Lithium ion battery

Abstract

The invention belongs to the field of new energy, and relates to a lithium ion battery. The lithium ion battery comprises a positive electrode, a negative electrode and an electrolyte, the positive electrode comprises a positive electrode active material, and the positive electrode active material contains Ni element; the electrolyte is prepared from fluorophosphate, sultone and lithium bis (fluorosulfonyl) imide; moreover, the lithium ion battery meets the following relational expression (1): 0.35 < = B * N / (A + C) < = 16.5 (1), in the formula (1), A is the mass percentage content of the fluorophosphate in the electrolyte, and the unit is wt%; b is the mass percentage content of sultone in the electrolyte, and the unit is wt%; c is the mass percentage content of lithium bis (fluorosulfonyl) imide in the electrolyte, and the unit is wt%; n is the mass percentage content of the nickel element in the positive electrode active material, and the unit is wt%. According to the lithium ion battery, the energy density of the battery is improved, and meanwhile, the high-temperature cycle performance and the safety performance of the nickel-containing positive electrode battery are improved or improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of new energy, and relates to a lithium ion secondary battery which can be used in a power device or an energy storage device. BACKGROUND

[0002] With the vigorous development of new energy vehicles and energy storage industries, lithium ion batteries are facing higher requirements in terms of energy density, cycle life and safety performance. Increasing the nickel content of ternary cathode materials is an effective strategy to improve the energy density of batteries, but the increase in nickel content also poses a serious challenge to the cycle performance and safety performance of the battery. High-valence Ni elements (Ni 3+ / Ni 4+ ) in high-nickel cathode materials have strong oxidizing properties, which can cause continuous decomposition of the electrolyte, leading to instability of the cathode solid electrolyte interface film and dissolution of transition metal ions, and thus accelerating the capacity decay of the battery. At the same time, the intrinsic thermal stability of the cathode material decreases, the lattice oxygen precipitation temperature decreases, and the exothermic reaction with the electrolyte intensifies, significantly increasing the risk of thermal runaway.

[0003] The prior art alleviates these problems by surface coating or using electrolyte additives:

[0004] Some documents disclose a preparation method of a lithium nickel cobalt manganese oxide NCM523 ternary material, in which the NCM523 ternary material is mixed with lithium iron phosphate (LFP) by dry ball milling to obtain LFP-coated NCM523 ternary material; some documents disclose a lithium manganese iron phosphate-ternary material composite cathode material and a preparation method thereof, in which lithium manganese iron phosphate (LFMP) and lithium nickel cobalt aluminum oxide NCA ternary material are mechanically mixed at high speed by adding a binder to obtain LMFP-coated NCA material. However, simply mechanically mixing the single-factor coated material with the nickel-containing cathode material is difficult to effectively improve the cycle performance, and may also affect the low-temperature performance and capacity of the battery.

[0005] Some documents disclose a silane-based additive which can effectively reduce the water content and acidity of the electrolyte, and at the same time improve the cycle performance of the battery under high temperature and high pressure. However, when this method uses additives to solve the problems of nickel dissolution in the cathode and silicon-carbon anode expansion in the anode, it also causes a decrease in storage performance, thereby reducing the cycle life, and cannot meet the requirements of high energy density, long cycle life and high safety at the same time.

[0006] It can be seen that although the prior art has made some research on improving the cycle performance and safety performance of lithium ion batteries containing nickel cathodes, the research on lithium ion batteries that simultaneously meet the requirements of high energy density, long cycle life and high safety is still not sufficient, and there is still room for further development. SUMMARY

[0007] Problem to be solved by the invention

[0008] The present invention is mainly proposed for a lithium secondary battery with high energy density of a nickel-containing positive electrode material. As described above, although using a ternary material with a high content of nickel element as a battery positive electrode can improve the energy density of the battery, it has the problem of poor cycle performance and safety performance.

[0009] In order to improve the above performance, the prior art usually adopts methods such as surface coating or using electrolyte additives, however, the method of surface coating often sacrifices the energy density or rate performance of the battery; and for the optimization of the electrolyte system, it is difficult to improve the cycle performance and safety performance by a single additive, and how to combine various additives to improve the comprehensive performance of the battery still needs to be considered.

[0010] In view of the problems in the prior art, the present invention proposes to mix specific types of additives (fluorinated phosphate, sulfonic acid lactone and lithium bisfluorosulfonylimide) in the electrolyte of a lithium ion battery with a nickel-containing positive electrode material, and to establish a specific correlation between the amount of various additives and the content of nickel element in the positive electrode active material, thereby improving or improving the high-temperature cycle performance and safety performance of the lithium ion battery with a nickel-containing positive electrode material while improving the energy density of the battery.

[0011] Solution for solving the problem

[0012] The present invention provides a lithium ion battery comprising a positive electrode, a negative electrode and an electrolyte, wherein,

[0013] The positive electrode comprises a positive electrode active material, and the positive electrode active material contains Ni element;

[0014] The electrolyte comprises fluorinated phosphate, sulfonic acid lactone and lithium bisfluorosulfonylimide;

[0015] And the lithium ion battery satisfies the following relationship (1):

[0016] 0.35≤B×N / (A+C)≤16.5 (1),

[0017] In the formula (1),

[0018] A is the mass percentage content of fluorinated phosphate in the electrolyte, with the unit of wt%;

[0019] B is the mass percentage content of sulfonic acid lactone in the electrolyte, with the unit of wt%;

[0020] C is the mass percentage content of lithium bisfluorosulfonylimide in the electrolyte, with the unit of wt%;

[0021] N is the mass percentage content of nickel element in the positive electrode active material, in wt%.

[0022] The lithium ion battery according to the present application, wherein the formula (1) further satisfies one or more of the following conditions:

[0023] 3 wt%≤A≤35 wt%;

[0024] 0.2 wt%≤B≤2.2 wt%;

[0025] 1.5 wt%≤C≤13 wt%;

[0026] 30 wt%≤N≤60 wt%.

[0027] The lithium ion battery according to the present application, wherein the fluorinated phosphate ester has a structure as shown in formula (A):

[0028]

[0029] In the formula (A),

[0030] R1, R2 and R3 are the same or different at each occurrence, and each is independently selected from a hydrogen atom, a halogen, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, or a substituted or unsubstituted aryl group, and at least one of R1, R2 and R3 is a fluorine atom substituent group.

[0031] The lithium ion battery according to the present application, wherein the alkyl group comprises a C1-C 20 alkyl group; the alkenyl group comprises a C1-C 20 alkenyl group; and the aryl group comprises a C6-C 12 aryl group.

[0032] The lithium ion battery according to the present application, wherein R1, R2 and R3 are all fluorine atom substituted groups.

[0033] The lithium ion battery according to the present application, wherein the fluorinated phosphate ester comprises at least one of the following compounds:

[0034]

[0035] The lithium ion battery according to the present application, wherein the positive electrode active material in the positive electrode comprises Li a Ni x Co y Mn z X bA ternary material of O2; wherein, 0.9<=a<=1.1, 0.5<=x<1, x+y+z=1, 0<=b<=0.1, and X is selected from at least one of Al, Zr, Ti, Mo, W, Zn, Cu, Cr, Mg, Fe, Nb, and B.

[0036] The lithium ion battery according to the application, wherein the electrolyte further comprises a lithium salt and an organic solvent.

[0037] The lithium ion battery according to the application, wherein the lithium salt is selected from one or more of the salts formed by lithium ions and the following anions: PF6 - , BF4 - , P(C2FO4)2 - , Cl - , Br - , I - , ClO4 - , AsF6 - , SiF6 2- , AlCl4 - , B(C2O4)2 - , CH3CO2 - , CF3SO3 - , N(CF3SO2)2 - , C(CF2SO2)3 - , C2BF2O4 - , PO2F2 - ; and / or, the organic solvent is selected from one or more of cyclic carbonate solvents, linear carbonate solvents, ether solvents, ester solvents, nitrile solvents, and ketone solvents.

[0038] The lithium ion battery according to the application, wherein the lithium ion battery is at least one of a power battery and a battery for an energy storage system.

[0039] Effects of the application

[0040] By implementing the above technical solution, the application can at least achieve the following technical effects:

[0041] The application improves the energy density of the battery by using a positive electrode material containing nickel, and introduces specific additives fluorophosphates, sulfonic acid lactones, and lithium bisfluorosulfonimide into the electrolyte. By controlling the content of fluorophosphates, sulfonic acid lactones, and lithium bisfluorosulfonimide in the electrolyte and the content of nickel in the positive electrode active material to satisfy the relationship formula: 0.5<=BxN / (A+C)<=30, the synergistic effect of sulfonic acid lactones, lithium bisfluorosulfonimide, and fluorophosphates can effectively improve the high-temperature stability of the electrode / electrolyte interface film, greatly improving the high-temperature cycle performance and safety performance of the lithium ion battery. DETAILED DESCRIPTION

[0042] Hereinafter, the content of the present application will be described in detail. The description of the technical features described below is based on representative embodiments, specific examples of the present application, but the present application is not limited to these embodiments, specific examples. Note that:

[0043] In the present specification, the numerical range indicated by "numerical value A to numerical value B" means a range including the end point values A and B.

[0044] In the present specification, the numerical range indicated by "above" or "below" means a range including the numerical value.

[0045] In the present specification, the meaning indicated by "may" includes both the meaning of performing a certain process and the meaning of not performing a certain process.

[0046] In the present specification, "optionally" or "optional" indicates the use or non-use of certain substances, components, execution steps, applied conditions, and the like.

[0047] In the present specification, "ordinary temperature" or "room temperature" means an indoor environmental temperature of "23 ± 2°C".

[0048] In the present specification, the unit names used are international standard unit names, and if not specifically stated, "%" used means a weight or mass percentage content.

[0049] In the present specification, "substantially" or "essentially" means that the standard deviation from a theoretical model, theoretical data, or target data is within a numerical range of 2%, preferably 1%, and more preferably 0.8%.

[0050] In the present specification, the term "comprising" and / or "including" means that the presence of a feature, step, operation, device, component, and / or a combination thereof is indicated.

[0051] In the present specification, "some specific / preferred embodiments", "further specific / preferred embodiments", "embodiments", and the like mean that the specific elements (for example, features, structures, properties, and / or characteristics) described in relation to the embodiments are included in at least one embodiment described herein, and can be present in other embodiments or can not be present in other embodiments. In addition, it should be understood that the elements can be combined in various embodiments in any suitable manner.

[0052] The present application mainly provides a lithium ion battery, which can effectively improve the high-temperature cycle performance and safety performance of the lithium ion battery by using a positive electrode material containing nickel and a specific electrolyte additive and establishing a specific correlation between the amount of the additive and the nickel content in the positive electrode active material.

[0053] The present application is mainly obtained through the following insights:

[0054] In order to improve the energy density of the battery, a ternary positive electrode material with a high nickel content is usually used. However, with the increase of the content of nickel element, the probability of dissolution of the Ni element and other positive electrode elements in the positive electrode material during the charging and discharging process of the lithium ion battery also increases, thereby catalyzing the decomposition of the electrolyte to produce more byproduct, increasing the interface impedance, and deteriorating the high-temperature cycle performance of the battery. At the same time, a large amount of gas such as CO2 and CH4 is produced, which causes the battery to swell and increases the risk of thermal runaway of the battery, affecting the safety performance of the battery.

[0055] The inventors of the present application found that when fluorophosphates, sulfolactones and lithium bisfluorosulfonimide are used as additives in the electrolyte of a lithium ion battery containing a nickel-containing positive electrode material, and the content N of the nickel element of the positive electrode active material, the mass content A of the fluorophosphate in the electrolyte, the mass content B of the sulfolactone and the mass content C of the lithium bisfluorosulfonimide satisfy a certain relationship, the high-temperature cycle performance of the battery can be significantly improved, and the safety performance of the lithium ion battery can be effectively improved. The reason may be that the sulfolactone in the electrolyte can be preferentially oxidized and ring-opening polymerized on the positive electrode surface to generate a dense CEI (Cathode Electrolyte Interface) film rich in sulfonic acid groups, thereby effectively passivating the electrode and inhibiting the contact between the electrolyte and the highly active Ni 4+ The lithium bisfluorosulfonimide itself has a high thermal decomposition temperature and a high ionic conductivity, which can help to improve the thermal stability of the electrolyte itself and the high-temperature performance of the lithium ion battery. The fluorophosphate can release phosphorus-oxygen radicals under high temperature conditions, which can capture or eliminate hydrogen radicals and hydroxyl radicals generated during the exothermic process of the battery, effectively reducing the risk of thermal runaway. In addition, the fluorophosphate can form an interface film rich in fluorine and phosphorus during the charging and discharging process, which can improve the high-temperature stability of the electrode interface and help to improve the safety performance of the battery.

[0056] (lithium ion battery)

[0057] The lithium ion secondary battery according to the present application can be a power battery, i.e. a battery used to provide power for transportation or vehicles, or a secondary battery used for a storage system of wind power, hydroelectric power, solar power or traditional petrochemical energy power.

[0058] The lithium ion secondary battery according to the present application can include a positive electrode, a negative electrode, an electrolyte and a separator, etc. in terms of a single unit. In addition, the lithium ion secondary battery according to the present application can be a non-aqueous electrolyte lithium ion battery or a semi-solid lithium ion battery with a certain non-aqueous electrolyte.

[0059] (cathode)

[0060] For the cathode, a current collector and a cathode active material layer are included. For the current collector of the cathode, there is no particular restriction in principle, and for example, copper or aluminum, preferably aluminum, can be used.

[0061] For the cathode active material layer, it can include a cathode active material, a binder, and optionally a conductive agent, an auxiliary agent, and the like.

[0062] From the perspective of high capacity, the cathode active material of the present application selects a ternary layered transition metal oxide cathode material containing Ni element, which has a higher specific capacity and can better meet the demand for high energy density, and can include: Li a Ni x Co y Mn z X b O2 ternary material; wherein 0.9≤a≤1.1, 0.5≤x<1, x+y+z=1, 0≤b≤0.1, X is selected from at least one of Al, Zr, Ti, Mo, W, Zn, Cu, Cr, Mg, Fe, Nb, B;

[0063] Further, for the cathode active material, increasing the nickel content in the cathode active material can improve the capacity of the battery, thereby increasing the energy density of the battery, but too high nickel content will exacerbate the Ni 4+ catalytic decomposition of the electrolyte, increase the interface impedance, and also reduce the thermal stability of the cathode material itself, thereby causing the cycle performance and safety performance of the battery to deteriorate sharply; when the nickel content is too low, the effect of improving the energy density of the battery cannot be achieved. Therefore, in order to better balance the energy density and electrochemical performance of the battery, the mass N of the nickel element in the cathode active material in the present application is 30wt%≤N≤60wt%, for example, it can be 32wt%, 35wt%, 38wt%, 40wt%, 42wt%, 45wt%, 48wt%, 50wt%, 52wt%, 55wt%, etc.

[0064] In a further preferred embodiment of the present application, the cathode active material can include Li(Ni 0.5 Co 0.2 Mn 0.3 )O2, Li(Ni 0.6 Co 0.2 Mn 0.2 )O2, Li(Ni 0.6 Co 0.1 Mn 0.3 )O2, Li(Ni 0.7 Co 0.1 Mn 0.2)02, Li(Ni 0.8 Co 0.1 Mn 0.1 )02, Li(Ni 0.65 Co 0.15 Mn 0.2 )02, and Li(Ni 0.68 Co 0.09 Mn 0.23 )02, and the like.

[0065] Further, for other components in the positive electrode active material layer, there is no particular restriction in principle, and for example, a binder, a conductive agent, and an auxiliary agent, which are generally used in the art, can be used. For such a binder, for example, a fluorine-containing polyolefin, an acrylate, a cellulose-based binder can be used; for a usable conductive agent, for example, a carbon nanotube, a conductive metal particle, and the like can be used; and for a usable auxiliary agent, for example, a thickening agent, a dispersing aid, and the like can be used.

[0066] (negative electrode)

[0067] For the negative electrode of the battery, there is no particular restriction in principle, and a negative electrode generally used in the art can be used. Such a negative electrode includes a current collector and a negative electrode active material layer. For the current collector of the negative electrode, there is no particular restriction in principle, and for example, copper or aluminum, preferably copper, can be used.

[0068] For the negative electrode active material layer, it can include a negative electrode active material, a binder, and optionally an auxiliary agent, and the like.

[0069] For the negative electrode active material, there is no particular restriction, and for example, a carbon material, a silicon material, or a mixture thereof can be used.

[0070] Further, for other components in the negative electrode active material layer, for example, a binder, other auxiliary agents, and the like, they can be selected from conventional components in the art.

[0071] (separating membrane)

[0072] In some specific embodiments of the present application, the lithium ion battery further uses a separating membrane.

[0073] For the separating membrane, it can include a porous membrane and optionally a modification layer formed on one or both main surfaces of the porous membrane.

[0074] For the porous membrane layer, there is no particular restriction in principle, and for example, an olefin (polypropylene PP, polyethylene PE), a polyamide, and the like can be used. Such a porous membrane layer can be composed of one or more organic resin layers.

[0075] For the modification layer, there is no particular restriction in principle, and for example, a material including an organic heat-resistant particle, an inorganic particle, a conductive agent, a lithium supplement agent, a binder, and the like can be used.

[0076] The porosity of the separator can be typically 20 to 60 vol%, and preferably 30 to 46 vol%, and the thickness of the separator can be typically 30 μm or less.

[0077] (Electrolyte solution)

[0078] The electrolyte solution of the present application includes, in terms of composition, at least three kinds of additives, i.e., fluorinated phosphate, sulfone lactone and lithium bisfluorosulfonylimide, in addition to a nonaqueous organic solvent and a lithium salt which are generally used, and optionally, other kinds of additives can be included.

[0079] Nonaqueous organic solvent

[0080] The nonaqueous organic solvent of the present application is not particularly limited as long as it is a nonaqueous solvent generally used for nonaqueous electrolyte solutions.

[0081] In some specific embodiments, the nonaqueous solvent can be selected from one or more of cyclic carbonate solvents, linear carbonate solvents, ether solvents, ester solvents, nitrile solvents and ketone solvents.

[0082] Among them, the cyclic carbonate solvents can be selected from ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC) and the like; the linear carbonate solvents can be selected from diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), methyl trifluoroethyl carbonate (FEMC), di(2,2,2-trifluoroethyl) carbonate (DFDEC) and the like; the ester solvents can be selected from methyl formate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, methyl neopentanoate and the like; the ether solvents can be selected from dibutyl ether, tetrahydrofuran (THF), 2-methyltetrahydrofuran, ethylene glycol dimethyl ether (DME), ethylene glycol diethyl ether (DEE), dioxane (DX), dioxolane (DOL) and the like; the nitrile solvents can include acetonitrile; and the ketone solvents can be selected from polymethylvinyl ketone and the like. These nonaqueous solvents can be used alone or in the form of a mixture of two or more kinds.

[0083] In some preferred embodiments, the nonaqueous solvent can be selected from two or three kinds of the organic solvents selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl formate (MA), ethyl acetate (EA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB) and propyl butyrate (PB).

[0084] Lithium salt

[0085] The kind of lithium salt that can be used in the present application is not particularly limited, and can be a lithium salt commonly used in the art (a lithium salt different from the additive described below).

[0086] In some specific embodiments, the lithium salt can be selected from one or more of the salts formed by lithium ions and the following anions: - BF4 - P(C2FO4)2 - Cl - Br - I - ClO4 - AsF6 - SiF6 2- AlCl4 - B(C2O4)2 - CH3CO2 - CF3SO3 - N(CF3SO2)2 - C(CF2SO2)3 - C2BF2O4 - PO2F2 - and the like.

[0087] In some preferred embodiments, the lithium salt can be at least one of lithium hexafluorophosphate (LiPF6), lithium difluorophosphate (LiPO2F2), lithium tetrafluoroborate (LiBF4), lithium difluorodioxalate phosphate (LiDFOP), lithium difluorooxalate borate (LiDFOB), and lithium bisoxalate borate (LiBOB).

[0088] There is no particular limitation on the content of the lithium salt in principle. In some specific embodiments of the present application, the concentration of the lithium salt in the nonaqueous electrolyte can be 0.8 mol / L to 5 mol / L, preferably 1 mol / L to 1.5 mol / L, for example, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, 4 mol / L, 4.5 mol / L, etc., from the perspective of controlling the viscosity and cost of the electrolyte.

[0089] Additive

[0090] The additive of the present application at least includes three essential additive components, namely fluorophosphonate, sulfolactone, and lithium bisfluorosulfonylimide.

[0091] The fluorophosphonate has a structure as shown in formula (A):

[0092]

[0093] In the formula (A),

[0094] R1, R2and R3are the same or different at each occurrence and are each independently selected from a hydrogen atom, a halogen, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, or a substituted or unsubstituted aryl group, and at least one of R1, R2and R3is a fluorine atom substituent.

[0095] As for the kind of the halogen, there is no particular limitation in principle, and it can be a fluorine atom, a chlorine atom, a bromine atom, or the like, of which a fluorine atom is preferred.

[0096] As for the alkyl group, it can be a straight chain structure, or can have one or more branched alkyl groups having 1 to 20, preferably 1 to 10 carbon atoms, such as a methyl group, an ethyl group, a propyl group, a butyl group, an isopropyl group, a butyl group, an isobutyl group, a tert-butyl group, or the like, of which an ethyl group and a propyl group are preferred; as for the alkenyl group, it can be a straight chain structure, or can have one or more branched alkenyl groups having 1 to 20, preferably 1 to 10 carbon atoms; and as for the aryl group, it can be a carbon aryl group or a heteroaryl group, and in some specific embodiments, a carbon aryl group is preferred, such as a carbon aryl group having 6 to 12 carbon atoms, such as a benzene ring group, or the like.

[0097] As for the substituent group usable for the above-mentioned groups, it can be a halogen, and preferably a fluorine atom.

[0098] In some specific embodiments, R1, R2and R3are each a fluorine atom substituent.

[0099] In some preferred embodiments, the fluorinated phosphate ester includes at least one of the following compounds:

[0100]

[0101] As for the sulfolactone, it can be selected from one or more of 1,3-propane sulfolactone (PS), 1,4-butane sulfolactone (1,4-BS), 2,4-butane sulfolactone (2,4-BS), 1,3-propene sulfolactone (PST), of which 1,3-propane sulfolactone (PS) is preferred.

[0102] As for the amount of the fluorinated phosphate ester, the sulfolactone and the lithium bisfluorosulfonylimide, which are the three essential additive components in the electrolyte, there is no particular limitation in principle, as long as the above-mentioned relationship of formula (1) is satisfied.

[0103] In some specific embodiments, A represents the mass percentage content of fluorinated phosphate in the electrolyte, preferably 3wt%≤A≤35wt%, for example, it can be 5wt%, 8wt%, 10wt%, 12wt%, 15wt%, 18wt%, 20wt%, 22wt%, 25wt%, 28wt%, 30wt% and the like.

[0104] In some specific embodiments, B represents the mass percentage content of sulfonic acid lactone in the electrolyte, preferably 0.2wt%≤B≤2.2wt%, for example, it can be 0.3wt%, 0.5wt%, 0.8wt%, 1wt%, 1.2wt%, 1.5wt%, 1.8wt%, 2wt% and the like.

[0105] In some specific embodiments, C represents the mass percentage content of lithium bisfluorosulfonylimide in the electrolyte, preferably 1.5wt%≤C≤13wt%, for example, it can be 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, 11wt%, 12wt% and the like.

[0106] It should be noted that, under the condition of meeting the above three additive content ranges, the technical effects of the present application can be better achieved. However, outside these ranges, especially under some harsh or extreme conditions, the following concerns may exist:

[0107] When the content A of fluorinated phosphate in the electrolyte is too low, the phosphorus-oxygen free radicals released thereby may not be able to effectively quench the hydrogen free radicals and hydroxyl free radicals generated during the exothermic process of the battery, thereby making it difficult to effectively improve the thermal stability of the battery. When the content A of fluorinated phosphate in the electrolyte is too high, it may increase the viscosity of the electrolyte itself, thereby causing incomplete impregnation of the electrode active material, resulting in low battery capacity and reducing the energy density of the battery. In addition, too high a content of fluorinated phosphate may also damage the negative electrode interface, thereby affecting the cycle stability of the battery.

[0108] When the content B of sulfonic acid lactone in the electrolyte is too low, it may not be conducive to the formation of a dense and stable interface film on the positive electrode surface, and it may not be able to effectively inhibit the dissolution of Ni from the positive electrode material and improve the battery gas production. When the content B of sulfonic acid lactone in the electrolyte is too high, the interface film formed may be too thick, resulting in an increase in the internal resistance of the battery, which is not conducive to the cycle performance of the battery.

[0109] When the content C of lithium bisfluorosulfonylimide in the electrolyte is too low, it may not be conducive to improving the thermal stability of the lithium ion battery. When the content C of lithium bisfluorosulfonylimide in the electrolyte is too high, the electrolyte may be prone to oxidative decomposition at high potential, and it may also exacerbate the corrosion of the aluminum current collector.

[0110] Further, in the electrolyte of the present application, in addition to the above-mentioned additives, various other additives known in the art can be used, as long as the technical effects of the present application are not hindered.

[0111] As such other kinds of additives, ethylene carbonate (VC), fluoroethylene carbonate (FEC), 2-cyanoethyltriethoxysilane (TEOSCN), sulfur-containing additives other than the above-mentioned sulfonic acid lactone, or oxalate-containing additives, and the like can be exemplified. Among them, the sulfur-containing additives can be selected from the group consisting of vinyl sulfite (DTD), methane disulfonic acid methylene ester (MMDS), ethylene sulfite (ES), and the like; the oxalate-containing additives can be selected from the group consisting of lithium difluoro oxalate borate (LiDFOB), lithium bisoxalate borate (LiBOB), lithium tetrafluoro oxalate phosphate (LiTFOP), lithium difluoro bisoxalate phosphate (LiDFOP), and the like. These additives can be used alone or in the form of a mixture of two or more kinds.

[0112] Lithium ion battery characteristics

[0113] By using the above-mentioned combination of three specific additives and establishing a specific correlation between the content of these additives and the content of nickel element in the positive electrode active material, the lithium ion battery of the present application can improve or improve the high-temperature cycle performance and safety performance of the lithium ion battery containing nickel positive electrode material while improving the energy density of the battery.

[0114] Specifically, the lithium ion battery of the present application satisfies the following relationship (1):

[0115] 0.35≤B×N / (A+C)≤16.5 (1),

[0116] In the formula (1),

[0117] A is the mass percentage content of fluorinated phosphate ester in the electrolyte, with the unit of wt%;

[0118] B is the mass percentage content of sulfonic acid lactone in the electrolyte, with the unit of wt%;

[0119] C is the mass percentage content of lithium bisfluorosulfonylimide in the electrolyte, with the unit of wt%;

[0120] N is the mass percentage content of nickel element in the positive electrode active material, with the unit of wt%.

[0121] When B x N / (A+C) is too large (for example, greater than 16.5), it indicates that the positive active material contains too high Ni element content, and the high-temperature cycle performance and safety performance of the battery are poor; or the content of fluorinated phosphate and lithium bisfluorosulfonylimide in the electrolyte is too low, which cannot effectively improve the thermal stability of the electrolyte, causing the safety performance of the battery to deteriorate; or the content of sulfolactone in the electrolyte is too high, which may cause the interface film formed to be too thick, making it difficult to effectively improve the high-temperature performance and safety of the electrolyte.

[0122] When B x N / (A+C) is too small (for example, less than 0.35), it indicates that the positive active material contains low Ni element content, which is not conducive to improving the energy density of the battery; or the content of fluorinated phosphate in the electrolyte is too high, causing the viscosity of the electrolyte itself to increase, the electrode wettability to deteriorate, and the active material capacity to be low; or the content of lithium bisfluorosulfonylimide in the electrolyte is too high, causing the electrolyte to be prone to oxidative decomposition, and failing to effectively improve the cycle performance of the battery; or the content of sulfolactone in the electrolyte is too low, making it difficult to form a dense CEI film on the electrode surface, thereby making it difficult to improve the high-temperature performance and safety performance.

[0123] Use form of lithium ion battery

[0124] The various components described above, as well as other auxiliary components or components, if necessary, are assembled according to the usual assembly method in the art to obtain a usable lithium ion secondary battery.

[0125] For such a battery, in terms of a single unit, its form can be one or more of a cylindrical battery, a sheet-shaped battery, a plate-shaped battery, and a block-shaped battery.

[0126] Further, in some specific embodiments, the battery of the present application appears and is used in the form of a single unit, and in other specific embodiments, the battery of the present application can be used in parallel or in series in any number of scales, for example, a battery pack or a battery bank formed after packaging several battery units.

[0127] Examples

[0128] The embodiments of the present application will be described in detail below with reference to examples, but those skilled in the art will understand that the following examples are only for illustration of the present application and should not be regarded as limiting the scope of the present application. If the specific conditions are not specified in the examples, they are carried out according to the conventional conditions or the conditions recommended by the manufacturer. If the reagents or instruments used are not specified by the manufacturer, they are all conventional products that can be obtained by purchase on the market.

[0129] Example 1

[0130] Positive electrode sheet: The positive active material Li(Ni 0.8Co 0.1 Mn 0.1 )O2, conductive agent Super P, binder polyvinylidene fluoride (PVDF) and appropriate amount of N-methyl-2-pyrrolidone (NMP) are uniformly mixed to form a positive electrode slurry. After that, the formed positive electrode slurry is coated on an aluminum foil, and a positive electrode tab is formed by drying and roll pressing die cutting.

[0131] The negative electrode tab: graphite, conductive agent Super P, thickening agent CMC, and binder SBR are added to appropriate amount of deionized water in a mass ratio of 95:2:1:2, and the mixture is stirred to prepare a negative electrode slurry. After that, the formed negative electrode slurry is coated on a copper foil, and a negative electrode tab is formed by drying and roll pressing die cutting.

[0132] The electrolyte: in an argon glove box at room temperature, a non-aqueous electrolyte is prepared, the water content in the box is less than 1 ppm, organic solvents ethylene carbonate (EC), methyl ethyl carbonate (EMC) and diethyl carbonate (DEC) are mixed in a mass ratio of (EC: EMC: DEC = 30:50:20); lithium salt includes lithium bisfluorosulfonylimide (LiFSI) and lithium hexafluorophosphate (LiPF6), the lithium salt concentration in the electrolyte is controlled to be 1M; additives include compound 1 and 1,3-propane sultone, the organic solvent, lithium salt and additives are mixed to form an electrolyte; wherein the lithium bisfluorosulfonylimide accounts for 5% of the total mass of the electrolyte, the compound 1 accounts for 10% of the total mass of the electrolyte, and the 1,3-propane sultone accounts for 1% of the total mass of the electrolyte.

[0133] Preparation of lithium ion battery: the prepared negative electrode tab, separator and positive electrode tab are stacked in sequence, then tab welding is performed and the soft package dry battery is packaged with aluminum plastic film to obtain a soft package dry battery, which is placed in an oven at 90±2℃ for 18h, and finally the electrolyte prepared in the foregoing is injected into the battery, and static, formation and capacity distribution operations are performed to complete the preparation of the lithium ion battery.

[0134] Preparation of lithium ion battery: the prepared negative electrode tab, separator and positive electrode tab are stacked in sequence, then tab welding is performed and the soft package dry battery is packaged with aluminum plastic film to obtain a soft package dry battery, which is placed in an oven at 90±2℃ for 18h, and finally the electrolyte prepared in the foregoing is injected into the battery, and static, formation and capacity distribution operations are performed to complete the preparation of the lithium ion battery.

[0135] Examples 2-26

[0136] The types and mass percentages of fluorophosphates in the electrolyte, the mass percentages of 1,3-propane sultone and lithium bisfluorosulfonylimide, and the mass percentage of nickel in the positive active material correspond to the relationships shown in Table 1 Examples 2-26, and the lithium ion batteries of Examples 2-26 are prepared according to the preparation method in Example 1.

[0137] Comparative Examples 1-6

[0138] The type of fluorinated phosphate ester in the electrolyte and the mass percentage, the mass percentage of 1,3-propane sultone and lithium bisfluorosulfonylimide, and the mass percentage of nickel element in the positive active material correspond to the relationships shown in Table 1 for Comparative Examples 1-6, which were prepared according to the preparation method in Example 1.

[0139] Table 1 Battery parameters of examples and comparative examples

[0140]

[0141]

[0142] The performance of the lithium ion batteries obtained in the above examples and comparative examples was tested, and the specific testing methods and results are as follows:

[0143] 1. Cycle performance test: at 45±2℃, the above lithium ion battery was charged at 1C constant current to 4.25V, then charged at constant voltage to current of 0.05C, and after standing for half an hour, discharged at 1C constant current to 2.8V to obtain the initial discharge capacity of the first cycle of the battery and record it as C0, and then continue to charge and discharge in the above manner, and the capacity after discharging at the 500th week is recorded as C500. 500 , then the capacity retention rate (%) after 500 weeks of normal temperature cycle = C500 / C0x 100%. 500

[0144] 2. High temperature storage gas production test: at 25±2℃, the above lithium ion battery was charged at 1C constant current to 4.25V, then charged at constant voltage to current of 0.05C, and the initial volume V0 of the battery was tested by drainage method, then stored at 60℃ for 60D (days), and after the battery cooled to room temperature, the volume V1 after storage was tested, then the volume expansion rate (%) after 60D storage at 60℃ = (V1-V0) / V0x 100%.

[0145] 3. Hot box performance test: at 25±2℃, the above lithium ion battery was charged at 1C constant current to 4.25V, then charged at constant voltage to current of 0.05C, then the fully charged battery was placed in a constant temperature oven, heated at a rate of 5℃ / min until 135℃, and kept at 135℃ for 1h, the battery state was monitored, and if the lithium ion battery did not catch fire or explode, it was recorded as passing the test. The hot box test pass rate was recorded as "number of tests passed / number of tests".

[0146] The test results are shown in Table 2.

[0147] ​Table 2 Test results of performance of lithium ion batteries prepared in examples and comparative examples

[0148]

[0149] As can be seen from Table 1 and Table 2, the examples of the present application obtained by controlling the content of nickel element in the positive active material, the fluorinated phosphate in the electrolyte, 1,3-propane sultone and lithium bisfluorosulfonylimide to meet the condition of formula (1) effectively improve the high-temperature cycle performance and high-temperature storage performance of the battery, and at the same time improve the safety performance of the battery. The comparative examples which cannot meet the condition of formula (1) are insufficient in high-temperature cycle performance, high-temperature storage performance and safety performance.

[0150] It should be noted that although the technical solutions of the present application are described with specific examples, those skilled in the art can understand that the present application should not be limited thereto.

[0151] The above has described various embodiments of the present application, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes are obvious to those skilled in the art without departing from the scope and spirit of the described embodiments. The selection of terms used herein is intended to best explain the principles, practical applications or technical improvements in the market of the embodiments, or to enable other ordinary skilled persons in the art to understand the embodiments disclosed herein.

Claims

1. A lithium-ion battery comprising a positive electrode, a negative electrode and an electrolyte, characterized in that: The positive electrode includes a positive electrode active material, and the positive electrode active material contains Ni element; The electrolyte includes fluorophosphate, sultone and lithium bis(fluorosulfonyl)imide; Furthermore, the lithium-ion battery satisfies the following relationship (1): 0.35≤B×N / (A+C)≤16.5 (1), In the formula (1), A is the mass percentage of fluorophosphate in the electrolyte, in wt%; B is the mass percentage of sultone in the electrolyte, in wt%; C is the mass percentage of lithium bis(fluorosulfonyl)imide in the electrolyte, in wt%; N is the mass percentage of nickel element in the positive electrode active material, in wt%.

2. The lithium-ion battery according to claim 1, wherein The formula (1) further satisfies one or more of the following conditions: 3wt%≤A≤35wt%; 0.2wt%≤B≤2.2wt%; 1.5wt%≤C≤13wt%; 30wt%≤N≤60wt%.

3. The lithium-ion battery according to claim 1 or 2, characterized in that The fluorophosphate has a structure as shown in formula (A): In the formula (A), R1, R2 and R3 are the same or different each time they appear, and are independently selected from hydrogen atom, halogen, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, or substituted or unsubstituted aryl, and at least one of R1, R2 and R3 is a fluorine atom substituted group.

4. The lithium-ion battery according to claim 3, characterized in that The alkyl group includes C1 to C 20 The alkyl group includes C1~C 20 The aryl group includes C6~C 12 of aromatic groups.

5. The lithium-ion battery according to claim 3 or 4, characterized in that R1, R2 and R3 are all groups substituted with fluorine atoms.

6. The lithium-ion battery according to any one of claims 3 to 5, characterized in that The fluorophosphate comprises at least one of the following compounds:

7. The lithium-ion battery according to any one of claims 1 to 6, characterized in that The positive electrode active material in the positive electrode includes Li a Ni x Co y Mn z X b O2 ternary material; wherein, 0.9≤a≤1.1, 0.5≤x<1, x+y+z=1, 0≤b≤0.1, and X is selected from at least one of Al, Zr, Ti, Mo, W, Zn, Cu, Cr, Mg, Fe, Nb, and B.

8. The lithium ion battery according to any one of claims 1 to 7, characterized in that The electrolyte further includes a lithium salt and an organic solvent.

9. The lithium-ion battery according to claim 8, characterized in that The lithium salt is selected from one or more salts formed by lithium ions and the following anions: PF6 - 、BF4 - 、P(C2FO4)2 - 、Cl - Br - , I - 、ClO4 - 、AsF6 - 、SiF6 2- 、AlCl4 - 、B(C2O4)2 - 、CH3CO2 - CF3SO3 - 、N(CF3SO2)2 - 、C(CF2SO2)3 - 、C2BF2O4 - PO2F2 - ; and / or, the organic solvent is selected from one or more of cyclic carbonate solvents, linear carbonate solvents, ether solvents, ester solvents, nitrile solvents and ketone solvents.

10. The lithium-ion battery according to any one of claims 1 to 9, characterized in that The lithium-ion battery is at least one of a power battery and a battery for an energy storage system.

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