Secondary battery and electronic device including the same

Abstract

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

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electrochemistry, in particular to a secondary battery and an electronic device comprising the same. BACKGROUND

[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, small self-discharge, no memory effect and long cycle life. With the continuous expansion of the use of lithium ion batteries, their use scenarios are more diverse, and the market has higher requirements for the electrochemical performance of lithium ion batteries. SUMMARY

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

[0004] It should be noted that the present application is explained by taking lithium ion batteries as an example in the summary of the application, but the secondary battery of the present application is 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 comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the electrolyte comprises a compound represented by Formula I:

[0006]

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

[0008] The mass percentage content A% of the compound represented by Formula I based on the total mass of the electrolyte is 0.01≤A≤50, preferably 1≤A≤45; the positive electrode sheet comprises a positive electrode active material, and the positive electrode active material comprises lithium cobaltate containing M elements, wherein the M elements comprise at least one of Al, Mg, Ti, Nb, Cr, Y, Sr or Zr, and the mass percentage content of the M elements based on the total mass of the positive electrode active material is B%, 0.01≤B≤1, preferably 0.05≤B≤0.8. In the secondary battery of the present application, the electrolyte comprises the compound represented by Formula I, the positive electrode active material comprises lithium cobaltate containing M elements, and the values of A and B are regulated within the above range, which is beneficial to the formation of a low-impedance CEI film, thereby enabling the secondary battery to simultaneously have good high-temperature storage stability and low-temperature discharge performance.

[0009] In an 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 an 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, can better play the synergistic effect with the lithium cobalt oxide containing the element M, 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 an embodiment of the present application, the electrolyte includes a cyclic carbonate, the cyclic carbonate includes at least one of ethylene carbonate, propylene carbonate or fluoroethylene carbonate; the mass percentage content of the cyclic carbonate is C%, 3≤C≤40 based on the total mass of the electrolyte. The electrolyte includes the 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, while improving the high-temperature storage stability of the secondary battery.

[0014] In an 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 cyclic carbonate of the above kind, which can further improve the electrolyte conductivity, thereby further improving the low-temperature discharge performance of the secondary battery while taking into account the high-temperature storage stability of the secondary battery.

[0015] In an embodiment of the present application, the electrolyte includes a linear carbonate, the linear carbonate includes at least one of methyl ethyl 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; the mass percentage content of the linear carbonate is D%, 3≤D≤30 based on the total mass of the electrolyte. The electrolyte includes the 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 electrolyte conductivity, 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.

[0016] In an embodiment of the present application, the linear carbonate includes at least one of diethyl carbonate or ethyl difluoroethyl carbonate. The electrolyte including the linear carbonate of the above-mentioned kind 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 an embodiment of the present application, the electrolyte includes a linear carboxylic acid ester, the linear carboxylic acid ester 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; the mass percentage content of the linear carboxylic acid ester is E%, 10≤E≤55, based on the total mass of the electrolyte. The electrolyte including the linear carboxylic acid ester and regulating the value of E within the above-mentioned range is conducive to reducing the overall viscosity of the electrolyte and 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 being able to take into account the high-temperature storage stability of the secondary battery.

[0018] In an 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 including the linear carboxylic acid ester of the above-mentioned kind 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 an 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-mentioned range is conducive to further improving the high-temperature storage stability and low-temperature discharge performance of the secondary battery.

[0020] In an embodiment of the present application, the electrolyte includes a nitrile compound, the nitrile compound includes at least one of butanedinitrile, pentanedinitrile, methyl pentanedinitrile, hexanedinitrile, heptanedinitrile, octanedinitrile, nonanedinitrile, decanedinitrile, 1,3,5-pentane trinitrile, or 1,3,6-hexane trinitrile; the mass percentage content of the nitrile compound is F%, 1≤F≤8, based on the total mass of the electrolyte. The electrolyte including the nitrile compound of the above-mentioned kind and regulating the value of F within the above-mentioned range is conducive to better synergistic effect with the compound of Formula I and lithium cobalt oxide containing the element M, thereby further improving the high-temperature storage stability and low-temperature discharge performance of the secondary battery.

[0021] In an embodiment of the present application, the electrolyte comprises a compound containing a sulfur-oxygen double bond, the compound containing a sulfur-oxygen double bond comprises at least one of 1,3-propane sultone, 1,4-butane sultone, ethylene sulfate or 1,3-propanediol sulfate; the mass percentage of the compound containing a sulfur-oxygen double bond is G%, 0.01≤G≤3, based on the total mass of the electrolyte. The electrolyte comprises the compound containing a sulfur-oxygen double bond described above and regulates the value of G within the range described above, which is beneficial for the better synergistic effect of the compound represented by Formula I and the lithium cobalt oxide containing M elements, 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 comprising the secondary battery in any of the foregoing embodiments. Thus, the electronic device provided by the present application has good use performance.

[0023] The present application provides a secondary battery and an electronic device comprising the same, the secondary battery comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, the electrolyte comprising a compound represented by Formula I; the mass percentage of the compound represented by Formula I is A%, 0.01≤A≤50, based on the total mass of the electrolyte; the positive electrode sheet comprises a positive electrode active material, the positive electrode active material comprises lithium cobalt oxide, and the lithium cobalt oxide comprises M elements, wherein the M elements comprise at least one of Al, Mg, Ti, Nb, Cr, Y, Sr or Zr; the mass percentage of the M elements is B%, 0.01≤B≤1, based on the total mass of the positive electrode active material. In the secondary battery of the present application, the electrolyte comprises the compound represented by Formula I, the positive electrode active material comprises the lithium cobalt oxide containing M elements, and the values of A and B are regulated within the range described above, which is beneficial for the formation of a low-impedance CEI film, so that the secondary battery simultaneously has 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 the advantages described above at the same time. DETAILED DESCRIPTION

[0025] The technical solutions in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of the present application, not 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 embodiments of the present application, lithium ion batteries are used as examples 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] A secondary battery according to a first aspect of the present application includes a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte, the electrolyte including a compound of Formula I:

[0028]

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

[0030] A mass percentage content A% of the compound of Formula I, based on the total mass of the electrolyte, is 0.01 ≤ A ≤ 50, preferably 1 ≤ A ≤ 45, for example, 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 defined by any two of them; the positive electrode sheet includes a positive electrode active material, the positive electrode active material including lithium cobaltate, the lithium cobaltate containing M elements, wherein the M elements include at least one of Al, Mg, Ti, Nb, Cr, Y, Sr, or Zr; a mass percentage content of the M elements, based on the total mass of the positive electrode active material, is B%, 0.01 ≤ B ≤ 1, preferably 0.05 ≤ B ≤ 0.8, for example, 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 defined by any two of them.

[0031] The inventors found that the lithium cobalt oxide material is prone to metal ion dissolution under high temperature conditions, which destroys the structure of the lithium cobalt oxide material and reduces the stability of the lithium cobalt oxide material. Doping M elements can effectively improve the stability of the lithium cobalt oxide material and inhibit the structural damage of the lithium cobalt oxide material under high temperature and high SOC, but at the same time, it will cause the increase of the interface impedance of the positive electrode sheet, the difficulty of delithiation, and the limitation of the low-temperature discharge performance. The compound represented by formula I in the electrolyte of the present application can play a synergistic effect with the lithium cobalt oxide doped with M elements in the positive electrode active material, which is conducive to the formation of a low-impedance positive 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 effect with the positive electrode active material, and the interface impedance of the positive electrode sheet is large; when the value of A is too large, for example, greater than 50, the thickness of the formed CEI film increases too much, 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 sheet is too large and cannot control the metal ion dissolution sufficiently. In the secondary battery of the present application, the electrolyte includes the compound represented by formula I, the positive electrode active material includes lithium cobalt oxide containing M elements, 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, thereby enabling the secondary battery to simultaneously have 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 an 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 play a synergistic effect with the lithium cobalt oxide containing M elements and 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 an embodiment of the present application, the electrolyte comprises a cyclic carbonate, the cyclic carbonate comprises at least one of ethylene carbonate (EC), propylene carbonate or fluoroethylene carbonate (FEC); the mass percentage of the cyclic carbonate in the electrolyte 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 between any two of them. The electrolyte comprises the cyclic carbonate and regulates the value of C within the above range, which is conducive to promoting the dissociation of lithium salt, improving the conductivity of the electrolyte, and further improving the low-temperature discharge performance of the secondary battery, while being able to assist in forming a more stable SEI film, reducing the impact of transition metal ions on the negative electrode, thereby improving the high-temperature storage stability of the secondary battery.

[0036] In an embodiment of the present application, the cyclic carbonate comprises fluoroethylene carbonate and at least one of ethylene carbonate or propylene carbonate. The amount of fluoroethylene carbonate and at least one of ethylene carbonate or propylene carbonate used in the present application is not particularly limited as long as the purpose of the present application can be achieved, for example, when the cyclic carbonate comprises fluoroethylene carbonate and at least one of 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 comprises fluoroethylene carbonate, 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 comprises 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.

[0037] In an embodiment of the present application, the electrolyte comprises a linear carbonate, the linear carbonate comprises 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; the mass percentage of the linear carbonate in the electrolyte 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 between any two of them. The electrolyte comprises the 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 further improving the low-temperature discharge performance of the secondary battery, while being able to take into account the high-temperature storage stability of the secondary battery.

[0038] In an embodiment of the present application, the linear carbonate includes at least one of diethyl carbonate or ethyl difluoroethyl carbonate. The electrolyte including the linear carbonate of the above-mentioned kind 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 while taking into account the high-temperature storage stability of the secondary battery.

[0039] In an embodiment of the present application, the electrolyte includes a linear carboxylic acid ester, the linear carboxylic acid ester 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; the mass percentage content of the linear carboxylic acid ester is E% based on the total mass of the electrolyte, 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 formed by any two of them. The electrolyte including the linear carboxylic acid ester and regulating the value of E within the above-mentioned range is conducive to reducing the overall viscosity of the electrolyte and 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 an 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 including the linear carboxylic acid ester of the above-mentioned kind 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 while taking into account the high-temperature storage stability of the secondary battery.

[0041] In an 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 formed by any two of them. By regulating the value of A / (A+E) within the above-mentioned range, the interface impedance of the positive electrode sheet can be further reduced, the ion transmission of the interface is promoted, and the electrolyte has good bulk ion transmission capacity, thereby further improving the high-temperature storage stability and low-temperature discharge performance of the secondary battery.

[0042] In an embodiment of the present application, the electrolyte comprises a nitrile compound, the nitrile compound comprises at least one of succinonitrile, glutaronitrile, methylglutaronitrile, adiponitrile, pimelonitrile, suberonitrile, azelonitrile, sebonitrile, 1,3,5-pentanetricarbonitrile or 1,3,6-hexanetricarbonitrile; the mass percentage of the nitrile compound is F% based on the total mass of the electrolyte, 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 between any two of them. The electrolyte comprises the above-mentioned nitrile compound and regulates the value of F within the above-mentioned range, which is beneficial to better synergistic effect with the compound represented by formula I and lithium cobalt oxide containing element M, synergistically modifies the CEI film, thereby further improving the high-temperature storage stability and low-temperature discharge performance of the secondary battery.

[0043] In an embodiment of the present application, the electrolyte comprises a compound containing a sulfur-oxygen double bond, the compound containing a sulfur-oxygen double bond comprises at least one of 1,3-propanesultone, 1,4-butanesultone, ethylene sulfate or 1,3-propanediol sulfate; the mass percentage of the compound containing a sulfur-oxygen double bond is G% based on the total mass of the electrolyte, 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 between any two of them. The electrolyte comprises the above-mentioned compound containing a sulfur-oxygen double bond and regulates the value of G within the above-mentioned range, which is beneficial to better synergistic effect with the compound represented by formula I and lithium cobalt oxide containing element M, 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, the above-mentioned cyclic carbonate, linear carbonate, linear carboxylic acid ester, nitrile compound, compound containing a sulfur-oxygen double bond, etc. 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 further includes a lithium salt and a nonaqueous solvent. The lithium salt is not particularly limited in the present application as long as the object of the present application is achieved. For example, the lithium salt can 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(oxalato)borate (LiBOB), or lithium difluoroborate. The content of the lithium salt in the electrolyte is not particularly limited in the present application as long as the object of the present application is achieved. For example, the mass percentage of the lithium salt is 8% to 15% based on the total mass of the electrolyte.

[0046] The nonaqueous solvent is not particularly limited in the present application as long as the object of the present application is achieved, for example, the nonaqueous solvent can include, but is not limited to, at least one of an ether compound or other organic solvent. The above-mentioned ether compound can include, but is not limited to, at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran. The above-mentioned other organic solvent can include, but is not limited to, at least one of dipropyl carbonate, dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate. The content of the nonaqueous solvent in the electrolyte is not particularly limited in the present application as long as the object of the present application is achieved. For example, the mass percentage of the nonaqueous solvent is 0% to 91% based on the total mass of the electrolyte.

[0047] In an embodiment of the present application, the electrolyte includes the compound represented by Formula I, a lithium salt, and a nonaqueous solvent. Herein, the mass percentages of the compound represented by Formula I and the lithium salt are as described above, and the mass percentage of the nonaqueous solvent is 35% to 91% based on the total mass of the electrolyte. The electrolyte including the compound represented by Formula I, the secondary battery using the electrolyte of the present application has improved high-temperature storage stability and low-temperature discharge performance.

[0048] In an embodiment of the present application, the electrolyte includes the compound represented by Formula I, a cyclic carbonate, a lithium salt, and a nonaqueous solvent. Herein, the mass percentages of the compound represented by Formula I, the cyclic carbonate, and the lithium salt are as described above, and the mass percentage of the nonaqueous solvent is 0% to 88% based on the total mass of the electrolyte. The electrolyte including the compound represented by Formula I and the cyclic carbonate, the secondary battery using the electrolyte of the present application has further improved high-temperature storage stability and low-temperature discharge performance.

[0049] In an embodiment of the present application, the electrolyte comprises the compound shown in Formula I, linear carbonate, lithium salt, and non-aqueous solvent. Among them, the mass percentage of the compound shown in Formula I, linear carbonate, and lithium salt is as described above, and the mass percentage of the non-aqueous solvent is 5% to 88% based on the total mass of the electrolyte. The electrolyte comprises the compound shown in Formula I and 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 an embodiment of the present application, the electrolyte comprises the compound shown in Formula I, linear carbonate, lithium salt, and non-aqueous solvent. Among them, the mass percentage of the compound shown in Formula I, linear carbonate, and lithium salt is as described above, and the mass percentage of the non-aqueous solvent is 5% to 88% based on the total mass of the electrolyte. The electrolyte comprises the compound shown in Formula I and 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.

[0051] In an embodiment of the present application, the electrolyte comprises the compound shown in Formula I, linear carbonate, lithium salt, and non-aqueous solvent. Among them, the mass percentage of the compound shown in Formula I, linear carbonate, and lithium salt is as described above, and the mass percentage of the non-aqueous solvent is 5% to 88% based on the total mass of the electrolyte. The electrolyte comprises the compound shown in Formula I and 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.

[0052] In an embodiment of the present application, the electrolyte comprises the compound shown in Formula I, linear carbonate, lithium salt, and non-aqueous solvent. Among them, the mass percentage of the compound shown in Formula I, linear carbonate, and lithium salt is as described above, and the mass percentage of the non-aqueous solvent is 5% to 88% based on the total mass of the electrolyte. The electrolyte comprises the compound shown in Formula I and 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.

[0053] In an embodiment of the present application, the electrolyte comprises the compound shown in Formula I, linear carbonate, lithium salt, and non-aqueous solvent. Among them, the mass percentage of the compound shown in Formula I, linear carbonate, and lithium salt is as described above, and the mass percentage of the non-aqueous solvent is 5% to 88% based on the total mass of the electrolyte. The electrolyte comprises the compound shown in Formula I and 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.

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

[0055] In an embodiment of the present application, the electrolyte includes the compound represented by Formula I, a nitrile compound, a lithium salt, and a non-aqueous solvent. Among them, the mass percentage of the compound represented by 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% based on the total mass of the electrolyte. The electrolyte includes the compound represented by 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 an embodiment of the present application, the electrolyte includes the compound represented by Formula I, a compound containing a sulfur-oxygen double bond, a lithium salt, and a non-aqueous solvent. Among them, the mass percentage of the compound represented by 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% based on the total mass of the electrolyte. The electrolyte includes the compound represented by Formula I and the 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 an embodiment of the present application, the electrolyte includes the compound represented by Formula I, a nitrile compound, a compound containing a sulfur-oxygen double bond, a lithium salt, and a non-aqueous solvent. Among them, the mass percentage of the compound represented by 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% based on the total mass of the electrolyte. The electrolyte includes the compound represented by Formula I, the nitrile compound, and the 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.

[0058] In an embodiment of the present application, the electrolyte comprises the compound represented by Formula I, a cyclic carbonate, a nitrile compound, a compound containing a sulfur-oxygen double bond, a lithium salt, and a non-aqueous solvent. The mass percentage of the compound represented by Formula I, the cyclic carbonate, the nitrile compound, the compound containing a sulfur-oxygen double bond, and the lithium salt in the electrolyte is as described above, and the mass percentage of the non-aqueous solvent is 0% to 87% based on the total mass of the electrolyte. The electrolyte comprises the compound represented by Formula I, the cyclic carbonate, the nitrile compound, and the 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.

[0059] In an embodiment of the present application, the electrolyte comprises the compound represented by Formula I, a cyclic carbonate, a linear carbonate, a linear carboxylic acid ester, a nitrile compound, a compound containing a sulfur-oxygen double bond, a lithium salt, and a non-aqueous solvent. The mass percentage of the compound represented by Formula I, the cyclic carbonate, the linear carbonate, the linear carboxylic acid ester, the nitrile compound, the compound containing a sulfur-oxygen double bond, and the lithium salt in the electrolyte is as described above, and the mass percentage of the non-aqueous solvent is 0% to 74% based on the total mass of the electrolyte. The electrolyte comprises the compound represented by Formula I, the cyclic carbonate, the linear carbonate, the linear carboxylic acid ester, the nitrile compound, and the 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.

[0060] In the present application, the positive electrode tab comprises a positive electrode current collector and a positive electrode material layer disposed on at least one surface of the positive electrode current collector. The "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 the thickness direction of the positive electrode current collector, or can be disposed on two surfaces of the positive electrode current collector along the thickness direction of the positive electrode current collector. It should be noted that the "surface" herein can be the entire area of the surface of the positive electrode current collector, or can be part of the area of the surface of the positive electrode current collector, and the present application does not have a particular limitation as long as the purpose of the present application can be achieved. The present application does not have a particular limitation on the positive electrode current collector as long as the purpose of the present application can be achieved, for example, it can comprise an aluminum foil, an aluminum alloy foil, or a composite current collector (for example, an aluminum-carbon composite current collector), etc.

[0061] The positive electrode material layer comprises the positive electrode active material of the present application. The method for preparing lithium cobaltate is not particularly limited in the present application as long as the purpose of the present application can be achieved, and exemplarily, the method for preparing lithium cobaltate comprises:

[0062] The lithium source material and the transition metal source material are used as raw materials, the mass ratio thereof is controlled, the raw materials are dispersed in anhydrous ethanol, the solid content in the dispersion is adjusted to 30 wt% to 45 wt%, and the dispersion is uniformly ground. The ground solution is dried at 60°C to 80°C to obtain a uniform powder, the powder is subjected to first heat treatment at a temperature in the range of 500°C to 850°C, the first heat treatment is performed in an air atmosphere for 3 h to 5 h, and a transition metal oxide is obtained after the first heat treatment. The transition metal oxide and the source material of the doping M element are uniformly mixed, and the mixture is subjected to second heat treatment at a temperature in the range of 880°C to 1100°C in a nitrogen atmosphere to obtain a positive electrode active material lithium cobaltate including the doping M element. The source material of the doping M element is not particularly limited in the present application, as long as the purpose of the present application can be achieved. For example, the source material of the doping M element can 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, and the like. The mass ratio of the lithium source material and the transition metal source material, and the mass ratio of the transition metal oxide and the source material of the doping M element are not particularly limited in the present application, and can be selected as needed, as long as the purpose of the present application can be achieved. For example, the mass ratio of the lithium source material and the transition metal source material can be (6 to 15):26, and the mass ratio of the transition metal oxide and the source material of the doping M element can be (133 to 13280):10.

[0063] The positive electrode material layer can further include a conductive agent and a binder. The conductive agent is not particularly limited in the present application as long as the object of the present application can be achieved, for example, the conductive agent can include, but is not limited to, at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, flake graphite, graphene, a metal material, or a conductive polymer, and the conductive carbon black can include, but is not limited to, at least one of acetylene black or ketjen black. The above-mentioned carbon nanotubes can include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The above-mentioned carbon fibers can include, but are not limited to, vapor grown carbon fibers (VGCF) and / or nanocarbon fibers. The above-mentioned metal material can include, but is not limited to, metal powder and / or metal fibers, and specifically, the metal can include, but is not limited to, at least one of copper, nickel, aluminum, or silver. The above-mentioned conductive polymer can include, but is not limited to, at least one of polyphenylene derivative, polyaniline, polythiophene, polyacetylene, or polypyrrole. The binder is not particularly limited in the present application as long as the object of the present application can be achieved, for example, the binder can 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 mass ratio of the positive electrode active material, the conductive agent, and the binder in the positive electrode material layer is not particularly limited in the present application, and those skilled in the art can select according to actual needs as long as the object of the present application can be achieved.

[0064] The thickness of the positive electrode current collector and the positive electrode material layer is not particularly limited in the present application as long as the object 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 can further include a conductive layer between the positive electrode current collector and the positive electrode material layer. The composition of the conductive layer is not particularly limited and can be a commonly used conductive layer in the art. The conductive layer includes a conductive agent and a binder. The conductive agent and the binder in the conductive layer are not particularly limited in the present application, for example, can be at least one of the above-mentioned conductive agent and the above-mentioned binder.

[0066] In the present application, the negative electrode tab 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 "the 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 the thickness direction of the negative electrode current collector, or can be disposed 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" herein can be the entire area of the surface of the negative electrode current collector, or can be part of the area of the surface of the negative electrode current collector, which is not particularly limited in the present application as long as the purpose of the present application can be achieved. The negative electrode current collector is not particularly limited in the present application as long as the purpose of the present application can be achieved, for example, it can include a copper foil, a copper alloy foil, a nickel foil, a stainless steel foil, a titanium foil, a nickel foam, a copper foam or a composite current collector, and exemplarily, 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, which is not particularly limited in the present application as long as the purpose of the present application can be achieved, for example, the negative electrode active material can include but is not limited to at least one of natural graphite, artificial graphite, mesocarbon microbeads, 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 Li-Al alloy.

[0068] In some embodiments of the present application, the negative electrode material layer can further include a conductive agent and a binder, which are not particularly limited in kind in the present application as long as the purpose of the present application can be achieved, for example, can be at least one of the above-mentioned conductive agent and the above-mentioned binder. The mass ratio of the negative electrode active material, the conductive agent and the binder in the negative electrode material layer is not particularly limited in the present application, which can be selected by a person skilled in the art 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 can further include a conductive agent, a binder and a thickening agent, which are not particularly limited in kind in the present application as long as the purpose of the present application can be achieved, for example, the conductive agent and the binder can be at least one of the above-mentioned conductive agent and the above-mentioned binder. The thickening agent can include but is not limited to at least one of sodium carboxymethyl cellulose or lithium carboxymethyl cellulose. The mass ratio of the negative electrode active material, the conductive agent, the binder and the thickening agent in the negative electrode material layer is not particularly limited in the present application, which can be selected by a person skilled in the art according to actual needs as long as the purpose of the present application can be achieved.

[0070] The thickness of the negative electrode material layer is not particularly limited in the present application, as long as the object of the present application can be achieved, for example, the thickness of the single-sided negative electrode material layer is 30 to 120 μm. The thickness of the negative electrode current collector is not particularly limited in the present application, as long as the object of the present application can be achieved, for example, the thickness of the negative electrode current collector is 4 to 15 μm.

[0071] Optionally, the negative electrode tab can further include a conductive layer between the negative electrode current collector and the negative electrode material layer. The composition of the conductive layer is not particularly limited in the present application, and can be a commonly used conductive layer in the art. For example, the conductive layer includes a conductive agent and a binder. The conductive agent and the binder in the conductive layer are not particularly limited in the present application, and can be at least one of the above-mentioned conductive agents and the above-mentioned binders, for example.

[0072] The separator film is not particularly limited in the present application, as long as the object of the present application can be achieved. For example, the material of the separator film can include, but is not limited to, at least one of polyethylene (PE), polyolefin (PO) based on polypropylene (PP), polyester (for example, polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid. The type of the separator film can include at least one of a woven film, a non-woven film, a microporous film, a composite film, a calendered film, or a spunlaid film.

[0073] In some embodiments of the present application, the separator film can include a base layer and a surface treatment layer. The base layer can be a non-woven fabric, a film, or a composite film having a porous structure, and the material of the base layer can 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 can be used.

[0074] Optionally, at least one surface of the base layer is provided with a surface treatment layer, which can be a polymer layer or an inorganic layer, or a layer formed by mixing polymer and inorganic matter. In some embodiments of the present application, the inorganic layer includes inorganic particles and a binder. The inorganic particles are not particularly limited in the present application, and 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, for example. The binder is not particularly limited in the present application, and can be at least one of the above-mentioned binders, for example. 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, polyacrylic acid salt, polyvinylpyrrolidone, polyvinyl ether, or polyvinylidene fluoride or poly(vinylidene fluoride-hexafluoropropylene).

[0075] In the present application, the thickness of the separator film is not particularly limited as long as the object of the present application can be achieved, for example, the thickness of the separator film can be 3 μm to 30 μm.

[0076] In the present application, the secondary battery further comprises a housing for accommodating the positive electrode sheet, the separator film, the negative electrode sheet and the electrolyte, and other components known in the art of secondary batteries, and the present application does not limit the above-mentioned other components. The housing is not particularly limited in the present application, and can be a housing known in the art as long as the object of the present application can be achieved. For example, the housing can be a hard shell housing or a flexible housing. The material of the hard shell housing can be metal, and the type of metal is not limited in the present application, and a metal hard shell housing known in the art can be used as long as the object of the present application can be achieved. The flexible housing can be a metal plastic film, for example, 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 the present application is not particularly limited, for example, the preparation process of the secondary battery can include but is not limited to the following steps: stacking the positive electrode sheet, the separator film and the negative electrode sheet in order, and winding, folding, etc. according to the need to obtain a wound electrode assembly, placing the electrode assembly into the housing, injecting the electrolyte into the housing and sealing, to obtain the secondary battery. Alternatively, the positive electrode sheet, the separator film and the negative electrode sheet are stacked in order, and then the four corners of the entire stack structure are fixed with adhesive tape to obtain a stack structure electrode assembly, the electrode assembly is placed into the housing, the electrolyte is injected into the housing and sealed, to obtain the secondary battery. In addition, the overcurrent prevention element, the guide plate, etc. can also be placed in the housing according to the need, so as to prevent the pressure rise in the secondary battery and overcharge and discharge.

[0078] The type of secondary battery is not particularly limited in the present application, which can include any device that undergoes an electrochemical reaction. For example, the secondary battery can include but is not limited to: lithium metal secondary battery, lithium ion battery, sodium ion battery, lithium polymer secondary battery, lithium ion polymer secondary battery.

[0079] The second aspect of the present application provides an electronic device comprising the secondary battery of any one of the preceding 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 longer service life.

[0080] The kind of the electronic device is not particularly limited in the present application, and it can be any electronic device known in the art. In some embodiments of the present application, the electronic device can include, but is not limited to, a notebook computer, a pen input computer, a mobile computer, an electronic book player, a portable telephone, a portable facsimile, a portable copying machine, a portable printer, a headphone, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable audio player, a radio, a backup power supply, an electric motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, a lighting appliance, a toy, a game machine, a clock, an electric tool, a flashlight, a camera, a household large storage battery, a lithium ion capacitor, and the like.

[0081] Embodiment

[0082] Hereinafter, the embodiments of the present application are more specifically described by citing examples and comparative examples. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are on a mass basis.

[0083] Test methods and apparatus:

[0084] Measurement of content of M element in positive electrode active material

[0085] The positive electrode tab was obtained by disassembling a lithium ion battery, and the positive electrode tab was washed with dimethyl carbonate (DMC). The positive electrode material layer of the washed positive electrode tab was scraped off with a doctor blade, and dissolved with a mixed solvent. 0.4 g of the positive electrode material layer was dissolved with 10 mL of aqua regia (mixed with nitric acid and hydrochloric acid at a ratio of 1:1) and 2 mL of HF, and the volume was made up to 100 mL. The mass percentage content of M element in the solution was then measured using an ICP (Inductively Coupled Plasma) analyzer.

[0086] High-temperature storage test of lithium ion battery

[0087] Four batteries were taken from each group of lithium ion batteries of the examples and comparative examples, and were first charged at a constant current of 0.5 C to 4.5 V, and then charged at a constant voltage until the current was equal to 0.05 C. The batteries were then discharged at a constant current of 1 C to 3.0 V, and the discharge capacity was recorded as the capacity before storage. The batteries were then charged at a constant current of 0.5 C to 4.5 V, and then stored in an oven at 85°C for 24 hours. After the storage, the batteries were allowed to cool to room temperature, and were then discharged at a constant current of 1 C to 3.0 V. The discharge capacity was recorded as the capacity after storage.

[0088] 85°C high-temperature storage capacity retention rate = post-storage capacity / pre-storage capacity x 100%.

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

[0090] The lithium ion battery was placed in a high-low temperature chamber, the temperature was adjusted to 25°C, and the lithium ion battery was allowed to stand for 30 minutes to reach a constant temperature. The lithium ion battery that reached a constant temperature was discharged at a current of 0.5C to 3.0V, then charged to 4.5V at a current of 0.5C, and then constant voltage charged at the charging voltage until the current was equal to 0.05C. Similarly, at a temperature of 25°C, discharge at a current of 0.5C to 3.0V, at which time the discharge capacity is recorded as the initial discharge capacity. At a temperature of 25°C, charge to 4.5V at a current of 0.5C, and then constant voltage charge at the charging voltage until the current is equal to 0.05C. Then, the lithium ion battery was placed at a temperature of -10°C and allowed to stand for 30 minutes to allow the temperature of the lithium ion battery to match the temperature of the outside environment. At a temperature of -10°C, discharge at a current of 0.5C to 3.0V, at which time the discharge capacity is recorded 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 cobaltate

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

[0095] Preparation of positive electrode sheet

[0096] The lithium cobaltate prepared above, the conductive agent Super P, and the binder polyvinylidene fluoride were mixed in a mass ratio of 97.9:0.9:1.2, N-methyl pyrrolidone (NMP) was added as a solvent, and a slurry with a solid content of 75 wt% was prepared. After uniform stirring in a vacuum, a positive electrode slurry was obtained. The positive electrode slurry was uniformly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 10 μm, and dried at 120°C to obtain a positive electrode tab with a single-side coated positive electrode material layer. The coated weight of the positive electrode material layer was 246.8 mg / 1540 mm 2 . Then the above steps were repeated on the other surface of the aluminum foil to obtain a positive electrode tab with a double-side coated positive electrode material layer. After drying at 120°C and cold pressing, the tab was cut and the tab ears were welded to obtain a positive electrode tab with a size of 74 mm x 867 mm for use. The thickness of the single-side positive electrode material layer was 42 μm.

[0097] <Preparation of a negative electrode tab>

[0098] The 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, deionized water was added as a solvent, and a slurry with a solid content of 45 wt% was prepared. After uniform stirring in a vacuum, a negative electrode slurry was obtained. The negative electrode slurry was uniformly coated on one surface of a negative electrode current collector copper foil with a thickness of 6 μm, and dried at 120°C to obtain a negative electrode tab with a single-side coated negative electrode material layer. The coated weight of the negative electrode material layer was 142 mg / 1540 mm 2 . Then the above steps were repeated on the other surface of the copper foil to obtain a negative electrode tab with a double-side coated negative electrode material layer. After drying at 120°C and cold pressing, the tab was cut and the tab ears were welded to obtain a negative electrode tab with a size of 78 mm x 875 mm for use. The thickness of the single-side negative electrode material layer was 54.5 μm.

[0099] <Preparation of an electrolyte>

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

[0101] <Separator>

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

[0103] <Preparation of a lithium ion battery>

[0104] The positive electrode sheet, the separator, and the negative electrode sheet prepared above are stacked in order, with the separator between the positive electrode sheet and the negative electrode sheet to play a separating role, to obtain an electrode assembly by winding. The electrode assembly is put into an aluminum-plastic film packaging bag, and is dehydrated at 80°C, injected with the electrolyte prepared above, and subjected to vacuum packaging, standing, formation, degassing, edge cutting, and other processes to obtain a lithium ion battery. The upper limit voltage of formation is 4.15 V, the formation temperature is 70°C, and the standing time of formation is 2 h.

[0105] Examples 1-2 to 1-7

[0106] Except that the mass percentage content A% of the compound shown in Formula I and the mass percentage content of the non-aqueous solvent are changed according to Table 1 in the preparation of the electrolyte, and the mass percentage content of the lithium salt remains unchanged, the rest is the same as Example 1-1.

[0107] Examples 1-8 to 1-12

[0108] Except that the mass percentage content B% of Al element in the lithium cobaltate is shown in Table 1 by adjusting the mass ratio of transition metal oxide and Al(NO3)3 source material of doped M element in the preparation of lithium cobaltate, the rest is the same as Example 1-1.

[0109] Examples 1-13 to 1-16

[0110] Except that the type of compound shown in Formula I is adjusted according to Table 1 in the preparation of the electrolyte, the rest is the same as Example 1-1.

[0111] Examples 1-17 to 1-23

[0112] Except that the type and mass percentage content B% of M element in the lithium cobaltate are shown in Table 1 by adjusting the type of doped M element source material and the mass ratio of transition metal oxide and doped M element source material in the preparation of lithium cobaltate, 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] Examples 2-1 to 2-24

[0114] The same as Example 1-1 except that in the preparation of the electrolyte, the cyclic carbonate, the linear carbonate, the linear carboxylic acid ester, the nitrile compound, and the compound containing sulfur and oxygen double bond were added as shown in Table 3, and the kind and mass percentage of the cyclic carbonate C%, the kind and mass percentage of the linear carbonate D%, the kind and mass percentage of the linear carboxylic acid ester E%, the kind and mass percentage of the nitrile compound F%, and the kind and mass percentage of the compound containing sulfur and oxygen double bond G% were adjusted according to Table 3, the mass percentage of the nonaqueous solvent was changed accordingly, and the mass percentage of the compound of Formula I and the lithium salt was unchanged.

[0115] Examples 3-1 to 3-12

[0116] The same as Example 1-1 except that in the preparation of the electrolyte, the cyclic carbonate, the linear carbonate, the linear carboxylic acid ester, the nitrile compound, and the compound containing sulfur and oxygen double bond were added as shown in Table 3, and the kind and mass percentage of the cyclic carbonate C%, the kind and mass percentage of the linear carbonate D%, the kind and mass percentage of the linear carboxylic acid ester E%, the kind and mass percentage of the nitrile compound F%, and the kind and mass percentage of the compound containing sulfur and oxygen double bond G% were adjusted according to Table 3, the mass percentage of the nonaqueous solvent was changed accordingly, and the mass percentage of the compound of Formula I and the lithium salt was unchanged.

[0117] Comparative Example 1-1

[0118] The same as Example 1-1 except that in the preparation of the lithium cobaltate, no M element doping source material was added to obtain lithium cobaltate containing no M element, and in the preparation of the electrolyte, no compound of Formula I was added, the mass percentage of the nonaqueous solvent was changed accordingly, and the mass percentage of the lithium salt was unchanged.

[0119] Comparative Example 1-2

[0120] The same as Example 1-1 except that in the preparation of the electrolyte, no compound of Formula I was added, the mass percentage of the nonaqueous solvent was changed accordingly, and the mass percentage of the lithium salt was unchanged.

[0121] Comparative Example 1-3

[0122] The same as Example 1-1 except that in the preparation of the electrolyte, the mass percentage of the compound I-1 A% was adjusted according to Table 1, the mass percentage of the nonaqueous solvent was changed accordingly, and the mass percentage of the lithium salt was unchanged.

[0123] Comparative Example 1-4

[0124] The same as Example 1-1 except that in the preparation of the lithium cobaltate, no M element doping source material was added to obtain lithium cobaltate containing no M element.

[0125] Comparative Example 1-5

[0126] Example 1-1 was repeated except that in the preparation of the lithium cobaltate, the mass ratio of the transition metal oxide and the source material of the doping M element Al(NO3)3 was adjusted so that the mass percentage content B% of the Al element in the lithium cobaltate was as shown in Table 1.

[0127] Comparative Example 1-6

[0128] Example 1-1 was repeated except that in the preparation of the lithium cobaltate, the type of the source material of the doping M element and the mass ratio of the transition metal oxide and the source material of the doping M element were adjusted so that the type and mass percentage content B% of the M element in the lithium cobaltate were as shown in Table 1. Among them, the source material of the doping M element was Mn(NO3)2.

[0129] Table 1

[0130]

[0131] Note: " / " in Table 1 indicates that the corresponding substance or parameter does not exist.

[0132] As can be seen from Example 1-1 to Example 1-23 and Comparative Example 1-1 to Comparative Example 1-6, when the positive electrode tab includes the positive electrode active material lithium cobaltate and the content of the M element in the lithium cobaltate is within the range of the present application, the electrolyte includes the compound shown in Formula I and the value of the content A of the compound is 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 simultaneously has good high-temperature storage stability and low-temperature discharge performance.

[0133] The type of the compound shown in Formula I generally affects the high-temperature storage stability and low-temperature discharge performance of the lithium ion battery. As can be seen from Example 1-1, Example 1-13 to Example 1-16, the lithium ion battery selected from the compound shown in Formula I within the range of the present application can simultaneously have a higher high-temperature storage capacity retention rate and a low-temperature discharge capacity retention rate, indicating that the lithium ion battery simultaneously has good high-temperature storage stability and low-temperature discharge performance.

[0134] Table 2

[0135]

[0136] Note: " / " in Table 2 indicates that the corresponding substance or parameter does not exist.

[0137] The kind and content of cyclic carbonates, the kind and content of linear carbonates, the kind and content of linear carboxylic acid esters usually affect the high-temperature storage stability and low-temperature discharge performance of the lithium ion battery. As can be seen from Example 1-1, Example 2-1 to Example 2-24, when the electrolyte comprises at least one of the cyclic carbonates, the linear carbonates, the linear carboxylic acid esters in the kind and content range of the present application, the lithium ion battery can have 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 at the same time.

[0138] The value of A / (A+E) usually affects the high-temperature storage stability and low-temperature discharge performance of the lithium ion battery. As can be seen from Example 1-1, Example 2-12 to Example 2-20, when the value of A / (A+E) is regulated within the range of the present application, the lithium ion battery can have higher high-temperature storage capacity retention rate and higher low-temperature discharge capacity retention rate at the same time, indicating that the lithium ion battery has better high-temperature storage stability and low-temperature discharge performance at the same time.

[0139] Table 3

[0140]

[0141] Note: " / " in Table 3 means that the corresponding substance or parameter does not exist.

[0142] The kind and content of nitrile compounds, the kind and content of compounds containing sulfur-oxygen double bond usually affect the high-temperature storage stability and low-temperature discharge performance of the lithium ion battery. As can be seen from Example 1-1, Example 3-1 to Example 3-10, when the electrolyte comprises at least one of the nitrile compounds, the compounds containing sulfur-oxygen double bond in the kind and content range of the present application, the high-temperature storage capacity retention rate and the 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] As can be seen from Example 1-1, Example 2-1 to Example 2-24, Example 3-1 to Example 3-12, when the electrolyte comprises at least two of the cyclic carbonates, the linear carbonates, the linear carboxylic acid esters, the nitrile compounds, the compounds containing sulfur-oxygen double bond in the kind and content range of the present application, the high-temperature storage capacity retention rate and the low-temperature discharge capacity retention rate of the lithium ion battery can be further improved, indicating that the high-temperature storage stability and the low-temperature discharge performance of the lithium ion battery are further improved.

[0144] It should be noted that, as used in this document, the terms "comprises", "comprising", or any other variation thereof are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can also include other elements not expressly listed or inherent to such process, method, article, or apparatus.

[0145] The use of the terms "at least one", "one or more", or "and / or" in the context of a list of items refers to the use of any of the items in the list, or the use of some combination of items in the list. For example, "A, B, and / or C" means A alone, B alone, C alone, A and B, A and C, B and C, or A and B and C.

[0146] Each of the embodiments in the present specification is described in a related manner, and the same or similar parts between the embodiments can be referred to each other. Each of the embodiments focuses on the difference from other embodiments.

[0147] The above only describes the preferred embodiments of the present application, and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle 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, the electrolyte comprising a compound represented by Formula I: wherein R is selected from the group consisting of C2 to C6 alkyl unsubstituted or substituted with Ra, C6 to C12 aryl unsubstituted or substituted with Ra, and C5 to C12 nitrogen-containing heteroaryl unsubstituted or substituted with Ra; each of Ra is independently selected from the group consisting of halogen or halogen-substituted C1 to C3 alkyl, each of the halogen is independently selected from the group consisting of fluorine, chlorine, or bromine; a mass percentage content A% of the compound represented by Formula I, 0.01 ≤ A ≤ 50, based on the total mass of the electrolyte; the positive electrode sheet comprising a positive electrode active material, the positive electrode active material comprising lithium cobaltate containing M elements, wherein the M elements comprise at least one of Al, Mg, Ti, Nb, Cr, Y, Sr, or Zr; a mass percentage content B% of the M elements, 0.01 ≤ B ≤ 1, based on the total mass of the positive electrode active material. wherein The secondary battery satisfies at least one of the following conditions: a) 1 ≤ A ≤ 45; b) 0.05 ≤ B ≤ 0.

8. The compound represented by Formula I comprises at least one of the following compounds: The electrolyte comprises a cyclic carbonate comprising at least one of ethylene carbonate, propylene carbonate, or fluoroethylene carbonate; a mass percentage content C% of the cyclic carbonate, 3 ≤ C ≤ 40, based on the total mass of the electrolyte.

2. The secondary battery according to claim 1, wherein The cyclic carbonate comprises fluoroethylene carbonate and at least one of ethylene carbonate or propylene carbonate. The electrolyte comprises a linear carbonate comprising at least one of methyl ethyl 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; a mass percentage content D% of the linear carbonate, 3 ≤ D ≤ 30, based on the total mass of the electrolyte. The linear carbonate comprises at least one of diethyl carbonate or ethyl difluoroethyl carbonate.

3. The secondary battery according to claim 1, wherein The electrolyte comprises a linear carboxylic acid ester comprising 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; a mass percentage content E% of the linear carboxylic acid ester, 10 ≤ E ≤ 55, based on the total mass of the electrolyte.

4. The secondary battery according to any one of claims 1 to 3, wherein 0.02 ≤ A / (A + E) ≤ 0.

8. The linear carboxylic acid ester comprises at least one of ethyl propionate, propyl propionate, 2,2-difluoroethyl acetate, or 2,2,2-trifluoroethyl acetate.

5. The secondary battery according to claim 4, wherein The electrolyte comprises a nitrile compound comprising at least one of butanedinitrile, pentanedinitrile, methyl pentanedinitrile, hexanedinitrile, heptanedinitrile, octanedinitrile, nonanedinitrile, decanedinitrile, 1,3,5-pentane trinitrile, or 1,3,6-hexane trinitrile.

6. The secondary battery according to any one of claims 1 to 3, wherein ​ ​ 7. The secondary battery according to claim 6, wherein ​ 8. The secondary battery according to any one of claims 1 to 3, wherein ​ ​ 9. The secondary battery according to claim 8, wherein ​ 10. The secondary battery according to claim 8, wherein ​ 11. The secondary battery according to any one of claims 1 to 3, wherein ​ A mass percentage of the nitrile compound is F% based on a total mass of the electrolyte, and 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, ethylene sulfate, or 1,3-propanediol sulfate; A mass percentage of the compound containing a sulfur-oxygen double bond is G% based on a total mass of the electrolyte, and 0.01≤G≤3. 13.An electronic device comprising the secondary battery of any one of claims 1 to 12.

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