Secondary battery and electronic device

Abstract

The present application provides a secondary battery and an electronic device. The secondary battery includes a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte. The negative electrode sheet includes a negative electrode current collector and a negative electrode material layer provided on at least one surface of the negative electrode current collector. The negative electrode material layer includes a negative electrode active material. The specific surface area of ​​the negative electrode active material is cm 2 / g, the negative electrode active material includes a basal surface and an end surface, where the end surface accounts for a; the electrolyte includes a fluorinated linear ester, and the mass percentage of the fluorinated linear ester is d%, based on the mass of the electrolyte, 5≤d≤65, 0.0015≤c / d≤2, and 0.0015≤a / d≤0.12. The electrolyte includes a fluorinated linear ester, and regulating the values ​​of d, c / d, and a / d within the above ranges can improve the cycling performance of the secondary battery under high voltage and high temperature conditions, while also facilitating improved fast charging performance of the secondary battery.

Description

Technical Field

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

[0002] Secondary batteries, such as lithium-ion batteries, boast high specific energy, high operating voltage, low self-discharge, compact size, and light weight. They are widely used in various fields, including energy storage, portable electronic devices, and electric vehicles. With the continuous iterative development of consumer lithium-ion batteries in recent years, the market demand for charging speeds has become increasingly stringent. The proportion of fast-charging products has gradually increased, providing users with a superior user experience and greatly increasing convenience in daily life.

[0003] To meet the requirements of fast charging, the cycling performance of lithium-ion batteries at high voltages and high temperatures is affected. This is because side reactions in the electrolyte increase under these conditions. Therefore, how to improve the cycling performance of lithium-ion batteries at high voltages and high temperatures has become a technical problem that needs to be solved urgently by those skilled in the art. Summary of the Invention

[0004] The purpose of this application is to provide a secondary battery and an electronic device to improve the cycle performance of the secondary battery. The specific technical solution is as follows:

[0005] The first aspect of the present application provides a secondary battery comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the negative electrode sheet comprises a negative electrode current collector and a negative electrode material layer provided on at least one surface of the negative electrode current collector, wherein the negative electrode material layer comprises a negative electrode active material, and the specific surface area of ​​the negative electrode active material is cm 2 / g, the negative electrode active material includes a basal surface and an end surface, wherein the end surface accounts for a; the electrolyte includes a fluorinated linear ester, and the mass percentage of the fluorinated linear ester is d%, based on the mass of the electrolyte, 5≤d≤65, 0.0015≤c / d≤2; 0.0015≤a / d≤0.12. The electrolyte includes a fluorinated linear ester and the values ​​of d, c / d, and a / d are regulated within the above ranges. This can reduce side reactions between the negative electrode active material and the electrolyte, improve the gas production of the electrolyte under high voltage and high temperature, and thus improve the cycle performance of the secondary battery under high voltage and high temperature conditions. At the same time, it can also shorten the charging time of the secondary battery, which is beneficial to improving the fast charging performance of the secondary battery.

[0006] In some embodiments of the present application, 0.1 ≤ c ≤ 10, and 0.1 ≤ a ≤ 0.6. By regulating the values ​​of c and a within the above ranges, side reactions between the negative electrode active material and the electrolyte can be reduced, improving the gas production of the electrolyte under high voltage and high temperature conditions, thereby improving the cycle performance of the secondary battery under high voltage and high temperature conditions. At the same time, it can also shorten the charging time of the secondary battery, which is conducive to improving the fast charging performance of the secondary battery.

[0007] In some embodiments of the present application, the fluorinated linear ester includes at least one of the following compounds:

[0008]

[0009]

[0010] Selecting fluorinated linear esters within the above range is more conducive to improving the antioxidant properties of the electrolyte and improving the gas production of the electrolyte at high voltage and high temperature, thereby improving the cycle performance of the secondary battery under high voltage and high temperature conditions.

[0011] In some embodiments of the present application, the electrolyte further comprises fluoroethylene carbonate, and the mass percentage of fluoroethylene carbonate is g%, based on the mass of the electrolyte, and 0.01 ≤ g ≤ 15. The electrolyte comprising fluoroethylene carbonate and regulating the value of g within the above range can reduce interfacial side reactions between the negative electrode plate and the electrolyte, thereby improving the cycle performance of the secondary battery under high voltage and high temperature conditions.

[0012] In some embodiments of the present application, 0.0067≤a / g≤60. By regulating the value of a / g within the above range, better compatibility between the negative electrode active material and the electrolyte is achieved, thereby improving the cycle performance of the secondary battery under high voltage and high temperature conditions.

[0013] In some embodiments of the present application, the electrolyte further includes a wetting agent, and the mass percentage of the wetting agent is e%, 0.1≤e≤10 based on the mass of the electrolyte; the wetting agent includes C6 to C 12 Fluorinated aromatic hydrocarbons, C1 to C6 fluorinated ether compounds and C1 to C 12 The electrolyte includes a wetting agent, and regulating the value of e within the above range can reduce the surface tension of the electrolyte and improve the fluidity of the electrolyte, which is beneficial for the transmission of lithium ions in the negative electrode sheet, thereby achieving fast charging and improving the fast charging performance of the secondary battery.

[0014] In some embodiments of the present application, 0.0015 ≤ e / d ≤ 2. By regulating the value of e / d within the above range, the fluorolinear ester and the wetting agent can work together to improve the gas production of the electrolyte at high voltage and high temperature while achieving fast charging, thereby improving the cycle performance of the secondary battery under high voltage and high temperature conditions while improving its fast charging performance.

[0015] In some embodiments of the present application, the wetting agent includes at least one of fluorobenzene, 1,2-difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene, 1,3,5-trifluorobenzene, 1,2,3-trifluorobenzene, 1,2,4-trifluorobenzene, 1,2,3,5-tetrafluorobenzene, 1,2,4,5-tetrafluorobenzene, 1,2,3,4-tetrafluorobenzene, pentafluorobenzene, hexafluorobenzene, p-fluorotoluene, p-ditrifluorotoluene, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 2,2,2-trifluoroethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, difluoromethyl 2,2,3,3-tetrafluoropropyl ether, 1,1,1,3,3,3-hexafluoroisopropyl methyl ether or perfluorododecane. Selecting a wetting agent within the above range is beneficial to further reduce the surface tension of the electrolyte and improve the fluidity of the electrolyte, thereby achieving fast charging and improving the fast charging performance of the secondary battery.

[0016] In some embodiments of the present application, the secondary battery satisfies at least one of the following characteristics: (1) 15≤d≤50; (2) 0.015≤c / d≤0.33; (3) 0.0077≤a / d≤0.08; (4) 1≤c≤5; (5) 0.3≤a≤0.5; (6) the electrolyte further includes a wetting agent, the mass percentage of the wetting agent based on the mass of the electrolyte is e%, and 0.015≤e / d≤0.33; (7) the negative electrode active material includes at least one of natural graphite, artificial graphite, hard carbon, or soft carbon. The secondary battery having the above characteristics has good cycle performance under high voltage and high temperature conditions and good fast charging performance.

[0017] The second aspect of the present application provides an electronic device comprising the secondary battery of the first aspect of the present application. The secondary battery of the first aspect of the present application has good cycle performance under high voltage and high temperature conditions and good fast charging performance, so that the electronic device provided by the second aspect of the present application has good performance.

[0018] Beneficial effects of this application:

[0019] The present application provides a secondary battery and an electronic device. The secondary battery includes a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte. The negative electrode sheet includes a negative electrode current collector and a negative electrode material layer provided on at least one surface of the negative electrode current collector. The negative electrode material layer includes a negative electrode active material. The specific surface area of ​​the negative electrode active material is cm 2 / g, the negative electrode active material includes a basal surface and an end surface, wherein the end surface accounts for a; the electrolyte includes a fluorinated linear ester, and the mass percentage of the fluorinated linear ester is d%, based on the mass of the electrolyte, 5≤d≤65, 0.0015≤c / d≤2; 0.0015≤a / d≤0.12. The electrolyte includes a fluorinated linear ester, and regulating the values ​​of d, c / d, and a / d within the above ranges can reduce side reactions between the negative electrode active material and the electrolyte, improve the gas production of the electrolyte under high voltage and high temperature, and thus improve the cycle performance of the secondary battery under high voltage and high temperature conditions. It can also shorten the charging time of the secondary battery and improve its fast charging performance.

[0020] Of course, it is not necessary to achieve all the advantages described above at the same time when implementing any product or method of the present application. DETAILED DESCRIPTION

[0021] The technical solutions in the embodiments of the present application will be described clearly and completely below. Obviously, the embodiments described are only part of the embodiments of the present application, not all of the embodiments. All other embodiments obtained by those skilled in the art based on the present application are within the scope of protection of the present application.

[0022] It should be noted that in the following description, lithium-ion batteries are used as an example of secondary batteries to explain this application, but the secondary batteries of this application are not limited to lithium-ion batteries. The specific technical solutions are as follows:

[0023] The first aspect of the present application provides a secondary battery comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the negative electrode sheet comprises a negative electrode current collector and a negative electrode material layer provided on at least one surface of the negative electrode current collector, wherein the negative electrode material layer comprises a negative electrode active material, and the specific surface area of ​​the negative electrode active material is cm 2 / g, the negative electrode active material includes a basal surface and an end surface, wherein the proportion of the end surface is a; the electrolyte includes a fluorinated linear ester, and the mass percentage of the fluorinated linear ester based on the mass of the electrolyte is d%, 5≤d≤65, preferably 15≤d≤50; 0.0015≤c / d≤2, preferably 0.015≤c / d≤0.33; 0.0015≤a / d≤0.12, preferably 0.0077≤a / d≤0.08. For example, the value of d can be 5, 10, 12, 15, 18, 20, 25, 30, 35, 40, 45, 48, 50, 53, 55, 60, 65, or a range consisting of any two of these values; the value of c / d can be 0.0015, 0.002, 0.005, 0.008, 0.01, 0.015, 0.02, 0.03, 0.05, 0.06, 0.08, 0.1, 0.15, 0.2, 0.25, 0.3 , 0.33, 0.35, 0.5, 0.8, 1, 1.5, 2 or a range consisting of any two of the values ​​therein; the value of a / d can be 0.0015, 0.002, 0.003, 0.004, 0.005, 0.006, 0.0062, 0.007, 0.0077, 0.008, 0.009, 0.01, 0.03, 0.05, 0.08, 0.1, 0.12 or a range consisting of any two of the values ​​therein.

[0024] The inventors discovered that the electrolyte includes a fluorinated linear ester. Due to the high oxidation potential of the fluorinated linear ester, it can enhance the electrolyte's antioxidant properties and improve the gas production problem of the secondary battery under high voltage and high temperature conditions, thereby improving the cycle performance of the secondary battery under high voltage and high temperature conditions. When the value of d is too small, the electrolyte's antioxidant capacity is poor and cannot improve the gas production problem of the secondary battery under high voltage and high temperature conditions. When the value of d is too large, the viscosity of the electrolyte is too high, and its wettability with the negative electrode plate is poor, which affects the transmission of lithium ions in the electrolyte and the negative electrode plate, and prolongs the charging time of the secondary battery. In this application, the specific surface area of ​​the negative electrode active material represents the specific surface area of ​​the negative electrode active material powder particles, and the basal plane and end face represent the crystal structure characteristics of the negative electrode active material. The larger the specific surface area of ​​the negative electrode active material, the greater the defect content of the negative electrode active material. Lithium ions are primarily embedded within the negative electrode active material through the end faces and some defect sites. Side reactions between the electrolyte and the negative electrode active material primarily occur at the end faces, with the sum of the basal and end face ratios being 100%. A larger end face ratio (a) increases the electrolyte's susceptibility to side reactions. The ratios c / d and a / d reflect the compatibility between the fluorolinear ester and the negative electrode active material. Furthermore, negative electrode active materials with different specific surface areas and end face ratios exhibit different pore structures. When the specific surface area and end face ratio are within an appropriate range, the surface tension of the electrolyte containing the fluorolinear ester can be reduced, accelerating electrolyte wetting and ensuring uniform electrolyte distribution across different regions of the negative electrode sheet. By combining negative electrode active materials with different specific surface areas and end face ratios with appropriate fluorolinear esters, polarization during secondary battery charging can be reduced and fast-charging capability improved. When the c / d ratio is too small, the specific surface area of ​​the negative electrode active material is too small or the content of the fluoro-linear ester is too high, resulting in poor compatibility between the negative electrode active material and the electrolyte, which is not conducive to rapid lithium insertion of the negative electrode active material. Furthermore, the electrolyte viscosity is too high, resulting in poor fluidity and poor wettability of the negative electrode electrode sheet, which affects the transport of lithium ions between the electrolyte and the negative electrode sheet, and prolongs the charging time of the secondary battery. When the c / d ratio is too large, the specific surface area of ​​the negative electrode active material is too large or the content of the fluoro-linear ester is too low, resulting in incompatibility between the two and failing to improve the antioxidant properties of the electrolyte. Furthermore, the two are likely to increase side reactions between the negative electrode active material and the electrolyte, increasing gas production under high voltage and high temperature conditions, which is not conducive to the secondary battery's cycling performance. When the a / d ratio is too large, the proportion of the end face is too large or the content of the fluoro-linear ester is too low, resulting in poor compatibility between the negative electrode active material and the electrolyte, increasing side reactions between the fluoro-linear ester and the negative electrode active material, and affecting the cycling performance of the secondary battery under high voltage and high temperature conditions.When the value of a / d is too small, the proportion of the end face is too small or the content of the fluorinated linear ester is too high, the two are incompatible, which is not conducive to the rapid lithium insertion of the negative electrode active material, and the viscosity of the electrolyte is too large, and the wettability to the negative electrode plate is poor, which is not conducive to the rapid lithium insertion of the negative electrode active material and the transmission of lithium ions in the electrolyte, and the charging rate of the secondary battery slows down and the charging time is prolonged. Therefore, the electrolyte includes a fluorinated linear ester, and the values ​​of d, c / d, and a / d are regulated within the above ranges, which can reduce the side reactions between the negative electrode active material and the electrolyte, improve the gas production of the electrolyte at high voltage and high temperature, and thus improve the cycle performance of the secondary battery under high voltage and high temperature conditions. At the same time, it can also shorten the charging time of the secondary battery, which is beneficial to improving the fast charging performance of the secondary battery. In this application, high voltage refers to a voltage greater than or equal to 4.2V, and high temperature refers to a temperature greater than or equal to 40°C.

[0025] In some embodiments of the present application, 0.1≤c≤10, 0.1≤a≤0.6, preferably 1≤c≤5, 0.3≤a≤0.5. For example, the value of c can be 0.1, 0.3, 0.5, 0.8, 1, 2, 3, 4, 5, 6, 8, 10, or a range consisting of any two of these values; the value of a can be 0.1, 0.15, 0.2, 0.25, 0.3, 0.32, 0.35, 0.38, 0.4, 0.42, 0.45, 0.48, 0.5, 0.55, 0.6, or a range consisting of any two of these values; by regulating the values ​​of c and a within the above range, the side reaction between the negative electrode active material and the electrolyte can be reduced, and the gas production of the electrolyte at high voltage and high temperature can be improved, thereby improving the cycle performance of the secondary battery under high voltage and high temperature conditions. At the same time, it can also shorten the charging time of the secondary battery, which is beneficial to improving the fast charging performance of the secondary battery.

[0026] In some embodiments of the present application, the fluorinated linear ester includes at least one of the following compounds:

[0027]

[0028]

[0029] Selecting fluorinated linear esters within the above range is more conducive to improving the antioxidant properties of the electrolyte and improving the gas production of the electrolyte at high voltage and high temperature, thereby improving the cycle performance of the secondary battery under high voltage and high temperature conditions.

[0030] In some embodiments of the present application, the electrolyte further comprises fluoroethylene carbonate, and the mass percentage of fluoroethylene carbonate is g%, based on the mass of the electrolyte, and 0.01≤g≤15. For example, the value of g can be 0.01, 0.03, 0.05, 0.08, 1, 3, 5, 8, 10, 12, 15, or a range consisting of any two of these values. The electrolyte comprises fluoroethylene carbonate, and regulating the value of g within the above range can form a more stable solid electrolyte interface film on the surface of the negative electrode plate, reduce the interfacial side reactions between the negative electrode plate and the electrolyte, and thus improve the cycle performance of the secondary battery under high voltage and high temperature conditions.

[0031] In some embodiments of the present application, 0.0067≤a / g≤60. For example, the value of a / g can be 0.0067, 0.01, 0.027, 0.05, 0.1, 0.5, 1, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, or a range consisting of any two of these values. By regulating the value of a / g within the above range, the negative electrode active material and the electrolyte have good compatibility, wherein, since the electrolyte mainly reacts with the negative electrode active material at the end surface, and fluoroethylene carbonate can form a film on the end surface of the negative electrode active material, the formed solid electrolyte interface film can protect the negative electrode active material, reduce the side reaction between the negative electrode active material and the electrolyte, and improve the gas production of the electrolyte at high voltage and high temperature, thereby improving the cycle performance of the secondary battery under high voltage and high temperature conditions.

[0032] In some embodiments of the present application, the electrolyte further includes a wetting agent, and the mass percentage of the wetting agent is e%, 0.1≤e≤10 based on the mass of the electrolyte; the wetting agent includes C6 to C 12 Fluorinated aromatic hydrocarbons, C1 to C6 fluorinated ether compounds and C1 to C 12 At least one of the perfluoroalkanes. For example, the value of e can be 0.1, 0.3, 0.5, 0.8, 1, 2, 5, 6, 8, 10, or a range consisting of any two of these values. The electrolyte includes a wetting agent, and regulating the value of e within the above range can reduce the surface tension of the electrolyte, improve the electrolyte's ability to wet the negative electrode sheet, improve the kinetic properties of the negative electrode sheet, and facilitate the cycle performance of the secondary battery. It can also improve the fluidity of the electrolyte, facilitate the transmission of lithium ions in the negative electrode sheet, thereby achieving rapid charging and improving the fast charging performance of the secondary battery.

[0033] In some embodiments of the present application, 0.0015≤e / d≤2, preferably 0.015≤e / d≤0.33. For example, the value of e / d can be 0.0015, 0.002, 0.004, 0.005, 0.008, 0.01, 0.015, 0.03, 0.05, 0.08, 0.1, 0.2, 0.3, 0.33, 0.5, 1, 1.5, 2, or a range consisting of any two of these values. Since the fluorolinear ester has a large viscosity, the surface tension of the electrolyte can be reduced and the infiltration of the electrolyte can be accelerated by introducing an appropriate amount of wetting agent with low surface tension, so that the electrolyte in each area of ​​the negative electrode plate is well infiltrated and evenly distributed. By regulating the value of e / d within the above range, the fluorolinear ester and the wetting agent can work synergistically; the combination of the two can not only reduce the side reactions between the negative electrode active material and the electrolyte, but also improve the wetting ability of the electrolyte on the negative electrode plate, improve the gas production of the electrolyte at high voltage and high temperature, and achieve fast charging, thereby further improving the cycle performance of the secondary battery under high voltage and high temperature conditions while improving its fast charging performance.

[0034] In some embodiments of the present application, the wetting agent includes at least one of fluorobenzene, 1,2-difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene, 1,3,5-trifluorobenzene, 1,2,3-trifluorobenzene, 1,2,4-trifluorobenzene, 1,2,3,5-tetrafluorobenzene, 1,2,4,5-tetrafluorobenzene, 1,2,3,4-tetrafluorobenzene, pentafluorobenzene, hexafluorobenzene, p-fluorotoluene, p-ditrifluorotoluene, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 2,2,2-trifluoroethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, difluoromethyl 2,2,3,3-tetrafluoropropyl ether, 1,1,1,3,3,3-hexafluoroisopropyl methyl ether or perfluorododecane. Selecting a wetting agent within the above range is beneficial to further reduce the surface tension of the electrolyte, improve the electrolyte's wetting ability on the negative electrode sheet, improve the kinetic properties of the negative electrode sheet, and further improve the fluidity of the electrolyte, which is beneficial to the transmission of lithium ions in the negative electrode sheet, thereby achieving fast charging and better improving the fast charging performance of the secondary battery.

[0035] In some embodiments of the present application, the negative electrode active material includes at least one of natural graphite, artificial graphite, hard carbon or soft carbon. The above-mentioned negative electrode active material is selected. On the one hand, it has good compatibility with the fluoro-substituted linear ester. On the other hand, the above-mentioned negative electrode active materials with different specific surface areas and end face ratios have different pore structures. The above-mentioned negative electrode active materials are matched with the fluoro-substituted linear ester to reduce the polarization during charging of the secondary battery and improve the fast charging capability. Therefore, while achieving rapid lithium insertion of the negative electrode active material, the electrolyte's ability to wet the negative electrode sheet can be improved, which is beneficial to improving the cycle performance of the secondary battery under high voltage and high temperature conditions, and further improving the fast charging performance of the secondary battery. Generally, the particle size of the negative electrode active material can be changed by mechanical crushing (such as ball milling), thereby changing the value of the specific surface area c of the negative electrode active material. For example, when other conditions remain unchanged, extending the ball milling time will reduce the particle size of the negative electrode active material and increase c; shortening the ball milling time will increase the particle size of the negative electrode active material and decrease c.

[0036] In the present application, the negative electrode active material can be obtained by the following preparation methods: raw material pretreatment, granulation (pyrolysis, ball milling and screening), graphitization, ball milling and screening. Negative electrode active materials with different a values ​​can be prepared by regulating the synthesis process of the negative electrode active material, such as the use of high temperature and high pressure in the pyrolysis process, whether to coat the material, etc. When other conditions remain unchanged, within a certain range, increasing the temperature and pressure in the pyrolysis process will increase the a value; decreasing the temperature and pressure in the pyrolysis process will decrease the a value. For example, the proportion of the end face can be increased by coating, so that the a value is increased. In the present application, the temperature of the above-mentioned high temperature and high pressure can be 1200℃ to 1500℃, the pressure can be 2GPa to 5GPa, and the time can be 0.1h to 3h. The coating can be carried out using asphalt, and the coating amount can be 5% to 15% based on the mass of the negative electrode active material.

[0037] In the present application, negative electrode active materials with different a values ​​can be purchased, and the proportion a of the end face of the negative electrode active material can be tested in combination with the test method of "Test of the specific surface area and the proportion of the end face of the negative electrode active material" provided in the present application, and the negative electrode active material with the required a value can be selected.

[0038] In the present application, the electrolyte also includes lithium salts and non-aqueous solvents. The present application has no particular restrictions on lithium salts and non-aqueous solvents, as long as the purpose of the present application can be achieved. For example, the lithium salt may include but is not limited to at least one of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium difluorooxalatoborate (LiDFOB), lithium bis(oxalatoborate) (LiBOB), lithium nitrate (LiNO3) or lithium difluorophosphate (LiPO2F2). The present application has no particular restrictions on the mass percentage of the lithium salt in the electrolyte, as long as the purpose of the present application can be achieved. For example, based on the mass of the electrolyte, the mass percentage of the lithium salt is 8% to 15%. Exemplarily, the mass percentage of the lithium salt can be 8%, 9%, 10%, 11%, 13%, 15% or a range consisting of any two of these values. The non-aqueous solvent may include but is not limited to at least one of a carbonate compound, a carboxylate compound, an ether compound or other organic solvents. The above-mentioned carbonate compound may include but is not limited to at least one of a chain carbonate compound or a cyclic carbonate compound. The above-mentioned linear carbonate compound may include but is not limited to at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC) or methyl ethyl carbonate (MEC). The above-mentioned cyclic carbonate may include but is not limited to at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC) or vinyl ethylene carbonate (VEC). The above-mentioned carboxylate compound may include but is 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, decanoic acid, valerolactone or caprolactone. The above-mentioned ether compound may include but is 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 other organic solvents may include, but are not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate. Based on the mass of the electrolyte, the mass percentage of the non-aqueous solvent may be 0% to 87%, for example, 0%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 87%, or a range consisting of any two of these values.

[0039] In some embodiments, the electrolyte includes a fluorolinear ester, a lithium salt, and a non-aqueous solvent. The weight percentages of the fluorolinear ester and the lithium salt are as described above, and the weight percentage of the non-aqueous solvent is 20% to 87%. A secondary battery including this electrolyte can improve the cycling performance of the secondary battery under high voltage and high temperature conditions, and also improve the fast charging performance of the secondary battery.

[0040] In some embodiments, the electrolyte includes a fluorolinear ester, a lithium salt, a fluoroethylene carbonate, and a non-aqueous solvent. The weight percentages of the fluorolinear ester, the lithium salt, and the fluoroethylene carbonate are as described above, and the weight percentage of the non-aqueous solvent is 5% to 86%. A secondary battery including this electrolyte can improve the fast-charging performance of the secondary battery while further improving its cycling performance under high voltage and high temperature conditions.

[0041] In some embodiments, the electrolyte comprises a fluorolinear ester, a lithium salt, a wetting agent, and a non-aqueous solvent. The weight percentages of the fluorolinear ester, lithium salt, and wetting agent are as described above, and the weight percentage of the non-aqueous solvent is 10% to 86%. A secondary battery comprising such an electrolyte can improve the cycling performance of the secondary battery under high voltage and high temperature conditions while further improving its fast charging performance.

[0042] In some embodiments, the electrolyte comprises a fluorolinear ester, a lithium salt, a fluoroethylene carbonate, a wetting agent, and a non-aqueous solvent. The weight percentages of the fluorolinear ester, the lithium salt, the fluoroethylene carbonate, and the wetting agent are as described above, and the weight percentage of the non-aqueous solvent is 0% to 86%. A secondary battery including this electrolyte can further improve both the cycling performance and fast charging performance of the secondary battery under high voltage and high temperature conditions.

[0043] The present application has no particular restrictions on the negative electrode current collector, as long as the purpose of the present application can be achieved. For example, the negative electrode current collector may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, carbon-based current collector or composite current collector (such as carbon-copper composite current collector, nickel-copper composite current collector, titanium-copper composite current collector), etc. The present application has no particular restrictions on the thickness of the negative electrode current collector, as long as the purpose of the present application can be achieved. For example, the thickness of the negative electrode current collector is 4μm to 20μm. In the present application, there is no particular restriction on the thickness of the negative electrode material layer, as long as the purpose of the present application can be achieved. For example, the thickness of the single-sided negative electrode material layer is 30μm to 160μm. In the present application, the negative electrode material layer can be arranged on one surface in the thickness direction of the negative electrode current collector, or on two surfaces in the thickness direction of the negative electrode current collector. It should be noted that the "surface" here can be the entire area of ​​the negative electrode current collector or a partial area of ​​the negative electrode current collector. The present application has no particular restrictions, as long as the purpose of the present application can be achieved.

[0044] The negative electrode material layer of the present application may also include a negative electrode conductive agent, a negative electrode binder and a negative electrode dispersant. The present application has no particular restrictions on the negative electrode conductive agent and the negative electrode binder, as long as the purpose of the present application can be achieved. For example, the negative electrode conductive agent may include but is not limited to at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), graphite, carbon fiber, carbon nanowire, graphene, metal materials or conductive polymers, and the above-mentioned carbon nanotubes may include but are not limited to single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The above-mentioned carbon fibers may include but are not limited to vapor-grown carbon fibers (VGCF) and / or nano-carbon fibers. The above-mentioned metal materials may include but are not limited to metal powder and / or metal fibers. Specifically, the metal may include but is not limited to at least one of copper, nickel, aluminum or silver. The above-mentioned conductive polymer may include but is not limited to at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene or polypyrrole. The negative electrode dispersant may include sodium carboxymethyl cellulose.

[0045] In the present application, there is no particular limitation on the method for preparing the negative electrode sheet, as long as the purpose of the present application can be achieved. For example, it can be prepared by the following method: a negative electrode active material, a negative electrode binder, and a negative electrode dispersant are mixed, deionized water is added and stirred evenly, and a negative electrode slurry with a solid content of 55wt% to 70wt% is obtained. The negative electrode slurry is evenly coated on one surface of the negative electrode current collector, and after drying, a negative electrode sheet coated with a negative electrode material layer on one side is obtained. Then, the above coating steps are repeated on the other surface of the negative electrode current collector, and after drying, a negative electrode sheet coated with a negative electrode material layer on both sides is obtained. After coating, the negative electrode sheet is obtained by cold pressing and cutting.

[0046] The present application has no particular restrictions on the positive electrode sheet, as long as the purpose of the present application can be achieved. For example, the positive electrode sheet includes a positive electrode current collector and a positive electrode material layer provided on at least one surface of the positive electrode current collector. The present application has no particular restrictions on the positive electrode current collector, as long as the purpose of the present application can be achieved. For example, the positive electrode current collector may include aluminum foil, aluminum alloy foil or a composite current collector (such as an aluminum-carbon composite current collector), etc. The present application has no particular restrictions on the thickness of the positive electrode current collector, as long as the purpose of the present application can be achieved. For example, the thickness of the positive electrode current collector is 5μm to 20μm. In the present application, the positive electrode material layer includes a positive electrode active material, and the present application has no particular restrictions on the type of positive electrode active material, as long as the purpose of the present application can be achieved. The positive electrode active material includes a compound that reversibly intercalates and deintercalates lithium ions. In some embodiments, the positive electrode material layer includes a positive electrode active material having an operating potential of 4.5V or more relative to metallic lithium. That is, the positive electrode active material of the present application can operate under high voltage. In some embodiments, the positive electrode active material may include at least one of lithium nickel cobalt manganese oxide (NCM), lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide, lithium manganese oxide, or lithium iron manganese phosphate. Lithium nickel cobalt manganese oxide may include but is not limited to LiNi0.8 Co 0.1 Mn 0.1 O2(NCM811), LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM622), LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM523),LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2(NCM333) or LiNi 0.9 Co 0.05 Mn 0.05 At least one of O2 (NCM955). The above-mentioned positive electrode active material may be doped. In some embodiments, the elements used for doping may include at least one of K, Na, Ca, Mg, B, Al, Co, Si, V, Ga, Sn, or Zr. The present application has no particular restriction on the thickness of the positive electrode material layer, as long as the purpose of the present application can be achieved. For example, the thickness of the single-sided positive electrode material layer is 30μm to 120μm. In the present application, the positive electrode material layer can be arranged on one surface in the thickness direction of the positive electrode current collector, or on two surfaces in the thickness direction of the positive electrode current collector. It should be noted that the "surface" here can be the entire area of ​​the positive electrode current collector surface, or it can be a partial area of ​​the positive electrode current collector surface. This application has no particular restrictions, as long as the purpose of the present application can be achieved. The positive electrode material layer of the present application may also contain a positive electrode conductive agent and a positive electrode binder. This application has no particular restrictions on the positive electrode conductive agent and the positive electrode binder, as long as the purpose of the present application can be achieved. For example, the positive electrode conductive agent may be the same as the negative electrode conductive agent, and the positive electrode binder may be the same as the negative electrode binder.

[0047] In the present application, there is no particular restriction on the method for preparing the positive electrode sheet, as long as the purpose of the present application can be achieved. For example, it can be prepared by the following method: the positive electrode active material, the positive electrode conductive agent, and the positive electrode binder are mixed, N-methylpyrrolidone (NMP) is added and stirred evenly to obtain a positive electrode slurry with a solid content of 65wt% to 85wt%. The positive electrode slurry is evenly coated on one surface of the positive electrode collector, and after drying, a positive electrode sheet coated with a positive electrode material layer on one side is obtained. Then, the above coating steps are repeated on the other surface of the positive electrode collector, and after drying, a positive electrode sheet coated with a positive electrode material layer on both sides is obtained. After coating is completed, the positive electrode sheet is obtained by cold pressing and cutting.

[0048] In the present application, the secondary battery also includes a diaphragm, which is used to separate the positive electrode plate and the negative electrode plate, prevent internal short circuit of the secondary battery, allow electrolyte ions to pass freely, and do not affect the electrochemical charge and discharge process. The present application has no particular restrictions on the diaphragm, as long as the purpose of the present application can be achieved. For example, the material of the diaphragm may include but is not limited to polyethylene (PE), polypropylene (PP)-based polyolefins (PO), polyesters (for example, polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex or aramid at least one. Exemplarily, polyethylene includes at least one of high-density polyethylene, low-density polyethylene or ultra-high molecular weight polyethylene. The type of diaphragm may include at least one of a woven membrane, a non-woven membrane, a microporous membrane, a composite membrane, a rolled membrane or a spun membrane. In the present application, the thickness of the diaphragm is not particularly limited, as long as the purpose of the present application can be achieved. For example, the thickness of the diaphragm can be 5μm to 500μm.

[0049] In some embodiments, the separator may include a substrate layer and a surface treatment layer. The substrate layer may be a non-woven fabric, a film or a composite film having 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 film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric or a polypropylene-polyethylene-polypropylene porous composite film may be used. Optionally, 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 a mixed polymer and an inorganic material. For example, the inorganic layer includes inorganic particles and a binder. The above-mentioned inorganic particles are not particularly limited, for example, they may include at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide or barium sulfate. The above-mentioned binder is not particularly limited, for example, it may be at least one of the above-mentioned negative electrode binders. The polymer layer contains polymers, and the polymer material includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinyl pyrrolidone, polyvinyl ether, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene).

[0050] The secondary battery of this application also includes a packaging bag for containing the positive electrode sheet, separator, negative electrode sheet, and electrolyte, as well as other components of the secondary battery known in the art. This application does not limit these other components. This application does not specifically limit the packaging bag and can be any packaging bag known in the art, as long as it can achieve the purpose of this application.

[0051] The secondary battery of the present application is not particularly limited and may include any device that undergoes an electrochemical reaction. In one embodiment of the present application, the secondary battery may include, but is not limited to, a lithium ion secondary battery (lithium ion battery), a lithium metal secondary battery (lithium metal battery), a sodium ion secondary battery (sodium ion battery), a sodium metal secondary battery (sodium metal battery), a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

[0052] The preparation process of the secondary battery of the present application is well known to those skilled in the art, and is not particularly limited in the present application. For example, it may include but is not limited to the following steps: stacking the positive electrode sheets, diaphragms and negative electrode sheets in order, and winding, folding and other operations as needed to obtain an electrode assembly with a wound structure, placing the electrode assembly in a packaging bag, injecting the electrolyte into the packaging bag and sealing it to obtain a secondary battery. Alternatively, stacking the positive electrode sheets, diaphragms and negative electrode sheets in order, and then fixing the four corners of the entire stacked structure with tape to obtain an electrode assembly with a stacked structure, placing the electrode assembly in a packaging bag, injecting the electrolyte into the packaging bag and sealing it to obtain a secondary battery. In addition, as needed, overcurrent protection elements, guide plates, etc. may be placed in the packaging bag to prevent the pressure inside the secondary battery from rising and overcharging and discharging. The packaging bag is a packaging bag known in the art, and is not limited in the present application.

[0053] The second aspect of the present application provides an electronic device comprising the secondary battery of the first aspect of the present application. The secondary battery of the first aspect of the present application has good cycle performance under high voltage and high temperature conditions and good fast charging performance, so that the electronic device provided by the second aspect of the present application has good performance.

[0054] The present application does not particularly limit the type of electronic device, and it can be any electronic device known in the prior art. In some embodiments of the present application, the electronic device can include, but is not limited to, a laptop computer, a pen-type computer, a mobile computer, an electronic book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, an LCD television, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flashlight, a camera, a large household battery, and a lithium-ion capacitor.

[0055] Example

[0056] The following examples and comparative examples are provided to more specifically illustrate the embodiments of the present invention. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0057] Test methods and equipment:

[0058] Test of the specific surface area and end face ratio of the negative electrode active material:

[0059] The specific surface area of ​​the negative electrode active material was measured using a TriStar II 3020 surface area analyzer via nitrogen adsorption / desorption. The specific test was conducted in accordance with the national standard GB / T 19587-2017, "Determination of the Specific Surface Area of ​​Solids by the BET Method for Gas Adsorption."

[0060] The proportion of the end face is calculated based on the different gas adsorption energies of the end face and basal surface of the negative electrode active material. The adsorption energy of the end face of the negative electrode active material is between 20e / k and 50e / k, and the adsorption energy of the basal surface is between 50e / k and 80e / k. The end face or basal surface corresponding to different adsorption energies is fitted and processed by the analysis software of the specific surface area analyzer. The proportion a of the end face can be obtained. The adsorption energy curve of the negative electrode active material is fitted using the TriStar II3020 supporting software, and the integral area of ​​the adsorption energy curve from 20e / k to 80e / k is calculated, recorded as S; the integral area of ​​the adsorption energy curve from 20e / k to 50e / k is recorded as S1; the proportion of the end face = S1 / S.

[0061] Cyclic performance test:

[0062] The cycle performance of lithium-ion batteries under high voltage conditions is evaluated by the capacity retention rate measured at 25°C and a charge cut-off voltage of 4.4V. The higher the capacity retention rate, the better the cycle performance of the lithium-ion battery under high voltage. The lower the capacity retention rate, the worse the cycle performance of the lithium-ion battery under high voltage. The test process is as follows: the lithium-ion battery is placed in a 25°C constant temperature box and allowed to stand for 60 minutes. The lithium-ion battery is then charged at a constant current of 3C to a voltage of 4.3V, then charged at a constant current of 1C to 4.4V, then charged at a constant voltage to a current of 0.05C, allowed to stand for 15 minutes, and then discharged at 0.2C to 3.0V. This is one charge and discharge cycle. The first discharge capacity is recorded as C1, and the charge and discharge cycle is repeated 1000 times. The test is stopped and the discharge capacity at the 1000th time is recorded as C2. The 4.4V cycle capacity retention rate of the lithium-ion battery is C% = C2 / C1×100%.

[0063] The thickness expansion rate (TEX) of lithium-ion batteries measured at 45°C is used to evaluate the cycling performance of lithium-ion batteries under high-temperature conditions. A lower TEX indicates better cycling performance at high voltages; a higher TEX indicates poorer cycling performance at high voltages. The test procedure is as follows: The lithium-ion battery is placed in a 45°C incubator and allowed to rest for 60 minutes. The thickness (d1) of the lithium-ion battery at this time is recorded. The lithium-ion battery is then charged at a constant current of 3C to a voltage of 4.3V, then at a constant current of 1C to 4.35V, then charged at a constant voltage to a current of 0.05C, allowed to rest for 15 minutes, and then discharged at 0.2C to 3.0V. This constitutes one charge-discharge cycle. The charge-discharge cycle is repeated 500 times, with the initial discharge capacity set as 100%. The test is then terminated, and the thickness (d2) of the lithium-ion battery after 500 cycles is recorded. The TEX of the lithium-ion battery at 45°C (d%) = (d2 - d1) / d1 × 100%.

[0064] Fast charging performance test:

[0065] The fast-charging performance of lithium-ion batteries is evaluated by their charging time. Longer charging times indicate poorer fast-charging performance, while shorter charging times indicate better fast-charging performance. The test procedure is as follows: Place the lithium-ion battery in a 25°C constant-temperature chamber for 30 minutes. Charge the battery at a constant current of 3C to a voltage of 4.3V, then at a constant current of 1C to a voltage of 4.35V, and then at a constant voltage to a current of 0.05C. The charging time for this process is T min.

[0066] Example 1-1

[0067] <Preparation of negative electrode sheet>

[0068] Artificial graphite (average particle size of 13 μm) was pyrolyzed in a reactor at 1200°C and 2 GPa for 0.5 h in a nitrogen atmosphere. The specific surface area c and the end face ratio a of the obtained artificial graphite, a negative electrode active material, are shown in Table 1.

[0069] The artificial graphite negative electrode active material, the negative electrode binder styrene-butadiene rubber (SBR), and sodium carboxymethyl cellulose prepared above were mixed in a mass ratio of 97.4:1.2:1.4, and then deionized water was added as a solvent to prepare a slurry with a solid content of 70 wt%, and stirred evenly. The negative electrode slurry was evenly coated on one surface of an 8 μm thick copper foil and dried at 110°C. Thereafter, the above steps were repeated on the other surface of the copper foil to obtain a negative electrode sheet coated with a negative electrode active material layer on both sides. After cold pressing, a double-sided negative electrode sheet with a single-sided negative electrode active material layer thickness of 150 μm was obtained. The negative electrode sheet was cut into a specification of 78 mm × 875 mm and welded to the tabs for use.

[0070] <Preparation of positive electrode sheet>

[0071] The positive electrode active material LiNi 0.6 Co 0.2 Mn 0.2 O2, acetylene black (a positive electrode conductive agent), and polyvinylidene fluoride (PVDF) (a positive electrode binder) were mixed in a mass ratio of 96:2:2. N-methylpyrrolidone (NMP) was added as a solvent and stirred evenly in a vacuum mixer to obtain a positive electrode slurry with a solid content of 75 wt%. The positive electrode slurry was evenly coated on one side of a 12 μm thick positive electrode current collector aluminum foil and dried at 85°C. The above steps were then repeated on the other surface of the aluminum foil to obtain a positive electrode sheet coated on both sides with a positive electrode active material layer. After cold pressing, a double-sided coated positive electrode sheet with a single-sided positive electrode active material layer thickness of 100 μm was obtained. The positive electrode sheet was cut into a size of 74 mm × 867 mm and welded to the tabs for later use.

[0072] <Preparation of Electrolyte>

[0073] In a dry argon atmosphere glove box, ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed in a mass ratio of 1:1 to obtain a non-aqueous solvent. Fluorinated linear ester (27) and lithium salt LiPF6 were then added to the base organic solvent and mixed uniformly to obtain an electrolyte. The mass percentage of the lithium salt was 12.5% ​​based on the mass of the electrolyte, the mass percentage of the fluorolinear ester was d% as shown in Table 1, and the balance was the non-aqueous solvent.

[0074] <Isolation Film>

[0075] A polyethylene (PE) porous polymer film with a thickness of 15 μm (provided by Celgard) was used as the separator.

[0076] <Preparation of lithium-ion batteries>

[0077] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, with the separator placed between the positive and negative electrodes to serve as an isolation, and then wound to obtain an electrode assembly; the electrode assembly is placed in an aluminum-plastic film packaging bag, placed in an 85°C vacuum oven to dry for 12 hours to remove moisture, and the above-prepared electrolyte is injected. After vacuum packaging, standing, formation (0.02C constant current charging to 3.5V, then 0.1C constant current charging to 3.9V), shaping, capacity testing, secondary packaging and other processes, a lithium-ion battery is obtained.

[0078] Example 1-2 to Example 1-6

[0079] Except that the mass percentage d% of the fluorolinear ester is adjusted according to Table 1, the mass percentage of the non-aqueous solvent is changed accordingly, and the mass percentage of the lithium salt and the mass ratio of each component of the non-aqueous solvent remain unchanged, the rest is the same as Example 1-1.

[0080] Example 1-7 to Example 1-12

[0081] Except for adjusting the type of fluorinated linear ester according to Table 1, the rest is the same as Example 1-1.

[0082] Example 1-13 to Example 1-28

[0083] The process was identical to Example 1-10, except that the relevant parameters were adjusted according to Table 1 to achieve the values ​​of c / d and a / d as shown in Table 1. When the mass percentage d% of the fluorolinear ester was changed, the mass percentage of the non-aqueous solvent was also changed, while the mass percentage of the lithium salt and the mass ratios of the non-aqueous solvent components remained unchanged. The negative electrode active material was ball-milled for an adjusted milling time to achieve the specific surface area c shown in Table 1. The temperature and pressure of the pyrolysis treatment were adjusted to achieve the end face ratio a shown in Table 1.

[0084] Example 2-1 to Example 2-8

[0085] Except for further introducing fluoroethylene carbonate into the electrolyte and adjusting the parameters according to Table 2, the rest is the same as Example 1-4.

[0086] Example 2-9 to Example 2-17

[0087] Except for further introducing the wetting agent fluorobenzene into the electrolyte and adjusting the parameters according to Table 2, the rest is the same as Example 2-5.

[0088] Example 3-1 to Example 3-14

[0089] Except for further introducing a wetting agent into the electrolyte and adjusting the parameters according to Table 3, the rest is the same as Example 1-4.

[0090] Comparative Example 1

[0091] The electrolyte does not include fluorinated linear ester, the mass percentage of the non-aqueous solvent changes accordingly, and the mass percentage of the lithium salt and the mass ratio of each component of the non-aqueous solvent remain unchanged. The rest is the same as Example 1-13.

[0092] Comparative Example 2

[0093] The electrolyte does not include fluorinated linear ester, the mass percentage of the non-aqueous solvent changes accordingly, and the mass percentage of the lithium salt and the mass ratio of each component of the non-aqueous solvent remain unchanged, and the rest is the same as Example 1-1.

[0094] Comparative Examples 3 to 6

[0095] The process was identical to Example 1-13, except that the relevant parameters were adjusted according to Table 1 to achieve the values ​​of c / d and a / d as shown in Table 1. When the mass percentage d% of the fluorolinear ester was changed, the mass percentage of the non-aqueous solvent was also changed, while the mass percentage of the lithium salt and the mass ratios of the non-aqueous solvent components remained unchanged. The negative electrode active material was ball-milled for an adjusted milling time to achieve the specific surface area c shown in Table 1. The temperature and pressure of the pyrolysis treatment were adjusted to achieve the end face ratio a shown in Table 1.

[0096] The relevant parameters and performance tests of each embodiment and each comparative example are shown in Tables 1 to 3.

[0097] Table 1

[0098]

[0099]

[0100] Note: “ / ” in Table 1 indicates that there is no corresponding substance or parameter.

[0101] From Examples 1-1 to 1-28 and Comparative Examples 1 to 6, it can be seen that the electrolyte includes a fluorinated linear ester and the values ​​of d, c / d, and a / d are adjusted within the range of this application, which can enable the lithium-ion battery to have a higher 4.4V cycle capacity retention rate, a lower 45°C cycle thickness expansion rate, and a shorter charging time, indicating that the lithium-ion battery has better cycling performance and better fast charging performance under high voltage and high temperature conditions. The electrolytes of Comparative Examples 1 and 2 do not include a fluorinated linear ester, the c / d value of Comparative Example 3 is too small, the c / d value of Comparative Example 4 is too large, the d and a / d values ​​of Comparative Example 5 are too large, and the a / d value of Comparative Example 6 is too small. The lithium-ion batteries have a lower 4.4V cycle capacity retention rate, a higher 45°C cycle thickness expansion rate, and a longer charging time. This indicates that when at least one of d, c / d, and a / d is outside the range of this application, the lithium-ion battery has poor cycling performance and fast charging performance under high voltage and high temperature conditions.

[0102] The type of fluorinated linear ester typically affects the cycling and fast-charging performance of lithium-ion batteries under high-voltage and high-temperature conditions. Examples 1-1, 1-7, and 1-12 demonstrate that using fluorinated linear esters within the scope of this application results in lithium-ion batteries with higher 4.4V cycling capacity retention, lower 45°C cycling thickness expansion, and shorter charging times. This demonstrates that lithium-ion batteries exhibit better cycling and fast-charging performance under high-voltage and high-temperature conditions.

[0103] The values ​​of c and a generally affect the cycling performance and fast-charging performance of lithium-ion batteries under high voltage and high temperature conditions. As can be seen from Examples 1-13 to 1-28, by adjusting the values ​​of c and a within the scope of this application, the lithium-ion battery has a higher 4.4V cycling capacity retention rate, a lower 45°C cycling thickness expansion rate, and a shorter charging time, indicating that the lithium-ion battery has better cycling performance and better fast-charging performance under high voltage and high temperature conditions.

[0104] Table 2

[0105]

[0106] Note: “ / ” in Table 2 indicates that there is no corresponding substance or parameter.

[0107] The electrolyte includes fluoroethylene carbonate and the values ​​of g and a / g usually affect the cycling performance and fast charging performance of lithium-ion batteries under high voltage and high temperature conditions. As can be seen from Examples 1-4 and 2-1 to 2-8, when the electrolyte includes a fluorolinear ester, further introduces fluoroethylene carbonate, and regulates the values ​​of g and a / g within the scope of this application, the lithium-ion battery has a higher 4.4V cycle capacity retention rate, a lower 45°C cycle thickness expansion rate, and a shorter charging time, indicating that the lithium-ion battery has better cycling performance and better fast charging performance under high voltage and high temperature conditions.

[0108] It can be seen from Examples 2-5 and 2-9 to 2-17 that the electrolyte includes fluorinated linear ester and fluorinated ethylene carbonate, and a wetting agent is further introduced, and the values ​​of e and e / d are regulated within the scope of this application. The lithium-ion battery has a higher 4.4V cycle capacity retention rate, a lower 45°C cycle thickness expansion rate, and a shorter charging time, indicating that the lithium-ion battery has better cycle performance and better fast charging performance under high voltage and high temperature conditions.

[0109] Table 3

[0110]

[0111] Note: “ / ” in Table 3 indicates that there is no corresponding substance or parameter.

[0112] The electrolyte, including the wetting agent, and the values ​​of e and e / d generally affect the cycling performance and fast charging performance of the lithium-ion battery under high voltage and high temperature conditions. As can be seen from Examples 1-4 and 3-1 to 3-8, when the electrolyte includes a fluorinated linear ester, the wetting agent is further introduced, and the values ​​of e and e / d are regulated within the scope of this application, the lithium-ion battery has a higher 4.4V cycle capacity retention rate, a lower 45°C cycle thickness expansion rate, and a shorter charging time, indicating that the lithium-ion battery has better cycling performance and better fast charging performance under high voltage and high temperature conditions.

[0113] The type of wetting agent generally affects the cycling performance and fast-charging performance of lithium-ion batteries under high voltage and high temperature conditions. As can be seen from Examples 1-4, 3-9, and 3-14, using wetting agents within the scope of this application, lithium-ion batteries have higher 4.4V cycling capacity retention, lower 45°C cycling thickness expansion, and shorter charging times, indicating that lithium-ion batteries have better cycling performance and faster charging performance under high voltage and high temperature conditions.

[0114] Each embodiment in this specification is described in a related manner. The same or similar parts between the embodiments can be referred to each other. Each embodiment focuses on the differences from other embodiments.

[0115] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. A secondary battery comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the negative electrode sheet comprises a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode material layer comprises a negative electrode active material, and the specific surface area of ​​the negative electrode active material is cm 2 / g, 0.1≤c≤10, the negative electrode active material includes a base surface and an end surface, wherein, The proportion of the end surface is a, 0.1≤a≤0.6; The electrolyte includes a fluorinated linear ester, and based on the mass of the electrolyte, the mass percentage of the fluorinated linear ester is d%, 5≤d≤65, 0.0015≤c / d≤2; 0.0062≤a / d≤0.12; The electrolyte further includes a wetting agent. Based on the mass of the electrolyte, the mass percentage of the wetting agent is e%, and 0.1≤e≤10.

2. The secondary battery according to claim 1, wherein The fluorinated linear ester comprises at least one of the following compounds:

3. The secondary battery according to claim 1 or 2, wherein The electrolyte further includes fluoroethylene carbonate. Based on the mass of the electrolyte, the mass percentage of the fluoroethylene carbonate is g%, and 0.01≤g≤15.

4. The secondary battery according to claim 3, wherein 0.0067≤a / g≤60.

5. The secondary battery according to claim 1, wherein The infiltrant includes C6 to C 12 Fluorinated aromatic hydrocarbons, C1 to C6 fluorinated ether compounds and C1 to C 12 At least one of the perfluoroalkanes.

6. The secondary battery according to claim 5, wherein 0.0015≤e / d≤2.

7. The secondary battery according to claim 5, wherein The wetting agent includes at least one of fluorobenzene, 1,2-difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene, 1,3,5-trifluorobenzene, 1,2,3-trifluorobenzene, 1,2,4-trifluorobenzene, 1,2,3,5-tetrafluorobenzene, 1,2,4,5-tetrafluorobenzene, 1,2,3,4-tetrafluorobenzene, pentafluorobenzene, hexafluorobenzene, p-fluorotoluene, p-ditrifluorotoluene, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 2,2,2-trifluoroethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, difluoromethyl 2,2,3,3-tetrafluoropropyl ether, 1,1,1,3,3,3-hexafluoroisopropyl methyl ether or perfluorododecane.

8. The secondary battery according to claim 1 or 2, wherein The secondary battery satisfies at least one of the following characteristics: (1) 15≤d≤50; (2) 0.015≤c / d≤0.33; (3) 0.0077≤a / d≤0.08; (4)1≤c≤5； (5)0.3≤a≤0.5； (6) 0.015≤e / d≤0.33; (7) The negative electrode active material includes at least one of natural graphite, artificial graphite, hard carbon or soft carbon. 9 . An electronic device comprising the secondary battery according to claim 1 .

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