Secondary battery and electronic device

Abstract

The invention provides a secondary battery and an electronic device, and particularly relates to the technical field of batteries. The secondary battery comprises a positive electrode, a diaphragm, a negative electrode and an electrolyte, the negative electrode comprises a negative electrode current collector and a negative electrode active material layer arranged on at least one side of the negative electrode current collector, and the surface of the negative electrode active material layer is provided with active groups containing O and N elements; the electrolyte comprises a non-aqueous solvent, an electrolyte salt and an additive, wherein the additive comprises any one of R1, R2, R3, R4, R5 and R6 in a first additive formula, wherein the R1, R2, R3, R4, R5 and R6 in the first additive formula are independently selected from halogen, a cyano group, an isocyanate group, substituted or unsubstituted C1-C8 alkyl, substituted or unsubstituted C1-C8 alkoxy, substituted or unsubstituted C2-C6 alkylene and substituted or unsubstituted C2-C6 alkyne. The invention can reduce the gas production in the high-temperature storage process of the battery and effectively improve the cycle performance of the secondary battery.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more particularly to a secondary battery and electronic device. Background Technology

[0002] With the rapid development of the new energy vehicle industry, the market is placing increasingly stringent demands on the range and energy density of power batteries. As a core component of power batteries, the performance of the anode material directly affects the battery's energy density and cycle life. The specific capacity and compaction density of traditional graphite anode materials have approached their theoretical limits, making it difficult to achieve a breakthrough in energy density through improvements to graphite materials themselves in the short term. Silicon-based materials have a theoretical specific capacity more than 10 times that of graphite. Adding silicon to graphite to form a silicon-carbon composite anode can more than double the specific capacity of the anode. Therefore, silicon-carbon composite materials hold promise as a new generation of high-energy-density anode materials.

[0003] However, silicon-based materials face a severe volume expansion problem in practical applications: during lithium-ion insertion / extraction, the volume change of silicon-based materials can reach over 300%. This repeated volume expansion and contraction can cause silicon-carbon anode materials to pulverize, and the drastic volume changes can cause the solid electrolyte interphase (SEI) film on the anode surface to repeatedly rupture and regenerate, continuously consuming active lithium, leading to rapid capacity decay and severely affecting the cycle life of the battery.

[0004] To address the aforementioned issues, a common approach is to improve SEI film stability by adjusting electrolyte additives. For example, adding fluoroethylene carbonate (FEC) to the electrolyte allows it to decompose on the silicon anode surface, generating lithium fluoride (LiF) and oxygen-containing organic compounds (such as -CHF-OCO2-). These products help construct a more stable SEI film, thereby mitigating the negative impact of volume expansion of silicon-based materials. However, FEC has a high reduction barrier, making complete decomposition difficult in the early stages of cycling. Unreacted FEC continues to decompose and generate gas in subsequent cycles, exacerbating battery gas expansion and leading to secondary damage to the SEI film, further intensifying electrolyte decomposition and gas generation. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the present invention provides a secondary battery and electronic device to improve the technical problems of high-temperature gas generation and poor cycle stability of silicon anode batteries.

[0006] To achieve the above and other related objectives, the present invention provides a secondary battery, the secondary battery comprising: a positive electrode, a separator, a negative electrode, and an electrolyte; the negative electrode comprises a negative electrode current collector and a negative electrode active material layer disposed on at least one side of the negative electrode current collector, the surface of the negative electrode active material layer having active groups containing O and N elements; The electrolyte comprises a non-aqueous solvent, an electrolyte salt, and an additive, wherein the additive includes a first additive, the structural formula of which is shown in Formula I: Formula I; In Formula I, R1, R2, R3, R4, R5, and R6 are each independently selected from any one of halogen, cyano, isocyanate group, substituted or unsubstituted C1-C8 alkyl, substituted or unsubstituted C1-C8 alkoxy, substituted or unsubstituted C2-C6 olefin, and substituted or unsubstituted C2-C6 alkyne group; wherein the substituents of the alkyl, alkoxy, olefin, and alkyne groups are each independently selected from any one of halogen, cyano, and isocyanate group.

[0007] In one embodiment of the present invention, the first additive is selected from at least one of the following compounds: Formula I-1; Formula I-2; Formula I-3; Equation I-4; Formula I-5.

[0008] In one embodiment of the present invention, the mass of the first additive is 0.1% to 5% of the total mass of the electrolyte.

[0009] In one embodiment of the present invention, the additive further includes fluoroethylene carbonate, wherein the mass of the fluoroethylene carbonate is 0.5% to 10% of the total mass of the electrolyte.

[0010] In one embodiment of the present invention, the active groups containing O and N elements on the surface of the negative electrode active material layer are formed by treating the negative electrode sheet with glow discharge plasma; the conditions for the glow discharge plasma treatment include: the gas medium is selected from one or more of argon, helium, nitrogen, oxygen, hydrogen and ammonia; the applied power is 50~200W, the treatment time is 300~1800s, and the gas flow rate is 50~300ml / min.

[0011] In one embodiment of the present invention, the non-aqueous solvent includes one or more of cyclic carbonates, linear carbonates, and linear carboxylic acid esters, and the mass of the non-aqueous solvent is 70% to 85% of the total mass of the electrolyte; and / or, the electrolyte salt includes one or more of lithium hexafluorophosphate, lithium difluorosulfonylimide, lithium tetrafluoroborate, lithium difluorooxalate borate, lithium difluorooxalate phosphate, lithium dioxalate borate, and lithium difluorophosphate.

[0012] In one embodiment of the present invention, the second additive includes one or more of vinylene carbonate, 1,3-propanesulfonate lactone, vinyl sulfate, tris(trimethylsilane) phosphate, tetravinylsilane, lithium difluorophosphate, and lithium difluorooxalate phosphate.

[0013] In one embodiment of the present invention, the negative electrode active material layer includes a silicon-based active material, wherein the silicon-based active material is selected from at least one of silicon, silicon-carbon composite materials, and silicon oxide compounds.

[0014] In one embodiment of the present invention, the mass of the silicon-based active material is 70-98% of the total mass of the negative electrode active material layer.

[0015] The present invention also provides an electronic device comprising any of the rechargeable batteries described above. The beneficial effects of this invention are as follows: The secondary battery provided by this invention forms active groups containing O and N elements on the surface of the negative electrode through surface treatment. These active groups significantly enhance the surface polarity of the negative electrode, making it more compatible with the polarity of the electrolyte solvent, thereby enhancing the electrolyte's liquid absorption and retention capabilities. Simultaneously, a first additive is added to the electrolyte. The highly polar -P=O groups in the first additive undergo an affinity addition reaction with the active groups containing O and N elements on the negative electrode surface, forming phosphate esters and silicate derivatives that coat the negative electrode surface. Fluoride ions in the first additive are released during the reaction and simultaneously coat the negative electrode surface as LiF. This interfacial film composed of phosphate esters, silicate derivatives, and LiF has low impedance and high ionic conductivity. It not only isolates the electrolyte from direct contact with the active sites of the negative electrode, forming a good buffer for the negative electrode and effectively mitigating its volume changes to stabilize the negative electrode structure, but also improves the cycle performance of the secondary battery.

[0016] In addition, the first additive can reduce or replace the use of fluoroethylene carbonate in the electrolyte, thereby alleviating the gas generation problem during the high-temperature cycling process of secondary batteries. Detailed Implementation

[0017] 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. 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. In the absence of conflict, the following embodiments and features in the embodiments can be combined with each other.

[0018] 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.

[0019] The term “and / or” as used herein includes any and all combinations of one or more of the related listed items.

[0020] 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.

[0021] 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.

[0022] Unless otherwise specified, "wt%" and "%" in this article refer to the percentage content by mass.

[0023] 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 the chemical and physical properties of the molecule.

[0024] The volume expansion of silicon-based materials during lithium insertion / extraction can reach over 300%. This repeated volume expansion and contraction can cause silicon-carbon anode materials to become powdery. Furthermore, the drastic volume changes can cause the SEI film to repeatedly rupture and regenerate, continuously consuming active lithium, exacerbating battery capacity decay, and severely affecting the battery's cycle life.

[0025] To address these issues, the industry has been adding fluoroethylene carbonate (FEC) to the electrolyte and controlling the amount of FEC to induce electrochemical reduction and decomposition on the negative electrode surface, generating LiF and fluorinated oxygen-containing organic compounds (such as -CHF-OCO2-). The LiF and fluorinated oxygen-containing organic compounds synergistically form a uniform and dense solid electrolyte interphase (SEI) film, physically isolating the silicon negative electrode from direct contact with the electrolyte, preventing continuous electrolyte decomposition, reducing the loss of active materials, and thus improving the cycle stability of the silicon negative electrode. Simultaneously, the SEI film combines the structural stability of the inorganic phase with the flexibility of the organic phase, buffering the dramatic volume expansion during the charging and discharging process of the silicon negative electrode, inhibiting SEI film rupture and reconstruction, and reducing the consumption of active lithium.

[0026] However, the applicant discovered in their research that the high bond energy of the CF bond in the FEC molecular structure leads to a high energy barrier for its electrochemical reduction reaction. During the initial cycling phase (battery activation period), the electron transfer efficiency at the electrode surface is limited, insufficient to drive all FEC molecules to complete reduction and decomposition. Incompletely decomposed FEC remains in the electrolyte, becoming a potential source of subsequent gas generation. With increasing cycle count, especially under high-temperature conditions (where higher temperatures lower the reaction energy barrier), the remaining FEC gradually undergoes reduction and decomposition, releasing gases such as CO2 and HF. Gas accumulation can damage the integrity of the SEI film, exacerbate electrolyte decomposition and gas generation, and simultaneously cause poor electrode interface contact, leading to rapid battery capacity decay, bulging, and even safety risks.

[0027] Based on this, the present invention provides a secondary battery and electronic device, which can reduce gas generation during high-temperature storage and effectively improve the cycle performance of the secondary battery by adjusting the composition of the electrolyte and the structure of the negative electrode active material layer.

[0028] The secondary battery provided by the present invention includes a positive electrode, a separator, a negative electrode, and an electrolyte. The separator is located between the positive electrode and the negative electrode and plays an insulating role to prevent short circuits between the positive electrode and the negative electrode. The electrolyte fills the space between the positive electrode, the separator, and the negative electrode and plays a role in conducting ions.

[0029] Specifically, the negative electrode includes a negative electrode current collector and a negative electrode active material layer disposed on at least one side of the negative electrode current collector. The negative electrode current collector can be a foil material with good conductivity and mechanical strength, such as nickel, titanium, aluminum, silver, stainless steel, or carbon, formed by surface treatment. Besides foil materials, the negative electrode current collector can also be used in any combination of one or more forms, such as film, mesh, porous, foam, or non-woven fabric. There is no particular limitation on the thickness of the negative electrode current collector, as long as it achieves the purpose of this application. For example, the thickness of the negative electrode current collector is 5μm to 12μm. The negative electrode current collector has two surfaces arranged opposite to each other along its thickness direction. The negative electrode active material layer can be disposed on either one surface or on both surfaces. By surface treating the negative electrode active material layer, its surface has a large number of active groups containing O and N elements. The introduction of these active groups can significantly improve the surface polarity of the negative electrode, making it more compatible with the polarity of the electrolyte solvent, thereby enhancing the electrolyte's liquid absorption and retention capacity.

[0030] The electrolyte, serving as a medium for ion conduction, comprises a non-aqueous solvent, an electrolyte salt, and additives. The non-aqueous solvent, as the main component of the electrolyte, dissolves the electrolyte salt and additives. Upon dissolution in the non-aqueous solvent, the electrolyte salt releases a large number of active ions, resulting in good conductivity of the electrolyte. The additives include a first additive, the structural formula of which is shown in Formula I. Formula I; In Formula I, R1, R2, R3, R4, R5, and R6 are each independently selected from any one of the following: halogen, cyano, isocyanate group, substituted or unsubstituted C1-C8 alkyl, substituted or unsubstituted C1-C8 alkoxy, substituted or unsubstituted C2-C6 olefin, or substituted or unsubstituted C2-C6 alkyne group. The halogen is selected from fluorine, chlorine, bromine, iodine, etc. That is, the substituents R1, R2, R3, R4, R5, and R6 in Formula I are independent of each other and do not affect each other. These six substituents can be all the same, or partially the same; for example, R1 and R2 are the same, or R1, R2, and R3 are the same, etc., or they can be completely different substituents. For example, R1 to R6 are all fluorine atoms; or R1 is a cyano, R2 is an isocyanate group, R3 and R4 are C3 alkyl, R5 and R6 are C4 olefin, etc. The C1-C8 alkyl groups mentioned above refer to alkyl groups with 1 to 8 carbon atoms, such as alkyl groups with 1 carbon atom, alkyl groups with 4 carbon atoms, alkyl groups with 6 carbon atoms, or alkyl groups with 8 carbon atoms. Substituted or unsubstituted alkyl groups refer to alkyl groups that can be unsubstituted or substituted with other substituents. Similarly, C1-C8 alkoxy groups refer to alkoxy groups with 1 to 8 carbon atoms, such as alkoxy groups with 1 carbon atom, alkoxy groups with 4 carbon atoms, alkoxy groups with 6 carbon atoms, or alkoxy groups with 8 carbon atoms. Substituted or unsubstituted alkoxy groups refer to alkoxy groups that can be unsubstituted or substituted with other substituents. C2-C6 olefinic groups refer to olefinic groups with 2 to 6 carbon atoms, such as olefinic groups with 2 carbon atoms, olefinic groups with 4 carbon atoms, or olefinic groups with 6 carbon atoms, etc. Substituted or unsubstituted olefinic groups can be either unsubstituted or substituted with other substituents. C2-C6 alkynic groups refer to alkynic groups with 2 to 6 carbon atoms, such as alkynic groups with 2 carbon atoms, alkynic groups with 4 carbon atoms, or alkynic groups with 6 carbon atoms, etc. Substituted or unsubstituted alkynic groups can be either unsubstituted or substituted with other substituents. The substituents in the aforementioned substituted alkyl, substituted alkoxy, substituted olefinic, and substituted alkynic groups are each independently selected from any one of halogen, cyano, or isocyanate groups.

[0031] The negatively charged active groups on the negative electrode surface can orient the positive charge center. The first additive contains a highly polar -P=O group, which can undergo an affinity addition reaction with the active groups containing O and N elements on the negative electrode surface to form phosphate esters and silicate derivatives that coat the negative electrode surface. As the reaction proceeds, fluoride ions in the first additive are released and coated on the negative electrode surface in the form of LiF. This composite interface film containing phosphate esters, silicate derivatives, and LiF has low impedance and high ionic conductivity, balancing ion transport efficiency and interface stability. This composite interface film can isolate the electrolyte from direct contact with the negative electrode active sites, reducing side reactions; it also forms an effective buffer for the negative electrode, mitigating volume changes during charge and discharge, stabilizing the negative electrode structure, and thus improving the cycle performance of the secondary battery.

[0032] In some alternative embodiments, the first additive is selected from at least one of the compounds shown in formulas I-1, I-2, I-3, I-4, and I-5: Formula I-1; Formula I-2; Formula I-3; Equation I-4; Formula I-5.

[0033] The first additive can be any one of the compounds listed above, such as compound I-1, compound I-3, compound I-5, etc.; the first additive can also be any combination of two or more of the listed compounds, such as a combination of compounds I-1 and I-2, or a combination of I-3, I-4 and I-5, etc. When the first additive is a combination of two or more, the proportion of each component in the composition is not limited, and they can be mixed in any proportion.

[0034] The content of the primary additive in the electrolyte and the content of active groups on the negative electrode surface directly affect the quality of the composite interfacial film on the negative electrode surface. Insufficient content of the primary additive or the content of active groups on the negative electrode surface results in an insufficiently dense interfacial film formed by the directional reaction on the negative electrode surface, providing insufficient protection for the negative electrode and easily leading to accelerated capacity decay during cycling. Excessive content of active groups on the negative electrode surface may damage the surface structure of the negative electrode material, thereby deteriorating the cycle performance of the battery. Conversely, excessive content of the primary additive, without sufficient active groups to react with it or with an excessively thick interfacial film, will affect ion conduction, thus impacting the electrochemical performance of the battery.

[0035] In some embodiments, the mass of the first additive is 0.1% to 5% of the total mass of the electrolyte. For example, it can be 0.1%, 1%, 3%, or 5%, etc.

[0036] In one embodiment, active groups containing O and N elements on the surface of the negative electrode active material layer are formed by glow discharge plasma treatment of the negative electrode. During glow discharge plasma treatment of the negative electrode, a nanoscale uneven structure is formed on the surface of the negative electrode, and a large number of active groups containing O and N elements are simultaneously formed in these uneven structures. The content of active groups on the surface of the negative electrode can be controlled by adjusting parameters during glow discharge plasma treatment, such as the applied power and etching time. In this embodiment, the glow discharge plasma treatment of the negative electrode is carried out in one or a mixture of several of the gases selected from Ar, He, N2, O2, H2, and NH3. That is, the plasma treatment can use a single gas listed above, or a mixture of two or more gases, such as Ar, or O2, or a mixture of N2 and O2, etc. Preferably, the glow discharge plasma treatment of the negative electrode is carried out in an O2 atmosphere. During glow discharge plasma treatment, the applied power is 50~200W, the etching time is 300~1800s, and the gas flow rate is 50~300ml / min. For example, the applied power can be 50W, 100W, 150W, or 200W, etc.; the etching time can be 300s, 500s, 1000s, 1500s, or 1800s, etc.; the gas flow rate can be 50ml / min, 100ml / min, 200ml / min, or 300ml / min, etc. When the applied power is low and the etching time is short, there are fewer O and N active groups generated on the negative electrode surface, resulting in insufficient active groups participating in the addition reaction. This leads to an insufficiently dense interfacial film formed by the directional reaction of the first additive on the silicon-based negative electrode surface, providing insufficient protection for the negative electrode and easily causing accelerated capacity decay during cycling. When the applied power is high and the etching time is long, the uneven structure formed on the negative electrode surface is large, which may damage the surface structure of the silicon-based negative electrode material, thereby deteriorating the cycle performance of the battery.

[0037] Adding a first additive to the electrolyte can significantly reduce the amount of FEC used, alleviating the gas generation problem caused by the continuous decomposition of FEC during the high-temperature cycling process of the secondary battery. However, although the gas generation problem is alleviated after the first additive completely replaces FEC, the high-temperature cycling performance of the battery will also decline. Therefore, in some embodiments, the additive also includes FEC. FEC, as a synergistic additive to the first additive, undergoes electrochemical reduction and decomposition on the negative electrode surface to generate a composite SEI film composed of LiF and fluorine-containing oxygen-containing organic matter. This film layer combines the structural stability of the inorganic phase with the flexibility of the organic phase, which can effectively buffer the drastic volume expansion during the charging and discharging process of the negative electrode, and inhibit the rupture and repeated reconstruction of the SEI film, reducing the ineffective consumption of active lithium, thereby significantly improving the cycle stability of the secondary battery. At the same time, FEC can form a synergistic effect with the first additive, further optimizing the overall quality of the interface film oriented on the negative electrode surface.

[0038] In some embodiments, the mass of FEC is 0.5% to 10% of the total electrolyte mass, for example, it can be 0.5%, 1%, 3%, 5%, 7%, or 10%, etc. A complementary content control strategy is adopted between FEC and the first additive: when the content of the first additive is high, the FEC content is correspondingly reduced; conversely, when the content of the first additive is low, the FEC content is adaptively increased. Through this dynamic ratio, a high-quality SEI film can be constructed on the negative electrode surface, ultimately achieving the dual optimization goals of suppressing battery gas generation and improving high-temperature cycling performance.

[0039] In some other embodiments, the additive further includes a second additive, which includes one or more of vinylene carbonate (VC), 1,3-propanesulfonate lactone (PS), vinyl sulfate (DTD), tris(trimethylsilane) phosphate (TMSP), tetravinylsilane (TVSi), lithium difluorophosphate (LiPO2F2), and lithium difluorooxalate phosphate (LiDFOB). That is, those skilled in the art can select the corresponding second additive according to actual needs. The second additives listed above can be used alone or in combination. For example, the second additive may be VC, or DTD, or a combination of PS and TMSP, or a combination of TMSP, TVSi, and LiPO2F2, etc. The amount of the second additive is not limited here and can be added according to actual needs. For example, the mass of the second additive is 2-10% of the total mass of the electrolyte, and more specifically, it can be 3-8%, for example, 3%, 5%, 7%, or 8%, etc.

[0040] The non-aqueous solvent in the electrolyte of this invention can be any organic solvent suitable for batteries. In some embodiments, the non-aqueous solvent includes one or more combinations of cyclic carbonates, linear carbonates, and linear carboxylic acid esters. Cyclic carbonates include one or both of ethylene carbonate (EC) and propylene carbonate (PC), for example, cyclic carbonates can be ethylene carbonate or propylene carbonate, or a mixture of ethylene carbonate and propylene carbonate in any proportion. Linear carbonates include one or more of dimethyl carbonate (DMC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC), that is, linear carbonates can be any of the species listed above, for example, dimethyl carbonate, diethyl carbonate, or methyl ethyl carbonate; or a combination of any two or three of the species listed above mixed in any proportion, such as a combination of dimethyl carbonate and diethyl carbonate, or a combination of dimethyl carbonate and methyl ethyl carbonate, or a combination of diethyl carbonate and methyl ethyl carbonate. The linear carboxylic acid ester is selected from one or more of methyl formate, ethyl formate, butyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, and ethyl butyrate. That is, the linear carboxylic acid ester can be any of the solvents listed above, such as methyl formate, ethyl acetate, or propyl propionate, etc.; the linear carboxylic acid ester can also be a combination of any two or more of the solvents listed above, such as a combination of methyl formate and ethyl formate, or a combination of butyl formate, methyl acetate, and propyl propionate, etc. The non-aqueous solvent of the present invention can be any of the solvents listed above, or any combination of two or more. Preferably, the non-aqueous solvent is a combination of two or more of the solvents listed above. Combining these solvents can mutually enhance their advantages and improve the overall performance of the electrolyte. In some embodiments, the content of the non-aqueous solvent in the electrolyte is 70% to 85%, for example, 70%, 80%, or 85%.

[0041] In some embodiments, the mass of the cyclic carbonate is 10% to 30% of the total mass of the electrolyte, for example, it can be 10%, 20% or 30%, etc.

[0042] In some embodiments, the mass of linear carbonate is 10% to 50% of the total mass of the electrolyte, for example, it can be 10%, 20%, 30%, 40% or 50%, etc.

[0043] In some embodiments, the mass of the linear carboxylic acid ester is 10% to 40% of the total mass of the electrolyte, for example, it can be 10%, 20%, 30% or 40%, etc.

[0044] The electrolyte salt in the electrolyte is selected according to the type of secondary battery. Taking lithium-ion batteries as an example, any lithium salt suitable for lithium-ion batteries can be selected as the electrolyte salt. In some embodiments, the lithium salt includes one or a combination of at least two of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium tetrafluoroborate (LiBF4), lithium difluorooxalate borate (LiDFOB), lithium difluorooxalate phosphate (LiDFOP), lithium dioxalate borate (LiBOB), and lithium difluorophosphate (LiPF2O2). That is, these lithium salts can be used alone or in combination. For example, the lithium salt is lithium hexafluorophosphate, which has better overall performance, or a combination of lithium hexafluorophosphate with other lithium salts, such as a combination of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide, etc.

[0045] In some embodiments, the mass of the lithium salt is 8 to 20% of the total mass of the electrolyte, specifically 8%, 10%, 15%, or 20%.

[0046] In some embodiments, the negative electrode active material layer includes a negative electrode active material. The negative electrode active material of the present invention is a silicon-based active material, selected from at least one of silicon, silicon-carbon composite materials, or silicon oxide compounds. The silicon-carbon composite material includes at least one of carbon-coated nano-silicon material, carbon-coated micron-sized silicon material, or porous carbon-supported nano-silicon material. Exemplarily, the negative electrode active material is elemental silicon, a silicon oxide compound, a porous carbon-supported nano-silicon material, or a combination of a silicon oxide compound and a carbon-coated nano-silicon material, etc. Further, the silicon-based active material of the present invention can exist in particulate form, such as nanoparticles, micron-sized particles, etc. In some embodiments, based on the total mass of the negative electrode active material layer, the mass content of the silicon-based active material is 70-98%, exemplarily 70%, 80%, or 98%, etc.

[0047] The negative electrode active material layer also includes a negative electrode conductive agent, a negative electrode binder, and a thickener. The negative electrode conductive agent is selected from one or more of the following: carbon black, Ketjen black, acetylene black, graphene, carbon nanotubes, carbon nanofibers, porous carbon, etc., or a combination of two or more in any proportion. For example, carbon black, or Ketjen black, or a combination of carbon black and carbon nanotubes, etc. The negative electrode binder includes, but is not limited to, one or more of the following: polyvinyl alcohol, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, styrene-butadiene rubber, or acrylated styrene-butadiene rubber, or a combination of several in any proportion. For example, the negative electrode binder is polytetrafluoroethylene, or polyvinylidene fluoride, or styrene-butadiene rubber, etc. The thickener is selected from sodium carboxymethyl cellulose (CMC-Na) or lithium carboxymethyl cellulose (CMC-Li).

[0048] In some embodiments, the positive electrode 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 nonwoven fabric. The positive current collector has two surfaces disposed opposite each other along its thickness direction, and the positive active material layer can be disposed on one of the surfaces or on both surfaces.

[0049] The positive electrode active material layer includes a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder. 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 some embodiments, the positive electrode active material is selected from layered materials, such as one or more of lithium cobalt oxide (LCO), lithium nickel cobalt manganese oxide (NCM), and lithium nickel cobalt aluminum oxide (NCA); it can also be selected from olivine-structured positive electrode materials, such as at least one of lithium iron phosphate (LFP) and lithium manganese iron phosphate (LFMP); or it can be selected from spinel-structured positive electrode materials, such as at least one of lithium manganese oxide (LMO), lithium nickel manganese oxide (LNMO), and lithium-rich manganese (LMR). These materials can be used alone or in combination. Exemplarily, the positive electrode active material is a combination of lithium manganese iron phosphate and lithium nickel cobalt manganese oxide, or lithium nickel manganese oxide, or lithium cobalt oxide, etc. The positive electrode binder is selected from one or more of the following: polyvinylidene fluoride (PVDF), polyethylene oxide (PEO), polyamide (PA), polyacrylonitrile (PAN), polyacrylate, polyethylene ether, polymethyl methacrylate (PMMA), ethylene-propylene-diene terpolymer (EPDM), polyhexane-propylene, or styrene-butadiene rubber (SBR). The positive electrode conductive agent is selected from one or a combination of two or more of the following: conductive carbon black, Ketjen black, acetylene black, graphene, carbon nanotubes, carbon nanofibers, and porous carbon, in any proportion.

[0050] In some embodiments, the diaphragm may be a conventional diaphragm, a ceramic diaphragm, a polymer diaphragm, a nonwoven fabric diaphragm, or an inorganic-organic composite diaphragm. Exemplarily, the diaphragm may be a single-layer polypropylene (PP) membrane, a single-layer polyethylene (PE) membrane, a double-layer PP / PE membrane, a double-layer PP / PP membrane, or a triple-layer PP / PE / PP membrane. The specific parameters of the diaphragm are not limited; a suitable diaphragm can be selected according to actual needs.

[0051] Those skilled in the art will understand that secondary batteries also include other necessary features, such as a casing. Here, there are no restrictions on the specific structure and material of the casing, which can be selected according to the battery type. For example, if the secondary battery is a pouch battery, the casing can be made of aluminum-plastic film; if the secondary battery is a cylindrical battery, the casing can be made of cylindrical steel, and so on.

[0052] The preparation process of the above-mentioned secondary battery is illustrated below: (1) Preparation of positive electrode The positive electrode active material, positive electrode conductive agent and positive electrode binder are dispersed in a solvent (such as N-methylpyrrolidone, abbreviated as NMP) to form a uniform positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode is obtained.

[0053] (2) Preparation of negative electrode The negative electrode active material, negative electrode binder, emulsifier and negative electrode conductive agent are dispersed in deionized water to form a uniform negative electrode slurry. The negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, a negative electrode sheet is obtained. The negative electrode sheet is placed in a plasma chamber, and after setting parameters such as power, processing time and gas flow, plasma treatment is performed so that the surface of the negative electrode has active groups containing O and N.

[0054] (3) Electrolyte preparation The electrolyte is prepared in a glove box filled with inert argon gas. The actual oxygen content and moisture content in the glove box are less than 1 ppm. The cyclic carbonate, linear carbonate and linear carboxylic acid ester solvents, which are used as non-aqueous solvents, are mixed evenly. The electrolyte salt is added and mixed evenly. After the electrolyte salt is added, the additives are added after the temperature drops below 15°C. The mixture is then mixed evenly to prepare the electrolyte.

[0055] (4) Battery assembly The prepared positive electrode, separator, and negative electrode are placed sequentially, with the separator positioned between the positive and negative electrodes to provide insulation. The bare cell is then obtained by winding or stacking. The bare cell is installed in a casing, and electrolyte is injected into the casing in one or multiple injections to completely immerse the bare cell in the electrolyte. Afterwards, processes such as settling, hot and cold pressing, formation, clamping, and capacity testing are performed to obtain the finished secondary battery.

[0056] The present invention also provides an electronic device comprising the secondary battery described above. This secondary battery can be used in the form of a single cell, a battery module, or a battery pack to power an electronic device.

[0057] This invention does not limit the type of electronic device and can be used for any device that requires battery power, including but not limited to laptops, pen-based computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors, etc.

[0058] 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.

[0059] Example 1 This embodiment provides a secondary battery, which includes a positive electrode, a negative electrode, a separator, and an electrolyte. The specific composition of the battery is as follows: (1) Preparation of the negative electrode: A silicon-carbon composite material with a silicon content of 30% was used as the negative electrode active material, carbon nanotubes as the conductive agent, polyacrylic acid as the binder, and sodium carboxymethyl cellulose as the thickener. They were mixed in a mass ratio of 96:2:1:1, deionized water was added, and a negative electrode slurry was obtained under the action of a vacuum stirrer. The negative electrode slurry was uniformly coated on the negative electrode current collector copper foil. After that, the copper foil was dried at room temperature and then transferred to an oven for drying. After cold pressing and slitting, the negative electrode sheet was obtained.

[0060] (2) Negative electrode surface treatment: The negative electrode was placed in the plasma chamber, the power was set to 100W, and it was treated in an O2 atmosphere for 800s with a gas flow rate of 100ml / min to obtain a negative electrode with active groups on its surface.

[0061] (3) Preparation of the positive electrode: LiNi, the positive electrode active material 0.9 Co 0.05 Mn 0.05 O2, binder polyvinylidene fluoride and conductive agent SuperP are mixed in a mass ratio of 97:2:1, 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 the positive electrode current collector aluminum foil, and then the aluminum foil is dried at room temperature and transferred to an oven for drying. After cold pressing and slitting, the positive electrode sheet is obtained.

[0062] (4) Preparation of electrolyte: In a glove box filled with argon atmosphere, ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), and methyl acetate (MA) are mixed evenly to obtain a non-aqueous solvent. Dried lithium hexafluorophosphate (LiPF6) is added to the non-aqueous solvent and mixed evenly. Then, the compound shown in Formula I-1 as the first additive and FEC are added, along with the second additives vinylene carbonate (VC), vinyl sulfate (DTD), tris(trimethylsilane) phosphate (TMSP), tetravinylsilane (TVSi), and lithium difluorophosphate (LiPO2F2) to obtain the electrolyte. Of these, based on the total mass of the electrolyte as 100%, EC accounts for 25% by mass, EMC accounts for 29% by mass, DMC accounts for 15% by mass, EA accounts for 10% by mass, LiPF6 accounts for 13% by mass, the first additive (the compound shown in Formula I-1) accounts for 0.5% by mass, FEC accounts for 5% by mass, VC accounts for 0.5% by mass, DTD accounts for 0.5% by mass, TMSP accounts for 0.5% by mass, LiPO2F2 accounts for 0.8% by mass, and TVSi accounts for 0.2% by mass.

[0063] (5) Preparation of the diaphragm: A 12μm thick polypropylene (PP) membrane was selected as the separator.

[0064] (6) Preparation of secondary batteries: The prepared negative electrode, separator, and positive electrode are stacked sequentially, with the separator acting as an interlayer between the positive and negative electrodes. The stacked bare cells are then placed into an aluminum-plastic film and vacuum-dried at 100°C to remove moisture. The prepared electrolyte is then injected into the aluminum-plastic film and sealed, followed by electrolyte liquefaction to obtain a soft-pack secondary battery with a capacity of 1.5 Ah.

[0065] Examples 2-4 In each embodiment, when treating the negative electrode surface in step (2), the power applied by the plasma is set to 50W, 150W, and 200W respectively, and the rest is the same as in embodiment 1.

[0066] Examples 5-7 In each embodiment, when treating the negative electrode surface in step (2), the treatment time under O2 atmosphere is set to 300s, 1200s, and 1800s respectively, and the rest is the same as in embodiment 1.

[0067] Examples 8-10 In each embodiment, when treating the negative electrode surface in step (2), the gas flow rate is 50 ml / min, 200 ml / min, and 300 ml / min respectively, and the rest is the same as in embodiment 1.

[0068] Examples 11-14 In each embodiment, the content of the compound shown in Formula I-1 in the electrolyte is 0.1%, 0.3%, 1% and 5% respectively, and the content of FEC is 10%, 7%, 3% and 0.5% respectively. The changes in the content of the compound of Formula I-1 and FEC are compensated by adjusting the amount of non-aqueous solvent, and the proportion between the components in the non-aqueous solvent remains unchanged (that is, the content variable of the additive is proportionally distributed to the components of the non-aqueous solvent). The rest is the same as in Example 1.

[0069] Examples 15-18 In each embodiment, the first additive in the electrolyte is a compound represented by formula I-2, I-3, I-4 and I-5, respectively, and the rest is the same as in Example 1.

[0070] Comparative Example 1 In this comparative example, when treating the negative electrode surface in step (2), the applied power is 50W, the treatment is carried out in an O2 atmosphere for 300s, and the gas flow rate is 50ml / min. The rest is the same as in Example 1.

[0071] Comparative Example 2 In this comparative example, when treating the negative electrode surface in step (2), the applied power is 200W, the treatment is carried out in O2 atmosphere for 1800s, the gas flow rate is 300ml / min, and the rest is the same as in Example 1.

[0072] Comparative Examples 3-5 In each comparative example, the content of the first additive—the compound shown in Formula I-1—in the electrolyte was 0%, 0.05%, and 5%, respectively, and the content of FEC was 20%, 15%, and 0%, respectively. The changes in the content of the compound of Formula I-1 and FEC were compensated by adjusting the amount of non-aqueous solvent, and the proportions between the components in the non-aqueous solvent remained unchanged (i.e., the content variation of the additive was proportionally distributed to the components of the non-aqueous solvent). The rest was the same as in Example 1.

[0073] Comparative Example 6 In this comparative example, step (2) was not performed, that is, the negative electrode was not subjected to plasma treatment, and the rest was the same as in Example 1.

[0074] Comparative Example 7 In this comparative example, step (2) was not performed, that is, the negative electrode was not subjected to plasma treatment, and the rest was the same as in comparative example 3.

[0075] Table 1: Parameter table of Examples 1-18 and Comparative Examples 1-7

[0076] The performance of the soft-pack secondary batteries prepared in each embodiment and comparative example of this invention was tested. The test results are shown in Table 2, and the test methods are as follows: (1) High-temperature cycle life test: Adjust the temperature of the constant temperature chamber to 45℃, stabilize the battery in the chamber for 2 hours, then charge it at a constant current of 1C to 4.25V, then charge it at a constant voltage of 0.05C. After resting for 10 minutes, discharge it at a constant current of 1C to 2.5V. Repeat this charge-discharge cycle 800 times, and record the discharge capacity C1 of the cell at the end of each discharge cycle. Calculate the cycle capacity retention rate of the battery after 800 cycles at 45℃ using the following formula: Cyclic capacity retention (%) = C1 / C0 × 100%.

[0077] (2) Gas production rate during high-temperature storage: The temperature of the constant temperature chamber was adjusted to 25℃. After the battery was left to stand in the chamber for 1 hour, it was charged at a constant current of 0.33C to 4.25V. The initial volume V1 of the battery was recorded using the water displacement method. The battery was then transferred to a constant temperature chamber at 60℃ and stored for 90 days. During these 90 days, the battery was recharged every 15 days. Each time the battery was recharged, it was transferred to the 25℃ constant temperature chamber and left to stand for 2 hours, then charged at a constant current of 0.33C to 4.25V, and then charged at a constant current of 0.05C at 4.25V before being transferred back to the 60℃ constant temperature chamber for further storage. After 90 days of storage, the battery volume V2 was recorded using the water displacement method. The gas production rate during storage was calculated using the following formula: Storage gas production rate = (V2-V1) / V1×100%.

[0078] Table 2: Battery performance of Examples 1-18 and Comparative Examples 1-7

[0079] Refer to Tables 1 and 2: Examples 1-4, where the applied power during negative electrode plasma treatment was adjusted while keeping other conditions constant; Examples 1 and 5-7, where the etching time during negative electrode plasma treatment was adjusted while keeping other conditions constant; Examples 1 and 8-10, where the gas flow rate during negative electrode plasma treatment was adjusted while keeping other conditions constant. The test results show that when plasma treatment is applied to the negative electrode surface, if the applied power is 50-200W, the treatment time is 300-1800s, and the gas flow rate is 50-300ml / min, and these three parameters are within the above ranges and synergistically matched, an appropriate amount of active groups containing O and N can be formed on the negative electrode surface without damaging the surface structure of the negative electrode material. Under these conditions, the active groups on the negative electrode surface can undergo an addition reaction with the first additive to form a dense SEI film, effectively improving the high-temperature cycle stability of the secondary battery and reducing the gas generation during high-temperature storage.

[0080] If the applied power, processing time, and gas flow rate during plasma treatment are all too low (Comparative Example 1), the number of O and N active groups generated on the negative electrode surface will be insufficient, and the interfacial film formed by the reaction with the first additive will be poorly dense, failing to adequately protect the negative electrode. If the applied power, processing time, and gas flow rate during plasma treatment are all too high (Comparative Example 2), the uneven structure on the negative electrode surface will be excessively prominent, which may also damage the surface structure of the silicon-based negative electrode material, ultimately leading to a deterioration in battery cycle performance.

[0081] Compared to Example 1, Comparative Example 6 did not undergo glow discharge plasma treatment on the negative electrode, resulting in the absence of O and N active groups on the negative electrode surface. Although the first additive and FEC were also added to the electrolyte, the high-temperature storage gas production of the battery increased relatively, and the cycle stability decreased. The core reason is that the negative electrode surface lacks O and N active groups that can undergo addition reactions with the first additive, making it difficult for the first additive to form a sufficient amount of interfacial film on the negative electrode surface. Consequently, it cannot effectively protect the negative electrode, ultimately leading to increased gas production and decreased cycle performance.

[0082] In Examples 1 and 11-14, the ratio of the first additive and FEC was adjusted while keeping other conditions constant. The results showed that adding the first additive (compound I-1) to the electrolyte reduced the amount of FEC, thereby decreasing gas production during high-temperature storage. Furthermore, the content of the first additive and the FEC content were inversely correlated: when the first additive completely replaced FEC (Comparative Example 5), the high-temperature gas production reached its lowest level, but cycle stability decreased; when the first additive content was 0 (Comparative Example 3), the battery gas production was highest, and cycle stability was also poor; when only a small amount of the first additive was added and the FEC content was high (Comparative Example 4), compared to Comparative Example 3 without the first additive, the battery gas production was significantly reduced, and cycle stability was improved. Therefore, the first additive and FEC work synergistically, and the battery's overall performance is optimal when the first additive content is 0.1%–5% and the FEC content is 0.5%–10%.

[0083] Examples 1 and 15-18 were conducted with all other conditions remaining constant except for the type of the first additive. Test results showed that all types of the first additive could undergo addition reactions with the O- and N-containing active groups on the negative electrode surface, directionally constructing a dense interfacial protective film on the negative electrode surface. This effectively reduced gas generation during high-temperature battery storage and improved the battery's cycle stability.

[0084] In Comparative Example 7, only excess FEC was added to the electrolyte without any primary additive, resulting in significantly higher gas production during battery storage and poorer high-temperature cycling stability. Compared to Comparative Example 7, the overall performance of the batteries in Examples 1-18 and Comparative Examples 1-6 was significantly improved.

[0085] The secondary battery provided by this invention involves surface treatment of the negative electrode to form active groups containing O and N elements. These active groups significantly enhance the surface polarity of the negative electrode, making it more compatible with the polarity of the electrolyte solvent, thereby improving the electrolyte's absorption and retention capabilities. Simultaneously, a first additive is added to the electrolyte. The highly polar -P=O groups in the first additive undergo an affinity addition reaction with the O and N-containing active groups on the negative electrode surface, forming phosphate esters and silicate derivatives that coat the negative electrode surface. Fluoride ions in the first additive are released during the reaction and simultaneously coat the negative electrode surface as LiF. This interfacial film composed of phosphate esters, silicate derivatives, and LiF exhibits low impedance and high ionic conductivity. It effectively isolates the electrolyte from direct contact with the active sites of the negative electrode, providing a good buffer and mitigating volume changes to stabilize the negative electrode structure, while also improving the cycle performance of the secondary battery. Therefore, this invention effectively overcomes some practical problems in the prior art, thus possessing high utilization value and practical significance.

[0086] 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 secondary battery, characterized in that, include: Positive electrode, separator, negative electrode, and electrolyte; The negative electrode includes a negative electrode current collector and a negative electrode active material layer disposed on at least one side of the negative electrode current collector, wherein the surface of the negative electrode active material layer has active groups containing O and N elements. The electrolyte comprises a non-aqueous solvent, an electrolyte salt, and an additive, wherein the additive includes a first additive, the structural formula of which is shown in Formula I: In Formula I, R1, R2, R3, R4, R5, and R6 are each independently selected from any one of halogen, cyano, isocyanate group, substituted or unsubstituted C1-C8 alkyl, substituted or unsubstituted C1-C8 alkoxy, substituted or unsubstituted C2-C6 olefin, and substituted or unsubstituted C2-C6 alkyne group; wherein the substituents of the alkyl, alkoxy, olefin, and alkyne groups are each independently selected from any one of halogen, cyano, and isocyanate group.

2. The secondary battery according to claim 1, characterized in that, The first additive is selected from at least one of the following compounds:

3. The secondary battery according to claim 1, characterized in that, The mass of the first additive is 0.1% to 5% of the total mass of the electrolyte.

4. The secondary battery according to claim 1, characterized in that, The additive also includes fluoroethylene carbonate, wherein the mass of the fluoroethylene carbonate is 0.5% to 10% of the total mass of the electrolyte.

5. The secondary battery according to claim 1, characterized in that, The active groups containing O and N elements on the surface of the negative electrode active material layer are formed by treating the negative electrode with glow discharge plasma. The conditions for glow discharge plasma treatment include: the gas medium is selected from one or more of argon, helium, nitrogen, oxygen, hydrogen and ammonia; the applied power is 50 to 200 W, the treatment time is 300 to 1800 s, and the gas flow rate is 50 to 300 ml / min.

6. The secondary battery according to claim 1, characterized in that, The non-aqueous solvent includes one or more of cyclic carbonates, linear carbonates, and linear carboxylic acid esters, and the mass of the non-aqueous solvent is 70% to 85% of the total mass of the electrolyte; and / or, the electrolyte salt includes one or more of lithium hexafluorophosphate, lithium difluorosulfonylimide, lithium tetrafluoroborate, lithium difluorooxalate borate, lithium difluorooxalate phosphate, lithium dioxalate borate, and lithium difluorophosphate.

7. The secondary battery according to claim 1 or 4, characterized in that, The additive further includes a second additive, which includes one or more of vinylene carbonate, 1,3-propanesulfonate lactone, vinyl sulfate, tris(trimethylsilane) phosphate, tetravinylsilane, lithium difluorophosphate, and lithium difluorooxalate phosphate.

8. The secondary battery according to claim 1, characterized in that, The negative electrode active material layer includes a silicon-based active material, which is selected from at least one of silicon, silicon-carbon composite materials, and silicon oxide compounds.

9. The secondary battery according to claim 8, characterized in that, The mass of the silicon-based active material is 70-98% of the total mass of the negative electrode active material layer.

10. An electronic device, characterized in that, Includes the secondary battery as described in any one of claims 1 to 9.

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