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, wherein the electrolyte comprises propionate and a first additive, and the first additive comprises at least one of a compound of formula (Ia), a compound of formula (Ib), or a compound of formula (Ic). By regulating the electrolyte, the impedance of the secondary battery can be reduced while the low-temperature performance of the secondary battery is improved.

Description

Secondary battery and electronic device Technical Field

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

[0002] Lithium-ion batteries offer numerous advantages, including high specific energy density, long cycle life, high nominal voltage, low self-discharge, compact size, and light weight. They are widely used in portable electronic devices, electric bicycles, electric vehicles, and energy storage devices. Technologists are constantly improving the performance of lithium-ion batteries, and they will continue to play a key role in the consumer electronics sector for a long time.

[0003] During the use of lithium-ion batteries, temperature is a significant factor affecting their discharge performance. At low temperatures (e.g., below -10°C), the discharge voltage and SOC (State of Charge) of lithium-ion batteries decrease, resulting in a reduction in discharge capacity and an increase in impedance.

[0004] Summary of the Invention

[0005] The purpose of this application is to provide a secondary battery and an electronic device that can improve the low-temperature performance of the secondary battery while reducing the impedance of the secondary battery. The specific technical solution is as follows:

[0006] A first aspect of the present application provides a secondary battery comprising a positive electrode sheet, a negative electrode sheet, and an electrolyte, wherein the electrolyte comprises a propionate and a first additive, wherein the first additive comprises at least one of a compound of formula (Ia), a compound of formula (Ib), or a compound of formula (Ic).

[0007] Wherein, R1, R2, R3, and R4 are each independently selected from a single bond, a methylene group substituted or unsubstituted by Ra, and Ra in each group is each independently selected from F, Cl, Br, I, methyl, ethyl, propyl, isopropyl, butyl, tert-butyl, trifluoromethyl, and tetrafluoroethyl, and R1, R2, R3, and R4 are not all single bonds at the same time; R5 is selected from a single bond, -O-, C1-C3 alkylidene, C1-C3 haloalkylidene, or C1-C3 oxaalkylidene; R6, R7, R8, and R9 are each independently selected from a C1-C5 alkylidene group substituted or unsubstituted by Rb, or O, and Rb in each group is each independently selected from F, Cl, Br, I, methyl, ethyl, propyl, isopropyl, butyl, tert-butyl, trifluoromethyl, and tetrafluoroethyl. By regulating the electrolyte including the propionate and the first additive, and the type of the first additive within the scope of this application, the low-temperature performance of the secondary battery can be improved while reducing the impedance of the secondary battery.

[0008] In one embodiment of the present application, the electrolyte satisfies at least one of the following:

[0009] (1) The propionate ester includes at least one of ethyl propionate or propyl propionate;

[0010] (2) The compound of formula (Ib) comprises at least one of the following compounds:

[0011] (3) The compound of formula (Ic) comprises at least one of the following compounds:

[0012] (4) Based on the mass of the electrolyte, the mass percentage of the propionate is A, 0.01%≤A≤70%;

[0013] (5) Based on the mass of the electrolyte, the mass percentage of the first additive is C, 0.01%≤C≤4%.

[0014] Satisfying at least one of the above conditions can further improve the low-temperature performance of the secondary battery and reduce the impedance of the secondary battery.

[0015] In one embodiment of the present application, the electrolyte further includes a second additive, the second additive including at least one of lithium difluorophosphate, lithium fluorosulfonate, or bis(fluorosulfonyl)imide. By regulating the inclusion of the second additive in the electrolyte and the type of the second additive within the scope of the present application, the second additive can synergistically regulate the thickness of the positive electrode interface protective film and the thickness of the negative electrode interface protective film with the propionate and the first additive, thereby further improving the low-temperature performance of the secondary battery and reducing the impedance of the secondary battery.

[0016] In one embodiment of the present application, the mass percentage of the second additive is D, based on the mass of the electrolyte, and 0.01%≤D≤6%. By regulating the mass percentage D of the second additive within the range of this application, a more effective positive electrode interface protective film and a negative electrode interface protective film can be obtained, thereby further improving the low-temperature performance of the secondary battery and reducing the impedance of the secondary battery.

[0017] In one embodiment of the present application, the positive electrode sheet includes a positive electrode current collector and a positive electrode material layer provided on at least one surface of the positive electrode current collector, wherein the positive electrode material layer includes a positive electrode active material, and the chemical formula of the positive electrode active material is LiCo 1-a M aO2, M includes at least one of Mg, Al, Ti, Zr, Ce, La, Y, W, Ba, or Ca, and 0≤a≤0.2. Under low-temperature conditions, the electrolyte viscosity is high, the lithium ion migration rate is slow, and the low-temperature performance of the secondary battery is limited. Under high-temperature conditions, the migration path of lithium ions is disturbed, resulting in an increase in the impedance of the secondary battery. By selecting the above-mentioned positive electrode active materials, the migration rate of lithium ions can be effectively increased, improving the low-temperature performance of the secondary battery. It also has less interference with the migration path of lithium ions under high-temperature conditions, which can reduce the cycle impedance growth rate of the secondary battery, thereby reducing the impedance of the secondary battery.

[0018] In one embodiment of the present application, M includes Y, and based on the mass of the positive electrode active material, the mass percentage of Y is B, 400ppm≤B≤5000ppm. The doping element M can improve the crystal structure stability of the positive electrode active material. M includes Y, and by regulating the mass percentage B of Y within the scope of this application, the crystal structure stability of the positive electrode active material can be further improved, while the degree of interaction between different components in the electrolyte under low temperature conditions can be increased, the toughness of the positive electrode interface protective film can be optimized, and the low temperature performance of the secondary battery can be further improved while reducing the impedance of the secondary battery.

[0019] In one embodiment of the present application, M includes Y, and the mass percentage of Y based on the mass of the positive electrode active material is B. The mass percentage of the propionate based on the mass of the electrolyte is A, 0.1%≤A≤70%, and 0.2≤A / B≤800. By regulating the mass percentage of the propionate A and the value of A / B within the scope of this application, the mass percentage of the propionate can be matched with the mass percentage of Y in the positive electrode active material. The propionate can act synergistically with the positive electrode active material to promote the migration of lithium ions and avoid the occurrence of side reactions, thereby further improving the low-temperature performance of the secondary battery while reducing the impedance of the secondary battery.

[0020] In one embodiment of the present application, M includes at least one of La, Mg, or W, and the mass percentage of La, Mg, or W is independently 200 ppm to 10,000 ppm based on the mass of the positive electrode active material. By regulating M to include at least one of La, Mg, or W, and regulating the mass percentage of the doping elements La, Mg, or W to be independently within the range of the present application, the surface resistance of the positive electrode sheet can be increased to a certain extent, enabling lithium ions to have a suitable intercalation and deintercalation rate, thereby improving the structural stability and cycle performance of the secondary battery.

[0021] In one embodiment of the present application, M includes at least one of Ba or Ca, and the mass percentage of Ba or Ca is independently 100 ppm to 22,000 ppm based on the mass of the positive electrode active material. By regulating M to include at least one of Ba or Ca, and regulating the mass percentage of the doping element Ba or Ca to be independently within the scope of the present application, the high-temperature stability of the positive electrode active material can be improved, and the low-temperature performance of the secondary battery can be improved, the impedance of the secondary battery can be reduced, and the secondary battery can have better high-temperature performance.

[0022] 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.

[0023] Beneficial effects of this application:

[0024] 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 electrolyte includes a propionate and a first additive. The first additive includes at least one of a compound of formula (Ia), a compound of formula (Ib), or a compound of formula (Ic). By regulating the electrolyte to include the propionate and the first additive, and regulating the type of the first additive within the scope of the present application, the low-temperature performance of the secondary battery can be improved while reducing the impedance of the secondary battery.

[0025] 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

[0026] 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.

[0027] 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:

[0028] The present application provides a secondary battery comprising a positive electrode sheet, a negative electrode sheet, and an electrolyte, wherein the electrolyte comprises a propionate and a first additive, wherein the first additive comprises at least one of a compound of formula (Ia), a compound of formula (Ib), or a compound of formula (Ic).

[0029] Wherein, R1, R2, R3, and R4 are each independently selected from a single bond, a methylene group substituted or unsubstituted by R, and R in each group is each independently selected from F, Cl, Br, I, methyl, ethyl, propyl, isopropyl, butyl, tert-butyl, trifluoromethyl, and tetrafluoroethyl; R1, R2, R3, and R4 are not simultaneously single bonds; R5 is selected from a single bond, -O-, C1-C3 alkylidene, C1-C3 haloalkylidene, or C1-C3 oxaalkylidene; R6, R7, R8, and R9 are each independently selected from C1-C5 alkylidene substituted or unsubstituted by R, and O, and R in each group is each independently selected from F, Cl, Br, I, methyl, ethyl, propyl, isopropyl, butyl, tert-butyl, trifluoromethyl, and tetrafluoroethyl. In the present application, C1-C3 haloalkylidene may be -CCl-, -CH2CCl-, or -CH2CH2CCl-. The C1-C3 oxaalkylene group may be -OCH-, -CH2OCH-, or -CH2OCH2CH-. The C1-C5 alkylene group may be methylene, ethylene, propylene, butylene, or pentylene.

[0030] The inventors have discovered that because the propionate ester and the first additive have different chemical structures, they can synergistically improve the low-temperature performance and reduce the impedance of the secondary battery during cycling. The combination of the propionate ester and the first additive can produce a secondary battery with improved capacity characteristics under low-temperature conditions. By adjusting the electrolyte containing the propionate ester and the first additive, and the type of the first additive within the scope of this application, it is possible to improve the low-temperature performance of the secondary battery while reducing the impedance of the secondary battery.

[0031] In one embodiment of the present application, the propionate ester includes at least one of ethyl propionate or propyl propionate. By adjusting the type of propionate ester within the scope of the present application, the low-temperature performance of the secondary battery can be further improved and the impedance of the secondary battery can be reduced.

[0032] In one embodiment of the present application, based on the mass of the electrolyte, the mass percentage of propionate is A, 0.01%≤A≤70%. For example, A can be 0.01%, 0.05%, 0.1%, 0.5%, 1%, 1.3%, 1.7%, 2%, 2.3%, 2.7%, 3%, 3.3%, 3.7%, 4%, 4.3%, 4.7%, 5%, 5.3%, 5.7%, 6%, 6.3%, 6.7%, 7%, 7.3%, 7.7%, 8%, 8.3%, 8.7%, 9%, 9.3%, 9.7%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, or a range consisting of any two of the above values. By regulating the mass percentage A of the propionate within the scope of this application, the propionate can have an appropriate mass percentage. The mixture of the propionate and the first additive can further improve the low-temperature performance of the secondary battery while reducing the impedance of the secondary battery.

[0033] In one embodiment of the present application, the compound of formula (Ib) includes at least one of the following compounds:

[0034] By selecting the compound of formula (Ib), the low-temperature performance of the secondary battery can be further improved and the impedance of the secondary battery can be reduced.

[0035] In one embodiment of the present application, the compound of formula (Ic) includes at least one of the following compounds:

[0036] By selecting the compound of formula (Ic), the low-temperature performance of the secondary battery can be further improved and the impedance of the secondary battery can be reduced.

[0037] In one embodiment of the present application, based on the mass of the electrolyte, the mass percentage of the first additive is C, 0.01%≤C≤4%. For example, C can be 0.01%, 0.03%, 0.05%, 0.07%, 0.1%, 0.3%, 0.4%, 0.5%, 0.7%, 0.9%, 1%, 1.2%, 1.3%, 1.5%, 1.7%, 1.9%, 2%, 2.2%, 2.3%, 2.4%, 2.5%, 2.7%, 2.9%, 3%, 3.3%, 3.4%, 3.5%, 3.7%, 4%, or a range consisting of any two of the above values. By regulating the mass percentage C of the first additive within the scope of this application, the first additive can have an appropriate mass percentage, and the first additive can be mixed with the propionate ester to further improve the low-temperature performance of the secondary battery while reducing the impedance of the secondary battery. In the present application, the first additive includes a compound of formula (Ia), and the weight percentage of the compound of formula (Ia) may be 0.01% to 4%; the first additive includes a compound of formula (Ib), and the weight percentage of the compound of formula (Ib) may be 0.01% to 4%; the first additive includes a compound of formula (Ic), and the weight percentage of the compound of formula (Ic) may be 0.01% to 4%. When the first additive includes two or more compounds, the present application does not particularly limit the weight percentage of each compound, as long as the weight percentage of the first additive meets the scope of the present application.

[0038] In one embodiment of the present application, the electrolyte further includes a second additive comprising at least one of lithium difluorophosphate, lithium fluorosulfonate, or bis(fluorosulfonyl)imide. By regulating the inclusion of the second additive and the type of the second additive within the scope of the present application, the second additive can synergistically regulate the thickness of the positive electrode interface protective film and the thickness of the negative electrode interface protective film with the propionate and the first additive, thereby further improving the low-temperature performance of the secondary battery and reducing the impedance of the secondary battery.

[0039] In one embodiment of the present application, based on the mass of the electrolyte, the mass percentage of the second additive is D, 0.01%≤D≤6%. For example, D can be 0.01%, 0.05%, 0.1%, 0.5%, 1%, 1.5%, 1.7%, 2%, 2.3%, 2.5%, 3%, 3.5%, 4%, 4.2%, 4.5%, 5%, 5.5%, 6% or a range consisting of any two of the above values. By regulating the mass percentage D of the second additive within the scope of this application, a more effective positive electrode interface protective film and a negative electrode interface protective film can be obtained, thereby further improving the low temperature performance of the secondary battery and reducing the impedance of the secondary battery.

[0040] In one embodiment of the present application, the positive electrode sheet includes a positive electrode current collector and a positive electrode material layer provided on at least one surface of the positive electrode current collector. The above-mentioned "positive electrode material layer provided on at least one surface of the positive electrode current collector" means that the positive electrode material layer can be provided on one surface of the positive electrode current collector along its own thickness direction, or on two surfaces of the positive electrode current collector along its own thickness direction. 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. The positive electrode material layer includes a positive electrode active material, and the chemical formula of the positive electrode active material is LiCo 1-a M a O2, M includes at least one of Mg, Al, Ti, Zr, Ce, La, Y, W, Ba or Ca, 0≤a≤0.2. Exemplarily, a can be 0, 0.02, 0.04, 0.06, 0.08, 0.1, 0.12, 0.14, 0.16, 0.18, 0.2 or a range consisting of any two of the above values. Under low temperature conditions, the viscosity of the electrolyte is high, the migration rate of lithium ions is slow, and the improvement of the low temperature performance of the secondary battery is limited; under high temperature conditions, the movement path of lithium ions will be disturbed, resulting in an increase in the impedance of the secondary battery. By selecting the above-mentioned positive electrode active materials, the migration rate of lithium ions can be effectively improved, and the low temperature performance of the secondary battery can be improved; it also has less interference with the movement path of lithium ions under high temperature conditions, and can reduce the cycle impedance growth rate of the secondary battery, thereby reducing the impedance of the secondary battery. In this application, high temperature refers to a temperature above 40°C.

[0041] In one embodiment of the present application, M includes Y, and the mass percentage of Y is B based on the mass of the positive electrode active material, 400ppm≤B≤5000ppm. For example, B can be 400ppm, 500ppm, 750ppm, 1000ppm, 1200ppm, 1500ppm, 2000ppm, 2200ppm, 2500ppm, 3000ppm, 3200ppm, 3500ppm, 4000ppm, 4200ppm, 4500ppm, 5000ppm or a range consisting of any two of the above values. The doping element M can improve the crystal structure stability of the positive electrode active material. M includes Y, and by regulating the mass percentage B of Y within the scope of this application, the crystal structure stability of the positive electrode active material can be further improved, while the degree of interaction between different components in the electrolyte under low temperature conditions is increased, the toughness of the positive electrode interface protective film is optimized, and the low temperature performance of the secondary battery can be further improved while reducing the impedance of the secondary battery.

[0042] In one embodiment of the present application, M includes Y, based on the mass of the positive electrode active material, the mass percentage of Y is B, based on the mass of the electrolyte, the mass percentage of propionate is A, 0.1%≤A≤70%, 0.2≤A / B≤800. For example, A can be 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 8.7%, 9%, 9.3%, 9.7%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70% or a range consisting of any two of the above values; A / B can be 0.2, 1, 5, 10, 15, 25, 50, 700, 704, 746, 750, 754, 796, 800, or a range consisting of any two of the above values. By regulating the mass percentage A of propionate and the value of A / B within the scope of this application, the mass percentage of propionate can be matched with the mass percentage of Y in the positive electrode active material. Propionate can act synergistically with the positive electrode active material to promote the migration of lithium ions and avoid the occurrence of side reactions, thereby further improving the low-temperature performance of the secondary battery while reducing the impedance of the secondary battery.

[0043] In one embodiment of the present application, M includes at least one of La, Mg, or W. Based on the mass of the positive electrode active material, the mass percentage of La, Mg, or W is each independently 200 ppm to 10000 ppm. For example, the mass percentage of La can be 200ppm, 400ppm, 600ppm, 800ppm, 1000ppm, 1200ppm, 2000ppm, 2200ppm, 3000ppm, 3200ppm, 4000ppm, 4200ppm, 5000ppm, 5200ppm, 6000ppm, 6200ppm, 7000ppm, 7200ppm, 8000ppm, 8200ppm, 9000ppm, 9200ppm, 10000ppm or a range consisting of any two of the above values; the mass percentage of Mg can be 200ppm, 400ppm, 600ppm, 800ppm, 1000ppm, 1200ppm, 2000ppm, 2200ppm, 3000ppm, 3200ppm, 4000ppm, 4200ppm ppm, 8000ppm, 8200ppm, 9000ppm, 9200ppm, 10000ppm or a range consisting of any two of the above values; the mass percentage of W can be 200ppm, 400ppm, 600ppm, 800ppm, 1000ppm, 1200ppm, 2000ppm, 2200ppm, 3000ppm, 3200ppm, 4000ppm, 4200ppm, 5000ppm, 5200ppm, 6000ppm, 6200ppm, 7000ppm, 7200ppm, 8000ppm, 8200ppm, 9000ppm, 9200ppm, 10000ppm or a range consisting of any two of the above values. By regulating M to include at least one of La, Mg or W, and the mass percentage of the doping elements La, Mg or W independently within the scope of the present application, the surface resistance of the positive electrode sheet can be increased to a certain extent, so that lithium ions have a suitable insertion and extraction rate, and the structural stability and cycle performance of the secondary battery can be improved.

[0044] In one embodiment of the present application, M includes at least one of Ba or Ca, and the mass percentage of Ba or Ca is independently 100 ppm to 22000 ppm based on the mass of the positive electrode active material. For example, the mass percentage of Ba can be 100 ppm, 500 ppm, 1000 ppm, 1200 ppm, 2500 ppm, 4700 ppm, 5000 ppm, 5300 ppm, 7200 ppm, 7500 ppm, 7800 ppm, 9000 ppm, 9700 ppm, 10000 ppm, 10300 ppm, 14700 ppm, 15000 ppm, 15300 ppm, 19700 ppm, 20000 ppm, 20300 ppm, 21700 ppm, 22000 ppm or a combination of any two of the above values. Range; the mass percentage of Ca can be 100ppm, 500ppm, 1000ppm, 1200ppm, 2500ppm, 4700ppm, 5000ppm, 5300ppm, 7200ppm, 7500ppm, 7800ppm, 9000ppm, 9700ppm, 10000ppm, 10300ppm, 14700ppm, 15000ppm, 15300ppm, 19700ppm, 20000ppm, 20300ppm, 21700ppm, 22000ppm or a range consisting of any two of the above values. By regulating M to include at least one of Ba or Ca, and the mass percentage of the doping element Ba or Ca each independently within the scope of this application, the high temperature stability of the positive electrode active material can be improved, and the low temperature performance of the secondary battery can be improved, the impedance of the secondary battery can be reduced, and the secondary battery can have good high temperature performance.

[0045] In the present application, the electrolyte 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(oxalatoborate) (LiBOB), or lithium difluoroborate. The mass percentage E of the lithium salt is 0.1% to 90% based on the mass of the electrolyte.

[0046] 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, it may include but is not limited to at least one of carbonate compounds, other carboxylic acid ester compounds, ether compounds or other organic solvents. The above-mentioned carbonate compounds may include but are not limited to at least one of linear carbonate compounds, cyclic carbonate compounds or fluorocarbon compounds. The above-mentioned linear carbonate compounds may include but are not limited to at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC) or ethyl methyl carbonate (EMC). The above-mentioned cyclic carbonate compounds may include but are not limited to at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC) or vinyl ethylene carbonate (VEC). The fluorinated carbonate compounds may include, but are 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 other carboxylate compounds may include, but are not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, γ-butyrolactone, decanoic acid lactone, 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, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate.

[0047] In one embodiment of the present application, the electrolyte may include a propionate ester, a first additive, another non-aqueous solvent, and a lithium salt. The weight percentages of the propionate ester, the first additive, and the lithium salt are as described above. A secondary battery including the above electrolyte has good low-temperature performance and low impedance.

[0048] In one embodiment of the present application, the electrolyte may include a propionate ester, a first additive, a second additive, another non-aqueous solvent, and a lithium salt. The weight percentages of the propionate ester, the first additive, the second additive, and the lithium salt are as described above. A secondary battery including the above electrolyte has excellent low-temperature performance and low impedance.

[0049] The present application has no particular limitation on the positive electrode current collector, as long as the purpose of the present application can be achieved. For example, it may include aluminum foil, aluminum alloy foil or a composite current collector (such as an aluminum-carbon composite current collector).

[0050] This application is for the positive electrode active material LiCo 1-a M a There is no particular limitation on the preparation method of O2, as long as the purpose of this application can be achieved. For example, the positive electrode active material LiCo 1-a M a The preparation method of O2 may include the following steps: according to the chemical formula of the desired positive electrode active material, the mixed material of cobalt oxide, lithium carbonate and the compound containing the M element are mixed according to the element stoichiometric ratio in the chemical formula, and the positive electrode active material is obtained after sintering at 800°C to 1100°C for 11h to 13h. The present application has no particular restriction on the mixing method, as long as the purpose of the present application can be achieved. For example, the mixing method can be ball milling. The present application has no particular restriction on the compound containing the M element, as long as the purpose of the present application can be achieved. For example, the compound containing the M element can be an oxide or salt containing the M element. Specifically, the compound containing the M element can include MgO, La2O3, Y2O3, WO3, BaO or CaO.

[0051] When M is element Y, the preparation method of the positive electrode active material may include the following steps: mixing a mixture of cobalt trioxide, lithium carbonate, and a compound containing element Y in a certain proportion, and sintering at 800°C to 1100°C for 11 to 13 hours to obtain the positive electrode active material. The present application does not particularly limit the mixing method, as long as it can achieve the objectives of the present application. For example, the mixing method may be ball milling. The compound containing element Y may include Y2O3.

[0052] When M is La, Mg or W, the preparation method of the positive electrode active material may include the following steps: mixing a mixture of cobalt oxide, lithium carbonate and a compound containing La, or mixing a mixture of cobalt oxide, lithium carbonate and a compound containing Mg, or mixing a mixture of cobalt oxide, lithium carbonate and a compound containing W in a certain proportion, and sintering at 800°C to 1100°C for 11 hours to 13 hours to obtain the corresponding positive electrode active material. The present application has no particular limitation on the mixing method, as long as the purpose of the present application can be achieved. For example, the mixing method can be ball milling. The compound containing La can include La2O3. The compound containing Mg can include MgO. The compound containing W can include WO3.

[0053] When M is Ba or Ca, the preparation method of the positive electrode active material may include the following steps: mixing a mixture of cobalt oxide, lithium carbonate and a compound containing Ba, or mixing a mixture of cobalt oxide, lithium carbonate and a compound containing Ca in a certain proportion, and sintering them at 800°C to 1100°C for 11 hours to 13 hours to obtain the corresponding positive electrode active material. This application does not particularly limit the mixing method, as long as it can achieve the purpose of this application. For example, the mixing method can be ball milling. The compound containing Ba can include BaO. The compound containing Ca can include CaO.

[0054] The present application does not impose any particular restrictions on regulating the mass percentage of the M element in the positive electrode active material, as long as the purpose of the present application can be achieved. For example, the mass percentage of the M element in the positive electrode active material can be regulated by regulating the mass percentage of the added compound containing the M element.

[0055] The present application has no particular limitation on the method for regulating the mass percentage B of Y, as long as the purpose of the present application can be achieved. For example, the mass percentage B of Y can be regulated by regulating the mass percentage of the added compound containing the element Y.

[0056] The present application does not particularly limit the method for regulating A / B, as long as the purpose of the present application can be achieved. For example, the value of A / B can be regulated by regulating the values ​​of A and B, and the regulation method is as described above.

[0057] 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 type of 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 (Super P), 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 at least one of 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 polymer may include but is 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 (PVDF), polystyrene butadiene copolymer (styrene-butadiene rubber), sodium alginate, polyvinyl alcohol, polytetrafluoroethylene, polyacrylonitrile, sodium carboxymethyl cellulose, potassium carboxymethyl cellulose, sodium hydroxymethyl cellulose or potassium hydroxymethyl cellulose. At least one of the following: The present application has no particular restrictions on the mass ratio of the positive electrode active material, the conductive agent, and the binder in the positive electrode material layer. Those skilled in the art can select according to actual needs, as long as the purpose of the present application can be achieved.

[0058] This application does not particularly limit the thickness of the positive electrode current collector, as long as the purpose of this application can be achieved. For example, the thickness of the positive electrode current collector is 5μm to 20μm. This application does not particularly limit the thickness of the positive electrode material layer, as long as the purpose of this application can be achieved. For example, the thickness of the positive electrode material layer is 30μm to 250μm. This application does not particularly limit the thickness of the positive electrode sheet, as long as the purpose of this application can be achieved. For example, the thickness of the positive electrode sheet is 50μm to 500μm.

[0059] 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.

[0060] In the present application, the negative electrode plate includes a negative electrode current collector and a negative electrode material layer provided on at least one surface of the negative electrode current collector. The above-mentioned "negative electrode material layer provided on at least one surface of the negative electrode current collector" means that the negative electrode material layer can be provided on one surface of the negative electrode current collector along the thickness direction of the negative electrode current collector, or on two surfaces of the negative electrode current collector along 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. 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, stainless steel, aluminum, nickel, titanium, sintered carbon, aluminum-cadmium alloy, copper or stainless steel that has been surface-treated with one of carbon, nickel, titanium or silver. The type of negative electrode current collector may include at least one of a film, a sheet, a foil, a mesh, a porous body, a foam or a non-woven fabric.

[0061] The negative electrode material layer of the present application includes a negative electrode active material. The present application has no particular restrictions on the negative electrode active material, as long as the purpose of the present application can be achieved. For example, specific examples of the negative electrode active material can be the following substances: carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber and amorphous carbon; metal compounds that can form alloys with lithium such as silicon (Si), aluminum (Al), tin (Sn), lead (Pb), zinc (Zn), bismuth (Bi), indium (In), magnesium (Mg), gallium (Ga), cadmium (Cd), Si alloy, Sn alloy or Al alloy; metal oxides that can be doped or not doped with lithium such as SiO β (0<β<2), SnO2, vanadium oxide and lithium vanadium oxide; or a composite material comprising a metal compound and a carbonaceous material such as a Si-C composite material or a Sn-C composite material, and any one thereof or a mixture of two or more thereof can be used. In addition, a metallic lithium film can be used as the negative electrode active material. The present application has no particular limitation on the mass percentage of the negative electrode active material in the negative electrode material layer, as long as the purpose of the present application can be achieved. For example, based on the mass of the negative electrode material layer, the mass percentage of the negative electrode active material can be 80% to 99%.

[0062] 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, as long as the purpose of the present application can be achieved. For example, the binder can be at least one of the above-mentioned binders. The present application has no special restrictions on the conductive agent, as long as the purpose of the present application can be achieved. For example, the conductive agent can be at least one of the above-mentioned conductive agents. The present application has no special restrictions on the mass percentage of the binder in the negative electrode material layer, as long as the purpose of the present application can be achieved. For example, based on the mass of the negative electrode material layer, the mass percentage of the binder can be 0.1% to 10%. The present application has no special restrictions on the mass percentage of the conductive agent in the negative electrode material layer, as long as the purpose of the present application can be achieved. For example, based on the mass of the negative electrode material layer, the mass percentage of the conductive agent can be 0.9% to 10%.

[0063] This application does not particularly limit the thickness of the negative electrode current collector, as long as the purpose of this application can be achieved. For example, the thickness of the negative electrode current collector is 5μm to 15μm. This application does not particularly limit the thickness of the negative electrode material layer, as long as the purpose of this application can be achieved. For example, the thickness of the negative electrode material layer is 30μm to 250μm. This application does not particularly limit the thickness of the negative electrode pole piece, as long as the purpose of this application can be achieved. For example, the thickness of the negative electrode pole piece is 50μm to 500μm.

[0064] 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.

[0065] 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 circuit of the secondary battery, allow electrolyte ions to pass freely, and do not affect the electrochemical charge and discharge process. The present application has no special 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.

[0066] 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 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 binder, and for example, it may be at least one of the aforementioned binders. The polymer layer includes 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).

[0067] 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.

[0068] In the present application, the secondary battery may include, but is not limited to, a lithium metal secondary battery, a lithium ion secondary battery (lithium ion battery), a lithium polymer secondary battery, or a lithium ion polymer secondary battery, etc.

[0069] 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, overcurrent protection elements, guide plates, etc. may also be placed in the packaging bag as needed to prevent the pressure inside the secondary battery from rising and overcharging and discharging. Among them, the packaging bag is a packaging bag known in the art, and the present application does not limit this.

[0070] 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.

[0071] 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.

[0072] Example

[0073] 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.

[0074] Test methods and equipment:

[0075] Test of the mass percentage of M in the positive electrode active material:

[0076] High-frequency inductively coupled plasma (ICP) emission mass spectrometry was used to determine the mass percentage of M element in the positive electrode active material.

[0077] Low temperature discharge performance test:

[0078] At 25°C, the lithium-ion battery was allowed to stand for 30 minutes, charged to 4.55V at a constant current of 0.5C, then charged to 0.05C at a constant voltage at 4.55V, and allowed to stand for 5 minutes, then discharged to 3.0V at 0.5C. After the discharge was completed, it was allowed to stand for 5 minutes, and the discharge capacity of the lithium-ion battery at 25°C was recorded as C0. Then at 25°C, the lithium-ion battery was charged to 4.55V at a constant current of 0.5C, then charged to 0.05C at a constant voltage at 4.55V, and allowed to stand for 5 minutes. After the lithium-ion battery was allowed to stand at -10°C for 4 hours, it was discharged to 3.0V at 0.5C. After the discharge was completed, it was allowed to stand for 5 minutes, and the discharge capacity of the lithium-ion battery at -10°C was recorded as C1.

[0079] The discharge capacity retention rate of a lithium-ion battery at -10°C = C1 / C0×100%.

[0080] High rate (1C) discharge performance test:

[0081] At 25°C, charge the lithium-ion battery at 0.1C to 4.3V, then charge it at a constant voltage at 4.3V to a current of 0.05C, let it stand for 5 minutes, and discharge it at a constant current of 0.2C to a voltage of 2.8V. The discharge capacity of the lithium-ion battery at this time is recorded as C2. Then charge the lithium-ion battery at 0.1C to 4.3V, then charge it at a constant voltage at 4.3V to a current of 0.05C, let it stand for 5 minutes, and discharge it at a constant current of 1C to a voltage of 2.8V. The discharge capacity of the lithium-ion battery at this time is recorded as C3.

[0082] High rate (1C) discharge capacity retention rate = C3 / C2×100%.

[0083] DC resistance (DCR) test:

[0084] At 25°C, the lithium-ion battery was charged at a constant current of 0.7C to 4.48V, then charged at a constant voltage of 4.48V to a current of 82.5mA, and then discharged at a constant current of 0.2C for 4h to make the lithium-ion battery state of charge (SOC) of 20%; then discharged at 0.1C for 10s to obtain a voltage of V0; discharged at 1C for 1s to obtain a voltage of V1; DCR (initial state at 25°C) = (V0-V1) / 0.1C. The lithium-ion battery is then charged to 4.48V at a constant current of 0.7C, and then charged to a current of 82.5mA at a constant voltage of 4.48V, and then discharged to 3.0V at a constant current of 0.2C. The above charge and discharge steps are cycled for 1000 cycles. After the lithium-ion battery cycle is completed, the lithium-ion battery is charged to 4.48V at a constant current of 0.7C, and then charged to a current of 82.5mA at a constant voltage of 4.48V, and then discharged at a constant current of 0.2C for 4h to discharge the lithium-ion battery to 20% SOC; then discharged at 0.1C for 10s to obtain a voltage V2; discharged at 1C for 1s to obtain a voltage V3; DCR (1000 cycles at 25°C) = (V2-V3) / 0.1C.

[0085] The DCR change rate at 20% SOC after 1000 cycles at 25°C = [DCR (1000 cycles at 25°C) / DCR (initial state at 25°C) - 1] × 100%.

[0086] At 45°C, the lithium-ion battery was charged at a constant current of 0.7C to 4.48V, then charged at a constant voltage of 4.48V to a current of 82.5mA, and then discharged at a constant current of 0.2C for 4h to make the lithium-ion battery state of charge (SOC) of 20%; then discharged at 0.1C for 10s to obtain a voltage of V4; discharged at 1C for 1s to obtain a voltage of V5; DCR (45°C initial state) = (V4-V5) / 0.1C. The lithium-ion battery was then charged to 4.48V at a constant current of 0.7C, and then charged to a current of 82.5mA at a constant voltage of 4.48V, and then discharged to 3.0V at a constant current of 0.2C. The above charge and discharge steps were cycled for 700 cycles. After the lithium-ion battery cycle was completed, the lithium-ion battery was charged to 4.48V at a constant current of 0.7C, and then charged to a current of 82.5mA at a constant voltage of 4.48V, and then discharged at a constant current of 0.2C for 4h to discharge the lithium-ion battery to 20% SOC; then discharged at 0.1C for 10s to obtain a voltage of V6; discharged at 1C for 1s to obtain a voltage of V7; DCR (700 cycles at 45°C) = (V6-V7) / 0.1C.

[0087] The DCR change rate at 20% SOC after 700 cycles at 45°C = [(DCR (700 cycles at 45°C)) / DCR (initial state at 45°C) - 1) × 100%.

[0088] Example 1-1

[0089] <Preparation of positive electrode sheet>

[0090] The mixture of cobalt trioxide, lithium carbonate, and Y2O3 was mixed evenly, then sintered at 990°C for 12 hours. After cooling, it was crushed and sieved to obtain a Y-doped lithium cobalt oxide positive electrode active material. Wherein, the mass percentage content B of Y based on the mass of the positive electrode active material is 1000ppm. The above-mentioned positive electrode active material, conductive carbon black as a conductive agent, and polyvinylidene fluoride as a binder were added to a stirring tank in a mass ratio of 97.2:1.5:1.3. NMP solvent was added and stirred evenly under the action of a vacuum mixer. The mixture was passed through a 200-mesh screen to obtain a positive electrode slurry, wherein the solid content of the positive electrode slurry was 75wt%. The positive electrode slurry is evenly coated on one side of a positive electrode current collector aluminum foil with a thickness of 10 μm, and dried at 120°C to obtain a positive electrode sheet coated with a positive electrode material layer with a thickness of 80 μm on one side. The above steps are repeated on the other side of the positive electrode current collector aluminum foil to obtain a positive electrode sheet coated with a positive electrode material layer on both sides. After cold pressing, cutting and slitting, the positive electrode sheet is obtained.

[0091] <Preparation of negative electrode sheet>

[0092] The negative electrode active material, artificial graphite, the binder, styrene-butadiene rubber, and the binder, sodium carboxymethyl cellulose, were mixed in a mass ratio of 95:2:3. Deionized water was added and the mixture was stirred evenly in a vacuum mixer to obtain a negative electrode slurry with a solid content of 75 wt%. The negative electrode slurry was evenly coated on one side of a 5 μm thick negative electrode current collector copper foil and dried at 85°C for 4 hours to obtain a negative electrode sheet coated on one side with a 130 μm thick negative electrode material layer. The above steps were repeated on the other side of the negative electrode current collector copper foil to obtain a negative electrode sheet coated on both sides with a negative electrode material layer. The negative electrode sheet was then cold pressed, cut, and slit.

[0093] <Preparation of Separator>

[0094] A porous polypropylene film with a thickness of 12 μm (provided by Celgard Company) was used.

[0095] <Preparation of Electrolyte>

[0096] 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 in a weight ratio of 3:5:2 to obtain a base mixture. Appropriate amounts of lithium salt LiPF6, ethyl propionate, and a first additive of formula (Ia) were then added to the base mixture, and the mixture was stirred to obtain an electrolyte. The weight percentage E of the lithium salt, the weight percentage A of the ethyl propionate, and the weight percentage C of the first additive, based on the weight of the electrolyte, was 12.5%, 5%, and 1.9%, respectively.

[0097] <Preparation of lithium-ion batteries>

[0098] The positive electrode sheet, separator, and negative electrode sheet are stacked in sequence, with the separator being placed between the positive and negative electrode sheets to act as an isolate. The electrodes are then wound into an electrode assembly, which is then placed in an aluminum-plastic film, injected with electrolyte, and sealed. The assembly then undergoes processes such as standing, forming, and shaping to obtain a lithium-ion battery.

[0099] Example 1-2 to Example 1-28

[0100] The preparation parameters were adjusted as in Table 1, and the remainder was the same as in Example 1-1. When the weight percentage of the added propionate or the first additive changed, the content of the base mixture changed accordingly, while the weight ratio of EC, EMC, and DEC and the weight percentage of the lithium salt remained unchanged.

[0101] Example 2-1

[0102] Except for preparing the electrolyte according to the following method, the rest is the same as Example 1-22.

[0103] <Preparation of Electrolyte>

[0104] 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) are mixed in a weight ratio of 3:5:2 to obtain a base mixture. Then, lithium salt LiPF6, propionate, a first additive, and a second additive, lithium difluorophosphate, are added to the base mixture and stirred to obtain an electrolyte. The propionate includes ethyl propionate and propyl propionate, and the first additive includes formula (Ib2) and formula (Ic2). Based on the mass of the electrolyte, the mass percentage E of the lithium salt is 12.5%, the mass percentage of ethyl propionate is 2.5%, the mass percentage of propyl propionate is 2.5%, the mass percentage of formula (Ib2) is 0.5%, the mass percentage of formula (Ic2) is 0.7%, and the mass percentage D of the second additive is 2.3%.

[0105] Example 2-2 to Example 2-5

[0106] The preparation parameters were the same as in Example 2-1, except that they were adjusted according to Table 2. When the weight percentage of the second additive was changed, the content of the base mixture changed accordingly, while the weight ratio of EC, EMC, and DEC and the weight percentage of the lithium salt remained unchanged.

[0107] Example 3-1 to Example 3-3

[0108] The preparation parameters were adjusted according to Table 3, and the mass percentage of the added compound containing the element M was adjusted in the "Preparation of the Positive Electrode Sheet" to achieve the mass percentage of Y, B, as shown in Table 3. The contents of the base mixture were changed accordingly when the mass percentage of the added propionate ester was changed, while the weight ratio of EC, EMC, and DEC and the mass percentage of the lithium salt remained unchanged.

[0109] Example 3-4 to Example 3-5

[0110] The preparation parameters were adjusted according to Table 3, and the mass percentage of the compound containing the element M was adjusted in the "Preparation of the Positive Electrode Sheet" to achieve the mass percentage of Y, B, as shown in Table 3. The contents of the base mixture were changed accordingly when the mass percentage of the added propionate ester was changed, while the weight ratio of EC, EMC, and DEC and the mass percentage of the lithium salt remained unchanged.

[0111] Example 3-6 to Example 3-12

[0112] Except for adjusting the relevant preparation parameters according to Table 3 and adjusting the mass percentage of the added compound containing the M element in <Preparation of the Positive Electrode> so that the mass percentage of the M element is as shown in Table 3, the rest is the same as Example 2-2.

[0113] Comparative Example 1

[0114] Except for preparing the electrolyte according to the following method, the rest is the same as Example 1-1.

[0115] <Preparation of Electrolyte>

[0116] 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 in a weight ratio of 3:5:2 to obtain a base mixture. LiPF6, a lithium salt, was then added to the base mixture and stirred to obtain an electrolyte. The weight percentage (E) of the lithium salt, based on the weight of the electrolyte, was 12.5%.

[0117] Comparative Example 2

[0118] Except for preparing the electrolyte according to the following method, the rest is the same as Example 1-1.

[0119] <Preparation of Electrolyte>

[0120] 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 in a weight ratio of 3:5:2 to obtain a base mixture. Lithium salt LiPF6 and ethyl propionate were then added to the base mixture and stirred to obtain an electrolyte. The weight percentage E of the lithium salt was 12.5%, and the weight percentage A of the ethyl propionate was 5%, based on the mass of the electrolyte.

[0121] Comparative Example 3

[0122] Except for preparing the electrolyte according to the following method, the rest is the same as Example 1-1.

[0123] <Preparation of Electrolyte>

[0124] 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 in a weight ratio of 3:5:2 to obtain a base mixture. A lithium salt, LiPF6, and a first additive of formula (Ia) were then added to the base mixture, and the mixture was stirred to obtain an electrolyte. The weight percentage E of the lithium salt, based on the weight of the electrolyte, was 12.5%, and the weight percentage C of the first additive was 2%.

[0125] The preparation parameters and electrical performance parameters of each embodiment and comparative example are shown in Tables 1 to 3.

[0126] Table 1 Note: (1) In Table 1, “ / ” indicates no relevant preparation parameters; (2) In Table 1, taking Example 1-5 as an example, the propionate ester is “ethyl propionate + propyl propionate”, and A (%) is “2.5% + 2.5%”, which means that 2.5% by weight of ethyl propionate and 2.5% by weight of propyl propionate are added to the electrolyte, and the same applies to other examples; (3) In Table 1, taking Example 1-17 as an example, the first additive is “Formula (Ia) + Formula (Ib1)”, and C (%) is “1.9% + 0.5%”, which means that 1.9% by weight of Formula (Ia) and 0.5% by weight of Formula (Ib1) are added to the electrolyte, and the same applies to other examples.

[0127] Referring to Table 1, it can be seen from Examples 1-1 to 1-28 and Comparative Examples 1 to 3 that by regulating the electrolyte to include propionate and the first additive, and the type of the first additive within the scope of this application, the lithium-ion battery has a higher discharge capacity retention rate at -10°C, a higher discharge capacity retention rate at a high rate (1C), a lower DCR change rate at 20% SOC after 1000 cycles at 25°C, and a lower DCR change rate at 20% SOC after 700 cycles at 45°C, indicating that the lithium-ion battery has better low-temperature performance and lower impedance. In Comparative Examples 1 to 3, the lithium-ion battery has a lower discharge capacity retention rate at -10°C, a lower discharge capacity retention rate at a high rate (1C), a higher DCR change rate at 20% SOC after 1000 cycles at 25°C, and a higher DCR change rate at 20% SOC after 700 cycles at 45°C, indicating that the lithium-ion battery has poor low-temperature performance and higher impedance.

[0128] The type of propionate ester typically affects the low-temperature performance and impedance of lithium-ion batteries. As shown in Examples 1-1 to 1-5, and 1-20 to 1-28, by adjusting the type of propionate ester within the scope of this application, the lithium-ion battery has a higher discharge capacity retention rate at -10°C, a higher high-rate (1C) discharge capacity retention rate, a lower DCR change rate at 20% SOC after 1000 cycles at 25°C, and a lower DCR change rate at 20% SOC after 700 cycles at 45°C. This indicates that the lithium-ion battery has good low-temperature performance and low impedance.

[0129] The type of the first additive typically affects the low-temperature performance and impedance of the lithium-ion battery. As shown in Examples 1-1, 1-8, and 1-22, by adjusting the type of the first additive within the scope of this application, the lithium-ion battery has a higher discharge capacity retention rate at -10°C, a higher high-rate (1C) discharge capacity retention rate, a lower DCR change rate at 20% SOC after 1000 cycles at 25°C, and a lower DCR change rate at 20% SOC after 700 cycles at 45°C. This indicates that the lithium-ion battery has better low-temperature performance and lower impedance.

[0130] The type of compound of formula (Ib) generally affects the low-temperature performance and impedance of lithium-ion batteries. As shown in Examples 1-8 to 1-10, by regulating the type of compound of formula (Ib) within the scope of this application, the lithium-ion battery has a high discharge capacity retention rate at -10°C, a high high-rate (1C) discharge capacity retention rate, a low DCR change rate at 20% SOC after 1000 cycles at 25°C, and a low DCR change rate at 20% SOC after 700 cycles at 45°C, indicating that the lithium-ion battery has good low-temperature performance and low impedance.

[0131] The type of compound of formula (Ic) generally affects the low-temperature performance and impedance of lithium-ion batteries. As shown in Examples 1-11 to 1-16, by regulating the type of compound of formula (Ic) within the scope of this application, the lithium-ion battery has a high discharge capacity retention rate at -10°C, a high high-rate (1C) discharge capacity retention rate, a low DCR change rate at 20% SOC after 1000 cycles at 25°C, and a low DCR change rate at 20% SOC after 700 cycles at 45°C, indicating that the lithium-ion battery has good low-temperature performance and low impedance.

[0132] The mass percentage A of propionate usually affects the low temperature performance and impedance of lithium ion batteries.

[0133] It can be seen from Examples 1-3 and 1-23 to 1-28 that by regulating the mass percentage A of propionate within the scope of this application, the discharge capacity retention rate of the lithium-ion battery at -10°C is higher, the discharge capacity retention rate at a high rate (1C) is higher, the DCR change rate of 20% SOC after 1000 cycles at 25°C is lower, and the DCR change rate of 20% SOC after 700 cycles at 45°C is lower, indicating that the low-temperature performance of the lithium-ion battery is better and the impedance of the lithium-ion battery is lower.

[0134] The mass percentage C of the first additive typically affects the low-temperature performance and impedance of the lithium-ion battery. As shown in Examples 1-1, 1-6, and 1-7, by regulating the mass percentage C of the first additive within the scope of this application, the lithium-ion battery has a high discharge capacity retention rate at -10°C, a high high-rate (1C) discharge capacity retention rate, a low DCR change rate at 20% SOC after 1000 cycles at 25°C, and a low DCR change rate at 20% SOC after 700 cycles at 45°C. This indicates that the lithium-ion battery has good low-temperature performance and low impedance.

[0135] Table 2 Note: In Table 2, “ / ” indicates no relevant preparation parameters.

[0136] The electrolyte also includes a second additive and the type of the second additive usually affects the low-temperature performance and impedance of the lithium-ion battery. From Example 2-1 to Example 2-3, it can be seen that by regulating the electrolyte to include a second additive and the type of the second additive within the scope of this application, the lithium-ion battery has a high discharge capacity retention rate at -10°C, a high discharge capacity retention rate at a high rate (1C), a low DCR change rate at 20% SOC after 1000 cycles at 25°C, and a low DCR change rate at 20% SOC after 700 cycles at 45°C, indicating that the lithium-ion battery has good low-temperature performance and low impedance.

[0137] The mass percentage D of the second additive typically affects the low-temperature performance and impedance of the lithium-ion battery. As shown in Examples 2-1, 2-4, and 2-5, by regulating the mass percentage D of the second additive within the scope of this application, the lithium-ion battery has a high discharge capacity retention rate at -10°C, a high high-rate (1C) discharge capacity retention rate, a low DCR change rate at 20% SOC after 1000 cycles at 25°C, and a low DCR change rate at 20% SOC after 700 cycles at 45°C, indicating that the lithium-ion battery has good low-temperature performance and low impedance.

[0138] Table 3 Note: In Table 3, “ / ” indicates no relevant preparation parameters.

[0139] The type of positive electrode active material, M including Y, and the mass percentage B of Y generally affect the low-temperature performance and impedance of the lithium-ion battery. As shown in Examples 2-2, 3-1, and 3-3, by regulating the type of positive electrode active material, M including Y, and the mass percentage B of Y within the scope of this application, the lithium-ion battery has a high discharge capacity retention rate at -10°C, a high high-rate (1C) discharge capacity retention rate, a low DCR change rate at 20% SOC after 1000 cycles at 25°C, and a low DCR change rate at 20% SOC after 700 cycles at 45°C, indicating that the lithium-ion battery has good low-temperature performance and low impedance.

[0140] The mass percentage A of the propionate and the value of A / B generally affect the low-temperature performance and impedance of lithium-ion batteries. As shown in Examples 3-4 and 3-5, by adjusting the mass percentage A of the propionate and the value of A / B within the scope of this application, the lithium-ion battery has a high discharge capacity retention rate at -10°C, a high high-rate (1C) discharge capacity retention rate, a low DCR change rate at 20% SOC after 1000 cycles at 25°C, and a low DCR change rate at 20% SOC after 700 cycles at 45°C. This indicates that the lithium-ion battery has good low-temperature performance and low impedance.

[0141] M includes at least one of La, Mg, or W, and the mass percentage of each of La, Mg, or W generally affects the structural stability and cycle performance of the lithium-ion battery. From Examples 3-6 to 3-8, and 3-10, it can be seen that by regulating M to include at least one of La, Mg, or W, and the mass percentage of each of La, Mg, or W within the scope of this application, the lithium-ion battery has a high discharge capacity retention rate at -10°C, a high rate (1C) discharge capacity retention rate, a low DCR change rate at 20% SOC after 1000 cycles at 25°C, and a low DCR change rate at 20% SOC after 700 cycles at 45°C, indicating that the cycle impedance of the lithium-ion battery is low and the lithium-ion battery has good cycle performance.

[0142] M includes at least one of Ba or Ca, and the mass percentage of Ba or Ca generally affects the low-temperature performance, impedance, and high-temperature performance of the lithium-ion battery. From Examples 3-9, 3-11, and 3-12, it can be seen that by regulating M to include at least one of Ba or Ca, and the mass percentage of Ba or Ca within the scope of this application, the lithium-ion battery has a high discharge capacity retention rate at -10°C, a high rate (1C) discharge capacity retention rate, a low DCR change rate at 20% SOC after 1000 cycles at 25°C, and a low DCR change rate at 20% SOC after 700 cycles at 45°C, indicating that the lithium-ion battery has good low-temperature performance, low impedance, and good high-temperature performance.

[0143] 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, wherein the electrolyte comprises a propionate and a first additive, wherein the first additive comprises at least one of a compound of formula (Ia), a compound of formula (Ib) or a compound of formula (Ic), in, R1, R2, R3, and R4 are each independently selected from a single bond, a methylene group substituted or unsubstituted by Ra, Ra in each group is each independently selected from F, Cl, Br, I, methyl, ethyl, propyl, isopropyl, butyl, tert-butyl, trifluoromethyl, and tetrafluoroethyl, and R1, R2, R3, and R4 are not single bonds at the same time; R5 is selected from a single bond, -O-, C1-C3 alkylene, C1-C3 haloalkylene, or C1-C3 oxaalkylene; R6, R7, R8, and R9 are each independently selected from C1-C5 alkylene substituted or unsubstituted by Rb, and O, and Rb in each group is each independently selected from F, Cl, Br, I, methyl, ethyl, propyl, isopropyl, butyl, tert-butyl, trifluoromethyl, and tetrafluoroethyl.

2. The secondary battery according to claim 1, wherein The electrolyte satisfies at least one of the following conditions: (1) The propionate ester includes at least one of ethyl propionate or propyl propionate; (2) The compound of formula (Ib) comprises at least one of the following compounds: (3) The compound of formula (Ic) comprises at least one of the following compounds: (4) Based on the mass of the electrolyte, the mass percentage of the propionate is A, 0.01%≤A≤70%; (5) Based on the mass of the electrolyte, the mass percentage of the first additive is C, 0.01%≤C≤4%.

3. The secondary battery according to claim 1, wherein The electrolyte further includes a second additive, wherein the second additive includes at least one of lithium difluorophosphate, lithium fluorosulfonate, or bis(fluorosulfonyl)imide.

4. The secondary battery according to claim 3, wherein Based on the mass of the electrolyte, the mass percentage of the second additive is D, and 0.01%≤D≤6%.

5. The secondary battery according to claim 1, wherein The positive electrode sheet includes a positive electrode current collector and a positive electrode material layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode material layer includes a positive electrode active material, and the chemical formula of the positive electrode active material is LiCo 1-a M a O2, M includes at least one of Mg, Al, Ti, Zr, Ce, La, Y, W, Ba or Ca, 0≤a≤0.

2.

6. The secondary battery according to claim 5, wherein M includes Y. Based on the mass of the positive electrode active material, the mass percentage of Y is B, and 400ppm≤B≤5000ppm.

7. The secondary battery according to claim 5, wherein M includes Y, based on the mass of the positive electrode active material, the mass percentage of Y is B, based on the mass of the electrolyte, the mass percentage of the propionate is A, 0.1%≤A≤70%, 0.2≤A / B≤800.

8. The secondary battery according to claim 5, wherein M includes at least one of La, Mg or W, and the mass percentage of La, Mg or W is independently 200 ppm to 10000 ppm based on the mass of the positive electrode active material.

9. The secondary battery according to claim 5, wherein M includes at least one of Ba and Ca, and the mass percentage of Ba and Ca is independently 100 ppm to 22000 ppm based on the mass of the positive electrode active material. 10 . An electronic device comprising the secondary battery according to claim 1 .

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