Lithium ion battery

Abstract

In order to solve the problem of continuous consumption of electrolytes caused by unstable film formation of negative electrodes of existing batteries, the present invention provides a lithium ion battery which comprises a positive electrode, a negative electrode and a non-aqueous electrolyte. The positive electrode comprises a positive electrode material layer, and the positive electrode material layer comprises a positive electrode active material and a lithium-rich oxide LixMm yOz, wherein M is at least one of Si, Cu, Co, Ni, Mn, Mo, Ru and Fe, 2≤x≤6, 0<y≤1, 2≤z≤4, and x+my-2z=0. The non-aqueous electrolyte comprises a non-aqueous organic solvent, a lithium salt and an additive, and the additive comprises vinylene carbonate, a boron-containing compound A and a boron-containing compound B. The boron-containing compound A is selected from compounds represented by structural formula 1; and the boron-containing compound B is selected from compounds represented by structural formula 2. The lithium ion battery provided has excellent cycle life and high temperature performance.

Description

A lithium-ion battery Technical Field

[0001] The present invention belongs to the technical field of energy storage components, and in particular relates to a lithium-ion battery. Background Art

[0002] The expansion of the new energy market is accelerating the evolution of lithium-ion battery technology, and applications are placing higher demands on the cycle life of lithium-ion batteries. Currently, commercial lithium-ion batteries face a cycle life bottleneck. Batteries for consumer electronics generally have a lifespan of no more than five years, electric vehicles typically no more than eight years, and energy storage batteries have a lifespan of ten years. Battery lifespans need to be further improved.

[0003] The service life of a battery is related to the functional loss of the easily consumable parts inside the battery, which conforms to the "short board effect" and usually depends on the parts that wear out the fastest. During the cyclic charge and discharge process, the positive electrode, electrolyte, and negative electrode in the battery all suffer from loss. The structure of commercial positive and negative electrode materials is usually relatively stable. As a medium between the positive and negative electrodes, the loss of electrolyte at the electrode interface is the main factor that limits the battery capacity in the middle and late stages of the cycle. Reducing the loss of electrolyte at the electrode interface is a key strategy to improve the cycle life of the battery. In the prior art, various film-forming additives are added to form a solid electrolyte film on the negative electrode interface, thereby forming a protective effect on the negative electrode. However, according to existing research, the performance of solid electrolyte films formed by different film-forming additives in different states varies greatly. The rupture of the solid electrolyte film during the cycle will further consume the electrolyte at the rupture position and increase its thickness, thereby leading to increased impedance and decreased capacity in the later stages of the cycle.

[0004] Summary of the Invention

[0005] In order to solve the problem that the negative electrode film formation of existing batteries is unstable, resulting in continuous consumption of electrolyte, the present invention provides a lithium-ion battery.

[0006] The technical solutions adopted by the present invention to solve the above technical problems are as follows:

[0007] The present invention provides a lithium ion battery, comprising a positive electrode, a negative electrode and a non-aqueous electrolyte, wherein the positive electrode comprises a positive electrode material layer, the positive electrode material layer comprises a positive electrode active material and a lithium-rich oxide Li x M m y O z , wherein M is at least one of Si, Cu, Co, Ni, Mn, Mo, Ru, and Fe, 2≤x≤6, 0<y≤1, 2≤z≤4, and x+my-2z=0; the non-aqueous electrolyte comprises a non-aqueous organic solvent, a lithium salt, and an additive, wherein the additive comprises vinylene carbonate, a boron-containing compound A, and a boron-containing compound B;

[0008] The boron-containing compound A is selected from the compound shown in structural formula 1:

[0009] wherein R1 and R2 are each independently selected from halogen or cyano;

[0010] The boron-containing compound B is selected from the compound shown in structural formula 2:

[0011] Wherein, R3, R4 and R5 are each independently selected from C1-C5 alkyl, C2-C5 alkenyl, and C3-C6 silyl.

[0012] Optionally, the lithium-rich oxide Li x M m y O z Including one or more of Li5FeO4, Li2MoO3, Li6CoO4, and Li2NiO2.

[0013] Optionally, the boron-containing compound A includes one or more of lithium difluorooxalatoborate and lithium dicyanooxalatoborate.

[0014] Optionally, the boron-containing compound B includes one or more of tri-tert-butyl borate, triethyl borate, triallyl borate, and tris(trimethylsilyl)borate.

[0015] Optionally, based on the total mass of the positive electrode material layer being 100%, the lithium-rich oxide Li x M m y O z The mass percentage is 0.1% to 4%.

[0016] Optionally, based on the total mass of the non-aqueous electrolyte as 100%, the mass percentage of the vinylene carbonate is 0.2% to 10%, the mass percentage of the boron-containing compound A is 0.02% to 1%, and the mass percentage of the boron-containing compound B is 0.01% to 0.8%.

[0017] Optionally, in the non-aqueous electrolyte, the mass ratio of the vinylene carbonate, the boron-containing compound A and the boron-containing compound B is (0.5-8): (0.05-0.9): (0.02-0.6).

[0018] Optionally, the lithium salt includes LiPF6, LiTFSI, LiDFOP, LiPO2F2, LiBF4, LiSbF6, LiAsF6, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiC(SO2CF3)3, LiClO4, LiAlCl4, LiCF3SO3, LiSO3F, Li2B 10 Cl 10 , lithium chloroborane, lithium tetrafluorooxalophosphate, lithium trioxalophosphate, a lower aliphatic carboxylic acid lithium having 4 or less carbon atoms, or lithium tetraphenylborate, wherein the concentration of the lithium salt is 0.1 mol / L to 4 mol / L.

[0019] Optionally, the additive further includes at least one of a cyclic sulfate compound, a sultone compound, a phosphate compound and a nitrile compound.

[0020] Optionally, the cyclic sulfate ester compound includes at least one of vinyl sulfate, propylene sulfate, and methyl vinyl sulfate; and / or

[0021] The sultone compound includes at least one of 1,3-propane sultone, 1,4-butane sultone, and 1,3-propene sultone; and / or

[0022] The phosphate compound includes at least one of tris(trimethylsilyl)phosphate, tris(triethylsilyl)phosphate or the compound shown in structural formula 3:

[0023] In the structural formula 3, R 31 、R 32 、R 33 Each independently selected from C1-C5 saturated hydrocarbon group, C1-C5 unsaturated hydrocarbon group, C1-C5 halogenated hydrocarbon group, -Si(C m H 2m+1 )3, m is a natural number from 1 to 3, and R 31 、R 32 、R 33 At least one of them is an unsaturated hydrocarbon group; and / or

[0024] The nitrile compound includes at least one of succinonitrile, glutaronitrile, hexanetrinitrile, adiponitrile, pimelonitrile, suberonitrile, azelaic acid dinitrile and sebacononitrile.

[0025] According to the lithium ion battery provided by the present invention, vinylene carbonate, boron-containing compound A and boron-containing compound B are simultaneously used as additives to the non-aqueous electrolyte to participate in the formation of the negative electrode solid electrolyte membrane. In the formation stage, vinylene carbonate and boron-containing compound A are decomposed together on the negative electrode interface to form a solid electrolyte membrane containing Li2CO3 and B-containing compound. Since the boron-containing compound B has multiple branched structures, its decomposition products can form crosslinking points in the solid electrolyte membrane, playing a crosslinking role, thereby facilitating the formation of a tough solid electrolyte membrane with good ion permeability. At the same time, since the formation of the solid electrolyte membrane requires the consumption of a large amount of lithium ions, conventional positive electrode active materials are difficult to supply in the early stage of formation. Therefore, lithium-rich oxide Li is added to the positive electrode material layer. x M m y O z , which plays a role in quickly supplying lithium ions in the early stage of formation, thereby ensuring the density and stability of the solid electrolyte membrane, effectively inhibiting the side reaction at the interface between the non-aqueous electrolyte and the negative electrode, and avoiding the rupture of the solid electrolyte membrane during the cycle. On the other hand, lithium-rich oxide Li x M m y O z The lithium and oxygen released during the formation stage diffuse to the negative electrode interface and also trigger the vinylene carbonate chain growth reaction, ensuring the rapid formation and stability of the solid electrolyte membrane. DETAILED DESCRIPTION

[0026] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0027] An embodiment of the present invention provides a lithium-ion battery, comprising a positive electrode, a negative electrode and a non-aqueous electrolyte, wherein the positive electrode comprises a positive electrode material layer, wherein the positive electrode material layer comprises a positive electrode active material and a lithium-rich oxide Li x M m y O z , wherein M is at least one of Si, Cu, Co, Ni, Mn, Mo, Ru, and Fe, 2≤x≤6, 0<y≤1, 2≤z≤4, and x+my-2z=0; the non-aqueous electrolyte comprises a non-aqueous organic solvent, a lithium salt, and an additive, wherein the additive comprises vinylene carbonate, a boron-containing compound A, and a boron-containing compound B;

[0028] The boron-containing compound A is selected from the compound shown in structural formula 1:

[0029] wherein R1 and R2 are each independently selected from halogen or cyano;

[0030] The boron-containing compound B is selected from the compound shown in structural formula 2:

[0031] Wherein, R3, R4 and R5 are each independently selected from C1-C5 alkyl, C2-C5 alkenyl, and C3-C6 silyl.

[0032] The lithium-ion battery simultaneously uses vinylene carbonate, boron-containing compound A and boron-containing compound B as additives to the non-aqueous electrolyte to participate in the formation of the negative electrode solid electrolyte membrane. In the formation stage, vinylene carbonate and boron-containing compound A decompose together on the negative electrode interface to form a solid electrolyte membrane containing Li2CO3 and B-containing compound. Since the boron-containing compound B has multiple branched structures, its decomposition products can form crosslinking points in the solid electrolyte membrane, playing a crosslinking role, thereby facilitating the formation of a tough solid electrolyte membrane with good ion permeability. At the same time, since the formation of the solid electrolyte membrane requires the consumption of a large amount of lithium ions, conventional positive electrode active materials are difficult to supply in the early stage of formation. Therefore, lithium-rich oxide Li is added to the positive electrode material layer. x M m y O z , which plays a role in quickly supplying lithium ions in the early stage of formation, thereby ensuring the density and stability of the solid electrolyte membrane, effectively inhibiting the side reaction at the interface between the non-aqueous electrolyte and the negative electrode, and avoiding the rupture of the solid electrolyte membrane during the cycle. On the other hand, lithium-rich oxide Li x M m y O z The lithium and oxygen released during the formation stage diffuse to the negative electrode interface and also trigger the vinylene carbonate chain growth reaction, ensuring the rapid formation and stability of the solid electrolyte membrane.

[0033] In some embodiments, the lithium-rich oxide Li x M m y O z Including one or more of Li5FeO4, Li2MoO3, Li6CoO4, and Li2NiO2.

[0034] The above compounds are used as lithium-rich oxides Li x M m y O z It can quickly release lithium ions during the formation stage to ensure the lithium source supply of the solid electrolyte membrane at the negative electrode interface, thereby avoiding the capacity loss of the positive electrode active material and improving the initial efficiency of the battery.

[0035] In some embodiments, the boron-containing compound A includes one or more of lithium difluorooxalatoborate and lithium dicyanooxalatoborate.

[0036] The boron-containing compound A has a cyclic oxalylboric acid structure and decomposes on the surface of the negative electrode to form a dense boron-containing polymer to form one of the main components of the negative electrode solid electrolyte membrane.

[0037] In some embodiments, the boron-containing compound B includes one or more of tri-tert-butyl borate, triethyl borate, triallyl borate, and tris(trimethylsilyl)borate.

[0038] The boron-containing compound B is a multi-branched borate structure centered on the B atom, wherein each branch can be integrated into the solid electrolyte membrane skeleton formed by the boron-containing compound A, playing a good three-dimensional cross-linking role, thereby improving the overall toughness of the solid electrolyte membrane.

[0039] In some embodiments, based on the total mass of the positive electrode material layer being 100%, the lithium-rich oxide Li x M m y O z The mass percentage is 0.1% to 4%.

[0040] In a specific embodiment, based on the total mass of the positive electrode material layer being 100%, the lithium-rich oxide Li x M m y O z The mass percentage can be 0.1%, 0.2%, 0.3%, 0.6%, 0.8%, 1%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8% or 4%.

[0041] Positive electrode lithium-rich oxide Li x M m y O z When the mass fraction of Li is within the above range, the released lithium and oxygen are conducive to the reaction of the electrolyte additives to form a good solid electrolyte membrane to protect the negative electrode. x M m y O z When the mass percentage of is too low, the released lithium and oxygen are insufficient to diffuse to the negative electrode to participate in the formation of the negative electrode passivation film, the coverage of the formed solid electrolyte film is insufficient, the negative electrode protection effect is poor, and the cycle life is reduced; and the negative electrode passivation layer lithium content is insufficient, the internal resistance is large, and the rate performance is reduced; when the lithium-rich oxide Li x M m y Oz When the mass percentage of is too high, too much lithium and oxygen will be released in a short period of time, the vinylene carbonate chain growth reaction will be too intense, a thick and loose interface layer will be formed at the negative electrode, and gas production during high-temperature storage of the battery will be aggravated. Optionally, based on the total mass of the non-aqueous electrolyte as 100%, the mass percentage of the vinylene carbonate is 0.2% to 10%, the mass percentage of the boron-containing compound A is 0.02% to 1%, and the mass percentage of the boron-containing compound B is 0.01% to 0.8%.

[0042] In some embodiments, in the non-aqueous electrolyte, the mass ratio of the vinylene carbonate, the boron-containing compound A, and the boron-containing compound B is (0.5-8): (0.05-0.9): (0.02-0.6).

[0043] When the mass ratio of the vinylene carbonate, the boron-containing compound A and the boron-containing compound B is within the above range, it is beneficial to optimize the film-forming quality of the solid electrolyte membrane and improve the battery cycle performance; when the proportion of the boron-containing compound A or the boron-containing compound B is too high, there are too many cross-linking points in the process of forming the solid electrolyte membrane, resulting in insufficient flexibility of the solid electrolyte membrane and poor ion transport performance, thereby reducing the rate performance; when the proportion of the boron-containing compound A or the boron-containing compound B is too low, the formed solid electrolyte membrane is not stable enough, the reconstruction of the interface layer during the cycle leads to electrolyte consumption, and the cycle life improvement effect is poor.

[0044] In some embodiments, the lithium salt includes LiPF6, LiTFSI, LiDFOP, LiPO2F2, LiBF4, LiSbF6, LiAsF6, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiC(SO2CF3)3, LiClO4, LiAlCl4, LiCF3SO3, LiSO3F, Li2B 10 Cl 10 , lithium chloroborane, lithium tetrafluorooxalophosphate, lithium trioxalophosphate, a lower aliphatic lithium carboxylate having 4 or less carbon atoms, or at least one of lithium tetraphenylborate.

[0045] 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 may 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.

[0046] In some embodiments, based on the total mass of the non-aqueous electrolyte being 100%, the mass content of the non-aqueous organic solvent is 65% to 90%.

[0047] 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%.

[0048] In some embodiments, the non-aqueous organic solvent includes at least one of an ether solvent, a nitrile solvent, a carbonate solvent, a carboxylate solvent, and a sulfone solvent.

[0049] In some embodiments, the ether solvent includes a cyclic ether or a chain ether, preferably a chain ether with 3 to 10 carbon atoms and a cyclic ether with 3 to 6 carbon atoms. The cyclic ether may be, but is not limited to, at least one of 1,3-dioxolane (DOL), 1,4-dioxolane (DX), a crown ether, tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-CH3-THF), and 2-trifluoromethyltetrahydrofuran (2-CF3-THF). The chain ether may be, but is not limited to, dimethoxymethane, diethoxymethane, ethoxymethoxymethane, ethylene glycol di-n-propyl ether, ethylene glycol di-n-butyl ether, and diethylene glycol dimethyl ether. Because chain ethers have high solvation ability with lithium ions and can improve ion dissociation, dimethoxymethane, diethoxymethane, and ethoxymethoxymethane are particularly preferred because they have low viscosity and can impart high ionic conductivity. The ether compound may be used alone or in any combination and ratio. The amount of the ether compound added is not particularly limited and is any amount that does not significantly impair the effects of the high-density lithium-ion battery of the present invention. The amount is typically 1% or more by volume, preferably 2% or more by volume, and more preferably 3% or more by volume, based on 100% by volume of the non-aqueous solvent. Furthermore, the amount is typically 30% or less by volume, preferably 25% or less by volume, and more preferably 20% or less by volume.

[0050] In some embodiments, the nitrile solvent may be, but is not limited to, at least one of acetonitrile, glutaronitrile, and malononitrile.

[0051] In some embodiments, the carbonate solvent includes a cyclic carbonate or a chain carbonate. The cyclic carbonate can be, but is not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), γ-butyrolactone (GBL), and butylene carbonate (BC); the chain carbonate can 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 the range that does not significantly damage the effect of the lithium-ion battery of the present invention. However, when using one alone, the lower limit of its content is generally 3% or more by volume, preferably 5% or more by volume, relative to the total amount of solvent in the non-aqueous electrolyte. By setting this range, the decrease in conductivity due to the decrease in the dielectric constant of the non-aqueous electrolyte can be avoided, and it is easy to achieve a good range of high current discharge characteristics, stability relative to the negative electrode, and cycle characteristics of the non-aqueous electrolyte battery. In addition, the upper limit is generally 90% or less by volume, preferably 85% or less by volume, and more preferably 80% or less by volume. By setting this scope, the oxidation / reduction tolerance of nonaqueous electrolyte can be improved, thereby contributing to the stability during high temperature storage. The content of linear carbonate is not particularly limited, and relative to the total amount of solvent of nonaqueous electrolyte, is usually more than 15% by volume, preferably more than 20% by volume, and more preferably more than 25% by volume. In addition, usually the volume ratio is less than 90%, preferably less than 85% by volume, and more preferably less than 80% by volume. By making the content of linear carbonate in the above-mentioned scope, it is easy to make the viscosity of nonaqueous electrolyte reach appropriate range, suppress the reduction of ionic conductivity, and then contribute to the output characteristics of nonaqueous electrolyte battery reach good scope. When using two or more linear carbonates in combination, make the total amount of linear carbonate meet the above-mentioned scope.

[0052] In certain embodiments, also can preferably use the linear carbonates with fluorine atoms (hereinafter referred to as " fluorinated linear carbonate ").The number of the fluorine atoms possessed by fluorinated linear carbonate is as long as being more than 1 then has no particular restrictions, but is generally below 6, preferably below 4.When fluorinated linear carbonate has a plurality of fluorine atoms, these fluorine atoms can be bonded on the same carbon, also can be bonded on different carbons.As fluorinated linear carbonate, can enumerate, fluorinated dimethyl carbonate derivatives, fluorinated ethyl methyl carbonate derivatives, fluorinated diethyl carbonate derivatives etc.

[0053] Carboxylate solvents include cyclic carboxylates and / or chain carbonates. Examples of cyclic carboxylates 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.

[0054] In some embodiments, the sulfone solvent includes a cyclic sulfone and a chain sulfone. Preferably, in the case of a cyclic sulfone, the compound generally has 3 to 6 carbon atoms, preferably 3 to 5 carbon atoms; in the case of a chain sulfone, the compound generally has 2 to 6 carbon atoms, preferably 2 to 5 carbon atoms. There is no particular limitation on the amount of sulfone solvent added, and it can be any amount that does not significantly impair the effect of the lithium-ion battery of the present invention. The volume ratio relative to the total amount of solvent in the non-aqueous electrolyte is generally 0.3% or more, preferably 0.5% or more, and more preferably 1% or more. Furthermore, the volume ratio is generally 40% or less, preferably 35% or less, and more preferably 30% or less. When two or more sulfone solvents are used in combination, the total amount of the sulfone solvents can be adjusted to meet the above range. When the amount of sulfone solvent added is within the above range, a non-aqueous electrolyte with excellent high-temperature storage stability tends to be obtained.

[0055] In a preferred embodiment, the non-aqueous organic solvent comprises a mixture of cyclic carbonate and chain carbonate.

[0056] In some embodiments, the additive further comprises at least one of a cyclic sulfate compound, a sultone compound, a phosphate compound, and a nitrile compound.

[0057] In some embodiments, based on the total mass of the non-aqueous electrolyte being 100%, the content of the additive is 0.01% to 10%.

[0058] In some embodiments, the cyclic sulfate ester compound includes at least one of vinyl sulfate, propylene sulfate, and methyl vinyl sulfate.

[0059] In some embodiments, the sultone compound includes at least one of 1,3-propane sultone, 1,4-butane sultone, and 1,3-propene sultone.

[0060] In some embodiments, the phosphate compound includes at least one of tris(trimethylsilyl)phosphate, tris(triethylsilyl)phosphate, or a compound represented by formula 3:

[0061] In the structural formula 3, R 31 、R 32 、R 33 Each independently selected from C1-C5 saturated hydrocarbon group, C1-C5 unsaturated hydrocarbon group, C1-C5 halogenated hydrocarbon group, -Si(C m H 2m+1 )3, m is a natural number from 1 to 3, and R 31 、R 32 、R 33At least one of them is an unsaturated hydrocarbon group.

[0062] In a preferred embodiment, the phosphate compound shown in the structural formula 3 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.

[0063] In some embodiments, the nitrile compound includes at least one of succinonitrile, glutaronitrile, hexanetrionitrile, adiponitrile, pimelonitrile, suberonitrile, azelaic acid dinitrile, and sebacononitrile.

[0064] In other embodiments, the additives may also include other additives that can improve battery performance: for example, additives that enhance battery safety, such as flame retardant additives such as fluorophosphates and cyclophosphazenes, or overcharge prevention additives such as tert-amylbenzene and tert-butylbenzene.

[0065] It should be noted that, unless otherwise specified, under normal circumstances, the content of any one of the optional substances in the additives in the non-aqueous electrolyte is less than 10%, preferably, the content is 0.01-5%, and more preferably, the content is 0.1% to 2%. Specifically, the content of any one of the optional substances in the additives can be 0.01%, 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%.

[0066] In some embodiments, the additive includes fluoroethylene carbonate, and based on the total mass of the non-aqueous electrolyte being 100%, the added amount of the fluoroethylene carbonate is 0.01% to 30%.

[0067] In some embodiments, the positive electrode active material includes LiFe 1-x’ M' x’ PO4、LiMn 2-y’ M y’ O4 and LiNi x Co y Mn z M1-x-y-z O2, wherein M' includes one or more of Mn, Mg, Co, Ni, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, V, Nb, Ce, Zr, W or Ti, M includes one or more of Fe, Co, Ni, Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, V, Nb, Ce, Zr, W or Ti, and 0≤x'<1, 0≤y'≤1, 0≤y≤1, 0≤x≤1, 0≤z≤1, x+y+z≤1.

[0068] In some embodiments, the positive electrode material layer further includes a positive electrode binder and a positive electrode conductor, the positive electrode active material, the lithium-rich oxide Li x M m y O z , the positive electrode binder and the positive electrode conductor are mixed to obtain the positive electrode material layer.

[0069] The positive electrode binder includes polyvinylidene fluoride, a copolymer of vinylidene fluoride, polytetrafluoroethylene, a copolymer of vinylidene fluoride-hexafluoropropylene, a copolymer of tetrafluoroethylene-hexafluoropropylene, a copolymer of tetrafluoroethylene-perfluoroalkyl vinyl ether, a copolymer of ethylene-tetrafluoroethylene, a copolymer of vinylidene fluoride-tetrafluoroethylene, a copolymer of vinylidene fluoride-trifluoroethylene, a copolymer of vinylidene fluoride-trichloroethylene, a copolymer of vinylidene fluoride-fluoroethylene, a copolymer of vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene, thermoplastic polyimide, a thermoplastic resin such as polyethylene and polypropylene; an acrylic resin; and at least one of styrene butadiene rubber.

[0070] The positive electrode conductive agent includes at least one of conductive carbon black, conductive carbon balls, conductive graphite, conductive carbon fibers, carbon nanotubes, graphene, or reduced graphene oxide.

[0071] In some embodiments, the positive electrode current collector includes a metal material that can conduct electrons. Preferably, the positive electrode current collector includes at least one of Al, Ni, tin, copper, and stainless steel. In a more preferred embodiment, the positive electrode current collector is selected from aluminum foil.

[0072] In some embodiments, the negative electrode includes a negative electrode active material layer, wherein the negative electrode active material layer includes a negative electrode active material, and the negative electrode active material includes at least one of a carbon-based negative electrode, a silicon-based negative electrode, a tin-based negative electrode, and a lithium negative electrode. Carbon-based negative electrodes may include graphite, hard carbon, soft carbon, graphene, mesocarbon microbeads, etc.; silicon-based negative electrodes may include silicon materials, silicon oxides, silicon-carbon composite materials, and silicon alloy materials; tin-based negative electrodes may include tin, tin-carbon, tin-oxygen, and tin metal compounds; and lithium negative electrodes may include metallic lithium or a lithium alloy. Specifically, the lithium alloy may 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.

[0073] 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.

[0074] 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.

[0075] In some embodiments, the negative electrode further comprises a negative electrode current collector, and the negative electrode active material layer covers the surface of the negative electrode current collector. The negative electrode current collector comprises an electron-conducting metal material. Preferably, the negative electrode current collector comprises 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.

[0076] In some embodiments, the negative electrode active 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 together to form the negative electrode active material layer. The negative electrode binder and the negative electrode conductive agent may be the same as the positive electrode binder and the positive electrode conductive agent, respectively, and are not further described here.

[0077] In some embodiments, the battery further includes a separator, which is located between the positive electrode and the negative electrode.

[0078] The diaphragm can be an existing conventional diaphragm, which can be a ceramic diaphragm, a polymer diaphragm, a non-woven fabric, an inorganic-organic composite diaphragm, etc., 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 diaphragms.

[0079] The present invention is further described below with reference to the following examples.

[0080] Table 1

[0081] Example 1

[0082] This embodiment is used to illustrate the preparation method of the lithium ion battery disclosed in the present invention, which includes the following steps:

[0083] 1) Preparation of non-aqueous electrolyte:

[0084] An electrolyte was prepared by mixing a solvent, a lithium salt, and an additive. The solvent was a mixture of ethylene carbonate and dimethyl carbonate in a mass ratio of 30%:70%. Based on the total weight of the non-aqueous electrolyte being 100%, 13% lithium hexafluorophosphate and vinylene carbonate, boron-containing compound A, and boron-containing compound B as shown in Table 1 were added.

[0085] 2) Preparation of positive electrode:

[0086] The positive electrode active material, LiFePO4, conductive carbon black Super-P, and binder PVDF were mixed in a mass ratio of 96:2:2. The lithium-rich oxide was then added in the mass proportions shown in Table 1 and dispersed in N-methyl-2-pyrrolidone to produce a positive electrode slurry. The slurry was evenly coated on both sides of aluminum foil, dried, rolled, and vacuum-dried to obtain the positive electrode.

[0087] 3) Preparation of negative electrode:

[0088] The negative electrode active material, conductive carbon black Super-P, and a mixture of binders SBR and CMC (mass ratio 97:1:2) are mixed in deionized water to create a negative electrode slurry. The slurry is then coated on both sides of copper foil and dried, rolled, and vacuum-dried to produce a negative electrode plate.

[0089] 4) Lithium-ion battery production: The positive electrode with welded tabs, the separator, and the negative electrode with welded tabs are stacked in order, wound, and encapsulated with aluminum-plastic film to obtain a battery cell. The above-mentioned electrolyte is injected into the battery cell, and the battery cell is prepared into a lithium-ion battery after aging, formation, fixture shaping, and secondary sealing.

[0090] Examples 2 to 12

[0091] Examples 2 to 12 are used to illustrate the lithium-ion battery and the preparation method thereof disclosed in the present invention, and include most of the operating steps in Example 1, except that:

[0092] In Examples 2 to 12, vinylene carbonate, boron-containing compound A and boron-containing compound B and their addition amounts in the non-aqueous electrolyte, and lithium-rich oxide and its addition amount in the positive electrode material layer are shown in Table 1.

[0093] Comparative Examples 1 to 5

[0094] Comparative Examples 1 to 5 are used to illustrate the lithium ion battery and the preparation method thereof disclosed in the present invention, and include most of the operating steps in Example 1, except that:

[0095] In Comparative Examples 1 to 5, vinylene carbonate, boron-containing compound A and boron-containing compound B and their addition amounts in the non-aqueous electrolyte, and lithium-rich oxide and its addition amount in the positive electrode material layer are shown in Table 1.

[0096] Performance Testing

[0097] The lithium-ion battery prepared above was subjected to the following performance tests:

[0098] 1. Rate discharge retention rate test: Place the battery at room temperature, charge it at 0.2C constant current and constant voltage to 3.65V, then discharge it at 0.05C and 0.2C to 2.5V. The discharge capacity is calculated as C1. Charge it at 0.2C constant current and constant voltage to 3.65V, then 0.05C and 2C to 2.5V. The discharge capacity is calculated as C2. Rate discharge retention rate = C2 / C1*100%.

[0099] 2. Normal temperature cycle life test: The battery is placed at room temperature, charged at 0.5C constant current and constant voltage to 3.65V, and discharged at 0.05C, 0.5C to 2.5V. The discharge capacity is counted as C3. The discharge capacity is counted as Cn for the nth charge and discharge cycle, and the normal temperature cycle life is n (Cn / C3=70%).

[0100] 3. High temperature cycle life test: The battery is placed at a high temperature of 45°C, charged at a constant current and constant voltage of 0.5C to 3.65V, and then discharged at 0.05C and 0.5C to 2.5V. The discharge capacity is counted as C4; the discharge capacity is counted as Cm for the mth charge and discharge cycle, and the high temperature cycle life is m (Cm / C4=70%).

[0101] 4. High-temperature storage gas production rate test: Place the battery at room temperature, let it stand for 2 hours, test the volume V1, transfer it to 60℃ and store it for 7 days, let it stand at room temperature for 2 hours, and test the volume V2; high-temperature storage gas production rate = (V2-V1) / V1*100%.

[0102] (1) The test results obtained in Examples 1 to 7 and Comparative Examples 1 to 5 are entered in Table 2.

[0103] Table 2

[0104] From the test results of Examples 1 to 7 and Comparative Examples 1 to 5, it can be seen that compared with Comparative Examples 1 to 5, the electrolyte combination provided by the present invention is combined with the addition of lithium-rich oxide Li x M m y O zThe positive electrode material layer of the obtained lithium-ion battery has significantly improved the performance in rate discharge performance, cycle life and high temperature working conditions, indicating that the combination of vinylene carbonate, boron-containing compound A and boron-containing compound B has a synergistic effect on the formation of the negative electrode solid electrolyte membrane. The obtained solid electrolyte membrane has good density and stability, as well as high ion permeability. At the same time, the lithium-rich oxide Li x M m y O z The addition of provides lithium source support and promotes the chain growth reaction for the formation of the negative electrode solid electrolyte membrane.

[0105] From the test results of Examples 1 to 7, it can be seen that when different lithium-rich oxides Li x M m y O z Different boron-containing compounds A or different boron-containing compounds B are still applicable to the battery system of the present invention and can effectively improve the cycle life and high-temperature electrochemical performance of lithium-ion batteries.

[0106] (2) The test results obtained in Examples 1 to 4 and Examples 8 to 12 are entered in Table 3.

[0107] Table 3

[0108] It can be seen from the test results of Examples 1 to 4 and Examples 8 to 12 that when the mass ratio of vinylene carbonate, boron-containing compound A and boron-containing compound B meets the conditions of (0.5 to 8): (0.05 to 0.9): (0.02 to 0.6), it is beneficial to optimize the density and high-temperature stability of the solid electrolyte membrane on the surface of the negative electrode material layer, can effectively inhibit the continuous consumption of non-aqueous electrolyte during the battery cycle, improve the battery high-temperature cycle capacity retention rate, thereby extending the cycle life of the battery, and solve the flatulence problem caused by the decomposition of the non-aqueous electrolyte. At the same time, the solid electrolyte membrane has a high ionic conductivity, can adapt to the ion exchange requirements of high-rate discharge, and reduce battery impedance and heat.

[0109] 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 in the scope of protection of the present invention.

Claims

1. A lithium-ion battery, characterized in that, It includes a positive electrode, a negative electrode and a non-aqueous electrolyte. The positive electrode includes a positive electrode material layer, and the positive electrode material layer includes a positive electrode active material and a lithium-rich oxide Li x M m y O z , where M is at least one of Si, Cu, Co, Ni, Mn, Mo, Ru, Fe, 2 ≤ x ≤ 6, 0 < y ≤ 1, 2 ≤ z ≤ 4, and x + my - 2z = 0; the non-aqueous electrolyte includes a non-aqueous organic solvent, a lithium salt and an additive, and the additive includes vinylene carbonate, a boron-containing compound A and a boron-containing compound B; The boron-containing compound A is selected from the compounds shown in Structural Formula 1: wherein R1 and R2 are each independently selected from halogen or cyano; The boron-containing compound B is selected from the compounds shown in Structural Formula 2: wherein R3, R4 and R5 are each independently selected from C1-C5 alkyl, C2-C5 alkenyl, C3-C6 silyl.

2. The lithium-ion battery according to claim 1, wherein, The lithium-rich oxide Li x M m y O z includes one or more of Li5FeO4, Li2MoO3, Li6CoO4, and Li2NiO2.

3. The lithium ion battery according to claim 1, characterized in that, The boron-containing compound A includes one or more of lithium difluorooxalate borate and lithium dicyanooxalate borate.

4. The lithium-ion battery according to claim 1, characterized in that, The boron-containing compound B includes one or more of tri-tert-butyl borate, triethyl borate, triallyl borate, and tris(trimethylsilyl) borate.

5. The lithium ion battery according to claim 1, characterized in that, Based on the total mass of the positive electrode material layer being 100%, the mass percentage of the lithium-rich oxide Li x M m y O z is 0.1% to 4%.

6. The lithium ion battery according to claim 1, characterized in that, Based on the total mass of the non-aqueous electrolyte being 100%, the mass percentage of vinylene carbonate is 0.2% to 10%.

7. The lithium ion battery according to claim 1, characterized in that, Based on the total mass of the non-aqueous electrolyte being 100%, the mass percentage of the boron-containing compound A is 0.02% to 1%.

8. The lithium-ion battery according to claim 1, characterized in that, Based on the total mass of the non-aqueous electrolyte being 100%, the mass percentage of the boron-containing compound B is 0.01% to 0.8%.

9. The lithium ion battery according to claim 1, characterized in that, In the non-aqueous electrolyte, the mass ratio of vinylene carbonate, the boron-containing compound A, and the boron-containing compound B is (0.5-8):(0.05-0.9):(0.02-0.6).

10. The lithium ion battery according to claim 1, characterized in that, The lithium salts include at least one of LiPF6, LiTFSI, LiDFOP, LiPO2F2, LiBF4, LiSbF6, LiAsF6, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiC(SO2CF3)3, LiClO4, LiAlCl4, LiCF3SO3, LiSO3F, Li2B 10 Cl 10 , lithium chloroborane, lithium tetrafluoroxalate phosphate, lithium trioxalate phosphate, lithium lower aliphatic carboxylate having 4 or less carbon atoms, or lithium tetraphenylborate.

11. The lithium ion battery according to claim 1, wherein, The concentration of the lithium salt is 0.1 mol / L to 4 mol / L.

12. The lithium-ion battery according to claim 1, wherein, The additive further includes at least one of cyclic sulfate compounds, sultone compounds, phosphate compounds, and nitrile compounds.

13. The lithium-ion battery according to claim 12, characterized in that, The cyclic sulfate compounds include at least one of ethylene sulfate, propylene sulfate, and methyl ethylene sulfate.

14. The lithium ion battery according to claim 12, characterized in that, The sultone compounds include at least one of 1,3-propane sultone, 1,4-butane sultone, and 1,3-propene sultone.

15. The lithium-ion battery according to claim 12, wherein, The phosphate ester compounds include at least one of tris(trimethylsilyl) phosphate, tris(triethylsilyl) phosphate or the compound shown in Structural Formula 3: In the structural formula 3, R 31 , R 32 , R 33 are each independently selected from a saturated hydrocarbon group having 1 to 5 carbon atoms, an unsaturated hydrocarbon group having 1 to 5 carbon atoms, a halogenated hydrocarbon group having 1 to 5 carbon atoms, -Si(C m H 2m+1 )3, m is a natural number from 1 to 3, and at least one of R 31 , R 32 , R 33 is an unsaturated hydrocarbon group.

16. The lithium-ion battery according to claim 12, wherein The nitrile compounds include at least one of succinonitrile, glutaronitrile, hexane trinitrile, adiponitrile, pimelonitrile, suberonitrile, azelaonitrile, and sebaconitrile.

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