WO2022252055A1

WO2022252055A1 - Electrochemical device and electronic device

Info

Publication number: WO2022252055A1
Application number: PCT/CN2021/097407
Authority: WO
Inventors: 唐超; 彭谢学
Original assignee: 宁德新能源科技有限公司
Priority date: 2021-05-31
Filing date: 2021-05-31
Publication date: 2022-12-08
Also published as: CN114450834A

Abstract

Provided in the present application are an electrochemical device and an electronic device. The electrochemical device comprises a positive electrode, a negative electrode, a separator and an electrolyte solution, wherein the electrolyte solution comprises phosphorus oxytrifluoride and a polycyano compound, which comprises at least two cyano groups. The electrolyte solution can form a dense and stable protective film on the surface of the positive electrode, so as to inhibit the decomposition reaction of the electrolyte solution under a high voltage. The electrochemical device comprising the electrolyte solution has good high-temperature safety performance and cycling performance.

Description

A kind of electrochemical device and electronic device

technical field

The present application relates to the field of electrochemistry, in particular to an electrochemical device and an electronic device.

Background technique

Lithium-ion batteries have the advantages of high energy storage density, high open circuit voltage, low self-discharge rate, long cycle life, and good safety. They have been widely used as power sources in cameras, mobile phones, drones, laptops, and smart watches product. At present, increasing the charging cut-off voltage of lithium-ion batteries to increase the amount of delithiation of positive electrode materials is an effective means to increase the energy density of lithium-ion batteries.

However, the increase of the charge cut-off voltage of lithium-ion batteries is likely to cause the lithium-ion battery to be flat, the cycle capacity rapidly decays at high temperature, and thermal runaway at high temperature causes safety problems. This is because under high voltage, the positive electrode surface of lithium-ion batteries has a strong electrochemical oxidation activity. Once the electrochemical window of the electrolyte is exceeded, the electrolyte will be oxidized and decomposed, resulting in capacity decay, gas production, heat release, etc. Phenomenon. In view of this, developing a suitable lithium ion battery has become a technical problem to be solved urgently by those skilled in the art.

Contents of the invention

The purpose of the present application is to provide an electrochemical device and an electronic device to improve the high-temperature safety performance and cycle performance of the electrochemical device.

In a first aspect, the application provides an electrochemical device comprising a positive electrode, a negative electrode, a separator, and an electrolyte, the positive electrode comprising a positive electrode current collector and a positive electrode active material disposed on at least one surface of the positive electrode current collector layer, the positive electrode active material layer contains a positive electrode active material; the electrolyte contains phosphorus oxyfluoride and a polycyano compound, and the polycyano compound contains at least two cyano groups.

According to some embodiments of the present application, based on the total mass of the electrolyte, the mass percentage A of the phosphorus oxyfluoride is 0.001% to 5%.

According to some embodiments of the present application, based on the total mass of the electrolyte, the mass percentage A of the phosphorus oxyfluoride is 0.001% to 3%.

According to some embodiments of the present application, based on the total mass of the electrolyte, the mass percentage B of the polycyano compound is 0.1% to 10%.

According to some embodiments of the present application, based on the total mass of the electrolyte, the mass percentage B of the polycyano compound is 2% to 8%.

According to some embodiments of the present application, based on the total mass of the electrolyte, the mass percentage of the phosphorus oxyfluoride is A, and the mass percentage of the polycyano compound is B, satisfying: 0.15%≤ A+B≤11%.

According to some embodiments of the present application, the polycyano compound includes at least one of the compounds shown in structural formula (I):

Wherein, R is selected from C ₁ to C ₁₅ alkane group, C ₁ to C ₁₅ alkene group or C ₁ to C ₁₅ alkyne group; a and c are each independently 0 or a positive integer, and a and c is different from 0 at the same time, 2≤a+c≤7, 0≤b≤6, and the number b of the alkylene groups connected to each cyano group can be the same or different.

According to some embodiments of the present application, the polycyano compound includes any one of the following formula (1) to formula (62):

According to some embodiments of the present application, the electrolyte solution further includes at least one of a fluoroester compound, a cyclic sulfonate, or a cyclic carbonate containing an unsaturated bond.

According to some embodiments of the present application, based on the total mass of the electrolyte, the mass percentage C of the fluoroester compound is 0.1% to 15%.

According to some embodiments of the present application, based on the total mass of the electrolyte, the mass percentage D of the cyclic sulfonic acid ester is 0.1% to 5%.

According to some embodiments of the present application, based on the total mass of the electrolyte, the mass percentage E of the unsaturated bond-containing cyclic carbonate is 0.01% to 2%.

According to some embodiments of the present application, the mass percentage A of the phosphorus oxyfluoride and the mass percentage D of the cyclic sulfonic acid ester satisfy: 0.1%≤A+D≤20%.

According to some embodiments of the present application, the fluoroester compound comprises fluoroethylene carbonate, difluoroethylene carbonate, ethylmethyl fluorocarbonate, dimethyl fluorocarbonate, diethyl fluorocarbonate, fluorine Ethyl fluoropropionate, propyl fluoropropionate, methyl fluoropropionate, ethyl fluoroacetate, methyl fluoroacetate, propyl fluoroacetate, fluoroethylene carbonate, difluoroethylene carbonate , at least one of trifluoromethylethylene carbonate.

According to some embodiments of the present application, the cyclic sulfonic acid ester comprises at least one of 1,3-propane sultone or 1,4-butane sultone.

According to some embodiments of the present application, the cyclic carbonate containing an unsaturated bond includes at least one of vinylene carbonate or vinyl vinyl carbonate.

According to some embodiments of the present application, the electrolytic solution includes a fluoroester compound and a cyclic sulfonate.

According to some embodiments of the present application, the electrolytic solution includes a fluoroester compound, a cyclic sulfonate, or a cyclic carbonate containing an unsaturated bond.

According to some embodiments of the present application, the difference between the mass percent content F of the metal elements in the positive electrode active material except lithium in the positive electrode active material and the mass percent content A of the phosphorus oxyfluoride in the electrolyte is Time to meet: 600>F/A>10.

According to some embodiments of the present application, the metal elements other than lithium include Fe, Co, Ni, Mn, Ti, Mg, Al, Zr, La, Y, V, Cr, Ge, Ru, Sn, Ti, Nb , Mo at least one.

In a second aspect, the present application provides an electronic device, including the electrochemical device according to the first aspect of the present application.

Detailed ways

In order to make the purpose, technical solution, and advantages of the present application clearer, the following examples are given to further describe the present application in detail. Apparently, the described embodiments are only some of the embodiments of this application, not all of them. All other technical solutions obtained by persons of ordinary skill in the art based on the embodiments in this application belong to the protection scope of this application.

It should be noted that, in the content of the present application, the lithium-ion battery is used as an example of the electrochemical device to explain the present application, but the electrochemical device of the present application is not limited to the lithium-ion battery. The specific technical scheme is as follows:

The first aspect of the present application provides an electrochemical device, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, the positive electrode includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, the positive electrode The active material layer contains positive active material; the electrolyte contains phosphorus oxyfluoride and a polycyano compound, and the polycyano compound contains at least two cyano groups.

In one embodiment of the present application, the electrolyte contains phosphorus oxyfluoride (POF ₃ ) and polycyano compounds, wherein, phosphorus oxyfluoride can form a dense protective film in passivation reaction at the positive electrode, and the polycyano compounds It can form a stable adsorption coordination on the surface of the positive electrode, and the synergistic effect of phosphorus oxyfluoride and polycyano compounds can form a dense and stable protective film, which can inhibit the oxidation and decomposition reaction of the electrolyte under high voltage, so as to avoid capacity decay and gas production , heat release and other phenomena, so as to effectively prevent lithium-ion battery flatulence, rapid loss of cycle capacity at high temperature, and safety problems caused by thermal runaway at high temperature, and have a significant effect on the improvement of high-temperature safety performance and cycle performance of lithium-ion batteries.

In one embodiment of the present application, phosphorus oxyfluoride (POF ₃ ) can be produced by decomposing an additive in the electrolyte, such as lithium hexafluorophosphate.

The present application has no special limitation on the number of cyano groups in the polycyano compound, as long as it contains at least two cyano groups, the purpose of the present application can be achieved. For example, 2, 3, 4, 5, 6 or 7 cyano groups may be included in the polycyano compound. Different polycyano compound molecules have different spatial structures and have different improvement effects on lithium-ion batteries.

The electrochemical device provided by the present application includes a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector. The positive electrode active material layer contains a positive electrode active material. Wherein, the electrolytic solution contains phosphorus oxyfluoride and polycyano compounds, and the polycyano compounds contain at least two cyano groups. The electrolyte can form a dense and stable protective film on the surface of the positive electrode, inhibit the oxidative decomposition of the electrolyte under high voltage, and prevent the lithium-ion battery from capacity decay, gas production, and heat release caused by the decomposition reaction of the electrolyte under high voltage. The phenomenon is greatly reduced, thereby effectively improving the high-temperature safety performance and cycle performance of the electrochemical device.

In one embodiment of the present application, based on the total mass of the electrolyte, the mass percentage A of phosphorus oxyfluoride is 0.001% to 5%. In one embodiment of the present application, based on the total mass of the electrolyte, the mass percentage A of phosphorus oxyfluoride is 0.01% to 3%. In one embodiment of the present application, based on the total mass of the electrolyte, the mass percentage A of phosphorus oxyfluoride is 0.01% to 0.95%. In one embodiment of the present application, based on the total mass of the electrolyte, the mass percent content B of the polycyano compound is 0.1% to 10%. In one embodiment of the present application, based on the total mass of the electrolyte, the mass percentage B of the polycyano compound is 2% to 8%. For example, the lower limit of the mass percentage A of phosphorus oxyfluoride may include the following values: 0.001%, 0.2%, 0.5% or 1%; the upper limit of the mass percentage A of phosphorus oxyfluoride may include Among the following values: 3% or 5%. The lower limit value of the mass percentage content B of polycyano compound can be included in the following values: 0.1%, 0.5%, 1%, 2% or 3%; The upper limit value of the mass percentage content B of polycyano compound can be Included in the following values: 5%, 7%, 8% or 10%. Without being limited to any theory, by controlling the mass percentage A of phosphorus oxyfluoride within the above range, phosphorus oxyfluoride can fully exert its effect when the positive electrode is lithiated to compensate for protection defects. By controlling the mass percent content B of the polycyano compound within the above range, the polycyano compound forms stable adsorption coordination on the surface of the positive electrode. Controlling the mass percentage content A of phosphorus oxyfluoride and the mass percentage content B of the polycyano compound within the above-mentioned preferred ranges can obtain correspondingly better effects.

In one embodiment of the present application, the mass percentage content A of phosphorus oxyfluoride and the mass percentage content B of the polycyano compound satisfy: 0.15%≤A+B≤11%. In one embodiment of the present application, the mass percentage content A of phosphorus oxyfluoride and the mass percentage content B of the polycyano compound satisfy 2.5%≤A+B≤10%. For example, the lower limit of the sum of A and B may be included in the following values: 0.15%, 1.5%, 2%, 2.2%, 2.5%, 3%, 4% or 5%; the upper limit of the sum of A and B It can be included in the following values: 6%, 7%, 8%, 9% or 10%. Without being limited to any theory, by controlling the sum of A and B within the above range, the synergistic adsorption reaction of phosphorus oxyfluoride and polycyano compounds has high film formation efficiency, and can quickly form a dense, stable and low-impedance interface protection film.

In one embodiment of the present application, the polycyano compound comprises at least one of the compounds shown in structural formula (I):

Preferably, the compound represented by structural formula (I) includes any one of the following formula (1) to formula (62):

In one embodiment of the present application, the electrolytic solution includes at least one of formula (1) to formula (9), and at least one of formula (10) to formula (62). Polycyano compounds with different structures work together to further improve the high-temperature safety performance and cycle performance of lithium-ion batteries without affecting other performances.

In one embodiment of the present application, based on the total mass of the electrolyte, the total content of at least one polycyano compound in formula (1) to formula (9) is B1%, formula (10) to formula (62 The total content of at least one polycyano compound in ) is B2%, satisfying B1>B2. When the content satisfies the above range, the electrolyte solution has a relatively suitable viscosity value, and the comprehensive performance of the lithium-ion battery is better.

In one embodiment of the present application, the electrolytic solution includes at least one of formula (1) to formula (9), and at least one of formula (14) to formula (23).

In one embodiment of the present application, the electrolyte comprises at least one of formula (1) to formula (9), at least one of formula (14) to formula (23), and comprises formula (38) to at least one of formula (48). The polycyano compound with ether bond and the polycyano compound compound without ether bond work together to make the performance of the lithium ion battery reach a better state.

In one embodiment of the present application, the electrolytic solution further includes at least one of a fluoroester compound, a cyclic sulfonate, or a cyclic carbonate containing an unsaturated bond. When at least one of the above-mentioned fluoroester compound, cyclic sulfonic acid ester or unsaturated bond-containing cyclic carbonate is included in the electrolytic solution, the electrolytic solution can form a stable protective layer at both the positive and negative electrodes, which will be more Effectively improve the high-temperature safety performance and cycle performance of lithium-ion batteries.

In one embodiment of the present application, based on the total mass of the electrolyte, the mass percentage C of the fluoroester compound is 0.1% to 15%, and/or the mass percentage D of the cyclic sulfonic acid ester is 0.1 % to 5%, and/or the mass percentage content E of the unsaturated bond-containing cyclic carbonate is 0.01% to 2%. For example, the lower limit of the mass percentage C of the fluoroester compound may include the following values: 0.1%, 5% or 7.6%; the upper limit of the mass percentage C of the fluoroester compound may include the following values : 8%, 10% or 15%. The lower limit value of the mass percentage content D of cyclic sulfonic acid ester can be included in the following numerical value: 0.1%, 1% or 2.5%; The upper limit value of the mass percentage content D of cyclic sulfonic acid ester can be included in the following numerical value : 3% or 5%. The lower limit of the mass percentage content E of the cyclic carbonate containing unsaturated bonds can be included in the following values: 0.01%, 0.1% or 0.5%; the mass percentage content E of the cyclic carbonate containing unsaturated bonds The upper limit may be included in the following values: 1.4% or 2%. Not limited to any theory, by controlling the mass percentage C of the fluoroester compound, the mass percentage D of the cyclic sulfonic acid ester and the mass percentage E of the cyclic carbonate containing unsaturated bonds within the above range , can further improve the stability of the electrolyte under high voltage, and more effectively avoid the decomposition reaction of the electrolyte under high voltage, thereby further significantly improving the high-temperature safety performance and cycle performance of the lithium-ion battery.

In one embodiment of the present application, the mass percentage content A of phosphorus oxyfluoride and the mass percentage content D of the cyclic sulfonic acid ester satisfy: 0.1%≤A+D≤20%. For example, the lower limit of the sum of A and D may include the following values: 0.1%, 1%, 3.001%, 3.05%, 3.2%, 3.5%, 4%, 6% or 8%; the sum of A and D The upper limit may be included in the following values: 10%, 15% or 20%. Without being limited to any theory, by controlling the sum of A and D within the above range, the synergistic effect of the cyclic sulfonate and phosphorus oxyfluoride can improve the composition of the positive electrode protective film, and can more effectively enhance the formation of phosphorus oxyfluoride on the positive electrode. Reactive passivation compensates for protection deficiencies.

In one embodiment of the present application, there is no particular limitation on the type of the fluoroester compound, as long as the purpose of the present application can be achieved. For example, the fluoroester compound may include fluoroethylene carbonate (FEC), difluoroethylene carbonate, ethyl methyl fluorocarbonate, dimethyl fluorocarbonate, diethyl fluorocarbonate, ethyl fluoropropionate ester, propyl fluoropropionate, methyl fluoropropionate, ethyl fluoroacetate, methyl fluoroacetate, propyl fluoroacetate, fluoroethylene carbonate, difluoroethylene carbonate, trifluoromethyl at least one of ethylene carbonate.

In another embodiment of the present application, there is no particular limitation on the type of cyclic sulfonate, as long as the purpose of the present application can be achieved. For example, the cyclic sulfonate may contain at least one of 1,3-propane sultone (PS) or 1,4-butane sultone.

In yet another embodiment of the present application, there is no particular limitation on the type of unsaturated bond-containing cyclic carbonate, as long as the purpose of the present application can be achieved. For example, the unsaturated bond-containing cyclic carbonate may contain at least one of vinylene carbonate (VC) or vinyl vinyl carbonate.

In one embodiment of the present application, the electrolytic solution includes a fluoroester compound and a cyclic sulfonic acid ester.

In one embodiment of the present application, 0.2≦C+D≦15. For example, the sum of C and D may be 0.3, 0.5, 1.5, 2, 4, 5, 7, 9, 11, 12 or 15, or a range composed of any two values therein.

In one embodiment of the present application, the electrolytic solution includes a fluoroester compound, a cyclic sulfonic acid ester, and a cyclic carbonate containing an unsaturated bond. When the electrolyte contains the above substances at the same time, the negative electrode can be better protected and the performance of the lithium-ion battery can be improved.

In one embodiment of the present application, the mass percentage content F of the metal elements in the positive electrode active material except lithium in the positive electrode active material and the mass percentage content A of phosphorus oxyfluoride in the electrolyte satisfy : 600>F/A>10. For example, the lower limit of F/A may include the following values: 12, 20, 60, 120 or 300; the upper limit of F/A may include the following values: 400, 500 or 600. In the present application, there is no particular limitation on the types of metal elements other than lithium, as long as the purpose of the present application can be achieved. For example, at least one of Fe, Co, Ni, Mn, Ti, Mg, Al, Zr, La, Y, V, Cr, Ge, Ru, Sn, Ti, Nb, and Mo may be included. Not limited to any theory, by limiting the relationship between the mass percentage F of the transition metal element in the positive active material in the positive active material and the mass percentage A of phosphorus oxyfluoride in the electrolyte, it can be more optimal Play the passivation protection effect of phosphorus oxyfluoride on the positive electrode surface.

The electrolytic solution of the present application also includes a lithium salt and a non-aqueous solvent. The present application has no particular limitation on the lithium salt, as long as the purpose of the present application can be achieved. For example, lithium salts may include lithium hexafluorophosphate (LiPF ₆ ), LiBF ₄ , LiB(C ₆ H ₅ ) ₄ , LiCH ₃ SO ₃ , LiCF ₃ SO ₃ , LiN(SO ₂ CF ₃ ) ₂ , LiC(SO ₂ CF ₃ ) _3. At least one of LiSiF ₆ , LiBOB or lithium difluoroborate. Preferably, the lithium salt may contain LiPF ₆ because LiPF ₆ may give high ion conductivity and improve cycle performance of the lithium ion battery. The present application has no special limitation on the non-aqueous solvent, as long as the purpose of the present application can be achieved. For example, the nonaqueous solvent may contain at least one of carbonate compounds, carboxylate compounds, ether compounds, or other organic solvents. The above-mentioned carbonate compound may be at least one of a chain carbonate compound or a cyclic carbonate compound. Examples of the above-mentioned chain carbonate compound are dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC) or carbonic acid At least one of methyl ethyl ester (MEC). An example of the cyclic carbonate compound is at least one of ethylene carbonate (EC), propylene carbonate (PC), or butylene carbonate (BC). An example of the above-mentioned carboxylic acid ester compound is at least one of ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, and propyl propionate. Examples of the aforementioned ether compounds are dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethyl At least one of oxyethane, 2-methyltetrahydrofuran or tetrahydrofuran. Examples of the aforementioned other organic solvents are dimethylsulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, At least one of formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate or phosphoric acid ester.

The positive electrode of the present application includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector. The present application has no special limitation on the positive electrode current collector, as long as the purpose of the present application can be achieved. For example, the positive electrode current collector may include aluminum foil, aluminum alloy foil, or a composite current collector. The positive electrode active material layer of the present application contains a positive electrode active material. The present application has no particular limitation on the type of positive electrode active material, as long as the purpose of the present application can be achieved. For example, the positive electrode active material may include lithium nickel cobalt manganese oxide (811, 622, 523, 111), lithium nickel cobalt aluminate, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide, lithium manganese oxide, lithium iron manganese phosphate Or at least one of lithium titanate and the like. In the present application, the positive electrode active material may also contain non-metallic elements, such as fluorine, phosphorus, boron, chlorine, silicon, sulfur and other elements, which can further improve the stability of the positive electrode active material. In the present application, there is no particular limitation on the thickness of the positive electrode current collector and the positive electrode active material layer, as long as the purpose of the present application can be achieved. For example, the thickness of the positive electrode collector is 5 μm to 20 μm, or 6 μm to 18 μm. The thickness of the positive electrode active material layer on one side is 30 μm to 120 μm. In the present application, the positive electrode active material layer can be arranged on one surface (first surface) in the thickness direction of the positive electrode current collector, or can be arranged on two surfaces (the first surface and the second surface) in the thickness direction of the positive electrode current collector. )superior. It should be noted that the "surface" here may refer to the entire area of the positive electrode collector or a partial area of the positive electrode collector. This application is not particularly limited, as long as the purpose of this application can be achieved. Optionally, the positive electrode sheet may further include a conductive layer, and the conductive layer is located between the positive electrode current collector and the positive electrode active material layer. The composition of the conductive layer is not particularly limited, and may be a commonly used conductive layer in the field. The conductive layer includes a conductive agent and a binder.

The negative electrode of the present application is not particularly limited, as long as the purpose of the present application can be achieved. For example, the negative electrode includes a negative electrode current collector and a negative electrode active material layer. The present application has no particular limitation on the negative electrode collector, as long as the purpose of the present application can be achieved. For example, the negative electrode current collector may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or a composite current collector. The anode active material layer of the present application contains an anode active material. The present application has no particular limitation on the type of the negative electrode active material, as long as the purpose of the present application can be achieved. For example, the negative electrode active material can include natural graphite, artificial graphite, mesophase microcarbon spheres (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, _SiOx (0<x<2), Li-Sn alloy , Li-Sn-O alloy, Sn, SnO, SnO ₂ , lithium titanate Li ₄ Ti ₅ O ₁₂ with a spinel structure, Li-Al alloy, and metallic lithium. In the present application, there is no particular limitation on the thickness of the negative electrode current collector and the negative electrode active material layer, as long as the purpose of the present application can be achieved. For example, the thickness of the negative electrode current collector is 6 μm to 10 μm, and the thickness of the negative electrode active material layer is 30 μm to 120 μm. In the present application, the negative electrode active material layer can be arranged on one surface (first surface) in the thickness direction of the negative electrode current collector, or can be arranged on two surfaces (the first surface and the second surface) in the thickness direction of the negative electrode current collector. )superior. It should be noted that the "surface" here may be the entire area of the negative electrode collector, or a partial area of the negative electrode collector. This application is not particularly limited, as long as the purpose of this application can be achieved. Optionally, the negative electrode sheet may further include a conductive layer, and the conductive layer is located between the negative electrode current collector and the negative electrode active material layer. The composition of the conductive layer is not particularly limited, and may be a commonly used conductive layer in the field. The conductive layer includes a conductive agent and a binder.

The conductive agent mentioned above is not particularly limited, as long as the purpose of the present application can be achieved. For example, the conductive agent can include at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon nanofibers, flake graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes or graphene A sort of. For example, the binder may include polyacryl alcohol, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyimide, polyamideimide, styrene-butadiene rubber (SBR), polyvinyl alcohol ( PVA), polyvinylidene fluoride, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl butyral (PVB), water-based acrylic resin, carboxymethyl cellulose (CMC) or carboxymethyl At least one of base cellulose sodium (CMC-Na) and the like.

The lithium ion battery of the present application also includes a separator, which is used to separate the positive electrode and the negative electrode, prevent the internal short circuit of the lithium ion battery, allow electrolyte ions to pass through freely, and complete the electrochemical charging and discharging process. The separator in the present application is not particularly limited, as long as the purpose of the present application can be achieved. For example, polyethylene (PE), polypropylene (PP)-based polyolefin (PO)-based release film, polyester film (such as polyethylene terephthalate (PET) film), cellulose film, polyamide Imine film (PI), polyamide film (PA), spandex or aramid film, woven film, non-woven film (non-woven fabric), microporous film, composite film, separator paper, rolled film, spun film, etc. at least one of the For example, a separator may include a substrate layer and a surface treatment layer. The substrate layer can be a non-woven fabric, a film or a composite film with a porous structure, and the material of the substrate layer can include at least one of polyethylene, polypropylene, polyethylene terephthalate and polyimide, etc. kind. Optionally, 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 may be used. Optionally, at least one surface of the substrate layer is provided with a surface treatment layer, and the surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic material. For example, the inorganic layer includes inorganic particles and a binder, and the inorganic particles are not particularly limited, for example, they can be selected from aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium oxide, tin oxide, cerium oxide, nickel oxide , zinc oxide, calcium oxide, zirconia, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide and barium sulfate. The binder is not particularly limited, for example, it can be selected from polyvinylidene fluoride, a copolymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinyl pyrene One or a combination of rolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene and polyhexafluoropropylene. The polymer layer comprises a polymer, and the polymer material includes polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride or poly( at least one of vinylidene fluoride-hexafluoropropylene) and the like.

The electrochemical device of the present application is not particularly limited, and it may include any device that undergoes an electrochemical reaction. In some embodiments, the electrochemical device may include, but is not limited to, a lithium metal secondary battery, a lithium ion secondary battery (lithium ion battery), a lithium polymer secondary battery, or a lithium ion polymer secondary battery, and the like.

The preparation process of an electrochemical device is well known to those skilled in the art, and there is no particular limitation in this application, as long as the purpose of this application can be achieved. For example, an electrochemical device can be manufactured through the following process: a separator is placed between the positive pole piece and the negative pole piece, and it is wound or stacked as required and put into the case, and the electrolyte is injected into the case and sealed, wherein The isolation film used is the above-mentioned isolation film provided by the present application. In addition, anti-overcurrent elements, guide plates, etc. can also be placed in the casing as needed, so as to prevent pressure rise and overcharge and discharge inside the electrochemical device.

The second aspect of the present application provides an electronic device comprising the electrochemical device described in the embodiments of the present application, the electronic device has good high-temperature safety performance and cycle performance.

The electronic device of the present application is not particularly limited, and it may be used in any electronic device known in the prior art. In some embodiments, electronic devices may include, but are not limited to, notebook computers, pen-based computers, mobile computers, e-book players, cellular phones, portable fax machines, portable copiers, portable printers, headsets, VCRs, LCD TVs, portable cleaners, portable CD players, mini discs, transceivers, electronic organizers, calculators, memory cards, portable tape recorders, radios, backup power supplies, motors, cars, motorcycles, power-assisted bicycles, bicycles, Lighting appliances, toys, game consoles, clocks, electric tools, flashlights, cameras, large household storage batteries and lithium-ion capacitors, etc.

The application provides an electrochemical device and an electronic device, the electrochemical device comprises a positive electrode, a negative electrode, a separator and an electrolyte, the electrolyte contains phosphorus oxyfluoride and a polycyano compound, the polycyano compound contains at least two a cyano group. The electrolyte can form a dense and stable protective film on the surface of the positive electrode, and inhibit the decomposition reaction of the electrolyte under high voltage. The electrochemical device containing the electrolyte has good high-temperature safety performance and cycle performance.

Example

Hereinafter, the embodiment of the present application will be described more specifically with reference to examples and comparative examples. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, "part" and "%" are based on mass.

Test method and equipment:

Cycle performance test:

At 25°C, let the lithium-ion battery stand for 30 minutes, then charge it to 4.45V at a rate of 1C, then charge it at a constant voltage of 4.45V to 0.05C, and let it stand for 5 minutes, then discharge it at a rate of 0.5C to 3.0V , which is a discharge cycle process. The discharge capacity this time is the first discharge capacity of the lithium-ion battery, and then 500 charge-discharge cycles are performed.

The capacity retention rate (%) of the lithium-ion battery after N charge-discharge cycles = the discharge capacity of the Nth cycle/the first discharge capacity × 100%.

High temperature safety performance test:

At 25°C, let the lithium-ion battery stand for 30 minutes, then charge it to 4.45V with a constant current of 1C rate, and then charge it to 0.05C with a constant voltage of 4.45V; place the fully charged lithium-ion battery in an oven at 5°C Heating at a heating rate of /min, monitoring the temperature on the surface of the lithium-ion battery, and recording the temperature of the oven when the lithium-ion battery is thermally runaway and burned.

In a dry argon atmosphere, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC) and ethyl propionate (EP) were mixed according to the mass ratio EC:PC:DEC:EP=20: 10:40:30 mixing to obtain a non-aqueous organic solvent. Add LiPF ₆ , and optionally POF ₃ , polycyano compound, fluoroester compound, cyclic sulfonate and unsaturated bond-containing cyclic carbonate to a non-aqueous organic solvent to obtain a LiPF ₆ concentration of 1.1 mol/L, the contents of POF ₃ , polycyano compounds, fluoroester compounds, cyclic sulfonic acid esters and cyclic carbonates containing unsaturated bonds are shown in Table 1.

Weigh 2kg of solvent N-methyl-2-pyrrolidone (NMP), 1.5kg of binder polyvinylidene fluoride solvent (PVDF, the mass percentage of polyvinylidene fluoride is 10%), 0.15kg of conductive agent Carbon black (Super P) and 9.7kg of positive electrode active material lithium cobaltate (LiCoO ₂ ) were thoroughly mixed and stirred to obtain positive electrode slurry. Wherein, the mass percentage F of the cobalt element in the positive electrode active material in LiCoO ₂ is 60%. The positive electrode slurry was evenly coated on the first surface of the positive electrode current collector aluminum foil with a thickness of 12 μm, and baked at 120° C. for 1 hour to obtain a positive electrode coated with the positive electrode slurry on one side. Then, repeat the above steps on the second surface of the positive electrode to obtain a positive electrode with positive electrode slurry coated on both sides. After the coating is completed, it is compacted and cut to obtain a positive electrode with a size of 74mm×867mm for use.

Thickener sodium carboxymethyl cellulose (CMC, the mass percentage composition of carboxymethyl cellulose sodium is 1.5%), 0.2kg binder styrene-butadiene rubber emulsion (mass percentage of styrene-butadiene rubber) of 2.0kg content of 50%) and 4.8 kg of negative electrode active material graphite powder (average particle diameter Dv50 is 11.5 μm) were uniformly mixed to obtain negative electrode slurry. The negative electrode slurry was evenly coated on the first surface of the negative electrode current collector copper foil with a thickness of 8 μm, and baked at 120° C. for 1 hour to obtain a negative electrode coated with the negative electrode slurry on one side. Then, repeat the above steps on the second surface of the negative electrode to obtain a negative electrode with negative electrode slurry coated on both sides. After the coating is completed, it is compacted and cut to obtain a negative electrode with a size of 76mm×851mm for use.

Aluminum oxide and polyvinylidene fluoride were mixed according to a mass ratio of 90:10 and dissolved in deionized water to form a ceramic slurry with a solid content of 50%. Subsequently, the ceramic slurry was uniformly coated on one side of the porous substrate (polypropylene, thickness 7 μm, average pore diameter 0.073 μm, porosity 26%) by dimple coating method, and dried to obtain a ceramic coating The thickness of the ceramic coating is 50 μm with the double-layer structure of the porous substrate.

Polyvinylidene fluoride (PVDF) and polyacrylate were mixed in a mass ratio of 96:4 and dissolved in deionized water to form a polymer slurry with a solid content of 50%. Subsequently, the polymer slurry is uniformly coated on the two surfaces of the above-mentioned ceramic coating layer and the porous substrate double-layer structure by a dimple coating method, and is dried to obtain a separator, wherein the single layer formed by the polymer slurry The coating thickness is 2 μm.

The positive electrode, separator, and negative electrode prepared above are stacked in order, so that the separator is in the middle of the positive and negative electrodes to play the role of isolation, and the electrode assembly is obtained by winding. Put the electrode assembly into an aluminum foil packaging bag, bake it at 80°C to remove water, inject the electrolyte solution prepared above, and go through processes such as vacuum packaging, standing, chemical formation, and shaping to obtain a lithium-ion battery.

Example 1 to Example 57, Comparative Example 1 to Comparative Example 6, <Preparation of Electrolyte>, <Preparation of Positive Electrode>, <Preparation of Negative Electrode>, <Preparation of Separator> and <Preparation of Lithium-ion Battery> The preparation steps are all the same as the above-mentioned preparation steps, and the changes of relevant preparation parameters are as shown in Table 1:

Table 1

Note: "/" in Table 1 indicates that the corresponding preparation parameter does not exist.

From Examples 1 to 9 and Comparative Example 1 and Comparative Example 5, it can be seen that the high-temperature safety performance and cycle performance of lithium-ion batteries change with the change of the mass percentage A of phosphorus oxyfluoride in the electrolyte. The lithium-ion battery whose mass percentage content A of phosphorus oxyfluoride in the electrolyte is within the content range of the application is selected, and its high-temperature safety performance and cycle performance are obviously better.

From Example 7, Example 19 to Example 23 and Comparative Example 2, it can be seen that the high-temperature safety performance and cycle performance of lithium-ion batteries change with the change of the mass percentage B of the polycyano compound in the electrolyte. A lithium-ion battery whose mass percentage B of the polycyano compound in the electrolyte is selected within the scope of the application has significantly better high-temperature safety performance and cycle performance.

The types and mass percentages of fluoroester compounds, cyclic sulfonate compounds, and unsaturated bond-containing cyclic carbonates in the electrolyte usually also affect the high-temperature safety performance and cycle performance of lithium-ion batteries. As can be seen from Example 39 to Example 51, as long as the types and contents of the fluorinated ester compound, cyclic sulfonic acid ester compound and unsaturated bond-containing cyclic carbonate in the electrolyte are within the scope of the application, the A lithium-ion battery with good high-temperature safety performance and cycle performance can be obtained.

The sum of the mass percentage A of phosphorus oxyfluoride and the mass percentage B of polycyano compounds A+B, the mass percentage A of phosphorus oxyfluoride and the mass percentage D of cyclic sulfonic acid esters And A+D usually also affect the high-temperature safety performance and cycle performance of lithium-ion batteries. It can be seen from Table 1 that A+B or A+D is within the scope of this application, and a lithium-ion battery with good high-temperature safety performance and cycle performance can be obtained.

The ratio F/A of the mass percent content F of transition metal elements in the positive electrode active material in the positive electrode active material to the mass percent content A of phosphorus oxyfluoride in the electrolyte will also generally affect the high temperature safety performance of lithium-ion batteries. and cycle performance. It can be seen from Example 7, Example 53 to Example 57 that the obtained F/A is within the scope of the present application, and a lithium-ion battery with good high-temperature safety performance and cycle performance can be obtained.

Based on the above analysis, it can be seen that the electrochemical device provided by the present application includes a positive electrode, a negative electrode, a separator, and an electrolyte, the electrolyte includes phosphorus oxyfluoride and a polycyano compound, and the polycyano compound contains at least two cyano groups. The electrolyte can form a dense and stable protective film on the surface of the positive electrode, and inhibit the decomposition reaction of the electrolyte under high voltage. The electrochemical device containing the electrolyte has good high-temperature safety performance and cycle performance.

The above descriptions are only preferred embodiments of the application, and are not intended to limit the application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the application shall be included in the protection of the application. within the range.

Claims

An electrochemical device comprising a positive electrode, a negative electrode, a separator and an electrolyte, the positive electrode comprising a positive electrode current collector and a positive electrode active material layer arranged on at least one surface of the positive electrode current collector, the positive electrode active material layer comprising Positive electrode active material; the electrolyte contains phosphorus oxyfluoride and a polycyano compound, and the polycyano compound contains at least two cyano groups.
The electrochemical device according to claim 1, wherein, based on the total mass of the electrolyte, the mass percentage A of the phosphorus oxyfluoride is 0.001% to 5%, and the mass percentage of the polycyano compound is The component content B is 0.1% to 10%.
The electrochemical device according to claim 1, wherein, based on the total mass of the electrolyte, the mass percentage of the phosphorus oxyfluoride is A, and the mass percentage of the polycyano compound is B, Satisfy: 0.15%≤A+B≤11%.
The electrochemical device according to claim 1, wherein the polycyano compound comprises at least one of the compounds shown in structural formula (I):

Wherein, R is selected from C 1 to C 15 alkane group, C 1 to C 15 alkene group or C 1 to C 15 alkyne group; a and c are each independently 0 or a positive integer, and a and c is different from 0 at the same time, 2≤a+c≤7, 0≤b≤6, and the number b of the alkylene groups connected to each cyano group can be the same or different.
The electrochemical device according to claim 1, wherein the polycyano compound comprises any one of the following formulas (1) to (62):
The electrochemical device according to claim 1, wherein the electrolytic solution further comprises at least one of a fluoroester compound, a cyclic sulfonate, or a cyclic carbonate containing an unsaturated bond.
The electrochemical device according to claim 6, wherein, based on the total mass of the electrolyte, the mass percentage C of the fluoroester compound is 0.1% to 15%, and/or the cyclic sulfonic acid The mass percentage content D of the ester is 0.1% to 5%, and/or the mass percentage content E of the unsaturated bond-containing cyclic carbonate is 0.01% to 2%.
The electrochemical device according to claim 7, wherein, the mass percentage A of the phosphorus oxyfluoride and the mass percentage D of the cyclic sulfonic acid ester satisfy: 0.1%≤A+D≤ 20%.
The electrochemical device according to claim 6, wherein the fluoroester compound comprises fluoroethylene carbonate, difluoroethylene carbonate, ethyl methyl fluorocarbonate, dimethyl fluorocarbonate, fluorocarbonic acid Diethyl ester, ethyl fluoropropionate, propyl fluoropropionate, methyl fluoropropionate, ethyl fluoroacetate, methyl fluoroacetate, propyl fluoroacetate, fluoroethylene carbonate, di At least one of fluoroethylene carbonate and trifluoromethylethylene carbonate;

The cyclic sulfonate contains at least one of 1,3-propane sultone or 1,4-butane sultone;

The unsaturated bond-containing cyclic carbonate includes at least one of vinylene carbonate or vinyl vinyl carbonate.
The electrochemical device according to any one of claims 1 to 9, wherein the mass percent content F of metal elements other than lithium in the positive electrode active material is the same as that of the phosphorus oxyfluoride in the positive electrode active material The mass percentage content A in the electrolyte solution satisfies: 600>F/A>10.
An electronic device comprising the electrochemical device according to any one of claims 1 to 10.