Secondary batteries and electronic devices containing them

Abstract

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 the element silicon, and the mass percentage of the element silicon is C% based on the total mass of the negative electrode material layer, where 1 ≤ C ≤ 20. The electrolyte comprises a first component and a second component, (1) the first component is a boron-containing lithium salt, and the mass percentage of the first component is B% based on the total mass of the electrolyte, where 0.1 ≤ B ≤ 5, and (2) the second component comprises at least one of a compound represented by formula I and a compound represented by formula II, and the mass percentage of the second component is A% based on the total mass of the electrolyte, where 25 ≤ A ≤ 70. The secondary battery of the present invention has good high-temperature, high-voltage cycle stability.

Description

[Technical Field]

[0001] This application claims priority to the Chinese patent application filed on May 31, 2024, with the Intellectual Property Administration of China, application number 202410708509.5, and titled "Secondary Battery and Electronic Device Including the Same." All contents of the said Chinese patent application are incorporated herein by reference.

[0002] This invention relates to the field of electrochemistry, 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 plants due to their high energy density, high power density, low self-discharge, lack of memory effect, and long cycle life. As the range of applications for lithium-ion batteries continues to expand, their use cases are becoming more diverse, and the market is placing higher demands on the electrochemical performance of lithium-ion batteries. [Overview of the Initiative]

[0004] The present invention aims to provide a secondary battery and an electronic device including the same in order to improve the high-temperature, high-voltage cycle stability of secondary batteries. Specific technical proposals are as follows.

[0005] A first aspect of the present invention is a secondary battery, the secondary battery including a positive electrode sheet, a negative electrode sheet, a separator, and an electrolytic solution, the negative electrode sheet including a negative electrode material layer, the negative electrode material layer including a silicon-containing active material, the silicon-containing active material including a silicon element, and based on the total mass of the negative electrode material layer, the mass percentage of the silicon element being C%, where 1 ≦ C ≦ 20, the electrolytic solution including a first component and a second component, (1) the first component being a boron-containing lithium salt, the boron-containing lithium salt including at least one of lithium tetrafluoroborate, lithium difluorooxalate borate, lithium bisoxalate borate, lithium difluoroborate, lithium tetracyano borate, lithium tetra(trifluoromethyl) borate, lithium dicyanooxalate borate, lithium tetramethoxy borate, lithium tetraethoxy borate, lithium perfluorotertiarybutoxy trifluoroborate, lithium bis(difluorophosphonooxy) difluoroborate, pentafluoroethyl trifluoroborate, methoxytricyano borate, and lithium bis(trifluoroborate) bis(sulfate), and based on the total mass of the electrolytic solution, the mass percentage of the first component being B%, where 0.1 ≦ B ≦ 5, (2) the second component including at least one of a compound represented by formula I and a compound represented by formula II,

Chemical formula

[0006] 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 controlling the values ​​of A, B, and C within the above range, good protection is formed for the positive electrode and the negative electrode, and the synergistic effect of the first component and the second component is exerted, thereby providing the secondary battery with good high-temperature, high-voltage cycle stability.

[0007] In some embodiments, 0.01 ≤ B / A ≤ 0.12. By controlling the value of B / A within the above range, the synergistic effect of the first and second components can be better realized, and as a result, the high-temperature, high-voltage cycle stability of the secondary battery can be further improved.

[0008] In some embodiments, 0.01 ≤ B / C ≤ 3. By controlling the B / C value within this range, the protective effect on the positive and negative electrodes can be further improved, and the high-temperature, high-voltage cycle stability of the secondary battery can be further enhanced.

[0009] In some embodiments, 1 ≤ C ≤ 15. By controlling the value of C within this range, the high-temperature, high-voltage cycle stability of the secondary battery can be further improved.

[0010] In some embodiments, 0.5 ≤ B ≤ 3. By controlling the value of B within this range, the high-temperature, high-voltage cycle stability of the secondary battery can be further improved.

[0011] In some embodiments, 40 ≤ A ≤ 70. By controlling the value of A within the above range, the high-temperature, high-voltage cycle stability of the secondary battery can be further improved.

[0012] In some embodiments, the compound represented by the formula I includes at least one of the compounds represented by the following formulas I-1 to I-25.

Chemical formula

[0013] The electrolyte containing the second component within the above range can participate in the formation of a CEI film with better stability, improve the protective effect on the positive electrode, and as a result, further improve the high-temperature and high-voltage cycle stability of the secondary battery.

[0014] In some embodiments, the compound represented by the formula II includes at least one of the compounds represented by the following formulas II-1 to II-20.

Chemical formula

[0015] The electrolyte containing the second component within the above range can participate in the formation of a CEI film with better stability, improve the protective effect on the positive electrode, and as a result, further improve the high-temperature and high-voltage cycle stability of the secondary battery.

[0016] In some embodiments, the electrolyte further includes fluoroethylene carbonate, and based on the total mass of the electrolyte, the mass percentage of the fluoroethylene carbonate is D%, and 0.05 ≤ B / D ≤ 1.5. By including fluoroethylene carbonate in the electrolyte and controlling the value of B / D within the above range, the protective effect on the interface of the silicon-containing negative electrode can be improved, and the amount of cycle gas generation can be reduced. As a result, the high-temperature and high-voltage cycle stability of the secondary battery can be improved.

[0017] In some embodiments, the electrolyte further contains lithium difluorophosphate, and based on the total mass of the electrolyte, the mass percentage of lithium difluorophosphate is E%, where 0.1 ≦ E ≦ 5. By including lithium difluorophosphate in the electrolyte and controlling the value of E within the above range, lithium difluorophosphate can suppress side reactions between the positive and negative electrodes and the electrolyte, reduce the interfacial resistance during different charge states and long cycle processes, form a stable interfacial film on the surface of the positive electrode, and effectively suppress the oxidative decomposition of the electrolyte. As a result, the high-temperature and high-voltage cycle stability of the secondary battery can be improved.

[0018] In some embodiments, the electrolyte further contains fluoropyridine, and based on the total mass of the electrolyte, the mass percentage of fluoropyridine is F%, where 0.01 ≦ F ≦ 2. By including fluoropyridine in the electrolyte and controlling the value of F within the above range, the high-temperature and high-voltage cycle stability of the secondary battery can be further improved.

[0019] In some embodiments, the electrolyte further contains a third component, and the third component includes adiponitrile and at least one of vinylene carbonate, ethylene sulfate, 1,3-propane sultone, and propenyl-1,3-propane sultone. Based on the total mass of the electrolyte, the mass percentage of the third component is G%, where 0.1 ≦ G ≦ 8. By including the third component in the electrolyte and controlling the value of G within the above range, the protective ability against the positive electrode can be improved, and the protection of the interface of the silicon-containing negative electrode can be strengthened. As a result, the high-temperature and high-voltage cycle stability of the secondary battery can be improved.

[0020] In some embodiments, 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 improving the high-temperature and high-voltage cycle stability of the secondary battery.

[0021] A second aspect of the present invention provides an electronic device including a secondary battery in any of the embodiments described above. As a result, the electronic device of the present invention has a long service life.

[0022] 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, the mass percentage of silicon element is C% based on the total mass of the negative electrode material layer, and 1 ≤ C ≤ 20, and the electrolyte comprises a first component and a second component, (1) the first component is a boron-containing lithium salt, the mass percentage of the first component is B% based on the total mass of the electrolyte, and 0.1 ≤ B ≤ 5, and (2) the second component comprises at least one of a compound represented by formula I and a compound represented by formula II, the mass percentage of the second component is A% based on the total mass of the electrolyte, and 25 ≤ A ≤ 70, and provides a secondary battery and an electronic device including the same. 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 controlling the values ​​of A, B, and C within the above range, good protection can be formed for the positive and negative electrodes, and a synergistic effect can be exerted between the first component and the second component. As a result, the secondary battery can be given good high-temperature, high-voltage cycle stability.

[0023] Of course, it is not necessary to achieve all of the above-mentioned advantages simultaneously by implementing any of the products or methods of the present invention. [Modes for carrying out the invention]

[0024] The following describes the technical concepts in the embodiments of the present invention clearly and completely. Clearly, the embodiments described are only a part of the embodiments of the present invention, not all embodiments. All other embodiments that can be obtained by those skilled in the art based on the present invention are included within the scope of protection of the present invention.

[0025] In the specific embodiments of the present invention, a lithium-ion battery is used as an example of a secondary battery to explain the present invention, but the secondary battery of the present invention is not limited to a lithium-ion battery. Specific technical ideas are as follows.

[0026] 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 elements, and the mass percentage of silicon elements is C% based on the total mass of the negative electrode material layer, and 1 ≤ C ≤ 20. For example, the value of C is 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 within the range of any two of the above values. The electrolyte comprises a first component and a second component. The first component is a boron-containing lithium salt, which includes at least one of the following: lithium tetrafluoroborate (LiBF4), lithium difluorooxalate borate (LiDFOB), lithium bisoxalate borate (LiBOB), lithium difluoroborate, lithium tetracyanoborate (LiTCB), lithium tetra(trifluoromethyl)borate, lithium dicyanooxalate borate, lithium tetramethoxyborate, lithium tetraethoxyborate, lithium perfluorotertiarybutoxytrifluoroborate, lithium bis(difluorophosphonooxy)difluoroborate, lithium pentafluoroethyltrifluoroborate, lithium methoxytricyanoborate, and lithium bis(trifluoroborate)bis(sulfate). The mass percentage of the first component is B% based on the total mass of the electrolyte, and 0.1 ≤ B ≤ 5. For example, the value of B may be 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 it may be within the range of any two of the above values. The second component includes at least one compound represented by formula I and one represented by formula II. [ka] Here, R 11and R 12 These are, independently, fluorine-substituted or unsubstituted C1-C 10 It is an alkyl group, R 11 and R 12 At least one of them is substituted with fluorine, R 21 and R 22 These are, independently, fluorine-substituted or unsubstituted C1-C 10 It is an alkyl group, R 21 and R 22 At least one of these is substituted with fluorine. The mass percentage of the second component is A% based on the total mass of the electrolyte, and 25 ≤ A ≤ 70. For example, the value of A may be 25, 27, 28, 30, 32, 33, 35, 36, 38, 40, 42, 45, 48, 50, 52, 55, 58, 60, 62, 65, 68, 70, or within the range of any two of the above values. In this invention, "high temperature" means a temperature of 45°C or higher, and "high voltage" or "high voltage" means a voltage between the positive and negative electrodes of 4.2V or higher.

[0027] The inventors have found the following: If the value of C is too large, for example, greater than 20, the reaction at the negative electrode-electrolyte interface becomes vigorous, which is detrimental to improving the high-temperature, high-voltage cycle stability of the secondary battery. If the value of B is too small, for example less than 0.1, it is insufficient to improve the high-temperature, high-voltage cycle stability of the secondary battery. If the value of B is too large, for example greater than 5, the first component continues to react and consume lithium ions, resulting in a thicker interfacial film and increased resistance, which is detrimental to improving the high-temperature, high-voltage cycle stability of the secondary battery. If the value of A is too small, for example less than 25, it is difficult to effectively protect the positive electrode interface, the lithium ion desorption energy barrier is high, and it is difficult to improve the high-temperature, high-voltage cycle stability of the secondary battery. If the value of A is too large, for example greater than 70, the lithium ion transport capacity is insufficient, which is detrimental to improving the high-temperature, high-voltage cycle stability of the secondary battery. In the secondary battery of the present invention, the electrolyte comprises a first component and a second component. The first component, a boron-containing lithium salt, is involved in the formation of a solid electrolyte interface (SEI) film with high ion conductivity, low conductivity, and high temperature resistance during the initial charge, and can be involved in the formation of an oxidation-resistant positive electrode electrolyte interface (CEI) film. The second component can improve the high-pressure resistance of the electrolyte, reduce the desorption or binding energy barrier of lithium ions during the cycle process, and reduce the desorption resistance at the lithium ion interface. At the same time, the negative electrode material layer contains a silicon-containing active material, and by controlling the values ​​of A, B, and C within the above range, good protection is formed for the positive and negative electrodes, and the synergistic effect of the first and second components can provide the secondary battery with good high-temperature, high-voltage cycle stability.

[0028] In one embodiment of the present invention, the second component includes a compound represented by formula I, and the mass percentage of the compound represented by formula I is 25% to 70% based on the total mass of the electrolyte.

[0029] In another embodiment of the present invention, the second component comprises a compound represented by formula II, wherein the mass percentage of the compound represented by formula II is 25% to 70% based on the total mass of the electrolyte.

[0030] In another embodiment of the present invention, the second component comprises a compound represented by formula I and a compound represented by formula II, wherein the sum of the mass percentages of the compound represented by formula I and the compound represented by formula II is 25% to 70% based on the total mass of the electrolyte. 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).

[0031] In some embodiments, 0.01 ≤ B / A ≤ 0.12. For example, the value of B / A may be 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.12, or within the range of any two of the above values. By controlling the value of B / A within the above range, the synergistic effect of the first and second components can be better realized, and as a result, the high-temperature, high-voltage cycle stability of the secondary battery can be further improved.

[0032] In some embodiments, 0.01 ≤ B / C ≤ 3. For example, the value of B / C 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, or within the range of any two of the above values. By controlling the value of B / C within the above range, the protective effect on the positive and negative electrodes can be further improved, and the high-temperature, high-voltage cycle stability of the secondary battery can be further enhanced.

[0033] In some embodiments, 1 ≤ C ≤ 15. By controlling the value of C within this range, the high-temperature, high-voltage cycle stability of the secondary battery can be further improved.

[0034] In some embodiments, 0.5 ≤ B ≤ 3. By controlling the value of B within this range, the high-temperature, high-voltage cycle stability of the secondary battery can be further improved.

[0035] In some embodiments, 40 ≤ A ≤ 70. By controlling the value of A within the above range, the high-temperature, high-voltage cycle stability of the secondary battery can be further improved.

[0036] In some embodiments, the compound represented by formula I includes at least one of the compounds represented by the following formulas I-1 to I-25. [ka]

[0037] An electrolyte containing a second component within the above range can contribute to the formation of a CEI film with better stability, improving the protective effect on the positive electrode, and consequently further improving the high-temperature, high-voltage cycle stability of the secondary battery.

[0038] In some embodiments, the compound represented by formula II includes at least one of the compounds represented by formulas II-1 to II-20 below. [ka]

[0039] An electrolyte containing a second component within the above range can contribute to the formation of a CEI film with better stability, improving the protective effect on the positive electrode, and consequently further improving the high-temperature, high-voltage cycle stability of the secondary battery.

[0040] In some embodiments, the electrolyte further contains fluoroethylene carbonate (FEC), and the mass percentage of fluoroethylene carbonate is D% based on the total mass of the electrolyte, where 0.05 ≤ B / D ≤ 1.5. For example, the B / D value may be 0.05, 0.07, 0.1, 0.15, 0.2, 0.25, 0.3, 0.4, 0.5, 0.6, 0.8, 1, 1.1, 1.2, 1.3, 1.4, 1.5, or within the range of any two of the above values. By including FEC in the electrolyte and controlling the B / D value within the above range, the protective effect on the interface of the silicon-containing negative electrode can be improved, and the amount of cycle gas generated can be reduced, thereby improving the high-temperature, high-voltage cycle stability of the secondary battery.

[0041] In some embodiments, 2 ≤ D ≤ 12. For example, the value of D may be 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 within the range of any two of the above values. The electrolyte contains FEC, and controlling the value of D within the above range is advantageous for improving the high-temperature, high-voltage cycle stability of the secondary battery.

[0042] In some embodiments, the electrolyte further comprises lithium difluorophosphate. The mass percentage of lithium difluorophosphate is E% based on the total mass of the electrolyte, where 0.1 ≤ E ≤ 5. For example, the value of E may be 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 within the range of any two of the above values. The electrolyte contains lithium difluorophosphate, and by controlling the value of E within the above range, lithium difluorophosphate suppresses side reactions between the positive and negative electrodes and the electrolyte, reduces interfacial resistance in different charge states and long cycle processes, and generates a stable interfacial film on the surface of the positive electrode, effectively suppressing oxidative decomposition of the electrolyte. As a result, the high-temperature, high-voltage cycle stability of the secondary battery can be improved.

[0043] In some embodiments, the electrolyte further contains fluoropyridine. The mass percentage of fluoropyridine relative to the total mass of the electrolyte is F%, where 0.01 ≤ F ≤ 2. 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, or within the range of any two of the above values. By containing fluoropyridine in the electrolyte and controlling the value of F within the above range, the fluoropyridine forms an SEI film together with the first and second components, and the fluoropyridine is reduced to form a nitrogen-containing polymer, contributing to the construction of a "mosaic" type interfacial film, which can reduce the sustained degradation of the SEI film during the cycling process, and as a result, the high-temperature, high-voltage cycling stability of the secondary battery can be further improved. In the present invention, fluoropyridine is at least one selected from 2-fluoropyridine, 3-fluoropyridine, and 4-fluoropyridine.

[0044] In some embodiments, the electrolyte further comprises a third component, the third component comprising adiponitrile and at least one of vinylene carbonate (VC), ethylene sulfate (DTD), 1,3-propanesultone (PS), and propenyl-1,3-propanesultone (PES). The mass percentage of the third component, based on the total mass of the electrolyte, is G%, and 0.1 ≤ G ≤ 8. For example, the value of G may be 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, 5.3, 5.5, 5.7, 6, 6.3, 6.5, 6.8, 7, 7.2, 7.5, 7.8, 8, or it may be within the range of any two of the above values. The electrolyte contains a third component, and by controlling the value of G within the above range, the nitrile groups of adiponitrile form complexes with metal ions, suppressing the elution of metal ions and improving the protective ability for the positive electrode. At the same time, at least one of the VC, DTD, PS, and PES used participates in the formation of a reduction-resistant SEI film during the initial formation process, strengthening the interfacial protection of the silicon-containing negative electrode, and as a result, improving the high-temperature, high-voltage cycle stability of the secondary battery.

[0045] In some embodiments, the mass percentage of adiponitrile is G1% based on the total mass of the electrolyte, and the total mass percentage of vinylene carbonate, ethylene sulfate, 1,3-propanesultone, and propenyl-1,3-propanesultone is G2%. In the present invention, the value of the ratio of G1 to G2, i.e., the value of G1:G2, is not particularly limited as long as the objective of the present invention is achieved. Exemplarily, G1:G2 is 1:(0.5~1.5).

[0046] In the present invention, fluoroethylene carbonate, lithium difluorophosphate, fluoropyridine, a third component, etc., within the above range can be used in any combination as long as the objective of the present invention is achieved.

[0047] In some embodiments, the silicon-containing active material includes at least one of a silicon-oxygen composite material and a silicon-carbon composite material. Exemplarily, the silicon-oxygen composite material is, for example, SiOx (0 < x ≤ 2), and the silicon-carbon composite material is, for example, SiC. A silicon-oxygen composite material or a silicon-carbon composite material known or commercially available in the art may be used. For example, in a commercially available silicon-carbon composite material, the mass percentage of silicon element in the silicon-carbon composite material is usually 40% to 60%. Without being limited to any theory, when the negative electrode sheet includes the above types of silicon-containing active materials, the processing of the negative electrode slurry and the negative electrode sheet can be made more convenient, the energy density of the secondary battery can be improved, and it is advantageous for improving the high-temperature and high-voltage cycle stability of the secondary battery.

[0048] In the present invention, the electrolytic solution further includes an electrolyte salt and a non-aqueous solvent. In the present invention, the electrolyte salt is not particularly limited as long as the object of the present invention can be achieved. For example, the electrolyte salt may include at least one of LiPF6, LiAsF6, LiClO4, LiCH3SO3, LiCF3SO3, LiC(SO2CF3)3, and Li2SiF6, but is not limited thereto. The content of the electrolyte salt in the electrolytic solution of the present invention is not particularly limited as long as the object of the present invention can be achieved. For example, based on the mass of the electrolytic solution, the mass percentage of the electrolyte salt is 8% to 15%.

[0049] In the present invention, the non-aqueous solvent is not particularly limited as long as the objective of the present invention is achieved. The non-aqueous solvent may, but is not limited to, at least one of carbonate compounds, carboxylate compounds, ether compounds, and other organic solvents. The carbonate compound may, but is not limited to, at least one of linear carbonate compounds and cyclic carbonate compounds. The linear carbonate compound may, but is not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), and ethyl methyl carbonate (MEC). The cyclic carbonate may, but is not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), and vinylethylene carbonate (VEC). The carboxylate compound may include, but is not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decalactone, valerolactone, and caprolactone. The ether compound may include, but is not limited to, at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran, and tetrahydrofuran. The other organic solvent may include, but is not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, and trioctyl phosphate. The content of the non-aqueous solvent in the electrolyte of the present invention is not particularly limited, as long as the objectives of the present invention are achieved.For example, relative to the total mass of the electrolyte, the mass percentage of the non-aqueous solvent ranges from 0% to 66%.

[0050] In one embodiment of the present invention, the electrolyte comprises a first component, a second component, an electrolyte salt, and a non-aqueous solvent. Based on the total mass of the electrolyte, the mass percentages of the first component, the second component, and the electrolyte salt are as described above, and the mass percentage of the non-aqueous solvent is 10% to 66%. A secondary battery using an electrolyte containing the first component and the second component of the present invention exhibits improved high-temperature, high-voltage cycle stability.

[0051] 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. Based on the total mass of the electrolyte, the mass percentages of the first component, the second component, fluoroethylene carbonate, and the electrolyte salt are as described above, and the mass percentage of the non-aqueous solvent is 0% to 64%. A secondary battery using the electrolyte comprising the first component, the second component, and fluoroethylene carbonate of the present invention exhibits further improved high-temperature, high-voltage cycle stability.

[0052] In one embodiment of the present invention, the electrolyte comprises a first component, a second component, lithium difluorophosphate, an electrolyte salt, and a non-aqueous solvent. Based on the total mass of the electrolyte, the mass percentages of the first component, the second component, lithium difluorophosphate, and the electrolyte salt are as described above, and the mass percentage of the non-aqueous solvent is 5% to 66%. A secondary battery using the electrolyte comprising the first component, the second component, and lithium difluorophosphate of the present invention exhibits further improved high-temperature, high-voltage cycle stability.

[0053] In one embodiment of the present invention, the electrolyte comprises a first component, a second component, fluoropyridine, an electrolyte salt, and a non-aqueous solvent. Based on the total mass of the electrolyte, the mass percentages of the first component, the second component, fluoropyridine, and the electrolyte salt are as described above, and the mass percentage of the non-aqueous solvent is 8% to 66%. A secondary battery using the electrolyte comprising the first component, the second component, and fluoropyridine of the present invention exhibits further improved high-temperature, high-voltage cycle stability.

[0054] 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. Based on the total mass of the electrolyte, the mass percentages of the first component, the second component, the third component, and the electrolyte salt are as described above, and the mass percentage of the non-aqueous solvent is 2% to 66%. A secondary battery using an electrolyte comprising the first component, the second component, and the third component of the present invention exhibits further improved high-temperature, high-voltage cycle stability.

[0055] In one embodiment of the present invention, the electrolyte comprises a first component, a second component, fluoroethylene carbonate, lithium difluorophosphate, an electrolyte salt, and a non-aqueous solvent. Based on the total mass of the electrolyte, the mass percentages of the first component, the second component, fluoroethylene carbonate, lithium difluorophosphate, and electrolyte salt are as described above, and the mass percentage of the non-aqueous solvent is 0% to 64%. A secondary battery using an electrolyte comprising the first component, the second component, fluoroethylene carbonate, and lithium difluorophosphate of the present invention exhibits further improved high-temperature, high-voltage cycle stability.

[0056] In one embodiment of the present invention, the electrolyte comprises a first component, a second component, fluoroethylene carbonate, fluoropyridine, an electrolyte salt, and a non-aqueous solvent. Based on the total mass of the electrolyte, the mass percentages of the first component, the second component, fluoroethylene carbonate, fluoropyridine, and electrolyte salt are as described above, and the mass percentage of the non-aqueous solvent is 0% to 64%. A secondary battery using an electrolyte comprising the first component, the second component, fluoroethylene carbonate, and fluoropyridine of the present invention exhibits further improved high-temperature, high-voltage cycle stability.

[0057] 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. Based on the total mass of the electrolyte, the mass percentages of the first component, the second component, fluoroethylene carbonate, the third component, and the electrolyte salt are as described above, and the mass percentage of the non-aqueous solvent is 0% to 64%. A secondary battery using an electrolyte comprising the first component, the second component, fluoroethylene carbonate, and the third component of the present invention exhibits further improved high-temperature, high-voltage cycle stability.

[0058] In one embodiment of the present invention, the electrolyte comprises a first component, a second component, lithium difluorophosphate, fluoropyridine, an electrolyte salt, and a non-aqueous solvent. Based on the total mass of the electrolyte, the mass percentages of the first component, the second component, lithium difluorophosphate, fluoropyridine, and electrolyte salt are as described above, and the mass percentage of the non-aqueous solvent is 3% to 66%. A secondary battery using the electrolyte comprising the first component, the second component, lithium difluorophosphate, and fluoropyridine of the present invention exhibits further improved high-temperature, high-voltage cycle stability.

[0059] In one embodiment of the present invention, the electrolyte comprises a first component, a second component, lithium difluorophosphate, a third component, an electrolyte salt, and a non-aqueous solvent. Based on the total mass of the electrolyte, the mass percentages of the first component, the second component, lithium difluorophosphate, the third component, and the electrolyte salt are as described above, and the mass percentage of the non-aqueous solvent is 0% to 66%. A secondary battery using an electrolyte comprising the first component, the second component, lithium difluorophosphate, and the third component of the present invention exhibits further improved high-temperature, high-voltage cycle stability.

[0060] In one embodiment of the present invention, the electrolyte comprises a first component, a second component, fluoropyridine, a third component, an electrolyte salt, and a non-aqueous solvent. Based on the total mass of the electrolyte, the mass percentages of the first component, the second component, fluoropyridine, the third component, and the electrolyte salt are as described above, and the mass percentage of the non-aqueous solvent is 0% to 66%. A secondary battery using the electrolyte comprising the first component, the second component, fluoropyridine, and the third component of the present invention exhibits further improved high-temperature, high-voltage cycle stability.

[0061] In one embodiment of the present invention, the electrolyte comprises a first component, a second component, fluoroethylene carbonate, lithium difluorophosphate, fluoropyridine, an electrolyte salt, and a non-aqueous solvent. Based on the total mass of the electrolyte, the mass percentages of the first component, the second component, fluoroethylene carbonate, lithium difluorophosphate, fluoropyridine, and electrolyte salt are as described above, and the mass percentage of the non-aqueous solvent is 0% to 64%. A secondary battery using an electrolyte comprising the first component, the second component, fluoroethylene carbonate, lithium difluorophosphate, and fluoropyridine of the present invention exhibits further improved high-temperature, high-voltage cycle stability.

[0062] In one embodiment of the present invention, the electrolyte comprises a first component, a second component, fluoroethylene carbonate, lithium difluorophosphate, a third component, an electrolyte salt, and a non-aqueous solvent. Based on the total mass of the electrolyte, the mass percentages of the first component, the second component, fluoroethylene carbonate, lithium difluorophosphate, the third component, and the electrolyte salt are as described above, and the mass percentage of the non-aqueous solvent is 0% to 64%. A secondary battery using an electrolyte comprising the first component, the second component, fluoroethylene carbonate, lithium difluorophosphate, and the third component of the present invention exhibits further improved high-temperature, high-voltage cycle stability.

[0063] In one embodiment of the present invention, the electrolyte comprises a first component, a second component, fluoroethylene carbonate, fluoropyridine, a third component, an electrolyte salt, and a non-aqueous solvent. Based on the total mass of the electrolyte, the mass percentages of the first component, the second component, fluoroethylene carbonate, fluoropyridine, the third component, and the electrolyte salt are as described above, and the mass percentage of the non-aqueous solvent is 0% to 64%. A secondary battery using an electrolyte comprising the first component, the second component, fluoroethylene carbonate, fluoropyridine, and the third component of the present invention exhibits further improved high-temperature, high-voltage cycle stability.

[0064] In one embodiment of the present invention, the electrolyte comprises a first component, a second component, lithium difluorophosphate, fluoropyridine, a third component, an electrolyte salt, and a non-aqueous solvent. Based on the total mass of the electrolyte, the mass percentages of the first component, the second component, lithium difluorophosphate, fluoropyridine, the third component, and the electrolyte salt are as described above, and the mass percentage of the non-aqueous solvent is 0% to 66%. A secondary battery using an electrolyte comprising the first component, the second component, lithium difluorophosphate, fluoropyridine, and the third component of the present invention exhibits further improved high-temperature, high-voltage cycle stability.

[0065] In one embodiment of the present invention, the electrolyte comprises a first component, a second component, fluoroethylene carbonate, lithium difluorophosphate, fluoropyridine, a third component, an electrolyte salt, and a non-aqueous solvent. Based on the total mass of the electrolyte, the mass percentages of the first component, the second component, fluoroethylene carbonate, lithium difluorophosphate, fluoropyridine, the third component, and the electrolyte salt are as described above, and the mass percentage of the non-aqueous solvent is 0% to 64%. A secondary battery using an electrolyte comprising the first component, the second component, fluoroethylene carbonate, lithium difluorophosphate, fluoropyridine, and the third component of the present invention exhibits further improved high-temperature, high-voltage cycle stability.

[0066] 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 "a negative electrode material layer 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 along the thickness direction of the negative electrode current collector itself, or on two surfaces along the thickness direction of the negative electrode current collector itself. The term "surface" here 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 the present invention is not particularly limited as long as it achieves the objective of the present invention.

[0067] In the present invention, the negative electrode current collector is not particularly limited as long as it can achieve the objectives of the present invention. The negative electrode current collector may include, for example, 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.

[0068] 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 as long as they can achieve the objectives of the present invention. For example, the other negative electrode active materials are natural graphite, artificial graphite, mesocarbon microbeads, hard carbon, soft carbon, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, and lithium-ionized TiO2-Li4Ti5O with a spinel structure. 12 The system may include, but is not limited to, at least one of the following: and Li-Al alloys.

[0069] In this invention, the mass percentage of silicon in the negative electrode material layer can also be controlled by controlling the mass ratio of the silicon-containing active material to other negative electrode active materials.

[0070] 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, the types of conductive agents and binders are not particularly limited 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. The conductive carbon black may include, but is not limited to, at least one of acetylene black and Ketjen 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 nanocarbon fibers. The metallic material may include, but is not limited to, metal powder and / or metal fibers. Specifically, the metal may include, but is not limited to, at least one of copper, nickel, aluminum, and silver. The conductive polymer 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, the mass ratio of the negative electrode active material, the conductive agent, and the binder in the negative electrode material layer is not particularly limited and can be selected by those skilled in the art as needed, insofar as the objectives of the present invention are achieved. The negative electrode material layer may further contain a thickening agent. In the present invention, the content and type of the thickening agent are not particularly limited and can be the usual types and content known in the art, insofar as the objectives of the present invention are achieved.

[0071] In the present invention, the thickness of the negative electrode material layer is not particularly limited as long as the objectives of the present invention are 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 as long as the objectives of the present invention are achieved. For example, the thickness of the negative electrode current collector is 4 μm to 15 μm.

[0072] Optionally, the negative electrode piece may further include a 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 conductive layer commonly used in the art. For example, 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 be, for example, at least one of the conductive agent and the binder.

[0073] 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 along the thickness direction of the positive electrode current collector itself, or on two surfaces along the thickness direction of the positive electrode current collector itself. The term "surface" here may refer to the entire surface of the positive electrode current collector, or to a portion of the surface of the positive electrode current collector, and the present invention is not particularly limited as long as it achieves the objective of the present invention.

[0074] In the present invention, the positive electrode current collector is not particularly limited as long as it can achieve the objectives of the present invention. The positive electrode current collector may include, for example, aluminum foil, aluminum alloy foil, or a composite current collector (e.g., an aluminum-carbon composite current collector).

[0075] The positive electrode material layer includes a positive electrode active material. In the present invention, the positive electrode active material is not particularly limited as long as it can achieve the objectives of the present invention. For example, the positive electrode active material may include, but is not limited to, at least one of the following: lithium nickel cobalt manganese oxide (e.g., NCM811, NCM622, NCM523, NCM111), lithium nickel cobalt aluminate, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium iron manganese phosphate, and lithium titanate.

[0076] The positive electrode material layer may further contain a conductive agent and a binder. In the present invention, the types of conductive agent and binder are not particularly limited as long as the objectives of the present invention are achieved, and for example, at least one of the conductive agent and the binder may be used. The mass ratio of the positive electrode active material, conductive agent and binder in the positive electrode material layer of the present invention is not particularly limited, and those skilled in the art can select them according to their actual needs as long as the objectives of the present invention are achieved.

[0077] In the present invention, the thickness of the positive electrode current collector and the positive electrode material layer is not particularly limited, as long as the objectives of the present invention can be achieved. For example, the thickness of the positive electrode current collector is 5 μm to 20 μm. For example, the thickness of the positive electrode material layer is 30 μm to 120 μm.

[0078] 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 conductive layer commonly used 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 be, for example, at least one of the conductive agent and the binder.

[0079] In the present invention, the secondary battery further includes a separator. In the present invention, the separator is not particularly limited as long as it can 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 consisting 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 spun film.

[0080] 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 membrane having a porous structure. The material of the base layer may include at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. Optionally, the base layer may be a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane.

[0081] Optionally, a surface treatment layer is provided 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 obtained by mixing a polymer and an inorganic material.

[0082] 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 aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium oxide, tin oxide, cerium oxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate. In the present invention, the binder is not particularly limited and may include, for example, at least one of the aforementioned binders. In some embodiments of the present invention, the polymer layer comprises a polymer. The polymer material includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene).

[0083] In the present invention, the thickness of the separator is not particularly limited as long as it is a thickness that can achieve the objective of the present invention. For example, the thickness of the separator may be 3 μm to 30 μm.

[0084] In the present invention, the secondary battery further includes a case 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, and the present invention does not limit such other components. In the present invention, the case is not particularly limited and may be a case known in the art as long as it can achieve the objectives of the present invention. For example, the case may be a rigid case or a flexible case. The material of the rigid case may be metal. In the present invention, the type of metal is not particularly limited and may be a rigid metal case known in the art as long as it can achieve the objectives of the present invention. A flexible case may include a metal-plastic film such as an aluminum-plastic film or a steel-plastic film.

[0085] In the present invention, the preparation process for the secondary battery is not particularly limited and is a preparation process well known to those skilled in the art. For example, the manufacturing process for a secondary battery may include, but is not limited to, the following steps: A positive electrode piece, a separator, and a negative electrode piece are stacked in order, and a wound electrode assembly is obtained by winding, folding, or other operations as needed, the electrode assembly is placed in a case, the electrolyte is injected into the case and sealed, and a secondary battery is obtained. Alternatively, a positive electrode piece, a separator, and a negative electrode piece are stacked in order, and then the four corners of the entire stacked structure are fixed with tape to obtain a stacked electrode assembly, the electrode assembly is placed in a case, the electrolyte is injected into the case and sealed, and a secondary battery is obtained. In addition, to prevent pressure rise inside the secondary battery, overcharging and overdischarging, etc., an overcurrent prevention element, lead plates, etc. may be placed in the case as needed.

[0086] In the present invention, the type of secondary battery is not particularly limited and may include any device that generates an electrochemical reaction. 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.

[0087] A second aspect of the present invention provides an electronic device including a secondary battery in any of the embodiments described above. Since the secondary battery according to the present invention has high temperature and high voltage cycle stability, the electronic device according to the present invention has a long service life.

[0088] In the present invention, the type of electronic device is not particularly limited and may be any electronic device known in the prior art. In some embodiments of the present invention, the electronic device includes, but is not limited to, notebook computers, pen-input computers, mobile computers, e-book players, mobile phones, portable facsimile machines, portable copiers, portable printers, stereo headsets, video recorders, LCD televisions, portable cleaners, portable CD players, MiniDiscs, transceivers, electronic notebooks, calculators, memory cards, portable tape recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric assist bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household storage batteries, and lithium-ion capacitors.

[0089] Examples The embodiments of the present invention will be described in more detail below with reference to examples and comparative examples. Various tests and evaluations will be carried out as follows. Unless otherwise specified, "parts" and "%" are based on mass.

[0090] Measurement method and apparatus Measurement of the mass percentage of silicon element A lithium-ion battery discharged to 3.0V at 0.5C was disassembled, the negative electrode piece was removed, immersed in dimethyl carbonate (DMC) for 20 minutes, and then washed once each with DMC and acetone. The negative electrode piece was then placed in an oven and baked at 80°C for 12 hours to obtain the negative electrode piece. The negative electrode piece was dried in a vacuum oven at 100°C for 24 hours, the negative electrode material layer on the negative electrode piece was scraped off with a blade, and then the mass percentage of silicon element in the negative electrode material layer was measured using an inductively coupled plasma (ICP) analyzer. Measurement of high-temperature, high-voltage cycling performance A lithium-ion battery was placed in a constant temperature test chamber at 45°C and left undisturbed for 30 minutes to allow the battery to reach a constant temperature. It was then charged with a constant current of 0.5C up to 4.45V, followed by constant voltage charging until the current reached 0.025C. After leaving it undisturbed for 5 minutes, it was discharged with a constant current of 0.5C up to 3.0V, and the initial discharge capacity C1 was recorded. This charge-discharge process was repeated, recording the discharge capacity C2 for each cycle, and the cycle capacity retention rate of the lithium-ion battery was calculated. The cycle capacity retention rate was calculated as C2 / C1 × 100%. Measurement was stopped when the cycle capacity retention rate was ≤ 80%, and the number of cycles at that point was recorded.

[0091] Example 1-1 <Preparation of the negative electrode piece> A Si / C composite material (in which Si is supported in carbon nanopores; commercially available, the mass percentage of silicon in silicon-carbon composite materials is 50%), artificial graphite, lithium polyacrylate (PAA-Li) as a binder, and carbon nanotubes as a conductive agent were mixed in a mass ratio of 2:88:7:3. Deionized water was added, and the mixture was uniformly mixed using a vacuum stirrer to obtain a negative electrode slurry with a solid content of 30 wt%. The negative electrode slurry was uniformly coated onto one side of a copper foil, which served as a negative electrode current collector and had a thickness of 12 μm. It was dried at 120°C to obtain a negative electrode piece with a negative electrode material layer coated on one side, resulting in a coating layer thickness of 143 μm. The above steps were repeated on the other side of the copper foil to obtain a negative electrode piece with negative electrode material layers coated on both sides. After cold pressing and cutting, a negative electrode piece with dimensions of 78 mm × 875 mm was obtained. Here, the thickness of the negative electrode material layer on one side after cold pressing was 80 μm. Based on the total mass of the negative electrode material layer, the mass percentage of Si (C%) was 1%. <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 mixture was stirred with a vacuum stirrer until the system became a homogeneous positive electrode slurry. The positive electrode slurry was uniformly coated onto one surface of an aluminum foil, which served as the positive electrode current collector, with a thickness of 10 μm, and dried at 85°C to obtain a positive electrode piece with the positive electrode active material coated on one side, resulting in a positive electrode material layer thickness of 90 μm. Subsequently, the above steps were repeated on the other surface of the 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 for use. The compressed density of the positive electrode piece was 4 g / cm³. 3 That was the case. <Preparation of Electrolyte> In a glove box under an argon atmosphere with a water content of less than 10 ppm, ethyl methyl carbonate was used as a non-aqueous solvent. Then, lithium difluoroborate (the first component), I-3 (the second component), and LiPF6 (the electrolyte salt) were added to the non-aqueous solvent and mixed uniformly to obtain an electrolyte. Based on the total mass of the electrolyte, the mass percentage B% of the first component was 3%, the mass percentage A% of the second component was 40%, the mass percentage of the electrolyte salt was 12.5%, and the remainder was the non-aqueous solvent. <Separator> A porous polyethylene (PE) membrane with a thickness of 5 μm (manufactured by Shanghai SEMCORP Co., Ltd.) was used. <Preparation of Lithium-ion Batteries> The positive electrode piece, separator, and negative electrode piece prepared above were stacked in order, with the separator interposed between the positive and negative electrode pieces to provide isolation. The assembly was then wound up to obtain the electrode assembly. After welding the tabs, the electrode assembly was placed in an aluminum plastic film packaging case and dried in an 85°C vacuum oven for 12 hours to remove moisture. The electrolyte prepared above was then injected, and a lithium-ion battery was obtained through processes such as vacuum packaging, standing, formation (charging to 3.5V with a constant current of 0.02C, then charging to 3.9V with a constant current of 0.1C), shaping, and capacity measurement.

[0092] Examples 1-2 to 1-23 In the <Preparation of the Negative Electrode Piece>, the mass ratio of silicon-containing active material to artificial graphite was adjusted to the mass percentage C% of silicon element in the negative electrode material layer as shown in Table 1 (however, the total mass of both remained unchanged). Then, in the <Preparation of the Electrolyte>, the type and mass percentage B% of the first component and the type and mass percentage A% of the second component were adjusted according to Table 1, and the procedure was carried out in the same manner as in Example 1-1, except that the mass percentage of the non-aqueous solvent changed accordingly, while the mass percentage of the electrolyte salt remained unchanged.

[0093] Examples 1-24 In the preparation of the negative electrode piece, the procedure was the same as in Examples 1-3, except that the type of silicon-containing active material was adjusted to a silicon-oxygen composite material (commercially available), as shown in Table 1.

[0094] Examples 2-1 to 2-3 In the <Preparation of Electrolyte Solution>, fluoroethylene carbonate was added as shown in Table 2, and the mass percentage D% of fluoroethylene carbonate was adjusted according to Table 2, so 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. The procedure was the same as in Examples 1-10.

[0095] Examples 2-4 to 2-30 In the <Preparation of Electrolyte Solution>, fluoroethylene carbonate, lithium difluorophosphate, 2-fluoropyridine (fluoropyridine), and a third component were added as shown in Table 2. The mass percentages of fluoroethylene carbonate (D%), lithium difluorophosphate (E%), fluoropyridine (F%), and the type and mass percentage of the third component (G%) were adjusted according to Table 2. 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 percentages of the first component, the second component, and the electrolyte salt remained unchanged.

[0096] Comparative Examples 1-1 to 1-10 The procedure was the same as in Example 1-1, except that the preparation parameters were adjusted as shown in Table 1. When silicon was not present, the negative electrode active material was replaced from a silicon-containing active material to artificial graphite. When the mass percentage B% of the first component and / or the mass percentage A% of the second component changed, the mass percentage of the non-aqueous solvent changed accordingly, while the mass percentage of the electrolyte salt remained unchanged. In the <Preparation of the negative electrode piece>, the mass percentage C% of silicon in the negative electrode material layer was set as shown in Table 1 by adjusting their mass ratio while keeping the total mass of the silicon-containing active material and artificial graphite constant.

[0097] [Table 1]

[0098] [Table 2]

[0099] As can be seen from Examples 1-1 to 1-24 and Comparative Examples 1-1 to 1-10, when the negative electrode piece contains a silicon-containing active material, and the value of the silicon element content C in the negative electrode material layer is controlled within the range of the present invention, and the electrolyte contains a first component and a second component, and the values ​​of B and A are controlled within the range of the present invention, the lithium-ion battery has a high number of high-temperature, high-voltage cycles, which indicates that the lithium-ion battery has good high-temperature, high-voltage cycle stability.

[0100] The B / A value typically affects the high-temperature, high-voltage cycle stability of lithium-ion batteries. As can be seen from Examples 1-3 and 1-6 to 1-15, when the B / A value is controlled within the range of the present invention, lithium-ion batteries have a high number of high-temperature, high-voltage cycles, which indicates that lithium-ion batteries have good high-temperature, high-voltage cycle stability.

[0101] The B / C value typically affects the high-temperature, high-voltage cycle stability of lithium-ion batteries. As can be seen from Examples 1-1 to 1-5 and Examples 1-16 to 1-18, when the B / C value is controlled within the range of the present invention, lithium-ion batteries have a high number of high-temperature, high-voltage cycles, which indicates that lithium-ion batteries have good high-temperature, high-voltage cycle stability.

[0102] The type of the first component, the second component, and the silicon-containing active material typically affects the high-temperature, high-voltage cycle stability of lithium-ion batteries. As can be seen from Examples 1-3 and Examples 1-19 to 1-24, when a lithium-ion battery is selected in which the type of the first component, the second component, and the silicon-containing active material are within the scope of the present invention, the lithium-ion battery has a high number of high-temperature, high-voltage cycles, which indicates that the lithium-ion battery has good high-temperature, high-voltage cycle stability.

[0103] The B / D value typically affects the high-temperature, high-voltage cycle stability of lithium-ion batteries. As can be seen from Examples 1-3, 1-10, and 2-1 to 2-7, when the B / D value is controlled within the range of the present invention, lithium-ion batteries have a higher number of high-temperature, high-voltage cycles, which indicates that lithium-ion batteries have better high-temperature, high-voltage cycle stability.

[0104] The content of lithium difluorophosphate and fluoropyridine typically affects the high-temperature, high-voltage cycle stability of lithium-ion batteries. As can be seen from Examples 2-8 to 2-18, when the electrolyte contains lithium difluorophosphate or fluoropyridine within the content range of the present invention, the lithium-ion battery has a higher number of high-temperature, high-voltage cycles, which indicates that the lithium-ion battery has better high-temperature, high-voltage cycle stability.

[0105] The type and content of the third component typically affect the high-temperature, high-voltage cycle stability of lithium-ion batteries. As can be seen from Examples 1-3 and 2-19 to 2-24, when the electrolyte contains a third component within the range of type and content of the present invention, the lithium-ion battery has a higher number of high-temperature, high-voltage cycles, which indicates that the lithium-ion battery has better high-temperature, high-voltage cycle stability.

[0106] Different types of electrolytes typically affect the high-temperature, high-voltage cycle stability of lithium-ion batteries. As can be seen from Examples 1-3 and Examples 2-1 to 2-30, when an electrolyte combining fluoroethylene carbonate, lithium difluorophosphate, fluoropyridine, and a third component of the present invention is selected, the number of high-temperature, high-voltage cycles of the lithium-ion battery is further improved, which indicates that the high-temperature, high-voltage cycle stability of the lithium-ion battery is further improved.

[0107] In this specification, relational terms such as "first" and "second" are used solely to distinguish one entity or operation from another, and do not necessarily require or imply any actual relationship or order between these entities or operations. Furthermore, the terms "include," "contain," or any other variation thereof are intended to cover non-exclusive inclusion, so that a process, method, or article containing a set of elements includes not only those elements but also other elements not expressly enumerated, or other elements specific to such a process, method, or article.

[0108] Elements connected by the terms "one of," "one of," "a type of," or other similar terms refer to any one of the enumerated elements. For example, "a type of A and B" refers to A only or B only, and as another example, "a type of A, B, and C" refers to A only, B only, or C only. Elements connected by the terms "at least one of," "at least one of," "at least one type of," or other similar terms refer to any combination of the enumerated elements. For example, "at least one of A and B" refers to A only, B only, and both A and B. As another example, "at least one of A, B, and C" refers to A only, B only, C only, A and B only, A and C only, B and C only, and all of A, B, and C.

[0109] Each example in this specification is described using the relevant method, and any identical or similar parts between the examples may be referenced to one another, while each example focuses on explaining the differences from the other examples.

[0110] The foregoing describes merely better embodiments of the present invention and does not limit it. Any modifications, equivalent substitutions, or improvements made within the scope of the spirit and principles of the present invention are all within the scope of the protections claimed by the present invention.

Claims

1. It is a secondary battery, The aforementioned secondary battery includes 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. With respect to the total mass of the negative electrode material layer, the mass percentage of the silicon element is C%, and 1 ≤ C ≤ 20. The electrolyte comprises a first component and a second component. (1) The first component is a boron-containing lithium salt, The boron-containing lithium salt comprises at least one of the following: lithium tetrafluoroborate, lithium difluorooxalate borate, lithium bisoxalate borate, lithium difluoroborate, lithium tetracyanoborate, lithium tetra(trifluoromethyl)borate, lithium dicyanooxalate borate, lithium tetramethoxyborate, lithium tetraethoxyborate, lithium perfluorotertoxytrifluoroborate, lithium bis(difluorophosphonooxy)difluoroborate, lithium pentafluoroethyltrifluoroborate, lithium methoxytricyanoborate, and lithium bis(trifluoroborate)bis(sulfate). With respect to the total mass of the electrolyte, the mass percentage of the first component is B%, and 0.1 ≤ B ≤ 5. (2) The second 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 are each independently a fluorine-substituted or unsubstituted C １ to C １０ alkyl group, and at least one of R １１ and R １２ is substituted with fluorine, and R ２１ and R ２２ are each independently a fluorine-substituted or unsubstituted C １ to C １０ alkyl group, and at least one of R ２１ and R ２２ is substituted with fluorine, A secondary battery in which the mass percentage of the second component is A% based on the total mass of the electrolyte, and 25 ≤ A ≤ 70.

2. The secondary battery according to claim 1, wherein 0.01 ≤ B / A ≤ 0.

12.

3. The secondary battery according to claim 1, wherein 0.01 ≤ B / C ≤ 3.

4. The aforementioned secondary battery is a) 1 ≤ C ≤ 15, b) 0.5 ≤ B ≤ 3, and c) 40 ≤ A ≤ 70 A secondary battery according to claim 1, satisfying at least one of the following conditions.

5. The secondary battery according to claim 1, wherein the compound represented by formula I includes at least one of the compounds represented by the following formulas I-1 to I-25. 【Chemistry 2】

6. The secondary battery according to claim 1, wherein the compound represented by formula II includes at least one of the compounds represented by formulas II-1 to II-20 below. 【Transformation 3】

7. The electrolyte further contains fluoroethylene carbonate, A secondary battery according to any one of claims 1 to 6, wherein the mass percentage of the fluoroethylene carbonate is D% based on the total mass of the electrolyte, and 0.05 ≤ B / D ≤ 1.

5.

8. The electrolyte further contains lithium difluorophosphate, The secondary battery according to any one of claims 1 to 6, wherein the mass percentage of lithium difluorophosphate is E% based on the total mass of the electrolyte, and 0.1 ≤ E ≤ 5.

9. The electrolyte further contains fluoropyridine, The secondary battery according to any one of claims 1 to 6, wherein the mass percentage of fluoropyridine is F% based on the total mass of the electrolyte, and 0.01 ≤ F ≤ 2.

10. The electrolyte further comprises a third component, The third component comprises adiponitrile and at least one of vinylene carbonate, ethylene sulfate, 1,3-propanesultone, and propenyl-1,3-propanesultone. The secondary battery according to any one of claims 1 to 6, wherein the mass percentage of the third component is G%, with respect to the total mass of the electrolyte, and 0.1 ≤ G ≤ 8.

11. 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.

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

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