Lithium ion secondary battery, cell, and electric device

Abstract

The invention provides a lithium ion secondary battery, a battery cell and an electric device. The lithium ion secondary battery comprises a positive pole piece, a negative pole piece and an electrolyte, a negative active layer of the negative pole piece comprises a silicon-based material, the electrolyte comprises a lithium salt, a solvent and a first additive, the solvent comprises a fluoro-carbonic ester solvent, the first additive comprises a reductive negative pole film-forming additive, and in the electrolyte, the first additive comprises a silicon-based material and a silicon-based material. The mass percent of the reducing negative electrode film-forming additive is 0%-4.5%; the electrolyte further comprises a second additive, and the second additive comprises a deacidification additive. The lithium ion secondary battery has a relatively long cycle life.

Description

Technical Field

[0001] The present application relates to the technical field of secondary batteries, and in particular to a lithium-ion secondary battery, a battery cell, and an electrical device. Background Art

[0002] In recent years, the application scope of secondary batteries such as lithium-ion batteries has become increasingly wide, and they have been widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, as well as power tools, electric bicycles, electric motorcycles, electric vehicles and other fields. As secondary batteries have made great progress, higher requirements have been put forward for their energy density, cycle performance and safety performance.

[0003] The theoretical specific capacity of silicon is as high as 4200mAh / g, which is more than 10 times that of carbon-based materials such as graphite (theoretical specific capacity is about 372mAh / g). This means that with the same mass, silicon-based materials can store more lithium ions, thereby providing batteries with higher energy density, which is of great significance for improving the range of secondary batteries and meeting the needs of electronic devices with high energy requirements. However, silicon-based materials have a large volume expansion during the lithium insertion process, and are prone to pulverization and breakage of material particles, which in turn destroys the SEI film on the surface of the negative electrode, reducing the cycle life of the secondary battery. There is a method to introduce fluorocarbonate solvents into the electrolyte in order to improve the stability of the SEI film on the surface of the negative electrode, but the improvement in the cycle life of the secondary battery is limited. Summary of the invention

[0004] Based on this, the present application provides a lithium-ion secondary battery, a battery cell and an electrical device with a good cycle life.

[0005] In a first aspect of the present application, a lithium-ion secondary battery is provided, comprising a positive electrode plate, a negative electrode plate and an electrolyte, wherein the negative electrode active layer of the negative electrode plate comprises a silicon-based material, the electrolyte comprises a lithium salt, a solvent and a first additive, the solvent comprises a fluorocarbonate solvent, the first additive comprises a reducing negative electrode film-forming additive, and the mass percentage of the reducing negative electrode film-forming additive in the electrolyte is 0% to 4.5%.

[0006] The present application is directed to lithium-ion secondary batteries containing silicon-based materials, and the synergistic use of fluorocarbonate solvents and reducing negative electrode film-forming additives can significantly improve the cycle life of the lithium-ion secondary batteries.

[0007] In some embodiments, the mass percentage of the fluorocarbonate solvent in the solvent is 0.1% to 50%. Reasonable control of the mass percentage of the fluorocarbonate solvent in the solvent is beneficial to the dissociation of the solvent from the lithium salt, improving the conductivity, improving the liquid phase transmission of lithium ions and the charge and discharge capacity of the battery, and also achieving good high temperature storage performance while obtaining a better battery cycle life.

[0008] In some embodiments, in the solvent, the mass percentage of the fluorocarbonate solvent is 2% to 30%.

[0009] In some embodiments, the fluorocarbonate solvent includes one or more of fluoroethylene carbonate, difluoroethylene carbonate, trifluoroethylene carbonate, tetrafluoroethylene carbonate, 4-trifluoromethylethylene carbonate, 1-fluoromethylethylene carbonate, fluoroethyl methyl carbonate, fluorodimethyl carbonate, di(2,2,2-trifluoroethyl)carbonate, 2,2,2-trifluoroethyl methyl carbonate, difluoromethyl methyl carbonate, trifluoromethyl methyl carbonate and difluoromethyl ethyl carbonate. By using a suitable type of fluorocarbonate solvent, an SEI film containing inorganic lithium fluoride with high Young's modulus and highly elastic polycarbonate compounds can be generated on the electrode surface, and the oxidation stability of the film itself is good, thereby improving the interface stability between the electrode and the electrolyte, reducing the reduction of lithium salts and solvents, thereby reducing the polarization inside the electrode and improving the cycle performance.

[0010] In some embodiments, the fluorocarbonate solvent includes one or more of fluoroethylene carbonate, fluorodimethyl carbonate and fluoroethyl methyl carbonate.

[0011] In some embodiments, the solvent further comprises one or more of a cyclic carbonate solvent, a chain carbonate solvent, and a chain carboxylate solvent.

[0012] In some embodiments, the mass percentage of the reducing negative electrode film-forming additive in the electrolyte is 0-2.5%. Reasonable control of the mass percentage of the reducing negative electrode film-forming additive is conducive to forming a stable SEI film and improving cycle performance while reducing the impedance of the electrolyte / electrode interface.

[0013] In some embodiments, the reducing negative electrode film-forming additive includes one or more of a lithium salt additive and a thioester additive. Using a suitable type of reducing negative electrode film-forming additive can better improve the cycle life of the battery.

[0014] In some embodiments, the lithium salt additive includes one or more of lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium tetrafluoroborate, lithium tetrafluorooxalatophosphate, lithium difluorophosphate, lithium fluorosulfonate, lithium bis(trifluoromethanesulfonylimide), lithium bis(fluorosulfonylimide) and lithium bis(oxalatoborate)difluorophosphate; and / or

[0015] The thioester additive includes one or more compounds having structural features shown in the following formula (II-1), formula (II-2) and formula (III) or their derivatives:

[0016] Formula (II-1),

[0017] Formula (II-2),

[0018] Formula (III),

[0019] In the compounds having the structural characteristics shown in formula (II-1) and formula (II-2), R 21 , R 22 , R 23 and R 24 Each independently includes H, F, C1~C10 saturated hydrocarbon group, fluorine-substituted C1~C10 saturated hydrocarbon group, C2~C10 unsaturated hydrocarbon group, fluorine-substituted C2~C10 unsaturated hydrocarbon group, aryl group, fluorine-substituted aryl group, carbonyl group, carboxyl group, ester group, nitrile group, silane group or ether group; n2 each independently includes 0, 1, 2 or 3; M2 includes O or CH2;

[0020] In the compound having the structural characteristics shown in formula (III), R 31 , R 32 , R 33 and R 34 Each independently includes H, F, C1~C10 saturated hydrocarbon group, fluorine-substituted C1~C10 saturated hydrocarbon group, C2~C10 unsaturated hydrocarbon group, fluorine-substituted C2~C10 unsaturated hydrocarbon group, aryl group, fluorine-substituted aryl group, carbonyl group, carboxyl group, ester group, nitrile group, silane group or ether group; n3 includes 0, 1, 2 or 3; M3 includes O or CH2.

[0021] In some embodiments, the lithium salt additive includes lithium difluorooxalate borate; and / or,

[0022] The thioester additive includes one or more of 1,3-propane sultone, vinyl sulfate and vinyl sulfite.

[0023] In some embodiments, the electrolyte further comprises a second additive, wherein the second additive comprises an acid-removing additive. The acid-removing additive can effectively remove proton hydrogen in the system, reduce the acidity of the electrolyte, and thus improve the cycle life of the lithium-ion secondary battery containing silicon-based materials.

[0024] In some embodiments, the acid removal additive includes one or more of a cyclic anhydride additive and a chain isocyanate additive. The use of suitable types of cyclic anhydride additives and / or chain isocyanate additives can reduce the reactivity of proton hydrogen by reacting with water, thereby reducing its damage to the electrolyte and the electrolyte / electrode interface, thereby improving the cycle life of the battery.

[0025] In some embodiments, the cyclic anhydride additive includes one or more of maleic anhydride, citraconic anhydride, trifluoromethylmaleic anhydride, succinic anhydride and glutaric anhydride;

[0026] And / or, the chain isocyanate additive includes one or more compounds having the structural characteristics shown in the following formula (I):

[0027] R 11 (N=C=O)n1 (I),

[0028] Among them, R 11 Including C1~C10 saturated hydrocarbon group, C2~C10 unsaturated hydrocarbon group, fluorine-substituted C1~C10 saturated hydrocarbon group, fluorine-substituted C2~C10 unsaturated hydrocarbon group, C3~C10 cycloalkyl group, C6~C20 aryl group, fluorine-substituted C6~C20 aryl group, carboxyl group, ester group or carbonyl group;

[0029] n1 includes 1, 2 or 3.

[0030] In some embodiments, the cyclic anhydride additive includes succinic anhydride;

[0031] And / or, the chain isocyanate additive includes one or more of hexamethylene diisocyanate, 1,4-cyclohexyl diisocyanate, isophenyl diisocyanate and isocyanoethyl methacrylate.

[0032] In some embodiments, the mass percentage of the acid removal additive in the electrolyte is 0.001% to 3%. Reasonable control of the mass percentage of the second additive can achieve a better proton hydrogen removal effect, improve the cycle life, reduce the impedance of the electrolyte / electrode interface, and also achieve good high temperature storage performance.

[0033] In some embodiments, in the electrolyte, the mass percentage of the acid-scavenging additive in the electrolyte is 0.01%~1%.

[0034] In some embodiments, the lithium salt has one or more of the following characteristics:

[0035] (1) The total molar concentration of the lithium salt in the electrolyte is 0.5 mol / L to 2 mol / L;

[0036] (2) The lithium salt includes lithium hexafluorophosphate.

[0037] In some embodiments, the lithium salt further comprises bis(fluorosulfonyl)imide lithium salt, and in the electrolyte, the concentration of the bis(fluorosulfonyl)imide lithium salt is 0.05 mol / L to 0.4 mol / L. Reasonable control of the concentration of the bis(fluorosulfonyl)imide lithium salt can achieve better cycle performance.

[0038] In some embodiments, in the electrolyte, the concentration of the bis(fluorosulfonyl)imide lithium salt is 0.1 mol / L to 0.2 mol / L.

[0039] In some embodiments, the silicon-based material has one or more of the following characteristics:

[0040] (1) The silicon-based material includes a silicon-carbon material, and the silicon-carbon material has one or more of the following characteristics:

[0041] (1.1) The silicon-carbon material comprises a porous carbon matrix and nano-silicon deposited in the pores of the porous carbon matrix;

[0042] (1.2) In the silicon-carbon material, the mass ratio of silicon element to carbon element is (4-6):(6-4);

[0043] (1.3) The mass ratio of the silicon-carbon material in the negative electrode active layer is 20% to 90%;

[0044] (2) The mass proportion of the silicon-based material in the negative electrode active layer is 10% to 100%.

[0045] According to a second aspect of the present application, a battery cell is provided, comprising a positive electrode plate, a negative electrode plate and an electrolyte, wherein the negative electrode active layer of the negative electrode plate comprises a silicon-based material, the electrolyte comprises a lithium salt, a solvent and a first additive, the solvent comprises a fluorocarbonate solvent, and the first additive comprises a reducing negative electrode film-forming additive.

[0046] In some embodiments, the fluorinated carbonate solvent has at least one of the following characteristics:

[0047] (1) In the solvent, the mass percentage of the fluorocarbonate solvent is 0.1% to 50%;

[0048] (2) The fluorocarbonate solvent includes one or more of fluoroethylene carbonate, difluoroethylene carbonate, trifluoroethylene carbonate, tetrafluoroethylene carbonate, 4-trifluoromethylethylene carbonate, 1-fluoromethylethylene carbonate, fluoroethyl methyl carbonate, fluorodimethyl carbonate, di(2,2,2-trifluoroethyl) carbonate, 2,2,2-trifluoroethyl methyl ester, difluoromethyl methyl carbonate, trifluoromethyl methyl carbonate and difluoromethyl ethyl carbonate.

[0049] In some embodiments, the reductive negative electrode film-forming additive has at least one of the following characteristics:

[0050] (1) The reducing negative electrode film-forming additive includes one or more of a lithium salt additive and a thioester additive;

[0051] (2) In the electrolyte, the mass percentage of the reducing negative electrode film-forming additive is 0.01%~5%.

[0052] In some embodiments, the electrolyte further includes a second additive, wherein the second additive includes an acid-scavenging additive.

[0053] In some embodiments, the acid scavenging additive has at least one of the following characteristics:

[0054] (1) The acid removal additive includes one or more of a cyclic acid anhydride additive and a chain isocyanate additive;

[0055] (2) In the electrolyte, the mass percentage of the acid removal additive is 0.01%~5%.

[0056] In some embodiments, the lithium salt has one or more of the following characteristics:

[0057] (1) The total molar concentration of the lithium salt in the electrolyte is 0.5 mol / L to 2 mol / L;

[0058] (2) The lithium salt includes lithium hexafluorophosphate.

[0059] In some embodiments, the lithium salt further comprises bis(fluorosulfonyl)imide lithium salt, and in the electrolyte, the concentration of the bis(fluorosulfonyl)imide lithium salt is 0.05 mol / L to 0.4 mol / L.

[0060] A third aspect of the present application provides an electrical device comprising the lithium-ion secondary battery described in the first aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] In order to better describe and illustrate the embodiments or examples provided by the present application, reference may be made to one or more drawings. The additional details or examples used to describe the drawings should not be considered as limiting the scope of the disclosed application, the embodiments or examples currently described, and any of the best modes of these applications currently understood. Moreover, the same reference numerals are used throughout the drawings to represent the same components. In the drawings:

[0062] Figure 1 It is a schematic diagram of a secondary battery according to one embodiment of the present application.

[0063] Figure 2 for Figure 1 An exploded view of a secondary battery according to an embodiment of the present application is shown.

[0064] Figure 3 FIG. 1 is a schematic diagram of an electrical device using a secondary battery according to an embodiment of the present application as a power source.

[0065] Description of reference numerals:

[0066] 1. Secondary battery; 11. Casing; 12. Electrode assembly; 13. Cover plate; 2. Electrical device. DETAILED DESCRIPTION

[0067] In order to facilitate the understanding of the present application, the present application will be described more fully below with reference to the relevant drawings. The preferred embodiments of the present application are given in the drawings. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present application more thorough and comprehensive.

[0068] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0069] The "range" disclosed in the present application can be limited in the form of a lower limit and an upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The range limited in this way can be including or excluding end values, and any end value can be included or not included independently, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a range. For example, if a range of 60 to 120 and 80 to 110 is listed for a specific parameter, it is understood that the range of 60 to 110 and 80 to 120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are also listed, the following ranges can all be expected: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4 and 2 to 5. In the present application, unless otherwise specified, the numerical range "a to b" represents the abbreviation of any real number combination between a and b, wherein a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to listing the parameter as, for example, integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For example, when a parameter is expressed as an integer selected from "2-10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9 and 10.

[0070] In the present application, "plurality", "multiple" and the like, unless otherwise specified, refer to a number greater than or equal to 2. For example, "one or more" means one or greater than or equal to two.

[0071] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0072] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment or implementation of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments. The "implementation methods" mentioned herein have a similar understanding.

[0073] Those skilled in the art will appreciate that, in the methods of each embodiment or example, the order in which each step is written does not mean a strict order of execution and does not constitute any limitation on the implementation process, and the detailed order of execution of each step should be determined by its function and possible internal logic. If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or steps (b) and (a) performed sequentially. For example, the method may also include step (c), indicating that step (c) can be added to the method in any order, for example, the method may include steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0074] In this application, unless otherwise specified, A (such as B) means that B is a non-limiting example of A, and it can be understood that A is not limited to B.

[0075] In this application, "optionally", "optional", and "optional" mean optional, that is, any one of the two parallel schemes of "yes" or "no". If there are multiple "options" in a technical solution, unless otherwise specified and there is no contradiction or mutual restriction, each "option" is independent.

[0076] In the present application, the term "saturated hydrocarbon group" refers to a monovalent residue formed by the loss of a hydrogen atom from a saturated hydrocarbon containing a primary (normal) carbon atom, a secondary carbon atom, a tertiary carbon atom, a quaternary carbon atom, or a combination thereof. A phrase containing the term, for example, "C1-C10 saturated hydrocarbon group" refers to a saturated hydrocarbon group containing 1 to 10 carbon atoms, and each occurrence may be independently a C1 saturated hydrocarbon group, a C2 saturated hydrocarbon group, a C3 saturated hydrocarbon group, a C4 saturated hydrocarbon group, a C5 saturated hydrocarbon group, a C6 saturated hydrocarbon group, a C7 saturated hydrocarbon group, a C8 saturated hydrocarbon group, or a C9 saturated hydrocarbon group. Suitable examples include, but are not limited to, methyl (Me, -CH3), ethyl (Et, -CH2CH3), 1-propyl (n-Pr, n-propyl, -CH2CH2CH3), 2-propyl (i-Pr, i-propyl, -CH(CH3)2), 1-butyl (n-Bu, n-butyl, -CH2CH2CH2CH3), 2-methyl-1-propyl (i-Bu, i-butyl, -CH2CH(CH3)2), 2-butyl (s-Bu, s-butyl, -CH(C H3)CH2CH3), 2-methyl-2-propyl (t-Bu, t-butyl, -C(CH3)3), 1-pentyl (n-pentyl, -CH2CH2CH2CH2CH3), 2-pentyl (-CH(CH3)CH2CH2CH3), 3-pentyl (-CH(CH2CH3)2), 2-methyl-2-butyl (-C(CH3)2CH2CH3), 3-methyl-2-butyl (-CH(CH3)CH(CH3)2), 3-methyl-1-butyl (- CH2CH2CH(CH3)2), 2-methyl-1-butyl (-CH2CH(CH3)CH2CH3), 1-hexyl (-CH2CH2CH2CH2CH2CH3), 2-hexyl (-CH(CH3)CH2CH2CH2CH3), 3-hexyl (-CH(CH2CH3)(CH2CH2CH3)), 2-methyl-2-pentyl (-C(CH3)2CH2CH2CH3), 3-methyl-2-pentyl (-CH(CH3)CH( 2), 2-methyl-3-pentyl (-CH(CH2CH3)CH(CH3)2), 2,3-dimethyl-2-butyl (-C(CH3)2CH(CH3)2), 3,3-dimethyl-2-butyl (-CH(CH3)C(CH3)3 and octyl (-(CH2)7CH3).

[0077] In the present application, the term "unsaturated hydrocarbon group" refers to a "saturated hydrocarbon group" containing at least one unsaturated site, such as a carbon-carbon double bond or a carbon-carbon triple bond.

[0078] In the present application, the term "cycloalkyl" refers to a non-aromatic hydrocarbon containing ring carbon atoms, which can be a monocyclic hydrocarbon group, a spirocyclic hydrocarbon group, or a bridged hydrocarbon group. The phrase comprising the term, for example, "C3~C10 cycloalkyl" refers to a cycloalkyl group containing 3~10 carbon atoms, and each occurrence can be independently of each other C3 cycloalkyl, C4 cycloalkyl, C5 cycloalkyl, C6 cycloalkyl, C7 cycloalkyl, C8 cycloalkyl, C9 cycloalkyl or C10 cycloalkyl. Suitable examples include but are not limited to: cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl and cycloheptyl. In addition, "cycloalkyl" can also contain one or more double bonds, and representative examples of the cycloalkyl containing double bonds include cyclopentenyl, cyclohexenyl, cyclohexadienyl and cyclobutadienyl.

[0079] In the present application, the term "aryl" refers to an aromatic hydrocarbon group derived from an aromatic ring compound by removing a hydrogen atom, which may be a monocyclic aryl, a condensed ring aryl, or a polycyclic aryl. For polycyclic rings, at least one is an aromatic ring system. For example, "C6-C20 aryl" refers to an aryl group containing 6 to 20 carbon atoms, and each occurrence may be independently C6 aryl, C10 aryl, C14 aryl, C18 aryl or C20 aryl. Suitable examples include, but are not limited to, benzene, biphenyl, naphthalene, anthracene, phenanthrene, perylene, triphenylene and their derivatives.

[0080] An embodiment of the present application provides a lithium-ion secondary battery, comprising a positive electrode plate, a negative electrode plate and an electrolyte, wherein the negative electrode active layer of the negative electrode plate comprises a silicon-based material, the electrolyte comprises a lithium salt, a solvent and a first additive, the solvent comprises a fluorocarbonate solvent, the first additive comprises a reducing negative electrode film-forming additive, and the mass percentage of the reducing negative electrode film-forming additive in the electrolyte is 0% to 4.5%.

[0081] During the research process, the present applicant discovered that for lithium-ion secondary batteries containing silicon-based materials, the coordinated use of fluorocarbonate solvents and reducing negative electrode film-forming additives can significantly improve the cycle life of lithium-ion secondary batteries.

[0082] Without limitation, the possible principle for improving the cycle life of lithium-ion secondary batteries containing silicon-based materials by combining fluorocarbonate solvents with reductive negative electrode film-forming additives is that fluorocarbonate solvents and reductive negative electrode film-forming additives can cooperate with each other to form a more stable SEI film on the surface of the negative electrode plate, reduce the damage to the SEI film caused by the expansion of silicon-based materials, and thereby improve the cycle life of lithium-ion secondary batteries.

[0083] The study also found that in some other embodiments, for lithium-ion secondary batteries containing silicon-based materials, the coordinated use of fluorocarbonate solvents and reducing negative electrode film-forming additives can also effectively improve the capacity retention rate of the battery stored under high temperature conditions, and reduce the increase of DC internal resistance during the cycle process, thereby achieving better rate performance.

[0084] It can be understood that the above principle analysis should not be used as a limitation on the technical solution and technical effect of the present application. The synergistic effect of the compounding of fluorocarbonate solvents and reducing negative electrode film-forming additives in the present application can be verified through examples.

[0085] It should be noted that the reductive negative electrode film-forming additive may no longer exist in the lithium-ion secondary battery (the corresponding mass percentage is 0%). This is because during the formation or recycling process of the finished lithium-ion secondary battery, the fluorocarbonate solvent and the reductive negative electrode film-forming additive cooperate with each other to form a stable SEI film on the surface of the negative electrode plate. During this period, the reductive negative electrode film-forming additive has been consumed. When the added amount is small, after formation or recycling, its mass percentage in the finished lithium-ion secondary battery may be 0%.

[0086] For ease of understanding, the present application refers to the battery after formation or recycling as a "lithium-ion secondary battery", and the battery before formation and recycling as a "battery cell". The mass percentage or concentration of the components will be explained from these two aspects below.

[0087] Corresponding to the above-mentioned lithium-ion secondary battery "the mass percentage of the reducing negative electrode film-forming additive in the electrolyte is 0%~4.5%", in the battery cell "the mass percentage of the reducing negative electrode film-forming additive in the electrolyte is 0.01%~5%".

[0088] In some embodiments, the fluorocarbonate solvent includes one or more of fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), trifluoroethylene carbonate, tetrafluoroethylene carbonate, 4-trifluoromethylethylene carbonate, 1-fluoromethylethylene carbonate, fluoroethyl methyl carbonate (FEMC), fluorodimethyl carbonate (FDMC), di(2,2,2-trifluoroethyl) carbonate, 2,2,2-trifluoroethyl methyl carbonate, difluoromethyl methyl carbonate, trifluoromethyl methyl carbonate and difluoromethyl ethyl carbonate. By using a suitable type of fluorocarbonate solvent, an SEI film containing inorganic lithium fluoride with high Young's modulus and highly elastic polycarbonate compounds can be generated on the electrode surface, and the oxidation stability of the SEI film is good, thereby improving the interface stability between the electrode and the electrolyte, reducing the reduction of lithium salts and solvents, thereby reducing the polarization inside the electrode and improving the cycle performance.

[0089] Further, the fluorocarbonate solvent includes one or more of fluoroethylene carbonate (FEC), fluorodimethyl carbonate (FDMC) and fluoroethylmethyl carbonate (FEMC).

[0090] In some embodiments, in the solvent, the mass percentage of the fluorocarbonate solvent is 0.1% to 50%. Specifically, the mass percentage of the fluorocarbonate solvent includes but is not limited to: 0.1%, 0.5%, 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50% or the range between any two of the foregoing. Reasonable control of the mass percentage of the fluorocarbonate solvent in the solvent is beneficial to the dissociation of the solvent to the lithium salt, while obtaining a better battery cycle life, improving the conductivity, improving the liquid phase transmission of lithium ions and the charge and discharge capacity of the battery, and also achieving good high temperature storage performance. Further before and after formation, in the solvent, the mass percentage of the fluorocarbonate solvent is 2% to 30%. It can be understood that during formation and recycling, the mass percentage of the fluorocarbonate solvent changes less, so the mass percentages of the lithium ion secondary battery and the fluorocarbonate solvent are both within the above range.

[0091] In some embodiments, the solvent also includes one or more of a cyclic carbonate solvent, a chain carbonate solvent, and a chain carboxylate solvent. Among them, the cyclic carbonate solvent is conducive to the dissociation of lithium salts and improves the conductivity of the electrolyte; the chain carbonate solvent and the chain carboxylate solvent can reduce the viscosity of the electrolyte, which is conducive to improving the liquid phase transmission performance of lithium ions. Therefore, these solvents are used in combination with fluorocarbonate solvents to obtain better charge and discharge capabilities. It is understandable that, unless otherwise specified, cyclic carbonate solvents, chain carbonate solvents, chain carboxylate solvents, etc. are all non-fluorinated.

[0092] Without limitation, the cyclic carbonate solvent includes one or more of ethylene carbonate, propylene carbonate and butylene carbonate. Further, the cyclic carbonate solvent includes one or more of ethylene carbonate and propylene carbonate.

[0093] Without limitation, the linear carbonate solvent includes one or more of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate and ethyl propyl carbonate. Further, the linear carbonate solvent includes one or more of dimethyl carbonate and ethyl methyl carbonate.

[0094] Without limitation, the chain carboxylate solvent includes one or more of methyl formate, ethyl acetate, propyl acetate, methyl propionate and ethyl propionate. Further, the chain carboxylate solvent includes one or more of ethyl acetate and methyl acetate.

[0095] In some embodiments, the reducing negative electrode film-forming additive includes one or more of a lithium salt additive and a thioester additive. The use of a suitable type of reducing negative electrode film-forming additive can better improve the cycle life of the battery. Furthermore, the reducing negative electrode film-forming additive includes a lithium salt additive and a thioester additive, and the two reducing negative electrode film-forming additives are used in synergy. The generated SEI film has corresponding organic components and inorganic components at the same time, which can obtain a better cycle life improvement effect.

[0096] In some embodiments, the lithium salt additive includes one or more of lithium bis(oxalate borate) (LiBOB), lithium difluorooxalate borate (LiODFB), lithium tetrafluoroborate (LiBF4), lithium tetrafluorooxalate phosphate (LiTFOP), lithium difluorophosphate (LiPO2F2), lithium fluorosulfonate (LiFSO3), lithium bis(trifluoromethanesulfonyl imide) (LiTFSI), lithium bis(fluorosulfonyl imide) (LiFSI) and lithium bis(oxalate borate) difluorophosphate (LiBODFP). The use of suitable types of lithium salt additives can form a good inorganic salt SEI film on the surface of the pole piece, improve the lithium conductivity, reduce the interface impedance, and thus improve the cycle life of the battery. Further, the lithium salt additive includes lithium difluorooxalate borate (LiODFB).

[0097] In some embodiments, the thioester additive includes one or more compounds having structural features shown in the following formula (II-1), formula (II-2) and formula (III) or their derivatives:

[0098] Formula (II-1),

[0099] Formula (II-2),

[0100] Formula (III),

[0101] In the compounds having the structural characteristics shown in formula (II-1) and formula (II-2), R 21 , R 22 , R 23 and R 24 Each independently includes H, F, C1~C10 saturated hydrocarbon group, fluorine-substituted C1~C10 saturated hydrocarbon group, C2~C10 unsaturated hydrocarbon group, fluorine-substituted C2~C10 unsaturated hydrocarbon group, aryl group, fluorine-substituted aryl group, carbonyl group, carboxyl group, ester group, nitrile group, silane group or ether group; n2 each independently includes 0, 1, 2 or 3; M2 includes O or CH2;

[0102] In the compound having the structural characteristics shown in formula (III), R 31 , R32 , R 33 and R 34 Each independently includes H, F, C1~C10 saturated hydrocarbon group, fluorine-substituted C1~C10 saturated hydrocarbon group, C2~C10 unsaturated hydrocarbon group, fluorine-substituted C2~C10 unsaturated hydrocarbon group, aryl group, fluorine-substituted aryl group, carbonyl group, carboxyl group, ester group, nitrile group, silane group or ether group; n3 includes 0, 1, 2 or 3; M3 includes O or CH2.

[0103] The use of suitable types of thioester additives can form interface components containing sulfates, sulfites and sulfur-containing organic matter on the surface of the electrode. Among them, sulfates and sulfites can improve the lithium ion conduction properties of the electrode interface and reduce the interface impedance; sulfur-containing organic matter can adapt to the volume effect of the electrode material during lithium ion insertion and extraction, which is beneficial to improve the interface stability, effectively protect the electrode material, and improve the cycle stability of the battery.

[0104] Furthermore, in the compound having the structural features shown in formula (II-1) or formula (II-2), n2 includes 0 or 1, that is, it is a five-membered or six-membered ring compound.

[0105] Furthermore, in the compound having the structural characteristics shown in formula (II-1) or formula (II-2), R 21 , R 22 , R 23 and R 24 Each independently comprises H or F.

[0106] Furthermore, in the compound having the structural characteristics shown in formula (III), n3 includes 0 or 1, that is, it is a five-membered or six-membered ring compound.

[0107] When the thioester additive is a five-membered or six-membered ring compound, on the one hand, it can exist relatively stably in the electrolyte, and on the other hand, it has good reaction activity, which is beneficial to the formation of the SEI film and improves the cycle stability of the battery.

[0108] Furthermore, in the compound having the structural characteristics shown in formula (III), R 31 , R 32 , R 33 and R 34 Each independently comprises H or F.

[0109] Without limitation, the derivative includes at least two compounds with structural features shown in formula (II-1) connected by a connecting group, at least two compounds with structural features shown in formula (II-2) connected by a connecting group, and at least two compounds with structural features selected from formula (II-1), formula (II-2) and formula (III) connected by a connecting group, and the connecting groups each independently include a single bond or a C1~C8 saturated hydrocarbon group.

[0110] In some embodiments, the thioester additive includes one or more of 1,3-propane sultone (PS), vinyl sulfite (ES), diethyl sulfate (DTD), propenyl-1,3-sultone (PES) and 3-fluoro-1,3-propane sultone (FPS). Further, the thioester additive includes one or more of 1,3-propane sultone, vinyl sulfate and vinyl sulfite.

[0111] In some embodiments, in the electrolyte, the mass percentage of the reductive negative electrode film-forming additive is 0~4.5%. Reasonable control of the mass percentage of the reductive negative electrode film-forming additive is conducive to the formation of a stable SEI film, improving the cycle performance, and reducing the impedance of the electrolyte / electrode interface. Specifically, the mass percentage of the reductive negative electrode film-forming additive includes but is not limited to: 0%, 0.01%, 0.05%, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5% or a range between any two of the foregoing. Further, the mass percentage of the reductive negative electrode film-forming additive is 0~2.5%. Correspondingly, in the battery cell, "the mass percentage of the reductive negative electrode film-forming additive in the electrolyte is 0.1%~3%".

[0112] In addition, in some embodiments, the electrolyte further includes a second additive, and the second additive includes an acid-removing additive. Fluorinated carbonate solvents or lithium salts such as lithium hexafluorophosphate are easy to generate acid, while silicon-based materials are more sensitive to acid, and acidic substances will increase the dissolution of transition metal ions in the positive electrode active material and destroy the SEI film on the surface of the negative electrode plate, thereby intensifying the reaction between the negative electrode active material and the electrolyte, causing capacity decay during the cycle storage process and reducing the cycle life. The acid-removing additive used in this application can effectively remove proton hydrogen in the system, reduce the acidity of the electrolyte, and thereby increase the cycle life of the lithium-ion secondary battery containing silicon-based materials.

[0113] In some embodiments, the acid scavenging additive includes one or more of a cyclic anhydride additive and a chain isocyanate additive.

[0114] Furthermore, the use of suitable types of cyclic anhydride additives and / or chain isocyanate additives can reduce the reactivity of proton hydrogen by reacting with water, thereby reducing its damage to the electrolyte and the electrolyte / electrode interface, thereby improving the cycle life of the battery.

[0115] In some embodiments, the cyclic acid anhydride additive includes one or more of maleic anhydride, citraconic anhydride, trifluoromethyl maleic anhydride, succinic anhydride and glutaric anhydride. Further, the cyclic acid anhydride additive includes succinic anhydride.

[0116] In some embodiments, the chain isocyanate additive includes one or more compounds having the structural features shown in the following formula (I):

[0117] R 11 (N=C=O)n1 (I),

[0118] Among them, R 11 Including C1~C10 saturated hydrocarbon group, C2~C10 unsaturated hydrocarbon group, fluorine-substituted C1~C10 saturated hydrocarbon group, fluorine-substituted C2~C10 unsaturated hydrocarbon group, C3~C10 cycloalkyl group, C6~C20 aryl group, fluorine-substituted C6~C20 aryl group, carboxyl group, ester group or carbonyl group; n1 includes 1, 2 or 3. It can be understood that in formula (I), the isocyanate group "-N=C=O" is directly bonded to the group R 11 In the above, when n1 is 1, it corresponds to monoisocyanate, when n1 is 2, it corresponds to diisocyanate, and when n1 is an integer of 3, it corresponds to triisocyanate.

[0119] In some embodiments, the compound having the structural characteristics shown in formula (I) In the compound having the structural characteristics shown in formula (I), n1 is 2, R 11 Including C2~C8 saturated hydrocarbon group, C3~C10 cyclic hydrocarbon group, phenyl group or ester group. Further, the chain isocyanate additive includes one or more of 1,6-hexamethylene diisocyanate, 1,4-cyclohexyl diisocyanate, m-phenylene diisocyanate and isocyanoethyl methacrylate. Further, the chain isocyanate additive includes 1,6-hexamethylene diisocyanate.

[0120] In some embodiments, in the electrolyte, the mass percentage of the acid-removing additive is 0.001%~3%. Reasonable control of the mass percentage of the second additive can obtain a better proton hydrogen removal effect, improve the cycle life, reduce the impedance of the electrolyte / electrode interface, and also achieve good high-temperature storage performance. Specifically, the mass percentage of the acid-removing additive includes but is not limited to: 0.001%, 0.005%, 0.01%, 0.05%, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3% or a range between any two of the foregoing. Correspondingly, in the battery cell, "the mass percentage of the acid-removing additive in the electrolyte is 0.01%~5%". Further, the mass percentage of the acid-removing additive is 0.01%~1%. Correspondingly, in the battery cell, "the mass percentage of the acid-removing additive in the electrolyte is 0.1%~2%".

[0121] In some embodiments, the concentration of the lithium salt in the electrolyte is 0.5mol / L~2mol / L. Specifically, the concentration of the lithium salt in the electrolyte includes but is not limited to: 0.5mol / L, 1mol / L, 1.5mol / L, 2mol / L or a range between any two of the foregoing. It is understandable that the concentration of the lithium salt in the electrolyte remains substantially unchanged during the formation or circulation process, so correspondingly, in the battery cell, "the concentration of the lithium salt in the electrolyte is 0.5mol / L~2mol / L".

[0122] In some embodiments, the lithium salt includes lithium hexafluorophosphate (LiPF6).

[0123] In some embodiments, the lithium salt also includes lithium bis(fluorosulfonyl)imide (LiFSI). Lithium hexafluorophosphate is easy to decompose and produce acid. Compared with it, lithium bis(fluorosulfonyl)imide has better stability, and lithium bis(fluorosulfonyl)imide can participate in the formation of SEI film, improve the stability of SEI film, and at the same time, lithium bis(fluorosulfonyl)imide can dissociate lithium salt well, which can improve liquid phase conductivity. Therefore, lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide are used in combination to obtain better cycle performance, and good high temperature storage performance and rate performance can also be achieved. Further, in the electrolyte, the concentration of lithium bis(fluorosulfonyl)imide is 0.05mol / L~0.4mol / L. Excessive concentration of lithium bis(fluorosulfonyl)imide has a certain degree of corrosion to metal current collectors such as aluminum foil in the pole piece, especially in the case of silicon-based materials. The expansion of silicon-based materials will pull the pole piece, the corrosion risk is higher, and the cycle performance is deteriorated. Therefore, the concentration of lithium bis(fluorosulfonyl)imide can be reasonably controlled to obtain better cycle performance. Specifically, the concentration of the bisfluorosulfonyl imide lithium salt includes, but is not limited to, 0.05 mol / L, 0.1 mol / L, 0.15 mol / L, 0.2 mol / L, 0.25 mol / L, 0.3 mol / L, 0.35 mol / L, 0.4 mol / L, or a range between any two of the foregoing. Further, the concentration of the bisfluorosulfonyl imide lithium salt is 0.1 mol / L to 0.2 mol / L.

[0124] Without limitation, the silicon-based material includes one or more of nano-silicon, micro-silicon, silicon-oxygen material and silicon-carbon material.

[0125] In some embodiments, the mass proportion of the silicon-based material in the negative electrode active layer is 10% to 100%. Specifically, the mass proportion of the silicon-based material in the negative electrode active layer includes but is not limited to: 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100% or any two of the foregoing.

[0126] In some embodiments, the silicon-based material includes a silicon-carbon material. Silicon has a high specific capacity, which is helpful for the design of high energy density batteries, but the system effect of silicon is large. The use of silicon-carbon materials can combine the advantages of silicon and carbon to a certain extent. In some embodiments, in the silicon-carbon material, the mass ratio of silicon element to carbon element is (4~6):(6~4). Specifically, the mass ratio of silicon element to carbon element includes but is not limited to: 6:4, 5.5:4.5, 5:5, 4.5:5.5, 4:6 or a range between any two of the foregoing.

[0127] Without limitation, the silicon content test in silicon-carbon materials: the silicon content is determined by emission spectroscopy (Inductively coupled plasma, ICP), as follows: a silicon-carbon material sample is taken, the sample is digested with aqua regia and hydrofluoric acid HF, the solution digested for 15 minutes and the solution completely digested are taken for ICP testing, the silicon content in the solution digested for 45 minutes is the silicon content in the "peripheral area of ​​the silicon-carbon material", and the difference in the silicon content in the solution completely digested and that digested for 1 hour is the silicon content in the "central area of ​​the silicon-carbon composite". The carbon content test in silicon-carbon composite materials: infrared absorption method carbon-sulfur content analysis, tested in accordance with the GB / T20123-2006 test standard, as follows: a silicon-carbon material is taken as a sample, the carbon content at 20 minutes of testing is the carbon content in the "peripheral area of ​​the silicon-carbon material", and the difference in the carbon content at 20 minutes of testing and at the end of the test is the carbon content in the "central area of ​​the silicon-carbon material".

[0128] In some embodiments, the silicon-carbon material includes a porous carbon matrix and nano-silicon deposited in the pores of the porous carbon matrix. The pores in the porous carbon matrix can provide space for the expansion of silicon and limit the expansion of silicon, improve the structural stability of the material, improve the cycle life, and at the same time, the content of silicon can be regulated by controlling the pores. Further, the porous carbon matrix includes mesopores and micropores. In some embodiments, the number of mesopores is greater than the number of micropores. Further, the number of mesopores accounts for ≥50%, and the number of micropores accounts for <50%. Regulating the number of micropores and mesopores in the porous carbon matrix can, on the one hand, form a porous carbon material with a relatively high specific surface area, and on the other hand, provide more space for the expansion of silicon. Among them, "mesopores" refer to pores with an average pore size of P1, 2nm≤P1≤10nm, and "micropores" refer to pores with an average pore size of P2, P2<2nm.

[0129] Without limitation, the proportion of the number of mesopores and micropores can be measured by using conventional testing instruments in the field to test the distribution of each pore and obtain the specific number through statistics. For example, the test instrument is ASAP2460-physical adsorption analyzer, the porous carbon material sample after drying and degassing is placed in liquid nitrogen, and different test pressures are adjusted to measure the adsorption amount of nitrogen respectively, and the adsorption and desorption isotherms are drawn. The shape of the pores is determined according to the shape of the hysteresis loop, the pore distribution is calculated according to different pore models, the pore size distribution curves of mesopores and macropores are fitted using the BJH model, and the pore size distribution curves of micropores are fitted using the DFT model.

[0130] In some embodiments, when the silicon-based material is a silicon-carbon material, the mass percentage of the silicon-carbon material in the negative electrode active layer is 20% to 90%. Reasonably control the mass percentage of the silicon-carbon material in the negative electrode active layer. On the one hand, a higher energy density can be obtained, and on the other hand, the damage to the pole piece due to the expansion of the silicon-carbon material can be reduced. Specifically, in the negative electrode active layer, the mass percentage of the silicon-carbon material includes but is not limited to: 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or a range between any two of the foregoing. When the silicon-based material is other silicon-based materials other than silicon-carbon materials, in the negative electrode active layer, the mass percentage of the silicon-based material is ≤10%. It can be understood that the negative electrode active layer also contains carbon-based materials. Furthermore, the carbon-based material includes one or more of artificial graphite, natural graphite, soft carbon and hard carbon.

[0131] In some other embodiments of the present application, an electrical device is provided, comprising the lithium-ion secondary battery as described above.

[0132] The lithium ion secondary battery (hereinafter referred to as secondary battery) and the electric device of the present application will be described below with reference to the drawings as appropriate.

[0133] Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator. During the battery charging and discharging process, active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays the role of conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is set between the positive electrode sheet and the negative electrode sheet, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing ions to pass through.

[0134] Furthermore, the positive electrode plate includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode film layer includes a positive electrode active material.

[0135] As a non-limiting example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode active material layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

[0136] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector may be obtained by forming a metal material on a polymer material substrate. In the positive electrode current collector, non-limiting examples of the metal material may include one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. In the positive electrode current collector, non-limiting examples of the polymer material substrate may include one or more of substrates such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0137] In some embodiments, the positive electrode active material may be a positive electrode active material for a battery known in the art. As a non-limiting example, the positive electrode active material may include one or more of the following materials: a lithium-containing phosphate with an olivine structure, a lithium transition metal oxide, and their respective modified compounds. However, the present application is not limited to these materials, and other conventional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Among them, examples of lithium transition metal oxides may include, but are not limited to, one or more of lithium cobalt oxide (such as LiCoO2), lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their modified compounds. Non-limiting examples of lithium-containing phosphates with an olivine structure may include, but are not limited to, one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon. Non-limiting examples of lithium cobalt oxides may include LiCoO2; non-limiting examples of lithium nickel oxides may include LiNiO2; non-limiting examples of lithium manganese oxides may include LiMnO2, LiMn2O4, etc.; non-limiting examples of lithium nickel cobalt manganese oxides may include LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM 333 )、LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 )、LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 )、LiNi 0.6 Co 0.2 Mn0.2 O2 (also referred to as NCM 622 )、LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ) etc. Non-limiting examples of lithium nickel cobalt aluminum oxide may include LiNi 0.8 Co 0.15 Al 0.05 O2.

[0138] In some embodiments, the positive electrode active material layer may further optionally include a binder. As non-limiting examples, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0139] In some embodiments, the positive electrode active material layer may further optionally include a conductive agent. As non-limiting examples, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0140] In some embodiments, the positive electrode sheet can be prepared in the following manner: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent to form a positive electrode slurry; the positive electrode slurry is coated on at least one side of the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained. The type of solvent can be selected from but not limited to any one of the aforementioned embodiments, such as N-methylpyrrolidone (NMP). The surface of the positive electrode collector coated with the positive electrode slurry can be on a single surface of the positive electrode collector or on both surfaces of the positive electrode collector. The surface of the positive electrode collector coated with the positive electrode slurry can be on a single surface of the positive electrode collector or on both surfaces of the positive electrode collector. The solid content of the positive electrode slurry can be 40wt%~80wt%. The viscosity of the positive electrode slurry at room temperature can be adjusted to 5000mPa·s~25000mPa·s. When applying the positive electrode slurry, the coating unit surface density based on dry weight (excluding solvent) can be 15 mg / cm 2 ~35mg / cm 2 The compaction density of the positive electrode can be 3.0g / cm 3 ~3.6g / cm 3 , optional 3.3g / cm 3 ~3.5g / cm 3 .

[0141] The negative electrode sheet includes a negative electrode current collector and a negative electrode active layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode active layer includes a negative electrode active material.

[0142] As a non-limiting example, the negative electrode current collector has two surfaces opposite to each other in its own thickness direction, and the negative electrode active layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

[0143] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be obtained by forming a metal material on a polymer material substrate. In the negative electrode current collector, non-limiting examples of the metal material may include one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. In the negative electrode current collector, non-limiting examples of the polymer material substrate may include one or more of substrates such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0144] In some embodiments, the negative electrode active material is as described above and will not be described in detail herein.

[0145] In some embodiments, the negative electrode active layer may further include a binder, which may include one or more of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0146] In some embodiments, the negative electrode active layer may further include a conductive agent, which may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0147] In some embodiments, the negative electrode active layer may further include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0148] In some embodiments, the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (a non-limiting example of the solvent is deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on at least one side of the surface of the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained. The surface of the negative electrode collector coated with the negative electrode slurry can be on a single surface of the negative electrode collector or on both surfaces of the negative electrode collector. The solid content of the negative electrode slurry can be 30wt%~60wt%. The viscosity of the negative electrode slurry at room temperature can be adjusted to 2000mPa·s~10000mPa·s. When coating the negative electrode slurry, the coating unit surface density on a dry weight basis (excluding the solvent) can be 75g / m 2 ~220g / m 2 The compaction density of the negative electrode sheet can be 1.0g / cm 3 ~ 1.8g / cm 3 .

[0149] In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical stability and mechanical stability can be selected.

[0150] In some embodiments, the material of the isolation membrane may include one or more of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation membrane may be a single-layer film or a multi-layer composite film, without particular limitation. When the isolation membrane is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0151] In some embodiments, the isolation film has a thickness of 6 μm to 40 μm, and may be 12 μm to 20 μm.

[0152] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly by a winding process or a lamination process.

[0153] In some embodiments, the secondary battery may include an outer package, which may be used to encapsulate the electrode assembly and the electrolyte.

[0154] In some embodiments, the outer packaging of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, and further, non-limiting examples of plastic may include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0155] The secondary battery includes at least one battery cell. The secondary battery may include one or more battery cells.

[0156] In this application, unless otherwise specified, "battery cell" refers to a basic unit that can realize the mutual conversion of chemical energy and electrical energy, and further, generally speaking, at least includes a positive electrode sheet, a negative electrode sheet and an electrolyte. During the battery charging and discharging process, active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays the role of conducting active ions between the positive electrode sheet and the negative electrode sheet.

[0157] The present application has no particular limitation on the shape of the battery cell, which may be cylindrical, square or any other shape. Figure 1 The secondary battery 1 is a square structure as an example.

[0158] In some of these embodiments, reference Figure 2 , the outer packaging may include a shell 11 and a cover plate 13. Among them, the shell 11 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 11 has an opening connected to the receiving cavity, and the cover plate 13 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly 12 through a winding process or a lamination process. The electrode assembly 12 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 12. The number of electrode assemblies 12 contained in the secondary battery 1 can be one or more, and those skilled in the art can select according to actual needs.

[0159] The secondary battery may be a battery module or a battery pack.

[0160] The battery module includes at least one battery cell. The number of battery cells contained in the battery module can be one or more, and those skilled in the art can select a suitable number according to the application and capacity of the battery module.

[0161] In the battery module, the plurality of battery cells may be arranged in sequence along the length direction of the battery module. Of course, they may also be arranged in any other manner. Further, the plurality of battery cells may be fixed by fasteners.

[0162] Optionally, the battery module may further include a housing having an accommodation space, and the plurality of battery cells are accommodated in the accommodation space.

[0163] In some of the embodiments, the battery modules may be assembled into a battery pack. The battery pack may contain one or more battery modules. Those skilled in the art may select a suitable number according to the application and capacity of the battery pack.

[0164] The battery pack may include a battery box and a plurality of battery modules disposed in the battery box. The battery box includes an upper box body and a lower box body, and the upper box body can be covered on the lower box body to form a closed space for accommodating the battery modules. The plurality of battery modules can be arranged in the battery box in any manner.

[0165] In addition, the present application also provides an electrical device, which includes a secondary battery provided by the present application. The secondary battery can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto. Among them, the mobile device may be, for example, a mobile phone, a laptop computer, etc.; the electric vehicle may be, for example, a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc., but are not limited thereto.

[0166] As an electrical device, a secondary battery can be selected according to its usage requirements.

[0167] Figure 3 The power consumption device 2 is taken as an example. The power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the power consumption device's requirements for high power and high energy density of secondary batteries, a battery pack or a battery module can be used.

[0168] As another example, the device may be a mobile phone, a tablet computer, a notebook computer, etc. The device is usually required to be light and thin, and a battery cell may be used as a power source.

[0169] In order to make the technical problems, technical solutions and beneficial effects solved by the present application clearer, the present application will be further described in detail below in conjunction with the embodiments and drawings. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present application and its applications. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application.

[0170] If no specific techniques or conditions are specified in the examples, the techniques or conditions described in the literature in the field or the product instructions are used. If no manufacturer is specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0171] The battery performance test methods of the embodiments and comparative examples are as follows:

[0172] (1) Cycle life:

[0173] At 45°C, the prepared secondary battery (full battery) is charged to 4.25V at 0.5C, and then discharged to 2.5V at 1C. This is a cyclic charge and discharge process. The discharge capacity at this time is recorded as the initial discharge capacity. The secondary battery is further subjected to cyclic charge and discharge tests according to the above method, and the discharge capacity after each cycle is recorded until the discharge capacity of the secondary battery decays to 80% of the initial discharge capacity. The number of cycles at this time is recorded.

[0174] (2) Rate performance:

[0175] At 45°C, the prepared secondary battery (full battery) is charged to 4.25V at 1C, and then discharged to 2.5V at 1C. This is a cycle charge and discharge process. The DC internal resistance at this time is recorded as the initial DC internal resistance. The secondary battery is subjected to 500 cycles of charge and discharge test according to the above method, and the DC internal resistance after 500 cycles is recorded. The DC internal resistance growth rate after 500 cycles at 1C rate is calculated.

[0176] (3) High temperature capacity retention rate:

[0177] At 25°C, the prepared secondary battery was charged at a constant current of 0.5C to a charge cutoff voltage of 4.25V, then charged at a constant voltage to a current of ≤0.05C, left to stand for 5 minutes, and then discharged at a constant current of 0.33C to a discharge cutoff voltage of 2V, left to stand for 5 minutes, which was a charge and discharge cycle. Then, the battery was charged at a constant current of 0.5C to a charge cutoff voltage of 4.25V, then charged at a constant voltage to a current of ≤0.05C, and the battery was stored at 60°C for 100 days. The battery was subjected to a cyclic charge and discharge test according to the above method, and the capacity retention rate of the lithium-ion battery after 100 days of storage was calculated.

[0178] Example 1

[0179] 1) Preparation of positive electrode

[0180] The positive electrode active material LiNi 0.9 Co 0.05 Mn 0.05 O2 (NCM955), conductive agent acetylene black and binder PVDF are dispersed in solvent NMP in a weight ratio of 94%:3%:3% and mixed evenly to obtain positive electrode slurry; the positive electrode slurry is evenly coated on the double-side surfaces of the positive electrode current collector aluminum foil, and after drying and cold pressing, the positive electrode sheet is obtained.

[0181] 2) Preparation of negative electrode

[0182] Silicon-carbon material, graphite, conductive carbon black, and binder polyacrylic acid are mixed in a mass ratio of 40%:40%:10%:10%, deionized water is added and stirred thoroughly, and negative electrode slurry is obtained under the action of a vacuum mixer; the negative electrode slurry is evenly coated on the double-sided surface of the copper foil, dried, and then cold pressed and cut to obtain negative electrode sheets. Among them, the silicon-carbon porous material includes a porous carbon matrix and silicon nanoparticles loaded in the pores of the porous carbon matrix, and the pores include mesopores (average pore size P1, 2nm≤P1≤10nm) and micropores (average pore size P2, P2<2nm), the number of mesopores accounts for 60% of the pores, the number of micropores accounts for 40% of the pores, and the mass ratio of silicon element to carbon element is 5:5.

[0183] 3) Isolation film

[0184] A 12μm thick polypropylene isolation film was selected.

[0185] 4) Preparation of electrolyte

[0186] In an argon atmosphere glove box (H2O<0.1ppm, O2<0.1ppm), the organic solvents FEC, EMC, and DMC were mixed uniformly in a mass ratio of 15%:55%:30%, propenyl-1,3-sultone, LiDFOB, and succinic anhydride were added, and LiFSI and LiPF6 were dissolved in the organic solvent and stirred uniformly to obtain an electrolyte, wherein the mass percentage of propenyl-1,3-sultone was 1%, the mass percentage of LiDFOB was 1%, the mass percentage of succinic anhydride was 1%, the concentration of LiFSI was 0.2 mol / L, and the concentration of LiPF6 was 0.8 mol / L;

[0187] 5) Preparation of batteries

[0188] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, so that the separator is between the positive and negative electrodes to play an isolating role, and then wound into a square bare cell, loaded with aluminum plastic film, dried, and injected with electrolyte to prepare the cell. The cell is vacuum packaged, left to stand, formed, and shaped to obtain the finished battery. The formation process is: at 45°C, 0.02C constant current charging to 3.4V, standing for 5 minutes, and 0.1C constant current charging to 3.75V.

[0189] The battery preparation methods of Examples 2 to 5 are the same as those of Example 1, with the main difference being that the mass percentage of FEC in the organic solvent is changed, the mass percentage of EMC and DMC is adjusted accordingly, and the ratio of EMC:DMC is kept constant at 5.5:3. The details are shown in Table 1 below:

[0190] Table 1

[0191]

[0192] The battery preparation method of Example 6 is the same as that of Example 1, with the main difference being that FDMC is used to replace FEC in equal amounts. The details are shown in Table 2 below:

[0193] Table 2

[0194]

[0195] The battery preparation methods of Examples 7 to 11 are the same as those of Example 1, with the main difference being that different types of acid-removing additives are used to replace succinic anhydride in equal amounts. The details are shown in Table 3 below:

[0196] Table 3

[0197]

[0198] The battery preparation methods of Examples 12 to 14 are the same as those of Example 1, with the main difference being that different mass percentages of acid removal additives are used. The details are shown in Table 4 below:

[0199] Table 4

[0200]

[0201] The battery preparation method of Example 15 is the same as that of Example 1, except that different types of reducing film-forming additives are used to replace propenyl-1,3-sultone in equal amounts. The details are shown in Table 5 below:

[0202] Table 5

[0203]

[0204] The battery preparation method of Examples 16-17 is the same as that of Example 1, with the main difference being that different concentrations of LiPF6 and LiFSI are used. The details are shown in Table 6 below:

[0205] Table 6

[0206]

[0207] The battery preparation method of Comparative Example 1 is the same as that of Example 1, with the main difference being that FEC is not used in the organic solvent, the mass percentages of EMC and DMC are adjusted accordingly, and the ratio of EMC:DMC is kept unchanged at 5.5:3.

[0208] The battery preparation method of Comparative Example 2 is the same as that of Example 1, the main difference being that no reducing film-forming additive is used.

[0209] The details are shown in Table 7 below:

[0210] Table 7

[0211]

[0212] By comparing the embodiment and comparative examples 1 and 2, it can be seen that by synergistically using fluorocarbonate solvents and reducing negative electrode film-forming additives, the cycle life of the battery can be improved, and it also has good high-temperature storage capacity retention and rate performance.

[0213] Furthermore, through the comparison between Examples 1 to 5, it can be seen that reasonable control of the mass percentage of the fluorocarbonate solvent in the solvent can achieve better cycle life, capacity retention rate of high temperature storage and rate performance.

[0214] Furthermore, through the comparison between Examples 1 and 6, it can be seen that the use of different types of fluorocarbonate solvents can achieve good cycle life, capacity retention rate of high temperature storage and rate performance.

[0215] Furthermore, by comparing Examples 1 and 7 to 11, it can be seen that the use of different types of acid scavenging additives can achieve good cycle life, capacity retention rate of high temperature storage and rate performance, among which for cyclic anhydride additives, succinic anhydride is better, and for chain isocyanate additives, 1,6-hexamethylene diisocyanate is better.

[0216] Furthermore, by comparing Examples 1 and 14, it can be seen that the addition of the acid-scavenging additive can achieve better cycle life, capacity retention rate of high temperature storage and rate performance. At the same time, by comparing Examples 1 and 12-13, it can be seen that the reasonable control of the mass percentage of the acid-scavenging additive can achieve better cycle life, capacity retention rate of high temperature storage and rate performance.

[0217] Furthermore, through the comparison between Examples 1 and 16-17, it can be seen that the combination of LiFSI and LiPF6 and the reasonable control of the concentration of LiFSI can achieve better cycle life, capacity retention rate of high temperature storage and rate performance.

[0218] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0219] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the attached claims.

Claims

1. A lithium ion secondary battery, characterized in that: It comprises a positive electrode sheet, a negative electrode sheet and an electrolyte, wherein the negative electrode active layer of the negative electrode sheet comprises a silicon-based material, the electrolyte comprises a lithium salt, a solvent and a first additive, the solvent comprises a fluorocarbonate solvent, the first additive comprises a reducing negative electrode film-forming additive, and the mass percentage of the reducing negative electrode film-forming additive in the electrolyte is 0% to 4.5%; The electrolyte further includes a second additive, wherein the second additive includes an acid-scavenging additive.

2. The lithium ion secondary battery according to claim 1, characterized in that: In the solvent, the mass percentage of the fluorocarbonate solvent is 0.1% to 50%.

3. The lithium ion secondary battery according to claim 2, characterized in that: In the solvent, the mass percentage of the fluorocarbonate solvent is 2% to 30%.

4. The lithium-ion secondary battery according to claim 1, characterized in that: The fluorocarbonate solvent includes one or more of fluoroethylene carbonate, difluoroethylene carbonate, trifluoroethylene carbonate, tetrafluoroethylene carbonate, 4-trifluoromethylethylene carbonate, 1-fluoromethylethylene carbonate, fluoroethyl methyl carbonate, fluorodimethyl carbonate, di(2,2,2-trifluoroethyl) carbonate, 2,2,2-trifluoroethyl methyl ester, difluoromethyl methyl carbonate, trifluoromethyl methyl carbonate and difluoromethyl ethyl carbonate.

5. The lithium ion secondary battery according to claim 4, characterized in that: The fluorocarbonate solvent includes one or more of fluoroethylene carbonate, fluorodimethyl carbonate and fluoroethyl methyl carbonate.

6. The lithium ion secondary battery according to claim 1, characterized in that: The solvent further comprises one or more of a cyclic carbonate solvent, a chain carbonate solvent and a chain carboxylate solvent.

7. The lithium ion secondary battery according to claim 1, characterized in that: The reductive negative electrode film-forming additive has one or more of the following characteristics: (1) The reducing negative electrode film-forming additive includes one or more of a lithium salt additive and a thioester additive; (2) In the electrolyte, the mass percentage of the reducing negative electrode film-forming additive is 0-2.5%.

8. The lithium ion secondary battery according to claim 7, characterized in that: The lithium salt additive includes one or more of lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium tetrafluoroborate, lithium tetrafluorooxalatophosphate, lithium difluorophosphate, lithium fluorosulfonate, lithium bis(trifluoromethanesulfonylimide), lithium bis(fluorosulfonylimide) and lithium bis(oxalatoborate)difluorophosphate; and / or The thioester additive includes one or more compounds having structural features shown in the following formula (II-1), formula (II-2) and formula (III) or their derivatives: Formula (II-1), Formula (II-2), Formula (III), In the compounds having the structural characteristics shown in formula (II-1) and formula (II-2), R 21 , R 22 , R 23 and R 24 Each independently includes H, F, C1~C10 saturated hydrocarbon group, fluorine-substituted C1~C10 saturated hydrocarbon group, C2~C10 unsaturated hydrocarbon group, fluorine-substituted C2~C10 unsaturated hydrocarbon group, aryl group, fluorine-substituted aryl group, carbonyl group, carboxyl group, ester group, nitrile group, silane group or ether group; n2 each independently includes 0, 1, 2 or 3; M2 includes O or CH2; In the compound having the structural characteristics shown in formula (III), R 31 , R 32 , R 33 and R 34 Each independently includes H, F, C1~C10 saturated hydrocarbon group, fluorine-substituted C1~C10 saturated hydrocarbon group, C2~C10 unsaturated hydrocarbon group, fluorine-substituted C2~C10 unsaturated hydrocarbon group, aryl group, fluorine-substituted aryl group, carbonyl group, carboxyl group, ester group, nitrile group, silane group or ether group; n3 includes 0, 1, 2 or 3; M3 includes O or CH2.

9. The lithium ion secondary battery according to claim 8, characterized in that: The lithium salt additive includes lithium difluorooxalate borate; and / or, The thioester additive includes one or more of 1,3-propane sultone, vinyl sulfate and vinyl sulfite.

10. The lithium ion secondary battery according to any one of claims 1 to 9, characterized in that: The acid scavenging additive includes one or more of a cyclic anhydride additive and a chain isocyanate additive.

11. The lithium ion secondary battery according to claim 10, characterized in that: The cyclic anhydride additive includes one or more of maleic anhydride, citraconic anhydride, trifluoromethylmaleic anhydride, succinic anhydride and glutaric anhydride; And / or, the chain isocyanate additive includes one or more compounds having the structural characteristics shown in the following formula (I): R 11 (N=C=O)n1 (I), Among them, R 11 Including C1~C10 saturated hydrocarbon group, C2~C10 unsaturated hydrocarbon group, fluorine-substituted C1~C10 saturated hydrocarbon group, fluorine-substituted C2~C10 unsaturated hydrocarbon group, C3~C10 cycloalkyl group, C6~C20 aryl group, fluorine-substituted C6~C20 aryl group, carboxyl group, ester group or carbonyl group; n1 includes 1, 2 or 3.

12. The lithium ion secondary battery according to claim 11, characterized in that: The cyclic anhydride additive includes succinic anhydride; And / or, the chain isocyanate additive includes one or more of hexamethylene diisocyanate, 1,4-cyclohexyl diisocyanate, isophenyl diisocyanate and isocyanoethyl methacrylate.

13. The lithium ion secondary battery according to claim 10, characterized in that: In the electrolyte, the mass percentage of the acid removal additive is 0.001%~3%.

14. The lithium ion secondary battery according to claim 13, characterized in that: In the electrolyte, the mass percentage of the acid-scavenging additive in the electrolyte is 0.01%~1%.

15. The lithium ion secondary battery according to any one of claims 1 to 9, characterized in that: The lithium salt has one or more of the following characteristics: (1) The total molar concentration of the lithium salt in the electrolyte is 0.5 mol / L to 2 mol / L; (2) The lithium salt includes lithium hexafluorophosphate.

16. The lithium ion secondary battery according to claim 15, characterized in that: The lithium salt further comprises bis(fluorosulfonyl)imide lithium salt. In the electrolyte, the concentration of the bis(fluorosulfonyl)imide lithium salt is 0.05 mol / L to 0.4 mol / L.

17. The lithium ion secondary battery according to claim 16, characterized in that: In the electrolyte, the concentration of the bis(fluorosulfonyl)imide lithium salt is 0.1 mol / L to 0.2 mol / L.

18. The lithium ion secondary battery according to any one of claims 1 to 9, characterized in that: The silicon-based material has one or more of the following characteristics: (1) The silicon-based material includes a silicon-carbon material, and the silicon-carbon material has one or more of the following characteristics: (1.1) The silicon-carbon material comprises a porous carbon matrix and nano-silicon deposited in the pores of the porous carbon matrix; (1.2) In the silicon-carbon material, the mass ratio of silicon element to carbon element is (4-6):(6-4); (1.3) The mass ratio of the silicon-carbon material in the negative electrode active layer is 20% to 90%; (2) The mass proportion of the silicon-based material in the negative electrode active layer is 10% to 100%.

19. A battery cell, characterized in that: It comprises a positive electrode sheet, a negative electrode sheet and an electrolyte, wherein the negative electrode active layer of the negative electrode sheet comprises a silicon-based material, the electrolyte comprises a lithium salt, a solvent and a first additive, the solvent comprises a fluorocarbonate solvent, and the first additive comprises a reducing negative electrode film-forming additive; The electrolyte further includes a second additive, wherein the second additive includes an acid-scavenging additive.

20. The battery cell according to claim 19, characterized in that: The fluorinated carbonate solvent has at least one of the following characteristics: (1) In the solvent, the mass percentage of the fluorocarbonate solvent is 0.1% to 50%; (2) The fluorocarbonate solvent includes one or more of fluoroethylene carbonate, difluoroethylene carbonate, trifluoroethylene carbonate, tetrafluoroethylene carbonate, 4-trifluoromethylethylene carbonate, 1-fluoromethylethylene carbonate, fluoroethyl methyl carbonate, fluorodimethyl carbonate, di(2,2,2-trifluoroethyl) carbonate, 2,2,2-trifluoroethyl methyl ester, difluoromethyl methyl carbonate, trifluoromethyl methyl carbonate and difluoromethyl ethyl carbonate.

21. The battery cell according to claim 19, characterized in that: The reducing negative electrode film-forming additive has at least one of the following characteristics: (1) The reducing negative electrode film-forming additive includes one or more of a lithium salt additive and a thioester additive; (2) In the electrolyte, the mass percentage of the reducing negative electrode film-forming additive is 0.01%~5%.

22. The battery cell according to any one of claims 19 to 21, characterized in that: The acid removal additive has at least one of the following characteristics: (1) The acid removal additive includes one or more of a cyclic acid anhydride additive and a chain isocyanate additive; (2) In the electrolyte, the mass percentage of the acid removal additive is 0.01%~5%.

23. The battery cell according to any one of claims 19 to 21, characterized in that: The lithium salt has one or more of the following characteristics: (1) The total molar concentration of the lithium salt in the electrolyte is 0.5 mol / L to 2 mol / L; (2) The lithium salt includes lithium hexafluorophosphate.

24. The battery cell according to claim 23, characterized in that: The lithium salt further comprises bis(fluorosulfonyl)imide lithium salt. In the electrolyte, the concentration of the bis(fluorosulfonyl)imide lithium salt is 0.05 mol / L to 0.4 mol / L.

25. An electrical device, characterized in that: A lithium ion secondary battery comprising any one of claims 1 to 18.

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