Secondary battery and device

Abstract

The invention relates to a secondary battery and an apparatus. The secondary battery comprises a positive pole piece, a negative pole piece and an electrolyte, wherein the positive pole piece comprises a positive active material selected from lithium-nickel transition metal oxides; the electrolyte comprises a solvent and a lithium salt, wherein the solvent comprises non-fluoro carbonate, fluoro carbonate and a cyclic sulfone compound; relative to every 100g of nickel element in the positive electrode active material, the content of the cyclic sulfone compound is Ag; relative to every 100g of nickel element in the positive electrode active material, the content of the fluoro-carbonic ester is Bg; wherein 0.1 < = A < = 5, 1 < = B < = 7.5, and 1.3 < = A + 0.25 * B < = 3.3. The electrolyte can effectively improve the problem of high-temperature gas production of the nickel-containing positive electrode battery, improve the out-of-control temperature of a battery hot box, reduce the maximum rate of instantaneous pressure change of a battery combustion bomb, and ensure the normal-temperature cycle capacity retention rate and the high-temperature storage capacity recovery rate of the nickel-containing positive electrode battery.

Description

Technical Field

[0001] The present application relates to the field of energy storage, and in particular to a secondary battery and a device. Background Art

[0002] With the continuous advancement of science and technology, people's demand for high-energy-density lithium-ion batteries with long cycle life and high safety has become more and more obvious. However, high-energy-density lithium-ion batteries often bring higher safety risks and shorter cycle life.

[0003] Medium-high nickel cathode systems can enable lithium-ion batteries to achieve higher capacity and energy density. However, the instability of nickel accelerates the decay of lithium-ion battery cycle capacity and brings great safety risks. Therefore, finding an electrolyte with more electrochemical stability and better thermal safety for nickel-containing cathode batteries has become an urgent problem to be solved. Summary of the invention

[0004] In view of the shortcomings of existing medium- and high-nickel lithium-ion batteries, the present application provides a secondary battery and related devices. The secondary battery of the present application aims at the nickel content in the positive electrode active material lithium nickel transition metal oxide, and introduces an appropriate amount of cyclic sulfone compounds and fluorocarbonates to effectively improve the high-temperature gas production problem of nickel-containing positive electrode batteries, and increases the runaway temperature of the battery hot box, reduces the harmfulness of the battery after thermal runaway, and takes into account the room temperature capacity retention rate and high temperature storage capacity recovery rate of the nickel-containing positive electrode battery.

[0005] The first aspect of the present application provides a secondary battery, which includes a positive electrode plate, a negative electrode plate and an electrolyte, wherein the positive electrode plate contains a positive electrode active material selected from lithium nickel transition metal oxides; the electrolyte contains a solvent and a lithium salt, and the solvent includes non-fluorinated carbonates, fluorinated carbonates and cyclic sulfone compounds; the content of the cyclic sulfone compound is Ag per 100g of nickel element in the positive electrode active material; the content of the fluorinated carbonate is Bg per 100g of nickel element in the positive electrode active material; wherein 0.1≤A≤5, 1≤B≤7.5, 1.3≤A+0.25×B≤3.3.

[0006] A second aspect of the present application provides a device, which includes the secondary battery described in the first aspect.

[0007] The beneficial effects of this application are:

[0008] The secondary battery of the present application targets the nickel content in the lithium-nickel transition metal oxide of the positive electrode plate and introduces appropriate amounts of cyclic sulfone compounds and fluorocarbonates, thereby effectively improving the high-temperature gas production problem of the nickel-containing positive electrode battery, reducing the volume expansion rate of the battery cell after high-temperature storage, and increasing the runaway temperature of the battery hot box, reducing the maximum rate of instantaneous pressure change of the battery combustion bomb, and mitigating the harmfulness of the battery after thermal runaway. At the same time, it also ensures the room temperature cycle capacity retention rate and high-temperature storage capacity recovery rate of the nickel-containing positive electrode battery. DETAILED DESCRIPTION

[0009] For simplicity, this application only specifically discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form an undefined range; and any lower limit can be combined with other lower limits to form an undefined range, and any upper limit can be combined with any other upper limit to form an undefined range. In addition, each separately disclosed point or single value can itself be combined as a lower limit or upper limit with any other point or single value or with other lower limits or upper limits to form an undefined range.

[0010] Unless otherwise specified, the terms used in this application have the commonly known meanings generally understood by those skilled in the art. Unless otherwise specified, the numerical values ​​of the various parameters mentioned in this application can be measured using various measurement methods commonly used in the art (for example, they can be tested according to the methods given in the examples of this application).

[0011] A list of items connected by the terms "at least one of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single component or multiple components. Item B may contain a single component or multiple components. Item C may contain a single component or multiple components.

[0012] The optional scope of the term "and / or" includes any one of two or more related listed items, and also includes any and all combinations of the related listed items, wherein any and all combinations include any combination of two related listed items, any more related listed items, or all related listed items.

[0013] The term "includes" or "comprising" is an open description, including closed technical solutions consisting of the listed features, and also including open technical solutions containing the listed features.

[0014] The present application is further described below in conjunction with specific implementations. It should be understood that these specific implementations are only used to illustrate the present application and are not used to limit the scope of the present application.

[0015] Primary and secondary batteries

[0016] The secondary battery provided in the present application includes a positive electrode plate, a negative electrode plate and an electrolyte, wherein the positive electrode plate contains a positive electrode active material selected from lithium nickel transition metal oxides; the electrolyte contains a solvent and a lithium salt, and the solvent includes non-fluorinated carbonates, fluorinated carbonates and cyclic sulfone compounds; the content of the cyclic sulfone compound is Ag per 100g of nickel element in the positive electrode active material; the content of the fluorinated carbonate is Bg per 100g of nickel element in the positive electrode active material; wherein 0.1≤A≤5, 1≤B≤7.5, 1.3≤A+0.25×B≤3.3.

[0017] In the present application, the solvent mainly has the function of dissolving lithium salts, and any solvent that can dissolve lithium salts can be used as a solvent.

[0018] In some embodiments, A is illustratively 0.1, 0.3, 0.5, 0.8, 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3, 3.2, 3.5, 3.8, 4, 4.2, 4.5, 4.8, 5 or a range consisting of any two of these values. In some embodiments, 0.5≤A≤4. If A is too low, the oxidation resistance of the electrolyte is poor, which will accelerate the side reaction of the electrolyte with the nickel-containing positive electrode under high pressure / high temperature conditions, thereby deteriorating the high temperature stability and safety of the battery. If A is too high, the high viscosity of the sulfone compound itself will deteriorate the fluidity of the electrolyte and deteriorate the kinetic performance of the battery. At the same time, the excessively high content of the cyclic sulfone compound cannot further improve the ionic conductivity of the electrolyte, but deteriorates its dissociation of the lithium salt, resulting in a decrease in ionic conductivity.

[0019] In some embodiments, B is illustratively 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3, 3.2, 3.5, 3.8, 4, 4.2, 4.5, 4.8, 5, 5.2, 5.5, 5.8, 6, 6.2, 6.5, 6.8, 7, 7.2, 7.5 or a range consisting of any two of these values. In some embodiments, 2.5≤B≤6. If B is too low, there is not enough fluorocarbonate to repair the interface film in a long cycle period, which makes the transition metal ions dissolved by the nickel-containing positive electrode active material in the cycle more significantly damaged to the negative electrode structure, thereby accelerating the decay of the battery capacity and deteriorating the battery cycle performance. If B is too high, the disadvantages caused by the instability of the fluorocarbonate itself will be magnified. Because fluorocarbonate itself is easily oxidized, it is easily catalytically decomposed by the highly oxidizing nickel-containing positive electrode under high pressure / high temperature conditions to produce more gas, thereby deteriorating the performance and safety of the battery cell. At the same time, the electrolyte system corresponding to an excessively high content of fluorocarbonate has higher heat, and the corresponding battery has greater hazards after thermal runaway.

[0020] In some embodiments, A+0.25×B is exemplarily 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3, 3.1, 3.2, 3.3 or a range consisting of any two of these values. In some embodiments, 1.4≤A+B≤3.3. If A+B is too small, there are too few cyclic sulfone compounds or too few fluorocarbonates. The electrolyte system composed of too few cyclic sulfone compounds has poor stability, and the high oxidizability of the nickel-containing positive electrode system will accelerate the decomposition of the electrolyte, thereby affecting the thermal stability and safety of the battery. At the same time, the electrolyte system corresponding to the low content of cyclic sulfone compounds has limited dissociation ability for lithium salts, thereby reducing the ionic conductivity of the electrolyte; too few fluorocarbonates are not enough to ensure the continuous repair of the interface film during the long cycle of the battery, so that the cycle performance of the battery cannot be effectively guaranteed. If A+B is too large, there will be too many cyclic sulfone compounds or too many fluorocarbonates. Too many cyclic sulfone compounds will easily cause high viscosity of the electrolyte, thereby deteriorating the kinetic performance of the battery. Too many fluorocarbonates will increase the heat of the electrolyte system and reduce the oxidation resistance of the electrolyte, thereby deteriorating the high temperature storage performance and safety performance of the battery.

[0021] In some embodiments, the non-fluorinated carbonate includes at least one of a non-fluorinated chain carbonate and a non-fluorinated cyclic carbonate. The non-fluorinated chain carbonate exemplarily includes at least one of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate and ethyl propyl carbonate, and the non-fluorinated cyclic carbonate includes at least one of ethylene carbonate, propylene carbonate and butylene carbonate.

[0022] In some embodiments, the mass proportion of the non-fluorinated linear carbonate in the non-fluorinated carbonate is more than 98%, for example, more than 98.5%, more than 98.8%, more than 99%, more than 99.2%, more than 99.5%, more than 99.8%. In some embodiments, the non-fluorinated carbonate does not include the non-fluorinated cyclic carbonate, such as ethylene carbonate and / or propylene carbonate. Here, "does not include" means that the mass proportion of non-fluorinated cyclic carbonate in non-fluorinated carbonate is less than 1%, for example, less than 0.8%, less than 0.5%, less than 0.3%, less than 0.1%.

[0023] In some embodiments, the content of the non-fluorinated carbonate is Cg, 25≤C≤35, relative to every 100g of nickel element in the positive electrode active material. C is exemplarily 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, or a range consisting of any two of these values. In some embodiments, 27≤C≤32.

[0024] In some embodiments, the fluorinated carbonate includes at least one of a fluorinated cyclic carbonate and a fluorinated linear carbonate.

[0025] In some embodiments, the fluorinated cyclic carbonate comprises at least one of the compounds represented by Formula I-1,

[0026]

[0027] In formula I-1, R1, R2, R3 and R4 are independently selected from hydrogen atom, fluorine atom, C1-C6 alkyl group or fluorinated C1-C6 alkyl group, and at least one of R1, R2, R3 and R4 is a fluorine atom or a fluorinated C1-C6 alkyl group, Q1 does not exist or Q1 is selected from C1-C6 alkylene group.

[0028] In the present application, C1-C6 alkyl includes but is not limited to methyl, ethyl, n-propyl, isopropyl, cyclopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, cyclobutyl, n-pentyl, isopentyl, neopentyl, cyclopentyl, n-hexyl, isohexyl, and cyclohexyl.

[0029] In the present application, fluorinated C1-C6 alkyl includes but is not limited to fluoromethyl, fluoroethyl, fluoro n-propyl, fluoro isopropyl, fluoro n-butyl, fluoro isobutyl, fluoro tert-butyl, fluoro n-pentyl, fluoro isopentyl, fluoro n-hexyl. Wherein, fluoro means that at least one hydrogen atom in C1-C6 alkyl is replaced by a fluorine atom. In some embodiments, fluorinated C1-C6 alkyl is selected from monofluoromethyl, difluoromethyl, trifluoromethyl, monofluoroethyl, difluoroethyl, trifluoroethyl, pentafluoroethyl or hexafluoro isopropyl.

[0030] In the present application, C1-C6 alkylene includes but is not limited to methylene, ethylene, n-propylene, isopropylene, cyclopropylene, n-butylene, isobutylene, sec-butylene, tert-butylene, cyclobutylene, n-pentylene, isopentylene, neopentylene, cyclopentylene, n-hexylene, isohexylene, and cyclohexylene.

[0031] In some embodiments, in formula I-1, R1, R2, R3, and R4 are independently selected from a hydrogen atom, a fluorine atom, a C1-C4 alkyl group, or a fluorinated C1-C4 alkyl group, and at least one of R1, R2, R3, and R4 is a fluorine atom, and Q1 does not exist or Q1 is selected from a methylene group or an ethylene group.

[0032] In some embodiments, in formula I-1, R1, R2, R3, and R4 are independently selected from hydrogen atoms, fluorine atoms, methyl groups, ethyl groups, trifluoromethyl groups, or 2,2,2-trifluoroethyl groups, at least one of R1, R2, R3, and R4 is a fluorine atom, and Q1 does not exist or Q1 is selected from methylene groups or ethylene groups.

[0033] In some embodiments, the fluorinated cyclic carbonate includes at least one of fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), and trifluoropropylene carbonate (TFPC).

[0034] In some embodiments, the fluorinated linear carbonate comprises at least one of the compounds represented by Formula I-2,

[0035]

[0036] In formula I-2, R5 and R6 are independently selected from C1-C6 alkyl or fluorinated C1-C6 alkyl, and at least one of R5 and R6 is a fluorinated C1-C6 alkyl.

[0037] In some embodiments, in Formula I-2, R5 and R6 are the same or different, and are independently selected from C1-C4 alkyl or fluorinated C1-C4 alkyl, and at least one of R5 and R6 is fluorinated C1-C4 alkyl.

[0038] In some embodiments, in formula I-2, R5 and R6 are the same or different, and are independently selected from methyl, ethyl, n-propyl, isopropyl, trifluoromethyl or 2,2,2-trifluoroethyl, and at least one of R5 and R6 is trifluoromethyl or 2,2,2-trifluoroethyl.

[0039] In some embodiments, the fluorinated linear carbonate includes at least one of methyl-2,2,2-trifluoroethyl carbonate (MTFEC) and bis(2,2,2-trifluoroethyl) carbonate (TFEC).

[0040] In some embodiments, the cyclic sulfone compound includes at least one compound selected from the group consisting of compounds represented by Formula II,

[0041]

[0042] In Formula II, R7, R8, R9 and R 10 Independently selected from a hydrogen atom, a halogen atom, a C1-C6 alkyl group, a C2-C6 alkenyl group, a C2-C6 alkynyl group, a halogenated C1-C6 alkyl group, a halogenated C2-C6 alkenyl group or a halogenated C2-C6 alkynyl group.

[0043] In the present application, C2-C6 alkenyl includes, but is not limited to, vinyl, propenyl, allyl, isopropenyl, n-butenyl, isobutenyl, tert-butenyl, n-pentenyl, isopentenyl, hexenyl, and cyclohexenyl.

[0044] C2-C6 alkynyl groups include, but are not limited to, ethynyl, n-propynyl, isopropynyl, n-butynyl, isobutynyl, n-pentynyl, isopentenyl, and hexynyl.

[0045] Halogen includes fluorine, chlorine, bromine and iodine.

[0046] In some embodiments, in Formula II, R7, R8, R9 and R 10 Independently selected from a hydrogen atom, a halogen atom, a C1-C6 alkyl group or a halogenated C1-C6 alkyl group.

[0047] In some embodiments, in Formula II, R7, R8, R9 and R 10 Independently selected from a hydrogen atom, a fluorine atom, a C1-C4 alkyl group or a fluorinated C1-C4 alkyl group.

[0048] In some embodiments, in Formula II, R7, R8, R9 and R 10 are independently selected from a hydrogen atom, a fluorine atom, a methyl group, an ethyl group, a trifluoromethyl group or a 2,2,2-trifluoroethyl group.

[0049] In some embodiments, the cyclic sulfone compound includes at least one of sulfolane (SL), methylsulfolane (MSL), and 2-fluorosulfolane (FSL).

[0050] In some embodiments, the lithium salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium trifluoromethanesulfonyl (LiOTf), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), lithium (trifluoromethylsulfonyl)(perfluorobutylsulfonyl)imide (LiFNFSI), lithium bis(pentafluoroethylsulfonate)imide (LiBETI), lithium bis(oxalatoborate) (LiBOB), lithium difluorooxalatoborate (LiDFOB), lithium difluorophosphate (LiDFP), lithium bis(oxalatodifluorophosphate) (LiODFP), lithium tetrafluoroborate (LiBF4), lithium bis(fluoromalonate)borate (LiBFMB), and lithium 4,5-dicyano-2-(trifluoromethyl)imidazole (LiTDI).

[0051] In some embodiments, the lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium difluorophosphate, and lithium bis(oxalatodifluorophosphate).

[0052] In some embodiments, the concentration of the lithium salt in the electrolyte is 0.8 mol / L-2 mol / L. The concentration of the lithium salt is illustratively 0.8 mol / L, 0.9 mol / L, 1 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L, 1.6 mol / L, 1.8 mol / L, 2 mol / L or a range consisting of any two of these values.

[0053] In some embodiments, the electrolyte may further include additives as long as they do not impair the purpose of the present invention. The additives exemplarily include vinylene carbonate (VC) and vinyl ethylene carbonate (VEC).

[0054] In some embodiments, based on the mass of the electrolyte, the mass percentage of the additive is 0.1%-10%, and exemplarily is 0.2%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or a range consisting of any two of these values.

[0055] In some embodiments, the positive electrode active material includes a LiNi selected from the formula m Co n A (1-m-n)O2 represents at least one of the lithium nickel transition metal oxides, wherein A is selected from at least one of manganese, aluminum, magnesium, zirconium, strontium, yttrium, lanthanum, molybdenum, silver, niobium, iron, titanium, copper, zinc, chromium, calcium, barium and tungsten, 0.5≤m≤1, 0≤n≤0.5, m+n≤1. In some embodiments, the chemical formula of the lithium nickel transition metal oxide is as follows: LiNi m Co n A (1-m-n) O2, wherein A is selected from at least one of manganese, aluminum, magnesium, zirconium, strontium, yttrium, lanthanum, molybdenum, silver, niobium, chromium and calcium, 0.5≤m≤1, 0≤n≤0.5, m+n≤1.

[0056] In some embodiments, m is 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1, or a range consisting of any two of these values. In some embodiments, n is 0, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, or a range consisting of any two of these values.

[0057] In some embodiments, the lithium nickel transition metal oxide includes at least one of NCM523, NCM622, NCM811, Ni90 (ie, NCM90), Ni92 (ie, NCM92), and Ni95 (ie, NCM900).

[0058] In some embodiments, the chemical formula of the lithium nickel transition metal oxide is as follows: m Co n A (1-m-n) O2, wherein A is selected from at least one of manganese, aluminum, magnesium, zirconium, strontium, yttrium, lanthanum, molybdenum, silver, niobium, iron, titanium, copper, zinc, chromium, calcium, barium and tungsten, 0.7≤m≤1, 0≤n≤0.3, m+n≤1. In some embodiments, the chemical formula of the lithium nickel transition metal oxide is as follows: LiNi m Co n A (1-m-n) O2, wherein A is selected from at least one of manganese, aluminum, magnesium, zirconium, strontium, yttrium, lanthanum, molybdenum, silver, niobium, chromium and calcium, 0.7≤m≤1, 0≤n≤0.3, m+n≤1.

[0059] In some embodiments, the lithium nickel transition metal oxide includes at least one of primary particles and secondary particles. In the present application, "primary particles" refer to crystals within a scale range of several μm, excluding grain boundaries, and the crystallographic orientation of each part of the crystal is basically the same, such as the so-called single crystal material. "Secondary particles" refer to a collection of primary particles of many oriented grains, and the interior of the secondary particles is based on a lattice periodic structure, but is isotropic, such as the so-called polycrystalline material.

[0060] In some embodiments, the lithium nickel transition metal oxide includes primary particles but no secondary particles. In some embodiments, the lithium nickel transition metal oxide includes secondary particles but no primary particles.

[0061] In order to take into account the normal temperature cycle capacity retention rate, high temperature storage capacity recovery rate and power performance of the battery such as low temperature discharge capacity retention rate, the primary particles and secondary particles of the lithium nickel transition metal oxide can be compounded. In some embodiments, the lithium nickel transition metal oxide includes primary particles and secondary particles, and the mass ratio of the primary particles to the secondary particles is 1:4 to 1:1. In some embodiments, the mass ratio of the primary particles of the lithium nickel transition metal oxide to the secondary particles is 1:4, 2:7, 1:3, 2:5, 3:7, 1:2, 2:3, 1:1 or a range consisting of any two of these ratios.

[0062] In some embodiments, the lithium nickel transition metal oxide may further include a coating layer, wherein the coating layer may be composed of one or more of lithium metaaluminate, aluminum oxide, lithium borate, or lithium boride.

[0063] In some embodiments, the positive electrode active material includes at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide.

[0064] In some embodiments, the positive electrode plate further comprises a binder and a conductive agent. In some embodiments, the binder includes but is not limited to polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl pyrrolidone. In some embodiments, the conductive agent includes but is not limited to carbon nanotubes, natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber.

[0065] In some embodiments, the positive electrode plate further includes a positive electrode current collector, and the positive electrode current collector includes: aluminum foil or a polymer substrate coated with a conductive metal.

[0066] In some embodiments, the negative electrode plate includes a negative electrode active material, and the negative electrode active material includes at least one of a silicon-based material and a carbon-based material. The silicon-based material includes at least one of silicon, a silicon alloy, a silicon oxide compound, and a silicon carbon compound, in particular a silicon oxide compound and / or a silicon carbon compound. The carbon-based material includes at least one of natural graphite, artificial graphite, soft carbon, hard carbon, carbon nanotubes, and graphene. In some embodiments, the negative electrode active material includes a silicon-based material and a carbon-based material, the silicon-based material includes a silicon oxide compound and / or a silicon carbon compound, and the carbon-based material includes natural graphite and / or artificial graphite.

[0067] In some embodiments, based on the mass of the negative electrode active material, the mass content g% of the silicon-based material satisfies: 8≤g≤50. In some embodiments, g is 8, 10, 12, 14, 16, 18, 20, 22, 25, 28, 30, 32, 35, 38, 40, 42, 45, 48, 50 or a range consisting of any two of these values. In some embodiments, 10≤g≤50. In other embodiments, 12≤g≤35.

[0068] In some embodiments, the negative electrode plate further comprises a binder and a conductive agent. In some embodiments, the binder includes butadiene styrene rubber, acrylated butadiene styrene rubber, polyacrylic acid, polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl pyrrolidone. In some embodiments, the conductive agent includes but is not limited to carbon nanotubes, natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber.

[0069] In some embodiments, the negative electrode plate further includes a negative electrode current collector, and the negative electrode current collector includes: copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, or any combination thereof.

[0070] In some embodiments, a separator is provided between the positive electrode plate and the negative electrode plate to prevent short circuit. The material and shape of the separator that can be used in the embodiments of the present application are not particularly limited, and it can be any technology disclosed in the prior art. In some embodiments, the separator includes a polymer or an inorganic substance formed of a material that is stable to the electrolyte of the present application.

[0071] For example, the diaphragm may include a substrate layer and a surface treatment layer. The substrate layer is a non-woven fabric, a film or a composite film having a porous structure, and the material of the substrate layer includes at least one of polyethylene, polypropylene, polyethylene terephthalate, polyimide or aramid. A surface treatment layer is provided on at least one surface of the substrate layer, and the surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by a mixed polymer and an inorganic substance.

[0072] In some embodiments, the secondary battery is a lithium secondary battery or a sodium secondary battery. In some embodiments, the lithium secondary battery includes but is not limited to: a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery or a lithium ion polymer secondary battery.

[0073] In some embodiments, the secondary battery may include an outer package, which may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the secondary battery may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, such as one or more of polypropylene, polybutylene terephthalate, polybutylene succinate, etc.

[0074] In some embodiments, the shape of the secondary battery is not particularly limited, and it can be cylindrical, square, or any other shape.

[0075] In some embodiments, the present application further provides a battery module. The battery module includes the above-mentioned secondary battery. The battery module of the present application uses the above-mentioned secondary battery, and therefore has at least the same advantages as the secondary battery. The number of secondary batteries contained in the battery module of the present application can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.

[0076] In some embodiments, the present application further provides a battery pack, which includes the above-mentioned battery module. The number of battery modules included in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0077] 2. Device

[0078] The present application also provides a device, which includes at least one of the above-mentioned secondary battery, battery module or battery pack as a power source.

[0079] In some embodiments, the device includes, but is not limited to: electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, power storage systems, etc. In order to meet the device's requirements for high power and high energy density of secondary batteries, a battery pack or battery module may be used.

[0080] In other embodiments, the device may be a mobile phone, a tablet computer, a laptop computer, etc. The device is usually required to be light and thin, and a secondary battery may be used as a power source.

[0081] Example

[0082] In this application, unless otherwise specified, all materials or reagents used are commercially available, and all methods used are conventional methods in the art.

[0083] Test Method

[0084] 1. Battery 25℃ cycle performance test

[0085] At 25°C, the lithium-ion battery was charged to 4.25V at 0.5C constant current, then charged to 0.05C at 4.25V, and then discharged to 2.5V at 1C constant current. After 400 cycles of charge and discharge, the capacity retention rate after the 400th cycle at 25°C was calculated according to the following formula: discharge capacity after the 400th cycle / discharge capacity in the first cycle × 100%.

[0086] 2. Capacity recovery rate test after battery storage at 60°C for 56 days

[0087] At 25°C, charge the lithium-ion battery to 4.25V at a constant current of 0.5C, charge it to 0.05C at a constant voltage at 4.25V, and then discharge it to 2.5V at a constant current of 1C, and record the discharge capacity Q1. Then charge the lithium-ion battery to 4.25V at a constant current of 0.5C, charge it to 0.05C at a constant voltage at 4.25V, and place the fully charged battery in a constant temperature box, and set the temperature of the incubator to 60°C±2°C. After being stored at 60°C for 56 days, discharge it to 2.5V at a constant current of 1C, then charge the lithium-ion battery to 4.25V at a constant current of 0.5C, charge it to 0.05C at a constant voltage at 4.25V, and then discharge it to 2.5V at a constant current of 1C, and record the discharge capacity Q2 at this time.

[0088] The capacity recovery rate of the battery after storage at 60°C for 56 days was calculated using the following formula: Q2 / Q1×100%.

[0089] 3. Gas production test after battery storage at 60°C for 56 days

[0090] The lithium-ion battery was discharged at 1C constant current to 2.5V at 25°C, then charged at 0.5C constant current to 4.25V, and then charged at 4.25V to 0.05C at constant voltage. The full-charge thickness of the battery at this time was measured using a PPG soft-pack battery thickness gauge and recorded as a. The battery stored at 60°C for 56 days according to the above test method 2 was charged at 0.5C constant current to 4.25V, and then charged at 4.25V to 0.05C at constant voltage. The full-charge thickness of the battery at this time was measured using a PPG soft-pack battery thickness gauge and recorded as b. The calculation formula for the expansion rate of the battery cell thickness after 56 days of storage at 60°C is: (ba) / a×100%.

[0091] 4. Battery -20℃ discharge capacity retention rate test

[0092] At 25°C, the lithium-ion battery is charged to 4.25V at a constant current of 0.33C, then charged to 0.05C at a constant voltage of 4.25V, and then discharged to 2.5V at a constant current of 0.33C, and the discharge capacity Q1 is recorded. Then the lithium-ion battery is charged to 4.25V at a constant current of 0.33C,

[0093] Constant voltage charge to 0.05C at 4.25V. The fully charged battery cell is placed in a -20°C constant temperature oven, left for 16h to reach thermal equilibrium, and then discharged at a constant current of 0.1C to 2.0V. Record the discharge capacity Q2. The calculation formula for the discharge capacity retention rate at -20°C is: Q2 / Q1×100%.

[0094] 5. Battery Thermal Chamber Test

[0095] The thermal chamber test steps are as follows: Under the condition of 25°C, calibrate the battery cell capacity at 1 / 3C and fully charge it; Clamp the fully charged battery cell, with a pre-tightening force of 1.5 Nm; Put the lithium-ion battery into the temperature chamber, and the temperature chamber rises from the ambient temperature to 130°C ± 2°C at a speed of 5°C / min and maintain this temperature for 60 min; The temperature chamber continues to rise by 10°C at a speed of 5°C / min and maintain this temperature for 60 min; Until out of control, record the battery cell temperature corresponding to the out-of-control situation.

[0096] 6. Battery Combustion Bomb Test

[0097] The combustion bomb test steps are as follows: Under the condition of 25°C, calibrate the battery cell capacity at 1 / 3C and fully charge it; Replace the atmosphere with nitrogen and evacuate and refill the atmosphere in the combustion bomb cavity twice; Set up data acquisition to record voltage and chamber pressure data. Lateral heat the battery cell with a heating sheet of size 50×50mm and power 300W at a constant power until the battery cell gets out of control. After thermal runaway, wait for the air pressure in the chamber to stabilize to complete the test. Differentiate the air domain temperature data during the test, record the change in the instantaneous ejection pressure dP / dt, and record the maximum value dP / dt(max) of the instantaneous pressure change dP / dt.

[0098] Example 1

[0099] The preparation steps of the positive electrode plate are as follows: Mix the positive active material NCM811 single crystal and NCM811 polycrystal mixture (the mass ratio of single crystal to polycrystal is 3:7), conductive agent carbon nanotubes, conductive agent carbon black, and binder polyvinylidene fluoride in a mass ratio of 95:2:1:2, and then disperse them in N-methyl-2-pyrrolidone to obtain a positive electrode slurry. Coat the positive electrode slurry evenly on both sides of a 12μm thick aluminum foil current collector, and after drying, rolling, and slitting, obtain the positive electrode plate.

[0100] The preparation steps of the negative electrode plate are as follows: Mix silicon oxide-graphite composite (the mass ratio of silicon oxide SiOx (0.5 < x < 1.5) to artificial graphite is 14:86), conductive agent acetylene black, binder styrene-butadiene rubber, thickener sodium carboxymethyl cellulose, and binder polyacrylic acid in a mass ratio of 95:2:1.5:1:0.5, and then disperse them in deionized water to obtain a negative electrode slurry. Coat the negative electrode slurry on both sides of an 8μm thick copper foil current collector, and after drying, rolling, and slitting, obtain the negative electrode plate.

[0101] Diaphragm: PP / PE / PP three-layer composite diaphragm.

[0102] Preparation of electrolyte: In an argon-protected glove box (H2O<0.1ppm, O2<0.1ppm), solvents ethyl methyl carbonate (EMC), fluoroethylene carbonate (FEC) and cyclopentane (SL) are mixed in proportion, wherein the amount of EMC is 30.702g, the amount of FEC is 4.284g, and the amount of SL is 0.714g per 100g of nickel element in the positive electrode active material, lithium hexafluorophosphate (LiPF6) is added to prepare a solution with a lithium salt concentration of 1 mol / L, and then 1.5wt% of the additive vinylene carbonate (VC) relative to the mass of the electrolyte is added, and stirred evenly to obtain the lithium ion battery electrolyte of Example 1.

[0103] Preparation of lithium-ion battery (battery cell): stack the prepared positive electrode sheet, separator, and negative electrode sheet in order, with the separator placed between the positive and negative electrode sheets, and wind them to obtain a bare battery cell; place the bare battery cell in an aluminum-plastic film outer package, inject the prepared lithium-ion battery electrolyte after sufficient drying, and obtain a lithium-ion battery with a rated capacity of ~110Ah after formation, secondary sealing and capacity division.

[0104] Examples 2 to 17 and Comparative Examples 1 to 5

[0105] Examples 2 to 17 and Comparative Examples 1 to 5 are achieved by adjusting the type and single-polycrystalline blending ratio of lithium nickel transition metal oxide, the type and content of cyclic sulfone compound, and the type and content of fluorocarbonate on the basis of Example 1. Among them, the total content of cyclic sulfone compound, fluorocarbonate and ethyl methyl carbonate in each example and comparative example is the same. Specific adjustment measures and detailed data are shown in Table 1. The performance of the corresponding lithium ion battery is shown in Table 2.

[0106] Table 1

[0107]

[0108] a: It means that it contains only single crystals and no polycrystals;

[0109] b: Indicates that it contains only polycrystals and no single crystals.

[0110] Table 2

[0111]

[0112]

[0113] *: Indicates that the battery capacity retention rate is less than 60% at a cycle before 400 cycles.

[0114] Although some exemplary embodiments of the present application have been illustrated and described, the present application is not limited to the disclosed embodiments. On the contrary, those skilled in the art will recognize that some modifications and changes may be made to the described embodiments without departing from the spirit and scope of the present application as described in the appended claims.

Claims

1. A secondary battery, comprising a positive electrode sheet, a negative electrode sheet and an electrolyte, wherein: The positive electrode plate comprises a positive electrode active material selected from lithium nickel transition metal oxides; The electrolyte comprises a solvent and a lithium salt, wherein the solvent comprises a non-fluorinated carbonate, a fluorinated carbonate and a cyclic sulfone compound; the content of the cyclic sulfone compound is Ag for every 100 g of nickel element in the positive electrode active material; the content of the fluorinated carbonate is Bg for every 100 g of nickel element in the positive electrode active material; wherein 0.1≤A≤5, 1≤B≤7.5, and 1.3≤A+0.25×B≤3.

3.

2. The secondary battery according to claim 1, characterized in that: 0.5≤A≤4, and / or, 2.5≤B≤6.

3. The secondary battery according to claim 1 or 2, wherein the lithium nickel transition metal oxide comprises a lithium nickel transition metal oxide selected from the formula LiNi m Co n A (1-m-n) At least one of the lithium nickel transition metal oxides shown in O2, wherein A is selected from at least one of manganese, aluminum, magnesium, zirconium, strontium, yttrium, lanthanum, molybdenum, silver, niobium, iron, titanium, copper, zinc, chromium, calcium, barium and tungsten, 0.5≤m≤1, 0≤n≤0.5, m+n≤1.

4. The secondary battery according to claim 1 or 2, characterized in that: The lithium nickel transition metal oxide includes at least one of primary particles and secondary particles.

5. The secondary battery according to claim 4, characterized in that: The lithium nickel transition metal oxide includes primary particles and secondary particles, and a mass ratio of the primary particles to the secondary particles is 1:4 to 1:

1.

6. The secondary battery according to claim 1 or 2, characterized in that: The fluorinated carbonate comprises at least one of a fluorinated cyclic carbonate and a fluorinated linear carbonate, wherein: The fluorinated cyclic carbonate comprises at least one of the compounds represented by formula I-1, In formula I-1, R1, R2, R3 and R4 are independently selected from hydrogen atoms, fluorine atoms, C1-C6 alkyl groups or fluorinated C1-C6 alkyl groups, and at least one of R1, R2, R3 and R4 is a fluorine atom or a fluorinated C1-C6 alkyl group, Q1 is absent or is selected from C1-C6 alkylene groups, The fluorinated linear carbonate comprises at least one of the compounds shown in formula I-2, In formula I-2, R5 and R6 are independently selected from C1-C6 alkyl or fluorinated C1-C6 alkyl, and at least one of R5 and R6 is fluorinated C1-C6 alkyl; and / or, The cyclic sulfone compound comprises at least one compound selected from the group consisting of compounds shown in Formula II, In Formula II, R7, R8, R9 and R 10 Independently selected from a hydrogen atom, a halogen atom, a C1-C6 alkyl group, a C2-C6 alkenyl group, a C2-C6 alkynyl group, a halogenated C1-C6 alkyl group, a halogenated C2-C6 alkenyl group or a halogenated C2-C6 alkynyl group.

7. The secondary battery according to claim 6, characterized in that: The fluorinated cyclic carbonate comprises at least one of fluoroethylene carbonate, difluoroethylene carbonate and trifluoropropylene carbonate, and / or, The fluorinated linear carbonate comprises at least one of methyl-2,2,2-trifluoroethyl carbonate and di(2,2,2-trifluoroethyl) carbonate, and / or, The cyclic sulfone compound includes at least one of sulfolane, methyl sulfolane and 2-fluorosulfolane.

8. The secondary battery according to claim 1 or 2, characterized in that: The secondary battery meets at least one of the following conditions: (a) the content of the non-fluorinated carbonate is Cg, 25≤C≤35, relative to every 100g of nickel element in the positive electrode active material; (b) the non-fluorinated carbonate comprises at least one of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, ethylene carbonate, propylene carbonate and butylene carbonate; (c) the mass proportion of non-fluorinated chain carbonate in the non-fluorinated carbonate is more than 98%, and the non-fluorinated chain carbonate includes at least one of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate and ethyl propyl carbonate; (d) The non-fluorinated carbonate does not include a non-fluorinated cyclic carbonate, and the non-fluorinated cyclic carbonate includes at least one of ethylene carbonate, propylene carbonate and butylene carbonate.

9. The secondary battery according to claim 1 or 2, characterized in that: The secondary battery meets at least one of the following conditions; (e) the lithium salt comprises at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium difluorophosphate and lithium bis(oxalatodifluorophosphate); (f) the concentration of lithium salt in the electrolyte is 0.8 mol / L-2 mol / L; (g) The negative electrode plate includes a negative electrode active material, the negative electrode active material includes at least one of a silicon-based material and a carbon-based material, the silicon-based material includes at least one of silicon, a silicon alloy, a silicon oxide compound and a silicon carbon compound, and the carbon-based material includes at least one of natural graphite, artificial graphite, soft carbon, hard carbon, carbon nanotubes and graphene.

10. A device comprising the secondary battery according to any one of claims 1 to 9.

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