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, the electrolyte comprises a lithium salt, a solvent and an additive, the solvent comprises 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 fluorinated carbonate; the negative electrode plate 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 content of fluorine in the solid electrolyte interface film is B% by adopting an energy disperse spectroscopy test; wherein 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, 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] The nickel-containing positive electrode system combined with the silicon-based negative electrode system can enable lithium-ion batteries to achieve higher capacity and energy density. However, the instability of the nickel element and the high volume change rate of the silicon-based negative electrode accelerate the decay of the cycle capacity of lithium-ion batteries and bring great safety risks. Summary of the invention

[0004] In response to the safety hazards and cycle attenuation of lithium-ion batteries with nickel-containing positive electrodes and silicon-based negative electrodes, the present application replaces the non-fluorinated saturated cyclic carbonate solvent with a certain proportion of highly resistant to oxidation and low in heat cyclic sulfone compound solvents, introduces fluorinated carbonate additives and controls the content of fluorine in the solid electrolyte interface film (SEI film) on the surface of the negative electrode active material layer, thereby improving the room temperature cycle performance and high temperature cycle performance of lithium-ion batteries, alleviating the gas production problem in high temperature cycles of lithium-ion batteries, delaying the thermal runaway temperature of the battery, and improving the battery safety.

[0005] The first aspect of the present application provides a secondary battery, comprising a positive electrode plate, a negative electrode plate 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 plate 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 the fluorine element in the solid electrolyte interface film is B% when tested by an energy spectrometer; wherein 0.4≤0.01×A×B≤4.

[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 introduces a combined solvent of non-fluorinated linear carbonate and cyclic sulfone compound and a fluorinated carbonate additive into the electrolyte, and controls the content of the cyclic sulfone compound and the content ratio of the fluorine element in the negative electrode SEI film, which 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 interface film that is conducive to lithium ion conduction. Under the premise of ensuring that the power performance and room temperature cycle performance of the lithium ion battery are not deteriorated, the high-temperature gas production problem of the lithium ion battery is effectively improved, the thermal runaway temperature of the battery is delayed, and the safety of the battery is significantly improved. 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 first aspect of the present application provides a secondary battery, comprising a positive electrode plate, a negative electrode plate 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 plate 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 the fluorine element in the solid electrolyte interface film is B% when tested by an energy spectrometer; wherein 0.4≤0.01×A×B≤4.

[0017] In the present 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 the present application, the mass percentage of fluorine in the solid electrolyte interface film refers to the mass percentage of fluorine in the entire solid electrolyte interface film region on the surface of the negative electrode active material layer, not the mass percentage of fluorine in the interface film in a portion of the interface film depth region at a distance from the interface film and the electrolyte interface side, but the mass percentage of fluorine in the interface film in the entire interface film depth region. In the present application, the mass percentage of fluorine in the solid electrolyte interface film refers to the mass percentage of fluorine in the interface film to the mass percentage of all elements between Be and U.

[0019] In this application, the mass percentage of fluorine in the solid electrolyte interface film is detected by EDS. EDS uses the different energies of X-ray quanta, which are received by the detector and then sent to the multi-channel pulse analyzer after amplification and shaping by the amplifier, and then the pulse number and pulse height curve are displayed on the picture tube. The energy resolution is 132eV, and the element content between Be and U can be detected. Usually, the mass percentage error of the elements tested by EDS is within the range of ±5%.

[0020] In some embodiments, 10≤A≤40. A is illustratively 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 a range consisting of any two 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 not sufficient to effectively dissociate the lithium salt, resulting in low secondary battery capacity. If A is too high, the viscosity of the electrolyte will be too large, and the migration speed of lithium ions will slow down, thereby significantly reducing the power performance and room temperature cycle performance of the electrolyte.

[0021] In some embodiments, 1≤B≤12. B is illustratively 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 a range consisting of any two of these values. In some embodiments, 2.5≤B≤10. If B is too low, a dense and stable interface film cannot be formed, and the corrosion of the negative electrode by the cyclic sulfone compound cannot be avoided, affecting the cycle performance of the secondary battery. When B is too high, it is easy to cause gas production problems during high-temperature cycles. Increased gas production will reduce the thermal stability of the battery, deteriorate the safety of the battery, and also aggravate the hazards after thermal runaway of the battery.

[0022] In some embodiments, 0.01×A×B is illustratively 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 a range consisting of any two of these values. In some embodiments, 1≤0.01×A×B≤3. If 0.01×A×B is too small, the mass percentage of the cyclic sulfone compound in the corresponding electrolyte is too low or the mass percentage of the fluorine element in the SEI film is too low, which makes the safety performance and / or cycle performance of the secondary battery unable to be effectively improved. If 0.01×A×B is too large, the mass percentage of the cyclic sulfone compound in the corresponding electrolyte is too high or the mass percentage of the fluorine element in the SEI film is too high, and the safety performance and / or cycle performance of the secondary battery cannot be effectively improved.

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

[0024]

[0025] In formula I, R1, R2, R3 and R4 are 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.

[0026] 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.

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

[0028] Halogen includes fluorine, chlorine, bromine and iodine.

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

[0030] In some embodiments, in Formula I, 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.

[0031] In some embodiments, in Formula I, R1, R2, R3 and R4 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.

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

[0033] In the present application, the non-fluorinated linear carbonate is a solvent conventionally used as a secondary battery in the art. In some embodiments, the non-fluorinated linear carbonate includes at least one of 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 of dimethyl carbonate, ethyl methyl carbonate and diethyl carbonate.

[0034] In some embodiments, the total mass of the non-fluorinated linear carbonate and the cyclic sulfone compound accounts for more than 98% of the mass of the solvent, such as 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 solvent does not include ether.

[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 proportion 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%, less than 0.1%. The inventors of the present application found that although non-fluorinated saturated cyclic carbonates are beneficial to the normal temperature cycle performance of secondary batteries, they are not conducive to the thermal safety of secondary batteries. Surprisingly, replacing non-fluorinated saturated cyclic carbonate solvents with cyclic sulfone compound solvents and controlling the content of cyclic sulfone compounds and the content ratio of fluorine element in the negative electrode SEI film can improve the thermal safety of secondary batteries while ensuring that the normal temperature cycle performance of secondary batteries is not deteriorated.

[0036] In some embodiments, the fluorinated carbonate includes at least one of a fluorinated cyclic carbonate and a fluorinated linear carbonate.

[0037] In some embodiments, the fluorinated cyclic carbonate comprises at least one of the compounds represented by Formula II-1,

[0038]

[0039] In formula II-1, R5, R6, R7 and R8 are independently selected from hydrogen atom, fluorine atom, 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, Q1 does not exist or Q1 is selected from C1-C6 alkylene.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] In some embodiments, in formula II-1, R5, R6, R7 and R8 are independently selected from hydrogen atoms, fluorine atoms, C1-C4 alkyl groups or fluorinated C1-C4 alkyl groups, and at least one of R5, R6, R7 and R8 is a fluorine atom, Q1 does not exist or Q1 is 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 groups, ethyl groups, trifluoromethyl groups or 2,2,2-trifluoroethyl groups, at least one of R5, R6, R7 and R8 is a fluorine atom, and Q1 does not exist or Q1 is selected from methylene groups or ethylene groups.

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

[0046] In some embodiments, the fluorinated linear carbonate comprises at least one of the compounds represented by Formula II-2,

[0047]

[0048] In formula II-2, R9 and R 10 are 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 embodiments, in Formula II-2, R9 and R 10 are the same or different and are 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 embodiments, in Formula II-2, R9 and R 10 are the same or different and are 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 mass percentage of fluorocarbonate in the electrolyte is 0.5%-8%. Exemplarily, it is 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 the range composed of any two of these values.

[0053] In some embodiments, the solvent comprises 60%-90% of non-fluorinated linear carbonates and 10%-40% of cyclic sulfone compounds, the percentages being based on the total mass of the solvent. In some embodiments, the solvent comprises 70%-85% of non-fluorinated linear carbonates and 15%-30% of 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(trifluoromethylsulfonyl)imide (LiTFSI), lithium (trifluoromethylsulfonyl)(perfluorobutylsulfonyl)imide (LiFNFSI), and lithium bis(pentafluoroethylsulfonic acid)imide (LiBETI).

[0055] In some embodiments, the lithium salt comprises at least one of 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 the lithium salt in the electrolyte is 0.8 mol / L-2 mol / L. Wherein, the concentration represents the number of moles of lithium salt contained in a unit volume of the electrolyte. The concentration of the 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 a range consisting of any two of these values.

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

[0058] In some embodiments, the electrolyte may further include a second additive, as long as it does not impair the realization of the purpose of the invention of the present application. The second additive exemplarily includes vinylene carbonate (VC), vinyl ethylene carbonate (VEC), propane sultone (PS), propene sultone (PST), methylene disulfonate (MMDS), vinyl sulfate (DTD), lithium difluorophosphate (LiDFOP), lithium bis(oxalatoborate) (LiBOB), lithium difluoroborate (LiDFOB), lithium bis(oxalatodifluorophosphate) (LiODFP), tris(trimethylsilyl) phosphate (TMSP).

[0059] 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, for example 0.1%-8%.

[0060] In some embodiments, the electrolyte includes 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, which 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 of a carbon-based material, a tin-based material, a phosphorus-based material, and metallic lithium. The carbon-based material includes at least one of artificial graphite, natural graphite, soft carbon, hard carbon, carbon nanotubes, and graphene. The tin-based material includes at least one of tin, tin oxide, and tin alloy. The phosphorus-based material includes phosphorus and / or a 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 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.

[0065] 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.

[0066] In some embodiments, the positive electrode sheet includes a positive electrode active material, wherein 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, 0.1≤m≤1, 0≤n≤0.9, m+n≤1. In some embodiments, the chemical formula of the lithium nickel transition metal oxide is as 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, 0.1≤m≤1, 0≤n≤0.9, m+n≤1.

[0067] In some embodiments, m is 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 a range consisting of 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, 0.6, 0.7, 0.8, 0.9, or a range consisting of two of these values.

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

[0069] 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, 0.5≤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.

[0070] In some embodiments, the lithium nickel transition metal oxide may further include a coating layer, wherein the coating layer may be composed of at least one of lithium metaaluminate, aluminum oxide, lithium borate, or lithium boride.

[0071] In some embodiments, the positive electrode active material includes a LiMn selected from the formula k B (1-k) At least one of the phosphate compounds shown in PO4, wherein 0≤k≤1, B is selected from at least one of iron, cobalt, magnesium, calcium, zinc, chromium and lead. In some embodiments, k is 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 a range consisting of any two 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 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.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] In some embodiments, the method for preparing the secondary battery includes providing an electrode assembly, injecting, packaging, and forming. In some embodiments, the temperature of the formation is 40°C to 50°C. In some embodiments, the temperature of the formation is 40°C, 41°C, 42°C, 43°C, 44°C, 45°C, 46°C, 47°C, 48°C, 49°C, 50°C, or a range consisting of any two of these values.

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

[0078] In some embodiments, the charge current of the formation is 0.02C-0.33C, and the discharge current of the formation is 0.05C-0.5C. In some embodiments, the charge current of the formation 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 consisting of any two of these values. In some embodiments, the charge current of the formation is 0.03C-0.2C. In some embodiments, the discharge current of the formation 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 a range consisting of any two of these values. In some embodiments, the discharge current of the formation is 0.1C-0.3C.

[0079] In some embodiments, the charge voltage of the formation is 4.0V-4.4V, such as 4.0V, 4.1V, 4.2V, 4.3V, 4.4V. In some embodiments, the discharge voltage of the formation is 2.8V-3.2V, such as 2.8V, 2.9V, 3.0V, 3.1V, 3.2V.

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

[0081] In some embodiments, the secondary battery is formed. In some embodiments, the solid electrolyte interface membrane is obtained by the formation of the secondary battery. During the formation process of the secondary battery, the electrolyte is reduced to form a film on the surface of the negative electrode active material to form a SEI membrane, which inhibits the continuous reaction between the electrolyte and the negative electrode active material. After the secondary battery has been cycled for many times, the absolute content of fluorine in the SEI membrane will be slightly different from the absolute content of silicon in the SEI membrane after formation, but the relative content, that is, the mass percentage of fluorine in the SEI membrane, is still between 1% and 12%.

[0082] In some embodiments, the injection coefficient of the injection is 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 the present application, 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: a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery or a lithium ion polymer secondary battery.

[0084] 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.

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

[0086] 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.

[0087] 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.

[0088] 2. Device

[0089] 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.

[0090] 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.

[0091] 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.

[0092] Example

[0093] In this application, unless otherwise specified, all materials or reagents used are commercially available, and all methods used are conventional methods in the art.

[0094] Test Method

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

[0096] The fluorine content in the SEI film was tested using an energy dispersive spectrometer (EDS). The specific test steps are as follows: The lithium-ion battery was discharged to 2.5V at a current of 0.1C, and the lithium-ion battery was disassembled in an argon-filled glove box to obtain the electrode sheet. The obtained negative electrode sheet was cut into pieces with an area of ​​about 20mm 2 The test sample of different sizes was soaked and cleaned with a low-boiling dimethyl carbonate (DMC) solvent for half an hour. After it was completely dried, it was quickly transferred to the conductive glue of the EDS sample stage, so that the surface of the negative electrode active material layer away from the current collector was facing upward, and the possible dust on the sample surface was removed with an ear-cleaning ball. The sample was injected for detection, and the detection depth was about 500nm~1μm. The element content between Be and U in the SEI film was detected, and the mass percentage of fluorine in the SEI film was calculated. Among them, the test energy resolution was 132eV.

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

[0098] 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 200th cycle at 25°C was calculated according to the following formula: discharge capacity after the 200th cycle / discharge capacity in the first cycle × 100%.

[0099] 3. Battery 45℃ cycle performance test

[0100] At 45°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 45°C was calculated according to the following formula: discharge capacity after the 400th cycle / discharge capacity in the first cycle × 100%.

[0101] 4. Battery gas production test at 45℃ for 400 cycles

[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. The full-charge thickness of the battery at this time is measured using a PPG soft-pack battery thickness gauge and denoted as a. After cycling the battery 400 times at 45°C according to the above test method 2, the battery is charged at a constant current of 0.5C to 4.25V, and then charged at a constant voltage of 4.25V to 0.05C. After that, the full-charge thickness of the battery is measured using a PPG soft-pack battery thickness gauge and denoted as b. The calculation formula for the swelling rate of the cell thickness 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 thermal runaway occurs, record the cell temperature corresponding to thermal runaway.

[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, and then disperse them in N-methyl-2-pyrrolidone to obtain a positive electrode slurry. The positive electrode slurry is evenly coated on both sides of a 12-μm-thick aluminum foil current collector, and after drying, rolling, and slitting, a positive electrode sheet is obtained.

[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, thickener carboxymethyl cellulose sodium CMCNa, and binder polyacrylic acid PAA 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. The negative electrode slurry is coated on both sides of an 8-μm-thick copper foil current collector, and after drying, rolling, and slitting, a negative electrode sheet is obtained.

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

[0109] Preparation of electrolyte: In an argon-protected glove box (H2O<0.1ppm, O2<0.1ppm), the solvents ethyl methyl carbonate (EMC), diethyl carbonate (DEC) and cyclopentane (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, and then 3 wt% of the additive fluoroethylene carbonate (FEC) relative to the mass of the electrolyte was added and stirred evenly to obtain the lithium ion battery electrolyte of Example 1.

[0110] Preparation of lithium-ion battery (cell): stack the prepared positive electrode, separator and negative electrode in order, so that the separator is in the middle of the positive and negative electrode, and wind to obtain a bare cell; place the bare cell in an aluminum plastic film outer package, and inject the prepared lithium-ion battery electrolyte after sufficient drying, with an injection coefficient of 1.7g / Ah. After the battery is left at 45℃ for 48h, formed in a high-temperature fixture (formation conditions are: temperature 45℃, pressure 210kgf, 0.05C current charging to 4.2V, standing for 60min, then 0.1C charging to 4.2V and then 0.2C discharge to 3.0V, and so on, repeated twice), and secondary sealing, conventional capacity division is performed, and finally a lithium-ion battery with a rated capacity of ~4Ah is obtained.

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

[0112] Examples 2 to 14 and Comparative Examples 1 to 6 are based on Example 1 by adjusting the contents of EMC and DEC in the solvent, the type and content of the cyclic sulfone compound, the type and concentration of the lithium salt, and the type and content of the additive fluorocarbonate. Specific adjustment measures and detailed data are shown in Table 1.

[0113] Table 1

[0114]

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

[0116] Table 2

[0117]

[0118]

[0119] a: Indicates that the battery capacity retention rate is lower than 60% at a cycle before 400 cycles;

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

[0121] 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 electrolyte comprises a lithium salt, a solvent and an additive, wherein 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 plate includes a negative electrode active material layer and a solid electrolyte interface film located on the surface of the negative electrode active material layer. The mass percentage of fluorine element in the solid electrolyte interface film is B% as measured by an energy spectrometer. Among them, 0.4≤0.01×A×B≤4.

2. The secondary battery according to claim 1, characterized in that: The secondary battery meets at least one of the following conditions: (a) 10≤A≤40, (b) 1≤B≤12, (c)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: (d) 15 ≤ A ≤ 30, (e)2.5≤B≤10.

4. The secondary battery according to claim 1 or 2, characterized in that: The total mass of the non-fluorinated linear carbonate and the cyclic sulfone compound 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 comprises at least one compound selected from the group consisting of compounds shown in Formula I, In Formula I, R1, R2, R3 and R4 are 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; 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 II-1, In formula II-1, R5, R6, R7 and R8 are independently selected from hydrogen atom, fluorine atom, C1-C6 alkyl group or fluorinated C1-C6 alkyl group, and at least one of R5, R6, R7 and R8 is fluorine atom or fluorinated C1-C6 alkyl group, Q1 is absent or Q1 is selected from C1-C6 alkylene group, The fluorinated linear carbonate comprises at least one of the compounds shown in formula II-2, In formula II-2, R9 and R 10 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.

6. The secondary battery according to claim 5, characterized in that: The cyclic sulfone compound includes at least one of sulfolane, methyl sulfolane and 2-fluorosulfolane, and / or, 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 mass percentage of the fluorinated carbonate in the electrolyte is 0.5%-8%.

7. The secondary battery according to claim 1 or 2, characterized in that: The negative electrode plate comprises a negative electrode active material selected from silicon-based materials, wherein the silicon-based material comprises at least one of silicon, silicon alloy, silicon oxide compound and silicon carbon compound, and the mass percentage of the silicon-based material in the negative electrode active material is 10%-40%; and / or, The positive electrode sheet includes a positive electrode active material, wherein the positive electrode active material includes a LiNi selected from the formula m Co n A (1-m-n) O2 is a lithium nickel transition metal oxide or a LiMn k B (1-k) At least one of the phosphate compounds shown in PO4, 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, B is selected from at least one of iron, cobalt, magnesium, calcium, zinc, chromium and lead, 0≤k≤1.

8. The secondary battery according to claim 1 or 2, characterized in that: The negative electrode active material includes a silicon-based material and a carbon-based material. The silicon-based material includes a silicon-oxygen compound and / or a silicon-carbon compound. The carbon-based material includes artificial graphite and / or natural graphite.

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

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

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