Non-aqueous electrolyte and lithium ion battery

Abstract

The application provides a nonaqueous electrolyte and a lithium ion battery, and particularly relates to the technical field of electrolytes.The nonaqueous electrolyte comprises an organic solvent, a lithium salt and an additive, wherein the additive comprises a compound of formula I, wherein R1, R2, R3 and R4 are each independently selected from a substituent with 1-6 carbon atoms, 0-4 unsaturation and 0-3 heteroatoms, and the heteroatoms are selected from any one of nitrogen atoms, sulfur atoms, oxygen atoms, boron atoms and phosphorus atoms.The addition of the compound can effectively improve the high-temperature cycle performance of the battery.

Description

Technical Field

[0001] This invention relates to the field of electrolyte technology, specifically to a non-aqueous electrolyte and a lithium-ion battery. Background Technology

[0002] With the depletion of fossil fuels and escalating environmental pollution, the automotive industry faces challenges and urgently needs new, environmentally friendly, and efficient energy sources. Lithium-ion batteries, due to their high energy density, small size, ability to provide long-lasting power for electric vehicles, low self-discharge rate (retaining charge even after prolonged periods of inactivity), high voltage, and strong power output, have broad application prospects. However, the safety of lithium-ion batteries cannot be ignored. Gases generated during charging and discharging can cause battery expansion, affecting performance and lifespan, increasing polarization risk, generating more heat, and potentially even causing explosions or fires, threatening life and property. Therefore, when promoting lithium-ion batteries, safety must be given high priority. Risks must be mitigated through optimized design, improved processes, and strengthened supervision to ensure safe and stable operation.

[0003] Currently, the electrolyte commonly used in lithium-ion batteries primarily consists of lithium hexafluorophosphate (LiPF6) as the electrolyte salt, combined with a mixture of cyclic and chain carbonates in organic solvents. However, this electrolyte has some shortcomings in practical applications. In particular, after prolonged cycling at high temperatures, the capacity retention and recovery rates of lithium-ion batteries decrease significantly, severely impacting their cycle life. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the present invention provides a non-aqueous electrolyte and a lithium-ion battery to improve the high-temperature cycle performance of lithium-ion batteries.

[0005] To achieve the above and other related objectives, the present invention provides a non-aqueous electrolyte, comprising: an organic solvent, a lithium salt, and an additive; wherein the additive comprises a compound represented by Formula I:

[0006]

[0007] In Formula I, R1, R2, R3, and R4 are each independently selected from substituents having 1-6 carbon atoms, an unsaturation degree of 0-4, and a heteroatom number of 0-3. The heteroatom is selected from any one of nitrogen, sulfur, oxygen, boron, and phosphorus atoms.

[0008] In one example of the present invention, R1, R2, R3, and R4 in Formula I are each independently selected from alkyl, alkenyl, alkynyl, carbonyl, ester, amino, or heterocyclic groups, wherein the heterocyclic group is selected from any one of pyridine, pyrrole, thiophene, thiazole, and furan.

[0009] In one example of the present invention, the content of the compound represented by Formula I in the non-aqueous electrolyte is from 0.05% to 3%.

[0010] In one example of the present invention, the content of the compound represented by Formula I in the non-aqueous electrolyte is 0.5% to 1.5%.

[0011] In one example of the present invention, the compound represented by Formula I includes any one or more of the following compounds:

[0012]

[0013]

[0014] In one example of the present invention, the additive further includes tris(trimethylsilyl)phosphate, wherein the content of tris(trimethylsilyl)phosphate in the non-aqueous electrolyte is 0.5% to 1%; and / or, the additive further includes one or more of fluoroethylene carbonate, propylene-1,3-sulfonyl lactone, and tetravinylsilane.

[0015] In one example of the present invention, the organic solvent includes one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, fluoroethylene carbonate, ethyl formate, ethyl acetate, propyl acetate, ethyl propionate, ethylene glycol dimethyl ether, diethanol diethyl ether, acetonitrile, propionitrile, butyronitrile, and valerate; the content of the organic solvent in the non-aqueous electrolyte is 70% to 80%.

[0016] In one example of the present invention, the lithium salt includes one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethyl)sulfonylimide, lithium acetate, lithium methanesulfonate, and lithium trifluoromethylsulfonate, and the lithium salt content in the non-aqueous electrolyte is 14% to 16%.

[0017] In another aspect, the present invention provides a lithium-ion battery, the lithium-ion battery comprising a positive electrode, a negative electrode, a separator, and any of the above-described non-aqueous electrolytes.

[0018] In one example of the present invention, the negative electrode sheet includes a negative current collector and a negative active material layer disposed on at least one side surface of the negative current collector, the negative active material layer including a negative active material, the negative active material including a silicon-based active material.

[0019] The non-aqueous electrolyte of this invention introduces a compound represented by Formula I as an additive. This additive molecule contains a tertiary amino group and unsaturated double bonds. The tertiary amino group can interact with acidic substances in the electrolyte. This interaction can, on the one hand, adjust the pH of the electrolyte, making the chemical environment of the electrolyte more stable; on the other hand, the salts generated by the reaction of the amino group with acidic substances can participate in the membrane formation process, increasing the ionic conductivity and stability of the membrane. The unsaturated double bonds can undergo polymerization in the electrolyte. During battery charging, the electric field and oxidative environment on the electrode surface trigger the opening of these double bonds, which then copolymerize with other components in the electrolyte (such as solvent molecules, other additives, etc.) to form a polymer film. This polymer film can cover the electrode surface, protecting the electrode, reducing side reactions between the electrode and the electrolyte, preventing direct contact between the electrolyte and the negative electrode, reducing irreversible lithium ion consumption, thereby improving the battery's cycle performance and coulombic efficiency.

[0020] Furthermore, the compound molecules shown in Formula I can also be adsorbed onto the electrode surface through physical or chemical adsorption. Cross-linking reactions can occur between molecules or with other components in the electrolyte, forming a cross-linked network structure. This cross-linked structure enhances the mechanical strength and stability of the membrane, enabling it to better resist volume changes and mechanical stresses generated during battery charging and discharging, thereby protecting the integrity of the electrode structure.

[0021] Furthermore, tris(trimethylsilyl)phosphate (TMSP) is added as another additive to the non-aqueous electrolyte. The trimethylsilyl (TMS) group in the TMSP molecule has certain steric hindrance and electronic effects, making some chemical bonds on the phosphate group relatively susceptible to nucleophilic attack. The nitrogen atom in the compound shown in Formula I has a lone pair of electrons, which can act as a nucleophile to perform a nucleophilic substitution reaction on the phosphate group in TMSP. The compound shown in Formula I attacks the phosphorus-oxygen bond in the phosphate group, causing the phosphorus-oxygen bond to break, and the nitrogen atom forms a new chemical bond with the phosphorus atom, simultaneously replacing some of the groups originally attached to the phosphorus atom. Subsequently, through a series of structural adjustments and rearrangements, a thermally stable SEI film is formed, thereby improving the battery's cycle performance and lifespan. Detailed Implementation

[0022] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that, unless otherwise specified, the following embodiments and features described therein can be combined with each other.

[0023] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0024] In this document, when referring to numerical ranges, unless otherwise specified, the distribution of selectable values ​​within a numerical range is considered continuous, including the two endpoints of the range (i.e., the minimum and maximum values), and every value between these two endpoints. When multiple numerical ranges are provided to describe a feature or property, these numerical ranges can be combined.

[0025] In this document, terms such as "multiple," "various," and "repeatedly" are used unless otherwise specified, referring to a quantity greater than or equal to 2. For example, "one or more" indicates one or more types. Terms such as "further," "even further," and "particularly" are used to describe purposes and indicate differences in content, but should not be construed as limiting the scope of protection of this invention.

[0026] Unless otherwise specified, "%" in this article refers to the percentage content by mass.

[0027] In this article, substituents refer to atoms or groups of atoms that replace those on the main chain or rings of organic compounds. They can replace a hydrogen atom or other atoms in a molecule, affecting its chemical and physical properties. The type and position of substituents have a significant impact on the reactivity, polarity, solubility, and other properties of a molecule.

[0028] Unsaturation, also known as the hydrogen deficiency index or cycloaddition double bond index, is a quantitative indicator of the degree of unsaturation in organic compound molecules. Its molecular formula is C2. n H m The hydrocarbon and its molecular formula is C n H m O x For hydrocarbon derivatives, if m < 2n + 2, then the hydrocarbon and its hydrocarbon group have a certain degree of unsaturation Ω. That is, compared with open-chain alkanes with the same number of carbon atoms, the degree of unsaturation of the organic compound increases by 1 for every 2 hydrogen atoms removed.

[0029] Number of heteroatoms: In organic chemistry, non-carbon atoms are collectively referred to as heteroatoms. The most common heteroatoms are nitrogen, sulfur and oxygen atoms.

[0030] As a crucial component of lithium-ion batteries, the performance of the electrolyte significantly impacts the battery's electrochemical performance, including cycle life, high-temperature storage, and safety. High-temperature environments (45–60°C) accelerate side reactions at the electrolyte / electrode interface. These reactions consume active lithium ions, leading to increased reversible capacity loss. Furthermore, the decomposition, rupture, or dissolution of the solid electrolyte interphase (SEI) film is more pronounced at high temperatures, thus accelerating the battery's aging process.

[0031] Based on this, the present invention provides a non-aqueous electrolyte and a lithium-ion battery. By introducing compounds containing tertiary amino groups and unsaturated double bonds as additives into the non-aqueous electrolyte, the tertiary amino groups are used to adjust the pH of the electrolyte, thereby increasing the ionic conductivity and stability of the membrane. The unsaturated double bonds are used to copolymerize with the components in the electrolyte to form a polymer membrane, thereby reducing the irreversible consumption of lithium ions and improving the cycle performance of the battery.

[0032] The first aspect of this invention provides a non-aqueous electrolyte comprising an organic solvent, a lithium salt, and additives. The organic solvent serves as the main component of the non-aqueous electrolyte and is used to dissolve the lithium salt and additives. After the lithium salt dissolves in the organic solvent, it can release a large number of active lithium ions, giving the electrolyte good conductivity. The additives serve as auxiliary substances for the electrolyte and can be selected according to actual needs, such as film-forming additives, flame-retardant additives, high-voltage additives, etc.

[0033] In this invention, the additive includes the compound represented by Formula I:

[0034]

[0035] In Formula I, R1, R2, R3, and R4 are each independently selected from substituents with 1-6 carbon atoms, an unsaturation degree of 0-4, and 0-3 heteroatoms. That is, the types of substituents R1, R2, R3, and R4 in Formula I do not affect each other; they can be completely identical substituents, or partially identical substituents, such as R1 and R2 being the same, or R1, R2, and R3 being the same, etc., or they can be completely different substituents. The number of carbon atoms in the above substituents can be any value from 1-6, such as 1, 3, 5, or 6, and the degree of unsaturation can be any value from 0-4, such as 0, 1, 3, or 4. Heteroatoms are non-carbon atoms, selected from any one of nitrogen (N), sulfur (S), oxygen (O), boron (B), and phosphorus (P) atoms. For example, a heteroatom can be a nitrogen atom, a sulfur atom, or an oxygen atom, but is not limited to these. The number of heteroatoms can be any value from 0-3. For example, 0, 1, 2, or 3.

[0036] In some embodiments, R1, R2, R3, and R4 in Formula I are each independently selected from alkyl, alkenyl, alkynyl, carbonyl, ester, amino, or heterocyclic groups. A heterocyclic group refers to a ring whose constituent atoms include at least one non-carbon atom in addition to a carbon atom; these non-carbon atoms are called heteroatoms. As an example, heterocyclic groups include, but are not limited to, any one of pyridine, pyrrole, thiophene, thiazole, and furan. For example, a heterocyclic group can be pyridine, thiophene, or furan, etc. That is, R1, R2, R3, and R4 can all be selected from any one of alkyl, alkenyl, alkynyl, carbonyl, ester, amino, and heterocyclic groups; they can be all the same, partially the same, or all different. As an example, R1, R2, R3, and R4 can all be alkyl; or R1 and R2 can be alkyl, R3 can be alkenyl, and R4 can be alkynyl; or R1 can be alkyl, R2 can be ester, R3 can be amino, and R4 can be alkenyl; and so on.

[0037] The compound shown in Formula I contains a tertiary amino group (R3N, where R represents an alkyl group, and the tertiary amino group is formed by the combination of a trimethyl group and an amino group (NH2)). Due to the lone pair of electrons on the nitrogen atom, the tertiary amino group exhibits basicity and can chemically react with acidic substances in the electrolyte (such as acidic substances produced by the decomposition of lithium salts). This can, on the one hand, adjust the pH of the electrolyte, making the chemical environment of the electrolyte more stable; on the other hand, the salts formed by the amino group and acidic substances can participate in the membrane formation process, increasing the ionic conductivity and stability of the membrane. Furthermore, the compound shown in Formula I also contains unsaturated double bonds. During battery charging, the electric field and oxidative environment on the electrode surface will trigger the opening of these double bonds, which then undergo copolymerization reactions with other components in the electrolyte (such as solvent molecules, other additives, etc.) to form a polymer film. This polymer film can cover the electrode surface, protecting the electrode, reducing side reactions between the electrode and the electrolyte, preventing direct contact between the electrolyte and the negative electrode, reducing irreversible lithium ion consumption, and thus improving the battery's cycle performance and coulombic efficiency.

[0038] In addition, the compound molecules shown in Formula I can also be adsorbed onto the electrode surface through physical adsorption or chemical adsorption, and cross-linking reactions can occur between molecules or between molecules and other components in the electrolyte to form a cross-linked network structure. This cross-linked structure can enhance the mechanical strength and stability of the membrane, enabling it to better resist volume changes and mechanical stresses generated during battery charging and discharging, thereby protecting the integrity of the electrode structure.

[0039] Further, the compound represented by Formula I is selected from one or a combination of two or more of compounds I-1, I-2, I-3, and I-4. Preferably, the compound represented by Formula I is selected from compound I-1.

[0040]

[0041]

[0042] Although the addition of the compound shown in Formula I is beneficial to improving the electrochemical performance of the battery, more is not necessarily better. The inventors of this application discovered in their research that when the content of the compound shown in Formula I in the non-aqueous electrolyte is too high, a thicker SEI film will form at the negative electrode interface, adversely affecting the cell's kinetics and interface stability, and consequently impacting the battery's cycle performance. Therefore, in one embodiment of this invention, the content of the compound shown in Formula I in the non-aqueous electrolyte is 0.05% to 3%, for example, 0.05%, 0.1%, 0.5%, 1%, 2%, or 3%. Further, the content of the compound shown in Formula I in the non-aqueous electrolyte is 0.5% to 1.5%, and even further, the content of the compound shown in Formula I in the non-aqueous electrolyte is 0.8% to 1%.

[0043] In one embodiment, the non-aqueous electrolyte additive also includes tris(trimethylsilyl)phosphate (TMSP). The trimethylsilyl (TMS) group in the TMSP molecule has certain steric hindrance and electronic effects, making some chemical bonds on the phosphate group relatively susceptible to nucleophilic attack. The nitrogen atom of the tertiary amino group in the compound shown in Formula I has a lone pair of electrons. When tris(trimethylsilyl)phosphate is used in combination with the compound shown in Formula I, the compound shown in Formula I can act as a nucleophile to perform a nucleophilic substitution reaction on the phosphate group in the TMSP molecule. That is, the compound shown in Formula I attacks the phosphorus-oxygen bond in the phosphate group, causing the phosphorus-oxygen bond to break, and the nitrogen atom forms a new chemical bond with the phosphorus atom, while simultaneously replacing some of the groups originally attached to the phosphorus atom. Subsequently, after a series of structural adjustments and rearrangements, a thermally stable SEI film is formed, thereby improving the high-temperature cycle performance and lifespan of the battery.

[0044] In one embodiment, the content of tris(trimethylsilyl)phosphate in the non-aqueous electrolysis is 0.5% to 1%, specifically 0.5%, 0.8%, or 1%. The inventors discovered that when the addition amount of tris(trimethylsilyl)phosphate exceeds 1%, the resulting SEI film is thicker, which is detrimental to cell dynamics and interface stability, thereby affecting the battery's cycle performance.

[0045] In other embodiments, the additive may also include one or more of fluoroethylene carbonate (FEC), propylene-1,3-sulfonyl lactone (PST), and tetravinylsilane (TVSI). The specific choice can be made according to actual production needs.

[0046] The organic solvent of this invention can be any solvent conventionally used in lithium-ion batteries. In some embodiments, the organic solvent includes one or more of carbonates, carboxylic esters, ethers, and nitriles, wherein the carbonate is selected from one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and fluoroethylene carbonate; the carboxylic ester is selected from one or more of ethyl formate, ethyl acetate, propyl acetate, and ethyl propionate; the ether is selected from ethylene glycol dimethyl ether and / or diethyl glycol diethyl ether; and the nitriles include one or more of acetonitrile, propionitrile, butyronitrile, and valerate. That is, the organic solvent can be selected from any one of the solvents listed above, or any two or a combination of two. For example, the organic solvent is a combination of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate, or a combination of ethyl formate and ethylene carbonate, etc. The content of the organic solvent in the non-aqueous electrolyte is typically 70% to 80%, for example, 70%, 80%, or 75%.

[0047] The lithium salt of this invention can be any type of lithium salt conventional in the art. To obtain a superior electrolyte, the lithium salt typically needs to possess the following characteristics: low dissociation energy and high solubility. Low dissociation energy ensures that the electrolyte formed after the lithium salt dissolves has high conductivity, thereby achieving a high rate of operation; high solubility ensures sufficient lithium ions for transport in the electrolyte. Good stability is also crucial, ensuring that the lithium salt does not react with other components when the battery operates at high voltage and high temperature. Excellent SEI film-forming properties are necessary to ensure that the electrolyte is not continuously consumed during subsequent cycles. Furthermore, it provides good passivation for aluminum current collectors, preventing corrosion of the aluminum foil under high voltage.

[0048] In one embodiment, the lithium salt includes one or more of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethyl)sulfonylimide (LiTFSI), lithium acetate (CH3COOLi), lithium methanesulfonate (CH3SO3Li), and lithium trifluoromethylsulfonate (CF3SO3Li). Further, lithium hexafluorophosphate, with its superior overall performance, is selected as the main lithium salt, and lithium bis(fluorosulfonyl)imide is used as the auxiliary lithium salt. Compared to lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide has higher conductivity and better thermal stability. Therefore, the addition of lithium bis(fluorosulfonyl)imide can provide better ion transport performance, thereby improving the charge and discharge efficiency and stability of the battery, and enhancing the overall performance of the electrolyte.

[0049] In some embodiments, the lithium salt content in the non-aqueous electrolyte is 12% to 16%, specifically 12%, 14%, or 16%, etc. As an example, the lithium salt is a composition of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide, wherein the mass ratio of lithium hexafluorophosphate to lithium bis(fluorosulfonyl)imide can be 14:1, 14:2, or 13:2, etc.

[0050] The non-aqueous electrolyte of this invention can be prepared using conventional methods. As an example, in a glove box under an argon atmosphere with a water content of <10 ppm, an organic solvent is mixed uniformly according to a predetermined ratio. Then, a thoroughly dried lithium salt and additives are added to the organic solvent and mixed uniformly to prepare the non-aqueous electrolyte. The content of each component in the non-aqueous electrolyte is a weight percentage calculated based on the total weight of the non-aqueous electrolyte.

[0051] A second aspect of this invention provides a lithium-ion battery comprising a positive electrode, a negative electrode, a separator, and the non-aqueous electrolyte described above. The separator is disposed between the positive and negative electrodes, serving as an isolation layer. During charging and discharging, lithium ions repeatedly insert and extract between the positive and negative electrodes, while the non-aqueous electrolyte conducts lithium ions between them. The lithium-ion battery can be, for example, a primary or secondary battery. A secondary battery can be, for example, a pouch battery, a prismatic battery, or a cylindrical battery. This invention does not limit the type of lithium-ion battery.

[0052] Specifically, the positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one side of the positive current collector. The positive current collector is, for example, a foil formed by surface treatment of materials such as nickel, titanium, aluminum, silver, stainless steel, or carbon. Besides foil, the positive current collector can also be used in any one or more combinations of various forms such as film, mesh, porous, foam, or non-woven fabric. The thickness of the positive current collector is, for example, 8 μm to 15 μm. In this embodiment, the positive current collector is, for example, aluminum foil, and the thickness of the aluminum foil is, for example, 13 μm. The positive active material layer includes a positive active material, a conductive agent, and a binder. No specific limitations are placed on the positive active material, conductive agent, and binder here; those skilled in the art can select them according to actual needs.

[0053] The positive electrode active material can be any material suitable for lithium-ion batteries, i.e., compounds that can reversibly insert and deintercalate lithium ions. In this invention, the positive electrode active material is selected from ternary positive electrode materials, lithium iron phosphate (LFP) positive electrode materials, etc., wherein the ternary positive electrode material is, for example, nickel-cobalt-manganese ternary material (NCM) or nickel-cobalt-aluminum ternary material (NCA), and the lithium iron phosphate (LFP) positive electrode material is, for example, lithium iron phosphate (LFP) or lithium manganese iron phosphate (LMFP). The binder for the positive electrode is selected from any one or more of polyvinylidene fluoride (PVDF), polyethylene oxide (PEO), polyamide (PA), polyacrylonitrile (PAN), polyacrylate (polyacrylate), polyvinyl ether (polyvinyl ether), polymethyl methacrylate (PMMA), ethylene-propylene-diene terpolymer (EPDM), polyhexanefluoropropylene (polyhexafluoropropylene), or polymerized styrene-butadiene rubber (SBR). The conductive agent of the positive electrode is selected from one or at least two of conductive carbon black (Super P), acetylene black, graphene, carbon nanotubes, carbon nanofibers, etc.

[0054] The negative electrode includes a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector. The negative current collector is selected from, for example, a copper foil current collector, a composite copper foil current collector, a carbon current collector, a foamed copper current collector, or a stainless steel current collector, and its thickness is, for example, 8 μm to 15 μm. In this embodiment, copper foil is selected as the negative current collector, and the thickness of the copper foil is, for example, 13 μm. The negative current collector has two surfaces opposite each other in its own thickness direction, and the negative active material layer is disposed on either or both of the two opposite surfaces of the negative current collector. The negative active material layer includes a negative active material, a conductive agent, a binder, and a thickener. The specific types of negative active material, conductive agent, and binder are not specifically limited here; materials known in the art for use in lithium-ion batteries can be used, and those skilled in the art can select them according to actual needs.

[0055] The negative electrode active material is selected from compounds capable of intercalating and deintercalating lithium ions. For example, graphite-based or silicon-based negative electrode materials can be selected. Graphite-based negative electrode materials include, but are not limited to, natural graphite, artificial graphite, soft carbon, and hard carbon; silicon-based negative electrode materials include silicon oxide compounds (SiO₂). x(0 < x < 2), silicon-carbon composites, silicon单质, etc. In one embodiment, the negative electrode active material adopts a combination of graphite-based negative electrode materials and silicon-based negative electrode materials. The theoretical specific capacity of graphite is relatively low (372 mAh / g), while the theoretical specific capacity of silicon (up to 4200 mAh / g) is much higher than that of graphite. Using graphite-based negative electrode materials in combination with silicon-based negative electrode materials can effectively improve the energy density of the battery and meet the requirements of high-energy-density batteries. At the same time, silicon expands significantly in volume during charge and discharge, and carbon materials such as graphite have good flexibility and mechanical strength, which can be used as a buffer coating layer for silicon-based negative electrode materials to effectively relieve the volume expansion effect of silicon and improve the cycle stability of the battery. The conductive agent of the negative electrode is selected from one of carbon black, acetylene black, graphene, carbon nanotubes, carbon nanofibers, etc. or a combination of two or more in any proportion. The binder of the negative electrode is selected from any one of polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), styrene-butadiene rubber (SBR), etc. or a combination of several in any proportion; the thickener is selected from sodium carboxymethyl cellulose (CMC-Na) or lithium carboxymethyl cellulose (CMC-Li).

[0056] The separator is selected from conventional types in the art, for example, polyethylene film (Polyethylene, PE), polypropylene film (Polypropylene, PP), glass fiber film, polyethylene film or composite film, etc. The thickness of the separator is 9 to 18 μm, the air permeability is 180 s / 100 mL to 380 s / 100 mL; the porosity is 30% to 50%.

[0057] The lithium-ion battery can be prepared according to the conventional methods in the art, as exemplified below:

[0058] (1) Preparation of the positive electrode sheet

[0059] Disperse the above positive electrode active material, conductive agent and binder in a solvent (such as N-methylpyrrolidone, abbreviated as NMP) to form a uniform positive electrode slurry; coat the positive electrode slurry on the positive electrode current collector, and after processes such as drying and cold pressing, obtain the positive electrode sheet. Among them, the proportions between the components in the positive electrode slurry can be set according to conventional proportions and are not limited here.

[0060] (2) Preparation of the negative electrode sheet

[0061] Disperse the above negative electrode active material, binder, thickener and conductive agent in deionized water to form a uniform negative electrode slurry: coat the negative electrode slurry on the negative electrode current collector, and after processes such as drying and cold pressing, obtain the negative electrode sheet. Among them, the proportions between the components in the negative electrode slurry can be set according to conventional proportions and are not limited here.

[0062] (3) Battery assembly

[0063] The prepared positive electrode, separator, and negative electrode are placed sequentially, with the separator positioned between the positive and negative electrodes to provide isolation. The bare cell is then obtained by winding or stacking the electrodes. The bare cell is wrapped in an aluminum-plastic film, transferred to a vacuum oven, and dried at 120°C. The prepared electrolyte is injected at a rate of 3.0 g / Ah, and the cell is sealed. Electrolysis is then performed to produce a 1Ah soft-pack battery (lithium-ion battery).

[0064] The lithium-ion battery of the present invention includes the non-aqueous electrolyte of the present invention, which can reduce the irreversible consumption of lithium ions and improve the cycle performance and coulombic efficiency of the battery.

[0065] The lithium-ion battery of this invention can be used in the form of a single cell, a battery module, or a battery pack to power electronic devices. Electronic devices include, but are not limited to, mobile phones, tablets, laptops, electric toys, electric vehicles, new energy vehicles, ships, spacecraft, etc. Electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc. Spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc. New energy vehicles can be pure electric vehicles, hybrid electric vehicles, or range-extended electric vehicles, etc.

[0066] The technical solution of the present invention will be described in detail below through several specific embodiments and comparative examples. Unless otherwise stated, the raw materials and reagents used in the following embodiments are all commercially available products, or can be prepared by conventional methods in the art, and the instruments used in the embodiments are all commercially available.

[0067] Example 1

[0068] This embodiment provides a non-aqueous electrolyte comprising an organic solvent, a lithium salt, and additives. The organic solvent is a composition of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of EC:DMC:EMC = 3:5:2. The lithium salt is a composition of lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI) mixed in a mass ratio of 14:1. The types and contents of the additives are shown in Table 1. In Table 1, the additive contents are weight percentages calculated based on the total weight of the non-aqueous electrolyte.

[0069] The preparation process of the non-aqueous electrolyte is as follows: In an argon atmosphere glove box with a water content of <10ppm, ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) are first mixed in a volume ratio of 3:5:2 to form an organic solvent; then lithium salts lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI) and additives are added to the organic solvent, wherein the amount of lithium hexafluorophosphate added is 14% of the total weight of the non-aqueous electrolyte, and the amount of lithium bis(fluorosulfonyl)imide added is 1% of the total weight of the non-aqueous electrolyte. After mixing evenly, the non-aqueous electrolyte is obtained. The types and amounts of additives are shown in Table 1.

[0070] This embodiment also provides a lithium-ion battery, which includes a positive electrode, a separator, a negative electrode, and the non-aqueous electrolyte of this embodiment. The preparation process of the lithium-ion battery is as follows:

[0071] Positive electrode preparation: LiNi 0.9 Co 0.05 Mn 0.05 O2, polyvinylidene fluoride, and conductive carbon black (Super P) are mixed in a mass ratio of 98:1:1. N-methylpyrrolidone (NMP) is added, and the mixture is stirred under vacuum until the system is homogeneous and transparent to obtain a positive electrode slurry. The positive electrode slurry is uniformly coated onto aluminum foil, dried at room temperature, and then transferred to an oven for drying. The positive electrode sheet is then produced through cold pressing, slitting, and other processes.

[0072] Negative electrode preparation: Negative electrode active material (90% artificial graphite + 10% silicon-carbon composite), conductive carbon black (Super P), lithium carboxymethyl cellulose (CMC-Li), and styrene-butadiene rubber (SBR) are mixed in a mass ratio of 96:1:1:2. Deionized water is added, and the mixture is thoroughly stirred and mixed evenly under the action of a vacuum stirrer to obtain a negative electrode slurry. The negative electrode slurry is uniformly coated on copper foil, dried at room temperature, and then transferred to an oven for drying. The negative electrode is then obtained through cold pressing, slitting, and other processes.

[0073] Selection of diaphragm: 12μm polypropylene film (PP) was used as the diaphragm.

[0074] Battery assembly: The positive electrode, separator, and negative electrode are placed sequentially, with the separator positioned between the positive and negative electrodes to provide insulation. The cells are then wound to form a bare cell. An aluminum-plastic film is then wrapped around the cell, and the cell is dried in a vacuum oven at 120°C. The prepared electrolyte is injected at a rate of 3.0 g / Ah, and the cell is sealed. Electrolysis is then performed to obtain a 1Ah soft-pack lithium-ion battery.

[0075] The present invention also provides Examples 2-12 and Comparative Examples 1-2, wherein the content of additives in the non-aqueous electrolytes of Examples 2-12 and Comparative Examples 1-2 is shown in Table 1, and the other steps are the same as those in Example 1.

[0076] Table 1: Types, contents, and battery performance of additives in Examples 1 to 12 and Comparative Examples 1 to 2

[0077]

[0078]

[0079] The lithium-ion batteries of Examples 1-12 and Comparative Examples 1-2 were subjected to performance tests, and the test results are shown in Table 1. The test methods are as follows:

[0080] (1) Beginning of Life Direct Current Resistance (BOL DCR) Test

[0081] Set the temperature of the constant temperature chamber to 25℃ and let it stand for 10 minutes. Charge the battery with a constant current of 0.33C to 4.25V, then charge it with a constant current of 0.05C at 4.25V, and let it stand for 30 minutes. Discharge the battery with a constant current of 0.33C to 2.5V, and let it stand for 10 minutes. Repeat this cycle twice, and record the discharge capacity of the last discharge as C0. Charge the battery with a constant current of 0.33C to 4.25V, then charge it with a constant current of 0.05C, and let it stand for 30 minutes. Discharge the battery with a constant current of 0.33C to 50% C0, and let it stand for 1 hour. Record the voltage V0 at the end of the standing period. Discharge the battery with a constant current of 4C0 for 30 seconds and record the voltage V1. Then, BOL DCR = (V0 - V1) / 4C0.

[0082] (2) Loop Test

[0083] Adjust the temperature of the constant temperature chamber to 45℃ and stabilize it for 30 minutes; charge at a constant current of 1C to 4.25V, then charge at a constant voltage of 0.05C, let it stand for 10 minutes, and then discharge at a constant current of 1C to 2.5V. After cycling this charge and discharge cycle 500 times, record the discharge capacity C1 of the cell on the 500th cycle. Then the capacity retention rate after 500 cycles at 45℃ is C1 / C0×100%.

[0084] Referring to Table 1, comparing Examples 1-5 and Comparative Examples 1 and 2, it can be concluded that adding Compound I-1 to the non-aqueous electrolyte improves both the BOL DCR value and the high-temperature cycle capacity retention of the battery. However, the improvement effect is closely related to the amount of Compound I-1 added: under the same conditions, as the amount of Compound I-1 added to the non-aqueous electrolyte increases, the BOL DCR value of the battery first gradually decreases, and then gradually increases after reaching a certain value; the high-temperature cycle capacity retention of the battery first gradually increases, and then gradually decreases after reaching the optimal value. This indicates that adding an appropriate amount of Compound I-1 to the non-aqueous electrolyte can improve the battery kinetics, thereby improving the high-temperature cycle performance of the battery. When the addition amount exceeds 3%, a thicker SEI film will form at the negative electrode interface, which will adversely affect the cell kinetics and interface stability, and will instead affect the cycle performance of the battery. The test results show that the addition amount of 0.05%-3% is reasonable, and the addition amount of 0.5%-1.5% has the best effect.

[0085] Comparing Examples 3, 6, 7, and 8, it can be concluded that compounds I-1, I-2, I-3, and I-4 can all improve the high-temperature cycle performance of batteries. Furthermore, at the same dosage, compound I-1 shows the most significant improvement.

[0086] Comparing Examples 4 and 9 to 12, it can be seen that adding an appropriate amount of TMSP along with Compound I-1 improves the battery's BOL DCR and high-temperature cycle capacity retention. However, when the TMSP content exceeds 1%, the BOL DCR value begins to increase, and the capacity retention begins to decrease. This is because Compound I-1 attacks the phosphorus-oxygen bond in the phosphate ester group, causing the phosphorus-oxygen bond to break. The nitrogen atom forms a new chemical bond with the phosphorus atom, replacing some of the groups originally attached to the phosphorus atom. Subsequently, through a series of structural adjustments and rearrangements, a thermally stable SEI film is formed, thereby improving the battery's cycle performance and lifespan. When the TMSP content is too high, the formed SEI film thickens, increasing the resistance of lithium ions through the film and thus increasing the battery's internal resistance, affecting the battery's efficiency. At the same time, it also consumes too many lithium ions, leading to battery capacity decay and affecting the battery's cycle life.

[0087] In summary, this invention introduces a compound of formula I as an additive into a non-aqueous electrolyte. This additive molecule contains a tertiary amino group and unsaturated double bonds. The tertiary amino group can interact with acidic substances in the electrolyte, adjusting the electrolyte's pH and stabilizing its chemical environment. It can also participate in membrane formation, increasing the membrane's ionic conductivity and stability. The unsaturated double bonds can also copolymerize with the electrolyte's Kizaru components to form a polymer film that covers the electrode surface, protecting the electrode, reducing side reactions between the electrode and the electrolyte, preventing direct contact between the electrolyte and the negative electrode, and reducing irreversible lithium-ion consumption. This improves the battery's cycle performance and coulombic efficiency. Therefore, this invention effectively overcomes some practical problems in the prior art, thus possessing high utilization value and practical significance.

[0088] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A non-aqueous electrolyte, characterized in that, include: Organic solvents, lithium salts, and additives; wherein the additives include compounds represented by Formula I or Formula I-3: Formula I; Formula I-3; In Formula I, R1, R2, R3, and R4 are each independently selected from substituents having 1-6 carbon atoms, an unsaturation degree of 0-4, and a heteroatom number of 0-3. The heteroatom is selected from any one of nitrogen, sulfur, oxygen, boron, and phosphorus atoms.

2. The non-aqueous electrolyte according to claim 1, characterized in that, In Formula I, R1, R2, R3, and R4 are each independently selected from alkyl, alkenyl, alkynyl, carbonyl, ester, or heterocyclic groups, wherein the heterocyclic group is selected from any one of pyridine, pyrrole, thiophene, thiazole, and furan.

3. The non-aqueous electrolyte according to claim 1, characterized in that, The content of the compound represented by Formula I or the compound represented by Formula I-3 in the non-aqueous electrolyte is from 0.05% to 3%.

4. The non-aqueous electrolyte according to claim 3, characterized in that, The content of the compound represented by Formula I or the compound represented by Formula I-3 in the non-aqueous electrolyte is 0.5% to 1.5%.

5. The non-aqueous electrolyte according to claim 1, characterized in that, The compound represented by Formula I includes any one or more of the following compounds: Ⅰ-1； Ⅰ-2； Ⅰ-4。 6. The non-aqueous electrolyte according to claim 1, characterized in that, The additive further includes tris(trimethylsilyl)phosphate, wherein the content of tris(trimethylsilyl)phosphate in the non-aqueous electrolyte is 0.5% to 1%; and / or, the additive further includes one or more of fluoroethylene carbonate, propylene-1,3-sulfonyl lactone, and tetravinylsilane.

7. The non-aqueous electrolyte according to claim 1, characterized in that, The organic solvent includes one or more of the following: ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, fluoroethylene carbonate, ethyl formate, ethyl acetate, propyl acetate, ethyl propionate, ethylene glycol dimethyl ether, diethanol diethyl ether, acetonitrile, propionitrile, butyronitrile, and valerate; the content of the organic solvent in the non-aqueous electrolyte is 70% to 80%.

8. The non-aqueous electrolyte according to claim 1, characterized in that, The lithium salt includes one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethyl)sulfonylimide, lithium acetate, lithium methanesulfonate, and lithium trifluoromethylsulfonate, and the lithium salt content in the non-aqueous electrolyte is 14% to 16%.

9. A lithium-ion battery, characterized in that, It includes a positive electrode, a negative electrode, a separator, and the non-aqueous electrolyte as described in any one of claims 1 to 8.

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

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