Non-aqueous electrolyte and lithium ion battery containing same

Abstract

The invention provides a non-aqueous electrolyte and a lithium ion battery containing the same, and belongs to the technical field of lithium ion batteries. The non-aqueous electrolyte comprises electrolyte salt, an organic solvent, a nitrile additive and a compound A; complementary construction of an interfacial film is achieved through the synergistic effect of the nitrile additive and fluorosilane, and decomposition of an electrolyte and corrosion of an electrode material are prevented; a lithium ion conduction path is optimized, and the charging and discharging efficiency of the battery in a high-temperature and high-pressure circulation process is improved; transition metal ion migration is inhibited, and the cycle performance at high temperature and high pressure is improved; gas and by-products generated by thermal decomposition are reduced, so that the volume expansion rate of the battery at high temperature and high pressure is reduced, and stable performance of the battery in a high-temperature cycle process is ensured; the volume expansion rate under high-temperature storage is reduced; and the capacity recovery rate is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries, and particularly relates to a non-aqueous electrolyte and a lithium-ion battery containing the same. Background Art

[0002] Lithium-ion batteries have become an important pillar of new energy technologies due to their high energy density, long cycle life, and environmental friendliness. However, with the continuous improvement of market requirements for battery performance, traditional graphite anode materials have gradually approached their theoretical capacity limit (372 mAh / g), making it difficult to meet the high energy density requirements.

[0003] Lithium cobalt oxide (LiCoO2, LCO) is a mainstream cathode material for lithium-ion batteries and is widely used due to its high theoretical capacity (274 mAh / g) and excellent electrochemical performance. However, its charging cut-off voltage is usually limited to below 4.5 V to avoid structural instability and safety issues at high voltages. At the same time, silicon-carbon anode materials are regarded as an ideal choice for next-generation anode materials due to their high theoretical capacity (4200 mAh / g) and low-cost advantages. Combining lithium cobalt oxide cathodes with silicon-carbon anodes is expected to significantly improve the energy density and comprehensive performance of lithium-ion batteries.

[0004] However, this technical path still faces many challenges. For example, under high-voltage conditions, the crystal lattice structure of the lithium cobalt oxide cathode is prone to irreversible phase transformation, resulting in the loss of active materials and thus affecting the battery cycle life; the silicon-carbon anode undergoes a huge volume change (up to 300%) during charge and discharge, causing damage to the electrode structure and leading to rapid capacity decay; at the same time, the compatibility between lithium cobalt oxide and the silicon-carbon anode in the electrolyte is poor, and interfacial side reactions occur frequently, not only consuming active lithium but also increasing the battery internal resistance and reducing the charge and discharge efficiency of the battery; in addition, under high-temperature environments, the internal chemical reactions in the battery intensify, further deteriorating the battery's cycle capacity retention rate, and the volume expansion of the anode is more obvious, posing a serious threat to the safety and structural stability of the battery.

[0005] Therefore, in-depth research on lithium-ion batteries with lithium cobalt oxide and silicon-carbon anodes, and solving the problems of silicon volume expansion and the structural instability of lithium cobalt oxide at high voltages from the electrolyte direction, so as to improve the high-temperature and high-pressure performance and reliability of lithium-ion batteries, is of great significance. Summary of the Invention

[0006] Aiming at the deficiencies of the existing technology, the present invention aims to provide a non-aqueous electrolyte and a lithium-ion battery containing the same.

[0007] One of the objectives of the present invention is to provide a non-aqueous electrolyte for a lithium-ion battery, characterized in that the electrolyte comprises an electrolyte salt, an organic solvent, a nitrile additive, and Compound A; Compound A is shown as Formula 1:

[0008] Wherein R1, R2, R3, R4, and R5 are each independently selected from any one of hydrogen, halogen, and substituted or unsubstituted C1-C4 alkyl groups.

[0009] Preferably, based on the total mass of the electrolyte being 100%, the proportion of the nitrile additive in the electrolyte is 0.5% to 5%; the proportion of the compound A in the electrolyte is 0.1% to 4.0%.

[0010] Preferably, R1, R2, R3, R4, and R5 are each independently selected from any one of fluorine, -CH3, -CH2CH3, -CH(CH3)2, or -C(CH3)3.

[0011] Preferably, the compound A includes at least one of the following compounds:

[0012] Preferably, the nitrile additive includes one or more of succinonitrile, glutarodinitrile, adiponitrile, trans-butenedinitrile, trans-hexenedinitrile, 1,2-bis(cyanoethoxy)ethane, 1,3,6-hexanetricarbonitrile, 1,2,3-tris(cyanoethoxy)propane.

[0013] Preferably, based on the total mass of the electrolyte being 100%, the proportion of the electrolyte salt in the electrolyte is 0.2 to 3.0%; The electrolyte salt includes one or more of lithium bis(fluorosulfonyl)imide, lithium difluoro(oxalato)borate, lithium tetrafluoroborate, bis(oxalato)borate, lithium difluorobis(oxalato)phosphate, or lithium hexafluorophosphate.

[0014] Preferably, the non-aqueous electrolyte of the lithium ion battery further includes a film-forming agent. Based on the mass of the non-aqueous electrolyte being 100%, the proportion of the film-forming agent in the electrolyte is 0.5 to 11%; The film-forming agent is one or more of vinylene carbonate (VC), 1,3-propane sultone (PS), fluoroethylene carbonate (FEC), ethylene sulfite (ES), ethylene sulfate (DTD), methylene methanedisulfonate (MMDS), vinylene ethylene carbonate (VEC), tris(trimethylsilyl) phosphate (TMSP), or tris(trimethylsilyl) borate (TMSB).

[0015] Preferably, based on the mass of the non-aqueous electrolyte being 100%, the proportion of the organic solvent in the electrolyte is 75% to 94%; Preferably, the organic solvent includes carbonate organic solvents and / or carboxylate organic solvents; Preferably, the carbonate organic solvent includes cyclic carbonate and / or chain carbonate; Preferably, the cyclic carbonate includes any one or a combination of at least two of ethylene carbonate, propylene carbonate or butylene carbonate; Preferably, the chain carbonate includes any one or a combination of at least two of diethyl carbonate, ethyl methyl carbonate, dimethyl carbonate or methyl propyl carbonate; Preferably, the carboxylic acid ester organic solvent includes any one or a combination of at least two of ethyl propionate, propyl propionate, ethyl acetate, ethyl n-butyrate, methyl acetate, propyl acetate, methyl propionate or γ-butyrolactone; Preferably, the non-aqueous organic solvent accounts for 75% - 94% of the total weight of the non-aqueous electrolyte of the lithium-ion battery.

[0016] The second object of the present invention is to provide a lithium-ion battery, which includes the non-aqueous electrolyte of the lithium-ion battery as described above.

[0017] Preferably, the positive electrode of the lithium-ion battery includes a positive electrode active material, a conductive agent and a binder. The active material of the positive electrode is at least one of LiCoO2, LiNix'L'y'Mn(2-x”-y')O4; where L is at least one of Al, Sr, Mg, Ti, Ca, Zr, Zn, Si, Fe; 5≤x≤1, 0≤y<1, 0≤z≤1, 0<x + y + z≤1, 0<x'≤1, 0.01≤y'≤0.2, and L' is at least one of Co, Al, Sr, Mg, Ti, Ca, Zr, Zn, Si, Fe; The negative electrode plate of the lithium-ion battery includes a negative electrode active material, and the negative electrode active material includes one or a combination of at least two of natural graphite, artificial graphite, soft carbon, hard carbon, mesophase carbon microspheres, graphene, graphyne, metallic lithium, nano-carbon, carbon nanotubes, elemental silicon, silicon oxide, silicon / copper oxide composite, AG composite, silicon alloy, elemental tin, tin oxide, tin-carbon composite, tin alloy or lithium titanate.

[0018] The negative electrode active material includes a combination of graphite and a silicon-based material, and the silicon-based material includes any one or a combination of at least two of elemental silicon, silicon oxide, silicon / copper oxide composite, silicon alloy; The mass percentage content of the silicon-based material in the negative electrode active material is 10% - 20%; The material of the separator of the lithium-ion battery includes one of polyethylene, polypropylene or a composite ceramic membrane.

[0019] The beneficial effects of the present invention: The present invention provides a non-aqueous electrolyte for a lithium-ion battery, which comprises an electrolyte salt, an organic solvent, a nitrile additive, and a compound A represented by Formula 1. Through the synergistic effect of the nitrile additive and the fluorosilane, the cyano group of the nitrile additive is preferentially adsorbed and reacts on the surface of the positive electrode to form an initial SEI film layer, effectively blocking the further side reactions between the electrolyte and the positive electrode. The silane part in the compound A can form a film on the surface of the negative electrode, and the polar groups in the SEI film formed by the nitrile additive can interact with the silicon-oxygen structure in the film layer formed by the compound A through intermolecular forces, making the SEI film at the entire electrode-electrolyte interface more continuous and complete, further preventing the decomposition of the electrolyte and the corrosion of the electrode material, and improving the overall cycle stability of the battery; The film formed by the nitrile additive has certain ion conduction characteristics, and the ion channels inside it can promote the transport of lithium ions near the positive electrode. The Si-O-Si cross-polymerization network constructed by the compound A on the surface of the negative electrode also forms a channel conducive to the conduction of lithium ions. The synergistic effect of the two optimizes the conduction path of lithium ions from the positive electrode to the negative electrode in the entire battery system, reduces the hindrance of lithium ions during the transport process, reduces the internal resistance of the battery, and improves the charge-discharge efficiency of the battery during the high-temperature and high-pressure cycle process, thereby improving the cycle performance; The cyano group of the nitrile additive can complex with the transition metal cobalt ions in the lithium cobaltate positive electrode material, reduce its solubility in the electrolyte, inhibit the dissolution of cobalt ions from the positive electrode, and reduce the migration amount of cobalt ions in the electrolyte. The Si-O-Si cross-polymerization network formed by the compound A on the surface of the negative electrode makes it difficult for the adsorption and deposition of transition metal ions such as dissolved cobalt ions on the surface of the negative electrode, indirectly inhibiting the adverse effects of transition metal ions on the surface of the negative electrode. In cooperation with the effect of the nitrile additive in inhibiting the dissolution of transition metal ions from the positive electrode, it reduces the battery performance decline caused by the migration of transition metal ions and improves the cycle performance under high temperature and high pressure; The nitrile additive improves the stability of the electrolyte, reduces the by-products generated by the decomposition of the electrolyte and the volume change of the silicon-based negative electrode caused by uneven electric fields; the Si-O-Si cross-polymerization network with high mechanical strength and flexibility formed by the compound A on the surface of the negative electrode, the synergistic effect of the two enables the battery to still maintain good structural integrity and electrochemical performance after experiencing multiple volume change cycles of the silicon-based negative electrode, reduces the volume expansion rate under high-temperature storage and improves the capacity recovery rate; Nitrile additives themselves have high thermal stability and are not easily decomposed in high-temperature environments. At the same time, the film layer formed on the positive electrode surface can also play a certain heat insulation role, reducing the heat transfer from the positive electrode to the electrolyte and lowering the overall thermal decomposition rate of the electrolyte. The Si-O-Si bond in Compound A has a high bond energy and good thermal stability at high temperatures. The cross-linked polymer network structure formed on the negative electrode surface can not only adapt to the volume change of silicon but also maintain stability in high-temperature environments, reducing structural damage and decomposition caused by high temperatures. The two work together to improve the thermal stability of the electrolyte under high-temperature conditions, reduce the gases and by-products generated by thermal decomposition, and further lower the volume expansion rate of the battery under high temperature and high pressure, ensuring the performance stability of the battery during high-temperature cycling. Detailed implementation mode

[0020] According to the first aspect of the present invention, a non-aqueous electrolyte for a lithium-ion battery is provided, comprising an electrolyte salt, an organic solvent, a nitrile additive, and Compound A; Compound A is shown in Formula 1:

[0021] Wherein R1, R2, R3, R4, and R5 are each independently selected from any one of hydrogen, halogen, substituted or unsubstituted C1-C4 alkyl groups.

[0022] In the present invention, the nitrile additive preferentially adsorbs and reacts on the positive electrode surface by virtue of the cyano group to form an initial SEI film layer rich in nitrogen-containing compounds, which effectively blocks the further side reactions between the electrolyte and the positive electrode. The silane part in Compound A can form a film on the negative electrode surface. When lithium ions shuttle between the positive and negative electrodes, the films formed by the two complement each other at the electrode-electrolyte interface. The polar groups in the SEI film formed by the nitrile additive can interact with the silicon-oxygen structure in the film layer formed by Compound A through intermolecular forces, making the SEI film at the entire electrode-electrolyte interface more continuous and complete, further preventing the decomposition of the electrolyte and the corrosion of the electrode material, and improving the overall cycle stability of the battery.

[0023] The film formed by the nitrile additive has certain ion conduction characteristics, and the ion channels inside it can promote the transport of lithium ions near the positive electrode. The Si-O-Si cross-linked polymer network constructed by Compound A on the negative electrode surface also forms a channel conducive to lithium ion conduction. The two work together to optimize the conduction path of lithium ions from the positive electrode to the negative electrode in the entire battery system, reduce the hindrance of lithium ions during transmission, lower the internal resistance of the battery, and improve the charge-discharge efficiency of the battery during high-temperature and high-pressure cycling, thereby improving the cycle performance.

[0024] The cyano group of nitrile additives can complex with transition metal cobalt ions in the lithium cobalt oxide cathode material, reduce its solubility in the electrolyte, and inhibit the dissolution of cobalt ions from the cathode. When cobalt ions dissolve out, they will migrate in the electrolyte and may deposit on the surface of the anode, triggering side reactions such as lithium deposition on the anode and reducing the battery performance. Nitrile additives reduce the migration amount of cobalt ions in the electrolyte through complexation. The Si-O-Si cross-polymerized network formed by Compound A on the surface of the anode changes the chemical environment and electronic structure of the anode surface. This structure makes it difficult for the anode surface to adsorb and deposit transition metal ions such as dissolved cobalt ions, indirectly inhibiting the adverse effects of transition metal ions on the anode surface. Cooperating with the role of nitrile additives in inhibiting the dissolution of transition metal ions from the cathode, it jointly maintains the structural stability of the cathode and anode materials of the battery, reduces the decline of battery performance caused by the migration of transition metal ions, and improves the cycling performance under high temperature and high pressure.

[0025] Although nitrile additives mainly act on the cathode, in the battery system, their improvement of the overall properties of the electrolyte also indirectly helps to address the volume change problem of the silicon-based anode. Nitrile additives improve the stability of the electrolyte and reduce the additional interference of by-products generated by electrolyte decomposition on the volume change of the silicon-based anode. At the same time, the stable film layer formed on the cathode ensures the stability of the cathode during charge and discharge, makes the internal electric field distribution of the battery more uniform, reduces the abnormal local volume change of the silicon-based anode caused by uneven electric field, and assists Compound A to better cope with the volume expansion and contraction of the silicon-based anode. The Si-O-Si cross-polymerized network with high mechanical strength and flexibility formed by Compound A on the surface of the anode is the main line of defense against the volume change of the silicon-based anode. It can deform to a certain extent without breaking when the silicon-based anode expands in volume and can recover part of its shape when the volume contracts, effectively alleviating the stress concentration of silicon during the cycling process. The two work together, enabling the battery to still maintain good structural integrity and electrochemical performance after experiencing multiple volume change cycles of the silicon-based anode, reducing the volume expansion rate under high temperature storage and increasing the capacity recovery rate.

[0026] Nitrile additives themselves have high thermal stability and are not easily decomposed in high-temperature environments. Their cyano structure can consume part of the thermal energy through intramolecular electron delocalization and other means at high temperatures, preventing the thermal decomposition reactions of themselves and the surrounding electrolyte components. At the same time, the film layer formed on the positive electrode surface can also play a certain heat insulation role, reducing the heat transfer from the positive electrode to the electrolyte and lowering the overall thermal decomposition rate of the electrolyte. The Si-O-Si bond in Compound A has a high bond energy and good thermal stability at high temperatures. The cross-linked polymer network structure formed on the negative electrode surface can not only adapt to the volume change of silicon but also maintain stability in high-temperature environments, reducing the structural damage and decomposition caused by high temperatures. The two work together to improve the thermal stability of the electrolyte under high-temperature conditions, reduce the gases and by-products generated by thermal decomposition, and then lower the volume expansion rate of the battery under high temperature and high pressure, ensuring the performance stability of the battery during high-temperature cycling.

[0027] In a preferred embodiment of the present invention, based on the total mass of the electrolyte being 100%, the proportion of the nitrile additive in the electrolyte is 0.5% - 5%; the proportion of Compound A in the electrolyte is 0.1% - 4.0%.

[0028] In the present invention, when the proportion of the nitrile additive is less than 0.5%, the amount of the SEI film formed on the positive electrode surface is too small to effectively complex the transition metal cobalt ions in the lithium cobaltate positive electrode material. A small amount of nitrile additive is difficult to form a continuous and dense film layer on the positive electrode surface, resulting in relatively more dissolution of the positive electrode transition metal ions, which will trigger side reactions such as electrolyte decomposition and lithium deposition on the negative electrode, and cannot fully play the role of improving the oxidation resistance of the electrolyte and stabilizing the positive electrode material. The cycling performance and volume expansion control ability of the battery under high temperature and high pressure will deteriorate. If the proportion of the nitrile additive exceeds 5%, on the one hand, it will significantly increase the viscosity of the electrolyte, resulting in an increase in the migration resistance of lithium ions in the electrolyte, an increase in the internal resistance of the battery, and a decrease in the charge-discharge efficiency, affecting the power performance of the battery. On the other hand, too much nitrile additive may undergo excessive reactions on the electrode surface, forming an overly thick film layer, which will not only hinder the transmission of lithium ions but also may cause problems such as peeling and cracking of the film layer during battery cycling, damaging the stability of the electrode-electrolyte interface, and instead having a negative impact on the cycling performance and volume expansion control of the battery. In the range of 0.5% - 5%, the improvement effect on battery performance and the adverse effects on electrolyte properties can be better balanced.

[0029] When the proportion of Compound A in the electrolyte is less than 0.1%, the amount of it reacting with natural silanol groups on the surface of the silicon-based anode is too small to form a sufficient cross-linked polymerization network of organosilicon or Si-O-Si bonds. In this way, it is impossible to effectively improve the mechanical strength and flexibility of the SEI film, and it cannot well adapt to the volume expansion and contraction of silicon during cycling. The silicon-based anode is prone to structural damage due to stress concentration during cycling, resulting in rapid attenuation of battery capacity, a decrease in the capacity recovery rate under high-temperature storage, and the volume expansion rate cannot be effectively controlled. If the proportion of Compound A exceeds 4.0%, it will cause a significant increase in the cost of the electrolyte. Moreover, excessive Compound A may undergo unnecessary side reactions with other components in the electrolyte, changing the electrochemical properties of the electrolyte and affecting the stability of the electrolyte. In addition, an overly thick film layer may form on the anode surface, hindering the insertion and extraction of lithium ions, increasing the internal resistance of the battery, and reducing the charge-discharge efficiency and cycling performance of the battery. In the proportion range of 0.1% - 4.0%, Compound A can not only effectively improve the relevant performance of the silicon-based anode, but also take into account the cost and the overall stability of the electrolyte.

[0030] The proportion of nitrile additives in the electrolyte is 0.5% - 5%, and the proportion of Compound A in the electrolyte is 0.1% - 4.0%. The amount of the film formed by nitrile additives on the positive electrode and Compound A on the negative electrode is appropriate. The two can be connected and supplemented with each other through intermolecular interactions, making the SEI film at the electrode-electrolyte interface more complete and continuous. If the proportion is improper, the insufficient amount of the film cannot be effectively connected, and too much film will cause problems such as hindered interfacial ion conduction, which are not conducive to the synergistic construction of a high-quality interfacial film. Within the above range, nitrile additives complex the transition metal ions of the positive electrode, and Compound A changes the surface environment of the negative electrode to inhibit ion deposition, and the synergistic effect of the two is the best. If the proportion is unbalanced, for example, too little nitrile additive results in insufficient complexing ability, and no matter how much Compound A there is, it is difficult to make up for it; on the contrary, too much nitrile additive affects the properties of the electrolyte, and the synergism of the two will also be affected.

[0031] Within the above range, nitrile additives assist in coping with silicon volume changes by improving the stability of the electrolyte, and the network structure formed by Compound A on the negative electrode bears the main load. An inappropriate proportion will prevent the two from effectively cooperating in aspects such as relieving stress and reducing interference, affecting the battery's ability to cope with silicon volume changes. Within the above range, the thermal stability advantages of nitrile additives and Compound A themselves and their inhibitory effects on the thermal decomposition of the electrolyte can be synergistically exerted. An improper ratio will cause an imbalance in the contribution of thermal stability. Too much of one additive may mask the thermal stability effect of the other additive, or trigger other side reactions to reduce the overall thermal stability.

[0032] In the present invention, the proportion of the nitrile additive in the electrolyte is, for example, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3.0%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9%, 4.0%, 4.1%, 4.2%, 4.3%, 4.4%, 4.5%, 4.6%, 4.7%, 4.8%, 4.9% and 5.0%; the proportion of compound A in the electrolyte is, for example, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3.0%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9% or 4.0%.

[0033] In a preferred embodiment of the present invention, each of R1, R2, R3, R4, and R5 is independently selected from any one of fluorine, -CH3, -CH2CH3, -CH(CH3)2 or -C(CH3)3.

[0034] In a preferred embodiment of the present invention, compound A includes at least one of the following compounds:

[0035] In the present invention, fluorine atoms have a strong electronegativity and a high C-F bond energy. Under harsh conditions of high temperature and high pressure, compound A is not easily decomposed, maintaining its own structural stability, continuously functioning as an effective additive, and ensuring stable battery performance. During the film formation process on the electrode surface, trifluoromethyl can participate in the construction of the SEI film. The SEI film containing trifluoromethyl has excellent chemical stability and antioxidant properties, which can effectively prevent further side reactions between the electrolyte and the electrode, reducing electrode material corrosion and electrolyte decomposition. At the same time, the presence of fluorine atoms endows the film with good ionic conductivity, facilitating the rapid passage of lithium ions during charge and discharge, reducing the battery internal resistance, and improving the cycle performance under high temperature and high pressure. The introduction of trifluoromethyl can reduce the flammability of the electrolyte and improve battery safety. In extreme situations such as thermal runaway that may be triggered by high temperature and high pressure, the risk of fire and explosion is reduced, meeting the safety requirements of the battery under harsh conditions. The spatial structure and electronegativity of trifluoromethyl will affect the interactions between compound A molecules and other components of the electrolyte. It promotes the more ordered arrangement and reaction of compound A on the surface of the silicon-based negative electrode, facilitating the formation of a uniform and dense SEI film, effectively preventing further side reactions between the electrolyte and the negative electrode. The silicon atoms in silane or fluorosilane can react with silanol groups on the surface of the negative electrode to form a cross-linked polymer network structure of Si-O-Si bonds. This network structure has high mechanical strength and flexibility, and can effectively adapt to the huge volume expansion and contraction of the silicon-based negative electrode during charge and discharge under high temperature and high pressure, relieve stress concentration, prevent the destruction of the negative electrode structure, reduce the battery performance degradation caused by the change of the negative electrode structure, and reduce the volume expansion rate under high temperature storage. The SEI film formed by the participation of silane or fluorosilane has channels conducive to lithium ion conduction inside. Under high temperature and high pressure, it can ensure the efficient transmission of lithium ions between the electrode and the electrolyte, maintain the normal charge and discharge reaction of the battery, and improve the charge and discharge efficiency and cycle performance of the battery. Silane or fluorosilane can adjust the chemical and physical properties of the electrolyte-electrode interface. By interacting with the electrode surface, it optimizes the electric field distribution and charge transfer process at the interface, reduces interface side reactions, and enhances the stability of the battery in a high temperature and high pressure environment.

[0036] In a preferred embodiment of the present invention, compound A includes the following compounds:

[0037] When R4 is methyl, it can have a positive impact on the performance of lithium cobalt oxide silicon-carbon anode lithium-ion batteries. The reasons mainly involve the structural characteristics of methyl and its changes in the behavior of compound A in the battery system, mainly reflected in the balance of steric hindrance and reactivity. The volume of methyl is relatively small, and during the process of compound A participating in the reaction to form the SEI film, it will not generate excessive steric hindrance, enabling compound A to react more smoothly with the natural silanol groups on the surface of the silicon-based anode. At the same time, methyl has a certain electron-donating ability, which can appropriately increase the electron cloud density on the silicon atom, optimize the reactivity of compound A with the silanol groups, and contribute to the formation of a cross-linked polymerization network of Si-O-Si bonds on the anode surface. The formation of this structure is the key to improving the performance of the SEI film and lays the foundation for adapting to the volume change of silicon. It can also enhance the flexibility of the SEI film. In the cross-linked polymerization network of Si-O-Si bonds formed, the presence of methyl helps to adjust the flexibility of the network. Silicon undergoes significant volume expansion and contraction during the charge-discharge cycle, and the flexible structure of methyl can buffer this stress change to a certain extent. Compared with other possible substituents, methyl can endow the SEI film with better flexibility, making it not easily break when the silicon volume changes, maintaining the integrity of the SEI film, thereby ensuring the stability of the internal structure of the battery and improving the capacity recovery rate of the battery under high-temperature storage. When R4 is methyl, it can also optimize the stability of the SEI film. The chemical properties of methyl are relatively stable and are not prone to side reactions such as decomposition in a high-temperature environment. When it participates in the formation of the SEI film as part of compound A, it can enhance the stability of the SEI film at high temperatures. During the high-temperature storage of lithium cobalt oxide silicon-carbon anode lithium-ion batteries, a stable SEI film can effectively prevent further side reactions between the electrolyte and the anode, reduce the generation of gas, and thus reduce the volume expansion rate of the battery. At the same time, it can also improve the interfacial compatibility. Methyl has good compatibility with other components inside the battery. In the battery system, it can promote the interfacial compatibility between the SEI film, the silicon-carbon anode, and the electrolyte, making the transmission of lithium ions between the interfaces more smooth. This helps to improve the charge-discharge efficiency of the battery, reduce irreversible capacity loss, has a positive effect on the improvement of the capacity recovery rate of the battery under high-temperature storage, and is also beneficial to reducing the volume expansion rate of the battery and maintaining the stability of the battery performance.

[0038] In a preferred embodiment of the present invention, the nitrile additive includes one or more of succinonitrile, glutarodinitrile, adiponitrile, trans-butenedinitrile, trans-hexenedinitrile, 1,2-bis(cyanoethoxy)ethane, 1,3,6-hexanetricarbonitrile, or 1,2,3-tris(cyanoethoxy)propane.

[0039] In the present invention, nitrile additives are, for example, succinonitrile, glutaronitrile, adiponitrile, fumarodinitrile, trans - hexenedinitrile, 1,2 - bis(cyanoethoxy)ethane, 1,3,6 - hexanetricarbonitrile, 1,2,3 - tris(cyanoethoxy)propane, combinations of succinonitrile and glutaronitrile, glutaronitrile and adiponitrile, adiponitrile and fumarodinitrile, trans - hexenedinitrile and 1,2 - bis(cyanoethoxy)ethane, 1,2 - bis(cyanoethoxy)ethane and 1,3,6 - hexanetricarbonitrile, combinations of succinonitrile, 1,3,6 - hexanetricarbonitrile and 1,2,3 - tris(cyanoethoxy)propane, or combinations of glutaronitrile, 1,2 - bis(cyanoethoxy)ethane and 1,3,6 - hexanetricarbonitrile.

[0040] In a preferred embodiment of the present invention, based on the total mass of the electrolyte solution being 100%, the proportion of the electrolyte salt in the electrolyte solution is 0.2 - 3.0%; the electrolyte salt includes one or more of lithium bis(fluorosulfonyl)imide, lithium difluoro(oxalato)borate, lithium tetrafluoroborate, bis(oxalato)borate, lithium difluorobis(oxalato)phosphate, or lithium hexafluorophosphate.

[0041] In the present invention, the proportion of the electrolyte salt in the electrolyte solution is, for example, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, or 3.0%.

[0042] In the present invention, the electrolyte salt is, for example, lithium bis(fluorosulfonyl)imide, lithium difluoro(oxalato)borate, lithium tetrafluoroborate, bis(oxalato)borate, lithium difluorobis(oxalato)phosphate, lithium hexafluorophosphate, combinations of lithium bis(fluorosulfonyl)imide and lithium difluoro(oxalato)borate, lithium difluoro(oxalato)borate and lithium tetrafluoroborate, bis(oxalato)borate and lithium difluorobis(oxalato)phosphate, lithium difluorobis(oxalato)phosphate and lithium hexafluorophosphate, combinations of lithium bis(fluorosulfonyl)imide, lithium difluoro(oxalato)borate and lithium tetrafluoroborate, or combinations of bis(oxalato)borate, lithium difluorobis(oxalato)phosphate and lithium hexafluorophosphate.

[0043] In a preferred embodiment of the present invention, the electrolyte salt includes lithium hexafluorophosphate.

[0044] In a preferred embodiment of the present invention, the non-aqueous electrolyte of the lithium-ion battery further includes a film-forming agent. Based on the mass of the non-aqueous electrolyte being 100%, the proportion of the film-forming agent in the electrolyte is 0.5-11%; the film-forming agent is one or more of vinylene carbonate (VC), 1,3-propane sultone (PS), fluoroethylene carbonate (FEC), ethylene sulfite (ES), ethylene sulfate (DTD), methylene methanedisulfonate (MMDS), vinylene ethylene carbonate (VEC), tris(trimethylsilyl) phosphate (TMSP), and tris(trimethylsilyl) borate (TMSB).

[0045] In the present invention, the proportion of the film-forming additive in the electrolyte is, for example, 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, 5.5%, 6.0%, 6.5%, 7.0%, 7.5%, 8.0%, 8.5%, 9.0%, 9.5%, 10.0%, 10.5% or 11.0%.

[0046] In the present invention, the film-forming agent is, for example, vinylene carbonate (VC), 1,3-propane sultone (PS), fluoroethylene carbonate (FEC), ethylene sulfite (ES), ethylene sulfate (DTD), methylene methanedisulfonate (MMDS), vinylene ethylene carbonate (VEC), tris(trimethylsilyl) phosphate (TMSP), tris(trimethylsilyl) borate (TMSB), a combination of vinylene carbonate (VC) and 1,3-propane sultone (PS), 1,3-propane sultone (PS) and fluoroethylene carbonate (FEC), fluoroethylene carbonate (FEC) and ethylene sulfite (ES), ethylene sulfate (DTD) and methylene methanedisulfonate (MMDS), methylene methanedisulfonate (MMDS) and vinylene ethylene carbonate (VEC), vinylene ethylene carbonate (VEC) and tris(trimethylsilyl) phosphate (TMSP), tris(trimethylsilyl) borate (TMSB), a combination of vinylene carbonate (VC) and 1,3-propane sultone (PS), vinylene ethylene carbonate (VEC), tris(trimethylsilyl) phosphate (TMSP) and tris(trimethylsilyl) borate (TMSB), or a combination of vinylene carbonate (VC), 1,3-propane sultone (PS) and fluoroethylene carbonate (FEC).

[0047] In a preferred embodiment of the present invention, based on the mass of the non-aqueous electrolyte being 100%, the proportion of the organic solvent in the electrolyte is 75% - 94%; The organic solvent includes carbonate organic solvents and / or carboxylate organic solvents; Preferably, the carbonate organic solvent includes cyclic carbonate and / or chain carbonate; Preferably, the cyclic carbonate includes any one or a combination of at least two of ethylene carbonate, propylene carbonate, or butylene carbonate; Preferably, the chain carbonate includes any one or a combination of at least two of diethyl carbonate, ethyl methyl carbonate, dimethyl carbonate, or methyl propyl carbonate; Preferably, the carboxylic acid ester organic solvent includes any one or a combination of at least two of ethyl propionate, propyl propionate, ethyl acetate, ethyl n-butyrate, methyl acetate, propyl acetate, methyl propionate, or γ-butyrolactone.

[0048] According to a second aspect of the present invention, a lithium-ion battery is provided, and the lithium-ion battery includes the non-aqueous electrolyte of the lithium-ion battery as described above.

[0049] In a preferred embodiment of the present invention, the lithium-ion battery further includes a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode.

[0050] In the present invention, the positive electrode of the lithium-ion battery includes a positive electrode active material, a conductive agent, and a binder. The positive electrode active material is at least one of LiCoO2, LiNix'L'y'Mn(2-x”-y')O4; where L is at least one of Al, Sr, Mg, Ti, Ca, Zr, Zn, Si, Fe; 5≤x≤1, 0≤y<1, 0≤z≤1, 0<x+y+z≤1, 0<x'≤1, 0.01≤y'≤0.2, and L' is at least one of Co, Al, Sr, Mg, Ti, Ca, Zr, Zn, Si, Fe; preferably, the positive electrode active material is LiCoO2.

[0051] The negative electrode plate of the lithium-ion battery includes a negative electrode active material, and the negative electrode active material includes one or a combination of at least two of natural graphite, artificial graphite, soft carbon, hard carbon, mesophase carbon microspheres, graphene, graphyne, metallic lithium, nano-carbon, carbon nanotubes, elemental silicon, silicon oxide compounds, silicon / copper oxide composites, AG composites, silicon alloys, elemental tin, tin oxide compounds, tin-carbon composites, tin alloys, or lithium titanate.

[0052] The negative electrode active material includes a combination of graphite and a silicon-based material, and the silicon-based material includes any one or a combination of at least two of elemental silicon, silicon oxide compounds, silicon / copper oxide composites, or silicon alloys; The mass percentage content of the silicon-based material in the negative electrode active material is 10%-20%; The material of the separator of the lithium-ion battery includes one of polyethylene, polypropylene, or a composite ceramic membrane.

[0053] Examples The present invention provides 14 examples and 4 comparative examples.

[0054] The preparation methods of the lithium-ion batteries in the examples and comparative examples include the following steps: (1) Preparation of the positive electrode sheet: Polyvinylidene fluoride (PVDF) is uniformly dissolved in N-methylpyrrolidone (NMP), and then conductive agent Super P is added and fully mixed. Then, positive electrode active material LiCoO2 powder is gradually added (where the mass ratio of LiCoO2 powder, PVDF, and conductive agent Super P is 97.4:1.3:1.3) to obtain a positive electrode slurry (the solid content of the discharged positive electrode slurry is 63.1%). The positive electrode slurry is coated on the current collector, and then dried, roll-pressed, and slit to obtain a positive electrode sheet that can be directly stacked.

[0055] (2) Preparation of the negative electrode sheet: Artificial graphite, conductive carbon, silicon oxide powder, and sodium carboxymethyl cellulose with a mass ratio of 80.9:2.9:15:1.2 are fed and premixed, stirred at a speed of 250 rpm for 140 min to obtain a negative electrode slurry. Then, the negative electrode slurry is transferred to deionized water for dispersion, and after being mixed evenly, the negative electrode slurry is sieved (180 mesh). Finally, the sieved negative electrode slurry is coated on the negative current collector, and then dried, roll-pressed, and slit to obtain a negative electrode sheet that can be directly stacked.

[0056] (3) Preparation of the electrolyte: The electrolyte is prepared in a MIKRONA glove box (the internal filling gas is argon, and the gaseous water is less than 10 ppm). First, organic solvents ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are uniformly mixed according to EC:EMC = 3:7 (vol:vol). In the uniformly mixed solvent package, a film-forming additive, a nitrile additive, and compound A are added successively. Finally, 12.5 g of LiPF6 is added, and the mixture is stirred until there is no residue at the bottom of the lithium salt and the electrolyte is clear and not turbid, that is, an electrolyte with normal chromaticity is obtained and stored in a -10°C refrigerator. The component ratios of each group are shown in Table 1.

[0057] (4) Cell manufacturing: The slit positive electrode sheet and negative electrode sheet are stacked on a stacker, and the separator is made of three layers of PP / PE / PP to form a soft-pack cell.

[0058] (5) Liquid injection, formation, and aging: After the battery cells are dried at high temperature, the electrolytes of the examples and comparative examples are injected into the soft-pack battery cells. After the electrolyte injection, the lithium battery undergoes initial packaging, surface cleaning and other preliminary processes to complete the preliminary work, and is left at room temperature for one day. The formation is carried out using a step-by-step formation method. The first step is a formation current of 0.05C, and constant current charging is applied for 2 hours. The second step is a formation current of 0.1C, and constant current charging is applied until the voltage reaches 3.85V. After formation, it is aged at 50°C for one day, cooled to room temperature and finally sealed.

[0059] Table 1 Composition ratios of Examples and Comparative Examples

[0060] Battery performance test: After the battery is assembled, it is placed in a room temperature chamber for 10 hours to allow the electrolyte to fully penetrate the battery electrodes, and then taken for the following tests.

[0061] ①25℃ normal temperature cycle test: In a constant temperature room at 25℃, constant current charge and discharge are performed at a current density of 1C at rated capacity. The cycle number is 1000. The test voltage range is 2.75V-4.2V and the charge cut-off current is 0.05C. After the test, the capacity retention rate at the 1000th week is calculated based on the discharge capacity in the first week.

[0062] The calculation formula for the capacity retention rate after 1000 cycles at room temperature is as follows: 1000th cycle capacity retention rate (%) = (1000th room temperature cycle discharge capacity / first discharge capacity) * 100%.

[0063] ②45℃ high temperature cycle test: In a constant temperature 45℃ forced air oven, constant current charge and discharge are performed at a current density of 1C at the rated capacity. The cycle number is 1000. The test voltage range is 2.75V-4.2V and the charge cut-off current is 0.05C. After the test, the capacity retention rate at the 1000th week is calculated based on the discharge capacity in the first week.

[0064] The calculation formula for 1000-cycle high-temperature cycle capacity retention rate is as follows: 1000th cycle capacity retention rate (%) = (1000th high-temperature cycle discharge capacity / first discharge capacity)*100%.

[0065] ③ Lithium-ion Battery High-Temperature Gas Generation Performance Test: Constant current charge and discharge were performed at a current density of 1C at the rated capacity in a 25°C constant temperature chamber. Subsequently, constant voltage charging was performed at 4.2V to a current of 0.05C. After full charge, the initial volume of the battery was measured using the water displacement method. The battery was then placed in a 60°C oven for 7 days, removed, and allowed to stand at room temperature for 60 minutes. After cooling to room temperature, the battery volume was measured using the water displacement method.

[0066] Perform the storage test according to the above steps until 28 days of storage. Take the battery volume measured before storage as the benchmark, and calculate the volume expansion rate of the battery as a function of storage time.

[0067] The volume expansion rate of the battery after 28 days of high-temperature storage = ((the volume after 28 days of high-temperature storage - the initial volume of the battery) / the initial volume of the battery) * 100%.

[0068] The test results of the examples and comparative examples are shown in Table 2: Table 2 Test Results of Examples and Comparative Examples

[0069] According to the data of Examples 1 to 14, it can be obtained that the electrolyte of the present invention enables the secondary lithium-ion battery to have good room-temperature capacity retention and high high-temperature capacity retention by adding nitrile additives and Compound A, and can greatly inhibit the volume expansion of the battery during storage. As can be seen from Examples 1 to 14, the capacity retention rate of the secondary lithium-ion battery assembled with the electrolyte is 89.2% to 94.7% under the test conditions of 25 °C and 1C, and the capacity retention rate is 79.4% to 88.2% under the test conditions of 45 °C and 1C. The volume expansion rate after 28 days of storage at 60 °C is 6.9 - 10.1%. From the data, it can be seen that the nitrile additive is preferably adiponitrile, and Compound A is preferably the structure shown in Formula 2. When the ratio of the nitrile additive to Compound A is in the range of 1 to 5:1, the battery has better performance, and the effect is the best when the ratio is 1:1. When the total addition amount of the nitrile additive and Compound A is between 0.6% and 9%, the battery has better performance. As the total addition amount increases, the performance gradually decreases, and the performance is better when the total addition amount is between 0.6% and 2%.

[0070] Analysis of the examples and comparative examples shows that only when the nitrile additive and Compound A are used in combination can the comprehensive performance of the battery be improved.

[0071] The present invention elaborates in detail the application details of the present invention through the above examples and data. However, the present invention is not limited to the listed examples. It should be understood that the present invention can greatly improve the battery performance in the field of cobalt lithium oxide silicon carbon lithium-ion battery electrolytes. Those skilled in the art should know that replacing the details of the present invention or by simple means without departing from the technical solution of the present invention should be within the scope of protection of the present invention.

Claims

1. A non-aqueous electrolyte for a lithium-ion battery, characterized in that, The electrolyte solution includes an electrolyte salt, an organic solvent, a nitrile additive, and Compound A; Compound A is shown as Formula 1: wherein R1, R2, R3, R4, and R5 are each independently selected from any one of hydrogen, halogen, substituted or unsubstituted C1-C4 alkyl groups.

2. The non-aqueous electrolyte for a lithium ion battery according to claim 1, wherein Based on the total mass of the electrolyte solution being 100%, the proportion of the nitrile additive in the electrolyte solution is 0.5% - 5%; the proportion of Compound A in the electrolyte solution is 0.1% - 4.0%.

3. The non-aqueous electrolyte for a lithium ion battery according to claim 1, wherein R1, R2, R3, R4, and R5 are each independently selected from any one of fluorine, -CH3, -CH2CH3, -CH(CH3)2, or -C(CH3)3.

4. The non-aqueous electrolyte for a lithium ion battery according to claim 3, characterized in that Compound A includes at least one of the following compounds:

5. The non-aqueous electrolyte for a lithium-ion battery according to claim 2, characterized in that, The nitrile additive includes one or more of succinonitrile, glutarodinitrile, adiponitrile, trans-butenedinitrile, trans-hexenedinitrile, 1,2-bis(cyanoethoxy)ethane, 1,3,6-hexanetricarbonitrile, or 1,2,3-tris(cyanoethoxy)propane.

6. The non-aqueous electrolyte for a lithium ion battery according to claim 1, wherein Based on the total mass of the electrolyte solution being 100%, the proportion of the electrolyte salt in the electrolyte solution is 0.2 - 3.0%; The electrolyte salt includes one or more of lithium difluoromethanesulfonate, lithium difluoro(oxalato)borate, lithium tetrafluoroborate, bis(oxalato)borate, lithium difluoro(bisoxalato)phosphate, or lithium hexafluorophosphate.

7. The non-aqueous electrolyte for a lithium ion battery according to claim 1, wherein The non-aqueous electrolyte solution of the lithium-ion battery further includes a film-forming agent. Based on the mass of the non-aqueous electrolyte solution being 100%, the proportion of the film-forming additive in the electrolyte solution is 0.5 - 11%; The film-forming agent is one or more of vinylene carbonate, 1,3-propane sultone, fluoroethylene carbonate, ethylene sulfite, ethylene sulfate, methylene methanedisulfonate, ethylene vinylene carbonate, tris(trimethylsilyl) phosphate, or tris(trimethylsilyl) borate.

8. The non-aqueous electrolyte for a lithium ion battery according to claim 1, characterized in that, Based on the mass of the non-aqueous electrolyte solution being 100%, the proportion of the organic solvent in the electrolyte solution is 75% - 94%; The organic solvent includes carbonate organic solvents and / or carboxylate organic solvents; Preferably, the carbonate organic solvents include cyclic carbonates and / or chain carbonates; Preferably, the cyclic carbonate includes any one or a combination of at least two of ethylene carbonate, propylene carbonate, or butylene carbonate; Preferably, the chain carbonate includes any one or a combination of at least two of diethyl carbonate, ethyl methyl carbonate, dimethyl carbonate, or methyl propyl carbonate; Preferably, the carboxylate organic solvents include any one or a combination of at least two of ethyl propionate, propyl propionate, ethyl acetate, ethyl n-butyrate, methyl acetate, propyl acetate, methyl propionate, or γ-butyrolactone.

9. A lithium-ion battery, characterized in that, The lithium-ion battery includes the non-aqueous electrolyte solution of the lithium-ion battery according to any one of claims 1 - 8.

10. The lithium ion battery according to claim 9, characterized in that, The positive electrode of the lithium-ion battery includes a positive electrode active material, a conductive agent, and a binder. The active material of the positive electrode is at least one of LiCoO2 and LiNix'L'y'Mn(2-x”-y'); where L is at least one of Al, Sr, Mg, Ti, Ca, Zr, Zn, Si, Fe; 5≤x≤1, 0≤y<1, 0≤z≤1, 0<x + y + z≤1, 0<x'≤1, 0.01≤y'≤0.2, and L' is at least one of Co, Al, Sr, Mg, Ti, Ca, Zr, Zn, Si, Fe; The negative electrode plate of the lithium-ion battery includes a negative electrode active material, and the negative electrode active material includes one or at least two combinations of natural graphite, artificial graphite, soft carbon, hard carbon, mesophase carbon microspheres, graphene, graphyne, metallic lithium, nano-carbon, carbon nanotubes, elemental silicon, silicon oxide compounds, silicon / copper oxide composites, AG composites, silicon alloys, elemental tin, tin oxide compounds, tin-carbon composites, tin alloys, or lithium titanate; The negative electrode active material includes a combination of graphite and a silicon-based material, and the silicon-based material includes any one or at least two combinations of elemental silicon, silicon oxide compounds, silicon / copper oxide composites, and silicon alloys; The mass percentage content of the silicon-based material in the negative electrode active material is 10%-20%; The material of the separator of the lithium-ion battery includes one of polyethylene, polypropylene, or a composite ceramic membrane.

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