An electrolyte and a lithium ion battery comprising the same

Abstract

The application relates to the technical field of lithium ion batteries, in particular to an electrolyte and a lithium ion battery comprising the electrolyte. The electrolyte comprises a lithium salt, an organic solvent and an additive; the additive comprises an additive A and an additive B; the additive A is a sulfonamide compound or a sulfinamide compound; and the additive B is a thiophene silicon cyanide compound. Through the synergistic effect of the sulfonamide compound and / or the sulfinamide compound and the thiophene silicon cyanide compound, the high-pressure resistance of the battery can be effectively improved, and the low-temperature performance and the cycle performance of the battery can be considered.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion batteries, in particular to an electrolyte and a lithium ion battery comprising the same. BACKGROUND

[0002] Lithium ion batteries are widely used due to their high operating voltage, large specific energy, long cycle life and no memory effect. At present, lithium ion batteries have been widely used in 3C digital consumer electronics product field. With the increasing demand for lithium ion battery capacity of electrical equipment, people's expectations for the energy density of lithium ion batteries are getting higher and higher. Especially for smart phones, tablet computers, notebook computers and other portable devices, lithium ion batteries with small size and long standby time are required. Similarly, in other electrical equipment, such as energy storage equipment, electric tools, electric vehicles, etc., lithium ion batteries with lighter weight, smaller size, higher output voltage and power density are also being developed, so the development of high energy density lithium ion batteries is an important research direction of lithium battery industry.

[0003] Increasing the charge cut-off voltage of lithium ion batteries is one of the important means to increase the energy density. However, high-voltage lithium ion batteries have made great contributions to the improvement of the energy density of the battery, but there are still many problems. At high voltage, the oxidation activity of the positive electrode material increases and the stability decreases, which leads to continuous oxidative decomposition reaction of the electrolyte on the surface of the positive electrode, constantly consuming active lithium ions, resulting in deterioration of the high-temperature storage performance of the battery; at the same time, the transition metal elements in the positive active material will be dissolved due to the oxidation-reduction reaction, leading to further deterioration of the lithium ion battery.

[0004] Therefore, it is of great significance to provide an electrolyte to improve the high-voltage resistance, low-temperature performance and cycle performance of lithium ion batteries. SUMMARY

[0005] Therefore, it is necessary to provide an electrolyte and a lithium ion battery comprising the same to effectively improve the high-voltage resistance of the battery while taking into account the low-temperature performance and cycle performance of the battery.

[0006] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0007] In a first aspect, the present application provides an electrolyte comprising a lithium salt, an organic solvent and an additive. The additive comprises an additive A and an additive B, the additive A is a sulfonamide compound and / or a sulfilimine compound, and the additive B is a thiophene silane compound.

[0008] The structure of the sulfilimine compound is shown as formula I, and the structure of the sulfonamide compound is shown as formula II:

[0009]

[0010] wherein R1 to R4 are each independently selected from at least one of a hydrogen atom, a halogen atom, an alkyl group having 1 to 5 carbon atoms, an alkenyl group having 2 to 5 carbon atoms, an aryl group having 6 to 12 carbon atoms, and a group formed by substituting an alkyl group having 1 to 5 carbon atoms, an alkenyl group having 2 to 5 carbon atoms, or an aryl group having 6 to 12 carbon atoms with a cyano group or a halogen atom;

[0011] The structure of the thiophene silane compound is shown in Formula III:

[0012]

[0013] wherein R5 to R6 are each independently selected from at least one of a hydrogen atom, a halogen atom, an alkyl group having 1 to 5 carbon atoms, an alkenyl group having 2 to 5 carbon atoms, an aryl group having 6 to 12 carbon atoms, and a group formed by substituting an alkyl group having 1 to 5 carbon atoms, an alkenyl group having 2 to 5 carbon atoms, or an aryl group having 6 to 12 carbon atoms with a cyano group or a halogen atom;

[0014] wherein R is selected from at least one of an alkyl group having 0 to 5 carbon atoms, an alkenyl group having 2 to 5 carbon atoms, an aryl group having 6 to 12 carbon atoms, and a group formed by substituting an alkyl group having 1 to 5 carbon atoms, an alkenyl group having 2 to 5 carbon atoms, or an aryl group having 6 to 12 carbon atoms with a cyano group or a halogen atom.

[0015] Further, the sulfonamide compound is selected from at least one of the following compounds:

[0016]

[0017] Further, the sulfonamide compound is selected from at least one of the following compounds:

[0018]

[0019] Further, the thiophene silane compound is selected from at least one of the following compounds:

[0020]

[0021] Further, the additive further comprises at least one of vinylene carbonate, 1,4-butane sultone, 1,3-propane sultone, fluoroethylene carbonate, vinyl ethylene carbonate, vinyl sulfate, methylene methane disulfonate, butanedinitrile, hexanedinitrile, 1,3,6-hexane trinitrile, 1,2,3-tris(2-cyanoethoxy)propane, ethylene glycol bis(propionitrile) ether, and tripropargyl phosphate (TPP).

[0022] Further, the mass of the additive is 0.5-15wt% of the total mass of the electrolyte.

[0023] Preferably, the mass of the additive B is 1-3wt% of the total mass of the electrolyte.

[0024] Further, the lithium salt comprises at least one of LiPF6, LiBF4, LiClO4, LiFSI, LiTFSI, LiBOB, LiDFOB, LiFAP, LiSbF6, LiCF3SO3, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiN(SO2CF3)2, LiN(SO2C4F9)2, LiC(SO2CF3)3, LiPF3(C3F7)3, LiB(CF3)4, and LiBF3(C2F5).

[0025] Further, the mass of the lithium salt is 8-20wt% of the total mass of the electrolyte.

[0026] Further, the organic solvent is at least one of ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl methyl carbonate, ethyl propionate, propyl propionate, ethyl acetate, ethyl n-butyrate, and γ-butyrolactone.

[0027] Further, the mass of the organic solvent is 50-90wt% of the total mass of the electrolyte.

[0028] In a second aspect, the present application provides a lithium ion battery, comprising a positive electrode, a negative electrode, a separator, and the electrolyte as described above.

[0029] Further, the active material in the positive electrode comprises at least one of LiCoO2, LiNiO2, LiVO2, LiCrO2, LiMn2O4, LiCoMnO4, LiNiMnO4, LiCoPO4, LiMnPO4, LiFePO4, LiNiPO4, LiCoFSO4, CuS2, FeS2, MoS2, NiS, TiS2, and LiCoPO4. i2 LiNiMn3O8, LiNi 0.5 Mn 1.5 O4, LiCoPO4, LiMnPO4, LiFePO4, LiNiPO4, LiCoFSO4, CuS2, FeS2, MoS2, NiS, TiS2, and LiCoPO4.

[0030] Preferably, the active material in the positive electrode is subjected to a modification treatment, and the modification treatment comprises at least one of coating and doping; and the material used in the modification treatment comprises at least one of Al, B, P, Zr, Si, Ti, Ge, Sn, Mg, Ce, and W.

[0031] Further, the active material in the negative electrode includes, but is not limited to, at least one of graphite, soft carbon, hard carbon, carbon fiber, mesocarbon microbead, silicon-based material, tin-based material, lithium titanate or other metal capable of forming an alloy with lithium.

[0032] Preferably, the graphite includes at least one of artificial graphite, natural graphite and modified graphite; the silicon-based material includes at least one of elemental silicon, silicon oxide compound, silicon-carbon composite and silicon alloy; and the tin-based material includes at least one of elemental tin, tin oxide compound and tin alloy.

[0033] Further, the separator includes, but is not limited to, at least one of polyethylene, polypropylene, polyvinylidene fluoride, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester and natural fiber.

[0034] Advantages

[0035] 1. The sulfonic acid / sulfinic acid group of the additive A in the electrolyte can be preferentially reduced to form a low-impedance SEI film containing sulfur structure, thereby improving the low-temperature performance of the battery; the amide group contained therein can neutralize HF in the electrolyte due to its Lewis base property, thereby reducing the corrosion of the positive electrode material by HF; and the thiophene group of the additive B in the electrolyte can be preferentially reduced on the surface of the negative electrode to form a low-impedance SEI film containing a large amount of dimer sulfur compounds, thereby improving the low-temperature performance and rate performance of the battery.

[0036] 2. The silane group of the additive B in the electrolyte can form a dense and stable SEI film on the surface of the negative electrode, better adapt to the volume change of the negative electrode during charging and discharging, improve the electrode / electrolyte interface of the high-voltage lithium ion battery and slow down the occurrence of side reactions at the positive / negative electrode interface during the cycle process; and the silane structure is also a Lewis base, which can hydrolyze or polymerize with HF and H2O containing active protons in the electrolyte, thereby removing H2O and inhibiting HF, further improving the thermal stability of LiPF6 and the high-temperature performance of the battery. The cyano group in the additive B in the electrolyte can be complexed with positive metal ions to protect the positive electrode, thereby greatly improving the high-temperature performance of the battery at high voltage.

[0037] 3. The sulfonamide / sulfinamide compound and the thiophene silane compound can effectively improve the high-voltage performance of the battery, and also take into account the low-temperature performance and cycle performance of the battery. DETAILED DESCRIPTION

[0038] In order to make the objects, technical solutions and advantages of the present application clearer, the following will further clearly and completely describe the technical solutions of the present application with reference to the embodiments of the present application. It should be explained that the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0039] The present application provides an electrolyte additive, an electrolyte and a lithium ion battery.

[0040] An electrolyte comprises a lithium salt, an organic solvent and an additive. The additive comprises an additive A and an additive B, the additive A is a sulfonamide compound and / or a sulfinamide compound, and the additive B is a thiophene silicon cyanide compound.

[0041] The structure of the sulfinamide compound is shown as formula I, and the structure of the sulfonamide compound is shown as formula II:

[0042]

[0043] wherein R1-R4 are each independently selected from at least one of a hydrogen atom, a halogen atom, an alkyl group with 1-5 carbon atoms, an alkenyl group with 2-5 carbon atoms, an aryl group with 6-12 carbon atoms, and a group formed by substituting the alkyl group with 1-5 carbon atoms, the alkenyl group with 2-5 carbon atoms, or the aryl group with 6-12 carbon atoms with a cyano group or a halogen atom;

[0044] The structure of the thiophene silicon cyanide compound is shown as formula III:

[0045]

[0046] wherein R5-R6 are each independently selected from at least one of a hydrogen atom, a halogen atom, an alkyl group with 1-5 carbon atoms, an alkenyl group with 2-5 carbon atoms, an aryl group with 6-12 carbon atoms, and a group formed by substituting the alkyl group with 1-5 carbon atoms, the alkenyl group with 2-5 carbon atoms, or the aryl group with 6-12 carbon atoms with a cyano group or a halogen atom;

[0047] wherein R is selected from at least one of an alkyl group with 0-5 carbon atoms, an alkenyl group with 2-5 carbon atoms, an aryl group with 6-12 carbon atoms, and a group formed by substituting the alkyl group with 1-5 carbon atoms, the alkenyl group with 2-5 carbon atoms, or the aryl group with 6-12 carbon atoms with a cyano group or a halogen atom.

[0048] R is selected from an alkyl group with 0 carbon atoms, i.e. R is not contained in formula III.

[0049] In some embodiments, the sulfonamide compound is selected from at least one of the following compounds:

[0050]

[0051] In some embodiments, the sulfonamide compound is selected from at least one of the following compounds:

[0052]

[0053] In some embodiments, the thiophenesilane compound is selected from at least one of the following compounds:

[0054]

[0055] In some embodiments, the additive further comprises at least one of vinylene carbonate, 1,4-butane sulfonic acid lactone, 1,3-propylene sulfonic acid lactone, fluoroethylene carbonate, vinyl ethylene carbonate, vinyl sulfate, methylene methane disulfonic acid, butanedinitrile, hexanedinitrile, 1,3,6-hexane trinitrile, 1,2,3-tris(2-cyanato)propane, ethylene glycol bis(propionitrile) ether, and tripropynyl phosphate (TPP).

[0056] In some embodiments, the mass of the additive is 0.5-15 wt% of the total mass of the electrolyte.

[0057] In some embodiments, the lithium salt comprises at least one of LiPF6, LiBF4, LiClO4, LiFSI, LiTFSI, LiBOB, LiDFOB, LiFAP, LiSbF6, LiCF3SO3, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiN(SO2CF3)2, LiN(SO2C4F9)2, LiC(SO2CF3)3, LiPF3(C3F7)3, LiB(CF3)4, and LiBF3(C2F5).

[0058] In some embodiments, the mass of the lithium salt is 8-20 wt% of the total mass of the electrolyte.

[0059] In some embodiments, the organic solvent is at least one of vinyl carbonate, propylene carbonate, diethyl carbonate, ethyl methyl carbonate, ethyl propionate, propyl propionate, ethyl acetate, ethyl n-butyrate, and γ-butyrolactone.

[0060] In some embodiments, the mass of the organic solvent is 50-90 wt% of the total mass of the electrolyte.

[0061] A lithium ion battery comprising a positive electrode, a negative electrode, a separator, and the electrolyte described above.

[0062] In some embodiments, the active material in the cathode includes, but is not limited to, at least one of LiCoO2, LiNiO2, LiVO2, LiCrO2, LiMn2O4, LiCoMnO4, LiFeMnO4, Li2MnO4, Li2CrO4, Li2NiO4, Li2VO4, Li2CoO4, Li2MnPO4, Li2CoPO4, Li2FePO4, Li2NiPO4, Li2CoFSO4, CuS2, FeS2, MoS2, NiS, TiS2. i2 Li2NiMn3O8, Li2Ni 0.5 Mn 1.5 O4, LiCoPO4, LiMnPO4, LiFePO4, LiNiPO4, LiCoFSO4, CuS2, FeS2, MoS2, NiS, TiS2.

[0063] In some embodiments, the active material in the cathode is modified, and the modification includes, but is not limited to, coating or doping; and the material used for the modification includes, but is not limited to, at least one of Al, B, P, Zr, Si, Ti, Ge, Sn, Mg, Ce, W.

[0064] In some embodiments, further, the active material in the anode includes, but is not limited to, at least one of graphite, soft carbon, hard carbon, carbon fiber, mesocarbon microbead, silicon-based material, tin-based material, lithium titanate, or other metal capable of forming alloy with lithium.

[0065] In some embodiments, the graphite includes one or more of artificial graphite, natural graphite, and modified graphite; the silicon-based material includes one or more of elemental silicon, silicon oxide compound, silicon-carbon composite, silicon alloy; and the tin-based material includes one or more of elemental tin, tin oxide compound, tin alloy.

[0066] In some embodiments, the separator includes, but is not limited to, at least one of polyethylene, polypropylene, polyvinylidene fluoride, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester, and natural fiber.

[0067] The compound used in the embodiments of the present application can be synthesized by using conventional chemical methods, and the present application is not particularly limited as long as the compound structure is satisfied.

[0068] In the description of the present application, it should be noted that, if the specific conditions are not specified in the embodiments, the conventional conditions or the conditions recommended by the manufacturer are used. If the manufacturers of the reagents or instruments are not specified, the conventional products that can be purchased on the market are used.

[0069] Example 1

[0070] 1. Preparation of electrolyte

[0071] In an argon-filled glove box, the water content <5 ppm, the oxygen content <5 ppm, ethylene carbonate (EC), propylene carbonate (PC), propyl propionate (PP), diethyl carbonate (DEC) were mixed according to the mass ratio of 1:1:2:1 to obtain an organic solvent; the organic solvent was mixed with lithium hexafluorophosphate, wherein the lithium hexafluorophosphate was 14.0 wt% of the total mass of the electrolyte; then an additive was added and uniformly mixed, the additive was 4.0 wt% of 1,3-propylene sulfite, 10.0 wt% of fluoroethylene carbonate, 2 wt% of 1,3,6-hexanetricarbonitrile (HTCN), 0.2 wt% of compound I-2 and 2 wt% of compound III-10. The mass fraction in the example was the percentage of the additive in the total mass of the electrolyte.

[0072] 2. Preparation of the positive electrode

[0073] The positive electrode active material LiCoO2, conductive carbon black Super-P and the binder polyvinylidene fluoride (PVDF) were mixed according to the mass ratio of 97:1.8:1.2, and then they were dispersed in N-methyl-2-pyrrolidone (NMP) to obtain a positive electrode slurry. The slurry was uniformly coated on both sides of an aluminum foil, and then the positive electrode plate was obtained after drying, calendering and vacuum drying, and welding an aluminum lead wire by an ultrasonic welding machine, and the thickness of the electrode sheet was 120-150 μm.

[0074] 3. Preparation of the negative electrode

[0075] The negative electrode active material artificial graphite, conductive carbon black Super-P, the binder styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) were mixed according to the mass ratio of 96:0.8:1.6:1.6, and then they were dispersed in ionized water to obtain a negative electrode slurry. The slurry was coated on both sides of a copper foil, and then the negative electrode plate was obtained after drying, calendering and vacuum drying, and welding a nickel lead wire by an ultrasonic welding machine, and the thickness of the electrode sheet was 120-150 μm.

[0076] 4. Preparation of the lithium ion battery

[0077] The positive electrode, the separator and the negative electrode were stacked in order, the separator was between the positive electrode and the negative electrode to play a role of isolation, and then they were placed in an outer packaging foil. The electrolyte was injected into the dried battery, and then the preparation of the lithium ion battery was completed after vacuum packaging, standing, formation, shaping and other processes.

[0078] Example 2

[0079] The difference between Example 2 and Example 1 was that the additive was 4.0 wt% of 1,3-propylene sulfite, 10.0 wt% of fluoroethylene carbonate, 2 wt% of 1,3,6-hexanetricarbonitrile (HTCN), 0.5 wt% of compound I-2 and 2 wt% of compound III-10. The rest was the same.

[0080] Example 3

[0081] The difference from Example 1 is that the additives are 4.0 wt% of 1,3- propenesultone, 10.0 wt% of fluoroethylene carbonate, 2 wt% of 1,3,6-hexanetricarboxylic acid (HTCN), 1 wt% of Compound I-2 and 2 wt% of Compound III-10. The rest are all the same.

[0082] Example 4

[0083] The difference from Example 1 is that the additives are 4.0 wt% of 1,3- propenesultone, 10.0 wt% of fluoroethylene carbonate, 2 wt% of 1,3,6-hexanetricarboxylic acid (HTCN), 2 wt% of Compound I-2 and 2 wt% of Compound III-10. The rest are all the same.

[0084] Example 5

[0085] The difference from Example 1 is that the additives are 4.0 wt% of 1,3- propenesultone, 10.0 wt% of fluoroethylene carbonate, 2 wt% of 1,3,6-hexanetricarboxylic acid (HTCN), 1 wt% of Compound II-2 and 2 wt% of Compound III-10. The rest are all the same.

[0086] Example 6

[0087] The difference from Example 1 is that the additives are 4.0 wt% of 1,3- propenesultone, 10.0 wt% of fluoroethylene carbonate, 2 wt% of 1,3,6-hexanetricarboxylic acid (HTCN), 1 wt% of Compound I-2 and 0.5 wt% of Compound III-10. The rest are all the same.

[0088] Example 7

[0089] The difference from Example 1 is that the additives are 4.0 wt% of 1,3- propenesultone, 10.0 wt% of fluoroethylene carbonate, 2 wt% of 1,3,6-hexanetricarboxylic acid (HTCN), 1 wt% of Compound I-2 and 1 wt% of Compound III-10. The rest are all the same.

[0090] Example 8

[0091] The difference from Example 1 is that the additives are 4.0 wt% of 1,3- propenesultone, 10.0 wt% of fluoroethylene carbonate, 2 wt% of 1,3,6-hexanetricarboxylic acid (HTCN), 1 wt% of Compound I-2 and 3 wt% of Compound III-10. The rest are all the same.

[0092] Example 9

[0093] The difference from Example 1 is that the additives are 4.0 wt% of 1,3- propene sultone, 10.0 wt% of fluoroethylene carbonate, 2 wt% of 1,3,6-hexanetricarboxylic acid (HTCN), 1 wt% of compound I-2, and 5 wt% of compound III-10. The rest are the same.

[0094] Example 10

[0095] The difference from Example 1 is that the additives are 4.0 wt% of 1,3- propene sultone, 10.0 wt% of fluoroethylene carbonate, 2 wt% of 1,3,6-hexanetricarboxylic acid (HTCN), 1 wt% of compound I-2, and 2 wt% of compound III-1. The rest are the same.

[0096] Example 11

[0097] The difference from Example 1 is that the additives are 4.0 wt% of 1,3- propene sultone, 10.0 wt% of fluoroethylene carbonate, 1 wt% of compound I-2, and 2 wt% of compound III-10. The rest are the same.

[0098] Example 12

[0099] The difference from Example 1 is that the additives are 4.0 wt% of 1,3- propene sultone, 10.0 wt% of fluoroethylene carbonate, 2 wt% of 1,3,6-hexanetricarboxylic acid (HTCN), 1 wt% of compound I-2, 1 wt% of compound II-2, and 2 wt% of compound III-10. The rest are the same.

[0100] Example 13

[0101] The difference from Example 1 is that the additives are 4.0 wt% of 1,3- propene sultone, 10.0 wt% of fluoroethylene carbonate, 2 wt% of 1,3,6-hexanetricarboxylic acid (HTCN), 1 wt% of compound I-2, 2 wt% of compound III-1, and 2 wt% of compound III-10. The rest are the same.

[0102] Example 14

[0103] The difference from Example 1 is that the additives are 4.0 wt% of 1,3- propene sultone, 10.0 wt% of fluoroethylene carbonate, 2 wt% of 1,3,6-hexanetricarboxylic acid (HTCN), 0.5 wt% of compound I-2, 0.5 wt% of compound II-2, and 2 wt% of compound III-10. The rest are the same.

[0104] Example 15

[0105] The difference from Example 1 is that the additives are 4.0 wt% of 1,3-propanesultone, 10.0 wt% of fluoroethylene carbonate, 2 wt% of 1,3,6-hexanetricarbonitrile (HTCN), 1 wt% of compound I-2, 1 wt% of compound III-1 and 1 wt% of compound III-10. The rest are the same.

[0106] Example 16

[0107] The difference from Example 1 is that the additives are 4.0 wt% of 1,3-propanesultone, 10.0 wt% of fluoroethylene carbonate, 2 wt% of 1,3,6-hexanetricarbonitrile (HTCN), 0.5 wt% of compound I-2, 0.5 wt% of compound II-2, 1 wt% of compound III-1 and 1 wt% of compound III-10. The rest are the same.

[0108] Comparative Example 1

[0109] The difference from Example 1 is that the additives are 4.0 wt% of 1,3-propanesultone, 10.0 wt% of fluoroethylene carbonate. The rest are the same.

[0110] Comparative Example 2

[0111] The difference from Example 1 is that the additives are 4.0 wt% of 1,3-propanesultone, 10.0 wt% of fluoroethylene carbonate, 2 wt% of 1,3,6-hexanetricarbonitrile (HTCN). The rest are the same.

[0112] Comparative Example 3

[0113] The difference from Example 1 is that the additives are 4.0 wt% of 1,3-propanesultone, 10.0 wt% of fluoroethylene carbonate, 2 wt% of 1,3,6-hexanetricarbonitrile (HTCN), 1 wt% of compound I-2. The rest are the same.

[0114] Comparative Example 4

[0115] The difference from Example 1 is that the additives are 4.0 wt% of 1,3-propanesultone, 10.0 wt% of fluoroethylene carbonate, 2 wt% of 1,3,6-hexanetricarbonitrile (HTCN), 2 wt% of compound III-10. The rest are the same.

[0116] Lithium ion battery performance test

[0117] The lithium ion batteries prepared in Comparative Examples 1-4 and Examples 1-16 are respectively subjected to cycle performance test, low-temperature discharge performance test and high-temperature storage performance test, and the test methods are as follows:

[0118] 1) 45℃ cycle performance test

[0119] The battery was first charged to 4.5 V at a constant current of 0.5 C at 45 °C, then charged to a current of 0.025 C at a constant voltage of 4.5 V, and discharged to 3.0 V at a constant current of 0.5 C, which was one charge-discharge cycle process. The discharge capacity of the 500th cycle C2 was detected, and the capacity retention rate of the battery after cycling was calculated by the following formula. Capacity retention rate of the battery after 500 cycles (%) = C2 / C1*100%.

[0120] 2) Low-temperature discharge performance test

[0121] The battery was first charged to 4.5 V at a constant current of 0.5 C at 25 °C, then charged to a current of 0.025 C at a constant voltage of 4.5 V, and discharged to 3.0 V at a constant current of 0.5 C, and the discharge capacity C3 was recorded. The battery was charged to 4.5 V at a constant current of 0.5 C again, then charged to a current of 0.025 C at a constant voltage of 4.5 V, and discharged to 3.0 V at a constant current of 0.2 C after being placed in an environment of -20 °C for 24 h. The low-temperature discharge rate at -20 °C (%) = C4 / C3*100%.

[0122] 3) High-temperature storage performance test

[0123] The volume change rate of the battery before and after storage was used to represent the high-temperature storage performance of the battery.

[0124] The battery was first charged to 4.5 V at a constant current of 0.5 C at 25 °C, then charged to a current of 0.025 C at a constant voltage of 4.5 V, and the initial volume of the battery was measured in deionized water by the drainage method. The initial volume of the battery at this time was taken as the volume V1 of the battery before storage. Then the battery was stored at 85 °C for 6 h. After the storage was completed, the volume V2 of the battery after high-temperature storage was tested, and the volume change rate of the battery was calculated by the following formula. Volume change rate of the battery (%) = V2 / V1*100%.

[0125] Table 1 Performance of lithium ion battery

[0126]

[0127]

[0128] As can be seen from the comparison of Examples 1-4, with the increase of the content of sulfenamide compounds, the cycle performance of the battery is obviously improved, but when the content is too high, the cycle life tends to decrease, which is mainly because too much sulfenamide compounds hinder the transport of lithium ions, thus the cycle performance of the battery cannot be effectively improved.

[0129] As can be seen from the comparison of Example 3 and Examples 6-9, with the increase of the content of thiophene silyl cyanide compounds, the high-temperature storage performance of the battery is obviously improved, but the low-temperature discharge performance gradually deteriorates, therefore, the content of thiophene silyl cyanide compounds is preferably controlled at 1-3 wt%.

[0130] As can be seen from the comparison of Comparative Examples 3-4 and Examples 1-10, sulfonamide compounds and / or sulfenamide compounds and thiophene silyl cyanide compounds have a synergistic effect to improve the comprehensive performance of the lithium ion battery.

[0131] As can be seen from the comparison of Comparative Examples 1-2 and Examples 3-11, HTCN can also improve the cycle performance and high-temperature storage performance to some extent, and after the synergistic effect of HTCN and sulfonamide compounds / sulfenamide compounds and thiophene silyl cyanide compounds in the present embodiment, the comprehensive performance of the lithium ion battery is better.

[0132] The above-described examples only express several embodiments of the present application, and the description is more specific and detailed, but it should not be understood as limiting the scope of the present patent. It should be noted that for ordinary skilled persons in the art, without departing from the concept of the present application, several modifications and improvements can be made, which are all within the protection scope of the present application. Therefore, the protection scope of the present patent should be subject to the appended claims.

Claims

1. An electrolyte, characterized in that: The invention comprises a lithium salt, an organic solvent and an additive; the additive comprises an additive A and an additive B, the additive A is a sulfonamide compound and / or a sulfenamide compound, and the additive B is a thiophene silicon nitrile compound; The structural formula of the sulfenamide compound is shown in Formula I, and the structural formula of the sulfonamide compound is shown in Formula II: wherein R1 to R4 are each independently selected from at least one of a hydrogen atom, a halogen atom, an alkyl group having 1 to 5 carbon atoms, an alkenyl group having 2 to 5 carbon atoms, an aryl group having 6 to 12 carbon atoms, and a group formed by replacing an alkyl group having 1 to 5 carbon atoms, an alkenyl group having 2 to 5 carbon atoms, or an aryl group having 6 to 12 carbon atoms with a cyano group or a halogen atom; The structural formula of the thiophene silicon nitrile compound is shown in Formula III: wherein R5 to R6 are each independently selected from at least one of a hydrogen atom, a halogen atom, an alkyl group having 1 to 5 carbon atoms, an alkenyl group having 2 to 5 carbon atoms, an aryl group having 6 to 12 carbon atoms, and a group formed by replacing an alkyl group having 1 to 5 carbon atoms, an alkenyl group having 2 to 5 carbon atoms, or an aryl group having 6 to 12 carbon atoms with a cyano group or a halogen atom; Wherein R is selected from at least one of an alkyl group having 0 to 5 carbon atoms, an alkenyl group having 2 to 5 carbon atoms, an aryl group having 6 to 12 carbon atoms, and a group formed by replacing an alkyl group having 1 to 5 carbon atoms, an alkenyl group having 2 to 5 carbon atoms, or an aryl group having 6 to 12 carbon atoms with a cyano group or a halogen atom.

2. The electrolyte according to claim 1, characterized in that The sulfenamide compound is selected from at least one of the following compounds:

3. The electrolyte according to claim 1, characterized in that The sulfonamide compound is selected from at least one of the following compounds:

4. The electrolyte according to claim 1, characterized in that The thiophene silicon nitrile compound is selected from at least one of the following compounds: Compound III-10 Compound III-11 Compound III-12.

5. The electrolyte according to claim 1, characterized in that The additives also include at least one of vinylene carbonate, 1,4-butane sultone, 1,3-propylene sultone, fluoroethylene carbonate, vinyl ethylene carbonate, vinyl sulfate, methylene methanedisulfonate, succinonitrile, adiponitrile, 1,3,6-hexanetrinitrile, 1,2,3-tris(2-cyano)propane, ethylene glycol bis(propionitrile) ether, and tripropynyl phosphate (TPP).

6. The electrolyte according to claim 1, characterized in that The mass of the additive is 0.5-15 wt % of the total mass of the electrolyte.

7. The electrolyte according to claim 1, characterized in that The lithium salt includes at least one of LiPF6, LiBF4, LiClO4, LiFSI, LiTFSI, LiBOB, LiDFOB, LiFAP, LiSbF6, LiCF3SO3, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiN(SO2CF3)2, LiN(SO2C4F9)2, LiC(SO2CF3)3, LiPF3(C3F7)3, LiB(CF3)4 and LiBF3(C2F5); the mass of the lithium salt is 8 to 20 wt% of the total mass of the electrolyte.

8. The electrolyte according to claim 1, characterized in that The organic solvent is at least one of ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl methyl carbonate, ethyl propionate, propyl propionate, ethyl acetate, ethyl butyrate, and γ-butyrolactone; the mass of the organic solvent is 50-90wt% of the total mass of the electrolyte.

9. A lithium-ion battery comprising a positive electrode, a negative electrode, a separator and the electrolyte according to any one of claims 1 to 8.

10. The lithium-ion battery according to claim 9, characterized in that The active materials in the positive electrode include LiCoO2, LiNiO2, LiVO2, LiCrO2, LiMn2O4, LiCoMnO4, L i2 NiMn3O8、LiNi 0.5 Mn 1.5 At least one of O4, LiCoPO4, LiMnPO4, LiFePO4, LiNiPO4, LiCoFSO4, CuS2, FeS2, MoS2, NiS, and TiS2; the active material in the negative electrode includes at least one of graphite, soft carbon, hard carbon, carbon fiber, mesophase carbon microbeads, silicon-based materials, tin-based materials, lithium titanate or other metals that can form alloys with lithium; the diaphragm includes at least one of polyethylene, polypropylene, polyvinylidene fluoride, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester and natural fiber.

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