Lithium-ion batteries

Abstract

Lithium-ion battery, characterized in that it consists of a cathode, an anode and a non-aqueous electrolyte; wherein the cathode comprises a cathode material layer containing an active cathode material, wherein the active cathode material comprises a compound represented by formula (A): Li x Ni a Co b M' 1-a-b O 2-y A y Formula (A) where in formula (A) -0.1 ≤ x ≤ 0.2, 0.8 ≤ a < 1, 0 ≤ b < 0.2, 0.8 ≤ a + b < 1, 0 ≤ y < 0.2 hold; where M' comprises one or both of the elements Mn or Al and zero, one or more of the elements Sr, Mg, Ti, Ca, Zr, Zn, Si, Fe, B, Ga, Cr, W, V, Nb and Ce; where A comprises one or more of S, N, F, B, Cl, Br and I; wherein the anode comprises an anode material layer containing an active anode material, wherein the active anode material comprises a silicon-based material; wherein the non-aqueous electrolyte comprises a lithium salt and an organic solvent, wherein the organic solvent comprises cyclic carbonate, and wherein the cyclic carbonate comprises fluorinated ethylene carbonate and propylene carbonate; where the lithium-ion battery meets the following conditions: 0.2 ≤ S / F ≤ 2 ,0 ,2 ≤ P / F ≤ 3 ,5 and 3 ≤ S ≤ 15 ,2 ≤ F ≤ 15 ,2 ≤ P ≤ 25 , 15 ≤ C ≤ 40; where S denotes the mass fraction of silicon in the anode material layer, expressed in wt.%; where F denotes the mass fraction of fluorinated ethylene carbonate in the non-aqueous electrolyte, expressed in wt.%; where P denotes the mass fraction of propylene carbonate in the non-aqueous electrolyte, expressed in wt.%; where C denotes the mass fraction of cyclic carbonate in the non-aqueous electrolyte, expressed in wt.%.

Description

[0001] The present disclosure is based on Chinese patent application no. 202311463178.5, filed on November 6, 2023, and claims priority to the Chinese patent application. The entire content of the Chinese patent application is hereby incorporated into the present application by reference. TECHNICAL AREA

[0002] The present application relates to the technical field of lithium-ion batteries, in particular a lithium-ion battery that improves high-temperature storage performance and optimizes high-temperature cycle performance. STATE OF THE ART

[0003] Due to their advantages such as high operating voltage, wide operating temperature range, high energy density, considerable output power, no memory effect and extended lifespan, lithium-ion batteries have not only found widespread use in 3C digital products such as mobile phones and laptops, but also have a huge application market in new energy vehicles and large-scale energy storage systems.

[0004] With the rapid advancement of new energy technologies, lithium-ion batteries with non-aqueous electrolytes have experienced exponential growth in their application. However, driven by the urgent consumer demand for greater range in new energy vehicles, further improvements in the energy density of high-performance batteries are essential.

[0005] From a materials science perspective, the most important approaches to improving battery energy density include: first, increasing the upper charge voltage limit of cathode materials to increase the specific capacitance of the cathode; second, developing cathode and anode materials with higher specific capacitances, such as ternary cathode materials with a high nickel content (≥ 80% nickel) and silicon-based anode materials. Among these, silicon-based anode materials represent a significant avenue for improving the energy density of lithium-ion batteries due to their theoretical specific capacitance, which is far greater than that of graphite anodes. However, compared to graphite anodes, silicon-based anodes exhibit considerable volume expansion (>300%) during the charge cycle.In lithium alloy batteries, the volume of silicon-based anodes undergoes significant changes, causing the solid electrolyte interphase (SEI) layer on their surface to continuously break down and regenerate during the battery cycle. This leads to electrolyte consumption, loss of active lithium, and increased interfacial impedance. Particularly in high-temperature environments, both cycle and storage performance deteriorate considerably. Simultaneously, the increasing thickness of the anode foil during charging and discharging exerts pressure on the battery casing, potentially leading to casing failure and posing safety risks. Furthermore, the increased thickness impairs the contact between the active material and the copper current collector foil, negatively affecting electron conductivity.As a result, the battery capacity decreases significantly in the later stages of the charging cycle, leading to the phenomenon known as "capacity drop".

[0006] Therefore, improving the performance of lithium-ion batteries that use high-nickel silicon-carbon systems represents an urgent challenge in this field. CONTENT OF THE PRESENT APPLICATION

[0007] To solve the aforementioned technical problems, the present application provides a lithium-ion battery that improves high-temperature storage performance and optimizes high-temperature cycle performance.

[0008] This application uses the following technical solution: a lithium-ion battery consisting of a cathode, an anode and a non-aqueous electrolyte; wherein the cathode comprises a cathode material layer containing an active cathode material, wherein the active cathode material comprises a compound represented by formula (A): Li 1x Ni a Co b M' 1-a-b O 2-y A y Formula (A) where in formula (A) -0.1 ≤ x ≤ 0.2, 0.8 ≤ a < 1, 0 ≤ b < 0.2, 0.8 ≤ a + b < 1, 0 ≤ y < 0.2 hold; where M' comprises one or both of the elements Mn or Al and zero, one or more of the elements Sr, Mg, Ti, Ca, Zr, Zn, Si, Fe, B, Ga, Cr, W, V, Nb and Ce; where A comprises one or more of S, N, F, B, Cl, Br and I; where the anode comprises an anode material layer containing an active anode material, the active anode material comprising a silicon-based material; wherein the non-aqueous electrolyte comprises a lithium salt and an organic solvent, wherein the organic solvent comprises cyclic carbonate, and wherein the cyclic carbonate comprises fluorinated ethylene carbonate and propylene carbonate; where the lithium-ion battery meets the following conditions: 0.2≤S / F≤2,0.2≤P / F≤3.5 and 3≤S≤15.2≤F≤15.2≤P≤25, 15≤C≤40; where S denotes the mass fraction of silicon in the anode material layer, expressed in wt.%; where F denotes the mass fraction of fluorinated ethylene carbonate in the non-aqueous electrolyte, expressed in wt.%; where P denotes the mass fraction of propylene carbonate in the non-aqueous electrolyte, expressed in wt.%; where C denotes the mass fraction of cyclic carbonate in the non-aqueous electrolyte, expressed in wt.%.

[0009] The present application uses a high-nickel cathode material in combination with a silicon-based anode material, effectively increasing the battery's energy density, with a theoretical energy density between 250 and 500 Wh / kg achievable. However, nickel ions exhibit high catalytic activity, accelerating the oxidative decomposition of non-aqueous electrolytes. This process degrades the solid electrolyte layer and causes transition metal ions to leach from the cathode surface. Simultaneously, the SEI layer on the anode surface is destroyed, allowing solvent molecules to co-intercalate and damage the anode material. Consequently, the battery becomes more susceptible to short circuits, compromising safety. While a silicon-based material can effectively improve battery energy density, its significant bulk effect should not be overlooked.These negative effects increase exponentially with increasing silicon content. Cyclic carbonate solvents in non-aqueous electrolytes possess high dielectric constants and ionic conductivity, which allows stable SEI layers to form on anode surfaces. However, their higher viscosity and lower electrochemical stability compared to linear carbonates limit their applications. In the present application, the content of cyclic carbonate in the non-aqueous electrolyte is limited to 15–40 wt.% to ensure both interfacial stability and electrochemical stability of the electrolyte. Specifically, the content of cyclic carbonate in the non-aqueous electrolyte is 15 wt.%, 18 wt.%, 20 wt.%, 25 wt.%, 28 wt.%, 29 wt.%, 30 wt.%, 33 wt.%, 36 wt.%, and 40 wt.%.-% or lies within a range formed by any of these values;; preferably the content C of cyclic carbonate in the non-aqueous electrolyte is 20 wt.% to 30 wt.%.

[0010] The fluorinated ethylene carbonate (FEC) within the cyclic carbonate can form a solid electrolyte layer with excellent elasticity on the surface of the silicon-based anode. This effectively bonds the silicon-based active material, suppresses its volume change during charging and discharging, ensures good contact between the particles, significantly improves the capacity retention rate of the lithium-ion battery, and reduces the thickness expansion rate of the anode foil. Specifically, the mass fraction S of silicon in the anode material layer is 3 wt%, 4 wt%, 5 wt%, 7 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, or lies within a range formed by any of these values; preferably, the mass fraction S of silicon in the anode material layer is 5 wt% to 12 wt%. The mass fraction F of fluorinated ethylene carbonate in the non-aqueous electrolyte is 2 wt.%, 3 wt.%.-%, 4 wt.%, 5 wt.%, 7 wt.%, 8 wt.%, 9 wt.%, 10 wt.%, 11 wt.%, 12 wt.%, 13 wt.%, 14 wt.%, 15 wt.%, or lies within a range formed by any of these values; preferably, the mass fraction F of fluorinated ethylene carbonate in the non-aqueous electrolyte is 4 wt.% to 10 wt.%. The higher the silicon content in the anode material layer, the greater the amount of fluorinated ethylene carbonate required to suppress the bulk effect. In particular, the S / F content ratio is 0.2, 0.3, 0.5, 0.7, 0.9, 1.0, 1.2, 1.5, 1.6, 1.8, 2.0; preferably, the S / F content ratio is 0.3 to 1.0.

[0011] The propylene carbonate (PC) in the cyclic carbonates undergoes reduction decomposition at the anode, resulting in a more compact and stable SEI layer. Furthermore, polycarbonate exhibits superior oxidation stability at high temperatures compared to other cyclic carbonates, thus providing improved high-temperature performance for polycarbonate solvent systems. Specifically, the mass fraction P of propylene carbonate in the non-aqueous electrolyte is 2 wt%, 3 wt%, 5 wt%, 6 wt%, 8 wt%, 10 wt%, 12 wt%, 15 wt%, 18 wt%, 20 wt%, 21 wt%, 22 wt%, 24 wt%, 25 wt%, or lies within a range of any of these values; preferably, the mass fraction P of propylene carbonate in the non-aqueous electrolyte is 5 wt% to 20 wt%.

[0012] In silicon-carbon anode materials, propylene carbonate intercalates with solvated lithium ions in graphite layers, leading to structural damage to the anode. This co-intercalation of propylene carbonate can, however, be avoided by significant amounts of anode film-forming additives. Specifically, the P / F mass ratio is 0.2, 0.3, 0.5, 0.7, 0.9, 1.0, 1.2, 1.5, 1.6, 1.8, 2.0, 2.2, 2.5, 2.6, 2.8, 3.0, 3.2, 3.3, 3.5; preferably, the P / F mass ratio is 0.5 to 2.6.

[0013] In some embodiments, the cyclic carbonate further comprises one or more of vinyl carbonate, difluorovinyl carbonate, and trifluoromethylvinyl carbonate. Ethylene carbonate has a molecular structure that lacks a methyl group compared to propylene carbonate. It decomposes at a voltage of slightly above 0.7 V to form a stable SEI layer, thereby inhibiting electrolyte decomposition at lower voltages and allowing normal lithium ion intercalation and ejection within the anode material. While fluorinated ethylene carbonate alone is insufficient to effectively inhibit propylene carbonate co-intercalation, its combination with ethylene carbonate suppresses reductive electrolyte decomposition below 0.7 V, thus protecting the overall battery performance.

[0014] In some embodiments, the organic solvent further comprises one or more of linear carbonates, carboxylate esters and ether compounds; In some preferred embodiments, the linear carbonates comprise one or more of dimethyl carbonates, diethyl carbonates, methyl ethyl carbonates and methyl propyl carbonates; In some preferred embodiments, the carboxylate esters comprise one or more of methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, methyl butyrate, methyl isobutyrate, methyl trimethyl acetate and ethyl trimethyl acetate. In some preferred embodiments, the ether compounds comprise one or more of ethylene glycol dimethyl ether, 1,3-dioxolane and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0015] In some embodiments, the silicon-based material comprises one or more of silicon materials, silicon oxide materials, silicon-carbon materials, and silicon alloy materials; In some preferred embodiments, the silicon material is a nanoscale silicon material; In some preferred embodiments, the silicon oxide material is SiO₂. x -Material, where 0 ≤ x ≤ 2; In some preferred embodiments, the silicon-carbon material is a silicon-based material containing silicon and carbon material, and / or a silicon-based material containing SiO₂. y and contains carbon material, where 0 ≤ y ≤ 2; In some preferred embodiments, the silicon alloy material is an Mg2Si alloy material. and / or an Fe2Si alloy material.

[0016] The silicon-based material possesses a high specific capacity but, due to its lithium intercalation mechanism, is prone to volume expansion, leading to fractures and failures of the electrode material; the carbon-based material exhibits superior stability compared to the silicon-based material. In some preferred embodiments, the silicon-based material is a silicon-carbon material. The silicon and carbon in the silicon-carbon material form a complementary relationship, combining the high specific capacity of the silicon-based material with the cycle stability of the carbon-based material. This effectively solves problems with material expansion defects while maintaining favorable cycle performance. Even more preferably, the silicon-carbon material comprises a silicon-based material containing silicon monoxide and graphite.

[0017] In some embodiments, the non-aqueous electrolyte further comprises additives, wherein the additives include at least one of cyclic sulfate ester compounds, sulfonyl lactone compounds, cyclic carbonate compounds, phosphate ester compounds, borate ester compounds and nitrile compounds; in some preferred embodiments, the cyclic sulfate ester compounds include at least one of diethyl sulfate (DTD), 4-methyl sulfate and propylene sulfate; In some preferred embodiments, the sulfonyl lactone compounds comprise at least one of 1,3-propanesulfonyl lactone, 1,4-butanesulfonyl lactone and vinyl-1,3-sulfonyl lactone; In some preferred embodiments, the cyclic carbonate compounds comprise at least one of ethylene carbonate, ethylene vinyl carbonate, methylene ethylene carbonate, trifluoromethyl ethylene carbonate, difluoroethylene carbonate and a compound represented by the following structural formula 1: where in the structural formula 1 R 21 , R 22 , R 23 , R 24 , R 25 and R 26 Each is independently composed of hydrogen, halogen and a C1-C5 group; In some preferred embodiments, the compounds shown in structural formula 1 comprise at least one compound from compound 1-1 to compound 1-6: In some preferred embodiments, the phosphate ester compound comprises at least one of tri(trimethylsilyl) phosphate (TMSP), tri(triethylsilyl) phosphate and a compound represented by the following structural formula 2: where in the structural formula 2 R 31 , R 32 and R 33 each independently of one of saturated hydrocarbon groups, unsaturated hydrocarbon groups, halogenated hydrocarbon groups of C1-C5 and -Si(C m H 2m+1 )3 are, where m is a natural number from 1 to 3, and where at least one of R 31 , R 32 and R 33an unsaturated hydrocarbon group; preferably, the compound represented by structural formula 2 comprises at least one of phosphoric acid tri(propynyl) ester, di(propynyl)methyl phosphate, di(propynyl)ethyl phosphate, di(propynyl)propyl phosphate, di-allylpropyltrifluoromethyl phosphate, di-allylpropyl-2,2,2-trifluoroethyl phosphate, di-allylpropyl-3,3,3-trifluoropropyl phosphate, diallylhexafluoroisopropyl phosphate, triallyl phosphate, diallylmethyl phosphate, diallylethyl phosphate, diallylpropyl phosphate, diallyltrifluoromethyl phosphate, diallyl-2,2,2-trifluoroethyl phosphate, diallyl-3,3,3-trifluoropropyl phosphate, diallylhexafluoroisopropyl phosphate; In some preferred embodiments, the borate ester compound comprises at least one of tris(trimethylsilyl)borate and tris(triethylsilyl)borate; In some preferred embodiments, the nitrile compound comprises at least one of adiponitrile, glutaronitrile, ethylene glycol bis(propionitrile) ether, hexanitrile, adiponitrile, heptanitrile, octanitrile, nonanitrile and decanitrile.

[0018] In some embodiments, the additive content, based on the total mass of the non-aqueous electrolyte (100%), is 0.01 wt.% to 10 wt.%. Preferably, the content is 0.1% to 5%, and even more preferably 0.1% to 2%. In particular, the content of any optional substance in the additive can be 0.05%, 0.08%, 0.1%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 7.8%, 8%, 8.5%, 9%, 9.5% or 10%.

[0019] In some embodiments, the lithium salt comprises at least one of LiPF6, LiPO2F2, LiBF4, LiBOB, LiSbF6, LiAsF6, LiCF3SO3, LiDFOB, LiDFOP, LiN(SO2CF3)2, LiC(SO2CF3)3, LiN(SO2C2F5)2, LiN(SO2F)2, LiCl, LiBr, LiI, LiClO4, LiB 10 Cl 10Lithium salts include LiAlCl4, lithium chloroborane, lithium salts of lower aliphatic carboxylic acids with four or fewer carbon atoms, lithium tetraphenylborate, and lithium iminide. Specifically, lithium salts can be: inorganic electrolyte salts such as LiBF4, LiClO4, LiAlF4, LiSbF6, LiTaF6, and LiWF7; fluorophosphate electrolyte salts such as LiPF6; tungstate electrolyte salts such as LiWOF5; carboxylate electrolyte salts such as HCO2Li, CH3CO2Li, CH2FCO2Li, CHF2CO2Li, CF3CO2Li, CF3CH2CO2Li, CF3CF2CO2Li, CF3CF2CF2CO2Li, and CF3CF2CF2CF2CO2Li; and CH3SO3Li sulfonic acid electrolyte salts. LiN(FCO2)2, LiN(FCO)(FSO2), LiN(FSO2)2, LiN(FSO2)(CF3SO2), LiN(CF3SO2)2, LiN(C2F5SO2)2, cyclic 1,2-perfluoroethylenedisulfonylimide lithium, cyclic 1,3-perfluoropropanedisulfonylimide lithium, LiN(CF3SO2) (C4F9SO2) and other imide electrolyte salts; LiC(FSO2)3, LiC(CF3SO2)3, LiC(C2F5SO2)3 and other methyl electrolyte salts;Oxalate electrolyte salts, including difluorooxalate lithium borate, di(oxalate)lithium borate, tetrafluorooxalate lithium phosphate, difluorodi(oxalate)lithium phosphate, tri(oxalate)lithium phosphate; and LiPF4(CF3)2, LiPF4(C2F5)2, LiPF4(CF3SO2)2, LiPF4(C2F5SO2)2, LiBF3CF3, LiBF3C2F5, LiBF3C3F7, LiBF2(CF3)2, LiBF2(C2F5)2, LiBF2(CF3SO2)2, LiBF2(C2F5SO2)2 and other fluorinated organic electrolyte salts.

[0020] In some embodiments, the active cathode material comprises at least one of LiNi0,8Co0,1Mn0,1O2, LiNi0,8Co0, 15 Mn0, 05 O2, LiNiO0,9CoO, 05 Mno0, 05 O2, LiNi0,8Co0, 15 Al0, 05 O2, LiNio0.8Co0.1Al0.1O2, LiNio0.9Co0, 05 Al0, 05 O2, LiNi0, 95 CO0, 02 Mn0, 03 O2 and LiNiO0,8Co0,1MnO, 05 Al0, 05 O2.

[0021] In some embodiments, the cathode material layer further comprises a cathode binder and a cathode conductor, wherein the active cathode material, the cathode binder and the cathode conductor are mixed to form the cathode material layer.

[0022] The cathode binder comprises one or more of polyvinylidene fluoride, vinylidene fluoride copolymer, polytetrafluoroethylene, vinylidene fluoride-hexafluoropropylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, ethylene-tetrafluoroethylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-trichloroethylene copolymer, vinylidene fluoride-fluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, thermoplastic polyimide, polyethylene and polypropylene and other thermoplastic resins, acrylic resins and styrene-butadiene rubbers.

[0023] The cathode conductive material comprises one or more conductive carbon black, conductive carbon spheres, conductive graphite, conductive carbon fibers, carbon nanotubes, graphene or reduced graphene oxide.

[0024] In some embodiments, the anode further comprises an anode collector, wherein the anode material layer is arranged on the surface of the anode collector. The material of the anode collector can be identical to that of the cathode collector and is not discussed in detail here.

[0025] In some embodiments, the anode material layer further comprises an anode binder and an anode conductor, wherein the active anode material, the anode binder, and the anode conductor are mixed to form the anode material layer. The anode binder and the anode conductor may be identical to the cathode binder and the cathode conductor, respectively, and are not discussed in detail here.

[0026] In some embodiments, the lithium-ion battery further includes a separator located between the cathode and the anode.

[0027] The separator can be a conventional separator known in the art, such as a ceramic separator, a polymer separator, a nonwoven fabric or an inorganic-organic composite separator, including but not limited to single-layer PP (polypropylene) separators, single-layer PE (polyethylene) separators, two-layer PP / PE separators, two-layer PP / PP separators and three-layer PP / PE / PP separators.

[0028] The lithium-ion battery of the present application uses materials with a high nickel content for the cathode and silicon-based materials for the anode, employing cyclic carbonates such as fluorinated ethylene carbonate and propylene carbonate as organic solvents. This configuration increases the energy density of the battery while simultaneously ensuring electrochemical stability in the silicon-based, high-nickel system through a controlled content of cyclic carbonate. If the lithium-ion battery also meets the following conditions: 0.2 ≤ S / F ≤ 2, 0.2 ≤ P / F ≤ 3.5 and 3 ≤ S ≤ 15, 2 ≤ F ≤ 15, 2 ≤ P ≤ 25, and 15 ≤ C ≤ 40, the synergistic effect of fluorinated ethylene carbonate and propylene carbonate optimizes the high-temperature storage performance and high-temperature cycle life of the lithium-ion battery while simultaneously reducing storage gas evolution. DETAILED DESCRIPTION

[0029] In connection with the embodiments in the present application, the technical solutions in the embodiments of the present application are explained clearly and completely below. Obviously, the embodiments explained do not represent all embodiments, but only a subset of them. All other embodiments that a person skilled in the art in this field could obtain from the embodiments in the present application without any creative work should be considered to be covered by the scope of protection of the present application. Example 1

[0030] The method for manufacturing a lithium-ion battery in the present embodiment comprises the following steps: 1) Production of the cathode: Mixing the active cathode material LiNio0,8Co0,1MnO2, the conductive carbon black Super-P and the binder polyvinylidene fluoride (PVDF) with a mass ratio of 97:1.5:1.5 and then dispersing this mixture in N-methyl-2-pyrrolidone (NMP) to obtain the cathode slurry. 2) Production of the anode: Silicon-carbon material (silicon oxide + graphite mixture with a silicon content of 7 wt%), conductive carbon black Super-P, and the binders styrene-butadiene rubber (SBR) and carboxymethylcellulose (CMC) are mixed in a mass ratio of 94.3:1.2:3.0:1.5. This mixture is then dispersed in deionized water to obtain the anode slurry. The slurry is applied to both sides of a copper foil, subsequently dried, calendered, and vacuum-dried. Nickel connecting cables are attached using an ultrasonic welding device to form the negative electrode plate, which has a thickness between 120 and 150 µm. 3) Production of the electrolyte: Fluorinated ethylene carbonate (FEC), propylene carbonate (PC), and methyl ethyl carbonate (EMC) are mixed in specific mass ratios. Lithium hexafluorophosphate (LiPF6) is then added to achieve a molar concentration of 1.0 mol / L, followed by the incorporation of the functional additive lithium difluorophosphate (LiPO2F2). Based on a total weight of 100% non-aqueous electrolyte, the mass fraction of LiPO2F2 in the non-aqueous electrolyte is 1%. The mass fractions of fluorinated ethylene carbonate (FEC) and propylene carbonate (PC) in the non-aqueous electrolyte are listed in Table 1. 4) Production of the battery cell: A 20 µm thick, three-layer separator is positioned between the positive and negative electrode plates. This sandwich structure of positive electrode plate, negative electrode plate, and separator is then wound into a coil. The wound assembly is flattened and inserted into an aluminum-plastic housing. After welding the tabs, the aluminum-plastic housing is sealed to prepare the battery cell for electrolyte filling. 5) Filling the battery cell with electrolyte and formation: Electrolyte is injected into the cell in a glove compartment kept below a dew point of -40°C. After a one-hour resting period, the battery cell is sealed and conditioned for 48 hours at 45°C.

[0031] The conventional initial charging process is then carried out as follows: charging with a constant current of 0.05 C for 3 hours, charging with a constant current of 0.1 C for 2 hours, charging with a constant current of 0.2 C for 2 hours, resting for 1 hour, aging for 48 hours at 45°C, followed by further charging with a constant current of 0.2 C to 4.2 V, then discharging with a constant current of 0.2 C to 2.75 V. Examples of implementation 2-31 and comparative examples 1-16

[0032] These embodiments and comparative examples illustrate the lithium-ion battery described herein, which incorporates most of the steps from the preceding embodiments. The differences are as follows: the mass fraction of organic solvents such as fluorinated ethylene carbonate and propylene carbonate in the non-aqueous electrolyte, the composition of the active materials of the cathode and anode, and the silicon content in the anode material layer are listed in Table 1. Furthermore, the electrolyte in embodiment 29 additionally contains 1% DTD (diethyl terephthalate). The electrolyte in embodiment 30 additionally contains 1% PS (1,3-propanesulfonic acid lactone), while the electrolyte in embodiment 31 additionally contains 1% phosphoric acid tripropyl ester. Table 1 group Active cathode material Active anode material Silicon content S in the anode material layer / wt.% Content C ancyclic carbonate / wt% Content F of anfluorinated ethylene carbonate / wt.% Panpropylene carbonate content / wt% Other cyclic carbonate types and content / wt% S / F P / F Example 1 LiNi 0,8 Co 0,1 Mr 0,1 O2 Silicon monoxide + graphite 7 23 8 15 / / 0,88 1,88 Example 2 LiNi 0,8 Co 0,1 Mr 0,1 O2 Silicon monoxide + graphite 7 27 12 15 / / 0,58 1,25 Example 3 LiNi 0,8 Co 0,1 Mr 0,1 O2 Silicon monoxide + graphite 6 26 8 20 / / 0,75 2,50 Example 4 LiNi 0,8 Co 0,1 Mr 0,1 O2 Silicon monoxide + graphite 4 26 8 20 / / 0,50 2,50 Example 5 LiNi 0,8 Co 0,1 Mr 0,1 O2 Silicon monoxide + graphite 10 25 10 15 / / 1,00 1,50 Example 6 LiNi 0,8 Co 0,1 Mr 0,1 O2 Silicon monoxide + graphite 10 32 10 22 / / 1,00 2,20 Example 7 LiNi 0,8 Co 0,1 Mr 0,1 O2 Silicon monoxide + graphite 7 18 8 10 / / 0,88 1,25 Example 8 LiNi 0,8 Co 0,1 Mr 0,1 O2 Silicon monoxide + graphite 12 30 10 20 / / 1,20 2,00 Example 9 LiNi 0,8 Co 0,1 Mr 0,1 O2 Silicon monoxide + graphite 10 15 10 5 / / 1,00 0,50 Example 10 LiNi 0,8 Co 0,1 Mr 0,1 O2 Silicon monoxide + graphite 3 20 4,5 15,5 / / 0,67 3,44 Example 11 LiNi 0,8 Co 0,1 Mr 0,1 O2 Silicon monoxide + graphite 5 29 8 21 / / 0,63 2,63 Example 12 LiNi 0,8 Co 0,1 Mr 0,1 O2 Silicon monoxide + graphite 14 25 7 18 / / 2,00 2,57 Example 13 LiNi 0,8 Co 0,1 Mr 0,1 O2 Silicon monoxide + graphite 3 16 4 12 / / 0,75 3,00 Example 14 LiNi 0,8 Co 0,1 Mr 0,1 O2 Silicon monoxide + 15 40 15 25 / / 1,00 1,67 graphite Example 15 LiNi 0,8 Co 0,1 Mr 0,1 O2 Silicon monoxide + graphite 4 20 2 6 EC 12 2,00 3,00 Example 16 LiNi 0,8 Co 0,1 Mr 0,1 O2 Silicon monoxide + graphite 7 23 4 2 EC 17 1,75 0,50 Example 17 LiNi 0,8 Co 0,1 Mr 0,1 O2 Silicon monoxide + graphite 6 33 8 10 EC 15 0,75 1,25 Example 18 LiNi 0,8 Co 0,1 Mr 0,1 O2 Silicon monoxide + graphite 6 25 8 10 EC 7 0,75 1,25 Example 19 LiNi 0,8 Co 0,1 Mr 0,1 O2 Silicon monoxide + graphite 6 25 8 10 DFEC 7 0,75 1,25 Example 20 LiNi 0,8 Co 0,1 Mr 0,1 O2 Silicon monoxide + graphite 6 25 8 10 TFPC 7 0,75 1,25 Example 21 LiNi o ,8Co o ,1.5Mn 0,05 O2 Silicon monoxide + graphite 6 26 8 20 / / 0,75 2,50 Example 22 LiNio 0,9 Co 0, 0.5 Mno 0,05 O2 Silicon monoxide + graphite 6 26 8 20 / / 0,75 2,50 Example 23 LiNi 0,8 Co 0,15 Al 0,05 O2 Silicon monoxide + graphite 6 26 8 20 / / 0,75 2,50 Execution LiNio 0,8 Co 0, Silicon 6 26 8 20 / / 0,75 2,50 example 24 1Al 0,1 O2 noxide + graphite Example 25 LiNi 0,8 Co 0,1 Mr 0,1 O2 Nanosilicon 6 26 8 20 / / 0,75 2,50 Example 26 LiNi 0,8 Co 0,1 Mr 0,1 O2 Nanosilicon + Graphite 6 26 8 20 / / 0,75 2,50 Example 27 LiNi 0,8 Co 0,1 Mr 0,1 O2 silicon monoxide 6 26 8 20 / / 0,75 2,50 Example 28 LiNi 0,8 Co 0,1 Mr 0,1 O2 Mg2Si 6 26 8 20 / / 0,75 2,50 Example 29 LiNi 0,8 Co 0,1 Mr 0,1 O2 Silicon monoxide + graphite 6 26 8 20 / / 0,75 2,50 Example 30 LiNi 0,8 Co 0,1 Mr 0,1 O2 Silicon monoxide + graphite 6 26 8 20 / / 0,75 2,50 Example 31 LiNi 0,8 Co 0,1 Mr 0,1 O2 Silicon monoxide + graphite 6 26 8 20 / / 0,75 2,50 Comparative example 1 LiNi 0,8 Co 0,1 Mr 0,1 O2 Silicon monoxide + graphite 2 26 8 20 / / 0,25 2,50 Comparative example 2 LiNi 0,8 Co 0,1 Mr 0,1 O2 Silicon monoxide + graphite 16 26 8 20 / / 2,00 2,50 Comparative example 3 LiNi 0,8 Co 0,1 Mr 0,1 O2 Silicon monoxide + graphite 6 15 / 15 / / / / comparative LiNi 0,8 What 0,1 Silicon example 4 Mn 0,1 O2 noxide + graphite 6 26 / 20 EC 8 / / Comparative example 5 LiNi 0,8 Co 0,1 Mr 0,1 O2 Silicon monoxide + graphite 3 21,8 1,8 3 EC 17 1,67 1,67 Comparative example 6 LiNi 0,8 Co 0,1 Mr 0,1 O2 Silicon monoxide + graphite 6 32 16 15 / / 0,38 0,94 Comparative example 7 LiNi 0,8 Co 0,1 Mr 0,1 O2 Silicon monoxide + graphite 6 15 15 / / / 0,40 / Comparative example 8 LiNi 0,8 Co 0,1 Mr 0,1 O2 Silicon monoxide + graphite 6 26 8 / EC 20 0,75 / Comparative example 9 LiNi 0,8 Co 0,1 Mr 0,1 O2 Silicon monoxide + graphite 6 21,8 8 1,8 EC 12 0,75 0,23 Comparative example 10 LiNi 0,8 Co 0,1 Mr 0,1 O2 Silicon monoxide + graphite 6 34 8 26 / / 0,75 3,25 Comparative example 11 LiNi 0,8 Co 0,1 Mr 0,1 O2 Silicon monoxide + graphite 6 14 7 7 / 1 0,86 1,00 Comparative example 12 LiNi 0,8 Co 0,1 Mr 0,1 O2 Silicon monoxide + graphite 6 42 10 20 EC 12 0,60 2,00 Comparative example 13 LiNi 0,8 Co 0,1 Mr 0,1 O2 Silicon monoxide + graphite 3 27 17 10 / / 0,18 0,59 Comparative example 14 LiNi 0,8 Co 0,1 Mr 0,1 O2 Silicon monoxide + graphite 15 22 7 15 / / 2,14 2,14 Comparative example 15 LiNi 0,8 Co 0,1 Mr 0,1 O2 Silicon monoxide + graphite 6 17,5 15 2,5 / / 0,40 0,17 Comparative example 16 LiNi 0,8 Co 0,1 Mr 0,1 O2 Silicon monoxide + graphite 6 28 6 22 / / 1,00 3,67 Note: EC - ethylene carbonate; DFEC - difluoroethylene carbonate; TFPC - trifluoromethylethylene carbonate.

[0033] Performance tests are carried out on the lithium-ion batteries produced from each embodiment and comparison example using the following method: 1. High-temperature bearing performance

[0034] After formation, the batteries are charged at room temperature with a constant current / voltage of 1C to 4.2 V and then discharged with a constant current of 1C to 2.75 V. The initial capacity is recorded. The batteries are then charged again with a constant current / voltage of 1C to 4.2 V. The initial volume is measured using the displacement method. The batteries are then stored at 60°C for 30 days. After cooling to room temperature, they are discharged at 1C to 2.75 V to measure the residual capacity, and the volume after storage is recorded. The calculation formulas are as follows: Battery capacity maintenance rate (%) = residual capacity / initial capacity × 100%; Battery storage gas expansion rate (%) = (volume after storage − initial volume) / initial volume × 100%. 2. High-temperature cycle performance test

[0035] At 45°C, the battery, after formation, is charged to 4.2 V with a constant current of 1C and then discharged to 2.75 V with a constant current of 1C. After 1000 charge / discharge cycles, the capacity retention rate is calculated at the 1000th cycle. The calculation formula is as follows: Capacity conservation rate (%) at the 1000th cycle = Discharge capacity at the 1000th cycle / Discharge capacity at the 1st cycle × 100%.

[0036] (1) The test results of embodiments 1-20 and comparison examples 1-16 are listed in Table 2. Table 2 group Capacity retention rate after 30 days of storage at 60°C (%) Gas expansion rate after 30 days of storage at 60°C (%) Capacity maintenance rate after 1000 cycles at 45°C (%) Example 1 88,5 26,3 88,3 Example 2 89,2 29,2 89,4 Example 3 88,8 25,5 89,2 Example 4 87,1 26,8 88,4 Example 5 89,5 27,7 90,3 Example 6 89,4 26,3 87,4 Example 7 87,8 21,1 88,2 Example 8 88,5 28,9 90,2 Example 9 87,5 20,1 85,4 Example 10 87,3 27,4 86,2 Example 11 86,6 29,5 86,5 Example 12 86,2 32,6 87,2 Example 13 87,5 20,2 85,9 Example 14 85,6 40,6 86,2 Example 15 84,3 32,5 86,3 Example 16 80,2 34,2 84,2 Example 17 89,9 30,8 92,1 Example 18 89,0 33,2 90,1 Example 19 80,2 37,2 78,2 Example 20 78,5 35,4 82,3 Comparative example 1 71,2 42,3 92,1 Comparative example 2 74,2 34,2 Capacity drop Comparative example 3 upper limit of the extent upper limit of the extent Capacity drop not testable not testable Comparative example 4 Upper limit of the extent not testable Upper limit of the extent not testable Capacity drop Comparative example 5 63,2 56,3 73,2 Comparative example 6 Upper limit of the extent not testable Upper limit of the extent not testable 76,3 Comparative example 7 70,3 49,2 83,2 Comparative example 8 83,8 29,5 82,2 Comparative example 9 84,8 28,5 83,2 Comparative example 10 80,2 29,5 Capacity drop Comparative example 11 70,1 19,2 Capacity drop Comparative example 12 Upper limit of the extent not testable Upper limit of the extent not testable 73,2 Comparative example 13 Upper limit of the extent not testable Upper limit of the extent not testable 76,3 Comparative example 14 Upper limit of the extent not testable Upper limit of the extent not testable Capacity drop Comparative example 15 69,2 54,3 80,2 Comparative example 16 76,9 62,1 72,1

[0037] The test results of embodiments 1 to 20 show that when using high nickel cathode materials and silicon-based anode materials, cyclic carbonate is used as an organic solvent and the content of fluorinated ethylene carbonate (F), propylene carbonate (P), cyclic carbonate (C) and silicon (S) in the anode material is controlled such that 0.2 ≤ S / F ≤ 2, 0.2 ≤ P / F ≤ 3.5, and 3 ≤ S ≤ 15, 2 ≤ F ≤ 15, 2 ≤ P ≤ 25, 15 ≤ C ≤ 40 apply, thereby ensuring the electrochemical stability of silicon-based high nickel batteries and simultaneously improving the battery's energy density. The synergistic effect of fluorinated ethylene carbonate and propylene carbonate optimizes the high-temperature storage performance and high-temperature cycle life of lithium-ion batteries and reduces storage gas evolution.

[0038] Comparisons between embodiments 1 to 2, 3 to 4 and 5 to 6 show that when the content of fluorinated ethylene carbonate F, the content of propylene carbonate P, the content of cyclic carbonate C and the silicon content S in the anode material additionally meet the ranges 5 ≤ ​​S ≤ 12, 4 ≤ F ≤ 10, 5 ≤ P ≤ 20 and 20 ≤ C ≤ 30, the lithium-ion battery exhibits excellent high-temperature storage performance and high-temperature cycle life.

[0039] The test results for embodiments 1 to 14 show that when only fluorinated ethylene carbonate and propylene carbonate are selected as cyclic carbonate solvents, fluorinated ethylene carbonate (FEC) suppresses volume changes in silicon-based active anode materials during charge and discharge cycles, ensures good particle contact, and significantly improves the capacity retention rate of the lithium-ion battery. Propylene carbonate (PC) undergoes reductive decomposition at the anode, forming a denser and more stable SEI layer, resulting in excellent high-temperature performance for the propylene carbonate solvent system. The combined use of these two cyclic carbonates improves the high-temperature storage and cycle performance of silicon-based, high-nickel battery systems.

[0040] The test results of embodiments 15 to 20 show that when fluorinated ethylene carbonate and propylene carbonate are selected as solvents, their combined use with other cyclic carbonates such as ethylene carbonate, difluoroethylene carbonate, and trifluoromethylethylene carbonate helps to suppress electrolytic decomposition at lower potentials. This facilitates normal lithium ion insertion and removal at the negative electrode, thus ensuring the high-temperature performance of the battery. This suggests that other cyclic carbonates exhibit a synergistic effect with fluorinated ethylene carbonate and propylene carbonate solvents.

[0041] The test results of comparative examples 1 to 12 show that lithium-ion batteries cannot exhibit satisfactory high-temperature performance even when the S / F and P / F values ​​are within the specified range, provided that a single parameter—the content of fluorinated ethylene carbonate (F), propylene carbonate (P), cyclic carbonate (C), or silicon (S) in the anode material—exceeds the limits of the range. The test results of comparative examples 13 to 16 show that even when the content of fluorinated ethylene carbonate (F), propylene carbonate (P), cyclic carbonate (C), and silicon (S) in the anode material meets the specified ranges, if either the S / F or P / F ratio is too high or too low, it is impossible to achieve both high energy density and excellent high-temperature performance simultaneously.This shows a strong correlation between the content of fluorinated ethylene carbonate (F), the content of propylene carbonate (P), the content of cyclic carbonate (C) and the silicon content (S) in the anode material with regard to the improvement of high-temperature storage and high-temperature cycle performance of the battery.

[0042] (2) The test results of embodiment 3 and embodiments 21 to 24 are shown in Table 3. Table 3 group Capacity retention rate after 30 days of storage at 60°C (%) Gas expansion rate after 30 days of storage at 60°C (%) Capacity retention rate after 1000 cycles at 45°C (%) Example 3 88,8 25,5 89,2 Example 21 89,2 24,5 91,2 Example 22 86,2 26,4 87,3 Example 23 88,6 23,9 90,4 Example 24 89,1 24,7 86,9

[0043] The test results of embodiment 3 and embodiments 21 to 24 show that, within the battery system of the present application, the use of various high-nickel cathode materials enables good high-temperature storage and high-temperature cycle performance, provided that the content of fluorinated ethylene carbonate (F), propylene carbonate (P), cyclic carbonates (C), and silicon (S) in the cathode material meet appropriate conditions. Improvements in the high-temperature storage and high-temperature cycle performance of the lithium-ion battery can be achieved. This demonstrates the universality of the battery system of the present application for various high-nickel cathode materials.

[0044] (3) The test results of embodiment 3 and embodiments 25 to 28 are shown in Table 4. Table 4 group Capacity retention rate after 30 days of storage at 60°C (%) Gas expansion rate after 30 days of storage at 60°C (%) Capacity maintenance rate after 1000 cycles at 45°C (%) Example 3 88,8 25,5 89,2 Example 25 80,2 45,3 78,5 Example 26 85,3 28,3 83,2 Example 27 83,2 35,4 80,5 Example 28 78,3 43,2 76,4

[0045] The test results of embodiment 3 and embodiments 25 to 28 show that, within the battery system of the present application, the use of various silicon-based anode materials enables good high-temperature storage and high-temperature cycle performance, provided that the content of fluorinated ethylene carbonate (F), propylene carbonate (P), cyclic carbonates (C), and silicon (S) in the anode material meets appropriate conditions. Improvements in the high-temperature storage and high-temperature cycle performance of the lithium-ion battery can be achieved. This demonstrates the universality of the battery system of the present application for various silicon-based anode materials.

[0046] (4) The test results of embodiment 3 and embodiments 29 to 31 are shown in Table 5. Table 5 group Capacity retention rate after 30 days of storage at 60°C (%) Gas expansion rate after 30 days of storage at 60°C (%) Capacity maintenance rate after 1000 cycles at 45°C (%) Example 3 88,8 25,5 89,2 Example 29 84,3 27,4 90,3 Example 30 89,2 25,0 90,8 Example 31 92,1 32,1 86,4

[0047] The test results of embodiment 3 and embodiments 29 to 31 show that, in the battery system of the present application, the additional incorporation of diethyl sulfate (DTD) further improves the cycle capacity retention rate during storage at high temperatures. The additional incorporation of 1,3-propanesulfonic acid lactone (PS) further improves both the capacity retention rate and the cycle capacity retention rate during storage at high temperatures and simultaneously reduces gas evolution during storage. The additional incorporation of the additive tripropyl phosphorus further improves the capacity retention rate during storage at high temperatures, indicating a complementary interaction between cyclic carbonates such as fluorinated ethylene carbonate and propylene carbonate and conventional additives.

[0048] The foregoing has described the present application in more detail by means of specific exemplary embodiments.

[0049] It is understood, however, that the specific descriptions contained herein should not be interpreted as limiting the nature and scope of the present application. All modifications made by those skilled in the art to the above-mentioned embodiments after reading this description fall within the scope of protection of the present application. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] CN 202311463178.5

[0001]

Claims

[1] Lithium-ion battery, characterized by , that it consists of a cathode, an anode and a non-aqueous electrolyte; wherein the cathode comprises a cathode material layer containing an active cathode material, wherein the active cathode material comprises a compound represented by formula (A): Li x Ni a Co b M' 1-a-b O 2-y A y Formula (A) where in formula (A) -0.1 ≤ x ≤ 0.2, 0.8 ≤ a < 1, 0 ≤ b < 0.2, 0.8 ≤ a + b < 1, 0 ≤ y < 0.2 hold; where M' comprises one or both of the elements Mn or Al and zero, one or more of the elements Sr, Mg, Ti, Ca, Zr, Zn, Si, Fe, B, Ga, Cr, W, V, Nb and Ce; where A comprises one or more of S, N, F, B, Cl, Br and I; wherein the anode comprises an anode material layer containing an active anode material, wherein the active anode material comprises a silicon-based material; wherein the non-aqueous electrolyte comprises a lithium salt and an organic solvent, wherein the organic solvent comprises cyclic carbonate, and wherein the cyclic carbonate comprises fluorinated ethylene carbonate and propylene carbonate; where the lithium-ion battery meets the following conditions: 0.2≤S / F≤2,0.2≤P / F≤3.5 and 3≤S≤15.2≤F≤15.2≤P≤25, 15≤C≤40; where S denotes the mass fraction of silicon in the anode material layer, expressed in wt.%; where F denotes the mass fraction of fluorinated ethylene carbonate in the non-aqueous electrolyte, expressed in wt.%; where P denotes the mass fraction of propylene carbonate in the non-aqueous electrolyte, expressed in wt.%; where C denotes the mass fraction of cyclic carbonate in the non-aqueous electrolyte, expressed in wt.%. [2] Lithium-ion battery according to claim 1, characterized bythat the lithium-ion battery meets the following conditions: 0.3≤S / F≤1,0.5≤P / F≤2.

6. [3] Lithium-ion battery according to claim 1, characterized by , that the mass fraction F of fluorinated ethylene carbonate in the non-aqueous electrolyte is 4 wt.% to 10 wt.%. [4] Lithium-ion battery according to claim 1, characterized by , that the mass fraction P of propylene carbonate in the non-aqueous electrolyte is 5 wt.% to 20 wt.%. [5] Lithium-ion battery according to claim 1, characterized by , that the mass fraction S of silicon in the anode material layer is 5 wt.% to 12 wt.%. [6] Lithium-ion battery according to claim 1, characterized by , that the mass fraction C of cyclic carbonate in the non-aqueous electrolyte is 20 wt.% to 30 wt.%. [7] Lithium-ion battery according to claim 1, characterized by, that the silicon-based material comprises one or more of silicon materials, silicon oxide materials, silicon-carbon materials and silicon alloy materials; where the silicon material is a nanoscale silicon material; where the silicon oxide material is a SiO x -material, where 0 ≤ x ≤ 2; where the silicon-carbon material is a silicon-based material containing silicon and carbon material, and / or a silicon-based material containing SiO y and contains carbon material, where 0 ≤ y ≤ 2; wherein the silicon alloy material is an Mg2Si alloy material and / or an Fe2Si alloy material. [8] Lithium-ion battery according to claim 1, characterized by that the cyclic carbonate continues to comprise one or more of vinyl carbonate, difluorovinyl carbonate, and trifluoromethylvinyl carbonate. [9] Lithium-ion battery according to claim 1, characterized bythat the organic solvent continues to comprise one or more of linear carbonates, carboxylate esters, and ether compounds. [10] Lithium-ion battery according to claim 9, characterized by that the linear carbonates comprise one or more of dimethyl carbonates, diethyl carbonates, methyl ethyl carbonates and methyl propyl carbonates. [11] Lithium-ion battery according to claim 9, characterized by that the carboxylate esters comprise one or more of methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, methyl butyrate, methyl isobutyrate, methyl trimethyl acetate and ethyl trimethyl acetate. [12] Lithium-ion battery according to claim 9, characterized by that the ether compounds comprise one or more of ethylene glycol dimethyl ether, 1,3-dioxolane and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether. [13] Lithium-ion battery according to claim 1, characterized by, that the non-aqueous electrolyte further comprises additives, wherein the additives include at least one of cyclic sulfate ester compounds, sulfonyl lactone compounds, cyclic carbonate compounds, phosphate ester compounds, borate ester compounds and nitrile compounds. [14] Lithium-ion battery according to claim 13, characterized by , that the additive content is 0.01 wt.% to 10 wt.% based on the total mass of the non-aqueous electrolyte as 100%. [15] Lithium-ion battery according to claim 13, characterized by , that the cyclic sulfate ester compounds comprise at least one of diethyl sulfate, 4-methyl sulfate and propylene sulfate; wherein the sulfonyl lactone compounds comprise at least one of 1,3-propanesulfonyl lactone, 1,4-butanesulfonyl lactone and vinyl-1,3-sulfonyl lactone; wherein the cyclic carbonate compounds comprise at least one of ethylene carbonate, ethylene vinyl carbonate, methylene ethylene carbonate, trifluoromethyl ethylene carbonate, difluoroethylene carbonate and a compound represented by the following structural formula 1: where in the structural formula 1 R 21 , R 22 , R 23 , R 24 , R 25 and R 26 Each is independently composed of hydrogen, halogen and a C1-C5 group; wherein the phosphate ester compound comprises at least one of tri(trimethylsilyl) phosphate, tri(triethylsilyl) phosphate and a compound represented by the following structural formula 2: where in the structural formula 2 R 31 , R 32 and R 33 each independently of one of saturated hydrocarbon groups, unsaturated hydrocarbon groups, halogenated hydrocarbon groups of C1-C5 and -Si(C m H2m+1 )3 are, where m is a natural number from 1 to 3, and where at least one of R 31 , R 32 and R 33 an unsaturated hydrocarbon group; wherein the borate ester compound comprises at least one of tris(trimethylsilyl) borate and tris(triethylsilyl) borate; wherein the nitrile compound comprises at least one of adiponitrile, glutaronitrile, ethylene glycol bis(propionitrile) ether, hexanitrile, adiponitrile, heptanitrile, octanitrile, nonanitrile and decanitrile.