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 pyridine thiophosphate compound as a first additive; through energy level orbit calculation, the pyridine thiophosphate compound has low LUMO and high HOMO, which indicates that the pyridine thiophosphate compound is easy to generate an interface film through redox reaction at the interface of the positive and negative electrodes in the charging and discharging process, and the generated interface film is rich in S, P and N elements, effectively improves the interface ion conductivity, reduces the interface impedance, and simultaneously, the high inorganic component film can inhibit the side reaction caused by the expansion of the negative electrode material in the cycle process, and improves the normal temperature and high temperature cycle performance of the battery.

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] In recent years, with the continuous development of lithium-ion battery technology, it has been widely used in power tools, 3C digital products, energy storage, and other fields. Lithium-ion batteries have advantages such as fast charging speed, long cycle life, and high energy density, making them a key focus of the new energy market. As market demand continues to increase, high-voltage, high-energy-density fast-charging systems have become the mainstream. However, high-voltage, high-energy-density fast-charging systems suffer from reduced electrochemical stability and intensified side reactions between the electrolyte and active materials, leading to decreased cycle life and reduced safety. Therefore, developing an electrolyte that improves cycle performance and safety under high voltage is an important direction in current electrolyte development. Summary of the Invention

[0003] To address the issues of decreased cycle performance and reduced safety performance of batteries under high voltage, this invention provides an electrolyte and a battery comprising the electrolyte. By adding a pyridine thiophosphate compound as a first additive to the electrolyte, the cycle performance and safety performance of the electrolyte under high voltage are significantly improved.

[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 functional additive, wherein the functional additive comprises a first additive, which is a pyridine thiophosphate compound.

[0006] According to an embodiment of the present invention, the pyridine thiophosphate compound contains a pyridine group and a thiophosphate group, wherein the pyridine group and the thiophosphate group are directly linked.

[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] Formula I

[0009] Wherein, X is selected from halogen, cyano, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkoxy, substituted or unsubstituted aryl;

[0010] R1 and R2 may be the same or different, and are independently selected from hydrogen atoms, substituted or unsubstituted alkyl groups, substituted or unsubstituted alkenyl groups, and substituted or unsubstituted aryl groups.

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

[0012] According to embodiments of the present invention, X is selected from halogens, cyano groups, substituted or unsubstituted C groups. 1-10 Alkyl, substituted or unsubstituted C 2-10 alkenyl, substituted or unsubstituted C 1-10 Alkoxy, substituted or unsubstituted C 6-12 Aryl;

[0013] R1 and R2 may be the same or different, and are independently selected from hydrogen atoms, substituted or unsubstituted carbon atoms. 1-10 Alkyl, substituted or unsubstituted C 2-10 alkenyl, substituted or unsubstituted C 6-12 Aryl.

[0014] According to embodiments of the present invention, X is selected from halogens, cyano groups, substituted or unsubstituted C groups. 1-6 Alkyl, substituted or unsubstituted C 2-6 alkenyl, substituted or unsubstituted C 1-6 Alkoxy, substituted or unsubstituted C 6-10 Aryl;

[0015] R1 and R2 may be the same or different, and are independently selected from hydrogen atoms, substituted or unsubstituted carbon atoms. 1-6 Alkyl, substituted or unsubstituted C 2-6 alkenyl, substituted or unsubstituted C 6-10 Aryl.

[0016] According to embodiments of the present invention, X is selected from halogens, cyano groups, substituted or unsubstituted C groups. 1-3 Alkyl, substituted or unsubstituted C 2-3 alkenyl, substituted or unsubstituted C 1-3 Alkoxy, substituted or unsubstituted C 6-8 Aryl;

[0017] R1 and R2 may be the same or different, and are independently selected from hydrogen atoms, substituted or unsubstituted carbon atoms. 1-3 Alkyl, substituted or unsubstituted C 2-3 alkenyl, substituted or unsubstituted C 6-8 Aryl.

[0018] According to an embodiment of the present invention, n is 0, 1, 2, 3 or 4.

[0019] According to an embodiment of the present invention, the first additive is selected from at least one of the following compounds A1 to A4:

[0020] Compound A1;

[0021] Compound A2;

[0022] Compound A3;

[0023] Compound A4.

[0024] According to an embodiment of the present invention, the content of the first additive is 0.1 to 10 wt% of the total mass of the electrolyte, preferably 0.5 wt% to 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%, 3.5 wt%, 4 wt%, 4.5 wt%, 5 wt%, 5.5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt% or 10 wt%.

[0025] 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.

[0026] According to an embodiment of the present invention, the electrolyte salt is selected from lithium electrolyte salts.

[0027] 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).

[0028] 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%.

[0029] 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).

[0030] 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 89wt%, for example, 60wt%, 65wt%, 70wt%, 75wt%, 80wt%, 85wt%, or 89wt%.

[0031] According to an embodiment of the present invention, the functional additive further includes a second additive, wherein the second additive is selected from hexatrionitrile (HTCN).

[0032] According to an embodiment of the present invention, the content of the second additive is 1wt% to 5wt% of the total mass of the electrolyte, preferably 2wt% to 4wt%, for example, 1wt%, 1.2wt%, 1.3wt%, 1.5wt%, 1.6wt%, 1.8wt%, 2wt%, 2.2wt%, 2.4wt%, 2.5wt%, 2.6wt%, 2.8wt%, 3wt%, 3.3wt%, 3.5wt%, 3.8wt%, 4wt%, 4.2wt%, 4.5wt%, 4.8wt%, or 5wt%.

[0033] According to an embodiment of the present invention, the functional additive further includes a third additive, wherein the third additive is 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), and ethylene glycol bis(propionitrile) ether (EGBE).

[0034] According to an embodiment of the present invention, the content of the third additive is 1wt% to 15wt% of the total mass of the electrolyte, preferably 5wt% to 13wt%, for example, 0.1wt%, 0.2wt%, 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%, 2.6wt%, 2.8wt%, 3wt%, 3.3wt%, 3.5wt%, 3.8wt%, 4wt%, 4.2wt%, 4.5wt%, 4.8wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, or 15wt%.

[0035] The present invention also provides a method for preparing the above-mentioned electrolyte, the method comprising the following steps:

[0036] The electrolyte is obtained by mixing an organic solvent, an electrolyte salt, a first additive, an optional second additive, and an optional third additive.

[0037] The present invention also provides a battery comprising the electrolyte described above.

[0038] According to an embodiment of the present invention, the battery is a lithium-ion battery.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] According to an embodiment of the present invention, the mass percentage of each component in the positive electrode active material layer is: 80~99.8wt% positive electrode active material, 0.1~10wt% conductive agent, and 0.1~10wt% binder.

[0043] Preferably, the mass percentage of each component in the positive electrode active material layer is: 90~99.6wt% positive electrode active material, 0.2~5wt% conductive agent, and 0.2~5wt% binder.

[0044] According to an embodiment of the present invention, the mass percentage of each component in the negative electrode active material layer is: 80~99.8wt% negative electrode active material, 0.1~10wt% conductive agent, and 0.1~10wt% binder.

[0045] Preferably, the mass percentage of each component in the negative electrode active material layer is: 90~99.6wt% negative electrode active material, 0.2~5wt% conductive agent, and 0.2~5wt% binder.

[0046] 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 nanotubes, and metal powder.

[0047] According to an embodiment of the present invention, the adhesive is selected from at least one of sodium carboxymethyl cellulose, styrene-butadiene latex, polytetrafluoroethylene, and polyethylene oxide.

[0048] 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.

[0049] 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 oxides are 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 more of Mg, Zn, Ga, Ba, Al, Fe, Cr, Sn, V, Mn, Sc, Ti, Nb, Mo, Zr, Ta, W, B, F, Si.

[0050] Beneficial effects

[0051] The present invention provides an electrolyte and a battery including the electrolyte. The electrolyte includes a pyridylthiophosphate compound as a first additive. Through energy level orbital calculation, the pyridylthiophosphate compound has a low LUMO energy level and a high HOMO energy level, indicating that it is prone to redox reaction at the positive and negative electrode interfaces during charge and discharge to form an interfacial film, and the formed interfacial film is rich in S, P, and N elements, effectively improving the interfacial ionic conductivity, reducing the interfacial impedance. At the same time, the high-inorganic-component film can inhibit the side reactions caused by the expansion of the negative electrode material during the cycling process, and improve the room-temperature and high-temperature cycling performance of the battery. The pyridylthiophosphate compound can not only form a film on the positive and negative electrodes, but also stabilize oxygen free radicals and reduce the dissolution of transition metal ions. The tricyano structure of hexanenitrile, used as a second additive in combination with it, can better complex with the remaining transition metal sites, which enables a cross-locked structure to be formed between the pyridylthiophosphate compound and hexanenitrile, improving the stability of the positive electrode material and the stability of the electrolyte on the positive electrode side at the same time. Moreover, the interfacial film containing a phosphate ester structure formed by the pyridylthiophosphate compound on the positive electrode can also block the free radical reaction under thermal shock conditions, improve the thermal stability. At the same time, pyridine is a weak basic compound, which can capture the acidic compounds generated by the decomposition of the electrolyte under thermal shock conditions and reduce its attack on the positive electrode side. And the pyridine group will form a polymer at the interface of the active material under extreme conditions, covering the short-circuit point and improving the thermal shock resistance. Specific embodiments

[0052] 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.

[0053] 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.

[0054] 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.

[0055] Methods for preparing lithium-ion batteries include:

[0056] [Preparation of positive electrode sheet]

[0057] 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 it formed a homogeneous and fluid positive electrode slurry. 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.

[0058] [Preparation of negative electrode sheet]

[0059] 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.

[0060] [Electrolyte Preparation]

[0061] In a glove box filled with inert gas (H2O < 10 ppm, O2 < 5 ppm), ethylene carbonate, ethyl methyl carbonate, and propyl propionate were mixed at a mass ratio of EC:PC:PP = 1:1:3. Then, lithium hexafluorophosphate (LiPF6) at 13.75 wt% of the total electrolyte weight was slowly added to the mixture. After passing moisture and free acid tests, a basic electrolyte was obtained. Adding different amounts of additives listed in Table 1 to the basic electrolyte yielded electrolytes for the corresponding examples and comparative examples.

[0062] [Battery manufacturing]

[0063] 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.

[0064] Examples 1-10 and Comparative Examples 1-6 were prepared according to the preparation method described above.

[0065] Table 1. Composition of the electrolyte in the batteries of the examples and comparative examples.

[0066]

[0067] The structural formula of the pyrimidine thiophosphate used in Comparative Example 5 is as follows: .

[0068] The structural formula of the pyridazine thiophosphate used in Comparative Example 6 above is: .

[0069] Performance testing

[0070] The lithium-ion batteries and their electrolytes obtained in Examples 1-10 and Comparative Examples 1-6 were subjected to relevant performance tests.

[0071] (1) High-temperature cycle performance test: At 45℃, the battery after capacity grading was charged to 4.48V at a constant current and constant voltage of 0.7C, with a cutoff current of 0.05C, and then discharged to 3.0V at a constant current of 0.5C. This cycle was repeated for 500 charge-discharge cycles. The capacity retention rate at the 500th cycle was calculated using the following formula:

[0072] 500-week cycle capacity retention (%) = (500-week cycle discharge capacity / initial cycle discharge capacity) × 100%.

[0073] (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 cutoff 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-discharge cycles, the capacity retention rate on the 500th cycle is calculated. The calculation formula is as follows:

[0074] 500-week cycle capacity retention (%) = (500-week cycle discharge capacity / initial cycle discharge capacity) × 100%.

[0075] (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.

[0076] Table 2 shows the performance test results of the batteries in the examples and comparative examples.

[0077]

[0078] The test results of Comparative Examples 1-6 and Examples 1-10 in Table 2 show that the compounds with the structure shown in Formula I in the examples can effectively improve the room temperature and high temperature cycling performance and thermal shock performance of lithium-ion batteries.

[0079] A comparison of Comparative Examples 1-4 and Examples 1-4 shows that compounds with the structure shown in Formula I significantly improve the thermal shock performance of lithium-ion batteries. The improvement in thermal shock performance is more pronounced with increasing addition amount, suggesting that higher addition amounts lead to more significant improvements in thermal stability, thus resulting in a more significant improvement in the battery's thermal shock performance. Compounds with the structure shown in Formula I also significantly improve the cycle performance of lithium-ion batteries, presumably because they generate a stable interfacial film at the positive and negative electrode interfaces, suppressing side reactions between the electrolyte and active materials, thereby improving cycle performance. With increasing addition amount, the cycle performance shows a trend of first increasing and then decreasing, which is presumably due to the increased film thickness leading to excessive polarization and negatively impacting cycle performance.

[0080] Comparison of Examples 1-4 and Examples 1-10 shows that the compound with the structure shown in Formula I has a more significant effect on improving the furnace temperature in synergy with HTCN. It is speculated that the compound with the structure shown in Formula I and HTCN can both complex transition metal ions and stabilize the positive electrode interface, thus effectively improving the thermal shock performance of the battery.

[0081] Comparison of Examples 5-6 and Examples 1-7 shows that the thermal shock properties of pyrimidine thiophosphate and pyridazine thiophosphate are significantly worse than those of pyridine thiophosphate. Calculations show that the reduction resistance of pyrimidine and pyridazine is significantly worse than that of pyridine. It is speculated that due to their poor reduction resistance, they are reduced and decomposed prematurely during the formation process, and their structure is destroyed. Therefore, they cannot form a polymer film at the interface under thermal shock conditions, resulting in a significant deterioration in thermal shock properties.

[0082] In summary, the electrolyte provided by this invention can effectively improve the cycle performance and thermal shock performance of batteries, demonstrating extremely high application potential.

[0083] 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 includes an electrolyte salt, an organic solvent, and a functional additive, wherein the functional additive includes a first additive, which is a pyridine thiophosphate compound. The first additive is selected from at least one of the compounds shown in Formula 1: Formula I Wherein, X is selected from halogen, cyano, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkoxy, substituted or unsubstituted aryl; R1 and R2 may be the same or different, and are independently selected from hydrogen atoms, substituted or unsubstituted alkyl groups, substituted or unsubstituted alkenyl groups, and substituted or unsubstituted aryl groups. n is an integer between 0 and 4; The content of the first additive is 0.1~10 wt% of the total mass of the electrolyte; The functional additive also includes a second additive, wherein the second additive is selected as acetyltrionitrile; The content of the second additive is 1wt% to 5wt% of the total mass of the electrolyte.

2. The electrolyte according to claim 1, characterized in that, X is selected from halogen, cyano, substituted or unsubstituted C. 1-10 Alkyl, substituted or unsubstituted C 2-10 alkenyl, substituted or unsubstituted C 1-10 Alkoxy, substituted or unsubstituted C 6-12 Aryl; R1 and R2 may be the same or different, and are independently selected from hydrogen atoms, substituted or unsubstituted carbon atoms. 1-10 Alkyl, substituted or unsubstituted C 2-10 alkenyl, substituted or unsubstituted C 6-12 Aryl.

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

4. The electrolyte according to any one of claims 1-3, characterized in that, The functional additive further includes a third additive, which is selected from at least one of fluoroethylene carbonate, vinylene carbonate, 1,3-propanesulfonate lactone, vinyl sulfate, methanedisulfonate methylene, propylene sulfonate lactone, maleic anhydride, diethanolic anhydride, succinic anhydride, succinic anhydride, adiponitrile, and ethylene glycol bis(propionitrile) ether.

5. The electrolyte according to claim 4, characterized in that, The content of the third additive is 1wt% to 15wt% of the total mass of the electrolyte.

6. A battery, characterized in that, The battery includes the electrolyte according to any one of claims 1-5.

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