Lithium ion secondary battery, electrolyte, battery cell and electric device

Abstract

The invention provides a lithium ion secondary battery, an electrolyte, a battery cell and an electric device. The lithium ion secondary battery comprises an electrolyte, the electrolyte comprises a lithium salt, a first additive and an organic solvent, the lithium salt comprises lithium hexafluorophosphate, the first additive comprises 1, 3-propene sultone, the organic solvent comprises a first solvent, and the relative dielectric constant of the first solvent is larger than or equal to 30. The lithium ion secondary battery has a relatively high cycle capacity retention rate.

Description

Technical Field

[0001] The present application relates to the technical field of secondary batteries, and in particular to a lithium-ion secondary battery, an electrolyte, 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. They have been widely used in energy storage power systems such as hydropower, thermal, wind and solar power stations, as well as power tools, electric bicycles, electric motorcycles, electric vehicles and other fields.

[0003] 1,3-Propene sultone (PST) is an electrolyte additive for lithium-ion batteries, which can improve the cycle life of batteries to a certain extent. However, the cycle life of batteries currently using PST needs to be further improved. Summary of the invention

[0004] In order to achieve the above-mentioned objectives, the present application provides a lithium-ion secondary battery, an electrolyte, a battery cell and an electrical device with a relatively long cycle life.

[0005] In a first aspect of the present application, a lithium ion secondary battery is provided, comprising an electrolyte, wherein the electrolyte comprises a lithium salt, a first additive and an organic solvent, wherein the lithium salt comprises lithium hexafluorophosphate, the first additive comprises 1,3-propylene sultone, and the organic solvent comprises a first solvent, wherein the relative dielectric constant of the first solvent is ≥30.

[0006] The present application study found that using a first solvent with a relative dielectric constant (ε) ≥ 30 in a lithium-ion battery system using lithium hexafluorophosphate as a lithium salt and 1,3-propylene sultone as an additive can effectively reduce the decomposition of 1,3-propylene sultone, reduce the acidity of the system, and thereby improve the battery's cycle capacity retention rate, giving the battery a better cycle life.

[0007] In some embodiments, the relative dielectric constant of the first solvent is 30-85.

[0008] In some embodiments, the first solvent includes one or more of N,N-dimethylacetamide, N,N-dimethylformamide, N,N-dimethylpropionamide, N,N-dimethyltrifluoroacetamide, N,N-dimethylpentafluoropropionamide, N,N-diethyltrifluoroacetamide, formamide, acetamide and dimethyl sulfate.

[0009] In some embodiments, in the organic solvent, the mass percentage of the first solvent is 0.5% to 18%.

[0010] In some embodiments, in the organic solvent, the mass percentage of the first solvent is 1% to 6%.

[0011] In some embodiments, the organic solvent further comprises a second solvent, and the second solvent has one or both of the following characteristics:

[0012] (1) the second solvent comprises one or more of a carbonate solvent, a carboxylate solvent and a nitrile solvent;

[0013] (2) In the organic solvent, the mass percentage of the second solvent is 82% to 99.5%.

[0014] In some embodiments, the electrolyte further comprises a second additive, wherein the second additive comprises a silicon-containing acid-scavenging additive.

[0015] In some embodiments, the second additive has one or both of the following characteristics:

[0016] (1) The silicon-containing acid-removing additive includes one or more of tris(trimethylsilyl)phosphate, silazane, N-trimethylsilyl imidazole and tris(trimethylsilyl)borate;

[0017] (2) In the electrolyte, the mass concentration of the silicon-containing acid-removing additive is 0.01% to 0.5%.

[0018] In some embodiments, the electrolyte further comprises a third additive, wherein the third additive comprises a negative electrode film-forming additive containing a 5- to 6-membered heterocyclic ring.

[0019] In some embodiments, the third additive has one or both of the following characteristics:

[0020] (1) The negative electrode film-forming additive containing a 5- to 6-membered heterocyclic ring includes one or more of fluoroethylene carbonate, vinylene carbonate, vinylethylene carbonate, propane sultone, vinyl sulfate and methylene methane disulfonate;

[0021] (2) In the electrolyte, the mass concentration of the negative electrode film-forming additive containing a 5- to 6-membered heterocyclic ring is 0.5% to 5%.

[0022] In some embodiments, the electrolyte further comprises a fourth additive, wherein the fourth additive comprises a positive electrode film-forming additive containing phosphorus and / or boron.

[0023] In some embodiments, the fourth additive has one or both of the following characteristics:

[0024] (1) The positive electrode film-forming additive includes one or more of lithium difluorophosphate, lithium difluorooxalatoborate and lithium dioxalatoborate;

[0025] (2) In the electrolyte, the mass concentration of the positive electrode film-forming additive is 0.01%~2%.

[0026] In some embodiments, in the electrolyte, the mass concentration of lithium hexafluorophosphate is 8% to 16%.

[0027] In some embodiments, in the electrolyte, the mass concentration of 1,3-propene sultone is 0.1% to 1%.

[0028] In a second aspect of the present application, an electrolyte is provided, comprising a lithium salt, a first additive and an organic solvent, wherein the lithium salt comprises lithium hexafluorophosphate, the first additive comprises 1,3-propylene sultone, the organic solvent comprises a first solvent, and the relative dielectric constant of the first solvent is ≥30.

[0029] In some embodiments, the electrolyte is the electrolyte in the lithium-ion secondary battery described in the first aspect.

[0030] In a third aspect of the present application, a battery cell is provided, comprising an electrolyte, wherein the electrolyte comprises a lithium salt, a first additive and an organic solvent, wherein the lithium salt comprises lithium hexafluorophosphate, the first additive comprises 1,3-propylene sultone, and the organic solvent comprises a first solvent, wherein the relative dielectric constant of the first solvent is ≥30.

[0031] In some embodiments, the relative dielectric constant of the first solvent is 30-85.

[0032] In some embodiments, the first solvent includes one or more of N,N-dimethylacetamide, N,N-dimethylformamide, N,N-dimethylpropionamide, N,N-dimethyltrifluoroacetamide, N,N-dimethylpentafluoropropionamide, N,N-diethyltrifluoroacetamide, formamide, acetamide and dimethyl sulfate.

[0033] In some embodiments, in the organic solvent, the mass percentage of the first solvent is 1% to 20%.

[0034] In some embodiments, the electrolyte further comprises a second additive, wherein the second additive comprises a silicon-containing acid-scavenging additive.

[0035] In some embodiments, the second additive has one or both of the following characteristics:

[0036] (1) The silicon-containing acid-removing additive includes one or more of tris(trimethylsilyl)phosphate, silazane, N-trimethylsilyl imidazole and tris(trimethylsilyl)borate;

[0037] (2) In the electrolyte, the mass concentration of the silicon-containing acid-removing additive is 0.01% to 1%.

[0038] In some embodiments, the electrolyte further comprises a third additive, wherein the third additive comprises a negative electrode film-forming additive containing a 5- to 6-membered heterocyclic ring.

[0039] In some embodiments, the third additive has one or both of the following characteristics:

[0040] (1) The negative electrode film-forming additive containing a 5- to 6-membered heterocyclic ring includes one or more of fluoroethylene carbonate, vinylene carbonate, vinylethylene carbonate, propane sultone, vinyl sulfate and methylene methane disulfonate;

[0041] (2) In the electrolyte, the mass concentration of the negative electrode film-forming additive containing a 5- to 6-membered heterocyclic ring is 0.5% to 6%.

[0042] In some embodiments, the electrolyte further comprises a fourth additive, wherein the fourth additive comprises a positive electrode film-forming additive containing phosphorus and / or boron.

[0043] In some embodiments, the fourth additive has one or both of the following characteristics:

[0044] (1) The positive electrode film-forming additive includes one or more of lithium difluorophosphate, lithium difluorooxalatoborate and lithium dioxalatoborate;

[0045] (2) In the electrolyte, the mass concentration of the positive electrode film-forming additive is 0.01%~3%.

[0046] A fourth 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

[0047] 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:

[0048] Figure 1 It is a schematic diagram of a secondary battery according to one embodiment of the present application.

[0049] Figure 2 for Figure 1 An exploded view of a secondary battery according to an embodiment of the present application is shown.

[0050] 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.

[0051] Description of reference numerals:

[0052] 1. Secondary battery; 11. Casing; 12. Electrode assembly; 13. Cover plate; 2. Electrical device. DETAILED DESCRIPTION

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 1,3-Propene sultone (PST) is an electrolyte additive for lithium-ion batteries, which can improve the cycle life of the battery to a certain extent. However, lithium hexafluorophosphate is usually used as a lithium salt in lithium-ion batteries. Lithium hexafluorophosphate is easily decomposed to produce acid at high temperatures, and its decomposition products will also cause 1,3-propene sultone to decompose and produce acid, making it difficult for the two to play their own roles. At the same time, the acidity of the electrolyte is increased, and the corrosiveness to the material is increased, making it difficult to effectively improve the cycle life of the battery.

[0063] An embodiment of the present application provides a lithium-ion secondary battery, comprising an electrolyte, wherein the electrolyte comprises a lithium salt, a first additive and an organic solvent, wherein the lithium salt comprises lithium hexafluorophosphate (LiPF6), the first additive comprises 1,3-propene sultone (PST), the organic solvent comprises a first solvent, and the relative dielectric constant (ε) of the first solvent is ≥30.

[0064] The present application study found that using a first solvent with a relative dielectric constant (ε) ≥ 30 in a lithium-ion battery system using lithium hexafluorophosphate as a lithium salt and 1,3-propylene sultone as an additive can effectively reduce the decomposition of 1,3-propylene sultone, reduce the acidity of the system, and thereby improve the battery's cycle capacity retention rate, giving the battery a better cycle life.

[0065] The possible mechanism is that the first solvent with a relative dielectric constant (ε) ≥ 30 can solvate lithium hexafluorophosphate to a certain extent, reduce the acid production caused by self-decomposition at high temperature, and reduce the acid production of 1,3-propylene sultone induced by the self-decomposition products of lithium hexafluorophosphate. In this way, the role of 1,3-propylene sultone in improving the cycle life of the battery can be exerted, and the corrosion of the electrolyte to the material can be reduced, thereby comprehensively improving the cycle capacity retention rate of the battery.

[0066] Without limitation, 1,3-propene sultone and the first solvent in the electrolyte can be detected by organic gas chromatography.

[0067] It should be noted that during the formation or recycling process of the battery, the additives in the electrolyte may change. For ease of understanding, this 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 percentage or concentration of the components below will be explained from these two aspects.

[0068] In some embodiments, the relative dielectric constant of the first solvent is 30~85. If the relative dielectric constant of the first solvent is too high, the interaction force with the lithium ions is strong, the solvation effect is enhanced, the desolvation energy of the lithium ions is increased, the dissociation and circulation of the lithium ions are affected, and the cycle performance is reduced. Based on this, it is necessary to reasonably control the relative dielectric constant of the first solvent to be 30~85. Specifically, the relative dielectric constant of the first solvent includes but is not limited to: 30, 35, 36.7, 37.8, 39, 45, 48, 50, 55, 59, 84, 85 or a range between any two of the foregoing. Further, the relative dielectric constant of the first solvent is 35~45.

[0069] Without limitation, the first solvent includes one or more of N,N-dimethylacetamide (ε=37.8), N,N-dimethylformamide (ε=36.7), N,N-dimethylpropionamide (ε=39), formamide (ε=84), acetamide (ε=59), N,N-dimethyltrifluoroacetamide (ε=48), N,N-dimethylpentafluoropropionamide (ε=45), N,N-diethyltrifluoroacetamide (ε=50) and dimethyl sulfate (ε=55).

[0070] In some embodiments, in the organic solvent, the mass percentage of the first solvent is 0.5% to 18%. Correspondingly, in the battery cell, "the mass percentage of the first solvent in the organic solvent is 1% to 20%". Reasonable control of the mass percentage of the first solvent in the organic solvent can reduce gas production and deterioration of the negative electrode interface while obtaining a suitable degree of lithium hexafluorophosphate solvation, and comprehensively improve the cycle capacity retention rate of the battery. Specifically, the mass percentage of the first solvent in the organic solvent includes but is not limited to: 0.5%, 0.7%, 1%, 2%, 2.5%, 3%, 4%, 5%, 6%, 7%, 8%, 10%, 13%, 15%, 17%, 18% or a range between any two of the foregoing. Further, the mass percentage of the first solvent in the organic solvent is 1% to 6%. Correspondingly, in the battery cell, "the volume percentage of the first solvent in the organic solvent is 3% to 8%".

[0071] Without limitation, the mass percentage of the first solvent in the organic solvent can be detected by organic gas chromatography.

[0072] It is understandable that the organic solvent further includes a second solvent. Without limitation, the second solvent may include one or more of a carbonate solvent, a carboxylate solvent and a nitrile solvent.

[0073] In some embodiments, the second solvent includes a saturated and / or unsaturated carbonate solvent. Without limitation, the saturated carbonate includes one or more of ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC) and ethyl propyl carbonate (EPC); the unsaturated carbonate includes ethylene carbonate (EC, ), propylene carbonate (PC, ) and butylene carbonate ( )

[0074] In some embodiments, the second solvent includes ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DMC).

[0075] In some embodiments, the mass percentage of the second solvent in the organic solvent is 82% to 99.5%. Correspondingly, in the battery cell, "the mass percentage of the second solvent in the organic solvent is 80% to 99%". Specifically, the mass percentage of the second solvent in the organic solvent includes, but is not limited to, 99.5%, 98%, 97%, 96%, 95%, 94%, 93%, 92%, 90%, 87%, 85%, 83%, 82% or a range between any two of the foregoing.

[0076] In some embodiments, the electrolyte further comprises a second additive, wherein the second additive comprises a silicon-containing acid-removing additive. The silicon-containing acid-removing additive can effectively capture proton hydrogen generated by high-temperature decomposition of lithium hexafluorophosphate and hydrolysis of 1,3-propylene sultone in the electrolyte, thereby reducing the acidity of the electrolyte and improving the cycle capacity retention rate of the battery.

[0077] Furthermore, the silicon-containing acid-scavenging additive includes one or more of tris(trimethylsilyl)phosphate (TMSP), silazane, N-trimethylsilyl imidazole and tris(trimethylsilyl)borate.

[0078] Further, in the electrolyte, the mass concentration of the silicon-containing acid-removing additive is 0.01%~0.5%. Correspondingly, in the battery cell, "the mass concentration of the silicon-containing acid-removing additive in the electrolyte is 0.01%~1%". Reasonable control of the mass concentration of the silicon-containing acid-removing additive in the electrolyte can effectively capture the proton hydrogen in the electrolyte, reduce the acidity of the electrolyte, obtain a smaller impedance, and comprehensively improve the cycle capacity retention rate of the battery. Specifically, the mass concentration of the silicon-containing acid-removing additive in the electrolyte includes but is not limited to: 0.01%, 0.05%, 0.1%, 0.15%, 0.17%, 0.2%, 0.25%, 0.3%, 0.4%, 0.5% or a range between any two of the foregoing. Further, the mass concentration of the silicon-containing acid-removing additive in the electrolyte is 0.05%~0.25%. Correspondingly, in the battery cell, "the mass concentration of the silicon-containing acid-removing additive in the electrolyte is 0.05%~0.5%".

[0079] Without limitation, the mass concentration and type of the second additive may be detected by organic gas chromatography.

[0080] Furthermore, the increase in electrolyte acidity will destroy the protective film (CEI film / SEI film) on the surface of the positive and negative electrode plates, causing the battery's cycle capacity retention rate to decrease.

[0081] Based on this, in some embodiments, the electrolyte further comprises a third additive, and the third additive comprises a negative electrode film-forming additive containing a 5- to 6-membered heterocyclic ring. Without limitation, the heteroatoms in the 5- to 6-membered heterocyclic ring may include one or more of N, O, and S. By introducing a negative electrode film-forming additive containing a 5- to 6-membered heterocyclic ring, it can cooperate with 1,3-propene sultone to form a stable SEI film on the surface of the negative electrode plate, reduce the damage of the acidic electrolyte to the negative electrode plate, and improve the cycle capacity retention rate of the battery.

[0082] Furthermore, the negative electrode film-forming additive containing a 5- to 6-membered heterocyclic ring includes one or more of fluoroethylene carbonate (FEC), vinylene carbonate (VC), vinylethylene carbonate (VEC), propane sultone (PS), diethylene sulfate (DTD) and methylene methane disulfonate (MMDS).

[0083] Further, the mass concentration of the negative electrode film-forming additive containing 5-6-membered heterocycles in the electrolyte is 0.5% to 5%. Correspondingly, in the battery cell, "the mass concentration of the negative electrode film-forming additive containing 5-6-membered heterocycles in the electrolyte is 0.5% to 6%". Reasonable control of the mass concentration of the negative electrode film-forming additive containing 5-6-membered heterocycles in the electrolyte can improve the stability of the negative electrode while obtaining a smaller impedance, thereby comprehensively improving the cycle capacity retention rate of the battery. Specifically, the mass concentration of the negative electrode film-forming additive containing 5-6-membered heterocycles in the electrolyte includes, but is not limited to, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5% or a range between any two of the foregoing. Further, the mass concentration of the negative electrode film-forming additive containing 5-6-membered heterocycles in the electrolyte is 1% to 2%. Correspondingly, in the battery cell, "the mass concentration of the negative electrode film-forming additive containing 5-6-membered heterocycles in the electrolyte is 1% to 3%".

[0084] Without limitation, the mass concentration and type of the third additive may be detected by organic gas chromatography.

[0085] In some embodiments, the electrolyte further comprises a fourth additive, and the fourth additive comprises a positive electrode film-forming additive containing phosphorus and / or boron. By introducing a positive electrode film-forming additive containing phosphorus and / or boron, it can be combined with 1,3-propylene sultone to form a stable CEI film on the surface of the positive electrode plate, reduce the damage of the acidic electrolyte to the positive electrode plate, and improve the cycle capacity retention rate of the battery. Furthermore, when the positive active material includes a ternary material, the formation of a CEI film is more stable, and therefore it is more conducive to improving the cycle life of the battery including the positive electrode containing the ternary material.

[0086] Furthermore, the positive electrode film-forming additive includes one or more of lithium difluorophosphate (LiPO2F2), lithium difluorooxalatoborate (LiBOB) and lithium dioxalatoborate (LiDFOB).

[0087] Furthermore, in the electrolyte, the mass concentration of the positive electrode film-forming additive is 0.01%~2%. Correspondingly, in the battery cell, "the mass concentration of the positive electrode film-forming additive in the electrolyte is 0.01%~3%". Specifically, reasonable control of the mass concentration of the positive electrode film-forming additive in the electrolyte can improve the stability of the positive electrode while obtaining a smaller impedance, thereby comprehensively improving the cycle capacity retention rate of the battery. Specifically, the mass concentration of the positive electrode film-forming additive in the electrolyte includes but is not limited to: 0.01%, 0.05%, 0.1%, 0.3%, 0.5%, 1%, 1.5%, 2% or a range between any two of the foregoing. Further, the mass concentration of the positive electrode film-forming additive in the electrolyte is 0.05%~1%. Correspondingly, in the battery cell, "the mass concentration of the positive electrode film-forming additive in the electrolyte is 0.05%~2%".

[0088] Without limitation, the mass concentration and type of the fourth additive may be detected by organic gas chromatography.

[0089] Without limitation, in the electrolyte, the mass concentration of the lithium hexafluorophosphate is 8% to 16%. Specifically, the mass concentration of the lithium hexafluorophosphate in the electrolyte includes but is not limited to: 8%, 10%, 11%, 12%, 12.5%, 13%, 14%, 15%, 16% or a range between any two of the foregoing.

[0090] Without limitation, in the electrolyte, the mass concentration of 1,3-propylene sultone is 0.1% to 1%. Correspondingly, in the battery cell, "the mass concentration of 1,3-propylene sultone in the electrolyte is 0.1% to 5%". Specifically, the mass concentration of 1,3-propylene sultone in the electrolyte includes, but is not limited to, 0.1%, 0.2%, 0.3%, 0.5%, 0.7%, 1% or a range between any two of the foregoing.

[0091] In some other embodiments of the present application, an electrolyte is provided, comprising a lithium salt, a first additive and an organic solvent, wherein the lithium salt comprises lithium hexafluorophosphate, the first additive comprises 1,3-propylene sultone, the organic solvent comprises a first solvent, and the relative dielectric constant (ε) of the first solvent is ≥30.

[0092] It can be understood that the electrolyte has similar technical solutions and effects as the electrolyte in the aforementioned lithium-ion secondary battery, which will not be described in detail here.

[0093] In some other embodiments of the present application, an electrical device is provided, comprising the lithium-ion secondary battery as described above.

[0094] The secondary battery and the electric device of the present application will be described below with reference to the drawings as appropriate.

[0095] Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator. During the charge and discharge process of the battery, 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, and the electrolyte scheme is as described above. 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.

[0096] The positive electrode sheet 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.

[0097] 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.

[0098] 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.

[0099] 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 Mn 0.2 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.

[0100] 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.

[0101] 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.

[0102] 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 .

[0103] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer includes a negative electrode active material.

[0104] 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 material layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

[0105] 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.

[0106] In some embodiments, the negative electrode active material may adopt the negative electrode active material for the battery known in the art. As a non-limiting example, the negative electrode active material may include one or more of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. Silicon-based materials may include one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may include one or more of elemental tin, tin oxide compounds, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0107] In some embodiments, the negative electrode active material layer may further include a binder. The binder 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).

[0108] In some embodiments, the negative electrode active material 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.

[0109] In some embodiments, the negative electrode active material layer may further optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0110] 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 40wt%~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 .

[0111] 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.

[0112] 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.

[0113] In some embodiments, the isolation film has a thickness of 6 μm to 40 μm, and may be 12 μm to 20 μm.

[0114] 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.

[0115] In some embodiments, the secondary battery may include an outer package, which may be used to encapsulate the electrode assembly and the electrolyte.

[0116] 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.

[0117] The secondary battery includes at least one battery cell. The secondary battery may include one or more battery cells.

[0118] 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.

[0119] 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.

[0120] In some 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 are enclosed to form a accommodating cavity. The shell 11 has an opening connected to the accommodating cavity, and the cover plate 13 can be covered on the opening to close the accommodating 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 accommodating 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.

[0121] The secondary battery may be a battery module or a battery pack.

[0122] 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.

[0123] 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.

[0124] 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.

[0125] In some embodiments, the battery modules described above may also be assembled into a battery pack. The number of battery modules contained in the battery pack may be one or more. Those skilled in the art may select a suitable number according to the application and capacity of the battery pack.

[0126] 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.

[0127] 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.

[0128] As an electrical device, a secondary battery can be selected according to its usage requirements.

[0129] 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.

[0130] 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.

[0131] 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.

[0132] 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.

[0133] The performance test method of the battery in each embodiment and comparative example is as follows:

[0134] (1) HF content:

[0135] Add 20g electrolyte sample and 1g acid-base indicator (1% bromophenol blue solution) to the fluorination bottle and stir slowly until the solution is completely dispersed. Add 0.02mol / L triethylamine (Et3N) dimethyl carbonate solution to the acid-base burette and record the initial volume (V0); slowly add the reagent in the acid-base burette to the sample until the sample changes color, and record the volume of the solution in the acid-base burette after titration (V1). Calculate the HF content of the electrolyte according to the following formula:

[0136] (V0−V1)×0.02×20 / 20, unit: mg / g.

[0137] (2) Cycle capacity retention rate:

[0138] At 60°C, charge the battery cell at a constant current of 0.5C to 4.4V, and then discharge it at a constant current of 1C to 2.5V. This is a charge and discharge cycle. The discharge capacity is recorded as the discharge capacity C1 of the first cycle of the lithium-ion battery cell. Repeat this cycle step for the same battery cell. After 1000 cycles, record the discharge capacity C2 of the 1000th cycle. The cycle capacity retention rate of the 1000th cycle = C2 / C1×100%.

[0139] Example 1

[0140] 1) Preparation of positive electrode

[0141] The positive electrode active material (5 series ternary nickel-cobalt-manganese-lithium, LiNi 0.5 Co 0.2 Mn 0.3 O2), conductive carbon black SP and binder PVDF are dispersed in solvent NMP in a weight ratio of 98%:1%:1% and mixed evenly to obtain positive electrode slurry; the positive electrode slurry is evenly coated on the double-sided surface of the positive electrode current collector aluminum foil, and after drying and cold pressing, a positive electrode sheet is obtained, wherein the coating amount per unit area on both sides is 0.27g / 1540.25mm 2 .

[0142] 2) Preparation of negative electrode

[0143] The negative electrode active material (graphite), thickener sodium carboxymethyl cellulose, adhesive styrene butadiene rubber, and conductive agent acetylene black are mixed in a mass ratio of 97%:1%:1%:1%, and deionized water is added to obtain a negative electrode slurry under the action of a vacuum mixer; the negative electrode slurry is evenly coated on both sides of the copper foil; the copper foil is dried at room temperature and then transferred to a 120°C oven for drying for 1 hour, and then super-cold pressed and cut to obtain a negative electrode sheet, wherein the coating amount per unit area on both sides is 0.17g / 1540.25mm 2 .

[0144] 3) Isolation film

[0145] A 12μm thick polypropylene isolation film was selected.

[0146] 4) Preparation of electrolyte

[0147] The organic solvent is a mixture of N,N-dimethylacetamide (the first solvent, with a relative dielectric constant of 37.8), ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC), wherein the mass ratio of N,N-dimethylacetamide, EC, EMC and DEC is 5%:30%:25%:40%. In an argon atmosphere glove box with a water content of <10ppm, PST, TMSP, FEC, LiPO2F2 and fully dried lithium salt LiPF6 are dissolved in the organic solvent and mixed evenly to obtain an electrolyte. Among them, the mass percentage of lithium salt is 12.5%, the mass percentage of PST is 1%, the mass percentage of TMSP is 0.25%, the mass percentage of FEC is 2%, and the mass percentage of lithium difluorophosphate is 1%.

[0148] 5) Preparation of batteries

[0149] 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 an aluminum plastic film, and then baked at 80°C to remove water, 10g of the corresponding non-aqueous electrolyte is injected, and the cell is sealed to prepare the cell. After the cell is placed, hot and cold pressed, formed, clamped, and divided into capacities, the finished battery is obtained. The formation process is: 45°C, 0.02C constant current charging for 600min. After formation, in the electrolyte, the mass percentage of lithium salt is 12.5%, the mass percentage of PST is 0.2%, the mass percentage of TMSP is 0.17%, the mass percentage of FEC is 1.5%, and the mass percentage of lithium difluorophosphate is 0.3%.

[0150] The battery preparation methods of Examples 2-3 are the same as those of Example 1, with the main difference being that first solvents with different relative dielectric constants are used. The details are shown in Table 1:

[0151] Table 1

[0152]

[0153] The battery preparation methods of Examples 4 to 7 are the same as those of Example 1, with the main difference being that different mass percentages of the first solvent are used in the organic solvent, and the mass percentage of the EMC is adjusted accordingly to meet 100%. The details are shown in Table 2:

[0154] Table 2

[0155]

[0156] The battery preparation method of Example 8 is the same as that of Example 1, except that the second additive TMSP is not used. The details are shown in Table 3:

[0157] Table 3

[0158]

[0159] The battery preparation method of Example 9 is the same as that of Example 1, except that the third additive FEC is not used. The details are shown in Table 4:

[0160] Table 4

[0161]

[0162] The battery preparation method of Example 10 is the same as that of Example 1, except that the fourth additive, lithium difluorophosphate, is not used. The details are shown in Table 5:

[0163] Table 5

[0164]

[0165] The battery preparation method of Comparative Example 1 is the same as that of Example 1, except that a first solvent with a different relative dielectric constant is used. The details are shown in Table 6:

[0166] Table 6

[0167]

[0168] By comparing Examples 1 to 10 with Comparative Example 1, it can be seen that by using the first solvent with a relative dielectric constant of ≥30 F / m, acid can be effectively removed and the cycle capacity retention rate of the battery can be improved.

[0169] Comparison between Examples 1 to 3 shows that when the relative dielectric constant of the first solvent is within an appropriate range, a higher cycle capacity retention rate of the battery can be achieved.

[0170] By comparing Examples 1 and 4 to 7, it can be seen that the reasonable control of the mass percentage of the first solvent can further improve the acid removal effect and enhance the cycle capacity retention rate of the battery.

[0171] By comparing Examples 1 and 8, it can be seen that the addition of the silicon-containing acid-removing additive TMSP can further improve the acid-removing effect and enhance the cycle capacity retention rate of the battery.

[0172] By comparing Examples 1 and 9, it can be seen that the addition of FEC, a negative electrode film-forming additive containing a 5- to 6-membered heterocyclic ring, can further improve the cycle capacity retention rate of the battery.

[0173] By comparing Examples 1 and 10, it can be seen that the addition of lithium difluorophosphate, a positive electrode film-forming additive, can further improve the acid removal effect and enhance the cycle capacity retention rate of the battery.

[0174] 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.

[0175] 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 comprising an electrolyte, characterized in that: The electrolyte comprises a lithium salt, a first additive and an organic solvent, wherein the lithium salt comprises lithium hexafluorophosphate, the first additive comprises 1,3-propylene sultone, the organic solvent comprises a first solvent, and the relative dielectric constant of the first solvent is ≥30.

2. The lithium ion secondary battery according to claim 1, characterized in that: The relative dielectric constant of the first solvent is 30-85.

3. The lithium ion secondary battery according to claim 1, characterized in that: The first solvent includes one or more of N,N-dimethylacetamide, N,N-dimethylformamide, N,N-dimethylpropionamide, N,N-dimethyltrifluoroacetamide, N,N-dimethylpentafluoropropionamide, N,N-diethyltrifluoroacetamide, formamide, acetamide and dimethyl sulfate.

4. The lithium-ion secondary battery according to claim 1, characterized in that: In the organic solvent, the mass percentage of the first solvent is 0.5% to 18%.

5. The lithium ion secondary battery according to claim 4, characterized in that: In the organic solvent, the mass percentage of the first solvent is 1% to 6%.

6. The lithium ion secondary battery according to any one of claims 1 to 5, characterized in that: The organic solvent further comprises a second solvent, wherein the second solvent has one or two of the following characteristics: (1) the second solvent comprises one or more of a carbonate solvent, a carboxylate solvent and a nitrile solvent; (2) In the organic solvent, the mass percentage of the second solvent is 82% to 99.5%.

7. The lithium ion secondary battery according to any one of claims 1 to 5, characterized in that: The electrolyte further comprises a second additive, wherein the second additive comprises a silicon-containing acid-scavenging additive.

8. The lithium ion secondary battery according to claim 7, characterized in that: The second additive has one or both of the following characteristics: (1) The silicon-containing acid-removing additive includes one or more of tris(trimethylsilyl)phosphate, silazane, N-trimethylsilyl imidazole and tris(trimethylsilyl)borate; (2) In the electrolyte, the mass concentration of the silicon-containing acid-removing additive is 0.01% to 0.5%.

9. The lithium ion secondary battery according to any one of claims 1 to 5, characterized in that: The electrolyte further comprises a third additive, wherein the third additive comprises a negative electrode film-forming additive containing a 5- to 6-membered heterocyclic ring.

10. The lithium ion secondary battery according to claim 9, characterized in that: The third additive has one or two of the following characteristics: (1) The negative electrode film-forming additive containing a 5- to 6-membered heterocyclic ring includes one or more of fluoroethylene carbonate, vinylene carbonate, vinylethylene carbonate, propane sultone, vinyl sulfate and methylene methane disulfonate; (2) In the electrolyte, the mass concentration of the negative electrode film-forming additive containing a 5- to 6-membered heterocyclic ring is 0.5% to 5%.

11. The lithium ion secondary battery according to any one of claims 1 to 5, characterized in that: The electrolyte further comprises a fourth additive, wherein the fourth additive comprises a positive electrode film-forming additive containing phosphorus and / or boron.

12. The lithium ion secondary battery according to claim 11, characterized in that: The fourth additive has one or two of the following characteristics: (1) The positive electrode film-forming additive includes one or more of lithium difluorophosphate, lithium difluorooxalatoborate and lithium dioxalatoborate; (2) In the electrolyte, the mass concentration of the positive electrode film-forming additive is 0.01%~2%.

13. The lithium ion secondary battery according to any one of claims 1 to 5, characterized in that: In the electrolyte, the mass concentration of lithium hexafluorophosphate is 8% to 16%.

14. The lithium ion secondary battery according to any one of claims 1 to 5, characterized in that: In the electrolyte, the mass concentration of 1,3-propylene sultone is 0.1% to 1%.

15. An electrolyte, characterized in that: The invention comprises a lithium salt, a first additive and an organic solvent, wherein the lithium salt comprises lithium hexafluorophosphate, the first additive comprises 1,3-propylene sultone, the organic solvent comprises a first solvent, and the relative dielectric constant of the first solvent is ≥30.

16. The electrolyte according to claim 15, characterized in that The electrolyte in the lithium ion secondary battery according to any one of claims 2 to 14.

17. A battery cell comprising an electrolyte, characterized in that: The electrolyte comprises a lithium salt, a first additive and an organic solvent, wherein the lithium salt comprises lithium hexafluorophosphate, the first additive comprises 1,3-propylene sultone, the organic solvent comprises a first solvent, and the relative dielectric constant of the first solvent is ≥30.

18. The battery cell according to claim 17, characterized in that: The relative dielectric constant of the first solvent is 30-85.

19. The battery cell according to claim 17, characterized in that: The first solvent includes one or more of N,N-dimethylacetamide, N,N-dimethylformamide, N,N-dimethylpropionamide, N,N-dimethyltrifluoroacetamide, N,N-dimethylpentafluoropropionamide, N,N-diethyltrifluoroacetamide, formamide, acetamide and dimethyl sulfate.

20. The battery cell according to claim 17, characterized in that: In the organic solvent, the mass percentage of the first solvent is 1% to 20%.

21. The battery cell according to any one of claims 17 to 20, characterized in that: The electrolyte further comprises a second additive, wherein the second additive comprises a silicon-containing acid-scavenging additive.

22. The battery cell according to claim 21, characterized in that: The second additive has one or both of the following characteristics: (1) The silicon-containing acid-removing additive includes one or more of tris(trimethylsilyl)phosphate, silazane, N-trimethylsilyl imidazole and tris(trimethylsilyl)borate; (2) In the electrolyte, the mass concentration of the silicon-containing acid-removing additive is 0.01% to 1%.

23. The battery cell according to any one of claims 17 to 20, characterized in that: The electrolyte further comprises a third additive, wherein the third additive comprises a negative electrode film-forming additive containing a 5- to 6-membered heterocyclic ring.

24. The battery cell according to claim 23, characterized in that: The third additive has one or two of the following characteristics: (1) The negative electrode film-forming additive containing a 5- to 6-membered heterocyclic ring includes one or more of fluoroethylene carbonate, vinylene carbonate, vinylethylene carbonate, propane sultone, vinyl sulfate and methylene methane disulfonate; (2) In the electrolyte, the mass concentration of the negative electrode film-forming additive containing a 5- to 6-membered heterocyclic ring is 0.5% to 6%.

25. The battery cell according to any one of claims 17 to 20, characterized in that: The electrolyte further comprises a fourth additive, wherein the fourth additive comprises a positive electrode film-forming additive containing phosphorus and / or boron.

26. The battery cell according to claim 25, characterized in that: The fourth additive has one or two of the following characteristics: (1) The positive electrode film-forming additive includes one or more of lithium difluorophosphate, lithium difluorooxalatoborate and lithium dioxalatoborate; (2) In the electrolyte, the mass concentration of the positive electrode film-forming additive is 0.01%~3%.

27. An electrical device, characterized in that: A lithium ion secondary battery comprising any one of claims 1 to 14.

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