Secondary battery and electronic device

Abstract

The present application provides a secondary battery and an electronic device. The secondary battery comprises a positive electrode sheet, a negative electrode sheet, and an electrolyte, wherein the positive electrode sheet comprises a positive electrode material layer, the positive electrode material layer comprises lithium cobalt oxide, the lithium cobalt oxide comprises a nickel element, and the electrolyte comprises a boron trifluoride complex, lithium difluorophosphate and a boron-containing additive. The present application can improve the low-temperature cycle performance and the floating charge performance of the secondary battery.

Description

Secondary battery and electronic device

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on January 17, 2024, with application number 202410069506.1 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 cycle performance and floating charge 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 cycle performance and float charge 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, wherein the positive electrode plate includes a positive electrode material layer, the positive electrode material layer includes lithium cobalt oxide, the lithium cobalt oxide includes nickel, and the electrolyte includes a boron trifluoride complex, lithium difluorophosphate and a boron-containing additive. By regulating the positive electrode material layer to include lithium cobalt oxide, the lithium cobalt oxide includes the above elements, and the electrolyte includes a boron trifluoride complex, lithium difluorophosphate and a boron-containing additive, the secondary battery still has a high electrical conductivity and lithium ion migration rate under low temperature conditions, the boron trifluoride complex is an auxiliary agent, which can improve the solubility of the additive, and the various components in the electrolyte work synergistically to effectively inhibit the dissociation and dissolution of transition metals, and form a relatively uniform and stable protective film at the positive electrode interface, while effectively avoiding the increase in electrolyte viscosity and affecting the lithium ion migration rate. Therefore, the secondary battery provided by the present application has good low-temperature cycle performance and floating charge performance.

[0007] In some embodiments of the present application, the negative electrode plate includes a negative electrode material layer, the negative electrode material layer includes a carbon material and a silicon-based material, the carbon material includes artificial graphite and / or natural graphite, and the negative electrode material layer includes the above materials, which can further improve the low-temperature cycle performance and floating charge performance of the secondary battery.

[0008] In some embodiments of the present application, based on the mass of the electrolyte, the mass percentage of the boron trifluoride complex is X%, the mass percentage of the lithium difluorophosphate is A%, and the mass percentage of the boron-containing additive is B%, 0.01≤X≤2.7, 0.2≤A+B≤6. By regulating the mass percentage of the boron trifluoride complex and the sum of the mass percentages of the lithium difluorophosphate and the boron-containing additive within the scope of the present application, the boron trifluoride complex can further increase the solubility of the additive under low temperature or float charge conditions of the secondary battery, and the synergistic effect between the components in the electrolyte is further stabilized, thereby further improving the low-temperature cycling performance and float charge performance of the secondary battery.

[0009] In some embodiments of the present application, the electrolyte satisfies at least one of the following characteristics: (1) 0.1≤A≤3; (2) 0.01≤B≤3; (3) 0.1≤A / B≤30. The electrolyte satisfying at least one of the above characteristics can further improve the low-temperature cycle performance and floating charge performance of the secondary battery.

[0010] In some embodiments of the present application, the boron-containing additive includes at least one of lithium dioxalatoborate or lithium difluorooxalatoborate. Selecting the above-mentioned boron-containing additive can further inhibit the dissociation and dissolution of transition metals and ensure that the positive electrode interface protective film has a relatively suitable thickness, thereby further improving the low-temperature cycling performance and float charge performance of the secondary battery.

[0011] In some embodiments of the present application, the electrolyte further includes propylene carbonate, and the mass percentage of the propylene carbonate is D%, based on the mass of the electrolyte, and 5≤D≤20. By regulating whether the electrolyte further includes propylene carbonate and the mass percentage of propylene carbonate is within the scope of the present application, the electrolyte can effectively reduce the performance fluctuation of the secondary battery at different temperatures and cycle numbers, thereby further improving the low-temperature cycling performance and float charge performance of the secondary battery.

[0012] In some embodiments of the present application, the mass percentage of the lithium difluorophosphate is A%, based on the mass of the electrolyte, and 0.005 ≤ A / D ≤ 0.2. By adjusting the value of A / D within the scope of this application to match the mass percentage of the lithium difluorophosphate with the mass percentage of the propylene carbonate, the low-temperature cycle capacity retention rate and the float charge capacity retention rate of the secondary battery can be further improved, and the float charge volume expansion rate of the secondary battery can be further reduced, thereby further improving the low-temperature cycle performance and float charge performance of the secondary battery.

[0013] In some embodiments of the present application, the electrolyte further includes a first additive, the first additive including sodium dithionite, and the mass percentage of the first additive is E% based on the mass of the electrolyte, and 0.1≤E≤2.5. By regulating the inclusion of the first additive in the electrolyte, the type of the first additive, and its mass percentage within the scope of the present application, the positive electrode interface protective film can have a relatively suitable thickness and density, thereby further improving the low-temperature cycling performance and float charge performance of the secondary battery.

[0014] In some embodiments of the present application, the lithium cobalt oxide includes Li x Ni 1-y-z Co y M z O2, 0.95≤x≤1.1, 0.01≤y≤0.35, 0.01≤z≤0.5, and M includes at least one element selected from Al, Cr, Mn, Fe, Mg, La, Ce, Sr, or V. The lithium cobalt oxide is selected from the above compounds, and the composition of the electrolyte is within the scope of this application, which can further improve the low-temperature cycle performance and float charge performance of the secondary battery.

[0015] In some embodiments of the present application, the positive electrode material layer includes a positive electrode material having a specific surface area of ​​0.1 m 2 / g to 3.9m 2 By adjusting the specific surface area of ​​the positive electrode material within the scope of this application, the low-temperature cycle performance and floating charge performance of the secondary battery can be further improved.

[0016] The second aspect of the present application provides an electronic device, which includes the secondary battery according to any one of the aforementioned embodiments. Therefore, the electronic device provided by the present application has good performance.

[0017] Beneficial effects of this application:

[0018] The present application provides a secondary battery and an electronic device. The secondary battery includes a positive electrode sheet, a negative electrode sheet, and an electrolyte. The positive electrode sheet includes a positive electrode material layer, the positive electrode material layer includes lithium cobalt oxide, and the lithium cobalt oxide includes nickel. The electrolyte includes a boron trifluoride complex, lithium difluorophosphate, and a boron-containing additive. By adjusting the positive electrode material layer to include lithium cobalt oxide, the lithium cobalt oxide includes the aforementioned elements, and the electrolyte to include a boron trifluoride complex, lithium difluorophosphate, and a boron-containing additive, the secondary battery can have good low-temperature cycling performance and float charge performance.

[0019] 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

[0020] 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.

[0021] It should be noted that in the specific embodiments of this application, 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:

[0022] 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 cobalt oxide, the lithium cobalt oxide includes nickel element, and the electrolyte includes a boron trifluoride complex, lithium difluorophosphate and a boron-containing additive.

[0023] The inventors have found that by regulating the positive electrode material layer to include lithium cobalt oxide, the lithium cobalt oxide includes the above elements, and the electrolyte includes boron trifluoride complex, lithium difluorophosphate and boron-containing additives, the secondary battery still has a high conductivity and lithium ion migration rate under low temperature conditions. The boron trifluoride complex is an auxiliary agent that can improve the solubility of the additives in the electrolyte of this application. The synergistic effect of the various components in the electrolyte can effectively inhibit the dissociation and dissolution of transition metals and form a relatively uniform and stable protective film at the positive electrode interface. At the same time, it can effectively avoid the increase in the viscosity of the electrolyte and affect the lithium ion migration rate. Therefore, the secondary battery provided by this application has good low-temperature cycle performance and floating charge performance. In this application, low temperature refers to a temperature below 0°C. In this application, the positive electrode material layer includes a positive electrode material, the positive electrode material includes lithium cobalt oxide, and the lithium cobalt oxide includes nickel.

[0024] In one embodiment of the present application, the negative electrode plate includes a negative electrode material layer, the negative electrode material layer includes a carbon material and a silicon-based material, the carbon material includes artificial graphite and / or natural graphite. In one embodiment of the present application, the silicon-based material includes silicon (elemental substance) or a silicon compound, for example, 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 deinsertion of lithium ions. The negative electrode material layer includes the above-mentioned materials, which can further improve the low-temperature cycling performance and floating charge performance of the secondary battery. In the present application, the negative electrode material layer includes a negative electrode material, and the negative electrode material includes a carbon material and a silicon-based material.

[0025] In one embodiment of the present application, based on the mass of the electrolyte, the mass percentage of the boron trifluoride complex is X%, the mass percentage of the lithium difluorophosphate is A%, and the mass percentage of the boron-containing additive is B%. 0.01≤X≤2.7. For example, the value of X can be 0.01, 0.03, 0.05, 0.07, 0.09, 0.1, 0.3, 0.5, 0.7, 0.9, 1, 1.3, 1.5, 1.7, 1.9, 2, 2.3, 2.5, 2.7, or a range consisting of any two of the above values. 0.2≤A+B≤6. For example, the value of A+B can be 0.2, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, or a range consisting of any two of the above values. By regulating the mass percentage of the boron trifluoride complex and the sum of the mass percentages of lithium difluorophosphate and the boron-containing additive within the scope of this application, the boron trifluoride complex can further improve the solubility of the additive under low temperature or float charge conditions of the secondary battery, and the synergistic effect between the components in the electrolyte is further stabilized, thereby further improving the low-temperature cycle performance and float charge performance of the secondary battery.

[0026] In one embodiment of the present application, 0.1≤A≤3. Exemplarily, the value of A can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.9, 1, 1.3, 1.5, 1.7, 1.9, 2, 2.3, 2.5, 2.7, 2.9, 3 or a range consisting of any two of the above values. By regulating the value of A within the scope of this application, lithium difluorophosphate can have a suitable mass percentage, which can further improve the uniformity of the positive electrode interface protective film during the charge and discharge process, further improve the low-temperature cycle capacity retention rate and float charge capacity retention rate of the secondary battery, and further reduce the float charge volume expansion rate of the secondary battery, thereby further improving the low-temperature cycle performance and float charge performance of the secondary battery.

[0027] In one embodiment of the present application, 0.01≤B≤3. Exemplarily, the value of B can be 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.3, 0.5, 0.7, 0.9, 1, 1.3, 1.5, 1.7, 1.9, 2, 2.3, 2.5, 2.7, 2.9, 3 or a range consisting of any two of the above values. By regulating the value of B within the scope of this application, the boron-containing additive can have a suitable mass percentage, which can further inhibit the dissociation and dissolution of the transition metal and form a more uniform and stable protective film at the positive electrode interface, which can further improve the low-temperature cycle capacity retention rate and the float charge capacity retention rate of the secondary battery, and further reduce the float charge volume expansion rate of the secondary battery, thereby further improving the low-temperature cycle performance and float charge performance of the secondary battery.

[0028] In one embodiment of the present application, 0.1≤A / B≤30. For example, the value of A / B can be 0.1, 0.5, 1, 3, 5, 7, 9, 10, 11, 13, 15, 17, 19, 20, 21, 23, 25, 27, 29, 30, or a range consisting of any two of the above values. By regulating the value of A / B within the scope of the present application, the mass percentage of lithium difluorophosphate matches the mass percentage of the boron-containing additive, which can further improve the low-temperature cycle capacity retention rate and float charge capacity retention rate of the secondary battery, and further reduce the float charge volume expansion rate of the secondary battery, thereby further improving the low-temperature cycle performance and float charge performance of the secondary battery.

[0029] In one embodiment of the present application, the boron-containing additive includes at least one of lithium dioxalatoborate (LiBOB) or lithium difluorooxalatoborate (LiDFOB). The use of such a boron-containing additive can further inhibit the dissociation and dissolution of transition metals and ensure a suitable thickness of the positive electrode interface protective film, thereby further improving the low-temperature cycling performance and float charge performance of the secondary battery.

[0030] In one embodiment of the present application, the electrolyte further includes propylene carbonate (PC), and the mass percentage of propylene carbonate is D% based on the mass of the electrolyte, and 5≤D≤20. For example, the value of D can be 5, 7, 8, 10, 11, 12, 13, 15, 16, 19, 20 or a range consisting of any two of the above values. By regulating the electrolyte to also include propylene carbonate and the mass percentage of propylene carbonate within the scope of the present application, the electrolyte can effectively reduce the performance fluctuations of the secondary battery at different temperatures and cycle numbers, thereby further improving the low-temperature cycle performance and float charge performance of the secondary battery.

[0031] In one embodiment of the present application, based on the mass of the electrolyte, the mass percentage of lithium difluorophosphate is A%, 0.005≤A / D≤0.2. For example, the value of A / D can be 0.005, 0.01, 0.015, 0.02, 0.025, 0.03, 0.035, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.13, 0.15, 0.17, 0.2 or a range consisting of any two of the above values. By regulating the value of A / D within the scope of this application, the mass percentage of lithium difluorophosphate matches the mass percentage of propylene carbonate, which can further improve the low-temperature cycle capacity retention rate and float charge capacity retention rate of the secondary battery, and further reduce the float charge volume expansion rate of the secondary battery, thereby further improving the low-temperature cycle performance and float charge performance of the secondary battery.

[0032] In one embodiment of the present application, the electrolyte further includes a first additive, the first additive includes sodium dithionite (Na2O4S2), and the mass percentage of the first additive is E%, based on the mass of the electrolyte, 0.1≤E≤2.5. Exemplarily, the value of E can be 0.1, 0.3, 0.5, 0.7, 0.9, 1, 1.3, 1.5, 1.7, 1.9, 2, 2.3, 2.5 or a range consisting of any two of the above values. By regulating the electrolyte to also include the first additive, the type of the first additive and its mass percentage within the scope of this application, the positive electrode interface protective film can have a more suitable thickness and density, thereby further improving the low temperature cycle performance and floating charge performance of the secondary battery.

[0033] In one embodiment of the present application, lithium cobalt oxide includes Li x Ni 1-y-z Co y M z O2, 0.95≤x≤1.1, 0.01≤y≤0.35, 0.01≤z≤0.5, and M includes at least one element selected from Al, Cr, Mn, Fe, Mg, La, Ce, Sr, or V. The lithium cobalt oxide is selected from the above compounds, and the composition of the electrolyte is within the scope of this application, which can further improve the low-temperature cycle performance and float charge performance of the secondary battery.

[0034] In one embodiment of the present application, the positive electrode material layer includes a positive electrode material, and the specific surface area SSA of the positive electrode material is 0.1m 2 / g to 3.9m 2 / g. For example, the specific surface area SSA of the positive electrode material can be 0.1m 2 / g, 0.3m 2 / g, 0.5m 2 / g, 0.7m 2 / g, 0.9m 2 / g、1m 2 / g, 1.1m 2 / g, 1.3m 2 / g, 1.5m 2 / g, 1.7m 2 / g, 1.9m 2 / g, 2m 2 / g, 2.1m 2 / g, 2.3m 2 / g, 2.5m 2 / g, 2.7m 2 / g, 2.9m 2 / g、3m 2 / g, 3.1m 2 / g, 3.3m 2 / g, 3.5m2 / g, 3.7m 2 / g, 3.9m 2 By adjusting the specific surface area of ​​the positive electrode material within the scope of this application, the low-temperature cycle performance and floating charge performance of the secondary battery can be further improved.

[0035] The present application does not particularly limit the method for regulating the specific surface area of ​​the positive electrode material, as long as the objectives of the present application can be achieved. For example, the specific surface area of ​​the positive electrode material can be regulated by pulverizing the positive electrode material. For example, when other conditions remain unchanged, extending the pulverization time increases the specific surface area of ​​the positive electrode material; shortening the pulverization time decreases the specific surface area of ​​the positive electrode material.

[0036] In the present application, the positive electrode sheet includes a positive electrode current collector and a positive electrode material layer arranged on at least one surface of the positive electrode current collector. The above-mentioned "positive electrode material layer arranged on at least one surface of the positive electrode current collector" means that the positive electrode material layer can be arranged on one surface of the positive electrode current collector along the thickness direction of itself, or on two surfaces of the positive electrode current collector along the thickness direction of itself. 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. This application has no special restrictions, as long as the purpose of this application can be achieved. This application has no special restrictions on the positive electrode current collector, as long as the purpose of this application can be achieved. For example, it can include aluminum foil, aluminum alloy foil or a composite current collector (such as an aluminum-carbon composite current collector).

[0037] The positive electrode material layer of the present application includes lithium cobalt oxide. The positive electrode material layer of the present application also includes a conductive agent and a binder. The present application has no particular restrictions on the conductive agent, as long as the purpose of the present application can be achieved. For example, the conductive agent may include but is not limited to at least one of conductive carbon black, carbon nanotubes (CNTs), carbon fibers, flake graphite, graphene, metal materials or conductive polymers. The above-mentioned conductive carbon black may include but is not limited to acetylene black or Ketjen black. 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 polymers may include but are not limited to at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene or polypyrrole. The present application has no particular restrictions on the binder, as long as the purpose of the present application can be achieved, for example, the binder may include but is not limited to polyacrylate, polyimide, polyamide, polyamide-imide, polyvinylidene fluoride, polystyrene butadiene copolymer (styrene-butadiene rubber), sodium alginate, polyvinyl alcohol, polytetrafluoroethylene, polyacrylonitrile, sodium carboxymethyl cellulose, potassium carboxymethyl cellulose, lithium carboxymethyl cellulose, sodium hydroxymethyl cellulose or potassium hydroxymethyl cellulose at least one. The present application has no particular restrictions on the mass ratio of lithium cobalt oxide, conductive agent, and binder in the positive electrode material layer, and those skilled in the art can select according to actual needs, as long as the purpose of the present application can be achieved. For example, the mass ratio of lithium cobalt oxide, conductive agent, and binder in the positive electrode material layer can be (80 to 98): (0.5 to 10): (0.5 to 10).

[0038] The present application does not particularly limit 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. The present application does not particularly limit 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 or a partial area of ​​the positive electrode current collector. The present application does not particularly limit it, as long as the purpose of the present application can be achieved.

[0039] Optionally, the positive electrode sheet may further include a conductive layer, which is located between the positive electrode current collector and the positive electrode material layer. The present application does not particularly limit the composition of the conductive layer, and it can be a conductive layer commonly used in the art. The conductive layer includes a conductive agent and a binder. The present application does not particularly limit the conductive agent and binder in the conductive layer, and it can be at least one of the above-mentioned conductive agents and binders. The present application does not particularly limit the mass ratio of the conductive agent and binder in the conductive layer, and those skilled in the art can select according to actual needs, as long as the purpose of the present application can be achieved.

[0040] In the present application, the electrolyte also includes a lithium salt. The lithium salt may include various lithium salts commonly used in the art, such as at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, Li2SiF6, lithium bis(fluorosulfonyl imide), lithium bis(trifluoromethanesulfonyl imide) or lithium difluoroborate. In the present application, the electrolyte also includes other non-aqueous solvents. The present application has no particular restrictions on other non-aqueous solvents, as long as the purpose of the present application can be achieved. For example, other non-aqueous solvents may include but are not limited to at least one of carbonate compounds, carboxylate compounds, ether compounds or other organic solvents. The above-mentioned carbonate compounds may include but are not limited to at least one of chain carbonate compounds, cyclic carbonate compounds or fluorinated carbonate compounds. 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 ethyl methyl carbonate (EMC). The above-mentioned cyclic carbonate compound may include but is not limited to at least one of ethylene carbonate (EC), butylene carbonate (BC) or vinyl ethylene carbonate (VEC). The above-mentioned fluorocarbonate compound may include but is not limited to at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate or trifluoromethylethylene carbonate. The 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 ether compound may include, but is not limited to, at least one of dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran. The other organic solvent may include, but is not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate. The present application does not particularly limit the weight percentage of the lithium salt and other non-aqueous solvents, as long as the purpose of the present application can be achieved. For example, based on the mass of the electrolyte, the mass percentage F of the lithium salt is 8% to 15%, and the mass percentage G of the other non-aqueous solvent is 54% to 91%.

[0041] In one embodiment of the present application, the electrolyte may include a boron trifluoride complex, lithium difluorophosphate, a boron-containing additive, another non-aqueous solvent, and a lithium salt. The mass percentages of the boron trifluoride complex, lithium difluorophosphate, the boron-containing additive, and the lithium salt are as described above, and the mass percentage G of the other non-aqueous solvent is 77% to 91%. A secondary battery including this electrolyte exhibits excellent low-temperature cycling performance and float charge performance.

[0042] In one embodiment of the present application, the electrolyte may include a boron trifluoride complex, lithium difluorophosphate, a boron-containing additive, propylene carbonate, another non-aqueous solvent, and a lithium salt. The mass percentages of the boron trifluoride complex, lithium difluorophosphate, the boron-containing additive, propylene carbonate, and the lithium salt are as described above, and the mass percentage G of the other non-aqueous solvent is 57% to 86%. A secondary battery including this electrolyte exhibits excellent low-temperature cycling performance and float charge performance.

[0043] In one embodiment of the present application, the electrolyte may include a boron trifluoride complex, lithium difluorophosphate, a boron-containing additive, a first additive, another non-aqueous solvent, and a lithium salt. The mass percentages of the boron trifluoride complex, lithium difluorophosphate, the boron-containing additive, the first additive, and the lithium salt are as described above, and the mass percentage G of the other non-aqueous solvent is 74% to 91%. A secondary battery including this electrolyte has excellent low-temperature cycling performance and float charge performance.

[0044] In one embodiment of the present application, the electrolyte may include a boron trifluoride complex, lithium difluorophosphate, a boron-containing additive, propylene carbonate, a first additive, another non-aqueous solvent, and a lithium salt. The mass percentages of the boron trifluoride complex, lithium difluorophosphate, the boron-containing additive, propylene carbonate, the first additive, and the lithium salt are as described above, and the mass percentage G of the other non-aqueous solvent is 54% to 86%. A secondary battery including this electrolyte exhibits excellent low-temperature cycling performance and float charge performance.

[0045] In the present application, the negative electrode plate includes a negative electrode current collector and a negative electrode material layer arranged on at least one surface of the negative electrode current collector. The above-mentioned "negative electrode material layer arranged on at least one surface of the negative electrode current collector" means that the negative electrode material layer can be arranged on one surface of the negative electrode current collector along the thickness direction of itself, or can be arranged on two surfaces of the negative electrode current collector along the thickness direction of itself. 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. This application has no special restrictions, as long as the purpose of this application can be achieved. This application has no special restrictions on the negative electrode current collector, as long as the purpose of this application can be achieved. For example, it can include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foam nickel, foam copper or a composite current collector, etc.

[0046] The negative electrode material layer of the present application may also include at least one of lithium metal, alloys or intermetallic compounds of lithium metal and other metals, metal oxides, metal nitrides, tin (single 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 also includes a binder and a conductive agent. The present application has no special restrictions on the binder and the conductive agent in the negative electrode material layer, as long as the purpose of the present application can be achieved. For example, the binder in the negative electrode material layer may be at least one of the above-mentioned binders, and the conductive agent in the negative electrode material layer may be at least one of the above-mentioned conductive agents. The negative electrode material layer of the present application also includes a thickener. The present application has no special restrictions on the thickener in the negative electrode material layer, as long as the purpose of the present application can be achieved. For example, the thickener may include sodium carboxymethyl cellulose (CMC-Na).

[0047] The present application does not particularly limit 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 4 μm to 15 μm. The present application does not particularly limit 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 30 μm to 160 μm.

[0048] Optionally, the negative electrode plate may further include a conductive layer, which is located between the negative electrode current collector and the negative electrode material layer. The present application does not particularly limit the composition of the conductive layer, and it can be a conductive layer commonly used in the art. The conductive layer includes a conductive agent and a binder. The present application does not particularly limit the conductive agent and binder in the conductive layer, and it can be at least one of the above-mentioned conductive agents and binders. The present application does not particularly limit the mass ratio of the conductive agent and binder in the conductive layer, and those skilled in the art can select according to actual needs, as long as the purpose of the present application can be achieved.

[0049] In the present application, the secondary battery also includes a diaphragm. The diaphragm is used to separate the positive electrode plate and the negative electrode plate, prevent internal short circuits in 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; 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. For example, polyethylene includes at least one of high-density polyethylene, low-density polyethylene or ultra-high molecular weight polyethylene. Preferably, the material of the diaphragm may include polyethylene or polypropylene, which has a good effect on preventing short circuits and can improve the safety performance of the secondary battery through the shutdown effect.

[0050] In the present application, the diaphragm may include a substrate and a surface treatment layer. The substrate may be a non-woven fabric or a composite film having a porous structure, and the material of the substrate 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, 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 present application has no particular restrictions on the above-mentioned inorganic particles, and for example, it 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 present application has no particular restrictions on the above-mentioned binder, and for example, it may be at least one of the aforementioned binders. The polymer layer contains a polymer, and the material of the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyvinyl pyrrolidone, polyvinyl ether, polyvinylidene fluoride or poly(vinylidene fluoride-hexafluoropropylene). The surface treatment layer can be a porous layer, and the diameter of the pores of the porous layer can be 0.01μm to 1μm. The surface treatment layer can improve the heat resistance, oxidation resistance and electrolyte wetting performance of the diaphragm, and enhance the adhesion between the diaphragm and the positive electrode sheet, and the diaphragm and the negative electrode sheet. The present application does not particularly limit the thickness of the diaphragm, as long as the purpose of the present application can be achieved. For example, the thickness of the diaphragm can be 3μm to 30μm.

[0051] 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. For example, an aluminum-plastic film packaging bag can be used.

[0052] The present application does not particularly limit the type of secondary battery, which may include any device that undergoes an electrochemical reaction. In the present application, secondary batteries may include, but are not limited to: lithium metal secondary batteries, lithium ion secondary batteries (lithium ion batteries), lithium polymer secondary batteries or lithium ion polymer secondary batteries (lithium ion polymer batteries), etc.

[0053] 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. may be placed in the packaging bag to prevent pressure rise and overcharge and discharge inside the secondary battery.

[0054] The second aspect of the present application provides an electronic device, which includes the secondary battery according to any one of the aforementioned embodiments. Therefore, the electronic device provided by the present application has good performance.

[0055] The present application does not particularly limit the type of electronic device, and the electronic device may 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.

[0056] Example

[0057] 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.

[0058] Test methods and equipment:

[0059] Type and mass percentage of elements tested:

[0060] After discharging the lithium-ion battery to 2.5V, disassemble it to obtain the positive electrode sheet, and perform the following tests on the positive electrode sheet:

[0061] (1) Scraping off the positive electrode material layer on the surface of the positive electrode sheet and sintering it in a muffle furnace at 500°C for 6 hours, collecting the positive electrode material powder, and subjecting the collected positive electrode material powder to inductively coupled plasma (ICP) testing to obtain the type and mass percentage of the elements;

[0062] (2) Randomly select a small disc with a diameter of 14 mm on the positive electrode sheet, perform surface energy spectrum (EDS) test on the positive electrode material layer on the small disc, magnify the test area by 3000 times, and perform EDS test on the entire area after 3000 times magnification to obtain the type and mass percentage of elements in the positive electrode material;

[0063] The higher value of the above two test results is taken as the mass percentage of the element in the positive electrode material.

[0064] Specific surface area test:

[0065] In accordance with the national standard "Determination of the specific surface area of ​​solid substances by gas adsorption BET method" (GB / T 19587-2017), the specific surface area of ​​the positive electrode material was tested by nitrogen adsorption method using a specific surface area analyzer (model TristarⅡ3020M).

[0066] -10℃ low temperature cycle performance test:

[0067] Place the lithium-ion battery in a -10℃ constant temperature box and let it stand for 30 minutes to allow the lithium-ion battery to reach a constant temperature. Charge the lithium-ion battery that has reached a constant temperature at -10℃ at a constant current of 0.2C to 4.3V, charge it at a constant voltage at 4.3V to a current of 0.05C, let it stand for 5 minutes, then discharge it at a constant current of 0.2C to 3.0V, let it stand for 5 minutes, and record the first cycle discharge capacity as C11. Then charge it at a constant current of 0.5C to 4.3V, charge it at a constant voltage at 4.3V to a current of 0.3C; then charge it at a constant current of 0.3C to 4.3V, charge it at a constant voltage at 4.3V to a current of 0.05C (this is the cyclic charging step); let it stand for 5 minutes; then discharge it at a constant current of 0.2C to 3.0V (this is the cyclic discharge step), let it stand for 5 minutes; this is one charge and discharge cycle. According to the above-mentioned cyclic charging and discharging steps, 200 cycles of charge and discharge are performed. The discharge capacity of the lithium-ion battery after 200 cycles is tested to be C12. The capacity retention rate of the lithium-ion battery after 200 cycles at -10°C is calculated according to the following formula.

[0068] Capacity retention after 200 cycles at -10°C = C12 / C11×100%.

[0069] Float charge capacity retention rate test:

[0070] Place the lithium-ion battery in a constant temperature box at 60℃ and charge it to 4.3V at a constant current of 1.5C. Test the battery capacity C0 at this time. Charge it to 0.05C at a constant voltage at 4.3V, and then charge it at a low current of 0.05C for 500 hours. Test the battery capacity C1 after float charge. The float charge capacity retention rate = C1 / C0×100%.

[0071] Float charge volume expansion rate test:

[0072] In a 45°C constant temperature oven, charge at a constant current of 1C until the charge cutoff voltage reaches 4.3V, then charge at a constant voltage of 4.3V until the current drops to 0A. Float charge for 28 days. Record the volume before and after float charge. Calculate the volume expansion rate of the lithium-ion battery after storage as the float charge volume expansion rate using the following formula:

[0073] Float charge volume expansion rate = (volume after float charge - volume before float charge) / volume before float charge × 100%.

[0074] Example 1-1

[0075] <Preparation of positive electrode sheet>

[0076] Commercially available LiNi 0.8 Co 0.2O2 (brand: TCI), carbon nanotubes, acetylene black, and polyvinylidene fluoride are mixed with N-methylpyrrolidone (NMP) in a mass ratio of 97:0.5:0.5:2 and stirred evenly to obtain a positive electrode slurry. The positive electrode slurry is evenly coated on one surface of a 10μm thick positive electrode current collector aluminum foil, dried at 120°C, and then repeated on the other surface of the aluminum foil. The positive electrode sheet is then obtained through cold pressing, cutting, and welding of the tabs.

[0077] <Preparation of negative electrode sheet>

[0078] Artificial graphite, styrene-butadiene rubber, and lithium carboxymethyl cellulose were mixed with deionized water in a mass ratio of 96.5:2.5:1 and stirred thoroughly to produce a negative electrode slurry. The negative electrode slurry was evenly coated on one surface of an 8μm-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. The negative electrode sheet was then cold-pressed, cut, and welded to the tabs.

[0079] <Preparation of Electrolyte>

[0080] In an argon atmosphere glove box with a water content of less than 10 ppm, ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed to form a base solvent. Then, lithium hexafluorophosphate (LiPF6), a boron trifluoride complex, lithium difluorophosphate, and lithium bis(oxalatoborate) (LiBOB) were added to the base solvent and mixed thoroughly to form an electrolyte. The boron trifluoride complex was obtained by the complexation reaction of gaseous dimethyl carbonate (DMC) and gaseous boron trifluoride (BF3) in a 1:1 mass ratio. Based on the mass of the electrolyte, the mass percentage F of the lithium salt was 12.5%, the mass percentage X of the boron trifluoride complex was 0.02%, the mass percentage A of the lithium difluorophosphate was 0.1%, and the mass percentage B of the boron-containing additive was 0.1%. The remainder was ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate, with the mass ratio of ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate being 1:2:1.

[0081] <Preparation of Separator>

[0082] A porous polyethylene film with a thickness of 10 μm (supplied by Celgard) was used as a separator.

[0083] <Preparation of lithium-ion batteries>

[0084] The positive electrode sheet, separator, negative electrode sheet, and separator are stacked in order, with the separator positioned between the positive and negative electrodes to provide insulation. The electrodes are then wound to form an electrode assembly. After welding the tabs, the electrode assembly is placed in an aluminum-plastic film packaging bag. After dehydration at 80°C, the aforementioned electrolyte is injected. The lithium-ion battery is then vacuum packaged, allowed to stand, formed, shaped, and tested for capacity.

[0085] Example 1-2 to Example 1-11

[0086] Except for adjusting the relevant preparation parameters in "Preparation of Electrolyte" according to Table 1, the rest is the same as Example 1-1. Specifically, when the mass percentage of the boron trifluoride complex, the mass percentage of lithium difluorophosphate, and the mass percentage of the boron-containing additive changes, the mass percentage of ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate changes accordingly, the mass percentage of the lithium salt remains unchanged, and the mass ratio of ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate remains unchanged.

[0087] Examples 1-12

[0088] In addition to the LiNi 0.8 Co 0.2 O2 (brand: TCI) replaced with LiNi 0.6 Mn 0.2 Co 0.2 Except for O2 (brand: TCI), the rest is the same as Example 1-1.

[0089] Examples 1-13

[0090] In addition to the LiNi 0.8 Co 0.2 O2 (brand: TCI) replaced with LiNi 0.33 Mn 0.33 Co 0.33 Except for O2 (brand: TCI), the rest is the same as Example 1-1.

[0091] Examples 1-14

[0092] In addition to the LiNi 0.8 Co 0.2 O2 (brand: TCI) replaced with LiNi 0.8 Co 0.15 Al 0.05 Except for O2 (brand: TCI), the rest is the same as Example 1-1.

[0093] Example 1-15 to Example 1-18

[0094] Except for adjusting the relevant preparation parameters in "Preparation of Electrolyte" according to Table 1, the rest is the same as Example 1-1. Specifically, when the mass percentage of the boron trifluoride complex, the mass percentage of lithium difluorophosphate, and the mass percentage of the boron-containing additive changes, the mass percentage of ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate changes accordingly, the mass percentage of the lithium salt remains unchanged, and the mass ratio of ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate remains unchanged.

[0095] Examples 1-19

[0096] Except for preparing the negative electrode sheet according to the following preparation method, the rest is the same as Example 1-1.

[0097] <Preparation of negative electrode sheet>

[0098] preparing a first negative electrode material consisting of artificial graphite and silicon oxide (SiO2) in a weight ratio of 9:1;

[0099] The first negative electrode material, styrene-butadiene rubber, and lithium carboxymethyl cellulose were mixed with deionized water in a mass ratio of 96.5:2.5:1 and stirred evenly to obtain a negative electrode slurry. The negative electrode slurry was evenly coated on one surface of an 8μm-thick negative electrode current collector copper foil, then dried at 110°C. The above steps were repeated on the other surface of the negative electrode current collector. Cold pressing, sheet cutting, and tab welding were performed to obtain a negative electrode sheet.

[0100] Example 2-1 to Example 2-8

[0101] The process was the same as Example 1-1, except that propylene carbonate (PC) was further introduced in the preparation of the electrolyte and the relevant preparation parameters were adjusted according to Table 2. When the mass percentage of propylene carbonate and the mass percentage of lithium difluorophosphate changed, the mass percentage of ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate also changed, while the mass percentage of the boron trifluoride complex, the mass percentage of the boron-containing additive, and the mass percentage of the lithium salt remained unchanged, and the mass ratio of ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate remained unchanged.

[0102] Examples 2-9

[0103] The preparation method was the same as that of Example 1-1, except that ethyl methyl carbonate was not added in the preparation of the electrolyte. Based on the mass of the electrolyte, the mass percentage F of the lithium salt was 12.5%, the mass percentage X% of the boron trifluoride complex was 0.02%, the mass percentage A% of the lithium difluorophosphate was 0.1%, the mass percentage B% of the boron-containing additive was 0.1%, and the remainder was ethylene carbonate and diethyl carbonate, with the mass ratio of ethylene carbonate to diethyl carbonate being 1:1.

[0104] Example 3-1 to Example 3-3

[0105] The process was the same as Example 1-1, except that the first additive was added in the preparation of the electrolyte and the relevant preparation parameters were adjusted according to Table 3. When the mass percentage of the first additive changed, the sum of the mass percentages of ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate changed accordingly; the mass percentage of the boron trifluoride complex, the mass percentage of lithium difluorophosphate, the mass percentage of the boron-containing additive, and the mass percentage of the lithium salt remained unchanged; and the mass ratio of ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate remained unchanged.

[0106] Examples 3-4

[0107] The preparation process was the same as Example 1-1, except that the first additive and propylene carbonate were added in the preparation of the electrolyte and the relevant preparation parameters were adjusted according to Table 3. Based on the mass of the electrolyte, the mass percentage F of the lithium salt was 12.5%, the mass percentage X% of the boron trifluoride complex was 0.02%, the mass percentage A% of lithium difluorophosphate was 0.1%, the mass percentage B% of the boron-containing additive was 0.1%, the mass percentage of propylene carbonate was 15%, the mass percentage of the first additive was 1.5%, and the remainder was ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate, with the mass ratio of ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate being 1:2:1.

[0108] Example 4-1 to Example 4-4

[0109] The process was the same as in Example 1-1 except that the pulverization time was adjusted so that the specific surface area of ​​the lithium cobalt oxide was as shown in Table 4.

[0110] Comparative Example 1

[0111] Except for preparing the electrolyte according to the following preparation method, the rest is the same as Example 1-1.

[0112] <Preparation of Electrolyte>

[0113] In an argon atmosphere glove box with a water content of less than 10 ppm, ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed to form a base solvent. Lithium hexafluorophosphate (LiPF6) was then added to the base solvent and mixed thoroughly to form an electrolyte. The lithium salt (LiPF6) was present in a 12.5% ​​by weight percentage (based on the mass of the electrolyte), with the remainder consisting of ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate. The mass ratio of ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate was 1:2:1.

[0114] Comparative Example 2

[0115] Except for using LiCoO2 as the positive electrode material in <Preparation of Positive Electrode Sheet>, the rest is the same as Example 1-1.

[0116] Comparative Examples 3 to 5

[0117] The preparation method is the same as Example 1-1 except that no boron trifluoride complex, lithium difluorophosphate or boron-containing additive is added in the preparation of the electrolyte, the sum of the mass percentages of ethylene carbonate, ethyl methyl carbonate and diethyl carbonate changes accordingly, the mass percentage of the lithium salt remains unchanged, and the mass ratio of ethylene carbonate, ethyl methyl carbonate and diethyl carbonate remains unchanged.

[0118] Comparative Example 6

[0119] The preparation method is the same as Example 1-1 except that lithium difluorophosphate and boron-containing additives are not added in the preparation of the electrolyte, the sum of the mass percentages of ethylene carbonate, ethyl methyl carbonate and diethyl carbonate changes accordingly, the mass percentage of the lithium salt remains unchanged, and the mass ratio of ethylene carbonate, ethyl methyl carbonate and diethyl carbonate remains unchanged.

[0120] Comparative Example 7

[0121] The preparation method is the same as Example 1-1 except that the boron trifluoride complex and the boron-containing additive are not added in the preparation of the electrolyte, the sum of the mass percentages of ethylene carbonate, ethyl methyl carbonate and diethyl carbonate changes accordingly, the mass percentage of the lithium salt remains unchanged, and the mass ratio of ethylene carbonate, ethyl methyl carbonate and diethyl carbonate remains unchanged.

[0122] Comparative Example 8

[0123] The preparation method is the same as Example 1-1 except that boron trifluoride complex and lithium difluorophosphate are not added in the preparation of electrolyte, the sum of the mass percentages of ethylene carbonate, ethyl methyl carbonate and diethyl carbonate changes accordingly, the mass percentage of lithium salt remains unchanged, and the mass ratio of ethylene carbonate, ethyl methyl carbonate and diethyl carbonate remains unchanged.

[0124] The preparation parameters and electrical performance parameters of each embodiment and comparative example are shown in Tables 1 to 4.

[0125] Referring to Table 1, it can be seen from Examples 1-1 to 1-19 and Comparative Examples 1 to 8 that by regulating the positive electrode material layer to include lithium cobalt oxide, the lithium cobalt oxide including the above-mentioned elements, and the electrolyte to include a boron trifluoride complex, lithium difluorophosphate, and a boron-containing additive, the lithium-ion battery has a higher capacity retention rate and float charge capacity retention rate after 200 cycles at -10°C, and a lower float charge volume expansion rate, indicating that the lithium-ion battery has good low-temperature cycling performance and float charge performance. In contrast, in Comparative Examples 1 to 8, the capacity retention rate and float charge capacity retention rate of the lithium-ion battery after 200 cycles at -10°C are low, and the float charge volume expansion rate is high, indicating that the low-temperature cycling performance and float charge performance of the lithium-ion battery are poor.

[0126] The mass percentage of the boron trifluoride complex and the sum of the mass percentages of lithium difluorophosphate and the boron-containing additive affect the low-temperature cycling performance and float charge performance of the lithium-ion battery. From Examples 1-1 to 1-5, 1-8 to 1-11, and 1-15 to 1-18, it can be seen that by regulating the mass percentage of the boron trifluoride complex and the sum of the mass percentages of lithium difluorophosphate and the boron-containing additive within the scope of this application, the lithium-ion battery has a higher capacity retention rate and float charge capacity retention rate after 200 cycles at -10°C, and a lower float charge volume expansion rate, indicating that the lithium-ion battery has good low-temperature cycling performance and float charge performance.

[0127] The mass percentage (A%) of lithium difluorophosphate affects the low-temperature cycling and float charge performance of lithium-ion batteries. As shown in Examples 1-1, 1-8, and 1-9, by adjusting the mass percentage (A%) of lithium difluorophosphate within the scope of this application, the lithium-ion battery exhibits higher capacity retention and float charge capacity retention after 200 cycles at -10°C, and lower float charge volume expansion, indicating that the lithium-ion battery has better low-temperature cycling and float charge performance.

[0128] A boron-containing additive with a mass percentage of B% can affect the low-temperature cycling and float charge performance of lithium-ion batteries. As shown in Examples 1-1 and 1-5, by adjusting the mass percentage of the boron-containing additive to B% within the scope of this application, the lithium-ion battery has a higher capacity retention rate and float charge capacity retention rate after 200 cycles at -10°C, and a lower float charge volume expansion rate, indicating that the lithium-ion battery has better low-temperature cycling and float charge performance.

[0129] The ratio A / B of the mass percentage of lithium difluorophosphate to the mass percentage of the boron-containing additive affects the low-temperature cycling performance and float charge performance of the lithium-ion battery. From Examples 1-1, 1-5, 1-8, 1-11, 1-16, and 1-18, it can be seen that by regulating the ratio A / B of the mass percentage of lithium difluorophosphate to the mass percentage of the boron-containing additive within the scope of this application, the lithium-ion battery has a higher capacity retention rate and float charge capacity retention rate after 200 cycles at -10°C, and a lower float charge volume expansion rate, indicating that the lithium-ion battery has good low-temperature cycling performance and float charge performance.

[0130] The type of boron-containing additive affects the low-temperature cycling and float charge performance of lithium-ion batteries. As shown in Examples 1-1, 1-6, and 1-7, by adjusting the type of boron-containing additive within the scope of this application, the lithium-ion battery has a higher capacity retention rate and float charge capacity retention rate after 200 cycles at -10°C, and a lower float charge volume expansion rate, indicating that the lithium-ion battery has good low-temperature cycling and float charge performance.

[0131] The type of negative electrode material affects the low-temperature cycling and float charge performance of lithium-ion batteries. Comparing Example 1-1 with Example 1-19, it can be seen that the lithium-ion battery containing a negative electrode material including a carbon material and a silicon-based material has a higher capacity retention rate and float charge capacity retention rate after 200 cycles at -10°C, as well as a lower float charge volume expansion rate, indicating that the lithium-ion battery has better low-temperature cycling and float charge performance.

[0132] Table 2 Note: In Table 2, “ / ” indicates no relevant preparation parameters.

[0133] The electrolyte also includes propylene carbonate, and the mass percentage (D%) of propylene carbonate affects the low-temperature cycling performance and float charge performance of the lithium-ion battery. As shown in Examples 2-1 to 2-8, by adjusting the electrolyte to also include propylene carbonate and adjusting the mass percentage (D%) of propylene carbonate within the range of this application, the lithium-ion battery has a higher capacity retention rate and float charge capacity retention rate after 200 cycles at -10°C, and a lower float charge volume expansion rate, indicating that the lithium-ion battery has better low-temperature cycling performance and float charge performance.

[0134] The ratio (A / D) of the mass percentage of lithium difluorophosphate to the mass percentage of propylene carbonate affects the low-temperature cycling and float charge performance of lithium-ion batteries. As shown in Examples 2-1 to 2-8, by adjusting the ratio (A / D) of the mass percentage of lithium difluorophosphate to the mass percentage of propylene carbonate within the scope of this application, the lithium-ion battery exhibits higher capacity retention and float charge capacity retention after 200 cycles at -10°C, and lower float charge volume expansion, indicating that the lithium-ion battery has better low-temperature cycling and float charge performance.

[0135] Table 3 Note: In Table 3, “ / ” indicates no relevant preparation parameters.

[0136] The electrolyte also includes a first additive, and the mass percentage E% of the first additive affects the low-temperature cycling performance and float charge performance of the lithium-ion battery. As can be seen from Examples 3-1 and 3-4, by adjusting the electrolyte to also include the first additive, and the mass percentage E% of the first additive within the scope of this application, the lithium-ion battery has a higher capacity retention rate and float charge capacity retention rate after 200 cycles at -10°C, and a lower float charge volume expansion rate, indicating that the lithium-ion battery has good low-temperature cycling performance and float charge performance.

[0137] Table 4

[0138] The specific surface area (SSA) of the positive electrode material affects the low-temperature cycling and float charge performance of lithium-ion batteries. As shown in Examples 1-1, 4-1, and 4-4, by adjusting the specific surface area (SSA) of the positive electrode material within the scope of this application, the lithium-ion battery exhibits higher capacity retention and float charge capacity retention after 200 cycles at -10°C, and lower float charge volume expansion, indicating that the lithium-ion battery has better low-temperature cycling and float charge performance.

[0139] 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.

[0140] 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.

[0141] 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 and an electrolyte, the positive electrode sheet comprising a positive electrode material layer, the positive electrode material layer comprising lithium cobalt oxide, and the lithium cobalt oxide comprising nickel element. The electrolyte comprises a boron trifluoride complex, lithium difluorophosphate and a boron-containing additive.

2. The secondary battery according to claim 1, wherein, The negative electrode sheet comprises a negative electrode material layer, the negative electrode material layer comprising a carbon material and a silicon-based material, and the carbon material comprising artificial graphite and / or natural graphite.

3. The secondary battery according to claim 1, wherein, Based on the mass of the electrolyte, the mass percentage content of the boron trifluoride complex is X%, the mass percentage content of lithium difluorophosphate is A%, and the mass percentage content of the boron-containing additive is B%, where 0.01 ≤ X ≤ 2.7 and 0.2 ≤ A + B ≤ 6.

4. The secondary battery according to any one of claims 1 to 3, wherein, The electrolyte satisfies at least one of the following characteristics: (1) 0.1 ≤ A ≤ 3; (2) 0.01 ≤ B ≤ 3; (3) 0.1 ≤ A / B ≤ 30.

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

6. The secondary battery according to any one of claims 1 to 3, wherein, The electrolyte further comprises propylene carbonate, and based on the mass of the electrolyte, the mass percentage content of propylene carbonate is D%, where 5 ≤ D ≤ 20.

7. The secondary battery according to claim 6, wherein, Based on the mass of the electrolyte, the mass percentage content of lithium difluorophosphate is A%, and 0.005 ≤ A / D ≤ 0.

2.

8. The secondary battery according to any one of claims 1 to 3, wherein, The electrolyte further comprises a first additive, the first additive comprising sodium dithionite, and based on the mass of the electrolyte, the mass percentage content of the first additive is E%, where 0.1 ≤ E ≤ 2.

5.

9. The secondary battery according to any one of claims 1 to 3, wherein, The lithium cobalt oxide includes Li x Ni 1-y-z Co y M z O2, where 0.95 ≤ x ≤ 1.1, 0.01 ≤ y ≤ 0.35, 0.01 ≤ z ≤ 0.5, and M includes at least one element of Al, Cr, Mn, Fe, Mg, La, Ce, Sr, or V.

10. The secondary battery according to any one of claims 1 to 3, wherein, The positive electrode material layer includes a positive electrode material, and the specific surface area of the positive electrode material is 0.1 m 2 / g to 3.9 m 2 / g.

11. An electronic device, comprising the secondary battery according to any one of claims 1 to 10.

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