Electrolyte, secondary battery, and device

Abstract

The invention relates to an electrolyte, a secondary battery and a device. The electrolyte provided by the invention comprises a non-aqueous solvent, a lithium salt, a first overcharge additive, a second overcharge additive and a phosphate additive, the first overcharge additive is shown as a formula I, the second overcharge additive is shown as a formula II, and the phosphate additive is shown as a formula III. The phosphate ester additive is shown as a formula III-1 or a formula III-2 (groups in the formula I, the formula II, the formula III-1 and the formula III-2 are defined in the specification), the mass ratio of the first overcharge additive to the second additive is 1: (0.5-2.5), and the mass ratio of the first overcharge additive to the phosphate ester additive is 1: (0.1-1). According to the electrolyte provided by the invention, the secondary battery has excellent overcharge performance, high-temperature performance and safety performance. # imgabs0 #

Description

Technical Field

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

[0002] Lithium-ion batteries have been widely used in portable electronic devices, electric vehicles and other life fields due to their green and environmentally friendly nature and high energy density. They have also been maturely used in high-tech fields such as aerospace. Among them, the life and safety of lithium-ion batteries have always been the focus of researchers. It is well known that batteries will swell or even explode and catch fire during excessive abuse. This is due to serious exothermic reactions inside the battery (oxidative decomposition and combustion of the electrolyte, etc.). Overcharging is a type of battery abuse. In the early stage of overcharging, it will cause heating problems in the battery. When overcharging occurs, the organic electrolyte will undergo violent oxidative decomposition, producing high-temperature flammable gases, etc., leading to serious dangers such as fire and explosion.

[0003] At present, overcharge additives have become the main means to solve the overcharge problem due to their low cost and wide variety. The working principle of overcharge protection additives is to undergo oxidative polymerization at high potential to form an insulating polymer film covering the electrode surface to prevent the voltage from rising, or to undergo an oxidation reaction by losing electrons at the positive electrode through the redox shuttle, and then undergo a reduction reaction at the negative electrode, thereby consuming excess charge to suppress the voltage increase. However, the addition of overcharge additives will affect other battery properties such as cycle performance to a certain extent. Summary of the invention

[0004] The present application aims to provide an electrolyte for solving at least one problem existing in the related field. In particular, the electrolyte provided by the present application enables a secondary battery to have excellent overcharge performance, cycle performance, high temperature performance and safety performance. The present application also relates to a secondary battery including the electrolyte.

[0005] The first aspect of the present application provides an electrolyte, which includes a non-aqueous solvent, a lithium salt, a first overcharge additive, a second overcharge additive and a phosphate additive, wherein the first overcharge additive is represented by formula I, the second overcharge additive is represented by formula II, and the phosphate additive is represented by formula III-1 or formula III-1.

[0006]

[0007] In Formula I, R1 and R2 are each independently selected from hydrogen, C1-C6 alkyl with or without substituents, C1-C6 alkoxy with or without substituents, halogen and cyano; in Formula II, R3, R4, R5, R6, R7 and R8 are each independently selected from hydrogen, C1-C6 alkyl with or without substituents, C1-C6 alkoxy with or without substituents, halogen and cyano; in Formula III-1 and Formula III-2, R9, R 10 and R 11 Each is independently selected from a substituted or unsubstituted C1-C6 alkyl group, a substituted or unsubstituted C2-C6 alkenyl group, a substituted or unsubstituted C2-C6 alkynyl group, a substituted or unsubstituted mono-C1-C6 alkylsilyl group, a substituted or unsubstituted poly-C1-C6 alkylsilyl group, and halogen, and R9, R 10 and R 11 At least one of them is selected from a mono-C1-C6 alkylsilane group with or without a substituent, and a poly-C1-C6 alkylsilane group with or without a substituent; the substituent is selected from a halogen and / or a cyano group, wherein the mass ratio of the first overcharge additive to the second additive is 1:(0.5-2.5), and the mass ratio of the first overcharge additive to the phosphate additive is 1:(0.1-1).

[0008] A second aspect of the present application provides a secondary battery, which includes a positive electrode, a negative electrode, and the electrolyte described in the first aspect.

[0009] A third aspect of the present application provides a device, which includes the secondary battery described in the second aspect.

[0010] The beneficial effects of this application are:

[0011] When the secondary battery is overcharged, the first monobenzene overcharge additive and the second biphenyl overcharge additive in the electrolyte of the present application can be gradient polymerized to form a polymer film, which effectively suppresses the increase in voltage and improves its safety performance. At the same time, the phosphate additive containing silane can improve the cycle performance and high temperature performance of the secondary battery itself while cooperating with the overcharge effect of the monobenzene ring and biphenyl overcharge additives. In the early stage of battery overcharge abuse, it can also effectively suppress the side effects of overcharge on battery temperature rise, slow down the occurrence of thermal runaway and the hazard of thermal runaway. The first overcharge additive, the second overcharge additive and the phosphate additive in the electrolyte work synergistically, so that the secondary battery has excellent cycle performance, safety performance, rate performance and high temperature performance. DETAILED DESCRIPTION

[0012] For simplicity, this application only specifically discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form an undefined range; and any lower limit can be combined with other lower limits to form an undefined range, and any upper limit can be combined with any other upper limit to form an undefined range. In addition, each separately disclosed point or single value can itself be combined as a lower limit or upper limit with any other point or single value or with other lower limits or upper limits to form an undefined range.

[0013] Unless otherwise specified, the terms used in this application have the commonly known meanings generally 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 measurement methods commonly used in the art (for example, they can be tested according to the methods given in the examples of this application).

[0014] A list of items connected by the terms "at least one of," "at least one of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, the phrase "at least one of A, B, and 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 may contain a single component or multiple components. Item B may contain a single component or multiple components. Item C may contain a single component or multiple components.

[0015] The term "silicon-based material" is not particularly limited, as long as the material contains silicon. In the present application, the "silicon-based material" may be silicon, silicon alloys, silicon-oxygen compounds, silicon-carbon compounds, and any mixture of the above silicon-based materials.

[0016] The term "carbon-based material" is not particularly limited, and may be graphite, soft carbon, hard carbon, carbon nanotubes, graphene, and any mixture of the above carbon-based materials. The term "graphite" is not particularly limited, and may be artificial graphite and / or natural graphite.

[0017] The term "C1-C6 alkyl" may be methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, isopentyl or n-hexyl.

[0018] The term "C1-C6 alkoxy" may be methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, isobutoxy, tert-butoxy, n-pentoxy, isopentyloxy or n-hexyloxy.

[0019] The term "C2-C6 alkenyl" may be ethenyl, n-propenyl, isopropenyl, n-but-2-enyl, but-3-enyl or n-hex-3-enyl.

[0020] The term "C2-C6 alkynyl" may be ethynyl, n-propynyl, isopropynyl, n-but-2-ynyl, but-3-ynyl or n-hex-3-ynyl.

[0021] The term "halogen" may be fluorine, chlorine, bromine or iodine.

[0022] The present application is further described below in conjunction with specific implementations. It should be understood that these specific implementations are only used to illustrate the present application and are not used to limit the scope of the present application.

[0023] 1. Electrolyte

[0024] The electrolyte provided by the present application includes a non-aqueous solvent, a lithium salt, a first overcharge additive, a second overcharge additive and a phosphate additive, wherein the first overcharge additive is represented by formula I, the second overcharge additive is represented by formula II, and the phosphate additive is represented by formula III-1 or formula III-2.

[0025]

[0026] In Formula I, R1 and R2 are each independently selected from hydrogen, C1-C6 alkyl with or without substituents, C1-C6 alkoxy with or without substituents, halogen and cyano; in Formula II, R3, R4, R5, R6, R7 and R8 are each independently selected from hydrogen, C1-C6 alkyl with or without substituents, C1-C6 alkoxy with or without substituents, halogen and cyano; in Formula III-1 and Formula III-2, R9, R 10 and R 11 Each is independently selected from a substituted or unsubstituted C1-C6 alkyl group, a substituted or unsubstituted C2-C6 alkenyl group, a substituted or unsubstituted C2-C6 alkynyl group, a substituted or unsubstituted mono-C1-C6 alkylsilyl group, a substituted or unsubstituted poly-C1-C6 alkylsilyl group, and halogen, and R9, R 10 and R 11 At least one of the above-mentioned additives is selected from a mono-C1-C6 alkylsilyl group with or without a substituent, and a poly-C1-C6 alkylsilyl group with or without a substituent, wherein the mass ratio of the first overcharge additive to the second additive is 1:(0.5-2.5), and the mass ratio of the first overcharge additive to the phosphate additive is 1:(0.1-1).

[0027] The present application adds a first overcharge additive of the monobenzene type, a second overcharge additive of the biphenyl type and a phosphate ester additive to the electrolyte. On the one hand, when the secondary battery is overcharged, the first overcharge additive of the monobenzene ring type and the second overcharge additive of the biphenyl type can form a gradient polymerization effect, more effectively suppress the increase of voltage, protect the electrode and the electrolyte, and improve the safety characteristics of the secondary battery. Specifically, the oxidation potential of the first overcharge additive of the monobenzene ring type is relatively high, and the oxidation potential of the second overcharge additive of the biphenyl type is relatively low. When the two are added to the electrolyte in combination, when the secondary battery is overcharged, the second overcharge additive of the biphenyl type preferentially undergoes oxidative polymerization to form a layer of mesh polymer film attached to the surface of the electrode. The film has insulating properties, and the oxidation of the additives will also consume a large amount of charge, ultimately suppressing the increase of voltage. If the potential continues to increase slowly and reaches the oxidation potential of the first overcharge additive of the monobenzene ring type, the structure will take effect, and its electrons will undergo oxidative polymerization to form a denser polymer film, covering the surface of the original biphenyl polymer film. The polymer film finally formed has higher insulation and can further suppress the increase of voltage. On the other hand, phosphate additives containing silane can be used in conjunction with single benzene ring and biphenyl overcharge additives to better improve the overcharge effect. And it can improve the high temperature performance of the secondary battery itself. In the early stage of battery overcharge abuse, it can also effectively inhibit the side effects of overcharge on battery temperature rise, slow down the occurrence of thermal runaway and the harm of thermal runaway. The first overcharge additive, the second overcharge additive and the phosphate additive in the electrolyte work synergistically, so that the secondary battery has excellent safety performance, rate performance, cycle performance and high temperature performance.

[0028] In some embodiments, the mass ratio of the first overcharge additive to the second additive is 1:(0.5-2.5), for example, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:10, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, 1:2.0, 1:2.1, 1:2.2, 1:2.3, 1:2.4 or any value therebetween.

[0029] In some embodiments, the mass ratio of the first overcharge additive to the phosphate additive is 1:(0.1-1), for example, 1:0.15, 1:0.2, 1:0.25, 1:0.3, 1:0.35, 1:0.4, 1:0.45, 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9 or any value therebetween.

[0030] In some embodiments, based on the mass of the electrolyte, the mass content of the first overcharge additive is 0.5%-10%. In some embodiments, the mass content of the first overcharge additive is 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5.5%, 6%, 7%, 8%, 9% or any value therebetween. In some embodiments, the mass content of the first overcharge additive is 1%-5%.

[0031] In some embodiments, based on the mass of the electrolyte, the mass content of the second overcharge additive is 0.5%-10%. In some embodiments, the mass content of the second overcharge additive is 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5.5%, 6%, 7%, 8%, 9% or any value therebetween. In some embodiments, the mass content of the second overcharge additive is 1%-5%.

[0032] In some embodiments, based on the mass of the electrolyte, the mass content of the phosphate ester additive is 0.1%-5%. In some embodiments, the mass content of the phosphate ester additive is 0.3%, 0.5%, 0.7%, 1%, 1.3%, 1.5%, 1.7%, 2%, 2.3%, 2.5%, 2.7%, 3%, 3.5%, 4%, 4.5% or any value therebetween. In some embodiments, the mass content of the phosphate ester additive is 0.5%-3%.

[0033] In some embodiments, in Formula I, R1 is selected from C1-C4 alkyl with or without substituents, halogen and cyano, and R2 is selected from C1-C4 alkyl without substituents; in Formula II, R3, R4 and R5 are each independently selected from hydrogen, C1-C4 alkyl without substituents, halogen or cyano; R6, R7 and R8 are each independently selected from hydrogen, C1-C4 alkyl without substituents or halogen; in Formula III-1, R9, R 10 and R 11 Each is independently selected from hydrogen or C1-C4 alkyl without substituent; the substituent is selected from halogen, and the halogen is selected from fluorine.

[0034] In some embodiments, in Formula I, R1 is selected from C1-C4 alkyl with or without substituents, halogen and cyano, and R2 is selected from C1-C4 alkyl without substituents. In some embodiments, R1 is selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, monofluoromethyl, difluoromethyl, trifluoromethyl, difluoroethyl, trifluoroethyl, pentafluoroethyl, hexafluoroisopropyl, fluorine and cyano, and R2 is selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl and tert-butyl.

[0035] In some embodiments, in Formula II, R3, R4 and R5 are each independently selected from hydrogen, C1-C4 alkyl without substituents, halogen and cyano; R6, R7 and R8 are each independently selected from hydrogen, C1-C4 alkyl without substituents and halogen. In some embodiments, R3, R4 and R5 are each independently selected from hydrogen, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, fluorine or cyano; R6, R7 and R8 are each independently selected from hydrogen, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl or fluorine.

[0036] In some embodiments, in Formula III-1, R9, R 10 and R 11 are independently selected from C1-C4 alkyl groups without substituents, poly-C1-C4 alkylsilyl groups without substituents, and R9, R 10 and R 11 At least one of them is selected from poly-C1-C4 alkylsilyl groups without substituents. 10 is selected from a poly-C1-C4 alkylsilyl group having no substituent, R9 and R 11 are independently selected from a C1-C4 alkyl group without a substituent or a poly-C1-C4 alkylsilyl group without a substituent. 10 is selected from trimethylsilyl, triethylsilyl, tri-n-butylsilyl, triisopropylsilyl, tri-n-butylsilyl, triisobutylsilyl, tri-tert-butylsilyl; R9 and R 11 Independently selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, trimethylsilyl, triethylsilyl, tri-n-butylsilyl, triisopropylsilyl, tri-n-butylsilyl, triisobutylsilyl, tri-tert-butylsilyl.

[0037] In some embodiments, in Formula III-2, R9, R 10 and R 11 are independently selected from C1-C4 alkyl groups without substituents, poly-C1-C4 alkylsilyl groups without substituents, and R9, R 10 and R 11 At least one of the groups is selected from poly-C1-C4 alkylsilyl groups having no substituent.

[0038] In some embodiments, in Formula III-2, R9, R 10 and R 11 each of methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, trimethylsilyl, triethylsilyl, tri-n-butylsilyl, triisopropylsilyl, tri-n-butylsilyl, triisobutylsilyl, tri-tert-butylsilyl, and R9, R 10 and R 11At least one of the following is selected from trimethylsilyl, triethylsilyl, tri-n-butylsilyl, triisopropylsilyl, tri-n-butylsilyl, triisobutylsilyl and tri-tert-butylsilyl.

[0039] In some embodiments, the substituents are selected from halogens selected from fluorine.

[0040] In some embodiments, the first overcharge additive is selected from at least one of the following compounds:

[0041]

[0042] In some embodiments, the second overcharge additive is selected from at least one of the following compounds:

[0043]

[0044] In some embodiments, the phosphate ester additive is selected from at least one of the following compounds:

[0045]

[0046]

[0047] In some embodiments, the first overcharge additive is represented by Formula I-1,

[0048] wherein R1 is selected from hydrogen, fluorine or cyano, and R2 is selected from C1-C4 alkyl without substituents, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl or tert-butyl;

[0049] The second overcharge additive is represented by Formula II-1 or Formula II-2,

[0050] wherein R4 is selected from hydrogen, cyano and C1-C4 alkyl without substituents, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl or tert-butyl; in formula II-2, R7 is selected from hydrogen or cyano;

[0051] The phosphate additive is represented by formula III-1A,

[0052] wherein R9 is selected from a C1-C4 alkyl group without a substituent or a poly-C1-C4 alkylsilyl group without a substituent, R 11 In some embodiments, R9 is selected from methyl, ethyl, n-propyl, isopropyl, trimethylsilyl, triethylsilyl, tri-n-butylsilyl or triisopropylsilyl, R 11 Selected from trimethylsilyl, triethylsilyl, tri-n-butylsilyl or triisopropylsilyl.

[0053] In some embodiments, the first overcharge additive is The second overcharge additive is The mass content of the phosphate additive is 1%-3%.

[0054] In some embodiments, the first overcharge additive is The second overcharge additive is The mass content of the phosphate additive is 1%-3%.

[0055] In some embodiments, the first overcharge additive is The second overcharge additive is The mass content of the phosphate additive is 1%-3%.

[0056] According to some embodiments of the present application, the non-aqueous solvent includes at least one of a linear carbonate, a cyclic carbonate or a carboxylate.

[0057] In some embodiments, the linear carbonate comprises at least one of the compounds shown in Formula IV,

[0058]

[0059] In Formula IV, R 12 and R 13 The same or different, each independently selected from C1-C6 alkyl or fluorinated C1-C6 alkyl.

[0060] In some embodiments, the linear carbonate includes at least one of dimethyl carbonate, ethyl methyl carbonate (EMC), diethyl carbonate, methyl n-propyl carbonate, ethyl n-propyl carbonate, di-n-propyl carbonate, bis(fluoromethyl) carbonate, bis(difluoromethyl) carbonate, bis(trifluoromethyl) carbonate, bis(2-fluoroethyl) carbonate or bis(2,2-difluoroethyl) carbonate.

[0061] In some embodiments, the cyclic carbonate comprises at least one of the compounds shown in V,

[0062]

[0063] In formula V, R 14 , R 15 , R 16 , R 17 are each independently selected from a hydrogen atom or a C1-C6 alkyl group, and a is 0, 1, 2, 3 or 4.

[0064] In some embodiments, the cyclic carbonate includes at least one of ethylene carbonate (EC), propylene carbonate (PC), or butylene carbonate.

[0065] In some embodiments, the carboxylate comprises at least one of the compounds of Formula VI,

[0066]

[0067] In Formula VI, R 18 and R 19 Independently selected from C1-C6 alkyl.

[0068] In some embodiments, the carboxylic acid ester is selected from at least one of 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 or ethyl isobutyrate.

[0069] In some embodiments, the lithium salt includes at least one selected from lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium bis(fluorosulfonyl)imide (LiFSI), lithium (trifluoromethylsulfonyl)(perfluorobutylsulfonyl)imide (LiFNFSI), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), lithium bis(oxalatoborate) (LiBOB), lithium bis(fluoromalonate)borate (LiBFMB), lithium 4,5-dicyano-2-(trifluoromethyl)imidazolium (LiTDI), or lithium difluorooxalatoborate (LiDFOB).

[0070] In some embodiments, the concentration of the lithium salt is 0.5M (mol / L)-1.5M, for example, 0.5M, 0.75M, 0.8M, 0.9M, 0.95M, 1.05M, 1.1M, 1.2M, 1.3M, 1.4M or any value therebetween.

[0071] 2. Secondary battery

[0072] The present application also provides a secondary battery, which includes a positive electrode, a negative electrode and the above-mentioned electrolyte.

[0073] According to some embodiments of the present application, the positive electrode includes a positive electrode active material, and the positive electrode active material includes LiNi x Co y M (1-x-y)In the O2 material, M is selected from at least one of Mn, Al, Mg, Cr, Ca, Zr, Mo, Ag, and Nb, 0.8≤x≤1, 0≤y≤0.2, and x+y≤1. In some embodiments, 0.8≤x≤1, for example, x is 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, or any value therebetween. In some embodiments, 0.86≤x≤1. In some embodiments, 0.90≤x≤1.

[0074] In some embodiments, 0≤y≤0.2, for example, y is 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.12, 0.14, 0.15, 0.17, 0.19 or any value therebetween. In some embodiments, 0≤y≤0.14. In some embodiments, 0≤y≤0.1. In some embodiments, the positive electrode active material includes at least one of NCM811, Ni90 or Ni94.

[0075] In some embodiments, the positive electrode active material may also be at least one of lithium nickel oxide, lithium manganese oxide, lithium iron phosphate, or lithium manganese iron phosphate.

[0076] According to some embodiments of the present application, the silicon-based material is a silicon-oxygen compound and / or a silicon-carbon compound. In some embodiments, the carbon-based material is graphite.

[0077] According to some embodiments of the present application, based on the mass of the negative electrode active material, the mass content z% of the silicon-based material satisfies: 8≤z<100. In some embodiments, the mass content k% of the carbon-based material satisfies: 0<k≤92. In some embodiments, z is 9, 11, 13, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95 or any value therebetween. In some embodiments, 10≤z≤50, in particular 10≤z≤35.

[0078] In some embodiments, k is 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 87, 89, 91 or any value therebetween. In some embodiments, 50≤k≤90, in particular 65≤k≤90.

[0079] In some embodiments, the negative electrode active material may also be at least one of tin, tin oxide, tin alloy, phosphorus, phosphorus complex, metallic lithium, and a metal capable of forming an alloy with metallic lithium.

[0080] According to some embodiments of the present application, the positive electrode includes a positive electrode current collector and a positive electrode active material layer located on the positive electrode current collector, and the positive electrode active material layer includes the positive electrode active material described above.

[0081] In some embodiments, the positive electrode active material layer further includes a binder, and optionally a conductive material. The binder improves the bonding of the positive electrode active material particles to each other and also improves the bonding of the positive electrode active material to the current collector.

[0082] In some embodiments, the binder includes, but is not limited to: polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin or nylon, etc.

[0083] In some embodiments, 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 material is selected from natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based material is selected from metal powder, metal fiber, copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer is a polyphenylene derivative.

[0084] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer substrate.

[0085] According to some embodiments of the present application, the negative electrode includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector, and the negative electrode active material layer includes the above-mentioned negative electrode active material.

[0086] In some embodiments, 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.

[0087] In some embodiments, the negative electrode active material layer further comprises a binder and a conductive agent. In some embodiments, the binder includes, but is not limited to: polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylic (ester) styrene-butadiene rubber, epoxy resin or nylon, etc.

[0088] In some embodiments, 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 material is selected from natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based material is selected from metal powder, metal fiber, copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer is a polyphenylene derivative.

[0089] According to some embodiments of the present application, a separator is provided between the positive electrode and the negative electrode to prevent short circuit. The material and shape of the separator that can be used in the embodiments of the present application 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 that is stable to the electrolyte of the present application.

[0090] For example, the isolation film 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, polyethylene terephthalate or polyimide. 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.

[0091] A surface treatment layer is disposed on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic layer.

[0092] The inorganic layer includes inorganic particles and a binder, wherein the inorganic particles include at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide or barium sulfate. The binder includes at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene or polyhexafluoropropylene.

[0093] The polymer layer contains polymers, and the polymer material includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride or poly(vinylidene fluoride-hexafluoropropylene).

[0094] According to some embodiments of the present application, the secondary battery is a lithium secondary battery or a sodium secondary battery. In some embodiments, the lithium secondary battery includes, but is not limited to: a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery or a lithium ion polymer secondary battery.

[0095] According to some embodiments of the present application, the secondary battery may include an outer package, which may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the secondary battery may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), etc.

[0096] According to some embodiments of the present application, the shape of the secondary battery is not particularly limited, and it can be cylindrical, square, or any other shape.

[0097] In some embodiments, the present application further provides a battery module. The battery module includes the above-mentioned secondary battery. The battery module of the present application uses the above-mentioned secondary battery, and therefore has at least the same advantages as the secondary battery. The number of secondary batteries contained in the battery module of the present application can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.

[0098] In some embodiments, the present application further provides a battery pack, which includes the above-mentioned battery module. The number of battery modules included in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0099] 3. Device

[0100] The present application also provides a device, which includes at least one of the above-mentioned secondary battery, battery module or battery pack.

[0101] In some embodiments, the device includes, but is not limited to: electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, power storage systems, etc. In order to meet the device's requirements for high power and high energy density of secondary batteries, a battery pack or battery module may be used.

[0102] In other embodiments, the device may be a mobile phone, a tablet computer, a laptop computer, etc. The device is usually required to be light and thin, and a secondary battery may be used as a power source.

[0103] Examples and Comparative Examples

[0104] Example 1

[0105] In a nitrogen-protected glove box (water content <1ppm, oxygen content <1ppm), ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a weight ratio of 30:70, and lithium hexafluorophosphate (LiPF6) was added thereto at a concentration of 1.2 mol / L to prepare a basic electrolyte. A first overcharge additive compound 3 with a mass fraction of 4%, a second overcharge additive compound 11 with a mass fraction of 4wt%, and a phosphate additive compound 21 with a mass fraction of 0.5% were added to the basic electrolyte, and the lithium-ion battery electrolyte of this embodiment was obtained after stirring evenly.

[0106] Example 2 to Example 15, Comparative Example 1 to Comparative Example 13

[0107] The preparation method of the electrolyte is the same as that of Example 1, and the only difference is the type and mass content of the first overcharge additive, the second overcharge additive and the phosphate additive. For details, see Table 1.

[0108] Lithium-ion battery preparation

[0109] 1) Preparation of positive electrode sheet: LiNi 0.9 Co 0.05 Mn 0.05 O2, conductive agent carbon nanotube / acetylene black, binder polyvinylidene fluoride PVDF, by weight proportion LiNi 0.9 Co 0.05 Mn 0.05 O2:CNT / Super-P:PVDF=95:2.0 / 1.0:2 was fully slurried in an N-methylpyrrolidone solvent system, coated on a 12 μm thick aluminum current collector, dried, and roll-pressed to obtain a positive electrode sheet.

[0110] 2) Preparation of negative electrode sheet: negative electrode active materials: artificial graphite, silicon-oxygen (SiO x , x=0.8-1.2), conductive agent acetylene black, binder styrene butadiene rubber, thickener sodium carboxymethyl cellulose, and polyacrylic acid are fully slurried in deionized water solvent in a weight ratio of 86:10:2:1.5:1:0.5, coated on a 8μm thick copper current collector, dried, and rolled to obtain a negative electrode sheet.

[0111] 3) Isolation film: Use polyethylene isolation film.

[0112] 4) The battery assembly steps are as follows: stack the above-mentioned positive electrode plate, isolation membrane, and negative electrode plate in a Z-shaped stack in sequence, place the obtained bare battery cell in a punched aluminum-plastic film soft package shell, and inject the electrolyte prepared in the above-mentioned embodiments and comparative examples after drying, and finally obtain a lithium-ion battery after standing, forming, aging, degassing, shaping and other processes.

[0113] Test Method

[0114] The lithium ion batteries prepared in the above embodiments and comparative examples were subjected to cycle performance tests, and the test method was as follows:

[0115] Battery formation process: Place the soft-pack battery in an environment of 25°C, charge it to 3.0V at 0.05C constant current, charge it to 3.4V at 0.1C constant current, and charge it to 3.75V at 0.2C constant current.

[0116] Battery capacity division process: Place the soft-pack battery in an environment of 25°C, charge it to 4.25V at 0.33C constant current and constant voltage, discharge it to 3.0V at 0.33C constant current, and cycle it twice.

[0117] Normal temperature cycle: Place the soft pack battery in a 25°C environment, charge it to 4.25V with constant current and constant voltage, with a cut-off current of 0.01C, and then discharge it to 3V with constant current. Calculate the capacity retention rate and impedance growth rate after 500 cycles. The calculation formula is as follows:

[0118] Capacity retention rate (%) = discharge capacity after N cycles / first discharge capacity × 100%;

[0119] Impedance growth rate (%) = (impedance after cycle - impedance before cycle) / impedance before cycle × 100%.

[0120] Overcharge test: Place the soft-pack battery after formation and capacity division in a constant temperature box at 25°C and charge it to 200% SOC at a constant current of 1C; if thermal runaway occurs during the process (the standard for thermal runaway is: battery fire and explosion), end the test; if there is no runaway, continue the test.

[0121] Test Results

[0122] Table 1

[0123]

[0124]

[0125]

[0126]

[0127] Note: Fail means that the capacity retention rate has decayed to 60% at a certain cycle before 500 cycles at 25℃.

[0128] The above comparative examples and example results show that the battery containing single benzene ring and biphenyl overcharge protection additives has a higher overcharge SOC protection range. After adding phosphate ester additives containing silane, the battery overcharge effect is further improved, and the impedance growth rate becomes lower. It shows that single benzene ring and biphenyl and phosphate ester additives containing silane can effectively improve the overcharge performance of the battery, and can improve the high temperature performance of the battery and reduce the battery impedance growth rate. Single benzene ring and biphenyl overcharge protection additives have a synergistic effect with phosphate ester additives containing silane, which can better improve the overcharge abuse safety of the battery.

[0129] 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 skilled in the art will recognize that some modifications and changes may be made to the described embodiments without departing from the spirit and scope of the present application as described in the appended claims.

Claims

1. An electrolyte comprising a non-aqueous solvent, a lithium salt, a first overcharge additive, a second overcharge additive and a phosphate additive, wherein: The first overcharge additive is represented by Formula I, the second overcharge additive is represented by Formula II, and the phosphate additive is represented by Formula III-1 or Formula III-2. In formula I, R1 and R2 are each independently selected from hydrogen, a C1-C6 alkyl group which may be substituted or unsubstituted, a C1-C6 alkoxy group which may be substituted or unsubstituted, a halogen group and a cyano group; In formula II, R3, R4, R5, R6, R7 and R8 are each independently selected from hydrogen, a C1-C6 alkyl group which may be substituted or unsubstituted, a C1-C6 alkoxy group which may be substituted or unsubstituted, a halogen group and a cyano group; In Formula III-1 and Formula III-2, R9, R 10 and R 11 Each is independently selected from a substituted or unsubstituted C1-C6 alkyl group, a substituted or unsubstituted C2-C6 alkenyl group, a substituted or unsubstituted C2-C6 alkynyl group, a substituted or unsubstituted mono-C1-C6 alkylsilyl group, a substituted or unsubstituted poly-C1-C6 alkylsilyl group, and halogen, and R9, R 10 and R 11 At least one of them is selected from a mono-C1-C6 alkylsilyl group which may be substituted or not, and a poly-C1-C6 alkylsilyl group which may be substituted or not; The substituents are selected from halogen and / or cyano; Wherein, the mass ratio of the first overcharge additive to the second additive is 1:(0.5-2.5), and the mass ratio of the first overcharge additive to the phosphate additive is 1:(0.1-1).

2. The electrolyte according to claim 1, characterized in that Based on the mass of the electrolyte, the mass content of the first overcharge additive is 0.5%-10%, preferably 1%-5%; and / or The mass content of the second overcharge additive is 0.5%-10%, preferably 1%-5%; and / or The mass content of the phosphate additive is 0.1%-5%, preferably 0.5%-3%.

3. The electrolyte according to claim 1 or 2, characterized in that In formula I, R1 is selected from C1-C4 alkyl with or without substitution, halogen and cyano, and R2 is selected from C1-C4 alkyl without substitution; In formula II, R3, R4 and R5 are each independently selected from hydrogen, C1-C4 alkyl without substituents, halogen and cyano; R6, R7 and R8 are each independently selected from hydrogen, C1-C4 alkyl without substituents and halogen; In Formula III-1 and Formula III-2, R9, R 10 and R 11 are independently selected from C1-C4 alkyl groups without substituents, poly-C1-C4 alkylsilyl groups without substituents, and R9, R 10 and R 11 At least one of them is selected from poly-C1-C4 alkylsilyl groups without substituents; The substituent is selected from halogen, and the halogen is selected from fluorine.

4. The electrolyte according to any one of claims 1 to 3, characterized in that The first overcharge additive is selected from at least one of the following compounds: and / or The second overcharge additive is selected from at least one of the following compounds: and / or The phosphate additive is selected from at least one of the following compounds:

5. The electrolyte according to any one of claims 1 to 3, characterized in that The first overcharge additive is represented by formula I-1, wherein R1 is selected from hydrogen, fluorine or cyano, and R2 is selected from C1-C4 alkyl without substituent; The second overcharge additive is represented by Formula II-1 or Formula II-2, Wherein, R4 is selected from hydrogen, cyano and C1-C4 alkyl without substituent; In formula II-2, R7 is selected from hydrogen or cyano; The phosphate additive is represented by formula III-1A, wherein R9 is selected from a C1-C4 alkyl group without a substituent or a poly-C1-C4 alkylsilyl group without a substituent, R 11 Selected from poly-C1-C4 alkylsilyl groups having no substituent.

6. The electrolyte according to claim 5, characterized in that The first overcharge additive is The second overcharge additive is The mass content of the phosphate additive is 1%-3%; or The first overcharge additive is The second overcharge additive is The mass content of the phosphate additive is 1%-3%; or The first overcharge additive is The second overcharge additive is The mass content of the phosphate additive is 1%-3%.

7. The electrolyte according to any one of claims 1 to 6, characterized in that The non-aqueous solvent comprises at least one of a linear carbonate, a cyclic carbonate or a carboxylate; and / or The lithium salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium trifluorosulfonyl, lithium bis(fluorosulfonyl)imide, lithium (trifluoromethylsulfonyl)(perfluorobutylsulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(pentafluoroethylsulfonic acid)imide, lithium bis(oxalatoborate), lithium bis(fluoromalonate)borate, lithium 4,5-dicyano-2-(trifluoromethyl)imidazole or lithium difluorooxalatoborate.

8. A secondary battery comprising a positive electrode, a negative electrode and the electrolyte according to any one of claims 1 to 7.

9. The secondary battery according to claim 8, characterized in that: The positive electrode includes a positive electrode active material, and the positive electrode active material includes LiNi x Co y M (1-x-y) At least one of the O2 materials, M is selected from at least one of Mn, Al, Mg, Cr, Ca, Zr, Mo, Ag, Nb, 0.8≤x≤1, 0≤y≤0.2, x+y≤1 preferably, 0.86≤x≤1, 0≤y≤0.14, x+y≤1; and / or The negative electrode includes a negative electrode active material, and the negative electrode active material includes at least one of a silicon-based material and a carbon-based material. Preferably, the silicon-based material is a silicon oxide compound and / or a silicon carbon compound, and the carbon-based material is graphite. Preferably, based on the mass of the negative electrode active material, the mass content z% of the silicon-based material satisfies: 8≤z<100, and the mass content k% of the carbon-based material satisfies: 0<k≤92. 10 . A device comprising the secondary battery according to claim 8 or 9 .

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