Electrolyte, and secondary battery and device comprising same

Abstract

The invention relates to an electrolyte, a secondary battery containing the electrolyte and a device. The electrolyte comprises a lithium salt, a solvent and an additive, the solvent comprises non-fluorinated linear carbonate and a cyclic sulfone compound, the additive comprises fluorinated saturated cyclic carbonate, unsaturated cyclic carbonate, an oxalate compound and a sulfur-containing compound, the oxalate compound comprises at least one of lithium oxalato borate and lithium oxalato phosphate, and the sulfur-containing compound comprises at least one of lithium oxalato borate and lithium oxalato phosphate. The sulfur-containing compound comprises at least one of sulfonate and sulfate, the mass percentage content of the cyclic sulfone compound in the electrolyte is A%, the mass percentage content of the additive in the electrolyte is C%, A / C is larger than or equal to 2 and smaller than or equal to 6.5, and C is larger than or equal to 3 and smaller than or equal to 16. The electrolyte integrates the normal-temperature cycle performance and the high-temperature safety performance of the lithium ion battery.

Description

Technical Field

[0001] The present application relates to the field of energy storage, and in particular to an electrolyte, a secondary battery and a device containing the electrolyte. 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. Therefore, it is urgent to develop a high-safety, long-cycle electrolyte for high-energy-density lithium-ion batteries. Summary of the invention

[0003] In response to the safety hazards and cycle attenuation of high-energy-density lithium-ion batteries, the present application uses a combination solvent containing a highly resistant to oxidation, low-calorie cyclic sulfone compound and a non-fluorinated linear carbonate in combination with a combination additive containing a certain amount of fluorinated saturated cyclic carbonate, unsaturated cyclic carbonate, oxalate compound and sulfur-containing compound, taking into account both the room temperature cycle performance and high temperature safety performance of the lithium-ion battery.

[0004] The first aspect of the present application provides an electrolyte, comprising a lithium salt, a solvent and an additive, wherein the solvent comprises a non-fluorinated linear carbonate and a cyclic sulfone compound, the additive comprises a fluorinated saturated cyclic carbonate, an unsaturated cyclic carbonate, an oxalate compound and a sulfur-containing compound, the oxalate compound comprises at least one of lithium oxalatoborate and lithium oxalatophosphate, the sulfur-containing compound comprises at least one of a sulfonate and a sulfate, the mass percentage of the cyclic sulfone compound in the electrolyte is A%, the mass percentage of the additive in the electrolyte is C%, wherein 2≤A / C≤6.5, and 3≤C≤16.

[0005] A second aspect of the present application provides a secondary battery, comprising a positive electrode sheet, a negative electrode sheet and the electrolyte described in the first aspect.

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

[0007] The beneficial effects of this application are:

[0008] The electrolyte of the present application introduces a combined solvent of non-fluorinated linear carbonates and cyclic sulfone compounds and a combined additive of fluorinated saturated cyclic carbonates, unsaturated cyclic carbonates, oxalate compounds and sulfur-containing compounds, and controls the content ratio of the cyclic sulfone compounds and the additives. While ensuring the ability of the electrolyte to transport lithium ions, it also takes into account the room temperature cycle performance, thermal stability, high temperature storage safety and high temperature electrochemical stability of the lithium ion battery. On the premise of ensuring that the room temperature cycle performance of the lithium ion battery is not deteriorated, it effectively improves the high temperature gas production problem of the lithium ion battery, delays the thermal runaway temperature of the battery, and improves the high temperature capacity recovery rate of the battery. DETAILED DESCRIPTION

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

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

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

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

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

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

[0015] Primary and secondary batteries

[0016] The first aspect of the present application provides an electrolyte, comprising a lithium salt, a solvent and an additive, wherein the solvent comprises a non-fluorinated linear carbonate and a cyclic sulfone compound, the additive comprises a fluorinated saturated cyclic carbonate, an unsaturated cyclic carbonate, an oxalate compound and a sulfur-containing compound, the oxalate compound comprises at least one of lithium oxalate borate and lithium oxalate phosphate, the sulfur-containing compound comprises at least one of a sulfonate and a sulfate, the mass percentage of the cyclic sulfone compound in the electrolyte is A%, the mass percentage of the additive in the electrolyte is C%, wherein 2≤A / C≤6.5, and 3≤C≤16. When A / C is within the above range, the solvent and the additive can better cooperate with each other, so that the secondary battery has better thermal stability and safety while also having excellent cycle performance.

[0017] In some embodiments, 15≤A≤40. A is illustratively 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, 20≤A≤40. If A is too low, the thermal stability and 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 capacity of the secondary battery. If A is too high, the viscosity of the electrolyte will be too large, affecting the kinetic performance and room temperature cycle performance of the secondary battery.

[0018] In some embodiments, C is illustratively 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, 12.5, 13, 13.5, 14, 14.5, 15, 15.5, 16 or a range consisting of any two of these values. In some embodiments, 5≤C≤12. If C is too low, a dense, uniform solid interface film cannot be formed, thereby effectively alleviating the side reactions between the electrode and the electrolyte, and effectively improving the cycle performance of the secondary battery. If C is too high, it is easy to cause the interfacial impedance of the secondary battery to increase, the battery kinetic loss to increase, thereby deteriorating the power performance and cycle performance of the battery.

[0019] In some embodiments, A / C is illustratively 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5 or a range consisting of any two of these values. In some embodiments, 2.5≤A / C≤6. If A / C is too low, the ionic conductivity of the electrolyte is low, the lithium ion transmission performance is weak, the interface impedance of the secondary battery increases, and the safety and kinetic performance of the battery are poor. If A / C is too high, the solid interface film formed on the electrode surface has large defects, and the uneven interface film is also prone to lithium precipitation in the battery core, thereby affecting the safety of the battery. At the same time, during the long cycle process, the defects of the interface film cannot be repaired in time, thereby accelerating the decay of the battery capacity and deteriorating the cycle performance.

[0020] In some embodiments, the mass percentage of the fluorinated saturated cyclic carbonate in the electrolyte is B%, wherein 3≤A / B≤16. In some embodiments, A / B is illustratively 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 10, 10.5, 11, 11.5, 12, 12.5, 13, 13.5, 14, 14.5, 15, 15.5, 16 or a range consisting of any two of these values. In some embodiments, 5≤A / B≤14. If A / B is too small, then A is too low or B is too high, which will degrade the capacity, cycle performance, thermal stability and safety of the battery. If A / B is too large, then A is too high or B is too low, which will degrade the power performance and cycle performance of the battery.

[0021] In some embodiments, 1≤B≤10. 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 or a range consisting of any two of these values. In some embodiments, 1≤B≤8. If B is too low, the cycle performance of the secondary battery will be affected. If 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 thermal runaway of the battery.

[0022] 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.

[0023] In some embodiments, the mass percentage of the non-fluorinated linear carbonate in the electrolyte is 41%-83%. Exemplarily, it is 41%, 43%, 45%, 48%, 50%, 52%, 55%, 58%, 60%, 62%, 65%, 68%, 70%, 72%, 75%, 78%, 80%, 83% or a range consisting of any two of these values. In some embodiments, the mass percentage of the non-fluorinated linear carbonate in the electrolyte is 50%-80%.

[0024] 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.

[0025] In some embodiments, the solvent does not contain ethylene carbonate and / or propylene carbonate. Preferably, the solvent does not contain non-fluorinated saturated cyclic carbonate. Here, "does not contain" means that the mass proportion of 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%. The inventors of the present application have found that replacing the non-fluorinated saturated cyclic carbonate solvent with a cyclic sulfone compound solvent and controlling the content ratio of the cyclic sulfone compound and the fluorinated saturated cyclic carbonate can effectively improve the room temperature cycle performance, thermal stability and safety of the secondary battery.

[0026] In some embodiments, the cyclic sulfone compound comprises at least one compound selected from the group consisting of compounds represented by Formula I,

[0027]

[0028] 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.

[0029] 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.

[0030] C2-C6 alkynyl groups include, but are not limited to, ethynyl, n-propynyl, isopropynyl, n-butynyl, isobutynyl, n-pentynyl, isopentenyl, and hexynyl.

[0031] Halogen includes fluorine, chlorine, bromine and iodine.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] In some embodiments, the cyclic sulfone compound includes at least one of sulfolane (SL), methylsulfolane (MSL), and 2-fluorosulfolane (FSL).

[0036] In some embodiments, the fluorinated saturated cyclic carbonate comprises at least one of the compounds represented by Formula II,

[0037]

[0038] In formula II, 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 a fluorine atom or a fluorinated C1-C6 alkyl group, Q1 does not exist or Q1 is selected from C1-C6 alkylene group.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] In some embodiments, in Formula II, R5, R6, R7 and R8 are independently selected from a hydrogen atom, a fluorine atom, a C1-C4 alkyl group or a fluorinated C1-C4 alkyl group, and at least one of R5, R6, R7 and R8 is a fluorine atom, and Q1 is absent or Q1 is selected from a methylene group or an ethylene group.

[0043] In some embodiments, in Formula II, 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 is absent or Q1 is selected from methylene groups or ethylene groups.

[0044] In some embodiments, the fluorinated saturated cyclic carbonate includes at least one of fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), and trifluoropropylene carbonate (TFPC).

[0045] In some embodiments, the unsaturated cyclic carbonate comprises at least one of the compounds of formula III-1 and formula III-2,

[0046]

[0047] In formula III-1, R9 and R 10 Independently selected from a hydrogen atom or a C1-C6 alkyl group;

[0048] In Formula III-2, R 11 , R 12 , R 13 and R 14 are independently selected from a hydrogen atom, a C1-C6 alkyl group, a C2-C6 alkenyl group or a C2-C6 alkynyl group, and R 11 , R 12 , R 13 and R 14 At least one of them is C2-C6 alkenyl or C2-C6 alkynyl.

[0049] In some embodiments, in Formula III-1, R9 and R 10 are independently selected from hydrogen atom or C1-C4 alkyl; in formula III-2, R 11 , R 12 , R 13 and R 14 are independently selected from a hydrogen atom, a C1-C4 alkyl group, a C2-C4 alkenyl group or a C2-C4 alkynyl group, and R 11 , R 12 , R 13 and R 14 At least one of them is C2-C4 alkenyl or C2-C4 alkynyl.

[0050] In some embodiments, the unsaturated cyclic carbonate includes at least one of vinylene carbonate (VC) and vinyl ethylene carbonate (VEC).

[0051] In some embodiments, the mass percentage of the unsaturated cyclic carbonate in the electrolyte is 0.2%-2.5%, illustratively 0.2%, 0.4%, 0.6%, 0.8%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, 2.2%, 2.4%, 2.5% or a range consisting of any two of these values.

[0052] In some embodiments, the oxalate compound comprises at least one of the compounds of Formula IV-1, Formula IV-2 and Formula IV-3,

[0053]

[0054] In Formula IV-2, R 15 and R 16 Each is independently selected from substituted or unsubstituted C1-C6 alkyl, substituted or unsubstituted C1-C6 alkoxy or halogen, wherein the substituted substituent is selected from halogen, and the halogen is selected from fluorine, chlorine, bromine or iodine.

[0055] In some embodiments, in Formula IV-2, R 15 and R 16 Each is independently selected from fluorine-substituted C1-C4 alkyl, fluorine-substituted C1-C4 alkoxy or fluorine.

[0056] In some embodiments, the oxalate compound includes at least one of lithium dioxalatoborate (LiBOB), lithium difluorooxalatoborate (LiDFOB), and lithium difluorodioxalatophosphate (LiDFOP).

[0057] In some embodiments, the mass percentage of the oxalate compound in the electrolyte is 0.2%-2.5%, illustratively 0.2%, 0.4%, 0.6%, 0.8%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, 2.2%, 2.4%, 2.5%, or a range consisting of any two of these values.

[0058] In some embodiments, the sulfur-containing compound includes at least one of the sulfonates of Formula V-1 and Formula V-2,

[0059]

[0060] In formula V-1, Q2 and Q3 are independently selected from C1-C6 alkylene;

[0061] In formula V-2, R 17 , R18 , R 19 and R 20 Q4 is independently selected from a hydrogen atom or a C1-C6 alkyl group, Q4 is absent or Q4 is selected from a C1-C6 alkylene group, a C2-C6 alkenylene group.

[0062] In some embodiments, in Formula V-1, Q4 and Q5 are independently selected from C1-C4 alkylene, such as methylene or ethylene; in Formula V-2, R 17 , R 18 , R 19 and R 20 Q4 is independently selected from a hydrogen atom or a C1-C4 alkyl group, Q4 is absent or Q4 is selected from a C1-C4 alkylene group, a C2-C4 alkenylene group.

[0063] In some embodiments, the sulfonate includes at least one of methylene methyl disulfonate (MMDS), ethylene ethyl disulfonate, 1,3-propane sultone (1,3-PS), 1-propylene-1,3-sultone (PST), and 1,4-butane sultone (1,4-BS). In some embodiments, the sulfonate includes at least one of methylene methyl disulfonate, 1,3-propane sultone, and 1-propylene-1,3-sultone.

[0064] In some embodiments, the sulfur-containing compound includes at least one of the sulfates shown in Formula V-3,

[0065]

[0066] In formula V-3, R 21 , R 22 , R 23 and R 24 Q5 is independently selected from a hydrogen atom or a C1-C6 alkyl group, Q5 is absent or Q5 is selected from a C1-C6 alkylene group.

[0067] In some embodiments, in Formula V-3, R 21 , R 22 , R 23 and R 24 Q5 is independently selected from a hydrogen atom or a C1-C4 alkyl group, Q5 is absent or Q5 is selected from a C1-C4 alkylene group.

[0068] In some embodiments, in Formula VI, R 20 , R 21 , R 22 , R 23 are independently selected from hydrogen, methyl, ethyl, n-propyl or isopropyl, and Q7 is absent.

[0069] In some embodiments, the sulfate ester includes at least one of ethylene sulfate (DTD), 4-methylethylene sulfate (PCS), 4-ethylethylene sulfate (PES), 4-propylethylene sulfate (PEGLST) and propylene sulfate (TS). In some embodiments, the sulfate ester includes ethylene sulfate.

[0070] In some embodiments, the mass percentage of the sulfur-containing compound in the electrolyte is 0.6%-4%, illustratively 0.6%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, or a range consisting of any two of these values.

[0071] In some embodiments, the electrolyte includes a solvent and an additive, the solvent includes 41%-83% of the non-fluorinated linear carbonate and 15%-40% of the cyclic sulfone compound, the additive includes 1%-10% of the fluorinated saturated cyclic carbonate, 0.2%-2.5% of the unsaturated cyclic carbonate, 0.2%-2.5% of the oxalate compound and 0.6%-4% of the sulfur-containing compound, and the percentages are based on the total mass of the electrolyte.

[0072] In some embodiments, the electrolyte includes a solvent and an additive, the solvent includes 50%-80% of the non-fluorinated linear carbonate and 20%-40% of the cyclic sulfone compound, the additive includes 1%-8% of the fluorinated saturated cyclic carbonate, 0.2%-2.5% of the unsaturated cyclic carbonate, 0.2%-2.5% of the oxalate compound and 0.6%-4% of the sulfur-containing compound, and the percentages are based on the total mass of the electrolyte.

[0073] 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). In some embodiments, the lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethylsulfonyl)imide. In some embodiments, the lithium salt includes lithium hexafluorophosphate. In some embodiments, the lithium salt includes lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide.

[0074] In some embodiments, the concentration of the lithium salt in the electrolyte is 0.8mol / L-2mol / 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 0.8mol / L, 0.9mol / L, 1mol / L, 1.1mol / L, 1.2mol / L, 1.3mol / L, 1.4mol / L, 1.5mol / L, 1.6mol / L, 1.8mol / L, 2mol / L or a range consisting of any two of these values. In some embodiments, the concentration of the lithium salt in the electrolyte is 0.8mol / L-1.5mol / L.

[0075] In some embodiments, the electrolyte may further include other additives as long as they do not impair the achievement of the purpose of the invention of the present application.

[0076] A second aspect of the present application provides a secondary battery, which includes a positive electrode sheet, a negative electrode sheet, and the electrolyte described in the first aspect.

[0077] 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, 0.5≤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.

[0078] In some embodiments, m is 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1, or a range consisting of any two of these values. In some embodiments, n is 0, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, or a range consisting of any two of these values.

[0079] In some embodiments, the lithium nickel transition metal oxide includes at least one of NCM523, NCM622, NCM811, Ni90 (ie, NCM90), Ni92 (ie, NCM92), and Ni95 (ie, NCM900).

[0080] In some embodiments, the lithium nickel transition metal oxide may further include a coating layer. The components of the coating layer exemplarily include at least one of lithium metaaluminate, aluminum oxide, lithium borate, or lithium boride.

[0081] In some embodiments, the positive electrode active material includes at least one selected from phosphate-based compounds represented by the formula LiMn k B (1-k) PO4, where 0 ≤ k ≤ 1, and B is selected from at least one of iron, cobalt, magnesium, calcium, zinc, chromium, and lead. In some embodiments, k is 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 formed by any two of these values. In some embodiments, the phosphate-based compound includes lithium iron phosphate, LiMn 0.6 Fe 0.4 PO4, or LiMn 0.8 Fe 0.2 PO4, or at least one of them.

[0082] In some embodiments, the positive electrode sheet further includes a binder and a conductive agent. In some embodiments, the binder includes, but is not limited to, polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, and polyvinylpyrrolidone. In some embodiments, the conductive agent includes, but is not limited to, carbon nanotubes, natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, and carbon fiber.

[0083] In some embodiments, the positive electrode sheet 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.

[0084] In some embodiments, the negative electrode sheet includes a negative electrode active material selected from silicon-based materials. In some embodiments, the silicon-based material includes at least one of silicon oxides and silicon carbide compounds. In the present application, the silicon oxide refers to a compound having 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.

[0085] In some embodiments, the negative electrode active material further includes a carbon-based material. In some embodiments, the carbon-based material includes at least one of artificial graphite, natural graphite, soft carbon, hard carbon, carbon nanotubes, and graphene. In some embodiments, the carbon-based material includes artificial and / or natural graphite.

[0086] In some embodiments, the mass percentage of 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 consisting of any two of these values. In some embodiments, the mass percentage of silicon-based material in the negative electrode active material is 12%-35%.

[0087] 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.

[0088] 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.

[0089] 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.

[0090] 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.

[0091] A third aspect of the present application provides a device, which includes the secondary battery described in the second aspect.

[0092] 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.

[0093] 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.

[0094] In some embodiments, the shape of the secondary battery is not particularly limited, and it can be cylindrical, square, or any other shape.

[0095] 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.

[0096] 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.

[0097] 2. Device

[0098] 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.

[0099] 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.

[0100] 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.

[0101] Example

[0102] In this application, unless otherwise specified, all materials or reagents used are commercially available, and all methods used are conventional methods in the art.

[0103] Test Method

[0104] 1. Battery 25℃ cycle performance test

[0105] 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%.

[0106] 2. Capacity recovery test of battery stored at 55°C for 56 days

[0107] At 25°C, charge the lithium-ion battery to 4.25V at a constant current of 0.5C, charge it to 0.05C at a constant voltage at 4.25V, and then discharge it to 2.5V at a constant current of 1C, and record the discharge capacity Q1. Then charge the lithium-ion battery to 4.25V at a constant current of 0.5C, charge it to 0.05C at a constant voltage at 4.25V, and place the fully charged battery in a constant temperature box, and set the temperature of the incubator to 55°C±2°C. After being stored at 55°C for 56 days, discharge it to 2.5V at a constant current of 1C, then charge the lithium-ion battery to 4.25V at a constant current of 0.5C, charge it to 0.05C at a constant voltage at 4.25V, and then discharge it to 2.5V at a constant current of 1C, and record the discharge capacity Q2 at this time.

[0108] The capacity recovery rate of the battery after storage at 55°C for 56 days was calculated using the following formula: Q2 / Q1×100%.

[0109] 3. Gas production test of batteries stored at 55°C for 56 days

[0110] The lithium-ion battery was discharged to 2.5V at 1C constant current at 25°C, then charged to 4.25V at 0.5C constant current, and then charged to 0.05C at 4.25V. The full-charge thickness of the battery was measured using a PPG soft-pack battery thickness gauge and recorded as a. The battery stored at 55°C for 56 days according to the above test method 2 was charged to 4.25V at 0.5C constant current, and then charged to 0.05C at 4.25V. The full-charge thickness of the battery was measured using a PPG soft-pack battery thickness gauge and recorded as b. The calculation formula for the expansion rate of the battery cell thickness when the battery was stored at 55°C for 56 days is: (ba) / a×100%.

[0111] 4. Battery hot box test

[0112] 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.

[0113] Example 1

[0114] 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 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. Coat the positive electrode slurry evenly on both surfaces of a 12-μm-thick aluminum foil current collector, and after drying, rolling, and slitting, a positive electrode plate is obtained.

[0115] The preparation steps of the negative electrode plate are as follows: Mix silicon oxide-graphite composite (the mass ratio of silicon oxide SiOx (0.5 < x < 1.5) to artificial graphite is 20:80), conductive agent acetylene black, binder styrene-butadiene rubber SBR, thickener sodium carboxymethyl cellulose 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. Coat the negative electrode slurry on both surfaces of an 8-μm-thick copper foil current collector, and after drying, rolling, and slitting, a negative electrode plate is obtained.

[0116] Separator: Use a PP / PE / PP three-layer composite separator.

[0117] Electrolyte preparation: In a glove box under argon protection (H2O < 0.1 ppm, O2 < 0.1 ppm), mix the solvents ethylene methyl carbonate (EMC) and sulfolane (SL) in a mass ratio of EMC:SL = 73:20, add lithium hexafluorophosphate (LiPF6), and prepare a solution with a lithium salt concentration of 1 mol / L. Then add additives fluoroethylene carbonate (FEC) at 3 wt% of the electrolyte mass, vinylene carbonate (VC) at 1%, propane sultone (PS) at 1%, ethylene sulfate (DTD) at 1%, and lithium bis(oxalato)borate (LiBOB) at 1% with respect to the electrolyte mass, and stir evenly to obtain the lithium-ion battery electrolyte of Example 1.

[0118] Preparation of lithium-ion battery (cell): Stack the prepared positive electrode plate, separator, and negative electrode plate in sequence, with the separator in the middle of the positive and negative electrode plates, and wind them to obtain a bare cell; Place the bare cell in an aluminum-plastic film outer package, inject the prepared lithium-ion battery electrolyte after sufficient drying, and the injection coefficient is 1.7 g / Ah. After the battery is left standing at 45°C for 48 h, subjected to high-temperature fixture formation (formation conditions are: temperature 45°C, pressure 210 kgf, charge at 0.05C current to 4.2V, stand for 60 min, then charge at 0.1C to 4.2V, and then discharge at 0.2C to 3.0V, and repeat this twice), and secondary sealing, perform conventional capacity grading, and finally obtain a lithium-ion battery with a rated capacity of ~75 Ah.

[0119] Examples 2 to 10 and Comparative Examples 1 to 7

[0120] Examples 2 to 10 and Comparative Examples 1 to 7 are based on Example 1 by adjusting the content of EMC in the solvent, the type and content of the cyclic sulfone compound, the content of the additives FEC and VC, and the type and content of the sulfur-containing compound and the oxalate compound. Specific adjustment measures and detailed data are shown in Table 1.

[0121] Table 1

[0122]

[0123]

[0124] The test results of the lithium ion batteries of Examples 1-10 and Comparative Examples 1-7 are shown in Table 2.

[0125] Table 2

[0126]

[0127]

[0128] *: Indicates that the battery capacity retention rate is less than 60% at a cycle before 400 cycles.

[0129] 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. An electrolyte comprising a lithium salt, a solvent and an additive, wherein: The solvent includes a non-fluorinated linear carbonate and a cyclic sulfone compound, the additive includes a fluorinated saturated cyclic carbonate, an unsaturated cyclic carbonate, an oxalate compound and a sulfur-containing compound, the oxalate compound includes at least one of lithium oxalate borate and lithium oxalate phosphate, the sulfur-containing compound includes at least one of a sulfonate and a sulfate, The mass percentage of the cyclic sulfone compound in the electrolyte is A%, and the mass percentage of the additive in the electrolyte is C%, wherein 2≤A / C≤6.5, and 3≤C≤16.

2. The electrolyte according to claim 1, characterized in that: The electrolyte meets at least one of the following conditions: (a) 15≤A≤40, (b) 5≤C≤12, (c)2.5≤A / C≤6.

3. The electrolyte according to claim 1 or 2, characterized in that The mass percentage of the fluorinated saturated cyclic carbonate in the electrolyte is B%, wherein 3≤A / B≤16.

4. The electrolyte according to claim 3, characterized in that The electrolyte meets at least one of the following conditions: (d)1≤B≤10, (e)5≤A / B≤14.

5. The electrolyte 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.

6. The electrolyte according to claim 1 or 2, characterized in that: The electrolyte meets at least one of the following conditions: (f) the sulfone compound comprises at least one of sulfolane, methyl sulfolane and 2-fluorosulfolane, (g) the fluorinated saturated cyclic carbonate comprises at least one of fluoroethylene carbonate, difluoroethylene carbonate and trifluoropropylene carbonate, (h) the unsaturated cyclic carbonate comprises at least one of vinylene carbonate and vinyl ethylene carbonate, (i) the oxalate compound comprises at least one of lithium dioxalatoborate, lithium difluorooxalatoborate and lithium difluorodioxalatophosphate, (j) the sulfur-containing compound comprises at least one of methylene disulfonate, 1,3-propane sultone, 1-propylene-1,3-sultone and vinyl sulfate, (k) the non-fluorinated linear carbonate comprises at least one of dimethyl carbonate, ethyl methyl carbonate and diethyl carbonate, (l) the lithium salt comprises at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethylsulfonyl)imide, (m) The concentration of lithium salt in the electrolyte is 0.8 mol / L-2 mol / L.

7. The electrolyte according to claim 1 or 2, characterized in that: The mass percentage of the non-fluorinated linear carbonate in the electrolyte is 50%-80%, The mass percentage of the unsaturated cyclic carbonate in the electrolyte is 0.2%-2.5%, The mass percentage of the oxalate compound in the electrolyte is 0.2%-2.5%, The mass percentage of the sulfur-containing compound in the electrolyte is 0.6%-4%.

8. A secondary battery comprising a positive electrode sheet, a negative electrode sheet and the electrolyte according to any one of claims 1 to 7.

9. The secondary battery according to claim 8, characterized in that: 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, 0.5≤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; and / or, The negative electrode plate includes a negative electrode active material selected from silicon-based materials, the silicon-based material includes at least one of silicon oxide compounds and silicon carbon compounds, and the mass percentage of the silicon-based material in the negative electrode active material is 10%-40%. 10 . A device comprising the secondary battery according to claim 8 or 9 .

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