Electrolyte and secondary battery containing same

Abstract

The invention provides an electrolyte. The electrolyte comprises a dimethoxy compound as shown in a formula (1) and a phenylenediamine compound as shown in a formula (2). In the formula, R1, R2, R3, R4, R6, R7 and R8 are respectively and independently selected from H, F, C1-C6 alkyl groups and C1-C6 alkoxy groups, and R5 is selected from H and C1-C6 alkyl groups. According to the present invention, the dimethoxy compound and the phenylenediamine compound generate the chelation in the electrolyte, the protection film is formed on the surface of the positive electrode through the chelation, and the secondary battery using the electrolyte has advantages of excellent overcharge resistance and good safety performance.

Description

Technical Field

[0001] The present application relates to the technical field of energy storage, and in particular, to an electrolyte and a secondary battery including the electrolyte. Background Art

[0002] With the wide application of lithium-ion batteries in energy storage and vehicles, the usage environment has been continuously broadened, and the requirements for lithium-ion batteries have been continuously improved. While taking into account the performance, it is necessary to consider the safety issues during use. Extreme situations such as overcharging and over-discharging of lithium-ion batteries are likely to cause abnormal operation of lithium-ion batteries and even safety hazards such as fire and explosion.

[0003] The electrolyte is one of the important components of lithium-ion batteries, which directly affects the performance and safety characteristics of the battery. At present, to solve such problems, overcharge protection additives (such as biphenyl, cyclohexylbenzene, etc.) are added to the electrolyte to improve its overcharge safety hazard. However, the problems of these additives are as follows: when the usage amount is small, the overcharge inhibition ability is insufficient; when the usage amount is large, the battery performance is reduced. Therefore, it is necessary to develop a new type of lithium-ion battery electrolyte to prevent overcharging of lithium-ion batteries without affecting the battery performance. Summary of the Invention

[0004] To solve the above problems, an object of the present invention is to provide an electrolyte, which includes a dimethoxy compound represented by formula (1) and a phenylenediamine compound represented by formula (2).

[0005]

[0006] Wherein, R1, R2, R3, R4, R6, R7, R8 are each independently selected from H, F, C1-C6 alkyl, and R5 is selected from H, C1-C6 alkyl.

[0007] According to an embodiment of the present invention, based on the total mass of the electrolyte, the content of the dimethoxy compound is 0.5 wt% to 3 wt%.

[0008] According to an embodiment of the present invention, based on the total mass of the electrolyte, the content of the phenylenediamine compound is 0.5 wt% to 3 wt%.

[0009] According to an embodiment of the present invention, based on the total mass of the electrolyte, the sum of the contents of the dimethoxy compound and the phenylenediamine compound is 0.01 wt% to 10 wt%.

[0010] Another object of the present invention is to provide a secondary battery, which includes the aforementioned electrolyte.

[0011] Another object of the present invention is to provide a device, which includes the aforementioned secondary battery.

[0012] Beneficial effects:

[0013] With the overcharge-resistant electrolyte for lithium-ion batteries according to the present invention, both the dimethoxy compound and the phenylenediamine compound can inhibit the oxidative decomposition of the electrolyte at high temperatures, enabling the electrolyte to maintain stable performance when operating at a relatively high voltage, and can form an interfacial film CEI that is still very stable at high temperatures on the positive electrode surface, thereby weakening the dissolution of transition metals and inhibiting the damage of the positive electrode material. The dimethoxy group and the diamino group strengthen the phenyl activity, weaken the phenyl large Π bond, and promote the dimethoxy compound and the phenylenediamine compound to have stronger activity. The dimethoxy compound and the phenylenediamine compound undergo para-position chelation in the electrolyte, and a protective film is formed on the positive electrode surface through the chelation. Since the oxidation potential of the dimethoxy compound is slightly higher than the electrochemical polymerization potential of the phenylenediamine compound, the dimethoxy compound preferentially forms a protective film on the positive electrode, while increasing the decomposition potential of the electrolyte and inhibiting the decomposition of the electrolyte at high voltages. At the same time, the intermolecular hydrogen bond interaction between the dimethoxy compound and the phenylenediamine compound and the electrophilic activity of the amino group improve the film-forming stability of the negative electrode SEI film, reduce the possibility of the electrolyte being oxidized, avoid the formation of an overly thick film of the dimethoxy compound on the electrode surface, and avoid problems such as lithium deposition. Specific embodiments

[0014] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are some, but not all, of the embodiments of this application. The embodiments described herein are illustrative in nature and are used to provide a basic understanding of this application. The embodiments of this application should not be construed as a limitation of this application. All other embodiments obtained by those skilled in the art based on the technical solutions provided in this application and the given embodiments fall within the scope of protection of this application.

[0015] Unless otherwise specified, the terms used in this application have the well-known meanings commonly understood by those skilled in the art. Unless otherwise specified, the numerical values of the various parameters mentioned in this application can be measured using various commonly used measurement methods in the art (for example, they can be tested according to the methods given in the embodiments of this application).

[0016] A list of items joined by the term "at least one of", "at least one", "at least one kind of" or other similar terms can mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A or B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, then the phrase "at least one of A, B or C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A can include a single component or multiple components. Item B can include a single component or multiple components. Item C can include a single component or multiple components.

[0017] I. Electrolyte

[0018] The electrolyte of the present application includes a dimethoxy compound represented by formula (1) and a phenylenediamine compound represented by formula (2).

[0019]

[0020] Wherein, R1, R2, R3, R4, R6, R7, R8 are each independently selected from H, F, C1-C6 alkyl, and R5 is selected from H, C1-C6 alkyl.

[0021] In some embodiments of the present application, the dimethoxy compound includes at least one of 1,4-dimethoxybenzene, 1,4-difluoro-2,5-dimethoxybenzene, 1,4-dimethoxy-2-fluorobenzene, and 1,4-dimethoxy-2,3-methylbenzene. In some embodiments of the present application, the dimethoxy compound includes 1,4-dimethoxybenzene.

[0022] In some embodiments of the present application, based on the total mass of the electrolyte, the content of the dimethoxy compound is 0.5 wt% to 3 wt%. In some embodiments of the present application, based on the total mass of the electrolyte, the content of the dimethoxy compound is 0.5 wt%, 0.8 wt%, 1 wt%, 1.2 wt%, 1.5 wt%, 1.8 wt%, 2 wt%, 2.3 wt%, 2.5 wt%, 2.8 wt%, 3 wt% or any range composed of these values. Based on the total mass of the electrolyte, the content of 1,4-dimethoxybenzene is 1 wt% to 3 wt%.

[0023] In some embodiments of the present application, the phenylenediamine compound includes at least one of o-xylenediamine, 1-methyl-3,5-dimethylaminobenzene, 1-fluoro-3,5-dimethylaminobenzene, 1,5-dimethyl-2,4-dimethylaminobenzene, and 1,5-difluoro-2,4-dimethylaminobenzene. In some embodiments of the present application, the phenylenediamine compound includes o-xylenediamine.

[0024] In some embodiments of the present application, based on the total mass of the electrolyte, the content of the phenylenediamine compound is 0.5 wt% to 3 wt%. In some embodiments of the present application, based on the total mass of the electrolyte, the content of the phenylenediamine compound is 0.5 wt%, 0.8 wt%, 1 wt%, 1.2 wt%, 1.5 wt%, 1.8 wt%, 2 wt%, 2.3 wt%, 2.5 wt%, 2.8 wt%, 3 wt% or any range composed of these values. Based on the total mass of the electrolyte, the content of the phenylenediamine compound is 1 wt% to 1.5 wt%.

[0025] In some embodiments of the present application, the sum of the contents of the dimethoxy compound and the phenylenediamine compound is 0.01 wt% to 10 wt%. In some embodiments of the present application, the sum of the contents of the dimethoxy compound and the phenylenediamine compound is 0.01 wt%, 0.05 wt%, 0.1 wt%, 0.5 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt% or any range composed of these values. If the sum of the contents of the dimethoxy compound and the phenylenediamine compound is too low, a synergistic effect cannot be produced, the thickness of the SEI film generated decreases, and the overcharge protection effect cannot be achieved; if the sum of the contents of the dimethoxy compound and the phenylenediamine compound is too high, the thickness of the SEI film is too large, the resistance increases, and the cycle performance and rate performance of the battery cell are reduced.

[0026] In some embodiments of the present application, the sum of the contents of the dimethoxy compound and the phenylenediamine compound is 2 wt% to 6 wt%. In some embodiments of the present application, the sum of the contents of the dimethoxy compound and the phenylenediamine compound is 2 wt%, 2.2 wt%, 2.4 wt%, 2.6 wt%, 2.8 wt%, 3 wt%, 3.2 wt%, 3.4 wt%, 3.6 wt%, 3.8 wt%, 4 wt%, 4.2 wt%, 4.4 wt%, 4.6 wt%, 4.8 wt%, 5 wt%, 5.2 wt%, 5.4 wt%, 5.6 wt%, 5.8 wt%, 6 wt% or any range composed of these values.

[0027] In some embodiments of the present application, based on the total mass of the electrolyte, the mass ratio of the content of the dimethoxy compound to the content of the phenylenediamine compound is (0.5 - 2):1. If the ratio of the content of the dimethoxy compound to the content of the phenylenediamine compound is too low, there are too many aniline groups in the SEI film, the activity is too high, the structure is unstable, the decomposition rate is too fast, and the overcharge protection ability is reduced; if the ratio of the content of the dimethoxy compound to the content of the phenylenediamine compound is too high, there are too many methoxy groups in the SEI film, the SEI film structure is solidified, the SEI conductivity is reduced, and the electrochemical activity is inhibited.

[0028] In some embodiments of the present application, based on the total mass of the electrolyte, the mass ratio of the dimethoxy compound, phenylenediamine compound, lithium salt and solvent is (1 - 3):(1 - 3):(8 - 15):(79 - 90).

[0029] In some embodiments of the present application, the electrolyte further comprises a lithium salt, and the lithium salt used in the electrolyte of the present application is selected from one or more of inorganic lithium salts and organic lithium salts.

[0030] In some embodiments of the present application, the lithium salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium difluorooxalate borate, lithium bis(oxalato)borate, lithium 4,5-dicyano-2-trifluoromethylimidazole, lithium difluorophosphate, lithium perchlorate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium bis(fluorosulfonyl)amide, and lithium bis(trifluoromethylsulfonyl)amide. In some embodiments of the present application, the lithium salt includes lithium hexafluorophosphate. In some embodiments of the present application, based on the total mass of the electrolyte, the mass content of the lithium hexafluorophosphate is 8 wt% - 15 wt%.

[0031] In some embodiments of the present application, the concentration of the lithium salt in the electrolyte is 0.5 mol / L, 1.0 mol / L, 1.5 mol / L, 2.0 mol / L, 2.5 mol / L, 3 mol / L or any range composed of these values.

[0032] The solvent used in the electrolyte of the present application can be any organic solvent known in the prior art that can be used as an electrolyte solvent.

[0033] In some embodiments of the present application, the organic solvents include, but are not limited to, chain carbonates, chain carboxylates, and cyclic ethers.

[0034] In some embodiments of the present application, the chain carbonates include, but are not limited to, ethylene carbonate, fluoroethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate (DEC), methyl n-propyl carbonate, ethyl n-propyl carbonate, di-n-propyl carbonate and other chain carbonates. As the chain carbonates substituted by fluorine, for example, bis(fluoromethyl) carbonate, bis(difluoromethyl) carbonate, bis(trifluoromethyl) carbonate, bis(2-fluoroethyl) carbonate, bis(2,2-difluoroethyl) carbonate, bis(2,2,2-trifluoroethyl) carbonate, 2-fluoroethyl methyl carbonate, 2,2-difluoroethyl methyl carbonate and 2,2,2-trifluoroethyl methyl carbonate.

[0035] In some embodiments of the present application, the chain carboxylic acid esters include, but are not limited to, methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, sec-butyl acetate, isobutyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, isopropyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, methyl isobutyrate, ethyl isobutyrate, methyl valerate, ethyl valerate, methyl pivalate and ethyl pivalate. In some embodiments, some hydrogen atoms of the chain carboxylic acid esters can be substituted by fluorine. In some embodiments, the fluorine-substituted chain carboxylic acid esters include, but are not limited to, methyl trifluoroacetate, ethyl trifluoroacetate, propyl trifluoroacetate, butyl trifluoroacetate and 2,2,2-trifluoroethyl trifluoroacetate.

[0036] In some embodiments of the present application, the cyclic ethers include, but are not limited to, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 2-methyl-1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,3-dioxane, 1,4-dioxane and dimethoxypropane.

[0037] In some embodiments of the present application, the electrolyte further contains a solvent. In some embodiments of the present application, the solvent includes an organic solvent, and the boiling point of the organic solvent ≤ 250 °C.

[0038] In some embodiments of the present application, the chain carbonate includes at least one of ethylene carbonate, propylene carbonate, diethyl carbonate and fluoroethylene carbonate.

[0039] In some embodiments of the present application, the solvent includes ethylene carbonate, diethyl carbonate and fluoroethylene carbonate. In some embodiments of the present application, the mass ratio of the three is ethylene carbonate:diethyl carbonate:fluoroethylene carbonate = (1-4):(1-4):(0.5-1). For the non-aqueous solvent prepared according to the above ratio, a lower content of ethylene carbonate is beneficial to the high-temperature charge and discharge of the battery and improves the high-temperature performance of the battery.

[0040] In some embodiments of the present application, the total amount of the lithium salt is M (mol), the total volume of the solvent is V1 (L), and the molar concentration of the lithium salt in the solvent satisfies 0.5 mol / L ≤ M / V1 ≤ 1.2 mol / L.

[0041] In some embodiments of the present application, the electrolyte further includes other additives, and the other additives include at least one of cyclic carbonates containing carbon-carbon double bonds, phosphates containing silyl groups, borates containing silyl groups, nitrile compounds, pyridinium propane sulfonate, fluorinated carbonates, and sulfonates. In some embodiments of the present application, the other additives include at least one of vinylene carbonate (VC), ethylene vinylene carbonate (VEC), tris(trimethylsilyl) phosphate (TMSP), tris(trimethylsilyl) borate (TMSB), succinonitrile (SN), adiponitrile (ADN), glutaronitrile (GLN), hexane trinitrile (HTN), and 1,3-propane sultone (PS). In some embodiments of the present application, the other additives include at least one of tris(trimethylsilyl) phosphate (TMSP) and 1,3-propane sultone (PS).

[0042] In some embodiments of the present application, based on the total mass of the electrolyte, the mass content of the other additives is 0.05% - 10%. In some embodiments, based on the total mass of the electrolyte, the mass content of the other additives is 0.05%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 6%, 7%, 8%, 9%, 10% or any value therebetween. In some embodiments of the present application, based on the total mass of the electrolyte, the mass content of the other additives is 0.1% - 5%.

[0043] In some embodiments of the present application, based on the total mass of the electrolyte, the mass content of the negative electrode film-forming additive is 2 wt% - 6 wt%. If the content of the negative electrode film-forming additive is too high, too much additive will remain in the electrolyte; if the content of the negative electrode film-forming additive is too low, it will be difficult to form a complete and effective SEI film.

[0044] II. Secondary Battery

[0045] The secondary battery according to the present invention can be a secondary battery, such as a lithium secondary battery or a sodium secondary battery, including a lithium metal secondary battery, a lithium ion secondary battery, a sodium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery. In some embodiments, the secondary battery of the present application includes a positive electrode, a negative electrode, a separator, and an electrolyte.

[0046] The secondary battery according to the present invention can be applied in the device according to the present invention, including but not limited to, laptop computers, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, head-mounted stereo headphones, video recorders, liquid crystal TVs, portable cleaners, portable CD players, minidiscs, transceivers, electronic notebooks, calculators, memory cards, portable tape recorders, radios, backup power supplies, motors, automobiles, motorcycles, motorized bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household storage batteries, and lithium-ion capacitors, etc.

[0047] The electrolyte used in the lithium battery of the present application is any of the above electrolytes of the present application. In addition, the electrolyte used in the lithium battery of the present application may also contain other electrolytes within the scope not departing from the gist of the present application.

[0048] The materials, compositions, and manufacturing methods of the negative electrode sheet that can be used in the embodiments of the present application include the technologies disclosed in any prior art.

[0049] In some embodiments of the present application, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer. The negative electrode current collector includes: copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, or any combination thereof. In some embodiments of the present application, the negative electrode active material layer includes a negative electrode active material, and the negative electrode active material includes a silicon-based material, or a mixture of a silicon-based material and at least one material selected from a carbon-based material, a tin-based material, a phosphorus-based material, and metallic lithium.

[0050] In some embodiments of the present application, the silicon-based material includes at least one of silicon, silicon alloy, silicon oxide compound, and silicon carbide compound. In some embodiments of the present application, the carbon-based material includes at least one of graphite, soft carbon, hard carbon, carbon nanotubes, and graphene. In some embodiments of the present application, the tin-based material includes at least one of tin, tin oxide, and tin alloy. In some embodiments of the present application, the phosphorus-based material includes phosphorus and / or a phosphorus complex.

[0051] In some embodiments of the present application, based on the mass of the negative electrode active material, the mass content g% of the silicon-based material satisfies: 10 ≤ g ≤ 100. In some embodiments of the present application, g is 11, 13, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or any value between them.

[0052] In some embodiments of the present application, the negative electrode active material layer further includes a binder and a conductive agent. In some embodiments of the present application, the binder includes, but is not limited to: polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene 1,1-difluoroethylene, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin or nylon, etc.

[0053] In some embodiments of the present application, the conductive agent includes, but is not limited to: carbon-based materials, metal-based materials, conductive polymers and mixtures thereof. In some embodiments, the carbon-based materials are selected from natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber or any combination thereof. In some embodiments, the metal-based materials are selected from metal powder, metal fiber, copper, nickel, aluminum or silver. In some embodiments, the conductive polymer is a polyphenylene derivative.

[0054] In some embodiments of the present application, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer located on the positive electrode current collector.

[0055] In some embodiments of the present application, the positive electrode current collector can be a metal foil or a composite current collector. For example, aluminum foil can be used. The composite current collector can be formed by forming a metal material (such as copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate.

[0056] In some embodiments of the present application, the positive electrode active material includes at least one of nickel-cobalt-based ternary materials and phosphate-based materials.

[0057] In some embodiments of the present application, the nickel-cobalt-based ternary material includes LiNi m Co n A (1-m-n) O2 materials, where A is selected from at least one of manganese, aluminum, magnesium, chromium, calcium, zirconium, molybdenum, silver or niobium, 0.5 ≤ m ≤ 1, 0 ≤ n ≤ 0.5, and m + n ≤ 1. In some embodiments of the present application, m is 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95 or a range composed of any two of these values. In some embodiments of the present application, n is 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45 or a range composed of any two of these values.

[0058] In some embodiments of the present application, the nickel-cobalt-based ternary material includes at least one of NCA, NCM111, NCM523, NCM622, NCM811, Ni90, Ni92 or Ni95.

[0059] In some embodiments of the present application, the phosphate-based material includes LiMn k B (1-k) PO4, where 0 ≤ k ≤ 1, and the B element is selected from at least one of iron, cobalt, magnesium, calcium, zinc, chromium or lead. In some embodiments of the present application, k is 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95 or a range formed by any two of these values. In some embodiments of the present application, the phosphate-based material includes lithium iron phosphate, LiMn 0.6 Fe 0.4 PO4 or LiMn 0.8 Fe 0.2 PO4.

[0060] In some embodiments of the present application, the positive electrode active material includes at least one of lithium nickel oxide, lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese oxide, lithium nickel manganese cobalt magnesium oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium iron phosphate and lithium iron manganese phosphate.

[0061] According to a preferred embodiment of the present application, the positive electrode active material is Li[Ni 1-x-y Co x M y O2 (M = Mn, Al, etc., such as lithium nickel cobalt manganese oxide Li[Ni 1-x-y Co x Mn y O2, 1 - x - y ≥ 0.5, lithium nickel cobalt aluminum oxide Li[Ni 1-x-y Co x Al y O2, 1 - x - y ≥ 0.5).

[0062] In some embodiments of the present application, the positive electrode active material layer further includes a binder, and optionally includes a conductive material. The binder improves the binding between the positive electrode active material particles and also improves the binding between the positive electrode active material and the current collector. In some embodiments of the present application, the binder includes: polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene 1,1-difluoroethylene, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin or nylon, etc.

[0063] In some embodiments of the present application, the conductive material includes, but is not limited to: carbon-based materials, metal-based materials, conductive polymers, and mixtures thereof. In some embodiments, the carbon-based materials are selected from natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based materials are selected from metal powder, metal fiber, copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer is a polyphenylene derivative.

[0064] In the embodiments of the present invention, the material and shape of the separator used are not particularly limited, and it can be any technology disclosed in the prior art. In some embodiments, the separator includes a polymer or an inorganic substance formed of a material stable to the electrolyte of the present invention.

[0065] For example, the separator may include a substrate layer and a surface treatment layer. The substrate layer is a non-woven fabric, a film, or a composite film having a porous structure, and the material of the substrate layer includes at least one of polyethylene, polypropylene, and polyethylene terephthalate. Specifically, a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric, or a polypropylene-polyethylene-polypropylene porous composite film can be selected.

[0066] A surface treatment layer is provided on at least one surface of the substrate layer, and the surface treatment layer can be a polymer layer, an inorganic layer, or a layer formed by mixing a polymer and an inorganic substance.

[0067] The inorganic layer includes inorganic particles and a binder. The inorganic particles include at least one of alumina, silica, magnesia, titania, hafnium dioxide, tin dioxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconia, yttria, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate. The binder includes at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate salt, polyvinylpyrrolidone, polyethylene alkoxide, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene.

[0068] The polymer layer contains a polymer, and the material of the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate salt, polyvinylpyrrolidone, polyethylene alkoxide, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene).

[0069] In a preferred embodiment according to the present invention, the separator is a polyethylene (PE) separator double-sidedly coated with a ceramic layer, wherein the thickness of the PE layer is in the range of 5 to 20 μm, and the coating thickness of each ceramic layer is in the range of 0 to 5 μm.

[0070] In the following examples and comparative examples, the reagents, materials and instruments used can be obtained commercially without special instructions.

[0071] III. Electrochemical performance test

[0072] 1. Overcharge experiment: The batteries assembled in the examples and comparative examples were charged at a constant current of 3C to 5V, and the battery status was recorded.

[0073] 2. 45°C high-temperature cycle experiment: The batteries assembled in the examples and comparative examples were placed in a constant-temperature oven at 55°C and left to stand for 2 h. After the large surface temperature of the battery core reached 55°C, the battery core was charged at a constant current of 1C to 4.5V, the cut-off current was 0.05C, left to stand for 10 min, and then discharged at a constant current of 0.5C to 2.8V. The cycle was repeated 3 times, and the discharge capacity of the battery at the last time was recorded as the initial capacity Q. When the cycle reached the specified number of turns, the discharge capacity Q1 of the battery at the last time was recorded, the initial thickness T of the battery core was measured and recorded, and the thickness at the specified number of turns was T1. The results are shown in Table 2.

[0074] Calculation formula: Battery capacity retention rate (%) = Q1 / Q0×100%.

[0075] 3. The test methods for the capacity retention rate, capacity recovery rate and thickness expansion rate after storage at 60°C for 30 days include:

[0076] The formed battery was charged at a constant current and constant voltage of 1C to 4.5V at room temperature, the cut-off current was 0.01C, and then discharged at a constant current of 1C to 3.0V. The initial discharge capacity Q2 of the battery was measured. Then it was charged at a constant current and constant voltage of 1C to 4.5V again, the cut-off current was 0.01C, and the initial thickness T2 of the battery was measured. Then after storage at 60°C for 30 days, the thickness T3 of the battery was measured, and then discharged at a constant current of 1C to 3.0V, and the retained capacity Q3 of the battery was measured. Then it was charged at a constant current and constant voltage until the cut-off current was 0.01C, and then discharged at a constant current of 1C to 3.0V, and its recovery capacity Q4 was measured. The calculation formulas are as follows:

[0077] Battery capacity retention rate (%) = Q3 / Q2×100%

[0078] Battery thickness expansion rate (%) = (T3 - T2) / T2×100%.

[0079] Example 1

[0080] Preparation of electrolyte: A non-aqueous organic solvent was prepared according to a volume ratio of propylene carbonate (PC): ethylene carbonate (EC): diethyl carbonate (DEC): fluoroethylene carbonate (FEC) = 3:3:3:1. Then, lithium hexafluorophosphate with a final concentration of 1.2 mol / L was added thereto. The lithium salt content in the electrolyte was 12 wt%, and 1.0 wt% of 1,4-dimethoxybenzene and 1.0 wt% of o-xylenediamine were added, that is, the percentage of the additive in the total mass of the electrolyte, and the rest were solvents, additives, and other additives.

[0081] Examples 2-9

[0082] Examples 2-9 were carried out in the same manner as Example 1. The electrolyte components used in Examples 2-9 are shown in Table 1.

[0083] Comparative Examples 1-10

[0084] Comparative Examples 1-10 were carried out in the same manner as Example 1. The electrolyte components used in Comparative Examples 1-10 are shown in Table 1.

[0085] Table 1

[0086]

[0087]

[0088] Coulombic efficiency tests and cycle stability tests were carried out on Li / Cu batteries manufactured from the electrolytes obtained in Examples 1-9 and Comparative Examples 1-10. The test results are shown in Table 2.

[0089] Table 2

[0090]

[0091] As can be seen from Table 2, the non-aqueous electrolyte of the lithium-ion battery of the present invention has excellent overcharge resistance performance, showing good safety performance and high-temperature charge and discharge performance. Specifically, it can be seen from Examples 1-9 and Comparative Examples 1-10 that the dimethoxy compound can form a passivation film on the surface of the positive electrode. At the same time, the methoxy substituent of the dimethoxy compound has a strong molecular polarity, is easy to diffuse, the reaction activity increases, and the overcharge resistance performance is improved. The addition of the phenylenediamine compound can better play the role of overcharge resistance and form a stable SEI film with high ionic conductivity, ensuring excellent electrochemical performance while improving the overcharge performance.

[0092] Although some exemplary embodiments of the present application have been illustrated and described, the present application is not limited to the disclosed embodiments. On the contrary, those of ordinary skill in the art will recognize that some modifications and changes can be made to the described embodiments without departing from the spirit and scope of the present application as described in the appended claims, and these modifications and changes also fall within the scope of protection of the present invention.

Claims

1. An electrolyte, characterized in that, The electrolyte includes a dimethoxy compound represented by formula (1) and a phenylenediamine compound represented by formula (2), wherein R1, R2, R3, R4, R6, R7, R8 are each independently selected from H, F, C1-C6 alkyl, and R5 is selected from H, C1-C6 alkyl.

2. The electrolyte according to claim 1, characterized in that, The dimethoxy compound includes at least one of 1,4-dimethoxybenzene, 1,4-difluoro-2,5-dimethoxybenzene, 1,4-dimethoxy-2-fluorobenzene, and 1,4-dimethoxy-2,3-methylbenzene; and / or Based on the total mass of the electrolyte, the content of the dimethoxy compound is 0.5 wt% to 3 wt%.

3. The electrolyte according to claim 1, characterized in that, The phenylenediamine compound includes at least one of o-xylenediamine, 1-methyl-3,5-dimethylaminobenzene, 1-fluoro-3,5-dimethylaminobenzene, 1,5-dimethyl-2,4-dimethylaminobenzene, and 1,5-difluoro-2,4-dimethylaminobenzene; and / or Based on the total mass of the electrolyte, the content of the phenylenediamine compound is 0.5 wt% to 3 wt%.

4. The electrolyte according to claim 2, characterized in that, The dimethoxy compound includes 1,4-dimethoxybenzene; and / or Based on the total mass of the electrolyte, the content of the dimethoxy compound is 1 wt% to 3 wt%.

5. The electrolyte according to claim 3, characterized in that, The phenylenediamine compound includes o-xylenediamine; and / or Based on the total mass of the electrolyte, the content of the phenylenediamine compound is 1 wt% to 1.5 wt%.

6. The electrolyte according to claim 1, characterized in that, Based on the total mass of the electrolyte, the sum of the contents of the dimethoxy compound and the phenylenediamine compound is 0.01 wt% to 10 wt%.

7. The electrolyte according to claim 6, characterized in that, Based on the total mass of the electrolyte, the sum of the contents of the dimethoxy compound and the phenylenediamine compound is 2 wt% to 6 wt%.

8. The electrolyte according to claim 1, characterized in that, Based on the total mass of the electrolyte, the ratio of the content of the dimethoxy compound to the content of the phenylenediamine compound is (0.5-2):

1.

9. A secondary battery, characterized in that, The secondary battery includes the electrolyte according to any one of claims 1 to 8.

10. A device, characterized in that, The device includes the secondary battery according to claim 9.

Images