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 a second additive, the first additive is selected from a sulfonyl fluoride compound, and the second additive is selected from 3,3',3'',3'''-(ethane-1,1,2,2-tetraalkyltetra(oxy))tetrapropionitrile. There is a synergistic effect between the first additive and the second additive in the electrolyte, and the two can jointly generate a stable CEI film on the surface of the positive active material in the charging and discharging process.

Description

TECHNICAL FIELD

[0001] The present application relates to an electrolyte and a battery comprising the same, and belongs to the technical field of lithium ion batteries. BACKGROUND

[0002] Lithium ion batteries are widely used as energy storage devices in various 3C digital electronic products, power tools and other fields due to their high energy density and long cycle life. In recent years, they have also been widely used in electric vehicles and energy storage devices. With the rapid development of lithium ion battery technology and the continuous increase of market demand, higher performance requirements are put forward for lithium ion batteries, including higher energy density, faster charging speed and longer cycle life.

[0003] Increasing the charging voltage of the positive electrode material can effectively improve the energy density of the lithium ion battery, but it brings great challenges to the stability of the positive electrode material. The main improvement strategies currently include improving the structural stability of the positive electrode material at high voltage by surface doping and coating of the positive electrode material and optimizing the precursor structure, inhibiting the side reaction between the positive electrode material and the electrolyte, and optimizing the electrolyte system to improve the oxidation resistance of the electrolyte and improve the stability of the interface film between the positive electrode material and the electrolyte, thereby improving the stability of the battery system. However, as the voltage of the battery system continues to rise, the side reaction between the positive electrode material and the electrolyte also continues to increase, and when the voltage exceeds 4.5V, the conventional electrolyte system is difficult to guarantee the high-temperature cycle stability of the battery, and new additives need to be developed to optimize the performance of lithium ion batteries. SUMMARY

[0004] In order to solve the problems of poor oxidation resistance, high-temperature cycle, high-temperature storage and rapid capacity decay of one-day high-temperature cycle of the existing lithium ion battery system at high voltage, the present application provides an electrolyte and a battery comprising the same. The use of the electrolyte can effectively improve the oxidation resistance of the electrolyte at high voltage, inhibit the side reaction between the electrolyte and the positive electrode interface at high voltage, significantly improve the stability of the positive electrode material and the interface between the positive electrode material and the electrolyte at high voltage, improve the side reaction of the electrolyte during the cycle of the battery at high voltage, improve the stability of the positive electrode material, and significantly improve the problems of rapid capacity decay of one-day high-temperature cycle, high-temperature cycle and high-temperature storage at high voltage.

[0005] The purpose of the present application is achieved by the following technical solutions:

[0006] An electrolyte, comprising an organic solvent, an electrolyte salt and a functional additive, wherein the functional additive comprises a first additive and a second additive, the first additive is selected from sulfonyl fluoride compounds, and the second additive is selected from 3,3',3'',3'''-(ethane-1,1,2,2-tetraalkyltetra(oxy))tetrapropionitrile.

[0007] According to an embodiment of the present application, the sulfonyl fluoride compound is a compound containing a sulfonyl fluoride group (-S(=0)2-F).

[0008] According to an embodiment of the present application, the sulfonyl fluoride compound is selected from at least one compound represented by Formula I:

[0009]

[0010] In Formula I, R is selected from the group consisting of nothing (i.e., X is directly connected to S), substituted or unsubstituted C 1-10 alkylene, substituted or unsubstituted C 1-10 alkylene, substituted or unsubstituted C 2-10 alkylene, substituted or unsubstituted C 2-10 alkylene, substituted or unsubstituted 5-12 membered heteroarylene; if substituted, the substituent is a fluorine atom; and X is selected from the group consisting of a fluorine atom, difluoromethyl, and trifluoromethyl.

[0011] In Formula I, R is selected from the group consisting of nothing, substituted or unsubstituted C 1-6 alkylene, substituted or unsubstituted C 1-6 alkylene, substituted or unsubstituted C 2-6 alkylene, substituted or unsubstituted C 2-6 alkylene, substituted or unsubstituted 5-10 membered heteroarylene; if substituted, the substituent is a fluorine atom; and X is selected from the group consisting of a fluorine atom, difluoromethyl, and trifluoromethyl.

[0012] In Formula I, R is selected from the group consisting of nothing, substituted or unsubstituted C 1-3 alkylene, substituted or unsubstituted C 1-3 alkylene, substituted or unsubstituted C 2-3 alkylene, substituted or unsubstituted C 2-3 alkylene, substituted or unsubstituted 5-6 membered heteroarylene; if substituted, the substituent is a fluorine atom; and X is selected from the group consisting of a fluorine atom, difluoromethyl, and trifluoromethyl.

[0013] In Formula I, R is selected from the group consisting of nothing, fluorinated C 1-3 alkylene, fluorinated C 1-3 alkylene, fluorinated C 2-3 alkylene, 5-6 membered heteroarylene; if substituted, the substituent is a fluorine atom; and X is selected from the group consisting of a fluorine atom and trifluoromethyl.

[0014] According to an embodiment of the present application, the first additive is selected from at least one compound represented by Formulae 1-4:

[0015]

[0016] According to an embodiment of the present application, the second additive is a compound of formula II:

[0017]

[0018] According to an embodiment of the present application, the first additive is present in an amount of 0.5wt% to 2wt% of the total weight of the electrolyte, for example 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1wt%, 1.2wt%, 1.3wt%, 1.5wt%, 1.6wt%, 1.8wt%, 2wt%.

[0019] According to an embodiment of the present application, the second additive is present in an amount of 0.3wt% to 5wt% of the total weight of the electrolyte, for example 0.3wt%, 0.4wt%, 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1wt%, 1.2wt%, 1.4wt%, 1.5wt%, 1.6wt%, 1.8wt%, 2wt%, 2.5wt%, 2.6wt%, 2.8wt%, 3wt%, 3.4wt%, 3.7wt%, 3.9wt%, 4wt%, 4.5wt%, 5wt%.

[0020] According to an embodiment of the present application, the first additive is prepared by a method known in the art or is obtained by commercial purchase.

[0021] According to an embodiment of the present application, the second additive is prepared by a method known in the art or is obtained by commercial purchase.

[0022] According to an embodiment of the present application, the electrolyte salt is selected from electrolyte lithium salts selected from one or more of lithium hexafluorophosphate (LiPF6), lithium difluorophosphate (LiPO2F2), lithium difluoro oxalato borate (LiDFOB), lithium bisfluorosulfonylimide (LiTFSI), lithium bis-trifluoromethylsulfonylimide, lithium difluorobisoxalate phosphate, lithium tetrafluoroborate, lithium bisoxalate borate, lithium hexafluoroantimonate, lithium hexafluoroarsenate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(pentafluoroethylsulfonyl)imide, lithium tris(trifluoromethylsulfonyl)methide or lithium bis(trifluoromethylsulfonyl)imide.

[0023] According to an embodiment of the present application, the electrolyte salt is present in an amount of 10wt% to 15wt% of the total weight of the electrolyte, for example 10wt%, 11wt%, 12wt%, 13wt%, 14wt% or 15wt%.

[0024] According to an embodiment of the present application, the organic solvent is selected from carbonates and / or carboxylic acid esters, the carbonates being selected from one or several of the following fluorinated or non-substituted solvents: ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate, diethyl carbonate (DEC), methyl ethyl carbonate; the carboxylic acid esters being selected from one or several of the following fluorinated or non-substituted solvents: propyl acetate, n-butyl acetate, isobutyl acetate, n-pentyl acetate, isopentyl acetate, propyl propionate (PP), ethyl propionate (EP), methyl butyrate, ethyl n-butyrate.

[0025] According to an embodiment of the present application, the functional additive further comprises a third additive selected from at least one of the following compounds: fluorinated ethylene carbonate, 1,3-propane sultone, 1,3-propene sultone, butanedinitrile, hexanedinitrile, glycerol trinitrile, lithium difluoro(oxalato)borate, lithium difluorophosphate, lithium difluorodioxalato-phosphate.

[0026] According to an embodiment of the present application, the third additive is present in a weight amount of 0-15 wt% of the total weight 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%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt% or 15 wt%.

[0027] According to an embodiment of the present application, the electrolyte is used in a lithium ion battery.

[0028] According to an embodiment of the present application, the electrolyte is used in a lithium ion battery with lithium cobaltate as the positive active material.

[0029] The present application also provides a battery comprising the electrolyte as described above.

[0030] According to an embodiment of the present application, the lithium ion battery further comprises a positive electrode sheet comprising a positive active material, a negative electrode sheet comprising a negative active material, and a separator.

[0031] According to an embodiment of the present application, the positive electrode sheet comprises a positive current collector and a positive active material layer coated on one or both sides of the positive current collector, the positive active material layer comprising a positive active material, a conductive agent and a binder.

[0032] According to an embodiment of the present application, the negative electrode sheet comprises a negative current collector and a negative active material layer coated on one or both sides of the negative current collector, the negative active material layer comprising a negative active material, a conductive agent and a binder.

[0033] According to an embodiment of the present application, the mass percentage of each component in the positive electrode active material layer is: 80-99.8wt% of positive electrode active material, 0.1-10wt% of conductive agent, and 0.1-10wt% of binder.

[0034] Preferably, the mass percentage of each component in the positive electrode active material layer is: 90-99.6wt% of positive electrode active material, 0.2-5wt% of conductive agent, and 0.2-5wt% of binder.

[0035] According to an embodiment of the present application, the mass percentage of each component in the negative electrode active material layer is: 80-99.8wt% of negative electrode active material, 0.1-10wt% of conductive agent, and 0.1-10wt% of binder.

[0036] Preferably, the mass percentage of each component in the negative electrode active material layer is: 90-99.6wt% of negative electrode active material, 0.2-5wt% of conductive agent, and 0.2-5wt% of binder.

[0037] 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, metal powder, and carbon fiber.

[0038] According to an embodiment of the present application, the binder is selected from at least one of sodium carboxymethyl cellulose, styrene butadiene latex, polytetrafluoroethylene, and polyethylene oxide.

[0039] According to an embodiment of the present application, the negative electrode active material comprises carbon-based negative electrode material and / or silicon-based negative electrode material.

[0040] According to an embodiment of the present application, the carbon-based negative electrode material is selected from at least one of artificial graphite, natural graphite, mesocarbon microbeads, hard carbon, and soft carbon.

[0041] According to an embodiment of the present application, the silicon-based negative electrode material is selected from at least one of silicon-oxygen negative electrode material or silicon-carbon negative electrode material, such as Si, SiC, and SiOx(0

[0042] According to an embodiment of the present application, the positive electrode active material is selected from lithium cobaltate doped with Al element.

[0043] According to an embodiment of the present application, the battery satisfies: 14≥100×X+100×Y+Z / 1000≥8;

[0044] wherein X is the percentage of the weight of the first additive in the total weight of the electrolyte; Y is the percentage of the weight of the second additive in the total weight of the electrolyte; and Z is the doping amount of Al element in the positive electrode active material, in ppm.

[0045] According to an embodiment of the present application, X is 0.5wt% to 2wt%, for example 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1wt%, 1.2wt%, 1.3wt%, 1.5wt%, 1.6wt%, 1.8wt%, 2wt%.

[0046] According to an embodiment of the present application, Y is 0.3wt% to 5wt%, for example 0.3wt%, 0.4wt%, 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1wt%, 1.2wt%, 1.4wt%, 1.5wt%, 1.6wt%, 1.8wt%, 2wt%, 2.5wt%, 2.6wt%, 2.8wt%, 3wt%, 3.4wt%, 3.7wt%, 3.9wt%, 4wt%, 4.5wt%, 5wt%.

[0047] According to an embodiment of the present application, Z is 3000 to 8000ppm, for example 3000ppm, 4000ppm, 5000ppm, 6000ppm, 7000ppm or 8000ppm.

[0048] According to an embodiment of the present application, the charge cut-off voltage of the battery is 4.5V or higher.

[0049] The present application has the following advantages:

[0050] The present application provides an electrolyte and a battery comprising the same. The first additive and the second additive in the electrolyte have a synergistic effect. Both of them can generate a stable CEI film on the surface of the positive active material during charging and discharging. Specifically, the sulfonyl fluoride group and the ether nitrile (-O-CH2CH2-CN) structure act on the surface of the positive active material. The ether nitrile complex positive transition metal ions, improves the stability of the positive active material, and cooperates with the inorganic interface film generated by the reaction of the ether nitrile and the sulfonyl fluoride to isolate the side reaction between the electrolyte and the positive active material at high voltage, significantly improving the high-temperature cycle storage performance and 45℃ 1-day cycle of the battery. At the same time, the participation of the S-containing compound in the film formation reduces the mass transfer resistance at the interface, and the low-temperature performance is also considered. DETAILED DESCRIPTION

[0051] The present application will be further described in detail below with reference to 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 realized based on the above description of the present application is covered within the scope of protection intended by the present application.

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

[0053] To make the objectives, technical solutions, and advantages of the present application clearer, the following will be combined with embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative effort belong to the scope of the present application.

[0054] It can be understood that the lithium ion battery of the present application comprises a negative electrode sheet, an electrolyte, a positive electrode sheet, a separator, and an outer package. The positive electrode sheet, the separator, and the negative electrode sheet are stacked to obtain an electrode core or are stacked and then wound to obtain an electrode core. The electrode core is placed in the outer package, and the electrolyte is injected into the outer package to obtain the lithium ion battery of the present application.

[0055] Examples 1-8 and Comparative Examples 1-3

[0056] The lithium ion batteries of Examples 1-8 and Comparative Examples 1-3 are prepared by the following steps:

[0057] 1) Preparation of a positive electrode sheet

[0058] The positive electrode active material lithium cobalt oxide doped with aluminum, polyvinylidene fluoride (PVDF), SP (super P), and carbon nanotubes (CNT) are mixed in a mass ratio of 96:2:1.5:0.5, N-methyl pyrrolidone (NMP) is added, and stirring is performed under the action of a vacuum stirrer until the mixed system becomes a positive electrode active slurry with uniform fluidity; the positive electrode active slurry is uniformly coated on both surfaces of an aluminum foil; the coated aluminum foil is dried, and then subjected to rolling and slitting to obtain the required positive electrode sheet.

[0059] 2) Preparation of a negative electrode sheet

[0060] The negative electrode active material artificial graphite, silicon monoxide, sodium carboxymethyl cellulose (CMC-Na), butadiene rubber, conductive carbon black (SP), and single-walled carbon nanotubes (SWCNTs) are mixed in a mass ratio of 79.5:15:2.5:1.5:1:0.5, deionized water is added, and a negative electrode active slurry is obtained under the action of a vacuum stirrer; the negative electrode active slurry is uniformly coated on both surfaces of a copper foil; the coated copper foil is air-dried at room temperature, and then transferred to a 80℃ oven for drying for 10 h, followed by cold pressing and slitting to obtain the negative electrode sheet.

[0061] 3) Preparation of an electrolyte

[0062] In an argon-filled glove box (H2O < 0.1ppm, O2 < 0.1ppm), EC / PC / DEC / PP were mixed uniformly in a mass ratio of 10 / 20 / 40 / 30, and then 1 mol / L of fully dried lithium hexafluorophosphate (LiPF6) was quickly added thereto. After dissolution, 9 wt% of fluoroethylene carbonate, 2 wt% of 1,3-propane sultone, 1.5 wt% of adiponitrile, the first additive and the second additive (specific amounts and selections are described in Table 1) were added, stirred uniformly, and the desired electrolyte was obtained after passing the moisture and free acid tests.

[0063] 4) Preparation of lithium-ion batteries

[0064] The positive electrode sheet from step 1), the negative electrode sheet from step 2), and the separator are stacked in the order of positive electrode sheet, separator, and negative electrode sheet, and then wound to form a battery cell. The battery cell is placed in an outer aluminum foil package, and the electrolyte from step 3) is injected into the outer packaging. After vacuum packaging, standing, forming, shaping, and sorting, a lithium-ion battery is obtained. The battery of the present invention has a charge and discharge range of 3.0 to 4.5V.

[0065] The performance of the lithium-ion batteries obtained in the examples and comparative examples was tested, and the test results are shown in Table 2.

[0066] 1) 45℃ cycle performance test

[0067] The battery in Table 1 was charged and discharged for 1000 cycles at a rate of 1C within the charge and discharge cut-off voltage range at 45°C. The discharge capacity in the first week of the test was calculated as x1 mAh, and the discharge capacity in the Nth week was calculated as y1 mAh. The capacity in the Nth week was divided by the capacity in the first week to obtain the cycle capacity retention rate of the Nth week, R1 = y1 / x1. The number of cycles of the battery corresponding to the cycle capacity retention rate of 80% at 45°C was recorded.

[0068] 2) 45℃, 1-day cycle performance test

[0069] The battery in Table 1 was discharged to 3V at a rate of 0.5C at 45°C, left to rest for 10 minutes, and then fully charged to 0.05C at a rate of 0.7C. The battery was left to rest for 20 hours. This constituted a cycle. Repeat this process multiple times, and record the number of cycles until the capacity retention rate was less than 70%.

[0070] 3) 60°C, 14-day high temperature storage test:

[0071] The battery of Table 1 was charged and discharged at 0.5C at room temperature for 1 time, then the battery was charged to full capacity with constant current and constant voltage, the thickness d1 of the battery before high temperature storage was tested using a vernier caliper (two diagonal lines of the above battery were connected by straight lines respectively, and the intersection of the two diagonal lines was the test point of the thickness of the battery), the battery was placed in a 60°C constant temperature oven for 14 days, after the storage was completed, the battery was taken out and the thickness d2 of the battery after storage was tested, and the thickness expansion rate of the battery after 14 days of 60°C storage was calculated; the calculation formula is as follows:

[0072] Thickness expansion rate after 14 days of 60°C storage = (d2-d1) / d1*100%.

[0073] Composition of electrolyte additives in lithium ion batteries of examples and comparative examples of Table 1

[0074]

[0075] Performance test results of lithium ion batteries of examples and comparative examples of Table 2

[0076]

[0077]

[0078] As can be seen from Table 2, the 45°C cycle capacity retention rate 80% cycle number and the 45°C 1 day cycle capacity retention rate 70% cycle days of Comparative Examples 1-3 without adding additives or adding only the first additive or the second additive are significantly less than those of the examples with the first additive and the second additive, and the possible reason is that the first additive and the second additive have a synergistic effect on the positive electrode surface of the lithium ion battery, improving the stability of the positive electrode surface under high voltage and high temperature conditions, and improving the cycle and storage performance of the battery.

[0079] As can be seen from Example 8, when the amount of additive and the content of Al element in the positive active material are not within the range of 14≥100×X+100×Y+Z / 1000≥8, the excessive first additive and second additive do not have obvious improvement effect on the cycle performance, on the contrary, it may also deteriorate the cycle performance of the battery, and the possible reason is that under the condition of a certain amount of Al doping, the complexing sites provided by the first additive and the second additive are limited, and the addition of excessive additives cannot participate in the complex protection of the positive electrode, resulting in the generation of by-products that are not conducive to the cycle performance in the negative electrode side reaction.

[0080] As can be seen from Examples 1-3, appropriate addition of the first additive is beneficial to the improvement of the cycle performance of the battery, and when the amount of the first additive is excessive, the side effects begin to appear and the performance improvement effect decreases.

[0081] As can be seen from Example 2 and Example 4, the compounds represented by Formula 1 and Formula 3 both have the same effect of improving the normal temperature and high temperature cycle performance, and the cycle storage improvement effect of the compound represented by Formula 3 is slightly weaker than that of the compound represented by Formula 1, and it is speculated that the oxidation resistance of the ether group structure is reduced, and the stability at high voltage is reduced, resulting in performance degradation.

[0082] As can be seen from Example 1-Example 7, when the first additive and the second additive are used together, the greater the amount, the better the storage performance of the battery.

[0083] In summary, the electrolyte added with the first additive and the second additive of the present application can form a protective layer with synergistic coordination on the positive electrode surface, improve the high voltage resistance of the positive electrode interface, reduce the interface side reaction, inhibit the consumption of electrolyte, and significantly improve the cycle performance and storage performance of the lithium ion battery.

[0084] The above describes the embodiments of the present application. However, the present application is not limited to the above-described 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, characterized in that: The battery includes an electrolyte, a positive electrode sheet containing a positive electrode active material, and a negative electrode sheet containing a negative electrode active material; the electrolyte includes an organic solvent, an electrolyte salt, and a functional additive, wherein the functional additive includes a first additive and a second additive, the first additive is selected from sulfonyl fluoride compounds, and the second additive is selected from 3,3',3",3'''-(ethane-1,1,2,2-tetraalkyltetra(oxy))tetrapropionitrile; The sulfonyl fluoride compound is selected from at least one compound represented by formula I: Formula I In formula I, R is selected from absent, substituted or unsubstituted C 1-10 Alkylene, substituted or unsubstituted C 1-10 Alkyleneoxy; if substituted, the substituent is a fluorine atom; X is selected from a fluorine atom, a difluoromethyl group, and a trifluoromethyl group; The positive electrode active material is selected from Al-doped lithium cobalt oxide; The battery satisfies: 14≥100×X+100×Y+Z / 1000≥8; Wherein, X is the percentage of the weight of the first additive to the total weight of the electrolyte; Y is the percentage of the weight of the second additive to the total weight of the electrolyte; Z is the doping amount of Al element in the positive electrode active material, in ppm; X is 0.5wt%~2wt%; Y is 0.3wt%~5wt%; Z is 3000~8000ppm.

2. The battery according to claim 1, characterized in that In formula I, R is selected from absent, substituted or unsubstituted C 1-6 Alkylene, substituted or unsubstituted C 1-6 Alkyleneoxy; if substituted, the substituent is a fluorine atom; X is selected from a fluorine atom, a difluoromethyl group, and a trifluoromethyl group.

3. The battery according to claim 2, wherein The first additive is selected from at least one of the compounds shown in Formula 1 to Formula 2: Formula 1 Formula 2.

4. The battery according to any one of claims 1 to 3, characterized in that The charging cut-off voltage of the battery is above 4.5V.

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