An electrolyte, an electrochemical device comprising the electrolyte, and an electronic device

Abstract

The application provides an electrolyte, an electrochemical device containing the electrolyte and an electronic device. The electrolyte comprises ethylene carbonate, propylene carbonate and fluoroethylene carbonate. The mass percentage of ethylene carbonate is a, 1.0% <= a <= 20%, the mass percentage of propylene carbonate is b, 12% <= b <= 35%, based on the mass of the electrolyte. The electrolyte further comprises an additive B. The additive B comprises at least one of butanedinitrile, hexanedinitrile, 1,4-dicyano-2-butene, ethylene glycol dicyan ether, 1,3,6-hexanetrimethylnitrile or 1,2,3-tris(2-cyanooxy)propane. The mass percentage of the additive B is 0.5% to 4%, based on the mass of the electrolyte. The electrochemical device with the electrolyte has good high-temperature storage performance and cycle performance.

Description

[0001] This invention is a divisional application of application number 202111087759.4, filed on September 16, 2021, entitled "An electrolyte, an electrochemical device comprising the electrolyte and an electronic device". Technical Field

[0002] This application relates to the field of electrochemical technology, and in particular to an electrolyte, an electrochemical device comprising the electrolyte, and an electronic device. Background Technology

[0003] Lithium-ion batteries possess advantages such as high energy density, high open-circuit voltage, low self-discharge rate, long cycle life, and good safety, and are widely used in portable energy storage, electronic devices, electric vehicles, and other fields. However, this also places higher demands on the overall performance of lithium-ion batteries, such as simultaneously possessing high energy density, good high-temperature storage performance, and good cycle performance. However, high energy density is accompanied by a decline in high-temperature storage performance and cycle performance.

[0004] In related technologies, electrolyte additives are often used to improve the high-temperature storage performance and cycle performance of lithium-ion batteries. However, most additives improve high-temperature storage by forming a film on the positive electrode, but often their high viscosity or high film impedance severely degrades the low-temperature discharge performance and cycle performance of lithium-ion batteries. Conversely, some additives with low film impedance can easily worsen the high-temperature storage performance of lithium-ion batteries. Therefore, there is an urgent need to develop electrolytes that can effectively improve the high-temperature storage performance of lithium-ion batteries. Summary of the Invention

[0005] The purpose of this application is to provide an electrolyte, an electrochemical device containing the electrolyte, and an electronic device to improve the high-temperature storage performance of the electrochemical device.

[0006] The first aspect of this application provides an electrolyte comprising ethylene carbonate, propylene carbonate, and fluoroethylene carbonate. Based on the mass of the electrolyte, the mass percentage of ethylene carbonate is 'a', the mass percentage of propylene carbonate is 12% to 35% (b), and the mass percentage of fluoroethylene carbonate is 0.2% to 2.5% (c), satisfying 0.1 ≤ a / b ≤ 0.75. Without being limited to any theory, by adjusting the mass percentage of propylene carbonate (b) to 12% to 35%, the mass percentage of fluoroethylene carbonate (c) to 0.2% to 2.5%, and the mass ratio of ethylene carbonate to propylene carbonate (a / b) to 0.1 to 0.75, it is beneficial to improve the high-temperature storage performance and cycle performance of the electrochemical device.

[0007] In one embodiment of this application, 1.0% ≤ a ≤ 20%. By controlling the mass percentage 'a' of ethylene carbonate within the above range, it is beneficial to improve the cycle performance and capacity retention of the electrochemical device and reduce its volume expansion rate. In another embodiment of this application, the electrolyte may further include chain carbonates. Based on the mass of the electrolyte, the mass percentage of the chain carbonates is 'd'. The chain carbonates include at least one of dimethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, methyl butyl carbonate, diethyl carbonate, dipropyl carbonate, or dibutyl carbonate. The electrolyte satisfies 0.04 ≤ a / d ≤ 0.35. By controlling the value of a / d within the above range, it is beneficial for ethylene carbonate and chain carbonates to produce a synergistic effect, improving the cycle performance and high-temperature storage performance of the electrochemical device under high voltage.

[0008] In one embodiment of this application, 30% ≤ d ≤ 60%. By controlling the mass percentage content of the chain carbonate within the above range, it is beneficial to improve the overall performance of the electrochemical device under high voltage, such as cycle performance and rate performance.

[0009] In one embodiment of this application, the electrolyte may further include a sulfonyl lactone compound, which includes at least one of 1,3-propanesulfonyl lactone, 2,4-butanesulfonyl lactone, or 1,4-butanesulfonyl lactone, wherein the mass percentage e of the sulfonyl lactone compound is 0.5% to 5% based on the mass of the electrolyte.

[0010] In one embodiment of this application, c ≤ e. By controlling the mass percentage content of the sulfonyl lactone compound within the above range and greater than the mass percentage content of fluoroethylene carbonate, it is beneficial to improve the cycle performance and high-temperature storage performance of the electrochemical device and reduce the amount of gas generated during circulation. In this application, the positive electrode can refer to a positive electrode sheet, and the negative electrode can refer to a negative electrode sheet.

[0011] In one embodiment of this application, the electrolyte may further include additive A, which includes at least one of vinylene carbonate, vinyl ethylene carbonate, ethylene sulfate, lithium difluorophosphate, or lithium boron salt. Without being limited to any particular theory, selecting additive A can improve the cycling performance, high-temperature storage performance, and safety performance of the electrochemical device under high voltage.

[0012] In one embodiment of this application, the electrolyte satisfies at least one of the following relationships: (a) Additive A comprises vinylene carbonate, and the mass percentage A1 of vinylene carbonate is 0.01% to 2% based on the mass of the electrolyte; (b) Additive A comprises ethylene sulfate, and the mass percentage A2 of ethylene sulfate is 0.01% to 2% based on the mass of the electrolyte; (c) Additive A comprises a lithium boron salt, wherein the lithium boron salt comprises at least one of lithium tetrafluoroborate, lithium difluorooxalate borate, or lithium dioxalate borate, and the mass percentage A3 of the lithium boron salt is 0.01% to 2% based on the mass of the electrolyte; (d) The electrolyte comprises vinylene carbonate and ethylene sulfate, wherein the mass percentage of vinylene carbonate is A1 based on the mass of the electrolyte, and the mass percentage of ethylene sulfate is A2. (e) The electrolyte contains vinylene carbonate and ethylene sulfate. Based on the mass of the electrolyte, the mass percentage of vinylene carbonate is A1 and the mass percentage of ethylene sulfate is A2, satisfying 0.1 ≤ A2 / A1 ≤ 12; (f) The electrolyte contains vinylene carbonate and lithium boron salt. Based on the mass of the electrolyte, the mass percentage of vinylene carbonate is A1 and the mass percentage of lithium boron salt is A3, satisfying 0.01 ≤ A1 + A3 ≤ 3%; (g) The electrolyte contains vinylene carbonate and lithium boron salt. Based on the mass of the electrolyte, the mass percentage of vinylene carbonate is A1 and the mass percentage of lithium boron salt is A3, satisfying 0.1 ≤ A1 / A3 ≤ 10. If the electrolyte satisfies at least one of the above relationships, it is beneficial to form a more stable solid electrolyte interphase (SEI) film and positive electrode electrolyte interphase (CEI) film under high voltage, so that the substances form a good synergistic effect, thereby improving the high-temperature storage performance and cycle performance of the electrochemical device.

[0013] In one embodiment of this application, additive A may include vinylene carbonate, and the mass percentage of vinylene carbonate A1 is 0.01% to 2% based on the mass of the electrolyte.

[0014] In one embodiment of this application, additive A may include ethylene sulfate, and the mass percentage of ethylene sulfate A2 is 0.01% to 2% based on the mass of the electrolyte.

[0015] In one embodiment of this application, additive A may include vinylene carbonate and ethylene sulfate, satisfying 0.1 < A2 / A1 ≤ 12 and / or 0.02% ≤ A1 + A2 ≤ 3%. By controlling the mass percentage of ethylene sulfate within the above range, and satisfying 0.1 < A2 / A1 ≤ 12 and / or 0.02% ≤ A1 + A2 ≤ 3%, SEI and CEI with strong stability under high voltage can be formed, and they can form a good synergistic effect with ethylene carbonate and propylene carbonate, thereby improving the high-temperature storage performance and cycle performance of the electrochemical device.

[0016] In one embodiment of this application, additive A may include a lithium boron salt, which includes at least one of lithium tetrafluoroborate, lithium difluorooxalate borate, and lithium dioxalate borate. The mass percentage of the lithium boron salt A3 is 0.01% to 2% based on the mass of the electrolyte.

[0017] In one embodiment of this application, additive A may include vinylene carbonate and lithium boron salt satisfying 0.01% ≤ A1 + A3 ≤ 3% and / or 0.1 ≤ A1 / A3 ≤ 10. When the above-mentioned lithium boron salt is selected and its mass percentage content is controlled within the above range, while simultaneously satisfying 0.01% ≤ A1 + A3 ≤ 3% and / or 0.1 ≤ A1 / A3 ≤ 10, a solid electrolyte interface (SEI) and positive electrode electrolyte interface (CEI) with strong stability under high voltage can be formed, and a good synergistic effect can be formed with ethylene carbonate and propylene carbonate, thereby improving the high-temperature storage performance and cycle performance of the electrochemical device.

[0018] In one embodiment of this application, the electrolyte may further include additive B, wherein the mass percentage of additive B is 0.5% to 4% based on the mass of the electrolyte. Additive B includes succinic acid, adiponitrile, heptanonitrile, octanoic acid, 1,4-dicyano-2-butene, 1,4-dicyano-2-methyl-2-butene, 1,4-dicyano-2-ethyl-2-butene, 1,4-dicyano-2,3-dimethyl-2-butene, 1,4-dicyano-2,3-diethyl-2-butene, etc. The additive B comprises at least one of 1,6-dicyano-3-hexene, 1,6-dicyano-2-methyl-3-hexene, 1,6-dicyano-2-methyl-5-methyl-3-hexene, ethylene glycol diethyl cyanide, 1,3,6-hexanetricarbonitrile, or 1,2,3-tris(2-cyanoxy)propane. Preferably, additive B comprises at least one of butadionitrile, adiponitrile, 1,4-dicyano-2-butene, ethylene glycol diethyl cyanide, 1,3,6-hexanetricarbonitrile, or 1,2,3-tris(2-cyanoxy)propane. By controlling the mass percentage content of additive B within the above range, it is beneficial to improve the high-temperature storage performance and cycle performance of the electrochemical device and control production costs. Selecting additive B further improves the high-temperature storage performance and cycle performance of the electrochemical device.

[0019] In one embodiment of this application, the electrolyte comprises a sulfonyl lactone compound, lithium difluorophosphate, lithium tetrafluoroborate, and 1,3,6-hexanetricarbonyl nitrile.

[0020] In one embodiment of this application, the electrolyte comprises a sulfonyl lactone compound, lithium difluorophosphate, lithium dioxalatoborate, and 1,3,6-hexanetricarbonyl nitrile.

[0021] In one embodiment of this application, the electrolyte comprises a sulfonyl lactone compound, lithium difluorophosphate, vinyl sulfate, and 1,3,6-hexanetricarbonyl nitrile.

[0022] In one embodiment of this application, the electrolyte comprises ethylene carbonate, propylene carbonate, fluoroethylene carbonate, 1,3-propane sulpholactone, and vinylene carbonate, satisfying c ≥ 2A1 and c + 2A1 ≤ 2.5. When the electrolyte comprises the above components and the mass percentages of fluoroethylene carbonate and vinylene carbonate are controlled within the above ranges, the composition of the protective film formed on the surfaces of the positive and negative electrodes can be diversified, resulting in a stable protective film with a thickness within a suitable range. This is beneficial for further improving the high-temperature storage performance and cycle performance of the electrochemical device.

[0023] In one embodiment of this application, the electrolyte may further comprise a compound of formula (I), wherein the mass percentage of compound (I) is 0.01% to 2% (g) based on the mass of the electrolyte.

[0024]

[0025] Wherein, R is selected from unsubstituted or Ra-substituted C1 to C8 fluoroalkyl groups, unsubstituted or Ra-substituted C2 to C8 fluoroalkyl groups. 10 Fluoroalkenyl, unsubstituted or Ra-substituted C6 to C 10 Fluorinated aryl groups;

[0026] Each substituent Ra of each group independently includes at least one of cyano, carboxyl, or sulfate groups.

[0027] For example, the compound of formula (I) includes any one of the following structural compounds I-1 to I-9. In one embodiment of this application, the electrolyte may further include at least one of the following structural compounds I-1 to I-9:

[0028]

[0029]

[0030] A second aspect of this application provides an electrochemical device comprising a positive electrode, a negative electrode, a separator, and an electrolyte as described in any of the foregoing embodiments.

[0031] In one embodiment of this application, the electrochemical device further includes a positive electrode sheet, which comprises a positive electrode material layer, the positive electrode material layer comprising a positive electrode active material, and the particle size of the positive electrode active material satisfying 0.4 μm ≤ D V 50≤20μm, 2μm≤D V 90≤40μm. By adjusting the Dv50 and Dv90 of the positive electrode active material within the above range, the positive electrode active material is less likely to undergo side reactions with the electrolyte, thereby improving the cycle performance and safety performance of the electrochemical device and reducing the amount of gas generated during the cycle.

[0032] In one embodiment of this application, the D of the positive electrode active material V 50 is fμm, and the electrochemical device satisfies at least one of conditions (i) to (iii): (i) 0.05 ≤ c / f×100 ≤ 1; (ii) The electrolyte includes sulfonyl lactone compounds, with the mass percentage of sulfonyl lactone compounds being e based on the mass of the electrolyte, and 0.08 ≤ e / f×100 ≤ 3; (iii) The electrolyte includes compounds of formula (I), with the mass percentage of compounds of formula (I) being g based on the mass of the electrolyte, and 0.02 ≤ g / f×100 ≤ 1. When the electrolyte includes sulfonyl lactone compounds, adjusting the value of e / f×100 within the above range is beneficial to improving the cycle performance and high-temperature storage performance of the electrochemical device. When the electrolyte includes compounds of formula (I), adjusting the value of g / f×100 within the above range is beneficial to improving the high-temperature storage performance, cycle performance, and safety performance of the electrochemical device.

[0033] In one embodiment of this application, the positive electrode active material includes element M, which includes at least one of Al, Mg, Ti, Cr, B, Fe, Zr, Y, Na, W, F, or S. Based on the mass of the metal elements other than lithium in the positive electrode active material, the mass percentage of element M is less than or equal to 0.5%. By controlling the mass percentage of element M within the aforementioned range, it is beneficial to improve the cycle performance, capacity retention, and safety performance of the electrochemical device. Selecting element M within the aforementioned range is beneficial to improving the cycle performance and high-temperature storage performance of the electrochemical device.

[0034] In one embodiment of this application, the positive electrode active material includes a lithium-nickel transition metal oxide.

[0035] In one embodiment of this application, the charging cutoff voltage of the electrochemical device is greater than or equal to 4.2V.

[0036] This application provides an electrolyte, an electrochemical device comprising the electrolyte, and an electronic device. The electrolyte comprises ethylene carbonate, propylene carbonate, and fluoroethylene carbonate. Based on the mass of the electrolyte, the mass percentage of ethylene carbonate is 'a', the mass percentage of propylene carbonate is 12% to 35% (b), and the mass percentage of fluoroethylene carbonate is 0.2% to 2.5% (c), satisfying 0.1 ≤ a / b ≤ 0.75. By controlling the mass percentage of propylene carbonate to 12% to 35%, the mass percentage of fluoroethylene carbonate to 0.2% to 2.5%, and the ratio of ethylene carbonate to propylene carbonate to 0.1 to 0.75, it is beneficial to improve the high-temperature storage performance and cycle performance of the electrochemical device.

[0037] This application also provides an electronic device comprising any of the electrochemical devices described in this application.

[0038] Additional aspects and advantages of the embodiments of this application will be described, shown, or illustrated in part by way of implementation of the embodiments of this application in the following description. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided with reference to the embodiments. Obviously, the described embodiments are merely some embodiments of this application, and not all embodiments. All other technical solutions obtained by those skilled in the art based on the embodiments of this application are within the scope of protection of this application.

[0040] 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.

[0041] The purpose of this application is to provide an electrolyte, an electrochemical device containing the electrolyte, and an electronic device to improve the high-temperature storage performance of the electrochemical device.

[0042] The first aspect of this application provides an electrolyte comprising ethylene carbonate, propylene carbonate, and fluoroethylene carbonate. Based on the mass of the electrolyte, the mass percentage of ethylene carbonate is 'a', the mass percentage of propylene carbonate is 12% to 35% (b), and the mass percentage of fluoroethylene carbonate is 0.2% to 2.5% (c), satisfying 0.1 ≤ a / b ≤ 0.75. Without being limited to any theory, by adjusting the mass percentage of propylene carbonate (b) to 12% to 35%, the mass percentage of fluoroethylene carbonate (c) to 0.2% to 2.5%, and the mass ratio of ethylene carbonate to propylene carbonate (a / b) to 0.1 to 0.75, it is beneficial to improve the high-temperature storage performance and cycle performance of the electrochemical device.

[0043] For example, the mass percentage b of propylene carbonate can be 12%, 15%, 18%, 20%, 23%, 25%, 28%, 30%, 35%, or any range therein. When the mass percentage of propylene carbonate is too low (e.g., below 12%), the improvement in the kinetic performance of the electrochemical device is not significant. As the mass percentage of propylene carbonate increases, its high dielectric constant (69c / vm) is beneficial for improving the kinetic performance of the electrochemical device. When the mass percentage of propylene carbonate is too high (e.g., above 35%), the content of other components decreases, affecting the cycle performance and high-temperature storage performance of the electrochemical device. By controlling the mass percentage of propylene carbonate within the above range, it is beneficial to improve the cycle performance and high-temperature storage performance of the electrochemical device.

[0044] For example, the value of a / b can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.75, or any range thereof. By adjusting the value of a / b within the above range, it is beneficial for ethylene carbonate and propylene carbonate to produce a synergistic effect, improve the oxidation resistance of the electrolyte, reduce the gas production during the cycle of the electrochemical device, and improve the cycle performance and high-temperature storage performance of the electrochemical device.

[0045] For example, the mass percentage c of fluoroethylene carbonate can be 0.2%, 0.5%, 0.8%, 1%, 1.4%, 1.8%, 2%, 2.5%, or any range therein. Without being limited to any theory, when the mass percentage of fluoroethylene carbonate is too low (e.g., below 0.2%), the improvement in the performance of the electrochemical device is not significant. Increasing the mass percentage of fluoroethylene carbonate is beneficial for improving the cycle performance and capacity retention of the electrochemical device. When the mass percentage of fluoroethylene carbonate is too high (e.g., above 2.5%), the residual amount of fluoroethylene carbonate after formation is relatively large, which easily leads to gas generation during high-voltage cycling and storage, increasing the expansion rate of the electrochemical device. Therefore, by controlling the mass percentage of fluoroethylene carbonate within the above range, it is beneficial to improve the capacity retention of the electrochemical device, as well as its cycle performance and high-temperature storage performance under high voltage. In this application, high voltage refers to a charging cut-off voltage greater than or equal to 4.2V.

[0046] In one embodiment of this application, 0.1 ≤ a / b ≤ 0.5, and the mass percentage c of fluoroethylene carbonate is 0.2% to 1.8%. Within this range, the electrolyte exhibits good overall antioxidant properties, and the residual amount of fluoroethylene carbonate ester after electrochemical device formation is within a suitable range, making the electrolyte more well-matched and providing better cycling performance under high voltage and high-temperature storage performance.

[0047] In one embodiment of this application, 1.0% ≤ a ≤ 20%. For example, the mass percentage 'a' of ethylene carbonate can be 1.0%, 2%, 5%, 8%, 10%, 12%, 15%, 18%, 20%, or any range thereof. Without being limited to any theory, when the mass percentage of ethylene carbonate is too low (e.g., below 1.0%), it cannot effectively suppress the side reactions between the negative electrode active material and the electrolyte, thus deteriorating the cycle performance and high-temperature storage performance of the electrochemical device. As the mass percentage of ethylene carbonate increases, it is beneficial for the formation of a stable solid electrolyte interphase (SEI) film at the negative electrode, thereby suppressing the reaction between the negative electrode active material and the electrolyte, and improving the cycle performance and capacity retention of the electrochemical device. When the mass percentage of ethylene carbonate is too high (e.g., greater than 20%), it can easily lead to severe gas expansion in the electrochemical device during cycling, storage, and float charging under high voltage, resulting in an increased volume expansion rate of the electrochemical device. By controlling the mass percentage of ethylene carbonate within the above range, it is beneficial to improve the cycle performance and capacity retention of the electrochemical device and reduce the volume expansion rate of the electrochemical device.

[0048] In one embodiment of this application, the electrolyte may further comprise chain carbonates, wherein the mass percentage of the chain carbonates is d based on the mass of the electrolyte, and the chain carbonates include at least one of dimethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, methyl butyl carbonate, diethyl carbonate, dipropyl carbonate, or dibutyl carbonate, and the electrolyte satisfies 0.04 ≤ a / d ≤ 0.35 and / or 30% ≤ d ≤ 60%.

[0049] For example, the value of a / d can be 0.04, 0.08, 0.1, 0.13, 0.17, 0.2, 0.23, 0.27, 0.3, 0.35, or any range thereof. Without being limited to any particular theory, adjusting the value of a / d within the above range is beneficial for synergistic effects between ethylene carbonate and chain carbonates, improving the cycling performance and high-temperature storage performance of the electrochemical device under high voltage.

[0050] For example, the mass percentage d of the chain carbonate can be 30%, 35%, 40%, 45%, 50%, 55%, 60%, or any range thereof. Without being limited to any theory, when the mass percentage of the chain carbonate is too low (e.g., below 30%), the improvement in the performance of the electrochemical device is not significant. As the mass percentage of the chain carbonate increases, its good chemical stability helps improve the overall performance of the electrochemical device at high voltages. When the mass percentage of the chain carbonate is too high (e.g., above 60%), the viscosity of the electrolyte increases sharply, affecting lithium-ion transport and deteriorating the kinetic performance of the electrochemical device. Therefore, controlling the mass percentage of the chain carbonate within the above range is beneficial for improving the overall performance of the electrochemical device at high voltages, such as cycle performance and rate performance.

[0051] In one embodiment of this application, the electrolyte may further comprise a sulfonyl lactone compound, including at least one of 1,3-propanesulfonyl lactone, 2,4-butanesulfonyl lactone, or 1,4-butanesulfonyl lactone. Based on the mass of the electrolyte, the mass percentage e of the sulfonyl lactone compound is 0.5% to 5%, and c ≤ e. For example, the mass percentage of the sulfonyl lactone compound is 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or any range thereto, and is greater than the mass percentage of fluoroethylene carbonate.

[0052] Regardless of any specific theory, when the mass percentage of sulfonyl lactone compounds is too low (e.g., below 0.5%), the performance improvement of the electrochemical device is not significant. As the mass percentage of sulfonyl lactone compounds increases, it facilitates the formation of a stable SEI film at the negative electrode to suppress side reactions between the electrolyte and the negative electrode active material. Simultaneously, it facilitates the formation of a stable positive electrode electrolyte interface (CEI) film at the positive electrode to suppress phase transitions, thereby improving the cycle performance, gas production, and high-temperature storage performance of the electrochemical device. When the mass percentage of sulfonyl lactone compounds is too high (e.g., above 5%), both the kinetic and cycle performance of the electrochemical device deteriorate. Furthermore, when the content of sulfonyl lactone compounds is less than that of fluoroethylene carbonate, a stable SEI film cannot be formed to suppress the oxidative decomposition of fluoroethylene carbonate at the negative electrode, thus affecting the high-temperature storage performance, cycle performance, and gas production of the electrochemical device. By controlling the mass percentage of sulfonyl lactone compounds within the above-mentioned range and exceeding the mass percentage of fluoroethylene carbonate, it is beneficial to improve the cycle performance and high-temperature storage performance of the electrochemical device and reduce the amount of gas produced during circulation. In this application, "positive electrode" can refer to a positive electrode plate, and "negative electrode" can refer to a negative electrode plate.

[0053] In one embodiment of this application, the electrolyte may further include additive A, which includes at least one of vinylene carbonate, vinyl ethylene carbonate, ethylene sulfate, lithium difluorophosphate, or lithium boron salt. Without being limited to any particular theory, selecting additive A can improve the cycling performance, high-temperature storage performance, and safety performance of the electrochemical device under high voltage.

[0054] In one embodiment of this application, the electrolyte satisfies at least one of the following relationships: (a) Additive A comprises vinylene carbonate, and the mass percentage A1 of vinylene carbonate is 0.01% to 2% based on the mass of the electrolyte; (b) Additive A comprises ethylene sulfate, and the mass percentage A2 of ethylene sulfate is 0.01% to 2% based on the mass of the electrolyte; (c) Additive A comprises a lithium boron salt, wherein the lithium boron salt comprises at least one of lithium tetrafluoroborate, lithium difluorooxalate borate, or lithium dioxalate borate, and the mass percentage A3 of the lithium boron salt is 0.01% to 2% based on the mass of the electrolyte; (d) The electrolyte comprises vinylene carbonate and ethylene sulfate, wherein the mass percentage of vinylene carbonate is A1 based on the mass of the electrolyte, and the mass percentage of ethylene sulfate is A2. (e) The electrolyte contains vinylene carbonate and ethylene sulfate. Based on the mass of the electrolyte, the mass percentage of vinylene carbonate is A1 and the mass percentage of ethylene sulfate is A2, satisfying 0.1 ≤ A2 / A1 ≤ 12; (f) The electrolyte contains vinylene carbonate and lithium boron salt. Based on the mass of the electrolyte, the mass percentage of vinylene carbonate is A1 and the mass percentage of lithium boron salt is A3, satisfying 0.01 ≤ A1 + A3 ≤ 3%; (g) The electrolyte contains vinylene carbonate and lithium boron salt. Based on the mass of the electrolyte, the mass percentage of vinylene carbonate is A1 and the mass percentage of lithium boron salt is A3, satisfying 0.1 ≤ A1 / A3 ≤ 10. If the electrolyte satisfies at least one of the above relationships, it is beneficial to form a more stable SEI film and CEI film under high voltage, so that the substances can form a good synergistic effect, thereby improving the high-temperature storage performance and cycle performance of the electrochemical device.

[0055] In one embodiment of this application, additive A may include vinylene carbonate, and the mass percentage A1 of vinylene carbonate, based on the mass of the electrolyte, is 0.01% to 2%. For example, the mass percentage A1 of vinylene carbonate can be 0.01%, 0.05%, 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, or any range therebetween. By controlling the mass percentage of vinylene carbonate within the above range, it is beneficial for the formation of a stable SEI film at the negative electrode to suppress side reactions between the electrolyte and the negative electrode active material, and for the formation of a stable CEI film at the positive electrode to suppress phase transitions at the positive electrode, thereby improving the cycle performance, gas generation, and high-temperature storage performance of the electrochemical device. Simultaneously, by controlling the mass percentage of vinylene carbonate within the above range, it is possible to reduce the impact on battery impedance caused by excessively thick protective films due to excessively high vinylene carbonate content, and the insufficient protection of the positive or negative electrode caused by excessively low vinylene carbonate content.

[0056] In one embodiment of this application, additive A may include ethylene sulfate, and the mass percentage of ethylene sulfate, A2, is 0.01% to 2% based on the mass of the electrolyte. For example, the mass percentage of ethylene sulfate, A2, may be 0.01%, 0.05%, 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, or any range thereto.

[0057] In one embodiment of this application, additive A may include vinylene carbonate and ethylene sulfate. Based on the mass of the electrolyte, the mass percentage of vinylene carbonate is A1, and the mass percentage of ethylene sulfate is A2. The electrolyte satisfies 0.1 < A2 / A1 ≤ 12 and / or 0.02% ≤ A1 + A2 ≤ 3%. For example, the value of A2 / A1 can be 0.1, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, or any range thereof. For example, the value of A1 + A2 can be 0.02%, 0.05%, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, or any range thereof.

[0058] By controlling the mass percentages of vinylene carbonate and ethylene sulfate within the above-mentioned ranges, and satisfying 0.1 < A2 / A1 ≤ 12 and / or 0.02% ≤ A1 + A2 ≤ 3%, SEI and CEI films with strong stability under high voltage can be formed, and they can form a good synergistic effect with ethylene carbonate and propylene carbonate, thereby improving the high-temperature storage performance and cycle performance of the electrochemical device.

[0059] In one embodiment of this application, additive A may include vinylene carbonate and a lithium boron salt, wherein the lithium boron salt includes at least one selected from lithium tetrafluoroborate, lithium difluorooxalate borate, and lithium dioxalate borate. Based on the mass of the electrolyte, the mass percentage A3 of the lithium boron salt is 0.01% to 2%, and the electrolyte satisfies 0.01% ≤ A1 + A3 ≤ 3% and / or 0.1 ≤ A1 / A3 ≤ 10. For example, the mass percentage A3 of the lithium boron salt may be 0.01%, 0.05%, 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, or any range thereof. For example, the value of A1 + A3 may be 0.01%, 0.05%, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, or any range thereof. For example, the value of A1 / A3 can be 0.1, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or any range thereof.

[0060] Without being limited to any theory, when the above-mentioned boron lithium salts are selected and their mass percentage content is controlled within the above range, while satisfying 0.01%≤A1+A3≤3% and / or 0.1≤A1 / A3≤10, SEI and CEI films with strong stability under high voltage can be formed, and they can form a good synergistic effect with ethylene carbonate and propylene carbonate, thereby improving the high-temperature storage performance and cycle performance of electrochemical devices.

[0061] In one embodiment of this application, the electrolyte may further include additive B, wherein the mass percentage of additive B is 0.5% to 4% based on the mass of the electrolyte. Additive B includes succinic acid, adiponitrile, heptanonitrile, octanoic acid, 1,4-dicyano-2-butene, 1,4-dicyano-2-methyl-2-butene, 1,4-dicyano-2-ethyl-2-butene, 1,4-dicyano-2,3-dimethyl-2-butene, 1,4-dicyano-2,3-diethyl-2-butene, etc. The additive B comprises at least one of 1,6-dicyano-3-hexene, 1,6-dicyano-2-methyl-3-hexene, 1,6-dicyano-2-methyl-5-methyl-3-hexene, ethylene glycol diethyl cyanide, 1,3,6-hexanetricarbonitrile, or 1,2,3-tris(2-cyanoxy)propane. Preferably, additive B comprises at least one of butadionitrile, adiponitrile, 1,4-dicyano-2-butene, ethylene glycol diethyl cyanide, 1,3,6-hexanetricarbonitrile, or 1,2,3-tris(2-cyanoxy)propane. For example, the mass percentage of additive B may be 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, or any range thereof.

[0062] Without being limited to any theory, when the mass percentage of additive B is too low (e.g., below 0.5%), its effect on improving the structural stability of the CEI film is not significant. When the mass percentage of additive B is within a suitable range, the synergistic effect of additive B complexing with the transition metal in the positive electrode active material is beneficial for forming a more stable CEI film, thereby suppressing side reactions at the positive electrode interface and improving the high-temperature storage performance and cycle performance of the electrochemical device. When the mass percentage of additive B is too high (e.g., above 4%), it does not further improve the performance of the electrochemical device, resulting in a waste of additive B and increased production costs. By controlling the mass percentage of additive B within the above-mentioned range, it is beneficial to improve the high-temperature storage performance and cycle performance of the electrochemical device and control production costs. Without being limited to any theory, selecting the above-mentioned additive B is beneficial for further improving the high-temperature storage performance and cycle performance of the electrochemical device.

[0063] In one embodiment of this application, the electrolyte comprises a sulfonyl lactone compound, lithium difluorophosphate, lithium tetrafluoroborate, and 1,3,6-hexanetricarbonyl nitrile.

[0064] In one embodiment of this application, the electrolyte comprises a sulfonyl lactone compound, lithium difluorophosphate, lithium dioxalatoborate, and 1,3,6-hexanetricarbonyl nitrile.

[0065] In one embodiment of this application, the electrolyte comprises a sulfonyl lactone compound, lithium difluorophosphate, vinyl sulfate, and 1,3,6-hexanetricarbonyl nitrile. When the electrolyte contains the above components, the sulfonyl lactone compound, lithium difluorophosphate, vinyl sulfate, and 1,3,6-hexanetricarbonyl nitrile compound work together to improve the stability of the SEI membrane and CEI membrane, which is beneficial for further improving the high-temperature storage performance and cycle performance of the electrochemical device.

[0066] In one embodiment of this application, the electrolyte comprises ethylene carbonate, propylene carbonate, fluoroethylene carbonate, 1,3-propane sulpholactone, and vinylene carbonate, satisfying c ≥ 2A1 and c + 2A1 ≤ 2.5%. For example, the value of c + 2A1 can be 0.22%, 0.5%, 0.75%, 1%, 1.25%, 1.5%, 1.75%, 2%, 2.25%, 2.5%, or any range thereof. When the electrolyte contains the above components and the mass percentage of fluoroethylene carbonate and vinylene carbonate is controlled within the above range, the composition of the SEI membrane and CEI membrane can be diversified, and the stability and thickness are within a suitable range, which is beneficial to further improve the high-temperature storage performance and cycle performance of the electrochemical device.

[0067] In one embodiment of this application, the electrolyte may further comprise a compound of formula (I), wherein the mass percentage of compound (I) is 0.01% to 2% (g) based on the mass of the electrolyte.

[0068]

[0069] Wherein, R is selected from unsubstituted or Ra-substituted C1 to C8 fluoroalkyl groups, unsubstituted or Ra-substituted C2 to C8 fluoroalkenyl groups, and unsubstituted or Ra-substituted C6 to C8 fluoroalkyl groups. 10 Fluorinated aryl groups;

[0070] Each substituent Ra of each group independently includes at least one of cyano, carboxyl, or sulfate groups.

[0071] For example, the compound of formula (I) includes any one of the following structural compounds I-1 to I-9. In one embodiment of this application, the electrolyte may further include at least one of the following structural compounds I-1 to I-9:

[0072]

[0073] For example, the mass percentage g of compound (I) can be 0.01%, 0.05%, 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, or any range thereof. Without being limited to any theory, by controlling the mass percentage of compound (I) within the above range, due to its strong high-voltage stability and antioxidant properties, it is beneficial for the formation of a stable SEI film at the negative electrode to suppress side reactions between the electrolyte and the negative electrode active material, and also beneficial for the formation of a stable CEI film at the positive electrode to suppress phase transitions. Furthermore, it can continuously repair the SEI and CEI films during the cycling process of the electrochemical device, thereby improving the high-temperature storage performance, cycling performance, and safety performance of the electrochemical device under high voltage.

[0074] In one embodiment of this application, the electrolyte may further include at least one of ethylene carbonate, propylene carbonate, butyl carbonate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, methyl valerate, ethyl valerate, methyl neovalerate, ethyl neovalerate, and butyl neovalerate.

[0075] In one embodiment of this application, the electrolyte may further include a lithium salt, which includes at least one selected from lithium hexafluorophosphate (LiPF6), lithium bisfluorosulfonylimide (LiFSI), and lithium bis(trifluoromethanesulfonylimide) (LiTFSI). Preferably, the lithium salt includes LiPF6. This application does not impose any particular limitation on the concentration of the lithium salt, as long as the purpose of this application is achieved. For example, based on the mass of the electrolyte, the mass percentage of the lithium salt can be 8% to 18%, preferably 10% to 15%.

[0076] The second aspect of this application provides an electrochemical device, including a positive electrode, a negative electrode, a separator, and an electrolyte as described in any of the above embodiments of this application, wherein the resulting electrochemical device has good high-temperature storage performance and cycle performance.

[0077] In one embodiment of this application, the electrochemical device further includes a positive electrode sheet, which comprises a positive electrode material layer, the positive electrode material layer comprising a positive electrode active material, and the particle size of the positive electrode active material satisfying 0.4 μm ≤ D V 50≤20μm, 2μm≤D V 90 ≤ 40 μm. For example, the Dv50 of the positive electrode active material can be 0.4 μm, 1 μm, 5 μm, 8 μm, 10 μm, 13 μm, 15 μm, 18 μm, 20 μm, or any range thereof. The Dv90 of the positive electrode active material can be 2 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, or any range thereof. Without being limited to any theory, by controlling the Dv50 and Dv90 of the positive electrode active material within the above ranges, the positive electrode active material is less likely to undergo side reactions with the electrolyte, which can suppress gas generation during the cycling process of the electrochemical device. Simultaneously, it can reduce the content of additives in the electrolyte and form a stable CEI film, further suppressing the generation of side reactions, improving the cycling performance and safety performance of the electrochemical device, and reducing the amount of gas generated during the cycling process.

[0078] In one embodiment of this application, the D of the positive electrode active material V 50 is fμm, and the electrochemical device satisfies at least one of conditions (i) to (iii): (i) 0.05 ≤ c / f×100 ≤ 1; (ii) the electrolyte includes sulfonyl lactone compounds, with a mass percentage of e based on the mass of the electrolyte, and 0.08 ≤ e / f×100 ≤ 3; (iii) the electrolyte includes compounds of formula (I), with a mass percentage of g based on the mass of the electrolyte, and 0.02 ≤ g / f×100 ≤ 1. For example, the value of c / f×100 can be 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, or any range therein. For example, the value of e / f×100 can be 0.08, 0.1, 0.5, 1, 1.5, 2, 2.5, 3, or any range thereof. Similarly, the value of g / f×100 can be 0.02, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 9, 1, or any range thereof.

[0079] Without being limited to any particular theory, adjusting the c / f×100 value within the above range is beneficial for improving the cycle performance and high-temperature storage performance of electrochemical devices, and reducing the expansion rate of electrochemical devices. When the electrolyte includes sulfonyl lactone compounds, adjusting the e / f×100 value within the above range is beneficial for improving the cycle performance and high-temperature storage performance of electrochemical devices. When the electrolyte includes compounds of formula (I), adjusting the g / f×100 value within the above range is beneficial for improving the high-temperature storage performance, cycle performance, and safety performance of electrochemical devices.

[0080] In one embodiment of this application, the positive electrode active material includes element M, which includes at least one of Al, Mg, Ti, Cr, B, Fe, Zr, Y, Na, W, F, or S. Based on the mass of the metal elements other than lithium in the positive electrode active material, the mass percentage of element M is less than or equal to 0.5%. For example, the mass percentage of element M is 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, or 0.5%. Without being limited to any theory, when the mass percentage of element M is too high (e.g., above 0.5%), it is easy for the positive electrode active material to undergo side reactions with the electrolyte and produce gas, thereby affecting the cycle performance, capacity retention, and safety performance of the electrochemical device. Therefore, by controlling the mass percentage of element M within the above range, it is beneficial to improve the cycle performance, capacity retention, and safety performance of the electrochemical device. Selecting element M within the above range is beneficial to improving the cycle performance and high-temperature storage performance of the electrochemical device.

[0081] In one embodiment of this application, the positive electrode active material includes a lithium-nickel transition metal oxide.

[0082] In one embodiment of this application, the positive electrode active material includes lithium nickel cobalt manganese oxide.

[0083] In one embodiment of this application, the positive electrode active material further includes at least one of other elements, such as P, Si, Cu, etc.

[0084] In one embodiment of this application, the charging cut-off voltage of the electrochemical device in any of the foregoing embodiments is greater than or equal to 4.2V.

[0085] In one embodiment of this application, the charging cutoff voltage of the electrochemical device is 4.2V-5.0V.

[0086] In this application, the positive electrode typically includes a positive current collector and a positive electrode material layer. The positive current collector is not particularly limited, as long as it achieves the purpose of this application; for example, it may include, but is not limited to, aluminum foil, aluminum alloy foil, or composite current collectors. In this application, the thickness of the positive current collector is not particularly limited, as long as it achieves the purpose of this application; for example, a thickness of 6 μm to 18 μm is acceptable.

[0087] In this application, the positive electrode material layer may also include a conductive agent. This application does not impose any particular limitation on the conductive agent, as long as it can achieve the purpose of this application. For example, it may include, but is not limited to, at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, flake graphite, Ketjen black, graphene, metallic materials, or conductive polymers. The aforementioned carbon nanotubes may include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The aforementioned carbon fibers may include, but are not limited to, vapor-grown carbon fibers (VGCF) and / or carbon nanofibers. The aforementioned metallic materials may include, but are not limited to, metal powders and / or metal fibers; specifically, the metal may include, but is not limited to, at least one of copper, nickel, aluminum, or silver. The aforementioned conductive polymers may include, but are not limited to, at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, or polypyrrole.

[0088] In this application, the positive electrode material layer may also include a binder. This application does not have any particular limitation on the binder, as long as it can achieve the purpose of this application. For example, it may include, but is not limited to, at least one of polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyvinyl alcohol, carboxymethyl cellulose, sodium carboxymethyl cellulose, polyimide, polyamide-imide, styrene-butadiene rubber or polyvinylidene fluoride.

[0089] Optionally, the surface of the positive electrode material layer may also have a coating, wherein the coating may include, but is not limited to, at least one of the following: an oxide of the coating element, a hydroxide of the coating element, a hydroxy oxide of the coating element, an oxycarbonate of the coating element, or a hydroxycarbonate of the coating element. The aforementioned coating element may include, but is not limited to, at least one of Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, or Zr. This application does not impose any particular limitation on the method of preparing the coating, as long as it achieves the purpose of this application, such as spraying or impregnation. This application does not impose any particular limitation on the thickness of the coating, as long as it achieves the purpose of this application, such as a thickness of 1 μm to 10 μm.

[0090] Optionally, the positive electrode may further include a conductive layer located between the positive current collector and the positive electrode material layer. This application does not impose any particular limitation on the composition of the conductive layer; it can be a conductive layer commonly used in the art, such as, but not limited to, the conductive agent and the binder described above.

[0091] The electrochemical device of this application also includes a negative electrode. The negative electrode in this application is not particularly limited, as long as it achieves the purpose of this application. For example, the negative electrode typically includes a negative current collector and a negative electrode material layer. The negative current collector is not particularly limited, as long as it achieves the purpose of this application, and may include, but is not limited to, copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or composite current collectors. In this application, the thickness of the negative current collector is not particularly limited, as long as it achieves the purpose of this application, for example, a thickness of 4 μm to 18 μm.

[0092] In this application, the negative electrode material layer includes a negative electrode active material. The negative electrode active material is not particularly limited, as long as it achieves the purpose of this application. Examples include, but are not limited to, natural graphite, artificial graphite, mesophase microcarbon spheres, hard carbon, soft carbon, silicon, silicon-carbon composites, Li-Sn alloys, Li-Sn-O alloys, Sn, SnO, SnO2, and spinel-structured lithiated TiO2-Li4Ti5O. 12 At least one of Li-Al alloys.

[0093] In this application, the negative electrode material layer may also include a conductive agent. This application does not have any particular limitation on the conductive agent, as long as it can achieve the purpose of this application. For example, it may include, but is not limited to, at least one of the above-mentioned conductive agents.

[0094] In this application, the negative electrode material layer may also include an adhesive. This application does not have any particular restrictions on the adhesive, as long as it can achieve the purpose of this application. For example, it may include, but is not limited to, at least one of the above-mentioned adhesives.

[0095] Optionally, the negative electrode may further include a conductive layer located between the negative electrode current collector and the negative electrode material layer. This application does not impose any particular limitation on the composition of the conductive layer; it can be a conductive layer commonly used in the art, and may include, but is not limited to, the aforementioned conductive agent and binder.

[0096] The electrochemical device of this application 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, it can be at least one of the following: polyethylene (PE), polypropylene (PP), polyolefin (PO) membranes primarily composed of polytetrafluoroethylene, polyester membranes (e.g., polyethylene terephthalate (PET) membranes), cellulose membranes, polyimide (PI) membranes, polyamide (PA) membranes, spandex or aramid membranes, woven membranes, nonwoven membranes (non-woven fabrics), microporous membranes, composite membranes, separator paper, rolled membranes, or spun membranes. The separator membrane of this application can have a porous structure, and the pore size is not particularly limited, as long as it achieves the purpose of this application. For example, the pore size can be from 0.01 μm to 1 μm. In this application, the thickness of the separator membrane is not particularly limited, as long as it achieves the purpose of this application. For example, the thickness can be from 5 μm to 100 μm.

[0097] For example, the separator may include a substrate layer and a surface treatment layer. The substrate layer may be a nonwoven fabric, membrane, or composite membrane with a porous structure, and the material of the substrate layer may include, but is not limited to, 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. Optionally, a surface treatment layer is provided on at least one surface of the substrate layer, and the surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing polymers and inorganic materials.

[0098] The inorganic layer may include, but is not limited to, inorganic particles and binders. This application does not impose any particular limitation on the inorganic particles, which may include, for example, at least one of the following: 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 impose any particular limitation on the binder, which may include, but is not limited to, at least one of the following: polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, or polyhexafluoropropylene. The polymer layer contains a polymer, and the polymer material may include, but is not limited to, at least one of the following: polyamide, polyacrylonitrile, acrylate polymers, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, or poly(vinylidene fluoride-hexafluoropropylene).

[0099] The fabrication process of the electrochemical device is well known to those skilled in the art, and this application does not impose any particular limitations. For example, it may include, but is not limited to, the following steps: stacking the positive electrode, the separator, and the negative electrode in sequence, and then, as needed, winding, folding, or performing other operations, placing them into the housing, injecting the electrolyte into the housing, and sealing it. 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.

[0100] A third aspect of this application provides an electronic device, including the electrochemical device in any of the above embodiments of this application.

[0101] 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.

[0102] This application provides an electrolyte, an electrochemical device comprising the electrolyte, and an electronic device. The electrolyte comprises ethylene carbonate, propylene carbonate, and fluoroethylene carbonate. Based on the mass of the electrolyte, the mass percentage of ethylene carbonate is 'a', the mass percentage of propylene carbonate is 12% to 35% (b), and the mass percentage of fluoroethylene carbonate is 0.1% to 2.5% (c), satisfying 0.1 ≤ a / b ≤ 0.75. By controlling the mass percentage of propylene carbonate to 12% to 35%, the mass percentage of fluoroethylene carbonate to 0.1% to 2.5%, and the ratio of ethylene carbonate to propylene carbonate to 0.1 to 0.75, it is beneficial to improve the high-temperature storage performance and cycle performance of the electrochemical device.

[0103] Example

[0104] 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.

[0105] Test methods and equipment:

[0106] Cyclic performance test:

[0107] The lithium-ion battery was placed in a 25°C constant temperature chamber and left to stand for 30 minutes to allow it to reach a constant temperature. The battery was then charged at a constant current of 1C until the voltage reached 4.45V, followed by constant voltage charging at 4.45V until the current reached 0.05C. The thickness of the battery at this point was measured and recorded using a micrometer as the initial thickness. Next, the battery was discharged at a constant current of 1C until the voltage reached 2.8V, completing one charge-discharge cycle. The discharge capacity of this cycle was recorded as the initial discharge capacity. The charge-discharge cycles were repeated with the initial discharge capacity as 100% until the discharge capacity decreased to 80%. The test was then stopped, the number of cycles was recorded, and the thickness of the battery was measured and recorded as the thickness after the cycle.

[0108] The method for testing the cycle performance of lithium-ion batteries at 45°C is the same as that for the 25°C cycle performance test, except that the lithium-ion batteries are placed in a 45°C constant temperature chamber.

[0109] Thickness expansion rate = (thickness after cycle - initial thickness) / initial thickness × 100%.

[0110] High-temperature storage performance test:

[0111] The lithium-ion battery was placed in a 25°C constant temperature chamber and left to stand for 30 minutes to allow it to reach a constant temperature. It was then charged at a constant current of 1C until the voltage reached 4.45V, followed by constant voltage charging until the current reached 0.05C. It was then discharged at a constant current of 1C until the voltage reached 2.8V, and the discharge capacity was recorded as the initial capacity. Next, it was charged at a constant current of 0.5C until the voltage reached 4.45V, followed by constant voltage charging until the current reached 0.05C. The thickness of the lithium-ion battery was measured and recorded using a micrometer as the initial thickness. The tested lithium-ion battery was then transferred to a 60°C constant temperature chamber for storage for 90 days (D). During this period, the thickness of the lithium-ion battery was measured and recorded every 3 days. After 90 days of storage, the battery was transferred to a 25°C constant temperature chamber and left to stand for 60 minutes. It was then discharged at a constant current of 1C until the voltage reached 2.8V, and the discharge capacity was recorded as the post-storage discharge capacity. Then, charge the battery with a constant current of 1C until the voltage reaches 4.45V, charge it with a constant voltage until the current reaches 0.05C, and then discharge it with a constant current of 1C until the voltage reaches 2.8V. Record the discharge capacity as the recoverable capacity, and measure the thickness of the lithium-ion battery as the thickness after storage.

[0112] Expansion rate of 90D thickness stored at 60℃ = (Thickness after storage - Initial thickness) / Initial thickness × 100%

[0113] 90D capacity retention rate at 60℃ = (initial discharge capacity - recoverable capacity) / initial discharge capacity × 100%.

[0114] 0℃ DC Impedance (DCR) Test:

[0115] At 0°C, the lithium-ion battery was charged at a constant current of 0.1C to a voltage of 4.4V, then charged at a constant voltage of 4.45V to a current of 0.05C, and allowed to stand for 10 minutes. It was then discharged at a current of 0.1C to a voltage of 3.4V and allowed to stand for 5 minutes. It was then charged again at a constant current of 0.1C to a voltage of 4.4V, then charged at a constant voltage of 4.45V to a current of 0.05C, and allowed to stand for 10 minutes. Finally, it was discharged at a constant current of 0.1C for 7 seconds, and the voltage value was recorded as U1. Then, it was discharged at a current of 1C for 1 second, and the voltage value was recorded as U2.

[0116] The DC resistance of a lithium-ion battery at 0°C can be calculated using the following formula: R = (U2 - U1) / (1C - 0.1C), where "1C" refers to the current value required to completely discharge the lithium-ion battery within 1 hour.

[0117] Overcharge test:

[0118] The lithium-ion battery was discharged at 25°C with a constant current of 0.5C until the voltage reached 2.8V, then charged with a constant current of 3C until the voltage reached 5.7V, and then charged with a constant voltage for 2 hours. The surface temperature change of the lithium-ion battery was monitored. The passing standard was that the lithium-ion battery did not catch fire, burn, or explode. Ten lithium-ion batteries prepared in each example or comparative example were tested, and the number of those that passed was recorded.

[0119] Float charging performance test:

[0120] The lithium-ion battery was placed in a 25°C constant temperature chamber and left to stand for 30 minutes to allow it to reach a constant temperature. It was then charged at a constant current of 1C until the voltage reached 4.45V, followed by constant voltage charging until the current reached 0.05C. It was then discharged at a constant current of 1C until the voltage reached 2.8V, and the discharge capacity was recorded as the initial capacity of the lithium-ion battery. Next, it was charged at a constant current of 0.5C until the voltage reached 4.45V, followed by constant voltage charging until the current reached 0.05C. The battery thickness was measured and recorded using a micrometer as the initial thickness. The tested lithium-ion battery was transferred to a 45°C constant temperature chamber and charged at a constant voltage of 4.45V for 60 days. After 60 days, the battery was transferred to a 25°C constant temperature chamber and left to stand for 60 minutes. It was then discharged at a constant current of 1C until the voltage reached 2.8V, and the discharge capacity was recorded as the discharge capacity after storage. Then, it is charged at a constant current of 1C to a voltage of 4.45V, charged at a constant voltage to a current of 0.05C, and then discharged at a constant current of 1C to 2.8V. The discharge capacity is recorded as the recoverable capacity of the lithium-ion battery, and the thickness of the lithium-ion battery is measured as the thickness after float charging.

[0121] Float charge thickness expansion rate = (Float charge thickness - Initial thickness) / Initial thickness × 100%

[0122] Float charge capacity retention rate = (initial discharge capacity - recoverable capacity) / initial discharge capacity × 100%.

[0123] Calendar Lifetime Performance (ITC) Test:

[0124] The lithium-ion battery was placed in a 45°C constant temperature chamber and left to stand for 30 minutes to allow it to reach a constant temperature. The battery was then charged at a constant current of 1C to a voltage of 4.45V, followed by constant voltage charging at 4.45V to a current of 0.05C. The thickness of the battery at this point was measured and recorded using a micrometer as the initial thickness. The battery was left to stand in this state for 24 hours, followed by constant current discharging at 1C to a voltage of 2.8V. This constitutes one charge-discharge cycle. The initial discharge capacity was taken as 100%, and the charge-discharge cycles were repeated until the discharge capacity decreased to 80%. The number of cycles was recorded as the calendar life, and the thickness of the lithium-ion battery was measured and recorded as the thickness after the cycle.

[0125] ITC thickness expansion rate = (thickness after cycling - initial thickness) / initial thickness × 100%.

[0126] Example 1

[0127] <Preparation of the positive electrode>

[0128] The positive electrode active material, lithium nickel manganese cobalt ternary material (NCM613), conductive carbon black (Super P), and binder, polyvinylidene fluoride, were mixed at a mass ratio of 97:1.4:1.6. N-methylpyrrolidone (NMP) was added, and the mixture was stirred evenly under vacuum to obtain a positive electrode slurry with a solid content of 72%. The positive electrode slurry was uniformly coated onto one surface of a 10 μm thick aluminum foil current collector. The aluminum foil was dried at 85°C to obtain a single-sided positive electrode sheet with a 60 μm coating thickness. The above steps were repeated on the other surface of the aluminum foil to obtain a double-sided positive electrode sheet with the positive electrode active material. After cold pressing, cutting, slitting, and welding of tabs, the sheet was dried under vacuum at 85°C for 4 hours to obtain the positive electrode sheet. The Dv50 of the positive electrode active material was 1 μm. The lithium-nickel-manganese-cobalt ternary material (NCM613) contains Al, and the mass percentage of Al is 0.1% based on the mass of metal elements other than lithium in the positive electrode active material.

[0129] <Preparation of Negative Electrode Sheets>

[0130] Artificial graphite (anode active material), Super P (conductive agent), sodium carboxymethyl cellulose (CMC) (thickener), and styrene-butadiene rubber (SBR) (binder) were mixed in a mass ratio of 96.4:1.5:0.5:1.6. Deionized water was added, and the mixture was stirred under vacuum to obtain a cathode slurry with a solid content of 54%. The cathode slurry was uniformly coated onto one surface of a 10 μm thick copper foil current collector. The copper foil was dried at 85°C to obtain a cathode sheet with a single-sided coating of cathode material and a coating thickness of 70 μm. The above steps were repeated on the other surface of the aluminum foil to obtain a cathode sheet with double-sided coating of cathode active material. After cold pressing, cutting, slitting, and welding of tabs, the cathode sheet was dried under vacuum at 120°C for 12 hours to obtain the cathode sheet.

[0131] <Preparation of Electrolyte>

[0132] In a dry argon-atmospheric glove box, organic solvents ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a mass ratio of EC:PC:EMC:DEC = 6:34:20:40. Lithium salt LiPF6 was then added to the organic solvents and dissolved, and the mixture was thoroughly mixed. Fluorinated ethylene carbonate (FEC) was then added and dissolved to obtain the electrolyte. The electrolyte contained 12% LiPF6, 2% FEC, and the remainder was the mass percentage of the organic solvents. The total mass percentages of EC, PC, EMC, and DEC were 5.2%, 29.2%, 17.2%, and 34.4%, respectively.

[0133] <Preparation of the separating membrane>

[0134] A 7μm thick polyethylene (PE) film (supplied by Celgard) is used.

[0135] <Preparation of Lithium-ion Batteries>

[0136] The positive electrode, separator, and negative electrode prepared above are stacked in sequence, with the separator positioned between the positive and negative electrode to provide isolation. The electrode assembly is then wound to obtain the electrode assembly. The electrode assembly is placed in an aluminum-plastic film packaging bag, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, degassing, and edge trimming, a lithium-ion battery is obtained.

[0137] In Examples 2 to 12, the mass percentages of EC, PC, EMC, DEC, and FEC were adjusted according to Table 1, and the rest were the same as in Example 1.

[0138] In Examples 13 to 19, the mass percentages of EC, PC, EMC, and DEC were adjusted according to Table 2, and the rest were the same as in Example 1.

[0139] In Examples 20 to 30, except that sulfonyl lactone compounds were added along with FEC according to Table 3, the mass percentage of FEC c was adjusted according to Table 3, and the mass percentage of organic solvents was adjusted adaptively (the mass ratio of EC, PC, EMC, and DEC was the same as in Example 2), everything else was the same as in Example 2.

[0140] In Examples 31 to 53, except that additives A and B were optionally added according to Table 4 while adding FEC, and the mass percentage of FEC was adjusted according to Table 4, and the mass percentage of organic solvent was adjusted adaptively (the mass ratio of EC, PC, EMC, and DEC was the same as in Example 2), the rest were the same as in Example 2.

[0141] In Examples 54 to 59, the compounds of formula (I) were added according to Table 5 along with FEC, and the mass percentage of organic solvents was adjusted adaptively (the mass ratios of EC, PC, EMC, and DEC were the same as in Example 2). The rest were the same as in Example 2.

[0142] In Examples 60 to 75, the contents were the same as in Example 2, except that the mass percentage of FEC (c), the Dv50 particle size of the positive electrode active material (f), the mass percentage of sulfonyl lactone compound (e), the mass percentage of compound of formula (I) (g), and the mass percentage of organic solvent (EC, PC, EMC, DEC mass ratio was the same as in Example 2) were adjusted according to Table 6.

[0143] In Comparative Examples 1 to 3, the mass percentages of EC, PC, EMC, DEC, and FEC were adjusted according to Table 1, and the rest were the same as in Example 1.

[0144]

[0145]

[0146]

[0147]

[0148]

[0149]

[0150]

[0151] As can be seen from Table 1 Examples 1 to 12 and Comparative Examples 1 to 3, by adjusting the mass percentage of PC, the a / b value and the mass percentage of FEC within the range of this application, the obtained electrochemical device simultaneously has good cycle performance and high-temperature storage performance.

[0152] As can be seen from Examples 13 to 19 in Table 2, when the electrolyte includes the chain carbonates of this application, by adjusting the mass percentage content d of the chain carbonates and / or the value of a / d within the range of this application, the resulting electrochemical device has good cycle performance, high-temperature storage performance, float charging performance and safety performance.

[0153] Additives in the electrolyte can affect the performance of electrochemical devices. The electrochemical device provided in this application can optionally add sulfonyl lactone compound, additive A, additive B, and compound of formula (I) to the electrolyte, which can improve the cycle performance, high temperature storage performance, float charge performance and safety performance of the electrochemical device to varying degrees.

[0154] As can be seen from Examples 2, 20 to 30 in Table 3, when the electrolyte includes the sulfonyl lactone compound of this application, the cycle performance, high-temperature storage performance, float charge performance, and safety performance of the electrochemical device can be further improved. As can be seen from Examples 20 to 30, by adjusting the mass percentage content of the sulfonyl lactone compound within the range of this application, the obtained electrochemical device exhibits good cycle performance, high-temperature storage performance, float charge performance, and safety performance.

[0155] As can be seen from Examples 2, 31 to 53 in Table 4, when the electrolyte includes additive A and / or additive B, the cycle performance, high-temperature storage performance, calendar life, float charge performance and safety performance of the electrochemical device can be further improved.

[0156] As can be seen from Examples 2, 54 to 59 in Table 5, when the electrolyte includes the compound of formula (I) and its content is within the range of this application, the cycle performance, calendar life, high temperature storage performance, float charge performance and safety performance of the electrochemical device can be further improved.

[0157] The mass percentage c of FEC, the particle size f of the positive electrode active material, the mass percentage e of the sulfonyl lactone compound (1,3-propanesulfonyl lactone), and the mass percentage g of the compound of formula (I) generally also affect the overall performance of the electrochemical device, such as cycle performance, high-temperature storage performance, float charge performance, and safety performance. As can be seen from Examples 60 to 75 in Table 6, by adjusting the relationship between f and c, e, and g within the scope of this application, the obtained electrochemical device has good cycle performance, high-temperature storage performance, calendar life, float charge performance, and safety performance.

[0158] 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 electrolyte comprising ethylene carbonate, propylene carbonate, and fluoroethylene carbonate, wherein, based on the mass of the electrolyte, the mass percentage of ethylene carbonate is a, 1.0% ≤ a ≤ 20%, and the mass percentage of propylene carbonate is b, 12% ≤ b ≤ 35%; The electrolyte further includes additive A, which comprises at least one of vinylene carbonate and ethylene sulfate, wherein, based on the mass of the electrolyte, additive A satisfies at least one of the following relationships: (1) the mass percentage of vinylene carbonate A1 is 0.01% to 2%, (2) the mass percentage of ethylene sulfate A2 is 0.01% to 2%; and The electrolyte further includes additive B, which includes at least one selected from succinic anhydride, adiponitrile, 1,4-dicyano-2-butene, ethylene glycol diethyl cyanide, 1,3,6-hexanetricarbonyl or 1,2,3-tris(2-cyanoxy)propane, and the mass percentage of additive B is 0.5% to 4% based on the mass of the electrolyte.

2. The electrolyte according to claim 1, wherein 0.1 ≤ a / b ≤ 0.

75.

3. The electrolyte according to claim 1, further comprising a chain carbonate, wherein the chain carbonate comprises at least one selected from dimethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, methyl butyl carbonate, diethyl carbonate, dipropyl carbonate, or dibutyl carbonate, wherein the mass percentage of the chain carbonate is d based on the mass of the electrolyte, and the electrolyte satisfies 0.04 ≤ a / d ≤ 0.53 and / or 30% ≤ d ≤ 60%.

4. The electrolyte according to claim 3, wherein, The electrolyte meets the following conditions: 0.04 ≤ a / d ≤ 0.35 and / or 35% ≤ d ≤ 60%.

5. The electrolyte according to claim 1, wherein, Based on the mass of the electrolyte, the mass percentage c of the fluoroethylene carbonate is 0.2% to 2.5%. The electrolyte also includes a sulfonyl lactone compound, which further includes at least one of 1,3-propanesulfonyl lactone, 2,4-butanesulfonyl lactone, or 1,4-butanesulfonyl lactone, and the mass percentage e of the sulfonyl lactone compound is 0.5% to 5% based on the mass of the electrolyte.

6. The electrolyte according to claim 5, wherein, The mass percentage c of the fluoroethylene carbonate is 1.5% to 2.5%.

7. The electrolyte according to claim 5, wherein, The mass percentage e of the sulfonyl lactone compound is 3% to 5%.

8. The electrolyte according to claim 5, wherein, The mass percentage e of the sulfonyl lactone compound is 1% to 3%.

9. The electrolyte according to claim 5, wherein, c≤e.

10. The electrolyte according to claim 1, wherein, Additive A also includes at least one of vinyl ethylene carbonate, lithium difluorophosphate, or lithium boron salt.

11. The electrolyte according to claim 10, wherein it satisfies at least one of the following relationships: (a) The additive A further includes a lithium boron salt, which includes at least one of lithium tetrafluoroborate, lithium difluorooxalate borate, or lithium dioxalate borate, and the mass percentage A3 of the lithium boron salt is 0.01% to 2% based on the mass of the electrolyte; (b) The electrolyte comprises vinylene carbonate and ethylene sulfate, and based on the mass of the electrolyte, the mass percentage of vinylene carbonate is A1 and the mass percentage of ethylene sulfate is A2, satisfying 0.1 < A2 / A1 ≤ 12; (c) The electrolyte comprises vinylene carbonate and ethylene sulfate, wherein, based on the mass of the electrolyte, the mass percentage of vinylene carbonate is A1 and the mass percentage of ethylene sulfate is A2, satisfying 0.02% ≤ A1 + A2 ≤ 3%; (d) The electrolyte comprises vinylene carbonate and lithium boron salt. Based on the mass of the electrolyte, the mass percentage of vinylene carbonate is A1, and the mass percentage of lithium boron salt is A3, satisfying 0.01% ≤ A1 + A3 ≤ 3%. (e) The electrolyte contains vinylene carbonate and lithium boron salt. Based on the mass of the electrolyte, the mass percentage of vinylene carbonate is A1 and the mass percentage of lithium boron salt is A3, satisfying 0.1≤A1 / A3≤10.

12. The electrolyte according to claim 11, wherein it satisfies at least one of the following relationships: (a) The additive A further includes a lithium boron salt, which includes at least one of lithium tetrafluoroborate, lithium difluorooxalate borate, or lithium dioxalate borate, and the mass percentage A3 of the lithium boron salt is 0.3% to 1.2% based on the mass of the electrolyte; (b) The electrolyte comprises vinylene carbonate and ethylene sulfate, and based on the mass of the electrolyte, the mass percentage of vinylene carbonate is A1 and the mass percentage of ethylene sulfate is A2, satisfying 1≤A2 / A1≤2; (c) The electrolyte comprises vinylene carbonate and ethylene sulfate, wherein, based on the mass of the electrolyte, the mass percentage of vinylene carbonate is A1 and the mass percentage of ethylene sulfate is A2, satisfying 0.5% ≤ A1 + A2 ≤ 2%; (d) The electrolyte comprises vinylene carbonate and lithium boron salt. Based on the mass of the electrolyte, the mass percentage of vinylene carbonate is A1, and the mass percentage of lithium boron salt is A3, satisfying 1.3% ≤ A1 + A3 ≤ 1.7%. (e) The electrolyte contains vinylene carbonate and lithium boron salt. Based on the mass of the electrolyte, the mass percentage of vinylene carbonate is A1 and the mass percentage of lithium boron salt is A3, satisfying 0.42≤A1 / A3≤3.

33.

13. The electrolyte according to claim 1, further comprising the compound of formula (I), wherein the mass percentage (g) of the compound of formula (I) is 0.01% to 2% based on the mass of the electrolyte: ； in, R is selected from unsubstituted or Ra-substituted C1 to C8 fluoroalkyl groups, and unsubstituted or Ra-substituted C2 to C8 fluoroalkyl groups. 10 Fluoroalkenyl, unsubstituted or Ra-substituted C6 to C 10 Fluorinated aryl groups; Each substituent Ra of each group independently includes at least one of cyano, carboxyl, or sulfate groups.

14. The electrolyte according to claim 1, further comprising at least one of the following structural compounds I-1 to I-9: 。 15. An electrochemical device comprising an electrolyte according to any one of claims 1 to 14.

16. The electrochemical device according to claim 15, further comprising a positive electrode plate, the positive electrode plate comprising a positive electrode material layer, the positive electrode material layer comprising a positive electrode active material, the particle size of the positive electrode active material satisfying 0.4 μm ≤ D V 50≤20μm, 2 μm≤D V 90≤40 μm.

17. The electrochemical device according to claim 16, wherein, The positive electrode active material D V 50 is f μm, and the electrochemical device satisfies at least one of conditions (i) to (iii): (i) Based on the mass of the electrolyte, the mass percentage of the fluoroethylene carbonate is c, and 0.05≤c / f×100≤1; (ii) The electrolyte includes sulfonyl lactone compounds, and the mass percentage of the sulfonyl lactone is e, based on the mass of the electrolyte, where 0.08 ≤ e / f × 100 ≤ 3; (iii) The electrolyte comprises the compound of formula (I), and based on the mass of the electrolyte, the mass percentage of the compound of formula (I) is g, and 0.02≤g / f×100≤1; ； Wherein, R is selected from unsubstituted or Ra-substituted C1 to C8 fluoroalkyl groups, unsubstituted or Ra-substituted C2 to C8 fluoroalkyl groups. 10 Fluoroalkenyl, unsubstituted or Ra-substituted C6 to C 10 The fluoroaryl group; the substituent Ra of each group independently includes at least one of cyano, carboxyl or sulfate.

18. The electrochemical device according to claim 17, wherein, The electrochemical device satisfies at least one of conditions (i) to (iii): (i) 0.33 ≤ c / f × 100 ≤ 0.67; (ii) 0.2 ≤ e / f × 100 ≤ 1; (iii) 0.17≤g / f×100≤0.

33.

19. The electrochemical device according to claim 16, wherein, The positive electrode active material includes element M, which includes at least one of Al, Mg, Ti, Cr, B, Fe, Zr, Y, Na, W, F or S. The mass percentage of element M is less than or equal to 0.5%, based on the mass of the metal elements other than lithium in the positive electrode active material.

20. An electronic device comprising an electrochemical device according to any one of claims 15 to 19.

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