Lithium ion battery

Abstract

In order to solve the problem that an electrolyte is continuously consumed due to unstable film formation of an existing battery negative electrode, the invention provides a lithium ion battery, the lithium ion battery comprises a positive electrode, a negative electrode and a non-aqueous electrolyte, 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 LixMmyOz, M is at least one of Si, Cu, Co, Ni, Mn, Mo, Ru and Fe, x is greater than or equal to 2 and less than or equal to 6, y is greater than 0 and less than or equal to 1, and z is greater than or equal to 2 and less than or equal to 4. X + my-2z = 0; the non-aqueous electrolyte comprises a non-aqueous organic solvent, a lithium salt and an additive; the additive comprises vinylene carbonate, a boron-containing compound A and a boron-containing compound B; the boron-containing compound A is selected from a compound # imgabs 0 # as shown in a structural formula 1; and the boron-containing compound B is selected from a compound # imgabs 1 # as shown in a structural formula 2. The lithium ion battery provided by the invention has excellent cycle life and high-temperature performance.

Description

Technical Field

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

[0002] The expansion of the new energy market has accelerated the technological iteration of lithium-ion batteries, and the application side has put forward higher requirements for the cycle service life of lithium-ion batteries. At present, there are bottlenecks in the cycle life of commercial lithium-ion batteries. The service life of batteries for consumer electronics products is generally no more than five years, the service life of batteries for electric vehicles usually does not exceed eight years, and the service life of energy storage batteries is ten years. The service life of the battery needs to be further improved.

[0003] The service life of the battery is related to the loss of function of easily worn components inside the battery, which conforms to the "short board effect" and usually depends on the component with the fastest loss. During the cycle of charge and discharge, there are losses in the positive electrode, electrolyte, and negative electrode of the battery. The structures of commercial positive and negative electrode materials are usually relatively stable. As the medium between the positive electrode and the negative electrode, the loss of the electrolyte at the electrode interface is the main factor restricting the battery capacity in the middle and late stages of the cycle. Reducing the loss of the electrolyte at the electrode interface is the key strategy to improve the battery cycle life. In the prior art, various film-forming additives are added to form a solid electrolyte film on the negative electrode interface to protect the negative electrode. However, according to existing research, the performance differences of the solid electrolyte films formed by different film-forming additives in different states are relatively large. The rupture of the solid electrolyte film during the cycle will further consume the electrolyte and increase its thickness at the rupture position, resulting in an increase in impedance and a decrease in capacity in the late stage of the cycle. Summary of the Invention

[0004] Aiming at the problem that the film formation on the negative electrode of the existing battery is unstable, resulting in continuous consumption of the electrolyte, the present invention provides a lithium-ion battery.

[0005] The technical solutions adopted by the present invention to solve the above technical problems are as follows:

[0006] The present 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, 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, boron-containing compound A, and boron-containing compound B;

[0007] The boron-containing compound A is selected from the compound shown in Structural Formula 1:

[0008]

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

[0010] The boron-containing compound B is selected from the compounds shown in Structural Formula 2:

[0011]

[0012] Wherein, R3, R4 and R5 are each independently selected from C1-C5 alkyl, C2-C5 alkenyl, C3-C6 silyl.

[0013] Optionally, the lithium-rich oxide Li x M m y O z Includes one or more of Li5FeO4, Li2MoO3, Li6CoO4, Li2NiO2.

[0014] Optionally, the boron-containing compound A includes one or more of lithium difluorooxalate borate, lithium dicyanooxalate borate.

[0015] Optionally, the boron-containing compound B includes one or more of tri-tert-butyl borate, triethyl borate, triallyl borate, tris(trimethylsilyl) borate.

[0016] Optionally, 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%.

[0017] Optionally, based on the total mass of the non-aqueous electrolyte being 100%, the mass percentage of 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%.

[0018] Optionally, 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 to 8):(0.05 to 0.9):(0.02 to 0.6).

[0019] Optionally, the lithium salt includes 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 tetrafluorooxalate phosphate, lithium trioxalate phosphate, lithium lower aliphatic carboxylate having less than 4 carbon atoms, or lithium tetraphenylborate. The concentration of the lithium salt is 0.1 mol / L to 4 mol / L.

[0020] Optionally, the additive further includes at least one of cyclic sulfate compounds, sultone compounds, phosphate ester compounds, and nitrile compounds.

[0021] Optionally, the cyclic sulfate compounds include at least one of ethylene sulfate, propylene sulfate, and vinyl methyl sulfate; and / or

[0022] the sultone compounds include at least one of 1,3-propane sultone, 1,4-butane sultone, and 1,3-propene sultone; and / or

[0023] the phosphate ester compounds include at least one of tris(trimethylsilyl) phosphate, tris(triethylsilyl) phosphate, or the compound shown in Structural Formula 3:

[0024]

[0025] 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; and / or

[0026] the nitrile compounds include at least one of succinonitrile, glutaronitrile, hexane trinitrile, adiponitrile, pimelonitrile, suberonitrile, azelaonitrile, and sebaconitrile.

[0027] 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 in the non-aqueous electrolyte to participate in the formation of the solid electrolyte film on the negative electrode. During the formation stage, vinylene carbonate and boron-containing compound A decompose together at the negative electrode interface to form a solid electrolyte film containing Li2CO3 and boron-containing compound. Since boron-containing compound B has multiple branched structures, its decomposition products can form cross-linking points in the solid electrolyte film, playing a cross-linking role, thus facilitating the formation of a tough solid electrolyte film. This solid electrolyte film has good ion permeability. At the same time, since the formation of this solid electrolyte film consumes a large amount of lithium ions, conventional positive electrode active materials are difficult to supply in the early stage of formation. Therefore, a lithium-rich oxide Li x M m y O z is added to the positive electrode material layer, which plays a role in quickly supplying lithium ions in the early stage of formation, thus ensuring the film-forming density and stability of the solid electrolyte film, effectively suppressing the side reaction between the non-aqueous electrolyte and the negative electrode interface, and avoiding the rupture of the solid electrolyte film during the cycling process. On the other hand, the lithium and oxygen released by the lithium-rich oxide Li x M m y O z 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 film. Detailed Embodiments

[0028] In order to make the technical problems, technical solutions, and beneficial effects solved by the present invention clearer, the present invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0029] An embodiment of the present 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, 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, boron-containing compound A, and boron-containing compound B;

[0030] The boron-containing compound A is selected from the compounds shown in Structural Formula 1:

[0031]

[0032] wherein R1 and R2 are each independently selected from halogen or cyano;

[0033] The boron-containing compound B is selected from the compounds shown in Structural Formula 2:

[0034]

[0035] wherein, R3, R4 and R5 are each independently selected from C1-C5 alkyl, C2-C5 alkenyl, C3-C6 silyl.

[0036] In the lithium-ion battery, vinylene carbonate, boron-containing compound A and boron-containing compound B are simultaneously used as additives in the non-aqueous electrolyte to participate in the formation of the solid electrolyte film on the negative electrode. During the formation stage, vinylene carbonate and boron-containing compound A decompose together on the negative electrode interface to form a solid electrolyte film containing Li2CO3 and boron-containing compound. Since the boron-containing compound B has multiple branched structures, its decomposition products can form cross-linking points in the solid electrolyte film and play a cross-linking role, thus facilitating the formation of a solid electrolyte film with toughness. This solid electrolyte film has good ion permeability. At the same time, since the formation of this solid electrolyte film consumes a large amount of lithium ions, it is difficult for conventional positive electrode active materials to supply them in the early stage of formation. Therefore, a lithium-rich oxide Li x M m y O z is added to the positive electrode material layer, which plays a role in quickly supplying lithium ions in the early stage of formation, thus ensuring the film-forming compactness and stability of the solid electrolyte film, effectively suppressing the side reaction between the non-aqueous electrolyte and the negative electrode interface, and avoiding the rupture of the solid electrolyte film during the cycle. On the other hand, the lithium and oxygen released by the lithium-rich oxide Li x M m y O z 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 film.

[0037] In some embodiments, the lithium-rich oxide Li x M m y O z includes one or more of Li5FeO4, Li2MoO3, Li6CoO4, Li2NiO2.

[0038] Using the above compounds as the lithium-rich oxide Li x M m y O z, it can quickly release lithium ions during the formation stage, ensuring the lithium source supply for the solid electrolyte interphase on the negative electrode interface, thereby avoiding the capacity loss of the positive electrode active material and improving the initial efficiency of the battery.

[0039] In some embodiments, the boron-containing compound A includes one or more of lithium difluorooxalate borate and lithium dicyanooxalate borate.

[0040] The boron-containing compound A has a cyclic oxalate borate structure and decomposes on the surface of the negative electrode to form a dense boron-containing polymer, which is one of the main components of the solid electrolyte interphase on the negative electrode.

[0041] 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.

[0042] The boron-containing compound B has a multi-branched borate ester structure centered on a B atom, and each branch can be integrated into the solid electrolyte interphase framework formed by the boron-containing compound A, playing a good three-dimensional cross-linking role, thereby improving the overall toughness of the solid electrolyte interphase.

[0043] In some embodiments, 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%.

[0044] In a specific embodiment, 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 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%.

[0045] When the mass fraction of the positive electrode lithium-rich oxide Li x M m y O z is within the above range, the released lithium and oxygen are beneficial to the reaction of the electrolyte additive to form a good solid electrolyte interphase and protect the negative electrode. When the lithium-rich oxide Li x M m y O zWhen the mass percentage content is too low, the released lithium and oxygen are not sufficient to diffuse to the negative electrode to participate in the formation of the negative electrode passivation film, the coverage rate of the formed solid electrolyte film is insufficient, the negative electrode protection effect is poor, and the cycle life is reduced; moreover, the lithium content in the negative electrode passivation layer is insufficient, the internal resistance is large, and the rate performance is reduced; when the mass percentage content of the lithium-rich oxide Li x M m y O z is too high, too much lithium and oxygen will be released in a short time, the chain growth reaction of vinylene carbonate is too intense, a thick and loose interface layer is formed on the negative electrode, and the gas generation during the high-temperature storage of the battery is aggravated. Optionally, based on the total mass of the non-aqueous electrolyte being 100%, the mass percentage content of the vinylene carbonate is 0.2% to 10%, the mass percentage content of the boron-containing compound A is 0.02% to 1%, and the mass percentage content of the boron-containing compound B is 0.01 to 0.8%.

[0046] 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 to 8):(0.05 to 0.9):(0.02 to 0.6).

[0047] 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 film 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 during the formation of the solid electrolyte film, resulting in insufficient flexibility and poor ion transport performance of the solid electrolyte film, 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 film is not stable enough, and the electrolyte is consumed due to the reconstruction of the interface layer during the cycle, and the improvement effect of the cycle life is not good.

[0048] In some embodiments, the lithium salt includes 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 less than 4 carbon atoms, or lithium tetraphenylborate.

[0049] In some embodiments, in the non-aqueous electrolyte, the concentration of the lithium salt is 0.1 mol / L to 4 mol / L. In a preferred embodiment, in the non-aqueous electrolyte, the concentration of the lithium salt 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.

[0050] 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%.

[0051] Specifically, based on the total mass of the non-aqueous electrolyte being 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%, 90%.

[0052] 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.

[0053] In some embodiments, the ether solvent includes cyclic ethers or chain ethers, preferably chain ethers having 3 to 10 carbon atoms and cyclic ethers having 3 to 6 carbon atoms. The cyclic ethers may specifically be, but are not limited to, at least one of 1,3-dioxolane (DOL), 1,4-dioxane (DX), crown ether, tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-CH3-THF), and 2-trifluoromethyltetrahydrofuran (2-CF3-THF); the chain ethers may specifically be, but are not limited to, dimethoxymethane, diethoxymethane, ethoxymethoxymethane, ethylene glycol di-n-propyl ether, ethylene glycol di-n-butyl ether, and diethylene glycol dimethyl ether. Since chain ethers have a high solvation ability with lithium ions and can improve ion dissociation, dimethoxymethane, diethoxymethane, and ethoxymethoxymethane, which have low viscosity and can impart 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%, the volume ratio is generally 1% or more, preferably 2% or more, more preferably 3% or more. Additionally, the volume ratio is generally 30% or less, preferably 25% or less, more preferably 20% or less.

[0054] In some embodiments, the nitrile solvent may specifically be, but is not limited to, at least one of acetonitrile, glutarodinitrile, and malononitrile.

[0055] In some embodiments, the carbonate solvents include cyclic carbonates or chain carbonates. The cyclic carbonates may specifically but not limited to be at least one of ethylene carbonate (EC), propylene carbonate (PC), γ-butyrolactone (GBL), and butylene carbonate (BC); the chain carbonates may specifically but not limited to be 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 may be arbitrary within the range that does not significantly damage the effect of the lithium-ion battery of the present invention. However, when using a single type alone, the lower limit of its content is generally 3% or more, preferably 5% or more, by volume, relative to the total amount of the solvents of the non-aqueous electrolyte. By setting this range, it is possible to avoid a decrease in conductivity due to a decrease in the dielectric constant of the non-aqueous electrolyte, and it is easy to bring the high-current discharge characteristics, stability with respect to the negative electrode, and cycle characteristics of the non-aqueous electrolyte battery into a good range. In addition, the upper limit is generally 90% or less, preferably 85% or less, more preferably 80% or less, by volume. By setting this range, the oxidation / reduction resistance of the non-aqueous electrolyte can be improved, which helps to improve the stability during high-temperature storage. The content of the chain carbonate is not particularly limited and is generally 15% or more, preferably 20% or more, more preferably 25% or more, by volume, relative to the total amount of the solvents of the non-aqueous electrolyte. In addition, it is generally 90% or less, preferably 85% or less, more preferably 80% or less, by volume. By making the content of the chain carbonate within the above range, it is easy to bring the viscosity of the non-aqueous electrolyte into an appropriate range, suppress a decrease in ionic conductivity, and further helps to bring the output characteristics of the non-aqueous electrolyte battery into a good range. When using two or more chain carbonates in combination, it is only necessary to make the total amount of the chain carbonates satisfy the above range.

[0056] In some embodiments, it is also preferable to use chain carbonates having fluorine atoms (hereinafter simply referred to as "fluorinated chain carbonates"). The number of fluorine atoms in the fluorinated chain carbonate is not particularly limited as long as it is 1 or more, but is generally 6 or less, preferably 4 or less. When the fluorinated chain carbonate has a plurality of fluorine atoms, these fluorine atoms may be bonded to the same carbon or to different carbons. Examples of the fluorinated chain carbonate include fluorinated dimethyl carbonate derivatives, fluorinated ethyl methyl carbonate derivatives, fluorinated diethyl carbonate derivatives, etc.

[0057] The carboxylic acid ester solvents include cyclic carboxylic acid esters and / or chain carbonates. Examples of the cyclic carboxylic acid esters may include at least one of γ-butyrolactone, γ-valerolactone, and δ-valerolactone. Examples of the chain carbonates may include at least one of methyl acetate (MA), ethyl acetate (EA), propyl acetate (EP), butyl acetate, propyl propionate (PP), and butyl propionate.

[0058] In some embodiments, the sulfone solvents include cyclic sulfones and chain sulfones. Preferably, in the case of cyclic sulfones, they are usually compounds with 3 to 6 carbon atoms, preferably 3 to 5 carbon atoms; in the case of chain sulfones, they are usually compounds with 2 to 6 carbon atoms, preferably 2 to 5 carbon atoms. There is no special limitation on the addition amount of the sulfone solvents, and it can be arbitrary within the range that does not significantly damage the effect of the lithium-ion battery of the present invention. Relative to the total amount of the solvents in the non-aqueous electrolyte, the volume ratio is usually 0.3% or more, preferably 0.5% or more, more preferably 1% or more. Additionally, the volume ratio is usually 40% or less, preferably 35% or less, more preferably 30% or less. When two or more sulfone solvents are used in combination, the total amount of the sulfone solvents only needs to satisfy the above range. When the addition amount of the sulfone solvents is within the above range, it tends to obtain a non-aqueous electrolyte with excellent high-temperature storage stability.

[0059] In a preferred embodiment, the non-aqueous organic solvent includes a mixture of cyclic carbonates and chain carbonates.

[0060] In some embodiments, the additive further includes at least one of cyclic sulfate compounds, sultone compounds, phosphate compounds, and nitrile compounds.

[0061] 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%.

[0062] In some embodiments, the cyclic sulfate compounds include at least one of ethylene sulfate, propylene sulfate, and vinyl methyl sulfate.

[0063] In some embodiments, the sultone compounds include at least one of 1,3-propane sultone, 1,4-butane sultone, and 1,3-propene sultone.

[0064] In some embodiments, the phosphate compounds include at least one of tris(trimethylsilyl) phosphate, tris(triethylsilyl) phosphate, or the compound shown in Structural Formula 3:

[0065]

[0066] In the Structural Formula 3, R 31 , R 32 , R 33 are each independently selected from a C1-C5 saturated hydrocarbon group, a C1-C5 unsaturated hydrocarbon group, a C1-C5 halogenated hydrocarbon group, -Si(C m H 2m+1 )3, m is a natural number from 1 to 3, and R 31 , R32 , R 33 At least one of them is an unsaturated hydrocarbon group.

[0067] In a preferred embodiment, the phosphate compound shown in Structural Formula 3 may be at least one of triallyl phosphate, diallylmethyl phosphate, diallylethyl phosphate, diallylpropyl phosphate, diallyltrifluoromethyl phosphate, diallyl-2,2,2-trifluoroethyl phosphate, diallyl-3,3,3-trifluoropropyl phosphate, diallylhexafluoroisopropyl phosphate, tripropargyl phosphate, dipropargylmethyl phosphate, dipropargylethyl phosphate, dipropargylpropyl phosphate, dipropargyltrifluoromethyl phosphate, dipropargyl-2,2,2-trifluoroethyl phosphate, dipropargyl-3,3,3-trifluoropropyl phosphate, dipropargylhexafluoroisopropyl phosphate.

[0068] In some embodiments, the nitrile compound includes at least one of succinonitrile, glutarodinitrile, hexanetrinitrile, adiponitrile, pimelonitrile, suberonitrile, azelaonitrile, sebaconitrile.

[0069] In other embodiments, the additive may further include other additives that can improve battery performance: for example, additives that enhance battery safety performance, specifically flame retardant additives such as fluorophosphate esters and cyclophosphazenes, or overcharge prevention additives such as tert-amylbenzene and tert-butylbenzene.

[0070] It should be noted that, unless otherwise specified, generally, the content of any optional substance in the additive in the non-aqueous electrolyte is 10% or less, preferably 0.01 - 5%, and more preferably 0.1% - 2%. Specifically, the content of any optional substance in the additive 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%, 10%.

[0071] In some embodiments, the additive includes fluoroethylene carbonate, and based on the total mass of the non-aqueous electrolyte being 100%, the addition amount of the fluoroethylene carbonate is 0.01% - 30%.

[0072] In some embodiments, the positive electrode active material includes LiFe 1-x’ M’ x’ PO4, LiMn 2-y’ M y’ O4 and LiNi x Coy Mn z M 1-x-y-z One or more of 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.

[0073] 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 lithium-rich oxide Li x M m y O z , the positive electrode binder and the positive electrode conductive agent are blended to obtain the positive electrode material layer.

[0074] The positive electrode binder includes at least one of thermoplastic resins such as polyvinylidene fluoride, copolymers of vinylidene fluoride, polytetrafluoroethylene, copolymers of vinylidene fluoride - hexafluoropropylene, copolymers of tetrafluoroethylene - hexafluoropropylene, copolymers of tetrafluoroethylene - perfluoroalkyl vinyl ether, copolymers of ethylene - tetrafluoroethylene, copolymers of vinylidene fluoride - tetrafluoroethylene, copolymers of vinylidene fluoride - trifluoroethylene, copolymers of vinylidene fluoride - trichloroethylene, copolymers of vinylidene fluoride - fluoroethylene, copolymers of vinylidene fluoride - hexafluoropropylene - tetrafluoroethylene, thermoplastic polyimide, polyethylene and polypropylene; acrylic resins; and styrene - butadiene rubber.

[0075] The positive electrode conductive agent includes at least one of conductive carbon black, conductive carbon spheres, conductive graphite, conductive carbon fibers, carbon nanotubes, graphene or reduced graphene oxide.

[0076] In some embodiments, the positive electrode current collector includes a metal material capable of conducting 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.

[0077] In some embodiments, the negative electrode includes a negative electrode active material layer, 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. The carbon-based negative electrode may include graphite, hard carbon, soft carbon, graphene, mesocarbon microbeads, 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-oxygen, tin metal compounds; the lithium negative electrode may include metallic lithium or a lithium alloy. The lithium alloy may specifically be at least one of a lithium-silicon alloy, a lithium-sodium alloy, a lithium-potassium alloy, a lithium-aluminum alloy, a lithium-tin alloy, and a lithium-indium alloy.

[0078] In a more preferred embodiment, the negative electrode active material includes at least one of graphite, hard carbon, soft carbon, graphene, and a silicon-carbon composite material.

[0079] 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.

[0080] In some embodiments, the negative electrode further includes 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 includes a metal material that can conduct 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.

[0081] In some embodiments, the negative electrode active 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 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 will not be elaborated here.

[0082] In some embodiments, the battery further includes a separator, and the separator is located between the positive electrode and the negative electrode.

[0083] The separator may be an existing conventional separator, which may be a ceramic separator, a polymer separator, a non-woven fabric, an inorganic-organic composite separator, 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 separators.

[0084] The present invention will be further described below through examples.

[0085] Table 1

[0086]

[0087]

[0088] Example 1

[0089] This example is used to illustrate the preparation method of the lithium-ion battery disclosed in the present invention, including the following operating steps:

[0090] 1) Preparation of non-aqueous electrolyte:

[0091] Mix a solvent, a lithium salt, and an additive to prepare an electrolyte. The solvent is a mixture of ethylene carbonate and dimethyl carbonate with a mass ratio of 30%:70%. Based on the total weight of the non-aqueous electrolyte being 100%, add 13% lithium hexafluorophosphate, as well as vinylene carbonate, boron-containing compound A, and boron-containing compound B as shown in Table 1.

[0092] 2) Preparation of the positive electrode:

[0093] Mix the positive electrode active material LiFePO4, conductive carbon black Super-P, and binder PVDF in a mass ratio of 96:2:2, and then add the lithium-rich oxide in the mass ratio shown in Table 1. Disperse it in N-methyl-2-pyrrolidone to obtain a positive electrode slurry. Coat the slurry evenly on both sides of the aluminum foil, and obtain the positive electrode through drying, rolling, and vacuum drying.

[0094] 3) Preparation of the negative electrode:

[0095] Mix the negative electrode active material, conductive carbon black Super-P, and a mixture of binder SBR and CMC (mass ratio 97:1:2) in a certain mass ratio, disperse it in deionized water to obtain a negative electrode slurry. Coat the slurry on both sides of the copper foil, and obtain the negative electrode plate through drying, rolling, and vacuum drying.

[0096] 4) Fabrication of the lithium-ion battery: Stack the positive electrode with welded tabs, the separator, and the negative electrode with welded tabs in sequence, wind and encapsulate it with an aluminum-plastic film to obtain an electric core. Inject the above electrolyte into the electric core, and prepare the lithium-ion battery through aging, formation, fixture shaping, and secondary sealing.

[0097] Examples 2 to 12

[0098] Examples 2 to 12 are used to illustrate the lithium-ion battery and its preparation method disclosed in the present invention, including most of the operating steps in Example 1. The differences are as follows:

[0099] 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 the lithium-rich oxide and its addition amount in the positive electrode material layer are as shown in Table 1.

[0100] Comparative Examples 1 to 5

[0101] Comparative Examples 1 to 5 are used to illustrate the lithium-ion battery and its preparation method disclosed in the present invention, including most of the operation steps in Example 1, and the differences are as follows:

[0102] 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 the lithium-rich oxide and its addition amount in the positive electrode material layer are shown in Table 1.

[0103] Performance Test

[0104] The following performance tests are carried out on the lithium-ion battery prepared above:

[0105] 1. Rate discharge retention test: The battery is placed at room temperature, charged at a constant current and voltage of 0.2C to 3.65V, 0.05C, and discharged at 0.2C to 2.5V, and the discharge capacity is denoted as C1; charged at a constant current and voltage of 0.2C to 3.65V, 0.05C, and discharged at 2C to 2.5V, and the discharge capacity is denoted as C2; the rate discharge retention = C2 / C1 * 100%.

[0106] 2. Room temperature cycle life test: The battery is placed at room temperature, charged at a constant current and voltage of 0.5C to 3.65V, 0.05C, and discharged at 0.5C to 2.5V, and the discharge capacity is denoted as C3; during the nth cycle of charge and discharge, the discharge capacity is denoted as Cn, and the room temperature cycle life is n (Cn / C3 = 70%).

[0107] 3. High temperature cycle life test: The battery is placed at a high temperature of 45°C, charged at a constant current and voltage of 0.5C to 3.65V, 0.05C, and discharged at 0.5C to 2.5V, and the discharge capacity is denoted as C4; during the mth cycle of charge and discharge, the discharge capacity is denoted as Cm, and the high temperature cycle life is m (Cm / C4 = 70%).

[0108] 4. High temperature storage gas generation rate test: The battery is placed at room temperature, left standing for 2h, the volume V1 is measured, transferred to 60°C for storage for 7d, left standing at room temperature for 2h, and the volume V2 is measured; the high temperature storage gas generation rate = (V2 - V1) / V1 * 100%.

[0109] (1) The test results obtained from Examples 1 to 7 and Comparative Examples 1 to 5 are filled in Table 2.

[0110] Table 2

[0111]

[0112]

[0113] 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, using the electrolyte combination provided by the present invention and adding the lithium-rich oxide Li x Mm y O z The positive electrode material layer of the obtained lithium-ion battery has significantly improved performance in rate discharge performance, cycle life, and performance under high-temperature working conditions. This shows that the combination of vinylene carbonate, boron-containing compound A, and boron-containing compound B has a synergistic effect on the formation of the solid electrolyte film on the negative electrode. The obtained solid electrolyte film has good compactness and stability, as well as a high ion transmittance. At the same time, the addition of rich lithium oxide Li x M m y O z provides a lithium source support and promotes the chain growth reaction for the formation of this solid electrolyte film on the negative electrode.

[0114] It can be seen from the test results of Examples 1 to 7 that when different rich lithium oxides Li x M m y O z , different boron-containing compound A, or different boron-containing compound B are used, they are still applicable to the battery system of the present invention and can effectively improve the cycle life and high-temperature electrochemical performance of the lithium-ion battery.

[0115] (2) Fill the test results obtained from Examples 1 to 4 and Examples 8 to 12 into Table 3.

[0116] Table 3

[0117]

[0118] 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 satisfies the condition (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 film on the surface of the negative electrode material layer, can effectively inhibit the continuous consumption of the non-aqueous electrolyte during the battery cycle, improve the high-temperature cycle capacity retention rate of the battery, thereby extending the cycle life of the battery, solve the problem of gas expansion caused by the decomposition of the non-aqueous electrolyte, and at the same time, this solid electrolyte film has a high ionic conductivity, can meet the ion exchange requirements of high-rate discharge, and reduce the battery impedance and heat generation.

[0119] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope 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 compound 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 compound 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, characterized in that, 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 difluorooxalatoborate and lithium dicyanooxalatoborate.

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 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%.

7. The lithium-ion battery according to claim 1, wherein 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).

8. 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 less than 4 carbon atoms, or lithium tetraphenylborate, and the concentration of the lithium salt is 0.1 mol / L to 4 mol / L.

9. The lithium ion battery according to claim 1, characterized in that, The additive further comprises at least one of cyclic sulfate compounds, sultone compounds, phosphate compounds and nitrile compounds.

10. The lithium ion battery according to claim 9, characterized in that, The cyclic sulfate ester compound includes at least one of vinyl sulfate, propylene sulfate and methyl vinyl sulfate; and / or The sultone compound includes at least one of 1,3-propane sultone, 1,4-butane sultone and 1,3-propene sultone; and / or The phosphate compound includes at least one of tris(trimethylsilyl)phosphate, tris(triethylsilyl)phosphate or the compound shown in structural formula 3: In the said 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 R 31 、R 32 、R 33 At least one of them is an unsaturated hydrocarbon group; and / or The nitrile compound includes at least one of succinonitrile, glutaronitrile, hexanetrinitrile, adiponitrile, pimelonitrile, suberonitrile, azelaic acid dinitrile and sebacononitrile.

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