An electrolyte and a battery comprising the same

Abstract

The application provides an electrolyte and a battery comprising the electrolyte. The electrolyte provided by the application is added with an iodine-containing imidazole compound as a first additive. The iodine-containing imidazole compound can be reduced on the surface of a negative electrode to generate I ‑ / I 3‑ redox couples, reversible I ‑ / I 3‑ redox reactions are conducive to the reactivation of non-active lithium. The imidazole group can effectively form a dense solid electrolyte film protective layer on the surface of the negative electrode to prevent uncontrollable growth of lithium dendrites and protect the negative electrode. On this basis, after the second additive is added, it can jointly act with the first additive on the surface of the positive and negative electrodes to generate stable SEI films and CEI films, and inhibit the occurrence of side reactions between the electrode material and the electrolyte. Through the synergistic effect of the first additive and the second additive, the risk of lithium precipitation of the battery is reduced, the safety performance and the cycle performance of the battery are significantly improved, and the fast charging performance of the battery is further taken into account.

Description

TECHNICAL FIELD

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

[0002] With the development of new energy technology, lithium ion batteries have been widely applied in the field of new energy vehicles and mobile terminals due to their high energy density, fast charging, long cycle life and other advantages. However, with the continuous improvement of customer demand, there are higher requirements for the working voltage, energy density, service life and charging speed of lithium ion batteries, especially for the application scenarios such as electric vehicles and energy storage systems, which require lithium ion batteries to have higher energy density, longer life cycle and faster charging speed.

[0003] Research has found that lithium ion reaction kinetics has a decisive effect on the charging speed of lithium ion batteries, and the rate-limiting step in the charging process of lithium ion batteries is often the solvation and desolvation process of lithium ions, which is closely related to the properties of the electrolyte and the electrode interface.

[0004] In order to achieve faster charging speed, improving the charging rate is a common strategy, which requires lithium ion batteries to have better kinetic performance. Moreover, under fast charging conditions, the risk of lithium precipitation in lithium ion batteries will increase, resulting in loss of active lithium and rapid capacity decay of the battery. SUMMARY

[0005] In order to improve the rapid cycle capacity decay of lithium ion batteries caused by the loss of active lithium and reduce the risk of lithium precipitation in lithium ion batteries, the present application provides an electrolyte and a battery comprising the electrolyte. The electrolyte can improve the lithium precipitation of lithium ion batteries, and improve the cycle performance of lithium ion batteries while considering the fast charging performance of the battery.

[0006] The purpose of the present application is achieved by the following technical solutions:

[0007] An electrolyte, comprising a lithium salt, an organic solvent and a first additive; the first additive is selected from an iodine-containing imidazole compound, the iodine-containing imidazole compound is an imidazole compound substituted with at least two iodine atoms, and the hydrogen atoms on the imidazole ring are substituted by the iodine atoms.

[0008] According to an embodiment of the present application, the first additive is selected from at least one of the compounds shown in formula I:

[0009]

[0010] wherein R1, R2, R3and R4are the same or different and are independently selected from the group consisting of a hydrogen atom, a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, a cyano group, a sulfonic acid group (HO-S(=0)2-), a sulfonyl group (R-S(=0)2-, R is a C 1-10 alkyl group), a substituted or unsubstituted C 1-10 alkyl group, a substituted or unsubstituted C 1-10 alkoxy group, a substituted or unsubstituted C 6-20 aryl group, a substituted or unsubstituted C 2-10 alkenyl group; and if substituted, the substituent is a halogen, a cyano group, a C 1-10 alkyl group; at least one of R2, R3and R4is an iodine atom;

[0011] or, R1and R3form a 5-6 membered ring with the carbon atom and the nitrogen atom in the imidazole; and R2and R4are both iodine atoms.

[0012] According to an embodiment of the present application, R1, R2, R3and R4are the same or different and are independently selected from the group consisting of a hydrogen atom, a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, a cyano group, a sulfonic acid group (HO-S(=0)2-), a sulfonyl group (R-S(=0)2-, R is a C 1-5 alkyl group), a substituted or unsubstituted C 1-5 alkyl group, a substituted or unsubstituted C 1-5 alkoxy group, a substituted or unsubstituted C 6-10 aryl group, a substituted or unsubstituted C 2-5 alkenyl group; and if substituted, the substituent is a halogen, a cyano group, a C 1-5 alkyl group; at least one of R2, R3and R4is an iodine atom;

[0013] or, R1and R3form a 5-6 membered ring with the carbon atom and the nitrogen atom in the imidazole; and R2and R4are both iodine atoms.

[0014] According to an embodiment of the present application, R1, R2, R3and R4are the same or different and are independently selected from the group consisting of a hydrogen atom, a halogen, a cyano group, a sulfonic acid group (HO-S(=0)2-), a sulfonyl group (R-S(=0)2-, R is a C 1-3 alkyl group), a substituted or unsubstituted C 1-3 alkyl group, a substituted or unsubstituted C 1-3 alkoxy group, a substituted or unsubstituted C 6-8 aryl group, a substituted or unsubstituted C 2-3 alkenyl group; and if substituted, the substituent is a halogen, a cyano group, a C 1-3 alkyl group; at least two of R2, R3and R4are iodine atoms;

[0015] Alternatively, R1and R3form a 5-membered ring with the carbon and nitrogen atoms of the imidazole; and R2and R4are both iodine atoms.

[0016] According to an embodiment of the present application, R2is an iodine atom.

[0017] According to an embodiment of the present application, the first additive is selected from at least one of the following compounds A1-A6:

[0018]

[0019]

[0020] According to an embodiment of the present application, the first additive has a weight of 0.1-10.0 wt% of the total weight of the electrolyte, preferably 0.5-3 wt%, 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%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt% or 10 wt%.

[0021] According to an embodiment of the present application, the first additive can be prepared by methods known in the art or purchased commercially.

[0022] According to an embodiment of the present application, the electrolyte further comprises a second additive selected from at least one of fluoroethylene carbonate (FEC), vinylene carbonate (VC), 1,3-propane sultone (PS), vinyl sulfate (DTD), methylene methane disulfonate (MMDS), propene sultone (PST), maleic anhydride, diglycolic anhydride, succinic anhydride, succinonitrile (SN), adiponitrile (ADN), ethylene glycol bis(propyl nitrate) ether (EGBE) and hexane trinitrile (HTCN).

[0023] According to an embodiment of the present application, the second additive has a weight of 0.1 wt% to 15 wt% of the total weight of the electrolyte, preferably 5 wt% to 12 wt%, for example 0.1 wt%, 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, 5 wt%, 5.5 wt%, 6 wt%, 6.5 wt%, 7 wt%, 7.5 wt%, 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt% or 15 wt%.

[0024] According to an embodiment of the present application, the lithium salt is at least one of lithium hexafluorophosphate (LiPF6), lithium difluorophosphate (LiPF2O2), lithium difluorobisoxalate phosphate (LiPF2(C2O4)2), lithium tetrafluorooxalate phosphate (LiPF4C2O4), lithium oxalate phosphate (LiPO2C2O4), lithium bisoxalate borate (LiBOB), lithium difluoro oxalate borate (LiODFB), lithium tetrafluoroborate (LiBF4), lithium bisfluorosulfonylimide (LiTFSI) and lithium bisfluorosulfonylimide (LiFSI).

[0025] According to an embodiment of the present application, the lithium salt has a weight of 10 wt% to 15 wt% of the total weight of the electrolyte, for example 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt% or 15 wt%.

[0026] According to an embodiment of the present application, the organic solvent is at least one of ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl propionate (EP), propyl propionate (PP), ethyl acetate (EA), ethyl n-butyrate (EB) and gamma-butyrolactone (GBL) and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE).

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

[0028] The present application also provides a battery comprising the electrolyte described above.

[0029] According to an embodiment of the present application, the battery is a lithium ion battery.

[0030] According to an embodiment of the present application, the battery further comprises a positive electrode sheet, a negative electrode sheet 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 positive active material is selected from lithium cobaltate or lithium cobaltate doped with two or more elements selected from Al, Mg, Mn, Cr, Ti, and Zr, and has a chemical formula of Li x Co 1-y1-y2-y3-y4 A y1 B y2 C y3 D y4 O2; 0.95≤x≤1.05, 0.01≤y1≤0.1, 0.01≤y2≤0.1, 0≤y3≤0.1, 0≤y4≤0.1, A, B, C, D are selected from two or more elements selected from Al, Mg, Mn, Cr, Ti, and Zr.

[0033] 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 side or both sides of the negative current collector, and the negative active material layer comprises a negative active material, a conductive agent, and a binder.

[0034] According to an embodiment of the present application, the negative active material is selected from at least one of artificial graphite, natural graphite, mesocarbon microbeads, hard carbon, and soft carbon.

[0035] According to an embodiment of the present application, the compaction density of the negative electrode sheet is 1.5-1.8 g / cm 3 . The average particle size of the active material is 13-21 μm. The tap density of the negative active material is 0.9-1.2 g / cm 3 . The specific surface area of the negative active material is 1.5-2.5 m 2 / g.

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

[0037] Preferably, the mass percentage of each component in the positive active material layer is: 90-99.6 wt% of the positive 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 application, the mass percentage of each component in the negative active material layer is: 80-99.8 wt% of the negative active material, 0.1-10 wt% of the conductive agent, and 0.1-10 wt% of the binder.

[0039] Preferably, the mass percentage of each component in the negative electrode active material layer is: 90-99.6wt% of the negative electrode active material, 0.2-5wt% of the conductive agent, and 0.2-5wt% 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 carboxymethyl cellulose, styrene-butadiene latex, polytetrafluoroethylene, and polyethylene oxide.

[0042] Advantages of the present application:

[0043] The present application provides an electrolyte and a battery comprising the same.

[0044] The electrolyte provided by the present application adds an iodine-containing imidazole compound as a first additive, which can undergo a reduction reaction on the negative electrode surface to generate a solid electrolyte interface (SEI) film containing LiI. - / I 3- Redox couple (F, Cl, Br does not have -3 valence, and will not form the redox couple), reversible I- / I 3- The redox reaction is conducive to the reactivation of non-active lithium. The imidazole group can effectively form a dense solid electrolyte film protective layer on the negative electrode surface, prevent the uncontrollable growth of lithium dendrites, and protect the negative electrode. Further, the solid electrolyte film protective layer generated on the negative electrode surface is rich in LiI, has the characteristics of high lithium ion conductivity (about 3.5 mS / cm, which is 20 times that of the traditional inorganic SEI film component), and is conducive to the efficient transmission of Li + The redox reaction is conducive to the reactivation of non-active lithium. The imidazole group can effectively form a dense solid electrolyte film protective layer on the negative electrode surface, prevent the uncontrollable growth of lithium dendrites, and protect the negative electrode. Further, the solid electrolyte film protective layer generated on the negative electrode surface is rich in LiI, has the characteristics of high lithium ion conductivity (about 3.5 mS / cm, which is 20 times that of the traditional inorganic SEI film component), and is conducive to the efficient transmission of Li DETAILED DESCRIPTION

[0045] 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.

[0046] 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.

[0047] Method for preparing lithium ion battery

[0048] The positive active material lithium cobaltate (LCO), the binder polyvinylidene fluoride (PVDF), the conductive carbon black and the single-walled carbon nanotube are mixed in a weight ratio of 97.2:1.5:1.2:0.1, 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 slurry with uniform fluidity; the positive electrode slurry is uniformly coated on the current collector aluminum foil; the coated aluminum foil is baked in an oven with five different temperature gradients, then dried in an oven at 120°C for 8h, and then subjected to rolling and slitting to obtain the required positive electrode sheet.

[0049] The negative active material artificial graphite, the thickening agent sodium carboxymethyl cellulose (CMC-Na), the binder styrene-butadiene rubber and the conductive agent acetylene black are mixed in a weight ratio of 97:1:1:1, deionized water is added, and a negative electrode slurry is obtained under the action of a vacuum stirrer; the negative electrode slurry is uniformly coated on a high-strength carbon-coated copper foil to obtain an electrode sheet; the obtained electrode sheet is dried at room temperature, then transferred to a 80°C oven for drying for 10h, and then subjected to rolling and slitting to obtain a negative electrode sheet.

[0050] In an inert gas-filled glove box (H2O<10ppm, O2<5ppm), ethylene carbonate, propylene carbonate and diethyl carbonate are mixed in a mass ratio of EC:PC:DEC=1:1:3, then 13wt% of lithium hexafluorophosphate (LiPF6) and an additive (the type and amount of the additive are shown in Table 1) based on the total mass of the electrolyte are slowly added to the mixed solution, and after passing the moisture and free acid detection, an electrolyte is obtained.

[0051] The positive electrode sheet, the negative electrode sheet and the separator film prepared above are stacked in the order of positive electrode sheet, separator film and negative electrode sheet, and then wound to obtain a battery cell; the battery cell is placed in an outer packaging aluminum foil, the electrolyte prepared above is injected into the outer packaging, and then subjected to vacuum packaging, standing, formation, shaping, sorting and other processes to obtain a lithium ion battery.

[0052] Table 1 Composition of additives in electrolytes of examples and comparative examples

[0053]

[0054] The lithium ion batteries obtained in Examples 1-25 and Comparative Examples 1-2 above are subjected to relevant cycle performance tests.

[0055] Normal temperature cycle performance test:

[0056] After the battery is charged at 25℃ by constant current and constant voltage to 4.48V at 5C, the cutoff current is 0.05C, then discharged to 3.0V at 0.5C, and so on, the cycle capacity retention rate is calculated after 500 cycles, and the calculation formula is as follows: cycle capacity retention rate at 500th cycle (%) = (discharge capacity at 500th cycle / discharge capacity at first cycle) x 100%.

[0057] Lithium precipitation performance test: after the battery is cycled for 500 cycles, the battery is disassembled to observe whether lithium precipitation occurs on the negative electrode sheet.

[0058] Table 2 battery performance test results of examples and comparative examples

[0059] Capacity retention rate at room temperature cycle for 500 cycles Whether lithium is precipitated Example 1 85.61％ No Example 2 93.15％ No Example 3 93.61％ No Example 4 95.08％ No Example 5 94.83％ No Example 6 94.34％ No Example 7 93.68％ No Example 8 92.08％ No Example 9 89.66％ No Example 10 94.88％ No Example 11 95.38％ No Example 12 93.47％ No Example 13 94.29％ No Example 14 92.35％ No Example 15 92.93％ No Example 16 94.52％ No Example 17 94.16％ No Example 18 93.51％ No Example 19 92.79％ No Example 20 83.68％ No Example 21 81.57％ No Example 22 85.67％ No Example 23 91.83％ No Example 24 93.68％ No Example 25 92.26％ No Comparative Example 1 68.15％ No Comparative Example 2 75.23％ Yes

[0060] As can be seen from the comparison of the test results of Comparative Example 1 and Examples 1-21 in Table 2, the addition of the first additive can effectively improve the lithium precipitation and cycle performance of the lithium ion battery. Specifically, as can be seen from Comparative Examples 1-9, Examples 14-19 and Comparative Example 1, the addition of the first additive in an appropriate amount (0.5wt%-3wt%) can significantly improve the cycle performance of the lithium ion battery.

[0061] As can be seen from Comparative Examples 1-21 and Comparative Examples 1-2, the first additive in combination with the second additive can better balance the battery performance, because the first additive is conducive to promoting the reactivation of inactive lithium and inhibiting the formation of dead lithium, and the second additive is conducive to forming a stable electrode-electrolyte interface film and inhibiting the decomposition of the electrolyte on the surface of the electrode material.

[0062] As can be seen from Comparative Examples 20-21 and Comparative Example 2, when the substitution position of the iodine atom of the first additive is on R2, R3 or R4, it is easier to be reduced on the surface of the negative electrode to form an iodine-containing SEI film and I- / I 3- Redox couples, reduce the internal resistance and active lithium loss, thereby improving the capacity retention rate and reducing the risk of lithium precipitation.

[0063] As can be seen from Comparative Example 4 and Examples 22-25, the use of the second additives VC and FEC in combination can better improve the cycle capacity retention rate, because VC has a lower LUMO energy level and can be reduced on the negative electrode to form a film to protect the negative electrode material, and FEC has a higher HOMO energy level and can be oxidized on the positive electrode to form a film to protect the positive electrode material.

[0064] In summary, it can be seen that the electrolyte provided by the application and the lithium ion battery using the electrolyte have better safety performance and cycle performance, and show high application potential.

[0065] 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, and the like made within the spirit and principle of the present application should be included in the scope of the present application.

Claims

1. An electrolyte, comprising a lithium salt, an organic solvent, and a first additive; the first additive is selected from imidazoles containing iodine compounds, the imidazoles containing iodine compounds are imidazoles compounds substituted with at least two iodine atoms, and the hydrogen atoms on the imidazole ring are substituted by the iodine atoms; the first additive is selected from at least one of the compounds shown in formula I: Formula I wherein R1, R2, R3and R4are the same or different, independently selected from a hydrogen atom, a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, a cyano group, a sulfonic acid group, a sulfonyl group, a substituted or unsubstituted C 1-10 alkyl group, a substituted or unsubstituted C 1-10 alkoxy group, a substituted or unsubstituted C 6-20 aryl group, a substituted or unsubstituted C 2-10 alkenyl group; if substituted, the substituent is a halogen, a cyano group, a C 1-10 alkyl group; at least one of R2, R3and R4is an iodine atom; or, R1and R3form a 5-6 membered ring with the carbon atom and the nitrogen atom in the imidazole; R2and R4are both iodine atoms.

2. The electrolyte according to claim 1, characterized in that, R1, R2, R3, and R4 may be the same or different, and are independently selected from hydrogen, fluorine, chlorine, bromine, iodine, cyano, sulfonic acid, sulfonyl, substituted or unsubstituted C atoms. 1-5 Alkyl, substituted or unsubstituted C 1-5 Alkoxy, substituted or unsubstituted C 6-10 aryl, substituted or unsubstituted C 2-5 The alkenyl group; if substituted, the substituent is a halogen, cyano, or C. 1-5 Alkyl group; at least one of R2, R3 and R4 is an iodine atom; or, R1 and R3 form a 5-6 membered ring with the carbon and nitrogen atoms in the imidazole; R2 and R4 are both iodine atoms.

3. The electrolyte according to claim 2, characterized in that R 2 is an iodine atom.

4. The electrolyte according to claim 3, characterized in that the first additive is selected from at least one of the following compounds A1-A6: Compound A1; Compound A2; Compound A3; Compound A4; Compound A5; Compound A6.

5. The electrolyte according to any one of claims 1 to 4, characterized in that, the weight of the first additive is 0.1-10.0 wt% of the total weight of the electrolyte.

6. The electrolyte according to claim 5, characterized in that the weight of the first additive is 0.5-3 wt% of the total weight of the electrolyte.

7. The electrolyte according to any one of claims 1 to 4, characterized in that, the electrolyte further comprises a second additive, the second additive is selected from at least one of fluoroethylene carbonate, vinylene carbonate, 1,3-propane sultone, vinyl sulfate, methylene methane disulfonate, propene sultone, maleic anhydride, diglycolic anhydride, succinic anhydride, succinonitrile, adiponitrile, ethylene glycol bis (propionitrile) ether, and hexane trinitrile.

8. The electrolyte according to claim 7, characterized in that the weight of the second additive is 0.1 wt%-15 wt% of the total weight of the electrolyte.

9. The electrolyte of claim 8, wherein, the weight of the second additive is 5 wt%-12 wt% of the total weight of the electrolyte.

10. The electrolyte according to any one of claims 1 to 4, characterized in that, the lithium salt is at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium difluorobisoxalate phosphate, lithium tetrafluorooxalate phosphate, lithium oxalate phosphate, lithium bisoxalate borate, lithium difluorooxalate borate, lithium tetrafluoroborate, lithium bisfluorosulfonimide, and lithium bisfluorosulfonimide; and / or the organic solvent is selected from the group consisting of ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl propionate, propyl propionate, ethyl acetate, ethyl n-butyrate and gamma butyrolactone and at least one of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether. 11.A battery, comprising the electrolyte of any one of claims 1-10.

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