Secondary battery and electronic device comprising same

Abstract

The invention provides a secondary battery and an electronic device comprising the same, the secondary battery comprises a positive pole piece, a negative pole piece, an isolating membrane and an electrolyte, and the electrolyte comprises a compound as shown in a formula I; based on the total mass of the electrolyte, the mass percentage content of the compound shown in the formula I is A%, and A is larger than or equal to 0.01 and smaller than or equal to 50; the positive pole piece comprises a positive active material, the positive active material comprises lithium cobalt oxide, the lithium cobalt oxide comprises an element M, and the element M comprises at least one of Al, Mg, Ti, Nb, Cr, Y, Sr or Zr; based on the total mass of the positive electrode active material, the mass percentage of the M element is B%, and 0.01 < = B < = 1. In the secondary battery, the electrolyte comprises the compound shown in the formula I, the positive electrode active material comprises the lithium cobalt oxide containing the M element, and the values of A and B are regulated and controlled in the range, so that the formation of a low-impedance CEI film is facilitated, and the secondary battery has good high-temperature storage stability and low-temperature discharge performance at the same time.

Description

Technical Field

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

[0002] Electrochemical devices (lithium-ion batteries) are widely used in many fields such as 3C electronic products, electric vehicles and energy storage power stations due to their high energy density, high power density, low self-discharge, no memory effect and long cycle life. As the scope of use of lithium-ion batteries continues to expand and their use scenarios become more diverse, the market has put forward higher requirements on the electrochemical performance of lithium-ion batteries. Summary of the invention

[0003] The object of the present application is to provide a secondary battery and an electronic device including the same, so as to improve the high-temperature storage stability and low-temperature discharge performance of the secondary battery.

[0004] It should be noted that in the invention content 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:

[0005] The first aspect of the present application provides a secondary battery, which includes a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the electrolyte includes a compound represented by formula I:

[0006]

[0007] Wherein, R is selected from C2 to C6 alkyl which is unsubstituted or substituted by Ra, C6 to C12 aryl which is unsubstituted or substituted by Ra, C5 to C12 nitrogen-containing heteroaryl which is unsubstituted or substituted by Ra; each of the Ra is independently selected from halogen or halogen-substituted C1 to C3 alkyl, and each of the halogen is independently selected from fluorine, chlorine or bromine;

[0008] Based on the total mass of the electrolyte, the mass percentage of the compound shown in Formula I is A%, 0.01≤A≤50, preferably 1≤A≤45; the positive electrode plate includes a positive electrode active material, the positive electrode active material includes lithium cobalt oxide, and the lithium cobalt oxide contains an M element, wherein the M element includes at least one of Al, Mg, Ti, Nb, Cr, Y, Sr or Zr; based on the total mass of the positive electrode active material, the mass percentage of the M element is B%, 0.01≤B≤1, preferably 0.05≤B≤0.8. In the secondary battery of the present application, the electrolyte includes the compound shown in Formula I, the positive electrode active material includes lithium cobalt oxide containing the M element, and the values ​​of A and B are regulated within the above range, which is conducive to the formation of a low-impedance CEI film, so that the secondary battery has good high-temperature storage stability and low-temperature discharge performance at the same time.

[0009] In one embodiment of the present application, the secondary battery satisfies at least one of the following conditions: a) 1≤A≤45; b) 0.05≤B≤0.8. Satisfying at least one of the above conditions can further improve the high temperature storage stability and low temperature discharge performance of the secondary battery.

[0010] In one embodiment of the present application, the compound represented by formula I includes at least one of the following compounds:

[0011]

[0012] The electrolyte includes the compound represented by formula I within the above range, which can better exert the synergistic effect with lithium cobalt oxide containing M element to generate a CEI film with lower impedance, thereby further improving the high temperature storage stability and low temperature discharge performance of the secondary battery.

[0013] In one embodiment of the present application, the electrolyte includes a cyclic carbonate, and the cyclic carbonate includes at least one of ethylene carbonate, propylene carbonate, or fluoroethylene carbonate; based on the total mass of the electrolyte, the mass percentage of the cyclic carbonate is C%, 3≤C≤40. The electrolyte includes a cyclic carbonate and regulates the value of C within the above range, which is conducive to improving the low-temperature discharge performance of the secondary battery and improving the high-temperature storage stability of the secondary battery.

[0014] In one embodiment of the present application, the cyclic carbonate includes fluoroethylene carbonate and at least one of ethylene carbonate or propylene carbonate. The electrolyte includes the above-mentioned cyclic carbonate, which can further improve the conductivity of the electrolyte, thereby further improving the low-temperature discharge performance of the secondary battery and taking into account the high-temperature storage stability of the secondary battery.

[0015] In one embodiment of the present application, the electrolyte includes a linear carbonate, and the linear carbonate includes at least one of ethyl methyl carbonate, diethyl carbonate, methyl difluoroethyl carbonate, ethyl difluoroethyl carbonate, methyl trifluoroethyl carbonate, ethyl trifluoroethyl carbonate, methyl hexafluoroisopropyl carbonate or di(2,2,2-trifluoroethyl) carbonate; based on the total mass of the electrolyte, the mass percentage of the linear carbonate is D%, 3≤D≤30. The electrolyte includes a linear carbonate and regulates the value of D within the above range, which is conducive to reducing the overall viscosity of the electrolyte, improving the conductivity of the electrolyte, thereby increasing the kinetic performance of the secondary battery, and then improving the low-temperature discharge performance of the secondary battery, while taking into account the high-temperature storage stability of the secondary battery.

[0016] In one embodiment of the present application, the linear carbonate comprises at least one of diethyl carbonate or ethyl difluoroethyl carbonate. The electrolyte comprises the above-mentioned linear carbonate, which can further reduce the viscosity of the electrolyte and improve the conductivity of the electrolyte, thereby further improving the low-temperature discharge performance of the secondary battery and taking into account the high-temperature storage stability of the secondary battery.

[0017] In one embodiment of the present application, the electrolyte includes a linear carboxylate, and the linear carboxylate includes at least one of ethyl acetate, n-propyl acetate, methyl propionate, ethyl propionate, propyl propionate, 2,2-difluoroethyl acetate, 2,2,2-trifluoroethyl acetate, hexafluoroisopropyl acetate, 2,2-difluoroethyl propionate, 2,2,2-trifluoroethyl propionate, or hexafluoroisopropyl propionate; based on the total mass of the electrolyte, the mass percentage of the linear carboxylate is E%, 10≤E≤55. The electrolyte includes a linear carboxylate and regulates the value of E within the above range, which is conducive to reducing the overall viscosity of the electrolyte, improving the conductivity of the electrolyte, thereby increasing the kinetic performance of the secondary battery, and then improving the low-temperature discharge performance of the secondary battery, while taking into account the high-temperature storage stability of the secondary battery.

[0018] In one embodiment of the present application, the linear carboxylic acid ester includes at least one of ethyl propionate, propyl propionate, 2,2-difluoroethyl acetate or 2,2,2-trifluoroethyl acetate. The electrolyte includes the above-mentioned linear carboxylic acid esters, which can further reduce the viscosity of the electrolyte and improve the conductivity of the electrolyte, thereby further improving the low-temperature discharge performance of the secondary battery and taking into account the high-temperature storage stability of the secondary battery.

[0019] In one embodiment of the present application, 0.02≤A / (A+E)≤0.8. In the present application, regulating the value of A / (A+E) within the above range is conducive to further improving the high temperature storage stability and low temperature discharge performance of the secondary battery.

[0020] In one embodiment of the present application, the electrolyte includes a nitrile compound, and the nitrile compound includes at least one of succinonitrile, glutaronitrile, methylglutaronitrile, adiponitrile, pimelonitrile, suberonitrile, azelaic acid dinitrile, sebacate, 1,3,5-pentanetrinitrile or 1,3,6-hexanetrinitrile; based on the total mass of the electrolyte, the mass percentage of the nitrile compound is F%, 1≤F≤8. The electrolyte includes the above-mentioned types of nitrile compounds and regulates the value of F within the above range, which is conducive to better synergistic effect with the compound shown in formula I and lithium cobalt oxide containing the M element, and further improves the high temperature storage stability and low temperature discharge performance of the secondary battery.

[0021] In one embodiment of the present application, the electrolyte includes a compound containing a sulfur-oxygen double bond, and the compound containing a sulfur-oxygen double bond includes at least one of 1,3-propane sultone, 1,4-butane sultone, vinyl sulfate, or 1,3-propylene glycol sulfate; based on the total mass of the electrolyte, the mass percentage of the compound containing a sulfur-oxygen double bond is G%, and 0.01≤G≤3. The electrolyte includes the above-mentioned compound containing a sulfur-oxygen double bond and regulates the value of G within the above range, which is conducive to better synergistic effect with the compound shown in Formula I and lithium cobalt oxide containing the M element, and further improves the high temperature storage stability and low temperature discharge performance of the secondary battery.

[0022] The second aspect of the present application provides an electronic device, which comprises the secondary battery in any of the above embodiments. Therefore, the electronic device provided by the present application has good performance.

[0023] The present application provides a secondary battery and an electronic device containing the same, wherein the secondary battery comprises a positive electrode plate, a negative electrode plate, a separator and an electrolyte, wherein the electrolyte comprises a compound shown in Formula I; based on the total mass of the electrolyte, the mass percentage of the compound shown in Formula I is A%, 0.01≤A≤50; the positive electrode plate comprises a positive electrode active material, the positive electrode active material comprises lithium cobalt oxide, the lithium cobalt oxide comprises an M element, wherein the M element comprises at least one of Al, Mg, Ti, Nb, Cr, Y, Sr or Zr; based on the total mass of the positive electrode active material, the mass percentage of the M element is B%, 0.01≤B≤1. In the secondary battery of the present application, the electrolyte comprises a compound shown in Formula I, the positive electrode active material comprises lithium cobalt oxide containing the M element, and the values ​​of A and B are regulated within the above range, which is conducive to the formation of a low-impedance CEI film, so that the secondary battery has both good high-temperature storage stability and low-temperature discharge performance.

[0024] Of course, implementing any product or method of the present application does not necessarily require achieving all of the advantages described above at the same time. DETAILED DESCRIPTION

[0025] The technical solutions in the embodiments of the present application are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those skilled in the art based on the present application belong to the scope of protection of the present application.

[0026] It should be noted that in the specific implementation of the present application, lithium-ion batteries are used as an example of secondary batteries to explain the present application, but the secondary batteries of the present application are not limited to lithium-ion batteries. The specific technical solutions are as follows:

[0027] The first aspect of the present application provides a secondary battery, which includes a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the electrolyte includes a compound shown in Formula I:

[0028]

[0029] wherein R is selected from C2 to C6 alkyl which is unsubstituted or substituted by Ra, C6 to C12 aryl which is unsubstituted or substituted by Ra, C5 to C12 nitrogen-containing heteroaryl which is unsubstituted or substituted by Ra; Ra are each independently selected from halogen or halogen-substituted C1 to C3 alkyl, and halogen is each independently selected from fluorine, chlorine or bromine;

[0030] Based on the total mass of the electrolyte, the mass percentage content of the compound represented by Formula I is A%, 0.01≤A≤50, preferably 1≤A≤45, for example, the value of A can be 0.01, 0.02, 0.05, 0.1, 0.2, 0.5, 1, 2, 5, 10, 12, 14, 15, 16, 18, 20, 22, 25, 28, 30, 33, 35, 38, 40, 42, 45, 48, 50 or a range consisting of any two values ​​thereof; the positive electrode sheet includes a positive electrode active material, and the positive electrode active material includes cobalt oxide Lithium, lithium cobalt oxide contains M element, wherein M element includes at least one of Al, Mg, Ti, Nb, Cr, Y, Sr or Zr; based on the total mass of the positive electrode active material, the mass percentage of M element is B%, 0.01≤B≤1, preferably 0.05≤B≤0.8, for example, the value of B can be 0.01, 0.02, 0.03, 0.05, 0.07, 0.08, 0.1, 0.2, 0.3, 0.5, 0.6, 0.7, 0.8, 0.9, 1 or a range consisting of any two of the values.

[0031] The inventors found that under high temperature conditions, lithium cobalt oxide materials are prone to metal ion dissolution, which destroys the structure of lithium cobalt oxide materials and reduces the stability of lithium cobalt oxide materials. Doping with M elements can effectively improve the stability of lithium cobalt oxide materials and inhibit the structural destruction of lithium cobalt oxide materials under high temperature and high SOC, but at the same time it will lead to an increase in the interface impedance of the positive electrode plate, difficulty in delithiation, and limited low-temperature discharge performance. The compound shown in Formula I in the electrolyte of the present application can play a synergistic role with lithium cobalt oxide doped with M elements in the positive electrode active material, which is conducive to the formation of a low-impedance positive electrode electrolyte interface (CEI) film, thereby improving the high-temperature storage stability and low-temperature discharge performance of the secondary battery. When the value of A is too small, for example, less than 0.01, it is difficult to play a synergistic role with the positive electrode active material, and the interface impedance of the positive electrode plate is large; when the value of A is too large, for example, greater than 50, the thickness of the formed CEI film increases greatly, which is not conducive to ion conduction. When the value of B is too small, for example, less than 0.01, it is not enough to improve the stability of the positive electrode active material lithium cobalt oxide; when the value of B is too large, for example, greater than 1, the interface impedance of the positive electrode plate is too large and the dissolution of metal ions cannot be fully controlled. In the secondary battery of the present application, the electrolyte includes the compound shown in Formula I, the positive electrode active material includes lithium cobalt oxide containing the element M, and the values ​​of A and B are regulated within the above range, which is conducive to forming a low-impedance CEI film, so that the secondary battery has good high-temperature storage stability and low-temperature discharge performance. In the present application, "high temperature" refers to a temperature greater than or equal to 45°C, and low temperature refers to a temperature less than or equal to -10°C.

[0032] In one embodiment of the present application, the compound represented by formula I includes at least one of the following compounds:

[0033]

[0034] The electrolyte includes the compound represented by formula I within the above range, which can better exert the synergistic effect with lithium cobalt oxide containing M element to generate a CEI film with lower impedance, thereby further improving the high temperature storage stability and low temperature discharge performance of the secondary battery.

[0035] In one embodiment of the present application, the electrolyte includes a cyclic carbonate, and the cyclic carbonate includes at least one of ethylene carbonate (EC), propylene carbonate or fluoroethylene carbonate (FEC); based on the total mass of the electrolyte, the mass percentage of the cyclic carbonate is C%, 3≤C≤40, for example, the value of C can be 3, 5, 8, 10, 12, 14, 15, 16, 18, 20, 22, 25, 28, 30, 33, 35, 38, 40 or a range consisting of any two of the values. The electrolyte includes a cyclic carbonate and regulates the value of C within the above range, which is conducive to promoting the dissociation of lithium salts, improving the conductivity of the electrolyte, and thus improving the low-temperature discharge performance of the secondary battery. At the same time, it can assist in forming a more stable SEI film, reduce the influence of transition metal ions on the negative electrode, and thus improve the high-temperature storage stability of the secondary battery.

[0036] In one embodiment of the present application, the cyclic carbonate includes fluoroethylene carbonate, and at least one of ethylene carbonate or propylene carbonate. The present application has no particular restrictions on the usage ratio of fluoroethylene carbonate, and at least one of ethylene carbonate or propylene carbonate, as long as the purpose of the present application can be achieved. For example, when the cyclic carbonate includes fluoroethylene carbonate, and ethylene carbonate or propylene carbonate, the mass ratio of fluoroethylene carbonate and ethylene carbonate or propylene carbonate is 1: (0.5 to 1.5); when the cyclic carbonate includes fluoroethylene carbonate, and ethylene carbonate and propylene carbonate, the mass ratio of fluoroethylene carbonate, ethylene carbonate and propylene carbonate is 1: (0.5 to 1.5): (0.5 to 1.5). The electrolyte includes the above-mentioned types of cyclic carbonates, which can further improve the conductivity of the electrolyte, thereby further improving the low-temperature discharge performance of the secondary battery and taking into account the high-temperature storage stability of the secondary battery.

[0037] In one embodiment of the present application, the electrolyte includes a linear carbonate, and the linear carbonate includes at least one of methyl ethyl carbonate (MEC), diethyl carbonate (DEC), methyl difluoroethyl carbonate, ethyl difluoroethyl carbonate, methyl trifluoroethyl carbonate, ethyl trifluoroethyl carbonate, methyl hexafluoroisopropyl carbonate or di(2,2,2-trifluoroethyl) carbonate; based on the total mass of the electrolyte, the mass percentage of the linear carbonate is D%, 3≤D≤30, for example, the value of D can be 3, 4, 5, 6, 8, 10, 12, 14, 15, 16, 18, 20, 21, 22, 25, 26, 28, 30 or a range consisting of any two of the values. The electrolyte includes a linear carbonate and regulates the value of D within the above range, which is conducive to reducing the overall viscosity of the electrolyte, improving the conductivity of the electrolyte, thereby increasing the kinetic performance of the secondary battery, and then improving the low-temperature discharge performance of the secondary battery, while taking into account the high-temperature storage stability of the secondary battery.

[0038] In one embodiment of the present application, the linear carbonate includes at least one of diethyl carbonate or ethyl difluoroethyl carbonate. The electrolyte includes the above-mentioned linear carbonate, which can further reduce the viscosity of the electrolyte and improve the conductivity of the electrolyte, thereby further improving the low-temperature discharge performance of the secondary battery and taking into account the high-temperature storage stability of the secondary battery.

[0039] In one embodiment of the present application, the electrolyte includes linear carboxylates, and the linear carboxylates include at least one of ethyl acetate, n-propyl acetate, methyl propionate, ethyl propionate, propyl propionate, 2,2-difluoroethyl acetate, 2,2,2-trifluoroethyl acetate, hexafluoroisopropyl acetate, 2,2-difluoroethyl propionate, 2,2,2-trifluoroethyl propionate or hexafluoroisopropyl propionate; based on the total mass of the electrolyte, the mass percentage of the linear carboxylate is E%, 10≤E≤55, for example, the value of E can be 10, 12, 14, 15, 16, 18, 20, 21, 22, 25, 26, 28, 30, 32, 35, 36, 38, 40, 42, 45, 46, 48, 50, 52, 53, 55 or a range consisting of any two of the values. The electrolyte includes linear carboxylic acid esters and regulates the value of E within the above range, which is beneficial to reducing the overall viscosity of the electrolyte, improving the conductivity of the electrolyte, thereby increasing the kinetic performance of the secondary battery, and further improving the low-temperature discharge performance of the secondary battery, while taking into account the high-temperature storage stability of the secondary battery.

[0040] In one embodiment of the present application, the linear carboxylic acid ester includes at least one of ethyl propionate, propyl propionate, 2,2-difluoroethyl acetate or 2,2,2-trifluoroethyl acetate. The electrolyte includes the linear carboxylic acid esters of the above types, which can further reduce the viscosity of the electrolyte and improve the conductivity of the electrolyte, thereby further improving the low-temperature discharge performance of the secondary battery and taking into account the high-temperature storage stability of the secondary battery.

[0041] In one embodiment of the present application, 0.02≤A / (A+E)≤0.8, for example, the value of A / (A+E) can be 0.02, 0.03, 0.05, 0.06, 0.08, 0.1, 0.12, 0.15, 0.18, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8 or a range consisting of any two of the values. By regulating the value of A / (A+E) within the above range, the interface impedance of the positive electrode sheet can be further reduced, the ion transport of the interface can be promoted, and the electrolyte can have good bulk ion transport capacity, thereby further improving the high temperature storage stability and low temperature discharge performance of the secondary battery.

[0042] In one embodiment of the present application, the electrolyte includes a nitrile compound, and the nitrile compound includes at least one of succinonitrile, glutaronitrile, methylglutaronitrile, adiponitrile, pimelonitrile, suberonitrile, azelaic acid dinitrile, sebacinonitrile, 1,3,5-pentanetrinitrile or 1,3,6-hexanetrinitrile; based on the total mass of the electrolyte, the mass percentage of the nitrile compound is F%, and 1≤F≤8, for example, the value of F can be 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.6, 2.8, 3, 3.2, 3.5, 3.6, 3.8, 4, 4.2, 4.3, 4.5, 4.6, 4.8, 5, 5.2, 5.5, 5.8, 6, 6.2, 6.5, 6.8, 7, 7.2, 7.3, 7.5, 7.6, 7.8, 8 or a range consisting of any two of the values. The electrolyte includes the above-mentioned types of nitrile compounds and regulates the value of F within the above-mentioned range, which is conducive to better synergistic effect with the compound shown in formula I and lithium cobalt oxide containing the M element, and synergistically modifies the CEI film, thereby further improving the high temperature storage stability and low temperature discharge performance of the secondary battery.

[0043] In one embodiment of the present application, the electrolyte includes a compound containing a sulfur-oxygen double bond, and the compound containing a sulfur-oxygen double bond includes at least one of 1,3-propane sultone, 1,4-butane sultone, vinyl sulfate or 1,3-propylene glycol sulfate; based on the total mass of the electrolyte, the mass percentage of the compound containing a sulfur-oxygen double bond is G%, 0.01≤G≤3, for example, the value of G can be 0.01, 0.02, 0.03, 0.05, 0.07, 0.08, 0.1, 0.2, 0.3, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.2, 1.3, 1.5, 1.6, 1.8, 2, 2.2, 2.3, 2.5, 2.6, 2.8, 3 or a range consisting of any two of the values. The electrolyte includes the above-mentioned compound containing sulfur-oxygen double bonds and regulates the value of G within the above-mentioned range, which is conducive to better synergistic effect with the compound shown in formula I and lithium cobalt oxide containing the M element, and synergistically modifies the CEI film, thereby further improving the high temperature storage stability and low temperature discharge performance of the secondary battery.

[0044] In the present application, cyclic carbonates, linear carbonates, linear carboxylates, nitrile compounds, compounds containing sulfur-oxygen double bonds, etc. within the above range can be used in any combination as long as the purpose of the present application can be achieved.

[0045] In the present application, the electrolyte also includes a lithium salt and a non-aqueous solvent. The present application has no particular restrictions on the lithium salt, as long as the purpose of the present application can be achieved. For example, the lithium salt may include but is not limited to at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, Li2SiF6, lithium bis(oxalate borate) (LiBOB) or lithium difluoroborate. The present application has no particular restrictions on the content of the lithium salt in the electrolyte, as long as the purpose of the present application can be achieved. For example, based on the total mass of the electrolyte, the mass percentage of the lithium salt is 8% to 15%.

[0046] The present application has no particular restrictions on non-aqueous solvents, as long as the purpose of the present application can be achieved. For example, non-aqueous solvents may include but are not limited to at least one of ether compounds or other organic solvents. The above-mentioned ether compounds may include but are not limited to at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran or tetrahydrofuran. The above-mentioned other organic solvents may include but are not limited to at least one of dipropyl carbonate, dimethyl sulfoxide, 1,2-dioxolane, cyclopentane, methylcyclopentane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate or trioctyl phosphate. The present application has no particular restrictions on the content of non-aqueous solvent in the electrolyte, as long as the purpose of the present application can be achieved. For example, based on the total mass of the electrolyte, the mass percentage of the non-aqueous solvent is 0% to 91%.

[0047] In one embodiment of the present application, the electrolyte includes a compound shown in Formula I, a lithium salt, and a non-aqueous solvent. Wherein, based on the total mass of the electrolyte, the mass percentage of the compound shown in Formula I and the lithium salt is as described above, and the mass percentage of the non-aqueous solvent is 35% to 91%. The electrolyte includes the compound shown in Formula I, and the secondary battery using the electrolyte of the present application has improved high temperature storage stability and low temperature discharge performance.

[0048] In one embodiment of the present application, the electrolyte includes a compound shown in Formula I, a cyclic carbonate, a lithium salt, and a non-aqueous solvent. Wherein, based on the total mass of the electrolyte, the mass percentage of the compound shown in Formula I, the cyclic carbonate, and the lithium salt is as described above, and the mass percentage of the non-aqueous solvent is 0% to 88%. The electrolyte includes the compound shown in Formula I and the cyclic carbonate, and the secondary battery using the electrolyte of the present application has further improved high temperature storage stability and low temperature discharge performance.

[0049] In one embodiment of the present application, the electrolyte includes a compound shown in Formula I, a linear carbonate, a lithium salt, and a non-aqueous solvent. Wherein, based on the total mass of the electrolyte, the mass percentage of the compound shown in Formula I, the linear carbonate, and the lithium salt is as described above, and the mass percentage of the non-aqueous solvent is 5% to 88%. The electrolyte includes a compound shown in Formula I and a linear carbonate, and the secondary battery using the electrolyte of the present application has further improved high temperature storage stability and low temperature discharge performance.

[0050] In one embodiment of the present application, the electrolyte includes a compound shown in Formula I, a linear carboxylate, a lithium salt, and a non-aqueous solvent. Wherein, based on the total mass of the electrolyte, the mass percentage of the compound shown in Formula I, the linear carboxylate, and the lithium salt is as described above, and the mass percentage of the non-aqueous solvent is 0% to 81%. The electrolyte includes a compound shown in Formula I and a linear carboxylate, and the secondary battery using the electrolyte of the present application has further improved high temperature storage stability and low temperature discharge performance.

[0051] In one embodiment of the present application, the electrolyte includes a compound shown in Formula I, a cyclic carbonate, a linear carbonate, a lithium salt, and a non-aqueous solvent. Wherein, based on the total mass of the electrolyte, the mass percentage of the compound shown in Formula I, the cyclic carbonate, the linear carbonate, and the lithium salt is as described above, and the mass percentage of the non-aqueous solvent is 0% to 85%. The electrolyte includes a compound shown in Formula I, a cyclic carbonate, and a linear carbonate. The secondary battery using the electrolyte of the present application has further improved high temperature storage stability and low temperature discharge performance.

[0052] In one embodiment of the present application, the electrolyte includes a compound shown in Formula I, a cyclic carbonate, a linear carboxylate, a lithium salt, and a non-aqueous solvent. Wherein, based on the total mass of the electrolyte, the mass percentage of the compound shown in Formula I, the cyclic carbonate, the linear carboxylate, and the lithium salt is as described above, and the mass percentage of the non-aqueous solvent is 0% to 78%. The electrolyte includes a compound shown in Formula I, a cyclic carbonate, and a linear carboxylate. The secondary battery using the electrolyte of the present application has further improved high temperature storage stability and low temperature discharge performance.

[0053] In one embodiment of the present application, the electrolyte includes a compound shown in Formula I, a linear carbonate, a linear carboxylate, a lithium salt, and a non-aqueous solvent. Wherein, based on the total mass of the electrolyte, the mass percentage of the compound shown in Formula I, the linear carbonate, the linear carboxylate, and the lithium salt is as described above, and the mass percentage of the non-aqueous solvent is 0% to 78%. The electrolyte includes a compound shown in Formula I, a linear carbonate, and a linear carboxylate. The secondary battery using the electrolyte of the present application has further improved high temperature storage stability and low temperature discharge performance.

[0054] In one embodiment of the present application, the electrolyte includes a compound shown in Formula I, a cyclic carbonate, a linear carbonate, a linear carboxylate, a lithium salt, and a non-aqueous solvent. Wherein, based on the total mass of the electrolyte, the mass percentage of the compound shown in Formula I, the cyclic carbonate, the linear carbonate, the linear carboxylate, and the lithium salt is as described above, and the mass percentage of the non-aqueous solvent is 0% to 75%. The electrolyte includes a compound shown in Formula I, a cyclic carbonate, a linear carbonate, and a linear carboxylate. The secondary battery using the electrolyte of the present application has further improved high temperature storage stability and low temperature discharge performance.

[0055] In one embodiment of the present application, the electrolyte includes a compound shown in Formula I, a nitrile compound, a lithium salt, and a non-aqueous solvent. Wherein, based on the total mass of the electrolyte, the mass percentage of the compound shown in Formula I, the nitrile compound, and the lithium salt is as described above, and the mass percentage of the non-aqueous solvent is 27% to 90%. The electrolyte includes the compound shown in Formula I and the nitrile compound, and the secondary battery using the electrolyte of the present application has further improved high temperature storage stability and low temperature discharge performance.

[0056] In one embodiment of the present application, the electrolyte includes a compound shown in Formula I, a compound containing a sulfur-oxygen double bond, a lithium salt, and a non-aqueous solvent. Wherein, based on the total mass of the electrolyte, the mass percentage of the compound shown in Formula I, the compound containing a sulfur-oxygen double bond, and the lithium salt is as described above, and the mass percentage of the non-aqueous solvent is 32% to 91%. The electrolyte includes a compound shown in Formula I and a compound containing a sulfur-oxygen double bond, and the secondary battery using the electrolyte of the present application has further improved high temperature storage stability and low temperature discharge performance.

[0057] In one embodiment of the present application, the electrolyte includes a compound shown in Formula I, a nitrile compound, a compound containing a sulfur-oxygen double bond, a lithium salt, and a non-aqueous solvent. Wherein, based on the total mass of the electrolyte, the mass percentage of the compound shown in Formula I, the nitrile compound, the compound containing a sulfur-oxygen double bond, and the lithium salt is as described above, and the mass percentage of the non-aqueous solvent is 24% to 90%. The electrolyte includes a compound shown in Formula I, a nitrile compound, and a compound containing a sulfur-oxygen double bond. The secondary battery using the electrolyte of the present application has further improved high temperature storage stability and low temperature discharge performance.

[0058] In one embodiment of the present application, the electrolyte includes a compound shown in Formula I, a cyclic carbonate, a nitrile compound, a compound containing a sulfur-oxygen double bond, a lithium salt, and a non-aqueous solvent. Wherein, based on the total mass of the electrolyte, the mass percentage of the compound shown in Formula I, the cyclic carbonate, the nitrile compound, the compound containing a sulfur-oxygen double bond, and the lithium salt is as described above, and the mass percentage of the non-aqueous solvent is 0% to 87%. The electrolyte includes a compound shown in Formula I, a cyclic carbonate, a nitrile compound, and a compound containing a sulfur-oxygen double bond. The secondary battery using the electrolyte of the present application has further improved high temperature storage stability and low temperature discharge performance.

[0059] In one embodiment of the present application, the electrolyte includes a compound shown in Formula I, a cyclic carbonate, a linear carbonate, a linear carboxylate, a nitrile compound, a compound containing a sulfur-oxygen double bond, a lithium salt, and a non-aqueous solvent. Wherein, based on the total mass of the electrolyte, the mass percentage of the compound shown in Formula I, the cyclic carbonate, the linear carbonate, the linear carboxylate, the nitrile compound, the compound containing a sulfur-oxygen double bond, and the lithium salt is as described above, and the mass percentage of the non-aqueous solvent is 0% to 74%. The electrolyte includes a compound shown in Formula I, a cyclic carbonate, a linear carbonate, a linear carboxylate, a nitrile compound, and a compound containing a sulfur-oxygen double bond. The secondary battery using the electrolyte of the present application has further improved high temperature storage stability and low temperature discharge performance.

[0060] In the present application, the positive electrode plate includes a positive electrode current collector and a positive electrode material layer disposed on at least one surface of the positive electrode current collector. The above-mentioned "positive electrode material layer disposed on at least one surface of the positive electrode current collector" means that the positive electrode material layer can be disposed on one surface of the positive electrode current collector along its own thickness direction, or it can be disposed 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 surface of the positive electrode current collector, or it can be a partial area of ​​the surface 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).

[0061] The positive electrode material layer includes the positive electrode active material of the present application. The present application has no particular limitation on the preparation method of lithium cobalt oxide, as long as the purpose of the present application can be achieved. Exemplarily, the preparation method of lithium cobalt oxide includes:

[0062] The lithium source material and the transition metal source material are used as raw materials, and their mass ratio is controlled. The raw materials are dispersed in anhydrous ethanol, and the solid content in the dispersion is adjusted to 30wt% to 45wt%, and ground evenly. The ground solution is dried at 60°C to 80°C to obtain a uniform powder, and the powder is subjected to a first heat treatment in the range of 500°C to 850°C. The first heat treatment is carried out in an air atmosphere for 3h to 5h, and a transition metal oxide is obtained after the first heat treatment; the transition metal oxide and the doped M element source material are mixed evenly, and a second heat treatment is carried out at a temperature of 880°C to 1100°C in a nitrogen atmosphere to obtain a positive active material lithium cobalt oxide including doped M element. The present application has no particular restrictions on the source material doped with the M element, as long as the purpose of the present application can be achieved. For example, the doped M element source material may be at least one of Mg(NO3)2, Al(NO3)3, Zr(NO3)4, MgSO4, Al2(SO4)3, Ti(SO4)2, Nb(C2O4)2, Cr(C2H3O2)3, Y2(SO4)3, SrSO4, Zr(SO4)2, etc. The present application does not particularly limit the mass ratio of the lithium source material to the transition metal source material, and the mass ratio of the transition metal oxide to the doped M element source material. They can be selected according to actual needs as long as the purpose of the present application can be achieved. For example, the mass ratio of the lithium source material to the transition metal source material may be (6 to 15):26, and the mass ratio of the transition metal oxide to the doped M element source material may be (133 to 13280):10.

[0063] The positive electrode material layer may also include 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 (Super P), carbon nanotubes (CNTs), carbon fibers, flake graphite, graphene, metal materials or conductive polymers, and the 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 powders and / or metal fibers, and 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 at least one of polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyvinyl alcohol, carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, polyimide, polyamide-imide, styrene-butadiene rubber or polyvinylidene fluoride. 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 choose according to actual needs, as long as the purpose of the present application can be achieved.

[0064] The present application has no particular restrictions on the thickness of the positive electrode current collector and the positive electrode material layer, as long as the purpose of the present application can be achieved. For example, the thickness of the positive electrode current collector is 5 μm to 20 μm, and the thickness of the single-sided positive electrode material layer is 30 μm to 120 μm.

[0065] 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 composition of the conductive layer is not particularly limited, 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 has no particular restrictions on the conductive agent and the binder in the conductive layer, for example, it can be at least one of the above conductive agent and the above binder.

[0066] In the present application, the negative electrode plate includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector. The above-mentioned "negative electrode material layer is disposed on at least one surface of the negative electrode current collector" means that the negative electrode material layer can be disposed on one surface of the negative electrode current collector along its own thickness direction, or it can be disposed on two surfaces of the negative electrode current collector along its own thickness direction. It should be noted that the "surface" here can be the entire area of ​​the surface of the negative electrode current collector, or it can be a partial area of ​​the surface 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. For example, the composite current collector can be a lithium-copper composite current collector, a carbon-copper composite current collector, a nickel-copper composite current collector, a titanium-copper composite current collector, etc.

[0067] The negative electrode material layer includes a negative electrode active material. The present application has no particular limitation on the negative electrode active material as long as the purpose of the present application can be achieved. For example, the negative electrode active material may include but is not limited to natural graphite, artificial graphite, mesophase microcarbon beads, hard carbon, soft carbon, silicon, silicon-carbon composite, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel structured lithiated TiO2-Li4Ti5O 12 Or at least one of Li-Al alloy.

[0068] In some embodiments of the present application, the negative electrode material layer may further include a conductive agent and a binder. The present application does not particularly limit the types of the conductive agent and the binder, as long as the purpose of the present application can be achieved. For example, it may be at least one of the above conductive agent and the above binder. The present application does not particularly limit the mass ratio of the negative electrode active material, the conductive agent, and the binder in the negative electrode material layer. Those skilled in the art may select according to actual needs, as long as the purpose of the present application can be achieved.

[0069] In some embodiments of the present application, the negative electrode material layer may also include a conductive agent, a binder and a thickener. The present application does not particularly limit the types of the conductive agent, the binder and the thickener, as long as the purpose of the present application can be achieved. For example, the conductive agent and the binder may be at least one of the above conductive agent and the above binder. The thickener may include but is not limited to at least one of sodium carboxymethyl cellulose or lithium carboxymethyl cellulose. The present application does not particularly limit the mass ratio of the negative electrode active material, the conductive agent, the binder and the thickener in the negative electrode material layer. Those skilled in the art can choose according to actual needs, as long as the purpose of the present application can be achieved.

[0070] The present application has no particular limitation on the thickness of the negative electrode material layer, as long as the purpose of the present application can be achieved, for example, the thickness of the single-sided negative electrode material layer is 30 μm to 120 μm. The present application has no particular limitation on the thickness of the negative electrode current collector, as long as the purpose of the present application can be achieved, for example, the thickness of the negative electrode current collector is 4 μm to 15 μm.

[0071] Optionally, the negative electrode plate may further include a conductive layer, and the conductive layer is located between the negative electrode current collector and the negative electrode material layer. The present application has no particular restrictions on the composition of the conductive layer, and it may be a conductive layer commonly used in the art. For example, the conductive layer includes a conductive agent and a binder. The present application has no particular restrictions on the conductive agent and the binder in the conductive layer, and it may be at least one of the above conductive agent and the above binder.

[0072] The present application has no particular restrictions on the isolation membrane, as long as the purpose of the present application can be achieved. For example, the material of the isolation membrane may include, but is not limited to, polyethylene (PE), polypropylene (PP)-based polyolefins (PO), polyesters (e.g., polyethylene terephthalate (PET) membranes), cellulose, polyimide (PI), polyamide (PA), spandex or aramid. The type of isolation membrane 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.

[0073] In some embodiments of the present application, the isolation film may include a substrate layer and a surface treatment layer. The substrate layer may be a nonwoven fabric, a film or a composite film having a porous structure, and the material of the substrate layer may include at least one of polyethylene, polypropylene, polyethylene terephthalate or polyimide. Optionally, a polypropylene porous film, a polyethylene porous film, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric or a polypropylene-polyethylene-polypropylene porous composite film may be used.

[0074] Optionally, a surface treatment layer is provided on at least one surface of the substrate layer, and the surface treatment layer can be a polymer layer or an inorganic layer, or a layer formed by a mixed polymer and an inorganic substance. In some embodiments of the present application, the inorganic layer includes inorganic particles and a binder. The present application has no particular restrictions on inorganic particles, such as inorganic particles can 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 binders, such as binders can be at least one of the above-mentioned binders. In some embodiments of the present application, the polymer layer includes a polymer, and the material of the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinyl pyrrolidone, polyvinyl ether or polyvinylidene fluoride or poly (vinylidene fluoride-hexafluoropropylene).

[0075] In the present application, there is no particular limitation on the thickness of the isolation film, as long as the purpose of the present application can be achieved. For example, the thickness of the isolation film may be 3 μm to 30 μm.

[0076] In the present application, the secondary battery also includes a shell for accommodating a positive electrode plate, a separator, a negative electrode plate and an electrolyte, as well as other components known in the field of secondary batteries, and the present application does not limit the above-mentioned other components. The present application has no special restrictions on the shell, and it can be a shell known in the art, as long as the purpose of the present application can be achieved. For example, the shell can be a hard shell or a flexible shell. The material of the hard shell can be metal, and the present application does not limit the type of metal. A metal hard shell known in the art can be used, as long as the purpose of the present application can be achieved. The flexible shell can be a metal plastic film, such as an aluminum plastic film, a steel plastic film, etc.

[0077] The preparation process of the secondary battery of the present application is well known to those skilled in the art, and there is no particular limitation in the present application. For example, the preparation process of the secondary battery 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 of a winding structure, placing the electrode assembly in a shell, injecting the electrolyte into the shell and sealing it to obtain a secondary battery. Alternatively, stacking the positive electrode sheet, the separator and the negative electrode sheet in order, and then fixing the four corners of the entire laminated structure with tape to obtain an electrode assembly of a laminated structure, placing the electrode assembly in a shell, injecting the electrolyte into the shell and sealing it to obtain a secondary battery. In addition, overcurrent protection elements, guide plates, etc. may also be placed in the shell as needed to prevent the pressure inside the secondary battery from rising and overcharging and discharging.

[0078] The present application does not particularly limit the type of secondary battery, which may include any device that generates an electrochemical reaction. For example, the secondary battery may include, but is not limited to: a lithium metal secondary battery, a lithium ion battery, a sodium ion battery, a lithium polymer secondary battery, and a lithium ion polymer secondary battery.

[0079] The second aspect of the present application provides an electronic device, which comprises the secondary battery in any of the above embodiments. The secondary battery provided in the present application has good high temperature storage stability and low temperature discharge performance, so that the electronic device of the present application has a long service life.

[0080] The present application does not particularly limit the type of electronic device, and it can be used for any electronic device known in the prior art. In some embodiments of the present application, the electronic device may include, but is not limited to, a laptop computer, a pen-input computer, a mobile computer, an electronic book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, an electric tool, a flashlight, a camera, a large household battery and a lithium-ion capacitor, etc.

[0081] Example

[0082] The following examples and comparative examples are given to more specifically describe the embodiments of the present application. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0083] Test methods and equipment:

[0084] Test of the content of M element in positive electrode active materials

[0085] The lithium-ion battery was disassembled to obtain the positive electrode sheet, and the positive electrode sheet was cleaned with dimethyl carbonate (DMC). The positive electrode material layer of the cleaned positive electrode sheet was scraped off with a scraper and dissolved with a mixed solvent. 0.4 g of the positive electrode material layer was diluted to 100 mL with a mixed solvent of 10 mL (nitric acid and hydrochloric acid were mixed in a ratio of 1:1) aqua regia and 2 mL of HF, and then the mass percentage of the M element in the solution was tested using an ICP (Inductively coupled plasma) analyzer.

[0086] High temperature storage testing of lithium-ion batteries

[0087] Take 4 batteries from each group of the lithium-ion batteries of the embodiment and the comparative example, and in a room temperature environment, first use a current of 0.5C for constant current charging, charge to 4.5V, then charge at a constant voltage until the current is equal to 0.05C, and then discharge at a current of 1C until the current is discharged to 3.0V, and record the discharge capacity, which is recorded as the capacity before storage; charge to 4.5V with a constant current of 0.5C, charge at a constant voltage until the current is equal to 0.05C, store the lithium-ion batteries in an oven at 85°C for 24 hours, and then stand in a room temperature environment until the lithium-ion batteries cool to room temperature, and discharge at a discharge current of 1C until the current is discharged to 3.0V, and record the discharge capacity, which is recorded as the capacity after storage.

[0088] 85°C high temperature storage capacity retention rate = capacity after storage / capacity before storage × 100%.

[0089] Low temperature discharge performance test of lithium-ion batteries

[0090] Place the lithium-ion battery in a high and low temperature box, adjust the temperature to 25°C, and let it stand for 30 minutes to allow the lithium-ion battery to reach a constant temperature. The lithium-ion battery that has reached a constant temperature is discharged to 3.0V at a current of 0.5C, then charged to 4.5V at a current of 0.5C, and then charged to a current of 0.05C at a constant voltage with the charging voltage. Also at a temperature of 25°C, discharge to 3.0V at a current of 0.5C, and record the discharge capacity as the initial discharge capacity. At a temperature of 25°C, charge to 4.5V at a current of 0.5C, and then charge to a current of 0.05C at a constant voltage with the charging voltage. After that, place the lithium-ion battery at a temperature of -10°C and let it stand for 30 minutes to keep the temperature of the lithium-ion battery consistent with the outside temperature. At -10°C, discharge to 3.0V at a current of 0.5C, and record the discharge capacity as the low-temperature discharge capacity.

[0091] -10°C low-temperature discharge capacity retention rate = (low-temperature discharge capacity / initial discharge capacity) x 100%.

[0092] Example 1-1

[0093] <Preparation of lithium cobalt oxide>

[0094] The lithium source material Li2CO3 and the transition metal source material Co(NO3)2 are mixed in a mass ratio of 11:26, and then dispersed in anhydrous ethanol, the solid content in the dispersion is adjusted to 35wt%, and ground evenly. The ground solution is dried at 60°C to obtain a uniform powder, and the powder is subjected to a first heat treatment at 600°C, the first heat treatment is carried out in an air atmosphere for 3h, and a transition metal oxide is obtained after the first heat treatment; the transition metal oxide and the doped M element source material Al(NO3)3 are mixed evenly in a mass ratio of 332:5, and a second heat treatment is carried out at a temperature of 1000°C in a nitrogen atmosphere to obtain lithium cobalt oxide containing the element Al, and the mass percentage content B% of the Al element is 0.2%.

[0095] <Preparation of positive electrode sheet>

[0096] The positive electrode active material prepared above, lithium cobalt oxide, conductive agent Super P, and binder polyvinylidene fluoride were mixed in a mass ratio of 97.9:0.9:1.2, and N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solid content of 75wt%, and the positive electrode slurry was obtained after vacuum stirring. The positive electrode slurry was evenly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 10μm, and dried at 120°C to obtain a positive electrode sheet coated with a positive electrode material layer on one side, and the coating weight of the positive electrode material layer was 246.8mg / 1540mm 2 Then repeat the above steps on the other surface of the aluminum foil to obtain a positive electrode sheet with a positive electrode material layer coated on both sides. After drying at 120°C, cold pressing, cutting and welding the tabs, a positive electrode sheet with a specification of 74mm×867mm is obtained for standby use. The thickness of the single-sided positive electrode material layer is 42μm.

[0097] <Preparation of negative electrode sheet>

[0098] The negative electrode active material artificial graphite, the binder styrene butadiene rubber, and the conductive agent acetylene black were mixed in a mass ratio of 97.4:1.4:1.2, and deionized water was added as a solvent to prepare a slurry with a solid content of 45wt%. The negative electrode slurry was uniformly coated on one surface of a negative electrode current collector copper foil with a thickness of 6μm, and dried at 120°C to obtain a negative electrode sheet with a single-sided coating of a negative electrode material layer. The coating weight of the negative electrode material layer was 142mg / 1540mm 2 Then repeat the above steps on the other surface of the copper foil to obtain a negative electrode sheet with a negative electrode material layer coated on both sides. After drying at 120°C, cold pressing, cutting and welding the tabs, a negative electrode sheet with a specification of 78mm×875mm is obtained for standby use. The thickness of the single-sided negative electrode material layer is 54.5μm.

[0099] <Preparation of Electrolyte>

[0100] In an environment with a water content of less than 10 ppm, dipropyl carbonate is used as a non-aqueous solvent, and then the compound of formula I-1 and lithium salt LiPF6 are added to the non-aqueous solvent and mixed evenly to obtain an electrolyte. Wherein, based on the total mass of the electrolyte, the mass percentage content A% of the compound of formula I is 5%, the mass percentage content of the lithium salt is 12.5%, and the balance is the non-aqueous solvent.

[0101] <Isolation film>

[0102] A porous polyethylene film with a thickness of 7 μm (provided by Celgard Company) was used as the separator.

[0103] <Preparation of lithium-ion batteries>

[0104] The positive electrode sheet, separator, and negative electrode sheet prepared above are stacked in order, so that the separator is placed between the positive electrode sheet and the negative electrode sheet to play an isolating role, and the electrode assembly is wound. The electrode assembly is placed in an aluminum-plastic film packaging bag, and the water is removed at 80°C, and the prepared electrolyte is injected. After vacuum packaging, standing, formation, degassing, trimming and other processes, a lithium-ion battery is obtained. Among them, the formation upper limit voltage is 4.15V, the formation temperature is 70°C, and the formation standing time is 2h.

[0105] Example 1-2 to Example 1-7

[0106] Except that the mass percentage A% of the compound represented by Formula I is adjusted according to Table 1 in <Preparation of Electrolyte>, the mass percentage A% of the non-aqueous solvent is changed accordingly, and the mass percentage of the lithium salt remains unchanged, the rest is the same as Example 1-1.

[0107] Example 1-8 to Example 1-12

[0108] Except that the mass ratio of transition metal oxide and doped M element source material Al(NO3)3 is adjusted in <Preparation of lithium cobalt oxide> so that the mass percentage B% of Al element in lithium cobalt oxide is as shown in Table 1, the rest is the same as Example 1-1.

[0109] Example 1-13 to Example 1-16

[0110] Except for adjusting the type of the compound represented by Formula I according to Table 1 in <Preparation of Electrolyte>, the rest is the same as Example 1-1.

[0111] Example 1-17 to Example 1-23

[0112] Except that the type of doped M element source material and the mass ratio of transition metal oxide to doped M element source material are adjusted in <Preparation of lithium cobalt oxide>, so that the type and mass percentage B% of M element contained in lithium cobalt oxide are as shown in Table 1, the rest is the same as Example 1-1. The doped M element source materials of Examples 1-17 to 1-23 are Mg(NO3)2, Ti(SO4)2, Nb(C2O4)2, Cr(C2H3O2)3, Y2(SO4)3, SrSO4, and Zr(NO3)4, respectively.

[0113] Example 2-1 to Example 2-24

[0114] The preparation of the electrolyte is the same as that of Example 1-1, except that cyclic carbonate, linear carbonate and linear carboxylate are added as shown in Table 2, and the mass percentage A% of the compound represented by Formula I, the type and mass percentage C% of the cyclic carbonate, the type and mass percentage D% of the linear carbonate, the type and mass percentage E% of the linear carboxylate are adjusted as shown in Table 2, the mass percentage of the non-aqueous solvent is changed accordingly, and the mass percentage of the lithium salt remains unchanged.

[0115] Example 3-1 to Example 3-12

[0116] In addition to adding cyclic carbonates, linear carbonates, linear carboxylates, nitrile compounds, and compounds containing sulfur-oxygen double bonds as shown in Table 3 in <Preparation of Electrolyte>, and adjusting the type and mass percentage of cyclic carbonates (C%), the type and mass percentage of linear carbonates (D%), the type and mass percentage of linear carboxylates (E%), the type and mass percentage of nitrile compounds (F%), the type and mass percentage of compounds containing sulfur-oxygen double bonds (G%) according to Table 3, the mass percentage of the non-aqueous solvent changes accordingly, and the mass percentage of the compound represented by Formula I and the lithium salt remains unchanged, the rest is the same as Example 1-1.

[0117] Comparative Example 1-1

[0118] The present invention is the same as Example 1-1, except that no M element doping source material is added in the preparation of lithium cobalt oxide to obtain lithium cobalt oxide without M element, and no compound represented by formula I is added in the preparation of electrolyte, the mass percentage of non-aqueous solvent is changed accordingly, and the mass percentage of lithium salt remains unchanged.

[0119] Comparative Example 1-2

[0120] Except that the compound represented by formula I is not added in <Preparation of electrolyte>, the mass percentage of non-aqueous solvent is changed accordingly, and the mass percentage of lithium salt remains unchanged, the rest is the same as Example 1-1.

[0121] Comparative Examples 1-3

[0122] Except that the mass percentage A% of compound I-1 is adjusted according to Table 1 in <Preparation of electrolyte>, the mass percentage of non-aqueous solvent is changed accordingly, and the mass percentage of lithium salt remains unchanged, the rest is the same as Example 1-1.

[0123] Comparative Examples 1-4

[0124] Except that no M element doping source material is added in <Preparation of lithium cobalt oxide> to obtain lithium cobalt oxide without M element, the rest is the same as Example 1-1.

[0125] Comparative Examples 1-5

[0126] Except that the mass ratio of transition metal oxide and doped M element source material Al(NO3)3 is adjusted in <Preparation of lithium cobalt oxide> so that the mass percentage B% of Al element in lithium cobalt oxide is as shown in Table 1, the rest is the same as Example 1-1.

[0127] Comparative Examples 1-6

[0128] Except that the type of the doped M element source material and the mass ratio of the transition metal oxide to the doped M element source material are adjusted in <Preparation of lithium cobalt oxide>, so that the type and mass percentage B% of the M element contained in the lithium cobalt oxide are as shown in Table 1, the rest is the same as Example 1-1. Among them, the doped M element source material is Mn(NO3)2.

[0129] Table 1

[0130]

[0131] Note: “ / ” in Table 1 means there is no corresponding substance or parameter.

[0132] It can be seen from Examples 1-1 to 1-23 and Comparative Examples 1-1 to 1-6 that when the positive electrode plate includes the positive electrode active material lithium cobalt oxide and the content of the M element in the lithium cobalt oxide is within the range of the present application, and the electrolyte includes the compound shown in Formula I and the value of its content A is regulated within the range of the present application, the lithium ion battery can simultaneously have a higher high temperature storage capacity retention rate and a higher low temperature discharge capacity retention rate, indicating that the lithium ion battery has both good high temperature storage stability and low temperature discharge performance.

[0133] The type of compound represented by Formula I usually affects the high temperature storage stability and low temperature discharge performance of lithium ion batteries. It can be seen from Examples 1-1, 1-13 to 1-16 that lithium ion batteries using the type of compound represented by Formula I within the scope of the present application can simultaneously have a high high temperature storage capacity retention rate and a low temperature discharge capacity retention rate, indicating that the lithium ion battery has good high temperature storage stability and low temperature discharge performance.

[0134] Table 2

[0135]

[0136] Note: “ / ” in Table 2 means there is no corresponding substance or parameter.

[0137] The type and content of cyclic carbonates, the type and content of linear carbonates, and the type and content of linear carboxylates usually affect the high temperature storage stability and low temperature discharge performance of lithium ion batteries. It can be seen from Examples 1-1, 2-1 to 2-24 that when the electrolyte includes at least one of the cyclic carbonates, linear carbonates, and linear carboxylates within the type and content range of the present application, the lithium ion battery can have a higher high temperature storage capacity retention rate and low temperature discharge capacity retention rate, indicating that the lithium ion battery has better high temperature storage stability and low temperature discharge performance.

[0138] The value of A / (A+E) usually affects the high temperature storage stability and low temperature discharge performance of lithium ion batteries. It can be seen from Examples 1-1, 2-12 to 2-20 that when the value of A / (A+E) is adjusted within the scope of this application, the lithium ion battery can simultaneously have a higher high temperature storage capacity retention rate and a higher low temperature discharge capacity retention rate, indicating that the lithium ion battery has better high temperature storage stability and low temperature discharge performance.

[0139] Table 3

[0140]

[0141] Note: “ / ” in Table 3 means there is no corresponding substance or parameter.

[0142] The type and content of nitrile compounds and the type and content of compounds containing sulfur-oxygen double bonds usually affect the high-temperature storage stability and low-temperature discharge performance of lithium-ion batteries. It can be seen from Examples 1-1 and 3-1 to 3-10 that when the electrolyte includes at least one of the nitrile compounds and compounds containing sulfur-oxygen double bonds within the type and content range of the present application, the high-temperature storage capacity retention rate and low-temperature discharge capacity retention rate of the lithium-ion battery can be further improved, indicating that the lithium-ion battery has better high-temperature storage stability and low-temperature discharge performance at the same time.

[0143] It can be seen from Example 1-1, Example 2-1 to Example 2-24, and Example 3-1 to Example 3-12 that when the electrolyte includes at least two of the cyclic carbonates, linear carbonates, linear carboxylates, nitrile compounds, and compounds containing sulfur-oxygen double bonds within the types and content ranges of the present application, the high temperature storage capacity retention rate and low temperature discharge capacity retention rate of the lithium ion battery can be further improved, indicating that the high temperature storage stability and low temperature discharge performance of the lithium ion battery are further improved.

[0144] It should be noted that, in this article, the terms "comprises", "includes" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method or article that includes a series of elements includes not only those elements, but also includes other elements that are not explicitly listed, or also includes elements that are inherent to such process, method or article.

[0145] The terms "at least one of", "at least one of", "at least one of" or other similar terms connected to elements refer to any combination of the listed elements. For example, "at least one of A or B" refers to only A, only B, A and B. For another example, "at least one of A, B, or C" refers to only A, only B, only C, only A and B, only A and C, only B and C, A, B, and C.

[0146] Each embodiment in this specification is described in a related manner, and the same or similar parts between the embodiments can be referenced to each other, and each embodiment focuses on the differences from other embodiments.

[0147] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. A secondary battery comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the electrolyte comprises a compound represented by formula I: in, R is selected from C2 to C6 alkyl which is unsubstituted or substituted by Ra, C6 to C12 aryl which is unsubstituted or substituted by Ra, C5 to C12 nitrogen-containing heteroaryl which is unsubstituted or substituted by Ra; each of the Ra is independently selected from halogen or halogen-substituted C1 to C3 alkyl, and each of the halogen is independently selected from fluorine, chlorine or bromine; Based on the total mass of the electrolyte, the mass percentage of the compound represented by formula I is A%, 0.01≤A≤50; The positive electrode plate includes a positive electrode active material, the positive electrode active material includes lithium cobalt oxide, and the lithium cobalt oxide contains an M element, wherein the M element includes at least one of Al, Mg, Ti, Nb, Cr, Y, Sr or Zr; Based on the total mass of the positive electrode active material, the mass percentage of the M element is B%, and 0.01≤B≤1.

2. The secondary battery according to claim 1, wherein The secondary battery satisfies at least one of the following conditions: a)1≤A≤45; b)0.05≤B≤0.

8.

3. The secondary battery according to claim 1, wherein The compound represented by formula I includes at least one of the following compounds:

4. The secondary battery according to any one of claims 1 to 3, wherein: The electrolyte includes a cyclic carbonate, and the cyclic carbonate includes at least one of ethylene carbonate, propylene carbonate or fluoroethylene carbonate; Based on the total mass of the electrolyte, the mass percentage of the cyclic carbonate is C%, 3≤C≤40.

5. The secondary battery according to claim 4, wherein The cyclic carbonate includes fluoroethylene carbonate, and at least one of ethylene carbonate or propylene carbonate.

6. The secondary battery according to any one of claims 1 to 3, wherein: The electrolyte includes a linear carbonate, and the linear carbonate includes at least one of ethyl methyl carbonate, diethyl carbonate, methyl difluoroethyl carbonate, ethyl difluoroethyl carbonate, methyl trifluoroethyl carbonate, ethyl trifluoroethyl carbonate, methyl hexafluoroisopropyl carbonate or di(2,2,2-trifluoroethyl) carbonate; Based on the total mass of the electrolyte, the mass percentage of the linear carbonate is D%, 3≤D≤30.

7. The secondary battery according to claim 6, wherein The linear carbonate includes at least one of diethyl carbonate or ethyl difluoroethyl carbonate.

8. The secondary battery according to any one of claims 1 to 3, wherein: The electrolyte includes a linear carboxylate, and the linear carboxylate includes at least one of ethyl acetate, n-propyl acetate, methyl propionate, ethyl propionate, propyl propionate, 2,2-difluoroethyl acetate, 2,2,2-trifluoroethyl acetate, hexafluoroisopropyl acetate, 2,2-difluoroethyl propionate, 2,2,2-trifluoroethyl propionate or hexafluoroisopropyl propionate; Based on the total mass of the electrolyte, the mass percentage of the linear carboxylic acid ester is E%, and 10≤E≤55.

9. The secondary battery according to claim 8, wherein 0.02≤A / (A+E)≤0.

8.

10. The secondary battery according to claim 8, wherein The linear carboxylic acid ester includes at least one of ethyl propionate, propyl propionate, 2,2-difluoroethyl acetate or 2,2,2-trifluoroethyl acetate.

11. The secondary battery according to any one of claims 1 to 3, wherein: The electrolyte includes a nitrile compound, and the nitrile compound includes at least one of succinonitrile, glutaronitrile, methylglutaronitrile, adiponitrile, pimelonitrile, suberonitrile, azelaic acid dinitrile, sebacononitrile, 1,3,5-pentanetrinitrile or 1,3,6-hexanetrinitrile; Based on the total mass of the electrolyte, the mass percentage of the nitrile compound is F%, 1≤F≤8.

12. The secondary battery according to any one of claims 1 to 3, wherein: The electrolyte includes a compound containing a sulfur-oxygen double bond, and the compound containing a sulfur-oxygen double bond includes at least one of 1,3-propane sultone, 1,4-butane sultone, vinyl sulfate, or 1,3-propylene glycol sulfate; Based on the total mass of the electrolyte, the mass percentage of the compound containing sulfur-oxygen double bonds is G%, and 0.01≤G≤3. 13 . An electronic device comprising the secondary battery according to claim 1 .

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