Electrochemical device and electronic device

Abstract

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

Description

Technical Field

[0001] The present application relates to the field of electrochemistry, and in particular to an electrochemical device and an electronic device. Background Art

[0002] 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 are now widely used as power sources in electronic products such as cameras, mobile phones, drones, laptops and smart watches. At present, increasing the charging cut-off voltage of lithium-ion batteries to increase the amount of lithium removed from the positive electrode material is an effective means to increase the energy density of lithium-ion batteries.

[0003] However, the increase in the charging cut-off voltage of lithium-ion batteries can easily cause safety problems such as flatulence of lithium-ion batteries, rapid decay of cycle capacity at high temperatures, and thermal runaway at high temperatures. This is because the positive electrode surface of lithium-ion batteries has strong electrochemical oxidation activity at high voltages. Once the electrochemical window of the electrolyte is exceeded, the electrolyte will undergo oxidation and decomposition, resulting in capacity decay, gas production, heat release, etc. In view of this, the development of a suitable lithium-ion battery has become a technical problem that needs to be solved urgently by those skilled in the art. Summary of the invention

[0004] 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.

[0005] In a first aspect, the present application provides an electrochemical device comprising a positive electrode, a negative electrode, a separator and an electrolyte, wherein the positive electrode comprises a positive electrode collector and a positive electrode active material layer disposed on at least one surface of the positive electrode collector, wherein the positive electrode active material layer comprises a positive electrode active material; the electrolyte comprises phosphorus oxyfluoride and a polycyano compound, wherein the polycyano compound comprises at least two cyano groups.

[0006] 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%.

[0007] 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%.

[0008] 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%.

[0009] 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%.

[0010] 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%.

[0011] According to some embodiments of the present application, the polycyano compound includes at least one of the compounds represented by structural formula (I):

[0012]

[0013] Wherein, R is selected from C1 to C 15 Alkane, C1 to C 15 Alkenyl or C1 to C 15 a and c are each independently 0 or a positive integer, and a and c are not 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 may be the same or different.

[0014] According to some embodiments of the present application, the polycyano compound includes any one of the following formulas (1) to (62):

[0015]

[0016]

[0017]

[0018] According to some embodiments of the present application, the electrolyte further includes at least one of a fluorinated ester compound, a cyclic sulfonate, or a cyclic carbonate containing an unsaturated bond.

[0019] According to some embodiments of the present application, based on the total mass of the electrolyte, the mass percentage C of the fluorinated ester compound is 0.1% to 15%.

[0020] According to some embodiments of the present application, based on the total mass of the electrolyte, the mass percentage D of the cyclic sulfonate is 0.1% to 5%.

[0021] According to some embodiments of the present application, based on the total mass of the electrolyte, the mass percentage E of the cyclic carbonate containing an unsaturated bond is 0.01% to 2%.

[0022] According to some embodiments of the present application, the mass percentage A of the phosphorus oxyfluoride and the mass percentage D of the cyclic sulfonate satisfy: 0.1%≤A+D≤20%.

[0023] According to some embodiments of the present application, the fluorinated ester compound comprises at least one of fluoroethylene carbonate, difluoroethylene carbonate, ethyl methyl fluorocarbonate, dimethyl fluorocarbonate, diethyl fluorocarbonate, ethyl fluoropropionate, propyl fluoropropionate, methyl fluoropropionate, ethyl fluoroacetate, methyl fluoroacetate, propyl fluoroacetate, fluoroethylene carbonate, difluoroethylene carbonate, and trifluoromethylethylene carbonate.

[0024] According to some embodiments of the present application, the cyclic sulfonate comprises at least one of 1,3-propane sultone or 1,4-butane sultone.

[0025] According to some embodiments of the present application, the unsaturated bond-containing cyclic carbonate comprises at least one of vinylene carbonate or vinyl ethylene carbonate.

[0026] According to some embodiments of the present application, the electrolyte contains a fluorinated ester compound and a cyclic sulfonate.

[0027] According to some embodiments of the present application, the electrolyte contains a fluorinated ester compound, a cyclic sulfonate, or a cyclic carbonate containing an unsaturated bond.

[0028] According to some embodiments of the present application, the mass percentage F of the metal elements other than lithium in the positive electrode active material and the mass percentage A of the phosphorus oxyfluoride in the electrolyte satisfy: 600>F / A>10.

[0029] According to some embodiments of the present application, the metal element other than lithium includes at least one of Fe, Co, Ni, Mn, Ti, Mg, Al, Zr, La, Y, V, Cr, Ge, Ru, Sn, Ti, Nb, and Mo.

[0030] In a second aspect, the present application provides an electronic device, comprising the electrochemical device according to the first aspect of the present application. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical scheme, and advantages of the present application more clearly understood, the following embodiments are given to further describe the present application in detail. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other technical schemes obtained by ordinary technicians in the field belong to the scope of protection of the present application.

[0032] It should be noted that in the content of this application, lithium-ion batteries are used as an example of electrochemical devices to explain this application, but the electrochemical devices of this application are not limited to lithium-ion batteries. The specific technical solution is as follows:

[0033] The first aspect of the present application provides an electrochemical device comprising a positive electrode, a negative electrode, a separator and an electrolyte, wherein the positive electrode comprises a positive electrode collector and a positive electrode active material layer disposed on at least one surface of the positive electrode collector, wherein the positive electrode active material layer comprises a positive electrode active material; the electrolyte comprises phosphorus oxyfluoride and a polycyano compound, wherein the polycyano compound comprises at least two cyano groups.

[0034] In one embodiment of the present application, the electrolyte comprises phosphorus oxyfluoride (POF3) and a polycyano compound, wherein phosphorus oxyfluoride can undergo a passivation reaction at the positive electrode to form a dense protective film, and the polycyano compound can form a stable adsorption coordination on the surface of the positive electrode. The synergistic effect of phosphorus oxyfluoride and the polycyano compound can form a dense and stable protective film, which inhibits the oxidative decomposition reaction of the electrolyte at high voltage to avoid capacity decay, gas production, heat release and the like, thereby effectively preventing lithium-ion batteries from bloating, rapid decay of cycle capacity at high temperatures, and thermal runaway at high temperatures, and producing a significant effect on improving the high-temperature safety performance and cycle performance of lithium-ion batteries.

[0035] In one embodiment of the present application, phosphorus oxyfluoride (POF3) may be an additive in the electrolyte, for example, produced by decomposition of lithium hexafluorophosphate.

[0036] The present application does not particularly limit the number of cyano groups in the polycyano compound, as long as it contains at least two cyano groups and can achieve the purpose of the present application. For example, the polycyano compound may contain 2, 3, 4, 5, 6 or 7 cyano groups. Different polycyano compound molecules have different spatial structures and different improvement effects on lithium-ion batteries.

[0037] The electrochemical device provided by the present application comprises a positive electrode, a negative electrode, a separator and an electrolyte, wherein the positive electrode comprises a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode active material layer comprises a positive electrode active material. The electrolyte comprises phosphorus oxyfluoride and a polycyano compound, wherein the polycyano compound comprises 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 greatly reduce the capacity attenuation, gas production, heat release and other phenomena caused by the decomposition reaction of the electrolyte under high voltage in the lithium-ion battery, thereby effectively improving the high temperature safety performance and cycle performance of the electrochemical device.

[0038] 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 percentage 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 the following values: 3% or 5%. The lower limit of the mass percentage content B of the polycyano compound may include the following values: 0.1%, 0.5%, 1%, 2% or 3%; the upper limit of the mass percentage content B of the polycyano compound may include the following values: 5%, 7%, 8% or 10%. Without being limited to any theory, by controlling the mass percentage content A of phosphorus oxyfluoride within the above range, phosphorus oxyfluoride can fully exert its effect when the positive electrode is lithium-altered to make up for the protection defect. By controlling the mass percentage content B of the polycyano compound within the above range, the polycyano compound forms a stable adsorption coordination on the positive electrode surface. By controlling the mass percentage content A of phosphorus oxyfluoride and the mass percentage content B of the polycyano compound within the above preferred range, the corresponding better effect can be obtained.

[0039] In one embodiment of the present application, the mass percentage A of phosphorus oxyfluoride and the mass percentage B of the polycyano compound satisfy: 0.15%≤A+B≤11%. In one embodiment of the present application, the mass percentage A of phosphorus oxyfluoride and the mass percentage B of the polycyano compound satisfy 2.5%≤A+B≤10%. For example, the lower limit of the sum of A and B may include 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 may include 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 a high film-forming efficiency, and can quickly form a dense, stable and low-impedance interface protective film.

[0040] In one embodiment of the present application, the polycyano compound includes at least one of the compounds represented by structural formula (I):

[0041]

[0042] Wherein, R is selected from C1 to C 15 Alkane, C1 to C 15 Alkenyl or C1 to C 15 a and c are each independently 0 or a positive integer, and a and c are not 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 may be the same or different.

[0043] Preferably, the compound represented by structural formula (I) includes any one of the following formulas (1) to (62):

[0044]

[0045]

[0046]

[0047] In one embodiment of the present application, the electrolyte comprises at least one of formula (1) to formula (9), and comprises at least one of formula (10) to formula (62). The polycyano compounds with different structures work together to further improve the high temperature safety performance and cycle performance of the lithium ion battery without affecting other properties.

[0048] 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%, and the total content of at least one polycyano compound in formula (10) to formula (62) is B2%, satisfying B1>B2. When the content meets the above range, the electrolyte has a more suitable viscosity value, and the overall performance of the lithium ion battery is better.

[0049] In one embodiment of the present application, the electrolyte comprises at least one of Formulas (1) to (9), and comprises at least one of Formulas (14) to (23).

[0050] In one embodiment of the present application, the electrolyte comprises at least one of formulas (1) to (9), at least one of formulas (14) to (23), and at least one of formulas (38) to (48). The polycyano compound having an ether bond and the polycyano compound not containing an ether bond work together to achieve a better performance of the lithium ion battery.

[0051] In one embodiment of the present application, the electrolyte further comprises 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 sulfonate or a cyclic carbonate containing an unsaturated bond is included in the electrolyte, the electrolyte can form a stable protective layer at both the positive electrode and the negative electrode, which will more effectively improve the high temperature safety performance and cycle performance of the lithium ion battery.

[0052] 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 E of the cyclic carbonate containing an unsaturated bond 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 of the mass percentage D of the cyclic sulfonic acid ester may include the following values: 0.1%, 1% or 2.5%; the upper limit of the mass percentage D of the cyclic sulfonic acid ester may include the following values: 3% or 5%. The lower limit of the mass percentage content E of the cyclic carbonate containing unsaturated bonds may include the following values: 0.01%, 0.1% or 0.5%; the upper limit of the mass percentage content E of the cyclic carbonate containing unsaturated bonds may include the following values: 1.4% or 2%. Without being limited to any theory, by controlling the mass percentage content C of the fluoroester compound, the mass percentage content D of the cyclic sulfonic acid ester and the mass percentage content E of the cyclic carbonate containing unsaturated bonds within the above range, the stability of the electrolyte under high voltage can be further improved, and the decomposition reaction of the electrolyte under high voltage can be more effectively avoided, thereby further significantly improving the high temperature safety performance and cycle performance of the lithium-ion battery.

[0053] In one embodiment of the present application, the mass percentage A of phosphorus oxyfluoride and the mass percentage D of cyclic sulfonate 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 upper limit of the sum of A and D may include 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 cyclic sulfonate and phosphorus oxyfluoride synergistically act to improve the composition of the positive electrode protective film, and can more effectively enhance the passivation of phosphorus oxyfluoride in the positive electrode reaction to make up for the protection defects.

[0054] In one embodiment of the present application, there is no particular restriction on the type of fluoroester compound, as long as the purpose of the present application can be achieved. For example, the fluoroester compound can include at least one of fluoroethylene carbonate (FEC), difluoroethylene carbonate, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, ethyl fluoropropionate, propyl fluoropropionate, methyl fluoropropionate, ethyl fluoroacetate, methyl fluoroacetate, propyl fluoroacetate, fluoroethylene carbonate, difluoroethylene carbonate, and trifluoromethylethylene carbonate.

[0055] In another embodiment of the present application, there is no particular limitation on the type of the cyclic sulfonate, as long as the purpose of the present application can be achieved. For example, the cyclic sulfonate may include at least one of 1,3-propane sultone (PS) or 1,4-butane sultone.

[0056] In another embodiment of the present application, there is no particular limitation on the type of the cyclic carbonate containing unsaturated bonds, as long as the purpose of the present application can be achieved. For example, the cyclic carbonate containing unsaturated bonds may include at least one of vinylene carbonate (VC) or vinyl ethylene carbonate.

[0057] In one embodiment of the present application, the electrolyte contains a fluorinated ester compound and a cyclic sulfonic acid ester.

[0058] In one embodiment of the present application, 0.2≤C+D≤15. For example, the sum of C and D can be 0.3, 0.5, 1.5, 2, 4, 5, 7, 9, 11, 12 or 15, or a range consisting of any two values ​​therein.

[0059] In one embodiment of the present application, the electrolyte contains a fluorinated ester compound, a cyclic sulfonate ester and a cyclic carbonate ester containing an unsaturated bond. When the electrolyte contains the above substances at the same time, it can better protect the negative electrode and improve the performance of the lithium-ion battery.

[0060] In one embodiment of the present application, the mass percentage F of the metal elements other than lithium in the positive electrode active material and the mass percentage 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 restriction on the type 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. Without being limited to any theory, by limiting the relationship between the mass percentage F of the transition metal element in the positive electrode active material and the mass percentage A of phosphorus oxyfluoride in the electrolyte, the passivation protection effect of phosphorus oxyfluoride on the positive electrode surface can be better exerted.

[0061] The electrolyte of the present application also includes lithium salts and non-aqueous solvents. The present application has no particular restrictions on lithium salts, as long as the purpose of the present application can be achieved. For example, the lithium salt may include at least one of lithium hexafluorophosphate (LiPF6), LiBF4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, LiSiF6, LiBOB or lithium difluoroborate. Preferably, the lithium salt may include LiPF6, because LiPF6 can give high ionic conductivity and improve the cycle performance of lithium-ion batteries. The present application has no particular restrictions on non-aqueous solvents, as long as the purpose of the present application can be achieved. For example, the non-aqueous solvent may include at least one of a carbonate compound, a carboxylate compound, an ether compound 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 linear carbonate compounds are at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC) or ethyl methyl carbonate (MEC). Examples of cyclic carbonate compounds are at least one of ethylene carbonate (EC), propylene carbonate (PC) or butylene carbonate (BC). Examples of the above-mentioned carboxylic acid ester compounds are at least one of ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate and propyl propionate. Examples of the above-mentioned ether compounds are at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran or tetrahydrofuran. Examples of the other organic solvents include at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate or phosphoric acid esters.

[0062] The positive electrode of the present application includes a positive electrode current collector and a positive electrode active material layer provided on at least one surface of the positive electrode current collector. There is no particular limitation on the positive electrode current collector in the present application, 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, etc. The positive electrode active material layer of the present application contains a positive electrode active material. There is no particular limitation on the type of the positive electrode active material in the present application, as long as the purpose of the present application can be achieved. For example, the positive electrode active material may include at least one of lithium nickel cobalt manganate (811, 622, 523, 111), lithium nickel cobalt aluminate, lithium iron phosphate, lithium-rich manganese-based material, lithium cobaltate, lithium manganate, lithium manganese iron phosphate, or lithium titanate, etc. In the present application, the positive electrode active material may also contain non-metallic elements, such as elements like fluorine, phosphorus, boron, chlorine, silicon, sulfur, etc., 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 current collector is 5 μm to 20 μm, or 6 μm to 18 μm. The thickness of the single-sided positive electrode active material layer is 30 μm to 120 μm. In the present application, the positive electrode active material layer may be provided on one surface (the first surface) in the thickness direction of the positive electrode current collector, or may be provided on two surfaces (the first surface and the second surface) in the thickness direction of the positive electrode current collector. It should be noted that the "surface" here may be the entire area of the positive electrode current collector, or may be a partial area of the positive electrode current collector. There is no particular limitation in the present application, as long as the purpose of the present application can be achieved. Optionally, the positive electrode plate 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 art. The conductive layer includes a conductive agent and a binder.

[0063] There is no particular limitation on the negative electrode of the present application, 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. There is no particular limitation on the negative electrode current collector in the present application, 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, etc. The negative electrode active material layer of the present application contains a negative electrode active material. There is no particular limitation on the type of the negative electrode active material in the present application, as long as the purpose of the present application can be achieved. For example, the negative electrode active material may include natural graphite, artificial graphite, mesocarbon microbeads (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, SiO x (0 < x < 2), Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel-structured lithium titanate Li4Ti5O 12, Li-Al alloy and metallic lithium, etc. In the present application, there is no particular restriction 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 6μm to 10μm, and the thickness of the negative electrode active material layer is 30μm to 120μm. 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 on two surfaces (first surface and second surface) in the thickness direction of the negative electrode current collector. It should be noted that the "surface" here can be the entire area of ​​the negative electrode current collector or a partial area of ​​the negative electrode current collector. There is no particular restriction in the present application, as long as the purpose of the present application can be achieved. Optionally, the negative electrode sheet may also include a conductive layer, which 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 it may be a conductive layer commonly used in the art. The conductive layer includes a conductive agent and a binder.

[0064] The above-mentioned conductive agent is not particularly limited, as long as the purpose of the present application can be achieved. For example, the conductive agent may 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. For example, the binder may include at least one of polypropylene alcohol, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyimide, polyamide-imide, 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 sodium carboxymethyl cellulose (CMC-Na) etc.

[0065] The lithium-ion battery of the present application also includes a separator to separate the positive electrode and the negative electrode, prevent the internal short circuit of the lithium-ion battery, allow the electrolyte ions to pass freely, and complete the electrochemical charge and discharge 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, a polyolefin (PO) separator mainly composed of polyethylene (PE) and polypropylene (PP), a polyester film (such as polyethylene terephthalate (PET) film), a cellulose film, a polyimide film (PI), a polyamide film (PA), at least one of spandex or aramid film, a woven film, a non-woven film (non-woven fabric), a microporous film, a composite film, a diaphragm paper, a rolled film, a spinning film, etc. For example, the separator may include a substrate layer and a surface treatment layer. The substrate layer may be a non-woven fabric, a film or a composite film with a porous structure, and the material of the substrate layer may include at least one of polyethylene, polypropylene, polyethylene terephthalate and polyimide. Optionally, a polypropylene porous film, a polyethylene porous film, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric or a polypropylene-polyethylene-polypropylene porous composite film can be used. Optionally, a surface treatment layer is provided on at least one surface of the substrate layer, and the surface treatment layer can be a polymer layer or an inorganic layer, or a layer formed by a mixed polymer and an inorganic substance. 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 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 and barium sulfate. The binder is not particularly limited, for example, it can be selected from one or more combinations of polyvinylidene fluoride, a copolymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene and polyhexafluoropropylene. 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).

[0066] The electrochemical device of the present application is not particularly limited, and 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.

[0067] The preparation process of the electrochemical device is well known to those skilled in the art, and this application is not particularly limited, as long as the purpose of this application can be achieved. For example, the electrochemical device can be manufactured by the following process: inserting a separator between the positive electrode sheet and the negative electrode sheet, and winding or stacking them as needed and placing them in a housing, injecting the electrolyte into the housing and sealing it, wherein the separator used is the above-mentioned separator provided in this application. In addition, overcurrent protection elements, guide plates, etc. can also be placed in the housing as needed to prevent pressure rise and overcharge and discharge inside the electrochemical device.

[0068] A second aspect of the present application provides an electronic device, comprising the electrochemical device described in the embodiments of the present application, wherein the electronic device has good high-temperature safety performance and cycle performance.

[0069] The electronic device of the present application is not particularly limited, and it can be any electronic device known in the prior art. In some embodiments, the electronic device may include, but is not limited to, a laptop computer, a pen-input computer, a mobile computer, an electronic book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, an LCD TV, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, an electric tool, a flashlight, a camera, a large household battery and a lithium-ion capacitor, etc.

[0070] The present application provides an electrochemical device and an electronic device, wherein the electrochemical device comprises a positive electrode, a negative electrode, a separator and an electrolyte, wherein the electrolyte comprises phosphorus oxyfluoride and a polycyano compound, wherein the polycyano compound comprises at least two cyano groups. The electrolyte can form a dense and stable protective film on the surface of the positive electrode, inhibiting the decomposition reaction of the electrolyte under high voltage. The electrochemical device comprising the electrolyte has good high temperature safety performance and cycle performance.

[0071] Example

[0072] The following examples and comparative examples are given to more specifically describe the embodiments of the present application. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0073] Test methods and equipment:

[0074] Cycle performance test:

[0075] At 25°C, after the lithium-ion battery is allowed to stand for 30 minutes, it is charged to 4.45V at a constant current of 1C, then charged to 0.05C at a constant voltage of 4.45V and allowed to stand for 5 minutes, and then discharged to 3.0V at a constant current of 0.5C. This is a discharge cycle process. The discharge capacity this time is the first discharge capacity of the lithium-ion battery, and then 500 charge and discharge cycles are carried out.

[0076] The capacity retention rate (%) of a lithium-ion battery after N charge and discharge cycles = discharge capacity at the Nth cycle / first discharge capacity × 100%.

[0077] High temperature resistance safety performance test:

[0078] At 25°C, the lithium-ion battery was left to stand for 30 minutes, then charged to 4.45V at a constant current rate of 1C, and then charged to 0.05C at a constant voltage of 4.45V. The fully charged lithium-ion battery was placed in an oven, which was heated at a heating rate of 5°C / min. The temperature of the lithium-ion battery surface was monitored, and the oven temperature was recorded when the lithium-ion battery experienced thermal runaway combustion.

[0079] <Preparation of Electrolyte>

[0080] In a dry argon atmosphere, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC) and ethyl propionate (EP) are mixed at a mass ratio of EC:PC:DEC:EP=20:10:40:30 to obtain a non-aqueous organic solvent. LiPF6, and optionally POF3, polycyano compounds, fluoroester compounds, cyclic sulfonates and cyclic carbonates containing unsaturated bonds are added to the non-aqueous organic solvent to obtain a LiPF6 concentration of 1.1 mol / L, and the contents of POF3, polycyano compounds, fluoroester compounds, cyclic sulfonates and cyclic carbonates containing unsaturated bonds are shown in Table 1.

[0081] <Preparation of positive electrode>

[0082] 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 conductive carbon black (Super P) and 9.7kg of positive electrode active material lithium cobalt oxide (LiCoO2), mix and stir thoroughly to obtain positive electrode slurry. Among them, the mass percentage F of cobalt element in LiCoO2 in the positive electrode active material is 60%. The positive electrode slurry is evenly coated on the first surface of the positive electrode current collector aluminum foil with a thickness of 12μm, and baked at 120℃ for 1h to obtain a positive electrode coated with positive electrode slurry on one side. Then, repeat the above steps on the second surface of the positive electrode to obtain a positive electrode coated with positive electrode slurry on both sides. After coating, after compaction and cutting, a positive electrode with a specification of 74mm×867mm is obtained for standby use.

[0083] <Preparation of negative electrode>

[0084] Weigh 2.0kg of thickener sodium carboxymethyl cellulose (CMC, the mass percentage of sodium carboxymethyl cellulose is 1.5%), 0.2kg of binder styrene butadiene rubber latex (the mass percentage of styrene butadiene rubber is 50%) and 4.8kg of negative electrode active material graphite powder (average particle size Dv50 is 11.5μm) and mix them evenly to obtain negative electrode slurry. The negative electrode slurry is evenly coated on the first surface of the negative electrode current collector copper foil with a thickness of 8μm, and baked at 120℃ for 1h to obtain a negative electrode coated with negative electrode slurry on one side. Then, repeat the above steps on the second surface of the negative electrode to obtain a negative electrode coated with negative electrode slurry on both sides. After coating, after compaction and cutting, a negative electrode with a specification of 76mm×851mm is obtained for standby use.

[0085] <Preparation of Separator Film>

[0086] Alumina and polyvinylidene fluoride were mixed in a mass ratio of 90:10 and dissolved in deionized water to form a ceramic slurry with a solid content of 50%. The ceramic slurry was then evenly coated on one side of a porous substrate (polypropylene, thickness 7 μm, average pore size 0.073 μm, porosity 26%) using a micro-concave coating method, and dried to obtain a double-layer structure of a ceramic coating and a porous substrate, with a thickness of 50 μm.

[0087] 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%. The polymer slurry was then evenly coated on both surfaces of the double-layer structure of the ceramic coating and the porous substrate by a micro-concave coating method, and dried to obtain an isolation membrane, wherein the thickness of the single-layer coating formed by the polymer slurry was 2 μm.

[0088] <Preparation of lithium-ion batteries>

[0089] The positive electrode, separator, and negative electrode prepared above are stacked in order, with the separator placed between the positive and negative electrodes to play a role of isolation, and then wound to obtain an electrode assembly. The electrode assembly is placed in an aluminum foil packaging bag, baked at 80°C to remove water, and then injected with the electrolyte prepared above, and a lithium-ion battery is obtained through vacuum packaging, standing, forming, shaping, and other processes.

[0090] In Examples 1 to 57 and Comparative Examples 1 to 6, the preparation steps of <Preparation of Electrolyte>, <Preparation of Positive Electrode>, <Preparation of Negative Electrode>, <Preparation of Separator> and <Preparation of Lithium Ion Battery> are the same as the above preparation steps, and the changes of relevant preparation parameters are shown in Table 1:

[0091]

[0092]

[0093]

[0094]

[0095] It can be seen from Examples 1 to 9 and Comparative Examples 1 and 5 that the high temperature safety performance and cycle performance of the lithium ion battery change with the change of the mass percentage content A of phosphorus oxyfluoride in the electrolyte. The lithium ion battery in which the mass percentage content A of phosphorus oxyfluoride in the electrolyte is within the content range of the present application has significantly better high temperature safety performance and cycle performance.

[0096] It can be seen from Examples 7, 19 to 23 and Comparative Example 2 that the high temperature safety performance and cycle performance of the lithium ion battery change with the change of the mass percentage content B of the polycyano compound in the electrolyte. The lithium ion battery with the mass percentage content B of the polycyano compound in the electrolyte within the range of the present application has significantly better high temperature safety performance and cycle performance.

[0097] The types and mass percentages of the fluoroester compounds, cyclic sulfonate compounds and cyclic carbonates containing unsaturated bonds in the electrolyte usually also affect the high temperature safety performance and cycle performance of the lithium ion battery. It can be seen from Examples 39 to 51 that as long as the types and contents of the fluoroester compounds, cyclic sulfonate compounds and cyclic carbonates containing unsaturated bonds in the electrolyte are within the scope of this application, a lithium ion battery with good high temperature safety performance and cycle performance can be obtained.

[0098] The sum A+B of the mass percentage of phosphorus oxyfluoride A and the mass percentage of the polycyanide compound B, and the sum A+D of the mass percentage of phosphorus oxyfluoride A and the mass percentage of the cyclic sulfonate D usually also have an impact on the high temperature safety performance and cycle performance of the lithium ion battery. As can be seen from Table 1, A+B or A+D within the scope of this application can obtain a lithium ion battery with good high temperature safety performance and cycle performance.

[0099] The ratio F / A of the mass percentage content F of the transition metal element in the positive electrode active material to the mass percentage content A of phosphorus oxyfluoride in the electrolyte generally also affects the high temperature safety performance and cycle performance of the lithium ion battery. It can be seen from Example 7 and Example 53 to Example 57 that when F / A is within the scope of this application, a lithium ion battery with good high temperature safety performance and cycle performance can be obtained.

[0100] Based on the above analysis, the electrochemical device provided by the present application comprises a positive electrode, a negative electrode, a separator and an electrolyte, wherein the electrolyte comprises phosphorus oxyfluoride and a polycyano compound, wherein the polycyano compound comprises at least two cyano groups. The electrolyte can form a dense and stable protective film on the surface of the positive electrode, inhibiting the decomposition reaction of the electrolyte under high voltage. The electrochemical device comprising the electrolyte has good high temperature safety performance and cycle performance.

[0101] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. An electrochemical device comprising a positive electrode, a negative electrode, a separator and an electrolyte, wherein the positive electrode comprises a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode active material layer comprises a positive electrode active material; the electrolyte comprises phosphorus oxyfluoride and a polycyano compound, wherein the polycyano compound comprises at least two cyano groups; Based on the total mass of the electrolyte, the mass percentage A of the phosphorus oxyfluoride is 0.9% to 3%, the mass percentage B of the polycyano compound is 0.1% to 10%, and 1.5%≤A+B≤11%; The polycyano compound comprises at least one of the compounds represented by structural formula (I): in, R is selected from C1 to C 15 Alkane, C1 to C 15 Alkenyl or C1 to C 15 a and c are each independently 0 or a positive integer, and a and c are not 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 may be the same or different.

2. The electrochemical device according to claim 1, wherein: The polycyano compound includes any one of the following formulas (1) to (62):

3. The electrochemical device according to claim 1, wherein The electrolyte further comprises at least one of a fluorinated ester compound, a cyclic sulfonate ester, or a cyclic carbonate ester containing an unsaturated bond.

4. The electrochemical device according to claim 3, 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 mass percentage D of the cyclic sulfonate is 0.1% to 5%, and / or the mass percentage E of the cyclic carbonate containing an unsaturated bond is 0.01% to 2%.

5. The electrochemical device according to claim 4, wherein: The mass percentage A of the phosphorus oxyfluoride and the mass percentage D of the cyclic sulfonate satisfy the following relationship: 1%≤A+D≤7%.

6. The electrochemical device according to claim 3, wherein: The fluorinated ester compound comprises at least one of fluoroethylene carbonate, difluoroethylene carbonate, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, ethyl fluoropropionate, propyl fluoropropionate, methyl fluoropropionate, ethyl fluoroacetate, methyl fluoroacetate, propyl fluoroacetate, and trifluoromethylethylene carbonate; The cyclic sulfonate comprises 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 ethylene carbonate.

7. The electrochemical device according to any one of claims 1 to 6, wherein: The mass percentage F of the metal elements other than lithium in the positive electrode active material and the mass percentage A of the phosphorus oxyfluoride in the electrolyte satisfy the following relationship: 600>F / A>10.

8. An electronic device comprising the electrochemical device according to any one of claims 1 to 7.

Images