WO2026001074A1 - 硅碳复合材料、二次电池和电子装置 - Google Patents

硅碳复合材料、二次电池和电子装置

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Publication number
WO2026001074A1
WO2026001074A1 PCT/CN2025/081251 CN2025081251W WO2026001074A1 WO 2026001074 A1 WO2026001074 A1 WO 2026001074A1 CN 2025081251 W CN2025081251 W CN 2025081251W WO 2026001074 A1 WO2026001074 A1 WO 2026001074A1
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WO
WIPO (PCT)
Prior art keywords
silicon
carbon composite
composite material
conductive agent
carbon
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
PCT/CN2025/081251
Other languages
English (en)
French (fr)
Inventor
李鑫
苏义松
谢远森
葛童
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Ningde Amperex Technology Ltd
Original Assignee
Ningde Amperex Technology Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Ningde Amperex Technology Ltd filed Critical Ningde Amperex Technology Ltd
Publication of WO2026001074A1 publication Critical patent/WO2026001074A1/zh
Pending legal-status Critical Current
Anticipated expiration legal-status Critical

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H01M4/386—Silicon or alloys based on silicon
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/628—Inhibitors, e.g. gassing inhibitors, corrosion inhibitors
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • This application relates to the field of electrochemical energy storage, and in particular to a silicon-carbon composite material, a secondary battery using the silicon-carbon composite material, and an electronic device using the secondary battery.
  • rechargeable batteries such as lithium-ion batteries
  • the SEI film formed on the surface of the negative electrode decomposes and produces gas, which affects the cycle performance of lithium-ion batteries.
  • This application provides a silicon-carbon composite material that can improve cycle performance.
  • this application also provides a secondary battery and electronic device using silicon-carbon composite materials.
  • This application provides a silicon-carbon composite material, including a silicon matrix and a first layer at least partially located on the silicon matrix, the first layer including a conductive agent and a silicon-oxygen organic compound.
  • the siloxane groups (Si-O-) in the organic silicon-oxygen compound can react with hydrofluoric acid (HF) in the electrolyte, thereby reducing or eliminating the etching of the silicon substrate by HF, improving the interfacial stability between the silicon substrate and the electrolyte, and enhancing the cycle performance of the secondary battery. Simultaneously, it can also reduce the corrosion of the SEI film by HF, thus improving the stability of the SEI film.
  • HF hydrofluoric acid
  • the organic silicon-oxygen compound can also inhibit the decomposition of the solvent in the SEI film, reducing the organic components in the SEI film, thereby achieving high-voltage stability of the SEI film, reducing lithium plating, and reducing the decomposition and gas generation of the SEI film during over-discharge of the secondary battery, thus improving the gas generation problem during over-discharge.
  • Adding a conductive agent to the first layer helps improve the interfacial conductivity of the silicon-carbon composite material, thereby improving its kinetic performance.
  • the combination of organic silicon-oxygen compound and conductive agent in the silicon-carbon composite material results in excellent cycle performance, expansion performance, and kinetic performance.
  • organic silicon-oxygen compounds can form a network structure, which improves the toughness and strength of the silicon-carbon composite surface, thereby further enhancing the interfacial stability between SEI films and ultimately improving the cycling and expansion performance of the silicon-carbon composite.
  • Conductive agents dispersed within the network structure formed by organic silicon-oxygen compounds can further improve the interfacial conductivity of the silicon-carbon composite, thus enhancing its kinetic properties.
  • the siloxane organic material includes at least one of polymethylhydrosiloxane, polysilsesquioxane, vinyltrimethoxysilane, or vinyltriethoxysilane.
  • This siloxane and silane can reduce or eliminate HF etching of the silicon substrate, improve the interfacial stability between the silicon substrate and the electrolyte, thereby enhancing the cycle performance of the secondary battery. It can also reduce lithium plating and reduce the decomposition and gas generation of the SEI film during over-discharge of the secondary battery, thus improving the gas generation problem during over-discharge.
  • the conductive agent includes at least one of single-walled carbon nanotubes or multi-walled carbon nanotubes.
  • This conductive agent has good conductivity, which is beneficial for improving the conductivity of silicon-carbon composite materials, thus providing a good transport channel for active ions and improving the charge-discharge efficiency and cycle life of the secondary battery.
  • the silicon matrix includes a silicon-carbon material.
  • the silicon-carbon material may include porous carbon material and elemental silicon dispersed on the porous carbon material, wherein the porous carbon material is used to suppress the volume expansion of elemental silicon during cycling.
  • the mass ratio of silicon matrix to conductive agent is 100:(0.5 ⁇ 0.9). This is beneficial for improving the conductivity of silicon-carbon composite materials while also having good specific capacity, and for giving the coated silicon-carbon composite materials excellent kinetic properties.
  • the mass ratio of the conductive agent to the organic silicon oxide is (0.5-5):2. This facilitates the full coating of the organic silicon oxide onto the silicon substrate, improves the integrity of the coating, thereby significantly reducing the etching of the silicon substrate by the electrolyte, and giving the silicon-carbon composite material good conductivity, resulting in good kinetic and cycling performance.
  • the conductive agent has a linear structure with an average diameter of y nm, where 0.5 ⁇ y ⁇ 20. This is beneficial for improving the conductivity of the silicon-carbon composite material while simultaneously enhancing the dispersibility of the conductive agent, thereby improving the rate performance and cycle performance of the silicon-carbon composite material.
  • the average length of the conductive agent is L nm, where 500 ⁇ L ⁇ 1000. This is beneficial for improving the dispersibility of the conductive agent while ensuring that the active ions have good long-range conductivity, thus improving the kinetic properties of the silicon-carbon composite material.
  • the particle size Dv50 of the silicon-carbon composite material is D ⁇ m, 4 ⁇ D ⁇ 13, which helps to reduce the side reactions between the silicon-carbon composite material and the electrolyte, improve the cycle performance of the silicon-carbon composite material, and improve the gas release problem during overcharging of the secondary battery.
  • the thickness of the first layer is H nm, 5 ⁇ H ⁇ 100, which is beneficial to ensure that the silicon-carbon composite material has a good specific capacity, while also enabling the first layer to protect the silicon substrate and improve the gas release problem during overcharging of the secondary battery.
  • H and Dv50 satisfy the relationship: 0.55 ⁇ H/D ⁇ 12.5, which is beneficial for silicon-carbon composite materials to have both good rate performance and cycle performance, and also beneficial for improving the interfacial stability between silicon-carbon composite materials and electrolyte, thereby improving the problem of gas generation in SEI film when the secondary battery is overcharged.
  • the silicon matrix includes silicon-carbon materials, which include silicon and carbon elements. Based on the sum of the masses of silicon and carbon elements in the silicon matrix, the mass percentage of silicon is 41.8% to 57.9%. This is beneficial for the silicon matrix to have good electrical conductivity, while also maximizing the capacity contribution of silicon in the silicon matrix, and giving the silicon-carbon composite material good cycling performance.
  • the average diameter of the conductive agent is ⁇ nm, where 1 ⁇ H/y ⁇ 25. This allows the first layer to have a certain thickness while also possessing good conductivity, which is beneficial for improving the cycle stability and energy density of the secondary battery, as well as reducing over-discharge gas generation.
  • the second aspect of this application also provides a secondary battery, including a cell, the cell including a negative electrode, a positive electrode and an electrolyte, the negative electrode further including a silicon-carbon composite material, wherein the silicon-oxygen organic matter in the silicon-carbon composite material can improve the interfacial stability between the silicon matrix and the electrolyte, and reduce the decomposition and gas generation of the SEI film during secondary battery over-discharge, thereby improving the cycle performance of the secondary battery and improving the gas generation performance of the secondary battery.
  • the cell thickness is H ⁇ sub>0 ⁇ /sub> when the cell voltage is between 3V and 3.95V, and the cell thickness is H ⁇ sub>2 ⁇ /sub> when the cell is discharged to 0.5V, where 0.58 ⁇ H ⁇ sub> 2 ⁇ /sub> / H ⁇ sub>0 ⁇ /sub> ⁇ 1.36.
  • This improves the gas generation problem inside the cell, allowing it to maintain good stability, thereby improving the cycle performance and lifespan of the secondary battery.
  • a third aspect of this application provides an electronic device including a secondary battery.
  • the secondary battery powers the electronic device and includes a silicon-carbon composite material, which improves the cycle life of the secondary battery and thus extends the lifespan of the electronic device.
  • Figure 1 is a scanning electron microscope image of the silicon-carbon composite material prepared in Example 1.
  • Figure 2 is a scanning electron microscope image of the uncoated silicon substrate in Comparative Example 1.
  • Figure 3 is a graph showing the changes in cell thickness and voltage when the cell assembled from the silicon-carbon composite material prepared in Example 1 is discharged from 3.19V to 0.5V.
  • the negative electrode potential continues to rise to the oxidation potential of the solid electrolyte interphase (SEI) membrane, which causes the SEI membrane to oxidize and decompose, generating a large amount of gas, thus affecting the cycle performance and safety performance of the lithium-ion battery.
  • SEI solid electrolyte interphase
  • This application provides a silicon-carbon composite material, comprising a silicon matrix and a first layer at least partially located on the silicon matrix.
  • the first layer includes a conductive agent and a silicon-oxygen organic compound containing Si-O-R.
  • the siloxane groups (Si-O-) in the silicon-oxygen organic compound can react with hydrofluoric acid (HF) in the electrolyte, thereby reducing or eliminating the etching of the silicon matrix by HF, improving the interfacial stability between the silicon matrix and the electrolyte, and enhancing the cycle performance of the secondary battery.
  • HF hydrofluoric acid
  • the silicon-oxygen organic compound can also inhibit the decomposition of the solvent in the SEI film, reducing the organic components in the SEI film, thereby achieving high-voltage stability of the SEI film, reducing lithium plating, and reducing the decomposition and gas generation of the SEI film during over-discharge of the secondary battery, thus improving the gas generation problem during over-discharge of the secondary battery.
  • the addition of a conductive agent to the first layer is beneficial for improving the interfacial conductivity of the silicon-carbon composite material, thereby improving the kinetic performance of the silicon-carbon composite material.
  • the combination of silicon-oxygen organic compounds and conductive agents in silicon-carbon composites gives them excellent cycling performance, expansion performance, and kinetic performance.
  • the first layer may completely cover the outer surface of the silicon substrate, or the first layer may only cover a portion of the outer surface of the silicon substrate.
  • the surface area of the first layer may account for one-half or one-third of the outer surface area of the silicon substrate.
  • the siloxane organic compound includes at least one of polymethylhydrosiloxane, polysilsesquioxane, vinyltrimethoxysilane, or vinyltriethoxysilane.
  • the siloxane or Si-O bonds in this siloxane organic compound can reduce or eliminate the etching of the Si or silicon compound interface in the silicon matrix by HF, improving the interfacial stability between the silicon matrix and the electrolyte, thereby enhancing the cycle performance of the secondary battery. It can also reduce the decomposition and gas generation of the SEI film during over-discharge of the secondary battery, improving the gas generation problem during over-discharge.
  • the network structure formed by the aforementioned siloxane organic compound can also improve the toughness and strength of the silicon-carbon composite surface, thereby further improving the stability of the SEI film, and thus improving the cycle performance and expansion performance of the silicon-carbon composite.
  • the conductive agent dispersed in the network structure formed by the siloxane organic compound can further improve the interfacial conductivity of the silicon-carbon composite, thereby improving the kinetic properties of the silicon-carbon composite.
  • the conductive agent includes at least one of single-walled carbon nanotubes (SWCNTs) or multi-walled carbon nanotubes.
  • SWCNTs single-walled carbon nanotubes
  • This conductive agent exhibits good conductivity, which is beneficial for improving the conductivity of silicon-carbon composite materials. Therefore, it can provide a good transport channel for active lithium ions, reduce the internal resistance of the secondary battery, and thus improve the charge-discharge efficiency and cycle life of the secondary battery.
  • the silicon matrix comprises a silicon-carbon material.
  • the silicon-carbon material may include a porous carbon material and elemental silicon dispersed on the porous carbon material, the porous carbon material being used to suppress the volume expansion of the elemental silicon during cycling.
  • the mass ratio of silicon matrix to conductive agent is 100:(0.5 to 0.9).
  • a mass ratio of conductive agent to organic silicon oxide within this range is beneficial for improving the conductivity of the silicon-carbon composite material while also maintaining good specific capacity, resulting in excellent kinetic properties in the coated silicon-carbon composite material.
  • the mass ratio of conductive agent to organic silicon oxide can be 100:0.5, 100:0.6, 100:0.65, 100:0.7, 100:0.75, 100:0.8, 100:0.85, 100:0.9, or any ratio within the range of any two of the above sets of ratios.
  • the mass ratio of the conductive agent to the organic silicon oxide is (0.5–5):2. This mass ratio within the above range ensures that the organic silicon oxide can adequately coat the silicon substrate, improving the integrity of the coating and thus minimizing electrolyte etching of the silicon substrate. This also results in good conductivity in the silicon-carbon composite material, giving it both good kinetic and cycling performance.
  • the mass ratio of the conductive agent to the organic silicon oxide can be 0.5:2, 1:2, 1.5:2, 2:2, 2.5:2, 3:2, 3.5:2, 4:2, 4.5:2, 5:2, or any ratio within the range of any two of the above ratios.
  • the conductive agent has a linear structure with an average diameter of y nm, where 0.5 ⁇ y ⁇ 20. Within this length range, it is beneficial to improve the conductivity of the silicon-carbon composite material while simultaneously enhancing the dispersibility of the conductive agent, thereby improving the rate performance and cycle performance of the silicon-carbon composite material. If the average diameter of the conductive agent is too large, such as y > 20, it will reduce the conductivity of the silicon-carbon composite material and decrease its cycle performance.
  • the average diameter of the conductive agent is too small, such as y ⁇ 0.5, the dispersion of the conductive agent in the first layer will be poor, resulting in uneven charge distribution on the surface of the silicon-carbon composite material, reducing interfacial stability, thereby reducing the cycle performance of the silicon-carbon composite material, and worsening the over-emission gas generation.
  • the average diameter y of the conductive agent can be 0.5, 1, 2, 3, 5, 7, 9, 10, 12, 15, 17, 18, 20, or any value within the range of any two of the above values.
  • the average length of the conductive agent is L nm, where 500 ⁇ L ⁇ 1000.
  • An average length within this range is beneficial for improving the dispersibility of the conductive agent while ensuring good long-range conductivity of the active lithium ions.
  • the conductive agent is dispersed on the network structure of the silicon-oxygen organic compound, providing an excellent conductive network and improving the rate performance of the silicon-carbon composite material.
  • the average length of the conductive agent can be 500, 600, 700, 800, 900, 1000, or any value within the range of any two of the above values.
  • the particle size Dv50 of the silicon-carbon composite material is D ⁇ m, where 4 ⁇ D ⁇ 13. Within this range, it is beneficial to reduce side reactions between the silicon-carbon composite material and the electrolyte, improve the cycle performance of the silicon-carbon composite material, and alleviate the gas release problem during overcharging of the secondary battery.
  • the particle size D of the silicon-carbon composite material can be 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, or any value within the range of any two of the above values.
  • the thickness of the first layer of the silicon-carbon composite material is H nm, where 5 ⁇ H ⁇ 100. A thickness within this range is beneficial for achieving good specific capacity in the silicon-carbon composite material while also protecting the silicon matrix and mitigating gas release issues during overcharging of the secondary battery.
  • the thickness H of the first layer can be 5, 10, 15, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, or any value within the range of any two of the above values. Preferably, 6 ⁇ H ⁇ 63.
  • H and Dv50 satisfy the relationship: 0.55 ⁇ H/D ⁇ 12.5.
  • Adjusting the relationship between the thickness of the first layer and the particle size D of the silicon-carbon composite material within a suitable range is beneficial for the silicon-carbon composite material to possess both good rate performance and cycle performance.
  • silicon-based composite materials have relatively large particle sizes and strong stability, but weak kinetic performance. By reducing the thickness of the first layer, the silicon-based composite material can maintain good kinetic performance. Simultaneously, it also helps improve the interfacial stability between the silicon-carbon composite material and the electrolyte, thereby mitigating the gas generation problem of the SEI film during overcharging of the secondary battery.
  • the ratio between H and D can be 0.55, 0.8, 0.9, 1, 2, 5, 8, 10, 11, 12, 12.5, or any value within the range of any two of the above values.
  • H/y can be 1, 2, 5, 7, 8, 10, 12, 15, 17, 20, 23, 25, or any value within the range of any two of the above values.
  • the mass percentage of carbon is 38.2% to 61.3%, and the mass percentage of silicon in the silicon matrix is 38.7% to 61.8%.
  • the carbon and silicon content in the silicon matrix within these ranges is beneficial for the silicon matrix to possess good electrical conductivity while also maximizing the capacity contribution of silicon in the silicon matrix, resulting in good cycle performance of the silicon-carbon composite material.
  • the mass percentage of carbon elements in the silicon matrix can be 38.2%, 39%, 41%, 45%, 47%, 49%, 53%, 55%, 58%, 60%, 61.3%, or any value within the range of any two of the above values.
  • the mass percentage of silicon in the silicon matrix can be 38.7%, 39%, 41.8%, 43%, 45%, 48%, 51%, 54%, 56%, 57%, 57.9%, 59%, 61%, 61.8%, or any value within the range of any two of the above values.
  • the mass percentage of silicon is between 41.8% and 57.9%.
  • the preparation method of silicon-carbon composite materials may include, but is not limited to, the following steps: (1) dissolving and dispersing the conductive agent and the silicon-oxygen organic compound containing Si-O-R in a solvent and stirring evenly; (2) adding the silicon matrix material to step (1), stirring and dispersing evenly, and drying to obtain the silicon-carbon composite material.
  • the solvent used in step (1) includes at least one of water, ethanol, ethylene glycol, propylene glycol, and tetrahydrofuran.
  • step (2) the stirring time is 1h to 24h, the stirring speed is 500r/min to 2500r/min, the drying temperature is 92°C to 198°C, and the drying time is 2h to 24h.
  • the above-mentioned method for preparing the silicon substrate includes: using chemical vapor deposition, a silicon source gas is deposited on porous carbon to form silicon, and then a carbon source is introduced, causing the carbon source to form amorphous carbon on the surface of the silicon substrate, thereby obtaining the silicon substrate.
  • the carbon source gas may include, but is not limited to, at least one of methane, acetylene, ethylene, ethane, propyne, propylene, propane, butyne, butene, or butane.
  • the silicon source gas may include, but is not limited to, one or more of silane, disilane, propane, tetrasilane, chlorosilane, dichlorosilane, trichlorosilane, or tetrachlorosilane.
  • the silicon content in the silicon substrate can be adjusted by changing the introduction time of the silicon source gas.
  • the mass ratio of silicon to carbon in the silicon matrix and the mass ratio of silicon matrix, conductive agent, and siloxane organic compound affect the cycle performance, lithium plating performance, and over-discharge gas generation of the silicon-carbon composite material.
  • the mass ratio of silicon matrix to conductive agent is 100:(0.5-0.9); the mass ratio of conductive agent to siloxane organic compound is (0.5-5):2.
  • the mass ratio of silicon matrix, conductive agent, and siloxane organic compound is 100:0.5:2. Increasing the mass ratio of silicon matrix to conductive agent will reduce the cycle performance of the silicon-carbon composite material; decreasing the mass ratio of silicon matrix to conductive agent will reduce the specific capacity of the silicon-carbon composite material and reduce the energy density of the secondary battery.
  • Increasing the mass ratio of silicon matrix to siloxane organic compound will reduce the effect of the silicon-carbon composite material on improving over-discharge gas generation. Decreasing the mass ratio of silicon matrix to siloxane organic compound will reduce the kinetic properties (such as lithium plating performance) and cycle performance of the silicon-carbon composite material. Increasing the mass ratio of organic silicon oxides to conductive agents will reduce the kinetic and cycle performance of silicon-carbon composite materials, while decreasing the mass ratio of organic silicon oxides to conductive agents will reduce the performance of silicon-carbon composite materials in improving the over-discharge gas generation of secondary batteries.
  • the thickness H of the first layer can be changed by adjusting the stirring time and rate when the silicon matrix content is changed.
  • the average diameter y and average length L of the conductive agent can be changed by selecting conductive agent raw materials with different average diameters and average lengths.
  • One embodiment of this application provides a secondary battery, which includes a casing and a battery cell.
  • the battery cell is located inside the casing.
  • the outer casing can be a packaging bag sealed with an encapsulating film (such as aluminum-plastic film), for example, a soft-pack secondary battery.
  • the secondary battery can also be a steel-cased secondary battery, an aluminum-cased secondary battery, etc.
  • the battery cell includes an electrode assembly and an electrolyte.
  • the electrode assembly includes a positive electrode, a negative electrode, and a separator, with the separator disposed between the positive and negative electrode.
  • the electrode assembly can be a stacked structure, formed by stacking the positive electrode, separator, and negative electrode. In other embodiments, the electrode assembly can also be a wound structure, formed by winding the stacked positive electrode, separator, and negative electrode.
  • the negative electrode includes a negative current collector and a negative active layer disposed on the negative current collector.
  • the negative current collector can be at least one of copper foil, nickel foil, stainless steel foil, titanium foil, or carbon-based current collector, or any composite current collector disclosed in the prior art, such as, but not limited to, current collectors formed by combining the aforementioned conductive foil and polymer substrate.
  • the negative active layer contains a negative active material, including the silicon-carbon composite material described above.
  • the negative electrode active layer also includes a binder to bond the negative electrode active material particles, thereby facilitating the formation of the film layer and improving the bonding force between the negative electrode active layer and the negative electrode current collector.
  • the binder may include, but is not limited to, polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon, etc.
  • the negative electrode active layer may further include a conductive material, including but not limited to carbon-based materials, metal-based materials, conductive polymers, or any combination thereof.
  • carbon-based materials may include, but are not limited to, natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof.
  • metal-based materials may include, but are not limited to, metal powders or metal fibers, such as copper, nickel, aluminum, or silver.
  • the conductive polymer may be a polyphenylene derivative.
  • the negative electrode active layer can further contain graphite. Due to the flexibility of graphite, its combination with silicon-carbon composite materials can alleviate the overall volume expansion of the negative electrode active layer. At the same time, using graphite and silicon-carbon composite materials as negative electrode active materials can fully utilize the advantages of both silicon-carbon composite materials and graphite to achieve better electrochemical performance.
  • the positive electrode includes a positive current collector and a positive active layer disposed on the positive current collector.
  • the positive current collector can be aluminum foil or nickel foil, or any composite current collector disclosed in the prior art, such as, but not limited to, current collectors formed by combining the aforementioned conductive foil and polymer substrate.
  • the positive active layer contains a positive active material, which includes compounds that reversibly insert and extract lithium ions (i.e., lithiation intercalation compounds).
  • the positive active material may include a lithium transition metal composite oxide. This lithium transition metal composite oxide contains lithium and at least one element selected from cobalt, manganese, and nickel.
  • the positive active material may include, but is not limited to, lithium cobalt oxide, lithium nickel manganese cobalt oxide, lithium nickel manganese aluminum oxide, lithium iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium iron silicate, lithium vanadium silicate, lithium cobalt silicate, lithium manganese silicate, spinel-type lithium manganese oxide, spinel-type lithium nickel manganese oxide, and lithium titanate.
  • the positive electrode active layer also includes an adhesive for bonding the positive electrode active material particles to facilitate the formation of the film layer, and also to improve the bonding force between the positive electrode active layer and the positive electrode current collector.
  • the adhesive may include, but is not limited to, at least one of polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon.
  • the positive electrode active layer may also include a conductive material, including but not limited to carbon-based materials, metal-based materials, conductive polymers, or any combination thereof.
  • carbon-based materials may include, but are not limited to, natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof.
  • metal-based materials may include, but are not limited to, metal powders or metal fibers, such as copper, nickel, aluminum, or silver.
  • the conductive polymer may be a polyphenylene derivative.
  • the material and shape of the separator used in the electrochemical device of this application are not particularly limited, and can be any technology disclosed in the prior art.
  • the separator comprises a polymer or inorganic material formed from a material stable to the electrolyte of this application.
  • the separator may include a substrate layer and a surface treatment layer.
  • the substrate layer is a nonwoven fabric, membrane, or composite membrane with a porous structure, and the material of the substrate layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide.
  • a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane may be selected.
  • a surface treatment layer is disposed on at least one surface of the substrate layer.
  • the surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by a mixture of polymer and inorganic materials.
  • the inorganic layer includes inorganic particles and a binder.
  • the inorganic particles are selected from at least one of alumina, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate.
  • the binder is selected from at least one of polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl alkoxy, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene.
  • the polymer layer contains a polymer, the polymer material of which is selected from at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl alkoxy, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene).
  • the electrolyte includes an organic solvent, a lithium salt, and optional additives.
  • the organic solvent in the electrolyte of this application may be any organic solvent known in the prior art that can be used as an electrolyte solvent. There are no limitations on the electrolyte used in the electrolyte according to this application; it may be any electrolyte known in the prior art.
  • the additives in the electrolyte according to this application may be any additives known in the prior art that can be used as electrolyte additives.
  • the organic solvent includes, but is not limited to: ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), or ethyl propionate.
  • the organic solvent includes ether solvents, such as at least one selected from 1,3-dioxapentane (DOL) and dimethyl ethylene glycol (DME).
  • the lithium salt includes at least one selected from organic lithium salts or inorganic lithium salts.
  • the lithium salt includes, but is not limited to: lithium hexafluorophosphate ( LiPF6 ), lithium tetrafluoroborate ( LiBF4 ), lithium difluorophosphate ( LiPO2F2 ), lithium bis( trifluoromethanesulfonyl )imide LiN( CF3SO2 ) 2 ( LiTFSI ), lithium bis(fluorosulfonyl)imide Li(N( SO2F ) 2 ) (LiFSI), lithium bis( oxalato )borate LiB( C2O4 ) 2 ( LiBOB ), or lithium difluorooxalatoborate LiBF2 ( C2O4 ) (LiDFOB).
  • the additive includes at least one selected from fluoroethylene carbonate and adiponitrile.
  • the secondary battery of this application includes, but is not limited to, a lithium-ion battery.
  • the thickness of the battery cell is H0 when the voltage of the battery cell is between 3V and 3.95V, and the thickness of the battery cell is H2 when the battery cell is discharged to 0.5V, where 0.58 ⁇ H2 / H0 ⁇ 1.36.
  • the negative electrode in the battery cell includes the aforementioned silicon-carbon composite material.
  • H2 / H0 can be 0.59, 0.6, 0.63, 0.7, 0.8, 0.9, 0.95, 1, 1.1, 1.15, 1.16, 1.2, 1.23, 1.3, 1.32, 1.36, or any value within the range of any two of the above values.
  • the thickness variation of the aforementioned battery cell is related to the interfacial stability within the cell.
  • the Si content, Si-O bond content, and conductivity of the conductive agent in the silicon-carbon composite material affect the interfacial stability of the cell. This application modifies these influencing factors to change the cell thickness at 0.5V discharge, ensuring the H2 / H0 ratio is within a suitable range, thus achieving good interfacial stability.
  • the battery cell discharges from its initial voltage to 2.5V, the volume change of its silicon-carbon composite material will be affected. If the cell continues to discharge from 2.5V, the SEI film will be primarily affected.
  • the cell discharges from its initial voltage of 3V-3.95V to 0.5V, lithium ions are extracted from the negative electrode active layer, reducing the thickness of the negative electrode.
  • the first layer of the silicon-carbon composite material is formed on the silicon substrate, and the good stability of the silicon-carbon composite material itself, as well as the good interfacial stability between the silicon-carbon composite material and the electrolyte, reduces or eliminates the decomposition and gas production of the SEI film, thus reducing the cell thickness.
  • the SEI film's stability is poor, and it will decompose and produce gas, significantly increasing the cell thickness and thus affecting the H2 / H0 ratio.
  • This application also applies secondary batteries to electronic devices, whereby the secondary batteries power the load of the electronic devices.
  • the secondary batteries in the aforementioned electronic devices contain a negative electrode active material, which includes a silicon-carbon composite material.
  • the first layer of the silicon-carbon composite material can reduce the etching of the silicon substrate by HF, improve the stability of the SEI film, thereby improving the cycle performance and charging efficiency of the secondary battery, and consequently improving the lifespan and charging efficiency of the electronic device.
  • Electronic devices may include, but are 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.
  • Single-walled carbon nanotubes and polymethylhydrosiloxane were dissolved and dispersed in a mixed solvent of water and ethanol at a mass ratio of 0.5:2 and stirred evenly to obtain a mixed slurry; (2) 100g of silicon matrix (based on the sum of silicon and carbon elements in the silicon matrix, the mass ratio of carbon element is 50.7% and the mass ratio of silicon element is 49.3%) was added to the mixed slurry in step (1), the stirring speed was 1000r/min, and after stirring for 4h, the mixture was evenly dispersed and dried at 168°C to obtain a silicon-carbon composite material.
  • the Dv50 of the silicon-carbon composite material was 9 ⁇ m, the average diameter of the single-walled carbon nanotubes was 5nm, and the average length was 800nm.
  • the negative electrode sheet Preparation of the negative electrode sheet: The silicon-carbon composite material, artificial graphite, styrene-butadiene rubber (SBR) as the negative electrode binder, and carboxymethyl cellulose (CMC) as the negative electrode dispersant were mixed in a mass ratio of 10:88:1.6:0.4. Deionized water was then added as a solvent and stirred until homogeneous, resulting in a negative electrode slurry with a solid content of 45 wt%. The negative electrode slurry was uniformly coated onto one surface of a 6 ⁇ m thick copper foil used as the negative electrode current collector.
  • SBR styrene-butadiene rubber
  • CMC carboxymethyl cellulose
  • the copper foil was dried at 85°C for 4 hours to obtain a negative electrode sheet with a single-sided coating of the negative electrode active material layer, with a coating thickness of 80 ⁇ m. After cold pressing, cutting, and slitting, the sheet was dried under vacuum at 120°C for 12 hours to obtain a negative electrode sheet with dimensions of 76.6 mm ⁇ 875 mm.
  • the cold pressing pressure was 20 tons (t), and the compaction density of the negative electrode sheet was 1.78 g/ cm3 .
  • Lithium cobalt oxide positive electrode active material
  • acetylene black positive electrode conductive agent
  • PVDF polyvinylidene fluoride
  • NMP N-methylpyrrolidone
  • the positive electrode slurry was uniformly coated on one surface of a 13 ⁇ m thick aluminum foil for the positive electrode current collector and dried at 85 °C to obtain a single-sided positive electrode sheet with a positive electrode active material layer thickness of 130 ⁇ m.
  • the positive electrode sheet was dried under vacuum at 85 °C for 4 hours to obtain a positive electrode sheet with a size of 74 mm ⁇ 867 mm.
  • the cold pressing pressure was 20 t, and the compaction density of the positive electrode sheet was 4.15 g/ cm3 .
  • Electrolyte preparation In a dry argon-atmospheric glove box, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and ethyl propionate (EP) were mixed in a mass ratio of 3:1:3:3. Then, lithium salt LiPF6 was added and mixed thoroughly to obtain the electrolyte. Based on the mass of the electrolyte, the lithium salt content was 12.5%, with the remainder being organic solvent.
  • EC ethylene carbonate
  • PC propylene carbonate
  • DEC diethyl carbonate
  • EP ethyl propionate
  • Assembling lithium-ion batteries The prepared positive electrode, separator, and negative electrode are stacked sequentially, with the separator positioned between the positive and negative electrodes to provide isolation. The electrodes are then wound to form the electrode assembly. After welding the tabs, the electrode assembly is placed in an aluminum-plastic film packaging bag and dried in an 80°C vacuum oven for 12 hours to remove moisture. The prepared electrolyte is then injected. The battery undergoes vacuum sealing, settling, formation (0.02C constant current charging to 3.5V, then 0.1C constant current charging to 3.9V), degassing, and edge trimming processes to obtain the lithium-ion battery (i.e., the cell).
  • Example 2 The difference between Examples 2 to 7 and Example 1 is that the type of organic silicon oxide or the mass ratio of silicon matrix to conductive agent or the mass ratio of conductive agent to organic silicon oxide are changed, while the rest of the preparation process is the same as in Example 1.
  • Example 8 to 10 The difference between Examples 8 to 10 and Example 1 is that the mass ratio of silicon in the silicon matrix is changed, while the rest of the preparation process is the same as that of Example 1.
  • Example 11 The difference between Examples 11 and 12 and Example 1 is that the particle size Dv50 of the silicon-carbon composite material is changed, while the rest of the preparation process is the same as that of Example 1.
  • Example 13 The difference between Examples 13 to 16 and Example 1 is that the average diameter or average length of the conductive agent in the silicon-carbon composite material is changed, while the rest of the preparation process is the same as in Example 1.
  • Example 17 The difference between Example 17 and Example 1 is that the stirring time in step (2) of preparing the silicon-carbon composite material is changed.
  • the stirring time is 10 min at a stirring speed of 1000 r/min, and the thickness of the first layer is 5 nm.
  • the rest of the preparation process is the same as in Example 1.
  • Example 18 The difference between Example 18 and Example 1 is that the stirring time in step (2) of preparing the silicon-carbon composite material is changed.
  • the stirring time is 1h at a stirring speed of 1000r/min, and the thickness of the first layer is 36nm.
  • the rest of the preparation process is the same as in Example 1.
  • Example 19 The difference between Example 19 and Example 1 is that the stirring time in step (2) of preparing the silicon-carbon composite material is changed.
  • the stirring time is 8 hours at a stirring speed of 1000 r/min, and the thickness of the first layer is 72 nm.
  • the rest of the preparation process is the same as in Example 1.
  • Example 20 The difference between Example 20 and Example 1 is that the stirring time in step (2) of preparing the silicon-carbon composite material is changed.
  • the stirring speed is 1000 r/min and the stirring time is 24 h, resulting in a first layer with a thickness of 100 nm.
  • the rest of the preparation process is the same as in Example 1.
  • Example 1 The difference from Example 1 is that the surface of the silicon matrix was not coated during the preparation of the silicon-carbon composite material.
  • the specific material composition is shown in Table 1.
  • Example 1 The difference from Example 1 is that in the process of preparing silicon-carbon composite material, the surface of the silicon matrix is only coated with a conductive agent and not with silicon-oxygen organic matter.
  • the specific material composition is shown in Table 1.
  • Example 1 The difference from Example 1 is that in the process of preparing silicon-carbon composite material, the surface of the silicon matrix is only coated with silicon-oxygen organic matter and not with conductive agent.
  • the specific material composition is shown in Table 1.
  • the silicon-carbon composite materials and lithium-ion batteries prepared in the examples and comparative examples were subjected to the following tests, as shown in Tables 1 to 4.
  • the particle size distribution of the silicon-based composite material was tested using a Malvern particle size analyzer (Master Sizer 2000).
  • the sample preparation method was as follows: approximately 0.02 g of powder sample was added to a 50 ml clean beaker, followed by approximately 20 ml of deionized water. Then, 3 drops of sodium dodecyl sulfate surfactant were added to completely disperse the powder in the water. The mixture was then ultrasonically cleaned for 5 minutes using a 120W ultrasonic cleaner to obtain the powder particle size test sample. In the volumetric particle size distribution of the material, the particle size reaching 50% of the cumulative volume was defined as Dv50, starting from the smallest particle size.
  • the silicon-carbon composite material was sliced using focused ion beam (FIB) and characterized by high-resolution transmission electron microscopy (HRTEM, Talos F200X). Within the same selected area (500,000x magnification), the first layer in the particles was observed. The thickness of the first layer in the silicon-carbon composite material particles was measured. The thickness at fifty different locations in the first layer was randomly selected. The thickness could be obtained by measuring with a scale. The average of the fifty thickness values was calculated to obtain the thickness of the first layer.
  • FIB focused ion beam
  • HRTEM high-resolution transmission electron microscopy
  • a 30,000kx magnified image was captured using a scanning electron microscope (SEM). The image was processed using the image analysis software ImageJ. The length and diameter of 20 CNTs were then measured. The average length of the CNTs was calculated by taking the average length of the 20 CNTs, and the average diameter of the CNTs was calculated by taking the average diameter of the 20 CNTs.
  • the mass percentages of silicon and carbon elements can be obtained.
  • the lithium-ion battery was placed in a constant temperature chamber at 25°C ⁇ 1°C for 30 minutes, then charged at a constant current of 0.5C to 4.45V, and then charged at a constant voltage of 4.45V to 0.025C. After being placed in a constant temperature chamber for 5 minutes, it was discharged at 0.5C to 3.0V. This constitutes one charge-discharge cycle.
  • the initial cycle discharge capacity C0 of the lithium-ion battery was recorded. This cycle was then repeated 500 times.
  • the cycle discharge capacity C1 of the 500th cycle was recorded.
  • the 500-cycle capacity retention rate C1/C0 ⁇ 100%.
  • the initial thickness of the battery cell (with a voltage of 3V to 3.95V) is measured using a micrometer and recorded as H0. Then, the cell is discharged to 0.5V at 0.01C and the thickness of the cell is measured using a micrometer and recorded as H2 . The ratio of H2 to H0 is then calculated.
  • the lithium-ion batteries were charged to 50% SOC at 0.5C to obtain the 50% SOC state.
  • the length, width, and thickness of each lithium-ion battery at 50% SOC were measured, and the volume of the lithium-ion battery was calculated.
  • the volumetric energy density of the lithium-ion battery was calculated as follows: lithium-ion battery discharge capacity ⁇ average discharge voltage of lithium-ion battery / lithium-ion battery volume.
  • the upper limit of the charging voltage for the lithium-ion battery is 4.45V, and the discharge cutoff voltage is 3.0V.
  • the lithium-ion battery was placed in a constant temperature chamber at 25°C ⁇ 1°C for 30 minutes, then charged at a constant current of 1.2C to 4.45V, followed by constant voltage charging at 4.45V to 0.025C. After a 5-minute rest, it was discharged at 0.5C to 3.0V, completing one charge-discharge cycle. This cycle was repeated 10 times. Then, the battery was charged at a constant current of 4C to 4.45V, followed by constant voltage charging at 4.45V to 0.025C, and then rested for 5 minutes. The lithium-ion battery was then disassembled to observe lithium plating.
  • the 1.2C was adjusted to 1.6C, 2C, 2.4C, 2.6C, 2.8C, 3C, 3.1C, 3.2C, 3.4C, 3.8C, or 4C, and lithium plating was observed at different charging rates.
  • the determination is based on the contamination status of the separator in contact with the negative electrode during full-charge disassembly. If the separator in contact with the negative electrode is white as a whole and the area showing gray is less than 2%, it is determined that there is no lithium plating.
  • Figure 1 is a scanning electron microscope (SEM) image of the silicon-carbon composite material prepared in Example 1
  • Figure 2 is a SEM image of the uncoated silicon substrate in Comparative Example 1. From Figures 1 and 2, single-walled carbon nanotubes with a linear structure are formed on the surface of the silicon substrate, and the silicon substrate surface is coated with a first layer.
  • Figure 3 shows the battery cell assembled in Example 1, the trend of the initial voltage of the battery cell from 3.19V to 0.5V, and the trend of the battery cell thickness. During the discharge process, the thickness of the battery cell gradually decreases, reaching 4 mm at 0.5V.
  • Table 2 Note: In Tables 1 and 2, "/" indicates that no parameters have been added or there are no related parameters.
  • the first layer simultaneously contains a conductive agent and an organic silicon oxide compound, which improves the cycle retention rate of the lithium-ion battery and reduces lithium plating.
  • the first layer on the silicon substrate needs to simultaneously coat a conductive agent and an organic silicon oxide compound, as only one of the conductive agent and the organic silicon oxide compound will reduce the cycle retention rate or lithium plating performance of the lithium-ion battery.
  • the silicon-carbon composite material has both an organic silicon oxide compound and a conductive agent on the surface of the silicon substrate, the cycle performance of the silicon-carbon composite material is improved and lithium plating is reduced.
  • adjusting the mass ratio of the silicon substrate to the conductive agent, the mass ratio of the conductive agent to the organic silicon oxide compound, or using different types of organic silicon oxide compounds affects the Si-O bond content in the silicon-carbon composite material, which in turn affects the stability of the SEI film in the cell, thereby affecting the H2 / H0 ratio.
  • the H2 / H0 ratio decreased in Examples 1 to 7, which also indicates that the presence of both silicon-oxygen organic matter and conductive agent in the silicon-carbon composite material reduces or eliminates the decomposition gas generation of the SEI film.
  • adjusting the silicon and carbon content in the silicon matrix affects the cycle performance and lithium plating performance of the silicon-carbon composite material.
  • a suitable silicon content in the silicon matrix contributes to good cycle performance and lithium plating performance in the secondary battery.
  • adjusting the particle size Dv50 of the silicon-carbon composite material when both Dv50 and H/D are within suitable ranges, results in secondary batteries that exhibit good energy density while also maintaining good cycle performance and lithium plating performance.
  • the stirring time was adjusted to adjust the thickness of the first layer in the silicon-carbon composite material.
  • the thickness of the first layer is within a suitable range, the corresponding secondary battery has good energy density and also good cycle performance and lithium plating performance.

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Abstract

本申请提供一种硅碳复合材料、二次电池和电子装置。硅碳复合材料包括硅基体以及至少部分位于硅基体上的第一层，第一层包括导电剂和硅氧有机物。本申请提供的硅碳复合材料提高硅基体与电解液的界面稳定性，提升二次电池的循环性能，还能减少在二次电池过放时SEI膜的分解产气，改善二次电池过放时的产气问题。

Description

硅碳复合材料、二次电池和电子装置 技术领域
本申请涉及电化学储能领域，尤其是涉及一种硅碳复合材料、应用所述硅碳复合材料的二次电池以及应用所述二次电池的电子装置。
背景技术
近年来，二次电池(如锂离子电池)在新能源汽车和大规模储能领域得到了迅猛发展。然而，二次电池在充电过程中，负极表面形成的SEI膜会发生分解并产气，且影响锂离子电池的循环性能。
发明内容
本申请提供一种能够提高循环性能的硅碳复合材料。
另，本申请还提供一种应用硅碳复合材料的二次电池和电子装置。
本申请提供一种硅碳复合材料，包括硅基体以及至少部分位于硅基体上的第一层，第一层包括导电剂和硅氧有机物。
当本申请的硅碳复合材料应用于二次电池时，硅氧有机物中的硅氧基团(Si-O-)能够与电解液的氢氟酸(HF)发生反应，进而减少或消除HF对硅基体的刻蚀，提高硅基体与电解液的界面稳定性，提升二次电池的循环性能；同时也可以减少HF对SEI膜的腐蚀，从而提高SEI膜的稳定性。再者，硅氧有机物在提高SEI膜的稳定性的同时，还能够抑制SEI膜中溶剂的分解，减少SEI膜中的有机组分，进而实现SEI膜的高压稳定性，减少析锂，并减少二次电池过放时SEI膜的分解产气，改善二次电池过放时的产气问题。第一层中加入导电剂利于提高硅碳复合材料的界面导电性，从而利于提高硅碳复合材料的动力学性能。硅碳复合材料中结合硅氧有机物和导电剂，使得硅碳复合材料在具有良好的循环性能、膨胀性能以及动力学性能。同时，硅氧有机物能够形成网络结构，该网络结构能够提高硅碳复合材料表面的韧性和强度，从而进一步提高SEI膜之间的界面稳定性，进而提高硅碳复合材料的循环性能和膨胀性能。导电剂分散于硅氧有机物形成的网络结构中，能够进一步提高硅碳复合材料的界面导电性，从而提高硅碳复合材料的动力学性能。
基于第一方面，在一些可能的实施方式中，硅氧有机物包括聚甲基氢硅氧烷、聚倍半硅氧烷、乙烯基三甲氧基硅烷或乙烯基三乙氧基硅烷中的至少一种。该硅氧烷和硅烷能够减少或消除HF对硅基体的刻蚀，提高硅基体与电解液的界面稳定性，进而提升二次电池的循环性能，还能减少析锂并减少二次电池过放时SEI膜的分解产气，改善二次电池过放时的产气问题。
基于第一方面，在一些可能的实施方式中，导电剂包括单壁碳纳米管或多壁碳纳米管中的至少一种。该导电剂具有较好的导电性，利于提高硅碳复合材料的导电性，因此可为活性离子提供良好的传输通道，提高二次电池的充放电效率和循环寿命。基于第一方面，在一些可能的实施方式中，硅基体包括硅碳材料。硅碳材料可包括多孔碳材料和分散于多孔碳材料上的单质硅，多孔碳材料用于抑制单质硅在循环过程中的体积膨胀。
基于第一方面，在一些可能的实施方式中，硅基体和导电剂的质量比为100：(0.5～0.9)。利于在提高硅碳复合材料的导电性的同时还具有较好的比容量，并使得包覆后的硅碳复合材料具有优异的动力学性能。
基于第一方面，在一些可能的实施方式中，导电剂和硅氧有机物的质量比为(0.5～5)：2。利于硅氧有机物充分包覆于硅基体上，利于提高硅氧有机物包覆于硅基体上的完整性，从而以充分减少电解液对硅基体的刻蚀，并使得硅碳复合材料具有良好的导电性，使得硅碳复合材料兼具良好的动力学性能和循环性能。
基于第一方面，在一些可能的实施方式中，导电剂为线状结构，导电剂的平均直径为ynm，0.5≤y≤20，利于在提高导电剂的分散性的同时提高硅碳复合材料的电导率，从而提高硅碳复合材料的倍率性能和循环性能。导电剂的平均长度为Lnm，500≤L≤1000。利于在提高导电剂的分散性的同时使得活性离子具有良好的长程导电能力，提高硅碳复合材料的动力学性能。
基于第一方面，在一些可能的实施方式中，硅碳复合材料的粒径Dv50为Dμm，4≤D≤13，利于减小硅碳复合材料与电解液的副反应，提高硅碳复合材料的循环性能并改善二次电池过充时的放气问题。
基于第一方面，在一些可能的实施方式中，第一层的厚度为Hnm，5≤H≤100，利于在使得硅碳复合材料具有较好的克容量的同时，还可使得第一层能够保护硅基体并改善二次电池过充时的放气问题。
基于第一方面，在一些可能的实施方式中，H和Dv50之间满足关系式：0.55≤H/D≤12.5，利于使得硅碳复合材料兼具较好的倍率性能和循环性能，还利于提升硅碳复合材料和电解液的界面稳定性，进而改善在二次电池过充时SEI膜的产气问题。
基于第一方面，硅基体包括硅碳材料，硅碳材料包括硅元素和碳元素，基于硅基体中硅元素和碳元素的质量之和，硅元素的质量占比为41.8％至57.9％。利于使得硅基体具有良好的导电性的同时，利于发挥硅基体中硅的容量贡献，并使得硅碳复合材料具有良好的循环性能。
基于第一方面，在一些可能的实施方式中，导电剂的平均直径为ynm，1≤H/y≤25。利于第一层具有一定的厚度的同时，还具有良好的导电性，利于改善二次电池的循环稳性能、能量密度并改善二次电池的过放产气。
本申请第二方面还提供一种二次电池，包括电芯，电芯包括负极极片、正极极片和电解液，负极极片还包括硅碳复合材，硅碳复合材料中硅氧有机物能够提高硅基体与电解液的界面稳定性，并减少在二次电池过放下SEI膜的分解产气，提升二次电池的循环性能并改善二次电池的产气性能。
基于第二方面，在一些可能的实施方式中，在电芯电压为3V至3.95V时电芯的厚度为H0，电芯放电至0.5V时电芯的厚度为H2，0.58<H2/H0≤1.36。电芯内部的产气问题得到改善，其可保持良好的稳定性，从而提高二次电池的循环性能和使用寿命。
本申请第三方面提供一种电子装置，包括二次电池。二次电池为电子装置供电，二次电池中包括硅碳复合材料，能够提高二次电池的循环寿命，进而提高电子装置的使用寿命。
附图说明
本申请的上述和/或附加的方面和优点从结合下面附图对实施例的描述中将变得明显和容易理解，其中：
图1为实施例1制备的硅碳复合材料的扫描电子显微镜图。
图2为对比例1中未经任何包覆的硅基体的扫描电子显微镜图。
图3为实施例1制备的硅碳复合材料组装的电芯从3.19V放电至0.5V时，电芯厚度和电压变化的曲线图。
具体实施方式
下面对本申请实施例中的技术方案进行清楚、详细地描述，显然，所描述的实施例是本申请一部分实施例，而不是全部的实施例。除非另有定义，本文所使用的所有的技术和科学术语与属于本申请的技术领域的技术人员通常理解的含义相同。在本申请的说明书中所使用的术语只是为了描述具体的实施例的目的，不是旨在于限制本申请。
在相关技术中，锂离子电池在过放过程中，锂离子电池持续放电，负极电势持续升高至固体电解质界面膜(SEI膜)氧化分解的氧化电位，就会使SEI膜发生氧化分解并产生大量的气体，影响锂离子电池的循环性能和安全性能。
本申请提供一种硅碳复合材料，包括硅基体以及至少部分位于硅基体上的第一层，第一层包括导电剂和含有Si-O-R的硅氧有机物。当本申请的硅碳复合材料应用于二次电池时，硅氧有机物中的硅氧基团(Si-O-)能够与电解液的氢氟酸(HF)发生反应，进而减少或消除HF对硅基体的刻蚀，提高硅基体与电解液的界面稳定性，提升二次电池的循环性能；同时也可以减少HF对SEI膜的腐蚀，从而提高SEI膜的稳定性。硅氧有机物在提高SEI膜的稳定性的同时，还能够抑制SEI膜中溶剂的分解，减少SEI膜中的有机组分，进而实现SEI膜的高压稳定性，减少析锂，并减少二次电池过放时SEI膜的分解产气，改善二次电池过放时的产气问题。第一层中加入导电剂利于提高硅碳复合材料的界面导电性，从而利于提高硅碳复合材料的动力学性能。硅碳复合材料中结合硅氧有机物和导电剂，使得硅碳复合材料在具有良好的循环性能、膨胀性能以及动力学性能。
在一些实施例中，第一层可以完全包覆于硅基体的外表面，或者第一层仅包覆于硅基体的外表面的部分区域上，比如，第一层的表面积可以占硅基体的外表面积的二分之一或三分之一。
在一些实施例中，硅氧有机物包括聚甲基氢硅氧烷、聚倍半硅氧烷、乙烯基三甲氧基硅烷或乙烯基三乙氧基硅烷中的至少一种。该硅氧有机物中硅氧烷或Si-O键能够减少或消除HF对硅基体中Si或硅化合物材料界面的刻蚀，提高硅基体与电解液的界面稳定性，进而提升二次电池的循环性能，还能减少在二次电池过放时SEI膜的分解产气，改善二次电池过放时的产气问题。同时，上述硅氧有机物形成的网络结构还能够提高硅碳复合材料表面的韧性和强度，从而进一步提高SEI膜的稳定性，进而提高硅碳复合材料的循环性能和膨胀性能。导电剂分散于硅氧有机物形成的网络结构中，还能够进一步提高硅碳复合材料的界面导电性，从而提高硅碳复合材料的动力学性能。
在一些实施例中，导电剂包括单壁碳纳米管(SWCNT)或多壁碳纳米管中的至少一种。该导电剂具有较好的导电性，利于提高硅碳复合材料的导电性，因此可为活性锂离子提供良好的传输通道，降低二次电池的内阻，从而提高二次电池的充放电效率和循环寿命。
在一些实施例中，硅基体包括硅碳材料。硅碳材料可包括多孔碳材料和分散于多孔碳材料上的单质硅，多孔碳材料用于抑制单质硅在循环过程中的体积膨胀。
在一些实施例中，硅基体和导电剂的质量比为100：(0.5～0.9)。导电剂和硅氧有机物的质量比在上述范围内，利于在提高硅碳复合材料的导电性的同时还具有较好的比容量，并使得包覆后的硅碳复合材料具有优异的动力学性能。在一些实施例中，导电剂和硅氧有机物的质量比可以为100：0.5、100：0.6、100：0.65、100：0.7、100：0.75、100：0.8、100：0.85、100：0.9或在上述任意两组比值所组成的范围内的任一比值。
在一些实施例中，导电剂和硅氧有机物的质量比为(0.5～5)：2。导电剂和硅氧有机物的质量比在上述范围内，以使得硅氧有机物能够充分包覆于硅基体上，利于提高硅氧有机物包覆于硅基体上的完整性，从而以充分减少电解液对硅基体的刻蚀，并使得硅碳复合材料具有良好的导电性，使得硅碳复合材料兼具良好的动力学性能和循环性能。在一些实施例中，导电剂和硅氧有机物的质量比可以为0.5：2、1：2、1.5：2、2：2、2.5：2、3：2、3.5：2、4：2、4.5：2、5：2或在上述任意两组比值所组成的范围内的任一比值。
在一些实施例中，导电剂为线状结构，导电剂的平均直径为ynm，0.5≤y≤20；在上述长度范围内，利于在提高导电剂的分散性的同时提高硅碳复合材料的电导率，从而提高硅碳复合材料的倍率性能和循环性能。若导电剂的平均直径过大，如y＞20，会降低硅碳复合材料的电导率，降低硅碳复合材料的循环性能；若导电剂的平均直径过小，如y＜0.5，导电剂在第一层中的分散性不佳，使得硅碳复合材料表面的电荷分布不均匀，降低界面稳定性，从而降低硅碳复合材料的循环性能，且会恶化过放产气。在一些实施例中，导电剂的平均直径y可以为0.5、1、2、3、5、7、9、10、12、15、17、18、20或在上述任意两个数值所组成的范围内的任一值。
在一些实施例中，导电剂的平均长度为Lnm，500≤L≤1000。导电剂的平均长度在上述范围内，利于在提高导电剂的分散性的同时使得活性锂离子具有良好的长程导电能力，导电剂分散于硅氧有机物的网络结构上，使得导电剂提供优异的导电网络，提高硅碳复合材料的倍率性能。在一些实施例中，导电剂的平均长度可以为500、600、700、800、900、1000或在上述任意两个数值所组成的范围内的任一值。
在一些实施例中，硅碳复合材料的粒径Dv50为Dμm，4≤D≤13。在上述范围内，利于减小硅碳复合材料与电解液的副反应，提高硅碳复合材料的循环性能并改善二次电池过充时的放气问题。在一些实施例中，硅碳复合材料的粒径D可以为4、5、6、7、8、9、10、11、12、13或在上述任意两个数值所组成的范围内的任一值。
在一些实施例中，硅碳复合材料的第一层的厚度为Hnm，5≤H≤100。第一层的厚度在上述范围内，利于在使得硅碳复合材料具有较好的克容量的同时，还可使得第一层能够保护硅基体并改善二次电池过充时的放气问题。在一些实施例中，第一层的厚度H可以为5、10、15、25、30、35、40、45、50、60、70、80、90、100或在上述任意两个数值所组成的范围内的任一值。优选地，6≤H≤63。
在一些实施例中，H和Dv50之间满足关系式：0.55≤H/D≤12.5。调控第一层的厚度以及硅碳复合材料的粒径D的关系在合适的范围内，利于使得硅碳复合材料兼具较好的倍率性能和循环性能，如硅基复合材料粒径相对较大，稳定性强，但动力学性能较弱，通过减小第一层的厚度，使得硅基复合材料保持较好的动力学性能。同时，还利于提升硅碳复合材料和电解液的界面稳定性，进而改善在二次电池过充时SEI膜的产气问题。在一些实施例中，H和D之间的比值可以为0.55、0.8、0.9、1、2、5、8、10、11、12、12.5或在上述任意两个数值所组成的范围内的任一值。
在一些实施例中，1≤H/y≤25。当第一层的厚度和导电剂的平均直径之间的关系满足上述关系，以平衡第一层的厚度和导电剂的平均直径之间的关系，以利于第一层具有一定的厚度的同时，还具有良好的导电性，利于改善二次电池的循环稳性能、能量密度并改善二次电池的过放产气。在一些实施例中，H/y可以为1、2、5、7、8、10、12、15、17、20、23、25或在上述任意两个数值所组成的范围内的任一值。
在一些实施例中，基于硅基体中硅元素和碳元素的质量之和，碳元素的质量占比为38.2％至61.3％，硅基体中硅元素的质量占比为38.7％至61.8％。硅基体中碳元素和硅元素的含量在上述范围内，利于使得硅基体具有良好的导电性的同时，利于发挥硅基体中硅的容量贡献，并使得硅碳复合材料具有良好的循环性能。在一些实施例中，硅基体中碳元素的质量占比可以为38.2％、39％、41％、45％、47％、49％、53％、55％、58％、60％、61.3％或在上述任意两个数值所组成的范围内的任一值。硅基体中硅元素的质量占比可以为38.7％、39％、41.8％、43％、45％、48％、51％、54％、56％、57％、57.9％、59％、61％、61.8％或在上述任意两个数值所组成的范围内的任一值。优选地，硅元素的质量占比为41.8％至57.9％。
本申请对硅碳复合材料的制备方法没有特别限制，只要能实现本申请的目的即可。例如硅碳复合材料的制备方法可以包括但不限于以下步骤：(1)将导电剂和含有Si-O-R的硅氧有机物溶解分散于溶剂中，并搅拌均匀；(2)将硅基体材料加入到步骤(1)中，搅拌后分散均匀，干燥后得到硅碳复合材料。
在步骤(1)中所用的溶剂包括：水、乙醇、乙二醇、丙二醇、四氢呋喃中的至少一种。
在步骤(2)中，搅拌时间为1h至24h，搅拌转速为500r/min至2500r/min，干燥温度为92℃-198℃，干燥时间为2h-24h。
本申请对硅基体的制备方法没有特别限制，只要能实现本申请的目的即可。例如上述硅基体的制备方法包括：采用化学气相沉积法，硅源气体在多孔碳上沉积形成硅，然后再通入碳源，使得碳源在硅基体的表面形成无定型碳，从而得到硅基体。碳源气体可以包括但不限于甲烷、乙炔、乙烯、乙烷、丙炔、丙烯、丙烷、丁炔、丁烯或丁烷中的至少一种。硅源气体可以包括但不限于甲硅烷、乙硅烷、丙硅烷、四硅烷、氯硅烷、二氯硅烷、三氯硅烷或四氯硅烷中的一种或多种。通过改变硅源气体的通入时间可以调整硅基体中硅元素的含量。
硅碳复合材料的制备方法中，硅基体中硅元素和碳元素的质量比以及硅基体、导电剂和硅氧有机物三者的质量比影响硅碳复合材料的循环性能、析锂性能和过放产气。硅基体和导电剂的质量比为100：(0.5～0.9)；导电剂和硅氧有机物的质量比为(0.5～5)：2。优选地，硅基体、导电剂和硅氧有机物的三者质量比为100:0.5:2。增大硅基体和导电剂的质量比，会降低硅碳复合材料的循环性能，减小硅基体和导电剂的质量比，会降低硅碳复合材料的比容量，降低二次电池的能量密度。增大硅基体和硅氧有机物的质量比，会降低硅碳复合材料对改善过放产气的效果。减小硅基体和硅氧有机物的质量比，会降低硅碳复合材料的动力学性能(如析锂性能)和循环性能。增大硅氧有机物和导电剂的质量比，会降低硅碳复合材料的动力学性能和循环性能，减小硅氧有机物和导电剂的质量比，会降低硅碳复合材料对改善二次电池过放产气的性能。
基于上述硅基体、导电剂和硅氧有机物三者的质量比，在改变硅基体含量的情况下，可以通过调整搅拌时间和速率改变第一层的厚度H。
通过选择不同平均直径和平均长度的导电剂原料来改变导电剂的平均直径y的值和平均长度L的值。
本申请一实施方式提供一种二次电池，其包括外壳和电芯。电芯位于外壳内。
外壳可以是采用封装膜(如铝塑膜)封装得到的包装袋，如二次电池为软包二次电池。在另一些实施例中，二次电池也可以是钢壳二次电池、铝壳二次电池等。
电芯包括电极组件和电解液，电极组件包括正极极片、负极极片、隔离膜，隔离膜设于正极极片和负极极片之间。电极组件可以是叠片式结构，其由正极极片、隔离膜和负极极片层叠形成。在另一些实施例中，电极组件还可以是卷绕结构，其由正极极片、隔离膜和负极极片层叠后卷绕形成。
负极极片
负极极片包括负极集流体和设于负极集流体上的负极活性层。负极集流体可以使用铜箔、镍箔、不锈钢箔、钛箔或碳基集流体等中的至少一种，也可为任何现有技术中公开的复合集流体，例如但不仅限于前述导电箔和聚合物基底结合形成的集流体。负极活性层包含负极活性材料，负极活性材料包括上述描述的硅碳复合材料。
负极活性层还包含粘结剂，用以粘结负极活性材料颗粒从而便于形成膜层，同时还能够提高负极活性层与负极集流体之间的结合力。在一些实施例中，粘结剂可包括但不仅限于聚乙烯醇、羟丙基纤维素、二乙酰基纤维素、聚氯乙烯、羧化的聚氯乙烯、聚氟乙烯、含亚乙基氧的聚合物、聚乙烯吡咯烷酮、聚氨酯、聚四氟乙烯、聚偏1,1-二氟乙烯、聚乙烯、聚丙烯、丁苯橡胶、丙烯酸(酯)化的丁苯橡胶、环氧树脂或尼龙等。
负极活性层还可包括导电材料，导电材料包括但不限于基于碳的材料、基于金属的材料、导电聚合物或其任意组合。在一些实施例中，基于碳的材料可包括但不仅限于自天然石墨、人造石墨、碳黑、乙炔黑、科琴黑、碳纤维或其任意组合。在一些实施例中，基于金属的材料可包括但不仅限于金属粉或金属纤维，例如铜、镍、铝或银。在一些实施例中，导电聚合物可为聚亚苯基衍生物。
负极活性层还可进一步地包含石墨，由于石墨具有一定的柔韧性，其与硅碳复合材料配合能够缓解负极活性层整体的体积膨胀。同时，石墨与硅碳复合材料同时作为负极活性材料还能够充分利用硅碳复合材料和石墨两者的优势以达到较好的电化学性能。
正极极片
正极极片包括正极集流体和设于正极集流体上的正极活性层。正极集流体可以使用铝箔或镍箔等，也可为任何现有技术中公开的复合集流体，例如但不仅限于前述导电箔和聚合物基底结合形成的集流体。正极活性层包含正极活性材料，正极活性材料包括可逆地嵌入和脱嵌锂离子的化合物(即，锂化插层化合物)。在一些实施例中，正极活性材料可以包括锂过渡金属复合氧化物。该锂过渡金属复合氧化物含有锂以及从钴、锰和镍中选择的至少一种元素。在一些实施例中，正极活性材料可包括但不仅限于钴酸锂、镍锰钴酸锂、镍锰铝酸锂、磷酸铁锂、磷酸钒锂、磷酸钴锂、磷酸锰锂、磷酸锰铁锂、硅酸铁锂、硅酸钒锂、硅酸钴锂、硅酸锰锂、尖晶石型锰酸锂、尖晶石型镍锰酸锂和钛酸锂中的至少一种。
正极活性层还包含粘合剂，用以粘结正极活性材料颗粒从而便于形成膜层，同时还能够提高正极活性层与正极集流体之间的结合力。在一些实施例中，粘合剂可包括但不仅限于聚乙烯醇、羟丙基纤维素、二乙酰基纤维素、聚氯乙烯、羧化的聚氯乙烯、聚氟乙烯、含亚乙基氧的聚合物、聚乙烯吡咯烷酮、聚氨酯、聚四氟乙烯、聚偏1,1-二氟乙烯、聚乙烯、聚丙烯、丁苯橡胶、丙烯酸(酯)化的丁苯橡胶、环氧树脂或尼龙等中的至少一种。
正极活性层还可包含导电材料，导电材料包括但不限于基于碳的材料、基于金属的材料、导电聚合物或其任意组合。在一些实施例中，基于碳的材料可包括但不仅限于自天然石墨、人造石墨、碳黑、乙炔黑、科琴黑、碳纤维或其任意组合。在一些实施例中，基于金属的材料可包括但不仅限于金属粉或金属纤维，例如铜、镍、铝或银。在一些实施例中，导电聚合物可为聚亚苯基衍生物。
隔离膜
本申请的电化学装置中使用的隔离膜的材料和形状没有特别限制，其可为任何现有技术中公开的技术。在一些实施例中，隔离膜包括由对本申请的电解液稳定的材料形成的聚合物或无机物等。
例如隔离膜可包括基材层和表面处理层。基材层为具有多孔结构的无纺布、膜或复合膜，基材层的材料选自聚乙烯、聚丙烯、聚对苯二甲酸乙二醇酯和聚酰亚胺中的至少一种。具体的，可选用聚丙烯多孔膜、聚乙烯多孔膜、聚丙烯无纺布、聚乙烯无纺布或聚丙烯-聚乙烯-聚丙烯多孔复合膜。
基材层的至少一个表面上设置有表面处理层，表面处理层可以是聚合物层或无机物层，也可以是混合聚合物与无机物所形成的层。无机物层包括无机颗粒和粘结剂，无机颗粒选自氧化铝、氧化硅、氧化镁、氧化钛、二氧化铪、氧化锡、二氧化铈、氧化镍、氧化锌、氧化钙、氧化锆、氧化钇、碳化硅、勃姆石、氢氧化铝、氢氧化镁、氢氧化钙和硫酸钡中的至少一种。
粘结剂选自聚偏氟乙烯、偏氟乙烯-六氟丙烯的共聚物、聚酰胺、聚丙烯腈、聚丙烯酸酯、聚丙烯酸、聚丙烯酸盐、聚乙烯呲咯烷酮、聚乙烯烷氧、聚甲基丙烯酸甲酯、聚四氟乙烯和聚六氟丙烯中的至少一种。聚合物层中包含聚合物，聚合物的材料选自聚酰胺、聚丙烯腈、丙烯酸酯聚合物、聚丙烯酸、聚丙烯酸盐、聚乙烯呲咯烷酮、聚乙烯烷氧、聚偏氟乙烯、聚(偏氟乙烯-六氟丙烯)中的至少一种。
电解液
根据本申请的一些实施方式，电解液包括有机溶剂、锂盐和可选的添加剂。
本申请的电解液中的有机溶剂可为现有技术中已知的任何可作为电解液的溶剂的有机溶剂。根据本申请的电解液中使用的电解质没有限制，其可为现有技术中已知的任何电解质。根据本申请的电解液的添加剂可为现有技术中已知的任何可作为电解液添加剂的添加剂。在一些实施例中，有机溶剂包括，但不限于：碳酸乙烯酯(EC)、碳酸丙烯酯(PC)、碳酸二乙酯(DEC)、碳酸甲乙酯(EMC)、碳酸二甲酯(DMC)或丙酸乙酯。
在一些实施例中，有机溶剂包括醚类溶剂，例如包括1，3-二氧五环(DOL)和乙二醇二甲醚(DME)中的至少一种。在一些实施例中，锂盐包括有机锂盐或无机锂盐中的至少一种。在一些实施例中，锂盐包括，但不限于：六氟磷酸锂(LiPF6)、四氟硼酸锂(LiBF4)、二氟磷酸锂(LiPO2F2)、双三氟甲烷磺酰亚胺锂LiN(CF3SO2)2(LiTFSI)、双(氟磺酰)亚胺锂Li(N(SO2F)2)(LiFSI)、双草酸硼酸锂LiB(C2O4)2(LiBOB)或二氟草酸硼酸锂LiBF2(C2O4)(LiDFOB)。在一些实施例中，添加剂包括氟代碳酸乙烯酯和己二腈中的至少一种。
根据本申请的一些实施方式，本申请的二次电池包括，但不限于：锂离子电池。
由上述负极极片组合形成的电芯中，在电芯的电压为3V至3.95V时电芯的厚度为H0，电芯放电至0.5V时电芯的厚度为H2，0.58<H2/H0≤1.36。电芯中的负极极片包括所述的硅碳复合材料。电芯在放电前后的厚度之比在上述范围内，电芯内部的产气问题得到改善，其可保持良好的稳定性，从而提高电芯的循环性能和使用寿命。电芯的厚度为H0时，其对应的电压可以为3V、3.1V、3.2V、3.3V、3.4V、3.5V、3.6V、3.7V、3V、3.8V、3.95V或在上述任意两个数值所组成的范围内的任一值。在一些实施例中，H2/H0可以为0.59、0.6、0.63、0.7、0.8、0.9、0.95、1、1.1、1.15、1.16、1.2、1.23、1.3、1.32、1.36或在上述任意两个数值所组成的范围内的任一值。优选地，0.63≤H2/H0≤1.23，更优选地，0.9≤H2/H0≤1.16。
上述电芯的厚度变化和电芯中的界面稳定性相关，硅碳复合材料和电解液的界面稳定性越好，其电芯放电至0.5V时，电芯的厚度越小。硅碳复合材料中的Si元素的含量、Si-O键的含量以及导电剂的导电性影响着电芯的界面稳定性。本申请通过调控上述影响因素，以改变电芯在放电至0.5V时的厚度，使得H2/H0的比值处于合适的范围内，以使得电芯具有良好的界面稳定性。
若电芯从初始电压放电至2.5V电压时，其硅碳复合材料的体积变化会受到影响，电芯从2.5V继续放电，主要受影响的是SEI膜。电芯从3V～3.95V的初始电压放电至0.5V时，锂离子从负极活性层中脱出，负极极片的厚度变小，并结合硅碳复合材料中第一层形成于硅基体上，硅碳复合材料自身具有较好的稳定性以及硅碳复合材料和电解液之间具有较好的界面稳定性，减少或消除了SEI膜的分解产气，从而使得电芯的厚度变小。若电芯从初始电压放电至0.5V电压时，SEI膜的稳定性差，SEI膜会发生分解产气，电芯的厚度增加较大，从而影响H2/H0的比值。
本申请还将二次电池应用于电子装置中，二次电池为电子装置的负载供电。上述电子装置中二次电池包含有负极活性材料，负极活性材料中包括硅碳复合材料，硅碳复合材料中的第一层能够减少HF对硅基体的刻蚀，提高SEI膜的稳定性，从而提高二次电池的循环性能和充电效率，进而提高电子装置的使用寿命和充电效率。
其中，电子装置可包括但不仅限于笔记本电脑、笔输入型计算机、移动电脑、电子书播放器、便携式电话、便携式传真机、便携式复印机、便携式打印机、头戴式立体声耳机、录像机、液晶电视、手提式清洁器、便携CD机、迷你光盘、收发机、电子记事本、计算器、存储卡、便携式录音机、收音机、备用电源、电机、汽车、摩托车、助力自行车、自行车、照明器具、玩具、游戏机、钟表、电动工具、闪光灯、照相机、家庭用大型蓄电池和锂离子电容器等。
以下通过具体实施例和对比例对本申请进行说明。本领域技术人员应理解，本申请中描述的制备方法仅是实施例，其他任何合适的制备方法均在本申请的范围内。
实施例1
(1)制备硅碳复合材料：
将单壁碳纳米管和聚甲基氢硅氧烷以0.5:2质量比溶解分散于水和乙醇的混合溶剂中，并搅拌均匀，得到混合浆料；(2)将100g硅基体(基于硅基体中硅元素和碳元素之和，碳元素的质量占比为50.7％，硅元素的质量占比为49.3％)材料加入到步骤(1)中的混合浆料，搅拌转速为1000r/min，搅拌4h后分散均匀，168℃干燥后得到硅碳复合材料，硅碳复合材料的Dv50为9μm，单壁碳纳米管的平均直径为5nm，平均长度为800nm。
(2)制备锂离子电池：
负极极片的制备：将上述制备的硅碳复合材料、人造石墨、负极粘结剂丁苯橡胶(SBR)、负极分散剂羧甲基纤维素(CMC)按照质量比为10:88:1.6:0.4进行混合，然后加入去离子水作为溶剂并搅拌均匀，调配成固含量为45wt％的负极浆料。将负极浆料均匀涂覆于厚度为6μm的负极集流体铜箔的一个表面上，将铜箔在85℃下烘干处理4小时，得到涂层厚度为80μm的单面涂覆负极活性材料层的负极极片。经过冷压、裁片、分切后，在120℃的真空条件下干燥12小时，得到负极极片，规格为76.6mm×875mm。其中，冷压压力为20吨(t)，负极极片的压实密度为1.78g/cm3。
正极极片的制备：将正极活性材料钴酸锂、正极导电剂乙炔黑、正极粘结剂聚偏氟乙烯(PVDF)按照质量比96.3:2.2:1.5进行混合，加入N-甲基吡咯烷酮(NMP)作为溶剂并搅拌均匀，调配成固含量为75wt％的正极浆料。将正极浆料均匀涂覆在厚度为13μm的正极集流体铝箔的一个表面上，85℃条件下烘干，得到正极活性材料层厚度为130μm的单面涂布正极活性材料的正极极片。经过冷压、裁片、分切后，在85℃的真空条件下干燥4小时，得到正极极片，规格为74mm×867mm。其中，冷压压力为20t，正极极片的压实密度为4.15g/cm3。
电解液的制备：在干燥氩气气氛手套箱中，将有机溶剂碳酸乙烯酯(EC)、碳酸丙烯酯(PC)、碳酸二乙酯(DEC)、丙酸乙酯(EP)按照质量比3:1:3:3进行混合，然后加入锂盐LiPF6，混合均匀后获得电解液。基于电解液的质量，锂盐的质量百分含量为12.5％，余量为有机溶剂。
隔离膜的制备：采用厚度为15μm的多孔聚乙烯薄膜(Celgard公司提供)作为隔离膜。
组装锂离子电池：将上述制备的正极极片、隔离膜、负极极片按顺序依次叠好，使隔离膜处于正极极片和负极极片中间起到隔离的作用，然后卷绕得到电极组件。焊接极耳后将电极组件装入铝塑膜包装袋中，放置在80℃真空烘箱中干燥12小时脱去水分，注入上述配好的电解液，经过真空封装、静置、化成(0.02C恒流充电至3.5V，再以0.1C恒流充电至3.9V)、脱气、切边等工艺流程得到锂离子电池(即电芯)。
实施例2至实施例7
实施例2至实施例7与实施例1的区别在于，改变硅氧有机物的种类或硅基体和导电剂的质量比或导电剂和硅氧有机物的质量比，其余制备过程与实施例1相同。
实施例8至实施例10
实施例8至实施例10与实施例1的区别在于，改变硅基体中硅元素的质量占比，其余制备过程与实施例1相同。
实施例11至实施例12
实施例11至实施例12与实施例1的区别在于，改变硅碳复合材料的粒径Dv50，其余制备过程与实施例1相同。
实施例13至实施例16
实施例13至实施例16与实施例1的区别在于，改变硅碳复合材料中导电剂的平均直径或平均长度，其余制备过程与实施例1相同。
实施例17
实施例17与实施例1的区别在于，改变制备硅碳复合材料的步骤(2)过程中的搅拌时间，在搅拌转速为1000r/min下，搅拌时间为10min，得到第一层的厚度为5nm，其余制备过程与实施例1相同。
实施例18
实施例18与实施例1的区别在于，改变制备硅碳复合材料的步骤(2)过程中的搅拌时间，在搅拌转速为1000r/min下，搅拌时间为1h，得到第一层的厚度为36nm，其余制备过程与实施例1相同。
实施例19
实施例19与实施例1的区别在于，改变制备硅碳复合材料的步骤(2)过程中的搅拌时间，在搅拌转速为1000r/min下，搅拌时间为8h，得到第一层的厚度为72nm，其余制备过程与实施例1相同。
实施例20
实施例20与实施例1的区别在于，改变制备硅碳复合材料的步骤(2)过程中的搅拌时间，在搅拌转速为1000r/min下，搅拌时间为24h，得到第一层的厚度为100nm，其余制备过程与实施例1相同。
对比例1
与实施例1的区别在于，制备硅碳复合材料过程中，硅基体的表面未经任何包覆处理，具体材料组成见表1。
对比例2
与实施例1的区别在于，制备硅碳复合材料过程中，硅基体的表面仅包覆有导电剂，未包覆硅氧有机物，具体材料组成见表1。
对比例3
与实施例1的区别在于，制备硅碳复合材料过程中，硅基体的表面仅包覆有硅氧有机物，未包覆导电剂，具体材料组成见表1。
对实施例和对比例制备的硅碳复合材料以及锂离子电池进行以下测试，如表1至表4。
性能测试
(1)粉末粒径Dv50的测试方法：
采用马尔文粒度测试仪(仪器型号为Master Sizer 2000)测试硅基复合材料的粒径分布。制样方法如下：50ml洁净烧杯中加入约0.02g粉末样品，加入约20ml去离子水，再滴加3滴的表面活性剂十二烷基硫酸钠，使粉末完全分散于水中，120W超声清洗机中超声5分钟，得到粉末粒径测试样品。在材料的体积基准的粒度分布中，从小粒径测起，到达体积累积50％的粒径为Dv50。
(2)第一层的厚度的测量方法：
采用聚焦离子束(FIB)对硅碳复合材料进行切片，再通过高分辨透射电子显微镜(HRTEM，型号为Talos F200X)表征，在同样的选区范围(500000倍放大倍数)内，观察到颗粒中的第一层，测量硅碳复合材料的颗粒中第一层的厚度，并任选第一层中五十个不同位置处的厚度，其厚度可以根据标尺测量得到，并计算五十个厚度数值的平均值，获得第一层的厚度。
(3)导电剂的平均直径和平均长度的测试方法：
通过扫描电子显微镜(SEM)拍到30000k倍的放大图像，使用图像分析软件ImageJ对图像进行处理，然后分别测量20个CNT的长度和直径，然后取20个CNT的长度数值的平均值，计算即可得到CNT的平均长度，取20个CNT的直径数值的平均值，计算即可得到CNT的平均直径。
(4)硅基体中硅元素和碳元素质量占比的测试方法：
通过扫描电子显微镜(SEM)拍到1000倍的放大图像，选择硅碳材料中硅基体部分，进行EDS元素分析即可得到获得硅元素和碳元素的质量占比。
(5)扫描电子显微镜(SEM)的测试方法：
采用JEOL-JSM-6700F型扫描电镜，在5kV的电压和0.8nA的电流下，对硅基复合材料进行测试。
锂离子电池性能测试
(1)循环性能的测试方法：
将锂离子电池在25℃±1℃的恒温箱中静置30分钟，以0.5C电流恒流充电至4.45V，再以4.45V恒压充电至0.025C，静置5分钟，然后以0.5C放电至3.0V，此为一次充放电循环过程，记录锂离子电池的首次循环放电容量C0，之后，按照上述循环过程循环500圈。记录第500圈的循环放电容量C1。500圈循环容量保持率＝C1/C0×100％。
(2)电芯放电前后厚度的测量方法：
使用千分尺测量电芯(电芯的电压为3V至3.95V)的初始厚度记为H0，然后使用0.01C放电至0.5V，使用千分尺测量电芯的厚度记为H2，并计算H2/H0的比值。
(3)能量密度的测试方法或计算公式：
将每组被测锂离子电池各取5个，在25℃的环境中进行第一次充电和放电。在0.5C的充电电流下进行恒流充电，直到上限电压，之后恒压充电至0.02C，然后在0.2C的放电电流下恒流放电至截止电压，获得锂离子电池的放电容量，并计算锂离子电池的放电平均电压。
以0.5C充电至50％SOC，得到50％SOC下的锂离子电池。测量各锂离子电池50％SOC下的长宽厚，计算得到锂离子电池的体积，计算出锂离子电池的体积能量密度＝锂离子电池的放电容量×锂离子电池放电平均电压/锂离子电池体积。
其中，锂离子电池充电上限电压为4.45V，放电截至电压为3.0V。
(4)析锂性能的测试方法：
将锂离子电池在25℃±1℃的恒温箱中静置30分钟，以1.2C电流恒流充电至4.45V，再以4.45V恒压充电至0.025C，静置5分钟，然后以0.5C放电至3.0V，此为一次充放电循环过程，重复10次循环过程进行后，以4C电流恒流充电至4.45V，再以4.45V恒压充电至0.025C，静置5分钟，对锂离子电池进行拆解，以观测锂离子电池的析锂情况。依照上述方法，将1.2C分别调整为1.6C、2C、2.4C、2.6C、2.8C、3C、3.1C、3.2C、3.4C、3.8C或4C，观测锂离子电池在不同充电倍率下的析锂情况。充电倍率越高下出现析锂，表明锂离子电池的析锂性能越好。根据满充拆解负极相接触的隔离膜被污染的状态来判定，当负极相接触的隔离膜整体显示为白色且显示为灰色的面积<2％，则判定为不析锂。
图1为实施例1制备的硅碳复合材料的扫描电子显微镜图，图2为对比例1中未经任何包覆的硅基体的扫描电子显微镜图。从图1和图2中，硅基体表面形成有线状结构的单壁碳纳米管，硅基体表面包覆有第一层。图3为实施例1组装的电芯，电芯的初始电压从3.19V放电至0.5V的变化趋势以及电芯厚度的变化趋势，在放电过程中，电芯的厚度逐渐减小，放电至0.5V时，电芯的厚度为4mm。
表1

表2

注：表1和表2中“/”表示未添加或无相关参数。
如表1和表2中，相较于对比例1至3，在实施例1至7中，第一层同时含有导电剂和硅氧有机物，提高了锂离子电池的循环保持率并减少析锂。这表明，硅基体上的第一层中需同时包覆导电剂和硅氧有机物，其导电剂和硅氧有机物中仅有一者会降低锂离子电池的循环保持率或析锂性能。实施例1至7中硅碳复合材料在硅基体表面同时存在硅氧有机物和导电剂时，提高了硅碳复合材料的循环性能并减少了析锂。且在上述实施例中，调整硅基体和导电剂的质量比、导电剂和硅氧有机物的质量比或采用不同类型的硅氧有机物，其影响硅碳复合材料中的Si-O键的含量，会影响电芯中SEI膜的稳定性，从而影响H2/H0的比值。相较于对比例1至3，实施例1至7中，H2/H0的比值均有减小，这也表明硅碳复合材料中同时存在硅氧有机物和导电剂时，减小或消除了SEI膜的分解产气。
表3
表4
结合表1至表4，实施例8至实施例9中，调整硅基体中硅元素和碳元素的含量，会影响硅碳复合材料的循环性能和析锂性能。硅基体中硅元素的含量在适宜的范围内，利于使得二次电池具有良好的循环性能和析锂性能。实施例1、实施例11和实施例12中，调整硅碳复合材料的粒径Dv50，在硅碳复合材料的粒径Dv50以及H/D在适宜的范围内，其对应的二次电池在具有良好的能量密度下，还兼容良好的循环性能和析锂性能。
实施例1、实施例13至实施例16中，通过调整导电剂的平均直径和平均长度，其对应的二次电池在具有良好的能量密度下，还兼容良好的循环性能和析锂性能。
实施例1、实施例17至实施例20中，在制备硅碳复合材料时，调整搅拌时间，从而调整硅碳复合材料中第一层的厚度，第一层的厚度在合适范围内，其对应的二次电池在具有良好的能量密度下，还兼容良好的循环性能和析锂性能。
以上所揭露的仅为本申请较佳实施方式而已，当然不能以此来限定本申请，因此依本申请所作的等同变化，仍属本申请所涵盖的范围。

Claims (10)

  1. 一种硅碳复合材料，其特征在于，包括硅基体以及至少部分位于所述硅基体上的第一层，所述第一层包括导电剂和硅氧有机物。
  2. 如权利要求1所述的硅碳复合材料，其特征在于，所述硅氧有机物包括聚甲基氢硅氧烷、聚倍半硅氧烷、乙烯基三甲氧基硅烷或乙烯基三乙氧基硅烷中的至少一种。
  3. 如权利要求1或2所述的硅碳复合材料，其特征在于，所述导电剂包括单壁碳纳米管或多壁碳纳米管中的至少一种；
    和/或，
    所述硅基体包括硅碳材料。
  4. 如权利要求1至3中任一项所述的硅碳复合材料，其特征在于，所述硅基体和所述导电剂的质量比为100:(0.5～0.9)；所述导电剂和所述硅氧有机物的质量比为(0.5～5):2。
  5. 如权利要求1至4中任一项所述的硅碳复合材料，其特征在于，所述导电剂为线状结构，所述导电剂的平均直径为y nm，0.5≤y≤20；所述导电剂的平均长度为L nm，500≤L≤1000。
  6. 如权利要求1至5中任一项所述的硅碳复合材料，其特征在于，所述硅碳复合材料满足以下条件中的至少一者：
    (1)所述硅碳复合材料的粒径Dv50为Dμm，4≤D≤13；
    (2)所述第一层的厚度为H nm，5≤H≤100；
    (3)所述硅碳复合材料的粒径Dv50为Dμm，所述第一层的厚度为Hnm，0.55≤H/D≤12.5；
    (4)所述硅基体包括硅碳材料，所述硅碳材料包括硅元素和碳元素，基于所述硅基体中所述硅元素和所述碳元素的质量之和，所述硅元素的质量占比为41.8％至57.9％。
  7. 如权利要求1至6中任一项所述的硅碳复合材料，其特征在于，所述第一层的厚度为H nm，所述导电剂的平均直径为y nm，1≤H/y≤25。
  8. 一种二次电池，包括电芯，其特征在于，所述电芯包括负极极片、正极极片和电解液，所述负极极片还包括如权利要求1至7中任一项所述的硅碳复合材料。
  9. 如权利要求8所述的二次电池，其特征在于，在所述电芯电压为3V至3.95V时所述电芯的厚度为H0，所述电芯放电至0.5V时所述电芯的厚度为H2，0.58<H2/H0≤1.36。
  10. 一种电子装置，其特征在于，包括如权利要求8或9所述的二次电池。
PCT/CN2025/081251 2024-06-26 2025-03-07 硅碳复合材料、二次电池和电子装置 Pending WO2026001074A1 (zh)

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