An electrolyte comprising the electrolyte of a battery

Abstract

The application provides an electrolyte and a battery comprising the electrolyte, wherein a first additive in the electrolyte is a pyridine silane compound, the pyridine silane compound can generate a stable interface film at a positive electrode, and the cycle performance of the battery is significantly improved. On the other hand, the silane group in the first additive can participate in film formation to generate a CEI film rich in inorganic components at a thermal shock temperature, and the thermal stability of the positive electrode interface can be improved; meanwhile, the pyridine ring is a weak base substance, can react with a Lewis acid at a high temperature, inhibit the diffusion reaction of combustion process free radicals, improve the flame retardancy, and the pyridine structure can be polymerized at a short circuit point at the thermal shock temperature, and the thermal shock performance of the battery is further improved.

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] With the rapid development of new energy industry, the proportion of lithium ion batteries in the fields of digital, electric tools and energy storage is further improved. Its high energy density, long service life and other characteristics have become one of the current market mainstream green energy. With the widening of application fields, the market puts forward higher requirements for the performance of lithium ion batteries. How to further improve the energy density of the battery has become one of the current research topics.

[0003] There are multiple ways to improve energy density, such as battery limit design, compression of non-energy density space, improvement of the charging voltage of the positive electrode material, and realization of a wider charging and discharging voltage area. The representative of the current high-voltage positive electrode material is lithium cobaltate. With the increase of its voltage, its specific capacity gradually increases, so the energy density is improved. However, the limit design and the increase of the voltage of the material will deteriorate the safety performance of the battery. Under the limit design, the risk of short circuit of the battery increases, and the thermal shock performance deteriorates significantly. The increase of the voltage of the positive electrode material rapidly increases the side reaction with the electrolyte, and the cycle performance of the battery rapidly decays. Therefore, it is urgent to develop a new type of electrolyte to improve the cycle performance at high voltage while considering the safety performance. SUMMARY

[0004] In order to solve the problems of poor positive electrode interface stability, rapid high-temperature cycle decay and low safety reliability in the existing high-voltage battery, the present application provides an electrolyte and a battery comprising the same. The electrolyte can significantly improve the cycle performance and thermal shock performance of the battery.

[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 selected from a pyridine silane compound, the pyridine silane compound is a compound containing a silane group and a pyridine ring, and the silane group is directly connected to the pyridine ring.

[0007] According to an embodiment of the present application, the pyridine silane compound is selected from at least one of the compounds represented by formula (1):

[0008]

[0009] In formula (1), R1, R2 and R3 are the same or different, and are independently selected from hydrogen, halogen, substituted or unsubstituted C 1-10 alkyl, substituted or unsubstituted C 1-10 alkoxy, substituted or unsubstituted C2-10 alkenyl; if substituted, the substituent is halogen;

[0010] X is selected from halogen, substituted or unsubstituted C 1-10 alkyl, substituted or unsubstituted C 1-10 alkoxy, substituted or unsubstituted C 1-10 alkylthio, -Si(R4)(R5)(R6); R4, R5, R6are the same or different, independently from each other, selected from substituted or unsubstituted C 1-10 alkyl, substituted or unsubstituted C 2-10 alkenyl;

[0011] n is an integer between 0 and 4.

[0012] According to an embodiment of the present application, in formula (1), R1, R2, R3are the same or different, independently from each other, selected from hydrogen, halogen, substituted or unsubstituted C 1-6 alkyl, substituted or unsubstituted C 1-6 alkoxy, substituted or unsubstituted C 2-6 alkenyl; if substituted, the substituent is halogen;

[0013] X is selected from halogen, substituted or unsubstituted C 1-6 alkyl, substituted or unsubstituted C 1-6 alkoxy, substituted or unsubstituted C 1-6 alkylthio, -Si(R4)(R5)(R6); R4, R5, R6are the same or different, independently from each other, selected from substituted or unsubstituted C 1-6 alkyl, substituted or unsubstituted C 2-6 alkenyl;

[0014] n is an integer between 0 and 2.

[0015] According to an embodiment of the present application, in formula (1), R1, R2, R3are the same or different, independently from each other, selected from hydrogen, halogen, substituted or unsubstituted C 1-3 alkyl, substituted or unsubstituted C 1-3 alkoxy, substituted or unsubstituted C 2-3 alkenyl; if substituted, the substituent is halogen;

[0016] X is selected from halogen, substituted or unsubstituted C 1-3 alkyl, substituted or unsubstituted C 1-3 alkoxy, substituted or unsubstituted C 1-3 alkylthio, -Si(R4)(R5)(R6); R4, R5, R6are the same or different, independently from each other, selected from substituted or unsubstituted C 1-3 alkyl, substituted or unsubstituted C 2-3 alkenyl;

[0017] n is an integer between 0 and 1.

[0018] According to an embodiment of the application, the first additive is selected from at least one of the compounds of formula (2) to (13):

[0019]

[0020]

[0021] According to an embodiment of the application, the first additive has a weight comprised between 0.3wt% and 3wt% 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%, 1.3wt%, 1.5wt%, 1.6wt%, 1.8wt%, 2wt%, 2.2wt%, 2.4wt%, 2.5wt%, 2.7wt%, 3.0wt%.

[0022] According to an embodiment of the application, the first additive is prepared using methods known in the art or is obtained by purchase on the market.

[0023] According to an embodiment of the application, the electrolyte salt is selected from electrolyte lithium salts selected from one or more than one of lithium hexafluorophosphate (LiPF6), lithium difluorophosphate (LiPO2F2), lithium difluoro-oxalato-borate (LiDFOB), lithium bisfluorosulfonylimide (LiTFSI), lithium bis-trifluoromethylsulfonylimide, lithium difluorobisoxalate-phosphate, lithium tetrafluoroborate, lithium bisoxalato-borate, lithium hexafluoroantimonate, lithium hexafluoroarsenate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(pentafluoroethylsulfonyl)imide, lithium tris(trifluoromethylsulfonyl)methide or lithium bis(trifluoromethylsulfonyl)imide.

[0024] According to an embodiment of the application, the electrolyte salt has a weight comprised between 10wt% and 15wt% of the total weight of the electrolyte, for example 10wt%, 11wt%, 12wt%, 13wt%, 14wt% or 15wt%.

[0025] According to an embodiment of the application, the organic solvent is selected from carbonates and / or carboxylic esters, the carbonates being selected from one or more of the following fluorinated or unsubstituted solvents: ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate, diethyl carbonate (DEC), methyl ethyl carbonate; the carboxylic esters being selected from one or more of the following fluorinated or unsubstituted solvents: propyl acetate, n-butyl acetate, isobutyl acetate, n-pentyl acetate, isopentyl acetate, propyl propionate (PP), ethyl propionate (EP), methyl butyrate, ethyl n-butyrate.

[0026] According to an embodiment of the present application, the functional additive further comprises a second additive selected from at least one of fluoroethylene carbonate (FEC), vinylene carbonate (VC), 1,3-propane sultone (PS), vinyl sulfite (DTD), methylene methane disulfonate (MMDS), propene sultone (PST), maleic anhydride, diglycolic anhydride, succinic anhydride, succinonitrile (SN), adiponitrile (ADN), ethylene glycol bis(propionitrile) ether (EGBE), and hexane trinitrile (HTCN).

[0027] According to an embodiment of the present application, the second additive has a weight 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%, 15 wt%.

[0028] According to an embodiment of the present application, the electrolyte is used in a lithium ion battery.

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

[0030] According to an embodiment of the present application, the lithium ion 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.

[0031] 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.

[0032] 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.

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

[0034] Preferably, the mass percentage of each component in the positive electrode active material layer is: 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.

[0035] According to an embodiment of the present application, the mass percentage of each component in the negative active material layer is: 80-99.8wt% of negative 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 active material layer is: 90-99.6wt% of negative 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, butyl rubber latex, polytetrafluoroethylene, and polyethylene oxide.

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

[0040] According to an embodiment of the present application, the carbon-based negative 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 material is selected from at least one of silicon-oxygen negative material or silicon-carbon negative material, such as Si, SiC, and SiOx (0

[0042] According to an embodiment of the present application, the positive active material is selected from one or more of transition metal lithium oxide, lithium iron phosphate, and lithium manganate; the chemical formula of the transition metal lithium oxide is Li 1+x Ni y Co z M (1-y-z) O2, wherein -0.1≤x≤1, 0≤y≤1, 0≤z≤1, and 0≤y+z≤1; wherein M is one or more of Mg, Zn, Ga, Ba, Al, Fe, Cr, Sn, V, Mn, Sc, Ti, Nb, Mo, and Zr.

[0043] According to an embodiment of the present application, the charge cut-off voltage of the battery is 4.5V or higher.

[0044] The present application has the following advantages:

[0045] The electrolyte provided by the application and the battery comprising the electrolyte, wherein the first additive in the electrolyte is a pyridine silane compound, the pyridine silane compound can generate a stable interface film at the positive electrode, effectively inhibit the dissolution of metal ions at high voltage, reduce the decomposition of the electrolyte, inhibit the side reaction between the positive electrode interface and the electrolyte in the high-voltage battery, improve the oxidation resistance of the interface, improve the stability of the positive electrode, better protect the positive electrode interface, reduce the consumption of the electrolyte and the damage to the positive electrode structure during the battery cycle process, and significantly improve the cycle performance of the battery. On the other hand, the silane group in the first additive can participate in film formation to generate a CEI film rich in inorganic components at the thermal shock temperature, which can improve the thermal stability of the positive electrode interface; at the same time, the pyridine ring is a weak base substance, which can react with Lewis acid at high temperature to inhibit the diffusion reaction of free radicals in the combustion process, improve the flame retardancy, and the pyridine structure can be polymerized at the short-circuit point at the thermal shock temperature, further improving the thermal shock performance of the battery. DETAILED DESCRIPTION

[0046] The application will be described in further detail below with reference to specific examples. It should be understood that the following examples are only illustrative and explanatory of the application, and should not be interpreted as limiting the scope of protection of the application. Any technology achieved based on the above description of the application is covered within the scope of protection intended by the application.

[0047] 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.

[0048] To make the purpose, technical solutions and advantages of the application more clear, the technical solutions in the embodiments of the application will be described clearly and completely below with reference to the embodiments of the application. Obviously, the described embodiments are part of the embodiments of the application, rather than all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the application.

[0049] It can be understood that the lithium ion battery of the 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 application.

[0050] Examples 1-15 and Comparative Examples 1-2

[0051] The lithium ion batteries of Examples 1-15 and Comparative Examples 1-2 are prepared by the following steps:

[0052] 1) Preparation of positive electrode sheet

[0053] The positive electrode active material lithium cobaltate (LiCoO2), polyvinylidene fluoride (PVDF), SP (super P) and carbon nanotubes (CNT) were mixed in a mass ratio of 96:2:1.5:0.5, N-methyl pyrrolidone (NMP) was added, and stirring was performed under the action of a vacuum stirrer until the mixed system became a positive electrode active paste with uniform fluidity; the positive electrode active paste was uniformly coated on both surfaces of an aluminum foil; the coated aluminum foil was dried, then rolled, and cut to obtain the desired positive electrode sheet.

[0054] 2) Preparation of negative electrode sheet

[0055] 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) were mixed in a mass ratio of 79.5:15:2.5:1.5:1:0.5, deionized water was added, and a negative electrode active paste was obtained under the action of a vacuum stirrer; the negative electrode active paste was uniformly coated on both surfaces of a copper foil; the coated copper foil was air-dried at room temperature, then transferred to a 80℃ oven for drying for 10h, and then cold-pressed and cut to obtain the negative electrode sheet.

[0056] 3) Preparation of electrolyte

[0057] In an argon-filled glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), EC / PC / DEC / PP were mixed in a mass ratio of 10 / 20 / 40 / 30, then 1 mol / L of fully dried lithium hexafluorophosphate (LiPF6) was quickly added, after dissolution, 9wt% of fluoroethylene carbonate based on the total mass of the electrolyte, 2wt% of 1,3-propane sultone, 1.5wt% of adiponitrile, 2.5wt% of hexanettritrile, and the first additive (the specific selection and amount are shown in Table 1) were added, stirred uniformly, and after passing the water and free acid detection, the desired electrolyte was obtained.

[0058] 4) Preparation of lithium ion battery

[0059] The positive electrode sheet of step 1), the negative electrode sheet of step 2) and the separator were stacked in the order of positive electrode sheet, separator and negative electrode sheet, then wound to obtain a cell; the cell was placed in an outer packaging aluminum foil, the electrolyte of step 3) was injected into the outer packaging, and after vacuum packaging, standing, formation, shaping, sorting and other processes, a lithium ion battery was obtained. The battery of the present application has a charge-discharge range of 3.0-4.5V.

[0060] The lithium ion batteries obtained in the examples and comparative examples were subjected to 25℃ cycle performance test and 45℃ cycle performance test, and thermal shock test, respectively, and the test results are shown in Table 2.

[0061] 1) 25℃ cycle performance test

[0062] The battery of Table 1 was charged and discharged at 25℃ at a rate of 1C within the charge and discharge cut-off voltage range for 1000 cycles, the discharge capacity of the 1stweek was counted as x1mAh, the discharge capacity of the Nthcycle was counted as y1mAh; the capacity of the Nthweek was divided by the capacity of the 1stweek to obtain the cycle capacity retention rate R1 of the Nthweek = y1 / x1, and the cycle number of the battery corresponding to the 25℃ cycle capacity retention rate of 80% was recorded.

[0063] 2) 45℃ cycle performance test

[0064] The battery of Table 1 was charged and discharged at 45℃ at a rate of 1C within the charge and discharge cut-off voltage range for 1000 cycles, the discharge capacity of the 1stweek was counted as x2mAh, the discharge capacity of the Nthcycle was counted as y2mAh; the capacity of the Nthweek was divided by the capacity of the 1stweek to obtain the cycle capacity retention rate R2 of the Nthweek = y2 / x2, and the cycle number of the battery corresponding to the 45℃ cycle capacity retention rate of 80% was recorded.

[0065] 3) thermal shock performance test

[0066] The battery of Table 1 was charged to full under standard charging conditions at room temperature (1C standard charging to the limit voltage, cut-off 0.025C); the full battery (the inkjet code face was downward, and the deep pit face was upward) was placed horizontally in an oven, the oven temperature was increased to (135±2)℃ at a rate of (5±2)℃ / min and maintained for 60 min, the temperature in the middle of the battery (deep pit face) was monitored during the test process, and whether the battery caught fire or exploded was observed.

[0067] Composition of the electrolyte in the lithium ion battery of the examples and the comparative examples of Table 1

[0068]

[0069] Performance test results of the lithium ion battery of the examples and the comparative examples of Table 2

[0070]

[0071]

[0072] As can be seen from Table 2, the 25℃ cycle number and the 45℃ cycle number of the electrolyte added with the compounds shown in formula (2), formula (3) and formula (5) were both significantly improved compared with the comparative example 1 without adding the additive, which proved that the pyridine silane compound could form a stable interface film on the surface of the positive electrode (especially the lithium cobalt oxide positive electrode) after charging and discharging, so as to inhibit the oxidation reaction of the positive electrode material and the electrolyte under high voltage charging and discharging conditions, and achieve the effect of improving the cycle performance.

[0073] Further, it can be seen from Examples 1-4 that, as the amount of the first additive increases, the improvement of the room temperature and high temperature cycle performance first becomes stronger and then weaker, and when the amount of the first additive is ≥ 5wt%, the improvement effect is no longer obvious, and the cycle and thermal shock performance may even deteriorate, because excessive additives will cause the interfacial film to be too thick, the interfacial impedance to increase, and other side reactions to occur, thereby adversely affecting the cycle of the lithium ion battery.

[0074] Further, it can be seen from Examples 6-15 that the compounds represented by formula (2), formula (3) and formula (5) all have the same effect of improving the room temperature and high temperature cycle performance, and the improvement effect of the compounds represented by formula (3) and formula (5) is better than that of the compound represented by formula (2), which may be because the compounds represented by formula (3) and formula (5) further contain double bonds and fluorine atoms, and the introduction of these groups can further improve the film stability and inhibit the side reaction of the positive electrode material and the electrolyte.

[0075] In summary, the electrolyte added with the first additive of the present application can form a stable protective layer on the surface of the positive electrode, which can reduce the oxidation ability of the electrolyte on the surface of the positive electrode, significantly improve the stability of the electrolyte and material interface, reduce the consumption of the electrolyte and the destruction of the positive electrode structure during the cycle of the lithium ion battery, and significantly improve the cycle performance of the lithium ion battery. At the same time, the stable interfacial film formed by the additive under thermal shock conditions can improve the thermal shock stability, and the weakly basic pyridine compound can block the free radical reaction, thereby improving the thermal shock performance of the battery.

[0076] 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 by, The battery comprises an electrolyte; the electrolyte comprises an organic solvent, an electrolyte salt and a functional additive, wherein the functional additive comprises a first additive selected from a pyridine silane compound, the pyridine silane compound is a compound containing a silane group and a pyridine ring, and the silane group is directly connected to the pyridine ring; the pyridine silane compound is selected from at least one of the compounds shown in formula (1): Formula (1) In formula (1), R1, R2, R3 are the same or different and independently selected from substituted or unsubstituted C 1-6 alkyl, substituted or unsubstituted C 1-6 alkyl, substituted or unsubstituted C 2-6 alkenyl; if substituted, the substituents are halogen; X is selected from halogen, substituted or unsubstituted C 1-6 alkyl, substituted or unsubstituted C 1-6 alkoxy, substituted or unsubstituted C 1-6 alkylthio, -Si(R4)(R5)(R6); R4, R5, R6are identical or different and independently from each other selected from substituted or unsubstituted C 1-6 alkyl, substituted or unsubstituted C 2-6 alkenyl; n is an integer between 0 and 4; The weight of the first additive is 1.5wt%-2.5wt% of the total weight of the electrolyte; The charging cutoff voltage of the battery is 4.5V or more.

2. The battery of claim 1, wherein, In formula (1), n is an integer between 0 and 2.

3. The battery of claim 2, wherein, In formula (1), R1, R2, R3 are the same or different and independently selected from substituted or unsubstituted C 1-3 alkyl, substituted or unsubstituted C 1-3 alkoxy, substituted or unsubstituted C 2-3 alkenyl; if substituted, the substituents are halogen; X is selected from halogen, substituted or unsubstituted C 1-3 alkyl, substituted or unsubstituted C 1-3 alkoxy, substituted or unsubstituted C 1-3 alkylthio, -Si(R4)(R5)(R6); R4, R5, R6are identical or different, independently from each other selected from substituted or unsubstituted C 1-3 alkyl, substituted or unsubstituted C 2-3 alkenyl; n is an integer between 0 and 1.

4. The battery of claim 1, wherein, The first additive is selected from at least one of the compounds shown in formula (2)-formula (13): Formula (2) Formula (3) Formula (4) Formula (5) Equation (6) Equation (7) Formula (8) Formula (9) Equation (10) Equation (11) Equation (12) Equation (13).

5. The battery according to any one of claims 1 to 4, characterized in that, The functional additive further comprises a second additive selected from at least one of fluoroethylene carbonate, vinylene carbonate, 1,3-propane sulfone lactone, vinyl sulfate, methylene methane disulfonate, propylene sulfone lactone, maleic anhydride, diglycolic anhydride, succinic anhydride, butanedinitrile, hexanedinitrile, ethylene glycol bis(propionitrile) ether and hexane trinitrile.

6. The battery of claim 5, wherein, The weight of the second additive is 0-15wt% of the total weight of the electrolyte.

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