Electrolyte, secondary battery and device containing the same

Abstract

The application relates to an electrolyte, a secondary battery containing the electrolyte and a device. 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 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 a lithium oxalate borate and a 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. The electrolyte balances the normal-temperature cycle performance and the high-temperature safety performance of a lithium ion battery.

Description

TECHNICAL FIELD

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

[0002] With the increasing renewal of technology life, the demand for high specific energy lithium ion batteries with long cycle life and high safety is increasingly obvious. However, high specific energy lithium ion batteries often bring higher safety hazards and shorter cycle life. Therefore, it is urgent to develop a high safety and long cycle electrolyte for high specific energy lithium ion batteries. SUMMARY

[0003] In view of the safety hazards and cycle decay of high specific energy lithium ion batteries, the present application uses a combination solvent containing a high oxidation-resistant and low-heat cyclic sulfone compound and a non-fluorinated linear carbonate, and a combination additive containing a certain amount of fluorinated saturated cyclic carbonate, unsaturated cyclic carbonate, oxalate compound and sulfur-containing compound, which takes into account the room temperature cycle performance and high temperature safety performance of lithium ion batteries.

[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 oxalate borate and lithium oxalate 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%, wherein 2≤A / C≤6.5 and 3≤C≤16.

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

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

[0007] The beneficial effects of the present application are:

[0008] The electrolyte of the present application introduces a combined solvent of non-fluorinated linear carbonate and cyclic sulfone compound and a combined additive of fluorinated saturated cyclic carbonate, unsaturated cyclic carbonate, oxalate compound and sulfur-containing compound, and controls the content ratio of the cyclic sulfone compound and the additive, while ensuring the lithium ion transmission capacity of the electrolyte, taking into account the room temperature cycle performance, thermal stability, high temperature storage safety and high temperature electrochemical stability of the lithium ion battery. Under the premise of ensuring that the room temperature cycle performance of the lithium ion battery is 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 high temperature capacity recovery rate of the battery is improved. DETAILED DESCRIPTION

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

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

[0011] The list of items connected by the term "at least one of," "at least one," or other similar terms, can mean any combination of the listed items. For example, if the 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 can include a single component or multiple components. Item B can include a single component or multiple components. Item C can include a single component or multiple components.

[0012] The optional scope of the term "and / or" includes any one of two or more related listed items, as well as any and all combinations of the related listed items, including a combination of any two related listed items, any more related listed items, or all related listed items.

[0013] The term "comprising" or "including" is an open term that includes both the listed features and the optional features consisting of the listed features.

[0014] The present application is further described in the detailed description that follows, with an understanding that both the

[0015] Primary and secondary batteries

[0016] A first aspect of the present application provides an electrolyte solution 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 a lithium oxalate borate salt and a lithium oxalate phosphate salt, the sulfur-containing compound comprises at least one of a sulfonate and a sulfate, the mass percentage content of the cyclic sulfone compound in the electrolyte solution is A%, the mass percentage content of the additive in the electrolyte solution is C%, wherein 2≤A / C≤6.5 and 3≤C≤16. A / C within the above range can enable better synergy between the solvent and the additive, so that the secondary battery has more excellent thermal stability and safety while also having excellent cycle performance.

[0017] In some embodiments, 15≤A≤40. A is exemplarily 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 also insufficient to effectively dissociate the lithium salt, thereby resulting in low capacity development of the secondary battery. If A is too high, the viscosity of the electrolyte solution is too large, which affects the kinetic performance and room temperature cycle performance of the secondary battery.

[0018] In some embodiments, C is exemplarily 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 and uniform solid-state interfacial film cannot be formed, so that the side reaction between the electrode and the electrolyte solution cannot be effectively alleviated, and the cycle performance of the secondary battery cannot be effectively improved. If C is too high, the interfacial impedance of the secondary battery is easily increased, and the battery kinetic loss is increased, thereby degrading 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 transport performance is weak, the interface impedance of the secondary battery is increased, and both the safety and the kinetics 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 non-uniform interface film also easily causes lithium precipitation from the cell, thereby affecting the safety of the battery, and at the same time, in the long cycle process, the defects of the interface film cannot be repaired in time, thereby accelerating the capacity decay of the battery and degrading the cycle performance.

[0020] In some embodiments, the mass percentage content 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, corresponding to A being too low or B being too high, the capacity performance, cycle performance, thermal stability, and safety of the battery are degraded. If A / B is too large, corresponding to A being too high or B being too low, the power performance and cycle performance of the battery are degraded.

[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 is affected. If B is too high, gas production problems during high-temperature cycling are easily caused, and the intensified gas production reduces the thermal stability of the battery and degrades the safety of the battery, and at the same time, a too high content of fluorinated carbonate intensifies the harm after thermal runaway of the battery.

[0022] In this application, the non-fluorinated linear carbonate is a solvent commonly used in the art for secondary batteries. 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 non-fluorinated linear carbonate has a mass percentage in the electrolyte solution of 41-83%. Exemplary values include 41%, 43%, 45%, 48%, 50%, 52%, 55%, 58%, 60%, 62%, 65%, 68%, 70%, 72%, 75%, 78%, 80%, 83%, or a range defined by any two of these values. In some embodiments, the non-fluorinated linear carbonate has a mass percentage in the electrolyte solution of 50-80%.

[0024] In some embodiments, the total mass of the non-fluorinated linear carbonate and the cyclic sulfone compound is greater than 98% of the mass of the solvent, for example, greater than 98.5%, greater than 98.8%, greater than 99%, greater than 99.2%, greater than 99.5%, greater than 99.8%. In some embodiments, the solvent does not include an ether.

[0025] In some embodiments, the solvent does not include ethylene carbonate and / or propylene carbonate. Preferably, the solvent does not include a non-fluorinated saturated cyclic carbonate. Here, "does not include" 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%. The inventors have found that replacing a 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 includes at least one selected from the compounds shown in Formula I,

[0027]

[0028] In Formula I, R1, R2, R3, and R4are independently selected from a hydrogen atom, a halogen atom, a C1-C6alkyl group, a C2-C6alkenyl group, a C2-C6alkynyl group, a halogenated C1-C6alkyl group, a halogenated C2-C6alkenyl group, or a halogenated C2-C6alkynyl group.

[0029] In this application, C2-C6alkenyl groups include, but are not limited to, ethenyl, propenyl, allyl, isopropenyl, n-butenyl, isobutenyl, t-butenyl, n-pentenyl, isopentenyl, hexenyl, cyclohexenyl.

[0030] C2-C6alkynyl groups include, but are not limited to, ethynyl, n-propynyl, isopropynyl, n-butynyl, isobutynyl, n-pentynyl, isopentynyl, hexynyl.

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

[0032] In some embodiments, in Formula I, R1, R2, R3, and R4are independently selected from a hydrogen atom, a halogen atom, a C1-C6alkyl group, or a halo-C1-C6alkyl group.

[0033] In some embodiments, in Formula I, R1, R2, R3, and R4are independently selected from a hydrogen atom, a fluorine atom, a C1-C4alkyl group, or a fluoro-C1-C4alkyl group.

[0034] In some embodiments, in Formula I, R1, R2, R3, and R4are 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 comprises at least one of sulfolane (SL), methylsulfolane (MSL), and 2-fluorosulfolane (FSL).

[0036] In some embodiments, the fluoro-saturated cyclic carbonate compound comprises at least one of the compounds shown in Formula II,

[0037]

[0038] In Formula II, R5, R6, R7, and R8are independently selected from a hydrogen atom, a fluorine atom, a C1-C6alkyl group, or a fluoro-C1-C6alkyl group, and at least one of R5, R6, R7, and R8is a fluorine atom or a fluoro-C1-C6alkyl group, and Q1is absent or Q1is selected from a C1-C6alkylene group.

[0039] In this application, C1-C6alkyl includes, but is not limited to, methyl, ethyl, n-propyl, iso-propyl, cyclopropyl, n-butyl, iso-butyl, sec-butyl, tert-butyl, cyclobutyl, n-pentyl, iso-pentyl, neopentyl, cyclopentyl, n-hexyl, iso-hexyl, cyclohexyl.

[0040] In this application, fluoro-C1-C6alkyl includes, but is not limited to, fluoro-methyl, fluoro-ethyl, fluoro-n-propyl, fluoro-iso-propyl, fluoro-n-butyl, fluoro-iso-butyl, fluoro-tert-butyl, fluoro-n-pentyl, fluoro-iso-pentyl, fluoro-n-hexyl. Wherein, fluoro means at least one hydrogen atom in C1-C6alkyl is replaced by a fluorine atom. In some embodiments, fluoro-C1-C6alkyl is selected from monofluoromethyl, difluoromethyl, trifluoromethyl, monofluoroethyl, difluoroethyl, trifluoroethyl, pentafluoroethyl, or hexafluoro-iso-propyl.

[0041] In this application, C1-C6alkylene includes, but is not limited to, methylene, ethylene, n-propylene, iso-propylene, cyclopropylene, n-butylene, iso-butylene, sec-butylene, tert-butylene, cyclobutylene, n-pentylene, iso-pentylene, neopentylene, cyclopentylene, n-hexylene, iso-hexylene, cyclohexylene.

[0042] In some embodiments, in Formula II, R5, R6, R7, and R8are independently selected from a hydrogen atom, a fluorine atom, a C1-C4alkyl group, or a fluorinated C1-C4alkyl group, and at least one of R5, R6, R7, and R8is a fluorine atom, and Q1is absent or Q1is selected from a methylene group or an ethylene group.

[0043] In some embodiments, in Formula II, R5, R6, R7, and R8are 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, and at least one of R5, R6, R7, and R8is a fluorine atom, and Q1is absent or Q1is selected from a methylene group or an ethylene group.

[0044] In some embodiments, the fluorinated saturated cyclic carbonate includes at least one of fluorinated ethylene carbonate (FEC), difluorinated ethylene carbonate (DFEC), and trifluorinated propylene carbonate (TFPC).

[0045] In some embodiments, the unsaturated cyclic carbonate includes at least one of a compound described in Formula III-1 and Formula III-2,

[0046]

[0047] In Formula III-1, R9and R 10 are independently selected from a hydrogen atom or a C1-C6alkyl group;

[0048] In Formula III-2, R 11 , R 12 , R 13 , and R 14 are independently selected from a hydrogen atom, a C1-C6alkyl group, a C2-C6alkenyl group, or a C2-C6alkynyl group, and at least one of R 11 , R 12 , R 13 , and R 14 is a C2-C6alkenyl group or a C2-C6alkynyl group.

[0049] In some embodiments, in Formula III-1, R9and R 10 are independently selected from a hydrogen atom or a C1-C4alkyl group; and in Formula III-2, R 11 , R 12 , R 13 , and R 14 are independently selected from a hydrogen atom, a C1-C4alkyl group, a C2-C4alkenyl group, or a C2-C4alkynyl group, and at least one of R 11 , R 12 , R 13 , and R 14 is a C2-C4alkenyl group or a C2-C4alkynyl group.

[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% to 2.5%. Exemplary values are 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 between any two of these values.

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

[0053]

[0054] In Formula IV-2, R 15 and R 16 are each independently selected from substituted or unsubstituted C1-C6 alkyl, substituted or unsubstituted C1-C6 alkoxy, or halogen, wherein the substituents of the substitution are 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 are each 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 bis(oxalato)borate (LiBOB), lithium bis(fluorosulfonyl)oxalate (LiDFOB), and lithium difluorophosphate bis(oxalate) (LiDFOP).

[0057] In some embodiments, the mass percentage of the oxalate compound in the electrolyte is 0.2% to 2.5%. Exemplary values are 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 between any two of these values.

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

[0059]

[0060] In Formula V-1, Q2and Q3are independently selected from C1-C6 alkylene;

[0061] In Formula V-2, R 17 , R18 R 19 and R 20 are independently selected from a hydrogen atom or a C1-C6 alkyl group, and 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 a C1-C4 alkylene group, such as methylene or ethylene; in formula V-2, R 17 R 18 R 19 and R 20 are independently selected from a hydrogen atom or a C1-C4 alkyl group, and Q4 is absent or Q4 is selected from a C1-C4 alkylene group, a C2-C4 alkenylene group.

[0063] In some embodiments, the sulfonic acid ester comprises at least one of methylene methanedisulfonate (MMDS), ethylene ethanedisulfonate, 1,3-propane sultone (1,3-PS), 1-propene-1,3-sultone (PST), and 1,4-butane sultone (1,4-BS). In some embodiments, the sulfonic acid ester comprises at least one of methylene methanedisulfonate, 1,3-propane sultone, and 1-propene-1,3-sultone.

[0064] In some embodiments, the sulfur-containing compound comprises at least one of the sulfates of formula V-3,

[0065]

[0066] In formula V-3, R 21 R 22 R 23 and R 24 are independently selected from a hydrogen atom or a C1-C6 alkyl group, and 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 are independently selected from a hydrogen atom or a C1-C4 alkyl group, and 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 a hydrogen atom, a methyl group, an ethyl group, a n-propyl group, or an i-propyl group, and Q7 is absent.

[0069] In some embodiments, the sulfuric acid ester includes at least one of vinyl sulfate (DTD), 4-methyl ethylene sulfate (PCS), 4-ethyl ethylene sulfate (PES), 4-propyl ethylene sulfate (PEGLST), and propylene sulfate (TS). In some embodiments, the sulfuric acid ester includes vinyl sulfate.

[0070] In some embodiments, the mass percentage of the sulfur-containing compound in the electrolyte is 0.6% to 4%. Exemplary are 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 between any two of these values.

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

[0072] In some embodiments, the electrolyte includes a solvent and an additive, the solvent includes 41% to 83% of the non-fluorinated linear carbonate and 15% to 40% of the cyclic sulfone compound, the additive includes 1% to 10% of the fluorinated saturated cyclic carbonate, 0.2% to 2.5% of the unsaturated cyclic carbonate, 0.2% to 2.5% of the oxalate compound, and 0.6% to 4% of the sulfur-containing compound, the percentages being 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 triflate (LiOTf), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), lithium (trifluoromethylsulfonyl)(perfluorobutylsulfonyl)imide (LiFNFSI), and lithium bis(pentafluoroethylsulfonyl)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 0.8-2 mol / L. The concentration of the lithium salt is exemplarily 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.8, 2 mol / L or a range between any two of these values. In some embodiments, the concentration of the lithium salt in the electrolyte is 0.8-1.5 mol / L.

[0075] In some embodiments, the electrolyte can further include other additives as long as it does not impair the realization of the purpose of the application.

[0076] The second aspect of the application provides a secondary battery, which comprises a positive electrode sheet, a negative electrode sheet and the electrolyte of the first aspect.

[0077] In some embodiments, the positive electrode sheet comprises a positive electrode active material, which comprises at least one lithium nickel transition metal oxide selected from the group consisting of 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, 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 represented by 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, iron, titanium, copper, zinc, chromium, calcium, barium and tungsten, 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 between 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 between any two of these values.

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

[0080] In some embodiments, the lithium nickel transition metal oxide can further include a coating layer. The composition of the coating layer can illustratively include at least one of lithium meta-aluminate, aluminum oxide, lithium borate, or lithium boride.

[0081] In some embodiments, the positive active material includes at least one selected from the group consisting of lithium manganese phosphate compounds represented by the formula LiMn k B (1-k) 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 between any two of these values. In some embodiments, the lithium manganese phosphate compound includes lithium iron phosphate, LiMn 0.6 Fe 0.4 PO4, or LiMn 0.8 Fe 0.2 PO4.

[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, 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 fibers.

[0083] In some embodiments, the positive electrode sheet further includes a positive current collector, which includes an aluminum foil or a polymer substrate coated with a conductive metal.

[0084] In some embodiments, the negative electrode sheet includes a negative active material selected from a silicon-based material. In some embodiments, the silicon-based material includes at least one of a silicon oxide compound and a silicon carbon compound. In the present application, the silicon oxide compound refers to a compound having a general formula of SiOx, where 0.5

[0085] In some embodiments, the negative 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 the silicon-based material in the negative active material is 10-40%, illustratively 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, or a range defined by any two of these values. In some embodiments, the mass percentage of the silicon-based material in the negative active material is 12-35%.

[0087] In some embodiments, the negative electrode sheet further comprises 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, 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, carbon fibers.

[0088] In some embodiments, the negative electrode sheet further comprises a negative current collector, which comprises: a copper foil, a nickel foil, a stainless steel foil, a titanium foil, a nickel foam, a 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 sheet and the negative electrode sheet to prevent short circuiting. The material and shape of the separator that can be used in the embodiments of the present application are not particularly limited and can be any of the techniques disclosed in the prior art. In some embodiments, the separator comprises a polymer or inorganic substance formed of a material stable to the electrolyte of the present application, etc.

[0090] For example, the separator can include a base material layer and a surface treatment layer. The base material layer is a non-woven fabric, a film, or a composite film having a porous structure, and the material of the base material 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 base material layer, and the surface treatment layer can be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic substance.

[0091] The third aspect of the present application provides a device, which comprises the secondary battery of 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 can include an outer package, which can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the secondary battery can also be a soft package, such as a pouch soft package. The material of the soft package can 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, which can be cylindrical, square, or any other shape.

[0095] In some embodiments, the present application also 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 also provides a battery pack, which includes the above-mentioned battery module. The number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0097] II. 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, an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an energy storage system, etc. In order to meet the high power and high energy density requirements of the secondary battery for the device, a battery pack or a battery module can be used.

[0100] In other embodiments, the device can be a mobile phone, a tablet computer, a notebook computer, etc. The device usually requires thinning, and a secondary battery can be used as a power source.

[0101] Embodiments

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

[0103] Test methods

[0104] 1. Battery 25℃ cycle performance test

[0105] The lithium ion battery was charged at 0.5 C to 4.25 V at 25 °C, and then charged at 4.25 V to 0.05 C, and then discharged at 1 C to 2.5 V. After 400 cycles of charging and discharging, the capacity retention rate after 400 cycles at 25 °C was calculated according to the following formula: discharge capacity after 400 cycles / initial cycle discharge capacity x 100%.

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

[0107] The lithium ion battery was charged at 0.5 C to 4.25 V at 25 °C, and then charged at 4.25 V to 0.05 C, and then discharged at 1 C to 2.5 V, and the discharge capacity Q1 was recorded. The lithium ion battery was then charged at 0.5 C to 4.25 V, and then charged at 4.25 V to 0.05 C, and then placed in a constant temperature oven with a temperature of 55 °C ± 2 °C. After 56 days of storage at 55 °C, the battery was discharged at 1 C to 2.5 V, and then charged at 0.5 C to 4.25 V, and then charged at 4.25 V to 0.05 C, and then discharged at 1 C to 2.5 V, and the discharge capacity Q2 was recorded.

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

[0109] 3. Gas production test of battery 55 °C storage for 56 days

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

[0111] 4. Battery hot box test

[0112] The hot box test procedure is as follows: at 25 °C, the battery is charged at 1 / 3 C to the rated capacity and fully charged; the fully charged battery is clamped on the fixture with a pre-tightening force of 1.5 Nm; the lithium ion battery is placed in a temperature oven, and the temperature oven is raised from the ambient temperature to 130 °C ± 2 °C at a rate of 5 °C / min, and maintained at this temperature for 60 min; the temperature oven continues to rise at a rate of 5 °C / min for another 10 °C, and maintained at this temperature for 60 min; until the temperature is out of control, and the corresponding cell temperature is recorded.

[0113] Example 1

[0114] The positive electrode tab preparation procedure was as follows: mixing positive electrode active material LiNi0.8Co0.1Mn0.1O2, conductive agent carbon black SP and binder polyvinylidene fluoride PVDF in a mass ratio of 96:2:2, then dispersing in N-methyl-2-pyrrolidone to obtain a positive electrode slurry, uniformly coating the positive electrode slurry on both sides of a 12 μm thick aluminum foil current collector, and then drying, rolling, and slitting to obtain a positive electrode tab. 0.8 Co 0.1 Mn 0.1 O2, conductive agent carbon black SP and binder polyvinylidene fluoride PVDF, then dispersing in N-methyl-2-pyrrolidone to obtain a positive electrode slurry, uniformly coating the positive electrode slurry on both sides of a 12 μm thick aluminum foil current collector, and then drying, rolling, and slitting to obtain a positive electrode tab.

[0115] The negative electrode tab preparation procedure was as follows: mixing silicon-oxygen-graphite composite (mass ratio of silicon-oxygen compound SiOx (0.5 < x < 1.5) and artificial graphite 20:80), conductive agent acetylene black, binder styrene-butadiene rubber SBR, thickening agent sodium carboxymethyl cellulose CMCNa and binder polyacrylic acid PAA in a mass ratio of 95:2:1.5:1:0.5, then dispersing in deionized water to obtain a negative electrode slurry, coating the negative electrode slurry on both sides of an 8 μm thick copper foil current collector, and then drying, rolling, and slitting to obtain a negative electrode tab.

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

[0117] Electrolyte preparation: in an argon-protected glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), solvent ethyl methyl carbonate (EMC) and sulfolane (SL) were mixed in a mass ratio of EMC:SL = 73:20, lithium hexafluorophosphate (LiPF6) was added, and a solution with a lithium salt concentration of 1 mol / L was prepared, then 3 wt% of additive fluoroethylene carbonate (FEC), 1% of additive vinylene carbonate (VC), 1% of additive propane sulfone (PS), 1% of additive ethylene sulfate (DTD) and 1% of additive lithium bis(oxalato)borate (LiBOB) were added with respect to the mass of the electrolyte, and the mixture was stirred uniformly to obtain the lithium ion battery electrolyte of Example 1.

[0118] Lithium ion battery (cell) preparation: the prepared positive electrode tab, separator and negative electrode tab were stacked in order with the separator between the positive and negative electrode tabs, and a bare cell was obtained by winding; the bare cell was placed in an aluminum-plastic film outer package, and after being fully dried, the prepared lithium ion battery electrolyte was injected, and the injection coefficient was 1.7 g / Ah. After the battery was placed at 45°C for 48 h, high-temperature fixture formation (formation conditions: temperature 45°C, pressure 210 kgf, 0.05C current charging to 4.2V, standing for 60 min, then 0.1C charging to 4.2V and then 0.2C discharging to 3.0V, and so on, repeated twice) and secondary sealing, the battery was routinely distributed, and finally a lithium ion battery with a rated capacity of ~75 Ah was obtained.

[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 oxalate compound. The 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 capacity retention rate of the battery at a certain cycle before cycle 400 is already lower than 60%.

[0129] While certain example embodiments of the application have been described and illustrated, the application is not to be limited to the embodiments disclosed herein. Rather, the disclosure describes various example embodiments of the application and is understood to include any modifications and alterations within the spirit and scope of the application as described in the claims.

Claims

1. An electrolyte comprising a lithium salt, a solvent, and an additive, wherein, The solvent comprises non-fluorinated linear carbonates and cyclic sulfone compounds, and the additives comprise fluorinated saturated cyclic carbonates, unsaturated cyclic carbonates, oxalate compounds, and sulfur-containing compounds. The oxalate compounds comprise at least one of lithium oxalate borate and lithium oxalate phosphate, and the sulfur-containing compounds comprise at least one of sulfonates and sulfates. The electrolyte contains A% by mass, B% by mass, and C% by mass, of the cyclic sulfone compound, B% by mass, and C% by mass, of the additive, wherein 2 ≤ A / C ≤ 6.5 and 3 ≤ C ≤ 16. 15≤A≤40； 1≤B≤10； 3≤A / B≤16; The sulfone compound includes at least one of sulfolane, methyl sulfolane, and 2-fluorosulfolane. The fluorosaturated cyclic carbonates include at least one of fluoroethylene carbonate, difluoroethylene carbonate and trifluoropropylene carbonate. The unsaturated cyclic carbonate includes at least one of vinylene carbonate and ethylene ethylene carbonate; The oxalate compound includes at least one of lithium dioxalatoborate, lithium difluorooxalatoborate, and lithium difluorodioxalatophosphate. The sulfur-containing compound includes at least one of methylene disulfonate, 1,3-propanesulfonyl lactone, 1-propylene-1,3-sulfonyl lactone, and vinyl sulfate.

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

3. The electrolyte according to claim 1 or 2, characterized in that, The electrolyte meets at least one of the following conditions: (c) 5 ≤ A / B ≤ 14.

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

5. The electrolyte according to claim 1 or 2, characterized in that, The electrolyte meets at least one of the following conditions: (d) The non-fluorinated linear carbonate includes at least one of dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate. (e) The lithium salt comprises at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethylsulfonyl)imide. (f) The concentration of lithium salt in the electrolyte is 0.8 mol / L-2 mol / L.

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

7. A secondary battery comprising a positive electrode, a negative electrode, and an electrolyte according to any one of claims 1-6.

8. The secondary battery according to claim 7, characterized in that, The positive electrode includes a positive active material, which includes materials selected from LiNi as shown below. m Co n A (1-m-n) Lithium-nickel transition metal oxides represented by O2 or LiMn as shown in the formula. 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, and B is selected from at least one of iron, cobalt, magnesium, calcium, zinc, chromium, and lead, 0 ≤ k ≤ 1; and / or, The negative electrode sheet includes a negative electrode active material selected from silicon-based materials, wherein the silicon-based material includes at least one of silicon oxide and silicon carbide, and the mass percentage of the silicon-based material in the negative electrode active material is 10%-40%.

9. An apparatus comprising the secondary battery as claimed in claim 7 or 8.

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