Lithium ion battery

Abstract

In order to overcome the problems of battery expansion and capacity attenuation of the existing lithium ion battery under long-term high-temperature cycle, the application provides a lithium ion battery, which comprises a positive electrode, a negative electrode and a non-aqueous electrolyte, wherein the non-aqueous electrolyte comprises an additive A, an additive B and an additive C; the lithium ion battery satisfies the following condition: 0.015 <= (a+b+c)*V <= 0.09; when the lithium ion battery provided by the application satisfies the relationship of 0.015 <= (a+b+c)*V <= 0.09, the problem of gas production of the electrolyte under long-term high-temperature cycle can be effectively solved, the battery expansion rate is effectively reduced, and the additive can occur special oxidation response on the surface of the positive electrode under the catalysis of a higher voltage, so that a more stable and good positive electrode protection film is formed, the positive electrode is better protected, and the long-term high-temperature cycle capacity retention rate of the battery is effectively improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of energy storage battery devices, and particularly relates to a lithium ion battery. BACKGROUND

[0002] At present, lithium ion batteries have been widely used as power sources in life due to their irreplaceable advantages such as low self-discharge rate, long cycle life, high working voltage and small pollution. Lithium ion batteries have broad prospects in mobile communication, notebook computers and new energy vehicles. At the same time, users also have requirements such as high energy density and fast charging for lithium ion batteries. In the lithium ion battery system, continuously increasing the working voltage and working temperature of the battery will cause the decomposition of electrolyte to different degrees, thereby accelerating the deterioration and failure of the battery performance.

[0003] During the first charge-discharge process of the lithium ion battery, the electrolyte will partially decompose to form a passivation film on the surface of the electrode material, which is called a solid electrolyte interface film (SEI). The chemical composition and structure of the SEI film play a key role in improving the working voltage and working temperature of the battery and the cycle life. Adding a small amount of additives to the electrolyte to optimize the composition of the SEI film is the most economical and convenient method to improve the battery performance.

[0004] The existing electrolyte additives include cyclic sulfate, cyclic sulfonic acid lactone, silane phosphate ester, silane borate ester and fluorinated cyclic carbonate, etc. The inventors found that when the voltage of the lithium battery is greater than or equal to 4.2V, the combination of cyclic sulfate and / or cyclic sulfonic acid lactone compound and silane phosphate ester and / or silane borate ester compound, or the combination of cyclic sulfate and / or cyclic sulfonic acid lactone compound and fluorinated cyclic carbonate compound, although the electrolyte has the advantage of low initial impedance, but under long-term high-temperature cycling, the battery will swell, and there is a problem of high-temperature cycle performance degradation. The electrolyte added with the combination of silane phosphate ester and / or silane borate ester compound and fluorinated cyclic carbonate will cause the capacity retention rate to decay under long-term high-temperature cycling. Moreover, how to inhibit high-temperature gas production to reduce the safety risk during the battery cycle is also a place that needs to be further improved. SUMMARY

[0005] In view of the problems of capacity retention rate decay and battery swelling under long-term high-temperature cycling of the existing lithium ion battery, the application provides a lithium ion battery.

[0006] The technical scheme adopted by the application to solve the above technical problems is as follows:

[0007] The application 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, the negative electrode comprises a negative electrode material layer, the negative electrode material layer comprises a negative electrode active material, and the non-aqueous electrolyte comprises an additive A, an additive B and an additive C.

[0008] The additive A is selected from one or more of a cyclic sulfate compound and / or a cyclic sulfonate lactone compound.

[0009] The additive B is selected from one or more of a silane phosphate compound and / or a silane borate compound.

[0010] The additive C is selected from one or more of a fluorinated cyclic carbonate compound.

[0011] The lithium ion battery satisfies the following conditions:

[0012] 0.015≤(a+b+c)×V≤0.09

[0013] Wherein, a is the mass ratio of the additive A to the positive electrode active material;

[0014] b is the mass ratio of the additive B to the positive electrode active material;

[0015] c is the mass ratio of the additive C to the negative electrode active material;

[0016] V is the upper limit voltage of the lithium ion battery.

[0017] Preferably, the lithium ion battery satisfies the following conditions:

[0018] 0.04≤(a+b+c)×V≤0.09.

[0019] The mass ratio a of the additive A to the positive electrode active material is 0.0008-0.012;

[0020] The mass ratio b of the additive B to the positive electrode active material is 0.0008-0.0022;

[0021] The mass ratio c of the additive C to the negative electrode active material is 0.001-0.01;

[0022] The upper limit voltage V of the lithium ion battery is 4.2V-4.45V.

[0023] Preferably, the mass ratio a of the additive A to the positive electrode active material is 0.004-0.01;

[0024] The mass ratio b of the additive B to the positive electrode active material is 0.001-0.002;

[0025] The mass ratio c of the additive C to the negative electrode active material is 0.0015 to 0.0085.

[0026] Preferably, the cyclic sulfate compound is selected from one or more of the compounds represented by formula A-1, and the cyclic sulfonic acid lactone compound is selected from one or more of the compounds represented by formula A-2;

[0027]

[0028] wherein m is 1 or 2, R1, R2, R3, R4, are each independently selected from a hydrogen atom, a halogen atom, a C1-C3 saturated hydrocarbon group, an oxygen-containing hydrocarbon group, a silicon-containing hydrocarbon group, or a cyano-containing substituted hydrocarbon group; and R5 is selected from a substituted or unsubstituted linear alkylene group having a carbon number of 3 to 5, wherein the substituent is selected from one or more of an alkyl group having a carbon number of 1 to 3, a halogen atom;

[0029] The silane phosphate compound is selected from one or more of the compounds represented by formula B-1, and the silane borate compound is selected from one or more of the compounds represented by formula B-2:

[0030]

[0031] wherein R6, R7, R8, R9, R10, R11, R12, R13, R14 are each independently selected from a C1-C6 alkyl group or a halogenated alkyl group, and R15, R16, R17, R18, R19, R20, R21, R22, R23 are each independently selected from a C1-C6 alkyl group or a halogenated alkyl group;

[0032] The fluorinated cyclic carbonate compound is selected from one or more of the compounds represented by formula C-1:

[0033]

[0034] wherein R24 and R25 are each independently selected from a hydrogen atom, a fluorine atom, or one or more of a C1-C3 saturated hydrocarbon group, an oxygen-containing hydrocarbon group, or a fluorine-containing substituted hydrocarbon group, and at least one of R24 and R25 contains a fluorine atom.

[0035] Preferably, the cyclic sulfate compound is selected from one or more of the following compounds:

[0036]

[0037] The cyclic sulfonic acid lactone compound is selected from one or more of the following compounds:

[0038]

[0039] The silane phosphate compound is selected from one or more of the following compounds:

[0040]

[0041] The silane borate compound is selected from one or more of the following compounds:

[0042]

[0043] The fluorinated cyclic carbonate compound is selected from one or more of the following compounds:

[0044]

[0045] Preferably, the non-aqueous electrolyte further comprises a lithium salt and an organic solvent, the lithium salt is selected from one or more of LiPF6, LiPO2F2, LiBF4, LiBOB, LiClO4, LiCF3SO3, LiDFOB, LiN(SO2CF3)2, and LiN(SO2F)2;

[0046] The organic solvent is selected from one or more of carbonates, carboxylates, and ethers;

[0047] Preferably, the carbonates are selected from cyclic carbonates or chain carbonates, the cyclic carbonates are selected from one or more of vinylene carbonate, propylene carbonate, ethylene carbonate, and butylene carbonate;

[0048] The chain carbonates are selected from one or more of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and methyl propyl carbonate;

[0049] The carboxylates are selected from one or more of methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, methyl butyrate, methyl isobutyrate, methyl trimethylacetate, and ethyl trimethylacetate;

[0050] The ethers are selected from one or more of dimethyl ether of ethylene glycol, 1,3-dioxolane, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether;

[0051] The concentration of the lithium salt in the non-aqueous electrolyte is 0.5-3.5 mol / L, preferably 0.8-2.0 mol / L;

[0052] The non-aqueous electrolyte can further comprise an auxiliary additive, the auxiliary additive is selected from one or more of unsaturated cyclic carbonates and unsaturated phosphates;

[0053] The mass percentage of the auxiliary additive in the non-aqueous electrolyte is 0.1%-2%.

[0054] The unsaturated cyclic carbonate is selected from one or more of vinylene carbonate, vinyl ethylene carbonate, and methylene vinylene carbonate; the unsaturated phosphate ester is selected from one or both of triallyl phosphate or tripropargyl phosphate.

[0055] Preferably, the positive active material includes LiNi x Co y M z O2, wherein 0.5≤x≤1, 0≤y≤0.5, 0≤z≤0.5, x+y+z≤1, M is one or more of Mn, Al, Ti, Cr, Mo, and Zr;

[0056] The negative active material includes graphite.

[0057] Preferably, the positive material is selected from one or more of LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.7 Co 0.1 Mn 0.2 O2, LiNi 0.6 Co 0.1 Mn 0.3 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, and LiNi 0.5 Co 0.2 Mn 0.3 O2.

[0058] Advantages of the present application:

[0059] The lithium ion battery provided by the application can effectively solve the problem of gas production of electrolyte under long-term high-temperature cycling, effectively reduce the expansion rate of the battery, and improve the capacity retention rate of long-term high-temperature cycling when the lithium ion battery satisfies the relationship 0.015≤(a+b+c)×V≤0.09 by adding the additive A, the cyclic sulfate compound and / or the cyclic sulfonic acid lactone compound, the additive B, the silane phosphate compound and / or the silane borate compound, and the additive C, the fluorinated cyclic carbonate compound in the non-aqueous electrolyte. The inventors have found that the key to improving the high-temperature performance mainly lies in the stability and impedance of the positive and negative electrode SEI. The cyclic sulfate compound and / or the cyclic sulfonic acid lactone compound can effectively protect the positive electrode, but there is a problem of too much positive electrode film forming impedance. The silane phosphate compound and / or the silane borate compound has electron-withdrawing B and better P ion transmission, so the positive electrode SEI formed by the silane phosphate compound and / or the silane borate compound is thinner, has better ion transmission, and has low impedance, but the protection of the positive electrode is not enough. When the two coexist, the silane phosphate compound and / or the silane borate compound will preferentially form a film on the positive electrode during charging, forming a low-impedance inner layer film containing B / P, and then the cyclic sulfate compound will further generate a protective layer containing S component on the positive electrode, thereby further protecting the positive electrode. The ratio of the two to the positive active material needs to be strictly controlled, so as to realize the construction of a low-impedance and structurally stable positive electrode protection film. And under the catalysis of the high-voltage positive electrode material surface, the positive electrode protection layer is reorganized, and the two can form a more stable and good positive electrode SEI film, so that the positive electrode is better protected. The F contained in the fluorinated cyclic carbonate can promote the generation of LiF in the negative electrode SEI, and the structure is more stable. However, it is unstable at high temperature and easy to produce gas, so the ratio of the fluorinated cyclic carbonate to the negative active material needs to be strictly controlled to make it consume as much as possible in the negative electrode and reduce the residual amount in the electrolyte. The inventors have found through a large number of experiments that only when the three have a certain ratio to the positive and negative electrode materials (0.015≤(a+b+c)×V≤0.09) can the advantages be complementary, the positive electrode protection film formed contains B / P and S, and the ratio is reasonable, which can take into account the characteristics of low impedance and structural stability. The negative electrode protection film formed is rich in LiF, and the residual amount of fluorinated ethylene carbonate in the electrolyte is small, which can effectively avoid the problem of gas production, thereby effectively improving the long-term high-temperature cycling capacity retention rate of the battery and reducing the gas expansion. DETAILED DESCRIPTION

[0060] In order to make the technical problems, technical solutions and beneficial effects of the present application clearer, the following will further illustrate the present application with examples. It should be understood that the specific examples described herein are only used to explain the present application and not to limit the present application.

[0061] The application 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, the negative electrode comprises a negative electrode material layer, the negative electrode material layer comprises a negative electrode active material, and the non-aqueous electrolyte comprises an additive A, an additive B and an additive C.

[0062] The additive A is selected from one or more of a cyclic sulfate compound and / or a cyclic sulfonate lactone compound.

[0063] The additive B is selected from one or more of a silane phosphate compound and / or a silane borate compound.

[0064] The additive C is selected from one or more of a fluorinated cyclic carbonate compound.

[0065] The lithium ion battery satisfies the following conditions:

[0066] 0.015≤(a+b+c)×V≤0.09

[0067] Wherein a is the mass ratio of the additive A to the positive electrode active material;

[0068] b is the mass ratio of the additive B to the positive electrode active material;

[0069] c is the mass ratio of the additive C to the negative electrode active material;

[0070] V is the upper limit voltage of the lithium ion battery.

[0071] The cyclic sulfate compound and / or the cyclic sulfonate lactone compound added in the lithium battery electrolyte can preferentially assist the formation of the negative electrode interface SEI film, and the remaining unreacted cyclic sulfate compound and / or cyclic sulfonate lactone compound can respond at the positive electrode interface to form a positive electrode protection film; however, the thickness of the positive electrode protection film formed by excessive cyclic sulfate compound and / or cyclic sulfonate lactone compound increases, the battery impedance increases, and the high-temperature performance of the battery deteriorates. The silane phosphate and / or silane borate compound added in the electrolyte can preferentially modify the positive electrode protection film formed at the positive electrode interface during the charging and discharging process of the battery, but the protection of the positive electrode is not enough, and the battery will have a capacity decay problem during high-temperature cycling. The fluorinated cyclic carbonate compound added in the electrolyte can provide good protection for the negative electrode and improve the cycle, but it is easy to decompose under high-temperature conditions, causing gas production problems.

[0072] The inventor finds that when the lithium battery voltage is greater than or equal to 4.2V, the addition of the cyclic sulfate compound and / or the cyclic sulfonolactone compound and the silane phosphate compound and / or the silane borate compound in the lithium battery electrolyte, or the addition of the cyclic sulfate compound and / or the cyclic sulfonolactone compound and the fluorinated cyclic carbonate compound in the electrolyte, the battery prepared has increased gas production and battery swelling during long-term high-temperature cycling, and the battery swelling is mainly caused by the accelerated decomposition of the electrolyte under the action of electrochemistry. The addition of the silane phosphate compound and / or the silane borate compound and the fluorinated cyclic carbonate compound in the lithium battery electrolyte, the battery prepared has increased positive active lithium loss and gradually decaying battery capacity retention rate with the increase of the battery charge and discharge cycle number during long-term high-temperature cycling.

[0073] The lithium ion battery provided by the application adds the cyclic sulfate compound and / or the cyclic sulfonolactone compound, the silane phosphate compound and / or the silane borate compound and the fluorinated cyclic carbonate compound in the non-aqueous electrolyte. Through a large number of researches, it is found that when the lithium ion battery satisfies the relationship 0.015≤(a+b+c)×V≤0.09, the electrolyte can effectively solve the problem of gas production during long-term high-temperature cycling, effectively reduce the battery swelling rate, and at the same time, strictly control the content of the additive A and the additive B to form a more stable and good positive electrode protection film under the condition of higher voltage of the battery, so that the positive electrode is better protected, and the content of the additive C is strictly controlled to effectively improve the stability of the negative electrode SEI film, reduce the residual amount in the electrolyte and reduce the gas production rate, thereby effectively improving the long-term high-temperature cycling capacity retention rate of the battery and reducing the battery swelling rate.

[0074] In some preferred embodiments, the lithium ion battery satisfies the following condition: 0.04≤(a+b+c)×V≤0.09, in which range, the lithium ion battery prepared has a lower swelling rate and a higher long-term high-temperature cycling retention rate.

[0075] In some embodiments, the mass ratio a of the additive A to the positive active material is 0.0008-0.012;

[0076] The mass ratio b of the additive B to the positive active material is 0.0008-0.0022;

[0077] The mass ratio c of the additive C to the negative active material is 0.001-0.01;

[0078] The upper limit voltage V of the lithium ion battery is 4.2V-4.45V.

[0079] The lithium ion battery provided in the application is a high-voltage battery, and the upper limit voltage reaches 4.2V and above, that is, the upper limit voltage of the lithium ion battery is between 4.2V and 4.45V. The adding amount of the additive A and the additive B in the non-aqueous electrolyte is relative to the mass of the positive active material, for example, the mass ratio a of the additive A to the positive active material is 0.0008-0.0012, which means that 0.0008-0.0012g of the additive A is added in the non-aqueous electrolyte per gram of the positive active material. The mass ratio c of the additive C to the negative active material in the non-aqueous electrolyte is 0.001-0.01, which means that 0.001-0.01g of the additive C is added in the non-aqueous electrolyte per gram of the negative active material.

[0080] In some preferred embodiments, the mass ratio a of the additive A to the positive active material is 0.004-0.01;

[0081] The mass ratio b of the additive B to the positive active material is 0.001-0.002;

[0082] The mass ratio c of the additive C to the negative active material is 0.0015-0.0085. In some embodiments, the cyclic sulfate compound is selected from one or more of the compounds represented by the formula A-1;

[0083]

[0084] wherein m is 1 or 2, and R1, R2, R3, R4 are each independently selected from a hydrogen atom, a halogen atom, a C1-C3 saturated hydrocarbon group, an oxygen-containing hydrocarbon group, a silicon-containing hydrocarbon group or a cyano-containing substituted hydrocarbon group. The halogen atom can be selected from fluorine, chlorine, bromine and iodine. The saturated hydrocarbon group with 1-3 carbon atoms can be selected from one or more of a methyl group, an ethyl group and a propyl group; the oxygen-containing hydrocarbon group is a hydrocarbon group in which a hydrogen atom is replaced by an oxygen atom, such as a methoxy group; the silicon-containing hydrocarbon group is a hydrocarbon group in which a hydrogen atom is replaced by a silicon atom; and the cyano-containing substituted hydrocarbon group is a hydrocarbon group in which a hydrogen atom on the hydrocarbon group is replaced by a cyano group -CN.

[0085] In some preferred embodiments, the cyclic sulfate compound is selected from one or more of the following compounds:

[0086]

[0087] It should be noted that the application does not limit the type of the above-mentioned cyclic sulfate compound, as long as it is within the scope of the formula A-1, it belongs to the type of the cyclic sulfate compound of the application.

[0088] In some embodiments, the cyclic sulfonate lactone compound is selected from one or more of the compounds represented by the formula A-2;

[0089]

[0090] R5 is selected from substituted or unsubstituted straight-chain alkylene having 3 to 5 carbon atoms, wherein the substituent is selected from alkyl having 1 to 3 carbon atoms, halogen atom(s). As the unsubstituted straight-chain alkylene having 3 to 5 carbon atoms, propylene, butylene, pentylene can be exemplified as the alkyl.

[0091] In some preferred embodiments, the cyclic sulfonic acid lactone compound is selected from one or more of the following compounds:

[0092]

[0093] It is to be noted that the present application does not limit the above-mentioned cyclic sulfonic acid lactone compound species, as long as it is within the scope of the structural formula A-2, it belongs to the cyclic sulfonic acid lactone compound species of the present application.

[0094] In some embodiments, the silane phosphate compound is selected from one or more of the compounds represented by the structural formula B-1, and the silane borate compound is selected from one or more of the compounds represented by the structural formula B-2

[0095]

[0096] wherein R6, R7, R8, R9, R10, R11, R12, R13, R14 are each independently selected from C1-C6 alkyl or haloalkyl, and R15, R16, R17, R18, R19, R20, R21, R22, R23 are each independently selected from C1-C6 alkyl or haloalkyl.

[0097] C1-C6 alkyl, the alkyl can be a chain alkyl, or a cyclic alkyl, and the hydrogen atom on the ring of the cyclic alkyl can be substituted by an alkyl. As the alkyl, methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, s-butyl, t-butyl, n-pentyl, i-pentyl, neopentyl, hexyl, 2-methyl-pentyl, 3-methyl-pentyl, 1,1,2-trimethyl-propyl, 3,3-dimethyl-butyl can be exemplified.

[0098] In some preferred embodiments, the silane phosphate compound is selected from one or more of the following compounds:

[0099]

[0100] It is to be noted that the present application does not limit the above-mentioned silane phosphate compound species, as long as it is within the scope of the structural formula B-1, it belongs to the silane phosphate compound species of the present application.

[0101] The silane borate compound is selected from one or more of the following compounds:

[0102]

[0103] It should be noted that the application does not limit the above-mentioned alkyl borate compound types, as long as they are within the scope of the structural formula B-2, they belong to the alkyl borate compound types of the application.

[0104] In some embodiments, the fluorinated cyclic carbonate compound is selected from one or more of the compounds shown in formula C-1:

[0105]

[0106] wherein R24 and R25 are each independently selected from one or more of a hydrogen atom, a fluorine atom, or a C1-C3 saturated hydrocarbon group, an oxygen-containing hydrocarbon group, or a fluorine-containing substituted hydrocarbon group, and at least one of R24 and R25 contains a fluorine atom.

[0107] The fluorinated cyclic carbonate compound is selected from one or more of the following compounds:

[0108]

[0109] It should be noted that the application does not limit the above-mentioned fluorinated cyclic carbonate compound types, as long as they are within the scope of the structural formula C-1, they belong to the fluorinated cyclic carbonate compound types of the application.

[0110] Compared with single addition or combination of other existing additives, the addition of additive A, additive B and additive C together can effectively reduce the battery expansion rate during long-term high-temperature cycling of the battery, solve the problem of gas production during long-term high-temperature cycling of the battery; at the same time, strict control of the content of additive A and additive B under higher voltage conditions of the battery can modify and form a more stable and good positive electrode SEI film, so that the positive electrode is better protected, and strict control of the content of additive C can effectively improve the stability of the negative electrode SEI. Thus, the long-term high-temperature cycling capacity retention rate of the battery is effectively improved.

[0111] In some embodiments, the non-aqueous electrolyte further comprises a lithium salt, the lithium salt comprises one or more of LiPF6, LiPO2F2, LiBF4, LiBOB, LiClO4, LiCF3SO3, LiDFOB, LiN(SO2CF3)2 and LiN(SO2F)2; the concentration of the lithium salt in the non-aqueous electrolyte is 0.5-3.5 mol / L.

[0112] In some preferred embodiments, the concentration of the lithium salt in the non-aqueous electrolyte is 0.8-2.0 mol / L.

[0113] In the non-aqueous electrolyte, lithium ions are contained in the lithium salt, which is beneficial to the electrochemical response of the battery during charging and discharging, replenishes the consumption of a small amount of lithium ions, and promotes the cycle performance of the battery. In the non-aqueous electrolyte, the lithium salt affects the conductivity of the electrolyte, and plays a role in conducting electrons between the positive and negative electrodes of the battery. The concentration of the lithium salt affects the viscosity of the electrolyte. As the concentration of the lithium salt increases, the viscosity of the electrolyte increases, the ion transport rate decreases, the battery polarization increases, the battery impedance increases, and the battery performance decreases.

[0114] In some embodiments, the non-aqueous electrolyte further comprises an auxiliary additive, and the non-aqueous electrolyte auxiliary additive further comprises one or more of an unsaturated cyclic carbonate and an unsaturated phosphate ester, and the mass fraction of the auxiliary additive in the non-aqueous electrolyte is 0.1% to 2%.

[0115] In some preferred embodiments, the unsaturated cyclic carbonate is selected from one or more of vinylene carbonate, vinyl ethylene carbonate, and methylene vinyl carbonate; and the unsaturated phosphate ester is selected from one or both of triallyl phosphate and tripropargyl phosphate.

[0116] The content of the auxiliary additive in the non-aqueous electrolyte is set in this range to avoid a decrease in conductivity due to a decrease in the dielectric constant of the non-aqueous electrolyte, and to easily achieve a good range of large-current discharge characteristics, stability with respect to the negative electrode, and cycle characteristics of the non-aqueous electrolyte battery; and to improve the oxidation / reduction resistance of the non-aqueous electrolyte, thereby helping to improve the stability of the battery during high-temperature cycling and high-temperature storage.

[0117] In some embodiments, the non-aqueous electrolyte comprises an organic solvent selected from one or more of carbonates, carboxylic acid esters, and ethers;

[0118] In some preferred embodiments, the carbonates are selected from cyclic carbonates or chain carbonates, and the cyclic carbonates are selected from one or more of vinylene carbonate, propylene carbonate, ethylene carbonate, and butylene carbonate;

[0119] The chain carbonates are selected from one or more of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and methyl propyl carbonate;

[0120] The carboxylic acid esters are selected from one or more of methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, methyl butyrate, methyl isobutyrate, methyl trimethylacetate, and ethyl trimethylacetate;

[0121] The ethers are selected from one or more of ethylene glycol dimethyl ether, 1,3-dioxolane, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0122] In some embodiments, the positive electrode active material comprises LiNi xCo y M z O2, wherein 0.5≤x≤1, 0≤y≤0.5, 0≤z≤0.5, x+y+z≤1, M is one or more of Mn, Al, Ti, Cr, Mo and Zr;

[0123] The positive electrode material is selected from one or more of LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.7 Co 0.1 Mn 0.2 O2, LiNi 0.6 Co 0.1 Mn 0.3 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, and LiNi 0.5 Co 0.2 Mn 0.3 O2.

[0124] The negative electrode active material includes graphite; the graphite is selected from one or more of artificial graphite and natural graphite.

[0125] The negative electrode active material can be selected from graphite, non-graphitized carbon, amorphous carbon, a polymer compound sintered body (for example, a substance obtained by sintering and carbonizing a phenol resin, a furan resin, or the like), a coke (for example, pitch coke, needle coke, and petroleum coke), carbon fiber, and the like.

[0126] The application is further described below by way of examples.

[0127] The compounds shown in the following table are used as the additive A, the additive B, and the additive C in the following examples and comparative examples.

[0128]

[0129] Examples 1-15 and Comparative Examples 1-9

[0130] This example is used to illustrate the battery and the preparation method thereof disclosed in the application, wherein the positive electrode active material is LiNi 0.6 Co 0.2 Mn 0.2 O2, and the negative electrode active material is graphite.

[0131] (1) Preparation of the positive electrode sheet

[0132] The positive electrode active material is LiNi 0.6 Co 0.2 Mn 0.2O2, the positive active material, the conductive agent and the binder PVDF are dispersed into the solvent NMP to mix uniformly to obtain a positive electrode slurry; the positive electrode slurry is uniformly coated on the positive electrode current collector aluminum foil, and after drying, rolling, and cutting, a positive electrode sheet is obtained, wherein the mass ratio of the positive active material, the conductive carbon black and the binder PVDF is 97:1:2.

[0133] (2) Preparation of the negative electrode sheet

[0134] The negative active material graphite, the conductive agent, the binder CMC and SBR are dispersed in deionized water in a mass ratio of 95:1.2:1.4:2.4 to stir to obtain a negative electrode slurry; the negative electrode slurry is uniformly coated on the negative electrode current collector copper foil, and after drying, rolling, and cutting, a negative electrode sheet is obtained.

[0135] (3) Preparation of the electrolyte

[0136] The organic solvents EC and EMC are mixed uniformly in a mass ratio of 3:7, then lithium hexafluorophosphate (LiPF6) is added to a molar concentration of 1 mol / L, and then additives A, B and C are added, wherein the addition amounts of additives A, B and C are shown in Table 1. EC is ethylene carbonate, and EMC is methyl ethyl carbonate.

[0137] (4) Preparation of the lithium ion battery

[0138] The positive electrode sheet, the separator and the negative electrode sheet are stacked in turn by using the lamination process, and then after top side sealing and injection of a certain amount of electrolyte, a soft package battery is prepared.

[0139] Performance test

[0140] The lithium ion battery prepared above is subjected to the following performance test:

[0141] 1. High temperature cycle performance test: at 45℃, the formed battery is charged to the cut-off voltage with 1C constant current and constant voltage, and then charged to the current drop to 0.05C with constant voltage, and then discharged to 3.0V with 1C constant current, and this cycle is repeated for 1000 times, and the discharge capacity of the first time and the discharge capacity of the last time are recorded.

[0142] The capacity retention rate of high temperature cycle is calculated according to the following formula:

[0143] Capacity retention rate = discharge capacity of the last time / discharge capacity of the first time x 100%.

[0144] 2. The gas expansion rate of the battery after 1000 high temperature cycles: after the first high temperature cycle test, the battery was taken out at room temperature, and the volume V1 of the battery was tested by immersing the battery in deionized water using the Archimedes drainage method. After 1000 high temperature cycles, the battery was taken out again, and the volume V2 of the battery was tested by immersing the battery in deionized water using the Archimedes drainage method at room temperature;

[0145] The battery gas expansion rate = (V2-V1) / V1*100%.

[0146] The battery performance test results of Examples 1-15 and Comparative Examples 1-9 are shown in Table 1.

[0147] Table 1

[0148]

[0149]

[0150] From the test results of Examples 1-16 and Comparative Examples 1-11, when the mass ratio of additive A to positive active material is a, the mass ratio of additive B to positive active material is b, and the mass ratio of additive C to negative active material is c, and the relationship 0.015≤(a+b+c)×V≤0.09 is satisfied, the lithium ion battery has a higher high temperature cycle capacity retention rate and a lower gas expansion rate under long-term high temperature cycling.

[0151] From the test results of Examples 1-11, when the lithium ion battery satisfies the preset relationship 0.015≤(a+b+c)×V≤0.09, as the value of (a+b+c)×V increases, the high temperature cycle performance of the lithium ion battery gradually increases, and the gas expansion rate of the battery under long-term high temperature cycling gradually decreases, indicating that the amount of additive A, additive B, and additive C added in the electrolyte can effectively reduce the battery gas expansion rate and improve the battery high temperature cycle capacity retention rate under long-term high temperature cycling. Especially when 0.04≤(a+b+c)×V≤0.09, the lithium ion battery has a lower gas expansion rate and a higher high temperature cycle capacity retention rate.

[0152] Compared with Comparative Examples 1-6, Example 16 shows that adding additives A, B, and C alone to the non-aqueous electrolyte results in low long-term high-temperature cycle capacity retention and higher battery expansion rate in lithium-ion batteries. Adding additives A+B, B+C, or A+C to the non-aqueous electrolyte still results in low high-temperature cycle performance and high expansion rate. Adding additives A, B, and C simultaneously to the electrolyte significantly improves the long-term high-temperature cycle capacity retention and significantly reduces the battery gas expansion rate. This indicates that the simultaneous addition of additives A, B, and C to the non-aqueous electrolyte, under the catalysis of high battery voltage, can undergo a special oxidation reaction on the positive electrode surface, forming a more stable and effective positive electrode protective film, thus providing better protection for the positive electrode and effectively improving the long-term high-temperature cycle capacity retention. It also effectively solves the problem of electrolyte gas generation under long-term high-temperature cycling, effectively reducing the battery expansion rate.

[0153] Compared with Comparative Examples 7-8, Examples 1-16 show that although the mass ratio 'a' of additive A to the positive electrode active material is within the range of 0.0008 to 0.001, the overall content of additives A, B, and C in the electrolyte is not high. Therefore, they cannot effectively synergistically prevent electrolyte decomposition during long-term high-temperature cycling, and a stable and good positive electrode protective film cannot be formed on the positive electrode surface. Under long-term high-temperature cycling, the battery's gas expansion rate increases, and its capacity retention rate is low. In Examples 1-16 and Comparative Example 9, the amounts of additives A, B, and C meet the requirements of this application, but do not meet the requirements of the relationship (a+b+c)×V. The three additives cannot achieve a good balance. Although the high-temperature cycling performance of the battery is improved, possibly due to the formation of a positive electrode protective film at the positive electrode interface, it fails to better prevent electrolyte decomposition, and the battery's gas expansion rate remains high.

[0154] Compared with Comparative Example 10, it can be concluded that the additive A, the additive B and the additive C meet the range requirements of the present application and the range requirements of the relationship (a+b+c) x V, but the voltage is not in the range of 4.2-4.45 V, i.e. the high temperature capacity retention rate and the gas swelling rate of the battery at low voltage also have certain improvement effect. Compared with Comparative Example 11, it can be concluded that the high temperature cycle performance and the gas swelling rate of the battery also have certain modification effect at high voltage (i.e. the voltage is greater than 4.45 V). It is found by comparing Examples 12-16 that when the additive A, the additive B, the additive C and the voltage are in the range set by the present application and meet the range requirements of the relationship (a+b+c) x V, the high temperature cycle capacity retention rate of the battery can be obviously improved, and the gas swelling rate of the battery under long-term high temperature cycle can be effectively reduced. Examples 12-16 and Comparative Examples 10-11 show that under the catalysis of the battery high voltage range 4.2-4.45 V, the electrolyte can occur special oxidation reaction on the surface of the positive electrode to form a more stable and good positive electrode protection film, so that the positive electrode is better protected, thereby effectively improving the long-term high temperature cycle capacity retention rate of the battery; at the same time, the problem of electrolyte gas production under long-term high temperature cycle can also be effectively solved, and the battery swelling rate can be effectively reduced. Examples 17-20

[0155] Examples 17-20 are different from Example 16 in that the positive active material is different; the rest of the preparation method is the same. The specific amount of the additive A, the additive B and the additive C in the non-aqueous electrolyte of Examples 17-20 is shown in Table 2. The battery performance test data of Examples 17-20 is shown in Table 3.

[0156] Table 2

[0157]

[0158]

[0159] Table 3

[0160]

[0161] As can be seen from Table 2 and Table 3, as long as the additives A, additives B and additives C in the non-aqueous electrolyte satisfy the relationship 0.015≤(a+b+c)×V≤0.09, the effects are similar, and the problems of gas generation of the electrolyte under long-term high-temperature cycling and the battery expansion rate can be effectively solved; at the same time, the additives can occur special oxidation reaction on the surface of the positive electrode under the catalysis of higher voltage, form a more stable and good positive electrode protection film, and the positive electrode is better protected, thereby effectively improving the long-term high-temperature cycling capacity retention rate of the battery. It is proved that the relationship satisfied by the additives A, additives B and additives C provided by the application is applicable to different types of positive electrode active materials.

[0162] Examples 21-24

[0163] Examples 21-23 are different from Example 16 in that the structural formulas of the compounds selected for the additives A, additives B and additives C in the non-aqueous electrolyte are different; the rest of the preparation method is the same. The specific addition amounts of the additives A, additives B and additives C in the non-aqueous electrolyte of Examples 21-23 are shown in Table 5. The battery performance test data of Examples 17-20 are shown in Table 6.

[0164] The structural formulas of the compounds selected for the additives A, additives B and additives C in Examples 21-23 are different, and are shown in Table 4 below.

[0165] Table 4

[0166]

[0167] Table 5

[0168]

[0169] Table 6

[0170]

[0171] As can be seen from Table 4-6, as long as the additives A, additives B and additives C in the non-aqueous electrolyte satisfy the relationship 0.015≤(a+b+c)×V≤0.09, the effects are similar, and the problems of gas generation of the electrolyte under long-term high-temperature cycling and the battery expansion rate can be effectively solved; at the same time, the additives can occur special oxidation reaction on the surface of the positive electrode under the catalysis of higher voltage, form a more stable and good positive electrode protection film, and the positive electrode is better protected, thereby effectively improving the long-term high-temperature cycling capacity retention rate of the battery.

[0172] The above merely describes preferred embodiments of the present application, and is not used to limit the present application, any modification, equivalent replacement and improvement within the spirit and principle of the present application should be included in the protection scope of the present application.

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, which includes a positive electrode active material. The negative electrode includes a negative electrode material layer, which includes a negative electrode active material. The non-aqueous electrolyte includes additive A, additive B, and additive C. Additive A is selected from one or more of cyclic sulfate compounds and / or cyclic sulfonyl lactone compounds; The additive B is selected from one or more of silane phosphate compounds and / or silane borate compounds; The additive C is selected from one or more fluorocyclic carbonate compounds; The lithium-ion battery meets the following conditions: 0.015≤(a+b+c)×V≤0.09 Wherein, a is the mass ratio of the additive A to the positive electrode active material; b is the mass ratio of the additive B to the positive electrode active material; c is the mass ratio of the additive C to the negative electrode active material; V represents the upper limit voltage of a lithium-ion battery; The mass ratio a of the additive A to the positive electrode active material is 0.0008 to 0.012; The mass ratio b of the additive B to the positive electrode active material is 0.0008 to 0.0022; The mass ratio c of the additive C to the negative electrode active material is 0.001 to 0.01; The upper limit voltage V of the lithium-ion battery is 4.2V to 4.45V.

2. The lithium-ion battery according to claim 1, characterized in that, The lithium-ion battery meets the following conditions: 0.04≤(a+b+c)×V≤0.

09.

3. The lithium-ion battery according to claim 2, characterized in that, The mass ratio a of the additive A to the positive electrode active material is 0.004 to 0.01; The mass ratio b of the additive B to the positive electrode active material is 0.001 to 0.002; The mass ratio c of the additive C to the negative electrode active material is 0.0015 to 0.0085.

4. The lithium-ion battery according to claim 1, characterized in that, The cyclic sulfate compound is selected from one or more of the compounds shown in formula A-1, and the cyclic sulfonyl lactone compound is selected from one or more of the compounds shown in formula A-2; Wherein, m is 1 or 2, and R1, R2, R3, and R4 are each independently selected from hydrogen atoms, halogen atoms, C1-C3 saturated hydrocarbon groups, oxygen-containing hydrocarbon groups, silicon-containing hydrocarbon groups, or cyano-substituted hydrocarbon groups; R5 is selected from substituted or unsubstituted straight-chain alkylene groups with 3 to 5 carbon atoms, wherein the substituents are selected from one or more of alkyl groups and halogen atoms with 1 to 3 carbon atoms; The silane phosphate compound is selected from one or more of the compounds shown in Formula B-1, and the silane borate compound is selected from one or more of the compounds shown in Formula B-2. Among them, R6, R7, R8, R9, R10, R11, R12, R13, and R14 are each independently selected from C1 to C6 alkyl or haloalkyl, and R15, R16, R17, R18, R19, R20, R21, R22, and R23 are each independently selected from C1 to C6 alkyl or haloalkyl. The fluorocyclic carbonate compound is selected from one or more compounds of formula C-1: Formula C-1 R24 and R25 are each independently selected from one or more of hydrogen atoms, fluorine atoms, or C1-C3 saturated hydrocarbon groups, oxygen-containing hydrocarbon groups, or fluorine-substituted hydrocarbon groups, and at least one of R24 and R25 contains a fluorine atom.

5. The lithium-ion battery according to claim 4, characterized in that, The cyclic sulfate compound is selected from one or more of the following compounds: The cyclic sulfonyl lactone compound is selected from one or more of the following compounds: The silane phosphate compound is selected from one or more of the following compounds: The silane boronic acid ester compound is selected from one or more of the following compounds: The fluorocyclic carbonate compound is selected from one or more of the following compounds: 。 6. The lithium-ion battery according to claim 1, characterized in that, The non-aqueous electrolyte also includes lithium salts and organic solvents, wherein the lithium salts include one or more of LiPF6, LiPO2F2, LiBF4, LiBOB, LiClO4, LiCF3SO3, LiDFOB, LiN(SO2CF3)2 and LiN(SO2F)2; The organic solvent is selected from one or more of carbonates, carboxylic esters, or ethers.

7. The lithium-ion battery according to claim 6, characterized in that, The carbonate is selected from cyclic carbonates or chain carbonates, and the cyclic carbonate is selected from one or more of vinylene carbonate, propylene carbonate, ethylene carbonate, and butene carbonate. The chain carbonate is selected from one or more of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and methyl propyl carbonate; The carboxylic acid ester is selected from one or more of methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, methyl butyrate, methyl isobutyrate, methyl trimethylacetate, and ethyl trimethylacetate; The ethers are selected from one or more of ethylene glycol dimethyl ether, 1,3-dioxolane and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether; The concentration of lithium salt in the non-aqueous electrolyte is 0.5~3.5 mol / L.

8. The lithium-ion battery according to claim 1, characterized in that, The positive electrode active material includes LiNi x Co y M z O2, where 0.5≤x≤1, 0≤y≤0.5, 0≤z≤0.5, x+y+z≤1, and M is one or more of Mn, Al, Ti, Cr, Mo and Zr; The negative electrode active material includes graphite.

9. The lithium-ion battery according to claim 8, characterized in that, The cathode material is selected from LiNi. 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.7 Co 0.1 Mn 0.2 O2, LiNi 0.6 Co 0.1 Mn 0.3 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2 and LiNi 0.5 Co 0.2 Mn 0.3 One or more of O2; the graphite is selected from one or more of artificial graphite or natural graphite.

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