Secondary battery and electronic device comprising same

Abstract

A secondary battery and an electronic device comprising 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, where R is selected from an unsubstituted or Ra-substituted C2 to C6 alkyl, an unsubstituted or Ra-substituted C6 to C12 aryl, or an unsubstituted or Ra-substituted C5 to C12 nitrogen-containing heteroaryl; each Ra is independently selected from a halogen or a halogen-substituted C1 to C3 alkyl, and each 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%, where 0.01 ≤ A ≤ 50. The positive electrode sheet comprises a positive electrode active material. The positive electrode active material comprises lithium cobalt oxide comprising 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 element M is B%, where 0.01 ≤ B ≤ 1. The values of A and B are controlled within the above ranges to facilitate formation of a low-impedance CEI film, thereby enabling the secondary battery to achieve both good high-temperature storage stability and low-temperature discharge performance.

Description

Secondary batteries and electronic devices containing them

[0001] This application claims priority to Chinese Patent Application No. 202411207759.7, filed on August 30, 2024, entitled "Secondary Battery and Electronic Device Containing the Thereof", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of electrochemical technology, and in particular to a secondary battery and an electronic device comprising the same. Background Technology

[0003] 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 application scope of lithium-ion batteries continues to expand and their application scenarios become more diverse, the market is placing higher demands on the electrochemical performance of lithium-ion batteries. Summary of the Invention

[0004] The purpose of this application is to provide a secondary battery and an electronic device therein, so as to improve the high-temperature storage stability and low-temperature discharge performance of the secondary battery.

[0005] It should be noted that while this application uses lithium-ion batteries as an example of secondary batteries to explain the invention, the secondary batteries in this application are not limited to lithium-ion batteries. The specific technical solution is as follows:

[0006] A first aspect of this application provides a secondary battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the electrolyte comprises a compound represented by Formula I:

[0007] Wherein, R is selected from unsubstituted or Ra-substituted C2 to C6 alkyl, unsubstituted or Ra-substituted C6 to C12 aryl, and unsubstituted or Ra-substituted C5 to C12 nitrogen-containing heteroaryl; 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] Based on the total mass of the electrolyte, the mass percentage A% of the compound represented by Formula I is 0.01 ≤ A ≤ 50, preferably 1 ≤ A ≤ 45; the positive electrode includes a positive electrode active material, which includes lithium cobalt oxide, and the lithium cobalt oxide contains element M, wherein element M 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 B% of element M is 0.01 ≤ B ≤ 1, preferably 0.05 ≤ B ≤ 0.8. In the secondary battery of this application, the electrolyte includes the compound represented by Formula I, the positive electrode active material includes lithium cobalt oxide containing element M, and the values ​​of A and B are controlled within the above range, which is beneficial to the formation of a low-resistance CEI film, thereby enabling the secondary battery to simultaneously possess good high-temperature storage stability and low-temperature discharge performance.

[0009] In one embodiment of this 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 this application, the compound represented by Formula I includes at least one of the following compounds:

[0011] The electrolyte includes compounds of Formula I within the above-mentioned range, which can better exert the synergistic effect with lithium cobalt oxide containing element M, generating a CEI film with lower impedance, thereby further improving the high-temperature storage stability and low-temperature discharge performance of the secondary battery.

[0012] In one embodiment of this application, the electrolyte comprises a cyclic carbonate, which includes at least one selected from 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 inclusion of a cyclic carbonate in the electrolyte and the control of the C value within the above range are beneficial for improving the low-temperature discharge performance of the secondary battery, while also improving the high-temperature storage stability of the secondary battery.

[0013] In one embodiment of this application, the cyclic carbonate includes fluoroethylene carbonate, and at least one of ethylene carbonate or propylene carbonate. The electrolyte comprising the above-mentioned types of cyclic carbonates can further improve the electrolyte conductivity, thereby further improving the low-temperature discharge performance of the secondary battery while also ensuring the high-temperature storage stability of the secondary battery.

[0014] In one embodiment of this application, the electrolyte comprises a linear carbonate, which 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; based on the total mass of the electrolyte, the mass percentage of the linear carbonate is D%, 3 ≤ D ≤ 30. Including a linear carbonate in the electrolyte and controlling the value of D within the above range is beneficial for reducing the overall viscosity of the electrolyte, increasing 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 also ensuring the high-temperature storage stability of the secondary battery.

[0015] In one embodiment of this application, the linear carbonate includes at least one of diethyl carbonate or ethyl difluoroethyl carbonate. The electrolyte comprising the above-mentioned linear carbonates can further reduce electrolyte viscosity and increase electrolyte conductivity, thereby further improving the low-temperature discharge performance of the secondary battery while also ensuring its high-temperature storage stability.

[0016] In one embodiment of this application, the electrolyte comprises a linear carboxylic acid ester, which 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%, 10 ≤ E ≤ 55%. Including a linear carboxylic acid ester in the electrolyte and controlling the value of E within the above range is beneficial for reducing the overall viscosity of the electrolyte, increasing 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 also ensuring the high-temperature storage stability of the secondary battery.

[0017] In one embodiment of this application, the linear carboxylic acid ester includes at least one selected from ethyl propionate, propyl propionate, 2,2-difluoroethyl acetate, or 2,2,2-trifluoroethyl acetate. The electrolyte comprising the above-mentioned linear carboxylic acid esters can further reduce electrolyte viscosity and increase electrolyte conductivity, thereby further improving the low-temperature discharge performance of the secondary battery while also ensuring its high-temperature storage stability.

[0018] In one embodiment of this application, 0.02 ≤ A / (A+E) ≤ 0.8. In this application, adjusting the value of A / (A+E) within the above range is beneficial to further improve the high-temperature storage stability and low-temperature discharge performance of the secondary battery.

[0019] In one embodiment of this application, the electrolyte comprises a nitrile compound, including at least one selected from butadionitrile, glutaronitrile, methylglutaronitrile, adiponitrile, heptaonitrile, octadionitrile, anonadionitrile, sebaconitrile, 1,3,5-pentanetrionitrile, or 1,3,6-hexanetrionitrile; based on the total mass of the electrolyte, the mass percentage of the nitrile compound is F%, 1 ≤ F ≤ 8. The inclusion of the above-mentioned types of nitrile compounds in the electrolyte and the control of the value of F within the above range facilitate a better synergistic effect between the compound shown in Formula I and lithium cobalt oxide containing element M, further improving the high-temperature storage stability and low-temperature discharge performance of the secondary battery.

[0020] In one embodiment of this application, the electrolyte comprises a compound containing a sulfur-oxygen double bond, wherein the compound containing the sulfur-oxygen double bond includes at least one selected from 1,3-propanesulfonic acid lactone, 1,4-butanesulfonic acid lactone, vinyl sulfate, or 1,3-propanediol sulfate; based on the total mass of the electrolyte, the mass percentage of the compound containing the sulfur-oxygen double bond is G%, 0.01 ≤ G ≤ 3. The inclusion of the above-mentioned compound containing the sulfur-oxygen double bond in the electrolyte and the control of the value of G within the above range facilitates better synergistic effects between the compound shown in Formula I and lithium cobalt oxide containing element M, further improving the high-temperature storage stability and low-temperature discharge performance of the secondary battery.

[0021] A second aspect of this application provides an electronic device comprising a secondary battery as described in any of the foregoing embodiments. Therefore, the electronic device provided by this application has excellent performance.

[0022] This application provides a secondary battery and an electronic device comprising the same. The secondary battery includes a positive electrode, a negative electrode, a separator, and an electrolyte. The electrolyte includes a compound represented by Formula I. Based on the total mass of the electrolyte, the mass percentage of the compound represented by Formula I is A%, and 0.01 ≤ A ≤ 50%. The positive electrode includes a positive electrode active material, which includes lithium cobalt oxide. The lithium cobalt oxide contains element M, wherein element M 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 element M is B%, and 0.01 ≤ B ≤ 1. In the secondary battery of this application, the electrolyte includes a compound represented by Formula I, the positive electrode active material includes lithium cobalt oxide containing element M, and the values ​​of A and B are controlled within the above ranges, which is beneficial for forming a low-resistance CEI film, thereby enabling the secondary battery to simultaneously possess good high-temperature storage stability and low-temperature discharge performance.

[0023] Of course, implementing any product or method of this application does not necessarily require achieving all of the advantages described above at the same time. Detailed Implementation

[0024] The technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0025] It should be noted that, in the specific embodiments of this application, a lithium-ion battery is used as an example of a secondary battery to explain this application; however, the secondary battery in this application is not limited to lithium-ion batteries. The specific technical solution is as follows:

[0026] The first aspect of this application provides a secondary battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the electrolyte comprises a compound represented by Formula I:

[0027] Wherein, R is selected from unsubstituted or Ra-substituted C2 to C6 alkyl, unsubstituted or Ra-substituted C6 to C12 aryl, and unsubstituted or Ra-substituted C5 to C12 nitrogen-containing heteroaryl; Ra is each independently selected from halogen or halogen-substituted C1 to C3 alkyl, and each halogen is each independently selected from fluorine, chlorine or bromine.

[0028] Based on the total mass of the electrolyte, the mass percentage A% of the compound represented by Formula I is 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 of any two of these values; the positive electrode includes a positive active material, which includes cobalt acid. Lithium, lithium cobalt oxide contains an element M, wherein the element M 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 content of the element M 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 of any two values ​​therein.

[0029] The inventors have discovered that lithium cobalt oxide materials are prone to metal ion dissolution under high-temperature conditions, which damages the structure and reduces the stability of the lithium cobalt oxide material. Doping with element M can effectively improve the stability of lithium cobalt oxide materials and suppress structural damage under high temperature and high SOC conditions. However, this also leads to an increase in the interfacial impedance of the positive electrode, making delithiation difficult and limiting low-temperature discharge performance. In this application, the compound represented by formula I in the electrolyte can synergistically interact with the positive electrode active material, lithium cobalt oxide, which is doped with element M, to facilitate 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 exert a synergistic effect with the positive electrode active material, and the interfacial impedance of the positive electrode is large. When the value of A is too large, for example, greater than 50, the thickness of the formed CEI film increases significantly, which is not conducive to ion conduction. When the value of B is too small, for example, less than 0.01, it is insufficient 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 interfacial impedance of the positive electrode is too large and the dissolution of metal ions cannot be fully controlled. In this application's secondary battery, the electrolyte includes a compound represented by Formula I, and the positive electrode active material includes lithium cobalt oxide containing element M. The values ​​of A and B are adjusted within the aforementioned range to facilitate the formation of a low-resistance CEI film, thereby enabling the secondary battery to simultaneously possess excellent high-temperature storage stability and low-temperature discharge performance. In this application, "high temperature" refers to a temperature greater than or equal to 45°C, and "low temperature" refers to a temperature less than or equal to -10°C.

[0030] In one embodiment of this application, the compound represented by Formula I includes at least one of the following compounds:

[0031] The electrolyte includes compounds of Formula I within the above-mentioned range, which can better exert the synergistic effect with lithium cobalt oxide containing element M, generating a CEI film with lower impedance, thereby further improving the high-temperature storage stability and low-temperature discharge performance of the secondary battery.

[0032] In one embodiment of this application, the electrolyte comprises a cyclic carbonate, which includes at least one selected from 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 these values. The inclusion of a cyclic carbonate in the electrolyte and the control of the C value within the aforementioned range are beneficial for promoting the dissociation of lithium salts, increasing the electrolyte conductivity, and thus improving the low-temperature discharge performance of the secondary battery. Simultaneously, it can assist in the formation of a more stable SEI film, reducing the influence of transition metal ions on the negative electrode, thereby improving the high-temperature storage stability of the secondary battery.

[0033] In one embodiment of this application, the cyclic carbonate includes fluoroethylene carbonate and at least one of ethylene carbonate or propylene carbonate. This application does not impose any particular limitation on the amount ratio of fluoroethylene carbonate and at least one of ethylene carbonate or propylene carbonate, as long as the purpose of this application is achieved. For example, when the cyclic carbonate includes fluoroethylene carbonate and ethylene carbonate or propylene carbonate, the mass ratio of fluoroethylene carbonate to 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 including the above-mentioned types of cyclic carbonates can further improve the electrolyte conductivity, thereby further improving the low-temperature discharge performance of the secondary battery while also ensuring the high-temperature storage stability of the secondary battery.

[0034] In one embodiment of this application, the electrolyte comprises a linear carbonate, which 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 of any two of these values. Including a linear carbonate in the electrolyte and controlling the value of D within the above range helps to reduce the overall viscosity of the electrolyte, increase 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 also ensuring the high-temperature storage stability of the secondary battery.

[0035] In one embodiment of this application, the linear carbonate includes at least one of diethyl carbonate or ethyl difluoroethyl carbonate. The electrolyte comprising the aforementioned linear carbonates can further reduce electrolyte viscosity and increase electrolyte conductivity, thereby further improving the low-temperature discharge performance of the secondary battery while also ensuring its high-temperature storage stability.

[0036] In one embodiment of this application, the electrolyte comprises a linear carboxylic acid ester, which 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%, 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 these values. The electrolyte includes linear carboxylic acid esters and the value of E is adjusted within the above range, which helps to reduce the overall viscosity of the electrolyte and increase the conductivity of the electrolyte, thereby increasing the kinetic performance of the secondary battery and improving the low-temperature discharge performance of the secondary battery, while also taking into account the high-temperature storage stability of the secondary battery.

[0037] In one embodiment of this application, the linear carboxylic acid ester includes at least one selected from ethyl propionate, propyl propionate, 2,2-difluoroethyl acetate, or 2,2,2-trifluoroethyl acetate. The electrolyte comprising the above-mentioned linear carboxylic acid esters can further reduce electrolyte viscosity and increase electrolyte conductivity, thereby further improving the low-temperature discharge performance of the secondary battery while also ensuring its high-temperature storage stability.

[0038] In one embodiment of this 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 of any two values ​​therein. By adjusting the value of A / (A+E) within the above range, the interfacial impedance of the positive electrode can be further reduced, promoting ion transport at the interface and enabling the electrolyte to possess good bulk ion transport capabilities, thereby further improving the high-temperature storage stability and low-temperature discharge performance of the secondary battery.

[0039] In one embodiment of this application, the electrolyte comprises a nitrile compound, which includes at least one selected from succinic anionyl nitrile, glutaronitrile, methylglutaronitrile, adiponitrile, heptanonitrile, octanoic anionyl nitrile, nonadionitrile, sebaconitrile, 1,3,5-pentanetrionitrile, or 1,3,6-hexanetrionitrile. Based on the total mass of the electrolyte, the mass percentage of the nitrile compound is F%, 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 these values. The electrolyte includes the above-mentioned nitrile compounds and the value of F is adjusted within the above range, which is conducive to the better synergistic effect of the compound shown in Formula I and lithium cobalt oxide containing element M, synergistically modifying the CEI film, thereby further improving the high-temperature storage stability and low-temperature discharge performance of the secondary battery.

[0040] In one embodiment of this application, the electrolyte includes a compound containing a sulfur-oxygen double bond, which includes at least one of 1,3-propanesulfonic acid lactone, 1,4-butanesulfonic acid lactone, vinyl sulfate, or 1,3-propanediol sulfate. Based on the total mass of the electrolyte, the mass percentage of the compound containing the 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 of any two of these values. The electrolyte includes the above-mentioned compounds containing sulfur-oxygen double bonds and the value of G is adjusted within the above range, which is conducive to the better synergistic effect of the compound shown in Formula I and lithium cobalt oxide containing element M, synergistically modifying the CEI film, thereby further improving the high-temperature storage stability and low-temperature discharge performance of the secondary battery.

[0041] In this application, cyclic carbonates, linear carbonates, linear carboxylic esters, nitrile compounds, and compounds containing sulfur-oxygen double bonds within the above-mentioned scope can be used in any combination, as long as the purpose of this application can be achieved.

[0042] In this application, the electrolyte also includes lithium salts and non-aqueous solvents. This application does not impose any particular limitation on the lithium salt, as long as it achieves the purpose of this application. 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(oxalato)borate (LiBOB), or lithium difluoroborate. This application does not impose any particular limitation on the content of lithium salts in the electrolyte, as long as it achieves the purpose of this application. For example, based on the total mass of the electrolyte, the mass percentage of lithium salts is 8% to 15%.

[0043] This application does not impose any particular limitation on non-aqueous solvents, as long as they achieve the purpose of this application. For example, non-aqueous solvents may include, but are not limited to, at least one of ether compounds or other organic solvents. The aforementioned 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 aforementioned other organic solvents may include, but are not limited to, at least one of dipropyl carbonate, dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate. This application does not impose any particular limitation on the content of non-aqueous solvents in the electrolyte, as long as they achieve the purpose of this application. For example, based on the total mass of the electrolyte, the mass percentage of non-aqueous solvents may be 0% to 91%.

[0044] In one embodiment of this application, the electrolyte comprises a compound of Formula I, a lithium salt, and a non-aqueous solvent. The mass percentages of the compound of Formula I and the lithium salt, based on the total mass of the electrolyte, are as described above, and the mass percentage of the non-aqueous solvent is 35% to 91%. The secondary battery using the electrolyte of this application, comprising the compound of Formula I, exhibits improved high-temperature storage stability and low-temperature discharge performance.

[0045] In one embodiment of this application, the electrolyte comprises a compound of Formula I, a cyclic carbonate, a lithium salt, and a non-aqueous solvent. The mass percentages of the compound of Formula I, the cyclic carbonate, and the lithium salt, based on the total mass of the electrolyte, are as described above, and the mass percentage of the non-aqueous solvent is 0% to 88%. The electrolyte comprises the compound of Formula I and the cyclic carbonate. Secondary batteries using the electrolyte of this application exhibit further improved high-temperature storage stability and low-temperature discharge performance.

[0046] In one embodiment of this application, the electrolyte comprises a compound of Formula I, a linear carbonate, a lithium salt, and a non-aqueous solvent. The mass percentages of the compound of Formula I, the linear carbonate, and the lithium salt, based on the total mass of the electrolyte, are as described above, and the mass percentage of the non-aqueous solvent is 5% to 88%. The electrolyte comprises the compound of Formula I and the linear carbonate. Secondary batteries using the electrolyte of this application exhibit further improved high-temperature storage stability and low-temperature discharge performance.

[0047] In one embodiment of this application, the electrolyte comprises a compound of Formula I, a linear carboxylic acid ester, a lithium salt, and a non-aqueous solvent. The mass percentages of the compound of Formula I, the linear carboxylic acid ester, and the lithium salt, based on the total mass of the electrolyte, are as described above, and the mass percentage of the non-aqueous solvent is 0% to 81%. The electrolyte comprises the compound of Formula I and the linear carboxylic acid ester. Secondary batteries using the electrolyte of this application exhibit further improved high-temperature storage stability and low-temperature discharge performance.

[0048] In one embodiment of this application, the electrolyte comprises a compound of Formula I, a cyclic carbonate, a linear carbonate, a lithium salt, and a non-aqueous solvent. The mass percentages of the compound of Formula I, the cyclic carbonate, the linear carbonate, and the lithium salt, based on the total mass of the electrolyte, are as described above, and the mass percentage of the non-aqueous solvent is 0% to 85%. The secondary battery using the electrolyte of this application, comprising the compound of Formula I, the cyclic carbonate, and the linear carbonate, exhibits further improved high-temperature storage stability and low-temperature discharge performance.

[0049] In one embodiment of this application, the electrolyte comprises a compound of Formula I, a cyclic carbonate, a linear carboxylic acid ester, a lithium salt, and a non-aqueous solvent. The mass percentages of the compound of Formula I, the cyclic carbonate, the linear carboxylic acid ester, and the lithium salt, based on the total mass of the electrolyte, are as described above, and the mass percentage of the non-aqueous solvent is 0% to 78%. The secondary battery using the electrolyte of this application, comprising the compound of Formula I, the cyclic carbonate, and the linear carboxylic acid ester, exhibits further improved high-temperature storage stability and low-temperature discharge performance.

[0050] In one embodiment of this application, the electrolyte comprises a compound of Formula I, a linear carbonate, a linear carboxylic acid ester, a lithium salt, and a non-aqueous solvent. The mass percentages of the compound of Formula I, the linear carbonate, the linear carboxylic acid ester, and the lithium salt, based on the total mass of the electrolyte, are as described above, and the mass percentage of the non-aqueous solvent is 0% to 78%. The secondary battery using the electrolyte of this application, comprising the compound of Formula I, the linear carbonate, and the linear carboxylic acid ester, exhibits further improved high-temperature storage stability and low-temperature discharge performance.

[0051] In one embodiment of this application, the electrolyte comprises a compound of Formula I, a cyclic carbonate, a linear carbonate, a linear carboxylic acid ester, a lithium salt, and a non-aqueous solvent. The mass percentages of the compound of Formula I, the cyclic carbonate, the linear carbonate, the linear carboxylic acid ester, and the lithium salt, based on the total mass of the electrolyte, are as described above, and the mass percentage of the non-aqueous solvent is 0% to 75%. The secondary battery using the electrolyte of this application, comprising the compound of Formula I, the cyclic carbonate, the linear carbonate, and the linear carboxylic acid ester, exhibits further improved high-temperature storage stability and low-temperature discharge performance.

[0052] In one embodiment of this application, the electrolyte comprises a compound of Formula I, a nitrile compound, a lithium salt, and a non-aqueous solvent. The mass percentages of the compound of Formula I, the nitrile compound, and the lithium salt, based on the total mass of the electrolyte, are as described above, and the mass percentage of the non-aqueous solvent is 27% to 90%. The electrolyte comprises the compound of Formula I and the nitrile compound. Secondary batteries using the electrolyte of this application exhibit further improved high-temperature storage stability and low-temperature discharge performance.

[0053] In one embodiment of this application, the electrolyte comprises a compound of Formula I, a compound containing a sulfur-oxygen double bond, a lithium salt, and a non-aqueous solvent. The mass percentages of the compound of Formula I, the compound containing a sulfur-oxygen double bond, and the lithium salt, based on the total mass of the electrolyte, are as described above, and the mass percentage of the non-aqueous solvent is 32% to 91%. The electrolyte comprises the compound of Formula I and the compound containing a sulfur-oxygen double bond. Secondary batteries using the electrolyte of this application exhibit further improved high-temperature storage stability and low-temperature discharge performance.

[0054] In one embodiment of this application, the electrolyte comprises a compound of Formula I, a nitrile compound, a compound containing a sulfur-oxygen double bond, a lithium salt, and a non-aqueous solvent. The mass percentages of the compound of Formula I, the nitrile compound, the compound containing a sulfur-oxygen double bond, and the lithium salt, based on the total mass of the electrolyte, are as described above, and the mass percentage of the non-aqueous solvent is 24% to 90%. The secondary battery using the electrolyte of this application, comprising the compound of Formula I, the nitrile compound, and the compound containing a sulfur-oxygen double bond, exhibits further improved high-temperature storage stability and low-temperature discharge performance.

[0055] In one embodiment of this application, the electrolyte comprises a compound of 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 percentages of the compound of Formula I, the cyclic carbonate, the nitrile compound, the compound containing a sulfur-oxygen double bond, and the lithium salt, based on the total mass of the electrolyte, are as described above, and the mass percentage of the non-aqueous solvent is 0% to 87%. The secondary battery using the electrolyte of this application, comprising the compound of Formula I, the cyclic carbonate, the nitrile compound, and the compound containing a sulfur-oxygen double bond, exhibits further improved high-temperature storage stability and low-temperature discharge performance.

[0056] In one embodiment of this application, the electrolyte comprises a compound of 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 percentages of the compound of 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, based on the total mass of the electrolyte, are as described above, and the mass percentage of the non-aqueous solvent is 0% to 74%. The secondary battery using the electrolyte of this application, comprising the compound of 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, exhibits further improved high-temperature storage stability and low-temperature discharge performance.

[0057] In this application, the positive electrode includes a positive current collector and a positive electrode material layer disposed on at least one surface of the positive current collector. The phrase "positive electrode material layer disposed on at least one surface of the positive current collector" means that the positive electrode material layer can be disposed on one surface of the positive current collector along its thickness direction, or on two surfaces of the positive current collector along its thickness direction. It should be noted that "surface" here can be the entire surface area of ​​the positive current collector, or only a portion of the surface area; this application has no particular limitation, as long as the purpose of this application is achieved. This application also has no particular limitation on the positive current collector, as long as the purpose of this application is achieved; for example, it can include aluminum foil, aluminum alloy foil, or a composite current collector (e.g., an aluminum-carbon composite current collector).

[0058] The positive electrode material layer includes the positive electrode active material of this application. This application does not impose any particular limitation on the preparation method of lithium cobalt oxide, as long as it achieves the purpose of this application. Exemplarily, the preparation method of lithium cobalt oxide includes:

[0059] Using lithium source material and transition metal source material as raw materials, and controlling their mass ratio, the raw materials are dispersed in anhydrous ethanol, and the solid content in the dispersion is adjusted to 30wt% to 45wt%, then ground uniformly. The ground solution is dried at 60°C to 80°C to obtain a uniform powder. The powder is then subjected to a first heat treatment at 500°C to 850°C in an air atmosphere for 3 to 5 hours, resulting in a transition metal oxide. The transition metal oxide is then mixed uniformly with the M-doped source material, and subjected to a second heat treatment at 880°C to 1100°C in a nitrogen atmosphere to obtain lithium cobalt oxide, a positive electrode active material including M-doped element. This application does not impose any particular limitation on the M-doped source material, as long as it can achieve the purpose of this application. For example, the M-doped source material 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, etc. This application does not particularly limit the mass ratio of lithium source material to transition metal source material, or the mass ratio of transition metal oxide to M-doped source material; these ratios can be selected according to actual needs, as long as the purpose of this application is achieved. For example, the mass ratio of lithium source material to transition metal source material can be (6 to 15):26, and the mass ratio of transition metal oxide to M-doped source material can be (133 to 13280):10.

[0060] The positive electrode material layer may further include a conductive agent and a binder. This application does not impose any particular limitation on the conductive agent, as long as it achieves the purpose of this application. 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, metallic materials, or conductive polymers. The conductive carbon black may include, but is not limited to, at least one of acetylene black or Ketjen black. The aforementioned carbon nanotubes may include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The aforementioned carbon fibers may include, but are not limited to, vapor-grown carbon fibers (VGCF) and / or carbon nanofibers. The aforementioned metallic materials may include, but are not limited to, metal powders and / or metal fibers; specifically, the metal may include, but is not limited to, at least one of copper, nickel, aluminum, or silver. The aforementioned conductive polymers may include, but are not limited to, at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, or polypyrrole. This application does not impose any particular limitation on the binder, as long as it can achieve the purpose of this application. 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. This application does not impose any particular limitation on the mass ratio of the positive electrode active material, conductive agent, and binder in the positive electrode material layer. Those skilled in the art can choose according to actual needs, as long as the purpose of this application can be achieved.

[0061] This application does not impose any particular limitations on the thickness of the positive electrode current collector and the positive electrode material layer, as long as the purpose of this application can be achieved. For example, the thickness of the positive electrode current collector can be 5 μm to 20 μm, and the thickness of the single-sided positive electrode material layer can be 30 μm to 120 μm.

[0062] Optionally, the positive electrode may further include a conductive layer located between the positive current collector and the positive electrode material layer. The composition of the conductive layer is not particularly limited and can be any conductive layer commonly used in the art. The conductive layer includes a conductive agent and a binder. This application does not impose any particular limitation on the conductive agent and binder in the conductive layer; for example, it can be at least one of the aforementioned conductive agents and binders.

[0063] In this application, the negative electrode sheet 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 phrase "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 its thickness direction, or on two surfaces of the negative electrode current collector along its thickness direction. It should be noted that the "surface" here can be the entire surface area of ​​the negative electrode current collector, or only a portion of the surface area; this application has no particular limitation, as long as the purpose of this application is achieved. This application has no particular limitation on the negative electrode current collector, as long as the purpose of this application is achieved. For example, it can include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or a composite current collector. 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.

[0064] The negative electrode material layer includes a negative electrode active material. This application does not impose any particular limitation on the negative electrode active material, as long as it can achieve the purpose of this application. For example, the negative electrode active material may include, but is not limited to, natural graphite, artificial graphite, mesophase micro carbon spheres, hard carbon, soft carbon, silicon, silicon-carbon composites, Li-Sn alloys, Li-Sn-O alloys, Sn, SnO, SnO2, and spinel-structured lithiated TiO2-Li4Ti5O. 12 Or at least one of Li-Al alloys.

[0065] In some embodiments of this application, the negative electrode material layer may further include a conductive agent and a binder. This application does not impose any particular restrictions on the types of conductive agents and binders, as long as they achieve the purpose of this application. For example, it may be at least one of the aforementioned conductive agents and binders. This application does not impose any particular restrictions on the mass ratio of the negative electrode active material, conductive agent, and binder in the negative electrode material layer. Those skilled in the art can select according to actual needs, as long as the purpose of this application is achieved.

[0066] In some embodiments of this application, the negative electrode material layer may further include a conductive agent, a binder, and a thickener. This application does not particularly limit the types of conductive agents, binders, and thickeners, as long as they achieve the purpose of this application. For example, the conductive agent and binder may be at least one of the aforementioned conductive agents and binders. The thickener may include, but is not limited to, at least one of sodium carboxymethyl cellulose or lithium carboxymethyl cellulose. This application does not particularly limit the mass ratio of the negative electrode active material, conductive agent, binder, and thickener in the negative electrode material layer; those skilled in the art can select them according to actual needs, as long as the purpose of this application is achieved.

[0067] This application does not impose any particular limitation on the thickness of the negative electrode material layer, as long as it achieves the purpose of this application. For example, the thickness of the single-sided negative electrode material layer is 30 μm to 120 μm. This application also does not impose any particular limitation on the thickness of the negative electrode current collector, as long as it achieves the purpose of this application. For example, the thickness of the negative electrode current collector is 4 μm to 15 μm.

[0068] Optionally, the negative electrode sheet may further include a conductive layer located between the negative electrode current collector and the negative electrode material layer. This application does not impose any particular limitation on the composition of the conductive layer, which can be a conductive layer commonly used in the art. For example, the conductive layer may include a conductive agent and a binder. This application does not impose any particular limitation on the conductive agent and binder in the conductive layer; for example, it can be at least one of the aforementioned conductive agents and binders.

[0069] This application does not impose any particular limitation on the separator membrane, as long as it can achieve the purpose of this application. For example, the material of the separator membrane may include, but is not limited to, at least one of polyethylene (PE), polyolefins (PO) mainly composed of polypropylene (PP), polyester (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid. The type of separator membrane may include at least one of woven membrane, nonwoven membrane, microporous membrane, composite membrane, rolled membrane, or spun membrane.

[0070] In some embodiments of this application, the separator may include a substrate layer and a surface treatment layer. The substrate layer may be a nonwoven fabric, membrane, or composite membrane with 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 membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane may be used.

[0071] Optionally, a surface treatment layer is disposed on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by a mixture of polymer and inorganic materials. In some embodiments of this application, the inorganic layer includes inorganic particles and a binder. This application does not particularly limit the inorganic particles; for example, the inorganic particles may include at least one of alumina, 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. This application does not particularly limit the binder; for example, the binder may be at least one of the binders described above. In some embodiments of this application, the polymer layer includes a polymer, and the polymer material includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, or polyvinylidene fluoride or poly(vinylidene fluoride-hexafluoropropylene).

[0072] In this application, there is no particular limitation on the thickness of the separator, as long as it can achieve the purpose of this application. For example, the thickness of the separator can be from 3 μm to 30 μm.

[0073] In this application, the secondary battery also includes a casing for housing the positive electrode, separator, negative electrode, and electrolyte, as well as other components known in the field of secondary batteries. This application does not limit the scope of these other components. This application does not impose any particular limitation on the casing; it can be a casing known in the art, as long as it achieves the purpose of this application. For example, the casing can be a rigid casing or a flexible casing. The material of the rigid casing can be metal; this application does not limit the type of metal and can use known metal rigid casings, as long as they achieve the purpose of this application. The flexible casing can be a metal plastic film, such as aluminum-plastic film, steel-plastic film, etc.

[0074] The fabrication process of the secondary battery described in this application is well known to those skilled in the art, and this application does not impose any particular limitations. For example, the fabrication process of the secondary battery may include, but is not limited to, the following steps: stacking the positive electrode sheet, separator, and negative electrode sheet in sequence, and performing operations such as winding and folding as needed to obtain a wound electrode assembly; placing the electrode assembly into a housing; injecting electrolyte into the housing and sealing it to obtain the secondary battery. Alternatively, stacking the positive electrode sheet, separator, and negative electrode sheet in sequence, and then fixing the four corners of the entire stacked structure with tape to obtain a stacked electrode assembly; placing the electrode assembly into a housing; injecting electrolyte into the housing and sealing it to obtain the secondary battery. In addition, overcurrent protection elements, conductive plates, etc., may be placed in the housing as needed to prevent pressure rise and overcharging / discharging inside the secondary battery.

[0075] This application does not impose any particular limitation on the type of secondary battery, which may include any device in which an electrochemical reaction occurs. For example, secondary batteries may include, but are not limited to: lithium metal secondary batteries, lithium-ion batteries, sodium-ion batteries, lithium polymer secondary batteries, and lithium-ion polymer secondary batteries.

[0076] A second aspect of this application provides an electronic device comprising the secondary battery described in any of the foregoing embodiments. The secondary battery provided by this application exhibits good high-temperature storage stability and low-temperature discharge performance, thereby giving the electronic device a long service life.

[0077] This application does not specifically limit the type of electronic device; it can be any electronic device known in the prior art. In some embodiments of this application, the electronic device may include, but is not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors, etc.

[0078] Example

[0079] The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below. Furthermore, unless otherwise specified, "parts" and "%" are quality standards.

[0080] Test methods and equipment:

[0081] Test of M element content in positive electrode active material

[0082] The positive electrode sheet was obtained by disassembling the lithium-ion battery. 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 in a mixed solvent. 0.4g of the positive electrode material layer was diluted to 100mL with a mixed solvent of 10mL aqua regia (nitric acid and hydrochloric acid mixed in a 1:1 ratio) and 2mL HF. Then, the mass percentage of element M in the solution was tested using an ICP (Inductively Coupled Plasma) analyzer.

[0083] High-temperature storage test of lithium-ion batteries

[0084] Four lithium-ion batteries were taken from each group of the examples and comparative examples. In a room temperature environment, they were first charged with a constant current of 0.5C to 4.5V, and then charged with a constant voltage until the current was equal to 0.05C. Then, they were discharged with a constant current of 1C until 3.0V. The discharge capacity was recorded as the capacity before storage. The batteries were charged with a constant current of 0.5C to 4.5V, and then charged with a constant voltage until the current was equal to 0.05C. After storing the lithium-ion batteries in an 85°C oven for 24 hours, they were left to cool to room temperature. Then, they were discharged with a constant current of 1C until 3.0V. The discharge capacity was recorded as the capacity after storage.

[0085] 85℃ high-temperature storage capacity retention rate = (capacity after storage / capacity before storage) × 100%.

[0086] Low-temperature discharge performance test of lithium-ion batteries

[0087] Place the lithium-ion battery in a high-low temperature chamber, adjust the temperature to 25°C, and let it stand for 30 minutes to allow the lithium-ion battery to reach a constant temperature. Discharge the lithium-ion battery to 3.0V at a current of 0.5C, then charge it to 4.5V at a current of 0.5C, and then charge it at the same voltage until the current equals 0.05C. Again at 25°C, discharge it to 3.0V at a current of 0.5C; record this discharge capacity as the initial discharge capacity. At 25°C, charge it to 4.5V at a current of 0.5C, and then charge it at the same voltage until the current equals 0.05C. Then, place the lithium-ion battery at -10°C and let it stand for 30 minutes to allow the battery temperature to match the ambient temperature. At -10°C, discharge it to 3.0V at a current of 0.5C; record this discharge capacity as the low-temperature discharge capacity.

[0088] -10℃ low-temperature discharge capacity retention rate = (low-temperature discharge capacity / initial discharge capacity) × 100%.

[0089] Example 1-1

[0090] <Preparation of Lithium Cobalt Oxide>

[0091] Lithium source material Li₂CO₃ and transition metal source material Co(NO₃)₂ were mixed at a mass ratio of 11:26, then dispersed in anhydrous ethanol. The solid content of the dispersion was adjusted to 35 wt%, and the mixture was ground uniformly. The ground solution was dried at 60°C to obtain a uniform powder. The powder was then subjected to a first heat treatment at 600°C for 3 hours in an air atmosphere, resulting in a transition metal oxide. The transition metal oxide and the doped element Al(NO₃)₃ were mixed uniformly at a mass ratio of 332:5, and then subjected to a second heat treatment at 1000°C in a nitrogen atmosphere to obtain lithium cobalt oxide containing elemental Al, with an Al content (B%) of 0.2%.

[0092] <Preparation of the positive electrode>

[0093] The lithium cobalt oxide, the positive electrode active material 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-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solid content of 75 wt%. After vacuum stirring, a positive electrode slurry was obtained. The positive electrode slurry was uniformly coated on one surface of a 10 μm thick aluminum foil for the positive electrode current collector and dried at 120 °C to obtain a positive electrode sheet with a single-sided coating of positive electrode material layer. The coating weight of the positive electrode material layer was 246.8 mg / 1540 mm². 2 The above steps are then repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coating of positive electrode material. After drying at 120℃, it is cold-pressed, then cut and welded with tabs to obtain a positive electrode sheet with a size of 74mm×867mm for later use. The thickness of the single-sided positive electrode material layer is 42μm.

[0094] <Preparation of Negative Electrode Sheets>

[0095] Artificial graphite (negative electrode active material), styrene-butadiene rubber (binder), and acetylene black (conductive agent) were mixed in a mass ratio of 97.4:1.4:1.2. Deionized water was added as a solvent to prepare a slurry with a solid content of 45 wt%. The slurry was stirred evenly in a vacuum mixer to obtain the negative electrode slurry. The negative electrode slurry was uniformly coated onto one surface of a 6 μm thick copper foil used as a negative electrode current collector and dried at 120°C to obtain a negative electrode sheet with a single-sided negative electrode material layer. The coating weight of the negative electrode material layer was 142 mg / 1540 mm². 2 Then, the above steps are repeated on the other surface of the copper foil to obtain a negative electrode sheet with a double-sided coating of negative electrode material. After drying at 120℃, it is cold-pressed, then cut and welded with tabs to obtain a negative electrode sheet with a size of 78mm×875mm for use. The thickness of the single-sided negative electrode material layer is 54.5μm.

[0096] <Preparation of Electrolyte>

[0097] In an environment with a water content of less than 10 ppm, dipropyl carbonate is used as a non-aqueous solvent. Then, compound I-1 (as shown in Formula I) and lithium salt LiPF6 are added to the non-aqueous solvent and mixed thoroughly to obtain an electrolyte. Based on the total mass of the electrolyte, the mass percentage A% of the compound shown in Formula I is 5%, the mass percentage of the lithium salt is 12.5%, and the remainder is the non-aqueous solvent.

[0098] <Isolation membrane>

[0099] A porous polyethylene film with a thickness of 7μm (provided by Celgard) was used as the separator.

[0100] <Preparation of Lithium-ion Batteries>

[0101] The prepared positive electrode, separator, and negative electrode are stacked sequentially, with the separator positioned between the positive and negative electrodes to provide isolation. The electrode assembly is then wound to obtain the electrode assembly. The electrode assembly is placed in an aluminum-plastic film packaging bag and dehydrated at 80°C. The electrolyte prepared above is then injected, and the battery undergoes vacuum sealing, settling, formation, degassing, and edge trimming to obtain a lithium-ion battery. The formation upper limit voltage is 4.15V, the formation temperature is 70°C, and the formation settling time is 2 hours.

[0102] Examples 1-2 to Examples 1-7

[0103] Except for the following changes in the <Preparation of Electrolyte>: adjusting the mass percentage A% of the compound shown in Formula I according to Table 1, changing the mass percentage of the non-aqueous solvent accordingly, and keeping the mass percentage of the lithium salt unchanged, the rest is the same as in Examples 1-1.

[0104] Examples 1-8 to Examples 1-12

[0105] Except for adjusting the mass ratio of transition metal oxide and doped M element source material Al(NO3)3 in the <Preparation of Lithium Cobalt Oxide> so that the mass percentage of Al element in lithium cobalt oxide is as shown in Table 1, the rest is the same as in Example 1-1.

[0106] Examples 1-13 to Examples 1-16

[0107] Except for adjusting the types of compounds shown in Formula I according to Table 1 in the <Preparation of Electrolyte> section, the rest is the same as in Examples 1-1.

[0108] Examples 1-17 to Examples 1-23

[0109] Except for adjusting the type of doped M element source material and the mass ratio of transition metal oxide to doped M element source material in the <Preparation of Lithium Cobalt Oxide> section, so that the type and mass percentage (B%) of M element in lithium cobalt oxide are as shown in Table 1, the rest is the same as in Example 1-1. The doped M element source materials in Examples 1-17 to 1-23 are, in order, Mg(NO3)2, Ti(SO4)2, Nb(C2O4)2, Cr(C2H3O2)3, Y2(SO4)3, SrSO4, and Zr(NO3)4.

[0110] Examples 2-1 to 2-24

[0111] Except for the addition of cyclic carbonates, linear carbonates, and linear carboxylic acid esters as shown in Table 2 in the <Preparation of Electrolyte>, and the adjustment of the mass percentage A% of the compounds shown in Formula I, the type and mass percentage C% of the cyclic carbonates, the type and mass percentage D% of the linear carbonates, and the type and mass percentage E of the linear carboxylic acid esters according to Table 2, the mass percentage of the non-aqueous solvent is changed accordingly, and the mass percentage of the lithium salt remains unchanged, the rest is the same as in Examples 1-1.

[0112] Examples 3-1 to 3-12

[0113] Except for the addition of cyclic carbonates, linear carbonates, linear carboxylic esters, nitrile compounds, and compounds containing sulfur-oxygen double bonds as shown in Table 3 in the <Preparation of Electrolyte>, and the adjustment of the types and mass percentages of cyclic carbonates (C%), linear carbonates (D%), linear carboxylic esters (E%), nitrile compounds (F%), and compounds containing sulfur-oxygen double bonds (G%) according to Table 3, and the change of the mass percentage of non-aqueous solvents accordingly, and the unchanged mass percentages of compounds and lithium salts shown in Formula I, the rest is the same as in Examples 1-1.

[0114] Comparative Example 1-1

[0115] Except that in the <Preparation of Lithium Cobalt Oxide>, no M-doped source material is added to obtain lithium cobalt oxide without M element, and in the <Preparation of Electrolyte>, no compound of Formula I is added, 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 in Examples 1-1.

[0116] Comparative Examples 1-2

[0117] Except that the compound shown in Formula I is not added in the <Preparation of Electrolyte>, the mass percentage of the non-aqueous solvent is changed accordingly, and the mass percentage of lithium salt remains unchanged, the rest is the same as in Example 1-1.

[0118] Comparative Examples 1-3

[0119] Except for adjusting the mass percentage A% of compound I-1 according to Table 1 in the <Preparation of Electrolyte>, changing the mass percentage of non-aqueous solvent accordingly, and keeping the mass percentage of lithium salt unchanged, the rest is the same as in Example 1-1.

[0120] Comparative Examples 1-4

[0121] Except for the fact that no M-element source material was added in the <Preparation of Lithium Cobalt Oxide> to obtain lithium cobalt oxide without M element, the rest is the same as in Example 1-1.

[0122] Comparative Examples 1-5

[0123] Except for adjusting the mass ratio of transition metal oxide and doped M element source material Al(NO3)3 in the <Preparation of Lithium Cobalt Oxide> so that the mass percentage of Al element in lithium cobalt oxide is as shown in Table 1, the rest is the same as in Example 1-1.

[0124] Comparative Examples 1-6

[0125] Except for adjusting the type of dopant source material and the mass ratio of transition metal oxide to dopant source material in the <Preparation of Lithium Cobalt Oxide> section, so that the type and mass percentage (B%) of dopant element in lithium cobalt oxide are as shown in Table 1, the rest is the same as in Example 1-1. The dopant source material is Mn(NO3)2.

[0126] Table 1 Note: " / " in Table 1 indicates that the corresponding substance or parameter does not exist.

[0127] As can be seen from Examples 1-1 to 1-23 and Comparative Examples 1-1 to 1-6, when the positive electrode includes lithium cobalt oxide as the positive active material and the content of element M in lithium cobalt oxide is within the range of this application, and the electrolyte includes the compound shown in Formula I and the value of its content A is adjusted to be within the range of this application, the lithium-ion battery can simultaneously have a high high-temperature storage capacity retention rate and a high low-temperature discharge capacity retention rate, indicating that the lithium-ion battery has both good high-temperature storage stability and low-temperature discharge performance.

[0128] The types of compounds shown in Formula I typically affect the high-temperature storage stability and low-temperature discharge performance of lithium-ion batteries. From...

[0129] As can be seen from Examples 1-1, 1-13 to 1-16, lithium-ion batteries using compounds of Formula I within the scope of this application can simultaneously exhibit high high-temperature storage capacity retention and low-temperature discharge capacity retention, indicating that lithium-ion batteries have both good high-temperature storage stability and low-temperature discharge performance.

[0130] Table 2 Note: " / " in Table 2 indicates that the corresponding substance or parameter does not exist.

[0131] The type and content of cyclic carbonates, linear carbonates, and linear carboxylic esters typically affect the high-temperature storage stability and low-temperature discharge performance of lithium-ion batteries. As can be seen from Examples 1-1, 2-1 to 2-24, when the electrolyte includes at least one of the cyclic carbonates, linear carbonates, and linear carboxylic esters within the range of types and contents specified in this application, the lithium-ion battery can exhibit higher high-temperature storage capacity retention and low-temperature discharge capacity retention, indicating that the lithium-ion battery simultaneously possesses better high-temperature storage stability and low-temperature discharge performance.

[0132] The value of A / (A+E) typically affects the high-temperature storage stability and low-temperature discharge performance of lithium-ion batteries. As can be seen from Examples 1-1, 2-12 to 2-20, when the value of A / (A+E) is adjusted within the range of this application, the lithium-ion battery can simultaneously exhibit higher high-temperature storage capacity retention and higher low-temperature discharge capacity retention, indicating that the lithium-ion battery simultaneously possesses better high-temperature storage stability and low-temperature discharge performance.

[0133] Table 3 Note: " / " in Table 3 indicates that the corresponding substance or parameter does not exist.

[0134] The type and content of nitrile compounds, and the type and content of compounds containing sulfur-oxygen double bonds, typically affect the high-temperature storage stability and low-temperature discharge performance of lithium-ion batteries. As can be seen from Examples 1-1, 3-1 to 3-10, when the electrolyte includes at least one of the nitrile compounds and compounds containing sulfur-oxygen double bonds within the scope of this 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 simultaneously possesses better high-temperature storage stability and low-temperature discharge performance.

[0135] As can be seen from Examples 1-1, 2-1 to 2-24, and 3-1 to 3-12, when the electrolyte includes at least two of the cyclic carbonates, linear carbonates, linear carboxylic acid esters, nitrile compounds, and compounds containing sulfur-oxygen double bonds within the scope of this application, the high-temperature storage capacity retention rate and low-temperature discharge capacity retention rate of lithium-ion batteries can be further improved, indicating that the high-temperature storage stability and low-temperature discharge performance of lithium-ion batteries are further improved.

[0136] It should be noted that, in this document, the terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, or article that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, or article.

[0137] The element connected by the terms "at least one of," "at least one of," "at least one of," or other similar terms refers to any combination of the listed elements. For example, "at least one of A or B" means only A, only B, A and B. Similarly, "at least one of A, B, or C" means only A, only B, only C, only A and B, only A and C, only B and C, A and B and C.

[0138] The various embodiments in this specification are described in a related manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0139] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A secondary battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the electrolyte comprises a compound represented by Formula I: in, R is selected from unsubstituted or Ra-substituted C2 to C6 alkyl groups, unsubstituted or Ra-substituted C6 to C12 aryl groups, and unsubstituted or Ra-substituted C5 to C12 nitrogen-containing heteroaryl groups; each Ra is independently selected from a halogen or a halogen-substituted C1 to C3 alkyl group, and each 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%, and 0.01 ≤ A ≤ 50%. The positive electrode sheet includes a positive electrode active material, the positive electrode active material includes lithium cobalt oxide, the lithium cobalt oxide contains an element M, wherein the element M 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 element M 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 comprises cyclic carbonates, which include 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 carbonates include 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 comprises linear carbonates, which include 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. 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 comprises a linear carboxylic acid ester, which 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%, 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 comprises nitrile compounds, including at least one selected from butadionitrile, glutaronitrile, methylglutaronitrile, adiponitrile, heptaonitrile, octadionitrile, nonadionitrile, sebaconitrile, 1,3,5-pentanetrionitrile, or 1,3,6-hexanetrionitrile. 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 comprises a compound containing a sulfur-oxygen double bond, which includes at least one of 1,3-propanesulfonate lactone, 1,4-butanesulfonate lactone, vinyl sulfate, or 1,3-propanediol sulfate. Based on the total mass of the electrolyte, the mass percentage of the compound containing the sulfur-oxygen double bond is G%, and 0.01≤G≤3.

13. An electronic device comprising a secondary battery according to any one of claims 1 to 12.

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