Secondary battery and device

Abstract

The application relates to a secondary battery and a device. The secondary battery comprises a positive electrode sheet, a negative electrode sheet and an electrolyte, wherein the electrolyte comprises a lithium salt, a solvent and an additive, the solvent comprises a non-fluorinated linear carbonate and a cyclic sulfone compound, the mass percentage of the cyclic sulfone compound in the solvent is A%, and the additive comprises a fluorinated carbonate; the negative electrode sheet comprises a negative electrode active material layer and a solid-state electrolyte interface film on the surface of the negative electrode active material layer, the mass percentage of fluorine in the solid-state electrolyte interface film is B% by using an energy spectrum analyzer; and 0.4 <= 0.01 * A * B <= 4. The secondary battery has improved cycle performance and safety performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of energy storage. Specifically, the present application relates to a secondary battery and a device. BACKGROUND

[0002] With the increasing renewal of technology life, the demand for high-capacity lithium-ion batteries with long cycle life and high safety is increasingly evident. However, high-capacity lithium-ion batteries often bring higher safety hazards and shorter cycle life.

[0003] The nickel-containing positive electrode system combined with the silicon-based negative electrode system can make the lithium-ion battery have higher capacity and energy density. However, the instability of nickel element and the high volume change rate of silicon-based negative electrode accelerate the cycle capacity decay of lithium-ion battery and bring great safety hazards. SUMMARY

[0004] In view of the safety hazards and cycle decay of lithium-ion batteries containing nickel-containing positive electrodes and silicon-based negative electrodes, the present application uses a certain proportion of high-oxidation-resistant and low-heat cyclic sulfone compound solvent to replace non-fluorinated saturated cyclic carbonate solvent, introduces fluorinated carbonate additive and controls the content of fluorine element in the solid electrolyte interface film (SEI film) on the surface of the negative active material layer, improves the room temperature cycle performance and high temperature cycle performance of the lithium-ion battery, alleviates the gas generation problem in the high temperature cycle of the lithium-ion battery, delays the battery thermal runaway temperature, and improves the battery safety.

[0005] The first aspect of the present application provides a secondary battery comprising a positive electrode sheet, a negative electrode sheet and an electrolyte, wherein the electrolyte comprises a lithium salt, a solvent and an additive, the solvent comprises a non-fluorinated linear carbonate and a cyclic sulfone compound, the mass percentage content of the cyclic sulfone compound in the solvent is A%, and the additive comprises a fluorinated carbonate; the negative electrode sheet comprises a negative active material layer and a solid electrolyte interface film on the surface of the negative active material layer, the mass percentage content of fluorine element in the solid electrolyte interface film is B% tested by energy dispersive spectrometer; wherein 0.4≤0.01xAxB≤4.

[0006] The second aspect of the present application provides a device comprising the secondary battery of the first aspect.

[0007] The present application has the following beneficial effects:

[0008] The secondary battery of the present application introduces a combined solvent of a non-fluorinated linear carbonate and a cyclic sulfone compound and a fluorinated carbonate additive in the electrolyte, and controls the content ratio of the cyclic sulfone compound and the content of fluorine element in the negative electrode SEI film, not only ensures the dissociation of the solvent to the lithium salt, effectively improves the thermal stability and electrochemical stability of the electrolyte, but also obtains a stable, low impedance, and beneficial to lithium ion conduction interface film, effectively improves the high temperature gas production problem of the lithium ion battery, delays the battery thermal runaway temperature, and significantly improves the safety of the battery. DETAILED DESCRIPTION

[0009] For the sake of brevity, the present application only specifically discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form a range not explicitly recited; and any lower limit can be combined with other lower limits to form a range not explicitly recited, and likewise any upper limit can be combined with any other upper limit to form a range not explicitly recited. In addition, each individual disclosed point or single numerical value can itself be combined as a lower limit or an upper limit with any other point or single numerical value or with other lower limits or upper limits to form a range not explicitly recited.

[0010] Unless otherwise indicated, the terms used in the present application have the commonly understood meanings as understood by those skilled in the art. Unless otherwise indicated, the values of each parameter mentioned in the present application can be measured by various measurement methods commonly used in the art (for example, can be tested according to the methods given in the examples of the present application).

[0011] The list of items connected by the terms "at least one of," "one or more of," or other similar terms signifies 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 A alone; B alone; or A and B together. In another example, if items A, B, and C are listed, the phrase "at least one of A, B, and C" means A alone; B alone; C alone; A and B together (excluding C); A and C together (excluding B); B and C together (excluding A); or A, B, and C together. Item A can include a single component or multiple components. Item B can include a single component or multiple components. Item C can include 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, as well as any and all combinations of the related listed items, including a combination of any two related listed items, a combination of any more related listed items, or a combination of all related listed items.

[0013] The term "comprising" or "including" is an open-ended description that includes both closed-ended technical solutions consisting of the listed features and open-ended technical solutions that include the listed features.

[0014] The present application will be further described below with reference to specific embodiments. It should be understood that these specific embodiments are for illustrative purposes only and are not intended to limit the scope of the present application.

[0015] Primary and secondary batteries

[0016] The first aspect of this application provides a secondary battery, including a positive electrode, a negative electrode, and an electrolyte, wherein the electrolyte comprises a lithium salt, a solvent, and an additive, the solvent comprising non-fluorinated linear carbonates and cyclic sulfone compounds, the cyclic sulfone compounds in the solvent having a mass percentage of A%, and the additives comprising fluorinated carbonates; the negative electrode comprises a negative electrode active material layer and a solid electrolyte interface film located on the surface of the negative electrode active material layer, and the mass percentage of fluorine in the solid electrolyte interface film, as measured by energy dispersive spectroscopy, is B%; wherein 0.4 ≤ 0.01 × A × B ≤ 4.

[0017] In this application, the solid electrolyte interface membrane is a non-artificial membrane. In some embodiments, the solid electrolyte interface membrane is obtained by reducing the electrolyte on the surface of the negative electrode active material layer.

[0018] In this application, the mass percentage of fluorine in the solid electrolyte interfacial membrane refers to the mass percentage of fluorine in the entire solid electrolyte interfacial membrane region on the surface of the negative electrode active material layer, not the mass percentage of fluorine in the interfacial membrane within a certain depth region of the interfacial membrane at a distance from the interface between the interfacial membrane and the electrolyte. In this application, the mass percentage of fluorine in the solid electrolyte interfacial membrane refers to the mass percentage of fluorine in the interfacial membrane relative to the mass percentage of all elements from Be to U.

[0019] In this application, the mass percentage of fluorine in the solid electrolyte interface membrane is detected using EDS (Electrode Spectroscopy). EDS utilizes the different energies of X-ray quanta; the detector receives these quanta and outputs electrical pulse signals, which are then amplified, shaped, and sent to a multichannel pulse analyzer. The pulse number and pulse height curves are then displayed on a cathode ray tube. With an energy resolution of 132 eV, it can detect the content of elements from Be to U. Typically, the mass percentage of elements obtained using EDS has an error within ±5%.

[0020] In some embodiments, 10 ≤ A ≤ 40. A is exemplarily a range of 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, or any combination of these values. In some embodiments, 15 ≤ A ≤ 30. If A is too low, the safety of the secondary battery cannot be effectively improved, and the dissociation of the electrolyte solvent is insufficient to effectively dissociate the lithium salt, resulting in low capacity utilization of the secondary battery. If A is too high, the electrolyte viscosity will be too high, slowing down the migration rate of lithium ions, thereby significantly reducing the power performance and room temperature cycling performance of the electrolyte.

[0021] In some embodiments, 1 ≤ B ≤ 12. B is exemplarily a range of 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.5, 12, or any combination of these values. In some embodiments, 2.5 ≤ B ≤ 10. If B is too low, a dense and stable interface film cannot be formed, thus failing to prevent the erosion of the negative electrode by cyclic sulfone compounds, affecting the cycle performance of the secondary battery. When B is too high, it easily causes gas generation problems during high-temperature cycling. Increased gas generation reduces battery thermal stability, degrades battery safety, and also exacerbates the hazards after battery thermal runaway.

[0022] In some implementations, 0.01 × A × B is exemplarily a range of 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 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, 3, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4, or any combination of these values. In some implementations, 1 ≤ 0.01 × A × B ≤ 3. If 0.01×A×B is too small, it corresponds to an excessively low mass percentage of cyclic sulfone compounds in the electrolyte or an excessively low mass percentage of fluorine in the SEI membrane, which prevents the effective improvement of the safety and / or cycle performance of the secondary battery. If 0.01×A×B is too large, it corresponds to an excessively high mass percentage of cyclic sulfone compounds in the electrolyte or an excessively high mass percentage of fluorine in the SEI membrane, which also prevents the effective improvement of the safety and / or cycle performance of the secondary battery.

[0023] In some embodiments, the cyclic sulfone compound includes at least one selected from compounds shown in Formula I.

[0024]

[0025] In Formula I, R1, R2, R3 and R4 are independently selected from hydrogen atoms, halogen atoms, C1-C6 alkyl, C2-C6 alkenyl, C2-C6 alkynyl, halogenated C1-C6 alkyl, halogenated C2-C6 alkenyl or halogenated C2-C6 alkynyl.

[0026] In this application, C2-C6 alkenyl groups include, but are not limited to: vinyl, propenyl, allyl, isopropenyl, n-butenyl, isobutenyl, tert-butenyl, n-pentenyl, isopentenyl, hexenyl, and cyclohexenyl.

[0027] C2-C6 alkynyl groups include, but are not limited to: ethynyl, n-propynyl, isopropynyl, n-butynyl, isobutynyl, n-pentynyl, isopentenynyl, and hexynyl.

[0028] Halogens include fluorine, chlorine, bromine, and iodine.

[0029] In some embodiments, in Formula I, R1, R2, R3 and R4 are independently selected from hydrogen atoms, halogen atoms, C1-C6 alkyl groups or halogenated C1-C6 alkyl groups.

[0030] In some embodiments, in Formula I, R1, R2, R3 and R4 are independently selected from hydrogen atoms, fluorine atoms, C1-C4 alkyl groups or fluorinated C1-C4 alkyl groups.

[0031] In some embodiments, in Formula I, R1, R2, R3 and R4 are independently selected from hydrogen atoms, fluorine atoms, methyl, ethyl, trifluoromethyl or 2,2,2-trifluoroethyl.

[0032] In some embodiments, the cyclic sulfone compound includes at least one of sulfolane (SL), methyl sulfolane (MSL), and 2-fluorosulfolane (FSL).

[0033] In this application, the non-fluorinated linear carbonate is a solvent conventionally used in secondary batteries. In some embodiments, the non-fluorinated linear carbonate includes at least one selected from dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dipropyl carbonate, methyl propyl carbonate, and ethyl propyl carbonate. In some embodiments, the non-fluorinated linear carbonate includes at least one selected from dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate.

[0034] In some embodiments, the total mass percentage of the non-fluorinated linear carbonate and cyclic sulfone compound to the solvent is 98% or more, for example, 98.5% or more, 98.8% or more, 99% or more, 99.2% or more, 99.5% or more, or 99.8% or more. In some embodiments, the solvent does not include ethers.

[0035] In some embodiments, the solvent does not contain ethylene carbonate and / or propylene carbonate. Preferably, the solvent does not contain non-fluorinated saturated cyclic carbonates. Here, "does not contain" means that the mass percentage of non-fluorinated saturated cyclic carbonates in the solvent is less than 1%, for example less than 0.8%, less than 0.5%, less than 0.3%, or less than 0.1%. The inventors of this application have discovered that although non-fluorinated saturated cyclic carbonates are beneficial to the room temperature cycle performance of secondary batteries, they are detrimental to the thermal safety of secondary batteries. Surprisingly, by replacing the non-fluorinated saturated cyclic carbonate solvent with a cyclic sulfone compound solvent and controlling the content of the cyclic sulfone compound and the ratio of fluorine in the negative electrode SEI film, the thermal safety of the secondary battery can be improved while ensuring that the room temperature cycle performance of the secondary battery is not degraded.

[0036] In some embodiments, the fluorocarbonate includes at least one of fluorocyclic carbonates and fluorolinear carbonates.

[0037] In some embodiments, the fluorocyclic carbonate includes at least one of the compounds shown in Formula II-1.

[0038]

[0039] In Formula II-1, R5, R6, R7 and R8 are independently selected from hydrogen atoms, fluorine atoms, C1-C6 alkyl or fluorinated C1-C6 alkyl, and at least one of R5, R6, R7 and R8 is a fluorine atom or a fluorinated C1-C6 alkyl, and Q1 is absent or selected from C1-C6 alkylene.

[0040] In this application, C1-C6 alkyl groups include, but are 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.

[0041] In this application, fluorinated C1-C6 alkyl groups include, but are not limited to, fluorinated methyl, fluorinated ethyl, fluorinated n-propyl, fluorinated isopropyl, fluorinated n-butyl, fluorinated isobutyl, fluorinated tert-butyl, fluorinated n-pentyl, fluorinated isopentyl, and fluorinated n-hexyl. Fluorination indicates that at least one hydrogen atom in the C1-C6 alkyl group is substituted by a fluorine atom. In some embodiments, the fluorinated C1-C6 alkyl groups are selected from monofluoromethyl, difluoromethyl, trifluoromethyl, monofluoroethyl, difluoroethyl, trifluoroethyl, pentafluoroethyl, or hexafluoroisopropyl.

[0042] In this application, C1-C6 alkylene compounds include, but are 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.

[0043] In some embodiments, in Formula II-1, R5, R6, R7 and R8 are independently selected from hydrogen atoms, fluorine atoms, C1-C4 alkyl or fluorinated C1-C4 alkyl, and at least one of R5, R6, R7 and R8 is a fluorine atom, and Q1 is absent or selected from methylene or ethylene.

[0044] In some embodiments, in Formula II-1, R5, R6, R7 and R8 are independently selected from hydrogen atoms, fluorine atoms, methyl, ethyl, trifluoromethyl or 2,2,2-trifluoroethyl, at least one of R5, R6, R7 and R8 is a fluorine atom, and Q1 is absent or selected from methylene or ethylene.

[0045] In some embodiments, the fluorocyclic carbonate includes at least one of fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), and trifluoropropylene carbonate (TFPC).

[0046] In some embodiments, the fluorinated linear carbonate includes at least one of the compounds shown in Formula II-2.

[0047]

[0048] In Equation II-2, R9 and R 10 Independently selected from C1-C6 alkyl or fluorinated C1-C6 alkyl, and R9 and R 10 At least one of them is a fluorinated C1-C6 alkyl group.

[0049] In some implementations, in formula II-2, R9 and R 10 They are identical or different, independently selected from C1-C4 alkyl or fluorinated C1-C4 alkyl, and R9 and R 10 At least one of them is a fluorinated C1-C4 alkyl group.

[0050] In some implementations, in formula II-2, R9 and R 10 The same or different, independently selected from methyl, ethyl, n-propyl, isopropyl, trifluoromethyl or 2,2,2-trifluoroethyl, and R9 and R 10 At least one of them is trifluoromethyl or 2,2,2-trifluoroethyl.

[0051] 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).

[0052] In some embodiments, the electrolyte contains 0.5%-8% by mass of fluorocarbonate. Exemplary values ​​are 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%, 5.2%, 5.5%, 5.8%, 6%, 6.2%, 6.5%, 6.8%, 7%, 7.2%, 7.5%, 7.8%, 8%, or a range of any two of these values.

[0053] In some embodiments, the solvent comprises 60%-90% non-fluorinated linear carbonates and 10%-40% cyclic sulfone compounds, the percentages being based on the total mass of the solvent. In some embodiments, the solvent comprises 70%-85% non-fluorinated linear carbonates and 15%-30% cyclic sulfone compounds, the percentages being based on the total mass of the solvent.

[0054] In some embodiments, the lithium salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium trifluoromethanesulfonyl (LiOTf), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium (trifluoromethanesulfonyl)(perfluorobutylsulfonyl)imide (LiFNFSI), and lithium bis(pentafluoroethylsulfonic acid)imide (LiBETI).

[0055] In some embodiments, the lithium salt comprises at least one selected from lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethylsulfonyl)imide. In some embodiments, the lithium salt comprises lithium hexafluorophosphate. In some embodiments, the lithium salt comprises lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide.

[0056] In some embodiments, the concentration of lithium salt in the electrolyte is 0.8 mol / L to 2 mol / L. Here, concentration represents the number of moles of lithium salt contained in a unit volume of electrolyte. The concentration of lithium salt is exemplarily 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 any combination of these values.

[0057] In some embodiments, the lithium salt comprises lithium hexafluorophosphate, and the concentration of lithium hexafluorophosphate in the electrolyte is 0.8 mol / L-2 mol / L, for example, 0.8 mol / L-1.5 mol / L. In some embodiments, the lithium salt comprises lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide, the concentration of the lithium salt in the electrolyte is 0.8 mol / L-2 mol / L, the concentration of lithium hexafluorophosphate is 0.2 mol / L-1.2 mol / L, the concentration of lithium bis(fluorosulfonyl)imide is 0.2 mol / L-1.5 mol / L, and the concentration ratio of lithium hexafluorophosphate to lithium bis(fluorosulfonyl)imide is 3:1-1:3.

[0058] In some embodiments, the electrolyte may further include a second additive, provided that it does not impair the achievement of the purpose of this invention. Exemplary examples of the second additive include vinylene carbonate (VC), ethylene ethylene carbonate (VEC), propane sulfonate lactone (PS), propene sulfonate lactone (PST), methane disulfonate methylene ester (MMDS), vinyl sulfate (DTD), lithium difluorophosphate (LiDFOP), lithium bis(oxalate borate) borate (LiBOB), lithium difluorooxalate borate (LiDFOB), lithium di(oxalate difluorophosphate) bis(oxalate) phosphate (LiODFP), and tris(trimethylsilane) phosphate (TMSP).

[0059] In some embodiments, the additive is present in a mass percentage of 0.1%-10% based on the mass of the electrolyte, exemplarily in the range of 0.2%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any combination of these values, such as 0.1%-8%.

[0060] In some embodiments, the electrolyte contains a lithium salt, a solvent, and an additive. The lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethylsulfonyl)imide. The solvent includes a non-fluorinated linear carbonate and a cyclic sulfone compound. The additive includes a fluorinated carbonate and optionally a second additive. The fluorinated carbonate is selected from at least one of fluorinated ethylene carbonate, difluorinated ethylene carbonate, trifluorinated propylene carbonate, methyl-2,2,2-trifluoroethyl carbonate, and bis(2,2,2-trifluoroethyl) carbonate. The second additive is selected from at least one of lithium difluorophosphate, lithium difluorooxalate borate, lithium bis(oxalato)difluorophosphate, and tris(trimethylsilyl) phosphate. The concentration of the lithium salt in the electrolyte is 0.8 mol / L - 2 mol / L. The mass percentage of the non-fluorinated linear carbonate in the solvent is 60% - 90%, and the mass percentage of the cyclic sulfone compound is 10% - 40%. The mass percentage of the fluorinated carbonate in the electrolyte is 0.5% - 8%, and the mass percentage of the second additive is 0% - 8%.

[0061] In some embodiments, the negative electrode sheet includes a negative electrode active material selected from silicon-based materials. In some embodiments, the silicon-based materials include at least one of silicon, silicon alloy, silicon oxide compound, and silicon carbide compound. In some embodiments, the silicon-based materials include silicon oxide compound and / or silicon carbide compound. In the present application, the silicon oxide compound refers to a compound with the general formula SiOx, where 0.5 < x < 1.5. It can be a single pure substance or a mixture, as long as its average composition conforms to the above general formula.

[0062] In some embodiments, the negative electrode active material further includes a mixture of at least one material selected from carbon-based materials, tin-based materials, phosphorus-based materials, and metallic lithium. The carbon-based materials include at least one of artificial graphite, natural graphite, soft carbon, hard carbon, carbon nanotubes, and graphene. The tin-based materials include at least one of tin, tin oxide, and tin alloy. The phosphorus-based materials include phosphorus and / or phosphorus complex. In some embodiments, the negative electrode active material includes a carbon-based material, and the carbon-based material includes artificial and / or natural graphite.

[0063] In some embodiments, the mass percentage of the silicon-based material in the negative electrode active material is 10% - 40%, exemplarily 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, or a range composed of any two of these values. In some embodiments, the mass percentage of the silicon-based material in the negative electrode active material is 12% - 35%.

[0064] In some embodiments, the negative electrode sheet further includes a binder and a conductive agent. In some embodiments, the binder includes, but is not limited to, styrene-butadiene rubber, acrylated styrene-butadiene rubber, polyacrylic acid, polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, and polyvinylpyrrolidone. In some embodiments, the conductive agent includes, but is not limited to, carbon nanotubes, natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, and carbon fiber.

[0065] In some embodiments, the negative electrode sheet further includes a negative current collector, which 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.

[0066] In some embodiments, the positive electrode includes a positive active material, which includes materials selected from LiNi as shown below. 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, and 0.1 ≤ m ≤ 1, 0 ≤ n ≤ 0.9, m + n ≤ 1. In some embodiments, the chemical formula of the lithium-nickel transition metal oxide is as shown in LiNi. m Co n A (1-m-n) As shown in O2, A is selected from at least one of manganese, aluminum, magnesium, zirconium, strontium, yttrium, lanthanum, molybdenum, silver, niobium, chromium and calcium, with 0.1≤m≤1, 0≤n≤0.9, and m+n≤1.

[0067] In some implementations, m is a range of 0.1, 0.2, 0.3, 0.4, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1, or any combination of these values. In some implementations, n is a range of 0, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.6, 0.7, 0.8, 0.9, or any combination of these values.

[0068] In some embodiments, the lithium nickel transition metal oxide includes at least one of NCM333, NCM523, NCM622, NCM811, Ni90 (i.e., NCM90), Ni92 (i.e., NCM92), and Ni95 (i.e., NCM900).

[0069] In some embodiments, the lithium-nickel transition metal oxide has the chemical formula LiNi. m Co n A(1-m-n) As shown in O2, 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, with 0.5 ≤ m ≤ 1, 0 ≤ n ≤ 0.5, and m + n ≤ 1. In some embodiments, the chemical formula of the lithium nickel transition metal oxide is as shown in LiNi. m Co n A (1-m-n) As shown in O2, A is selected from at least one of manganese, aluminum, magnesium, zirconium, strontium, yttrium, lanthanum, molybdenum, silver, niobium, chromium and calcium, with 0.5≤m≤1, 0≤n≤0.5, and m+n≤1.

[0070] In some embodiments, the lithium-nickel transition metal oxide may further include a coating layer. The coating layer, exemplarily, includes at least one of lithium aluminate, alumina, lithium borate, or lithium boride.

[0071] In some embodiments, the positive electrode active material includes materials selected from LiMn. k B (1-k) At least one of the phosphate compounds shown in PO4, wherein 0 ≤ k ≤ 1, and B is selected from at least one of iron, cobalt, magnesium, calcium, zinc, chromium, and lead. In some embodiments, k is a range of 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, or any combination of these values. In some embodiments, the phosphate compound includes lithium iron phosphate, LiMn... 0.6 Fe 0.4 PO4 or LiMn 0.8 Fe 0.2 At least one of PO4.

[0072] In some embodiments, the positive electrode further includes 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, and polyvinylpyrrolidone. In some embodiments, the conductive agent includes, but is not limited to, carbon nanotubes, natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, and carbon fiber.

[0073] In some embodiments, the positive electrode sheet further includes a positive current collector, which includes an aluminum foil or a polymer substrate coated with a conductive metal.

[0074] In some embodiments, a separator is provided between the positive and negative electrode plates to prevent short circuits. The material and shape of the separator used in the embodiments of this application are not particularly limited, and can be any technology disclosed in the prior art. In some embodiments, the separator comprises a polymer or inorganic material formed from a material stable to the electrolyte of this application.

[0075] For example, the diaphragm may include a substrate layer and a surface treatment layer. The substrate layer is a nonwoven fabric, membrane, or composite membrane with a porous structure, and the material of the substrate layer includes at least one selected from polyethylene, polypropylene, polyethylene terephthalate, polyimide, or aramid. At least one surface of the substrate layer is provided with a surface treatment layer, which may be a polymer layer, an inorganic layer, or a layer formed by mixing polymers and inorganic materials.

[0076] In some embodiments, the method for preparing the secondary battery includes providing electrode assemblies, liquid injection, encapsulation, and formation. In some embodiments, the formation temperature is 40°C to 50°C. In some embodiments, the formation temperature is a range of 40°C, 41°C, 42°C, 43°C, 44°C, 45°C, 46°C, 47°C, 48°C, 49°C, 50°C, or any combination of these values.

[0077] In some embodiments, the formation pressure is from 150 kgf to 750 kgf. In some embodiments, the formation temperature is a range of 150 kgf, 160 kgf, 170 kgf, 180 kgf, 190 kgf, 200 kgf, 210 kgf, 220 kgf, 230 kgf, 240 kgf, 250 kgf, 260 kgf, 270 kgf, 280 kgf, 290 kgf, 300 kgf, 320 kgf, 350 kgf, 380 kgf, 400 kgf, 420 kgf, 450 kgf, 480 kgf, 500 kgf, 520 kgf, 550 kgf, 580 kgf, 600 kgf, 620 kgf, 650 kgf, 680 kgf, 700 kgf, 720 kgf, 750 kgf, or any combination of these values. In some embodiments, the formation pressure is from 150 kgf to 300 kgf.

[0078] In some embodiments, the formation charging current is 0.02C-0.33C, and the formation discharging current is 0.05C-0.5C. In some embodiments, the formation charging current is 0.02C, 0.03C, 0.05C, 0.07C, 0.09C, 0.1C, 0.12C, 0.14C, 0.16C, 0.18C, 0.2C, 0.22C, 0.24C, 0.26C, 0.28C, 0.3C, 0.32C, 0.33C, or a range of any two of these values. In some embodiments, the formation charging current is 0.03C-0.2C. In some embodiments, the formation discharge current is 0.05C, 0.07C, 0.1C, 0.12C, 0.15C, 0.18C, 0.2C, 0.22C, 0.25C, 0.28C, 0.3C, 0.32C, 0.35C, 0.38C, 0.4C, 0.42C, 0.45C, 0.48C, 0.5C, or any combination of these values. In some embodiments, the formation discharge current is 0.1C-0.3C.

[0079] In some embodiments, the charging voltage of the formation is 4.0V-4.4V, for example 4.0V, 4.1V, 4.2V, 4.3V, or 4.4V. In some embodiments, the discharging voltage of the formation is 2.8V-3.2V, for example 2.8V, 2.9V, 3.0V, 3.1V, or 3.2V.

[0080] In some embodiments, the formation includes: charging to 4.0V-4.4V, for example 4.2V, at a temperature of 40°C-50°C, for example 45°C, and a pressure of 150kgf-300kgf, for example 210kgf, with a current of 0.03C-0.08C, for example 0.05C, allowing it to stand, then charging to 4.0V-4.4V at 0.08C-0.2C, and then discharging to 2.8V-3.2V, for example 3.0V, at 0.1C-0.3C, for example 0.2C.

[0081] In some embodiments, the secondary battery undergoes formation. In some embodiments, the solid electrolyte interphase (SEI) membrane is obtained through the formation of the secondary battery. During the formation process, the electrolyte is reduced to form a film on the surface of the negative electrode active material, forming an SEI membrane, which inhibits the continuous reaction between the electrolyte and the negative electrode active material. After multiple cycles, the absolute content of fluorine in the SEI membrane will differ slightly from the absolute content of silicon in the SEI membrane after formation, but the relative content, i.e., the mass percentage of fluorine in the SEI membrane, remains between 1% and 12%.

[0082] In some embodiments, the electrolyte injection coefficient is from 1.5 g / Ah to 2.0 g / Ah, for example, 1.6 g / Ah, 1.7 g / Ah, 1.8 g / Ah, or 1.9 g / Ah. In this application, the electrolyte injection coefficient = electrolyte mass (g) / battery capacity (Ah).

[0083] 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, lithium metal secondary batteries, lithium-ion secondary batteries, lithium polymer secondary batteries, or lithium-ion polymer secondary batteries.

[0084] In some embodiments, the secondary battery may include an outer packaging, which may be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging may also be a soft pack, such as a pouch. The soft pack may be made of plastic, such as one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0085] In some embodiments, the shape of the secondary battery is not particularly limited; it can be cylindrical, square, or any other arbitrary shape.

[0086] In some embodiments, this application also provides a battery module. This battery module includes the aforementioned secondary battery. The battery module of this application uses the aforementioned secondary battery, and therefore has at least the same advantages as the aforementioned secondary battery. The battery module of this application can contain multiple secondary batteries, and the specific number can be adjusted according to the application and capacity of the battery module.

[0087] In some embodiments, this application also provides a battery pack that includes the aforementioned battery modules. The number of battery modules included in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0088] II. Apparatus

[0089] This application also provides an apparatus that includes at least one of the above-mentioned secondary battery, battery module or battery pack as a power source.

[0090] In some embodiments, the device includes, but is not limited to, electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and energy storage systems. To meet the device's requirements for high power and high energy density in secondary batteries, battery packs or battery modules may be used.

[0091] In other embodiments, the device can be a mobile phone, tablet computer, laptop computer, etc. This device typically requires a thin and light design and can use a rechargeable battery as its power source.

[0092] Example

[0093] Unless otherwise specified, all materials and reagents used in this application are commercially available, and all methods used are conventional methods in the field.

[0094] Test methods

[0095] 1. Determination of fluorine content in SEI membranes

[0096] The fluorine content in the SEI film was measured using energy dispersive spectroscopy (EDS). The specific testing procedures are as follows: The lithium-ion battery was discharged to 2.5V at a current of 0.1C. The lithium-ion battery was then disassembled in an argon-filled glove box to obtain the electrode sheets. The obtained negative electrode sheets were cut into pieces with an area of ​​approximately 20 mm². 2 Test samples of a certain size were immersed and cleaned in low-boiling-point dimethyl carbonate (DMC) solvent for half an hour. After complete drying, they were quickly transferred to the conductive adhesive on the EDS sample stage, with the surface of the negative electrode active material layer facing upwards, and any dust on the sample surface was removed with a syringe rubber bulb. Sample injection and detection were performed at a depth of approximately 500 nm to 1 μm to determine the elemental content of Be to U in the SEI film and calculate the mass percentage of fluorine in the SEI film. The energy resolution was 132 eV.

[0097] 2. Battery cycle performance test at 25°C

[0098] At 25°C, the lithium-ion battery was charged at a constant current of 0.5C to 4.25V, then charged at a constant voltage of 4.25V to 0.05C, and finally discharged at a constant current of 1C to 2.5V. After 400 charge-discharge cycles, the capacity retention rate after the 200th cycle at 25°C was calculated using the following formula: Discharge capacity after the 200th cycle / Discharge capacity of the first cycle × 100%.

[0099] 3. Battery 45℃ Cycle Performance Test

[0100] At 45°C, the lithium-ion battery was charged at a constant current of 0.5C to 4.25V, then charged at a constant voltage of 4.25V to 0.05C, and finally discharged at a constant current of 1C to 2.5V. After 400 charge-discharge cycles, the capacity retention rate after the 400th cycle at 45°C was calculated using the following formula: Discharge capacity after 400 cycles / Discharge capacity of the first cycle × 100%.

[0101] 4. Battery gas production test after 400 cycles at 45°C

[0102] The lithium-ion battery is discharged at a constant current of 1C to 2.5V at 25°C, then charged at a constant current of 0.5C to 4.25V, and then charged at a constant voltage of 4.25V to 0.05C. Use a PPG soft-pack battery thickness gauge to measure the full-charge thickness of the battery at this time and record it as a. After cycling the battery 400 times at 45°C according to the above test method 2, charge the battery at a constant current of 0.5C to 4.25V, and then charge it at a constant voltage of 4.25V to 0.05C. Then, use a PPG soft-pack battery thickness gauge to measure the full-charge thickness of the battery at this time and record it as b. The calculation formula for the cell thickness expansion rate of the battery after 400 cycles at 45°C is: (b - a) / a × 100%.

[0103] 5. Battery Thermal Chamber Test

[0104] The thermal chamber test steps are as follows: Under the condition of 25°C, calibrate the cell capacity at 1 / 3C and fully charge it; Clamp the fully charged cell, with a pre-tightening force of 1.5 Nm and 6 bolts; 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 cell temperature corresponding to the out-of-control.

[0105] Example 1

[0106] The preparation steps of the positive electrode sheet are as follows: Mix the positive electrode active material LiNi 0.6 Co 0.2 Mn 0.2 O2, conductive agent carbon black SP and binder polyvinylidene fluoride PVDF in a mass ratio of 96:2:2, then disperse them in N-methyl-2-pyrrolidone to obtain a positive electrode slurry. Coat the positive electrode slurry evenly on both sides of the surface of a 12-μm-thick aluminum foil current collector, and after drying, rolling, and slitting, obtain the positive electrode sheet.

[0107] The preparation steps of the negative electrode sheet are as follows: Mix silicon oxide-graphite composite (the mass ratio of silicon oxide SiOx (0.5 < x < 1.5) to artificial graphite is 10:90), conductive agent acetylene black, binder styrene-butadiene rubber SBR, thickening agent sodium carboxymethyl cellulose CMCNa and binder polyacrylic acid PAA in a mass ratio of 95:2:1.5:1:0.5, then disperse them in deionized water to obtain a negative electrode slurry. Coat the negative electrode slurry on both sides of the surface of an 8-μm-thick copper foil current collector, and after drying, rolling, and slitting, obtain the negative electrode sheet.

[0108] Separator: Use a PP / PE / PP three-layer composite separator.

[0109] Electrolyte preparation: In an argon-protected glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), solvents ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and sulfolane (SL) were mixed in a mass ratio of EMC:DEC:SL = 57:23:20. Lithium hexafluorophosphate (LiPF6) was added to prepare a solution with a lithium salt concentration of 1 mol / L. Then, 3 wt% of fluoroethylene carbonate (FEC) was added as an additive relative to the electrolyte mass, and the mixture was stirred evenly to obtain the lithium-ion battery electrolyte of Example 1.

[0110] Preparation of lithium-ion battery (cell): The prepared positive electrode sheet, separator, and negative electrode sheet are stacked in sequence, with the separator positioned between the positive and negative electrode sheets, and wound to obtain a bare cell. The bare cell is placed in an aluminum-plastic film outer packaging, and after thorough drying, it is injected with the prepared lithium-ion battery electrolyte at an injection coefficient of 1.7 g / Ah. After the battery is placed at 45℃ for 48 hours, formed in a high-temperature fixture (formation conditions are: temperature 45℃, pressure 210 kgf, charging to 4.2V at 0.05C, resting for 60 minutes, then charging to 4.2V at 0.1C, then discharging to 3.0V at 0.2C, repeating this process twice), and then sealed twice, it undergoes routine capacity testing to finally obtain a lithium-ion battery with a rated capacity of ~4Ah.

[0111] Examples 2 to 14 and Comparative Examples 1 to 6

[0112] Examples 2 to 14 and Comparative Examples 1 to 6 were based on Example 1, with adjustments made to the content of EMC and DEC in the solvent, the type and content of cyclic sulfone compounds, the type and concentration of lithium salts, and the type and content of fluorocarbonate additives. Specific adjustments and detailed data are shown in Table 1.

[0113] Table 1

[0114]

[0115] The test results of lithium-ion batteries in Examples 1-14 and Comparative Examples 1-6 are shown in Table 2.

[0116] Table 2

[0117]

[0118]

[0119] a: This indicates that the battery's capacity retention rate was already below 60% in one of the cycles before the 400th cycle.

[0120] b: indicates that no test was performed.

[0121] While some exemplary embodiments of this application have been described and illustrated, this application is not limited to the disclosed embodiments. Rather, those skilled in the art will recognize that modifications and changes may be made to the described embodiments without departing from the spirit and scope of this application as described in the appended claims.

Claims

1. A secondary battery, comprising a positive electrode, a negative electrode, and an electrolyte, wherein, The electrolyte comprises lithium salt, solvent, and additives. The solvent includes non-fluorinated linear carbonates and cyclic sulfone compounds, wherein the mass percentage of the cyclic sulfone compounds in the solvent is A%. The additives include fluorinated carbonates. The negative electrode sheet includes a negative electrode active material layer and a solid electrolyte interface film located on the surface of the negative electrode active material layer. Energy dispersive spectroscopy (EDS) analysis shows that the mass percentage of fluorine in the solid electrolyte interface film is B%. Where 0.4 ≤ 0.01 × A × B ≤ 4; 10≤A≤40； 1≤B≤12; The electrolyte contains 3%-8% by mass of fluorocarbonate. The cyclic sulfone compound includes at least one selected from the compounds shown in Formula I. Formula I In Formula I, R1, R2, R3 and R4 are independently selected from hydrogen atoms, halogen atoms, C1-C6 alkyl groups, and halo-C1-C6 alkyl groups; The fluorocarbonate includes at least one of fluorocyclic carbonate and fluorolinear carbonate. The fluorocyclic carbonates include at least one of fluoroethylene carbonate, difluoroethylene carbonate, and trifluoropropylene carbonate; The fluorinated linear carbonates include at least one of methyl-2,2,2-trifluoroethyl carbonate and bis(2,2,2-trifluoroethyl) carbonate.

2. The secondary battery according to claim 1, characterized in that, The secondary battery meets the following conditions: 1≤0.01×A×B≤3.

3. The secondary battery according to claim 1 or 2, characterized in that, The secondary battery meets at least one of the following conditions: (a) 15 ≤ A ≤ 30, (b) 2.5 ≤ B ≤ 10.

4. The secondary battery according to claim 1 or 2, characterized in that, The total mass percentage of the non-fluorinated linear carbonate and cyclic sulfone compounds accounts for more than 98% of the mass of the solvent, and / or, The solvent does not contain ethylene carbonate and / or propylene carbonate.

5. The secondary battery according to claim 1 or 2, characterized in that, The cyclic sulfone compound includes at least one of sulfolane, methylsulfolane, and 2-fluorosulfolane.

6. The secondary battery according to claim 1 or 2, characterized in that, The negative electrode sheet comprises a negative electrode active material selected from silicon-based materials, wherein the silicon-based material includes at least one of silicon, silicon alloys, silicon oxides, and silicon carbide compounds, and the mass percentage of the silicon-based material in the negative electrode active material is 10%-40%; and / or, The positive electrode includes a positive active material, which includes materials selected from LiNi as shown below. m Co n A (1-m-n) O2 represents lithium-nickel transition metal oxides or LiMn as shown in formula. k B (1-k) PO4 contains at least one of the following phosphate compounds, 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, with 0.5 ≤ m ≤ 1, 0 ≤ n ≤ 0.5, and m + n ≤ 1, and B is selected from at least one of iron, cobalt, magnesium, calcium, zinc, chromium, and lead, with 0 ≤ k ≤ 1.

7. The secondary battery according to claim 1 or 2, characterized in that, The negative electrode active material includes silicon-based materials and carbon-based materials. The silicon-based materials include silicon oxides and / or silicon-carbon compounds, and the carbon-based materials include artificial graphite and / or natural graphite.

8. The secondary battery according to claim 1 or 2, characterized in that, The secondary battery satisfies at least one of the following conditions: (c) The solvent comprises 60%-90% linear carbonate and 10%-40% cyclic sulfone compound, the percentages being based on the total mass of the solvent; (d) The linear carbonate includes at least one of dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, and ethyl propyl carbonate; (e) The lithium salt comprises at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethylsulfonyl)imide; (f) The concentration of lithium salt in the electrolyte is 0.8 mol / L-2 mol / L; (g) The electrolyte injection coefficient of the secondary battery is 1.5 g / Ah-2 g / Ah.

9. An apparatus comprising a secondary battery as described in any one of claims 1-8.

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