Secondary batteries and electronic devices containing them

Abstract

The present invention provides a secondary battery and an electronic device including the same. The secondary battery comprises a positive electrode piece, a negative electrode piece, a separator, and an electrolyte. The negative electrode piece comprises a negative electrode material layer, the negative electrode material layer comprises a silicon-containing active material, the silicon-containing active material comprises silicon element, and when the mass percentage of silicon element relative to the total mass of the negative electrode material layer is A%, A satisfies 1 ≤ A ≤ 20. The electrolyte comprises a first component comprising at least one of the compounds represented by formula I and the compounds represented by formula II, and a second component, and when the mass percentage of the first component relative to the total mass of the electrolyte is B%, and the mass percentage of the second component is C%, B and C satisfy 25 ≤ B ≤ 70 and 0.07 ≤ C / B ≤ 1. The secondary battery of the present invention has good cycle stability and low-temperature discharge characteristics.

Description

[Technical Field]

[0001] This invention claims priority based on a Chinese patent application filed with the China National Intellectual Property Administration on May 31, 2024, with application number 202410703741.X and the title of the invention "Secondary Battery and Electronic Device Including the Same," the entirety of which is incorporated into this application by reference.

[0002] The present invention relates to the field of electrochemical technology, and more particularly to secondary batteries and electronic devices including them. [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, lack of memory effect, and relatively long cycle life. As the range of applications for lithium-ion batteries expands, their application scenarios become even more diverse, and the industry is demanding higher levels of electrochemical performance from lithium-ion batteries. [Overview of the project]

[0004] The object of the present invention is to provide a secondary battery and an electronic device including the same for improving the cycle stability and low-temperature discharge characteristics of secondary batteries. The specific technical solutions are as follows.

[0005] A first aspect of the present invention provides a secondary battery comprising a positive electrode piece, a negative electrode piece, a separator, and an electrolyte, wherein the negative electrode piece comprises a negative electrode material layer, the negative electrode material layer comprises a silicon-containing active material, the silicon-containing active material comprises silicon element, and when the mass percentage of the silicon element is A% relative to the total mass of the negative electrode material layer, A satisfies 1 ≤ A ≤ 20, and the electrolyte comprises a first component and a second component, the first component comprises at least one of a compound represented by formula I and a compound represented by formula II. [ka]

[0006] Here, R 11 and R 12 Each of these is independently a fluorine-substituted or unsubstituted C1-C10 alkyl group, and R 11 and R 12 At least one of them is substituted with fluorine, R 21 and R 22 Each of these is independently a fluorine-substituted or unsubstituted C1-C10 alkyl group, and R 21 and R 22 At least one of the first and second components is substituted with fluorine, and the second component comprises at least one of ethyl formate, methyl acetate, ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), dimethyl carbonate (DMC), and diethyl carbonate (DEC). When the mass percentage of the first component is B% and the mass percentage of the second component is C% relative to the total mass of the electrolyte, B and C satisfy 25 ≤ B ≤ 70 and 0.07 ≤ C / B ≤ 1. In the secondary battery of the present invention, the negative electrode material layer comprises a silicon-containing active material, and the electrolyte comprises the first and second components. By adjusting the values ​​of A, B, and C / B within the above ranges, a good protective effect is achieved for the positive and negative electrodes, thereby providing the secondary battery with good cycle stability. At the same time, the binding energy between the first component and lithium ions is relatively low, and the second component reduces the viscosity of the electrolyte, thereby reducing the transport resistance of lithium ions. As a result, the secondary battery has good low-temperature discharge characteristics.

[0007] In one embodiment of the present invention, A satisfies 3 ≤ A ≤ 15. By adjusting the value of A within the above range, the cycle stability and low-temperature discharge characteristics of the secondary battery can be further improved.

[0008] In one embodiment of the present invention, B satisfies 30 ≤ B ≤ 60. By adjusting the value of B within the above range, the cycle stability and low-temperature discharge characteristics of the secondary battery can be further improved.

[0009] In one embodiment of the present invention, B and C satisfy 0.1 ≤ C / B ≤ 0.9. By adjusting the value of C / B within the above range, the cycle stability and low-temperature discharge characteristics of the secondary battery can be further improved.

[0010] In one embodiment of the present invention, A, B, and C satisfy 0.01 ≤ A / (B+C) ≤ 0.5. For example, the value of A / (B+C) may be in the range of 0.01, 0.02, 0.03, 0.05, 0.07, 0.08, 0.1, 0.12, 0.13, 0.15, 0.16, 0.18, 0.2, 0.22, 0.25, 0.28, 0.3, 0.32, 0.35, 0.38, 0.4, 0.45, 0.5, or any two of the above values. By adjusting the value of A / (B+C) to within the above range, the protective effect on the positive and negative electrodes can be further improved, the viscosity of the electrolyte can be further reduced, the transport resistance of lithium ions can be reduced, and thereby the cycle stability and low-temperature discharge characteristics of the secondary battery can be further improved.

[0011] In one embodiment of the present invention, the compound represented by formula I is [ka] It includes at least one of the following.

[0012] By containing a first component within the above range, the electrolyte contributes to the formation of a more stable cathode-electrolyte interface (CEI) film, improving the protective effect on the cathode, thereby further improving the cycle stability and low-temperature discharge characteristics of the secondary battery.

[0013] In one embodiment of the present invention, the compound represented by formula II is [ka] It includes at least one of the following.

[0014] By containing the first component within the above range, the electrolyte is involved in the formation of a more stable CEI film, improves the protective effect on the positive electrode, and thereby can further improve the cycle stability and low-temperature discharge characteristics of the secondary battery.

[0015] In one embodiment of the present invention, the electrolyte further contains fluoroethylene carbonate (FEC). When the mass percentage of the fluoroethylene carbonate is D% with respect to the total mass of the electrolyte, D satisfies 2 ≤ D ≤ 12. By the electrolyte containing FEC and adjusting the value of D within the above range, the protective effect on the negative electrode can be improved, and the amount of gas generated during cycling can be reduced, thereby improving the cycle stability and low-temperature discharge characteristics of the secondary battery.

[0016] In one embodiment of the present invention, the electrolyte further contains a third component. The third component includes at least one of succinonitrile, glutaronitrile, methylglutaronitrile, adiponitrile, pimelonitrile, suberonitrile, azelaonitrile, sebaconitrile, 1,2-bis(cyanoethoxy)ethane, 1,2,3-tris(2-cyanoethoxy)propane, 1,3,5-pentanetricarbonitrile, and 1,3,6-hexanetricarbonitrile. When the mass percentage of the third component is E% with respect to the total mass of the electrolyte, E satisfies 0.5 ≤ E ≤ 6. By the electrolyte containing the third component and adjusting the value of E within the above range, it is advantageous for improving the stability of the positive electrode interface, reducing the side reaction between the positive electrode sheet and the electrolyte, and thereby improving the cycle characteristics and low-temperature discharge characteristics of the secondary battery.

[0017] In one embodiment of the present invention, the electrolyte further includes a fourth component, the fourth component includes at least one of ethylene sulfate, vinylene carbonate, 1,3 - propane sultone, and 1 - propene 1,3 - sultone. When the mass percentage of the fourth component is F% with respect to the total mass of the electrolyte, F satisfies 0.01 ≤ F ≤ 5. By including the fourth component in the electrolyte and adjusting the value of F within the above range, the interface protection of the silicon - containing negative electrode sheet can be further strengthened, and it is possible to avoid a significant increase in the electrolyte resistance. Thereby, the cycle stability of the secondary battery can be further improved, and the low - temperature discharge characteristics of the secondary battery can be improved.

[0018] In one embodiment of the present invention, the silicon - containing active material includes at least one of a silicon - oxygen composite material and a silicon - carbon composite material. By including the silicon - containing active material of the above type in the negative electrode sheet, it is advantageous for simultaneously improving the cycle stability and low - temperature discharge characteristics of the secondary battery.

[0019] In one embodiment of the present invention, the electrolyte further includes a nitrogen - containing lithium salt, the nitrogen - containing lithium salt includes at least one of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium nitrate (LiNO3). When the mass percentage of the nitrogen - containing lithium salt is G% with respect to the total mass of the electrolyte, G satisfies 0.1 ≤ G ≤ 7. By including the nitrogen - containing lithium salt in the electrolyte and adjusting the value of G within the above range, it has good solubility and dissociation ability, and can further ensure the ion - conduction ability of the electrolyte. Thereby, the cycle stability and low - temperature discharge characteristics of the secondary battery can be further improved.

[0020] The second aspect of the present invention provides an electronic device including the secondary battery according to any one of the above embodiments. Thereby, the electronic device of the present invention has a relatively long service life.

[0021] The present invention provides a secondary battery and an electronic device including the same, wherein the secondary battery comprises a positive electrode piece, a negative electrode piece, a separator, and an electrolyte, the negative electrode piece comprises a negative electrode material layer, the negative electrode material layer comprises a silicon-containing active material, the silicon-containing active material comprises silicon element, and when the mass percentage of silicon element is A% with respect to the total mass of the negative electrode material layer, A satisfies 1 ≤ A ≤ 20, and the electrolyte comprises (1) a first component comprising at least one of a compound represented by formula I and a compound represented by formula II, and (2) a second component, when the mass percentage of the first component is B% with respect to the total mass of the electrolyte and the mass percentage of the second component is C%, B and C satisfy 25 ≤ B ≤ 70 and 0.07 ≤ C / B ≤ 1. In the secondary battery of the present invention, the negative electrode material layer contains a silicon-containing active material, and the electrolyte contains a first component and a second component. By adjusting the values ​​of A, B, and C / B within the above range, a good protective effect is achieved for the positive and negative electrodes, thereby giving the secondary battery good cycle stability. At the same time, the binding energy between the first component and lithium ions is relatively low, and the second component reduces the viscosity of the electrolyte, thereby reducing the transport resistance of lithium ions, and thus the secondary battery has good low-temperature discharge characteristics.

[0022] Of course, when implementing any one of the products or methods of the present invention, it is not necessarily required to achieve all of the above advantages simultaneously. [Modes for carrying out the invention]

[0023] The technical solutions in the embodiments of the present invention are described below clearly and completely. Obviously, the embodiments described are not all embodiments but only a portion of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the present invention are included within the scope of protection of the present invention.

[0024] In the embodiments for carrying out the present invention, lithium-ion batteries are used as an example of secondary batteries in the explanation of the present invention, but the secondary batteries of the present invention are not limited to lithium-ion batteries. The specific technical solutions are as follows.

[0025] The first aspect of the present invention provides a secondary battery including a positive electrode sheet, a negative electrode sheet, a separator, and an electrolytic solution. The negative electrode sheet includes a negative electrode material layer, the negative electrode material layer includes a silicon-containing active material, the silicon-containing active material includes silicon element, and when the mass percentage of the silicon element is A% with respect to the total mass of the negative electrode material layer, A satisfies 1≤A≤20. For example, the value of A may be 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 10.5, 11, 12, 12.5, 13, 14, 15, 15.5, 16, 17, 18, 19, 20 or a range composed of any two of the above numerical values. The electrolytic solution includes a first component and a second component, and the first component includes at least one of the compound represented by Formula I and the compound represented by Formula II, [Chemical Formula]

[0026] where R 11 and R 12 are each independently a fluorine-substituted or unsubstituted C1-C10 alkyl group, and at least one of R 11 and R 12 is substituted with fluorine, R 21 and R 22 are each independently a fluorine-substituted or unsubstituted C1-C10 alkyl group, R 21 and R 22At least one of the first components is substituted with fluorine, and the second component comprises at least one of ethyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, dimethyl carbonate, and diethyl carbonate. When the mass percentage of the first component is B% and the mass percentage of the second component is C% relative to the total mass of the electrolyte, B satisfies 25 ≤ B ≤ 70. For example, the values ​​of B are 25, 27, 28, 30, 32, 33, 35, 36, 38, 40, 42, 45, 48, 50, 52, 55, 58, 60, 62. , 65, 68, 70, or a range consisting of any two of the above numbers, and B and C satisfy 0.07 ≤ C / B ≤ 1, for example the value of C / B may be 0.07, 0.08, 0.1, 0.12, 0.13, 0.15, 0.16, 0.18, 0.2, 0.22, 0.25, 0.28, 0.3, 0.32, 0.35, 0.38, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.88, 0.9, 0.92, 0.95, 0.98, 1, or a range consisting of any two of the above numbers.

[0027] The inventors have found the following: If the value of A is too small, for example less than 1, the silicon content in the negative electrode material layer becomes relatively low, which is insufficient for improving the cycle stability and low-temperature discharge characteristics of the secondary battery. On the other hand, if the value of A is too large, for example greater than 20, the reaction at the negative electrode-electrolyte interface becomes vigorous, which is unfavorable for improving the cycle stability and low-temperature discharge characteristics of the secondary battery. If the value of B is too small, for example less than 25, it becomes difficult to effectively protect the positive electrode interface, the lithium ion desorption energy barrier becomes relatively high, and it becomes difficult to improve the cycle characteristics and low-temperature discharge characteristics of the secondary battery. On the other hand, if the value of B is too large, it becomes difficult for the electrolyte to supply sufficient lithium ions during the low-temperature discharge process, polarization increases, which is unfavorable for improving the cycle stability and low-temperature discharge characteristics of the secondary battery. If the value of C / B is too small, for example less than 0.07, it becomes difficult to reduce the viscosity of the electrolyte, the lithium ion transport resistance becomes relatively large, which is insufficient for improving the cycle stability and low-temperature discharge characteristics of the secondary battery. On the other hand, if the C / B value is too large, for example, if it exceeds 1, the protective effect on the positive electrode weakens, the lithium ion desorption energy barrier increases, and it is detrimental to improving the cycle stability and low-temperature discharge characteristics of the secondary battery. In the secondary battery of the present invention, the negative electrode material layer contains a silicon-containing active material, and the electrolyte contains a first component and a second component. By adjusting the values ​​of A, B, and C / B within the above range, a good protective effect is exerted on the positive and negative electrodes, thereby the secondary battery has good cycle capacity maintenance performance and good cycle stability. At the same time, the binding energy between the first component and lithium ions is relatively low, and the second component reduces the viscosity of the electrolyte and reduces the transport resistance of lithium ions, so the secondary battery has good low-temperature discharge characteristics. In the present invention, "low temperature" refers to a temperature of -10°C or lower.

[0028] In one embodiment of the present invention, A satisfies 3 ≤ A ≤ 15. By adjusting the value of A within the above range, the cycle stability and low-temperature discharge characteristics of the secondary battery can be further improved.

[0029] In one embodiment of the present invention, B satisfies 30 ≤ B ≤ 60. By adjusting the value of B within the above range, the cycle stability and low-temperature discharge characteristics of the secondary battery can be further improved.

[0030] In one embodiment of the present invention, B and C satisfy 0.1 ≤ C / B ≤ 0.9. By adjusting the value of C / B within the above range, the cycle stability and low-temperature discharge characteristics of the secondary battery can be further improved.

[0031] In one embodiment of the present invention, the first component comprises a compound represented by formula I, and the mass percentage of the compound represented by formula I is 25% to 70% of the total mass of the electrolyte. In one embodiment of the present invention, the mass percentage of the compound represented by formula I is 30% to 60%.

[0032] In another embodiment of the present invention, the first component comprises a compound represented by formula II, and the mass percentage of the compound represented by formula II is 25% to 70% of the total mass of the electrolyte. In one embodiment of the present invention, the mass percentage of the compound represented by formula II is 30% to 60%.

[0033] In another embodiment of the present invention, the first component comprises a compound represented by formula I and a compound represented by formula II, and the sum of the mass percentages of the compound represented by formula I and the compound represented by formula II is 25% to 70% of the total mass of the electrolyte. In one embodiment of the present invention, the sum of the mass percentages of the compound represented by formula I and the compound represented by formula II is 30% to 60%. In the present invention, the mass ratio of the compound represented by formula I to the compound represented by formula II is not particularly limited, as long as the objective of the present invention is achieved. For example, the mass ratio of the compound represented by formula I to the compound represented by formula II is 1:(0.5 to 1.5).

[0034] In one embodiment of the present invention, A, B, and C satisfy 0.01 ≤ A / (B+C) ≤ 0.5, for example, the value of A / (B+C) may be in the range of 0.01, 0.02, 0.03, 0.05, 0.07, 0.08, 0.1, 0.12, 0.13, 0.15, 0.16, 0.18, 0.2, 0.22, 0.25, 0.28, 0.3, 0.32, 0.35, 0.38, 0.4, 0.45, 0.5 or any two of the above values. By adjusting the value of A / (B+C) to within the above range, the protective effect on the positive and negative electrodes can be further improved, the viscosity of the electrolyte can be further reduced, the transport resistance of lithium ions can be reduced, and thereby the cycle stability and low-temperature discharge characteristics of the secondary battery can be further improved.

[0035] In one embodiment of the present invention, B and C satisfy 26 ≤ B + C ≤ 89, and for example, the value of B + C may be in the range of 26, 28, 30, 32, 33, 35, 36, 38, 40, 42, 45, 48, 50, 52, 55, 58, 60, 62, 65, 68, 70, 73, 75, 77, 80, 82, 85, 86, 89 or any two of the above values. By adjusting the value of B + C within the above range, the ion transport function of the electrolyte can be ensured, the viscosity of the electrolyte can be reduced, the transport resistance of lithium ions can be reduced, and thereby the cycle stability and low-temperature discharge characteristics of the secondary battery can be improved.

[0036] In one embodiment of the present invention, the compound represented by formula I is [ka] It includes at least one of the following.

[0037] By containing the first component within the above range, the electrolyte contributes to the formation of a more stable CEI film, improving the protective effect on the positive electrode, thereby further improving the cycle stability and low-temperature discharge characteristics of the secondary battery.

[0038] In one embodiment of the present invention, the compound represented by formula II is [ka] It includes at least one of the following.

[0039] By containing the first component within the above range, the electrolyte contributes to the formation of a more stable CEI film, improving the protective effect on the positive electrode, thereby further improving the cycle stability and low-temperature discharge characteristics of the secondary battery.

[0040] In one embodiment of the present invention, the electrolyte further comprises fluoroethylene carbonate, and when the mass percentage of fluoroethylene carbonate relative to the total mass of the electrolyte is D%, D satisfies 2 ≤ D ≤ 12. For example, the value of D may be in the range of 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.5, 12, or any two of the above values. By including FEC in the electrolyte and adjusting the value of D within the above range, the FEC and the silicon-containing negative electrode piece have good compatibility, forming a highly tough polymer protective layer crosslinked at the interface of the negative electrode during the formation process of the secondary battery. This improves the protective effect on the negative electrode piece, reduces gas generation during the cycle, and improves the cycle stability and low-temperature discharge characteristics of the secondary battery.

[0041] In one embodiment of the present invention, the electrolyte further comprises a third component, the third component comprising at least one of succinonitrile, glutaronitrile, methylglutaronitrile, adiponitrile, pimeronitrile, suberonitrile, azelanitrile, sebaconitrile, 1,2-bis(cyanoethoxy)ethane, 1,2,3-tris(2-cyanoethoxy)propane, 1,3,5-pentanetricarbonitride, and 1,3,6-hexanetricarbonitride, where E is the mass percentage of the third component relative to the total mass of the electrolyte, and E satisfies 0.5 ≤ E ≤ 6. For example, the value of E may be in the range of 0.5, 0.6, 0.8, 1, 1.2, 1.3, 1.5, 1.6, 1.8, 2, 2.2, 2.5, 2.8, 3, 3.2, 3.5, 3.8, 4, 4.2, 4.5, 4.7, 5, 5.2, 5.5, 5.8, 6, or any two of the above values. By including a third component in the electrolyte and adjusting the value of E within the above range, the third component is adsorbed onto the positive electrode interface, which is advantageous for improving the stability of the positive electrode interface, reducing side reactions between the positive electrode piece and the electrolyte, thereby improving the cycle characteristics and low-temperature discharge characteristics of the secondary battery.

[0042] In one embodiment of the present invention, the electrolytic solution further contains a fourth component, the fourth component contains at least one of ethylene sulfate, vinylene carbonate, 1,3 - propane sultone, and 1 - propene 1,3 - sultone. When the mass percentage of the fourth component is F% with respect to the total mass of the electrolytic solution, F satisfies 0.01 ≦ F ≦ 5. For example, the value of F may be 0.01, 0.03, 0.05, 0.07, 0.1, 0.15, 0.2, 0.25, 0.3, 0.4, 0.5, 0.6, 0.8, 1, 1.2, 1.5, 1.7, 1.8, 2, 2.2, 2.5, 2.6, 2.8, 3, 3.2, 3.3, 3.5, 3.8, 4, 4.2, 4.5, 4.6, 4.8, 5 or a range consisting of any two of the above numerical values. By including the fourth component in the electrolytic solution and adjusting the value of F within the above range, in the initial formation process of the secondary battery, it is involved in the formation of a solid electrolyte interface (SEI) film having reduction resistance, can further strengthen the interface protection of the silicon - containing negative electrode sheet, avoid excessive increase in the resistance of the electrolytic solution, thereby further improving the cycle stability of the secondary battery and maintaining the low - temperature discharge characteristics of the secondary battery.

[0043] In one embodiment of the present invention, the silicon - containing active material contains at least one of a silicon - oxygen composite material and a silicon - carbon composite material. Exemplarily, the silicon - oxygen composite material is SiOx where 0 < x ≦ 2, and the silicon - carbon composite material is SiC. Without being limited to any theory, by including the silicon - containing active material of the above types in the negative electrode sheet, the processing of the negative electrode slurry and the negative electrode sheet can be made simpler, and the energy density of the secondary battery can be improved, which is advantageous for simultaneously improving the cycle stability and low - temperature discharge characteristics of the secondary battery.

[0044] In the present invention, there are no particular limitations on the method for preparing the silicon-containing active material. For example, the method for preparing the silicon-containing active material may include, but is not limited to, the steps of dissolving a silicon material and lithium nitrate in a solvent, uniformly mixing them, drying to obtain a powder material, and then heat-treating the powder material in a carbon-containing gas to obtain the silicon-containing active material. Here, the drying temperature may be 80°C to 120°C, the heat treatment temperature 300°C to 800°C, the heating rate of the heat treatment 1°C / min to 10°C / min, the holding time of the heat treatment 0.5h to 6h, and the mass ratio of the silicon material to lithium nitrate (10 to 200):1. The silicon material may be a silicon-carbon material, a silicon-oxygen material, or a pre-lithium-treated silicon-oxygen material. The solvent may include, but is not limited to, at least one of ethanol, water, and acetone. The carbon-containing gas includes at least one of acetylene, methane, and propylene. The mass ratio of the powder material to the carbon-containing gas may be (20-100):1. In this invention, the mass percentage of silicon element in the silicon-containing active material can be adjusted by adjusting the mass ratio of the silicon material to lithium nitrate.

[0045] In one embodiment of the present invention, the electrolyte further comprises a nitrogen-containing lithium salt, the nitrogen-containing lithium salt comprising at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, and lithium nitrate, and when the mass percentage of the nitrogen-containing lithium salt is G% relative to the total mass of the electrolyte, G satisfies 0.1 ≤ G ≤ 7. For example, the value of G may be in the range of 0.1, 0.15, 0.2, 0.25, 0.3, 0.4, 0.5, 0.6, 0.8, 1, 1.2, 1.5, 1.7, 2, 2.2, 2.5, 2.8, 3, 3.3, 3.5, 3.8, 4, 4.2, 4.5, 4.8, 5, 5.2, 5.5, 5.7, 6, 6.3, 6.5, 6.8, 7, or any two of the above values. The electrolyte contains a nitrogen-containing lithium salt, and by adjusting the G value within the above range, it can have good solubility and dissociation ability, further ensuring the ion conductivity of the electrolyte. Furthermore, the nitrogen-containing lithium salt contributes to the formation of a stable electrolyte-electrode interface, thereby further improving the cycle stability and low-temperature discharge characteristics of the secondary battery.

[0046] In the present invention, fluoroethylene carbonate, the third component, the fourth component, and nitrogen-containing lithium salts within the above range can be used in any combination as long as the objective of the present invention is achieved.

[0047] In the present invention, the electrolyte further comprises an electrolyte salt and a non-aqueous solvent. In the present invention, the electrolyte salt is not particularly limited and should be any salt that can achieve the objectives of the present invention. For example, the electrolyte salt may include, but is not limited to, at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiC(SO2CF3)3, Li2SiF6, lithium bis(oxalato)borate (LiBOB), and lithium difluoroborate. In the present invention, the content of the electrolyte salt in the electrolyte is not particularly limited and should be any salt that can achieve the objectives of the present invention. For example, the mass percentage of the electrolyte salt relative to the mass of the electrolyte is 8% to 15%.

[0048] In the present invention, the non-aqueous solvent is not particularly limited and should be able to achieve the objectives of the present invention. For example, the non-aqueous solvent may include, but is not limited to, at least one of ether compounds and other organic solvents. The 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, and tetrahydrofuran. The other organic solvents may include, but are not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidine ketone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, and trioctyl phosphate. In the present invention, the content of the non-aqueous solvent in the electrolyte is not particularly limited and should be able to achieve the objectives of the present invention. For example, the mass percentage of the non-aqueous solvent relative to the total mass of the electrolyte is between 0% and 66%.

[0049] In one embodiment of the present invention, the electrolyte comprises a first component, a second component, an electrolyte salt, and a non-aqueous solvent. The mass percentages of the first component, the second component, and the electrolyte salt relative to the total mass of the electrolyte are as described above, and the mass percentage of the non-aqueous solvent is 0% to 66%. Since the electrolyte contains the first and second components, a secondary battery using the electrolyte of the present invention exhibits improved cycle stability and low-temperature discharge characteristics.

[0050] In one embodiment of the present invention, the electrolyte comprises a first component, a second component, fluoroethylene carbonate, an electrolyte salt, and a non-aqueous solvent. The mass percentages of the first component, the second component, fluoroethylene carbonate, and the electrolyte salt relative to the total mass of the electrolyte are as described above, and the mass percentage of the non-aqueous solvent is 0% to 64%. Because the electrolyte contains the first component, the second component, and fluoroethylene carbonate, a secondary battery using the electrolyte of the present invention exhibits further improved cycle stability and low-temperature discharge characteristics.

[0051] In one embodiment of the present invention, the electrolyte comprises a first component, a second component, a third component, an electrolyte salt, and a non-aqueous solvent. The mass percentages of the first component, the second component, the third component, and the electrolyte salt relative to the total mass of the electrolyte are as described above, and the mass percentage of the non-aqueous solvent is 0% to 65%. Since the electrolyte contains the first component, the second component, and the third component, a secondary battery using the electrolyte of the present invention exhibits further improved cycle stability and low-temperature discharge characteristics.

[0052] In one embodiment of the present invention, the electrolyte comprises a first component, a second component, a fourth component, an electrolyte salt, and a non-aqueous solvent. The mass percentages of the first component, the second component, the fourth component, and the electrolyte salt relative to the total mass of the electrolyte are as described above, and the mass percentage of the non-aqueous solvent is 0% to 65%. Since the electrolyte contains the first component, the second component, and the fourth component, a secondary battery using the electrolyte of the present invention exhibits further improved cycle stability and low-temperature discharge characteristics.

[0053] In one embodiment of the present invention, the electrolyte comprises a first component, a second component, a nitrogen-containing lithium salt, an electrolyte salt, and a non-aqueous solvent. The mass percentages of the first component, the second component, the nitrogen-containing lithium salt, and the electrolyte salt relative to the total mass of the electrolyte are as described above, and the mass percentage of the non-aqueous solvent is 0% to 65%. Because the electrolyte contains the first component, the second component, and the nitrogen-containing lithium salt, a secondary battery using the electrolyte of the present invention exhibits further improved cycle stability and low-temperature discharge characteristics.

[0054] In one embodiment of the present invention, the electrolyte comprises a first component, a second component, fluoroethylene carbonate, a third component, an electrolyte salt, and a non-aqueous solvent. The mass percentages of the first component, second component, fluoroethylene carbonate, third component, and electrolyte salt relative to the total mass of the electrolyte are as described above, and the mass percentage of the non-aqueous solvent is 0% to 63%. Because the electrolyte comprises a first component, a second component, fluoroethylene carbonate, and a third component, a secondary battery using the electrolyte of the present invention exhibits further improved cycle stability and low-temperature discharge characteristics.

[0055] In one embodiment of the present invention, the electrolyte comprises a first component, a second component, fluoroethylene carbonate, a fourth component, an electrolyte salt, and a non-aqueous solvent. The mass percentages of the first component, the second component, fluoroethylene carbonate, the fourth component, and the electrolyte salt relative to the total mass of the electrolyte are as described above, and the mass percentage of the non-aqueous solvent is 0% to 63%. Because the electrolyte comprises the first component, the second component, fluoroethylene carbonate, and the fourth component, a secondary battery using the electrolyte of the present invention exhibits further improved cycle stability and low-temperature discharge characteristics.

[0056] In one embodiment of the present invention, the electrolyte comprises a first component, a second component, fluoroethylene carbonate, a nitrogen-containing lithium salt, an electrolyte salt, and a non-aqueous solvent. The mass percentages of the first component, the second component, fluoroethylene carbonate, nitrogen-containing lithium salt, and electrolyte salt relative to the total mass of the electrolyte are as described above, and the mass percentage of the non-aqueous solvent is 0% to 63%. Because the electrolyte comprises a first component, a second component, fluoroethylene carbonate, and a nitrogen-containing lithium salt, a secondary battery using the electrolyte of the present invention exhibits further improved cycle stability and low-temperature discharge characteristics.

[0057] In one embodiment of the present invention, the electrolyte comprises a first component, a second component, a third component, a fourth component, an electrolyte salt, and a non-aqueous solvent. The mass percentages of the first component, the second component, the third component, the fourth component, and the electrolyte salt relative to the total mass of the electrolyte are as described above, and the mass percentage of the non-aqueous solvent is 0% to 65%. Because the electrolyte contains the first component, the second component, the third component, and the fourth component, a secondary battery using the electrolyte of the present invention exhibits further improved cycle stability and low-temperature discharge characteristics.

[0058] In one embodiment of the present invention, the electrolyte comprises a first component, a second component, a third component, a nitrogen-containing lithium salt, an electrolyte salt, and a non-aqueous solvent. The mass percentages of the first component, the second component, the third component, the nitrogen-containing lithium salt, and the electrolyte salt relative to the total mass of the electrolyte are as described above, and the mass percentage of the non-aqueous solvent is 0% to 65%. Because the electrolyte contains the first component, the second component, the third component, and a nitrogen-containing lithium salt, a secondary battery using the electrolyte of the present invention exhibits further improved cycle stability and low-temperature discharge characteristics.

[0059] In one embodiment of the present invention, the electrolyte comprises a first component, a second component, a fourth component, a nitrogen-containing lithium salt, an electrolyte salt, and a non-aqueous solvent. The mass percentages of the first component, the second component, the fourth component, the nitrogen-containing lithium salt, and the electrolyte salt relative to the total mass of the electrolyte are as described above, and the mass percentage of the non-aqueous solvent is 0% to 65%. Because the electrolyte contains the first component, the second component, the fourth component, and a nitrogen-containing lithium salt, a secondary battery using the electrolyte of the present invention exhibits further improved cycle stability and low-temperature discharge characteristics.

[0060] In one embodiment of the present invention, the electrolyte comprises a first component, a second component, fluoroethylene carbonate, a third component, a fourth component, an electrolyte salt, and a non-aqueous solvent. The mass percentages of the first component, the second component, fluoroethylene carbonate, the third component, the fourth component, and the electrolyte salt relative to the total mass of the electrolyte are as described above, and the mass percentage of the non-aqueous solvent is 0% to 63%. Because the electrolyte contains the first component, the second component, fluoroethylene carbonate, the third component, and the fourth component, a secondary battery using the electrolyte of the present invention exhibits further improved cycle stability and low-temperature discharge characteristics.

[0061] In one embodiment of the present invention, the electrolyte comprises a first component, a second component, fluoroethylene carbonate, a third component, a nitrogen-containing lithium salt, an electrolyte salt, and a non-aqueous solvent. The mass percentages of the first component, the second component, fluoroethylene carbonate, the third component, the nitrogen-containing lithium salt, and the electrolyte salt relative to the total mass of the electrolyte are as described above, and the mass percentage of the non-aqueous solvent is 0% to 63%. Because the electrolyte comprises a first component, a second component, fluoroethylene carbonate, a third component, and a nitrogen-containing lithium salt, a secondary battery using the electrolyte of the present invention exhibits further improved cycle stability and low-temperature discharge characteristics.

[0062] In one embodiment of the present invention, the electrolyte comprises a first component, a second component, fluoroethylene carbonate, a fourth component, a nitrogen-containing lithium salt, an electrolyte salt, and a non-aqueous solvent. The mass percentages of the first component, the second component, fluoroethylene carbonate, the fourth component, the nitrogen-containing lithium salt, and the electrolyte salt relative to the total mass of the electrolyte are as described above, and the mass percentage of the non-aqueous solvent is 0% to 63%. Because the electrolyte comprises a first component, a second component, fluoroethylene carbonate, a fourth component, and a nitrogen-containing lithium salt, a secondary battery using the electrolyte of the present invention exhibits further improved cycle stability and low-temperature discharge characteristics.

[0063] In one embodiment of the present invention, the electrolyte comprises a first component, a second component, a third component, a fourth component, a nitrogen-containing lithium salt, an electrolyte salt, and a non-aqueous solvent. The mass percentages of the first component, the second component, the third component, the fourth component, the nitrogen-containing lithium salt, and the electrolyte salt relative to the total mass of the electrolyte are as described above, and the mass percentage of the non-aqueous solvent is 0% to 65%. Because the electrolyte comprises a first component, a second component, a third component, a fourth component, and a nitrogen-containing lithium salt, a secondary battery using the electrolyte of the present invention exhibits further improved cycle stability and low-temperature discharge characteristics.

[0064] In one embodiment of the present invention, the electrolyte comprises a first component, a second component, fluoroethylene carbonate, a third component, a fourth component, a nitrogen-containing lithium salt, an electrolyte salt, and a non-aqueous solvent. The mass percentages of the first component, the second component, fluoroethylene carbonate, the third component, the fourth component, the nitrogen-containing lithium salt, and the electrolyte salt relative to the total mass of the electrolyte are as described above, and the mass percentage of the non-aqueous solvent is 0% to 63%. Because the electrolyte comprises a first component, a second component, fluoroethylene carbonate, a third component, a fourth component, and a nitrogen-containing lithium salt, a secondary battery using the electrolyte of the present invention exhibits further improved cycle stability and low-temperature discharge characteristics.

[0065] In the present invention, the negative electrode piece includes a negative electrode current collector and a negative electrode material layer provided on at least one surface of the negative electrode current collector. The phrase "the negative electrode material layer is provided on at least one surface of the negative electrode current collector" means that the negative electrode material layer may be provided on one surface of the negative electrode current collector in its thickness direction, or on both surfaces of the negative electrode current collector in its thickness direction. Here, "surface" may refer to the entire surface of the negative electrode current collector, or to a portion of the surface of the negative electrode current collector, and is not particularly limited as long as the objective of the present invention is achieved.

[0066] In the present invention, the negative electrode current collector is not particularly limited and only needs to be able to achieve the objectives of the present invention. For example, it may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foamed nickel, foamed copper, or a composite current collector. Exemplary examples of composite current collectors include lithium copper composite current collectors, carbon copper composite current collectors, nickel copper composite current collectors, titanium copper composite current collectors, and the like.

[0067] The negative electrode material layer may further contain other negative electrode active materials. In the present invention, the other negative electrode active materials are not particularly limited and should be able to achieve the objectives of the present invention. For example, the other negative electrode active materials may be natural graphite, artificial graphite, mesocarbon microbeads, hard carbon, soft carbon, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, or TiO2-Li4Ti5O with a spinel structure. 12The system may include, but is not limited to, at least one of the following: and Li-Al alloys.

[0068] In the present invention, the mass percentage of silicon element in the negative electrode material layer can be adjusted by adjusting the mass ratio of the silicon-containing active material to other negative electrode active materials.

[0069] In some embodiments of the present invention, the negative electrode material layer may further contain a conductive agent and a binder. In the present invention, there are no particular restrictions on the type of conductive agent and binder, as long as they can achieve the objectives of the present invention. 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, and conductive polymers, and the conductive carbon black may include, but is not limited to, at least one of acetylene black and Ketzelb black. The carbon nanotubes may include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The carbon fibers may include, but are not limited to, vapor-grown carbon fibers (VGCF) and / or carbon nanofibers. The metallic materials may include, but are not limited to, metal powders and / or metal fibers, and specifically, the metal may include, but is not limited to, at least one of copper, nickel, aluminum, and silver. The conductive polymer described above may, but is not limited to, at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, and polypyrrole. For example, the binder may, but is not limited to, at least one of polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyvinyl alcohol, carboxymethylcellulose, sodium carboxymethylcellulose, lithium carboxymethylcellulose, polyimide, polyamideimide, styrene-butadiene rubber, and polyvinylidene fluoride. In the present invention, there are no particular restrictions on the mass ratio of the negative electrode active material, the conductive agent, and the binder in the negative electrode material layer, and those skilled in the art can select them as needed, provided that the present invention can be achieved. The negative electrode material layer may further contain a thickening agent, and in the present invention, there are no particular restrictions on the content and type of the thickening agent, and commonly known types and content in the art may be used, provided that the objectives of the present invention can be achieved.

[0070] In the present invention, the thickness of the negative electrode material layer is not particularly limited and only needs to be such that the objective of the present invention is achieved. For example, the thickness of the negative electrode material layer is 30 μm to 120 μm. In the present invention, the thickness of the negative electrode current collector is not particularly limited and only needs to be such that the objective of the present invention is achieved. For example, the thickness of the negative electrode current collector is 4 μm to 15 μm.

[0071] Optionally, the negative electrode piece may further include a conductive layer, the conductive layer located between the negative electrode current collector and the negative electrode material layer. In the present invention, the composition of the conductive layer is not particularly limited and may be a conventional conductive layer in the art. For example, the conductive layer may include a conductive agent and a binder. In the present invention, the conductive agent and binder in the conductive layer are not particularly limited and may be, for example, at least one of the above-mentioned conductive agent and binder.

[0072] In the present invention, the positive electrode piece includes a positive electrode current collector and a positive electrode material layer provided on at least one surface of the positive electrode current collector. The phrase "positive electrode material layer provided on at least one surface of the positive electrode current collector" means that the positive electrode material layer may be provided on one surface of the positive electrode current collector in its thickness direction, or on both surfaces of the positive electrode current collector in its thickness direction. Here, "surface" may refer to the entire surface of the positive electrode current collector, or to a part of the surface of the positive electrode current collector, and is not particularly limited as long as the objective of the present invention is achieved.

[0073] In the present invention, the positive electrode current collector is not particularly limited and only needs to achieve the objectives of the present invention. For example, it may include aluminum foil, aluminum alloy foil, or composite current collectors (e.g., aluminum-carbon composite current collectors).

[0074] The positive electrode material layer contains a positive electrode active material. In the present invention, the positive electrode active material is not particularly limited and only needs to be able to achieve the objectives of the present invention. For example, the positive electrode active material may contain, but is not limited to, at least one of lithium nickel cobalt manganese oxide (e.g., NCM811, NCM622, NCM523, NCM111), lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based material, lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium iron manganese phosphate, and lithium titanate.

[0075] The positive electrode material layer may further contain a conductive agent and a binder. In the present invention, there are no particular restrictions on the types of conductive agents and binders, as long as the objectives of the present invention can be achieved, for example, at least one of the above-mentioned conductive agents and binders may be used. In the present invention, there are no particular restrictions on the mass ratio of the positive electrode active material, the conductive agent and the binder in the positive electrode material layer, and those skilled in the art can select them as needed, as long as the present invention can be achieved.

[0076] In this invention, there are no particular restrictions on the thickness of the positive electrode current collector and the positive electrode material layer, as long as the objective of the present invention can be achieved. For example, the thickness of the positive electrode current collector is 5 μm to 20 μm, and the thickness of the positive electrode material layer is 30 μm to 120 μm.

[0077] Optionally, the positive electrode piece may further include a conductive layer located between the positive electrode current collector and the positive electrode material layer. The composition of the conductive layer is not particularly limited and may be a conventional conductive layer in the art. The conductive layer includes a conductive agent and a binder. In the present invention, the conductive agent and binder in the conductive layer are not particularly limited and may, for example, be at least one of the above-mentioned conductive agent and binder.

[0078] In the present invention, the secondary battery further includes a separator. In the present invention, the separator is not particularly limited and should be able to achieve the objectives of the present invention. For example, the material of the separator 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, and aramid. The type of separator may include at least one of woven film, nonwoven film, microporous film, composite film, rolled film, and spinning film.

[0079] In some embodiments of the present invention, the separator may include a base layer and a surface treatment layer. The base layer may be a nonwoven fabric, film, or composite film having a porous structure, and the material of the base layer may include at least one of polyethylene, polypropylene, polyethylene terephthalate, and 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 film may be used.

[0080] Optionally, a surface treatment layer is provided on at least one surface of the base layer, and the surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic material.

[0081] In some embodiments of the present invention, the inorganic layer comprises inorganic particles and a binder. In the present invention, the inorganic particles are not particularly limited and may include, for example, 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 hydrogen oxide, calcium hydrogen oxide, and barium sulfate. In the present invention, the binder is not particularly limited and may include, for example, at least one of the above binders. In some embodiments of the present invention, the polymer layer comprises a polymer, the polymer material of which includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene).

[0082] In the present invention, the thickness of the separator is not particularly limited, and it is sufficient as long as the objective of the present invention is achieved. For example, the thickness of the separator may be 3 μm to 30 μm.

[0083] In the present invention, the secondary battery further includes a housing for housing a positive electrode piece, a separator, a negative electrode piece, and an electrolyte, as well as other components known in the field of secondary batteries. In the present invention, the above-mentioned other components are not limited. In the present invention, the housing is not particularly limited and may be a housing known in the art as long as it can achieve the objectives of the present invention. For example, the housing may be a rigid housing or a flexible housing. The material of the rigid housing may be metal. In the present invention, the type of metal is not limited and may be a rigid metal housing known in the art as long as it can achieve the objectives of the present invention. The flexible housing may be a metal-plastic laminate film such as an aluminum-plastic laminate film or a steel-plastic laminate film.

[0084] The preparation process for the secondary battery of the present invention is well known to those skilled in the art and is not particularly limited. The preparation process for the secondary battery may include, for example, the steps of stacking a positive electrode piece, a separator, and a negative electrode piece in this order, winding and folding them as necessary to obtain a wound electrode assembly, placing the electrode assembly in a housing, injecting electrolyte into the housing and sealing it to obtain a secondary battery, or stacking a positive electrode piece, a separator, and a negative electrode piece in this order, then fixing the four corners of the entire stacked structure with adhesive tape to obtain a stacked electrode assembly, placing the electrode assembly in a housing, injecting electrolyte into the housing and sealing it to obtain a secondary battery, but is not limited to these steps. Furthermore, in order to prevent pressure rise inside the secondary battery and overcharging and discharging, an overcurrent prevention element, lead plates, etc. may be provided in the housing as necessary.

[0085] In the present invention, there are no particular restrictions on the type of secondary battery, and any device for generating an electrochemical reaction may be included. For example, the secondary battery may include, but is not limited to, lithium metal secondary batteries, lithium-ion batteries, sodium-ion batteries, lithium polymer secondary batteries, and lithium-ion polymer secondary batteries.

[0086] A second aspect of the present invention provides an electronic device including a secondary battery described in any one of the above embodiments. The secondary battery provided in the present invention has good cycle stability and low-temperature discharge characteristics, and therefore the electronic device of the present invention has a relatively long service life.

[0087] In the present invention, the type of electronic device is not limited and may be any electronic device known in the prior art. In some embodiments of the present invention, the electronic device may include, but is not limited to, a notebook computer, a pen-input computer, a mobile computer, an e-book player, a mobile phone, a portable facsimile, a portable copier, a portable printer, a stereo headset, a video recorder, an LCD television, a portable cleaner, a portable CD player, a MiniDisc, a transceiver, an electronic notebook, a calculator, a memory card, a portable tape recorder, a radio, a backup power supply, a motor, an automobile, a motorcycle, an electric assist bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a strobe, a camera, a large household storage battery, and a lithium-ion capacitor. Examples

[0088] The embodiments of the present invention will be described in more detail below with reference to examples and comparative examples. Each measurement and evaluation is performed as follows. Unless otherwise specified, "parts" and "%" are based on mass.

[0089] Measurement method and equipment Measurement of the mass percentage of silicon element A lithium-ion battery discharged to 3.0V at 0.5C was disassembled, and a negative electrode piece was obtained. The negative electrode piece was immersed in dimethyl carbonate (DMC) for 20 minutes, and then washed once each with DMC and acetone in that order. The negative electrode piece was then placed in an oven and dried at 80°C for 12 hours to obtain a negative electrode piece. Subsequently, the negative electrode piece was placed in a vacuum oven and dried at 100°C for 24 hours. After scraping the negative electrode material layer from the negative electrode piece with a blade, the mass percentage of silicon element in the negative electrode material layer was measured using an ICP (Inductively Coupled Plasma) analyzer.

[0090] Measurement of room temperature cycling characteristics Under conditions of 25°C, a lithium-ion battery was charged with a constant current of 1.2C to 4.25V, then charged with a constant voltage of 0.7C at 4.25V, further charged with a constant current of 0.7C to 4.5V, then charged with a constant voltage of 0.05C at 4.5V, left to stand for 5 minutes, and then discharged with a constant current of 0.5C to 3.0V. This was considered the first cycle, and the discharge capacity was recorded. The lithium-ion battery was cycled multiple times according to the above conditions, and the discharge capacity of the lithium-ion battery at the end of each cycle was measured. The initial discharge capacity was set as 100%, and the charge-discharge cycle was repeated until the discharge capacity retention rate decreased to 80% of the initial discharge capacity, at which point the measurement was stopped. The number of cycles at this point was recorded and used as an index to evaluate the room-temperature cycle capacity retention rate of the lithium-ion battery. Discharge capacity retention rate = (Capacity after each discharge / Initial discharge capacity) × 100%.

[0091] Measurement of low-temperature discharge characteristics Under conditions of 25°C, the lithium-ion battery was charged with a constant current of 0.5C to a voltage of 4.5V, and then charged with a constant voltage of 0.025C at 4.5V. Under conditions of 25°C, the battery was discharged with a constant current of 0.2C to a voltage of 3.0V, and the discharge capacity was recorded as C0. Subsequently, under conditions of 25°C, the lithium-ion battery was charged with a constant current of 0.5C to a voltage of 4.5V, and then charged with a constant voltage of 0.025C at 4.5V. Under conditions of -20°C, the battery was discharged with a constant current of 0.2C to a voltage of 3.0V, and the discharge capacity was recorded as C1.

[0092] Low temperature discharge capacity maintenance rate = C1 / C0×100%.

[0093] Example 1-1 <Preparation of silicon-containing active material> A silicon-oxygen material, SiO2, and lithium nitrate were dispersed in ethanol, uniformly mixed, and then dried to obtain a powder material. The powder material was then heat-treated in methane to obtain a silicon-containing active material with amorphous carbon on its surface. The drying temperature was 100°C, the heat treatment temperature was 450°C, the heating rate was 5°C / min, the heat treatment holding time was 3.2 hours, the mass ratio of SiO2 to lithium nitrate was 36:1, and the mass ratio of the powder material to methane was 30:1. The mass percentage of silicon in the silicon-containing active material was 65%.

[0094] <Preparation of the negative electrode piece> The silicon-containing active material, artificial graphite, the conductive agents carbon nanotubes (CNT) and conductive carbon black (Super P), and the binder lithium polyacrylate (PAA-Li) were mixed according to a mass ratio of 1.54:88.46:1.5:0.5:8. Deionized water was then added as a solvent to prepare a negative electrode slurry with a solid content of 54%, and the slurry was stirred in a vacuum stirrer until it was uniform. The negative electrode slurry was uniformly coated onto one surface of a copper foil negative electrode current collector with a thickness of 8 μm, and dried at 85°C to obtain a negative electrode piece with a single-sided coating and a negative electrode material layer thickness of 100 μm. Subsequently, the above steps were repeated on the other surface of this negative electrode piece to obtain a negative electrode piece with a double-sided coating. After coating was completed, the negative electrode piece was cold-pressed and cut to a size of 76 mm × 851 mm, and the compressed density of the negative electrode piece was 1.4 g / cm³. 3 That was the case.

[0095] <Preparation of positive electrode piece> Lithium cobalt oxide (LiCoO2), the positive electrode active material, conductive carbon black (Super P), the conductive agent, and polyvinylidene fluoride (PVDF), the binder, were mixed in a mass ratio of 97:1.4:1.6. N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solid content of 75%, and the slurry was stirred in a vacuum stirrer until the positive electrode slurry was uniform. The positive electrode slurry was uniformly coated onto one surface of an aluminum foil positive electrode current collector with a thickness of 10 μm, and dried at 85°C to obtain a positive electrode piece with a positive electrode material layer thickness of 90 μm and the positive electrode active material coated on one side. Subsequently, the above steps were repeated on the other surface of this positive electrode piece to obtain a positive electrode piece with the positive electrode active material coated on both sides. After coating was completed, the positive electrode piece was cold-pressed and cut to a size of 74 mm × 867 mm, and the compressed density of the positive electrode piece was 4 g / cm³. 3 That was the case.

[0096] <Preparation of Electrolyte> In an argon gas-atmosphered glove box with a water content of less than 10 ppm, methyl ethyl carbonate was used as a non-aqueous solvent. Subsequently, the first component, compound I-3, the second component, propyl propionate, and the electrolyte salt, LiPF6, were added to the non-aqueous solvent and mixed uniformly to obtain an electrolyte. Of the total mass of the electrolyte, the mass percentage B% of the first component was 40%, the mass percentage C% of the second component was 8%, the mass percentage of the electrolyte salt was 12.5%, and the remainder was the non-aqueous solvent.

[0097] <Separator> A 5 μm thick porous polyethylene (PE) membrane (provided by Shanghai Energy New Materials Technology Co., Ltd.) was used.

[0098] <Preparation of Lithium-ion Batteries> The positive electrode piece, separator, and negative electrode piece prepared above were sequentially stacked and wound to obtain an electrode assembly, with the separator interposed between the positive electrode piece and the negative electrode piece to act as an isolation. After welding the tabs, the electrode assembly was placed in an aluminum-plastic laminate film packaging enclosure, placed in a vacuum oven at 85°C, dried for 12 hours to remove moisture, injected the electrolyte prepared above, and obtained a lithium-ion battery through processes such as vacuum packaging, standing, formation (constant current charging at 0.02C up to 3.5V, and then constant current charging at 0.1C up to 3.9V), molding, and capacity measurement.

[0099] Examples 1-2 to 1-5 In the preparation of the negative electrode piece, the procedure was the same as in Example 1-1, except that the mass ratio of silicon-containing active material to artificial graphite was adjusted so that the mass percentage A% of silicon element in the negative electrode material layer was set to the value shown in Table 1.

[0100] Examples 1-6 to 1-19 In the <Preparation of Electrolyte>, the type and mass percentage B% of the first component and the type and mass percentage C% of the second component were adjusted according to Table 1. The procedure was the same as in Examples 1-3, except that the mass percentage of the non-aqueous solvent changed accordingly, while the mass percentage of the electrolyte salt remained unchanged.

[0101] Examples 1-20 In the preparation of the negative electrode piece, the procedure was the same as in Examples 1-6, except that the mass ratio of silicon-containing active material to artificial graphite was adjusted so that the mass percentage A% of silicon element in the negative electrode material layer was set to the value shown in Table 1.

[0102] Examples 1-21 In the preparation of the silicon-containing active material, the procedure was the same as in Examples 1-3, except that the type of silicon material was changed to a silicon-carbon material (SiC), and the mass ratio of the silicon material to lithium nitrate was adjusted to determine the type of silicon-containing active material shown in Table 1.

[0103] Examples 2-1 to 2-38 In the preparation of the electrolyte, fluoroethylene carbonate, the third component, the fourth component, and a nitrogen-containing lithium salt were added according to Table 2, and the mass percentage of fluoroethylene carbonate (D%), the type and mass percentage of the third component (E%), the type and mass percentage of the fourth component (F%), and the type and mass percentage of the nitrogen-containing lithium salt (G%) were adjusted according to Table 2. The process was the same as in Examples 1-3, except that the mass percentage of the non-aqueous solvent changed accordingly, while the mass percentages of the first component, the second component, and the electrolyte salt remained unchanged.

[0104] Comparative Examples 1-1 to 1-13 The procedure was the same as in Example 1-1, except that the relevant preparation parameters were adjusted according to Table 1. When silicon element was not present, the silicon-containing active material of the negative electrode active material was replaced with artificial graphite. When the mass percentage B% of the first component and / or the mass percentage C% of the second component changed, the mass percentage of the non-aqueous solvent changed accordingly, while the mass percentage of the electrolyte salt did not change. By adjusting the mass ratio of the silicon-containing active material and artificial graphite in <Preparation of negative electrode piece>, the mass percentage A% of silicon element in the negative electrode material layer was set to the value shown in Table 1.

[0105] [Table 1]

[0106] Note: In Table 1, " / " indicates that there is no corresponding adjustment parameter.

[0107] [Table 2]

[0108] Note: In Table 2, " / " indicates that there is no corresponding adjustment parameter.

[0109] As can be seen from Examples 1-1 to 1-21 and Comparative Examples 1-1 to 1-13, by including a silicon-containing active material in the negative electrode piece, adjusting the silicon element content A in the negative electrode material layer to within the range of the present invention, and including a first and second component in the electrolyte, and adjusting the values ​​of B and C / B to within the range of the present invention, it is confirmed that the lithium-ion battery simultaneously has a relatively high number of room-temperature cycles and a low-temperature discharge capacity retention rate, and that the lithium-ion battery simultaneously has good cycle stability and low-temperature discharge characteristics.

[0110] The value of A / (B+C) typically affects the cycle stability and low-temperature discharge characteristics of lithium-ion batteries. As can be seen from Examples 1-1 to 1-6 and Example 1-20, by adjusting the value of A / (B+C) within the range of the present invention, it is confirmed that lithium-ion batteries simultaneously have a relatively high number of room-temperature cycles and a low-temperature discharge capacity retention rate, and that lithium-ion batteries simultaneously have good cycle stability and low-temperature discharge characteristics.

[0111] The types of the first component, second component, and silicon-containing active material typically affect the cycle stability and low-temperature discharge characteristics of lithium-ion batteries. As can be seen from Examples 1-3, 1-15 to 1-19, and 21, by using lithium-ion batteries in which the types of the first component, second component, and silicon-containing active material are within the scope of the present invention, it is confirmed that the lithium-ion battery simultaneously has a relatively high number of room-temperature cycles and a low-temperature discharge capacity retention rate, and thus possesses good cycle stability and low-temperature discharge characteristics.

[0112] The fluoroethylene carbonate content typically affects the cycle stability and low-temperature discharge characteristics of lithium-ion batteries. As can be seen from Examples 1-3 and 2-1 to 2-5, when the electrolyte contains fluoroethylene carbonate within the content range of the present invention, the lithium-ion battery has a higher number of room-temperature cycles and a lower low-temperature discharge capacity retention rate, and simultaneously exhibits better cycle stability and low-temperature discharge characteristics.

[0113] The type and content of the third component, the type and content of the fourth component, and the type and content of the nitrogen-containing lithium salt typically affect the cycle stability and low-temperature discharge characteristics of lithium-ion batteries. As can be seen from Examples 1-3 and 2-6 to 2-28, when the electrolyte contains the third component, the fourth component, or a nitrogen-containing lithium salt within the type and content range of the present invention, the lithium-ion battery simultaneously exhibits a higher number of room-temperature cycles and a lower low-temperature discharge capacity retention rate, and the lithium-ion battery simultaneously exhibits better cycle stability and low-temperature discharge characteristics.

[0114] Different types of electrolytes typically affect the cycle stability and low-temperature discharge characteristics of lithium-ion batteries. As can be seen from Examples 1-3 and 2-1 to 2-38, selecting an electrolyte that combines the fluoroethylene carbonate, third component, fourth component, and nitrogen-containing lithium salt of the present invention can further improve the number of room-temperature cycles and the low-temperature discharge capacity retention rate of lithium-ion batteries, and it has been confirmed that the cycle stability and low-temperature discharge characteristics of lithium-ion batteries are further improved.

[0115] In this specification, relational terms such as "First" and "Second" are used to distinguish one entity or operation from another, and do not necessarily require or imply any such relationship or order between these entities or operations. Furthermore, the terms "includes," "has," or any variation thereof are intended to refer to non-exclusive inclusion, so that a process, method, or article that includes a set of elements includes not only those elements but also other elements not explicitly enumerated or elements specific to such process, method, or article.

[0116] Elements connected by the terms "one of," "one of," "one of," or other similar terms mean any one of the listed elements. For example, "one of A and B" means A only or B only. Also, for example, "one of A, B, and C" means A only, B only, or C only. Elements connected by the terms "at least one of," "at least one of," "at least one of," or other similar terms mean any combination of the listed elements. For example, "at least one of A and B" means A only, B only, or a combination of A and B. Also, for example, "at least one of A, B, and C" means A only, B only, C only, a combination of A and B, a combination of A and C, a combination of B and C, or a combination of A, B, and C.

[0117] Each example in this specification is described in a related manner, and identical or similar parts of each example may be referenced to one another. Each example focuses on explaining the differences from the other examples.

[0118] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Any modifications, equivalent substitutions, improvements, etc., made within the scope of the spirit and principles of this application should be included within the scope of protection of the present invention.

Claims

1. A secondary battery comprising a positive electrode piece, a negative electrode piece, a separator, and an electrolyte, The aforementioned negative electrode piece includes a negative electrode material layer, The aforementioned negative electrode material layer contains a silicon-containing active material. The aforementioned silicon-containing active material contains the element silicon. When the mass percentage of the silicon element is A% relative to the total mass of the negative electrode material layer, A satisfies 1 ≤ A ≤ 20. The electrolyte comprises a first component and a second component, The first component comprises at least one of the compounds represented by formula I and the compounds represented by formula II. 【Chemistry 1】 Here, R １１ and R １２ Each of these is independently a fluorine-substituted or unsubstituted C1-C10 alkyl group, and R １１ and R １２ At least one of them is substituted with fluorine, R ２１ and R ２２ Each of these is independently a fluorine-substituted or unsubstituted C1-C10 alkyl group, and R ２１ and R ２２ At least one of them is substituted with fluorine, The second component comprises at least one of ethyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, dimethyl carbonate, and diethyl carbonate. A secondary battery in which, with respect to the total mass of the electrolyte, the mass percentage of the first component is B% and the mass percentage of the second component is C%, such that B and C satisfy 25 ≤ B ≤ 70 and 0.07 ≤ C / B ≤ 1.

2. A is a secondary battery according to claim 1, satisfying 3 ≤ A ≤ 15.

3. The aforementioned secondary battery is a) B satisfies 30 ≤ B ≤ 60, b) B and C satisfy 0.1 ≤ C / B ≤ 0.9, A secondary battery according to claim 1, satisfying at least one of the following conditions.

4. The secondary battery according to claim 1, wherein A, B, and C satisfy 0.01 ≤ A / (B + C) ≤ 0.

5.

5. The compound represented by the above formula I is 【Chemistry 2】 The secondary battery according to claim 1, comprising at least one of the following.

6. The compound represented by the above formula II is 【Transformation 3】 The secondary battery according to claim 1, comprising at least one of the following.

7. The electrolyte further contains fluoroethylene carbonate, The secondary battery according to any one of claims 1 to 6, wherein when the mass percentage of the fluoroethylene carbonate is D% with respect to the total mass of the electrolyte, D satisfies 2 ≤ D ≤ 12.

8. The electrolyte further comprises a third component, The third component includes at least one of succinonitrile, glutalonitrile, methylglutalonitrile, adiponitrile, pimelonitrile, suberonitrile, azeranitrile, sebaconitrile, 1,2-bis(cyanoethoxy)ethane, 1,2,3-tris(2-cyanoethoxy)propane, 1,3,5-pentanetricarbonitride and 1,3,6-hexanetricarbonitride, The secondary battery according to any one of claims 1 to 6, wherein when the mass percentage of the third component is E% with respect to the total mass of the electrolyte, E satisfies 0.5 ≤ E ≤ 6.

9. The electrolyte further comprises a fourth component, The fourth component comprises at least one of ethylene sulfate, vinylene carbonate, 1,3-propanesultone, and 1-propene-1,3-sultone. The secondary battery according to any one of claims 1 to 6, wherein, when the mass percentage of the fourth component is F% with respect to the total mass of the electrolyte, F satisfies 0.01 ≤ F ≤ 5.

10. The secondary battery according to any one of claims 1 to 6, wherein the silicon-containing active material comprises at least one of a silicon-oxygen composite material and a silicon-carbon composite material.

11. The electrolyte further contains a nitrogen-containing lithium salt, The nitrogen-containing lithium salt comprises at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, and lithium nitrate. The secondary battery according to any one of claims 1 to 6, wherein when the mass percentage of the nitrogen-containing lithium salt is G% relative to the total mass of the electrolyte, G satisfies 0.1 ≤ G ≤ 7.

12. An electronic device comprising a secondary battery according to any one of claims 1 to 11.

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