Electrolyte and application thereof

Abstract

The invention provides an electrolyte and application thereof, the electrolyte comprises a compound with a structure of formula 1, in the formula 1, X is H, halogen atom, substituted or unsubstituted C1-C30 alkyl, substituted or unsubstituted C2-C30 alkenyl, substituted or unsubstituted C2-C30 alkynyl; n = 2 or 3. The electrolyte comprises a special additive, so that the safety performance of the battery can be effectively improved, and the occurrence probability of thermal runaway when the battery is abused is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries, relates to an electrolyte, and particularly relates to an electrolyte and its application. Background Art

[0002] Lithium-ion batteries are widely used in fields such as portable electronic devices (such as smartphones, laptops, tablets, etc.), electric vehicles, and energy storage systems due to their advantages of high working voltage, high energy density, fast charging, no memory effect, and environmental friendliness. In recent years, with the continuous development of lithium-ion batteries, safety has become one of the key performance concerns for consumer batteries and power batteries.

[0003] During the operation of lithium-ion batteries, thermal runaway is one of the most common safety problems of lithium-ion batteries, and thermal runaway is often caused by battery abuse, which mainly includes high-temperature environment, extrusion, puncture, impact, etc. During the abuse process, due to the out-of-control chemical reactions inside the battery, a large amount of heat is released, and at the same time, there are also thermal decomposition reactions of the positive electrode, negative electrode, and electrolyte itself. A large amount of free acid is generated during this process, and these free acids will further react with the active materials and the interface film, exacerbating the thermal runaway of the battery. Moreover, the electrolytes in current batteries mainly adopt non-aqueous organic systems, including high-purity organic solvents, lithium salts, and additives, etc. Among them, the organic solvents usually include carbonate solvents, which have the characteristics of easy decomposition and flammability. When thermal runaway occurs, it will further exacerbate the severity of safety accidents, such as safety accidents such as fire or even explosion.

[0004] Therefore, it is necessary to develop a new electrolyte system to effectively inhibit the fire and explosion caused by thermal runaway during battery abuse. Summary of the Invention

[0005] Aiming at the above defects, the present invention provides an electrolyte, which includes a special additive, so that the safety performance of the battery can be effectively improved, and the probability of fire and explosion caused by thermal runaway during battery abuse can be reduced.

[0006] The present invention also provides a lithium-ion battery, which includes the above electrolyte, so that the lithium-ion battery has high safety performance and reduces the probability of thermal runaway during battery abuse.

[0007] In the first aspect of the present invention, an electrolyte is provided, and the electrolyte includes a compound with the structure of formula 1.

[0008]

[0009] In Formula 1, X is H, a halogen atom, a substituted or unsubstituted C1-C30 alkyl group, a substituted or unsubstituted C2-C30 alkenyl group, or a substituted or unsubstituted C2-C30 alkynyl group; n = 2 or n = 3.

[0010] The electrolyte as described above, wherein the mass percentage of the compound having the structure of Formula 1 in the electrolyte is X%, and X satisfies: 0.1 ≤ X ≤ 8.

[0011] The electrolyte as described above, wherein the compound having the structure of Formula 1 includes at least one of the following compounds,

[0012]

[0013] The electrolyte as described above, wherein the electrolyte further includes a nitrile compound;

[0014] Preferably, the mass percentage of the nitrile compound in the electrolyte is Y%, and Y satisfies: 0.5 ≤ Y ≤ 10;

[0015] Preferably, the nitrile compound includes a trinitrile compound, and the trinitrile compound includes at least one of 1,3,6-hexanetricarbonitrile, 1,2,6-hexanetricarbonitrile, 1,3,5-hexanetricarbonitrile, 1,3,5-pentanetricarbonitrile, 1,2,3-propanetricarbonitrile, glycerol trinitrile, 1,3,5-benzenetricarbonitrile, and 1,3,5-cyclohexanetricarbonitrile.

[0016] The electrolyte as described above, wherein the electrolyte satisfies: 0.2 ≤ X / Y ≤ 8.

[0017] The electrolyte as described above, wherein the electrolyte further includes a sulfur-containing additive;

[0018] Preferably, the sulfur-containing additive includes at least one of 1,3-propane sultone, 1,3-propene sultone, ethylene sulfate, vinylene sulfate, and the compound shown in Formula 2,

[0019]

[0020] Preferably, the mass percentage of the sulfur-containing additive in the electrolyte is 0.1-5%.

[0021] The electrolyte as described above, wherein the electrolyte further includes an organic solvent, and the organic solvent includes a fluorinated solvent;

[0022] Preferably, the fluorinated solvent includes at least one of 2,2-difluoroethyl acetate, ethyl trifluoroacetate, methyl ethyl fluorocarbonate, diethyl fluorocarbonate, diethyl fluorocarbonate, butenyl fluorocarbonate, methyl propyl fluorocarbonate, ethyl propyl fluorocarbonate, methyl trifluoroethyl carbonate, 3,3,3-trifluoropropylene carbonate;

[0023] Preferably, the mass percentage content of the fluorinated solvent in the organic solvent is 5-35%.

[0024] The electrolyte as described above, wherein the electrolyte further includes fluorinated ethylene carbonate;

[0025] Preferably, the mass percentage content of the fluorinated ethylene carbonate in the electrolyte is 5-25%.

[0026] The electrolyte as described above, wherein the electrolyte further includes lithium difluorooxalate borate;

[0027] Preferably, the mass percentage content of the lithium difluorooxalate borate in the electrolyte is 0.01-2%.

[0028] The second aspect of the present invention provides a lithium-ion battery, and the lithium-ion battery includes the electrolyte of the first aspect.

[0029] The lithium-ion battery as described above, wherein the lithium-ion battery includes a negative electrode sheet, the negative electrode sheet includes a negative electrode current collector and a negative electrode active layer provided on at least a part of the surface of the negative electrode current collector, the negative electrode active layer includes a negative electrode active material, and the negative electrode active material includes a silicon-based material.

[0030] The electrolyte in the present invention includes a compound with a structure of Formula 1, and this compound can effectively inhibit the fire and explosion caused by thermal runaway during battery abuse and improve the safety of the battery. This may be because the compound of Formula 1 can effectively inhibit the thermal runaway of lithium batteries through multi-stage actions: in the initial stage, the pyridine ring structure can capture the active free radicals (such as ·H, ·OH, etc.) generated by the decomposition of the electrolyte, block the chain reaction, and reduce the probability of triggering thermal runaway; as the temperature rises, the pyridine ring decomposes to expose the triazine ring structure, consume the free acids (such as HF, PF5, etc.) generated during thermal runaway, delay the decomposition of the electrolyte, and thus inhibit the temperature rise rate; when the temperature further rises, the remaining triazine ring decomposes to generate a large amount of nitrogen gas (N2), and these gases can not only dilute the concentration of combustible gases to inhibit combustion, but also cause the aluminum-plastic film to rupture through rapid pressure increase to achieve rapid heat release, and finally avoid the battery from undergoing a violent explosion. Detailed Embodiments

[0031] To make the objectives, technical solutions, and advantages of the present invention clearer, the following will, in combination with the embodiments of the present invention, clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0032] Lithium-ion batteries are widely used in various different technical fields due to their advantages such as high energy density, wide operating temperature range, no memory effect, and environmental friendliness. However, in practical applications, lithium batteries often need to work in various complex environments (such as high-temperature environments), and mechanical abuse may also occur during operation, which can all lead to thermal runaway of the battery and pose safety hazards.

[0033] As one of the key components of the battery, the electrolyte mainly plays the role of conducting ions, enabling the lithium-ion battery to achieve the charge and discharge functions. Currently, the commonly used electrolytes are generally carbonate-based electrolytes, which are easily decomposed and flammable at high temperatures and will further exacerbate the severity of safety accidents when the battery undergoes thermal runaway, such as safety accidents like fire or even explosion.

[0034] Therefore, it is necessary to further develop the electrolyte to effectively suppress the fire and explosion caused by thermal runaway of the battery during abuse.

[0035] In view of the above problems, the first aspect of the present invention provides an electrolyte, which includes a compound containing the structure of Formula 1,

[0036]

[0037] In Formula 1, X is H, a halogen atom, a substituted or unsubstituted C1-C30 alkyl group, a substituted or unsubstituted C2-C30 alkenyl group, or a substituted or unsubstituted C2-C30 alkynyl group; n = 2 or n = 3.

[0038] The "compound containing the structure of Formula 1" in the present invention includes a triazine ring and at least two pyridine rings. The pyridine ring includes a substituent X, and the substituent X includes H, a halogen atom, a substituted or unsubstituted C1-C30 alkyl group, a substituted or unsubstituted C2-C30 alkenyl group, or a substituted or unsubstituted C2-C30 alkynyl group. The halogen atom includes F, Cl, Br. Among them, the pyridine ring can replace the hydrogen atom at any position on the triazine ring, and the substituent X can replace the hydrogen atom at any position on the pyridine ring. It should be noted that the pyridine ring replaces the hydrogen atom in the triazine ring and is connected to the carbon atom, and the substituent X replaces the hydrogen atom in the pyridine ring and is connected to the carbon atom.

[0039] The "alkyl group with C1-C30" in the present invention refers to a cyclic alkyl group or a linear alkyl group containing 1 to 30 carbon atoms. The linear alkyl group can be a saturated straight-chain alkyl group or a saturated branched-chain alkyl group; it should be noted that the cyclic alkyl group contains 3 to 30 carbon atoms; for example, the cyclic alkyl group can be cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, decahydronaphthyl, etc.; the linear alkyl group can be methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, neopentyl, n-hexyl, isohexyl, n-heptyl, n-octyl, n-nonyl, n-decyl, etc. Specifically, the number of carbon atoms in the above alkyl group can be 1, 5, 10, 15, 20, 25, 30, etc.

[0040] The "alkenyl group with C2-C30" in the present invention refers to a linear alkenyl group or a branched alkenyl group containing 1 or more double bonds and having 2 to 30 carbon atoms. For example, vinyl, 1-propenyl, 2-propenyl, 1-butenyl, 2-butenyl, 3-butenyl, 1,3-butadienyl, 3-methyl-2-butenyl. Specifically, the number of carbon atoms in the above alkenyl group can be 1, 5, 10, 15, 20, 25, 30, etc.

[0041] The "alkynyl group with C2-C30" in the present invention refers to a linear alkynyl group or a branched alkynyl group containing 1 or more triple bonds and having 2 to 30 carbon atoms. For example, ethynyl, propynyl, butynyl. Specifically, the number of carbon atoms in the above alkynyl group can be 1, 5, 10, 15, 20, 25, 30, etc.

[0042] Furthermore, the above alkyl group is an alkyl group with C1-C10, the alkenyl group is an alkenyl group with C2-C10, and the alkynyl group is an alkynyl group with C2-C10.

[0043] The present invention does not specifically limit the substituents in the alkyl group, alkenyl group, and alkynyl group. For example, they can be selected from at least one of halogen atoms, cyano groups, amino groups, and hydroxyl groups. And the present invention does not specifically limit the substitution position of the substituents. Any hydrogen atom in the alkyl group, alkenyl group, and alkynyl group can be substituted, and the number of substituents substituted is not limited.

[0044] When n = 2 in the present invention, the compound shown in Formula 1 contains two pyridine rings; when n = 3, the compound shown in Formula 1 contains three pyridine rings.

[0045] The present invention does not specifically limit the sources of the components in the electrolyte. Products commercially available or prepared by conventional preparation methods well-known to those skilled in the art can be used.

[0046] Through analysis, the inventor found that the main cause of thermal runaway is that when the battery is abused, the chemical reactions inside the battery get out of control, generating a large amount of heat. At the same time, there are also thermal decomposition reactions of the positive electrode, negative electrode, and electrolyte itself. During this process, a large amount of free acid is generated, and these free acids will further react with the active materials and the interface film, exacerbating the thermal runaway of the battery and triggering safety accidents such as fire and explosion.

[0047] Through research, the inventor found that the triazine structure can react with free acid to eliminate free acid. However, this structure can react with free acid at a relatively low temperature (below about 60°C, the normal operating temperature of the battery). This means that even if a compound containing a triazine structure is added to the electrolyte, it will be gradually consumed during the cycle, and there will not be enough compound containing a triazine structure during thermal runaway, making it difficult to play a role.

[0048] The inventor further found that when the triazine-structure compound includes no less than two pyridine rings, that is, adding a compound with the structure of Formula 1 to the electrolyte can effectively solve the aforementioned problem. This is because: the pyridine rings therein can form a conjugated protection ring, enhancing the stability of the triazine-structure compound, protecting the triazine structure at the normal operating temperature of the battery, reducing the reactivity of the triazine structure, and reducing the consumption of the triazine structure by free acid and moisture during the cycle; initially, the pyridine ring structure can capture active free radicals (such as ·H, ·OH, etc.) generated by the decomposition of the electrolyte, blocking the chain reaction and reducing the probability of triggering thermal runaway; as the temperature rises, the pyridine ring decomposes, exposing the triazine structure, enabling some of the triazine structure to react with free acid, effectively reducing the damage of the free acid generated during thermal runaway to the active materials and the interface, delaying the occurrence time of thermal runaway and reducing the temperature rise; as the temperature continues to rise, the remaining triazine structure can decompose to generate a large amount of non-combustible gas nitrogen, which can not only inhibit fire but also directly break through the aluminum-plastic film, quickly release heat, and prevent the battery from catching fire and exploding.

[0049] Therefore, the electrolyte in the present invention can effectively inhibit the fire and explosion caused by thermal runaway during battery abuse, improving the safety of the battery.

[0050] In addition, the compound with the structure of Formula 1 can also capture metal ions such as Fe, Co, Ni, etc. (derived from the positive electrode active material) in the electrolyte, preventing the metal ions from dissolving out and depositing on the negative electrode side, damaging the SEI film structure, effectively improving the stability of the interface film, and improving the cycle performance of the battery. At the same time, the compound with the structure shown in Formula 1 can also participate in the formation of the SEI film, increasing the N content in the SEI film, which is not only beneficial to the transmission of lithium ions but also can improve the strength and toughness of the interface film, effectively inhibiting the continuous formation of the interface film, preventing the increase in impedance caused by the excessive thickness of the interface film, and improving the high-temperature cycle performance of the battery in a high-voltage system.

[0051] In a specific embodiment, the mass percentage content of the compound of formula 1 in the electrolyte is X%, and X satisfies: 0.1 ≤ X ≤ 8. In this range, the mass content of the compound of formula 1 in the electrolyte is more appropriate, which can not only ensure the safety of the battery, effectively improve the thermal runaway problem of the battery, but also further improve the high-temperature cycling performance of the battery.

[0052] Exemplarily, X can be 0.1, 0.5, 1, 2, 3, 4, 5, 6, 7, 8 or a range composed of any two of these values.

[0053] In a specific embodiment, the compound of formula 1 includes at least one of the following compounds,

[0054]

[0055] When the compound of formula 1 includes at least one of the above specific compounds, the safety performance of the battery can be further improved.

[0056] When the compound of formula 1 is a mixture of the above various specific compounds, the present invention does not make specific limitations on the ratio between the various specific compounds.

[0057] In a specific embodiment, the electrolyte further includes a nitrile compound; preferably, the mass percentage content of the nitrile compound in the electrolyte is Y%, and Y satisfies: 0.5 ≤ Y ≤ 10; preferably, the nitrile compound includes a trinitrile compound, and the trinitrile compound includes at least one of 1,3,6-hexanetricarbonitrile, glycerol trinitrile, 1,2,6-hexanetricarbonitrile, 1,3,5-hexanetricarbonitrile, 1,3,5-pentanetricarbonitrile, 1,2,3-propanetricarbonitrile, glycerol trinitrile, 1,3,5-benzenetricarbonitrile, 1,3,5-cyclohexanetricarbonitrile.

[0058] Although the compound of formula 1 can capture metal ions in the electrolyte, it cannot inhibit the dissolution of transition metal ions in the positive electrode active material from the root cause, and the improvement of the battery cycling performance is limited. By further adding a nitrile compound to the electrolyte, the nitrile compound complexes with the metal ions on the surface of the positive electrode active material and adsorbs on the surface of the positive electrode active material, effectively reducing the dissolution of transition metal ions in the positive electrode active material, improving the structural stability of the positive electrode active material, and reducing the collapse of the structure of the positive electrode active material caused by the dissolution of transition ions, thereby improving the cycling stability of the battery. Therefore, when the electrolyte further includes a nitrile compound, the nitrile compound can cooperate with the compound of formula 1 to further improve the cycling performance of the battery.

[0059] When the mass percentage Y% of the nitrile compound in the electrolyte is within the aforementioned range, it is possible to avoid the increase in interfacial impedance caused by excessive nitrile compounds, effectively reduce polarization, and further improve the cycle stability of the battery.

[0060] Exemplarily, Y can be 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or a range composed of any two of these values.

[0061] When the nitrile compound includes a trinitrile compound, it is helpful to better complex metal ions on the surface of the positive electrode active material, play a better role in inhibiting dissolution, and compared with other nitrile additives, the impedance brought by the polynitrile structure of the trinitrile compound is smaller, which is helpful to improve the cycle performance of the battery; at the same time, the trinitrile compound has better thermal stability and a wider electrochemical window, which can not only be adapted to high-voltage battery systems, but also further improve the safety of the battery.

[0062] When the trinitrile compound is a mixture of the above-mentioned various specific compounds, the present invention does not specifically limit the ratio between the various specific compounds.

[0063] In one embodiment, the nitrile compound further includes a dinitrile compound, and the dinitrile compound includes at least one of succinonitrile, glutarodinitrile, adiponitrile, pimelonitrile, suberonitrile, sebaconitrile, 1,2-bis(2-cyanoethoxy)ethane.

[0064] When the dinitrile compound is a mixture of the above-mentioned various specific compounds, the present invention does not specifically limit the ratio between the various specific compounds.

[0065] The present invention does not specifically limit the source of the nitrile compound, and commercially available products or products prepared by conventional preparation methods well-known to those skilled in the art can be used.

[0066] In a specific embodiment, the electrolyte satisfies: 0.2 ≤ X / Y ≤ 8. Exemplarily, X / Y can be 0.2, 0.5, 1, 2, 3, 4, 5, 6, 7, 8 or a range composed of any two of these values.

[0067] When X / Y < 0.2, there will be too many nitrile compounds and too few compounds with the structure of Formula 1 in the electrolyte. On the one hand, it will cause too much nitrile compounds to be adsorbed on the surface of the positive active material, affecting lithium ion transport, further increasing the interfacial impedance, polarization, and affecting the battery cycle performance and rate performance. On the other hand, too few compounds with the structure of Formula 1 cannot play their roles fully, and the improvement of the battery safety performance and cycle performance is limited. When X / Y > 8, there will be too few nitrile compounds and too many compounds with the structure of Formula 1 in the electrolyte. On the one hand, the improvement of the metal ion dissolution of the positive active material is limited. On the other hand, too many compounds with the structure of Formula 1 may cause the growth of the interfacial impedance between the electrode and the electrolyte, the increase in the difficulty of lithium ion transport, the increase in interfacial polarization, and affect the cycle performance of the battery.

[0068] Therefore, when 0.2 ≤ X / Y ≤ 8, the nitrile compounds and the compounds with the structure of Formula 1 can cooperate better, further improving the battery safety performance, cycle performance and rate performance.

[0069] In a specific embodiment, the electrolyte further includes a sulfur-containing additive; preferably, the sulfur-containing additive includes at least one of 1,3-propane sultone, 1,3-propene sultone, ethylene sulfate, vinylene sulfate and the compound shown in Formula 2.

[0070]

[0071] Preferably, the mass percentage content of the sulfur-containing additive in the electrolyte is 0.1-5%.

[0072] By including a sulfur-containing additive in the electrolyte to participate in the formation of the SEI film and obtain a sulfur-containing SEI film, it can not only make the battery have high high-temperature cycle performance, rate performance and safety performance, but also effectively reduce the charge transfer impedance, reduce the transport resistance of lithium ions, and is beneficial to improving the low-temperature performance of the battery.

[0073] When the sulfur-containing additive in the electrolyte is one or more of the above specific compounds, the low-temperature performance of the battery can be further improved.

[0074] When the sulfur-containing additive is a mixture of the above multiple specific compounds, the present invention does not specifically limit the ratio between the specific compounds.

[0075] The present invention does not specifically limit the source of the sulfur-containing additive, and commercially available products or products prepared by conventional preparation methods well-known to those skilled in the art can be used.

[0076] When the mass percentage content of the sulfur-containing additive in the electrolyte is within the aforementioned range, it can not only effectively improve the low-temperature performance of the battery, but also avoid side reactions occurring during the cycling process due to excessive sulfur-containing additives. Such side reactions will not only decompose to produce gases (such as SO2, H2S, etc.), leading to safety hazards, but also consume active lithium ions, resulting in battery capacity loss.

[0077] Exemplarily, the mass percentage content of the sulfur-containing additive in the electrolyte can be 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5% or a range composed of any two of these values.

[0078] In a specific embodiment, the electrolyte further includes an organic solvent, and the organic solvent includes a fluorinated solvent; preferably, the fluorinated solvent includes at least one of 2,2-difluoroethyl acetate, ethyl trifluoroacetate, methyl ethyl fluorocarbonate, propylene fluorocarbonate, diethyl fluorocarbonate, butene fluorocarbonate, methyl propyl fluorocarbonate, ethyl propyl fluorocarbonate, methyl trifluoroethyl carbonate, 3,3,3-trifluoropropylene carbonate; preferably, the mass percentage content of the fluorinated solvent in the organic solvent is 5-35%.

[0079] By making the electrolyte include a fluorinated solvent, the thermal stability of the electrolyte can be effectively improved, making the electrolyte less likely to explode and burn or even completely non-flammable, thereby improving the safety performance of the battery; at the same time, the fluorinated solvent can also improve the antioxidant property of the electrolyte, enabling the electrolyte to be adapted to a high-voltage battery system and improving the cycling stability of the battery.

[0080] Furthermore, when the fluorinated solvent includes the aforementioned specific compounds, the furnace temperature safety performance, energy density and cycling stability of the battery can be further improved.

[0081] The present invention does not specifically limit the source of the fluorinated solvent, and commercially available products or products prepared by conventional preparation methods well-known to those skilled in the art can be used.

[0082] Furthermore, when the mass percentage content of the fluorinated solvent in the organic solvent is within the aforementioned range, it can not only effectively improve the furnace temperature safety performance and cycling stability of the battery, but also avoid an increase in the viscosity of the electrolyte caused by too high a content, reduce the ion-conducting performance of the electrolyte, increase polarization, and deteriorate the battery capacity.

[0083] Exemplarily, the mass percentage content of the fluorinated solvent in the organic solvent can be 5%, 10%, 15%, 20%, 25%, 30%, 35% or a range composed of any two of these values.

[0084] In one embodiment, the organic solvent further includes a carbonate solvent and / or a carboxylate solvent. Among them, the carbonate solvent includes at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate; the carboxylate solvent includes at least one of propyl acetate, n-butyl acetate, isobutyl acetate, n-pentyl acetate, isopentyl acetate, ethyl propionate, propyl propionate, n-propyl propionate, methyl butyrate, ethyl butyrate, and n-ethyl butyrate.

[0085] In a specific embodiment, the electrolyte further includes fluoroethylene carbonate; preferably, the mass percentage content of fluoroethylene carbonate in the electrolyte is 5-25%.

[0086] When the electrolyte further includes fluoroethylene carbonate (FEC), FEC can participate in the formation of the SEI film to form an SEI film rich in lithium fluoride, further improving the lithium ion transport efficiency of the interface film. At the same time, the interface film containing lithium fluoride has high stability, which can further improve the long cycle performance of the battery.

[0087] The present invention does not specifically limit the source of fluoroethylene carbonate, and products commercially available or prepared by conventional preparation methods well-known to those skilled in the art can be used.

[0088] When the mass percentage content of fluoroethylene carbonate in the electrolyte is within the aforementioned range, it not only helps to improve the stability of the SEI film and further improve the long cycle performance of the battery, but also can avoid the problems of increased impedance and gas generation caused by too high a content of fluoroethylene carbonate.

[0089] Exemplarily, the mass percentage content of fluoroethylene carbonate in the electrolyte can be 5%, 7%, 9%, 11%, 13%, 15%, 17%, 19%, 21%, 23%, 25% or a range composed of any two of these values.

[0090] In a specific embodiment, the electrolyte further includes lithium difluoro(oxalato)borate; preferably, the mass percentage content of lithium difluoro(oxalato)borate in the electrolyte is 0.01-2%.

[0091] When the electrolyte further includes lithium difluoro(oxalato)borate (LiODFB), lithium difluoro(oxalato)borate can form a stable low-impedance interface film on the positive and negative electrodes. In cooperation with the compound containing the structure of Formula 1, it can effectively improve the cycle stability of the battery, inhibit the growth of impedance during cycling, and improve the cycle capacity retention rate of the battery.

[0092] The present invention does not specifically limit the source of lithium difluoro(oxalato)borate, and products commercially available or prepared by conventional preparation methods well-known to those skilled in the art can be used.

[0093] When the mass percentage content of lithium difluoro(oxalato)borate in the electrolyte is within the aforementioned range, the content of lithium difluoro(oxalato)borate is relatively appropriate, which can not only effectively improve the cycle capacity retention rate of the battery, but also reduce the impedance and improve the gas generation problem to a certain extent.

[0094] Exemplarily, the mass percentage content of lithium difluoro(oxalato)borate in the electrolyte can be 0.01%, 0.1%, 0.2%, 0.4%, 0.6%, 0.8%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2% or the range composed of any two of these values.

[0095] It can be understood that the electrolyte also includes a lithium salt; the lithium salt in the present invention is preferably at least one of lithium hexafluorophosphate (LiPF6), lithium difluorophosphate (LiPO2F2), lithium bis(fluorosulfonyl)imide, lithium difluorobis(oxalato)phosphate, lithium tetrafluoroborate, lithium bis(oxalato)borate, lithium hexafluoroantimonate, lithium hexafluoroarsenate, lithium bis(pentafluoroethylsulfonyl)imide, lithium tris(trifluoromethylsulfonyl)methyl, lithium bis(trifluoromethylsulfonyl)imide.

[0096] When the lithium salt is a mixture of the above-mentioned various specific compounds, the present invention does not specifically limit the ratio between the specific compounds.

[0097] The present invention does not specifically limit the source of the lithium salt, and commercially available products or products prepared by conventional preparation methods well-known to those skilled in the art can be used.

[0098] In the second aspect of the present invention, a lithium-ion battery is provided. The lithium-ion battery includes the electrolyte of the first aspect. Therefore, the lithium-ion battery has high safety performance.

[0099] The present invention does not specifically limit the preparation method of the lithium-ion battery, and it can be prepared by conventional methods in the art.

[0100] In a specific embodiment, the lithium-ion battery includes a negative electrode sheet. The negative electrode sheet includes a negative electrode current collector and a negative electrode active layer disposed on at least a part of the surface of the negative electrode current collector. The negative electrode active layer includes a negative electrode active material, and the negative electrode active material includes a silicon-based material.

[0101] Compared with other negative electrode active materials, the silicon-based material can provide a higher energy density, which can meet the demand of consumer electronics products for longer battery life. However, including a silicon-based negative electrode active material often accompanies a large volume change during the cycle. Since the compound containing the structure shown in Formula 1 can effectively improve the stability of the SEI film, therefore, the occurrence of side reactions on the surface of the silicon-based material can be reduced to a certain extent, thereby reducing the charge-discharge interface impedance of the silicon-based material particles, improving the lithium ion insertion / extraction efficiency, and making the battery have high cycle performance and rate performance.

[0102] In summary, when the negative electrode active material is a silicon-based material, it can not only ensure the cycle performance and rate performance of the battery, but also improve the energy density of the battery.

[0103] Preferably, the silicon-based material in the present invention includes at least one of nano-silicon (Si), silicon-oxide negative electrode material (SiO x , 0 < x < 2), and silicon-carbon negative electrode material.

[0104] When the silicon-based material is a mixture of the foregoing various specific materials, the present invention does not specifically limit the ratio between the various specific materials.

[0105] Preferably, the mass percentage content of silicon in the silicon-based material is 10-80%. In this range, a relatively high specific capacity and low expansion can be taken into account.

[0106] Exemplarily, the mass percentage content of silicon in the silicon-based material can be 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80% or a range composed of any two of these values.

[0107] The present invention does not specifically limit the source of the silicon-based material, and commercially available products or products prepared by conventional preparation methods well-known to those skilled in the art can be used.

[0108] The present invention does not specifically limit the type of the negative electrode current collector, and conventional negative electrode current collectors in the art can be used, such as copper foil.

[0109] In one embodiment, the negative electrode active material further includes a carbon-based material; preferably, the carbon-based material includes at least one of artificial graphite, natural graphite, mesophase carbon microspheres, hard carbon, and soft carbon.

[0110] When the carbon-based material is a mixture of the foregoing various specific materials, the present invention does not specifically limit the ratio between the various specific materials.

[0111] The present invention does not specifically limit the source of the carbon-based material, and commercially available products or products prepared by conventional preparation methods well-known to those skilled in the art can be used.

[0112] It can be understood that the negative electrode active layer further includes a binder and a conductive agent; the present invention does not specifically limit the types of the binder and the conductive agent, and conventional binders and conductive agents in the art can be used; for example, the binder can include at least one of polyvinylidene fluoride (PVDF), sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), and nitrile rubber (NBR); the conductive agent can include at least one of acetylene black, Ketjen black, graphite, graphene, and carbon nanotubes.

[0113] The present invention does not specifically limit the mass contents of the negative electrode active material, binder, and conductive agent in the negative electrode active layer, and appropriate mass ratios can be selected according to actual needs.

[0114] It can be conceived that the battery in the present invention further includes a positive electrode sheet and a separator.

[0115] The present invention does not specifically limit the composition of the positive electrode sheet. In one embodiment, the positive electrode sheet includes a positive electrode current collector and a positive electrode active layer provided on at least a part of the surface of the positive electrode current collector. The positive electrode active layer includes a positive electrode active material, a binder, and a conductive agent.

[0116] Among them, the positive electrode active material may include a layered lithium composite oxide, and the chemical composition of the layered lithium composite oxide is Li (1+x) Ni y Co z M (1-y-z) O2, where -0.1 ≤ x ≤ 1, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1, and 0 ≤ y + z ≤ 1; among them, M includes at least one of Mg, Zn, Ga, Ba, Al, Fe, Cr, Sn, V, Mn, Sc, Ti, Nb, Mo, and Zr.

[0117] The binder may include at least one of polyvinylidene fluoride, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate salt, polyvinyl pyrrolidone, polyethylene ether, polymethyl methacrylate, polytetrafluoroethylene, polyhexafluoropropylene, and styrene-butadiene rubber.

[0118] The conductive agent may include at least one of conductive carbon black, carbon nanotubes, conductive graphite, and graphene.

[0119] The present invention does not specifically limit the mass contents of the positive electrode active material, binder, and conductive agent in the positive electrode active layer, and appropriate mass ratios can be selected according to actual needs.

[0120] The present invention does not specifically limit the type of the positive electrode current collector, and conventional positive electrode current collectors in the art can be used, such as aluminum foil.

[0121] The present invention does not specifically limit the separator, and it can be a separator material commonly used in current lithium-ion batteries, such as any one of a polypropylene separator (PP), a polyethylene separator (PE), a polypropylene / polyethylene double-layer composite film (PP / PE), a polypropylene / polyethylene / polypropylene triple-layer composite film (PP / PE / PP), and a separator with a ceramic coating.

[0122] Hereinafter, the electrolyte provided by the present invention and the lithium-ion battery including the electrolyte will be introduced in detail through specific examples.

[0123] Example 1

[0124] 1) Preparation of the positive electrode sheet

[0125] Mix the positive electrode active material lithium cobaltate, binder polyvinylidene fluoride (PVDF), and conductive agent carbon black in a mass ratio of 95:3:2, add N-methylpyrrolidone (NMP), and stir under the action of a vacuum mixer to obtain a uniform positive electrode active slurry; uniformly coat the positive electrode active slurry on both surfaces of the aluminum foil; dry, roll, and slit the coated aluminum foil to obtain a positive electrode sheet with a double-sided areal density of 9.88 mg / cm 2 and a double-sided tap density of 4.2 g / cm 3 .

[0126] 2) Preparation of the negative electrode sheet

[0127] Mix graphite, silicon-carbon negative electrode active material (mass content of silicon element is 20%), binder styrene-butadiene rubber (SBR), and conductive agent carbon black in a mass ratio of 90:5:3:2, add deionized water, and obtain a negative electrode active slurry under the action of a vacuum mixer; uniformly coat the negative electrode active slurry on both surfaces of the copper foil; dry, cold-press, and slit the coated copper foil to obtain a negative electrode sheet with a double-sided areal density of 6.2 mg / cm 2 and a double-sided tap density of 1.7 g / cm 3 .

[0128] 3) Preparation of the electrolyte

[0129] In a glove box filled with argon (H2O < 0.1 ppm, O2 < 0.1 ppm), mix ethylene carbonate (EC), propylene carbonate (PC), propyl propionate (PP), and 2,2-difluoroethyl acetate (DFEA) evenly in a mass ratio of 10:15:55:20 to obtain a mixed solvent; then quickly add 15% of fully dried lithium hexafluorophosphate (LiPF6) based on the total mass of the electrolyte and 1% of lithium difluoro(oxalato)borate (LiODFB) based on the total mass of the electrolyte to the mixed solvent. After dissolution, add 5% of the compound shown in Formula 1-1 based on the total mass of the electrolyte, 5% of 1,3,6-hexanetricarbonitrile based on the total mass of the electrolyte, and 13 wt% of fluoroethylene carbonate (FEC) based on the total mass of the electrolyte. After stirring evenly and passing the moisture and free acid tests, obtain the required electrolyte; wherein, X / Y = 1.0.

[0130] 4) Separator

[0131] The separator is a polyethylene separator with a thickness of 8 μm.

[0132] 5) Preparation of the lithium-ion battery

[0133] After stacking the above positive electrode sheet, separator, and negative electrode sheet in sequence, winding is performed to obtain an electrode core; the electrode core is placed in an outer packaging aluminum foil, and the above electrolyte is injected into the outer packaging. After processes such as vacuum packaging, standing, formation, shaping, and sorting, a lithium-ion battery is obtained.

[0134] Example 2

[0135] The preparation method of the lithium-ion battery in this example is basically the same as that in Example 1, except that in step 3), the compound shown in Formula 1-1 in the electrolyte is replaced with the compound shown in Formula 1-2.

[0136] Example 3

[0137] The preparation method of the lithium-ion battery in this example is basically the same as that in Example 1, except that in step 3), the compound shown in Formula 1-1 in the electrolyte is replaced with the compound shown in Formula 1-3.

[0138] Example 4

[0139] The preparation method of the lithium-ion battery in this example is basically the same as that in Example 1, except that in step 3), the compound shown in Formula 1-1 in the electrolyte is replaced with the compound shown in Formula 1-4.

[0140] Example 5

[0141] The preparation method of the lithium-ion battery in this example is basically the same as that in Example 1, except that in step 3), the compound shown in Formula 1-1 in the electrolyte is replaced with the compound shown in Formula 1-5.

[0142] Example 6

[0143] The preparation method of the lithium-ion battery in this example is basically the same as that in Example 1, except that in step 3), the mass content of the compound shown in Formula 1-1 in the electrolyte is adjusted to 0.1%; then X / Y = 0.2.

[0144] Example 7

[0145] The preparation method of the lithium-ion battery in this example is basically the same as that in Example 1, except that in step 3), the mass content of the compound shown in Formula 1-1 in the electrolyte is adjusted to 2%; then X / Y = 0.4.

[0146] Example 8

[0147] The preparation method of the lithium-ion battery in this example is basically the same as that in Example 1, except that in step 3), the mass content of the compound shown in Formula 1-1 in the electrolyte is adjusted to 8%; then X / Y = 1.6.

[0148] Example 9

[0149] The preparation method of the lithium-ion battery in this embodiment is basically the same as that in Embodiment 1, except that in step 3), 1,3,6-hexanetricarbonitrile in the electrolyte is replaced by glycerol trinitrile.

[0150] Embodiment 10

[0151] The preparation method of the lithium-ion battery in this embodiment is basically the same as that in Embodiment 1, except that in step 3), the mass content of 1,3,6-hexanetricarbonitrile in the electrolyte is adjusted to 3%; then X / Y = 1.7.

[0152] Embodiment 11

[0153] The preparation method of the lithium-ion battery in this embodiment is basically the same as that in Embodiment 1, except that in step 3), the mass content of 1,3,6-hexanetricarbonitrile in the electrolyte is adjusted to 10%; then X / Y = 0.5.

[0154] Embodiment 12

[0155] The preparation method of the lithium-ion battery in this embodiment is basically the same as that in Embodiment 1, except that in step 3), the mass content of 1,3,6-hexanetricarbonitrile in the electrolyte is adjusted to 0.7%; then X / Y = 7.1.

[0156] Embodiment 13

[0157] The preparation method of the lithium-ion battery in this embodiment is basically the same as that in Embodiment 1, except that in step 3), the mass ratio of EC, PC, PP, and DFEA in the mixed solvent is 10:15:70:5.

[0158] Embodiment 14

[0159] The preparation method of the lithium-ion battery in this embodiment is basically the same as that in Embodiment 1, except that in step 3), the mass ratio of EC, PC, PP, and DFEA in the mixed solvent is 10:15:40:35.

[0160] Embodiment 15

[0161] The preparation method of the lithium-ion battery in this embodiment is basically the same as that in Embodiment 1, except that in step 3), the mass content of fluoroethylene carbonate in the electrolyte is adjusted to 5%.

[0162] Embodiment 16

[0163] The preparation method of the lithium-ion battery in this embodiment is basically the same as that in Embodiment 1, except that in step 3), the mass content of fluoroethylene carbonate in the electrolyte is adjusted to 25%.

[0164] Embodiment 17

[0165] The preparation method of the lithium-ion battery in this example is basically the same as that in Example 1, except that in step 3), the mass content of lithium difluoro(oxalato)borate in the electrolyte is adjusted to 0.01%.

[0166] Example 18

[0167] The preparation method of the lithium-ion battery in this example is basically the same as that in Example 1, except that in step 3), the mass content of lithium difluoro(oxalato)borate in the electrolyte is adjusted to 2%.

[0168] Example 19

[0169] The preparation method of the lithium-ion battery in this example is basically the same as that in Example 1, except that in step 3), the electrolyte further includes the sulfur-containing additive vinylene sulfate, and the mass content of vinylene sulfate in the electrolyte is 1%.

[0170] Example 20

[0171] The preparation method of the lithium-ion battery in this example is basically the same as that in Example 19, except that in step 3), the mass content of vinylene sulfate in the electrolyte is 0.1%.

[0172] Example 21

[0173] The preparation method of the lithium-ion battery in this example is basically the same as that in Example 19, except that in step 3), the mass content of vinylene sulfate in the electrolyte is 5%.

[0174] Example 22

[0175] The preparation method of the lithium-ion battery in this example is basically the same as that in Example 1, except that in step 3), the mass content of the compound shown in Formula 1-1 in the electrolyte is adjusted to 0.5 wt%, and then X / Y = 0.1.

[0176] Example 23

[0177] The preparation method of the lithium-ion battery in this example is basically the same as that in Example 1, except that in step 3), the mass content of 1,3,6-hexanetricarbonitrile in the electrolyte is adjusted to 0.5 wt%, and then X / Y = 10.0.

[0178] Example 24

[0179] The preparation method of the lithium-ion battery in this example is basically the same as that in Example 1, except that in step 3), there is no 2,2-difluoroethyl acetate in the mixed solvent, and the mass ratio of EC, PC, and PP in the mixed solvent is 10:15:75.

[0180] Example 25

[0181] The preparation method of the lithium-ion battery in this example is basically the same as that in Example 1, except that in step 3), fluoroethylene carbonate is absent in the electrolyte.

[0182] Example 26

[0183] The preparation method of the lithium-ion battery in this example is basically the same as that in Example 1, except that in step 3), lithium difluoro(oxalato)borate is absent in the electrolyte.

[0184] Comparative Example 1

[0185] The preparation method of the lithium-ion battery in this comparative example is basically the same as that in Example 1, except that in step 3), the compound shown in Formula 1-1 is replaced with 2,4,6-tris(trifluoromethyl)-1,3,5-triazine.

[0186] Comparative Example 2

[0187] The preparation method of the lithium-ion battery in this comparative example is basically the same as that in Example 1, except that in step 3), the compound shown in Formula 1-1 is replaced with 2,4,6-tris(pentafluoroethyl)-1,3,5-triazine.

[0188] Comparative Example 3

[0189] The preparation method of the lithium-ion battery in this comparative example is basically the same as that in Example 1, except that in step 3), the compound shown in Formula 1-1 is replaced with the compound shown in Formula 3 (CAS No. 111359-79-6).

[0190]

[0191] Test Example

[0192] 1. Test the electrochemical performance of the lithium-ion batteries prepared in the above examples and comparative examples, including the following steps:

[0193] 1) High-temperature cycle performance

[0194] At an ambient temperature of 45 °C, discharge the divided-capacity batteries prepared in the above examples and comparative examples at a current of 0.2C to 3.0V, and let stand for 5 min; first charge at a constant current and constant voltage of 0.7C to 4.5V, with a cut-off current of 0.05C, and then discharge at a constant current of 0.5C to 3.0V, and record the initial discharge capacity as C0; perform cycling according to the aforementioned charge-discharge mechanism. After 500 cycles of charge and discharge, record the discharge capacity after cycling as C1, then the capacity retention rate (%) after 500 cycles = (C1 / C0) × 100%.

[0195] 2) Rate performance

[0196] The formed batteries prepared in the above-mentioned examples and comparative examples were placed in a constant temperature environment of 25°C, left standing for 10 min, discharged at 0.2C to 3.0V, and left standing for 10 min; charged at a rate of 3C to 4.45V to obtain the constant current charge capacity; then charged at a constant voltage until the cut-off current was 0.02C, record the constant voltage charge capacity, left standing for 10 min; then discharged at 0.2C to 3.0V and left standing for 10 min. In the present invention, the rate performance is represented by the constant current charge ratio, and the constant current charge ratio (%) = constant current charge capacity ÷ (constant voltage charge capacity + constant current charge capacity) × 100%, where the sum of the constant voltage charge capacity and the constant current charge capacity is the total charge capacity.

[0197] 3) Furnace temperature test

[0198] Under the environmental condition of 25°C, the battery was discharged at a current of 0.2C to 3.0V; left standing for 5 min; then charged at a charging current of 0.2C to 4.45V. When the cell voltage reached 4.45V, it was changed to constant voltage charging at 4.45V until the charging current was less than or equal to the cut-off current of 0.05C, and the state of the battery before the test was recorded by taking pictures. The aforementioned battery was left standing for 1 h and then placed in an oven. The temperature of the oven was raised to 132 ± 2°C at a rate of 5 ± 2°C / min and kept for 30 min and then stopped. The passing standard was that the battery did not catch fire or explode. Six batteries were taken as a group for testing in each example and comparative example, and the number of passes among the six batteries was recorded. For example, when 4 out of the 6 batteries participating in the test passed the test, it was recorded as 4 / 6 PASS.

[0199] 4) Penetration test

[0200] Under the environmental condition of 25°C, the battery was discharged at a current of 0.2C to 3.0V and left standing for 5 min; then charged at a charging current of 0.5C to 4.45V. When the cell voltage reached 4.45V, it was changed to constant voltage charging at 4.45V until the charging current was less than or equal to the cut-off current of 0.02C to obtain a fully charged battery. A steel needle (with a diameter of 4 mm and a sharp angle taper of 15°) was used to pierce through the center position of the cell surface at a descending speed of 30 mm / s. After piercing, the cell temperature dropped to 20% lower than the peak value, and the test ended.

[0201] The test results are shown in Table 1.

[0202] Table 1

[0203]

[0204]

[0205] As can be seen from Table 1:

[0206] Compared with Comparative Examples 1 - 3, the lithium-ion batteries in Examples 1 - 26 have higher comprehensive performance. Among them, the lithium-ion battery in Example 1 has high safety performance, with the number of furnace temperature test passes being 6 / 6 PASS and the number of needle penetration test passes being 6 / 6 PASS; and it also has a high high-temperature cycle capacity retention rate and rate performance. Among them, the high-temperature cycle capacity retention rate is 85.33%, and the rate performance is 90.38%. It can be seen from this that the electrolyte in the present invention can effectively improve the safety performance of the battery and reduce the probability of fire and explosion caused by thermal runaway during battery abuse.

[0207] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An electrolyte, characterized in that, The electrolyte includes a compound having the structure of Formula 1, wherein in Formula 1, X is H, a halogen atom, a substituted or unsubstituted C1-C30 alkyl group, a substituted or unsubstituted C2-C30 alkenyl group, or a substituted or unsubstituted C2-C30 alkynyl group; n = 2 or n = 3.

2. The electrolyte according to claim 1, wherein The mass percentage content of the compound having the structure of Formula 1 in the electrolyte is X%, where X satisfies: 0.1 ≤ X ≤ 8; and / or, the compound having the structure of Formula 1 includes at least one of the following compounds, 3. The electrolyte according to claim 1 or 2, characterized in that, The electrolyte further includes a nitrile compound; Preferably, the mass percentage content of the nitrile compound in the electrolyte is Y%, where Y satisfies: 0.5 ≤ Y ≤ 10; Preferably, the nitrile compound includes a trinitrile compound, and the trinitrile compound includes at least one of 1,3,6-hexanetricarbonitrile, 1,2,6-hexanetricarbonitrile, 1,3,5-hexanetricarbonitrile, 1,3,5-pentanetricarbonitrile, 1,2,3-propanetricarbonitrile, glycerol trinitrile, 1,3,5-benzenetricarbonitrile, 1,3,5-cyclohexanetricarbonitrile.

4. The electrolyte according to claim 3, characterized in that, The electrolyte satisfies: 0.2 ≤ X / Y ≤ 8.

5. The electrolyte according to any one of claims 1-4, characterized in that, The electrolyte further includes a sulfur-containing additive; Preferably, the sulfur-containing additive includes at least one of 1,3-propane sultone, 1,3-propene sultone, ethylene sulfate, vinylene sulfate, and the compound shown in Formula 2, Preferably, the mass percentage content of the sulfur-containing additive in the electrolyte is 0.1-5%.

6. The electrolyte according to any one of claims 1-5, characterized in that The electrolyte further includes an organic solvent, and the organic solvent includes a fluorinated solvent; Preferably, the fluorinated solvent includes at least one of 2,2-difluoroethyl acetate, ethyl trifluoroacetate, ethyl methyl fluorocarbonate, diethyl fluorocarbonate, diethyl fluorocarbonate, butenyl fluorocarbonate, methylpropyl fluorocarbonate, ethylpropyl fluorocarbonate, methyltrifluoroethyl carbonate, 3,3,3-trifluoropropene carbonate; Preferably, the mass percentage content of the fluorinated solvent in the organic solvent is 5-35%.

7. The electrolyte according to any one of claims 1-6, characterized in that The electrolyte further includes fluoroethylene carbonate; Preferably, the mass percentage content of the fluoroethylene carbonate in the electrolyte is 5-25%.

8. The electrolyte according to any one of claims 1-7, characterized in that, The electrolyte further includes lithium difluorooxalate borate; Preferably, the mass percentage content of the lithium difluorooxalate borate in the electrolyte is 0.01-2%.

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

10. The lithium ion battery according to claim 9, characterized in that, The lithium ion battery includes a negative electrode sheet, the negative electrode sheet includes a negative electrode current collector and a negative electrode active layer provided on at least a part of the surface of the negative electrode current collector, the negative electrode active layer includes a negative electrode active material, and the negative electrode active material includes a silicon-based material.

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