Lithium ion battery electrolyte and lithium ion battery

Abstract

The present invention relates to a lithium ion battery electrolyte and a lithium ion battery, which mainly solves the problem of poor high and low temperature performance of lithium ion batteries. The present invention adds a first additive to the electrolyte, and the first additive is selected from one or more compounds shown in structural formula A, wherein R1, R2, and R3 are independently selected from hydrogen atoms, halogen atoms, substituted or unsubstituted alkyl, alkenyl, alkynyl, cyano, phenyl, halogenated phenyl, carbonyl, phenoxy, thiophenyl, amide, thiophene-2-ylthio, or any two of the R1, R2, and R3 form a substituted or unsubstituted cyclic alkenyl group, and the substituted groups include halogen atoms and amino groups, so that the lithium ion battery has better high temperature cycle, high temperature shelf and low temperature performance, and the first additive can also synergize with other additives to further improve the high and low temperature performance of the lithium ion battery.

Description

Technical Field

[0001] The invention relates to a lithium ion battery electrolyte and a lithium ion battery. Background Art

[0002] As portable electronic products develop towards miniaturization and multi-functionality, and power batteries have higher requirements for driving range and application environment, the performance of lithium-ion batteries is facing higher challenges.

[0003] In order to improve the energy density of lithium-ion batteries, the simplest approach is to change the positive and negative electrode materials of lithium-ion batteries. Nickel-cobalt-manganese ternary positive electrode materials with high energy density are used. However, this positive electrode material is prone to dissolution of cobalt ions / manganese ions during the cycle process or high-temperature storage, resulting in a decrease in battery performance. Compared with the current mainstream negative electrode material graphite (theoretical maximum energy density of 372mAh / g), silicon has a theoretical gram capacity of 4200mAh / g, and the earth's reserves are high. Silicon-based materials that combine the electrical conductivity and stability of carbon materials and the high capacity of silicon materials have great development potential. However, due to the large volume expansion effect of silicon-based materials, especially during high-temperature storage and circulation, it is easy to cause high-temperature gas production / battery voltage to drop sharply, thereby deteriorating battery performance. Therefore, it is necessary to improve the performance of lithium-ion batteries such as high-temperature cycling and high-temperature shelving. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a lithium ion battery electrolyte and a lithium ion battery, wherein the lithium ion battery electrolyte can improve the high temperature cycle capacity of the lithium ion battery, inhibit battery swelling after high temperature storage, improve capacity retention rate, and improve rate discharge at low temperature.

[0005] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] The present invention provides a lithium ion battery electrolyte, comprising an organic solvent, a lithium salt and an additive, wherein the additive comprises a first additive, the first additive is selected from one or more compounds represented by structural formula A, and the structural formula A is Wherein, the R1, R2, and R3 are independently selected from hydrogen atoms, halogen atoms, substituted or unsubstituted alkyl groups, alkenyl groups, alkynyl groups having 1 to 6 carbon atoms, cyano groups, phenyl groups, halogenated phenyl groups, carbonyl groups, phenoxy groups, thiophenyl groups, amide groups, thiophen-2-ylthio groups, or any two of the R1, R2, and R3 form a substituted or unsubstituted cyclic alkenyl group, and the substituted groups include halogen atoms and amino groups.

[0007] Preferably, R1, R2, and R3 are independently selected from a hydrogen atom, a substituted or unsubstituted alkyl group having 1 to 3 carbon atoms, a halogenated phenyl group, a carbonyl group having 2 to 6 carbon atoms, a thiophenyl group, and a thiophen-2-ylthio group, or any two of R1, R2, and R3 form a substituted or unsubstituted cyclic alkenyl group having 3 to 6 carbon atoms, and the substituted group is selected from a halogen atom and an amino group, and the halogen atom is selected from one or more of fluorine, chlorine, and bromine.

[0008] Further preferably, the first additive is selected from one or more of the following structural formulas:

[0009] Preferably, the first additive accounts for 0.5% to 2.0% of the total weight of the electrolyte.

[0010] Further preferably, the first additive accounts for 0.9% to 1.5% of the total weight of the electrolyte, for example, it may be 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, etc.

[0011] Preferably, the additive further comprises a second additive and a third additive, wherein the second additive is selected from one or more phosphorus-fluorinated lithium salts; and the third additive is selected from one or more compounds represented by structural formula C, wherein structural formula C is Wherein, the R4 is a group containing one or more of a borate group, a phosphate group, a phosphite group, an isocyanate group, a heterocyclic group, an amine group, and a sulfate group.

[0012] More preferably, the second additive is selected from one or more of lithium difluorophosphate, lithium difluorobisoxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0013] Further preferably, the third additive is selected from one or more of the following structural formulas:

[0014]

[0015] Preferably, the second additive accounts for 0.1% to 2.0% of the total weight of the electrolyte.

[0016] Further preferably, the second additive accounts for 0.4% to 1.0% of the total weight of the electrolyte, for example, it may be 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, etc.

[0017] Preferably, the third additive accounts for 0.1% to 2.0% of the total weight of the electrolyte.

[0018] Further preferably, the third additive accounts for 0.4% to 1.0% of the total weight of the electrolyte, for example, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, etc.

[0019] Preferably, the additives also include other additives, and the other additives are selected from one or more of cyclic carbonates containing double bonds, cyclic carbonates containing halogens, sulfonates, sulfates, sulfites, anhydrides, benzene compounds, fluorobenzene compounds, nitrile compounds, phosphates, phosphites, boron compounds, amine compounds, silicon-containing compounds, and heterocyclic compounds.

[0020] Further preferably, the other additives include vinyl carbonate, ethylene carbonate, fluoroethylene carbonate, vinyl sulfate, methylene methanedisulfonate, vinyl sulfite, 1,3-propane sultone, biphenyl, succinic anhydride, glutaric anhydride, cyclohexylbenzene, tert-butylbenzene, tert-amylbenzene, m-fluorotoluene, 3,4-difluorotoluene, 4-bromo-2-fluoroanisole, p-fluorotoluene, p-xylene, 1,2-dimethoxy-4-nitrobenzene, N-phenylmaleimide One or more of imine, pentafluoroanisole, 2,5-di-tert-butyl, 1,4-dimethoxybenzene, adiponitrile, hexanetrinitrile, succinonitrile, 1,2,3-tris(2-cyanoethoxy)propane, n-butylamine, ethanolamine, N,N-dicyclohexylcarbodiimide, N,N-diethylaminotrimethylsilane, hexamethyldisilazane, triphenyl phosphate, pimelonitrile, 2-ethoxy-2,4,4,6,6-pentafluorotripolyphosphazene, 2-fluoropyridine, and 1,3-dioxane.

[0021] More preferably, the other additives account for 0.5% to 5% of the total weight of the electrolyte, for example, 0.5%, 0.7%, 1.0%, 1.2%, 1.5%, 1.7%, 2%, 2.3%, 2.5%, 2.7%, 3%, 3.5%, 4%, 4.5%, etc.

[0022] Preferably, the organic solvent comprises one or more of substituted or unsubstituted carbonates, substituted or unsubstituted carboxylates, substituted or unsubstituted ethers, substituted or unsubstituted sulfones, substituted or unsubstituted sulfoxides, substituted or unsubstituted benzenes, and the substituted groups comprise fluorine atoms.

[0023] More preferably, the organic solvent accounts for 70% to 85% of the total weight of the electrolyte, for example, 70%, 75%, 80%, 85%, etc.

[0024] According to some preferred embodiments, the organic solvent is a mixture of two or more of fluoroethylene carbonate, difluoroethylene carbonate, trifluoroethyl carbonate, fluoroethyl sulfone, tetrafluoroethyl tetrafluoropropyl ether, trifluoroethyl hexafluoropropyl ether, dimethyl carbonate, diethyl carbonate, ethylene carbonate, propylene carbonate, ethyl methyl carbonate, ethylene glycol dimethyl ether, r-butyrolactone, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, propyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, cyclopentane, methyl ethyl sulfone, dimethyl sulfoxide, and fluorobenzene.

[0025] Preferably, the lithium salt comprises a mixture of at least one of lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, lithium bis(oxalatoborate) and lithium oxalatodifluoroborate and lithium hexafluorophosphate.

[0026] More preferably, the lithium salt accounts for 10% to 25% of the total weight of the electrolyte, for example, 12%, 15%, 17%, 20%, 22%, 25%, etc.

[0027] More preferably, the lithium hexafluorophosphate accounts for 10% to 15% of the total weight of the electrolyte.

[0028] A second aspect of the present invention provides a lithium ion battery comprising the electrolyte as described above.

[0029] Preferably, the lithium-ion battery comprises a positive electrode and a negative electrode, the positive electrode comprises a positive electrode active material, and the positive electrode active material comprises LiNi x Co y Mn 1-x-y O2 or LiCoO2, wherein the value of x is 0.3-1, and the value of y is 0-0.4; the negative electrode comprises a negative electrode active material, and the negative electrode active material comprises metallic lithium, metal oxide, metal alloy, graphite, modified carbon material, silicon, silicon oxygen or silicon oxygen carbon.

[0030] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0031] The present invention can improve the high-temperature cycle capacity of a lithium-ion battery, inhibit battery swelling after being stored at high temperature, improve capacity retention, and improve rate discharge at low temperatures by adding a first additive to the electrolyte; the first additive can synergize with other additives to further improve the high and low temperature performance of the lithium-ion battery. DETAILED DESCRIPTION

[0032] As the application scenarios of lithium-ion batteries expand, it is necessary to further improve the high-temperature cycle capacity of lithium-ion batteries, inhibit battery swelling after high-temperature storage, improve capacity retention, and improve rate discharge at low temperatures. Therefore, the inventors conducted in-depth research and a large number of experiments to obtain this solution, which is further discussed below.

[0033] According to some preferred embodiments, a lithium ion battery electrolyte includes an organic solvent, a lithium salt and an additive, wherein the additive includes a first additive, a second additive and a third additive, wherein the first additive is selected from one or more compounds represented by structural formula A. Structural formula A is Wherein, R1, R2, and R3 are independently selected from hydrogen atoms, halogen atoms, substituted or unsubstituted alkyl groups, alkenyl groups, alkynyl groups having 1 to 6 carbon atoms, cyano groups, phenyl groups, halogenated phenyl groups, carbonyl groups, phenoxy groups, thiophenyl groups, amide groups, thiophen-2-ylthio groups, or any two of said R1, R2, and R3 form a substituted or unsubstituted cyclic alkenyl group, and said substituted groups include halogen atoms and amino groups;

[0034] The second additive is selected from one or more phosphorus-fluorine-lithium salts;

[0035] The third additive is selected from one or more compounds represented by structural formula C, wherein structural formula C is Wherein, R4 is a group containing one or more of a borate group, a phosphate group, a phosphite group, an isocyanate group, a heterocyclic group, an amine group, and a sulfate group;

[0036] The first additive accounts for 0.5% to 2.0% of the total weight of the electrolyte; the second additive accounts for 0.1% to 2.0% of the total weight of the electrolyte; and the third additive accounts for 0.1% to 2.0% of the total weight of the electrolyte.

[0037] Furthermore, a lithium-ion battery includes the electrolyte as described above. Specifically, the lithium-ion battery includes a housing, a battery cell contained in the housing, and a non-aqueous electrolyte, wherein the battery cell includes a positive electrode, a negative electrode, and a separator between the positive electrode and the negative electrode.

[0038] According to the present invention, the positive electrode includes a positive electrode current collector and a positive electrode material located on the surface of the positive electrode current collector. The positive electrode material includes a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder. The positive electrode active material can be a common type LiNi x Co y Mn 1-x-y O2, ordinary LiNi x Co y Al 1-x-y O2, ordinary LiCoO2, high voltage LiNi x Co y Mn 1-x-yO2, high voltage LiCoO2; the positive electrode conductive agent is acetylene black or carbon nanotubes; the positive electrode binder is polyvinylidene fluoride.

[0039] According to the present invention, the negative electrode includes a negative electrode current collector and a negative electrode material located on the surface of the negative electrode current collector, the negative electrode material includes a negative electrode active substance and a negative electrode binder, and the negative electrode material may also selectively include a negative electrode conductive agent, which may be the same as or different from the positive electrode conductive agent, and both are conductive agents commonly used in the art; the negative electrode active substance and the negative electrode binder may be negative electrode active substances and negative electrode binders conventionally used in the art, for example, the negative electrode active substance may be metallic lithium, metal oxides, metal alloys, graphite and modified carbon materials, silicon and its silicon oxygen, silicon carbon or silicon oxygen carbon.

[0040] According to the present invention, the separator may be a separator conventionally used in the art, and the present invention is not particularly limited thereto.

[0041] The solution of the present invention has at least the following advantages:

[0042] (1) The first additive in the present invention can improve the high-temperature cycle capacity of lithium-ion batteries to a certain extent, inhibit battery swelling after high-temperature storage, improve capacity retention, and improve rate discharge at low temperatures. It can achieve effects comparable to those of additives in the prior art. The use of the first additive expands the types of additives and provides more possibilities for the selection of additives.

[0043] (2) The present invention adds a first additive, a second additive, a third additive and other additives to the electrolyte, so that during the charge and discharge process of the lithium ion battery, the structural stability of the positive and negative electrode materials and the interface stability between the positive electrode and the electrolyte, and between the negative electrode and the electrolyte are improved through the synergistic effect between the additives, thereby improving the high and low temperature performance of the lithium ion battery.

[0044] The present invention is further described below in conjunction with the examples. However, the present invention is not limited to the following examples. The implementation conditions used in the examples can be further adjusted according to the different requirements of specific use, and the implementation conditions not specified are conventional conditions in the industry. The technical features involved in each embodiment of the present invention can be combined with each other as long as they do not conflict with each other.

[0045] Preparation of electrolyte:

[0046] The specific embodiments and comparative examples of the present invention prepare battery electrolytes in a glove box according to the formulas described in Table 1 and Table 2. The substances involved in the table include ethylene carbonate (EC), dimethyl carbonate (DEC), ethyl methyl carbonate (EMC), propylene carbonate (PC), fluoroethylene carbonate (FEC), lithium bis(fluorosulfonyl)imide (LiFSI), lithium difluoroborate oxalate (LiODFB), 1,3-propane sultone (PS), vinyl sulfate (DTD), and lithium hexafluorophosphate (LiPF6);

[0047] The structural formula of A1 is:

[0048] The structural formula of A2 is:

[0049] The structural formula of A3 is:

[0050] The structural formula of A4 is:

[0051] The structural formula of A5 is:

[0052] The structural formula of A6 is:

[0053] The structural formula of A7 is:

[0054] The structural formula of A8 is:

[0055] B1 is lithium difluorophosphate (LiDFP); B2 is lithium difluorobisoxalate phosphate (LiDFOP); B3 is lithium tetrafluorooxalate phosphate (LiTFOP);

[0056] The structural formula of C1 is:

[0057] The structural formula of C2 is:

[0058] The structural formula of C3 is:

[0059] The structural formula of C4 is:

[0060] The structural formula of C5 is:

[0061] The structural formula of C6 is:

[0062] The structural formula of C7 is:

[0063] Table 1

[0064]

[0065]

[0066]

[0067] Table 2

[0068]

[0069] Preparation of the battery:

[0070] The electrolytes obtained in Examples 1 to 46 and Comparative Examples 1 to 12 were injected into the same batch of LiNi 0.6 Co 0.2 Mn 0.2 The following tests were performed on the O2 (NCM622) || Silicon Oxygen Carbon (420mAh) polymer soft pack battery:

[0071] 1) When the battery is tested at 45°C, voltage between 2.75-4.3V, and current of 1C, the capacity retention rate after 500 charge and discharge cycles is L1% (discharge capacity after 500 cycles / average discharge capacity before 5 weeks*100);

[0072] 2) After the test battery is fully charged at 4.3V and placed at 60°C for 7 days, the battery swelling rate is H% (thickness before placing - thickness after placing) / thickness before placing * 100), and the capacity retention rate is L2% (discharge capacity after placing / discharge capacity before placing * 100);

[0073] 3) When the battery is tested at a low temperature of 0°C and the voltage is between 2.75-4.3V and the current is 2C, the capacity retention rate after 200 charge and discharge cycles is L3% (discharge capacity after 200 cycles / average discharge capacity before 5 weeks*100);

[0074] The experimental results are shown in Table 3.

[0075] Table 3

[0076]

[0077]

[0078]

[0079] Table 3 shows that in LiNi 0.6 Co 0.2 Mn 0.2In O2 (NCM622) || Silicon Oxycarbon (420mAh) 1Ah polymer soft-pack battery, the use of the first additive can improve the high and low temperature performance of the lithium-ion battery. When used in combination with the second additive, the third additive, etc., the high-temperature cycle, high-temperature shelf performance, and low-temperature discharge of the battery can be further improved.

[0080] The above detailed description of the present invention is intended to enable persons familiar with the art to understand the contents of the present invention and implement them. It does not limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A lithium ion battery electrolyte, comprising an organic solvent, a lithium salt and an additive, characterized in that: The additives include a first additive, a second additive and a third additive, The first additive is selected from one or more of the following structural formulas: ； The second additive is selected from one or more of lithium difluorophosphate, lithium difluorobisoxalate phosphate, and lithium tetrafluorooxalate phosphate; The third additive is selected from one or more of the following structural formulas: ， The first additive accounts for 0.5% to 2.0% of the total weight of the electrolyte, the second additive accounts for 0.1% to 2.0% of the total weight of the electrolyte, and the third additive accounts for 0.1% to 2.0% of the total weight of the electrolyte.

2. The lithium-ion battery electrolyte according to claim 1, characterized in that: The first additive accounts for 0.9% to 1.5% of the total weight of the electrolyte.

3. The lithium ion battery electrolyte according to claim 1, characterized in that: The second additive accounts for 0.4% to 1.0% of the total weight of the electrolyte; the third additive accounts for 0.4% to 1.0% of the total weight of the electrolyte.

4. The lithium-ion battery electrolyte according to claim 1, characterized in that: The additives also include other additives, which are selected from one or more of cyclic carbonates containing double bonds, cyclic carbonates containing halogens, sulfonates, sulfates, sulfites, anhydrides, benzene compounds, nitrile compounds, phosphates, phosphites, boron compounds, amine compounds, silicon-containing compounds, and heterocyclic compounds.

5. The lithium ion battery electrolyte according to claim 4, characterized in that: The other additives include vinyl carbonate, ethylene carbonate, fluoroethylene carbonate, vinyl sulfate, methylene methanedisulfonate, vinyl sulfite, 1,3-propane sultone, biphenyl, succinic anhydride, glutaric anhydride, cyclohexylbenzene, tert-butylbenzene, tert-amylbenzene, m-fluorotoluene, 3,4-difluorotoluene, 4-bromo-2-fluoroanisole, p-fluorotoluene, p-xylene, 1,2-dimethoxy-4-nitrobenzene, N-phenylmaleimide One or more of amine, pentafluoroanisole, 1,4-dimethoxybenzene, adiponitrile, hexanetrinitrile, succinonitrile, 1,2,3-tris(2-cyanoethoxy)propane, n-butylamine, ethanolamine, N,N-dicyclohexylcarbodiimide, N,N-diethylaminotrimethylsilane, hexamethyldisilazane, triphenyl phosphate, pimelonitrile, 2-ethoxy-2,4,4,6,6-pentafluorotripolyphosphazene, 2-fluoropyridine, and 1,3-dioxane; and / or, The other additives account for 0.5% to 5% of the total weight of the electrolyte.

6. The lithium ion battery electrolyte according to claim 1, characterized in that: The organic solvent comprises one or more of substituted or unsubstituted carbonate, substituted or unsubstituted carboxylate, substituted or unsubstituted ether, substituted or unsubstituted sulfone, substituted or unsubstituted sulfoxide, substituted or unsubstituted benzene, the substituted group comprises fluorine atom, and the organic solvent accounts for 70% to 85% of the total weight of the electrolyte; and / or, The lithium salt includes a mixture of at least one of lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, lithium bis(oxalatoborate) and lithium oxalatodifluoroborate and lithium hexafluorophosphate, and the lithium salt accounts for 10% to 25% of the total weight of the electrolyte.

7. The lithium ion battery electrolyte according to claim 6, characterized in that: The organic solvent is a mixture of two or more of fluoroethylene carbonate, difluoroethylene carbonate, trifluoroethyl carbonate, fluoroethyl sulfone, tetrafluoroethyl tetrafluoropropyl ether, trifluoroethyl hexafluoropropyl ether, dimethyl carbonate, diethyl carbonate, ethylene carbonate, propylene carbonate, ethyl methyl carbonate, ethylene glycol dimethyl ether, r-butyrolactone, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, propyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, cyclopentane, methyl ethyl sulfone, dimethyl sulfoxide, and fluorobenzene.

8. A lithium ion battery, characterized in that: The lithium-ion battery comprises the electrolyte according to any one of claims 1 to 7.

9. The lithium-ion battery according to claim 8, characterized in that: The lithium-ion battery comprises a positive electrode and a negative electrode, wherein the positive electrode comprises a positive electrode active material, and the positive electrode active material comprises LiNi x Co y Mn 1-ｘ-y O2 or LiCoO2, wherein the value of x is 0.3~1, and the value of y is 0~0.4; the negative electrode includes a negative electrode active material, and the negative electrode active material includes metallic lithium, metal oxides, metal alloys, graphite, modified carbon materials, silicon, silicon oxygen or silicon oxygen carbon.

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