A lithium-ion battery

Abstract

The application relates to the technical field of batteries, and particularly discloses a lithium ion battery. The lithium ion battery comprises a positive electrode, a negative electrode, a diaphragm and a non-aqueous electrolyte; the positive electrode active material comprises lithium cobaltate, and the negative electrode active material comprises silicon-carbon material; the non-aqueous electrolyte comprises a compound shown in structural formula 1, a compound shown in structural formula 2 and fluorinated ethylene carbonate; the battery satisfies 2.5 <= A / (C1+C2) <= 10, 0.4 <= C3xR / 100D <= 1.4, 0.05 <= C1 <= 4, 0.05 <= C2 <= 5, 10 <= C3 <= 25, 5 <= A <= 50, 5 <= D <= 20 and 36 <= R <= 50. The compound shown in structural formula 1 inhibits cobalt dissolution and oxygen precipitation, the compound shown in structural formula 2 cooperates with the fluorinated ethylene carbonate to construct a stable SEI film, and the silicon content of the negative electrode is matched, so that the volume expansion of the silicon-carbon material is relieved, the interface bonding force is enhanced, and electrolyte decomposition, electrode crosstalk and active layer peeling are inhibited. While the energy density is improved, the cycle performance, high-temperature performance and safety performance are optimized, and the comprehensive electrochemical performance and safety of the battery are significantly improved.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and specifically to a lithium-ion battery based on a lithium cobalt oxide system that combines high voltage stability, low volume expansion, and high safety. Background Technology

[0002] Lithium cobalt oxide (LiCoO2), as the earliest commercially available cathode material in the field of lithium-ion batteries, has become a dominant material in lithium-ion batteries for high-end consumer electronics products such as smartphones, laptops, and wearable devices, thanks to its excellent high compaction density, stable layered crystal structure, mature industrial preparation process, and good electrochemical kinetic performance. It has become a core material supporting the lightweight and miniaturization development of the consumer electronics industry.

[0003] With the market's continuous demand for higher battery energy density, the industry generally adopts two core technological paths to improve battery energy density: one is to increase the charging cut-off voltage of lithium cobalt oxide cathodes to fully tap their lithium-ion intercalation / deintercalation potential; the other is to incorporate high-specific-capacity silicon-based materials into the anode material to replace traditional graphite anodes and increase the theoretical capacity of the anode. However, both of these technological paths face significant technical bottlenecks in practical applications, severely restricting the commercialization of high-energy-density lithium cobalt oxide / silicon-based battery systems.

[0004] On the one hand, when the charging cut-off voltage of the lithium cobalt oxide cathode is increased to above 4.5 V, its crystal structure stability is severely compromised: excessive extraction of lithium ions from the lattice leads to an irreversible phase transition in the layered structure, gradually transforming into a spinel or rock salt phase, which in turn causes irreversible capacity decay and significantly shortens the battery's cycle life. Simultaneously, the high-voltage environment exacerbates interfacial side reactions between the electrolyte and the delithiated lithium cobalt oxide cathode. This not only accelerates the dissolution of cobalt ions from the cathode lattice but also allows the dissolved cobalt ions to migrate to the anode and deposit, disrupting the anode's interfacial stability. More critically, these interfacial side reactions also induce oxygen release from the cathode lattice, leading to increased internal heat accumulation and a significantly higher risk of thermal runaway, seriously threatening battery safety.

[0005] On the other hand, silicon-based materials are considered the most promising high-capacity anode materials due to their extremely high theoretical specific capacity. However, silicon undergoes a volume expansion of over 300% during lithium intercalation. This inherent defect brings a series of problems: the dramatic volume expansion generates enormous mechanical stress and strain, causing the silicon-based anode material to pulverize and detach, damaging the integrity of the electrode. Simultaneously, the volume expansion causes repeated breakage and regeneration of the solid electrolyte interphase (SEI) film on the anode surface, consuming not only electrolyte and lithium ions but also exacerbating the increase in interfacial impedance, leading to a deterioration in battery rate performance and cycle performance. Generally speaking, the higher the silicon content in a silicon-based anode, the higher the theoretical energy density of the battery, but the resulting volume expansion problem becomes increasingly severe, creating a contradiction between "capacity improvement and structural stability."

[0006] Based on this, when a silicon-carbon composite anode is coupled with a high-voltage lithium cobalt oxide cathode, the battery's interface compatibility, structural stability, and thermal safety are further deteriorated under the combined stress of high voltage-induced cathode structural instability, intensified interfacial side reactions, and high volume expansion-induced anode structural damage and interface failure. This significantly amplifies the potential for battery thermal runaway and severely limits the practical application of high-energy-density lithium cobalt oxide / silicon-based battery systems.

[0007] Therefore, developing a lithium cobalt oxide / silicon-based battery system that combines high voltage stability, low volume expansion, and high safety is crucial for overcoming the performance limitations of existing high-energy-density batteries and promoting the upgrading of lithium-ion battery technology. Summary of the Invention

[0008] To address the aforementioned technical problems, this invention provides a lithium-ion battery based on a lithium cobalt oxide / silicon system that combines high voltage stability, low volume expansion, and high safety.

[0009] The present invention adopts the following technical solution: A lithium-ion battery includes a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte; The positive electrode includes a positive electrode current collector and a positive electrode material layer covering at least one surface of the positive electrode current collector, the positive electrode material layer including a positive electrode active material, the positive electrode active material including lithium cobalt oxide; The negative electrode includes a negative electrode current collector and a negative electrode material layer covering at least one surface of the negative electrode current collector. The negative electrode material layer includes a negative electrode active material, which is a silicon-carbon material. The thickness of the negative electrode current collector is D μm, and its dyn value is R dyn / cm. The mass percentage of silicon in the negative electrode material layer is A%. The non-aqueous electrolyte comprises the compound shown in structural formula 1, the compound shown in structural formula 2, and fluoroethylene carbonate: Structural Formula 1; R1, R2, and R3 are each independently selected from C1-C10 alkyl, C2-C10 alkenyl, C2-C10 alkynyl, C1-C10 alkoxy, C1-C10 fluoroalkyl, C1-C10 fluoroalkoxy, C2-C10 cyano, and C2-C10 isocyanate groups. Structural Formula 2; Where X is selected from or R4 and R5 are each independently selected from H, or R4 and R5 are not both selected from H, and X, R4, and R5 contain at least one sulfur atom; Based on the mass of the non-aqueous electrolyte, the mass percentage of the compound shown in structural formula 1 is C1wt%, and the mass percentage of the compound shown in structural formula 2 is C2wt%. The lithium-ion battery meets the following conditions: 0.05≤C1≤4, 0.05≤C2≤5, 10≤C3≤25, 5≤A≤50, 5≤D≤20, 36≤R≤50, 2.5≤A / (C1+C2)≤10, 0.4≤C3×R / 100D≤1.4.

[0010] The lithium-ion battery of the present invention uses lithium cobalt oxide as the positive electrode active material and adopts silicon-carbon composite negative electrode to significantly improve the battery energy density. At the same time, the silicon content in the negative electrode material layer is controlled, and the compound shown in structural formula 1, the compound shown in structural formula 2 and fluoroethylene carbonate are synergistically added to the non-aqueous electrolyte. Through extensive research, the inventors discovered that when the mass percentages of the compound shown in structural formula 1 (C1), the compound shown in structural formula 2 (C2), and the fluoroethylene carbonate (C3) in the non-aqueous electrolyte, along with the thickness of the negative electrode current collector (D) and the dyne value (R), and the mass percentage of silicon in the negative electrode material layer (A) satisfy the following conditions: 0.05≤C1≤4, 0.05≤C2≤5, 10≤C3≤25, 5≤A≤50, 5≤D≤20, 36≤R≤50, 2.5≤A / (C1+C2)≤10, and 0.4≤C3×R / 100D≤1.4, the prepared lithium-ion battery can achieve a high local energy density while also possessing excellent high voltage stability, low volume expansion, and high safety.

[0011] First, the compound shown in Formula 1 undergoes an oxidative polymerization reaction on the positive electrode side during the first charge of the battery, forming a cross-linked polymer interface film. This interface film can significantly suppress the dissolution of Co ions and the evolution of reactive oxygen species from the lithium cobalt oxide positive electrode under high voltage conditions, reducing electrochemical failure on the positive electrode side from the source. Simultaneously, the cyanuric acid structure contained in this compound can form large π bonds through a conjugation effect. When the interface protective film is subjected to energy disturbances such as external thermal shock and electrochemical oxidation, it can dissipate energy through a resonance effect, significantly improving the shock resistance of the lithium-ion battery and enhancing battery safety performance. Meanwhile, the compound shown in Formula 2 can form a stable and dense solid electrolyte interface film containing sulfate / sulfonate on the negative electrode side, effectively reducing the direct contact between the negative electrode and the electrolyte in the lithium-intercalated state, thus giving the lithium-ion battery good cycle stability. In the electrolyte system, although fluoroethylene carbonate can optimize ion conduction and interfacial compatibility, its protective effect on the high-voltage positive electrode is limited when used alone, and it poses a risk of gas generation, easily leading to cycle degradation and safety hazards. The addition of compounds shown in Structural Formulas 1 and 2 effectively compensates for the aforementioned defects: the compound shown in Structural Formula 1 can form a stable cross-linked polymer interface film on the positive electrode side, compensating for the insufficient positive electrode protection capability of fluoroethylene carbonate under high voltage; the compound shown in Structural Formula 2 can form a dense and stable SEI film on the negative electrode side, solving the problems of poor negative electrode protection and insufficient high-temperature stability of fluoroethylene carbonate. The synergistic effect of the three compounds optimizes the formation efficiency, density, and stability of the positive and negative electrode interface films. By limiting the lithium-ion battery to 2.5≤A / (C1+C2)≤10, the solid electrolyte interface film formed by this invention provides good protection for both the positive and negative electrodes. It effectively reduces the oxidative decomposition of the electrolyte under high voltage and avoids electrode crosstalk between the positive and negative electrodes, thereby significantly improving the battery's thermal safety and high-voltage stability. At the same time, it effectively reduces the battery's K value and the generation of negative electrode black spots during high-temperature cycling, achieving a synergistic improvement in battery safety and cycle performance.

[0012] When the mass percentage of the compound shown in structural formula 1 (C1), the mass percentage of the compound shown in structural formula 2 (C2), and the silicon content of the negative electrode (A) are related by A / (C1+C2) < 2.5, it indicates that the proportion of silicon in the negative electrode material layer is too low, or the content of the compounds shown in structural formulas 1 and 2 is too high, making it difficult to form a stable solid electrolyte interface film that can protect both positive and negative electrodes and is compatible with the high-voltage lithium cobalt oxide-high silicon negative electrode coupling system. If the value of A is too small, the silicon content of the negative electrode is insufficient, resulting in poor matching with the high-voltage lithium cobalt oxide positive electrode and limiting the overall capacity of the battery. If the value of C1 is too high, it is easy to damage the uniformity of the interface film, which will reduce the shock resistance of the electrode. If the value of C2 is too high, it will lead to a significant increase in interface impedance, which will hinder lithium-ion transport. Overall, this further amplifies the failure risk and safety hazards of the high-voltage lithium cobalt oxide-high silicon negative electrode system.

[0013] When the mass percentage of the compound shown in structural formula 1 (C1) and the mass percentage of the compound shown in structural formula 2 (C2) in the non-aqueous electrolyte are related to the silicon content A of the negative electrode (A / (C1+C2)) > 10, it indicates that the proportion of silicon in the negative electrode material layer is too high, or the content of the compounds shown in structural formulas 1 and 2 is too low. If the value of A is too large, the volume effect of the high-silicon negative electrode itself is significant, which can easily aggravate electrode pulverization and interface damage, and amplify the failure risk after coupling with the high-voltage lithium cobalt oxide positive electrode. If the value of C1 is too low, the interface protective film is difficult to effectively dissipate heat through resonance and resist external energy impacts such as electrochemical oxidation, resulting in poor battery impact resistance. If the value of C2 is too low, a sufficient amount of stable and dense sulfate / sulfonate solid electrolyte interface film cannot be formed on the negative electrode side, increasing the direct contact between the lithium-intercalated negative electrode and the electrolyte, and significantly reducing high-temperature stability. Overall, this will lead to aggravated oxidation and decomposition of the electrolyte under high voltage, severe electrode crosstalk, and deterioration of battery thermal safety and high-voltage cycle stability.

[0014] Preferably, the mass percentage of the compound represented by structural formula 1 (C1) and the mass percentage of the compound represented by structural formula 2 in the non-aqueous electrolyte are related to the silicon content A of the negative electrode, which satisfies 3 ≤ A / (C1+C2) ≤ 9.

[0015] Secondly, based on the mass of the non-aqueous electrolyte, the mass percentage of the fluoroethylene carbonate is C3wt%, the dyn value of the negative electrode current collector is R dyn / cm, and the thickness of the negative electrode current collector is D μm; The lithium-ion battery described satisfies the following conditions: 0.4≤C3×R / 100D≤1.4, 10≤C3≤25, 5≤D≤20, 36≤R≤50. Under these conditions, the prepared lithium-ion battery achieves both high local energy density and excellent electrolyte wettability with low volume expansion. It is speculated that the synergistic effect of the surface energy and thickness design of the negative electrode current collector, combined with the precise matching of the content of key electrolyte additives, jointly constructs a dual-effect protection system for both positive and negative electrodes, effectively balancing the structural integrity of the high-silicon-content negative electrode and the battery's energy density.

[0016] When the mass percentage of fluoroethylene carbonate in the non-aqueous electrolyte is C3, the dyne value of the negative electrode current collector is R, and the thickness of the negative electrode current collector is D, the relationship between C3×R / 100D < 0.4 indicates insufficient interfacial bonding strength of the negative electrode sheet. When the peeling driving force, such as drying shrinkage stress or mechanical external force, exceeds the limit that the interfacial adhesion force can withstand, the electrode sheet is prone to coating peeling. If the D value is too large, although the excessive thickness of the current collector can reduce process risks, it will sacrifice energy density. At the same time, the thick foil has high stiffness and high internal stress during winding, which will increase the peeling force on the interface. Uneven heating during coating will also amplify shrinkage stress. If the R value is too small, it indicates that the dyne value of the negative electrode current collector is relatively low compared to the silicon content. The wettability and surface tension of the negative electrode surface are insufficient, which cannot meet the interfacial bonding requirements of the high silicon content negative electrode. This directly leads to poor bonding strength between the negative electrode material layer and the current collector, making it easy for active materials to fall off and peel off, resulting in battery cycle performance degradation and increased impedance.

[0017] When the mass percentage of fluoroethylene carbonate in the non-aqueous electrolyte is C3, the dyne value of the negative electrode current collector is R, and the thickness D of the negative electrode current collector is C3×R / 100D>1.4, it means that the adhesion force between the coating and the current collector is much greater than the peeling stress generated during the process. Although this can ensure that the electrode does not shed powder, "over-bonding" will also cause cracks and slag to easily form at the edges when the electrode is die-cut, posing a risk of short circuit and self-discharge. If the D value is too small, the mechanical strength and support capacity of the current collector itself are insufficient, making it difficult to withstand the drastic volume expansion and contraction of the high-silicon negative electrode during lithium insertion and extraction, which can easily lead to deformation, wrinkles, or even breakage of the current collector. If the R value is too large, the negative electrode slurry spreads too quickly and penetrates too deeply into the current collector, and drying can easily form "thick edges" or excessive "pinning", which is not conducive to the uniformity of the electrode.

[0018] Preferably, the mass percentage of fluoroethylene carbonate in the non-aqueous electrolyte is C3, and the relationship between the dyne value R of the negative electrode current collector and the thickness D of the negative electrode current collector satisfies 0.5≤C3×R / 100D≤1.1.

[0019] The compound of structural formula 1 in the non-aqueous electrolyte of the lithium-ion battery of the present invention can undergo oxidative polymerization on the positive electrode side during the first charging process to form a cross-linked polymer interface film, which can significantly suppress the dissolution of Co ions and the evolution of active oxygen from the high-voltage lithium cobalt oxide positive electrode; at the same time, the cyanuric acid structure contained therein can form conjugated large π bonds, which can effectively dissipate energy through conjugated resonance when the interface protective film is subjected to external energy impacts such as heat and electrochemical oxidation, thereby endowing the lithium-ion battery with excellent impact resistance characteristics. If the amount of the compound shown in Formula 1 is insufficient, it is difficult to form a complete and continuous cross-linked polymer interface film on the positive electrode surface, which significantly reduces the inhibition effect on Co ion dissolution and reactive oxygen evolution. In addition, the content of conjugated large π bonds is too low, which cannot effectively dissipate external energy impacts, resulting in poor battery impact resistance and deterioration of positive electrode interface stability under high voltage. If the amount of the compound shown in Formula 1 is excessive, it is easy to accumulate on the electrode surface, resulting in an excessively thick and loosely structured interface film, which increases the battery interface impedance and hinders the rapid transport of lithium ions. At the same time, excessive additives are prone to triggering side reactions, causing electrolyte decomposition and increased battery gas production, which in turn leads to decreased cycle stability and excessively rapid increase in internal resistance, which is not conducive to the overall performance of the battery. Specifically, in some embodiments of the present invention, the mass percentage C1wt% of the compound represented by structural formula 1 in the non-aqueous electrolyte is 0.05wt%, 0.08wt%, 0.1wt%, 0.5wt%, 0.8wt%, 1.0wt%, 1.2wt%, 1.5wt%, 1.7wt%, 2.0wt%, 2.2wt%, 2.5wt%, 2.8wt%, 3wt%, 3.2wt%, 3.5wt%, 3.7wt%, 4wt%, or any combination of these values; preferably, the mass percentage C1wt% of the compound represented by structural formula 1 in the non-aqueous electrolyte is 0.1wt% to 3wt%.

[0020] The compound shown in Structural Formula 2 in the non-aqueous electrolyte of the lithium-ion battery of the present invention can form a stable and dense solid electrolyte interface film containing sulfate / sulfonate on the negative electrode side, effectively blocking direct contact between the lithium-intercalated negative electrode and the electrolyte, reducing the continuous reduction and decomposition of the electrolyte at high temperatures, thereby giving the lithium-ion battery good high-temperature stability. If the amount of the compound shown in Structural Formula 2 is insufficient, it is difficult to form a continuous and dense sulfate / sulfonate interface film on the negative electrode surface, resulting in weak protection for the negative electrode. The lithium-intercalated negative electrode and the electrolyte are still prone to side reactions, leading to poor high-temperature stability of the battery and problems such as negative electrode black spots and rapid capacity decay during high-temperature cycling. If the amount of the compound shown in Structural Formula 2 is excessive, it will cause the negative electrode interface film to grow excessively and have uneven thickness, significantly increasing the battery interface impedance, hindering the insertion and extraction of lithium ions and transport, causing a decrease in rate performance and increased polarization. At the same time, excessive additives are prone to triggering side reactions in the electrolyte, leading to increased gas production and battery expansion, thereby deteriorating cycle life and safety performance. Specifically, in some embodiments of the present invention, the mass percentage C2wt% of the compound represented by structural formula 2 in the non-aqueous electrolyte is 0.05 wt%, 0.08 wt%, 0.1 wt%, 0.5 wt%, 0.8 wt%, 1.0 wt%, 1.2 wt%, 1.5 wt%, 1.7 wt%, 2.0 wt%, 2.2 wt%, 2.5 wt%, 2.8 wt%, 3 wt%, 3.2 wt%, 3.5 wt%, 3.7 wt%, 4 wt%, 4.2 wt%, 4.5 wt%, 4.7 wt%, 5 wt%, or any combination of these values; preferably, the mass percentage C2wt% of the compound represented by structural formula 2 in the non-aqueous electrolyte is 0.1 wt% to 4 wt%.

[0021] The addition of fluoroethylene carbonate (FEC) to the non-aqueous electrolyte of the lithium-ion battery of this invention can improve the ionic conductivity of the electrolyte and enhance rate performance. During the first charge, it preferentially reduces at the negative electrode, participating in the formation of a dense and stable SEI film, blocking contact between the lithium-intercalated negative electrode and the electrolyte, and inhibiting electrolyte decomposition. The fluorinated groups can enhance the high-temperature resistance and damage resistance of the SEI film, adapt to the volume effect of high-silicon negative electrodes, help improve the stability of high-voltage lithium cobalt oxide positive electrodes, and at the same time improve the compatibility between the electrolyte and the electrode and reduce the interfacial impedance. If the amount of fluoroethylene carbonate added is insufficient, an effective SEI film cannot be formed, resulting in insufficient negative electrode protection, aggravated electrolyte side reactions, and a decrease in battery cycle life, rate performance, and high-temperature stability. Excessive FEC will increase electrolyte viscosity, reduce ionic conductivity, lead to an excessively thick SEI film, increase interfacial impedance, and also cause side reaction gas generation, battery expansion, deteriorate cycle stability and safety, and affect the compatibility of positive and negative electrode coupling. Specifically, in some embodiments of the present invention, the mass percentage (C3wt%) of fluoroethylene carbonate in the non-aqueous electrolyte is 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt%, 20 wt%, 21 wt%, 22 wt%, 23 wt%, 24 wt%, 25 wt%, or any combination of these values; preferably, the mass percentage (C3wt%) of fluoroethylene carbonate in the non-aqueous electrolyte is 12 wt% to 20 wt%.

[0022] Controlling the mass percentage (A%) of silicon in the negative electrode material layer can improve the theoretical capacity and energy density of the battery while avoiding excessive volume expansion during charging and discharging due to excessive silicon content. By reasonably limiting the mass percentage of silicon, the structural stress caused by silicon expansion can be effectively alleviated, reducing cracking, peeling, and current collector deformation of the negative electrode material layer, thereby improving the battery's cycle stability and lifespan. Precise control of the silicon content can also balance the battery's rate performance and interface stability, preventing increased internal impedance due to excessive expansion, and achieving synergistic optimization of high capacity and structural reliability. In some embodiments of the present invention, the mass percentage A% of silicon in the negative electrode material layer is specifically 5%, 7%, 9%, 10%, 12%, 14%, 15%, 17%, 19%, 20%, 22%, 24%, 25%, 27%, 29%, 30%, 32wt%, 34%, 35%, 37%, 39%, 40%, 42%, 45%, 47%, 49%, 50%, or any combination of these values; preferably, the mass percentage A% of silicon in the negative electrode material layer is 10% to 35%.

[0023] Specifically, in some embodiments of the present invention, the method for determining the silicon content in the negative electrode material layer is as follows: After discharging the battery to 0% SOC, the negative electrode is disassembled and removed. It is then immersed in dimethyl carbonate solvent for cleaning to remove lithium salt residue. After vacuum drying of the electrode sheet, it is subjected to high-temperature treatment at 400°C in an inert atmosphere for 2 hours to peel off the negative electrode material. The negative electrode material is then subjected to a thermogravimetric analyzer with an oxygen-filled atmosphere, heated from room temperature to 900°C and maintained for 40 minutes, allowing the non-silicon components in the negative electrode material layer to volatilize while the silicon is fully oxidized to silicon dioxide. The remaining substance is the ash content of the negative electrode material layer. The mass content of silicon in the negative electrode material layer can be calculated based on the mass of the ash content using the formula: Silicon content = 7 × mass of ash / (15 × mass of test sample).

[0024] The thickness D of the negative electrode current collector plays a crucial balancing role in the performance of lithium-ion batteries. If the thickness is too small, it reduces mechanical strength and heat dissipation capacity, making it unable to withstand the severe volume expansion stress during charging and discharging of the silicon negative electrode, easily causing current collector deformation and material layer peeling. If the thickness is too large, it becomes too rigid, making it difficult to buffer expansion stress through elastic deformation, while simultaneously compressing the space of the active material and reducing energy density. Therefore, reasonably controlling the current collector thickness can balance energy density and structural stability, effectively adapting to the large volume expansion characteristics of silicon-based negative electrodes, and improving battery cycle reliability. In some embodiments of the present invention, the thickness D μm of the negative electrode current collector is specifically 5 μm, 7 μm, 8 μm, 9 μm, 10 μm, 12 μm, 14 μm, 15 μm, 17 μm, 19 μm, 20 μm, or any combination of these values; preferably, the thickness of the negative electrode current collector is 8 μm to 15 μm.

[0025] Specifically, in some embodiments of the present invention, the method for determining the thickness of the negative electrode current collector is as follows: After discharging the sample battery to 0% SOC, disassemble and remove the negative electrode, immerse it in water or ethyl propionate solvent, and sonicate it at 60°C for 10 minutes. The active material layer will naturally detach due to the swelling of the binder. If there is still material residue on the current collector, gently wipe it off with a cotton swab, and finally rinse it with alcohol and air dry. After initial calibration with a standard block using a high-precision digital micrometer (MDH-25MB), 10 points are uniformly selected on the obtained bare foil, and the thickness at multiple points is measured and the average value is taken.

[0026] The dyn value of the negative electrode current collector represents its wettability. Controlling the dyn value R of the negative electrode current collector allows its surface tension to match that of the negative electrode active material particles, ensuring a suitable bonding strength between them. A suitable dyn value can inhibit the swelling and shedding of the active material layer in the electrolyte, improving the stability of the electrode structure. By rationally controlling the dyn value of the negative electrode, the lithium-ion battery ultimately achieves excellent cycle stability and low interfacial impedance. In some embodiments of the present invention, the dyn value R dyn / cm of the negative electrode current collector is specifically 36 dyn / cm, 38 dyn / cm, 40 dyn / cm, 42 dyn / cm, 44 dyn / cm, 45 dyn / cm, 47 dyn / cm, 48 dyn / cm, 49 dyn / cm, 50 dyn / cm, or any combination of these values; preferably, the dyn value R of the negative electrode current collector is 38 dyn / cm to 48 dyn / cm.

[0027] Specifically, in some embodiments of the present invention, the method for determining the dyne value of the negative electrode current collector is as follows: Using a dyne pen with different dyne values, lines are drawn on the surface of the copper foil along the running surface and in the direction perpendicular to it. If the straight line does not shrink within 3 seconds, the dyne value is considered achieved. The test is performed three times using a dyne pen with the same dyne value. If the straight line does not shrink within 3 seconds in each test, then the dyne value is the surface tension of the copper foil. In lithium-ion batteries, the foil near the tab of the negative electrode current collector is relatively flat. After disassembling the lithium-ion battery, the soldered tab is torn off, and the negative electrode current collector at the tab location is taken for testing.

[0028] Specifically, in some embodiments of the present invention, the compound represented by structural formula 1 includes at least one of the following compounds: .

[0029] Specifically, in some embodiments of the present invention, the compound represented by structural formula 2 includes at least one of the following compounds: .

[0030] Specifically, in some embodiments of the present invention, the negative electrode active material layer further includes a negative electrode adhesive and a negative electrode conductive agent. The negative electrode adhesive includes at least one of polyacrylic acid, polyurethane, styrene-butadiene rubber, and carboxymethyl cellulose; the negative electrode conductive agent includes at least one of carbon nanotubes, conductive carbon black, and graphene.

[0031] Specifically, in some embodiments of the present invention, the non-aqueous electrolyte further includes lithium salt, organic solvent and auxiliary additives.

[0032] Specifically, in some embodiments of the present invention, the lithium salt includes lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), LiPO₂F₂, LiBF₄, LiBOB, LiSbF₆, LiAsF₆, LiCF₃SO₃, LiDFOB, LiDFOP, LiN(SO₂CF₃)₂, LiC(SO₂CF₃)₃, LiN(SO₂C₂F₅)₂, LiCl, LiBr, LiI, LiClO₄, and LiB₂. 10 Cl 10 At least one of the following: LiAlCl4, lithium chloroborane, lithium lower aliphatic carboxylic acids having four or fewer carbon atoms, and lithium tetraphenylborate.

[0033] Specifically, in some embodiments of the present invention, the organic solvent includes at least one of cyclic carbonate solvents, linear carbonate solvents, carboxylic acid ester solvents, and ether solvents.

[0034] In some preferred embodiments, the cyclic carbonate solvent includes at least one of vinylene carbonate, propylene carbonate, ethylene carbonate, and butene carbonate.

[0035] In some preferred embodiments, the linear carbonate solvent includes at least one of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and methyl propyl carbonate.

[0036] In some preferred embodiments, the carboxylic acid ester solvent includes at least one selected from methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, methyl butyrate, methyl isobutyrate, methyl trimethylacetate, and ethyl trimethylacetate.

[0037] In some preferred embodiments, the ether solvent includes at least one of ethylene glycol dimethyl ether, 1,3-dioxolane, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0038] Specifically, in some embodiments of the present invention, the non-aqueous electrolyte further includes auxiliary additives, which include at least one of sulfate ester compounds, sulfonyl lactone compounds, phosphate ester compounds, borate ester compounds, and nitrile compounds.

[0039] In some preferred embodiments, the sulfate ester compound includes at least one of vinyl sulfate, 4-methyl vinyl sulfate, and propylene sulfate.

[0040] In some preferred embodiments, the sulfonyl lactone compound includes at least one of 1,3-propanesulfonyl lactone, 1,4-butanesulfonyl lactone, and propenyl-1,3-sulfonyl lactone.

[0041] In some preferred embodiments, the phosphate ester compound includes at least one of tris(trimethylsilane) phosphate, tris(triethylsilane) phosphate, triargyl phosphate, and triphenyl phosphate.

[0042] In some preferred embodiments, the borate ester compound includes at least one of tris(trimethylsilane)borate and tris(triethylsilane)borate.

[0043] In some preferred embodiments, the nitrile compound includes at least one selected from succinic anion, glutaronitrile, hexanetrionitrile, adiponitrile, 1,2-bis(cyanoethoxy)ethane, 1,2,3-tris(cyanoethoxy)propane, and 1,2,3,4-tetra(cyanoethoxy)butane.

[0044] Specifically, in some embodiments of the present invention, the auxiliary additives further include any one of LiPO2F2 (lithium difluorophosphate), LiDFOB (lithium difluorooxalate borate), LiBF4, LiBOB (lithium oxalate borate), LiFSI, and LiTFSI.

[0045] The silicon-carbon material is a silicon-based material containing silicon and carbon materials and / or containing SiO2. y Silicon-based materials and carbon materials.

[0046] Specifically, in some embodiments of the present invention, the negative electrode current collector includes a metallic material capable of conducting electrons, preferably, the negative electrode current collector includes one or more of aluminum, nickel, tin, copper, and stainless steel.

[0047] Specifically, in some embodiments of the present invention, the material of the positive current collector may be the same as that of the negative current collector, which will not be described in detail here.

[0048] Specifically, in some embodiments of the present invention, the positive electrode material layer further includes a positive electrode binder and a positive electrode conductive agent, and the positive electrode active material, the positive electrode binder, and the positive electrode conductive agent are blended to obtain the positive electrode material layer. The positive electrode binder and the positive electrode conductive agent can be the same as the negative electrode binder and the negative electrode conductive agent, respectively, and will not be described in detail here.

[0049] In the lithium-ion battery of the present invention, the separator can be a conventional separator, such as a ceramic separator, a polymer separator, a non-woven fabric separator, an inorganic-organic composite separator, etc., including but not limited to single-layer PP (polypropylene), single-layer PE (polyethylene), double-layer PP / PE, double-layer PP / PP and triple-layer PP / PE / PP separators.

[0050] The lithium-ion battery of this invention is a lithium cobalt oxide system. Its non-aqueous electrolyte contains the compound shown in structural formula 1, the compound shown in structural formula 2, and fluoroethylene carbonate. The content of the compound shown in structural formula 1 (C1), the content of the compound shown in structural formula 2 (C2), and the content of fluoroethylene carbonate (C3) in the non-aqueous electrolyte, and the mass percentage A of silicon in the negative electrode material layer of the battery, are limited to satisfying the following conditions: 2.5 ≤ A / (C1+C2) ≤ 10, 0.4 ≤ C3×R / 100D ≤ 1.4, 0.05 ≤ C1 ≤ 4, 0.05 ≤ C2 ≤ 5, 10 ≤ C3 ≤ 25, 5 ≤ A ≤ 50, 5 ≤ D ≤ 20, and 36 ≤ R ≤ 50. When these conditions are met, the parameters are mutually compatible and mutually supportive. The compounds in Formula 1 form a stable and impact-resistant interfacial film at the positive electrode, effectively inhibiting cobalt ion dissolution and reactive oxygen evolution. Formula 2, combined with fluoroethylene carbonate, constructs a dense and stable SEI film at the negative electrode, improving both the battery's high-temperature stability and reducing electrolyte oxidation and decomposition and electrode crosstalk under high voltage. The precise definition and synergistic interaction of these parameters significantly enhance the energy density of the lithium-ion battery while effectively improving its cycle stability, high-temperature reliability, and thermal safety performance. This also reduces the battery's K-value and suppresses black spots on the negative electrode during high-temperature cycling, comprehensively improving the overall electrochemical performance and safety of the lithium-ion battery. Detailed Implementation

[0051] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0052] Example 1 The method for preparing the lithium-ion battery in this embodiment includes the following steps: 1) Preparation of the positive electrode Lithium cobalt oxide (LCO), polyvinylidene fluoride (PVDF), carbon black (SP), and single-walled carbon nanotubes (CNTs) were mixed uniformly in a weight ratio of 97:1:1.5:0.5. N-methylpyrrolidone (NMP) was added, and the mixture was stirred under vacuum until it formed a uniform and fluid positive electrode slurry. The positive electrode slurry was uniformly coated on both surfaces of the positive electrode current collector aluminum foil. The coated positive electrode sheet was dried at 85°C and then cold-pressed. It was then trimmed, cut into strips, and dried under vacuum at 85°C for 4 hours. The tabs were then welded to obtain the positive electrode.

[0053] 2) Preparation of the negative electrode The negative electrode active material graphite (AG), active material silicon carbide (SiC), binder polyacrylic acid (PAA), conductive agent carbon black (SP), conductive agent carbon nanotubes (CNT), and thickener sodium carboxymethyl cellulose (CMC) were mixed in a weight ratio of 94.7:3:1.5:0.3:0.5. Deionized water was added, and the mixture was stirred in a vacuum mixer to obtain a negative electrode slurry. The negative electrode slurry was uniformly coated onto a copper foil negative electrode current collector, dried at 85°C, and then cold-pressed. The slabs were trimmed, cut, and slit. After slitting, the slabs were dried at 85°C under vacuum for 4 hours, and then the tabs were welded to obtain the negative electrode sheet. The silicon content A in the negative electrode material layer, the thickness D of the negative electrode current collector, and the dyne value R of the negative electrode current collector are shown in Table 1.

[0054] 3) Preparation of non-aqueous electrolyte In an argon-filled glove box (moisture <10 ppm, oxygen <10 ppm), solvents ethylene carbonate (EC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), and propyl propionate (PP) were mixed uniformly at a mass ratio of EC:DEC:EMC:PP = 10:20:15:55. Thoroughly dried 15% lithium hexafluorophosphate was rapidly added to the mixed solvent, followed by fluoroethylene carbonate, compound 1-1, compound 2-1, and auxiliary additives. After passing moisture and free acid tests, a non-aqueous electrolyte was obtained. The contents of fluoroethylene carbonate, compound 1-1, and compound 2-1, based on 100% by weight of the non-aqueous electrolyte, are shown in Table 1. The auxiliary additives included 1% 1,3-propanesulfonyl lactone (PS), 0.5% lithium difluorooxalate borate (LiDFOB), 2% succinic anionyl (SN), and 3% 1,3,6-hexanetrionitrile (HTCN).

[0055] 4) Preparation of the diaphragm A three-layer separator membrane consisting of polypropylene, polyethylene, and polypropylene is used, with a thickness of 20 μm.

[0056] 5) Preparation of lithium-ion batteries The positive electrode, negative electrode, and separator prepared by the above process are assembled into a stacked soft-pack battery cell, vacuum baked at 75°C for 10 hours, and then injected with the electrolyte prepared above. After standing at 45°C for 48 hours, the battery is placed in an environment of 80°C and subjected to a pressure of 6 kg / cc. After formation, shaping, and sorting, the battery is obtained.

[0057] Examples 2-35 and Comparative Examples 1-12 Examples 2-35 and Comparative Examples 1-12 are used to illustrate the lithium-ion battery disclosed in this invention. They include most of the operating steps in Example 1 above, but differ in the composition and content of the non-aqueous electrolyte, the mass percentage of silicon in the negative electrode material layer, the thickness of the negative electrode current collector, the dyne value of the negative electrode current collector, and the values ​​of the relationship A / (C1+C2) and C3×R / 100D, as shown in Table 1.

[0058] The lithium-ion batteries prepared in each embodiment and comparative example were subjected to performance testing according to the following methods: 1. Battery high-temperature cycle performance test After the battery was placed in a constant temperature environment of 45±2℃ for 2 hours, it was charged according to a stepped charging program: ① 2.5C constant current charging to 4.25V; ② 1.5C constant current charging to 4.3V; ③ 1.2C constant current and constant voltage charging to 4.45V, with a cutoff current of 1C; ④ 1C constant current and constant voltage charging to 4.55V, with a cutoff current of 2 / 3C; ⑤ 2 / 3C constant current and constant voltage charging to 4.55V, with a cutoff current of 0.05C; ⑥ Place for 5 minutes, then discharge at a constant current of 0.7C to 2.8V; ⑦ Place for 5 minutes, and repeat the above charge-discharge cycle 400 times. Record the charge-discharge capacity on the 1st and 400th cycles.

[0059] Constant current charging ratio = Constant current charging capacity at 400th cycle / Total charging capacity at 400th cycle × 100%; Discharge retention rate = (Discharge capacity at 400th cycle / Discharge capacity at 1st cycle) × 100%; And calculate the average value of the parallel samples.

[0060] 2. Battery thermal abuse test After the battery is placed in a constant temperature environment of 25±2℃ for 2 hours, the following test procedures are followed according to GB 31241: ① Charge the battery at a constant current and voltage of 0.2C to 4.55V, with a cutoff current of 0.05C; ② Let it rest for 5 minutes, then discharge it at a constant current of 0.2C to 2.8V; ③ Cycle the battery through a 25℃ constant temperature cycle for 3 times using this procedure, and calculate the battery discharge capacity, requiring a discharge capacity deviation of ±10mAh / g; ④ Let it rest for 5 minutes, then charge it at a constant current and voltage of 0.2C to 4.55V, with a cutoff current of 0.05C, which is considered the fully charged state of the battery; ⑤ Place the fully charged battery in a thermal shock test chamber and heat it from 30℃ to the specified temperature at a rate of 5℃ / min according to the set program, maintaining the temperature for 60 minutes. If the battery does not explode or catch fire during this period, it is considered to have passed the thermal abuse test and is recorded as OK; otherwise, it is recorded as NG.

[0061] Test Results: Table 1 shows the parameters required for preparing lithium-ion batteries in Examples 1-18 and Comparative Examples 1-18. The differences between Examples 2-18 and Comparative Examples 1-18 and Example 1 lie in the relevant parameters in Table 1. Specifically, the differences are: the mass percentage C1 of the compound shown in structural formula 1 (compound 1-1), the mass percentage C2 of the compound shown in structural formula 2 (compound 2-1), the mass percentage C3 of fluoroethylene carbonate, the mass percentage A of silicon in the negative electrode material layer, the thickness D of the negative electrode current collector, the dyne value R of the negative electrode current collector, and the values ​​of the relationships A / (C1+C2) and C3×R / 100D. The remaining parameters and preparation steps are the same as those described in Example 1. Table 1 also shows the performance test results of the lithium-ion batteries prepared in Examples 1-18 and Comparative Examples 1-18.

[0062] Table 1 In the table: "-" indicates that the item is not present; "OK" indicates that the test passed; "NG" indicates that the test failed; "Plummeting" indicates that the battery capacity retention rate rapidly declines and cannot complete the normal test.

[0063] As shown in the test results in Table 1, the lithium-ion battery provided by this invention can achieve a comprehensive improvement in both electrochemical performance and safety when the mass percentages of the compound shown in structural formula 1 (C1wt%), the compound shown in structural formula 2 (C2wt%), and the fluoroethylene carbonate (C3wt%) in the non-aqueous electrolyte, the mass percentage of silicon in the negative electrode material layer (A%), the thickness of the negative electrode current collector (Dμm), and the dyn value (Rdyn / cm) satisfy the following conditions: 2.5≤A / (C1+C2)≤10, 0.4≤C3×R / 100D≤1.4, 0.05≤C1≤4, 0.05≤C2≤5, 10≤C3≤25, 5≤A≤50, 5≤D≤20, and 36≤R≤50.

[0064] The test results of Example 1 and Comparative Examples 1-14 show that when any one or two of the following parameters in a lithium-ion battery—the mass percentage of the compound shown in Structural Formula 1 (C1wt%), the mass percentage of the compound shown in Structural Formula 2 (C2wt%), the mass percentage of fluoroethylene carbonate (C3wt%), the mass percentage of silicon in the negative electrode material layer (A%), the thickness of the negative electrode current collector (D μm), and the dyn value (R dyn / cm)—do not meet the specified range, the compound shown in Structural Formula 1, the compound shown in Structural Formula 2, and fluoroethylene carbonate cannot form a synergistic effect. Therefore, a battery system with dual protection for both positive and negative electrodes cannot be constructed, and a lithium-ion battery with excellent high voltage stability, low volume expansion, and high safety cannot be obtained.

[0065] When the mass percentages of the compound shown in structural formula 1 (C1), the compound shown in structural formula 2 (C2), and the fluoroethylene carbonate (C3) in the lithium-ion battery structure, along with the mass percentage of silicon in the negative electrode material layer (A), the thickness of the negative electrode current collector (D), and the dyne value (R), further satisfy the following conditions: 3≤A / (C1+C2)≤9, 0.5≤C3×R / 100D≤1.1, 0.1≤C1≤3, 0.1≤C2≤4, 12≤C3≤20, 10≤A≤35, 8≤D≤15, and 38≤R≤48, the efficiency of the compound shown in structural formula 1 and the compound shown in structural formula 2 in forming a dense and stable interface film at the positive and negative electrodes is optimized. This better solves the problems of poor protection effect and insufficient high-temperature stability of fluoroethylene carbonate on the negative electrode.

[0066] Table 2 shows the performance test results of the lithium-ion batteries prepared in Examples 1 and 19-26. The difference between Examples 19-26 and Example 1 is the type of compound shown in Structural Formula 1 in Table 2. The other parameters and preparation steps are the same as those described in Example 1.

[0067] Table 2 As shown in Table 2, when the mass percentages of the compound shown in Structural Formula 1 (C1wt%), the compound shown in Structural Formula 2 (C2wt%), and the fluoroethylene carbonate (C3wt%) in the non-aqueous electrolyte meet the corresponding conditions, the mass percentage of silicon in the negative electrode material layer (A%), the thickness of the negative electrode current collector (D μm), and the dyn value (R dyn / cm), adding different compounds shown in Structural Formula 1 can still result in lithium-ion batteries with comprehensively improved electrochemical performance and safety. This demonstrates that the battery system provided by this invention has universal applicability to the compounds shown in Structural Formula 1.

[0068] Table 3 shows the performance test results of the lithium-ion batteries prepared in Examples 1 and 27-32. The difference between Examples 27-32 and Example 1 is the type of compound shown in structural formula 2 in Table 3. The other parameters and preparation steps are the same as those described in Example 1.

[0069] Table 3 As shown in Table 3, when the mass percentages of the compound shown in Structural Formula 1 (C1wt%), the compound shown in Structural Formula 2 (C2wt%), and the fluoroethylene carbonate (C3wt%) in the non-aqueous electrolyte meet the corresponding conditions, the mass percentage of silicon in the negative electrode material layer (A%), the thickness of the negative electrode current collector (D μm), and the dyn value (R dyn / cm), adding different compounds shown in Structural Formula 2 can still result in lithium-ion batteries with comprehensively improved electrochemical performance and safety. This demonstrates that the battery system provided by this invention has universal applicability to compounds shown in Structural Formula 2.

[0070] Table 4 shows the performance test results of the lithium-ion batteries prepared in Examples 1 and 33-34. The difference between Examples 33-34 and Example 1 is the auxiliary additives and their contents shown in Table 4. The other parameters and preparation steps are the same as those described in Example 1.

[0071] Table 4 Note: In the table, "TPP" represents triphenyl phosphate; "DTD" represents vinyl sulfate; "ADN" represents adiponitrile; and "RPS" represents 1,3-propenesulfonyl lactone.

[0072] As shown in Table 4, when the mass percentages of the compound shown in structural formula 1 (C1wt%), the compound shown in structural formula 2 (C2wt%), and the fluoroethylene carbonate (C3wt%) in the non-aqueous electrolyte meet the corresponding conditions, and the mass percentages of silicon (A%), negative electrode current collector (Dμm), and dyn value (Rdyn / cm) in the negative electrode material layer satisfy the corresponding conditions, lithium-ion batteries with improved comprehensive electrochemical performance and safety can still be obtained by adding different types of auxiliary additives. This demonstrates that the battery system provided by this invention has universal applicability to different types of auxiliary additives.

[0073] The present invention has been further described above with reference to specific embodiments. However, it should be understood that the specific description herein should not be construed as limiting the nature and scope of the present invention. Various modifications made to the above embodiments by those skilled in the art after reading this specification are all within the scope of protection of the present invention.

Claims

1. A lithium-ion battery, characterized by, Includes positive electrode, negative electrode, membrane, and non-aqueous electrolyte; The positive electrode includes a positive electrode current collector and a positive electrode material layer covering at least one surface of the positive electrode current collector, the positive electrode material layer including a positive electrode active material, the positive electrode active material including lithium cobalt oxide; The negative electrode includes a negative electrode current collector and a negative electrode material layer covering at least one surface of the negative electrode current collector. The negative electrode material layer includes a negative electrode active material, which is a silicon-carbon material. The thickness of the negative electrode current collector is D μm, and its dyn value is R dyn / cm. The mass percentage of silicon in the negative electrode material layer is A%. The non-aqueous electrolyte comprises the compound shown in structural formula 1, the compound shown in structural formula 2, and fluoroethylene carbonate: Structure 1; R1, R2, and R3 are each independently selected from C1-C10 alkyl, C2-C10 alkenyl, C2-C10 alkynyl, C1-C10 alkoxy, C1-C10 fluoroalkyl, C1-C10 fluoroalkoxy, C2-C10 cyano, and C2-C10 isocyanate groups. Structural Formula 2; Where X is selected from or R4 and R5 are each independently selected from H, or R4 and R5 are not both selected from H, and X, R4, and R5 contain at least one sulfur atom; Based on the mass of the non-aqueous electrolyte, the mass percentage of the compound shown in structural formula 1 is C1 wt%, the mass percentage of the compound shown in structural formula 2 is C2 wt%, and the mass percentage of the fluoroethylene carbonate is C3 wt%. The lithium-ion battery meets the following conditions: 0.05≤C1≤4, 0.05≤C2≤5, 10≤C3≤25, 5≤A≤50, 5≤D≤20, 36≤R≤50, 2.5≤A / (C1+C2)≤10, 0.4≤C3×R / 100D≤1.

4.

2. The lithium-ion battery of claim 1, wherein, The lithium-ion battery satisfies: 3≤A / (C1+C2)≤9.

3. The lithium-ion battery of claim 1, wherein the lithium-ion battery is a lithium-ion battery. The lithium-ion battery satisfies: 0.5≤C3×R / 100D≤1.

1.

4. The lithium-ion battery of claim 1, wherein, The mass percentage of the compound C1 shown in structural formula 1 in the non-aqueous electrolyte is 0.1 wt% to 3 wt%; and / or, The mass percentage of the compound C2 shown in structural formula 2 in the non-aqueous electrolyte is 0.1 wt% to 4 wt%; and / or, The non-aqueous electrolyte contains 12 wt% to 20 wt% fluoroethylene carbonate (C3); and / or, The mass percentage A of silicon in the negative electrode material layer is 10%~35%.

5. The lithium-ion battery of claim 1, wherein, The thickness D of the negative electrode current collector is 8 μm to 15 μm.

6. The lithium-ion battery of claim 1, wherein, The dyn value R of the negative electrode current collector is 38 dyn / cm to 48 dyn / cm.

7. The lithium-ion battery of claim 1, wherein, The compound shown in structural formula 1 includes at least one of the following compounds: 。 8. The lithium-ion battery as described in claim 1, characterized in that, The compound shown in structural formula 2 includes at least one of the following compounds: 。 9. The lithium-ion battery as described in claim 1, characterized in that, The non-aqueous electrolyte further includes auxiliary additives, which include at least one selected from sulfate esters, sulfonyl lactones, phosphate esters, borate esters, and nitrile compounds; and / or, The sulfate ester compounds include at least one of vinyl sulfate, 4-methylvinyl sulfate, and propylene sulfate; and / or, The sulfonyl lactone compounds include at least one selected from 1,3-propanesulfonyl lactone, 1,4-butanesulfonyl lactone, and 1,3-propenesulfonyl lactone; and / or, The phosphate ester compounds include at least one of tris(trimethylsilane) phosphate, tris(triethylsilane) phosphate, and triphenyl phosphate; and / or, The borate ester compounds include at least one of tris(trimethylsilane)borate and tris(triethylsilane)borate; and / or, The nitrile compounds include at least one of butadionitrile, glutaronitrile, adiponitrile, hexanetrionitrile, 1,2-bis(cyanoethoxy)ethane, 1,2,3-tris(cyanoethoxy)propane, and 1,2,3,4-tetra(cyanoethoxy)butane.

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