An electrolyte and an electrochemical device comprising the same

Abstract

The application provides an electrolyte and an electrochemical device comprising the electrolyte, the electrolyte comprising a lithium salt, an organic solvent and a first additive, the first additive comprising a seleninic acid compound, the seleninic acid compound having at least one of the structural formulas shown in formula I: the electrolyte and the electrochemical device comprising the electrolyte have the characteristics of good high-temperature cycle performance and good high-temperature storage performance.

Description

Technical Field

[0001] This invention relates to the field of electrochemical technology, and more particularly to an electrolyte and an electrochemical device including the electrolyte. Background Technology

[0002] Lithium-ion batteries, as typical modern energy storage devices, have been widely used in various consumer electronics and transportation equipment. The performance and safety of lithium-ion batteries are affected by various factors during use, including operating temperature, battery structure, and electrode materials. Among these, the high-temperature stability, thermal shock, and drop performance of lithium-ion batteries have consistently troubled manufacturers. To address these issues, the electrolyte is one of the key factors determining the high-temperature stability of lithium-ion batteries.

[0003] In existing lithium-ion battery structures, the electrolyte involves various components, among which nitrile additives are crucial, playing a role in improving the thermal stability and conductivity of lithium-ion batteries and inhibiting the growth of the SEI film on the electrode surface. Generally, excessive addition of these additives increases the viscosity of the electrolyte, which may reduce the lithium-ion transport rate and affect electrochemical performance. Insufficient addition may lead to inadequate protection of other materials, exacerbating side reactions and resulting in poor battery performance. Therefore, developing an electrolyte for lithium-ion batteries that possesses both excellent electrochemical performance and safe performance is currently an important research direction. Summary of the Invention

[0004] To address the poor high-temperature cycling and storage performance of existing electrolytes and electrochemical devices including such electrolytes, this invention provides an electrolyte and an electrochemical device including such electrolyte. The electrolyte and the electrochemical device including such electrolyte exhibit good high-temperature cycling and storage performance.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] An electrolyte comprising a lithium salt, an organic solvent, and a first additive, wherein the first additive comprises a selenonitrile compound.

[0007] According to an embodiment of the present invention, the selenonitrile compound has at least one of the structural formulas shown in Formula I:

[0008]

[0009] In Formula I, X1 is selected from alkyl, alkoxy, and alkenyl groups that are absent, substituted, or unsubstituted. If substituted, the substituent is alkyl, alkenyl, cyano, or halogen.

[0010] R is selected from substituted or unsubstituted alkyl, substituted or unsubstituted heteroaryl, substituted or unsubstituted aryl, and if substituted, the substituent is alkyl, cyano or halogen.

[0011] According to embodiments of the present invention, research has found that by adding selenonitrile compounds to the electrolyte, stable interfacial films can be formed on the surfaces of the positive and negative electrodes. The inorganic interfacial film, rich in Se, exhibits high stability, high ionic conductivity, and low electronic conductivity, effectively reducing side reactions in the negative electrode active material and capturing free nitrile groups, thus improving SEI film stability. On the positive electrode side, the selenonitrile structure has strong adsorption capacity and can be effectively adsorbed onto the positive electrode surface. Furthermore, the resulting inorganic-metal interface can form a reversible alloy phase with active lithium, mitigating phase transitions in the positive electrode active material under high voltage and improving positive electrode stability. In summary, the addition of selenonitrile compounds can improve the stability of the positive and negative electrode interfaces, thereby enhancing the high-temperature cycle performance and high-temperature storage performance of lithium-ion batteries.

[0012] According to an embodiment of the present invention, in Formula I, X1 is selected from C that is absent, substituted, or unsubstituted. 1-12 Alkyl, C 1-12 Alkoxy, C 2-12 Alkenyl groups, if substituted, have a C substituent. 1-12 Alkyl, C 2-12 Alkenyl, cyano, or halogen;

[0013] R is selected from substituted or unsubstituted C. 1-12 Alkyl, substituted or unsubstituted 5-12-membered heteroaryl, substituted or unsubstituted C 6-12 aryl groups, if substituted, have a substituent of C. 1-12 Alkyl, cyano or halogen.

[0014] According to an embodiment of the present invention, in Formula I, X1 is selected from C that is absent, substituted, or unsubstituted. 1-6 Alkyl, C 1-6 Alkoxy, C 2-6 Alkenyl groups, if substituted, have a C substituent. 1-6 Alkyl, C 2-6 Alkenyl, cyano, or halogen;

[0015] R is selected from substituted or unsubstituted C. 1-6 Alkyl, substituted or unsubstituted 5-8 membered heteroaryl, substituted or unsubstituted C 6-10 aryl groups, if substituted, have a substituent of C. 1-6 Alkyl, cyano or halogen.

[0016] According to an embodiment of the present invention, in Formula I, X1 is selected from C that is absent, substituted, or unsubstituted. 1-3 Alkyl, C 1-3 Alkoxy, C 2-3Alkenyl groups, if substituted, have a C substituent. 1-3 Alkyl, C 2-3 Alkenyl, cyano, or halogen;

[0017] R is selected from substituted or unsubstituted C. 1-3 Alkyl, substituted or unsubstituted 5-6 membered heteroaryl, substituted or unsubstituted C 6-8 aryl groups, if substituted, have a substituent of C. 1-3 Alkyl, cyano or halogen.

[0018] According to an embodiment of the present invention, in Formula I, X1 is selected from C that is absent, substituted, or unsubstituted. 1-3 Alkyl, C 1-3 Alkoxy, C 2-3 Alkenyl groups, if substituted, have a C substituent. 1-3 Alkyl, C 2-3 Alkenyl, cyano, or halogen;

[0019] R is selected from substituted or unsubstituted C. 1-3 Alkyl, substituted or unsubstituted pyridyl, substituted or unsubstituted phenyl, and if substituted, the substituent is C. 1-3 Alkyl, cyano or halogen.

[0020] According to an embodiment of the present invention, the selenonitrile compound includes at least one of the following compounds 1 to 6:

[0021]

[0022] According to embodiments of the present invention, when the selenonitrile compounds selected are compounds 1 to 6, the stability of the positive and negative electrode interfaces can be significantly improved, thereby enhancing the high-temperature cycle performance and high-temperature storage performance of lithium-ion batteries.

[0023] According to an embodiment of the present invention, the electrolyte further includes a second additive, which includes an ether nitrile compound.

[0024] According to embodiments of the present invention, research has found that adding selenonitrile compounds to the electrolyte, and further combining them with ether nitrile compounds, can better stabilize the positive electrode active material. Simultaneously, the ether nitrile compounds exhibit low impedance and high ionic conductivity. When used in combination, the two additives can simultaneously complex with the positive electrode surface, forming a more stable interfacial film. This effectively suppresses phase transitions in the positive electrode active material and further improves the wettability of the positive electrode surface, reduces side reactions, and enhances battery performance, such as reducing gas generation. The combination of selenonitrile and ether nitrile compounds can improve the battery's high-temperature cycle performance, high-temperature storage performance, and thermal shock resistance.

[0025] According to an embodiment of the present invention, the second additive has at least one of the structural formulas shown in Formula ⅠI;

[0026]

[0027] In Formula ⅠI, R0, R1, R2, and R3 may be the same or different, and are independently selected from hydrogen, At least one of them, wherein R4-R 10 They may be the same or different, and are independently selected from alkylene groups.

[0028] According to an embodiment of the present invention, R4-R 10 Same or different, selected independently from C 1-5 Alkylene; preferably, R4-R 10 Same or different, selected independently from C 1-3 Alkylene; R4-R 10 They may be the same or different, and are independently selected from methylene or ethylene.

[0029] According to embodiments of the present invention, the ether nitrile compound includes at least one of the following compounds 7 to 11:

[0030]

[0031] According to an embodiment of the present invention, the mass percentage A of the first additive to the total mass of the electrolyte satisfies: 0.05% ≤ A ≤ 8%, preferably 1% ≤ A ≤ 4%. Exemplarily, A is 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 5%, 6%, 7%, or 8%. When the mass percentage of the first additive is less than 0.05%, due to the insufficient content of the first additive, it cannot generate a sufficient and stable interfacial film on the positive and negative electrode surfaces, thus failing to effectively reduce the side reactions of the negative electrode active material. Simultaneously, there is not enough interfacial film to capture free nitrile groups, failing to improve the stability of the SEI film; it also cannot be effectively adsorbed onto the positive electrode surface, resulting in a weak ability to improve the phase transition of the positive electrode active material under high voltage, and failing to improve the stability of the positive electrode. Therefore, its introduction has little effect on improving battery performance. When the mass percentage of the first additive is greater than 8%, due to the excessive content of the first additive, the battery impedance is high, and excessive interfacial polarization leads to deterioration of the stability of the active material, affecting the high-temperature cycle performance of the battery.

[0032] According to an embodiment of the present invention, the mass percentage B of the second additive to the total mass of the electrolyte satisfies: 0.05% ≤ B ≤ 10%, preferably, 1% ≤ B ≤ 6%. Exemplarily, B is 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%. When the mass percentage of the second additive is less than 0.05%, due to its insufficient content, it cannot form a complexation reaction with the first additive on the positive electrode surface, nor can it cooperate with the first additive to further improve the stability of the interfacial film on the positive electrode surface in the presence of the first additive, nor can it further inhibit the phase transition of the positive electrode active material in the presence of the first additive, nor can it improve the wettability of the positive electrode surface, reduce the side reactions on the positive electrode surface, or inhibit the performance improvement of the battery gas generation. It can only play the role of the first additive. When the mass percentage of the second additive is greater than 10%, the viscosity of the electrolyte will increase significantly, and the significant increase in interfacial impedance will also lead to excessive interfacial polarization, affecting the high-temperature cycle performance of the battery.

[0033] According to an embodiment of the present invention, the first additive may be prepared by a method known in the art or obtained through commercial purchase.

[0034] According to an embodiment of the present invention, the second additive may be prepared by a method known in the art or obtained through commercial purchase.

[0035] The present invention also provides an electrochemical device comprising the electrolyte described above.

[0036] According to an embodiment of the present invention, the electrochemical device further includes a negative electrode and a positive electrode;

[0037] The positive electrode sheet includes a positive electrode active material;

[0038] The electrochemical device satisfies:

[0039] 0.4 ≤ 2(A+B)×100 / C ≤ 2.9

[0040] Where A is the mass percentage of the first additive in the electrolyte, in wt%; B is the mass percentage of the second additive in the electrolyte, in wt%; and C is the median particle size of the positive electrode active material, in μm.

[0041] For example, 2(A+B)×100 / C can be 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, or 2.8. Preferably, 0.5≤2(A+B)×100 / C≤2.

[0042] Research has found that when the electrochemical device satisfies 0.4≤2(A+B)×100 / C≤2.9, that is, by adjusting the content of the two additives in the electrolyte of the electrochemical device and the particle size of the positive electrode active material, not only can significantly improved high-temperature cycling performance be obtained, but more importantly, the thermal shock performance of the battery can also be significantly improved. This is mainly because when the electrochemical device satisfies 0.4≤2(A+B)×100 / C≤2.9, the two additives can be fully utilized, allowing the selenonitrile compounds and ether nitrile compounds to complex with the positive electrode surface. The two work together on the positive electrode surface to form a more stable interfacial film, effectively suppressing the phase transition of the positive electrode active material. Furthermore, it can also improve the wettability of the positive electrode surface, reduce side reactions on the positive electrode surface, and suppress battery gas production, thus improving performance. This not only achieves good high-temperature cycling performance, but more importantly, it can also significantly improve the thermal shock performance of the battery. When the electrochemical device satisfies 0.4 ≤ 2(A+B)×100 / C ≤ 2.9, it can effectively ensure the interface protection and performance balance of the two additives, avoiding the side reactions caused by excessive additives that exacerbate performance degradation, and the phenomenon that insufficient additives result in insignificant improvement. Furthermore, compared to 2(A+B)×100 / C < 0.4, when the electrochemical device satisfies 0.4 ≤ 2(A+B)×100 / C ≤ 2.9, it can also improve the high-temperature storage performance of the battery.

[0043] According to embodiments of the present invention, the median particle size of the positive electrode active material is 4-20 μm, for example 6-12 μm, such as 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, or 20 μm. When the median particle size of the positive electrode active material is <4 μm, the material particle size is too small, resulting in an excessively large specific surface area, leading to excessively fast side reaction rates and a sharp decrease in material collapse at the initial stage of testing, causing a sharp deterioration in the battery's high-temperature cycle performance, high-temperature storage performance, and thermal shock performance. When the median particle size of the positive electrode active material is >20 μm, the excessively large particle size leads to an excessively long diffusion path, significantly deteriorating the rate performance. Simultaneously, the high expansion caused by the large particle size leads to a decrease in electrode stability, significantly worsening the battery's high-temperature cycle performance and high-temperature storage performance, and also reducing the battery's thermal shock performance.

[0044] According to an embodiment of the present invention, the electrochemical device is a lithium-ion battery.

[0045] According to an embodiment of the present invention, the charging cutoff voltage of the electrochemical device is 4.48V or higher. This indicates that the electrochemical device has good high-voltage resistance, meaning it performs well even at high voltages.

[0046] The beneficial effects of this invention are:

[0047] The present invention provides an electrolyte and an electrochemical device including the electrolyte, wherein the electrolyte and the electrochemical device including the electrolyte have the characteristics of good high-temperature cycling performance and good high-temperature storage performance. Detailed Implementation

[0048] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0049] Studies have found that during thermal shock testing of electrochemical devices, the test temperature is typically above 100°C. At such high temperatures, the stability of the positive electrode interface is significantly reduced, leading to substantial decomposition of the electrolyte on the positive electrode side. Simultaneously, the positive electrode active material layer undergoes a phase transition, causing structural collapse. A large number of metal ions deposit on the negative electrode side, triggering interface failure and resulting in a violent electrolyte reaction at the negative electrode interface. Ultimately, the continuous heat accumulation at the positive and negative electrode interfaces leads to combustion or explosion of the electrochemical device.

[0050] This application provides an electrolyte and an electrochemical device including the electrolyte. The electrolyte is protected against both the positive and negative electrodes by adding selenonitrile compounds and optionally, ether nitrile compounds. Furthermore, by matching the particle size of the positive electrode active material in a specific ratio, the relationship between the amount of additives and the particle size is balanced, maintaining the thermal stability of the positive and negative electrode interfaces while simultaneously considering electrochemical performance and thermal shock resistance. The electrochemical device of this invention can improve the thermal shock resistance of the electrochemical device from three dimensions: the positive electrode active material, the positive electrode interface, and the negative electrode interface.

[0051] The electrochemical device provided in this application includes a positive electrode, a negative electrode, and an electrolyte. The positive electrode includes a positive current collector and a positive active material layer disposed on the surface of the positive current collector. The negative electrode includes a negative current collector and a negative active material layer disposed on the surface of the negative current collector. The electrolyte contacts the positive active material layer and the negative active material layer respectively and performs ion exchange, so that the electrochemical device can be charged and discharged.

[0052] According to an embodiment of the present invention, the electrolyte includes a first additive, the first additive including a selenonitrile compound having at least one of the structural formulas shown in Formula I.

[0053] According to an embodiment of the present invention, the electrolyte includes a second additive, the second additive including an ether nitrile compound having at least one of the structural formulas shown in Formula ⅠI.

[0054] According to an embodiment of the present invention, the electrolyte includes a third additive, which includes at least one of fluoroethylene carbonate (FEC) and vinylene carbonate (VC).

[0055] According to an embodiment of the present invention, the electrolyte comprises a lithium salt and an organic solvent.

[0056] The embodiments of this application do not impose any particular limitation on lithium salts. Any lithium salt known in the art can be used as long as it can achieve the purpose of this application. For example, lithium salts may include at least one of LiTFSI, LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3), LiC(SO2CF3)3, or LiPO2F2.

[0057] This application does not impose any particular limitation on organic solvents, as long as they can achieve the purpose of this application. For example, organic solvents may include at least one of carbonate compounds, carboxylic acid ester compounds, ether compounds, or other organic solvents. Carbonate compounds may include at least one of ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), propylene carbonate (PC), butyl carbonate (BC), vinyl ethylene carbonate (VEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, or trifluoromethylethylene carbonate. Carboxylic acid ester compounds include at least one of the following: methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, isobutyl propionate, pentyl propionate, isopentyl propionate, ethyl isopropionate, ethyl butyrate, ethyl isobutyrate, butyl butyrate, butyl isobutyrate, pentyl butyrate, isopentyl butyrate, ethyl valerate, ethyl isovalerate, propyl valerate, propyl isovalerate, and compounds in which the foregoing carboxylic acid ester compounds are partially or completely substituted by one or more of F, Cl, Br, and I. The ether compound includes at least one of substituted or unsubstituted alkyl ethers, wherein the substituent is a halogen; and more preferably at least one of substituted or unsubstituted C1-12 alkyl ethers; the alkyl ether may be a cyclic ether compound or a chain ether compound, wherein the number of oxygen atoms in the ether compound may be 1, 2, 3 or 4; preferably, the ether compound may be substituted with at least one halogen atom, wherein the halogen atom is F, Cl or Br.

[0058] According to an embodiment of the present invention, the positive electrode active material layer includes a positive electrode active material.

[0059] The positive electrode active material includes at least one of lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide or lithium nickel manganese oxide, and lithium-rich manganese-based oxide.

[0060] The positive electrode active material layer further includes a positive electrode conductive agent and / or a positive electrode binder. This application embodiment does not particularly limit the positive electrode conductive agent, as long as it achieves the purpose of this application. For example, the positive electrode conductive agent may include at least one of conductive carbon black, acetylene black, Ketjen black, sheet graphite, graphene, carbon nanotubes, or carbon fibers. This application embodiment also does not particularly limit the positive electrode binder, as long as it achieves the purpose of this application. For example, the positive electrode binder may include at least one of polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, styrene-acrylate copolymer, styrene-butadiene copolymer, polyamide, sodium carboxymethyl cellulose, polyvinyl acetate, polyvinylpyrrolidone, polyvinyl ether, polytetrafluoroethylene, polyhexafluoropropylene, or polymethyl methacrylate.

[0061] There are no particular limitations on the positive current collector in this application. The positive current collector can be any positive current collector known in the art, such as aluminum foil, aluminum alloy foil, or composite current collector.

[0062] According to an embodiment of the present invention, the negative electrode active material layer includes a negative electrode active material.

[0063] The negative electrode active material includes at least one of crystalline carbon, amorphous carbon, natural graphite, artificial graphite, intermediate carbon phase microspheres, silicon, silicon oxides, silicon carbide compounds, and silicon alloys.

[0064] The negative electrode active material layer further includes a negative electrode conductive agent and / or a negative electrode binder. This application embodiment does not particularly limit the negative electrode conductive agent, as long as it achieves the purpose of this application. For example, the negative electrode conductive agent may include at least one of carbon black, acetylene black, Ketjen black, sheet graphite, graphene, carbon nanotubes, carbon fibers, or carbon nanowires. This application embodiment also does not particularly limit the negative electrode binder, as long as it achieves the purpose of this application. For example, the negative electrode binder may include at least one of carboxymethyl cellulose (CMC), polyacrylic acid, polyacrylate, polyacrylate, polyvinylpyrrolidone, polyaniline, polyimide, polyamide-imide, polysiloxane, styrene-butadiene rubber, epoxy resin, polyester resin, polyurethane resin, or polyfluorene.

[0065] The embodiments of this application do not have any particular limitations on the negative electrode current collector, as long as it can achieve the purpose of this application. For example, the negative electrode current collector may include at least one of copper foil, nickel foil or carbon-based current collector.

[0066] According to an embodiment of the present invention, the electrochemical device further includes a separator membrane disposed between the positive electrode and the negative electrode to prevent short circuit between the positive and negative electrode. The separator membrane may be a polyethylene (PE) film or a polypropylene (PP) film.

[0067] According to an embodiment of the present invention, the electrochemical device further includes a positive electrode tab, a negative electrode tab, and an outer packaging. The positive electrode sheet, the separator, and the negative electrode sheet are sequentially stacked or stacked on one side and wound together. The positive electrode sheet is connected to the positive electrode tab, and the negative electrode sheet is connected to the negative electrode tab, forming an electrode assembly. The electrode assembly is disposed within the internal space of the outer packaging, and the positive and negative electrode tabs are led out from the internal space of the outer packaging to the external space of the outer packaging so that the positive and negative electrode tabs can be electrically connected to an external circuit. Then, an electrolyte is injected into the internal space of the outer packaging, and the outer packaging is sealed to obtain the electrochemical device. The outer packaging can be an aluminum-plastic film outer packaging.

[0068] I. Lithium-ion Battery Performance Testing Methods

[0069] (1) Thermal shock test: The lithium-ion battery under test is charged to 4.48V at a constant current of 0.5C at 25℃, and the CV (constant-voltage) is maintained until the current is 0.025C. The lithium-ion battery under test is then placed vertically in the chamber and heated to the specified temperature at a rate of 5±2℃ and maintained for 100 minutes. The criterion for passing is that the lithium-ion battery under test does not catch fire or explode during the 100-minute constant temperature process. Three batteries are tested in each group. If all three batteries pass, the lithium-ion battery group is considered to have met the thermal shock test requirements at the specified temperature.

[0070] (2) 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:

[0071] 500-week cycle capacity retention (%) = (500-week cycle discharge capacity / initial cycle discharge capacity) × 100%.

[0072] (3) The specific test method for the 60℃ high-temperature storage test is as follows:

[0073] The battery was placed at room temperature (25℃) and charged and discharged once at 0.5C (4.48V-3.0V). The discharge capacity C0 before storage was recorded. Then, the battery was charged at constant current and constant voltage to a full charge of 4.48V. The thickness d1 of the battery before high-temperature storage was measured using a PPG battery thickness gauge (500g). The battery was then stored in a 60℃ constant temperature chamber. After several days of storage, the battery was removed and the thermal thickness d2 of the battery after storage was measured. The battery thickness expansion rate after 60℃ storage was calculated using the formula: 60℃ storage thickness expansion rate = (d2-d1) / d1×100%. When the 60℃ storage thickness expansion rate is ≥20%, gas production is considered to have occurred. The number of days corresponding to gas production was recorded.

[0074] II. Preparation methods of lithium-ion batteries

[0075] 1. Preparation of positive electrode sheet

[0076] Lithium cobalt oxide (LiCoO2), the positive electrode active material, polyvinylidene fluoride (PVDF), the positive electrode binder, and conductive carbon black (Super-P) were dissolved in N-methylpyrrolidone (NMP) at a mass ratio of 96:2:2 and mixed evenly to prepare a positive electrode slurry. The positive electrode slurry was uniformly coated onto a 12 μm thick aluminum foil for the positive electrode current collector and baked at 120 °C for 1 hour. After that, it was compacted and slit to obtain the positive electrode sheet.

[0077] 2. Preparation of negative electrode sheet

[0078] Artificial graphite (anode active material), sodium carboxymethyl cellulose (CMC) (anode binder), styrene-butadiene rubber (styrene-butadiene rubber) (anode binder), and conductive carbon black (anode conductive agent) were dissolved in water at a mass ratio of 85:2:8:5 and thoroughly mixed to obtain a cathode slurry. The cathode slurry was then uniformly coated onto a copper foil with a cathode current collector thickness of 12 μm and baked at 120°C for 1 hour to obtain a cathode sheet. After compaction and slitting, the cathode sheet was obtained.

[0079] 3. Preparation of electrolyte

[0080] Ethylene carbonate and diethyl carbonate were mixed at a mass ratio of 3:7, and 1M LiPF6 was added simultaneously to obtain the electrolyte base. A first additive and a second additive were then added to the electrolyte base to obtain the electrolytes of the examples and comparative examples.

[0081] 4. Preparation of lithium-ion batteries

[0082] Polypropylene film is used as the separator. The positive electrode, separator, and negative electrode are stacked sequentially, with the separator positioned between the positive and negative electrodes to isolate them. They are then wound, with the positive tab connected to the positive electrode and the negative tab connected to the negative electrode, thus obtaining the electrode assembly. The electrode assembly is placed inside an aluminum foil bag, with the positive and negative tabs extended from the inside to the outside of the outer packaging. After baking at 80°C to remove moisture, electrolyte is injected into the inner space of the outer packaging. Following vacuum sealing, settling, formation, and shaping processes, a lithium-ion battery is obtained.

[0083] The lithium-ion batteries of the examples and comparative examples were prepared according to the above method and then tested.

[0084] Table 1. Composition and performance test results of the electrolytes in the examples and comparative examples.

[0085]

[0086]

[0087] As shown in Table 1, embodiments of the present invention provide an electrolyte and an electrochemical device including the electrolyte. The addition of selenonitrile compounds and optionally added ether nitrile compounds to the electrolyte protects both the positive and negative electrodes. Furthermore, by matching the particle size of the positive electrode active material in a specific ratio, the relationship between the amount of additives and the particle size is balanced, maintaining the thermal stability of the positive and negative electrode interfaces while simultaneously considering electrochemical performance and thermal shock resistance. The electrochemical device of the present invention can improve the thermal shock resistance of the electrochemical device from three dimensions: the positive electrode active material, the positive electrode interface, and the negative electrode interface.

[0088] Specifically, a comparison of Example 32 and Comparative Examples 1-2 shows that by adding selenonitrile compounds to the electrolyte, stable interfacial films can be formed on the surfaces of the positive and negative electrodes. The inorganic interfacial film, rich in Se, exhibits high stability, high ionic conductivity, and low electronic conductivity, effectively reducing side reactions in the negative electrode active material and capturing free nitrile groups, thus improving SEI film stability. On the positive electrode side, the selenonitrile structure has strong adsorption capacity and can effectively adsorb onto the positive electrode surface. Furthermore, the resulting inorganic-metal interface can form a reversible alloy phase with active lithium, mitigating phase transitions in the positive electrode active material under high voltage and improving positive electrode stability. In summary, the addition of selenonitrile compounds can improve the stability of the positive and negative electrode interfaces, thereby enhancing the high-temperature cycle performance and high-temperature storage performance of lithium-ion batteries.

[0089] The comparison of Examples 1-32 shows that further combination with ether nitrile compounds further stabilizes the positive electrode active material. Ether nitrile compounds have low impedance and high ionic conductivity. When used together, the two additives can simultaneously complex with the positive electrode surface, forming a more stable interfacial film that effectively suppresses phase transitions in the positive electrode active material. Furthermore, it improves the wettability of the positive electrode surface, reduces side reactions, and enhances battery performance by suppressing gas generation. The combination of selenonitrile and ether nitrile compounds improves the battery's high-temperature cycle performance, high-temperature storage performance, and thermal shock resistance.

[0090] In summary, the electrolyte and the electrochemical device including the electrolyte of the present invention have the advantages of good high-temperature cycling performance and good high-temperature storage performance.

[0091] 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 comprising a lithium salt, an organic solvent, and a first additive, wherein the first additive comprises a selenonitrile compound; The selenonitrile compound has at least one of the structural formulas shown in Formula I: Formula I In Formula I, X1 is selected from substituted or unsubstituted C 1-12 Alkyl, C 1-12 Alkoxy, C 2-12 Alkenyl groups, if substituted, have a C substituent. 1-12 Alkyl, C 2-12 Alkenyl, cyano, or halogen; R is selected from substituted or unsubstituted C. 1-12 Alkyl, substituted or unsubstituted 5-12-membered heteroaryl, substituted or unsubstituted C 6-12 aryl groups, if substituted, have a substituent of C. 1-12 Alkyl, cyano, or halogen; The electrolyte also includes a second additive, which includes ether nitrile compounds; The mass percentage A of the first additive to the total mass of the electrolyte satisfies: 0.05% ≤ A ≤ 8%; the mass percentage B of the second additive to the total mass of the electrolyte satisfies: 0.05% ≤ B ≤ 10%.

2. The electrolyte according to claim 1, wherein, In Formula I, X1 is selected from substituted or unsubstituted C 1-6 Alkyl, C 1-6 Alkoxy, C 2-6 Alkenyl groups, if substituted, have a C substituent. 1-6 Alkyl, C 2-6 Alkenyl, cyano, or halogen; R is selected from substituted or unsubstituted C. 1-6 Alkyl, substituted or unsubstituted 5-8 membered heteroaryl, substituted or unsubstituted C 6-10 aryl groups, if substituted, have a substituent of C. 1-6 Alkyl, cyano or halogen.

3. The electrolyte according to claim 2, wherein, In Formula I, X1 is selected from substituted or unsubstituted C 1-3 Alkyl, C 1-3 Alkoxy, C 2-3 Alkenyl groups, if substituted, have a C substituent. 1-3 Alkyl, C 2-3 Alkenyl, cyano, or halogen; R is selected from substituted or unsubstituted C. 1-3 Alkyl, substituted or unsubstituted 5-6 membered heteroaryl, substituted or unsubstituted C 6-8 aryl groups, if substituted, have a substituent of C. 1-3 Alkyl, cyano or halogen.

4. The electrolyte according to claim 3, wherein, In Formula I, X1 is selected from substituted or unsubstituted C 1-3 Alkyl, C 1-3 Alkoxy, C 2-3 Alkenyl groups, if substituted, have a C substituent. 1-3 Alkyl, C 2-3 Alkenyl, cyano, or halogen; R is selected from substituted or unsubstituted C. 1-3 Alkyl, substituted or unsubstituted pyridyl, substituted or unsubstituted phenyl, and if substituted, the substituent is C. 1-3 Alkyl, cyano or halogen.

5. The electrolyte according to claim 4, wherein, The selenonitrile compounds include at least one of the following compounds 1 to 6: Compound 1 Compound 2 Compound 4 Compound 5 Compound 6.

6. The electrolyte according to any one of claims 1-5, wherein, The mass percentage A of the first additive to the total mass of the electrolyte satisfies: 1% ≤ A ≤ 4%.

7. The electrolyte according to any one of claims 1-5, wherein, The second additive has at least one of the structural formulas shown in Formula II; Formula II In Formula II, R0, R1, R2, and R3 may be the same or different, and are independently selected from hydrogen, , , , At least one of them, wherein R4-R 10 They may be the same or different, and are independently selected from alkylene groups.

8. The electrolyte according to claim 7, wherein, R4-R 10 Same or different, selected independently from C 1-5 Alkylene.

9. The electrolyte according to claim 8, wherein, R4-R 10 Same or different, selected independently from C 1-3 Alkylene.

10. The electrolyte according to claim 9, wherein, R4-R 10 They may be the same or different, and are independently selected from methylene or ethylene.

11. The electrolyte according to claim 7, wherein, The ether nitrile compounds include at least one of the following compounds 7 to 11: Compound 7 Compound 8 Compound 9 Compound 10 Compound 11.

12. The electrolyte according to any one of claims 1-5, wherein, The mass percentage B of the second additive to the total mass of the electrolyte satisfies: 1% ≤ B ≤ 6%.

13. An electrochemical device comprising the electrolyte according to any one of claims 1-12.

14. The electrochemical device according to claim 13, wherein, The electrochemical device further includes a negative electrode and a positive electrode; the positive electrode includes a positive electrode active material; The electrochemical device satisfies: 0.4 ≤ 2(A+B)×100 / C ≤ 2.9 Where A is the mass percentage of the first additive in the electrolyte, in wt%; B is the mass percentage of the second additive in the electrolyte, in wt%; and C is the median particle size of the positive electrode active material, in μm.

15. The electrochemical device according to claim 14, wherein, The median particle size of the positive electrode active material is 4-20 μm.

16. The electrochemical device according to any one of claims 13-15, wherein, The charging cutoff voltage of the electrochemical device is above 4.48V.

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