Electrolyte and battery

Abstract

The invention provides an electrolyte and a battery, the electrolyte comprises a solvent, a first additive and a second additive, the solvent comprises ethylene carbonate, the first additive comprises a chalcogenide cyclic compound, and the second additive comprises a boron nitrile compound; based on the total mass of the electrolyte as 100%, the ethylene carbonate is A%; the first additive is B%; the second additive is C%; the ratio of A to B to C is (5-12): (2-6): (0.5-1); 9 < = (A + B + C) < = 16; by accurately regulating and controlling the ratio and the total amount of the ethylene carbonate, the first additive and the second additive, the problems of gas production and expansion of the high-energy-density lithium ion battery in the later stage of nested circulation are specifically solved while the good electrochemical performance is guaranteed, the long-term reliability and safety of the battery are remarkably improved, and the application prospect is wide. And the method is particularly suitable for application scenes with strict requirements on interface stability, such as a high-voltage lithium cobalt oxide / silicon carbon system.

Description

Technical Field

[0001] This invention relates to the field of secondary battery technology, specifically to an electrolyte and a battery. Background Technology

[0002] With the increasing demands for energy density, cycle life, and safety performance from electric vehicles, portable electronic devices, and large-scale energy storage systems, lithium-ion batteries are rapidly developing towards high-voltage, high-nickel cathodes and silicon-based anodes. However, these high-energy-density systems generally face serious gas generation and battery expansion problems in the later stages of long-term cycling, especially high-temperature or high-rate "nested cycling" (i.e., a cycling mode simulating actual usage conditions with alternating charging, discharging, and storage).

[0003] Gas generation primarily stems from the oxidative decomposition of the electrolyte on the high-potential positive electrode surface and the continuous reduction side reactions on the negative electrode surface. For example, while ethylene carbonate (EC), the main solvent in conventional electrolytes, can form a solid electrolyte interphase (SEI) film during the initial cycle, in later stages of cycling, especially during the repeated volume expansion / contraction of the silicon-based negative electrode leading to SEI rupture and regeneration, EC continuously undergoes ring-opening and decarboxylation side reactions, generating large amounts of gases such as CO2, C2H4, and CH4. Simultaneously, lithium hexafluorophosphate readily hydrolyzes in the presence of trace amounts of water to produce HF, further corroding the positive electrode material, initiating transition metal dissolution and chain side reactions, exacerbating gas generation. Currently, gas generation is mainly mitigated by reducing the voltage of the positive electrode material or lowering the CB value, but this degrades energy density and increases costs. Therefore, overcoming these technical problems and defects is a key issue that needs to be addressed. Summary of the Invention

[0004] In response to the common problem of severe gas production and battery expansion in rechargeable batteries during long-term cycling, especially in the later stages of high-temperature or high-rate "nested cycling", this invention provides an electrolyte and a battery.

[0005] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows: This invention provides an electrolyte comprising a solvent, a first additive, and a second additive. The solvent comprises ethylene carbonate, the first additive comprises a sulfide cyclic compound, and the second additive comprises a boron nitrile compound. The total mass of the electrolyte is denoted as 100%, the percentage of ethylene carbonate in the electrolyte is denoted as A; the percentage of the first additive in the electrolyte is denoted as B; and the percentage of the second additive in the electrolyte is denoted as C. The values ​​A, B, and C satisfy the following condition: Equation 1: A:B:C = (5~12): (2~6): (0.5~1); Equation 2: 9≤(A+B+C)≤16.

[0006] Optionally, the electrolyte satisfies at least one of the following conditions: Equation 3: A = 5~12; Equation 4: B = 2~6; Equation 5: C = 0.5~1.

[0007] Optionally, the chalcogenide cyclic compound includes at least one of the following compounds: , , .

[0008] Optionally, the chalcogenide cyclic compound includes one or both of compound 1 and compound 3.

[0009] Optionally, the boron nitrile compound includes at least one of the following compounds: , , , .

[0010] Optionally, the electrolyte further includes an electrolyte salt, wherein the electrolyte salt accounts for 6% to 28% of the electrolyte.

[0011] Optionally, the electrolyte salt includes one or more of lithium hexafluorophosphate, lithium difluorooxalate borate, lithium bis(oxalate borate), lithium difluorodi(oxalate phosphate), lithium tetrafluoroborate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, and lithium difluorophosphate.

[0012] Optionally, the electrolyte further includes a film-forming additive, wherein the film-forming additive accounts for 8% to 20% of the electrolyte.

[0013] Optionally, the film-forming additive includes one or more of fluoroethylene carbonate, vinylene carbonate, and nitrile compounds.

[0014] Optionally, the nitrile compound includes one or more of butadionitrile, glutaronitrile, adiponitrile, ethylene glycol bis(propionitrile) ether, 1,3,6-hexanetrionitrile, glycerol trionitrile, and 3,3',3",3"'(ethane 1,1,2,2 tetraalkyltetra(oxy))tetrapropionitrile.

[0015] Optionally, the electrolyte further includes an organic solvent, wherein the organic solvent accounts for 30% to 70% of the electrolyte.

[0016] Optionally, the organic solvent further includes two or more of the following: propylene carbonate, diethyl carbonate, methyl ethyl carbonate, ethyl propionate, propyl propionate, ethyl fluorocarbonate, methyl ethyl fluorocarbonate, dimethyl fluorocarbonate, and propylene fluorocarbonate.

[0017] Another aspect of the present invention provides a battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte as described above.

[0018] According to the electrolyte provided by the present invention, by rationally controlling the types and ratios of ethylene carbonate, the first additive (sulfur-based cyclic compound), and the second additive (boron nitrile compound), and ensuring that their mass percentage content satisfies A:B:C=(5~12):(2~6):(0.5~1) and 9≤A+B+C≤16, ethylene carbonate, as a basic film-forming additive, preferentially reduces to form the initial SEI layer during the first charge-discharge process; the sulfur-based cyclic compound continuously participates in SEI repair during cycling, improving the film density and flexibility; the boron nitrile compound has strong Lewis acidity, can complex trace amounts of water and HF, and simultaneously forms a boron-nitrogen protective layer on the positive electrode surface, inhibiting the dissolution and oxidative decomposition of transition metals; under long-term deep cycling or high-temperature storage conditions, conventional electrolytes are prone to excessive reduction of EC and PF6. - Hydrolysis or solvent oxidation produces gases such as CO2, C2H4, and CH4. In this invention, the synergistic effect of sulfide cyclic compounds and boron nitrile compounds effectively passivates the active sites on the negative electrode surface, blocking the continuous ring-opening polymerization and decomposition pathway of ethylene carbonate. Simultaneously, the boron nitrile compounds remove HF and inhibit the thermal decomposition of LiPF6, reducing the generation of acidic gases (such as HF) and secondary gases (such as CO2) at the source. This significant reduction in gas generation directly translates into reduced battery thickness growth. Expansion uniformity is also improved, avoiding mechanical stress concentration and safety risks caused by localized bulging. In summary, this invention, through precise control of the ratio and total amount of the three types of additives, effectively solves the gas generation and expansion problems faced by high-energy-density lithium-ion batteries in the later stages of nested cycling, while ensuring good electrochemical performance. This significantly improves the long-term reliability and safety of the battery, making it particularly suitable for applications with stringent requirements for interface stability, such as high-voltage lithium cobalt oxide / silicon-carbon systems. Detailed Implementation

[0019] To make the technical problems solved, technical solutions, and beneficial effects of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0020] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; the materials and reagents used are commercially available unless otherwise specified.

[0021] In one embodiment, the present invention provides an electrolyte comprising a solvent, a first additive, and a second additive. The solvent comprises ethylene carbonate, the first additive comprises a sulfide cyclic compound, and the second additive comprises a boron nitrile compound. The total mass of the electrolyte is denoted as 100%, the percentage of ethylene carbonate in the electrolyte is denoted as A, the percentage of the first additive in the electrolyte is denoted as B, and the percentage of the second additive in the electrolyte is denoted as C. The values ​​A, B, and C satisfy the following condition: Equation 1: A:B:C = (5~12): (2~6): (0.5~1); Equation 2: 9≤(A+B+C)≤16.

[0022] Specifically, the ratios of A:B:C are 5:3:1, 5:4:1, 5:5:1, 5:6:1, 5:4:0.5, 5:5:0.5, 5:6:0.5, 7:2:1, 7:3:1, 7:4:1, 7:5:1, 7:6:1, 7:2:0.5, 7:3:0.5, 7:4:0.5, 7:5:0.5, 7:6:0.5, 10:2:1, 10:3:1, The range of any one value or any two point values ​​in 10:4:1, 10:5:1, 10:2:0.5, 10:3:0.5, 10:4:0.5, 10:5:0.5, 12:2:1, 12:3:1, 12:4:1, 12:2:0.5 or 12:3:0.5; in a preferred embodiment, the ratio of A:B:C is (6~10): (3~5): (0.5~1).

[0023] When the ratio of A:B:C is (5~12):(2~6):(0.5~1), the electrolyte can form a stable and dense SEI film in lithium-ion batteries; significantly improve high-temperature cycling performance and storage stability; inhibit electrolyte decomposition and gas generation; improve low-temperature discharge capability and rate performance; moreover, the synergistic effect of boron nitrile compounds and sulfide cyclic compounds enhances interface protection; and ethylene carbonate, as the basic component for film formation, provides a good initial SEI.

[0024] Specifically, the value of A+B+C is any one point or a range of any two points from 9, 10, 11, 12, 13, 14, 15 or 16; in a preferred embodiment, the value of A+B+C is 10-14.

[0025] When the value of A+B+C is 9-16, the electrolyte can form a stable and dense SEI film in lithium-ion batteries, significantly improving high-temperature cycling performance and storage stability; inhibiting electrolyte decomposition and gas generation; improving low-temperature discharge capability and rate performance; moreover, the synergistic effect of boron nitrile compounds and sulfide cyclic compounds enhances interface protection; ethylene carbonate, as the main solvent, provides a foundation for ion transport due to its high dielectric properties. When the value of A+B+C is less than 9, the total amount of solvent, first additive, and second additive is insufficient, failing to maintain effective interface protection in the later stages of cycling, leading to continuous EC decomposition and gas generation, and exacerbating expansion. When the value of A+B+C is greater than 16, the solvent, first additive, and second additive are in excess, which may lead to side reactions (such as oxidation of sulfide compounds and hydrolysis of boron nitrile), introducing new gas sources, and high viscosity hinders lithium-ion transport, exacerbating side reactions due to local polarization, which also worsens expansion behavior.

[0026] In the electrolyte system provided by this invention, by rationally controlling the types and ratios of the solvent (ethylene carbonate), the first additive (sulfuric cyclic compound), and the second additive (boron nitrile compound), and ensuring that their mass percentage content satisfies A:B:C=(5~12):(2~6):(0.5~1) and 9≤A+B+C≤16, ethylene carbonate serves as the main solvent, and its high dielectric properties lay the foundation for ion transport; the sulfuric cyclic compound continuously participates in SEI repair during cycling, improving the film's density and flexibility; the boron nitrile compound has strong Lewis acidity, can complex trace amounts of water and HF, and simultaneously forms a boron-nitrogen protective layer on the positive electrode surface, inhibiting the dissolution and oxidative decomposition of transition metals; under long-term deep cycling or high-temperature storage conditions, conventional electrolytes are prone to excessive reduction of EC and PF6. - Hydrolysis or solvent oxidation produces gases such as CO2, C2H4, and CH4. In this invention, the synergistic effect of sulfide cyclic compounds and boron nitrile compounds effectively passivates the active sites on the negative electrode surface, blocking the continuous ring-opening polymerization and decomposition pathway of ethylene carbonate. Simultaneously, the boron nitrile compounds remove HF and inhibit the thermal decomposition of LiPF6, reducing the generation of acidic gases (such as HF) and secondary gases (such as CO2) at the source. This significant reduction in gas generation directly translates into reduced battery thickness growth. Expansion uniformity is also improved, avoiding mechanical stress concentration and safety risks caused by localized bulging. In summary, this invention, through precise control of the ratio and total amount of solvent, first additive, and second additive, effectively solves the gas generation and expansion problems faced by high-energy-density lithium-ion batteries in the later stages of nested cycling, while ensuring good electrochemical performance. This significantly improves the long-term reliability and safety of the battery, making it particularly suitable for applications with stringent requirements for interface stability, such as high-voltage lithium cobalt oxide / silicon-carbon systems.

[0027] In one embodiment, the electrolyte satisfies at least one of the following conditions: Equation 3: A = 5~12; Equation 4: B = 2~6; Equation 5: C = 0.5~1.

[0028] Specifically, the value of A is any one value or any two values ​​from 5%, 6%, 7%, 8%, 9%, 10%, 11%, or 12%; in a preferred embodiment, the value of A is 6% to 10%.

[0029] When the value of A is in the range of 5% to 12%, the electrolyte can achieve an optimal balance between dielectric properties, viscosity characteristics, and interfacial film formation effect. When the value of A is less than 5%, the content of ethylene carbonate is insufficient to provide a sufficiently high dielectric environment, the lithium salt is not fully dissolved, and the ionic conductivity of the electrolyte drops significantly, failing to meet the ion transport requirements during normal battery charging and discharging. When the value of A is greater than 12%, the high viscosity characteristics of ethylene carbonate become prominent, the overall fluidity of the electrolyte deteriorates, the ion migration activation energy increases significantly, and the rate performance of the battery deteriorates sharply.

[0030] Specifically, the value of B is any one value or any two values ​​from 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5% or 6%; in a preferred embodiment, the value of B is 3% to 5%.

[0031] When the value of B is in the range of 2% to 6%, it helps to suppress the oxidative decomposition of the electrolyte under high voltage and improve the stability of the positive electrode interface. When the value of B is less than 2%, the protection effect on the positive electrode is insufficient, and the capacity decay of the battery is accelerated during high-voltage cycling. When the value of B is greater than 6%, it may cause an increase in side reactions, serious gas production, and lead to battery swelling or decreased safety performance.

[0032] Specifically, the value of C is any one point or any two points from 0.5%, 0.6%, 0.7%, 0.8%, 0.9% or 1%; in a preferred embodiment, the value of C is 0.5% to 0.8%.

[0033] When the value of C is in the range of 0.5% to 1%, it can effectively remove trace amounts of water and HF from the electrolyte, while synergistically improving the compactness of the SEI / CEI membrane. When the value of C is less than 0.5%, the deacidification and stabilization effects are not obvious, and its protective function cannot be fully utilized; when the value of C is greater than 1%, it may introduce excessive impurities or byproducts, which may damage the interfacial membrane structure and reduce the battery cycle life.

[0034] In one embodiment, the chalcogenide cyclic compound includes at least one of the following compounds: , , .

[0035] In one embodiment, the sulfide cyclic compound is selected from compound 1 (1,3-propanesulfonyl lactone (PS)), compound 2 (ethylene sulfate (DTD)) and compound 3 (mannitol carbonate sulfate). Both 1,3-propanesulfonyl lactone and ethylene sulfate can effectively block ethylene carbonate, reducing the generation of gases such as CO2 and C2H4 at the source. The mannitol carbonate sulfate molecule contains multiple -OH-derived cyclic sulfate structures, which can complex trace water molecules and remove HF, inhibiting the chain gas generation reaction initiated by LiPF6 hydrolysis. Because gas generation is greatly suppressed, especially with the introduction of ethylene sulfate and mannitol carbonate sulfate, a high-modulus, low-porosity interfacial film can be formed, preventing bulging caused by local gas accumulation.

[0036] By limiting the sulfur-based cyclic compound to at least one of 1,3-propanesulfonyl lactone, vinyl sulfate, and mannitol carbonate sulfate, this invention not only ensures high rate and long cycle performance but also specifically solves the problem of gas generation and expansion caused by interfacial side reactions in high-energy-density lithium-ion batteries during long-term use. It is especially suitable for applications with stringent safety and lifespan requirements, such as electric vehicles and energy storage systems.

[0037] In one embodiment, the chalcogenide cyclic compound includes one or both of compound 1 and compound 3.

[0038] 1,3-Propanesulfonyl lactone is preferentially reduced on the surface of the negative electrode (such as graphite or silicon carbon) during the initial charge-discharge process, generating a flexible SEI layer rich in -SO3Li, Li2S, and organic sulfides, effectively passivating active sites and inhibiting continuous solvent decomposition; mannitol carbonate sulfate molecules contain multiple hydroxyl-derived cyclic sulfate structures, which can participate in interfacial reactions at multiple points under electrochemical action, forming a cross-linked network composite film that combines inorganic rigidity and organic elasticity, significantly improving the mechanical strength and self-healing ability of the SEI film; both Whether used alone or in combination, it can effectively alleviate the volume expansion stress of silicon-based anodes during the lithiation / delithiation process and prevent the loss of active lithium caused by SEI cracking and regeneration. Moreover, 1,3-propanesulfonyl lactone can effectively block the ring-opening polymerization and decarboxylation pathway of ethylene carbonate, reducing the generation of CO2 and C2H4. The residual hydroxyl groups and cyclic sulfate structures in mannitol carbonate ester molecules can complex trace amounts of water, remove HF, and inhibit the chain side reaction initiated by LiPF6 hydrolysis, thereby reducing the generation of acidic gases and secondary gases from the source.

[0039] In one embodiment, the boronitrile compound includes at least one of the following compounds: , , , .

[0040] Boronitrile compounds possess strong Lewis acidity, capable of complexing trace amounts of moisture and HF, while simultaneously forming a boron-nitrogen protective layer on the positive electrode surface, inhibiting transition metal dissolution and oxidative decomposition. Under long-term deep cycling or high-temperature storage conditions, conventional electrolytes are prone to excessive reduction by EC and PF6. - Hydrolysis or solvent oxidation produces gases such as CO2, C2H4, and CH4. In this invention, the synergistic effect of sulfide cyclic compounds and boron nitrile compounds effectively passivates the active sites on the negative electrode surface, blocking the continuous ring-opening polymerization and decomposition pathway of ethylene carbonate. At the same time, boron nitrile compounds remove HF and inhibit the thermal decomposition of LiPF6, reducing the generation of acidic gases (such as HF) and secondary gases (such as CO2) from the source. The significant reduction in gas generation directly translates into the inhibition of battery thickness growth. Expansion uniformity is also improved, avoiding mechanical stress concentration and safety risks caused by local bulging.

[0041] In one embodiment, the electrolyte further includes an electrolyte salt, which accounts for 6% to 28% of the electrolyte content.

[0042] Specifically, the percentage content of electrolyte salt in the electrolyte is any one value or a range of any two values ​​from 6%, 8%, 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, or 28%; in a preferred embodiment, the percentage content of electrolyte salt in the electrolyte is 10% to 24%.

[0043] When the electrolyte salt content in the electrolyte is 6% to 28%, it exhibits good ionic conductivity, a stable electrochemical window, and excellent battery cycle performance and safety. When the electrolyte salt content is less than 6%, it leads to insufficient ion concentration, a significant decrease in electrolyte conductivity, and an increase in battery internal resistance, thereby affecting charge / discharge efficiency and rate performance, and even causing severe battery polarization and accelerated capacity decay. When the electrolyte salt content is greater than 28%, it leads to a significant increase in electrolyte viscosity, hindering ion migration and thus reducing ionic conductivity.

[0044] In one embodiment, the electrolyte salt includes one or more of lithium hexafluorophosphate, lithium difluorooxalate borate, lithium bis(oxalate borate), lithium difluorodioxalate phosphate, lithium tetrafluoroborate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, and lithium difluorophosphate.

[0045] By rationally selecting one or more of the above electrolyte salts for compounding, high voltage tolerance, excellent interface stability, wide temperature range adaptability and high safety can be achieved simultaneously without sacrificing ionic conductivity. It is particularly suitable for advanced energy storage systems such as high energy density lithium-ion batteries, silicon-based anode batteries, lithium metal batteries and power batteries.

[0046] In one embodiment, the electrolyte further includes a film-forming additive, which accounts for 8% to 20% of the electrolyte content.

[0047] Specifically, the percentage content of the film-forming additive in the electrolyte is any one value or a range of any two values ​​from 8%, 10%, 12%, 14%, 16%, 18% or 20%; in a preferred embodiment, the percentage content of the film-forming additive in the electrolyte is 10%-18%.

[0048] When the percentage of film-forming additives in the electrolyte is 8% to 20%, it effectively promotes the formation of a stable and dense SEI / CEI film, improves cycle life and initial coulombic efficiency, and enhances adaptability to high voltage or low temperature. When the percentage of film-forming additives in the electrolyte is less than 8%, the SEI / CEI film will be thin and porous, making it difficult to prevent solvent molecules from co-intercalating or continuously decomposing, exacerbating interfacial side reactions, and resulting in a lower initial coulombic efficiency. When the percentage of film-forming additives in the electrolyte is greater than 20%, the interfacial film will be too thick or have too high impedance, hindering lithium-ion transport, increasing battery polarization, and reducing rate performance.

[0049] In one embodiment, the film-forming additive includes one or more of fluoroethylene carbonate (FEC), vinylene carbonate (VC), and nitrile compounds.

[0050] Fluorinated ethylene carbonate, vinylene carbonate, and nitrile compounds preferentially decompose over the solvent during the initial charge-discharge process, forming a dense, uniform, and inorganic / organic composite solid electrolyte interface (SEI) film in situ on the surface of the negative electrode (especially silicon-based or graphite-silicon composite negative electrodes). This film possesses both good ion conductivity and electronic insulation, effectively suppressing continuous side reactions of the electrolyte.

[0051] Silicon materials undergo drastic volume changes during lithium insertion / extraction, easily leading to the rupture and repeated regeneration of traditional SEI films, resulting in irreversible consumption of active lithium and electrolyte. Fluorinated ethylene carbonate can form a flexible SEI component rich in LiF, vinylene carbonate provides a high-mechanical-strength polycarbonate network, and nitrile compounds participate in polymerization through -CN functional groups, endowing the SEI with excellent elasticity and self-healing capabilities. The three components synergistically alleviate film cracking, forming a dense, stable, low-impedance, and highly self-healing composite interface film, significantly extending battery cycle life.

[0052] In one embodiment, the nitrile compound includes one or more of butadionitrile, glutaronitrile, adiponitrile, ethylene glycol bis(propionitrile) ether, 1,3,6-hexanetrionitrile, glycerol trionitrile, and 3,3',3",3"'(ethane 1,1,2,2 tetraalkyltetra(oxy))tetrapropionitrile.

[0053] Nitrile compounds can significantly improve the electrochemical stability of electrolytes. Nitrile groups (–C≡N) have strong polarity and coordination ability, which can form a stable solvation structure with lithium ions, regulate lithium ion deposition behavior, and inhibit dendrite growth. At the same time, they participate in the formation of an SEI film rich in nitrides and cyano polymers on the negative electrode surface. This film has high mechanical strength and ion conductivity, which helps to alleviate the interfacial rupture problem caused by the volume expansion of silicon negative electrodes and improve cycle life. Polynitrile compounds (such as trinitrile and tetranitrile) have high boiling points, low volatility, and excellent thermal decomposition temperatures, which can effectively improve the overall thermal stability of the electrolyte and reduce the risk of gas generation and combustion under high-temperature storage or abuse conditions.

[0054] In one embodiment, the electrolyte further includes an organic solvent, which accounts for 30% to 70% of the electrolyte content.

[0055] Specifically, the percentage of organic solvent in the electrolyte is any one value or a range of any two values ​​from 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, or 70%; in a preferred embodiment, the percentage of organic solvent in the electrolyte is 40%-60%.

[0056] When the organic solvent accounts for 30% to 70% of the electrolyte, within this range, it can fully dissolve the lithium salt and effectively dissociate it, forming a high concentration of free lithium ions while maintaining low viscosity, thus ensuring excellent ion migration capability of the electrolyte. An appropriate amount of organic solvent helps form a uniform, dense, and stable solid electrolyte interphase (SEI) film and positive electrode electrolyte interphase (CEI) film on the positive and negative electrode surfaces, suppressing side reactions and improving cycle life. When the organic solvent accounts for less than 30% of the electrolyte, it leads to insufficient dissolution of the lithium salt, a significant decrease in ionic conductivity, an increase in battery internal resistance, and deterioration in rate performance and low-temperature performance. Insufficient electrolyte wettability also makes it difficult to fully wet the separator and electrodes. Porosity affects lithium-ion transport paths, leading to accelerated capacity decay; incomplete interfacial film formation and poor SEI / CEI film quality can easily cause continuous electrolyte decomposition and loss of active lithium, reducing initial coulombic efficiency and cycle stability; when the percentage of organic solvent in the electrolyte exceeds 70%, it can lead to increased viscosity or volatility, potentially causing poor electrolyte flowability or easy vaporization at high temperatures, affecting battery sealing and long-term reliability; the electrochemical window narrows, especially in high-voltage systems, where excessive organic solvent may undergo oxidative decomposition on the cathode surface, generating gas and accelerating capacity decay; safety decreases, as some organic solvents (such as carbonates) are highly flammable, and excessive content increases the risk of thermal runaway, reducing battery safety performance.

[0057] In one embodiment, the organic solvent further includes two or more of the following: propylene carbonate (PC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), ethyl propionate (EP), propyl propionate (PP), ethyl fluorocarbonate (DFEA), methyl ethyl fluorocarbonate (FEMC), dimethyl fluorocarbonate (FDMC), and propylene fluorocarbonate (FPC).

[0058] Using a variety of organic solvents in combination can effectively broaden the operating temperature range of the electrolyte. For example, propylene carbonate has a high dielectric constant, which is beneficial for lithium salt dissociation; while linear carbonates (such as DEC and EMC) and propionates (such as EP and PP) have low viscosity and melting point, which can significantly improve low-temperature performance, allowing the battery to maintain good ionic conductivity and cycle stability in low-temperature environments.

[0059] Introducing fluorinated solvents (such as methyl fluoride carbonate, dimethyl fluoride carbonate, propylene fluoride carbonate, etc.) can improve the antioxidant capacity of the electrolyte and enhance its stability on the surface of high-voltage cathode materials (such as high-voltage lithium cobalt oxide, lithium-rich manganese-based materials, etc.), thereby improving the energy density and cycle life of the battery.

[0060] In summary, using two or more of the above-mentioned organic solvent combinations can significantly improve the electrochemical performance, safety, and environmental adaptability of lithium-ion batteries without significantly increasing costs, and has good application prospects.

[0061] In a preferred embodiment, the organic solvent is selected from propylene carbonate (PC), diethyl carbonate (DEC), ethyl propionate (EP), and propyl propionate (PP).

[0062] In one embodiment, another aspect of the present invention provides a battery including a positive electrode, a negative electrode, a separator, and an electrolyte as described above.

[0063] In one embodiment, the positive electrode includes a positive current collector and a positive active material layer disposed on the positive current collector. The positive active material layer includes a positive active material, which includes, but is not limited to, transition metal oxides; the transition metal oxides are LiCoO2, LiMn2O4, LiMnO2, Li2MnO4, LiFePO4, LiCo 1-x-y Mn x Ni y One or more of (0≤x<1, 0≤y<1).

[0064] In this application, there is no particular limitation on the type of positive electrode current collector; it can be any known material suitable for use as a positive electrode current collector. In one embodiment, the positive electrode current collector includes metallic materials such as aluminum, stainless steel, magnesium plating, titanium, and tantalum, as well as carbon materials such as carbon cloth and carbon paper. In one embodiment, the positive electrode current collector is a metallic material.

[0065] In some embodiments, the positive electrode active material layer also includes a positive electrode conductive agent and a positive electrode binder.

[0066] In some embodiments, the type of positive conductive agent mentioned in this invention is not limited, and any known conductive agent can be used.

[0067] In some embodiments, the positive electrode conductive agent mentioned in this invention includes at least one of carbon materials such as natural graphite, artificial graphite, acetylene black, needle coke, carbon nanotubes, and graphene.

[0068] In one embodiment, the type of positive electrode binder mentioned in this invention is not limited, and any known positive electrode binder can be used.

[0069] In some embodiments, the positive electrode binder includes at least one of polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, and nitrocellulose.

[0070] In one embodiment, the negative electrode sheet includes a negative current collector and a negative active material layer disposed on the negative current collector. The negative active material layer includes a negative active material, which includes, but is not limited to, one or more combinations of graphite, hard carbon, silicon, silicon suboxide, silicon-carbon composite material, and lithium titanate. Preferably, it is designed in conjunction with the positive electrode and functionalized electrolyte to maximize the overall performance of the battery. In this invention, there are no particular limitations on the negative electrode current collector, as long as it can achieve the purpose of this application. For example, it can be copper foil, copper alloy foil, magnesium foil, stainless steel foil, titanium foil, foamed magnesium, foamed copper, or composite current collector, etc.

[0071] In some preferred embodiments, the negative current collector comprises copper foil.

[0072] In some embodiments, the negative electrode active material layer is disposed on at least one side surface of the negative electrode current collector, and the negative electrode active material layer further includes a negative electrode conductive agent, a negative electrode binder, a negative electrode thickener, and a negative electrode solvent.

[0073] The negative electrode conductive agent includes at least one of the following carbon materials: natural graphite, artificial graphite, acetylene black, needle coke, carbon nanotubes, and graphene.

[0074] Negative electrode binders include styrene-butadiene latex, etc. Negative electrode thickeners include CMC, etc. Negative electrode solvents include deionized water, etc.

[0075] In one embodiment, a separator is also included, which is located between the positive electrode and the negative electrode.

[0076] This application does not impose any particular restrictions on the material and shape of the diaphragm, as long as it does not significantly impair the effectiveness of this application.

[0077] In some embodiments, the diaphragm includes a porous sheet-like or non-woven material with excellent liquid retention properties. The diaphragm includes resin or glass fiber diaphragm materials, including but not limited to polyolefins, aromatic polyamides, polytetrafluoroethylene, polyethersulfone, etc.

[0078] In some embodiments, the lithium-ion battery may include an outer packaging that can be used to encapsulate the electrode assembly and electrolyte described above.

[0079] In one embodiment, another aspect of the present invention provides an electrical device including a battery as described above.

[0080] Specifically, the aforementioned electrical devices may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited to these.

[0081] The beneficial effects of the present invention will be further illustrated below with reference to the embodiments.

[0082] To make the inventive objectives, technical solutions, and beneficial effects of this invention clearer, the invention is further described in detail below with reference to embodiments. However, it should be understood that the embodiments of this invention are merely for illustrative purposes and not for limiting the invention, and the embodiments are not limited to those given in the specification. Materials not specified in the embodiments were prepared under conventional conditions or according to the conditions recommended by the material supplier.

[0083] Furthermore, it should be understood that the one or more method steps mentioned in this invention do not preclude the existence of other method steps before or after the combination steps, or the insertion of other method steps between these explicitly mentioned steps, unless otherwise stated. It should also be understood that the combination connection relationship between one or more devices / apparatus mentioned in this invention does not preclude the existence of other devices / apparatus before or after the combination of devices / apparatus, or the insertion of other devices / apparatus between these explicitly mentioned devices / apparatus, unless otherwise stated. Moreover, unless otherwise stated, the numbering of each method step is merely a convenient tool for identifying each method step, and not for limiting the order of the method steps or limiting the scope of the invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the invention.

[0084] In the following embodiments, the reagents, materials and instruments used, unless otherwise specified, are commercially available or can be obtained through synthesis methods known in the art.

[0085] Table 1. Design of negative electrode parameters for Examples 1-8 and Comparative Examples 1-15; This embodiment illustrates the negative electrode sheet and battery disclosed in this invention; it includes the following operational steps: Electrolyte preparation: The electrolyte preparation steps are as follows: In an argon atmosphere with a water content of <10ppm, PC / DEC / EP / PP are mixed in a glove box at a ratio of 20:20:20:40, 1.2M LiPF6 is added, and based on the total mass of the electrolyte, 4W of nitrile compounds and 12W of fluoroethylene carbonate are added; the contents of ethylene carbonate, the first additive, and the second additive are shown in Table 1.

[0086] Production of positive electrode plates: The positive electrode active material lithium cobalt oxide (LiCoO2), conductive agent CNT, and binder PVDF are thoroughly mixed in NMP solvent at a weight ratio of 97:1.5:1.5. This slurry is coated onto aluminum foil and then processed through drying, cold pressing, slitting, sheet forming, welding, and tab bonding to produce a positive electrode sheet that meets the winding requirements.

[0087] Production of negative electrode plates: The negative electrode active material graphite, silicon carbide, conductive agent SP, thickener CMC, and binder SBR are mixed in a mass ratio of 91.26:4:1.24:1.5:2.0 in an appropriate amount of deionized water solvent to form a uniform negative electrode slurry. This slurry is then coated onto the negative electrode current collector Cu foil, and after drying, cold pressing, slitting, sheet forming, welding of tabs, and adhesive bonding, a negative electrode sheet that meets the winding requirements is produced.

[0088] Preparation of the diaphragm: PE porous polymer film is used as the membrane substrate.

[0089] The manufacturing process of lithium-ion batteries: The above-mentioned positive electrode sheet, separator, and negative electrode sheet are wound together to obtain a bare cell. The bare cell is then placed in a pre-punched aluminum-plastic film to complete the top and side sealing. After processes such as high-temperature baking, electrolyte injection, settling, formation, capacity testing, and inspection, the battery manufacturing is completed.

[0090] Examples 2-8 Examples 2-8 illustrate the electrolyte and battery disclosed in this invention, including most of the operating steps in Example 1, with the following differences: The parameters of the electrolyte shown in Table 1 were used.

[0091] Comparative Examples 1-15 Comparative Examples 1-15 are used to illustrate the electrolyte and battery disclosed in this invention, including most of the operating steps in Example 1, the difference being: The parameters of the electrolyte shown in Table 1 were used.

[0092] Performance testing The following performance tests were performed on the batteries prepared in Examples 1-8 and Comparative Examples 1-15: Lithium-ion battery performance testing 45℃ Nested Cycle Test: At 25℃, discharge to 3.0V at 0.2C, rest for 10 minutes, charge at 0.5C constant current for 36 minutes, rest for 10 minutes, and then remove from the cabinet. The cell thickness H0 is measured using a 650g PPG sample. At 45℃, charge to 4.55V at 1.2C constant current and constant voltage, cutoff current 0.05C, rest for 24 hours, and then discharge to 3.0V at 0.5C. The discharge capacity C0 is recorded as the initial value, and this process is repeated for 60 cycles. The final capacity C after 60 cycles is obtained. 60 Then the capacity retention rate = C 60 / C0.

[0093] During the 45℃ nested cycle process, every 10 weeks, the cell thickness H was tested using a 650g PPG battery after a full charge. n (n represents the number of cycles), for example, thickness expansion over 60 cycles = (H) 60 -H0) / H0.

[0094] The test results are shown in Table 2.

[0095] Table 2. Battery electrochemical performance test results As can be seen from Examples 1-8 and Comparative Example 1, adding ethylene carbonate, sulfide cyclic compounds, and boron nitrile compounds to the electrolyte can reduce nested cycle thickness expansion and improve battery capacity retention.

[0096] As can be seen from Examples 1-8 and Comparative Example 2, when ethylene carbonate is lacking in the electrolyte, the battery capacity retention rate decreases and gas expansion problems occur.

[0097] As can be seen from Examples 1-8 and Comparative Example 3, when boron nitrile compounds are lacking in the electrolyte, the battery capacity retention rate decreases and the nested cycle thickness expansion rate is high.

[0098] As can be seen from Examples 1-8 and Comparative Examples 4 and 13-15, when the electrolyte lacks sulfide cyclic compounds, the battery capacity retention rate decreases and the nested cycle thickness expansion rate is high.

[0099] The test results from Examples 1-3 and Comparative Examples 5-6 show that when the value of A is in the range of 5% to 12%, the nested cycle thickness expansion can be reduced and the battery capacity retention rate can be improved. When the value of A is less than 5%, the battery capacity retention rate is significantly reduced and the nested cycle thickness expansion rate is high; when the value of A is greater than 12%, the battery capacity retention rate is reduced and the nested cycle thickness expansion rate is significantly increased.

[0100] The test results of Examples 1, 4-5 and Comparative Examples 7-8 show that when the value of B is in the range of 2% to 6%, the nested cycle thickness expansion can be reduced and the battery capacity retention rate can be improved; when the value of B is less than 2%, the battery capacity retention rate decreases and the nested cycle thickness expansion rate increases significantly; when the value of B is greater than 6%, the battery capacity retention rate decreases significantly and the nested cycle thickness expansion rate is high.

[0101] The test results from Examples 1, 6-7, and Comparative Examples 9-10 show that when the value of C is in the range of 0.5% to 1%, it can reduce the nested cycle thickness expansion and improve the battery capacity retention rate; when the value of C is less than 0.5%, the battery capacity retention rate decreases and the nested cycle thickness expansion rate is high; when the value of C is greater than 1%, the battery capacity retention rate decreases significantly and the nested cycle thickness expansion rate increases significantly.

[0102] The test results of Examples 1-8 and Comparative Examples 11-12 show that when the value of A+B+C is 9-16, the nested cycle thickness expansion can be reduced and the battery capacity retention rate can be improved; when the value of A+B+C is less than 9, the battery capacity retention rate is significantly reduced and the nested cycle thickness expansion rate is significantly increased; when the value of A+B+C is greater than 16, the battery capacity retention rate is reduced and the nested cycle thickness expansion rate is increased.

[0103] In summary, the electrolyte of this invention, by rationally controlling the types and ratios of the solvent (ethylene carbonate), the first additive (sulfur-based cyclic compound), and the second additive (boron nitrile compound), and ensuring that their mass percentage content satisfies A:B:C=(5~12):(2~6):(0.5~1) and 9≤A+B+C≤16, can significantly improve the capacity retention rate and thickness expansion during nested cycles. This may be related to the fact that an appropriate amount of ethylene carbonate provides high ion conductivity without affecting gas production, and that an appropriate amount of sulfur-containing compounds and boron nitrile compounds balance impedance and provide interface protection. Therefore, the three components work together within a certain range to significantly inhibit the decomposition of the electrolyte and the generation of gas at high temperatures, thereby improving the capacity retention rate and thickness expansion during high-temperature storage.

[0104] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements 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 a solvent, a first additive, and a second additive. The solvent includes ethylene carbonate, the first additive includes a sulfide cyclic compound, and the second additive includes a boron nitrile compound. The total mass of the electrolyte is denoted as 100%, the percentage of ethylene carbonate in the electrolyte is denoted as A; the percentage of the first additive in the electrolyte is denoted as B; and the percentage of the second additive in the electrolyte is denoted as C. The values ​​A, B, and C satisfy the following condition: Equation 1: A:B:C = (5~12): (2~6): (0.5~1); Equation 2: 9≤(A+B+C)≤16.

2. The electrolyte according to claim 1, characterized in that: The electrolyte satisfies at least one of the following conditions: Equation 3: A = 5~12; Equation 4: B = 2~6; Equation 5: C = 0.5~1.

3. The electrolyte according to claim 1, characterized in that: The chalcogenide cyclic compound includes at least one of the following compounds: 、 、 。 4. The electrolyte according to claim 3, characterized in that: The chalcogenide cyclic compounds include one or both of compound 1 and compound 3.

5. The electrolyte according to claim 1, characterized in that: The boron nitrile compounds include at least one of the following compounds: 、 、 、 。 6. The electrolyte according to claim 1, characterized in that: The electrolyte also includes an electrolyte salt, which accounts for 6% to 28% of the electrolyte content.

7. The electrolyte according to claim 6, characterized in that: The electrolyte salt includes one or more of lithium hexafluorophosphate, lithium difluorooxalate borate, lithium bis(oxalate borate), lithium difluorodi(oxalate phosphate), lithium tetrafluoroborate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, and lithium difluorophosphate.

8. The electrolyte according to claim 1, characterized in that: The electrolyte also includes film-forming additives, which account for 8% to 20% of the electrolyte content.

9. The electrolyte according to claim 8, characterized in that: The film-forming additives include one or more of fluoroethylene carbonate, vinylene carbonate, and nitrile compounds.

10. The electrolyte according to claim 9, characterized in that: The nitrile compounds include one or more of succinic anion, glutaronitrile, adiponitrile, ethylene glycol bis(propionitrile) ether, 1,3,6-hexanetrionitrile, glycerol trionitrile, and 3,3',3",3"'(ethane 1,1,2,2 tetraalkyltetra(oxy))tetrapropionitrile.

11. The electrolyte according to claim 1, characterized in that: The electrolyte also includes an organic solvent, which accounts for 30% to 70% of the electrolyte.

12. The electrolyte according to claim 11, characterized in that: The organic solvent also includes two or more of the following: propylene carbonate, diethyl carbonate, methyl ethyl carbonate, ethyl propionate, propyl propionate, ethyl fluorocarbonate, methyl ethyl fluorocarbonate, dimethyl fluorocarbonate, and propylene fluorocarbonate.

13. A battery, characterized in that: It includes a positive electrode, a negative electrode, a separator, and an electrolyte as described in any one of claims 1-12.

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