An electrolyte and a battery comprising the same

Abstract

The application provides an electrolyte and a battery comprising the electrolyte, wherein the electrolyte comprises a sulfuryl bipyridine compound as a first additive, the first additive has a lower LUMO orbital and a higher HOMO orbital, is easy to be oxidized and reduced, and generates an interface film on the surface of the positive and negative electrodes, the interface film has the characteristics of high inorganic component content, high stability, and rich in S atoms and N atoms, can improve the transmission efficiency of lithium ions, and thus can improve the cycle performance of the battery; meanwhile, the first additive and the pyridine derivative which has formed a film are easy to have a polymerization reaction under the limit working condition of thermal shock, delay the short circuit of the positive and negative electrodes, block the aggravation of the side reaction, and effectively improve the thermal shock performance.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, specifically relating to an electrolyte and a battery including the electrolyte. Background Technology

[0002] Lithium-ion batteries have become a major component of the new energy market due to their advantages such as fast charging speed, high energy density, and wide voltage range. However, with the continuous increase in voltage, battery stability has decreased, and side reactions between the interface and electrolyte have intensified, leading to problems such as reduced battery life, gas generation during storage, and susceptibility to failure due to thermal shock. In recent years, the pursuit of higher battery voltage and energy density, along with the continuous introduction of cathode materials that match high voltage, has made the research on electrolytes that match high voltage materials a top priority. When the voltage exceeds the carrying capacity of the material system, excessive side reactions will accelerate electrolyte consumption, seriously affecting the lifespan of lithium-ion battery products and causing battery safety hazards. Therefore, developing electrolytes suitable for high voltage systems is an important direction in current electrolyte development. Summary of the Invention

[0003] To match the high-voltage system of lithium-ion batteries, suppress side reactions between electrode materials and electrolytes, reduce electrolyte consumption, and improve the service life and safety performance of lithium-ion battery products, this invention provides an electrolyte and a battery including the electrolyte; the electrolyte has good ambient and high-temperature cycling performance while also taking into account the thermal shock performance of the battery.

[0004] The objective of this invention is achieved through the following technical solution:

[0005] An electrolyte comprising an electrolyte salt, an organic solvent, and a first additive, wherein the first additive is a sulfonyl bipyridine compound.

[0006] According to an embodiment of the present invention, the sulfonyl bipyridine compound is a compound containing a sulfonyl group and two pyridyl groups, wherein the two pyridyl groups are directly connected to the sulfonyl group.

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

[0008]

[0009] Wherein, X1 and X2 may be the same or different, and each is independently selected from hydrogen, halogen, cyano, substituted or unsubstituted aryl, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkoxy; if substituted, the substituent is alkyl, halogen, or cyano;

[0010] n1 and n2 may be the same or different, and each is an independent integer between 0 and 4.

[0011] According to embodiments of the present invention, X1 and X2 may be the same or different, and are each independently selected from hydrogen, halogen, cyano, substituted or unsubstituted C. 6-12 aryl, substituted or unsubstituted C 1-12 Alkyl, substituted or unsubstituted C 2-12 alkenyl, substituted or unsubstituted C 1-12 alkoxy group; if substituted, the substituent is C. 1-12 Alkyl, halogen, cyano.

[0012] According to embodiments of the present invention, X1 and X2 may be the same or different, and are each independently selected from hydrogen, halogen, cyano, substituted or unsubstituted C. 6-10 aryl, substituted or unsubstituted C 1-6 Alkyl, substituted or unsubstituted C 2-6 alkenyl, substituted or unsubstituted C 1-6 alkoxy group; if substituted, the substituent is C. 1-6 Alkyl, halogen, cyano.

[0013] According to embodiments of the present invention, X1 and X2 may be the same or different, and are each independently selected from hydrogen, halogen, cyano, substituted or unsubstituted C. 6-8 aryl, substituted or unsubstituted C 1-3 Alkyl, substituted or unsubstituted C 2-3 alkenyl, substituted or unsubstituted C 1-3 alkoxy group; if substituted, the substituent is C. 1-3 Alkyl, halogen, cyano.

[0014] According to embodiments of the present invention, X1 and X2 may be the same or different, and each is independently selected from hydrogen, trifluoromethyl, fluorine, and cyano.

[0015] According to an embodiment of the present invention, n1 and n2 may be the same or different, and each can be 0, 1, 2, 3 or 4 independently.

[0016] According to an embodiment of the present invention, the first additive is selected from at least one of the following compounds A1 to A5:

[0017] Compound A1;

[0018] Compound A2;

[0019] Compound A3;

[0020] Compound A4;

[0021] Compound A5.

[0022] According to an embodiment of the present invention, the content of the first additive is 0.5wt% to 3wt% of the total mass 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%, 2.2wt%, 2.4wt%, 2.5wt%, 2.6wt%, 2.8wt%, or 3wt%.

[0023] According to an embodiment of the present invention, the first additive can be obtained through commercial purchase or prepared by methods known in the art.

[0024] According to an embodiment of the present invention, the electrolyte salt is selected from lithium electrolyte salts.

[0025] According to an embodiment of the present invention, the electrolyte lithium salt is selected from at least one of lithium hexafluorophosphate (LiPF6), lithium difluorophosphate (LiPF2O2), lithium difluorobis(oxalate) phosphate (LiPF2(C2O4)2), lithium tetrafluorooxalate phosphate (LiPF4C2O4), lithium oxalate phosphate (LiPO2C2O4), lithium bis(oxalate) borate (LiBOB), lithium difluorooxalate borate (LiODFB), lithium tetrafluoroborate (LiBF4), lithium bis(fluorosulfonyl)imide (LiTFSI), and lithium bis(fluorosulfonyl)imide (LiFSI).

[0026] According to an embodiment of the present invention, the content of the electrolyte salt as a percentage of the total mass of the electrolyte is 10wt% to 15wt%, for example, 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, or 15wt%.

[0027] According to an embodiment of the present invention, the organic solvent is selected from at least one of ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl propionate (EP), propyl propionate (PP), ethyl acetate (EA), ethyl butyrate (EB), and γ-butyrolactone (GBL).

[0028] According to an embodiment of the present invention, the content of the organic solvent as a percentage of the total mass of the electrolyte is 60wt% to 90wt%, for example, 60wt%, 65wt%, 70wt%, 75wt%, 80wt%, 85wt%, or 90wt%.

[0029] According to an embodiment of the present invention, the electrolyte further includes a second additive, the second additive being selected from at least one of fluoroethylene carbonate (FEC), vinylene carbonate (VC), 1,3-propanesulfonate lactone (PS), vinyl sulfate (DTD), methanedisulfonate methylene ester (MMDS), propenesulfonate lactone (PST), maleic anhydride, diethanolic anhydride, succinic anhydride, succinic anhydride, succinic nitrile (SN), adiponitrile (ADN), ethylene glycol bis(propionitrile) ether (EGBE), and hexanetrionitrile (HTCN).

[0030] According to an embodiment of the present invention, the content of the second additive is 1 wt% to 15 wt% of the total mass of the electrolyte, preferably 5 wt% to 13 wt%, for example, 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%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, or 15 wt%.

[0031] The present invention also provides a method for preparing the above-mentioned electrolyte, the method comprising the following steps:

[0032] The electrolyte is obtained by mixing an organic solvent, an electrolyte salt, a first additive, and optionally a second additive.

[0033] The present invention also provides a battery comprising the electrolyte described above.

[0034] According to an embodiment of the present invention, the battery is a lithium-ion battery.

[0035] According to an embodiment of the present invention, the battery further includes a positive electrode sheet containing a positive electrode active material, a negative electrode sheet containing a negative electrode active material, and a separator.

[0036] According to an embodiment of the present invention, the positive electrode sheet includes a positive current collector and a positive active material layer coated on one or both surfaces of the positive current collector, wherein the positive active material layer includes a positive active material, a conductive agent, and a binder.

[0037] According to an embodiment of the present invention, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer coated on one or both surfaces of the negative electrode current collector, wherein the negative electrode active material layer includes a negative electrode active material, a conductive agent, and a binder.

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

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

[0040] According to an embodiment of the present invention, the mass percentage content of each component in the negative electrode active material layer is: 80 to 99.8 wt% of negative electrode active material, 0.1 to 10 wt% of conductive agent, and 0.1 to 10 wt% of binder.

[0041] Preferably, the mass percentage content of each component in the negative electrode active material layer is: 90 to 99.6 wt% of negative electrode active material, 0.2 to 5 wt% of conductive agent, and 0.2 to 5 wt% of binder.

[0042] According to an embodiment of the present invention, the conductive agent is selected from at least one of conductive carbon black, acetylene black, Ketjen black, conductive graphite, conductive carbon fiber, carbon nanotube, and metal powder.

[0043] According to an embodiment of the present invention, the binder is selected from at least one of sodium carboxymethyl cellulose, styrene-butadiene latex, polytetrafluoroethylene, and polyethylene oxide.

[0044] According to an embodiment of the present invention, the negative electrode material is selected from at least one of nano-silicon (Si), silicon-oxygen negative electrode material (SiO x (0 < x < 2)), silicon-carbon negative electrode material, artificial graphite, natural graphite, mesophase carbon microspheres, hard carbon, soft carbon, lithium metal, and lithium titanate.

[0045] According to an embodiment of the present invention, the positive electrode active material is selected from lithium transition metal composite oxides, and the lithium transition metal oxide is selected from LiMO2 (M = Ni, Co, Mn), LiMn2O4, LiMPO4 (M = Fe, Mn, Co), LiNi x Mn 1-x O2 (M = Co, Mn), LiNixCo y M1 x y O2, where 0 ≤ x, y ≤ 1 and x + y ≤ 1; where 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.

[0046] Beneficial effects

[0047] This invention provides an electrolyte and a battery comprising the electrolyte. The electrolyte includes a sulfonyl bipyridine compound as a first additive. The first additive has a low LUMO orbital and a high HOMO orbital, making it easily oxidized and reduced to form an interfacial film on the positive and negative electrode surfaces. This interfacial film is characterized by high inorganic content, high stability, and rich in S and N atoms, which can improve the lithium-ion transport efficiency and thus enhance the cycle performance of the battery. At the same time, both the first additive and the already formed pyridine derivative readily undergo polymerization reactions under extreme thermal shock conditions, delaying short circuits at the positive and negative electrodes, preventing the aggravation of side reactions, and effectively improving thermal shock performance. Detailed Implementation

[0048] The present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0049] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0050] In the description of this invention, it should be noted that the terms "first," "second," etc., are used for descriptive purposes only and are not intended to indicate or imply relative importance.

[0051] Methods for preparing lithium-ion batteries include:

[0052] [Preparation of positive electrode sheet]

[0053] Lithium cobalt oxide (LCO), polyvinylidene fluoride (PVDF), conductive carbon black, and single-walled carbon nanotubes were mixed in a weight ratio of 97.2:1.5:1.2:0.1. N-methylpyrrolidone (NMP) was added, and the mixture was stirred under vacuum until a homogeneous and fluid positive electrode slurry was formed. The positive electrode slurry was uniformly coated onto a current collector aluminum foil. The coated aluminum foil was baked in an oven with five different temperature gradients, and then dried in an oven at 120°C for 8 hours. Finally, it was rolled and slit to obtain the desired positive electrode sheet.

[0054] [Preparation of negative electrode sheet]

[0055] Artificial graphite (anode active material), sodium carboxymethyl cellulose (CMC-Na) (thickener), styrene-butadiene rubber (binder), and acetylene black (conductive agent) were mixed in a weight ratio of 97:1:1:1. Deionized water was added, and the mixture was stirred in a vacuum mixer to obtain a cathode slurry. The cathode slurry was uniformly coated onto a high-strength carbon-coated copper foil to obtain an electrode sheet. After the obtained electrode sheet was dried at room temperature, it was transferred to an 80°C oven to dry for 10 hours. Then, it was rolled and slit to obtain a cathode sheet.

[0056] [Electrolyte Preparation]

[0057] In a glove box filled with inert gas (H2O < 10 ppm, O2 < 5 ppm), ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate were mixed at a mass ratio of EC:PC:DEC = 1:2:4. Then, lithium hexafluorophosphate (LiPF6) at 13.75 wt% of the total electrolyte weight was slowly added to the mixed solution. After passing moisture and free acid tests, a basic electrolyte was obtained. Different amounts of the first and second additives listed in Table 1 were added to the basic electrolyte to obtain electrolytes for the corresponding examples and comparative examples.

[0058] [Battery manufacturing]

[0059] Stack the prepared positive electrode, separator (9-micron thick PP film), and negative electrode in sequence, ensuring that the separator is between the positive and negative electrodes to provide isolation. Place the bare cell in the aluminum-plastic film outer packaging, inject the prepared electrolyte into the dried battery, and then encapsulate, let stand, form, shape, and perform capacity testing to complete the preparation of the lithium-ion soft pack battery.

[0060] Examples 1-10 and Comparative Examples 1-4 were prepared according to the preparation method described above.

[0061] Table 1. Composition of the electrolyte in the batteries of the examples and comparative examples.

[0062] First additive and its content Second additive and its content Example 1 Compound A1: 0.5 wt% FEC: 8.0 wt% / PS: 3.0 wt% Example 2 Compound A1: 1.0 wt% FEC: 8.0 wt% / PS: 3.0 wt% Example 3 Compound A1: 2.0 wt% FEC: 8.0 wt% / PS: 3.0 wt% Example 4 Compound A1: 3.0 wt% FEC: 8.0 wt% / PS: 3.0 wt% Example 5 Compound A2: 1.0 wt% FEC: 8.0 wt% / PS: 3.0 wt% Example 6 Compound A3: 1.0 wt% FEC: 8.0 wt% / PS: 3.0 wt% Example 7 Compound A4: 1.0 wt% FEC: 8.0 wt% / PS: 3.0 wt% Example 8 Compound A5: 1.0 wt% FEC: 8.0 wt% / PS: 3.0 wt% Example 9 Compound A1: 1.0 wt% FEC: 8.0wt% Example 10 Compound A1: 1.0 wt% PS: 3.0wt% Comparative Example 1 / / Comparative Example 2 / FEC: 8.0wt% Comparative Example 3 / PS: 3.0wt% Comparative Example 4 / FEC: 8.0 wt% / PS: 3.0 wt%

[0063] Performance testing

[0064] The lithium-ion batteries and their electrolytes obtained in the above embodiments and comparative examples were subjected to relevant performance tests.

[0065] (1) High temperature cycle performance test: At 45℃, the battery after capacity division is charged to 4.48V at a constant current and constant voltage of 0.7C and the cut-off current is 0.05C. Then it is discharged to 3.0V at a constant current of 0.5C. This cycle is repeated. After 500 charge and discharge cycles, the capacity retention rate of the 500th cycle is calculated. The calculation formula is as follows: Capacity retention rate of the 500th cycle (%) = (500th cycle discharge capacity / first cycle discharge capacity) × 100%.

[0066] (2) Room temperature cycle performance test: At 25℃, the battery after capacity division is charged to 4.48V at a constant current and constant voltage of 0.7C and the cut-off current is 0.05C. Then it is discharged to 3.0V at a constant current of 0.5C. This cycle is repeated. After 500 charge and discharge cycles, the capacity retention rate of the 500th cycle is calculated. The calculation formula is as follows: Capacity retention rate of the 500th cycle (%) = (500th cycle discharge capacity / first cycle discharge capacity) × 100%.

[0067] (3) Thermal shock performance: At 25℃, discharge to 3.0V with a given current of 0.2C; rest for 5 minutes; charge to 4.48V with a charging current of 0.2C. When the cell voltage reaches 4.48V, switch to constant voltage charging at 4.48V until the charging current is less than or equal to the given cutoff current of 0.05C; after resting for 1 hour, put the cell into an oven. The oven temperature rises to 135±2℃ at a rate of 5±2℃ / min and is maintained for 30 minutes before stopping. The judgment criterion is that the cell does not catch fire or explode.

[0068] Table 2 shows the performance test results of the batteries in the examples and comparative examples.

[0069]

[0070] As can be seen from the comparison of the test results of Comparative Example 4 and Examples 1-10 in Table 2, the addition of the first additive in the examples can effectively improve the room temperature and high temperature cycling performance and thermal shock performance of lithium-ion batteries.

[0071] Comparing Comparative Examples 1-4 and Examples 1-10, it can be seen that the addition of the first additive can significantly improve the thermal shock performance of the battery. Moreover, the improvement in thermal shock performance is more obvious with the increase of the amount added. The possible reason is that under thermal shock conditions, the accelerated polymerization of the first additive can isolate the positive and negative electrodes. At the same time, the higher the amount of the first additive added, the more significant the blocking effect is, thus effectively improving the thermal shock performance of the battery.

[0072] Comparing Comparative Example 4 with Examples 1-3, it can be seen that the first additive improves the cycle performance in an appropriate range (0.5-3wt%). However, the cycle performance does not improve significantly when the amount added is excessive. This may be because the increased amount of additive leads to excessive polarization due to increased film thickness, which has a negative effect on the cycle performance.

[0073] In summary, it can be seen that the electrolyte provided by this invention can effectively improve cycling and thermal shock performance, demonstrating extremely high application potential.

[0074] The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An electrolyte, characterized in that, The electrolyte comprises an electrolyte salt, an organic solvent, and a first additive, wherein the first additive is a sulfonyl bipyridine compound. The first additive is selected from at least one of the compounds shown in Formula 1: Formula I Wherein, X1 and X2 may be the same or different, and each is independently selected from hydrogen, halogen, cyano, substituted or unsubstituted aryl, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkoxy; if substituted, the substituent is alkyl, halogen, or cyano; n1 and n2 may be the same or different, and each is an independent integer between 0 and 4; The content of the first additive is 0.5wt% to 3wt% of the total mass of the electrolyte.

2. The electrolyte according to claim 1, characterized in that, The first additive is selected from at least one of the following compounds A1 to A5: Compound A1; Compound A2; Compound A3; Compound A4; Compound A5.

3. The electrolyte according to claim 1, characterized in that, The electrolyte salt is selected from lithium electrolyte salts, specifically lithium hexafluorophosphate (LiPF6), lithium difluorophosphate (LiPF2O2), lithium difluorobis(oxalate) phosphate (LiPF2(C2O4)2), lithium tetrafluorooxalate phosphate (LiPF4C2O4), lithium oxalate phosphate (LiPO2C2O4), lithium bis(oxalate) borate (LiBOB), lithium difluorooxalate borate (LiODFB), lithium tetrafluoroborate (LiBF4), lithium bis(fluorosulfonyl)imide (LiTFSI), and lithium bis(fluorosulfonyl)imide (LiFSI); and / or, the content of the electrolyte salt is 10wt% to 15wt% of the total mass of the electrolyte.

4. The electrolyte according to claim 1, characterized in that, The organic solvent is selected from at least one of ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl propionate (EP), propyl propionate (PP), ethyl acetate (EA), ethyl butyrate (EB), and γ-butyrolactone (GBL); and / or, the content of the organic solvent is 60wt% to 90wt% of the total mass of the electrolyte.

5. The electrolyte according to any one of claims 1-4, characterized in that, The electrolyte further includes a second additive selected from at least one of fluoroethylene carbonate (FEC), vinylene carbonate (VC), 1,3-propanesulfonate lactone (PS), vinyl sulfate (DTD), methanedisulfonate methylene ester (MMDS), propenesulfonate lactone (PST), maleic anhydride, diethanolic anhydride, succinic anhydride, succinic anhydride, succinic anhydride (SN), adiponitrile (ADN), ethylene glycol bis(propionitrile) ether (EGBE), and hexanetrionitrile (HTCN).

6. The electrolyte according to claim 5, characterized in that, The content of the second additive is 1wt% to 15wt% of the total mass of the electrolyte.

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

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