An electrolyte and a battery comprising the same

Abstract

The application provides an electrolyte and a battery comprising the electrolyte, the electrolyte comprising an organic solvent, an electrolyte salt and a functional additive, wherein the functional additive comprises a first additive, and the first additive is a diazo ester compound. The diazo ester compound in the electrolyte can decompose to generate a large amount of inert gas in advance before the electrolyte solvent is massively volatilized to produce gas during the oven temperature test, and the inert gas is flushed out from the tab, thereby avoiding the heat accumulation in the interior to cause thermal runaway, and significantly improving the safety of the battery under the thermal runaway condition. In addition, through the calculation of the orbital energy level, the HOMO energy level of the diazo ester compound is higher than that of the solvent molecule, and the oxidation reaction of the diazo ester compound occurs at the anode interface to form a CEI film in advance, thereby inhibiting the side reaction at the anode interface, and the high-temperature cycle performance is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electrolyte for lithium ion battery, and particularly relates to a high-safety electrolyte and a battery comprising the electrolyte. BACKGROUND

[0002] Lithium ion battery is an excellent energy storage device, which is widely used in portable electronic devices, electric vehicles and energy storage fields. In recent years, the vigorous development of electric vehicles has brought great convenience to people's travel, but accidents of combustion and explosion occur from time to time in the use process, and the safety of lithium ion battery has become the focus of attention. Studies have shown that lithium ion battery is prone to abnormal temperature rise in the battery under the conditions of overcharge, internal and external short circuit, forced high-rate discharge and high-temperature environment, and when the internal heat production rate is higher than the heat dissipation rate, the battery will cause thermal runaway, and cause the battery to produce combustion or explosion and other unsafe behaviors. Although the battery management system can accurately monitor and manage the voltage, current and temperature of the battery in the use process, and cut off the external current through the battery in abnormal conditions, it can improve the safety of the battery to a certain extent in the use process, but it is often helpless to the thermal runaway of the battery caused by internal short circuit. In addition, the test requirement of battery oven temperature in the national standard is to heat the battery to 130 DEG C by continuous heating, and keep the temperature at this temperature for 30 min, and the battery cannot catch fire and explode during this period. When the battery is heated to 130 DEG C, the temperature inside the battery will be higher, the battery will produce gas and deform, and the separator will shrink seriously, causing internal short circuit of the battery, especially for soft package battery without pressure relief valve, which causes the gas to be discharged in time, and the heat is gathered in the internal, further triggering thermal runaway. These requirements of lithium ion battery for safety promote researchers to combine more effective means to further improve the safety of the battery. SUMMARY

[0003] In order to improve the safety of the battery in use, the application provides an electrolyte capable of improving the oven temperature performance of lithium ion battery and a battery comprising the electrolyte, the electrolyte comprises a first additive, the first additive is a diazo ester compound, and the battery assembled by the electrolyte can safely pass the oven temperature test, significantly improving the safety of the battery under thermal runaway conditions, and the use of the electrolyte can also improve the high-temperature cycle performance of the battery.

[0004] The purpose of the application is realized by the following technical scheme:

[0005] An electrolyte, the electrolyte comprises an organic solvent, an electrolyte salt and a functional additive, wherein the functional additive comprises a first additive, and the first additive is a diazo ester compound.

[0006] According to embodiments of the present application, the first additive is selected from at least one of the compounds of Formula I:

[0007]

[0008] In Formula I, R1is selected from substituted or unsubstituted heteroaryl, substituted or unsubstituted aryl; if substituted, the substituents are halogen, alkyl, haloalkyl, alkoxy and cyano; R2is selected from substituted or unsubstituted alkyl; if substituted, the substituents are halogen, alkyl, haloalkyl.

[0009] According to embodiments of the present application, R1is selected from substituted or unsubstituted 5-12 heteroaryl, substituted or unsubstituted C 6-12 aryl; if substituted, the substituents are halogen, C 1-12 alkyl, haloC 1-12 alkyl, C 1-12 alkoxy and cyano; R2is selected from substituted or unsubstituted C 1-12 alkyl; if substituted, the substituents are halogen, C 1-12 alkyl, haloC 1-12 alkyl.

[0010] According to embodiments of the present application, R1is selected from substituted or unsubstituted 5-8 heteroaryl, substituted or unsubstituted C 6-8 aryl; if substituted, the substituents are halogen, C 1-6 alkyl, haloC 1-6 alkyl, C 1-6 alkoxy and cyano; R2is selected from substituted or unsubstituted C 1-6 alkyl; if substituted, the substituents are halogen, C 1-6 alkyl, haloC 1-6 alkyl.

[0011] According to embodiments of the present application, R1is selected from substituted or unsubstituted 5-6 heteroaryl, substituted or unsubstituted phenyl; if substituted, the substituents are halogen, C 1-3 alkyl, haloC 1-3 alkyl, C 1-3 alkoxy and cyano; R2is selected from substituted or unsubstituted C 1-3 alkyl; if substituted, the substituents are halogen, C 1-3 alkyl, haloC 1-3 alkyl.

[0012] According to embodiments of the present application, R1is selected from substituted or unsubstituted thienyl, substituted or unsubstituted furanyl, substituted or unsubstituted phenyl; if substituted, the substituents are halogen, C 1-3 alkyl, haloC 1-3 alkyl; R2is selected from substituted or unsubstituted C 1-3alkyl; if substituted, the substituents are halogen, C 1-3 alkyl, halogenated C 1-3 alkyl.

[0013] According to embodiments of the present application, the first additive is selected from at least one of the compounds shown in formula I-1 to formula I-6:

[0014]

[0015]

[0016] According to embodiments of the present application, the first additive can be prepared by methods known in the art or can be purchased through commercial channels.

[0017] According to embodiments of the present application, 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 application, the organic solvent is selected from one or more of carbonic acid ester solvents, carboxylic acid ester solvents, ether solvents and their corresponding one or more fluorine-substituted fluorides.

[0019] Illustratively, the carbonic acid ester solvent is selected from at least one of vinyl carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate.

[0020] Illustratively, 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, ethyl n-butyrate.

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

[0022] According to an embodiment of the present application, the mass of the organic solvent is 60wt% to 90wt% of the total mass of the electrolyte, for example 60wt%, 65wt%, 70wt%, 75wt%, 80wt%, 85wt% or 90wt%.

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

[0024] According to an embodiment of the present application, the lithium salt is selected from one or more of lithium hexafluorophosphate (LiPF6), lithium hexafluoroantimonate (LiSbF6), lithium hexafluoroarsenate (LiAsF6), lithium perchlorate (LiClO4), lithium difluorophosphate (LiPO2F2), lithium tetrafluoroborate (LiBF4), lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiODFB), lithium difluorobis(oxalato)phosphate (LiDFBP), lithium tetrafluoro(oxalato)phosphate (LiOTFP), lithium bisfluorosulfonylimide (LiFSI), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), lithium bis(pentafluoroethylsulfonyl)imide (LiBETI), lithium 4,5-dicyano-2-trifluoromethyl-imidazole (LiTDI), lithium trifluoromethanesulfonate or lithium perfluorobutylsulfonate.

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

[0026] According to an embodiment of the present application, the functional additive further comprises a second additive selected from at least one of 1,3-propane sultone, 1,3- propene sultone, butanedinitrile, hexanedinitrile, glycerol trinitrile, 1,3,6-hexanetrinitrile, lithium difluoro(oxalato)borate, lithium difluorophosphate, lithium difluorobis(oxalato)phosphate.

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

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

[0029] The electrolyte is obtained after mixing the organic solvent, the electrolyte salt, the first additive, and optionally the second additive.

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

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

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

[0033] According to an embodiment of the present application, the battery further comprises a positive electrode sheet comprising a positive electrode active material, a negative electrode sheet comprising a negative electrode active material, and a separator.

[0034] According to an embodiment of the present application, the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer coated on one side or both sides of the positive electrode current collector, the positive electrode active material layer comprising a positive electrode active material, a conductive agent, and a binder.

[0035] According to an embodiment of the present application, the negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer coated on one side or both sides of the negative electrode current collector, the negative electrode active material layer comprising a negative electrode active material, a conductive agent, and a binder.

[0036] According to an embodiment of the present application, the mass percentage of each component in the positive electrode active material layer is: 80 to 99.8wt% of the positive electrode active material, 0.1 to 10wt% of the conductive agent, and 0.1 to 10wt% of the binder.

[0037] Preferably, the mass percentage of each component in the positive electrode active material layer is: 90 to 99.6wt% of the positive electrode active material, 0.2 to 5wt% of the conductive agent, and 0.2 to 5wt% of the binder.

[0038] According to an embodiment of the present application, the mass percentage of each component in the negative electrode active material layer is: 80 to 99.8wt% of the negative electrode active material, 0.1 to 10wt% of the conductive agent, and 0.1 to 10wt% of the binder.

[0039] Preferably, the mass percentage of each component in the negative electrode active material layer is: 90 to 99.6wt% of the negative electrode active material, 0.2 to 5wt% of the conductive agent, and 0.2 to 5wt% of the binder.

[0040] According to an embodiment of the present application, 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 application, the binder is selected from at least one of sodium carboxymethylcellulose, styrene butadiene latex, polytetrafluoroethylene, polyethylene oxide.

[0042] According to an embodiment of the present application, the positive current collector is a substance having electrical conductivity without causing adverse chemical changes in the secondary battery, including, but not limited to, aluminum.

[0043] According to an embodiment of the present application, the positive active material is selected from a transition metal composite oxide of lithium, the transition metal oxide including 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, wherein 0≤x, y≤1 and x+y≤1; wherein M is one or several of Mg, Zn, Ga, Ba, Al, Fe, Cr, Sn, V, Mn, Sc, Ti, Nb, Mo, Zr, Ta, W, B, F, Si.

[0044] According to an embodiment of the present application, the negative current collector is a substance having electrical conductivity without causing adverse chemical changes in the secondary battery, and can be selected from copper, stainless steel, aluminum, nickel, titanium, carbon cloth, or a composite thereof.

[0045] According to an embodiment of the present application, the negative active material is selected from one or several composites of lithium metal, carbon-based material, silicon-based material, lithium titanate.

[0046] According to an embodiment of the present application, the carbon-based material includes, but is not limited to, artificial graphite, natural graphite, hard carbon, soft carbon, mesocarbon microbead.

[0047] According to an embodiment of the present application, the silicon-based material includes, but is not limited to, Si, SiO x (0

[0048] According to an embodiment of the present application, the separator is a porous polymer film, including a polyolefin-based polymer film (e.g., polyethylene, polypropylene, ethylene / butylene copolymer, ethylene / methacrylate copolymer), a glass fiber film, a polytetrafluoroethylene film, a cellulose film, a polyimide film, a polyamide film, a spandex or aramid film, and a porous polymer film having a polymer or / and oxide coating on the surface thereof.

[0049] According to an embodiment of the present application, the polymer in the porous polymer film having a polymer coating includes polymethyl methacrylate, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinylidene fluoride-trifluorochloroethylene copolymer, polyethylene oxide, etc.

[0050] According to an embodiment of the present application, the oxide in the oxide-coated porous polymer film can be selected from one or more of Al2O3, MO2 (M = Si, Ti, Zn, Mg, Ca, Zr, Mn, W).

[0051] Advantages of the present application:

[0052] The present application provides an electrolyte and a battery comprising the same. The diazo ester compound in the electrolyte can decompose to generate a large amount of inert gas in advance before a large amount of gas is generated by volatilization of the electrolyte solvent during the oven temperature test, and the inert gas can be flushed out from the tab. As the temperature continues to rise to the temperature at which a large amount of gas is generated by volatilization of the electrolyte solvent, the gas generated by volatilization of the electrolyte solvent can be quickly discharged from the tab. On the one hand, a large amount of flammable gas is discharged from the inside of the battery, and the heat generated inside is released in time, avoiding the accumulation of heat inside and causing thermal runaway. On the other hand, the volatilization of the electrolyte solvent will close the ion channel inside the battery, stop the side reaction, and finally make the battery safely pass the oven temperature test, significantly improving the safety of the battery under thermal runaway conditions. In addition, through orbital energy level calculation, the HOMO energy level of the diazo ester compound is higher than that of the solvent molecule, and the oxidation reaction at the positive electrode interface to form the CEI film is preferentially generated at the positive electrode interface, which inhibits the side reaction at the positive electrode interface, thereby improving the high-temperature cycle performance. DETAILED DESCRIPTION

[0053] The present application will be further described in conjunction with specific examples. It should be understood that the following examples are only illustrative and explanatory of the present application, and should not be interpreted as limiting the scope of protection of the present application. Any technology implemented based on the above description of the present application is covered within the scope of the present application.

[0054] The experimental methods used in the following examples are conventional methods unless otherwise specified. The reagents, materials, etc. used in the following examples can be obtained from commercial channels unless otherwise specified.

[0055] Example 1

[0056] Preparation of electrolyte

[0057] In an argon-filled glove box (H2O, O2<10 ppm), ethylene carbonate (EC), propylene carbonate (PC), propyl propionate (PP), fluoroethylene carbonate (FEC) were mixed in a mass ratio of 1:2:7:1, then 1 mol / L lithium hexafluorophosphate (LiPF6) and 2 wt.% of 1,3-propane sultone, 2 wt.% of 1,3,6-hexanetricarbonitrile, and 2 wt.% of the diazotate compound represented by formula I-1 based on the total mass of the electrolyte were added, and finally stirred at 15°C until uniform, to obtain the electrolyte.

[0058] Preparation of the positive electrode

[0059] Lithium cobalt oxide (LCO), polyvinylidene fluoride (PVDF), and acetylene black were mixed in a weight ratio of 97:1.5:1.5, N-methyl pyrrolidone (NMP) was added and stirred until uniform to obtain a positive electrode slurry; then the positive electrode slurry was uniformly coated on an aluminum foil, which was dried in an oven at 120°C for 8h, then rolled and cut to obtain a positive electrode sheet.

[0060] Preparation of the negative electrode

[0061] 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, deionized water was added and stirred until uniform to obtain a negative electrode slurry; then the negative electrode slurry was uniformly coated on a copper foil, which was dried in an oven at 80°C for 10h, then rolled and cut to obtain a negative electrode sheet.

[0062] The separator was a polypropylene (PP) separator.

[0063] Preparation of the lithium ion battery

[0064] The positive electrode sheet, the separator, and the negative electrode sheet prepared above were wound to obtain a bare cell, which was then placed in an outer aluminum plastic film to obtain a non-liquid injected battery, and then the electrolyte prepared above was injected into the battery in a glove box. The battery after injection was subjected to processes such as standing, pre-charging, aging, and capacity grading to obtain the required lithium ion battery. The battery of the present application has a charge-discharge range of 3.0-4.5V.

[0065] Example 2

[0066] The non-aqueous electrolyte of the present example is the same as that of Example 1, except that the diazotate compound additive is the compound represented by formula I-2.

[0067] Example 3

[0068] The non-aqueous electrolyte of the present example is the same as that of Example 1, except that the diazotate compound additive is the compound represented by formula I-3.

[0069] Example 4

[0070] The nonaqueous electrolyte of this example is the same as that of Example 1, except that the diazo ester compound additive is the compound shown in formula II-4.

[0071] Example 5

[0072] The nonaqueous electrolyte of this example is the same as that of Example 1, except that the diazo ester compound additive is the compound shown in formula II-5.

[0073] Example 6

[0074] The nonaqueous electrolyte of this example is the same as that of Example 1, except that the diazo ester compound additive is the compound shown in formula II-6.

[0075] Example 7

[0076] The nonaqueous electrolyte of this example is the same as that of Example 1, except that the diazo ester compound additive is the compound shown in formula II-6, and the amount of the diazo ester compound additive added is 0.05 wt%.

[0077] Example 8

[0078] The nonaqueous electrolyte of this example is the same as that of Example 1, except that the diazo ester compound additive is the compound shown in formula II-6, and the amount of the diazo ester compound additive added is 6 wt%.

[0079] Comparative Example 1

[0080] The nonaqueous electrolyte of this example is the same as that of Example 1, except that no diazo ester compound is added to the electrolyte.

[0081] (1) Furnace temperature test of lithium ion battery

[0082] The battery in a full charge state was placed in a blast oven, and was heated to 130°C, 132°C and 135°C at a heating rate of 5°C / min, respectively, and was kept at the corresponding temperature for one hour, and the gas production of the battery and whether the battery caught fire and burned during the process were observed, and the results were recorded in Table 1.

[0083] (2) 45°C cycle performance test

[0084] The batteries obtained in the above examples and comparative examples were placed in an environment of (45±2) °C, and left to stand for 2-3 hours. When the battery body reached (45±2) °C, the battery was charged at 1C constant current and constant voltage to 4.5V with a cut-off current of 0.05C. After the battery was fully charged, it was left to stand for 5 min, and then discharged at 1C constant current to a cut-off voltage of 3.0V. The highest discharge capacity of the first three cycles was recorded as the initial capacity Q. When the cycle reached the required number of times, the discharge capacity of the last cycle was recorded as Q1. The results are shown in Table 1.

[0085] The calculation formula used is as follows: capacity retention rate (%) = Q1 / Q x 100%.

[0086] Table 1: Furnace temperature and 45 °C cycle performance test results of lithium ion batteries of examples and comparative examples

[0087]

[0088] From the test results in Table 1, it can be seen that the diazo ester compound can reduce the opening temperature of the battery, improve the furnace temperature pass rate of the battery, and has a certain effect on improving the safety of the battery. It is also found that the battery with a higher opening temperature can still catch fire during the furnace temperature test at 135 °C, which may be because the gas generated by the evaporation of the electrolyte cannot be discharged in time, causing heat accumulation and triggering thermal runaway. In addition, the diazo ester compound can also preferentially form a CEI film on the positive electrode interface by oxidizing the solvent, thereby inhibiting the side reaction on the positive electrode interface and improving the high-temperature cycle performance.

[0089] The above describes the embodiments of the present application. However, the present application is not limited to the above embodiments. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A battery comprising an electrolyte, the electrolyte comprising an organic solvent, an electrolyte salt, and a functional additive, wherein, The functional additive comprises a first additive, which is a diazo ester compound; The first additive is selected from at least one of the compounds shown in Formula I: Formula I In Formula I, R1 is selected from substituted or unsubstituted heteroaryl, substituted or unsubstituted aryl, and if substituted, the substituent is halogen, alkyl, haloalkyl, alkoxy and cyano; R2 is selected from substituted or unsubstituted alkyl, and if substituted, the substituent is halogen, alkyl, haloalkyl; The mass of the first additive is 0.1wt%-5.0wt% of the total mass of the electrolyte; The battery further comprises a negative electrode sheet containing a negative electrode active material, which is selected from one or more of lithium metal, carbon-based material, silicon-based material.

2. The battery of claim 1, wherein, R1is selected from substituted or unsubstituted heteroaryl, substituted or unsubstituted C 6-12 aryl, and if substituted, with halogen, C 1-12 alkyl, halogeno C 1-12 alkyl, C 1-12 alkoxy and cyano; R2is selected from substituted or unsubstituted C 1-12 alkyl, and if substituted, with halogen, C 1-12 alkyl, halogeno C 1-12 alkyl.

3. The battery of claim 2, wherein, R1is selected from substituted or unsubstituted heteroaryl, substituted or unsubstituted C 6-8 aryl, and if substituted, with halogen, C 1-6 alkyl, halogeno C 1-6 alkyl, C 1-6 alkoxy, and cyano; R2is selected from substituted or unsubstituted C 1-6 alkyl, and if substituted, with halogen, C 1-6 alkyl, halogeno C 1-6 alkyl.

4. The battery of claim 3, wherein, R1is selected from substituted or unsubstituted heteroaryl, substituted or unsubstituted phenyl, if substituted, the substituents are halo, C 1-3 alkyl, haloC 1-3 alkyl, C 1-3 alkoxy and cyano; R2is selected from substituted or unsubstituted C 1-3 alkyl, if substituted, the substituents are halo, C 1-3 alkyl, haloC 1-3 alkyl.

5. The battery of claim 4, wherein, said first additive is selected from the group consisting of compounds of formula I 1~formula I 6at least one of the compounds shown below Formula I 1 Formula I 2 Formula I 3 Formula I 4 Formula I 5 Formula I 6.

6. The battery according to any one of claims 1 to 5, wherein The functional additive further comprises a second additive, which is selected from at least one of 1,3-propane sulfite, 1,3-propylene sulfite, butanedinitrile, hexanedinitrile, glycerol trinitrile, 1,3,6-hexanetricarboxylic acid, lithium difluoro(oxalato)borate, lithium difluorophosphate, lithium difluorodioxalate phosphate.

7. The battery of claim 6, wherein, The mass of the second additive is 0.5-10wt% of the total mass of the electrolyte.

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