: 0.3 ≤ F ≤ 4.

9. The lithium-ion battery according to claim 8, characterized in that, The non-aqueous electrolyte satisfies the following condition: 0.05 ≤ (F + B) / C ≤ 0.

5.

10. The lithium-ion battery according to claim 1, characterized in that, The additive further includes at least one of cyclic sulfate compounds, sultone compounds, unsaturated cyclic carbonate compounds, silane phosphate compounds, and nitrile compounds; The cyclic sulfate compounds include at least one of propylene sulfate and vinyl methyl sulfate; and / or The sultone compounds include at least one of 1,3-propane sultone, 1,4-butane sultone, and 1,3-propene sultone; and / or The unsaturated cyclic carbonate compounds include at least one of vinylene carbonate, ethylene vinylene carbonate, and methylene vinylene carbonate; and / or The silane phosphate compounds include at least one of tris(trimethylsilyl)phosphate and tris(triethylsilyl)phosphate; and / or The nitrile compounds include at least one of succinonitrile, glutaronitrile, hexane trinitrile, adiponitrile, pimelonitrile, suberonitrile, azelaonitrile, and sebaconitrile.

11. The lithium-ion battery according to claim 1, characterized in that, The non-aqueous organic solvent further includes one or more of chain carbonates, carboxylic ester solvents, and ether solvents.

12. The lithium-ion battery according to claim 1, characterized in that, The positive electrode active material includes at least one of the compounds shown in Formula (A) or Formula (B): LiNi x M 2-x A y O r B p Formula (A) nLi2MnO3·(1 - n)LiMO2 Formula (B) In Formula (A), 0 ≤ x ≤ 1, 0 ≤ 2 - x ≤ 2, 0 ≤ y ≤ 0.05, 1 ≤ r ≤ 4, 0 ≤ p ≤ 4, r + p ≤ 4, M is selected from at least one of Mn or Al, A is selected from at least one of Mg, Cu, Zn, Sn, B, Ga, Cr, Sr, V, Nb, Ce, Zr, W, Ti, and B is selected from at least one of F, Cl, Br; In Formula (B), 0 < n < 1, and M is selected from at least one of Ni, Mn, or Al.

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