Electrolyte, lithium ion battery and electronic device

Abstract

The application discloses an electrolyte, a lithium ion battery and an electronic device. The electrolyte comprises a compound shown in formula I and a fluorinated carbonate; formula I wherein R1 and R2 are each independently a substituent group with 1-6 carbon atoms, 0-4 unsaturations and 0-3 heteroatoms. The lithium ion battery using the electrolyte has excellent low-temperature kinetic performance and high-temperature cycle performance.

Description

TECHNICAL FIELD

[0001] The present application provides an electrolyte, a lithium ion battery and an electronic device. BACKGROUND

[0002] With the increasing demand for electric vehicles and portable devices, the development of lithium ion batteries is also changing rapidly. In commercial lithium ion batteries, the positive electrode material is a key factor that determines the energy density and cost of lithium ion batteries. Among the many candidate positive electrode materials, high-nickel positive electrode material LiNi x M 1-x O2(M = Mn, Co, Al, etc.) has the potential to achieve high energy density and is the most mature in development, with an energy density ranging from 650 Wh kg -1 to more than 850 Wh kg -1 At the same time, the cycle life is also quite considerable, reaching 1500-3000 cycles.

[0003] However, high-nickel positive electrodes have a structure collapse phenomenon, which may be caused by two types of side reactions: one is the decomposition reaction of lithium-related compounds (such as LiOH, LiHCO3 and Li2CO3) remaining on the surface and the side reaction with the acidic environment of the system; the other is the oxidation reaction between the electrolyte and the high-nickel positive electrode in the high delithiation state. This will cause damage to the material structure, mechanical failure of the battery shell, and even battery explosion, so there is a certain risk in safety performance.

[0004] The existing means to solve the transition metal overflow of high-nickel positive electrodes are mainly: 1) coating the material; 2) adjusting the solvent ratio in the electrolyte. The coating of the material is mainly through the method of atomic layer deposition to coat a layer of oxide protective film on the material or the electrode sheet level, but such a method will affect the energy density of the system, and has a negative effect on the dynamics of the material. On the other hand, adjusting the solvent ratio in the electrolyte reduces the use of ethylene carbonate (EC), which can reduce the oxidation side reaction of EC on the positive electrode side, thereby reducing high-temperature gas production, but the reduction of EC also has a serious impact on the dynamics. SUMMARY

[0005] The present application provides an electrolyte, a lithium ion battery and an electronic device. The electrolyte of the present application contains a specific additive, and the lithium ion battery using the electrolyte has excellent low-temperature dynamics and high-temperature cycle performance.

[0006] In order to achieve the above purpose, the present application adopts the following technical solutions:

[0007] The first aspect of the present application provides an electrolyte, which comprises a compound represented by formula I and a fluorinated carbonate;

[0008]

[0009] Formula I

[0010] wherein R1 and R2 are each independently a substituent having 1 to 6 carbon atoms, 0 to 4 degrees of unsaturation, and 0 to 3 numbers of heteroatoms.

[0011] A second aspect of the present application provides a lithium ion battery including the electrolyte described above.

[0012] A third aspect of the present application provides an electronic device including the lithium ion battery described above.

[0013] The positive progress effect of the present application is that:

[0014] The present application can form a phosphate-carbonate copolymer SEI film containing LiF on the electrode surface during the operation of the lithium ion battery by adding a specific cyanophosphonate compound as an additive in the electrolyte, in combination with fluorocarbonates, through complexation of metal ions and nucleophilic substitution reactions, while improving the low-temperature kinetic performance and high-temperature cycle performance of the lithium ion battery. DETAILED DESCRIPTION

[0015] The present application will be further described below by way of examples, but the present application is not limited to the scope of the examples described. In the following examples, the experimental methods not specified in the specific conditions are selected according to the conventional methods and conditions, or according to the instructions of the goods.

[0016] In the electrolyte described in the first aspect of the present application, the electrolyte includes a compound represented by Formula I and a fluorocarbonate;

[0017]

[0018] Formula I

[0019] wherein R1 and R2 are each independently a substituent having 1 to 6 carbon atoms, 0 to 4 degrees of unsaturation, and 0 to 3 numbers of heteroatoms.

[0020] In the present application, the compound shown in formula I is a cyanophosphonate compound, the structure containing cyanogen, the mechanism of complexing metal ions mainly involving coordination chemistry and structural characteristics, the N atom having lone pair of electrons, which can be coordinated with metal ions as Lewis base; and the P atom having empty 3d orbital, which can participate in π backbonding or auxiliary coordination, and also can have the function of complexing transition metal. The cyanophosphonate compound shown in formula I is used in combination with fluorocarbonate, and the phosphorus atom in fluorocarbonate (due to the strong electron-withdrawing effect of cyanogen, the P=O bond is polarized, and the phosphorus is positively charged) can become the nucleophilic attack site of the fluorine atom in fluorocarbonate. The C-F bond in fluorocarbonate is replaced under the action of nucleophilic reagents (such as ethoxy or cyanogen) to generate fluorine-containing phosphonate derivatives and release LiF. The nucleophilic group (such as ethoxy or cyanogen) in the cyanophosphonate compound attacks the carbonyl carbon of fluorocarbonate, leading to ring opening of the cyclic carbonate, forming a phosphonate-carbonate covalent compound SEI film containing LiF.

[0021] In some embodiments, R1and R2are each independently one or more of alkyl, alkenyl, alkynyl, carbonyl, ester, amino-substituted alkyl, and heterocyclyl having 1-6 carbon atoms, 0-4 degrees of unsaturation, and 0-3 heteroatoms. Note that "having 1-6 carbon atoms, 0-4 degrees of unsaturation, and 0-3 heteroatoms" defines "alkyl, alkenyl, alkynyl, carbonyl, ester, amino-substituted alkyl, and heterocyclyl" and not just "alkyl."

[0022] In some preferred embodiments, the compound shown in formula I is selected from one or more of compounds 1-4;

[0023] Compound 1 , compound 2 ,

[0024] Compound 3 , compound 4 .

[0025] In some embodiments, the content of the compound shown in formula I is 0.05wt.%-3wt.%, preferably 0.1wt.%-1wt.%, for example 0.3wt.% or 3.5wt.%, and wt.% is the mass percentage of the compound shown in formula I in the electrolyte.

[0026] In some embodiments, the fluorocarbonate is fluoroethylene carbonate (FEC).

[0027] In some embodiments, the content of the fluorocarbonate is 0.5wt.%-8wt.%, preferably 0.5wt.%-5wt.%, and wt.% is the mass percentage of the fluorocarbonate in the electrolyte.

[0028] In some embodiments, the total content of the compound of Formula I and the fluorinated carbonate is 0.6 wt.% - 10 wt.%, for example 0.8 wt.%, 5.05 wt.%, 5.3 wt.%, 6 wt.%, 8 wt.%, 8.3 wt.% or 8.5 wt.%, wt.% is the sum of the mass of the compound of Formula I and the fluorinated carbonate, as a percentage of the mass of the electrolyte.

[0029] In some preferred embodiments, the content of the compound of Formula I is 0.05 wt.% - 3 wt.% and the content of the fluorinated carbonate is 0.5 wt.% - 8 wt.%.

[0030] In some specific embodiments, the compound of Formula I is Compound 1 and the fluorinated carbonate is fluorinated ethylene carbonate.

[0031] In some specific embodiments, the compound of Formula I is Compound 1 and the fluorinated carbonate is fluorinated ethylene carbonate, the content of Compound 1 is 0.3 wt.% and the content of fluorinated ethylene carbonate is 5 wt.%.

[0032] In some specific embodiments, the compound of Formula I is Compound 1 and the fluorinated carbonate is fluorinated ethylene carbonate, the content of Compound 1 is 0.3 wt.% and the content of fluorinated ethylene carbonate is 0.5 wt.%.

[0033] In some specific embodiments, the compound of Formula I is Compound 1 and the fluorinated carbonate is fluorinated ethylene carbonate, the content of Compound 1 is 1 wt.% and the content of fluorinated ethylene carbonate is 5 wt.%.

[0034] In some specific embodiments, the compound of Formula I is Compound 1 and the fluorinated carbonate is fluorinated ethylene carbonate, the content of Compound 1 is 3 wt.% and the content of fluorinated ethylene carbonate is 5 wt.%.

[0035] In some specific embodiments, the compound of Formula I is Compound 1 and the fluorinated carbonate is fluorinated ethylene carbonate, the content of Compound 1 is 0.05 wt.% and the content of fluorinated ethylene carbonate is 5 wt.%.

[0036] In some specific embodiments, the compound of Formula I is Compound 1 and the fluorinated carbonate is fluorinated ethylene carbonate, the content of Compound 1 is 3.5 wt.% and the content of fluorinated ethylene carbonate is 5 wt.%.

[0037] In some embodiments, the compound of Formula I is Compound 1, the fluorinated carbonate is fluoroethylene carbonate, and the Compound 1 is present in an amount of 0.3 wt.%, and the fluoroethylene carbonate is present in an amount of 8 wt.%.

[0038] In some embodiments, the compound of Formula I is Compound 2, the fluorinated carbonate is fluoroethylene carbonate.

[0039] In some embodiments, the compound of Formula I is Compound 2, the fluorinated carbonate is fluoroethylene carbonate, and the Compound 2 is present in an amount of 0.3 wt.%, and the fluoroethylene carbonate is present in an amount of 5 wt.%.

[0040] In some embodiments, the compound of Formula I is Compound 3, the fluorinated carbonate is fluoroethylene carbonate.

[0041] In some embodiments, the compound of Formula I is Compound 3, the fluorinated carbonate is fluoroethylene carbonate, and the Compound 3 is present in an amount of 0.3 wt.%, and the fluoroethylene carbonate is present in an amount of 5 wt.%.

[0042] In some embodiments, the compound of Formula I is Compound 4, the fluorinated carbonate is fluoroethylene carbonate.

[0043] In some embodiments, the compound of Formula I is Compound 4, the fluorinated carbonate is fluoroethylene carbonate, and the Compound 4 is present in an amount of 0.3 wt.%, and the fluoroethylene carbonate is present in an amount of 5 wt.%.

[0044] In some embodiments, the solvent in the electrolyte is selected from one or more of diethyl carbonate, dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), trifluoroethyl methyl carbonate, difluoroethyl acetate, ethers, and nitriles.

[0045] In some embodiments, the solvent in the electrolyte is selected from one or more of diethyl carbonate, dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), trifluoroethyl methyl carbonate, difluoroethyl acetate, ethers, and nitriles.

[0046] In some embodiments, the solvent in the electrolyte is selected from one or more of diethyl carbonate, dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), trifluoroethyl methyl carbonate, difluoroethyl acetate, ethers, and nitriles.

[0047] In some embodiments, the solvent in the electrolyte is selected from one or more of diethyl carbonate, dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), trifluoroethyl methyl carbonate, difluoroethyl acetate, ethers, and nitriles.

[0048] In some embodiments, the content of the solvent in the electrolyte is 70wt.%-80wt.%, wt.% is the mass percentage of the solvent in the electrolyte.

[0049] In some embodiments, the lithium salt in the electrolyte is selected from one or more of lithium hexafluorophosphate, lithium bisfluorosulfonimide, lithium bis(trifluoromethyl)sulfonimide, lithium acetate, lithium methylsulfonate and lithium trifluoromethylsulfonate.

[0050] In some embodiments, the lithium salt comprises lithium hexafluorophosphate.

[0051] In some embodiments, the lithium salt comprises lithium hexafluorophosphate and lithium bisfluorosulfonimide. Wherein the mass ratio of the lithium hexafluorophosphate and the lithium bisfluorosulfonimide is 14: (1-3), for example 14:1, 14:2 or 13:2.

[0052] In some embodiments, the content of the lithium salt in the electrolyte is 12wt.%-16wt.%, for example 12.5wt.%, wt.% is the mass percentage of the lithium salt in the electrolyte.

[0053] In some embodiments, the electrolyte further comprises one or more of vinyl sulfate (DTD), propenyl-1,3-sultone (PST), tetraethenylsilane (TVSI) and tris(trimethylsilyl) phosphate (TMSP).

[0054] In some embodiments, the electrolyte further comprises tris(trimethylsilyl) phosphate, the content of the tris(trimethylsilyl) phosphate is preferably 0.1wt.%-1.0wt.%, for example 0.5wt.%.

[0055] In some specific embodiments, the electrolyte comprises 0.3wt.% of compound 1, 5wt.% of fluoroethylene carbonate and 0.5wt.% of tris(trimethylsilyl) phosphate.

[0056] In some embodiments, the electrolyte further comprises propenyl-1,3-sultone, the content of the propenyl-1,3-sultone is preferably 0.1wt.%-1.0wt.%, for example 0.5wt.%.

[0057] In some specific embodiments, the electrolyte comprises 0.3wt.% of compound 1, 5wt.% of fluoroethylene carbonate and 0.5wt.% of propenyl-1,3-sultone.

[0058] In some embodiments, the electrolyte further comprises tetraethenylsilane, the content of the tetraethenylsilane is preferably 0.1wt.%-1.0wt.%, for example 0.5wt.%.

[0059] In some embodiments, the electrolyte comprises 0.3 wt.% of Compound 1, 5 wt.% of fluoroethylene carbonate, and 0.5 wt.% of tetra-vinyl silane.

[0060] In a second aspect of the present application, a lithium ion battery is provided, wherein the lithium ion battery comprises the electrolyte as described above.

[0061] In the present application, the lithium ion battery comprises a positive electrode sheet, a negative electrode sheet, a separator, and the electrolyte as described above.

[0062] Positive electrode sheet

[0063] In the present application, the positive electrode sheet can comprise a positive electrode current collector and a positive electrode material layer disposed on at least one surface of the positive electrode current collector; the positive electrode material layer comprises a positive electrode material.

[0064] In some embodiments, the positive electrode material is a nickel-containing positive electrode material.

[0065] In some embodiments, the nickel-containing positive electrode material has a chemical formula of LiNi x M 1-x O2, wherein M is selected from one or more of Mn, Co, and Al, and x is 0.4-0.95.

[0066] In some embodiments, the nickel-containing positive electrode material has a chemical formula of LiNi 0.9 Mn 0.05 Co 0.05 O2.

[0067] In some embodiments, the positive electrode material layer further comprises a conductive agent. The conductive agent is an agent used to ensure that the electrode has good charge and discharge performance. It can be optionally selected from graphite-based materials such as natural graphite, artificial graphite, carbon black-based materials such as acetylene black, ketjen black, channel black, furnace black, lamp black, thermal cracking black, conductive fibers such as carbon fibers, metal fibers, metal powders such as fluorinated carbon powder, aluminum powder, nickel powder, conductive whiskers such as zinc oxide, potassium titanate, and conductive metal oxides such as titanium dioxide, or polyphenylene derivatives, for example, conductive carbon black.

[0068] In some embodiments, the positive electrode material layer further comprises a binder. The binder can be a component that facilitates the binding between the positive electrode material and the conductive agent and facilitates the binding between the positive electrode material and the positive electrode current collector. It can be typically selected from the group consisting of polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butadiene rubber, fluoro rubber, and various copolymers, for example, PVDF.

[0069] In some embodiments, the positive electrode material layer comprises a positive electrode material, polyvinylidene fluoride, and conductive carbon black.

[0070] In some specific embodiments, the mass ratio of the positive electrode material, polyvinylidene fluoride, and conductive carbon black is 8:1:1.

[0071] In the present application, the positive electrode current collector can be a conventional positive electrode current collector in the art. For the positive electrode current collector, a material that does not cause chemical changes and has high electrical conductivity can be used without limitation. For example, stainless steel, aluminum, nickel, titanium, or calcined carbon, or an aluminum or stainless steel material surface-treated with carbon, nickel, titanium, silver, or the like can be typically used. In order to enhance adhesion, micro-embossing can be formed on the surface of the positive electrode current collector. The positive electrode current collector can be used in various forms, such as a film, a sheet, a foil, a mesh, or a porous body, etc.

[0072] In some alternative embodiments, the positive electrode current collector is an aluminum foil.

[0073] In some alternative embodiments, the thickness of the positive electrode current collector can be 8-16 μm, for example, 10 μm.

[0074] In the present application, the positive electrode sheet can be prepared using a conventional method in the art.

[0075] In some alternative embodiments, the method of preparing the positive electrode sheet comprises the following steps:

[0076] After mixing the positive electrode material, the binder, and the conductive agent in a certain mass ratio, a solvent is added and mixed uniformly to obtain a positive electrode slurry; then the positive electrode slurry is uniformly coated on at least one surface of the positive electrode current collector; and then the positive electrode sheet is prepared through processes such as drying, rolling, and slitting.

[0077] Negative electrode sheet

[0078] In the present application, the negative electrode sheet can comprise a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector, the negative electrode material layer comprising a negative electrode material.

[0079] In the present application, the negative material in the negative material layer can be a negative material commonly used in the art, such as a graphite-based negative material, a silicon-oxygen-based negative material, or a silicon-carbon-based negative material.

[0080] In some embodiments, the negative material includes one or more of artificial graphite, natural graphite, soft carbon, hard carbon, mesocarbon microbeads, silicon monoxide, and silicon-carbon material.

[0081] In some embodiments, the negative material layer further includes a conductive agent.

[0082] The conductive agent is not particularly limited as long as it has conductivity and does not cause chemical changes in the battery. For example, graphite such as natural graphite or artificial graphite; carbon-based materials such as conductive carbon black (Super P, referred to as SP), carbon nanotubes (CNT), acetylene black, ketjen black, slot black, furnace black, lamp black, thermal carbon black, or carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, or silver; conductive whiskers such as zinc oxide whiskers or potassium titanate whiskers; conductive metal oxides such as titanium dioxide; or conductive polymers such as polyphenylene derivatives can be used, for example.

[0083] In some specific embodiments, the conductive agent in the negative material layer is acetylene black.

[0084] In some embodiments, the negative material layer further includes a binder.

[0085] The type of binder is not particularly limited and can be selected from polyvinylidene fluoride, polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid (PAA), ethylene-propylene-diene terpolymer and its sulfonated product, styrene butadiene rubber (SBR), fluororubber, and various copolymers, for example, SBR.

[0086] In some embodiments, the negative material layer further includes a thickening agent.

[0087] The addition of the thickening agent can increase the system viscosity of the components in the negative slurry, and can be a thickening agent commonly used in the art for preparing negative sheets, for example, sodium carboxymethyl cellulose (CMC).

[0088] In the present application, the negative current collector can be a conventional negative current collector in the art. The negative current collector serves as a substrate to support the negative material layer, and is usually a metal foil having a thickness of 3-500 μm. There is no particular limitation on the material, as long as it has high electrical conductivity and does not chemically react in the system of the secondary battery. For example, it can be a foil formed after surface treatment of nickel, titanium, aluminum, nickel, silver, stainless steel, carbon, etc. The negative current collector is usually smooth, but fine lines or the like can be formed on its surface to improve the adhesion between the negative material layer and the current collector. In addition to the foil, the negative current collector can also take any one or a combination of multiple forms of film, mesh, porous, foam or non-woven fabric, etc. Generally, the negative current collector is a copper foil.

[0089] In some embodiments, the method for preparing the negative sheet comprises the following steps: coating the negative slurry obtained by thoroughly mixing the components of the negative material layer in a solvent on at least one surface of the negative current collector, drying, cold pressing, and slitting to obtain the negative sheet.

[0090] Separator

[0091] In some alternative embodiments, the separator can be a polypropylene film or a polyethylene film.

[0092] In the present application, the method for preparing the lithium ion battery can be a conventional preparation method in the art, which can be to sequentially wind the positive sheet, the separator and the negative sheet to obtain a battery cell, then package the battery cell with a packaging shell and inject the electrolyte; or to sequentially stack the positive sheet, the separator and the positive sheet to obtain a battery cell, then package the battery cell with a packaging shell and inject the electrolyte; and then go through the processes of standing, hot and cold pressing, formation, clamping, and capacity grading to obtain the lithium ion battery.

[0093] In the electronic device according to the third aspect of the present application, the electronic device comprises the lithium ion battery.

[0094] Exemplarily, the electronic device according to the present application can be, but is not limited to, a mobile device (such as a mobile phone, a tablet computer, a notebook computer, a video recorder, a portable printer / copier, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system and a backup power supply, etc.

[0095] On the basis of common sense in the art, the above-mentioned preferred conditions can be combined arbitrarily to obtain various preferred examples of the present application.

[0096] The reagents and raw materials used in the following examples and comparative examples are commercially available. Example 1

[0097] (1) Preparation of electrolyte

[0098] In a glove box with nitrogen content of 99.999%, actual oxygen content of 0.1 ppm, and moisture content of 0.1 ppm, compound 1 was mixed with fluoroethylene carbonate (FEC) and a solvent (EC:DMC:EMC = 3:5:2, by volume) to obtain a mixture, and then lithium hexafluorophosphate dried sufficiently was added to prepare an electrolyte; wherein, based on the total mass of the electrolyte being 100 wt.%, the content of compound 1 was 0.3 wt.%, the content of FEC was 5 wt.%, and the content of lithium hexafluorophosphate was 12.5 wt.%.

[0099] (2) Preparation of positive electrode sheet

[0100] The positive electrode material LiNi 0.9 Mn 0.05 Co 0.05 O2, the conductive agent acetylene black, and the binder polyvinylidene fluoride were mixed uniformly in the N-methylpyrrolidone solvent, coated on an aluminum foil, dried, and cold-pressed to obtain a positive electrode sheet.

[0101] (3) Preparation of negative electrode sheet

[0102] The artificial graphite, the natural graphite, the silicon-carbon material, the conductive agent acetylene black, the binder styrene-butadiene rubber, and the thickening agent sodium carboxymethyl cellulose were mixed uniformly in a deionized water solvent system according to a mass ratio of 43:43:10:2:1:1, coated on a copper foil, dried, and cold-pressed to obtain a negative electrode sheet.

[0103] (4) Preparation of separator

[0104] A polyethylene with a thickness of 9 μm was used as a base film, and a nanometer alumina coating with a thickness of 3 μm was coated on the base film to obtain a separator.

[0105] (5) Assembly of lithium ion battery

[0106] The positive electrode sheet, the separator, and the negative electrode sheet prepared in the foregoing steps were stacked in sequence to obtain a bare cell, and the separator was arranged between the positive electrode sheet and the negative electrode sheet to play a role of isolation, thereby obtaining a bare cell. The bare cell was then loaded into an aluminum plastic film, and then baked at 80 o C to remove water, and then the electrolyte prepared in step (1) was injected and sealed, and then the lithium ion battery was obtained after the processes of standing, hot and cold pressing, formation, clamp, and capacity distribution.

[0107] Examples 2-12 and Comparative Examples 1-4

[0108] Examples 2-10 and Comparative Examples 1-3 are the same as Example 1 except that the content of the compound of Formula I and fluoroethylene carbonate in the electrolyte is different from that of Example 1. The content of the compound of Formula I and fluoroethylene carbonate in the electrolyte of Examples 1-10 and Comparative Examples 1-3 is shown in Table 1.

[0109] In Examples 11-13, the electrolyte further includes tris(trimethylsilyl) phosphate, propenyl-1,3-sultone or tetra-vinylsilane, and the remaining steps and conditions are the same as Example 1. In Comparative Example 4, the remaining steps and conditions are the same as Example 1 except that vinylene carbonate (VC) is used instead of fluoroethylene carbonate in the electrolyte. The components in Examples 11-13 and Comparative Example 4 are shown in Table 2.

[0110] Table 1

[0111]

[0112] Note: " / " means that the component is not included.

[0113] Table 2

[0114]

[0115] Note: " / " means that the component is not included.

[0116] Effect Examples

[0117] 1. Impedance DCR at -20°C

[0118] Adjust the temperature of the thermostat to -20°C, stand for 2 h, charge at 0.33 C to 4.25 V, then charge at 4.25 V to 0.05 C cut-off, stand for 30 min, then discharge at 0.33 C to 2.5 V; cycle the charge and discharge at 0.33 C for 2 times, record the discharge capacity at the last time as Co; stand for 30 min, then discharge at 0.33 C to 50% Co, adjust the SOC of the cell to 50%, stand for 30 min, record the end voltage V1, discharge at Co for 30 s, record the end voltage V2 and the current I, calculate DCR = (V1-V2) / I. The test results are shown in Table 3.

[0119] Table 3

[0120]

[0121] 2. Capacity retention rate of high temperature cycle at 45°C

[0122] The temperature of the environmental box was adjusted to 45℃, and the lithium ion battery was rested for 1h, then charged at 0.5C constant current to 4.4V, and then charged at 4.4V constant voltage until the current was less than 0.05C, rested for 10 min, then discharged at 1.0C constant current to 2.8V, rested for 10 min, and then the discharge capacity of the lithium ion battery at this time was recorded as the discharge capacity of the first cycle; the battery was cycled multiple times under the above conditions, and the capacity retention rate of the battery after 800 cycles was calculated.

[0123] The cycle capacity retention rate was calculated according to the following formula:

[0124] Capacity retention rate (%) = (discharge capacity corresponding to 800 cycles / discharge capacity of the first cycle) x 100%.

[0125] The test results are shown in Table 3.

[0126] As shown in Table 3, the lithium ion battery prepared by using the electrolyte of the present application has excellent low-temperature kinetic performance and high-temperature cycle performance, the DCR at -20℃ is less than 550Ω, more preferably less than 500Ω, and the capacity retention rate after 800 cycles at 45℃ is 81% or more, more preferably 85% or more. The electrolyte in Comparative Example 1 does not add a cyanophosphonate compound or a fluorinated carbonate; Comparative Example 2 only adds a cyanophosphonate compound, and Comparative Example 3 only adds a fluorinated carbonate; although Comparative Example 4 adds a cyanophosphonate compound, it uses an equivalent amount of vinylene carbonate to replace the fluorinated carbonate; the low-temperature kinetic performance and high-temperature cycle performance of Comparative Examples 1-4 cannot simultaneously achieve the effect of the present application.

[0127] The above specific embodiments further illustrate the purpose, technical solutions and beneficial effects of the present application, and it should be understood that the above description is only for specific embodiments of the present application and is not intended to limit the present application, and any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A lithium-ion battery, characterized in that: The lithium-ion battery includes an electrolyte, and the electrolyte includes a compound and a fluorocarbonate; the compound is compound 2 and / or compound 3; Compound 2 , compound 3 ; The mass percentage of the fluorinated carbonate in the electrolyte is 5wt.%-8wt.%; the mass percentage of the total mass of the compound and the fluorinated carbonate in the electrolyte is 5.05wt.%-10wt.%; The solvent in the electrolyte includes ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate; The lithium-ion battery further comprises a positive electrode sheet, a negative electrode sheet and a separator. The positive electrode sheet comprises a positive electrode current collector and a positive electrode material layer. The positive electrode material layer is provided on at least one surface of the positive electrode current collector. The positive electrode material layer comprises a positive electrode material. The positive electrode material is a nickel-containing positive electrode material. The chemical formula of the nickel-containing positive electrode material is LiNi x M 1-x O2, wherein M is selected from one or more of Mn, Co and Al, and x is 0.9-0.

95.

2. The lithium-ion battery according to claim 1, wherein The mass percentage of the compound in the electrolyte is 0.05 wt.%-3 wt.%.

3. The lithium-ion battery according to claim 1, wherein The fluorinated carbonate is fluorinated ethylene carbonate.

4. The lithium-ion battery according to claim 1, wherein The mass percentage of the solvent in the electrolyte is 70 wt.%-80 wt.%.

5. The lithium-ion battery according to claim 1, wherein The lithium salt in the electrolyte is selected from one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethyl)sulfonylimide, lithium acetate, lithium methanesulfonate and lithium trifluoromethylsulfonate; And / or, the mass percentage of the lithium salt in the electrolyte is 12 wt.%-16 wt.%.

6. The lithium-ion battery according to claim 1, wherein The electrolyte further comprises one or more of vinyl sulfate, propenyl-1,3-sultone, tetravinylsilane and tris(trimethylsilyl)phosphate.

7. An electronic device, characterized in that: The electronic device comprises the lithium-ion battery according to any one of claims 1 to 6.

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