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 solvent and a lithium salt, the solvent comprises non-fluorinated linear carbonic ester, fluorinated carbonic ester and a cyclic sulfone compound, the mass percentage content of the cyclic sulfone compound in the solvent is A%, the mass percentage content of the fluorinated carbonic ester in the solvent is B%, the mass percentage content of the lithium salt in the solvent is A%, and the mass percentage content of the lithium salt in the solvent is A%. 0.05 < = A / B < = 2; the negative pole piece comprises a negative active material selected from a silicon-based material, the mass percentage content of the silicon-based material in the negative active material is C%, and C / A is greater than or equal to 2 and less than or equal to 18. The electrolyte can effectively improve the high-temperature gas production problem of the silicon-based negative electrode secondary battery, improve the thermal runaway temperature of the battery, reduce the thermal runaway damage of the battery, and ensure the excellent normal-temperature cycle performance and high-temperature cycle performance of the battery.

Description

Technical Field

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

[0002] As a representative of the new energy field, lithium-ion batteries have been widely used in daily life and high-tech fields due to their green and environmentally friendly characteristics and high specific energy. With the demand for scientific and technological life, lithium-ion batteries with higher specific energy are an inevitable trend of development. However, the application of high-specific energy lithium-ion batteries cannot ignore the safety hazards they bring, especially lithium-ion batteries with silicon-based negative electrodes correspond to greater safety hazards.

[0003] As the blood of lithium-ion batteries, electrolyte not only carries the connection between positive and negative electrode materials, but also plays a key role in the safety of lithium-ion batteries. The composition of electrolyte mainly includes solvent and lithium salt, among which conventional solvent is a combination of non-fluorinated cyclic carbonate (such as ethylene carbonate (EC), propylene carbonate (PC), etc.) and non-fluorinated linear carbonate (such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), etc.). Non-fluorinated cyclic carbonate solvents can effectively dissociate lithium salts and ensure the ability of lithium ion transmission, but it cannot be ignored that non-fluorinated carbonate solvents are the main source of heat in thermal runaway. More noteworthy is that non-fluorinated cyclic carbonate solvents account for a larger proportion of the source of heat after thermal runaway. Therefore, establishing an electrolyte that does not contain non-fluorinated cyclic carbonates is the most effective strategy to improve the safety performance of silicon-based negative electrode batteries. Summary of the invention

[0004] In response to the thermal safety hazards of lithium-ion batteries containing non-fluorinated cyclic carbonate solvents, the present application replaces the non-fluorinated cyclic carbonate solvents with low-calorie, high-dissociation solvents, specifically, uses a combination solvent of fluorinated carbonates and cyclic sulfone compounds in a certain dosage ratio to replace the non-fluorinated cyclic carbonates, which not only ensures the dissociation of the solvent to the lithium salt, but also effectively improves the gas production problem of silicon-based negative electrode batteries in high-temperature cycles, delays the thermal runaway temperature of the battery, and reduces the harmfulness of the battery after thermal runaway, while taking into account the room temperature cycle performance and high temperature cycle performance of the silicon-based negative electrode battery.

[0005] The first aspect of the present application provides a secondary battery, which includes a positive electrode plate, a negative electrode plate and an electrolyte, wherein the electrolyte contains a solvent and a lithium salt, the solvent includes a non-fluorinated linear carbonate, a fluorinated carbonate and a cyclic sulfone compound, the mass percentage of the cyclic sulfone compound in the solvent is A%, the mass percentage of the fluorinated carbonate in the solvent is B%, and 0.05≤A / B≤2; the negative electrode plate contains a negative electrode active material selected from silicon-based materials, the mass percentage of the silicon-based material in the negative electrode active material is C%, wherein 2≤C / A≤18.

[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 combination solvent of non-fluorinated linear carbonates, fluorinated carbonates and cyclic sulfone compounds into the electrolyte. Compared with the traditional combination solvent of non-fluorinated cyclic carbonates and non-fluorinated linear carbonates, the high-temperature gas production problem of the secondary battery can be effectively improved, the volume expansion rate of the battery cell after high-temperature cycling of the battery can be reduced, the thermal runaway temperature of the battery can be increased, the maximum rate of instantaneous temperature rise of the battery combustion bomb can be reduced, and the thermal runaway hazard of the battery can be reduced, thereby significantly improving the safety of the battery, and at the same time ensuring that the silicon-based negative electrode battery has excellent room temperature cycling performance and high temperature cycling performance. DETAILED DESCRIPTION

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

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

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

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

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

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

[0015] Primary and secondary batteries

[0016] The secondary battery provided in the present application includes a positive electrode plate, a negative electrode plate and an electrolyte, wherein the electrolyte contains a solvent and a lithium salt, the solvent includes a non-fluorinated linear carbonate, a fluorinated carbonate and a cyclic sulfone compound, the mass percentage of the cyclic sulfone compound in the solvent is A%, the mass percentage of the fluorinated carbonate in the solvent is B%, and 0.05≤A / B≤2; the negative electrode plate contains a negative electrode active material selected from silicon-based materials, the mass percentage of the silicon-based material in the negative electrode active material is C%, wherein 2≤C / A≤18.

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

[0018] In some embodiments, A / 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 or a range consisting of any two of these values. In some embodiments, 0.1≤A / B≤1.5. If A / B is too small, there is too much fluorocarbonate or too little cyclic sulfone compound in the corresponding electrolyte, which reduces the thermal stability of the electrolyte and increases the heat. The gas production of the corresponding battery in the high temperature cycle process is aggravated, the thermal safety of the battery is deteriorated, and the risk of thermal runaway is increased. If A / B is too large, there will be too little fluorocarbonate or too much cyclic sulfone compound in the corresponding electrolyte, which will cause the performance of the solid electrolyte interface film (SEI film) formed on the negative electrode side to deteriorate. The SEI film formed during a long cycle period cannot effectively protect the silicon-based negative electrode side, thereby accelerating the decay of the battery cycle capacity.

[0019] In some embodiments, 1≤A≤10. A is illustratively 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3, 3.2, 3.5, 3.8, 4, 4.2, 4.5, 4.8, 5, 5.2, 5.5, 5.8, 6, 6.2, 6.5, 6.8, 7, 7.2, 7.5, 7.8, 8, 8.2, 8.5, 8.8, 9, 9.2, 9.5, 9.8, 10 or a range consisting of any two of these values. In some embodiments, 2≤A≤8. If A is too low, the high temperature stability and safety of the secondary battery cannot be effectively improved. If A is too high, the film forming property of the electrolyte deteriorates, and a dense and uniform SEI film cannot be formed on the surface of the negative electrode, thereby significantly deteriorating the cycle performance of the battery, especially the room temperature cycle performance.

[0020] In some embodiments, 5≤B≤20. B is illustratively 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or a range consisting of any two of these values. In some embodiments, 8≤B≤15. If B is too low, there is not enough fluorocarbonate to repair the SEI film in a long cycle period, thereby failing to effectively improve the cycle performance of the silicon-based negative electrode 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 and deteriorate the safety of the battery. At the same time, the fluorocarbonate content is too high, and the corresponding higher heat will aggravate the hazards after the battery thermal runaway.

[0021] In some embodiments, C / A is, for example, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, or a range formed by any two of these values. In some embodiments, 3 ≤ C / A ≤ 15. If C / A is too large, the content of the silicon-based material in the corresponding negative electrode is too high or the introduction amount of the cyclic sulfone compound is too small. The insufficient cyclic sulfone compound cannot dissociate the lithium salt sufficiently, and the ionic conductivity of the corresponding electrolyte system decreases, and the capacity of the battery corresponding to the high-silicon negative electrode system cannot be fully exerted, and at the same time, the power performance of the battery is affected. If C / A is too small, the content of the silicon-based material in the corresponding negative electrode is too small, and the introduction amount of the cyclic sulfone compound is too large. The excessive sulfone compound will increase the viscosity of the electrolyte and reduce the fluidity of the electrolyte, thereby affecting the cycle performance and power performance of the battery.

[0022] In some embodiments, 0 < C ≤ 50. C is, for example, 2, 5, 8, 10, 12, 15, 18, 20, 22, 25, 28, 30, 32, 35, 38, 40, 42, 45, 48, 50, or a range formed by any two of these values. In some embodiments, 10 ≤ C ≤ 40.

[0023] In some embodiments, the total mass percentage of the non-fluorinated linear carbonate, fluorinated carbonate, and cyclic sulfone compound in the solvent is more than 98%, for example, more than 98.5%, more than 98.8%, more than 99%, more than 99.2%, more than 99.5%, more than 99.8%.

[0024] 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 the non-fluorinated saturated cyclic carbonate 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%.

[0025] In some embodiments, the fluorinated carbonate includes at least one of a fluorinated cyclic carbonate and a fluorinated linear carbonate.

[0026] In some embodiments, the fluorinated cyclic carbonate includes at least one of the compounds shown in Formula I-1,

[0027]

[0028] In Formula I-1, R 1 , R 2 , R 3 and R 4 are independently selected from a hydrogen atom, a fluorine atom, a C1-C6 alkyl group, or a fluorinated C1-C6 alkyl group, and R 1 , R 2, R 3 and R 4 At least one of them is a fluorine atom or a fluorinated C1-C6 alkyl group, Q 1 Not present or Q 1 Selected from C1-C6 alkylene.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] In some embodiments, in Formula I-1, R 1 , R 2 , R 3 , R 4 are independently selected from a hydrogen atom, a fluorine atom, a C1-C4 alkyl group or a fluorinated C1-C4 alkyl group, and R 1 , R 2 , R 3 , R 4 At least one of them is a fluorine atom, Q 1 Not present or Q 1 Selected from methylene or ethylene.

[0033] In some embodiments, in Formula I-1, R 1 , R 2 , R 3 , R 4 R 1 , R 2 , R 3 , R 4 At least one of them is a fluorine atom, Q 1 Not present or Q1 Selected from methylene or ethylene.

[0034] In some embodiments, the fluorinated cyclic carbonate includes at least one of fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), and trifluoropropylene carbonate (TFPC).

[0035] In some embodiments, the fluorinated linear carbonate comprises at least one of the compounds represented by Formula I-2,

[0036]

[0037] In Formula I-2, R 5 and R 6 are independently selected from C1-C6 alkyl or fluorinated C1-C6 alkyl, and R 5 and R 6 At least one of them is a fluorinated C1-C6 alkyl group.

[0038] In some embodiments, in Formula I-2, R 5 and R 6 are the same or different and are independently selected from C1-C4 alkyl or fluorinated C1-C4 alkyl, and R 5 and R 6 At least one of them is a fluorinated C1-C4 alkyl group.

[0039] In some embodiments, in Formula I-2, R 5 and R 6 are the same or different and are independently selected from methyl, ethyl, n-propyl, isopropyl, trifluoromethyl or 2,2,2-trifluoroethyl, and R 5 and R 6 At least one of them is trifluoromethyl or 2,2,2-trifluoroethyl.

[0040] 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).

[0041] In some embodiments, the cyclic sulfone compound includes at least one compound selected from the group consisting of compounds represented by Formula II,

[0042]

[0043] In Formula II, R 7 , R 8 , R 9 and R 10Independently 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.

[0044] 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.

[0045] C2-C6 alkynyl groups include, but are not limited to, ethynyl, n-propynyl, isopropynyl, n-butynyl, isobutynyl, n-pentynyl, isopentenyl, and hexynyl.

[0046] Halogen includes fluorine, chlorine, bromine and iodine.

[0047] In some embodiments, in Formula II, R 7 , R 8 , R 9 and R 10 Independently selected from a hydrogen atom, a halogen atom, a C1-C6 alkyl group or a halogenated C1-C6 alkyl group.

[0048] In some embodiments, in Formula II, R 7 , R 8 , R 9 and R 10 Independently selected from a hydrogen atom, a fluorine atom, a C1-C4 alkyl group or a fluorinated C1-C4 alkyl group.

[0049] In some embodiments, in Formula II, R 7 , R 8 , R 9 and R 10 are independently selected from a hydrogen atom, a fluorine atom, a methyl group, an ethyl group, a trifluoromethyl group or a 2,2,2-trifluoroethyl group.

[0050] In some embodiments, the cyclic sulfone compound includes at least one of sulfolane, methylsulfolane, and 2-fluorosulfolane.

[0051] 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.

[0052] In some embodiments, the solvent comprises 70%-94% of non-fluorinated linear carbonates, 5%-20% of fluorinated carbonates, and 1%-10% of cyclic sulfone compounds, the percentages being based on the total mass of the solvent. In some embodiments, the solvent comprises 77%-90% of non-fluorinated linear carbonates, 8%-15% of fluorinated carbonates, and 2%-8% of cyclic sulfone compounds, the percentages being based on the total mass of the solvent.

[0053] In some embodiments, the lithium salt includes lithium hexafluorophosphate (LiPF 6 ), lithium bis(fluorosulfonyl)imide (LiFSI), lithium trifluoromethanesulfonyl (LiOTf), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), lithium (trifluoromethylsulfonyl)(perfluorobutylsulfonyl)imide (LiFNFSI), lithium bis(pentafluoroethylsulfonate)imide (LiBETI), lithium bis(oxalatoborate) (LiBOB), lithium difluorooxalatoborate (LiDFOB), lithium difluorophosphate (LiDFP), lithium bis(oxalatodifluorophosphate) (LiODFP), lithium tetrafluoroborate (LiBF 4 ), at least one of lithium bis(fluoromalonate)borate (LiBFMB) and lithium 4,5-dicyano-2-(trifluoromethyl)imidazole (LiTDI).

[0054] In some embodiments, the lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium difluorophosphate, and lithium bis(oxalatodifluorophosphate).

[0055] In some embodiments, the concentration of the lithium salt in the electrolyte is 0.8 mol / L-2 mol / L. The concentration of the lithium salt is illustratively 0.8 mol / L, 0.9 mol / L, 1 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L, 1.6 mol / L, 1.8 mol / L, 2 mol / L or a range consisting of any two of these values.

[0056] In some embodiments, the electrolyte may further include additives as long as they do not impair the purpose of the present invention. The additives exemplarily include vinylene carbonate (VC) and vinyl ethylene carbonate (VEC).

[0057] 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.

[0058] In some embodiments, the silicon-based material includes at least one of silicon, silicon alloy, silicon oxide compound, and silicon carbide compound. In some embodiments, the silicon-based material includes 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.

[0059] In some embodiments, the negative electrode active material further includes a mixture of at least one material among carbon-based material, tin-based material, 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 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.

[0060] 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.

[0061] In some embodiments, the negative electrode sheet 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.

[0062] In some embodiments, the positive electrode sheet includes a positive electrode active material, and the positive electrode active material includes at least one selected from lithium nickel transition metal oxides represented by the formula LiNi m Co n A (1-m-n) O 2 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, and m + n ≤ 1. In some embodiments, the chemical formula of the lithium nickel transition metal oxide is as shown in the formula LiNi m Co n A (1-m-n) O 2 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, and m + n ≤ 1.

[0063] 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.

[0064] 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).

[0065] In some embodiments, the chemical formula of the lithium nickel transition metal oxide is as follows: m Co n A (1-m-n) O 2 As shown, 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 shown in the formula LiNi m Co n A (1-m-n) O 2 As shown, wherein A is selected from at least one of manganese, aluminum, magnesium, zirconium, strontium, yttrium, lanthanum, molybdenum, silver, niobium, chromium and calcium, 0.7≤m≤1, 0≤n≤0.3, m+n≤1.

[0066] In some embodiments, the lithium nickel transition metal oxide may further include a coating layer, wherein the coating layer may be composed of one or more of lithium metaaluminate, aluminum oxide, lithium borate or lithium boride.

[0067] In some embodiments, the positive electrode active material includes at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide.

[0068] In some embodiments, the positive electrode active material includes a LiMn selected from the formula k B (1-k) PO 4At least one of the phosphate compounds shown, 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 PO 4 or LiMn 0.8 Fe 0.2 PO 4 At least one of .

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] In some embodiments, the shape of the secondary battery is not particularly limited, and it can be cylindrical, square, or any other shape.

[0076] 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.

[0077] 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.

[0078] 2. Device

[0079] 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.

[0080] 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.

[0081] 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.

[0082] Example

[0083] In this application, unless otherwise specified, all materials or reagents used are commercially available, and all methods used are conventional methods in the art.

[0084] Test Method

[0085] 1. Battery 25℃ cycle performance test

[0086] At 25°C, the lithium-ion battery was charged to 4.25V at 0.5C constant current, then charged to 0.05C at 4.25V, and then discharged to 2.5V at 1C constant current. After 400 cycles of charge and discharge, the capacity retention rate after the 400th cycle at 25°C was calculated according to the following formula: discharge capacity after the 400th cycle / discharge capacity in the first cycle × 100%.

[0087] 2. Battery 45℃ cycle performance test

[0088] 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%.

[0089] 3. Battery gas production test at 45℃ for 400 cycles

[0090] The lithium-ion battery is discharged at 1C constant current to 2.5V at 25°C, then charged at 0.5C constant current to 4.25V, and then charged at 4.25V to 0.05C at constant voltage. The full-charge thickness of the battery at this time is measured using a PPG soft-pack battery thickness gauge and recorded as a. The battery that has been cycled 400 times at 45°C according to the above test method 2 is charged at 0.5C constant current to 4.25V, and then charged at 4.25V to 0.05C at constant voltage. The full-charge thickness of the battery at this time is measured using a PPG soft-pack battery thickness gauge and recorded as b. The calculation formula for the expansion rate of the battery cell thickness after 400 cycles at 45°C is: (ba) / a×100%.

[0091] 4. Battery hot box test

[0092] The hot box test process steps are as follows: at 25°C, calibrate the cell capacity at 1 / 3C and fully charge the cell; clamp the fully charged cell with a preload of 1.5Nm; place the lithium-ion battery in a temperature box, and heat the temperature box from ambient temperature to 130°C±2°C at a rate of 5°C / min, and maintain this temperature for 60 minutes; the temperature box continues to heat up by 10°C at a rate of 5°C / min, and maintains this temperature for 60 minutes; until it gets out of control, record the cell temperature corresponding to the out-of-control.

[0093] 5. Battery incendiary bomb test

[0094] The test steps of the incendiary bomb are as follows: Under the condition of 25 °C, calibrate the capacity of the battery cell at 1 / 3C and fully charge it; displace the atmosphere with nitrogen and evacuate and fill the atmosphere in the combustion bomb cavity twice; set the data acquisition to record the voltage and temperature data, and laterally heat the battery cell with a constant power heating sheet with a size of 50×50 mm and a power of 300 W until the battery cell gets out of control. After thermal runaway, wait for the temperature and pressure in the cavity to stabilize to complete the test. Differentiate the air domain temperature data during the test process, record the change in the instantaneous temperature rise dT / dt of the instantaneous eruption, and record the maximum value dT / dt(max) of the instantaneous temperature rise dT / dt.

[0095] Example 1

[0096] The preparation steps of the positive electrode plate are as follows: Mix the positive electrode active material LiNi 0.8 Co 0.1 Mn 0.1 O 2 , conductive agent carbon black and binder polyvinylidene fluoride, and then disperse them in N-methyl-2-pyrrolidone to obtain a positive electrode slurry. Coat the positive electrode slurry evenly on both sides of a 12-μm-thick aluminum foil current collector, and after drying, rolling, and slitting, obtain the positive electrode plate.

[0097] The preparation steps of the negative electrode plate are as follows: Mix silicon oxy-graphite composite (the mass ratio of silicon oxide SiOx (0.5 < x < 1.5) to artificial graphite is 30:70), conductive agent acetylene black, binder styrene-butadiene rubber, thickener sodium carboxymethyl cellulose, and binder polyacrylic acid according to the mass ratio of 95:2:1.5:1:0.5, and then disperse them in deionized water to obtain a negative electrode slurry. Coat the negative electrode slurry on both sides of an 8-μm-thick copper foil current collector, and after drying, rolling, and slitting, obtain the negative electrode plate.

[0098] Separator: Use a PP / PE / PP three-layer composite separator.

[0099] Electrolyte preparation: In a glove box under argon protection (H 2 O < 0.1 ppm, O 2 < 0.1 ppm), mix the solvents ethylene methyl carbonate (EMC), fluoroethylene carbonate (FEC), and sulfolane (SL) according to the mass ratio of EMC:FEC:SL = 86:12:2, add lithium hexafluorophosphate (LiPF 6 ), prepare a solution with a lithium salt concentration of 1 mol / L, and then add 1.5 wt% of additive vinylene carbonate (VC) relative to the mass of the electrolyte, and stir evenly to obtain the lithium-ion battery electrolyte of Example 1.

[0100] Preparation of lithium-ion batteries (cells): stack the prepared positive electrode sheets, separators, and negative electrode sheets in order, with the separators placed between the positive and negative electrode sheets, and wind them to obtain bare cells; place the bare cells in an aluminum-plastic film outer package, inject the prepared lithium-ion battery electrolyte after sufficient drying, and obtain a lithium-ion battery with a rated capacity of ~75Ah after formation, secondary sealing, and capacity division.

[0101] Examples 2 to 14 and Comparative Examples 1 to 8

[0102] Examples 2 to 14 and Comparative Examples 1 to 8 are achieved by adjusting the content of ethyl methyl carbonate in the solvent, the type and content of the cyclic sulfone compound, the type and content of the fluorocarbonate, the content of the negative electrode silicon oxide compound, and whether ethylene carbonate is added on the basis of Example 1. Specific adjustment measures and detailed data are shown in Table 1.

[0103] Table 1

[0104]

[0105] The test results of the lithium ion batteries of Examples 1-14 and Comparative Examples 1-8 are shown in Table 2.

[0106] Table 2

[0107]

[0108]

[0109] *: Indicates that the battery capacity retention rate is less than 60% at a cycle before 400 cycles.

[0110] 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 solvent and a lithium salt, wherein the solvent comprises a non-fluorinated linear carbonate, a fluorinated carbonate and a cyclic sulfone compound, wherein the mass percentage of the cyclic sulfone compound in the solvent is A%, the mass percentage of the fluorinated carbonate in the solvent is B%, and 0.05≤A / B≤2; The negative electrode plate comprises a negative electrode active material selected from silicon-based materials, and the mass percentage of the silicon-based material in the negative electrode active material is C%, wherein 2≤C / A≤18.

2. The secondary battery according to claim 1, characterized in that: The secondary battery meets at least one of the following conditions: (a) 1≤A≤10, (b) 5≤B≤20, (c)0 <C≤50。 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)2≤A≤8, (e)8≤B≤15, (f) 10 ≤ C ≤ 40, (g) 0.1≤A / B≤1.5, (h)3≤C / A≤15.

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

6. The secondary battery according to claim 5, characterized in that: The fluorinated cyclic carbonate comprises at least one of fluoroethylene carbonate, difluoroethylene carbonate and trifluoropropylene carbonate, and / or, The fluorinated linear carbonate comprises at least one of methyl-2,2,2-trifluoroethyl carbonate and di(2,2,2-trifluoroethyl) carbonate, and / or, The cyclic sulfone compound includes at least one of sulfolane, methyl sulfolane and 2-fluorosulfolane.

7. The secondary battery according to claim 1 or 2, characterized in that: The silicon-based material includes at least one of silicon, silicon alloy, silicon oxide compound and silicon carbon compound; and / or, The negative electrode active material further includes a carbon-based material, and the carbon-based material includes at least one of artificial graphite, natural graphite, soft carbon, hard carbon, carbon nanotubes, and graphene.

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, and the carbon-based material includes artificial graphite and / or natural graphite; 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) Lithium nickel transition metal oxide represented by O2 or 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, 0.1≤m≤1, 0≤n≤0.9, m+n≤1, B is selected from at least one of iron, cobalt, magnesium, calcium, zinc, chromium and lead, 0≤k≤1.

9. The secondary battery according to claim 1 or 2, characterized in that: The secondary battery satisfies at least one of the following conditions: (i) the solvent comprises 77% to 90% of a non-fluorinated linear carbonate, 8% to 15% of a fluorinated carbonate and 2% to 8% of a cyclic sulfone compound, the percentages being based on the total mass of the solvent; (j) the non-fluorinated linear carbonate comprises at least one of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate and ethyl propyl carbonate; (k) the lithium salt comprises at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium difluorophosphate and lithium bis(oxalatodifluorophosphate); (l) The concentration of lithium salt in the electrolyte is 0.8 mol / L-2 mol / L.

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

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