WO2026001073A1 - 硅基复合材料、二次电池和电子装置 - Google Patents

硅基复合材料、二次电池和电子装置

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Publication number
WO2026001073A1
WO2026001073A1 PCT/CN2025/081250 CN2025081250W WO2026001073A1 WO 2026001073 A1 WO2026001073 A1 WO 2026001073A1 CN 2025081250 W CN2025081250 W CN 2025081250W WO 2026001073 A1 WO2026001073 A1 WO 2026001073A1
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WO
WIPO (PCT)
Prior art keywords
silicon
based composite
composite material
lithium
layer
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/CN2025/081250
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
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Filing date
Publication date
Application filed by Ningde Amperex Technology Ltd filed Critical Ningde Amperex Technology Ltd
Publication of WO2026001073A1 publication Critical patent/WO2026001073A1/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-based composite material, a secondary battery using the silicon-based composite material, and an electronic device using the secondary battery.
  • Secondary batteries such as lithium-ion batteries
  • Secondary batteries typically use silicon as the anode material. Due to its high theoretical specific capacity (Li ⁇ sub>15 ⁇ /sub> Si ⁇ sub>4 ⁇ /sub> , 3579 mAh/g) and suitable operating voltage ( ⁇ 0.5 V vs. Li/Li ⁇ sup> + ⁇ /sup> ), silicon is considered the most promising anode material to replace graphite. However, its low conductivity and the significant volume expansion during alloying/dealloying processes affect the cycle performance of secondary batteries.
  • This application provides a silicon-based composite material that can improve cycle performance.
  • this application also provides a secondary battery and electronic device using silicon-based composite materials.
  • This application provides a silicon-based composite material, including a silicon matrix and a first layer located on at least a portion of the surface of the silicon matrix.
  • the first layer includes a conductive agent and a fluorinated lithium phosphate compound.
  • the thickness of the first layer is H nm, where 5 ⁇ H ⁇ 200 nm.
  • the fluorinated lithium phosphate compound in the first layer undergoes a reduction reaction during the charging process to form inorganic salt components such as LiF, Li3PO4 , or Li3P , which participate in the formation of the solid electrolyte interphase ( SEI ) film.
  • the inorganic salt components improve the strength and ionic conductivity of the SEI film, thereby improving its interfacial stability and enhancing the cycle performance and expansion performance of the silicon-based composite material.
  • the addition of a conductive agent in the first layer further improves the conductivity of the silicon-based composite material, thereby enhancing its kinetic performance.
  • the thickness of the first layer within the aforementioned range, it not only increases the specific capacity of the silicon-based composite material but also protects the silicon substrate, improves the interfacial stability of the SEI film, and further enhances the cycle performance and expansion performance of the silicon-based composite material.
  • the fluorinated lithium phosphate compound is selected from at least one of lithium difluorophosphate, lithium difluorobis(oxalato)phosphate, or lithium tetrafluoro(oxalato)phosphate. All of these fluorinated lithium phosphate compounds are capable of undergoing reduction reactions to form inorganic salt components such as LiF, Li3PO4 , or Li3P , thereby improving the interfacial stability of the SEI film and enhancing the cycling performance and expansion properties of the silicon-based composite material.
  • the conductive agent includes at least one of single-walled carbon nanotubes or multi-walled carbon nanotubes.
  • These conductive agents are all linear conductive agents, capable of providing better ion transport channels, improving the conductivity of silicon-based composite materials, and thus enhancing the kinetic properties of the silicon-based composite materials.
  • 5 ⁇ H ⁇ 64 which is beneficial to further improve the stability of the SEI film through the first layer and improve the cycle performance and expansion performance of the silicon-based composite material.
  • the particle size Dv50 of the silicon-based composite material is X ⁇ m, where 4 ⁇ X ⁇ 13. This helps to reduce the contact between the silicon-based composite material and the electrolyte, thereby reducing side reactions between the silicon-based composite material and the electrolyte, and thus improving the cycle performance of the silicon-based composite material.
  • 0.56 ⁇ H/X ⁇ 22.22 is beneficial for silicon-based composite materials to have good kinetic properties, cycling properties and expansion properties.
  • the conductive agent has a linear structure with an average diameter of y nm, where 1 ⁇ y ⁇ 30. This facilitates better dispersibility of the conductive agent and also improves the conductivity of the silicon-based composite material, thereby enhancing its kinetic and cycling performance.
  • the conductive agent has an average length of L nm, where 1000 ⁇ L ⁇ 2000. This facilitates better dispersibility of the silicon-based composite material and also enhances the long-range conductivity of the active ions, improving the rate performance of the silicon-based composite material.
  • 1 ⁇ H/y ⁇ 50 1 ⁇ H/y ⁇ 50.
  • the sphericity of the silicon substrate is S, where S ⁇ 0.8.
  • a higher sphericity of the silicon substrate is beneficial for improving the uniformity of active ion embedding in the silicon-based composite material, as well as the uniformity of the first layer coating and the stability of the silicon substrate, thereby improving the stability of the SEI film and ultimately enhancing the cycle performance of the silicon-based composite material.
  • 1052 ⁇ L/S ⁇ 2105.
  • gaps exist between silicon-based composite materials.
  • interconnected active ion transport channels are formed between the conductive agents, thereby improving the active ion transport rate and thus enhancing the rate performance of the silicon-based composite material.
  • the mass percentage of lithium in the first layer is A%, 0.1 ⁇ A ⁇ 4; the mass percentage of phosphorus in the first layer is B%, 0.03 ⁇ B ⁇ 1.2; and the mass percentage of fluorine in the first layer is C%, 0.1 ⁇ C ⁇ 4.
  • the first layer protects the silicon matrix, which is beneficial for the silicon-based composite material to have excellent specific capacity while improving the cycle performance and expansion performance of the silicon-based composite material.
  • the silicon matrix includes silicon-carbon materials, wherein the mass percentage of silicon is D%, 38 ⁇ D ⁇ 59%, and the mass percentage of carbon is E%, 40 ⁇ E ⁇ 61%, based on the mass of the silicon matrix.
  • This is beneficial for the silicon matrix to have good specific capacity and initial efficiency, while also improving the interfacial stability of the silicon-based composite material, thereby enhancing the cycle performance and expansion performance of the silicon-based composite material.
  • the lithium, phosphorus, and fluorine content in the first layer satisfies the above-mentioned relationship with the silicon content in the silicon matrix, allowing the elements in the first layer to fully participate in the formation of the SEI film, which is beneficial to improving the stability of the SEI film and enhancing the protection of the silicon matrix, thereby improving the cycle performance and expansion performance of the silicon-based composite material.
  • 0.104 ⁇ H/D ⁇ 4.16 This allows for adjusting the thickness of the first layer while ensuring a certain silicon content in the silicon matrix, reducing side reactions between the silicon matrix and the electrolyte, thereby improving the cycle performance of the silicon-based composite material.
  • a second aspect of this application provides a secondary battery, including a negative electrode, a positive electrode, and an electrolyte, wherein the negative electrode comprises a silicon-based composite material.
  • the fluorinated lithium phosphate compound in the first layer can improve the interfacial stability of the SEI film and enhance the cycle performance of the secondary battery.
  • a third aspect of this application provides an electronic device including a secondary battery.
  • the secondary battery supplies power to the electronic device and includes a negative electrode.
  • the negative electrode contains a silicon-based composite material, which improves the cycle performance of the secondary battery, thereby increasing the lifespan and charge/discharge rate of the electronic device.
  • Figure 1 is a scanning electron microscope image of the silicon substrate before coating in Embodiment 1 of this application.
  • Figure 2 is a scanning electron microscope image of the silicon-based composite material prepared after silicon substrate coating in Example 1 of this application.
  • One embodiment of this application provides a secondary battery, which includes a casing, an electrode assembly, and an electrolyte. Both the electrode assembly and the electrolyte are located within 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 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 layering 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 silicon-based composite materials.
  • the silicon-based composite material includes a silicon matrix and a first layer located on at least a portion of the surface of the silicon matrix.
  • the first layer includes a conductive agent and a fluorinated lithium phosphate compound.
  • the thickness of the first layer is H nm, where 5 ⁇ H ⁇ 200.
  • the fluorinated lithium phosphate compound in the first layer undergoes a reduction reaction during secondary battery charging to form inorganic salt components such as LiF, Li3PO4 , or Li3P .
  • inorganic salt components participate in the formation of the solid electrolyte interphase (SEI) film.
  • SEI solid electrolyte interphase
  • the inorganic salt components improve the strength and ionic conductivity of the SEI film, thereby improving the interfacial stability of the SEI film and enhancing the cycle performance and expansion performance of the silicon-based composite material.
  • the addition of a conductive agent in the first layer further improves the conductivity of the silicon-based composite material, which in turn enhances its rate performance and reduces lithium plating.
  • the silicon-based composite material can maintain a high specific capacity while protecting the silicon substrate, improving the interfacial stability of the SEI film, and further enhancing the cycle performance and expansion performance of the silicon-based composite material.
  • the thickness of the first layer is relatively small, resulting in weak protection of the silicon substrate.
  • the electrolyte may react with and etch the silicon substrate, thereby deteriorating the cycle performance and expansion performance of the silicon-based composite material.
  • H > 200 the thickness of the first layer is relatively large, affecting the specific capacity of the silicon-based composite material.
  • the thickness H of the first layer can be 5, 6, 10, 15, 20, 25, 30, 40, 50, 75, 90, 100, 120, 125, 130, 150, 175, 180, 190, 200, or any value within the range of any two of the above values.
  • 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 fluorinated lithium phosphate compound is selected from at least one of lithium difluorophosphate, lithium difluorobis(oxalato)phosphate, or lithium tetrafluoro(oxalato)phosphate. All of the above-mentioned fluorinated lithium phosphate compounds can undergo reduction reactions to form inorganic salt components such as LiF, Li3PO4 , or Li3P , thereby improving the interfacial stability of the SEI film and enhancing the cycling performance and expansion properties of the silicon-based composite material.
  • the conductive agent includes at least one of single-walled carbon nanotubes (SWCNTs) or multi-walled carbon nanotubes. All of the above conductive agents are linear conductive agents, capable of providing better ion transport channels, improving the conductivity of silicon-based composite materials, and thus enhancing the rate performance of silicon-based composite materials.
  • SWCNTs single-walled carbon nanotubes
  • All of the above conductive agents are linear conductive agents, capable of providing better ion transport channels, improving the conductivity of silicon-based composite materials, and thus enhancing the rate performance of silicon-based composite materials.
  • the particle size Dv50 of the silicon-based composite material is X ⁇ m, where 4 ⁇ X ⁇ 13. Within this range, it is beneficial to reduce the contact opportunities between the silicon-based composite material and the electrolyte, thereby reducing side reactions between the silicon-based composite material and the electrolyte, and thus improving the cycle performance and expansion performance of the silicon-based composite material.
  • the average particle size X of the silicon-based 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.
  • H/X can be 0.56, 0.6, 0.7, 0.8, 1, 2, 3, 5, 7, 9, 10, 12, 15, 17, 19, 20, 22.22, or any value within the range of any two of the above values.
  • the conductive agent has a linear structure with an average diameter of y nm, where 1 ⁇ y ⁇ 30. Within this length range, the conductive agent exhibits good dispersibility while simultaneously improving the conductivity of the silicon-based composite material, thereby enhancing its rate performance and cycle performance.
  • the average diameter y of the conductive agent can be 1, 2, 3, 5, 7, 9, 10, 12, 15, 17, 18, 20, 23, 25, 27, 30, or any value within the range of any two of the above values.
  • the average length of the conductive agent is L nm, where 1000 ⁇ L ⁇ 2000.
  • An average length within this range is beneficial for the silicon-based composite material to have good dispersibility, while also ensuring good long-range conductivity of active lithium ions, thus improving the kinetic properties of the silicon-based composite material.
  • the average length L of the conductive agent can be 1000, 1200, 1500, 1600, 1700, 1800, 1900, 2000, or any value within the range of any two of the above values.
  • 1 ⁇ H/y ⁇ 50 By adjusting the relationship between the thickness of the first layer and the average diameter of the conductive agent, the average diameter of the conductive agent can be within a set range when the first layer is thicker, thereby improving the overall stability and ionic conductivity of the silicon-based composite material.
  • H/y can be 1, 2, 3, 4, 5, 6, 10, 12, 15, 20, 25, 30, 35, 40, 45, 50, or any value within the range of any two of the above values.
  • the sphericity of the silicon substrate is S, where S ⁇ 0.8.
  • a higher sphericity of the silicon substrate is beneficial for improving the uniformity of active ion intercalation in the silicon-based composite material, as well as the uniformity of the first coating layer and the stability of the silicon substrate, thereby improving the stability of the SEI film and consequently enhancing the cycle performance and expansion performance of the silicon-based composite material.
  • the sphericity S can be 0.8, 0.85, 0.9, 0.95, 0.99, or any value within the range of any two of the above values. In some embodiments, 0.8 ⁇ S ⁇ 1.
  • 1052 ⁇ L/S ⁇ 2105 1052 ⁇ L/S ⁇ 2105.
  • the L/S ratio can be 1052, 1100, 1200, 1300, 1400, 1500, 1600, 1700, 1800, 1900, 2000, 2100, 2105, or any value within the range of any two of the above values.
  • the mass percentage of lithium in the first layer is A%, 0.1 ⁇ A ⁇ 4; the mass percentage of phosphorus in the first layer is B%, 0.03 ⁇ B ⁇ 1.2; and the mass percentage of fluorine in the first layer is C%, 0.1 ⁇ C ⁇ 4.
  • the contents of lithium, phosphorus, and fluorine are within an appropriate range, they can reflect the thickness of the first layer, so that the first layer protects the silicon matrix, which is beneficial for the silicon-based composite material to have excellent specific capacity while improving the cycle performance and expansion performance of the silicon-based composite material.
  • A can be 0.1, 0.2, 0.5, 0.8, 1, 1.2, 1.5, 2, 2.2, 2.5, 3, 3.2, 3.5, 4, or any value within the range of any two of the above values.
  • B can be 0.03, 0.05, 0.1, 0.2, 0.3, 0.5, 0.7, 0.9, 1, 1.2, or any value within the range of any two of the above values.
  • C can be 0.1, 0.2, 0.5, 0.8, 1, 1.2, 1.5, 2, 2.2, 2.5, 3, 3.2, 3.5, 4, or any value within the range of any two of the above values.
  • the silicon matrix comprises a silicon-carbon material, wherein the mass percentage of silicon is D%, 38 ⁇ D ⁇ 59%, and the mass percentage of carbon is E%, 40 ⁇ E ⁇ 61%, based on the mass of the silicon matrix.
  • the mass percentages of silicon and carbon in the silicon matrix within these ranges are beneficial for the silicon matrix to possess good specific capacity and initial efficiency while also improving the interfacial stability of the silicon-based composite material, thereby enhancing the cycle performance and expansion performance of the silicon-based composite material.
  • the mass percentage D of silicon can be 38, 40, 42, 45, 48, 50, 52, 55, 59, or any value within the range of any two of the above values.
  • the mass percentage E of carbon can be 40, 42, 45, 48, 50, 52, 55, 59, 61, or any value within the range of any two of the above values.
  • the ratio (A+B+C)/D can be 0.003, 0.005, 0.01, 0.03, 0.05, 0.1, 0.13, 0.15, 0.18, 0.19, or any value within the range of any two of the above values.
  • the H/D ratio can be 0.104, 0.11, 0.12, 0.15, 0.2, 0.3, 0.5, 0.6, 1, 1.2, 1.5, 1.8, 2, 2.3, 2.5, 2.8, 3, 3.2, 3.5, 3.8, 4, 4.16, or any value within the range of any two of the above values.
  • the silicon to carbon content ratio in the silicon matrix ranges from 0.623 to 1.475. Within this range, a certain mass ratio of silicon to carbon in the silicon matrix is achieved, thereby improving the specific capacity and initial efficiency of the silicon-based composite material. In some embodiments, the mass ratio of silicon to carbon in the silicon matrix can be 0.623, 0.65, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.475, or any value within the range of any two of the above values.
  • the preparation method of silicon-based composite materials may include, but is not limited to, the following steps: (1) dissolving and dispersing the conductive agent and the fluorinated lithium phosphate compound 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-based composite material.
  • step (2) the drying temperature is 80°C ⁇ 220°C and the drying time is 4h ⁇ 48h.
  • 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 thickness H of the first layer is adjusted by changing the mass ratio of the silicon matrix, conductive agent, and fluorinated lithium phosphate compound.
  • the mass ratio of silicon matrix, conductive agent, and fluorinated lithium phosphate compound is 100:(0.4–0.9):(0.5–5).
  • increasing the mass ratio of silicon matrix to conductive agent may affect the conductivity of the silicon-based composite material and its cycle performance; decreasing the mass ratio of silicon matrix to conductive agent will reduce the specific capacity of the silicon-based composite material and lower the energy density of the lithium-ion battery.
  • Increasing the mass ratio of silicon matrix to fluorinated lithium phosphate compound will affect the interfacial stability of the silicon-based composite material and lower the cycle performance of the lithium-ion battery; decreasing the mass ratio of silicon matrix to fluorinated lithium phosphate compound will reduce the initial efficiency of the silicon-based composite material and lower the energy density of the lithium-ion battery.
  • Increasing the mass ratio of fluorinated lithium phosphate compound to conductive agent will affect the conductivity of silicon-based composite materials and reduce the kinetic performance of lithium-ion batteries; decreasing the mass ratio of fluorinated lithium phosphate compound to conductive agent will affect the interfacial stability of silicon-based composite materials and reduce the cycle performance of lithium-ion batteries.
  • the content of lithium, phosphorus, and fluorine elements in the silicon substrate is adjusted by modifying the mass of the fluorinated lithium phosphate compound.
  • 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.
  • 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-based composite materials can alleviate the overall volume expansion of the negative electrode active layer. At the same time, using both graphite and silicon-based composite materials as negative electrode active materials can fully utilize the advantages of both silicon-based 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.
  • This application also applies secondary batteries to electronic devices, whereby the secondary batteries supply power to the loads within the electronic devices.
  • the secondary batteries in these electronic devices contain a negative electrode material, which includes a silicon-based composite material.
  • the fluorinated lithium phosphate compound in the silicon-based composite material is reduced to an inorganic salt during the charging and discharging process of the secondary battery, improving the strength and ionic conductivity of the SEI film, thereby enhancing the cycle performance and charging efficiency of the secondary battery, and consequently improving the lifespan and charging efficiency of the electronic device.
  • the electronic devices or apparatus described in this application are not particularly limited.
  • the electronic devices described in this application include, but are not limited to, laptops, pen input 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.
  • Preparation of the negative electrode sheet The silicon-based composite material prepared above was used as the active material, acetylene black as the conductive agent, and sodium alginate as the binder. The mass ratio of the active material, acetylene black, and sodium alginate was 96:2:2. The active material and acetylene black were thoroughly mixed in the specified ratio and ground evenly. An aqueous solution of sodium alginate was added in the specified ratio and stirred for 4 hours. Finally, the mixture was evenly coated onto copper foil and vacuum dried at 70°C for 12 hours to obtain the negative electrode sheet.
  • FEC fluoroethylene carbonate
  • HTCN 1,3,6-hexamethylenetrionitrile
  • Example 1-1 The difference between Examples 1-2 to 1-7 and Example 1-1 is that the amount of lithium difluorodioxalate phosphate added in the preparation of the silicon-based composite material is adjusted; the rest of the preparation process is exactly the same as in Example 1-1. Specific material preparation conditions are shown in Tables 1 and 2.
  • Examples 2-1 to 2-4 and Examples 1-7 The difference between Examples 2-1 to 2-4 and Examples 1-7 is that the sphericity of the silicon matrix or the mass ratio of silicon in the silicon matrix is adjusted in the silicon-based composite material; the rest of the preparation process is exactly the same as in Examples 1-7. Specific material preparation conditions are shown in Tables 3 to 5.
  • Examples 3-5 and Examples 3-3 The difference between Examples 3-5 and Examples 3-3 is that the particle size Dv50 of the silicon-based composite material was adjusted. The remaining preparation process is exactly the same as in Examples 3-3.
  • the difference between Examples 3-6 and Examples 3-4 is that the particle size Dv50 of the silicon-based composite material was adjusted. The remaining preparation process is exactly the same as in Examples 3-4.
  • the thickness of the first layer and the mass percentage of silicon are the same as in Examples 1-7. Specific material preparation conditions are shown in Table 6.
  • Example 3-4 The difference between Examples 3-7 and 3-8 and Example 3-4 is that the type of fluorinated lithium phosphate compound and the particle size Dv50 of the silicon-based composite material were adjusted; the rest of the preparation process was exactly the same as in Example 3-4. The thickness of the first layer and the mass percentage of silicon were the same as in Examples 1-7. Specific material preparation conditions are shown in Table 6.
  • Example 1-1 The difference from Example 1-1 is that the surface of the silicon matrix was not coated during the preparation of the silicon-based composite material.
  • the specific material preparation conditions are shown in Tables 1 and 2.
  • Comparative Example 1 is represented by “D1”
  • the comparative examples described below will be represented by the corresponding "D2", “D3”, “D4", and "D5".
  • Example 1-1 The difference from Example 1-1 is that, in the process of preparing silicon-based composite materials, the surface of the silicon matrix is only coated with the conductive agent SWCNT.
  • the specific material preparation conditions are shown in Table 1 and Table 2.
  • Example 1-1 The difference from Example 1-1 is that, in the process of preparing silicon-based composite materials, the surface of the silicon matrix is only coated with fluorinated lithium phosphate compound.
  • the specific material preparation conditions are shown in Table 1 and Table 2.
  • Example 1-1 The difference from Example 1-1 is that the amount of lithium difluorodioxalate phosphate added in the preparation of the silicon-based composite material is adjusted; the rest of the preparation process is exactly the same as in Example 1-1. Specific material preparation conditions are shown in Tables 1 and 2.
  • Example 1-1 The difference from Example 1-1 is that the amount of lithium difluorodioxalate phosphate added in the preparation of the silicon-based composite material is adjusted; the rest of the preparation process is exactly the same as in Example 1-1. Specific material preparation conditions are shown in Tables 1 and 2.
  • Powder particle size testing method 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 0.02g of powder sample was added to a 50ml clean beaker, followed by approximately 20ml of deionized water, and then 3 drops of the surfactant sodium dodecyl sulfate were added to completely disperse the powder in the water. The sample was then ultrasonically cleaned for 5 minutes in a 120W ultrasonic cleaner to obtain the powder particle size test sample. In the volumetric particle size distribution of the material, starting from the smallest particle size, the particle size reaching 50% of the cumulative volume is defined as Dv50.
  • the silicon-based composite material was sliced using focused ion beam (FIB) and characterized using a high-resolution transmission electron microscope (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-based 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.
  • HRTEM high-resolution transmission electron microscope
  • the mass percentages of silicon and carbon elements can be obtained.
  • the silicon-based composite material was sliced using focused ion beam (FIB) and then characterized by high-resolution transmission electron microscopy (HRTEM, model Talos F200X). EDS elemental analysis was performed within the same selected area (1000x magnification) to obtain the mass percentages of lithium, phosphorus, and fluorine.
  • FIB focused ion beam
  • HRTEM high-resolution transmission electron microscopy
  • the FPIA-2100 (manufactured by SYSMEX Co., Ltd.) was evaluated using a flow particle image analyzer through the following evaluation method.
  • a silicon substrate sample was dispersed in water containing a surfactant and introduced into a flow particle image analyzer via a syringe.
  • a CCD camera was used to capture an image of the sample (dispersed fine powder liquid) flowing in the core of the flow cell every 1/30 second, and the still images were processed in real time. Sphericity was calculated using the following formula.
  • 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 lithium-ion battery was charged at a constant current of 0.5C to 3.95V, which is the initial half-charge state.
  • the thickness of the lithium-ion battery at the initial half-charge state was measured with a micrometer and recorded as H0.
  • the lithium-ion battery was charged at a constant current of 0.5C to 4.45V (the fully charged state), and the thickness of the lithium-ion battery at this time was measured with a micrometer again and recorded as H1.
  • the expansion rate after 500 cycles (H1 - H0) / H0 ⁇ 100%.
  • 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 1C 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, constituting 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 1C was adjusted to 1.5C, 2C, 2.4C, 2.5C, 2.8C, 3C, 3.5C, 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.
  • 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 voltage for charging the lithium-ion battery is 4.45V, and the discharge cutoff voltage is 3.0V.
  • Figures 1 and 2 are scanning electron microscope images of the silicon substrate and the silicon-based composite material formed after coating the silicon substrate in Example 1, respectively. From Figures 1 and 2, the silicon substrate surface is coated with a coating material, increasing surface smoothness, and fluorinated lithium phosphate compound and conductive agent are attached to the silicon substrate.
  • Table 2 Note: In Tables 1 and 2, "/" indicates that no parameters have been added or there are no related parameters.
  • a conductive agent and a fluorinated lithium phosphate compound were formed on the surface of the silicon substrate, which improved the cycle performance and expansion performance of the lithium-ion battery and reduced the lithium plating performance of the lithium-ion battery.
  • the thickness H of the first layer affects the cycle performance and expansion performance of the lithium-ion battery. Compared to Comparative Examples 4 and 5, the thickness of the first layer in Examples 1-1 to 1-7 is within a suitable range, which is beneficial for improving the cycle performance and expansion performance of the lithium-ion battery.
  • the sphericity of the silicon substrate also affects the cycle performance and expansion performance of the lithium-ion battery.
  • a greater sphericity is beneficial to improving the uniformity of active ion embedding in silicon-based composite materials, which is beneficial to improving the stability of the SEI film, thereby improving the cycle performance and expansion performance of silicon-based composite materials.
  • the mass fractions of silicon and carbon also affect the cycle performance and expansion performance of lithium-ion batteries.
  • Table 5 shows that in Examples 1-7 and Examples 2-3 to 2-4, when the silicon content in the silicon matrix is within a suitable range and the (A+B+C)/D ratio is within a suitable range, the lithium-ion batteries exhibit good cycle performance, expansion performance, and reduced lithium plating.
  • the average diameter and average length of the conductive agent in the silicon-based composite material affect the cycle performance, expansion performance, and lithium plating performance of the lithium-ion battery.
  • Table 6 shows that in Examples 1-7 and Examples 3-1 to 3-4, when the average diameter and average length of the conductive agent are within a suitable range, the lithium-ion batteries exhibit good cycle performance, expansion performance, and reduced lithium plating.
  • the particle size Dv50 of silicon-based composite materials affects the cycle performance, expansion performance, and lithium plating performance of lithium-ion batteries.
  • Table 6 in Examples 3-5 to 3-8, the lithium-ion batteries of silicon-based composite materials exhibit good cycle performance and expansion performance at different particle sizes Dv50.

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Abstract

本申请提供一种硅基复合材料、二次电池和电子装置，硅基复合材料包括硅基体以及位于硅基体的至少部分表面的第一层，第一层包括导电剂和含氟的磷酸锂化合物，第一层的厚度为H nm，5≤H≤200。本申请提供的硅基复合材料中含氟的磷酸锂化合物能够改善SEI膜的界面稳定性，提高硅基复合材料的循环性能和膨胀性能。

Description

硅基复合材料、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，尤其是涉及一种硅基复合材料、应用所述硅基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。二次电池通常采用硅材料作为负极材料。硅材料由于较高的理论比容量(Li15Si4，3579mAh/g)和合适的工作电压(<0.5Vvs.Li/Li+)等特点，被认为是可以替代石墨的最有前途的负极材料。然而，低的导电性以及在合金化/去合金化过程中巨大的体积膨胀，影响了二次电池的循环性能。
发明内容
本申请提供一种能够提高循环性能的硅基复合材料。
另，本申请还提供一种应用硅基复合材料的二次电池和电子装置。
本申请提供一种硅基复合材料，包括硅基体以及位于硅基体的至少部分表面的第一层，第一层包括导电剂和含氟的磷酸锂化合物，第一层的厚度为H nm，5≤H≤200。
本申请的硅基复合材料应用于二次电池时，第一层中含氟的磷酸锂化合物在二次电池充电过程中会发生还原反应形成LiF、Li3PO4或Li3P等无机盐组分，并参与固体电解质界面膜(SEI膜)的形成，无机盐组分提高SEI膜的强度和离子导电性，从而能够改善SEI膜的界面稳定性，提高硅基复合材料的循环性能和膨胀性能。同时，第一层中导电剂的加入能够进一步改善硅基复合材料的导电性，进而提升硅基复合材料的动力学性能；在提高SEI膜稳定性的同时，还利于相对减小SEI膜的厚度，降低SEI膜的界面传输阻抗，从而改善析锂现象。第一层的厚度在上述范围内，在提高硅基复合材料的比容量的同时还能够保护硅基体，提高SEI膜的界面稳定性，进一步提高硅基复合材料的循环性能和膨胀性能。
基于第一方面，在一些可能的实施方式中，含氟的磷酸锂化合物选自二氟磷酸锂、二氟双草酸磷酸锂或四氟草酸磷酸锂中的至少一种。该含氟的磷酸锂化合物中均能够发生还原反应形成LiF、Li3PO4或Li3P等无机盐组分，以改善SEI膜的界面稳定性，提高硅基复合材料的循环性能和膨胀性能。
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。该导电剂均为线状导电剂，能够提供较好的离子传输通道，提升硅基复合材料的导电性，从而提升硅基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，5≤H≤64，利于进一步通过第一层提升SEI膜的稳定性，提高硅基复合材料的循环性能和膨胀性能。
基于第一方面，在一些可能的实施方式中，硅基复合材料的粒径Dv50为Xμm，4≤X≤13。利于减少硅基复合材料和电解液的接触，进而减小硅基复合材料与电解液的副反应，从而提高硅基复合材料的循环性能。
基于第一方面，在一些可能的实施方式中，0.56≤H/X≤22.22，利于使硅基复合材料兼具较好的动力学性能、循环性能和膨胀性能。
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，1≤y≤30。利于使导电剂具有较好的分散性的同时，还利于提高硅基复合材料的电导率，从而提高硅基复合材料的动力学性能和循环性能。导电剂的平均长度为Lnm，1000≤L≤2000。利于使硅基复合材料具有较好分散性的同时，还利于使活性离子具有良好的长程导电能力，提高硅基复合材料的倍率性能。
基于第一方面，在一些可能的实施方式中，1≤H/y≤50。通过调控第一层的厚度和导电剂的平均直径的关系，以在第一层厚度较厚时，导电剂能够保持合适的平均直径，从而利于提高硅基复合材料的整体稳定性以及离子导电性。
基于第一方面，在一些可能的实施方式中，硅基体的球形度为S，S≥0.8。硅基体的球形度越大，利于提高活性离子嵌入硅基复合材料的均匀性，也利于提高第一层包覆的均匀性以及硅基体的稳定性，从而利于提高SEI膜的稳定性，进而提高硅基复合材料的循环性能。
基于第一方面，在一些可能的实施方式中，1052≤L/S≤2105。较高的球形度下，硅基复合材料之间存在间隙，调整导电剂的平均长度和球形度之间的关系，在较高的球形度下，利用较长的导电剂长度，使得导电剂之间形成连通的活性离子传输通道，以利于提高活性离子传输速率，从而提高硅基复合材料的倍率性能。
基于第一方面，在一些可能的实施方式中，基于硅基复合材料的质量，第一层中锂元素的质量占比为A％，0.1≤A≤4；第一层中磷元素的质量占比为B％，0.03≤B≤1.2；第一层中氟元素的质量占比为C％，0.1≤C≤4；当锂元素、磷元素和氟元素含量在适应的范围内，以使得第一层保护硅基体，利于使硅基复合材料具有优异的比容量的同时，提高硅基复合材料的循环性能和膨胀性能。
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，基于硅基体的质量，硅元素的质量占比为D％，38≤D≤59，碳元素的质量占比为E％，40≤E≤61。利于使硅基体在具有较好的比容量和首次效率的同时，还可提高硅基复合材料的界面稳定性，进而提升硅基复合材料的循环性能和膨胀性能。
基于第一方面，在一些可能的实施方式中，0.003≤(A+B+C)/D≤0.19。第一层中的锂元素、磷元素和氟元素含量与硅基体中硅元素满足上述关系式，使得第一层中元素充分参与SEI膜的形成，利于提高SEI膜的稳定性并提高对硅基体的保护，从而提高硅基复合材料的循环性能和膨胀性能。
基于第一方面，在一些可能的实施方式中，0.104≤H/D≤4.16。利于在硅基体具有一定硅含量的同时，调整第一层的厚度，减少硅基体和电解液发生的副反应，从而利于提高硅基复合材料的循环性能。
本申请第二方面提供一种二次电池，包括负极极片、正极极片和电解液，负极极片包括硅基复合材料。第一层中的含氟的磷酸锂化合物能够改善SEI膜的界面稳定性，提高二次电池的循环性能。
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，二次电池包括负极极片，负极极片中硅基复合材料，能够提高二次电池的循环性能，进而提高电子装置的使用寿命和充放电速率。
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为本申请实施例1中硅基体在包覆前的扫描电子显微镜图。
图2为本申请实施例1中硅基体包覆后制备的硅基复合材料的扫描电子显微镜图。
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。
本申请一实施方式提供一种二次电池，其包括外壳、电极组件和电解液。电极组件和电解液均位于外壳内。
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。
电极组件包括正极极片、负极极片和隔离膜，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，负极活性材料包括硅基复合材料。
硅基复合材料包括硅基体以及位于硅基体上的至少部分表面的第一层，第一层包括导电剂和含氟的磷酸锂化合物，第一层的厚度为H nm，5≤H≤200。
本申请提供的硅基复合材料中，第一层中的含氟的磷酸锂化合物在二次电池充电过程中会发生还原反应，形成LiF、Li3PO4或Li3P等无机盐组分，并参与固体电解质界面膜(SEI膜)的形成，无机盐组分提高SEI膜的强度和离子导电性，从而能够改善SEI膜的界面稳定性，提高硅基复合材料的循环性能和膨胀性能。同时，第一层中导电剂的加入能够进一步改善硅基复合材料的导电性，进而利于提升硅基复合材料的倍率性能并减少析锂。通过调控第一层的厚度在上述范围内，以在硅基复合材料在兼具较高的比容量下还能够保护硅基体，提高SEI膜的界面稳定性，进一步提高硅基复合材料的循环性能和膨胀性能。
若H＜5，第一层的厚度较小，对硅基体的保护作用较弱，电解液可能会与硅基体反应，并蚀刻硅基体，从而恶化硅基复合材料的循环性能和膨胀性能；若H＞200，第一层的厚度较大，影响硅基复合材料的比容量。在一些实施例中，第一层的厚度H可以为5、6、10、15、20、25、30、40、50、75、90、100、120、125、130、150、175、180、190、200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，优选地，5≤H≤64。利于进一步通过第一层提升SEI膜的稳定性，提高硅基复合材料的循环性能和膨胀性能。
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等。
在一些实施例中，含氟的磷酸锂化合物选自二氟磷酸锂、二氟双草酸磷酸锂或四氟草酸磷酸锂中的至少一种。上述含氟的磷酸锂化合物中均能够发生还原反应形成LiF、Li3PO4或Li3P等无机盐组分，以改善SEI膜的界面稳定性，提高硅基复合材料的循环性能和膨胀性能。
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。上述导电剂均为线状导电剂，能够提供较好的离子传输通道，提升硅基复合材料的导电性，从而提升硅基复合材料的倍率性能。
在一些实施例中，硅基复合材料的粒径Dv50为Xμm，4≤X≤13。在上述范围内，利于减少硅基复合材料和电解液的接触机会，利于减小硅基复合材料与电解液发生的副反应，从而提高硅基复合材料的循环性能和膨胀性能。在一些实施例中，硅基复合材料的平均粒径X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，0.56≤H/X≤22.22，通过调整第一层的厚度和硅基复合材料的平均粒径之间的关系，利于使硅基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倍率性能。在一些实施例中，H/X可以为0.56、0.6、0.7、0.8、1、2、3、5、7、9、10、12、15、17、19、20、22.22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，导电剂为线状结构，导电剂的平均直径为y nm，1≤y≤30；在上述长度范围内，利于使导电剂具有较好的分散性的同时，利于提高硅基复合材料的电导率，从而提高硅基复合材料的倍率性能和循环性能。在一些实施例中，导电剂的平均直径y可以为1、2、3、5、7、9、10、12、15、17、18、20、23、25、27、30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L nm，1000≤L≤2000。导电剂的平均长度在上述范围内，利于使硅基复合材料具有较好分散性的同时，还利于活性锂离子具有良好的长程导电能力，提高硅基复合材料的动力学性能。在一些实施例中，导电剂的平均长度L可以为1000、1200、1500、1600、1700、1800、1900、2000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≤50。通过调控第一层的厚度和导电剂的平均直径的关系，以在第一层厚度较厚时，导电剂能够在设定的范围内的平均直径，从而利于提高硅基复合材料的整体稳定性以及离子导电性。在一些实施例中，H/y可以为1、2、3、4、5、6、10、12、15、20、25、30、35、40、45、50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，硅基体的球形度为S，S≥0.8，硅基体的球形度越大，利于提高活性离子嵌入硅基复合材料的均匀性，也利于提高第一层包覆的均匀性以及硅基体的稳定性，从而利于提高SEI膜的稳定性，进而提高硅基复合材料的循环性能和膨胀性能。在一些实施例中，球形度S可以为0.8、0.85、0.9、0.95、0.99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，0.8≤S＜1。
在一些实施例中，1052≤L/S≤2105，较高的球形度下，硅基复合材料之间存在间隙，调整导电剂的平均长度和球形度之间的关系，在较高的球形度下，利用较长的导电剂长度，使得导电剂之间形成连通的活性离子传输通道，以利于提高锂离子传输速率，从而提高硅基复合材料的倍率性能。在一些实施例中，L/S的比值可以为1052、1100、1200、1300、1400、1500、1600、1700、1800、1900、2000、2100、2105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，基于硅基复合材料的质量，第一层中锂元素的质量占比为A％，0.1≤A≤4；第一层中磷元素的质量占比为B％，0.03≤B≤1.2；第一层中氟元素的质量占比为C％，0.1≤C≤4；当锂元素、磷元素和氟元素含量在适应的范围内，能够反映第一层的厚度，以使得第一层保护硅基体，利于使硅基复合材料具有优异的比容量的同时，提高硅基复合材料的循环性能和膨胀性能。在一些实施例中，A可以为0.1、0.2、0.5、0.8、1、1.2、1.5、2、2.2、2.5、3、3.2、3.5、4或在上述任意两个数值所组成的范围内的任一值。B可以为0.03、0.05、0.1、0.2、0.3、0.5、0.7、0.9、1、1.2或在上述任意两个数值所组成的范围内的任一值。C可以为0.1、0.2、0.5、0.8、1、1.2、1.5、2、2.2、2.5、3、3.2、3.5、4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，硅基体包括硅碳材料，基于硅基体的质量，硅元素的质量占比为D％，38≤D≤59，碳元素的质量占比为E％，40≤E≤61。硅基体中，硅元素和碳元素的质量占比在上述范围内，利于使硅基体在具有较好的比容量和首次效率的同时，还可提高硅基复合材料的界面稳定性，进而提升硅基复合材料的循环性能和膨胀性能。在一些实施例中，硅元素的质量占比D可以为38、40、42、45、48、50、52、55、59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，碳元素的质量占比E可以为40、42、45、48、50、52、55、59、61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，0.003≤(A+B+C)/D≤0.19。通过调控第一层中锂元素、磷元素和氟元素的质量之和与硅基体中碳元素的质量比，能够反映出第一层对硅基体包覆的影响，第一层中的锂、磷和氟元素的质量之和与硅基体中硅元素满足上述关系式，使得第一层中元素充分参与SEI膜的形成，提高SEI膜的稳定性并提高第一层对硅基体的保护，从而提高硅基复合材料的循环性能和膨胀性能。若上述比值较小，第一层对SEI膜的改善效果不明显；若上述比值较大，硅基复合材料应用于二次电池时，在化成阶段会发生较多副反应，影响首次效率和能量密度。在一些实施例中，(A+B+C)/D的比值可以为0.003、0.005、0.01、0.03、0.05、0.1、0.13、0.15、0.18、0.19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，0.104≤H/D≤4.16。第一层的厚度与硅基体在上述关系下，利于在硅基体具有一定硅含量的同时，调整第一层的厚度，减少硅基体和电解液发生的副反应，从而提高硅基复合材料的循环性能。在一些实施例中，H/D的比值可以为0.104、0.11、0.12、0.15、0.2、0.3、0.5、0.6、1、1.2、1.5、1.8、2、2.3、2.5、2.8、3、3.2、3.5、3.8、4、4.16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，硅基体中硅元素和碳元素的含量比范围为0.623～1.475。在上述范围内，以使得硅基体中硅元素和碳元素满足一定的质量比，从而利于提高硅基复合材料的比容量和首次效率。在一些实施例中，硅基体中硅元素和碳元素的质量比可以为0.623、0.65、0.7、0.8、0.9、1、1.1、1.2、1.3、1.4、1.475或在上述任意两个数值所组成的范围内的任一值。
本申请对硅基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。例如硅基复合材料的制备方法可以包括但不限于以下步骤：(1)将导电剂和含氟的磷酸锂化合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，干燥后得到硅基复合材料。
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)中干燥的温度为80℃～220℃，干燥时间为4h～48h。
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。
硅基复合材料的制备方法中，通过改变硅基体、导电剂和含氟的磷酸锂化合物三者的质量比，以调整第一层的厚度H。硅基体、导电剂和含氟的磷酸锂化合物的质量比为100:(0.4～0.9):(0.5～5)，在上述合适比值范围内，若增大硅基体和导电剂的质量比，可能会影响硅基复合材料的导电性，影响硅基复合材料的循环性能；减小硅基体和导电剂的质量比，会降低硅基复合材料的克容量，降低锂离子电池的能量密度。若增大硅基体和含氟的磷酸锂化合物的质量比，会影响硅基复合材料界面稳定性，降低锂离子电池的循环性能；减小硅基体和含氟的磷酸锂化合物的质量比，会降低硅基复合材料的首效，降低锂离子电池的能量密度。若增大含氟的磷酸锂化合物和导电剂的质量比，会影响硅基复合材料的导电性，降低锂离子电池的动力学性能；减小含氟的磷酸锂化合物和导电剂的质量比，会影响硅基复合材料的界面稳定性，降低锂离子电池的循环性能。
通过调整含氟的磷酸锂化合物的质量，以调整含氟的磷酸锂化合物在硅基体上的锂元素、磷元素和氟元素的含量。
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。
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，其与硅基复合材料配合能够缓解负极活性层整体的体积膨胀。同时，石墨与硅基复合材料同时作为负极活性材料还能够充分利用硅基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。
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中的负载供电。上述电子装置中二次电池中包含有负极材料，负极材料中包括硅基复合材料，硅基复合材料中的含氟的磷酸锂化合物在二次电池充放电过程中还原形成无机盐，提高SEI膜的强度和离子导电性，从而提高二次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。
本申请的电子设备或装置没有特别限定。在一些实施例中，本申请的电子设备包括但不限于，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
(1)将0.4g单壁碳纳米管(SWCNT)和0.2g二氟二草酸磷酸锂溶解分散于水和乙醇的混合溶剂中，并搅拌均匀，SWCNT的平均直径为5nm，平均长度为1500nm；(2)将100g硅基体材料加入到步骤(1)中，硅基体的球形度为0.95，硅基体中硅元素和碳元素的质量比为48:51，搅拌后分散均匀，180℃下干燥24h后得到硅基复合材料。
制备锂离子电池：
负极极片的制备：采用上述制备得到的硅基复合材料作为活性材料，乙炔黑作为导电剂，海藻酸钠作为粘结剂。活性材料、乙炔黑、海藻酸钠的质量比为96：2：2。将活性材料、乙炔黑按比例充分混合后研磨均匀，按比例加入海藻酸钠水溶液并搅拌4h。最后将混合物浆料均匀涂布在铜箔上，并于70℃真空干燥下真空干燥12h，得到负极极片。
正极极片的制备：采用super-P为导电剂，PVDF为粘结剂，其中活性材料(钴酸锂)、super-P和PVDF的质量比为96：2：2。将活性材料与super-P按比例充分混合后研磨均匀，按比例加入已制备的PVDF溶液并搅拌4h。最后将混合物浆料均匀涂布在铝箔上，并于70℃真空干燥下真空干燥12h，得到正极极片。
其中，正极极片和负极极片的单位面积容量分别约为2.6mAh cm-2和2.7mAh cm-2，对应负/正极容量比(N/P)约为1.045。将上述正极极片和负极极片通过卷绕工艺使用7um的聚乙烯(PE)隔膜分离而成。其中，将体积比为1:1:1:1的碳酸乙烯酯/碳酸丙烯酯/碳酸二乙酯/丙酸丙酯(EC/PC/DEC/PP)混合，并在溶剂中加入1M LiPF6，混合均匀，在加入5wt.％的氟代碳酸乙烯酯(FEC)和2wt.％的1,3,6-己三腈(HTCN)作为电解质添加剂，电解液的保液系数为1.6g/Ah。经过陈化，化成，分容等工序后制成锂离子电池。
实施例1-2至实施例1-7
实施例1-2至实施例1-7与实施例1-1的区别在于：调整制备硅基复合材料中二氟二草酸磷酸锂的加入量，其余制备过程与实施例1-1完全相同。具体材料制备条件见表1和表2。
实施例2-1至2-4
实施例2-1至实施例2-4与实施例1-7的区别在于：调整硅基复合材料中硅基体的球形度或硅基体中硅元素的质量占比，其余制备过程与实施例1-7完全相同。具体材料制备条件见表3至表5。
实施例3-1至实施例3-4
实施例3-1至实施例3-4与实施例1-7的区别在于：调整硅基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1-7完全相同。第一层的厚度与硅的质量百分比与实施例1-7中的数值相同。具体材料制备条件见表6。
实施例3-5至实施例3-8
实施例3-5与实施例3-3的区别在于：调整硅基复合材料的粒径Dv50。其余制备过程与实施例3-3完全相同。实施例3-6与实施例3-4的区别在于：调整硅基复合材料的粒径Dv50。其余制备过程与实施例3-4完全相同。第一层的厚度与硅的质量百分比与实施例1-7中的数值相同。具体材料制备条件见表6。
实施例3-7至实施例3-8与实施例3-4的区别在于：调整含氟的磷酸锂化合物的种类并调整硅基复合材料的粒径Dv50，其余制备过程与实施例3-4完全相同。第一层的厚度与硅的质量百分比与实施例1-7中的数值相同。具体材料制备条件见表6。
对比例1
与实施例1-1的区别在于，制备硅基复合材料过程中，硅基体的表面未经任何包覆处理，具体材料制备条件见表1和表2。在表1和表2中，对比例1采用“D1”表示，以下描述的对比例后续均采用对应的“D2”、“D3”、“D4”、“D5”进行表示。
对比例2
与实施例1-1的区别在于，制备硅基复合材料过程中，硅基体的表面仅包覆有导电剂SWCNT，具体材料制备条件见表1和表2。
对比例3
与实施例1-1的区别在于，制备硅基复合材料过程中，硅基体的表面仅包覆有含氟的磷酸锂化合物，具体材料制备条件见表1和表2。
对比例4
与实施例1-1的区别在于，调整制备硅基复合材料中二氟二草酸磷酸锂的加入量，其余制备过程与实施例1-1完全相同。具体材料制备条件见表1和表2。
对比例5
与实施例1-1的区别在于，调整制备硅基复合材料中二氟二草酸磷酸锂的加入量，其余制备过程与实施例1-1完全相同。具体材料制备条件见表1和表2。
测试方法
(1)粉末粒径的测试方法：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)对硅基复合材料进行切片，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，测量硅基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，从而获得第一层的厚度。
(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)硅基复合材料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)硅基复合材料中锂元素、磷元素和氟元素的测试方法：
采用聚焦离子束(FIB)对硅基复合材料进行切片，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(1000倍放大倍数)内进行EDS元素分析即可得到锂元素、磷元素和氟元素的质量占比。
(6)球形度的测量方法：
利用流动颗粒图象分析仪，FPIA-2100(由SYSMEX Co.，Ltd生产)通过下述评估方法评估。
将硅基体试样分散于包含表面活性剂的水中并且通过注射器引入流动颗粒图像分析仪。利用CCD相机每1/30秒拍摄一张在流动池核心部分流动的试样(分散细粉的液体)的照片并且实时处理静态照片。通过下述公式计算球形度。
球形度＝(由相应圆环直径计算的周长)/(颗粒投影图像的周长)
“相应环的直径”是这样的完美的环的直径，其具有对应于实际拍摄的颗粒的投影图像的周长的面积。球形度是通过将其除以用实际拍摄的颗粒的投影图像的周长获得的值。例如，在理想圆环情况下，球形度为1，颗粒图像的形状越复杂，球形度的值越小。对于每个单独颗粒计算平均球形度。
(7)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。
锂离子电池的性能测试
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.膨胀性能测试方法：
将锂离子电池以0.5C流恒流充电至3.95V，为初始半充状态，用螺旋千分尺测试初始半充时锂离子电池的厚度为H0。以上述循环性能测试过程循环至500次时，将锂离子电池以0.5C流恒流充电至4.45V，为满充状态)，再用螺旋千分尺测试此时锂离子电池的厚度为H1。500圈循环膨胀率＝(H1-H0)/H0×100％。
3.析锂性能测试方法：
将锂离子电池在25℃±1℃的恒温箱中静置30分钟，以1C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1C分别调整为1.5C、2C、2.4C、2.5C、2.8C、3C、3.5C、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膜被污染的状态来判定，当负极相接触的隔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。
4.能量密度的测试方法：
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。
图1和图2分别为实施例1中硅基体以及硅基体包覆后形成硅基复合材料的扫描电子显微镜图。从图1和图2中，硅基体表面包覆有包覆物，表面光滑度增加，含氟的磷酸锂化合物和导电剂附着于硅基体上。
表1
表2

注：表1和表2中“/”表示未添加或无相关参数。
表3
表4
在表1和表2中，在实施例和对比例中，硅基体的表面形成有导电剂和含氟磷酸锂化合物，其提高了锂离子电池的循环性能、膨胀性能并降低了锂离子电池的析锂性能。
第一层的厚度H会影响锂离子电池的循环性能和膨胀性能。相较于对比例4和对比例5，实施例1-1至实施例1-7中第一层的厚度在适宜的范围内，其利于提高锂离子电池的循环性能和膨胀性能。硅基体的球形度也会影响锂离子电池的循环性能和膨胀性能。
在表3和表4中，在实施例1-7和实施例2-1至2-2中可知，球形度越大，利于提高活性离子嵌入硅基复合材料的均匀性，利于提高SEI膜的稳定性，从而利于提高硅基复合材料的循环性能和膨胀性能。
表5
硅元素和碳元素的质量分数也会影响锂离子电池的循环性能和膨胀性能。在表5中，在实施例1-7和实施例2-3至2-4中可知，硅基体中硅元素在合适的范围内以及(A+B+C)/D在合适的范围内，其锂离子电池均具有良好的循环性能、膨胀性能并减少析锂。
表6
硅基复合材料中导电剂的平均直径和平均长度影响锂离子电池的循环性能、膨胀性能以及析锂性能。在表6中，在实施例1-7和实施例3-1至实施例3-4可知，导电剂的平均直径和平均长度在合适的范围内，其锂离子电池均具有良好的循环性能、膨胀性能并减少了析锂。
硅基复合材料的粒径Dv50影响锂离子电池的循环性能、膨胀性能以及析锂性能。在表6中，实施例3-5至实施例3-8中，硅基复合材料在不同的粒径Dv50下，其锂离子电池均具有良好的循环性能和膨胀性能。
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 (11)

  1. 一种硅基复合材料，其中，包括硅基体以及位于所述硅基体的至少部分表面的第一层，所述第一层包括导电剂和含氟的磷酸锂化合物，所述第一层的厚度为H nm，5≤H≤200。
  2. 如权利要求1所述的硅基复合材料，其中，所述含氟的磷酸锂化合物选自二氟磷酸锂、二氟双草酸磷酸锂或四氟草酸磷酸锂中的至少一种；
    或/和
    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。
  3. 如权利要求1或2所述的硅基复合材料，其中，所述硅基复合材料满足以下条件中的至少一者：
    (1)5≤H≤64；
    (2)所述硅基复合材料的粒径Dv50为Xμm，4≤X≤13；
    (3)所述硅基复合材料的粒径Dv50为Xμm，0.56≤H/X≤22.22。
  4. 如权利要求1至3中任一项所述的硅基复合材料，其中，所述导电剂为线状结构，所述导电剂的平均直径为y nm，1≤y≤30；所述导电剂的平均长度为L nm，1000≤L≤2000。
  5. 如权利要求4所述的硅基复合材料，其中，1≤H/y≤50。
  6. 如权利要求1至5中任一项所述的硅基复合材料，其中，所述硅基体的球形度为S，S≥0.8。
  7. 如权利要求6所述的硅基复合材料，其中，所述导电剂的平均长度为Lnm，1052≤L/S≤2105。
  8. 如权利要求1至7中任一项所述的硅基复合材料，其中，所述硅基复合材料满足以下条件中的至少一者：
    (1)基于所述硅基复合材料的质量，所述第一层中锂元素的质量占比为A％，0.1≤A≤4；
    (2)基于所述硅基复合材料的质量，所述第一层中磷元素的质量占比为B％，0.03≤B≤1.2；
    (3)基于所述硅基复合材料的质量，所述第一层中氟元素的质量占比为C％，0.1≤C≤4；
    (4)所述硅基体包括硅碳材料，基于所述硅基体的质量，硅元素的质量占比为D％，38≤D≤59，碳元素的质量占比为E％，40≤E≤61；
    (5)0.003≤(A+B+C)/D≤0.19。
  9. 如权利要求8所述的硅基复合材料，其中，0.104≤H/D≤4.16。
  10. 一种二次电池，包括负极极片、正极极片和电解液，其中，所述负极极片包括如权利要求1至9中任一项所述的硅基复合材料。
  11. 一种电子装置，其中，包括如权利要求10所述的二次电池。
PCT/CN2025/081250 2024-06-26 2025-03-07 硅基复合材料、二次电池和电子装置 Pending WO2026001073A1 (zh)

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