Secondary battery and electronic device

Abstract

Provided are a secondary battery and an electronic device. The secondary battery comprises a positive electrode sheet, a negative electrode sheet and an electrolyte; the positive electrode sheet comprises a positive electrode material layer, the positive electrode material layer comprising lithium iron phosphate; and the electrolyte comprises a boron trifluoride-dimethyl carbonate complex, lithium difluorophosphate and a boron-containing additive. The positive electrode sheet and the electrolyte can work in conjunction with each other to simultaneously improve the low-temperature discharge performance and the high-temperature storage performance of the secondary battery.

Description

Secondary batteries and electronic devices

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on January 17, 2024, with application number 202410068550.0 and invention name “A Secondary Battery and Electronic Device”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the field of electrochemical technology, and in particular to a secondary battery and an electronic device. Background Art

[0003] Secondary batteries, such as lithium-ion batteries, have the advantages of high energy storage density, high open circuit voltage, low self-discharge rate, long cycle life and good safety. They are now widely used as power sources in various electronic products.

[0004] With the rapid development of electric vehicles and mobile electronic devices, people's performance requirements for lithium-ion batteries are becoming increasingly diverse. As an important component of lithium-ion batteries, electrolytes urgently need to be improved to obtain secondary batteries with good low-temperature discharge performance and high-temperature storage performance. Summary of the Invention

[0005] The purpose of this application is to provide a secondary battery and an electronic device to improve the low-temperature discharge performance and high-temperature storage performance of the secondary battery. The specific technical solution is as follows:

[0006] The first aspect of the present application provides a secondary battery, which includes a positive electrode plate, a negative electrode plate and an electrolyte, the positive electrode plate includes a positive electrode material layer, the positive electrode material layer includes lithium iron phosphate; the electrolyte includes a trifluoride boron dimethyl carbonate complex, lithium difluorophosphate (LiPO2F2) and a boron-containing additive. The positive electrode material layer includes lithium iron phosphate, and the electrolyte includes the above-mentioned trifluoride boron dimethyl carbonate complex and additives, which can improve the structural stability of the positive electrode material layer while suppressing the decomposition reaction of the electrolyte in a high temperature environment, so that the secondary battery of the present application has good thermal stability at high temperatures. At the same time, in a low temperature environment, the lithium iron phosphate in the present application can synergize with the above-mentioned components in the electrolyte, thereby suppressing the deterioration of the liquid circulation of the electrolyte toward the positive electrode plate and increasing the rate of lithium ion migration. Therefore, the secondary battery provided by the present application has good low-temperature discharge performance and high-temperature storage performance.

[0007] In some embodiments of the present application, the negative electrode plate includes a negative electrode material layer, which includes at least one of a carbon material or a silicon-based material, the carbon material includes at least one of a graphite material or amorphous carbon, and the graphite material includes at least one of artificial graphite or natural graphite. These materials have relatively stable crystalline structures during the intercalation and deintercalation of lithium ions. Including these materials in the negative electrode material layer can further improve the low-temperature discharge performance and high-temperature storage performance of the secondary battery.

[0008] In some embodiments of the present application, the carbon material includes a graphite material having amorphous carbon on at least a portion of its surface. The carbon material has the aforementioned characteristics, which can further suppress side reactions between the negative electrode surface and the electrolyte, thereby improving the low-temperature discharge performance and high-temperature storage performance of the secondary battery.

[0009] In some embodiments of the present application, the mass percentage of the boron trifluoride dimethyl carbonate complex is X%, based on the mass of the electrolyte, with 0.1≤X≤2.6. The boron trifluoride dimethyl carbonate complex, as an additive, can improve the solubility of lithium difluorophosphate and boron-containing additives. By regulating the value of X within the above range, the low-temperature discharge performance and high-temperature storage performance of the secondary battery can be further improved.

[0010] In some embodiments of the present application, based on the mass of the electrolyte, the mass percentage of lithium difluorophosphate is A%, the mass percentage of the boron-containing additive is B%, and based on the mass of the positive electrode material layer, the mass percentage of lithium iron phosphate is Y%, 13≤Y≤78; the positive electrode material layer includes a positive electrode material, and the specific surface area of ​​the positive electrode material is S m 2 / g, 9≤S≤18, 3S×Y / 800≤A+B≤3S×Y / 200. Meeting the above conditions can further improve the low-temperature discharge performance and high-temperature storage performance of the secondary battery.

[0011] In some embodiments of the present application, the secondary battery satisfies at least one of the following characteristics: (1) the mass percentage of lithium difluorophosphate based on the mass of the electrolyte is A%, 0.01≤A≤5; (2) the mass percentage of the boron-containing additive based on the mass of the electrolyte is B%, 0.01≤B≤10. Satisfying at least one of the above characteristics can further improve the low-temperature discharge performance and high-temperature storage performance of the secondary battery.

[0012] In some embodiments of the present application, the boron-containing additive includes at least one of lithium dioxalatoborate or lithium difluorooxalatoborate. Selecting the boron-containing additive within the above range further reduces the occurrence of side reactions in the electrolyte, thereby enabling the secondary battery to have good low-temperature discharge performance and high-temperature storage performance.

[0013] In some embodiments of the present application, the positive electrode material layer further includes LiMn2O4, LiNix Co y R z M (1-x-y-z) At least one of O2 or Li2MnO3·(1-α)LiQO2; 0≤x<1, 0≤y≤1, 0≤z≤1, x+y+z≤1, R comprises at least one of Mn or Al, M comprises at least one of Co, Ni, Mg, Cu, Zn, Sn, B, Ga, Cr, Sr, V, or Ti; 0<α<1, Q comprises at least one of Ni, Co, or Mn. The positive electrode material layer also includes the above materials, which can further improve the structural stability of the positive electrode material layer and enhance the synergistic effect between the positive electrode material layer and the electrolyte, thereby further improving the low-temperature discharge performance and high-temperature storage performance of the secondary battery.

[0014] In some embodiments of the present application, the electrolyte further includes a first additive, the first additive including at least one of trimethylfluorosilane or tris(trimethylsilyl)phosphate, and the mass percentage of the first additive based on the mass of the electrolyte is C%, and 0.1≤C≤7. The electrolyte includes the first additive and regulates the value of C within the above range, which can further reduce decomposition reactions in the electrolyte, thereby further improving the low-temperature discharge performance and high-temperature storage performance of the secondary battery.

[0015] In some embodiments of the present application, the electrolyte includes ethylene carbonate, and the mass percentage of ethylene carbonate is D%, based on the mass of the electrolyte, and 5≤D≤30. When the electrolyte includes ethylene carbonate and the value of D is adjusted within the above range, the low-temperature discharge performance and high-temperature storage performance of the secondary battery can be further improved.

[0016] In some embodiments of the present application, the mass percentage of lithium difluorophosphate is A%, based on the mass of the electrolyte, and 0.003 ≤ A / D ≤ 0.2. Controlling the A / D value within this range can better maximize the effects of lithium difluorophosphate and further improve the low-temperature discharge performance and high-temperature storage performance of the secondary battery.

[0017] In some embodiments of the present application, the electrolyte further includes ethyl propionate, and the mass percentage of ethyl propionate is E%, based on the mass of the electrolyte, and 0.1≤E≤20. The electrolyte further includes ethyl propionate and the value of E is regulated within the above range, which can further enhance the dissolution-promoting effect of the dimethyl boron trifluoride carbonate complex on lithium difluorophosphate, thereby further improving the low-temperature discharge performance and high-temperature storage performance of the secondary battery.

[0018] In some embodiments of the present application, the electrolyte includes an electrolyte salt, and the electrolyte salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, lithium difluorobis(oxalatophosphate), lithium tetrafluorobis(oxalatophosphate), lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium trifluoromethanesulfonate, or lithium perchlorate. The electrolyte includes the above electrolyte salt, which can improve the uniformity and stability of the electrolyte salt in the electrolyte, thereby further improving the low-temperature discharge performance and high-temperature storage performance of the secondary battery.

[0019] In some embodiments of the present application, the electrolyte salt includes lithium hexafluorophosphate, and the electrolyte further includes propylene carbonate. Based on the mass of the electrolyte, the mass percentage of lithium hexafluorophosphate is W%, and the mass percentage of propylene carbonate is F%, wherein 4≤W≤24, 4≤F≤24, and 0.5≤W / F≤2. By regulating the values ​​of W and F within the above ranges, the uniformity of the electrolyte salt concentration can be further improved, thereby improving the low-temperature discharge performance and high-temperature storage performance of the secondary battery.

[0020] The second aspect of the present application provides an electronic device comprising the secondary battery of any of the aforementioned embodiments. The secondary battery provided in the first aspect of the present application has good low-temperature discharge performance and high-temperature storage performance. Therefore, the electronic device provided in the present application has a long service life and a wide operating temperature range.

[0021] Beneficial effects of this application:

[0022] The present application provides a secondary battery and an electronic device. The secondary battery includes a positive electrode plate, a negative electrode plate and an electrolyte. The positive electrode plate includes a positive electrode material layer, and the positive electrode material layer includes lithium iron phosphate; the electrolyte includes a trifluoride boron dimethyl carbonate complex, lithium difluorophosphate and a boron-containing additive. The positive electrode material layer includes lithium iron phosphate, and the electrolyte includes the above-mentioned trifluoride boron dimethyl carbonate complex and additives, which can improve the structural stability of the positive electrode material while suppressing the decomposition reaction of the electrolyte in a high-temperature environment, so that the secondary battery of the present application has good thermal stability at high temperatures. At the same time, in a low-temperature environment, the lithium iron phosphate in the present application can synergistically act with the above-mentioned components in the electrolyte, thereby suppressing the deterioration of the liquid circulation of the electrolyte toward the positive electrode plate and increasing the rate of lithium ion migration. Therefore, the secondary battery provided by the present application has good low-temperature discharge performance and high-temperature storage performance.

[0023] 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

[0024] 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.

[0025] 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:

[0026] The present application provides a secondary battery, which includes a positive electrode plate, a negative electrode plate and an electrolyte, the positive electrode plate includes a positive electrode material layer, the positive electrode material layer includes lithium iron phosphate; the electrolyte includes a trifluoride boron dimethyl carbonate complex, lithium difluorophosphate (LiPO2F2) and a boron-containing additive. The positive electrode material layer includes lithium iron phosphate, and the electrolyte includes the above-mentioned trifluoride boron dimethyl carbonate complex and additives, which can improve the structural stability of the positive electrode material layer while suppressing the decomposition reaction of the electrolyte in a high temperature environment, so that the secondary battery of the present application has good thermal stability at high temperatures. At the same time, in a low temperature environment, the lithium iron phosphate in the positive electrode material layer can synergistically act with the above-mentioned components in the electrolyte, thereby suppressing the deterioration of the liquid circulation of the electrolyte toward the positive electrode plate and increasing the rate of lithium ion migration. Therefore, the secondary battery provided by the present application has good low-temperature discharge performance and high-temperature storage performance.

[0027] The inventors have discovered that although the lithium iron phosphate positive electrode system has the advantages of long cycle life and high operating voltage, its performance is poor in high and low temperature environments. The electrolyte includes a boron trifluoride dimethyl carbonate complex, the above-mentioned lithium difluorophosphate and a boron-containing additive, which helps to stabilize the crystal structure of lithium iron phosphate during charging and discharging, improve the stability of lithium iron phosphate, and reduce the decomposition reaction of the electrolyte in a high temperature environment, which is beneficial to improving the high temperature storage performance of the secondary battery. At the same time, in a low temperature environment, the above-mentioned components in the electrolyte can form a flexible protective film at the positive electrode interface and increase the migration rate of lithium ions, thereby improving the low temperature resistance of the lithium iron phosphate battery. In this application, high temperature refers to a temperature greater than or equal to 45°C, and low temperature refers to a temperature less than or equal to 0°C.

[0028] In the present application, there is no particular limitation on the preparation method of the boron trifluoride dimethyl carbonate complex (BMC). For example, the boron trifluoride dimethyl carbonate complex can be prepared by the following steps: liquid dimethyl carbonate can be converted into a gaseous state, and introduced into a complexation reactor in a mass ratio of gaseous dimethyl carbonate (DMC) to gaseous boron trifluoride (BF3) of 1:1, and the temperature in the reaction complexation reactor is controlled not to exceed 90°C, and a complexation reaction is carried out to generate a solid boron trifluoride dimethyl carbonate complex.

[0029] In some embodiments of the present application, the negative electrode sheet includes a negative electrode material layer, the negative electrode material layer includes at least one of a carbon material or a silicon-based material, the carbon material includes at least one of a graphite material or amorphous carbon, the graphite material includes at least one of artificial graphite or natural graphite, the silicon-based material includes silicon (elemental substance) or a silicon compound, and the silicon compound may include silicon carbon (SiC), silicon oxide (SiO n , 0<n≤2). The above-mentioned materials have a relatively stable crystalline structure during the insertion and extraction of lithium ions. The inclusion of the above-mentioned materials in the negative electrode material layer can further improve the low-temperature discharge performance and high-temperature storage performance of the secondary battery. This application does not particularly limit the mass percentage of the above-mentioned carbon material or silicon-based material in the negative electrode material layer. It can be selected according to actual needs, as long as it can achieve the purpose of this application.

[0030] In some embodiments of the present application, the carbon material includes a graphite material having amorphous carbon on at least a portion of its surface. The carbon material has the above-mentioned characteristics, which can further suppress the side reaction between the negative electrode surface and the electrolyte, and improve the low-temperature discharge performance and high-temperature storage performance of the secondary battery. The above-mentioned carbon material includes a graphite material having amorphous carbon on at least a portion of its surface, which means that the amorphous carbon can be present on part of the surface of the graphite material particles or on the entire surface of the graphite material particles, and this application does not impose any particular restrictions on this.

[0031] In some embodiments of the present application, based on the mass of the electrolyte, the mass percentage of the boron trifluoride dimethyl carbonate complex is X%, 0.1≤X≤2.6. For example, X can be 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6 or a range consisting of any two of the above values. The boron trifluoride dimethyl carbonate complex can be used as an auxiliary agent to increase the solubility of lithium difluorophosphate and boron-containing additives. By regulating the value of X within the above range, the low-temperature discharge performance and high-temperature storage performance of the secondary battery can be further improved.

[0032] In some embodiments of the present application, based on the mass of the electrolyte, the mass percentage of lithium difluorophosphate is A%, the mass percentage of the boron-containing additive is B%, and based on the mass of the positive electrode material layer, the mass percentage of lithium iron phosphate is Y%, 13≤Y≤78; the positive electrode material layer includes a positive electrode material, and the specific surface area of ​​the positive electrode material is S m 2 / g, 9≤S≤18, 3S×Y / 800≤A+B≤3S×Y / 200. Illustratively, Y may be 13, 17, 21, 26, 29, 33, 37, 41, 44, 48, 53, 56, 59, 62, 68, 71, 73, 78, or a range consisting of any two of the above values, S may be 9, 9.5, 10, 10.5, 11, 11.5, 12, 12.5, 13, 13.5, 14, 14.5, 15, 15.5, 16, 16.5, 17, 17.5, 18, or a range consisting of any two of the above values, and A+B may be 3S×Y / 800, 3S×Y / 700, 3S×Y / 600, 3S×Y / 500, 3S×Y / 400, 3S×Y / 300, 3S×Y / 200, or a range consisting of any two of the above values. Regulating the values ​​of S and Y within the scope of this application is beneficial to the role of additives in the electrolyte in reducing the occurrence of side reactions. It can also make the protective film formed by the electrolyte at the positive electrode interface have higher stability, forming an interface protective film of uniform thickness at the positive electrode, thereby enabling the secondary battery to have good low-temperature discharge performance and high-temperature storage performance. When A+B satisfies 3S×Y / 800≤A+B≤3S×Y / 200, the stability of the negative electrode solid electrolyte interface film (SEI film) and the positive electrode solid electrolyte interface film (CEI film) during temperature changes and charge and discharge processes, as well as the uniformity of the electrolyte, can be further improved, thereby improving the low-temperature discharge performance and high-temperature storage performance of the secondary battery.

[0033] In some embodiments of the present application, the positive electrode material layer further includes LiMn2O4, LiNi x Co y R z M (1-x-y-z)O2 or at least one of Li2MnO3·(1-α)LiQO2; 0≤x<1, 0≤y≤1, 0≤z≤1, x+y+z≤1, R includes at least one of Mn or Al, M includes at least one of Co, Ni, Mg, Cu, Zn, Sn, B, Ga, Cr, Sr, V or Ti; 0<α<1, Q includes at least one of Ni, Co or Mn. For example, x can be 0, 0.1, 0.3, 0.5, 0.6, 0.8, 0.9, 0.99 or a range consisting of any two of the above values, y can be 0, 0.1, 0.3, 0.5, 0.6, 0.8, 0.9, 1 or a range consisting of any two of the above values, z can be 0, 0.1, 0.3, 0.5, 0.6, 0.8, 0.9, 1 or a range consisting of any two of the above values, and α can be 0.01, 0.1, 0.3, 0.5, 0.6, 0.8, 0.9, 0.99 or a range consisting of any two of the above values. The positive electrode material layer also includes the above materials, which can further improve the structural stability of the positive electrode material layer and enhance the synergistic effect between the positive electrode material layer and the electrolyte, thereby further improving the low temperature discharge performance and high temperature storage performance of the secondary battery.

[0034] In this application, the positive electrode material includes lithium iron phosphate, the first material, and may also include a positive electrode binder and a positive electrode conductor. The first material includes the above-mentioned LiMn2O4, LiNi x Co y R z M (1-x-y-z)At least one of O2 or Li2MnO3·(1-α)LiQO2. The mass percentage of the first material is not particularly limited, as long as the purpose of this application can be achieved. Based on the mass of the positive electrode material layer, the mass percentage of the first material is Z%, 17≤Z≤83. For example, Z can be 17, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 83 or a range consisting of any two of the above values. The above-mentioned positive electrode conductor and positive electrode binder are not particularly limited, as long as the purpose of this application can be achieved. The positive electrode binder may include at least one of polytetrafluoroethylene, polyvinylidene fluoride, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, styrene-butadiene rubber (SBR), hydrogenated nitrile rubber (HNBR), carboxymethyl cellulose, methyl cellulose, cellulose phthalate, hydroxypropyl methylcellulose or polyvinyl alcohol. The positive electrode conductive agent may include at least one of acetylene black, Ketjen black, furnace black, carbon fiber, graphite (granular graphite, flaky graphite), or fluorinated graphite, preferably at least one of acetylene black or Ketjen black. In the present application, there is no particular limitation on the mass percentage of 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 mass percentage of the positive electrode conductive agent may be 0.5% to 1.5%, and the mass percentage of the positive electrode binder may be 2% to 5%.

[0035] Typically, the specific surface area S of the positive electrode material can be adjusted by changing the particle size of the positive electrode material through mechanical crushing (e.g., ball milling). When other conditions remain unchanged, extending the ball milling time will reduce the particle size of the positive electrode material and increase S; shortening the ball milling time will increase the particle size of the positive electrode material and reduce S. Alternatively, the specific surface area of ​​lithium iron phosphate can be changed by carbon coating the lithium iron phosphate, thereby changing the specific surface area S of the positive electrode material. Those skilled in the art can make adjustments according to actual needs, and this application does not impose any particular restrictions on this.

[0036] In some embodiments of the present application, the mass percentage of lithium difluorophosphate is A%, based on the mass of the electrolyte, 0.01≤A≤5, illustratively, A can be 0.01, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1 .6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, 5 or a range consisting of any two of the above values. By regulating the value of A within the above range, it is more conducive to forming a flexible protective film at the positive electrode interface, improving the stability of the lithium iron phosphate positive electrode system, thereby further improving the low temperature discharge performance and high temperature storage performance of the secondary battery.

[0037] In some embodiments of the present application, based on the mass of the electrolyte, the mass percentage of the boron-containing additive is B%, 0.01≤B≤10, and illustratively, B can be 0.01, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2. , 3.8, 3.9, 4, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, 5, 5.3, 5.6, 5.9, 6.2, 6.4, 6.7, 6.9, 7.1, 7.4, 7.7, 7.9, 8.3, 8.6, 8.8, 9.1, 9.3, 9.7, 10 or a range consisting of any two of the above values. By regulating the value of B within the above range, it is more conducive to improving the uniformity of the CEI film in the lithium iron phosphate positive electrode system, and can further improve the low temperature discharge performance and high temperature storage performance of the secondary battery.

[0038] In some embodiments of the present application, the boron-containing additive includes at least one of lithium dioxalatoborate (LiBOB) or lithium difluorooxalatoborate (LiDFOB). Selecting a boron-containing additive within the above range facilitates the formation of a stable CEI film on the surface of the positive electrode, further reducing the occurrence of side reactions in the electrolyte, thereby enabling the secondary battery to have excellent low-temperature discharge performance and high-temperature storage performance.

[0039] In some embodiments of the present application, the electrolyte further includes a first additive, the first additive including at least one of trimethylsilyl fluoride ((CH3)3SiF) or tris(trimethylsilyl) phosphate ([(CH3)3SiO]3P(O)), and the mass percentage of the first additive is C%, based on the mass of the electrolyte, 0.1≤C≤7. Exemplarily, C can be 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, 5, 5.1, 5.2, 5.3, 5.4, 5.5, 5.6, 5.7, 5.8, 5.9, 6, 6.1, 6.2, 6.3, 6.4, 6.5, 6.6, 6.7, 6.8, 6.9, 7 or a range consisting of any two of the above values. The electrolyte includes the above-mentioned first additive and regulates the value of C within the above-mentioned range, which is beneficial to further enhance the synergistic effect between lithium iron phosphate and the electrolyte, increase the migration rate of lithium ions, and further reduce the decomposition reaction in the electrolyte, thereby further improving the low-temperature discharge performance and high-temperature storage performance of the secondary battery.

[0040] In some embodiments of the present application, the electrolyte includes ethylene carbonate, and the mass percentage of ethylene carbonate (EC) is D%, based on the mass of the electrolyte, and 5≤D≤30. For example, D can be 5, 7, 8, 10, 12, 14, 15, 16, 18, 20, 21, 23, 25, 27, 30, or a range consisting of any two of the above values. The electrolyte includes ethylene carbonate and the value of D is regulated within the above range, which can further improve the low-temperature discharge performance and high-temperature storage performance of the secondary battery.

[0041] In some embodiments of the present application, based on the mass of the electrolyte, the mass percentage of lithium difluorophosphate is A%, 0.003≤A / D≤0.2. For example, A / D can be 0.003, 0.005, 0.01, 0.02, 0.03, 0.04, 0.05, 0.1, 0.13, 0.15, 0.17, 0.2, or a range consisting of any two of the above values. Regulating the value of A / D within the above range is more conducive to the role of lithium difluorophosphate, and can further improve the low-temperature discharge performance and high-temperature storage performance of the secondary battery.

[0042] In some embodiments of the present application, the electrolyte further comprises ethyl propionate, and the mass percentage of ethyl propionate based on the mass of the electrolyte is E%, 0.1≤E≤20. For example, E can be 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3, 3.1, 3.2, 3.3, 3.4, 3. , 4.5, 4.6, 4.7, 4.8, 4.9, 5, 5.3, 5.6, 5.9, 6.2, 6.4, 6.7, 6.9, 7.1, 7.4, 7.7, 7.9, 8.3, 8.6, 8.8, 9.1, 9.3, 9.7, 10, 12, 14, 15, 17, 19, 20, or a range consisting of any two of the above values. The electrolyte further includes ethyl propionate and the value of E is adjusted within the above range to further enhance the dissolution-promoting effect of the dimethyl boron trifluoride carbonate complex on lithium difluorophosphate, thereby further improving the low-temperature discharge performance and high-temperature storage performance of the secondary battery.

[0043] In some embodiments of the present application, the electrolyte includes an electrolyte salt, and the electrolyte salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium bis(fluorosulfonyl)imide (LiFSI), lithium difluorobis(oxalatophosphate) (LiDFOP), lithium tetrafluorobis(oxalatophosphate) (LiTFOP), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (Li(FSO2)2N), lithium trifluoromethanesulfonate (LiCF3SO3), or lithium perchlorate (LiClO4). The electrolyte includes the above-mentioned electrolyte salt, which can improve the uniformity and stability of the electrolyte salt in the electrolyte, facilitate the transmission of lithium ions, and thus further improve the low-temperature discharge performance and high-temperature storage performance of the secondary battery.

[0044] The present application has no particular restriction on the mass percentage of the electrolyte salt, 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 electrolyte salt is 4% to 30%. For example, the mass percentage of the electrolyte salt can be 4, 5, 6, 7, 8, 9, 10, 13, 15, 17, 20, 23, 25, 27, 30 or a range consisting of any two of the above values.

[0045] In some embodiments of the present application, the electrolyte salt includes lithium hexafluorophosphate, and the electrolyte further includes propylene carbonate (PC). Based on the mass of the electrolyte, the mass percentage of lithium hexafluorophosphate is W%, and the mass percentage of propylene carbonate is F%, 4≤W≤24, 4≤F≤24, 0.5≤W / F≤2, preferably 7≤W≤19, 6≤F≤20. For example, W can be 4, 5, 5.3, 5.6, 5.9, 6.2, 6.4, 6.7, 6.9, 7, 7.1, 7.4, 7.7, 7.9, 8, 8.3, 8.6, 8.8, 9.1, 9.3, 9.7, 10, 10.2, 10.4, 10.6, 10.8, 11.1, 11.3, 11.6, 11.9, 12.4, 12.8, 13. 2, 13.9, 14.4, 14.8, 15, 15.2, 15.7, 16.3, 16.8, 17.1, 17.6, 18.1, 18.3, 18.7, 18.9, 19, 19.2, 19.8, 20, 22, 24 or a range consisting of any two of the above values; F can be 4, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4 .8, 4.9, 5, 5.3, 5.6, 5.9, 6, 6.2, 6.4, 6.7, 6.9, 7.1, 7.4, 7.7, 7.9, 8.3, 8.6, 8.8, 9.1, 9.3, 9.7, 10, 10.2, 10.4, 10.7, 10.9, 11.4, 11.8, 12.2, 12.7, 13.3, 13.6, 14.1, 14.8, 15, 15.2, 15.7, 16.3, 16.8, 17, 17.6, 18.1, 18.3, 18.7, 18.9, 19.2, 19.8, 20, 22, 24, or a range consisting of any two of the above values; W / F can be 0.5, 0.6, 0.8, 1, 1.2, 1.4, 1.5, 1.6, 1.8, 2, or a range consisting of any two of the above values. By regulating the values ​​of W and F within the above ranges, the uniformity of the electrolyte salt concentration can be further improved, which is beneficial to the transmission of lithium ions, thereby further improving the low-temperature discharge performance and high-temperature storage performance of the secondary battery.

[0046] The electrolyte of the present application may also include other non-aqueous solvents, and other non-aqueous solvents may include but are not limited to at least one of dimethyl carbonate, ethyl methyl carbonate (EMC), diethyl carbonate (DEC), propyl propionate, ethyl acetate or methyl propionate. The present application has no particular restrictions on the mass percentage of other non-aqueous solvents, as long as the purpose of the present application can be achieved. Based on the mass of the electrolyte, the mass percentage of the above-mentioned other non-aqueous solvents is 0% to 95%, for example, the mass percentage of other non-aqueous solvents can be 0%, 5%, 10%, 20%, 30%, 31%, 38%, 40%, 41%, 46%, 48%, 50%, 53%, 56%, 60%, 63%, 70%, 75%, 80%, 85%, 90%, 92%, 94%, 95% or a range consisting of any two of the above values.

[0047] In some embodiments, the electrolyte includes a boron trifluoride dimethyl carbonate complex, lithium difluorophosphate, a boron-containing additive, an electrolyte salt, and the aforementioned other non-aqueous solvents. The weight percentages of the boron trifluoride dimethyl carbonate complex, lithium difluorophosphate, the boron-containing additive, and the electrolyte salt are as described above, and the weight percentage of the other non-aqueous solvent is 53% to 95%, based on the weight of the electrolyte. A secondary battery including this electrolyte can improve the low-temperature discharge performance and high-temperature storage performance of the secondary battery.

[0048] In some embodiments, the electrolyte includes a boron trifluoride dimethyl carbonate complex, lithium difluorophosphate, a boron-containing additive, a first additive, an electrolyte salt, and the aforementioned other non-aqueous solvents. Based on the mass of the electrolyte, the mass percentages of the boron trifluoride dimethyl carbonate complex, lithium difluorophosphate, the boron-containing additive, the first additive, and the electrolyte salt are as described above, and the mass percentage of the other non-aqueous solvent is 46% to 95%. A secondary battery including this electrolyte can further improve the low-temperature discharge performance and high-temperature storage performance of the secondary battery.

[0049] In some embodiments, the electrolyte includes a boron trifluoride dimethyl carbonate complex, lithium difluorophosphate, a boron-containing additive, ethylene carbonate, an electrolyte salt, and the other non-aqueous solvents described above. Based on the mass of the electrolyte, the mass percentages of the boron trifluoride dimethyl carbonate complex, lithium difluorophosphate, the boron-containing additive, the first additive, ethylene carbonate, and the electrolyte salt are as described above, and the mass percentage of the other non-aqueous solvent is 23% to 90%. A secondary battery including this electrolyte can further improve the low-temperature discharge performance and high-temperature storage performance of the secondary battery.

[0050] In some embodiments, the electrolyte includes a boron trifluoride dimethyl carbonate complex, lithium difluorophosphate, a boron-containing additive, a first additive, ethylene carbonate, an electrolyte salt, and the other non-aqueous solvents described above. Based on the mass of the electrolyte, the mass percentages of the boron trifluoride dimethyl carbonate complex, lithium difluorophosphate, the boron-containing additive, the first additive, ethylene carbonate, and the electrolyte salt are as described above, and the mass percentage of the other non-aqueous solvents is 16% to 90%. A secondary battery including this electrolyte can further improve the low-temperature discharge performance and high-temperature storage performance of the secondary battery.

[0051] In some embodiments, the electrolyte includes a boron trifluoride dimethyl carbonate complex, lithium difluorophosphate, a boron-containing additive, ethyl propionate, an electrolyte salt, and the aforementioned other non-aqueous solvents. Based on the mass of the electrolyte, the mass percentages of the boron trifluoride dimethyl carbonate complex, lithium difluorophosphate, the boron-containing additive, ethyl propionate, and the electrolyte salt are as described above, and the mass percentage of the other non-aqueous solvent is 33% to 95%. A secondary battery including this electrolyte can further improve the low-temperature discharge performance and high-temperature storage performance of the secondary battery.

[0052] In some embodiments, the electrolyte includes a boron trifluoride dimethyl carbonate complex, lithium difluorophosphate, a boron-containing additive, a first additive, ethyl propionate, an electrolyte salt, and the other non-aqueous solvents described above. Based on the mass of the electrolyte, the mass percentages of the boron trifluoride dimethyl carbonate complex, lithium difluorophosphate, the boron-containing additive, the first additive, ethyl propionate, and the electrolyte salt are as described above, and the mass percentage of the other non-aqueous solvents is 26% to 95%. A secondary battery including this electrolyte can further improve the low-temperature discharge performance and high-temperature storage performance of the secondary battery.

[0053] In some embodiments, the electrolyte includes a boron trifluoride dimethyl carbonate complex, lithium difluorophosphate, a boron-containing additive, ethylene carbonate, ethyl propionate, an electrolyte salt, and the other non-aqueous solvents described above. Optionally, the electrolyte also includes a first additive. Based on the mass of the electrolyte, the mass percentages of the boron trifluoride dimethyl carbonate complex, lithium difluorophosphate, a boron-containing additive, the first additive, ethylene carbonate, ethyl propionate, and the electrolyte salt are as described above, and the mass percentages of the other non-aqueous solvents are 0% to 90%. The secondary battery includes the above-mentioned electrolyte, which can further improve the low-temperature discharge performance and high-temperature storage performance of the secondary battery.

[0054] In some embodiments, the electrolyte includes a boron trifluoride dimethyl carbonate complex, lithium difluorophosphate, a boron-containing additive, propylene carbonate, an electrolyte salt, and the aforementioned other non-aqueous solvents. The mass percentages of the boron trifluoride dimethyl carbonate complex, lithium difluorophosphate, the boron-containing additive, propylene carbonate, and the electrolyte salt are as described above, and the mass percentage of the other non-aqueous solvents ranges from 29% to 91%, based on the mass of the electrolyte. A secondary battery including this electrolyte can further improve the low-temperature discharge performance and high-temperature storage performance of the secondary battery.

[0055] In some embodiments, the electrolyte includes a boron trifluoride dimethyl carbonate complex, lithium difluorophosphate, a boron-containing additive, a first additive, propylene carbonate, an electrolyte salt, and the other non-aqueous solvents described above. Based on the mass of the electrolyte, the mass percentages of the boron trifluoride dimethyl carbonate complex, lithium difluorophosphate, the boron-containing additive, the first additive, propylene carbonate, and the electrolyte salt are as described above, and the mass percentage of the other non-aqueous solvents ranges from 22% to 86%. A secondary battery including this electrolyte can further improve the low-temperature discharge performance and high-temperature storage performance of the secondary battery.

[0056] In some embodiments, the electrolyte includes a boron trifluoride dimethyl carbonate complex, lithium difluorophosphate, a boron-containing additive, ethyl propionate, propylene carbonate, an electrolyte salt, and the other non-aqueous solvents described above. Based on the mass of the electrolyte, the mass percentages of the boron trifluoride dimethyl carbonate complex, lithium difluorophosphate, the boron-containing additive, ethyl propionate, propylene carbonate, and the electrolyte salt are as described above, and the mass percentage of the other non-aqueous solvent is 9% to 91%. A secondary battery including this electrolyte can further improve the low-temperature discharge performance and high-temperature storage performance of the secondary battery.

[0057] In some embodiments, the electrolyte includes a boron trifluoride dimethyl carbonate complex, lithium difluorophosphate, a boron-containing additive, a first additive, ethyl propionate, propylene carbonate, an electrolyte salt, and the other non-aqueous solvents described above. Based on the mass of the electrolyte, the mass percentages of the boron trifluoride dimethyl carbonate complex, lithium difluorophosphate, the boron-containing additive, the first additive, ethyl propionate, propylene carbonate, and the electrolyte salt are as described above, and the mass percentage of the other non-aqueous solvents is 6% to 86%. A secondary battery including this electrolyte can further improve the low-temperature discharge performance and high-temperature storage performance of the secondary battery.

[0058] In some embodiments, the electrolyte includes a boron trifluoride dimethyl carbonate complex, lithium difluorophosphate, a boron-containing additive, ethylene carbonate, propylene carbonate, an electrolyte salt, and the other non-aqueous solvents described above. Optionally, the electrolyte also includes at least one of a first additive or ethyl propionate. Based on the mass of the electrolyte, the mass percentages of the boron trifluoride dimethyl carbonate complex, lithium difluorophosphate, the boron-containing additive, the first additive, ethylene carbonate, propylene carbonate, and the electrolyte salt are as described above, and the mass percentages of the other non-aqueous solvents are 0% to 86%. The inclusion of the above electrolyte in a secondary battery can further improve the low-temperature discharge performance and high-temperature storage performance of the secondary battery.

[0059] The positive electrode sheet of the present application also includes a positive electrode current collector. The present application has no special 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 or aluminum alloy foil, etc. In the present application, there is no special restriction on the thickness of the positive electrode current collector and the positive electrode material layer, as long as the purpose of the present application can be achieved. For example, the thickness of the positive electrode current collector is 5μm to 20μm. 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 or a partial area of ​​the positive electrode current collector. The present application has no special restrictions, as long as the purpose of the present application can be achieved.

[0060] In the present application, the negative electrode sheet also includes a negative electrode current collector. There is no particular limitation on the negative electrode current collector in the present application, as long as the purpose of the present application can be achieved. For example, the negative electrode current collector may include copper foil, copper alloy foil, nickel foil, titanium foil, nickel foam or copper foam, etc. In the present application, the negative electrode material layer may also include at least one of lithium metal, alloys or intermetallic compounds of lithium metal and other metals, metal oxides, metal nitrides, tin (elemental substance), tin compounds, and conductive polymers. The above-mentioned conductive polymers may include but are not limited to at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene or polypyrrole. The negative electrode material layer of the present application may also include a negative electrode conductive agent and a negative electrode binder. There is no particular limitation on the above-mentioned negative electrode conductive agent and negative electrode binder, as long as the purpose of the present application can be achieved. For example, the negative electrode conductive agent may include at least one of acetylene black, Ketjen black, carbon nanotubes (CNTs), carbon nanofibers, flake graphite, carbon dots or graphene, etc. The negative electrode binder may include at least one of polypropylene alcohol, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyamideimide, styrene-butadiene rubber (SBR), polyvinyl alcohol (PVA), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl butyral (PVB), aqueous acrylic resin, carboxymethyl cellulose (CMC) or sodium carboxymethyl cellulose (CMC-Na), etc.

[0061] In the present application, there is no particular restriction on the thickness of the negative electrode current collector and the negative electrode material layer, as long as the purpose of the present application can be achieved. For example, the thickness of the negative electrode current collector is 4μm to 15μm, and 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 provided 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. There is no particular restriction in the present application, as long as the purpose of the present application can be achieved.

[0062] The secondary battery of the present application also includes a separator to separate the positive electrode plate and the negative electrode plate, prevent the internal short circuit of the secondary battery, allow the electrolyte ions to pass freely, and do not affect the electrochemical charge and discharge process. The present application has no special restrictions on the separator, as long as it can achieve the purpose of the present application. For example, the material of the separator can include but is not limited to polyethylene, polypropylene, polytetrafluoroethylene-based polyolefin separators, polyester films (such as polyethylene terephthalate (PET) films), cellulose films, polyimide films, polyamide films, spandex or aramid films, etc. At least one of the types of separators can include but is not limited to woven membranes, non-woven membranes (non-woven fabrics), microporous membranes, composite membranes, rolled membranes or spun membranes, etc. The isolation membrane of the present application may have a porous structure, wherein a porous layer is provided on at least one surface of the isolation membrane, and the porous layer includes inorganic particles and a binder. The inorganic particles 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 binder may include at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polymethyl acrylate, polyethyl acrylate, polybutyl acrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinyl pyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, or polyhexafluoropropylene. The present application does not particularly limit the size of the pore size of the porous structure, as long as the purpose of the present application can be achieved. For example, the pore size may be 0.01 μm to 1 μm. In the present application, the thickness of the isolation film is not particularly limited as long as the purpose of the present application can be achieved. For example, the thickness of the isolation film can be 3 μm to 30 μm.

[0063] The secondary battery of the present application also includes a packaging bag for accommodating a positive electrode sheet, a separator, a negative electrode sheet and an electrolyte, as well as other components known in the art in the secondary battery. The present application has no particular restrictions on the above-mentioned other components. The present application has no particular restrictions on the packaging bag, which can be a packaging bag known in the art, as long as it can achieve the purpose of the present application. For example, an aluminum-plastic film packaging bag can be used. The secondary battery of the present application is not particularly limited, and it can 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 battery, a sodium-ion battery, a lithium polymer secondary battery or a lithium-ion polymer secondary battery, etc.

[0064] 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 sheet, the separator and the negative electrode sheet 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; or stacking the positive electrode sheet, the separator and the negative electrode sheet 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. can also be placed in the packaging bag to prevent pressure rise and overcharge and discharge inside the secondary battery.

[0065] The second aspect of the present application provides an electronic device comprising the secondary battery of any of the aforementioned embodiments. The secondary battery provided in the first aspect of the present application has good low-temperature discharge performance and high-temperature storage performance. Therefore, the electronic device provided in the present application has a long service life and a wide operating temperature range.

[0066] The electronic device of the present application is not particularly limited and can be any electronic device known in the art. In some embodiments, the electronic device may 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 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, an automobile, 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.

[0067] Example

[0068] 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.

[0069] Test methods and equipment:

[0070] Specific surface area test of positive electrode material:

[0071] The specific surface area of ​​the cathode material was measured using a surface area analyzer (TriStar II 3020M, provided by Micromeritics, USA) using nitrogen adsorption. 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."

[0072] Test of the content of each component in the electrolyte:

[0073] Gas chromatography-mass spectrometry (instrument model: Agilent 8890) and ion chromatography (instrument model: AQUION ion chromatography) were used for testing to obtain various components in the electrolyte and test their contents.

[0074] Low temperature discharge performance test:

[0075] The low-temperature discharge performance of the lithium-ion battery is evaluated by the -10°C discharge capacity retention rate. The higher the low-temperature discharge capacity retention rate, the better the low-temperature discharge performance of the lithium-ion battery. After the lithium-ion battery is charged to 4.2V at an ambient temperature of 25°C with a constant current of 990mA (0.3 hour rate), it is charged at a constant voltage of 4.2V with a termination current of 66mA. Then, it is discharged at a constant current of 3300mA (1.0 hour rate) to 3.0V, and the discharge capacity at this time is measured as the battery capacity at 25°C. Then, it is charged to 4.2V at an ambient temperature of 25°C with a constant current of 990mA (0.3 hour rate), and after it is charged at a constant voltage of 4.2V with a termination current of 66mA, it is placed in a -10°C environment for 2 hours. Then, constant current discharge was performed at an ambient temperature of -10°C at a constant current of 3300 mA (1.0 hour rate) to 3.0 V, and the discharge capacity at this time was measured as the battery capacity at -10°C. Then, the -10°C discharge capacity retention rate was calculated by the following formula: -10°C discharge capacity retention rate (%) = (battery capacity at -10°C / battery capacity at 25°C) × 100%.

[0076] High temperature storage performance test:

[0077] The high temperature storage performance of lithium-ion batteries is evaluated by the 80°C capacity retention rate. The higher the capacity retention rate after high temperature storage, the better the high temperature storage performance of the lithium-ion battery. After the lithium-ion battery is charged to 4.2V at an ambient temperature of 25°C with a constant current of 990mA (0.3 hour rate), it is charged at a constant voltage of 4.2V with a termination current of 66mA. Then, it is discharged at a constant current of 1650mA (0.5 hour rate) to 3.0V, and the discharge capacity at this time is measured as the battery capacity before storage. Then, it is charged to 4.2V at an ambient temperature of 25°C with a constant current of 990mA (0.3 hour rate), and charged at a constant voltage of 4.2V with a termination current of 66mA, and then kept in a constant temperature bath at 80°C for 3 days. After storage, the lithium-ion battery was removed from the thermostatic chamber and allowed to stand for 1 hour. The battery was then discharged to 3.0 V at a constant current of 1650 mA (0.5 hour rate) at an ambient temperature of 25°C. The discharge capacity at this point was measured as the battery capacity after storage at 80°C. The capacity retention rate after high-temperature storage was then calculated using the following formula: 80°C capacity retention rate (%) = (battery capacity after storage at 80°C / battery capacity before storage) × 100%.

[0078] Example 1-1

[0079] <Preparation of positive electrode sheet>

[0080] Lithium iron phosphate, a first material, LiMn2O4 (LMO), a positive electrode conductive agent, acetylene black, a positive electrode binder, polyvinylidene fluoride (PVDF), and hydrogenated nitrile rubber (HNBR) were mixed in a mass ratio of 45:50.4:0.8:3:0.8 to obtain a positive electrode material. N-methylpyrrolidone (NMP) was added and stirred uniformly. The mixture was then prepared using NMP as a solvent to form a positive electrode slurry with a solid content of 60 wt%. The positive electrode slurry was then coated on one surface of a 12 μm thick positive electrode current collector aluminum foil. The mixture was then dried at 85°C. The above steps were repeated on the other surface of the positive electrode current collector. After cold pressing and cutting, a double-sided coated positive electrode sheet with a single-sided positive electrode material layer thickness of 100 μm was obtained. The mass percentage of lithium iron phosphate (Y%), the specific surface area (S) of the positive electrode material, and the mass percentage (Z%) of the first material, LMO, are shown in Table 1.

[0081] <Preparation of negative electrode sheet>

[0082] The negative electrode active material, artificial graphite, and the negative electrode binder, PVDF, were mixed in a 90:10 mass ratio. NMP was added and stirred evenly. The resulting mixture was then prepared using the NMP solvent to create a negative electrode slurry with a solid content of 70 wt%. The slurry was evenly coated on one surface of an 8 μm thick copper foil negative electrode current collector. The mixture was then dried at 110°C. The above steps were repeated on the other surface of the negative electrode current collector. After cold pressing and cutting, the negative electrode sheets were obtained.

[0083] <Isolation Film>

[0084] A porous polyethylene film with a thickness of 12 μm (provided by Celgard) was used as the separator.

[0085] <Preparation of Electrolyte>

[0086] In a nitrogen atmosphere drying oven with a dew point below -50°C, ethylene carbonate (EC), preheated to 30°C, and other non-aqueous solvents, ethyl methyl carbonate (EMC), and diethyl carbonate (DEC), were mixed in a mass ratio of 3:5:2 to form a base solvent. The electrolyte salt LiPF6 was then added, followed by lithium difluorophosphate (LiPO2F2), a boron-containing additive (LiBOB), and a boron trifluoride dimethyl carbonate complex. The mixture was then mixed thoroughly to form an electrolyte. The boron trifluoride dimethyl carbonate complex was obtained by the complexation reaction of gaseous dimethyl carbonate (DMC) and gaseous boron trifluoride (BF3) in a mass ratio of 1:1. Based on the mass of the electrolyte, the mass percentage of LiPF6 (W%) was 12.5%, the mass percentage of lithium difluorophosphate (A%), the mass percentage of the boron-containing additive (B%), and the mass percentage of the boron trifluoride dimethyl carbonate complex (X%) were as shown in Table 1. The remainder was the base solvent.

[0087] <Preparation of lithium-ion batteries>

[0088] The positive electrode sheet, separator, and negative electrode sheet prepared above are stacked in order, with the separator placed between the positive electrode sheet and the negative electrode sheet to serve as an isolation. The electrode assembly is then wound and welded to the tabs. The electrode assembly is then placed in an aluminum-plastic film packaging bag and placed in an 85°C vacuum oven to dry for 12 hours to remove moisture. The prepared electrolyte is then injected, and a lithium-ion battery is obtained after vacuum packaging, standing, formation (charging at a constant current of 0.02C to 3.5V, then charging at a constant current of 0.1C to 3.9V), shaping, capacity testing, and secondary packaging.

[0089] Example 1-2 to Example 1-3

[0090] Except that the mass percentage of lithium iron phosphate is adjusted to Y% according to Table 1, the mass percentage of the first material is changed accordingly, and the mass percentages of the positive electrode conductor and the positive electrode binder remain unchanged, the rest is the same as Example 1-1.

[0091] Example 1-4 to Example 1-5

[0092] The process was the same as Example 1-1 except that the positive electrode material was ball-milled and the ball-milling time was adjusted so that the specific surface area S thereof had the value shown in Table 1.

[0093] Example 1-6 to Example 1-21

[0094] Except for adjusting the relevant parameters according to Table 1, the rest is the same as Example 1-1. When the mass percentage of the boron trifluoride dimethyl carbonate complex X%, the mass percentage of the lithium difluorophosphate A%, or the mass percentage of the boron-containing additive B% is changed, the mass percentage of the base solvent is changed accordingly, and the mass ratio of the components in the base solvent and the mass percentage of the electrolyte salt remain unchanged.

[0095] Examples 1-22

[0096] Except for adjusting the type of boron-containing additive according to Table 1, the rest is the same as Example 1-1.

[0097] Example 1-23 to Example 1-24

[0098] Except for adjusting the type of the first material according to Table 1, the rest is the same as Example 1-1.

[0099] Example 2-1 to Example 2-5

[0100] The process was identical to Example 1-1, except that the first additive was further introduced into the electrolyte and the parameters were adjusted according to Table 2. When the mass percentage C% of the first additive was changed, the mass percentage of the base solvent was also changed, while the mass ratios of the components in the base solvent and the mass percentage of the electrolyte salt remained unchanged.

[0101] Examples 2-6

[0102] Except for adjusting the type of the first additive according to Table 2, the rest is the same as Example 2-1.

[0103] Example 3-1 to Example 3-4

[0104] The same procedures as in Example 1-1 were followed except for adjusting the relevant parameters according to Table 3. When the mass percentage A% of lithium difluorophosphate and the mass percentage D% of ethylene carbonate were changed, the sum of the mass percentages of ethyl methyl carbonate and diethyl carbonate changed accordingly, while the mass ratio of the two and the mass percentage of the electrolyte salt remained unchanged.

[0105] Example 4-1 to Example 4-4

[0106] The process was the same as Example 1-1, except that ethyl propionate was further introduced into the electrolyte and the parameters were adjusted according to Table 4. When the mass percentage E% of ethyl propionate was changed, the mass percentage of the base solvent was changed accordingly, while the mass ratios of the components in the base solvent and the mass percentage of the electrolyte salt remained unchanged.

[0107] Example 5-1 to Example 5-8

[0108] The process was identical to Example 1-1, except that propylene carbonate was further introduced into the electrolyte and the weight percentage of the electrolyte salt was adjusted according to Table 5. When the weight percentage of propylene carbonate (F%) and the weight percentage of the electrolyte salt (W%) were changed, the weight percentage of the base solvent was changed accordingly, while the weight ratio of the components in the base solvent remained unchanged.

[0109] Examples 5-9

[0110] Except for adjusting the type of electrolyte salt according to Table 5, the rest is the same as Example 1-1.

[0111] Example 6-1

[0112] Except that ethyl propionate was further introduced into the electrolyte and its mass percentage was adjusted according to Table 6, the mass percentage of the base solvent was changed accordingly, and the mass ratio of each component in the base solvent and the mass percentage of the electrolyte salt remained unchanged, the rest was the same as Example 2-1.

[0113] Example 6-2

[0114] The same as Example 2-1 except that propylene carbonate was further introduced into the electrolyte and its mass percentage was adjusted according to Table 6, the mass percentage of the base solvent was changed accordingly, and the mass ratio of each component in the base solvent and the mass percentage of the electrolyte salt remained unchanged.

[0115] Example 6-3

[0116] The same as Example 4-1 except that propylene carbonate was further introduced into the electrolyte and its mass percentage was adjusted according to Table 6, the mass percentage of the base solvent was changed accordingly, and the mass ratio of each component in the base solvent and the mass percentage of the electrolyte salt remained unchanged.

[0117] Example 6-4

[0118] Except that ethyl propionate and propylene carbonate were further introduced into the electrolyte and their mass percentages were adjusted according to Table 6, the mass percentage of the base solvent was changed accordingly, and the mass ratio of each component in the base solvent and the mass percentage of the electrolyte salt remained unchanged, the rest was the same as Example 2-1.

[0119] Example 7-1

[0120] Except that the carbon material prepared in the following <Preparation of Negative Electrode Active Material> was used as the negative electrode active material, the rest was the same as Example 1-1.

[0121] <Preparation of negative electrode active material>

[0122] Natural graphite powder was heat-treated at 500°C for 2 hours in an air atmosphere to obtain heat-treated graphite powder. 10 wt% coal tar pitch was added to 90 wt% of the heat-treated graphite powder and mixed thoroughly. The mixture was then sintered at 600°C for 2 hours in a nitrogen atmosphere. The sintered powder was sieved through a 325-mesh sieve to obtain a graphite material having amorphous carbon on at least a portion of the surface of the negative electrode active material.

[0123] Comparative Example 1

[0124] Except that lithium iron phosphate is not added to the positive electrode material layer and the mass percentage Z% of the first material is adjusted according to Table 1, and the mass percentages of the positive electrode conductor and the positive electrode binder remain unchanged, the rest is the same as Example 1-1.

[0125] Comparative Example 2

[0126] The process is the same as Example 1-1 except that the boron trifluoride dimethyl carbonate complex is not added to the electrolyte, the mass percentage of the base solvent is changed accordingly, and the mass ratio of the components in the base solvent and the mass percentage of the electrolyte salt remain unchanged.

[0127] Comparative Example 3

[0128] The process is the same as Example 1-1 except that lithium difluorophosphate is not added to the electrolyte, the mass percentage of the base solvent is changed accordingly, and the mass ratio of each component in the base solvent and the mass percentage of the electrolyte salt remain unchanged.

[0129] Comparative Example 4

[0130] The process is the same as Example 1-1 except that no boron-containing additive is added to the electrolyte, the mass percentage of the base solvent is changed accordingly, and the mass ratio of each component in the base solvent and the mass percentage of the electrolyte salt remain unchanged.

[0131] The relevant parameters and performance test results of each embodiment and each comparative example are shown in Tables 1 to 7.

[0132] Table 1 Note: “ / ” in Table 1 indicates that there is no related substance or parameter; the chemical formula of the first material NCM in Table 1 is LiNi 0.8 Co0.1 Mn 0.1 O2, the chemical formula of NCA is LiNi 0.8 Co 0.15 Al 0.05 O2.

[0133] From Examples 1-1 to 1-24 and Comparative Examples 1 to 4, it can be seen that the positive electrode material layer includes lithium iron phosphate, and the electrolyte includes a boron trifluoride dimethyl carbonate complex, lithium difluorophosphate, and a boron-containing additive, which can enable the lithium-ion battery to have a higher -10°C discharge capacity retention rate and 80°C capacity retention rate, indicating that the lithium-ion battery has better low-temperature discharge performance and high-temperature storage performance. In Comparative Example 1, the positive electrode material layer does not include lithium iron phosphate, the electrolyte of Comparative Example 2 does not add a boron trifluoride dimethyl carbonate complex, the electrolyte of Comparative Example 3 does not add lithium difluorophosphate, and the electrolyte of Comparative Example 4 does not add a boron-containing additive. The lithium-ion batteries of Comparative Examples 1 to 4 have low -10°C discharge capacity retention rates and 80°C capacity retention rates, indicating that the low-temperature discharge performance and high-temperature storage performance of the lithium-ion battery are poor.

[0134] The value of Y typically affects the low-temperature discharge performance and high-temperature storage performance of lithium-ion batteries. As can be seen from Examples 1-1 to 1-3, when the value of Y is adjusted within the range of this application, the lithium-ion battery has a higher -10°C discharge capacity retention rate and 80°C capacity retention rate, indicating that the lithium-ion battery has better low-temperature discharge performance and high-temperature storage performance.

[0135] The value of S typically affects the low-temperature discharge performance and high-temperature storage performance of lithium-ion batteries. As can be seen from Examples 1-1, 1-4, and 1-5, when the value of S is adjusted within the range of this application, the lithium-ion battery has a higher -10°C discharge capacity retention rate and 80°C capacity retention rate, indicating that the lithium-ion battery has better low-temperature discharge performance and high-temperature storage performance.

[0136] The value of X generally affects the low-temperature discharge performance and high-temperature storage performance of lithium-ion batteries. As can be seen from Examples 1-1, 1-6, and 1-9, by adjusting the value of X within the scope of this application, the lithium-ion battery can have a high -10°C discharge capacity retention rate and 80°C capacity retention rate, indicating that the lithium-ion battery has good low-temperature discharge performance and high-temperature storage performance.

[0137] The value of A typically affects the low-temperature discharge performance and high-temperature storage performance of lithium-ion batteries. As can be seen from Examples 1-1, 1-10, and 1-13, by adjusting the value of A within the scope of this application, lithium-ion batteries can have high -10°C discharge capacity retention and 80°C capacity retention, indicating that lithium-ion batteries have good low-temperature discharge performance and high-temperature storage performance.

[0138] The value of B generally affects the low-temperature discharge performance and high-temperature storage performance of lithium-ion batteries. As can be seen from Examples 1-1, 1-14, and 1-17, by adjusting the value of B within the range of this application, the lithium-ion battery can have a high -10°C discharge capacity retention rate and 80°C capacity retention rate, indicating that the lithium-ion battery has good low-temperature discharge performance and high-temperature storage performance.

[0139] Whether A+B satisfies the relationship 3S×Y / 800≤A+B≤3S×Y / 200 typically affects the low-temperature discharge performance and high-temperature storage performance of lithium-ion batteries. As can be seen from Examples 1-1 to 1-21, when A+B satisfies this relationship, the lithium-ion battery can exhibit high -10°C discharge capacity retention and 80°C capacity retention, demonstrating excellent low-temperature discharge performance and high-temperature storage performance.

[0140] The type of boron-containing additive generally affects the low-temperature discharge performance and high-temperature storage performance of lithium-ion batteries. As can be seen from Examples 1-1 and 1-22, using boron-containing additives within the scope of this application can enable lithium-ion batteries to have high -10°C discharge capacity retention and 80°C capacity retention, demonstrating that lithium-ion batteries have good low-temperature discharge performance and high-temperature storage performance.

[0141] The composition of the positive electrode material layer generally affects the low-temperature discharge performance and high-temperature storage performance of lithium-ion batteries. As can be seen from Examples 1-1, 1-23, and 1-24, when the composition of the positive electrode material layer is within the range of this application, the lithium-ion battery can have a high -10°C discharge capacity retention rate and 80°C capacity retention rate, indicating that the lithium-ion battery has good low-temperature discharge performance and high-temperature storage performance.

[0142] Table 2 Note: “ / ” in Table 2 indicates that there is no relevant substance or parameter.

[0143] The electrolyte includes a first additive, and the mass percentage C% of the first additive generally affects the low-temperature discharge performance and high-temperature storage performance of the lithium-ion battery. As can be seen from Examples 1-1, 2-1, and 2-5, further introducing the first additive into the electrolyte and adjusting the value of C within the scope of this application can enable the lithium-ion battery to have a high -10°C discharge capacity retention rate and 80°C capacity retention rate, indicating that the lithium-ion battery has good low-temperature discharge performance and high-temperature storage performance.

[0144] The type of first additive typically affects the low-temperature discharge performance and high-temperature storage performance of lithium-ion batteries. As can be seen from Examples 2-1 and 2-6, using a first additive within the scope of this application can result in lithium-ion batteries with high -10°C discharge capacity retention and 80°C capacity retention, demonstrating that lithium-ion batteries have good low-temperature discharge performance and high-temperature storage performance.

[0145] Table 3

[0146] The mass percentage of ethylene carbonate, D%, and the A / D ratio generally affect the low-temperature discharge performance and high-temperature storage performance of lithium-ion batteries. As can be seen from Examples 1-1, 3-1, and 3-4, by adjusting the D and A / D ratios within the ranges of this application, lithium-ion batteries can exhibit high -10°C discharge capacity retention and 80°C capacity retention, demonstrating excellent low-temperature discharge performance and high-temperature storage performance.

[0147] Table 4 Note: “ / ” in Table 4 indicates that there is no relevant substance or parameter.

[0148] The inclusion of ethyl propionate in an electrolyte and the mass percentage (E%) of ethyl propionate generally affect the low-temperature discharge performance and high-temperature storage performance of a lithium-ion battery. As can be seen from Examples 1-1, 4-1, and 4-4, further introducing ethyl propionate into the electrolyte and adjusting the value of E within the scope of this application can result in a lithium-ion battery with a high -10°C discharge capacity retention rate and 80°C capacity retention rate, demonstrating that the lithium-ion battery has good low-temperature discharge performance and high-temperature storage performance.

[0149] Table 5 Note: “ / ” in Table 5 indicates that there is no relevant substance or parameter.

[0150] The mass percentage (W%) of lithium hexafluorophosphate typically affects the low-temperature discharge performance and high-temperature storage performance of lithium-ion batteries. As shown in Examples 1-1, 5-1, and 5-6, adjusting the W value within the range of this application can result in lithium-ion batteries with high -10°C discharge capacity retention and 80°C capacity retention, demonstrating excellent low-temperature discharge performance and high-temperature storage performance.

[0151] The mass percentage F% of propylene carbonate and the W / F ratio generally affect the low-temperature discharge performance and high-temperature storage performance of lithium-ion batteries. As shown in Examples 5-1 to 5-8, by adjusting the F and W / F ratios within the ranges of this application, lithium-ion batteries can exhibit high -10°C discharge capacity retention and 80°C capacity retention, demonstrating excellent low-temperature discharge performance and high-temperature storage performance.

[0152] The type of electrolyte salt generally affects the low-temperature discharge performance and high-temperature storage performance of lithium-ion batteries. As can be seen from Examples 1-1 and 5-9, using electrolyte salts within the scope of this application can enable lithium-ion batteries to have high -10°C discharge capacity retention and 80°C capacity retention, indicating that lithium-ion batteries have good low-temperature discharge performance and high-temperature storage performance.

[0153] Table 6 Note: “ / ” in Table 6 indicates that there is no relevant substance or parameter.

[0154] It can be seen from Examples 1-1, 2-1, 4-1, and 6-1 that the electrolyte simultaneously includes boron trifluoride dimethyl carbonate complex, lithium difluorophosphate, a boron-containing additive, a first additive, and ethyl propionate, which can enable the lithium-ion battery to have a higher -10°C discharge capacity retention rate and 80°C capacity retention rate, indicating that the lithium-ion battery has better low-temperature discharge performance and high-temperature storage performance.

[0155] It can be seen from Examples 1-1, 2-1, 5-1, and 6-2 that the electrolyte simultaneously includes boron trifluoride dimethyl carbonate complex, lithium difluorophosphate, a boron-containing additive, a first additive, and propylene carbonate, which can enable the lithium-ion battery to have a higher -10°C discharge capacity retention rate and 80°C capacity retention rate, indicating that the lithium-ion battery has better low-temperature discharge performance and high-temperature storage performance.

[0156] It can be seen from Examples 1-1, 4-1, 5-1, and 6-3 that the electrolyte simultaneously includes boron trifluoride dimethyl carbonate complex, lithium difluorophosphate, a boron-containing additive, ethyl propionate, and propylene carbonate, which can enable the lithium-ion battery to have a higher -10°C discharge capacity retention rate and 80°C capacity retention rate, indicating that the lithium-ion battery has better low-temperature discharge performance and high-temperature storage performance.

[0157] It can be seen from Examples 1-1, 2-1, 4-1, 5-1, and 6-4 that the electrolyte simultaneously includes boron trifluoride dimethyl carbonate complex, lithium difluorophosphate, a boron-containing additive, a first additive, ethyl propionate, and propylene carbonate, which can enable the lithium-ion battery to have a higher -10°C discharge capacity retention rate and 80°C capacity retention rate, indicating that the lithium-ion battery has better low-temperature discharge performance and high-temperature storage performance.

[0158] Table 7

[0159] The type of carbon material generally affects the low-temperature discharge performance and high-temperature storage performance of lithium-ion batteries. As can be seen from Examples 1-1 and 7-1, using carbon materials within the scope of this application can enable lithium-ion batteries to have high -10°C discharge capacity retention and 80°C capacity retention, demonstrating that lithium-ion batteries have good low-temperature discharge performance and high-temperature storage performance.

[0160] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, or article comprising a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, or article.

[0161] 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.

[0162] 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, which includes a positive electrode sheet, a negative electrode sheet, and an electrolyte, The positive electrode sheet includes a positive electrode material layer, and the positive electrode material layer includes lithium iron phosphate; The electrolyte includes boron trifluoride dimethyl carbonate complex, lithium difluorophosphate, and a boron-containing additive.

2. The secondary battery according to claim 1, wherein The negative electrode sheet includes a negative electrode material layer, and the negative electrode material layer includes at least one of a carbon material or a silicon-based material, The carbon material includes at least one of a graphite material or an amorphous carbon, and the graphite material includes at least one of artificial graphite or natural graphite.

3. The secondary battery according to claim 2, wherein, The carbon material includes a graphite material with at least part of its surface having amorphous carbon.

4. The secondary battery according to any one of claims 1 to 3, wherein, Based on the mass of the electrolyte, the mass percentage content of the boron trifluoride dimethyl carbonate complex is X%, and 0.1 ≤ X ≤ 2.

6.

5. The secondary battery according to any one of claims 1 to 3, wherein, Based on the mass of the electrolyte, the mass percentage content of the lithium difluorophosphate is A%, and the mass percentage content of the boron-containing additive is B%, Based on the mass of the positive electrode material layer, the mass percentage content of the lithium iron phosphate is Y%, and 13 ≤ Y ≤ 78, The positive electrode material layer includes a positive electrode material, and the specific surface area of the positive electrode material is Sm 2 / g, where 9 ≤ S ≤ 18, 3S × Y / 800 ≤ A + B ≤ 3S × Y / 200.

6. The secondary battery according to any one of claims 1 to 3, wherein, The secondary battery satisfies at least one of the following characteristics: (1) Based on the mass of the electrolyte, the mass percentage content of the lithium difluorophosphate is A%, and 0.01 ≤ A ≤ 5; (2) Based on the mass of the electrolyte, the mass percentage content of the boron-containing additive is B%, and 0.01 ≤ B ≤ 10.

7. The secondary battery according to any one of claims 1 to 3, wherein, The boron-containing additive includes at least one of lithium bis(oxalato)borate or lithium difluoro(oxalato)borate.

8. The secondary battery according to any one of claims 1 to 3, wherein, The positive electrode material layer further includes at least one of LiMn2O4, LiNi x Co y R z M (1-x-y-z) O2 or Li2MnO3·(1-α)LiQO2; 0≤x<1, 0≤y≤1, 0≤z≤1, x + y + z≤1, R includes at least one of Mn or Al, M includes at least one of Co, Ni, Mg, Cu, Zn, Sn, B, Ga, Cr, Sr, V or Ti; 0<α<1, Q includes at least one of Ni, Co or Mn.

9. The secondary battery according to any one of claims 1 to 3, wherein, The electrolyte further includes a first additive, and the first additive includes at least one of trimethylfluorosilane or tris(trimethylsilyl) phosphate, Based on the mass of the electrolyte, the mass percentage content of the first additive is C%, and 0.1 ≤ C ≤ 7.

10. The secondary battery according to any one of claims 1 to 3, wherein, The electrolyte includes ethylene carbonate, and based on the mass of the electrolyte, the mass percentage content of ethylene carbonate is D%, and 5 ≤ D ≤ 30.

11. The secondary battery according to claim 10, wherein, Based on the mass of the electrolyte, the mass percentage content of the lithium difluorophosphate is A%, and 0.003 ≤ A / D ≤ 0.

2.

12. The secondary battery according to any one of claims 1 to 3, wherein, The electrolyte further includes ethyl propionate, and based on the mass of the electrolyte, the mass percentage content of the ethyl propionate is E%, and 0.1 ≤ E ≤ 20.

13. The secondary battery according to any one of claims 1 to 3, wherein, The electrolyte includes an electrolyte salt, and the electrolyte salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, lithium difluorobis(oxalato)phosphate, lithium tetrafluorobis(oxalato)phosphate, lithium hexafluoroarsenate, bis(fluorosulfonyl)iminolithium, lithium trifluoromethanesulfonate, or lithium perchlorate.

14. The secondary battery according to claim 13, wherein, The electrolyte salt includes lithium hexafluorophosphate, and the electrolyte further includes propylene carbonate. Based on the mass of the electrolyte, the mass percentage content of lithium hexafluorophosphate is W%, the mass percentage content of propylene carbonate is F%, 4 ≤ W ≤ 24, 4 ≤ F ≤ 24, and 0.5 ≤ W / F ≤ 2.

15. An electronic device, which includes the secondary battery according to any one of claims 1 to 14.

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