Non-aqueous electrolyte and lithium secondary battery

Abstract

The invention relates to a non-aqueous electrolyte and a lithium secondary battery. In order to solve the problems of poor cycle performance, high impedance and serious gas production of a lithium secondary battery, the invention provides a non-aqueous electrolyte, the non-aqueous electrolyte comprises an organic solvent, a lithium salt and additives, the additives comprise a first additive, a second additive and a third additive, the first additive is selected from one or more of compounds shown in a formula I, and the third additive is selected from one or more of compounds shown in a formula II; the formula I is # imgabs0; the second additive is selected from a compound shown in a formula II and / or a formula III; the formula II is # imgabs 1 #, the formula III is # imgabs 2 #, and the third additive is selected from one or more of double-bond-containing cyclic carbonate, halogen-containing cyclic carbonate, sulfonate, sulfate, sulfite, anhydride, a benzene compound, a fluorobenzene compound, a nitrile compound, phosphate, phosphite, a boron compound, an amine compound, a silicon-containing compound and a heterocyclic compound. Through the synergistic effect of the three additives, the cycle performance of the battery is improved, the impedance of the battery is reduced, and the gas production of the battery is reduced.

Description

Technical Field

[0001] The invention relates to a non-aqueous electrolyte and a lithium secondary battery. Background Art

[0002] Lithium-ion batteries (or lithium secondary batteries) have the advantages of high energy density, good cycle performance, long storage time, and low self-discharge. As an ideal energy storage device, they are expected to gradually replace traditional energy storage devices such as lead-acid batteries, nickel-cadmium batteries, and nickel-metal hydride batteries. With the expansion of lithium-ion battery applications and the development of modern information technology, lithium-ion batteries have been challenged to a higher level, namely, the need to further improve the cycle performance of lithium-ion batteries, reduce their impedance, and reduce their gas production. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide a non-aqueous electrolyte that can improve battery cycle performance, reduce battery impedance and reduce battery gas production, and further provide a lithium secondary battery containing the non-aqueous electrolyte.

[0004] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0005] A non-aqueous electrolyte comprises an organic solvent, a lithium salt and an additive, wherein the additive comprises a first additive, a second additive and a third additive, wherein the first additive is selected from one or more compounds represented by formula I, wherein formula I is wherein R1, R2, R3, and R4 are independently selected from hydrogen, alkyl, haloalkyl, cyano, halo, -COCN, -COR8, alkenyl, haloalkenyl, alkynyl, or haloalkynyl, and at least one of R1, R2, R3, and R4 is cyano or -COCN, and R8 is selected from alkyl;

[0006] The second additive is selected from the compound represented by formula II and / or the compound represented by formula III, wherein formula II is Wherein, R5 and R6 are independently selected from hydrogen, a hydrocarbon group having 1 to 6 carbon atoms, a halogenated alkyl group or a cyano group; the formula III is Wherein, R7 is selected from hydrogen and an alkyl group having 1 to 6 carbon atoms;

[0007] The third additive is selected from one or more of cyclic carbonates containing double bonds, cyclic carbonates containing halogens, sulfonates, sulfates, sulfites, acid anhydrides, benzene compounds, fluorobenzene compounds, nitrile compounds, phosphates, phosphites, boron compounds, amine compounds, silicon-containing compounds, and heterocyclic compounds.

[0008] The present invention adds a first additive, a second additive and a third additive to the electrolyte, so that during the charge and discharge process of the battery, the stability of the positive and negative electrode material structures 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 of the above additives, thereby improving the normal temperature and high temperature cycle performance of the battery, reducing the impedance of the battery at normal temperature or high temperature, and reducing the gas production of the battery at high temperature. According to the present invention, the normal temperature refers to 25°C, and the high temperature refers to 45-60°C.

[0009] Preferably, R1 is selected from an alkyl group having 1 to 3 carbon atoms or a cyano group, R2 is selected from hydrogen or a cyano group, R3 is selected from hydrogen or a halogen group, R4 is selected from hydrogen, -COCN, -COR8 or an alkyl group having 1 to 3 carbon atoms, R8 is selected from an alkyl group having 2 to 4 carbon atoms, and the halogen group is fluorine.

[0010] Furthermore, the R1 is selected from methyl or cyano.

[0011] Furthermore, the R4 is selected from hydrogen, -COCN, -COC(CH3)3 or ethyl.

[0012] Preferably, the R5 is selected from an alkenyl group having 1 to 3 carbon atoms, a fluoroalkyl group having 1 to 3 carbon atoms, a cyano group or an alkyl group having 2 to 4 carbon atoms, and the R6 is selected from hydrogen or an alkenyl group having 1 to 3 carbon atoms.

[0013] Furthermore, the R5 is selected from vinyl, cyano, fluoromethyl or isopropyl.

[0014] Furthermore, the R6 is selected from hydrogen or vinyl.

[0015] Preferably, said R7 is selected from hydrogen, methyl, ethyl or propyl.

[0016] In some preferred embodiments, the formula I is

[0017] In some preferred embodiments, the formula II is

[0018] In some preferred embodiments, the formula III is In some specific and preferred embodiments, the first additive is a compound represented by formula I, wherein formula I is The second additive is a compound represented by formula III, wherein formula III is

[0019] Preferably, the first additive and the second additive each account for 0.05% to 5% of the total weight of the non-aqueous electrolyte.

[0020] Furthermore, the first additive and the second additive respectively account for 0.05% to 2% of the total weight of the non-aqueous electrolyte, for example, 0.05%, 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.3%, 1.5%, 1.8% or 2%.

[0021] Furthermore, the first additive and the second additive account for 1% to 3% of the total weight of the non-aqueous electrolyte, for example, 1%, 1.3%, 1.5%, 1.8%, 2%, 2.3%, 2.5%, 2.8%, 3%, etc.

[0022] Preferably, the third additive is selected from vinylene carbonate, vinyl 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 , 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, 1,3-dioxane or one or more thereof.

[0023] Preferably, the third additive accounts for 0.3% to 10% of the total weight of the non-aqueous electrolyte.

[0024] Furthermore, the third additive accounts for 0.5% to 8% of the total weight of the non-aqueous electrolyte, further 2% to 6%, and further 3% to 5%.

[0025] In some preferred embodiments, the third additive is vinylene carbonate and 1,3-propane sultone.

[0026] Furthermore, the mass ratio of vinylene carbonate to 1,3-propane sultone is 1:(0.5-1.5), for example, 1:0.5, 1:0.8, 1:1, 1:1.3, 1:1.5, etc.

[0027] Preferably, 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, and the substituted group comprises a fluorine atom.

[0028] Further, the organic solvent is selected from 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.

[0029] Preferably, the organic solvent accounts for 60% to 90% of the total weight of the non-aqueous electrolyte, further 70% to 85%, and further 75% to 80%.

[0030] In some specific embodiments, the organic solvent is ethylene carbonate, diethyl carbonate, ethyl methyl carbonate, fluoroethylene carbonate and propylene carbonate.

[0031] Furthermore, ethylene carbonate accounts for 15% to 25% of the total weight of the non-aqueous electrolyte, diethyl carbonate accounts for 5% to 15% of the total weight of the non-aqueous electrolyte, propylene carbonate accounts for 3% to 8% of the total weight of the non-aqueous electrolyte, ethyl methyl carbonate accounts for 35% to 45% of the total weight of the non-aqueous electrolyte, and fluoroethylene carbonate accounts for 3% to 8% of the total weight of the non-aqueous electrolyte.

[0032] Preferably, the lithium salt includes a first lithium salt and a second lithium salt, the first lithium salt is lithium hexafluorophosphate, and the second lithium salt is selected from one or more of lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, lithium dioxalatoborate, lithium oxalatodifluoroborate, lithium difluorooxalatophosphate, lithium tetrafluorooxalatophosphate, lithium fluorosulfonate and lithium 4,5-dicyano-2-trifluoromethylimidazole.

[0033] Preferably, the lithium salt accounts for 8% to 30% of the total weight of the non-aqueous electrolyte, further 10% to 20%, for example 10%, 12%, 14%, 16%, 18%, 20%, etc.

[0034] In some specific embodiments, the first lithium salt accounts for 10% to 15% of the total weight of the non-aqueous electrolyte, and the second lithium salt accounts for 1% to 5% of the total weight of the non-aqueous electrolyte.

[0035] Furthermore, the second lithium salt is lithium bis(fluorosulfonyl)imide and lithium oxalate difluoroborate.

[0036] Furthermore, lithium bis(fluorosulfonyl)imide accounts for 2% to 3% of the total weight of the non-aqueous electrolyte, and lithium oxalodifluoroborate accounts for 0.5% to 1.5% of the total weight of the non-aqueous electrolyte.

[0037] A second object of the present invention is to provide a lithium secondary battery comprising a positive electrode, a negative electrode and a separator disposed between the positive electrode and the negative electrode, wherein the lithium secondary battery further comprises the non-aqueous electrolyte as described above.

[0038] Preferably, the positive electrode active material in the positive electrode is LiNi x Co y Mn z O2 or LiNi x Co y Al z O2, wherein the value of x is 0-1, the value of y is 0-1, and the value of z is 0-1; the negative electrode active material in the negative electrode includes metallic lithium, metal oxides, lithium aluminum alloys, graphite, modified carbon materials, silicon, silicon oxygen or silicon oxygen carbon.

[0039] According to the present invention, the positive electrode includes a positive electrode collector and a positive electrode material located on the surface of the positive electrode collector. The positive electrode material includes a positive electrode active substance, a positive electrode conductor and a positive electrode binder. The positive electrode conductor may be, for example, acetylene black or carbon nanotubes, and the positive electrode binder may be, for example, polyvinylidene fluoride.

[0040] 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. The negative electrode material may also selectively include a negative electrode conductive agent. The negative electrode conductive agent 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 binder is a negative electrode binder conventionally used in the art, and the present invention does not impose any specific limitation.

[0041] 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.

[0042] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0043] The present invention improves the cycle performance of the battery, reduces the battery impedance and reduces the gas generation of the battery through the synergistic effect of the first additive, the second additive and the third additive. DETAILED DESCRIPTION

[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), diethyl 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), vinylene carbonate (VC), and lithium hexafluorophosphate (LiPF6);

[0047] The structural formula of A1 is: The structural formula of A2 is:

[0048] The structural formula of A3 is: The structural formula of A4 is: The structural formula of A5 is: The structural formula of B1 is: The structural formula of B2 is: The structural formula of B3 is: The structural formula of B4 is: The structural formula of B5 is: The structural formula of B6 is: The structural formula of B7 is:

[0049] Table 1

[0050]

[0051]

[0052]

[0053]

[0054] The wt% in Table 1 is a unit of weight percentage, which indicates weight ratio, that is, the proportion of one substance in the mixture.

[0055] Preparation of the battery:

[0056] The electrolytes obtained in Examples 1 to 41 and Comparative Examples 1 to 12 were injected into 1Ah 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:

[0057] 1) The test battery is charged and discharged for 500 cycles at 25°C and 45°C, voltage between 2.75-4.2V, and current of 1C. The capacity retention rates L1% and L2% (discharge capacity after 500 cycles / average discharge capacity before 5 weeks × 100) and the internal resistance growth rates R1% and R2% are measured.

[0058] 2) The test battery is fully charged to 4.2V and placed at 60°C for 28 days. The battery swelling rate is H% (thickness before placing - thickness after placing) / thickness before placing × 100).

[0059] The above experimental results are shown in Table 2.

[0060] Table 2

[0061]

[0062]

[0063]

[0064] Table 2 shows that in LiNi 0.6 Co 0.2 Mn 0.2 In O2(NCM622)||Silicon Oxycarbon(420mAh) 1Ah polymer soft pack battery, the combination of the first additive, the second additive and the third additive can further improve the battery cycle, impedance and gas production problems.

[0065] 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 non-aqueous 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, wherein the first additive is selected from one or more compounds represented by formula I, wherein formula I is wherein R1, R2, R3, and R4 are independently selected from hydrogen, alkyl, haloalkyl, cyano, halo, -COCN, -COR8, alkenyl, haloalkenyl, alkynyl, or haloalkynyl, and at least one of R1, R2, R3, and R4 is cyano or -COCN, and R8 is selected from alkyl; The second additive is selected from the compound represented by formula II and / or the compound represented by formula III, wherein formula II is Wherein, R5 and R6 are independently selected from hydrogen, a hydrocarbon group having 1 to 6 carbon atoms, a halogenated alkyl group or a cyano group; the formula III is Wherein, R7 is selected from hydrogen and an alkyl group having 1 to 6 carbon atoms; The third additive is selected from one or more of cyclic carbonates containing double bonds, cyclic carbonates containing halogens, sulfonates, sulfates, sulfites, acid anhydrides, benzene compounds, fluorobenzene compounds, nitrile compounds, phosphates, phosphites, boron compounds, amine compounds, silicon-containing compounds, and heterocyclic compounds.

2. The non-aqueous electrolyte according to claim 1, characterized in that: The R1 is selected from an alkyl group having 1 to 3 carbon atoms or a cyano group, the R2 is selected from hydrogen or a cyano group, the R3 is selected from hydrogen or a halogen group, the R4 is selected from hydrogen, -COCN, -COR8 or an alkyl group having 1 to 3 carbon atoms, the R8 is selected from an alkyl group having 2 to 4 carbon atoms, and the halogen group is fluorine; and / or, the R5 is selected from an alkenyl group having 1 to 3 carbon atoms, a fluoroalkyl group having 1 to 3 carbon atoms, a cyano group or an alkyl group having 2 to 4 carbon atoms, and the R6 is selected from hydrogen or an alkenyl group having 1 to 3 carbon atoms; and / or, The R7 is selected from hydrogen, methyl, ethyl or propyl.

3. The non-aqueous electrolyte according to claim 2, characterized in that: The formula I is and / or, The formula II is And / or, the formula III is 4. The non-aqueous electrolyte according to any one of claims 1 to 3, characterized in that: The first additive and the second additive each account for 0.05% to 5% of the total weight of the non-aqueous electrolyte.

5. The non-aqueous electrolyte according to claim 4, characterized in that: The first additive and the second additive account for 1% to 3% of the total weight of the non-aqueous electrolyte.

6. The non-aqueous electrolyte according to claim 1, characterized in that: The third additive is selected from vinylene 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, pentafluorobenzene One or more of methyl ether, 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; and / or, The third additive accounts for 0.3% to 10% of the total weight of the non-aqueous electrolyte.

7. The non-aqueous electrolyte according to claim 1, characterized in that: The organic solvent includes one or more of substituted or unsubstituted carbonates, substituted or unsubstituted carboxylates, substituted or unsubstituted ethers, substituted or unsubstituted sulfones, substituted or unsubstituted sulfoxides, and substituted or unsubstituted benzenes, and the substituted groups include fluorine atoms; and / or the organic solvent accounts for 60% to 90% of the total weight of the non-aqueous electrolyte.

8. The non-aqueous electrolyte according to claim 7, characterized in that: The organic solvent is selected from 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.

9. The non-aqueous electrolyte according to claim 1, characterized in that: The lithium salt comprises a first lithium salt and a second lithium salt, wherein the first lithium salt is lithium hexafluorophosphate, and the second lithium salt is selected from one or more of lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, lithium dioxalatoborate, lithium oxalatodifluoroborate, lithium difluorooxalatophosphate, lithium tetrafluorooxalatophosphate, lithium fluorosulfonate and lithium 4,5-dicyano-2-trifluoromethylimidazole; and / or, The lithium salt accounts for 8% to 30% of the total weight of the non-aqueous electrolyte.

10. The non-aqueous electrolyte according to claim 9, characterized in that: The first lithium salt accounts for 10% to 15% of the total weight of the non-aqueous electrolyte, and the second lithium salt accounts for 1% to 5% of the total weight of the non-aqueous electrolyte.

11. A lithium secondary battery comprising a positive electrode, a negative electrode and a separator disposed between the positive electrode and the negative electrode, characterized in that: The lithium secondary battery further comprises the nonaqueous electrolyte according to any one of claims 1 to 10.

12. The lithium secondary battery according to claim 11, characterized in that: The positive electrode active material in the positive electrode is LiNi x Co y Mn z O2 or LiNi x Co y Al z O2, wherein the value of x is 0-1, the value of y is 0-1, and the value of z is 0-1; the negative electrode active material in the negative electrode includes metallic lithium, metal oxide, lithium aluminum alloy, graphite, modified carbon material, silicon, silicon oxygen or silicon oxygen carbon.

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