Lithium ion secondary battery and electric device

Abstract

The invention provides a lithium ion secondary battery and an electric device. The lithium ion secondary battery comprises a positive pole piece, a negative pole piece and an electrolyte, a positive active layer in the positive pole piece comprises a ternary material, the ternary material comprises ternary metal elements, the ternary metal elements comprise a nickel element, the molar percentage of the nickel element in the total molar weight of the ternary metal elements is 50-70%, and the molar percentage of the negative pole piece is 50-70%. The electrolyte comprises a lithium salt, a first additive and a solvent, the first additive comprises 1, 3-propene sultone, and the solvent comprises ethylene carbonate with the mass percent of 5%-25%. 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 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, etc. Among them, high-voltage lithium-ion batteries have received more attention due to their fast charging capabilities.

[0003] High-voltage lithium-ion batteries usually use ternary materials with medium and low nickel (the molar proportion of nickel element is about 50%~70%) as positive electrode active materials. However, high-voltage lithium-ion batteries containing such positive electrode active materials have severe capacity decay and short cycle life. Summary of the invention

[0004] In order to achieve the above-mentioned purpose, the present application provides a lithium-ion secondary battery and an electrical device having good cycle capacity retention rate and a long 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 a positive electrode active layer in the positive electrode plate comprises a ternary material, wherein the ternary material comprises a ternary metal element, wherein the ternary metal element comprises a nickel element, wherein the molar percentage of the nickel element in the total molar amount of the ternary metal element is 50% to 70%, and wherein the electrolyte comprises a lithium salt, a first additive and a solvent, wherein the first additive comprises 1,3-propylene sultone, and the solvent comprises 5% to 25% by mass of ethylene carbonate.

[0006] The present application is directed to a high-voltage battery system using medium- and low-nickel ternary materials. By using 1,3-propylene sultone as an additive and reasonably controlling the mass percentage of ethylene carbonate in the solvent of the electrolyte, the two can work together to significantly reduce the occurrence of a "lithium-poor state", improve the cycle capacity retention rate of the lithium-ion battery, and enable the lithium-ion battery to have a longer cycle life.

[0007] In some embodiments, the mass percentage of the ethylene carbonate in the solvent is 13% to 18%, so that it can better cooperate with 1,3-propylene sultone to improve the cycle capacity retention rate of the battery.

[0008] In some embodiments, the mass concentration of 1,3-propylene sultone in the electrolyte is 0.1% to 1%, so that it can better cooperate with ethylene carbonate to improve the cycle capacity retention rate of the battery.

[0009] In some of the embodiments, the mass concentration of 1,3-propene sultone is 0.15% to 0.45%.

[0010] In some embodiments, the electrolyte further comprises a second additive, and the second additive comprises a fluorine-containing phosphate. The fluorine-containing phosphate can adhere to the surface of the positive electrode plate, adsorb lithium ions on the surface of the positive electrode plate, and cooperate with the aforementioned 1,3-propylene sultone and EC to better reduce the diffusion rate of lithium ions on the surface of the positive electrode plate, reduce the occurrence of "lithium-deficient state", and obtain a higher cycle capacity retention rate.

[0011] In some embodiments, the second additive includes one or more of lithium difluorophosphate, lithium monofluorophosphate, lithium difluorobisoxalate phosphate and lithium tetrafluorooxalate phosphate.

[0012] In some embodiments, the mass concentration of the fluorine-containing phosphate in the electrolyte is 0.01% to 1%. The mass concentration of the fluorine-containing phosphate in the electrolyte is reasonably controlled to produce a suitable adsorption effect on the lithium ions on the surface of the positive electrode, improve the "lithium-poor state", reduce excessive binding of lithium ions, obtain better lithium ion transmission performance, and then comprehensively improve the cycle capacity retention rate.

[0013] In some embodiments, the ternary metal element includes cobalt, and the molar percentage of the cobalt element in the total molar amount of the ternary metal element is 7% to 20%. The presence of cobalt in the ternary material can improve the migration of lithium ions in the bulk phase of the positive electrode sheet, accelerate its migration to the surface of the positive electrode sheet, and thus reduce the "lithium-poor state". At the same time, the presence of cobalt can also make the structure of the ternary material more stable. At the same time, its molar percentage should not be too high. Too high cobalt ions are easy to dissolve, destroying the structure of the ternary material, and the dissolved cobalt ions will be deposited on the negative electrode sheet, destroying the structure of the negative electrode sheet and reducing the cycle life. Therefore, it is necessary to reasonably control the molar percentage of the cobalt element.

[0014] In some of the embodiments, the molar percentage of cobalt element in the total molar amount of the ternary metal elements is 10%-15%.

[0015] In some embodiments, the primary particle size of the ternary material is 1 μm to 4 μm. Reasonable control of the primary particle size of the ternary material can shorten the solid phase migration path of lithium ions, accelerate their transmission in the cathode bulk phase, improve the "lithium-poor state", reduce side reactions, and comprehensively improve the cycle capacity retention rate.

[0016] In some of the embodiments, the ternary material includes one or more of lithium nickel cobalt manganese oxide and modified compounds thereof.

[0017] In some embodiments, the electrolyte further comprises a third additive, and the third additive comprises a fluorine-substituted compound containing a five-membered heterocyclic structure. The fluorine-substituted compound containing a five-membered heterocyclic structure can form a relatively stable SEI film on the negative electrode plate, protect the negative electrode plate structure, reduce damage to the negative electrode structure such as dissolution of cobalt ions, and thus improve the cycle capacity retention rate.

[0018] In some embodiments, the third additive includes one or more of fluoroethylene carbonate, fluoroethylene sulfate and bisfluoroethylene carbonate.

[0019] In some embodiments, the mass concentration of the fluorine-substituted compound containing a five-membered heterocyclic structure in the electrolyte is 0.01% to 5%. Reasonable control of the mass concentration of the fluorine-substituted compound containing a five-membered heterocyclic structure in the electrolyte can form a relatively stable SEI film while obtaining a lower impedance and comprehensively improving the cycle capacity retention rate.

[0020] In some embodiments, the lithium salt includes lithium hexafluorophosphate.

[0021] A second 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

[0022] 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:

[0023] Figure 1 It is a schematic diagram of a secondary battery according to one embodiment of the present application.

[0024] Figure 2 for Figure 1 An exploded view of a secondary battery according to an embodiment of the present application is shown.

[0025] 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.

[0026] Description of reference numerals:

[0027] 1. Secondary battery; 11. Casing; 12. Electrode assembly; 13. Cover plate; 2. Electrical device. DETAILED DESCRIPTION

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] High-voltage lithium-ion batteries usually use ternary materials with medium and low nickel (the molar proportion of nickel is about 50%~70%) as positive electrode active materials. During the cycle process, the positive electrode sheets made of such positive electrode active materials have poor lithium ion transmission performance in the bulk phase of the positive electrode sheets, and the high voltage environment makes the migration driving force of lithium ions on the surface of the positive electrode sheets larger, so that more lithium ions are released from the surface of the positive electrode sheets, but the lithium ions in the bulk phase are difficult to replenish to the surface of the positive electrode sheets in time, forming a "lithium-poor state" on the surface of the positive electrode sheets. The "lithium-poor state" causes serious loss of positive electrode active materials, deterioration of surface structure, and an increase in rock salt phase, which further increases the difficulty of lithium ion transmission in the bulk phase, causing serious capacity decay of lithium-ion batteries and shortened cycle life.

[0038] Based on this, 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 positive electrode active layer in the positive electrode plate comprises a ternary material, wherein the ternary material comprises a ternary metal element, wherein the ternary metal element comprises a nickel element, wherein the molar percentage of the nickel element in the total molar amount of the ternary metal element is 50% to 70%, wherein the electrolyte comprises a lithium salt, a first additive and a solvent, wherein the first additive comprises 1,3-propene sultone (PST), and the solvent comprises 5% to 25% by mass of ethylene carbonate (EC).

[0039] The study found that for high-voltage battery systems using medium- and low-nickel ternary materials, by using 1,3-propylene sultone as an additive and reasonably controlling the mass percentage of ethylene carbonate in the solvent of the electrolyte, the two can work together to significantly reduce the occurrence of "lithium-deficient state", improve the cycle capacity retention rate of lithium-ion batteries, and enable lithium-ion batteries to have a longer cycle life.

[0040] Without limitation, the principle of improving the "lithium-poor state" by 1,3-propylene sultone and a suitable mass percentage of ethylene carbonate may be that: 1,3-propylene sultone can form a film on the positive electrode, and the film components include inorganic and organic components, and the organic components have a stronger effect. Therefore, compared with before film formation, the transmission of lithium ions on the positive electrode surface is hindered, and the lithium ion diffusion on the surface of the positive electrode is reduced to a certain extent, thereby achieving the effect of improving the "lithium-poor state"; at the same time, the mass percentage of ethylene carbonate needs to be reasonably controlled to be 5%~25%. When it is too high, ethylene carbonate is easy to combine with the positive electrode. The lithium ions on the surface of the electrode accelerate their diffusion to the negative electrode in the electrolyte. Therefore, when its mass percentage is too high, the combined diffusion effect is serious, which will aggravate the "lithium-poor state" on the surface of the positive electrode. When it is too low, it is difficult to achieve effective dissociation of lithium salts, and it is not conducive to improving the battery cycle life. Therefore, controlling the mass percentage of ethylene carbonate to 5%~25% can effectively dissociate lithium salts while reducing the diffusion of lithium ions on the surface of the positive electrode, thereby improving the "lithium-poor state" and improving the cycle capacity retention rate of lithium-ion batteries, so that lithium-ion batteries have a longer cycle life.

[0041] Specifically, in the solvent, the mass percentage of the ethylene carbonate includes but is not limited to: 5%, 10%, 13%, 15%, 18%, 20%, 25% or a range between any two of the foregoing. Further, in the solvent, the mass percentage of the ethylene carbonate is 13% to 18%. This can better cooperate with 1,3-propylene sultone to improve the cycle capacity retention rate of the battery.

[0042] It is understandable that the solvent may include other solvents conventionally used in the art while including ethylene carbonate. Without limitation, other solvents may include one or more of propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane sulfone, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0043] In some embodiments, the solvent further comprises a saturated carbonate. Without limitation, the mass percentage of the saturated carbonate in the solvent is 75% to 95%. Specifically, in the solvent, the mass percentage of the saturated carbonate includes, but is not limited to, 95%, 90%, 87%, 85%, 82%, 80%, 75% or a range between any two of the foregoing.

[0044] In some embodiments, 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); optionally including ethyl methyl carbonate (EMC) and diethyl carbonate (DMC). Without limitation, in the solvent, the mass percentage of ethyl methyl carbonate (EMC) is 60% to 70%, and the mass percentage of diethyl carbonate (DMC) is 15% to 25%.

[0045] In some embodiments, in the electrolyte, the mass concentration of 1,3-propylene sultone is 0.1% to 1%. In this way, it can better cooperate with ethylene carbonate to improve the cycle capacity retention rate of the battery. Specifically, in the electrolyte, the mass concentration of 1,3-propylene sultone includes but is not limited to: 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, 0.65%, 0.7%, 0.75%, 0.8%, 0.85%, 0.9%, 0.95%, 1% or a range between any two of the foregoing. Further, the mass concentration of 1,3-propylene sultone is 0.15% to 0.45%.

[0046] Without limitation, the molar percentage of nickel in the ternary material can be detected by ICP; the mass concentrations of 1,3-propylene sultone and ethylene carbonate in the electrolyte can be detected by GC organic gas chromatography.

[0047] In some embodiments, the electrolyte further comprises a second additive, and the second additive comprises a fluorine-containing phosphate. The fluorine-containing phosphate can adhere to the surface of the positive electrode plate, adsorb lithium ions on the surface of the positive electrode plate, and cooperate with the aforementioned 1,3-propylene sultone and EC to better reduce the diffusion rate of lithium ions on the surface of the positive electrode plate, reduce the occurrence of "lithium-deficient state", and obtain a higher cycle capacity retention rate.

[0048] Without limitation, the cations in the fluorine-containing phosphate include one or more of lithium ions, sodium ions, potassium ions, magnesium ions, and calcium ions. In some embodiments, the cations in the fluorine-containing phosphate include lithium ions.

[0049] Furthermore, the second additive includes one or more of lithium difluorophosphate, lithium monofluorophosphate, lithium difluorobisoxalate phosphate and lithium tetrafluorooxalate phosphate.

[0050] Further, in the electrolyte, the mass concentration of the fluorine-containing phosphate is 0.01% to 1%. Specifically, in the electrolyte, the mass concentration of the fluorine-containing phosphate includes but is not limited to: 0.01%, 0.02%, 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1% or a range between any two of the foregoing. Reasonably control the mass concentration of the fluorine-containing phosphate in the electrolyte to produce a suitable adsorption effect on the lithium ions on the surface of the positive electrode plate, improve the "lithium-poor state" while reducing excessive binding of lithium ions, obtain better lithium ion transmission performance, and then comprehensively improve the cycle capacity retention rate. Further, in the electrolyte, the mass concentration of the fluorine-containing phosphate is 0.02% to 0.5%.

[0051] Without limitation, the mass concentration of the fluorine-containing phosphate in the electrolyte can be tested by IC ion chromatography.

[0052] In some embodiments, the molar percentage of cobalt in the total molar amount of the ternary metal element is 7% to 20%. The presence of cobalt in the ternary material can increase the migration of lithium ions in the bulk phase of the positive electrode sheet, accelerate its migration to the surface of the positive electrode sheet, and thus reduce the "lithium-poor state". At the same time, the presence of cobalt can also make the structure of the ternary material more stable. At the same time, its molar percentage should not be too high. Too high cobalt ions are easily dissolved, destroying the structure of the ternary material, and the dissolved cobalt ions will be deposited on the negative electrode sheet, destroying the structure of the negative electrode sheet, and reducing the cycle life. Therefore, it is necessary to reasonably control the molar percentage of the cobalt element. Specifically, the molar percentage of cobalt in the total molar amount of the ternary metal element includes but is not limited to: 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20% or any two of the foregoing range. Further, the molar percentage of cobalt in the total molar amount of the ternary metal element is 10% to 15%.

[0053] Without limitation, the molar percentage of the cobalt element in the ternary material can be detected by ICP.

[0054] Without limitation, the ternary material includes one or more of lithium nickel cobalt manganese oxide and its modified compounds. Non-limiting examples may include LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 )、LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 )、LiNi 0.55 Co 0.12 Mn 0.33 O2, etc.

[0055] In some embodiments, the electrolyte further comprises a third additive, and the third additive comprises a fluorine-substituted compound containing a five-membered heterocyclic structure. Without limitation, the heteroatom in the heterocyclic structure may be O, N, S, etc. The fluorine-substituted compound containing a five-membered heterocyclic structure can form a relatively stable SEI film on the negative electrode sheet, protect the negative electrode sheet structure, reduce damage to the negative electrode structure such as dissolution of cobalt ions, and thereby improve the cycle capacity retention rate.

[0056] Further, the third additive includes one or more of fluoroethylene carbonate (FEC), fluoroethylene sulfate and bisfluoroethylene carbonate.

[0057] Furthermore, in the electrolyte, the mass concentration of the fluorine-substituted compound containing a five-membered heterocyclic structure is 0.01% to 5%. Reasonable control of the mass concentration of the fluorine-substituted compound containing a five-membered heterocyclic structure in the electrolyte can form a relatively stable SEI film while obtaining a lower impedance and comprehensively improving the cycle capacity retention rate. Specifically, in the electrolyte, the mass concentration of the fluorine-substituted compound containing a five-membered heterocyclic structure includes but is not limited to: 0.01%, 0.05%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5% or a range between any two of the foregoing. Further, in the electrolyte, the mass concentration of the fluorine-substituted compound containing a five-membered heterocyclic structure is 1% to 3.5%.

[0058] Without limitation, the mass concentration of the fluorine-substituted compound containing a five-membered heterocyclic structure in the electrolyte can be detected by organic gas chromatography.

[0059] In some embodiments, the primary particle size of the ternary material is 1μm~4μm. Reasonable control of the primary particle size of the ternary material can shorten the solid phase migration path of lithium ions, accelerate its transmission in the positive electrode body phase, improve the "lithium-poor state", reduce side reactions, and comprehensively improve the cycle capacity retention rate. Specifically, the primary particle size of the ternary material includes but is not limited to: 1μm, 1.5μm, 2μm, 2.2μm, 2.5μm, 2.7μm, 3μm, 3.5μm, 4μm or a range between any two of the foregoing. Furthermore, the primary particle size of the ternary material is 2μm~3μm.

[0060] Without limitation, the primary particle size of the ternary material can be detected by SEM.

[0061] Without limitation, the lithium salt may include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorophosphate (LiPO2F2), lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorobis(oxalatophosphate) (LiDFOP) and lithium tetrafluorooxalatophosphate (LiTFOP).

[0062] In some embodiments, the lithium salt includes lithium hexafluorophosphate (LiPF6).

[0063] Without limitation, the concentration of the lithium salt in the electrolyte is 0.5 mol / L to 2 mol / L. Specifically, the concentration of the lithium salt in the electrolyte includes but is not limited to: 0.5 mol / L, 0.8 mol / L, 1 mol / L, 1.2 mol / L, 1.5 mol / L, 1.8 mol / L, 2 mol / L or a range between any two of the foregoing.

[0064] In some other embodiments of the present application, an electrical device is provided, comprising the lithium-ion secondary battery as described above.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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 .

[0073] 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.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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).

[0078] 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.

[0079] In some of the embodiments, the negative electrode active material layer may further include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0080] In some of the 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 .

[0081] 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.

[0082] 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.

[0083] In some embodiments, the isolation film has a thickness of 6 μm to 40 μm, and may be 12 μm to 20 μm.

[0084] In some of the embodiments, the positive electrode sheet, the negative electrode sheet and the separator can be formed into an electrode assembly by a winding process or a lamination process.

[0085] In some embodiments, the secondary battery may include an outer package, which may be used to encapsulate the electrode assembly and the electrolyte.

[0086] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery can also be a soft package, such as a bag-type soft package. The material of the soft package can be plastic, and further, non-limiting examples of plastic can include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0087] The secondary battery includes at least one battery cell. The secondary battery may include one or more battery cells.

[0088] 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.

[0089] 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.

[0090] 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.

[0091] The secondary battery may be a battery module or a battery pack.

[0092] 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.

[0093] 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.

[0094] 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.

[0095] 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.

[0096] 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.

[0097] 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.

[0098] As an electrical device, a secondary battery can be selected according to its usage requirements.

[0099] 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.

[0100] 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.

[0101] 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.

[0102] 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.

[0103] The test method of the cycle capacity retention rate in each embodiment and comparative example is as follows:

[0104] At 45°C, charge the battery cell at a constant current of 0.5C to 4.4V, then charge at a constant voltage of 4.4V to a cut-off current of 0.05C, and then discharge at a constant current of 1C to 2.5V. This is a charge and discharge cycle. The discharge capacity this time 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 600 cycles, record the discharge capacity C2 of the 600th cycle. The cycle capacity retention rate of the 600th cycle = C2 / C1*100%.

[0105] Example 1

[0106] 1) Preparation of positive electrode

[0107] The positive electrode active material (LiNi 0.55 Co 0.12 Mn 0.33 O2, primary particle size 2.2μm), 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 .

[0108] 2) Preparation of negative electrode sheet

[0109] The negative electrode active material graphite, the thickener sodium carboxymethyl cellulose, the binder styrene butadiene rubber, and the 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 .

[0110] 3) Isolation film

[0111] A 12μm thick polypropylene isolation film was selected.

[0112] 4) Preparation of electrolyte

[0113] The organic solvent is a mixed solution containing ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DMC), wherein the mass ratio of EC, EMC and DMC is 15%:65%:20%. In an argon atmosphere glove box with a water content of <10ppm, PST, lithium difluorophosphate, FEC and fully dried lithium salt LiPF6 are dissolved in the organic solvent and mixed evenly to obtain an electrolyte. Among them, the concentration of lithium salt is 1mol / L, the mass concentration of PST is 0.3%, the mass concentration of lithium difluorophosphate is 0.4%, and the mass concentration of FEC is 3%.

[0114] 5) Preparation of batteries

[0115] The positive electrode sheet, the isolation film, and the negative electrode sheet are stacked in order, so that the isolation film is placed between the positive and negative electrode sheets to play an isolating role. Then, they are wound into a square bare battery cell, loaded with an aluminum-plastic film, and then baked at 80°C to remove water. After that, 10g of the corresponding non-aqueous electrolyte is injected and sealed. After standing, hot and cold pressing, formation, clamping, capacity division and other processes, a finished battery is obtained.

[0116] The battery preparation methods provided in Examples 2 to 5 are the same as those in Example 1, with the main difference being that the mass percentage of EC in the organic solvent of the electrolyte is changed, and the mass percentage of EMC is adjusted accordingly to meet 100%, as shown in Table 1 below.

[0117] Table 1

[0118]

[0119] The battery preparation methods provided in Examples 6 to 8 are the same as those in Example 1, with the main difference being that the mass concentration of PST in the electrolyte is changed, as shown in Table 2 below.

[0120] Table 2

[0121]

[0122] The battery preparation method provided in Example 9 is the same as that in Example 1, except that no lithium difluorophosphate is added to the electrolyte, as shown in Table 3 below.

[0123] Table 3

[0124]

[0125] The battery preparation methods provided in Examples 10 and 11 are the same as those in Example 1, except that the molar percentage of the cobalt element in the ternary material is changed, that is, LiNi is used respectively. 0.55 Co 0.07 Mn 0.38 O2、LiNi 0.55 Co 0.20 Mn 0.25O2 replaces LiNi in equal amounts 0.55 Co 0.12 Mn 0.33 O2. As shown in Table 4 below.

[0126] Table 4

[0127]

[0128] The battery preparation method provided in Example 12 is the same as that in Example 1, except that no FEC is added to the electrolyte, as shown in Table 5 below.

[0129] Table 5

[0130]

[0131] The battery preparation method provided in Comparative Example 1 is the same as that in Example 1, except that the mass percentage of EC in the organic solvent of the electrolyte is changed to 30%, and the mass percentage of EMC is adjusted accordingly to meet 100%, as shown in Table 6 below.

[0132] The battery preparation method provided in Comparative Example 2 is the same as that in Example 1, except that PST is not added to the electrolyte, as shown in Table 6 below.

[0133] Table 6

[0134]

[0135] By comparing the embodiment with comparative examples 1 and 2, it can be seen that by using 1,3-propylene sultone as an additive and reasonably controlling the mass percentage of ethylene carbonate in the solvent of the electrolyte, the cycle capacity retention rate of the lithium ion battery can be significantly improved, so that the lithium ion battery has a longer cycle life.

[0136] Furthermore, through the comparison between Examples 1 to 5, it can be seen that a better cycle capacity retention rate can be obtained by reasonably controlling the mass percentage of EC in the organic solvent of the electrolyte.

[0137] Furthermore, by comparing Examples 1 and 6 to 8, it can be seen that a better cycle capacity retention rate can be obtained by properly controlling the mass concentration of PST in the electrolyte.

[0138] Furthermore, by comparing Examples 1 and 9, it can be seen that adding lithium difluorophosphate as an additive to the electrolyte can obtain a better cycle capacity retention rate.

[0139] Furthermore, through the comparison between Examples 1 and 10-11, it can be seen that a better cycle capacity retention rate can be obtained by reasonably controlling the molar percentage of the cobalt element in the ternary material.

[0140] Furthermore, through the comparison between Examples 1 and 12, it can be seen that adding FEC as an additive to the electrolyte can obtain a better cycle capacity retention rate.

[0141] 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.

[0142] 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: The invention comprises a positive electrode plate, a negative electrode plate and an electrolyte, wherein the positive electrode active layer in the positive electrode plate comprises a ternary material, wherein the ternary material comprises a ternary metal element, wherein the ternary metal element comprises a nickel element, wherein the molar percentage of the nickel element in the total molar amount of the ternary metal element is 50% to 70%, and the electrolyte comprises a lithium salt, a first additive and a solvent, wherein the first additive comprises 1,3-propylene sultone, and the solvent comprises ethylene carbonate in an amount of 5% to 25% by mass.

2. The lithium ion secondary battery according to claim 1, characterized in that: In the solvent, the mass percentage of ethylene carbonate is 13% to 18%.

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

4. The lithium ion secondary battery according to claim 3, characterized in that: The mass concentration of the 1,3-propylene sultone is 0.15% to 0.45%.

5. The lithium ion secondary battery according to any one of claims 1 to 4, characterized in that: The electrolyte further comprises a second additive, wherein the second additive comprises a fluorine-containing phosphate.

6. The lithium ion secondary battery according to claim 5, characterized in that: The second additive has one or both of the following characteristics: (1) The second additive includes one or more of lithium difluorophosphate, lithium monofluorophosphate, lithium difluorobisoxalate phosphate and lithium tetrafluorooxalate phosphate; (2) In the electrolyte, the mass concentration of the fluorine-containing phosphate is 0.01% to 1%.

7. The lithium ion secondary battery according to any one of claims 1 to 4, characterized in that: The ternary metal element includes cobalt, and the molar percentage of the cobalt element in the total molar amount of the ternary metal element is 7% to 20%.

8. The lithium ion secondary battery according to claim 7, characterized in that: The molar percentage of cobalt element in the total molar amount of the ternary metal elements is 10% to 15%.

9. The lithium ion secondary battery according to any one of claims 1 to 4, characterized in that: The ternary material has one or two of the following characteristics: (1) The primary particle size of the ternary material is 1 μm to 4 μm; (2) The ternary material includes one or more of lithium nickel cobalt manganese oxide and its modified compounds.

10. The lithium ion secondary battery according to any one of claims 1 to 4, characterized in that: The electrolyte further includes a third additive, wherein the third additive includes a fluorine-substituted compound containing a five-membered heterocyclic structure.

11. The lithium ion secondary battery according to claim 10, characterized in that: The third additive has one or two of the following characteristics: (1) The third additive includes one or more of fluoroethylene carbonate, fluoroethylene sulfate and bisfluoroethylene carbonate; (2) In the electrolyte, the mass concentration of the fluorine-substituted compound containing a five-membered heterocyclic structure is 0.01% to 5%.

12. The lithium ion secondary battery according to any one of claims 1 to 4, characterized in that: The lithium salt includes lithium hexafluorophosphate.

13. An electrical device, characterized in that: A lithium ion secondary battery comprising any one of claims 1 to 12.

Images