An electrochemical device and an electronic device

Abstract

This application provides an electrochemical device and an electronic device. The electrochemical device includes an electrolyte and a positive electrode. The electrolyte comprises a compound of formula I and lithium difluorophosphate. Based on the total mass of the electrolyte, the mass percentage of compound I is A, and the mass percentage of lithium difluorophosphate is B, where 0.005 ≤ A / B ≤ 500, and 0.01% < A+B ≤ 7%. The positive electrode includes a positive active material layer comprising a lithium nickel cobalt manganese oxide transition metal oxide. At least a portion of the surface of the lithium nickel cobalt manganese oxide transition metal oxide includes element M, which includes at least one of Al, Mg, Ti, Zn, Ge, Zr, W, or Si. The electrochemical device of this application exhibits good high-temperature cycling performance and high-temperature storage performance, and can reduce the DC impedance growth during the cycling process of the electrochemical device.

Description

Technical Field

[0001] This application relates to the field of electrochemical technology, and in particular to an electrochemical device and an electronic device. Background Technology

[0002] Lithium-ion batteries possess advantages such as high energy density, light weight, and long cycle life, making them widely used in consumer batteries. With the development of electronic products towards thinner and more portable designs, higher demands are being placed on battery energy density and high-temperature cycling performance. Using high-energy-density materials and increasing operating voltage are effective ways to improve the energy density of lithium-ion batteries. However, when lithium-ion batteries are subjected to high voltage, the oxidation activity of the positive electrode active material increases, and structural damage intensifies. Simultaneously, the electrolyte is also prone to decomposition under high voltage, especially electrochemical oxidation reactions on the positive electrode surface. This leads to increased positive electrode impedance, rapid electrolyte consumption, and reduced cycle performance, as well as decreased safety. Therefore, researching and improving the high-temperature cycling and high-temperature storage performance of lithium-ion batteries under high-voltage conditions is of great significance for their application. Summary of the Invention

[0003] The purpose of this application is to provide an electrochemical device and an electronic device to improve the high-temperature cycling performance and high-temperature storage performance of the electrochemical device and reduce the DC impedance growth during the cycling process of the electrochemical device.

[0004] It should be noted that while this application uses lithium-ion batteries as an example of an electrochemical device to explain the invention, the electrochemical device described herein is not limited to lithium-ion batteries. The specific technical solution is as follows:

[0005] The first aspect of this application provides an electrochemical device comprising an electrolyte and a positive electrode. The electrolyte comprises at least one of a compound of formula I and lithium difluorophosphate. Based on the total mass of the electrolyte, the mass percentage of the compound of formula I is A, the mass percentage of lithium difluorophosphate is B, 0.005 ≤ A / B ≤ 500, and 0.01% < A + B ≤ 7%.

[0006]

[0007] R1, R2, R3, and R4 are each independently selected from an oxygen atom or a methylene group, and at least one of R1, R2, R3, or R4 is selected from an oxygen atom; X1 and X2 are each independently selected from C-R5 or C2 to C. 10 The alkenyl group; R5 is selected from hydrogen atoms, C1 to C2. 10 Alkyl, C2 to C 10 alkenyl, C6 to C 12 aryl, C3 to C 10 Cycloalkane group, C3 to C10 Cycloolefinic groups or C3 to C 10 The aromatic heterocyclic group, wherein the heteroelement in the aromatic heterocyclic group includes at least one of O, S, N, B, P, or Si; the positive electrode includes a positive electrode active material layer, which includes a lithium nickel cobalt manganese oxide transition metal oxide, wherein at least a portion of the surface of the lithium nickel cobalt manganese oxide transition metal oxide includes element M, wherein element M includes at least one of Al, Mg, Ti, Zn, Ge, Zr, W, or Si. When at least a portion of the surface of the lithium nickel cobalt manganese oxide transition metal oxide includes the aforementioned element M, side reactions between the lithium nickel cobalt manganese oxide transition metal oxide and the electrolyte can be reduced, and the structural stability of the lithium nickel cobalt manganese oxide transition metal oxide itself can be improved, reducing the dissolution of metal ions therein, reducing the safety risk caused by the deposition of dissolved metal ions on the negative electrode, and simultaneously improving the conductivity of the positive electrode active material, thereby improving the high-temperature cycle stability of the positive electrode active material and reducing gas production. Adding the aforementioned compound of formula I to the electrolyte can effectively improve the high-temperature cycling performance of the electrochemical device and reduce gas generation during cycling. This is because compound of formula I preferentially oxidizes over the solvent, forming a relatively dense protective film on the surface of the positive electrode active material particles, reducing side reactions between the positive electrode active material and the electrolyte, and simultaneously reducing the dissolution of metal ions. Furthermore, compound of formula I preferentially reduces to form a film at the negative electrode during the first charge-discharge cycle, resulting in a denser film and reducing electrolyte decomposition at the negative electrode. LiPO2F2 can increase the LiF content in the SEI film and provide stability to the organic layer, thereby improving the high-temperature cycling performance of the electrochemical device and reducing DC impedance. When the values ​​of A / B and A+B are within the range of this application, combining the positive electrode and electrolyte of this application in the electrochemical device can further improve the high-temperature cycling and high-temperature storage performance of the electrochemical device and reduce the increase in DC impedance during cycling.

[0008] In one embodiment of this application, the compound of formula I includes at least one of the following compounds:

[0009]

[0010]

[0011] When the compound of formula I includes at least one of the above compounds, it can form a relatively dense protective film at the positive electrode interface and the negative electrode interface, reduce the side reactions between the positive electrode active material and the negative electrode active material and the electrolyte, and improve the high-temperature cycle performance and high-temperature storage performance of the electrochemical device.

[0012] In one embodiment of this application, based on the total mass of the electrolyte, the mass percentage A of compound I is 0.01% to 5%, preferably 0.1% to 2%; and the mass percentage B of lithium difluorophosphate is 0.01% to 2%, preferably 0.1% to 1%. When the mass percentage A of compound I is within the above range, the film-forming resistance of compound I at the positive and negative electrode interfaces is relatively small, enabling the formation of a denser protective film at the positive and negative electrode interfaces, reducing side reactions between the positive and negative electrode active materials and the electrolyte, thereby improving the high-temperature cycling performance and high-temperature storage performance of the electrochemical device. When the mass percentage B of lithium difluorophosphate is within the above range, the film-forming resistance of lithium difluorophosphate at the positive and negative electrode interfaces is relatively small, which can increase the LiF content in the solid electrolyte interphase (SEI) film and improve the stability of the organic layer, thereby improving the high-temperature cycling performance of the electrochemical device and reducing the DC impedance.

[0013] In one embodiment of this application, the mass percentage C of element M is 0.01% to 5%, preferably 0.05% to 3%, based on the total mass of the positive electrode active material layer. When at least a portion of the surface of the lithium nickel cobalt manganese oxide transition metal oxide includes element M, and the mass percentage C of element M is within the above range, the structural stability of the lithium nickel cobalt manganese oxide transition metal oxide can be increased, side reactions with the electrolyte can be reduced, and at the same time, there is better interfacial transport between the lithium nickel cobalt manganese oxide transition metal oxide and the electrolyte, thereby improving the kinetic performance, high-temperature cycling performance, and high-temperature storage performance of the electrochemical device.

[0014] In one embodiment of this application, 0.002 ≤ C / A ≤ 500, preferably 0.025 ≤ C / A ≤ 300. By adjusting the ratio C / A of the mass percentage content C of element M and the mass percentage content A of compound of formula I to be within the above range, not only can the side reactions between lithium nickel cobalt manganese oxide transition metal oxide and electrolyte be reduced, but also the increase in DC impedance during cycling can be reduced, as well as the capacity loss caused by excessive compounds containing element M on the surface of the positive electrode active material can be reduced, thereby improving the high-temperature cycling performance and high-temperature storage performance of the electrochemical device and reducing DC impedance.

[0015] In one embodiment of this application, the electrolyte includes a sulfonate compound, which includes at least one selected from 1,3-propanesulfonate lactone, 3-fluoro-1,3-propanesulfonate lactone, 1,4-butanesulfonate lactone, 1,3-propenesulfonate lactone, or methanedisulfonate methylene ester; the mass percentage of the sulfonate compound is 0.1% to 5% based on the total mass of the electrolyte. When the above-mentioned sulfonate compound is selected and the mass percentage of the sulfonate compound is controlled within the above range, the sulfonate compound can form an interfacial film with excellent mechanical stability at both the positive and negative electrode interfaces. This interfacial film can reduce side reactions at the positive and negative electrode interfaces, thereby improving the high-temperature cycling performance and high-temperature storage performance of the electrochemical device, and reducing the DC impedance of the electrochemical device.

[0016] In one embodiment of this application, the electrolyte further includes at least one of fluoroethylene carbonate, vinylene carbonate, or lithium dioxalate borate. Fluoroethylene carbonate and vinylene carbonate have better film-forming properties, making the structures of the positive and negative electrode active materials less susceptible to damage. Lithium dioxalate borate, due to its conjugated structure, has better thermal stability, and it participates in the film formation of both the positive and negative electrodes, thus protecting them from damage and improving the high-temperature cycling and high-temperature storage performance of the electrochemical device.

[0017] In one embodiment of this application, the electrolyte further includes fluoroethylene carbonate, and the mass percentage of fluoroethylene carbonate is 0.5% to 10% based on the total mass of the electrolyte. When the electrolyte includes fluoroethylene carbonate and the mass percentage of fluoroethylene carbonate is within the above range, fluoroethylene carbonate has better film-forming properties, making the structure of the positive and negative electrode active materials less susceptible to damage, thereby improving the high-temperature cycling performance and high-temperature storage performance of the electrochemical device.

[0018] In one embodiment of this application, the electrolyte further includes vinylene carbonate, and the mass percentage of vinylene carbonate is 0.01% to 5% based on the total mass of the electrolyte. When the electrolyte includes vinylene carbonate and the mass percentage of vinylene carbonate is within the above range, vinylene carbonate has better film-forming properties, making the structure of the positive and negative electrode active materials less susceptible to damage, thereby improving the high-temperature cycling performance and high-temperature storage performance of the electrochemical device.

[0019] In one embodiment of this application, the electrolyte further includes lithium dioxalate borate, and the mass percentage of lithium dioxalate borate is 0.01% to 5% based on the total mass of the electrolyte. When the electrolyte includes lithium dioxalate borate and the mass percentage of lithium dioxalate borate is within the above range, lithium dioxalate borate has better thermal stability due to its conjugated structure, and it participates in the film formation of both the positive and negative electrodes, thus protecting both electrodes from damage and improving the high-temperature cycling performance and high-temperature storage performance of the electrochemical device.

[0020] A second aspect of this application provides an electronic device comprising the electrochemical device of any of the foregoing embodiments. The electronic device of this application exhibits good high-temperature cycling performance and high-temperature storage performance, and is capable of reducing DC impedance growth during cycling.

[0021] The beneficial effects of this application are:

[0022] This application provides an electrochemical device and an electronic device. The electrochemical device includes an electrolyte and a positive electrode. The electrolyte includes at least one compound of formula I and lithium difluorophosphate. The positive electrode includes a positive active material layer comprising a lithium nickel cobalt manganese oxide transition metal oxide. At least a portion of the surface of the lithium nickel cobalt manganese oxide transition metal oxide includes element M, which includes at least one of Al, Mg, Ti, Zn, Ge, Zr, W, or Si. The inclusion of element M on at least a portion of the surface of the lithium nickel cobalt manganese oxide transition metal oxide can reduce side reactions between the lithium nickel cobalt manganese oxide and the electrolyte, and can improve the structural stability of the lithium nickel cobalt manganese oxide itself, reduce the dissolution of metal ions therein, reduce the safety risks caused by the deposition of dissolved metal ions on the negative electrode, and simultaneously improve the conductivity of the positive active material, thereby improving the high-temperature cycle stability of the positive active material and reducing gas production. Adding the aforementioned compound of formula I to the electrolyte can effectively improve the high-temperature cycling performance of the electrochemical device and reduce gas generation during cycling. This is because compound of formula I preferentially oxidizes over the solvent, forming a relatively dense protective film on the surface of the positive electrode active material particles, reducing side reactions between the positive electrode active material and the electrolyte, and simultaneously reducing the dissolution of metal ions. Furthermore, compound of formula I preferentially reduces to form a film at the negative electrode during the first charge-discharge cycle, resulting in a denser film and reducing electrolyte decomposition at the negative electrode. Lithium difluorophosphate (LiPO2F2) can increase the lithium fluoride (LiF) content in the SEI film while providing stability to the organic layer, thus improving the high-temperature cycling performance of the electrochemical device and reducing DC impedance. Combining the positive electrode and electrolyte of this application in an electrochemical device can further improve the high-temperature cycling and high-temperature storage performance of the electrochemical device and reduce the increase in DC impedance during cycling. Detailed Implementation

[0023] The technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0024] It should be noted that, in the specific embodiments 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.

[0025] The first aspect of this application provides an electrochemical device comprising an electrolyte and a positive electrode. The electrolyte comprises at least one compound of formula I and lithium difluorophosphate. Based on the total mass of the electrolyte, the mass percentage of the compound of formula I is A, the mass percentage of lithium difluorophosphate is B, 0.005 ≤ A / B ≤ 500, and 0.01% < A+B ≤ 7%. For example, the value of A / B can be 0.005, 0.1, 1, 10, 100, 200, 300, 400, 500, or a range of any two values ​​therein; the value of A+B can be 0.02%, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, or a range of any two values ​​therein.

[0026]

[0027] R1, R2, R3, and R4 are each independently selected from an oxygen atom or a methylene group, and at least one of R1, R2, R3, or R4 is selected from an oxygen atom; X1 and X2 are each independently selected from C-R5 or C2 to C. 10 The alkenyl group; R5 is selected from hydrogen atoms, C1 to C2. 10 Alkyl, C2 to C 10 alkenyl, C6 to C 12 aryl, C3 to C 10 Cycloalkane group, C3 to C 10 Cycloolefinic groups or C3 to C 10 The aromatic heterocyclic group, wherein the heteroelement in the aromatic heterocyclic group includes at least one of O, S, N, B, P or Si.

[0028] The positive electrode includes a positive active material layer, which includes a positive active material, which includes a lithium nickel cobalt manganese oxide transition metal oxide. At least a portion of the surface of the lithium nickel cobalt manganese oxide transition metal oxide includes element M, which includes at least one of Al, Mg, Ti, Zn, Ge, Zr, W, or Si. The phrase "at least a portion of the surface of the lithium nickel cobalt manganese oxide transition metal oxide includes element M" means that element M can be present on part or all of the surface of the lithium nickel cobalt manganese oxide transition metal oxide.

[0029] Without being limited to any particular theory, the inventors of this application have discovered that having at least a portion of the surface of lithium nickel cobalt manganese oxide transition metal oxide including the aforementioned element M can reduce side reactions between the lithium nickel cobalt manganese oxide transition metal oxide and the electrolyte, and can also improve the structural stability of the lithium nickel cobalt manganese oxide transition metal oxide itself, reduce the dissolution of metal ions therein, reduce the safety risks caused by the deposition of dissolved metal ions on the negative electrode, and at the same time improve the conductivity of the positive electrode active material, thereby improving the high-temperature cycle stability of the positive electrode active material and reducing gas production. Adding the aforementioned compound of formula I to the electrolyte can effectively improve the high-temperature cycle performance of the electrochemical device and reduce gas production during the cycle. This is because compound of formula I can preferentially undergo oxidation before the solvent, forming a relatively dense protective film on the surface of the positive electrode active material particles, reducing side reactions between the positive electrode active material and the electrolyte, and simultaneously reducing the dissolution of metal ions; and compound of formula I can preferentially reduce the formation of a film on the negative electrode during the first charge and discharge, resulting in a relatively dense film and reducing the decomposition reaction of the electrolyte on the negative electrode. LiPO2F2 can increase the LiF content in the SEI film and provide stability to the organic layer, thereby improving the high-temperature cycling performance and reducing the DC impedance of the electrochemical device. When the values ​​of A / B and A+B are within the range of this application, the combined use of the positive electrode and electrolyte of this application in the electrochemical device can further improve the high-temperature cycling performance and high-temperature storage performance of the electrochemical device and reduce the DC impedance growth during cycling. In this application, "high temperature" refers to a temperature ≥60℃.

[0030] In one embodiment of this application, the compound of formula I includes at least one of the following compounds:

[0031]

[0032]

[0033] When the compound of formula I includes at least one of the above compounds, it can form a relatively dense protective film at the positive electrode interface and the negative electrode interface, reduce the side reactions between the positive electrode active material and the negative electrode active material and the electrolyte, and improve the high-temperature cycle performance and high-temperature storage performance of the electrochemical device.

[0034] In one embodiment of this application, based on the total mass of the electrolyte, the mass percentage A of compound I is 0.01% to 5%, preferably 0.1% to 2%; the mass percentage B of lithium difluorophosphate is 0.01% to 2%, preferably 0.1% to 1%. For example, the mass percentage A of compound I can be 0.01%, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, or a range of any two values ​​therein; the mass percentage B of lithium difluorophosphate can be 0.01%, 0.1%, 0.5%, 1%, 1.5%, 2%, or a range of any two values ​​therein. When the mass percentage A of compound I is within the above range, the film-forming resistance of compound I at the positive and negative electrode interfaces is small, and it can form a relatively dense protective film at the positive and negative electrode interfaces, reducing side reactions between the positive and negative electrode active materials and the electrolyte, thereby improving the high-temperature cycling performance and high-temperature storage performance of the electrochemical device. When the mass percentage B of lithium difluorophosphate is within the above range, the film-forming resistance of lithium difluorophosphate at the positive and negative electrode interfaces is small, which can increase the LiF content in the solid electrolyte interphase (SEI) film, improve the stability of the organic layer, improve the high-temperature cycling performance of the electrochemical device, and reduce the DC impedance.

[0035] In one embodiment of this application, the mass percentage C of element M is 0.01% to 5%, preferably 0.05% to 3%, based on the total mass of the positive electrode active material layer. For example, the mass percentage C of element M can be 0.01%, 0.05%, 0.5%, 1%, 2%, 3%, 4%, 5%, or a range consisting of any two of these values. When at least a portion of the surface of the lithium nickel cobalt manganese oxide transition metal oxide includes element M, and the mass percentage C of element M is within the above range, the structural stability of the lithium nickel cobalt manganese oxide transition metal oxide can be increased, side reactions with the electrolyte can be reduced, and the lithium nickel cobalt manganese oxide transition metal oxide has better interfacial transport with the electrolyte, thereby improving the kinetic performance, high-temperature cycling performance, and high-temperature storage performance of the electrochemical device.

[0036] In one embodiment of this application, 0.002 ≤ C / A ≤ 500, preferably 0.025 ≤ C / A ≤ 300. For example, the value of C / A can be 0.002, 0.025, 0.1, 1, 10, 100, 200, 300, 400, 500, or a range of any two of these values. By adjusting the ratio C / A of the mass percentage content C of element M and the mass percentage content A of compound of formula I to be within the above range, not only can the side reactions between lithium nickel cobalt manganese oxide transition metal oxide and electrolyte be reduced, but also the increase in DC impedance during cycling can be reduced, as well as the capacity loss caused by excessive compounds containing element M on the surface of the positive electrode active material can be reduced, thereby improving the high-temperature cycling performance and high-temperature storage performance of the electrochemical device and reducing the DC impedance.

[0037] In one embodiment of this application, the chemical formula of the lithium nickel cobalt manganese oxide transition metal oxide is LiNi. x Co y Mn 1-x-y M z O2, where 0.03≤x≤0.96, 0.002≤y≤0.3, 0.001≤z≤0.15. For example, the value of x can be 0.03, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 0.96, or a range of any two of these values; the value of y can be 0.002, 0.005, 0.01, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, or a range of any two of these values; the value of z can be 0.001, 0.005, 0.01, 0.03, 0.05, 0.07, 0.09, 0.11, 0.13, 0.15, or a range of any two of these values. By selecting the aforementioned lithium nickel cobalt manganese oxide transition metal oxides, the high-temperature cycling performance and high-temperature storage performance of electrochemical devices can be improved.

[0038] In one embodiment of this application, the electrolyte includes a sulfonate compound, which includes at least one selected from 1,3-propanesulfonate lactone, 3-fluoro-1,3-propanesulfonate lactone, 1,4-butanesulfonate lactone, 1,3-propenesulfonate lactone, or methanedisulfonate methylene ester; the mass percentage of the sulfonate compound is 0.1% to 5% based on the total mass of the electrolyte. For example, the mass percentage of the sulfonate compound can be 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, or a range consisting of any two of these values. When the above-mentioned sulfonate compound is selected and its mass percentage is controlled within the above range, the sulfonate compound can form an interfacial film with excellent mechanical stability at both the positive and negative electrode interfaces. This interfacial film can reduce side reactions at the positive and negative electrode interfaces, thereby improving the high-temperature cycling performance and high-temperature storage performance of the electrochemical device, and reducing the DC impedance of the electrochemical device.

[0039] In one embodiment of this application, the electrolyte further includes at least one of fluoroethylene carbonate (FEC), vinylene carbonate (VC), or lithium bis(oxalato)borate (LiBOB). Fluoroethylene carbonate and vinylene carbonate exhibit superior film-forming properties, making the structures of the positive and negative electrode active materials less susceptible to damage. Lithium bis(oxalato)borate, due to its conjugated structure, possesses excellent thermal stability, and since it participates in the film formation of both the positive and negative electrodes, it can simultaneously protect both electrodes from damage, thereby improving the high-temperature cycling performance and high-temperature storage performance of the electrochemical device.

[0040] In one embodiment of this application, the electrolyte further includes fluoroethylene carbonate, and the mass percentage of fluoroethylene carbonate is 0.5% to 10% based on the total mass of the electrolyte. When the electrolyte includes fluoroethylene carbonate and the mass percentage of fluoroethylene carbonate is within the above range, fluoroethylene carbonate has better film-forming properties, making the structures of the positive and negative electrode active materials less susceptible to damage, thereby improving the high-temperature cycling performance and high-temperature storage performance of the electrochemical device.

[0041] In one embodiment of this application, the electrolyte further includes vinylene carbonate, and the mass percentage of vinylene carbonate is 0.01% to 5% based on the total mass of the electrolyte. When the electrolyte includes vinylene carbonate and the mass percentage of vinylene carbonate is within the above range, vinylene carbonate has better film-forming properties, making the structures of the positive and negative electrode active materials less susceptible to damage, thereby improving the high-temperature cycling performance and high-temperature storage performance of the electrochemical device.

[0042] In one embodiment of this application, the electrolyte further includes lithium dioxalate borate, and the mass percentage of lithium dioxalate borate is 0.01% to 5% based on the total mass of the electrolyte. When the electrolyte includes lithium dioxalate borate and the mass percentage of lithium dioxalate borate is within the above range, lithium dioxalate borate has better thermal stability due to its conjugated structure, and it participates in the film formation of both the positive and negative electrodes, thus protecting both electrodes from damage and improving the high-temperature cycling performance and high-temperature storage performance of the electrochemical device.

[0043] In this application, the electrolyte also includes lithium salts. There are no particular limitations on the lithium salts used; any lithium salt known in the art can be used, as long as it achieves the purpose of this application. For example, the lithium salt can be selected from at least one of lithium hexafluorophosphate (LiPF6), LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, or Li2SiF6. Based on the total mass of the electrolyte, the mass percentage of lithium salt can be from 8% to 20%, for example, the mass percentage of lithium salt can be 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, or a range consisting of any two of these values. There are no particular limitations on non-aqueous solvents used in this application, as long as they achieve the purpose of this application. For example, non-aqueous solvents can include, but are not limited to, at least one of carbonate compounds, carboxylic acid ester compounds, ether compounds, or other organic solvents.

[0044] The aforementioned carbonate compounds may include, but are not limited to, at least one of chain carbonate compounds or cyclic carbonate compounds. The aforementioned chain carbonate compounds may include, but are not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), or methyl ethyl carbonate (MEC). The aforementioned cyclic carbonate compounds may include, but are not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), or vinyl ethylene carbonate (VEC). The aforementioned carboxylic acid ester compounds may include, but are not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolactone, valproic acid lactone, or caprolactone. The aforementioned ether compounds may include, but are not limited to, at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran. The aforementioned other organic solvents may include, but are not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate.

[0045] This application does not impose any particular limitation on the content of non-aqueous solvents in the electrolyte, as long as the purpose of this application is achieved. For example, based on the total mass of the electrolyte, the mass percentage of non-aqueous solvents can be from 48% to 91.98%, such as 48%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 91.98%, or a range of any two of these values.

[0046] In one embodiment of this application, the electrolyte may include a compound of formula I, lithium difluorophosphate, a lithium salt, and a non-aqueous solvent. The mass percentages of the compound of formula I, lithium difluorophosphate, and lithium salt are as described above, and the mass percentage of the non-aqueous solvent is 73% to 91.98%. Electrochemical devices comprising the above-described electrolyte exhibit good high-temperature cycling performance, high-temperature storage performance, and low DC impedance.

[0047] In one embodiment of this application, the electrolyte may include a compound of formula I, lithium difluorophosphate, a sulfonate compound, a lithium salt, and a non-aqueous solvent. The mass percentages of the compound of formula I, lithium difluorophosphate, sulfonate compound, and lithium salt are as described above, and the mass percentage of the non-aqueous solvent is 68% to 91.88%. Electrochemical devices comprising the above-described electrolyte exhibit good high-temperature cycling performance, high-temperature storage performance, and low DC impedance.

[0048] In one embodiment of this application, the electrolyte may include a compound of formula I, lithium difluorophosphate, fluoroethylene carbonate, a lithium salt, and a non-aqueous solvent. The mass percentages of the compound of formula I, lithium difluorophosphate, fluoroethylene carbonate, and lithium salt are as described above, and the mass percentage of the non-aqueous solvent is 63% to 91.48%. Electrochemical devices comprising the above-described electrolyte exhibit good high-temperature cycling performance, high-temperature storage performance, and low DC impedance.

[0049] In one embodiment of this application, the electrolyte may include one of the following: a compound of formula I, lithium difluorophosphate, vinylene carbonate, or lithium dioxaborate, a lithium salt, and a non-aqueous solvent. The mass percentages of the compound of formula I, lithium difluorophosphate, vinylene carbonate, or lithium dioxaborate, and the lithium salt are as described above, and the mass percentage of the non-aqueous solvent is 68% to 91.87%. Electrochemical devices comprising the above-described electrolyte exhibit good high-temperature cycling performance, high-temperature storage performance, and low DC impedance.

[0050] In one embodiment of this application, the electrolyte may include a compound of formula I, lithium difluorophosphate, a sulfonate compound, fluoroethylene carbonate, a lithium salt, and a non-aqueous solvent. The mass percentages of the compound of formula I, lithium difluorophosphate, sulfonate compound, fluoroethylene carbonate, and lithium salt are as described above, and the mass percentage of the non-aqueous solvent is 58% to 91.38%. Electrochemical devices comprising the above-described electrolyte exhibit good high-temperature cycling performance, high-temperature storage performance, and low DC impedance.

[0051] In one embodiment of this application, the electrolyte may include one of the following: a compound of formula I, lithium difluorophosphate, a sulfonate compound, vinylene carbonate, or lithium dioxaborate, a lithium salt, and a non-aqueous solvent. The mass percentages of the compound of formula I, lithium difluorophosphate, sulfonate compound, vinylene carbonate, or lithium dioxaborate, and the lithium salt are as described above, and the mass percentage of the non-aqueous solvent is 63% to 91.87%. Electrochemical devices comprising the above-described electrolyte exhibit good high-temperature cycling performance, high-temperature storage performance, and low DC impedance.

[0052] In one embodiment of this application, the electrolyte may include one of the following: a compound of formula I, lithium difluorophosphate, fluoroethylene carbonate, vinylene carbonate, or lithium dioxalate borate, a lithium salt, and a non-aqueous solvent. The mass percentages of the compound of formula I, lithium difluorophosphate, fluoroethylene carbonate, vinylene carbonate, or lithium dioxalate borate, and the lithium salt are as described above, and the mass percentage of the non-aqueous solvent is 58% to 91.47%. Electrochemical devices comprising the above-described electrolyte exhibit good high-temperature cycling performance, high-temperature storage performance, and low DC impedance.

[0053] In one embodiment of this application, the electrolyte may include one of the following: a compound of formula I, lithium difluorophosphate, a sulfonate compound, fluoroethylene carbonate, vinylene carbonate, or lithium dioxaborate, a lithium salt, and a non-aqueous solvent. The mass percentages of the compound of formula I, lithium difluorophosphate, sulfonate compound, fluoroethylene carbonate, vinylene carbonate, or lithium dioxaborate, and the lithium salt are as described above, and the mass percentage of the non-aqueous solvent is 53% to 91.37%. Electrochemical devices comprising the above-described electrolyte exhibit good high-temperature cycling performance, high-temperature storage performance, and low DC impedance.

[0054] In one embodiment of this application, the electrolyte may include a compound of formula I, lithium difluorophosphate, a sulfonate compound, fluoroethylene carbonate, vinylene carbonate, lithium dioxaborate, a lithium salt, and a non-aqueous solvent. The mass percentages of the compound of formula I, lithium difluorophosphate, sulfonate compound, fluoroethylene carbonate, vinylene carbonate, lithium dioxaborate, and lithium salt are as described above, and the mass percentage of the non-aqueous solvent is 48% to 91.36%. Electrochemical devices comprising the above-described electrolyte exhibit good high-temperature cycling performance, high-temperature storage performance, and low DC impedance.

[0055] This application does not impose any particular limitation on the preparation method of lithium nickel cobalt manganese oxide transition metal oxide, as long as it achieves the purpose of this application, such as vapor deposition or sol-gel method. Exemplarily, the preparation method of lithium nickel cobalt manganese oxide transition metal oxide may include, but is not limited to, the following steps:

[0056] (1) Vapor deposition method: A metal precursor is placed in the deposition chamber of an atomic layer deposition system, and an element M source and an oxygen source are introduced. At a deposition temperature of 150°C to 250°C, element M is deposited on the surface of the metal precursor to obtain lithium nickel cobalt manganese oxide transition metal oxide. The element M source is a compound containing element M, and the oxygen source includes water.

[0057] (2) Sol-gel method: The metal precursor is dispersed in an aqueous solution containing ammonium bicarbonate (NH4HCO3) and polyethylene glycol. Then, under the conditions of water bath at 80°C to 100°C, a solution of the compound containing element M is added dropwise to the solution. After stirring for 3 to 5 hours, the mixture is filtered, washed and dried to obtain an intermediate product. Finally, the intermediate product is calcined in a tube furnace at 300°C to 500°C for 4 to 6 hours under a nitrogen atmosphere to obtain lithium nickel cobalt manganese oxide transition metal oxide.

[0058] In this application, the metal precursor may include, but is not limited to, LiNi. 0.33 Co 0.33 Mn 0.33 O2, LiNi 0.5 Co 0.2 Mn 0.3O2, LiNi 0.6 Co 0.1 Mn 0.3 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2 or LiNi 0.9 Co 0.05 Mn 0.05 At least one of O2; the compound containing element M may include, but is not limited to, at least one of oxides, hydroxides, fluorides, nitrates, or organic compounds containing element M. For example, the oxides containing element M include at least one of Al2O3, MgO, TiO2, ZnO, ZrO2, WO3, or SiO2; the hydroxides containing element M include at least one of Al(OH)3, Mg(OH)2, Zn(OH)2, Ge(OH)2, or Zr(OH)3; the fluorides containing element M include at least one of AlF3, MgF2, or GeF4; the nitrates containing element M include at least one of Al(NO3)3, Mg(NO3)2, or Zn(NO3)2; and the organic compounds containing element M include at least one of trimethylaluminum or tetramethylgermanium.

[0059] In this application, the mass percentage C of element M in the positive electrode active material layer can be controlled by adjusting the mass ratio of the compound containing element M to the metal precursor during the preparation of lithium nickel cobalt manganese oxide transition metal oxide. For example, increasing the mass ratio of the compound containing element M to the metal precursor increases the mass percentage of element M in the positive electrode active material layer; decreasing the mass ratio of the compound containing element M to the metal precursor decreases the mass percentage of element M in the positive electrode active material layer.

[0060] In this application, the positive electrode includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector. The phrase "positive active material layer disposed on at least one surface of the positive current collector" means that the positive active material layer can be disposed on one surface of the positive current collector along its thickness direction, or on two surfaces of the positive current collector along its thickness direction. It should be noted that "surface" here can refer to the entire surface area of ​​the positive current collector, or only a portion thereof; this application does not impose any particular limitation, as long as the purpose of this application is achieved.

[0061] This application does not impose any particular restrictions on the positive electrode current collector, as long as it can achieve the purpose of this application. For example, it may include aluminum foil, aluminum alloy foil, or composite current collector (such as aluminum-carbon composite current collector).

[0062] In this application, the positive electrode active material layer may further include a conductive agent and a binder. This application does not impose any particular limitation on the types of conductive agents and binders, as long as they achieve the purpose of this application. For example, the binder may include, but is not limited to, at least one of polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, a styrene-acrylate copolymer, a styrene-butadiene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinyl acetate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, or polyhexafluoropropylene. The conductive agent may include, but is not limited to, at least one of conductive carbon black, sheet graphite, graphene, carbon nanotubes, or carbon fibers. In this application, the conductive carbon black includes at least one of acetylene black or Ketjen black. This application does not impose any particular limitation on the mass ratio of the positive electrode active material, conductive agent, and binder in the positive electrode active material layer; those skilled in the art can select them according to actual needs, as long as the purpose of this application is achieved. For example, the mass ratio of positive electrode active material, conductive agent and binder in the positive electrode active material layer can be (93 to 97):(1 to 3):(2 to 5).

[0063] This application does not impose any particular limitations on the thickness of the positive electrode current collector and the positive electrode active material layer, as long as the purpose of this application can be achieved. For example, the thickness of the positive electrode current collector is 5 μm to 20 μm, and the thickness of the single-sided positive electrode active material layer is 30 μm to 120 μm.

[0064] Optionally, the positive electrode may further include a conductive layer located between the positive current collector and the positive active material layer. The composition of the conductive layer is not particularly limited and can be any conductive layer commonly used in the art. The conductive layer includes a conductive agent and a binder. This application does not impose any particular limitation on the conductive agent and binder in the conductive layer; for example, it can be at least one of the aforementioned conductive agents and binders.

[0065] In this application, the electrochemical device also includes a separator membrane. This application does not impose any particular limitation on the separator membrane, as long as it achieves the purpose of this application. For example, the material of the separator membrane may include, but is not limited to, at least one of polyethylene (PE), polyolefins (PO) primarily composed of polypropylene (PP), polyester (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid. The type of separator membrane may include at least one of woven membrane, nonwoven membrane, microporous membrane, composite membrane, rolled membrane, or spun membrane.

[0066] In some embodiments of this application, the separator may include a substrate layer and a surface treatment layer. The substrate layer may be a nonwoven fabric or composite membrane with a porous structure, and the material of the substrate layer may include at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Optionally, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane may be used.

[0067] Optionally, a surface treatment layer is provided on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing polymers and inorganic substances.

[0068] In some embodiments of this application, the inorganic layer comprises inorganic particles and a binder. This application does not particularly limit the inorganic particles; for example, the inorganic particles may include at least one selected from alumina, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. This application does not particularly limit the binder; for example, the binder may be at least one of the binders described above. In some embodiments of this application, the polymer layer comprises a polymer, the polymer material of which includes at least one selected from polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, or polyvinylidene fluoride or poly(vinylidene fluoride-hexafluoropropylene).

[0069] In some embodiments of this application, the inorganic layer may also include a thickener and a wetting agent. This application does not have any particular restrictions on the types of thickeners and wetting agents, as long as they can achieve the purpose of this application. For example, the thickener may include, but is not limited to, at least one of sodium carboxymethyl cellulose or lithium carboxymethyl cellulose; the wetting agent may include, but is not limited to, at least one of dimethylsiloxane, sodium dodecyl sulfate, trialkyl phosphate, methyl decanoate or dodecyl acetate.

[0070] In this application, there is no particular limitation on the thickness of the separator, as long as it can achieve the purpose of this application. For example, the thickness of the separator can be from 4 μm to 30 μm.

[0071] In the present application, the electrochemical device further includes a negative electrode plate, which includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. The above-mentioned "negative electrode active material layer disposed on at least one surface of the negative electrode current collector" means that the negative electrode active material layer can be disposed on one surface of the negative electrode current collector along its own thickness direction, or can be disposed on two surfaces of the negative electrode current collector along its own thickness direction. It should be noted that the "surface" here can be the entire area of the surface of the negative electrode current collector, or a partial area of the surface of the negative electrode current collector. There is no special limitation in the present application, as long as the purpose of the present application can be achieved.

[0072] The present application does not particularly limit the negative electrode current collector, as long as the purpose of the present application can be achieved. For example, it can include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam or composite current collector. Exemplarily, the composite current collector can be a lithium-copper composite current collector, a carbon-copper composite current collector, a nickel-copper composite current collector, a titanium-copper composite current collector, etc.

[0073] The negative electrode active material layer of the present application includes a negative electrode active material. The present application does not particularly limit 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, 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 or metallic lithium, or at least one of them.

[0074] The present application does not particularly limit 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 4 μm to 15 μm, and the thickness of the negative electrode active material layer is 30 μm to 120 μm.

[0075] In some embodiments of this application, the negative electrode active material layer may further include a binder and a thickener. This application does not particularly limit the types of binders and thickeners, as long as they achieve the purpose of this application. For example, the binder may include, but is not limited to, at least one of styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl butyral (PVB), waterborne acrylic resin, or carboxymethyl cellulose (CMC). The thickener may include, but is not limited to, at least one of carboxymethyl cellulose (CMC), sodium carboxymethyl cellulose, or lithium carboxymethyl cellulose. The negative electrode active material layer may also include a conductive agent. This application does not particularly limit the types of conductive agents, as long as they achieve the purpose of this application. For example, the conductive agent may include, but is not limited to, at least one of conductive carbon black, sheet graphite, graphene, carbon nanotubes, carbon fibers, or carbon nanowires.

[0076] This application does not impose any particular limitation on the mass ratio of negative electrode active material, binder, and thickener in the negative electrode active material layer. Those skilled in the art can choose according to actual needs, as long as the purpose of this application can be achieved. For example, the mass ratio of negative electrode active material, binder, and thickener in the negative electrode active material layer can be (93 to 97):(1 to 3):(2 to 5).

[0077] The electrochemical device also includes a housing for accommodating the positive electrode, separator, negative electrode, and electrolyte, as well as other components known in the field of electrochemical devices. This application does not limit the scope of these other components. This application does not impose any particular limitation on the housing; it can be a housing known in the art, as long as it achieves the purpose of this application. For example, the housing can be a rigid housing or a flexible housing. The material of the rigid housing can be metal; this application does not limit the type of metal and can use known metal rigid housings, as long as they achieve the purpose of this application. The flexible housing can be a metal-plastic film, such as aluminum-plastic film, steel-plastic film, etc.

[0078] The preparation process of the electrochemical device described in this application is well known to those skilled in the art, and this application does not impose any particular limitations. For example, the preparation process of the electrochemical device may include, but is not limited to, the following steps: stacking the positive electrode, the separator, and the negative electrode in sequence, and performing operations such as winding and folding as needed to obtain a wound electrode assembly; placing the electrode assembly into a housing; injecting electrolyte into the housing and sealing it to obtain the electrochemical device. Alternatively, stacking the positive electrode, the separator, and the negative electrode in sequence, and then fixing the four corners of the entire stacked structure with tape to obtain a stacked electrode assembly; placing the electrode assembly into a housing; injecting electrolyte into the housing and sealing it to obtain the electrochemical device. In addition, overcurrent protection elements, conductive plates, etc., may be placed in the housing as needed to prevent pressure rise and overcharging / discharging inside the electrochemical device.

[0079] A second aspect of this application provides an electronic device, which includes the electrochemical device in any of the foregoing embodiments.

[0080] The electronic device described in this application is not particularly limited and can be any electronic device known in the prior art. In some embodiments, the electronic device may include, but is not limited to, laptops, pen-based computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors, etc.

[0081] Example

[0082] The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below. Furthermore, unless otherwise specified, "parts" and "%" are quality standards.

[0083] Test methods and equipment:

[0084] M element content test

[0085] After discharging the lithium-ion battery to 3V at 0.2C, the positive electrode was removed. The positive electrode was cut into 10 small discs with a diameter of 16mm. The positive active material layer was scraped off from the current collector of each disc using a knife, yielding powder. 0.2g of the powder was weighed and digested with 10mL of aqua regia. The solution was then diluted to a volumetric flask with deionized water. An inductively coupled plasma analyzer (ICP, model AVIO-200) was used, with the RF generator frequency set to 40.68MHz, the argon secondary pressure to 0.6MPa, the RF power to 1400W, and the pump speed to 1.0mL / min. The content of each element in the positive active material layer of each disc was measured. The average content of each element from the 10 discs was taken to obtain the mass percentage of element M in the positive active material layer. The aqua regia was obtained by mixing concentrated nitric acid and concentrated hydrochloric acid in a 1:1 volume ratio.

[0086] Electrolyte composition testing

[0087] The lithium-ion battery was discharged to 3V at 0.2C and then disassembled to obtain positive and negative electrode plates. These plates were then centrifuged in centrifuge tubes to obtain the electrolyte. The mass percentage of each substance (e.g., compound of formula I, lithium difluorophosphate, sulfonate compounds, fluoroethylene carbonate, vinylene carbonate, and lithium dioxalate borate) in the electrolyte was determined using gas chromatography-mass spectrometry (GC-MS).

[0088] High-temperature cycling performance test

[0089] At 60℃, a lithium-ion battery is charged at a constant current of 1C to 4.4V, then charged at a constant voltage of 4.4V to 0.05C, and finally discharged at a constant current of 4C to 3V. This constitutes one charge-discharge cycle. This cycle is repeated 500 times. The discharge capacity after one cycle is recorded as the initial discharge capacity C0, and the discharge capacity after 500 cycles is recorded as C1. The cycle capacity retention rate after 500 cycles at 60℃ characterizes the high-temperature cycle performance of the lithium-ion battery. A higher cycle capacity retention rate after 500 cycles at 60℃ indicates better high-temperature cycle performance. Cycle capacity retention rate (%) = C1 / C0 × 100%.

[0090] High-temperature storage performance test

[0091] Take the lithium-ion battery to be tested, charge it at a constant current of 0.5C to 3.75V, and then charge it at a constant voltage of 3.75V to 0.05C. Measure the original thickness d0 of the lithium-ion battery at this point using a micrometer. At 25℃, charge the lithium-ion battery at a constant current of 0.5C to 4.4V, and then charge it at a constant voltage of 0.05C at 4.4V. The lithium-ion battery is in a fully charged state. Place the lithium-ion battery in a 60℃ constant temperature chamber for high-temperature storage for 15 days. Then measure the thickness d1 of the lithium-ion battery after storage using a micrometer. The thickness expansion rate of the lithium-ion battery after 15 days of storage at 60℃ characterizes the high-temperature storage performance of the lithium-ion battery. The smaller the thickness expansion rate of the lithium-ion battery after 15 days of storage at 60℃, the better the high-temperature storage performance of the lithium-ion battery. Thickness expansion rate (%) = (d1-d0) / d0 × 100%.

[0092] Cyclic impedance growth rate test

[0093] The lithium-ion battery was placed in a 25°C constant temperature chamber and left to stand for 1 hour to allow it to reach a constant temperature. The lithium-ion battery was then charged at a constant current of 1C to 4.4V, followed by a constant voltage charge at 4.4V to a current of 0.05C. After standing for 30 minutes, it was discharged at a constant current of 0.1C for 10 seconds, and then at a constant current of 1C for 360 seconds. At this point, the lithium-ion battery was at 80% state of charge (SOC). The DC impedance D0 of the lithium-ion battery at 80% SOC was then calculated. Following the charge-discharge cycle process in the high-temperature cycle performance test described above, the lithium-ion battery was subjected to 500 charge-discharge cycles. The DC impedance D1 of the lithium-ion battery at 80% SOC after 500 cycles was then measured and calculated using the same method. The DC impedance of the lithium-ion battery was calculated using the following formula: DC impedance = (0.1C discharge termination voltage - 1C discharge termination voltage) / (0.1C discharge termination current - 1C discharge termination current).

[0094] The cycle impedance growth rate of a lithium-ion battery can be calculated using the following formula: Cycle impedance growth rate (%) = (DC impedance D1 of the lithium-ion battery after 500 cycles - DC impedance D0 of the lithium-ion battery before cycling) / DC impedance D0 of the lithium-ion battery before cycling × 100%.

[0095] Example 1-1

[0096] <Preparation of Positive Electrode Active Materials>

[0097] LiNi metal precursor 0.6 Co 0.1 Mn 0.3 O2 particles were placed in the deposition chamber of the atomic layer deposition system, and an aluminum source (a compound containing elemental Al) trimethylaluminum and an oxygen source water were introduced. At a deposition temperature of 200°C, the metal precursor LiNi was deposited. 0.6 Co 0.1 Mn 0.3 Aluminum is deposited on the surface of O2 to obtain lithium nickel cobalt manganese oxide transition metal oxide with Al on the surface, which is the positive electrode active material.

[0098] <Preparation of the positive electrode>

[0099] The positive electrode active material, conductive agent carbon nanotubes (CNTs), and binder polyvinylidene fluoride prepared above were mixed at a mass ratio of 95:2:3. N-methylpyrrolidone (NMP) was added as the positive electrode solvent, and the mixture was stirred under vacuum until a homogeneous positive electrode slurry with a solid content of 75 wt% was formed. The positive electrode slurry was uniformly coated onto one surface of a 10 μm thick aluminum foil current collector and dried at 120 °C to obtain a positive electrode sheet with a single-sided coating of positive electrode active material layer. The coating weight of the positive electrode active material layer was 267.8 mg / 1540 mm². 2The above steps are then repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coating of positive active material. After drying at 120℃, it is cold-pressed, then cut and welded with tabs to obtain a positive electrode sheet with dimensions of 74mm × 867mm for later use. The compaction density of the positive active material layer is 4.15 g / cm³. 3 Based on the total mass of the positive electrode active material layer, the mass percentage of Al element C is 1.5%.

[0100] <Preparation of Negative Electrode Sheets>

[0101] Artificial graphite, styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) were mixed at a mass ratio of 95:2:3. Deionized water was then added as the negative electrode solvent to prepare a slurry with a solid content of 70 wt%. The slurry was stirred evenly in a vacuum mixer to obtain the negative electrode slurry. The negative electrode slurry was uniformly coated onto one surface of a 6 μm thick copper foil used as a negative electrode current collector and dried at 120°C to obtain a negative electrode sheet with a single-sided coating of the negative electrode active material layer. The coating weight of the negative electrode active material layer was 142 mg / 1540 mm². 2 The above steps are then repeated on the other surface of the copper foil to obtain a negative electrode sheet with a double-sided coating of negative electrode active material. After drying at 120℃ and cold pressing, the sheet is cut and tabs are welded to obtain a negative electrode sheet with dimensions of 78mm × 875mm for later use. The compaction density of the negative electrode active material layer is 1.74 g / cm³. 3 .

[0102] <Preparation of Electrolyte>

[0103] In an argon-atmospheric glove box with a water content of less than 10 ppm, ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) were uniformly mixed at a mass ratio of 10:30:60 to obtain a base solvent. Compound I-1, lithium difluorophosphate, and lithium salt LiPF6 were then added and stirred until homogeneous to obtain the electrolyte. Based on the total mass of the electrolyte, the mass percentage A of compound I-1 was 0.5%, the mass percentage B of lithium difluorophosphate was 0.8%, the mass percentage of lithium salt LiPF6 was 12.5%, and the remainder was the base solvent.

[0104] <Isolation membrane>

[0105] A 15μm thick porous polyethylene polymer film (manufacturer: Celgard Diaphragm Company, USA) was used as the separator.

[0106] <Preparation of Lithium-ion Batteries>

[0107] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide insulation. The electrode assembly is then wound to form an electrode assembly, which is placed in an aluminum-plastic film packaging bag and dehydrated at 80°C. A prepared electrolyte is then injected, followed by vacuum sealing, settling, formation, and shaping processes to obtain a lithium-ion battery. The formation temperature is 70°C, and the settling time is 2 hours.

[0108] Examples 1-2 to Examples 1-13

[0109] Except for the following in <Preparation of Electrolyte>: adjusting the type and mass percentage of compound I according to Table 1, the mass percentage of lithium difluorophosphate, and the mass percentage of the base solvent, while keeping the mass ratio of each component of the base solvent and the mass percentage of lithium salt unchanged, the rest is the same as in Example 1-1.

[0110] Examples 1-14 to Examples 1-17

[0111] Except for adjusting the relevant preparation parameters according to Table 1 and controlling the mass ratio of the compound containing element M and the metal precursor in the <Preparation of Positive Electrode Active Material> so that the mass percentage of element M in the positive electrode active material layer is as shown in Table 1, the rest is the same as in Example 1-1.

[0112] Examples 1-18

[0113] In addition to using LiNi in the <Preparation of Positive Electrode Active Materials> 0.33 Co 0.33 Mn 0.33 Except for O2 being used as a metal precursor, the rest is the same as in Example 1-1.

[0114] Examples 1-19

[0115] Except for the use of TiO2 as the compound containing element M in the <Preparation of Positive Electrode Active Material>, the rest is the same as in Example 1-1.

[0116] Examples 1-20

[0117] Except for the use of SiO2 as the compound containing element M in the <Preparation of Positive Electrode Active Material>, the rest is the same as in Example 1-1.

[0118] Examples 2-1 to 2-17

[0119] Except for the addition of at least one of the following in the <Preparation of Electrolyte> according to Table 2: sulfonate compound, fluoroethylene carbonate, vinylene carbonate, or lithium dioxalate borate, and the adjustment of the type and mass percentage of the sulfonate compound, the mass percentage of the fluoroethylene carbonate, the mass percentage of the vinylene carbonate, and the mass percentage of the lithium dioxalate borate, the mass percentage of the base solvent is changed accordingly, the mass ratio of each component of the base solvent remains unchanged, and the mass percentage of the lithium salt remains unchanged, the rest is the same as in Examples 1-1.

[0120] Comparative Example 1

[0121] Except that the compound of formula I is not added in the <Preparation of Electrolyte>, the mass percentage of the base solvent is changed accordingly, the mass ratio of each component of the base solvent remains unchanged, and the mass percentage of lithium salt remains unchanged, the rest is the same as in Example 1-1.

[0122] Comparative Example 2

[0123] Except that lithium difluorophosphate is not added in the <Preparation of Electrolyte>, the mass percentage of the base solvent is changed accordingly, the mass ratio of each component of the base solvent remains unchanged, and the mass percentage of lithium salt remains unchanged, the rest is the same as in Example 1-1.

[0124] Comparative Example 3

[0125] Except for adjusting the mass percentages of compound I and lithium difluorophosphate according to Table 1 in the <Preparation of Electrolyte>, changing the mass percentage of the base solvent accordingly, keeping the mass ratios of the components of the base solvent unchanged, and keeping the mass percentage of the lithium salt unchanged, everything else is the same as in Example 1-1.

[0126] Comparative Example 4

[0127] In addition to using the metallic precursor LiNi in the <Preparation of Positive Electrode> 0.6 Co 0.1 Mn 0.3 Except for O2 being used as the positive electrode active material, everything else is the same as in Example 1-1.

[0128] The preparation parameters and performance parameters of each embodiment and comparative example are shown in Tables 1 and 2.

[0129] Table 1

[0130]

[0131]

[0132] Note: " / " in Table 1 indicates that the corresponding preparation parameters or substances do not exist.

[0133] As can be seen from Examples 1-1 to 1-20 and Comparative Examples 1 to 4, the electrolyte contains a compound of Formula I and lithium difluorophosphate, and the positive electrode active material layer of the positive electrode sheet includes lithium nickel cobalt manganese oxide transition metal oxide. When the above electrolyte and positive electrode sheet are combined and applied to a lithium-ion battery, when the mass percentage content A of the compound of Formula I and the mass percentage content B of lithium difluorophosphate satisfy 0.005≤A / B≤500 and 0.01%<A+B≤7%, the lithium-ion battery exhibits a high cycle capacity retention rate, a low thickness expansion rate, and a low cycle impedance growth rate, indicating that the high-temperature cycle performance and high-temperature storage performance of the lithium-ion battery are improved. In Comparative Examples 1 to 4, the electrolyte does not contain a compound of Formula I or lithium difluorophosphate, or the value of A+B is outside the scope of this application, or the metal precursor LiNi is used. 0.6 Co 0.1 Mn 0.3 Using O2 as the positive electrode active material, the resulting lithium-ion battery exhibits low cycle capacity retention, high thickness expansion rate, and high cycle impedance growth rate, indicating that the lithium-ion battery has poor high-temperature cycle performance and high-temperature storage performance, while possessing a high cycle impedance growth rate.

[0134] As can be seen from Examples 1-1 to 1-13, when the type and mass percentage of compound I, the mass percentage of lithium difluorophosphate, the value of A / B, and the value of A+B are within the scope of this application, the lithium-ion battery has a high cycle capacity retention rate, a low thickness expansion rate, and a low cycle impedance growth rate. This indicates that the high-temperature cycle performance and high-temperature storage performance of the lithium-ion battery are improved while having a low cycle impedance growth rate.

[0135] As can be seen from Examples 1-1, 1-14 to 1-17, when the ratio C / A of the mass percentage content of element M to the mass percentage content of compound I is within the scope of this application, the lithium-ion battery has a high cycle capacity retention rate and a low thickness expansion rate and cycle impedance growth rate, indicating that the high-temperature cycle performance and high-temperature storage performance of the lithium-ion battery are improved while having a low cycle impedance growth rate.

[0136] As can be seen from Examples 1-1, 1-18 to 1-20, when the types of element M and lithium nickel cobalt manganese oxide transition metal oxides are within the scope of this application, the lithium-ion battery has a high cycle capacity retention rate, a low thickness expansion rate and a low cycle impedance growth rate, indicating that the high-temperature cycle performance and high-temperature storage performance of the lithium-ion battery are improved while having a low cycle impedance growth rate.

[0137] Table 2

[0138]

[0139] Note: " / " in Table 2 indicates that the corresponding preparation parameters or substances do not exist.

[0140] The type and mass percentage of sulfonate compounds typically affect the high-temperature cycle performance, high-temperature storage performance, and cycle impedance growth rate of lithium-ion batteries. As can be seen from Examples 2-1 to 2-4, when the type and mass percentage of sulfonate compounds are within the range of this application, the lithium-ion battery exhibits higher cycle capacity retention, lower thickness expansion rate, and lower cycle impedance growth rate, indicating that the high-temperature cycle performance and high-temperature storage performance of the lithium-ion battery are improved while maintaining a lower cycle impedance growth rate.

[0141] The mass percentage of FEC typically affects the high-temperature cycling performance, high-temperature storage performance, and cycle impedance growth rate of lithium-ion batteries. As can be seen from Examples 2-5 to 2-7, when the mass percentage of FEC is within the range specified in this application, the lithium-ion battery exhibits higher cycle capacity retention, lower thickness expansion rate, and lower cycle impedance growth rate, indicating that the high-temperature cycling performance and high-temperature storage performance of the lithium-ion battery are improved while maintaining a lower cycle impedance growth rate.

[0142] The mass percentage of VC typically affects the high-temperature cycle performance, high-temperature storage performance, and cycle impedance growth rate of lithium-ion batteries. As can be seen from Examples 2-8 to 2-10, when the mass percentage of VC is within the range of this application, the lithium-ion battery exhibits higher cycle capacity retention, lower thickness expansion rate, and lower cycle impedance growth rate, indicating that the high-temperature cycle performance and high-temperature storage performance of the lithium-ion battery are improved while maintaining a lower cycle impedance growth rate.

[0143] The mass percentage of LiBOB typically affects the high-temperature cycling performance, high-temperature storage performance, and cycle impedance growth rate of lithium-ion batteries. As can be seen from Examples 2-11 to 2-13, when the mass percentage of LiBOB is within the range specified in this application, the lithium-ion battery exhibits higher cycle capacity retention, lower thickness expansion rate, and lower cycle impedance growth rate. This indicates that the high-temperature cycling performance and high-temperature storage performance of the lithium-ion battery are improved while maintaining a lower cycle impedance growth rate.

[0144] As can be seen from Examples 2-14 to 2-17, when the electrolyte includes at least two of sulfonate compounds, FEC, VC, or LiBOB, the cycle capacity retention rate of the lithium-ion battery is further improved, and the thickness expansion rate and cycle impedance growth rate are further reduced. This indicates that the lithium-ion battery has good high-temperature cycle performance and high-temperature storage performance while having a low cycle impedance growth rate.

[0145] The terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, or article that comprises a list of elements includes not only those elements but also other elements not expressly listed or inherent to such process, method, or article.

[0146] The various embodiments in this specification are described in a related manner. For the same or similar parts between the various embodiments, please refer to each other. Each embodiment focuses on describing the differences from other embodiments.

[0147] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. An electrochemical device comprising an electrolyte and a positive electrode, the electrolyte comprising at least one of a compound of formula I and lithium difluorophosphate, wherein, based on the total mass of the electrolyte, the mass percentage A of the compound of formula I is 0.01% to 5%, the mass percentage B of the lithium difluorophosphate is 0.01% to 2%, 0.005 ≤ A / B ≤ 500, and 0.01% < A + B ≤ 7%; in, R1, R2, R3, and R4 are each independently selected from an oxygen atom or a methylene group, and at least one of R1, R2, R3, or R4 is selected from an oxygen atom; X1 and X2 are each independently selected from C-R5 or C2 to C5. 10 The alkenyl group; R5 is selected from hydrogen atoms, C1 to C2. 10 Alkyl, C2 to C 10 alkenyl, C6 to C 12 aryl, C3 to C 10 Cycloalkane group, C3 to C 10 Cycloolefinic groups or C3 to C 10 The aromatic heterocyclic group, wherein the heteroelement in the aromatic heterocyclic group includes at least one of O, S, N, B, P or Si; The positive electrode includes a positive active material layer, which comprises a lithium nickel cobalt manganese oxide transition metal oxide. At least a portion of the surface of the lithium nickel cobalt manganese oxide transition metal oxide includes element M, which includes at least one of Al, Mg, Ti, Zn, Ge, Zr, W, or Si. Based on the total mass of the positive active material layer, the mass percentage C of element M is 0.01% to 5%, and 0.002 ≤ C / A ≤ 500.

2. The electrochemical device according to claim 1, wherein, The compound of formula I includes at least one of the following compounds:

3. The electrochemical device according to claim 1, wherein, The electrochemical device satisfies at least one of the following characteristics: (1) Based on the total mass of the electrolyte, the mass percentage A of the compound of formula I is 0.1% to 2%, and the mass percentage B of the lithium difluorophosphate is 0.1% to 1%; (2) Based on the total mass of the positive electrode active material layer, the mass percentage C of element M is 0.05% to 3%; (3) Based on the total mass of the positive electrode active material layer, the mass percentage of element M is C, and 0.025≤C / A≤300.

4. The electrochemical device according to claim 1, wherein, The electrolyte comprises a sulfonate compound, which includes at least one selected from 1,3-propanesulfonate lactone, 3-fluoro-1,3-propanesulfonate lactone, 1,4-butanesulfonate lactone, 1,3-propenesulfonate lactone, or methanedisulfonate methylene ester; the sulfonate compound comprises 0.1% to 5% by mass based on the total mass of the electrolyte.

5. The electrochemical device according to claim 1, wherein, The electrolyte also includes at least one of fluoroethylene carbonate, vinylene carbonate, or lithium dioxalate borate.

6. The electrochemical device according to claim 5, wherein, The electrolyte satisfies at least one of the following characteristics: (1) The electrolyte also includes fluoroethylene carbonate, and the mass percentage of fluoroethylene carbonate is 0.5% to 10% based on the total mass of the electrolyte; (2) The electrolyte further includes vinylene carbonate, and the mass percentage of vinylene carbonate is 0.01% to 5% based on the total mass of the electrolyte; (3) The electrolyte also includes lithium dioxalate borate, and the mass percentage of lithium dioxalate borate is 0.01% to 5% based on the total mass of the electrolyte.

7. An electronic device comprising the electrochemical device according to any one of claims 1 to 6.

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