An electrolyte and a battery comprising the same

Abstract

The application provides an electrolyte and a battery comprising the electrolyte, wherein the diazonium salt compound in the electrolyte can be decomposed in advance to generate a large amount of inert gas before a large amount of organic solvent is volatilized to generate gas during a furnace temperature test, and the inert gas is discharged from the pole lug, so that the generated heat is timely released, heat accumulation in the interior is avoided, and heat runaway is avoided; on the other hand, the volatilization of the organic solvent can cause the ion channel in the battery to be closed, so that the side reaction is stopped, the battery can safely pass the furnace temperature test, and the safety of the battery under the condition of heat runaway is significantly improved. Meanwhile, the electron-deficient B element in the diazonium salt compound in the electrolyte has Lewis acidity, can accept an electron pair, can remove HF in the electrolyte, avoids the damage of HF to the interface protection film, and further improves the high-temperature storage performance of the battery.

Description

Technical Field

[0001] This invention belongs to the field of electrolyte technology for lithium-ion batteries, specifically relating to an electrolyte that can improve the furnace temperature performance and high-temperature storage performance of batteries, and a battery including the electrolyte. Background Technology

[0002] Lithium-ion batteries, as excellent energy storage devices, are widely used in portable electronic devices, electric vehicles, and energy storage. In recent years, the rapid development of electric vehicles has brought great convenience to people's travel; however, accidents involving combustion and explosion during use occur frequently, making the safety of lithium-ion batteries a current focus of attention. Research shows that lithium-ion batteries are prone to abnormal temperature increases under conditions such as overcharging, internal and external short circuits, forced high-rate discharge, and high-temperature environments. When the rate of internal heat generation exceeds the rate of heat release, the battery will experience thermal runaway, leading to unsafe behaviors such as combustion or explosion. Although battery management systems can accurately monitor and manage the voltage, current, and temperature of the battery during use and cut off the external current through the battery in abnormal situations, improving battery safety to some extent, they are often powerless against thermal runaway caused by internal short circuits. Furthermore, the national standard requires that the battery furnace temperature be tested by continuously heating the battery to 130°C and maintaining that temperature for 30 minutes, during which time the battery must not catch fire or explode. When a battery is heated to 130°C, the internal temperature becomes even higher, causing it to swell and deform due to gas production. Simultaneously, the separator contracts severely, leading to an internal short circuit. This is particularly problematic for pouch cells without a pressure relief valve, where gas cannot escape promptly, heat accumulates internally, and can trigger thermal runaway. These safety requirements for lithium-ion batteries necessitate researchers to combine more effective methods to further improve battery safety performance. Summary of the Invention

[0003] To improve battery safety, this invention provides an electrolyte that improves the furnace temperature performance of lithium-ion batteries and a battery comprising the electrolyte. The electrolyte includes a first additive, which is a diazonium salt of tetrafluoroborate. The battery assembled with the electrolyte can safely pass the furnace temperature test and significantly improves the battery's safety performance under thermal runaway conditions. Furthermore, the electrolyte can also improve the battery's high-temperature storage performance.

[0004] This invention is achieved through the following technical solutions:

[0005] An electrolyte comprising an organic solvent, an electrolyte salt, and a functional additive, wherein the functional additive comprises a first additive, which is a diazonium tetrafluoroborate compound.

[0006] According to an embodiment of the present invention, the diazonium salt of tetrafluoroborate is a compound containing a diazonium bond (-N=N-) and a tetrafluoroborate functional group (-BF4), and the diazonium bond (-N=N-) and the tetrafluoroborate functional group (-BF4) are directly connected.

[0007] According to an embodiment of the present invention, the first additive is selected from at least one of the compounds shown in formula (1):

[0008] RN = N - BF4 Equation (1)

[0009] In formula (1), R is selected from substituted or unsubstituted heteroaryl, substituted or unsubstituted aryl; if substituted, the substituent is halogen, alkyl, haloalkyl, alkoxy or cyano.

[0010] According to an embodiment of the present invention, in formula (1), R is selected from substituted or unsubstituted 5-12 member heteroaryl groups, substituted or unsubstituted C groups. 6-12 Aryl; if substituted, the substituent is a halogen or C. 1-12 Alkyl, fluorinated C 1-12 Alkyl, C 1-12 Alkyl or cyano groups.

[0011] According to an embodiment of the present invention, in formula (1), R is selected from substituted or unsubstituted 5-8 membered heteroaryl groups, substituted or unsubstituted C groups. 6-10 Aryl; if substituted, the substituent is a halogen or C. 1-6 Alkyl, fluorinated C 1-6 Alkyl, C 1-6 Alkyl or cyano groups.

[0012] According to an embodiment of the present invention, in formula (1), R is selected from substituted or unsubstituted 5-6 membered heteroaryl groups, substituted or unsubstituted C groups. 6-8 Aryl; if substituted, the substituent is a halogen or C. 1-3 Alkyl, fluorinated C 1-3 Alkyl, C 1-3 Alkyl or cyano groups.

[0013] According to an embodiment of the present invention, in formula (1), R is selected from substituted or unsubstituted thiophene group, substituted or unsubstituted phenyl group; if substituted, the substituent is fluorine, methyl, trifluoromethyl, methoxy or cyano.

[0014] According to an embodiment of the present invention, the first additive can be prepared by methods known in the art or can be obtained through commercial purchase.

[0015] According to an embodiment of the present invention, the first additive is selected from at least one of the compounds shown in Formula I-1 to Formula I-8:

[0016]

[0017] According to an embodiment of the present invention, the mass of the first additive is 0.1 wt% to 5.0 wt% of the total mass of the electrolyte, for example, 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, 1 wt%, 1.2 wt%, 1.3 wt%, 1.5 wt%, 1.6 wt%, 1.8 wt%, 2 wt%, 2.2 wt%, 2.4 wt%, 2.5 wt%, 2.6 wt%, 2.8 wt%, 3 wt%, 3.3 wt%, 3.5 wt%, 3.8 wt%, 4 wt%, 4.2 wt%, 4.5 wt%, 4.8 wt%, or 5 wt%.

[0018] According to embodiments of the present invention, the organic solvent is selected from one or more of carbonate solvents, carboxylic acid ester solvents, ether solvents, and one or more of their corresponding fluorinated fluorides.

[0019] For example, the carbonate solvent is selected from at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0020] For example, the carboxylic acid ester solvent is selected from at least one of γ-butyrolactone, methyl acetate, ethyl acetate, propyl acetate, n-butyl acetate, n-pentyl acetate, isoamyl acetate, isobutyl acetate, methyl propionate, ethyl propionate, n-propyl propionate, n-butyl propionate, methyl butyrate, and n-ethyl butyrate.

[0021] For example, the ether solvent is selected from at least one of 1,3-dioxolane, 1,3-dioxane, 1,4-dioxane, ethyl propyl ether, and ethylene glycol dimethyl ether.

[0022] According to an embodiment of the present invention, the mass of the organic solvent is 70 wt.% to 90 wt.% of the total mass of the electrolyte, for example, 70 wt.%, 75 wt.%, 80 wt.%, 85 wt.%, or 90 wt.%.

[0023] According to an embodiment of the present invention, the electrolyte salt is selected from lithium salts.

[0024] According to embodiments of the present invention, the lithium salt is selected from one or more of lithium hexafluorophosphate (LiPF6), lithium hexafluoroantimony oxide (LiSbF6), lithium hexafluoroarsenate (LiAsF6), lithium perchlorate (LiClO4), lithium difluorophosphate (LiPO2F2), lithium tetrafluoroborate (LiBF4), lithium bis(oxalate)borate (LiBOB), lithium difluorooxalateborate (LiODFB), lithium difluorobis(oxalate)phosphate (LiDFBP), lithium tetrafluorooxalate phosphate (LiOTFP), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethyl)sulfonyl)imide (LiTFSI), lithium bis(pentafluoroethyl)sulfonyl)imide (LiBETI), lithium 4,5-dicyano-2-trifluoromethyl-imidazolium (LiTDI), lithium trifluoromethanesulfonate, or lithium perfluorobutyl sulfonate.

[0025] According to an embodiment of the present invention, the mass of the electrolyte salt is 10 wt.% to 25 wt.% of the total mass of the electrolyte, for example, 10 wt.%, 12 wt.%, 13 wt.%, 14 wt.%, 15 wt.%, 16 wt.%, 17 wt.%, 18 wt.%, 19 wt.%, 20 wt.%, 21 wt.%, 22 wt.%, 23 wt.%, 24 wt.%, or 25 wt.%, and the corresponding molar concentration is 0.8 to 2 mol / L.

[0026] According to an embodiment of the present invention, the functional additive further includes a second additive, the second additive being selected from at least one of 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, succinate, adiponitrile, triacrylonitrile, 1,3,6-hexanetrionitrile, lithium difluorooxalate borate, lithium difluorophosphate, and lithium difluorodioxalate phosphate.

[0027] According to an embodiment of the present invention, the mass of the second additive is 0 to 10 wt% of the total mass of the electrolyte, for example, 0.5 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, or 10 wt%.

[0028] The present invention also provides a method for preparing the above-mentioned electrolyte, the method comprising the following steps:

[0029] The electrolyte is obtained by mixing an organic solvent, an electrolyte salt, a first additive, and optionally a second additive.

[0030] According to an embodiment of the present invention, the mixing temperature is -10℃ to 15℃, and the mixing method is stirring and / or ultrasonic mixing.

[0031] The present invention also provides a battery comprising the electrolyte described above.

[0032] According to an embodiment of the present invention, the battery is a lithium-ion battery.

[0033] According to an embodiment of the present invention, the battery further includes a positive electrode sheet containing a positive electrode active material, a negative electrode sheet containing a negative electrode active material, and a separator.

[0034] According to an embodiment of the present invention, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer coated on one or both surfaces of the positive electrode current collector, and the positive electrode active material layer includes a positive electrode active material, a conductive agent, and a binder.

[0035] According to an embodiment of the present invention, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer coated on one or both surfaces of the negative electrode current collector, and the negative electrode active material layer includes a negative electrode active material, a conductive agent, and a binder.

[0036] According to an embodiment of the present invention, the mass percentage contents of the components in the positive electrode active material layer are: 80-99.8 wt% of the positive electrode active material, 0.1-10 wt% of the conductive agent, and 0.1-10 wt% of the binder.

[0037] Preferably, the mass percentage contents of the components in the positive electrode active material layer are: 90-99.6 wt% of the positive electrode active material, 0.2-5 wt% of the conductive agent, and 0.2-5 wt% of the binder.

[0038] According to an embodiment of the present invention, the mass percentage contents of the components in the negative electrode active material layer are: 80-99.8 wt% of the negative electrode active material, 0.1-10 wt% of the conductive agent, and 0.1-10 wt% of the binder.

[0039] Preferably, the mass percentage contents of the components in the negative electrode active material layer are: 90-99.6 wt% of the negative electrode active material, 0.2-5 wt% of the conductive agent, and 0.2-5 wt% of the binder.

[0040] According to an embodiment of the present invention, the conductive agent is selected from at least one of conductive carbon black, acetylene black, Ketjen black, conductive graphite, conductive carbon fiber, carbon nanotube, and metal powder.

[0041] According to an embodiment of the present invention, the binder is selected from at least one of sodium carboxymethyl cellulose, styrene-butadiene latex, polytetrafluoroethylene, and polyethylene oxide.

[0042] According to an embodiment of the present invention, the negative electrode active material is selected from at least one of nano-silicon (Si), silicon-oxygen negative electrode material (SiO x (0 < x < 2)), silicon-carbon negative electrode material, artificial graphite, natural graphite, mesophase carbon microspheres, hard carbon, soft carbon, lithium metal, and lithium titanate.

[0043] According to an embodiment of the present invention, the positive electrode active material is selected from lithium transition metal composite oxides, wherein the lithium transition metal oxides are selected from LiMO2 (M = Ni, Co, Mn), LiMn2O4, LiMPO4 (M = Fe, Mn, Co), LiNi x Mn 1-x O2 (M = Co, Mn), LiNixCo y M 1-x-y O2, where 0≤x, y≤1 and x+y≤1; where M is one or more of Mg, Zn, Ga, Ba, Al, Fe, Cr, Sn, V, Mn, Sc, Ti, Nb, Mo, Zr, Ta, W, B, F, and Si.

[0044] According to an embodiment of the present invention, the diaphragm is a porous polymer membrane.

[0045] According to embodiments of the present invention, the diaphragm is selected from polyolefin-based polymer membranes (e.g., polyethylene, polypropylene, ethylene / butene copolymer, ethylene / methacrylate copolymer), glass fiber membranes, polytetrafluoroethylene membranes, cellulose membranes, polyimide membranes, polyamide membranes, spandex or aramid membranes, and porous polymer membranes having polymer and / or oxide coatings on their surfaces.

[0046] The polymer in the polymer-coated porous polymer membrane is selected from polymethyl methacrylate, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinylidene fluoride-trifluorochloroethylene copolymer, polyoxyethylene, etc.

[0047] The oxide in the porous polymer membrane with oxide coating is selected from one or more of Al2O3 and MO2 (M = Si, Ti, Zn, Mg, Ca, Zr, Mn, W).

[0048] The beneficial effects of this invention are:

[0049] This invention provides an electrolyte and a battery comprising the electrolyte. The tetrafluoroborate diazonium salt compound in the electrolyte decomposes preferentially before the organic solvent evaporates and generates a large amount of inert gas during furnace temperature testing, which escapes from the electrode tabs. As the temperature continues to rise to the point where the organic solvent evaporates and generates a large amount of gas, the gas generated by the evaporation of the organic solvent can be rapidly discharged from the electrode tabs. On the one hand, a large amount of flammable gas is discharged from the battery, releasing the internal heat in a timely manner and preventing heat accumulation that could lead to thermal runaway. On the other hand, the evaporation of the organic solvent closes the ion channels inside the battery, causing side reactions to stop, ultimately allowing the battery to safely pass the furnace temperature test, significantly improving the battery's safety under thermal runaway conditions. Simultaneously, the electron-deficient boron element in the tetrafluoroborate diazonium salt compound of the electrolyte exhibits Lewis acidity and can accept electron pairs, effectively removing HF from the electrolyte and preventing HF from damaging the interfacial protective film, thereby improving the battery's high-temperature storage performance.

[0050] In summary, the electrolyte can improve the high-temperature storage performance of the battery, and also improve the furnace temperature performance of the battery. Detailed Implementation

[0051] The present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0052] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0053] Example 1

[0054] Preparation of electrolyte

[0055] In an argon-filled glove box (H2O < 10 ppm, O2 < 10 ppm), ethylene carbonate (EC), propylene carbonate (PC), propyl propionate (PP), and fluoroethylene carbonate (FEC) were mixed in a mass ratio of 1:2:7:1. Then, 1 mol / L of lithium hexafluorophosphate (LiPF6), 2 wt.% of 1,3-propanesulfonate lactone, 2 wt.% of 1,3,6-hexanetrionitrile, and 2 wt.% of the diazonium salt of tetrafluoroborate shown in Formula I-1 were added. Finally, the mixture was stirred and mixed evenly at 15 °C to obtain the electrolyte.

[0056] Preparation of positive electrode

[0057] Lithium cobalt oxide (LCO), polyvinylidene fluoride (PVDF), and acetylene black were mixed in a weight ratio of 97:1.5:1.5, and N-methylpyrrolidone (NMP) was added and stirred evenly to obtain a positive electrode slurry. The positive electrode slurry was then uniformly coated onto aluminum foil and dried in an oven at 120°C for 8 hours. The positive electrode sheet was then obtained by rolling and slitting.

[0058] Preparation of negative electrode

[0059] Artificial graphite, sodium carboxymethyl cellulose (CMC-Na), styrene-butadiene rubber (SBR), and acetylene black were mixed in a weight ratio of 95:1.5:2:1.5, and deionized water was added and stirred evenly to obtain a negative electrode slurry. The negative electrode slurry was then uniformly coated onto copper foil and dried in an oven at 80°C for 10 hours. The negative electrode sheet was then obtained by rolling and slitting.

[0060] diaphragm

[0061] Polypropylene (PP) membranes are selected.

[0062] Preparation of lithium-ion batteries

[0063] The prepared positive electrode sheet, separator, and negative electrode sheet are wound to obtain a bare cell. The bare cell is then placed in an outer aluminum-plastic film to obtain an unfilled battery. The prepared electrolyte is then injected into the battery in a glove box. After electrolyte injection, the battery undergoes standing, pre-charging, aging, and capacity testing to obtain the desired lithium-ion battery. The charge / discharge range of the battery of this invention is 3.0–4.5V.

[0064] Example 2

[0065] The lithium-ion battery in this embodiment is the same as that in Embodiment 1, except that the tetrafluoroborate diazonium salt compound additive is as shown in Formula I-2.

[0066] Example 3

[0067] The lithium-ion battery in this embodiment is the same as that in Embodiment 1, except that the tetrafluoroborate diazonium salt compound additive is as shown in Formula I-3.

[0068] Example 4

[0069] The lithium-ion battery in this embodiment is the same as that in Embodiment 1, except that the tetrafluoroborate diazonium salt compound additive is as shown in Formula I-4.

[0070] Example 5

[0071] The lithium-ion battery in this embodiment is the same as that in Embodiment 1, except that the tetrafluoroborate diazonium salt compound additive is as shown in Formula I-5.

[0072] Example 6

[0073] The lithium-ion battery in this embodiment is the same as that in Embodiment 1, except that the tetrafluoroborate diazonium salt compound additive is as shown in Formula I-6.

[0074] Example 7

[0075] The lithium-ion battery in this embodiment is the same as that in Embodiment 1, except that the tetrafluoroborate diazonium salt compound additive is as shown in Formula I-7.

[0076] Example 8

[0077] The lithium-ion battery in this embodiment is the same as that in Embodiment 1, except that the tetrafluoroborate diazonium salt compound additive is as shown in Formula I-8.

[0078] Example 9

[0079] The lithium-ion battery in this embodiment is the same as that in Embodiment 1, except that the tetrafluoroborate diazonium salt compound additive is as shown in Formula I-8, and the amount of tetrafluoroborate diazonium salt compound added is 0.05%.

[0080] Example 10

[0081] The lithium-ion battery in this embodiment is the same as that in Embodiment 1, except that the tetrafluoroborate diazonium salt compound additive is as shown in Formula I-8, and the amount of tetrafluoroborate diazonium salt compound added is 6%.

[0082] Comparative Example 1

[0083] The lithium-ion battery in this embodiment is the same as that in Embodiment 1, except that the electrolyte does not contain tetrafluoroborate diazonium salt compound additives.

[0084] Performance testing of lithium-ion batteries:

[0085] (1) Furnace temperature test

[0086] The fully charged battery was placed in an explosion-proof oven and heated to 130℃, 132℃ and 135℃ respectively at a heating rate of 5℃ / min. The temperature was then kept constant for 1 hour at the corresponding temperature. During this process, the battery produced gas and whether it caught fire was observed.

[0087] (2) 60℃ High Temperature Storage Test

[0088] Under normal temperature (25℃) conditions, the thickness D0 of the fully charged cell was measured. The lithium-ion battery was charged and discharged once at 0.3C / 0.3C (the battery discharge capacity was recorded as C0), with an upper limit voltage of 4.5V. The battery was placed in a 60℃ constant temperature chamber for 30 days. The battery was then removed, and the thickness D1 of the fully charged cell was measured. The battery was placed in a 25℃ environment and discharged at 0.3C, with the discharge capacity recorded as C1. Then, the lithium-ion battery was charged and discharged once at 0.3C / 0.3C (the battery discharge capacity was recorded as C2), and the thickness of the battery was measured. The thickness expansion rate, capacity retention rate, and capacity recovery rate of the lithium-ion battery were calculated using the following formulas.

[0089] Capacity retention rate = (C1 / C0) * 100%;

[0090] Capacity recovery rate = (C2 / C0) * 100%;

[0091] Thickness expansion rate = (D1-D0) / D0*100%.

[0092] Table 1. Performance test results of lithium-ion batteries in the examples and comparative examples.

[0093]

[0094] The test results in Table 1 show that diazonium tetrafluoroborate compounds can reduce the battery's opening temperature and improve the furnace temperature pass rate, thus having a certain effect on improving battery safety. However, it was also found that batteries with higher opening temperatures still caught fire during the 135℃ furnace temperature test. This may be because the gases generated by electrolyte evaporation could not be discharged in time, leading to heat accumulation and thermal runaway.

[0095] The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An electrolyte, characterized in that, The electrolyte is composed of an organic solvent, an electrolyte salt, fluoroethylene carbonate (FEC), and a functional additive; the functional additive is composed of a first additive and a second additive, wherein the first additive is a diazonium salt of tetrafluoroborate; and the second additive is selected from at least one of 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, succinate, adiponitrile, triacrylonitrile, 1,3,6-hexanetrionitrile, lithium difluorooxalate borate, lithium difluorophosphate, and lithium difluorodioxalate phosphate. The first additive is selected from at least one of the compounds shown in formula (1): RN = N - BF4 Equation (1) In formula (1), R is selected from substituted or unsubstituted heteroaryl, substituted or unsubstituted aryl; if substituted, the substituent is halogen, alkyl, haloalkyl, alkoxy or cyano; The mass of the first additive is 0.1wt% to 5.0wt% of the total mass of the electrolyte.

2. The electrolyte according to claim 1, characterized in that, In formula (1), R is selected from substituted or unsubstituted 5-12 membered heteroaryl groups, substituted or unsubstituted C groups. 6-12 Aryl; if substituted, the substituent is a halogen or C. 1-12 Alkyl, fluorinated C 1-12 Alkyl, C 1-12 Alkyl or cyano groups.

3. The electrolyte according to claim 2, characterized in that, In formula (1), R is selected from substituted or unsubstituted 5-8 membered heteroaryl groups, substituted or unsubstituted C groups. 6-10 Aryl; if substituted, the substituent is a halogen or C. 1-6 Alkyl, fluorinated C 1-6 Alkyl, C 1-6 Alkyl or cyano groups.

4. The electrolyte according to claim 3, characterized in that, In formula (1), R is selected from substituted or unsubstituted 5-6 membered heteroaryl groups, substituted or unsubstituted C groups. 6-8 Aryl; if substituted, the substituent is a halogen or C. 1-3 Alkyl, fluorinated C 1-3 Alkyl, C 1-3 Alkyl or cyano groups.

5. The electrolyte according to claim 1, characterized in that, The mass of the second additive is greater than 0 and less than or equal to 10 wt% of the total mass of the electrolyte.

6. A battery, characterized in that, The battery includes the electrolyte according to any one of claims 1-5.

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