WO2024050799A1 - 负极活性材料及其制备方法、二次电池、电池模组、电池包及用电装置 - Google Patents

负极活性材料及其制备方法、二次电池、电池模组、电池包及用电装置 Download PDF

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WO2024050799A1
WO2024050799A1 PCT/CN2022/117986 CN2022117986W WO2024050799A1 WO 2024050799 A1 WO2024050799 A1 WO 2024050799A1 CN 2022117986 W CN2022117986 W CN 2022117986W WO 2024050799 A1 WO2024050799 A1 WO 2024050799A1
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active material
negative active
coating layer
silicon
mass
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PCT/CN2022/117986
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English (en)
French (fr)
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周益
吴启凡
张明
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宁德时代新能源科技股份有限公司
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    • 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
    • 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
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides

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  • This application belongs to the technical field of secondary batteries, and specifically relates to a negative active material and its preparation method, secondary batteries, battery modules, battery packs and electrical devices.
  • Secondary batteries are widely used in various consumer electronics and electric vehicles due to their outstanding characteristics such as light weight, no pollution, and no memory effect. With the continuous development of the new energy industry, customers have put forward higher demand for secondary batteries.
  • silicon-based materials As an anode active material, silicon-based materials have attracted widespread attention due to their high capacity. However, silicon-based materials have serious volume effects and will produce huge volume expansion during charging. Therefore, during the charging and discharging process, the surface of silicon-based materials It is difficult to form a stable SEI film, resulting in rapid capacity fading of the secondary battery, which in turn leads to poor cycle performance of the secondary battery.
  • this application provides a negative active material and its preparation method, a secondary battery and a power device, aiming to make the secondary battery containing it have better cycle performance.
  • a negative active material including:
  • Core materials including silicon-based materials
  • a first cladding layer is located on at least part of the surface of the core material, the first cladding layer includes SiO x , 1 ⁇ x ⁇ 2;
  • a second coating layer is located on at least a portion of the surface of the first coating layer, and the second coating layer includes a fluorinated carbon material.
  • this application at least includes the following beneficial effects:
  • a specific two-layer coating layer is formed on the surface of a specific core material, wherein the first coating layer includes SiOx and the second coating layer includes fluorocarbon material.
  • the SiOx precursor (silicic acid) is first formed in the first coating layer.
  • F-CNTs fluorocarbon material
  • SEI silicon oxide solid electrolyte interface
  • SiOx and lithium will generate electrochemically inert substances Li 2 O and Li 4 SiO 4 , which together with the fluoride carbon material inhibit the core material. Volume expansion. In this way, the rebound rate of the negative electrode plate of the secondary battery can be reduced, and the service life of the secondary battery and the cycle performance of the battery can be improved.
  • the fluorinated carbon material is selected from at least one of fluorinated graphene, fluorinated fullerene, fluorinated single-walled carbon nanotubes, and fluorinated multi-walled carbon nanotubes.
  • the volume average particle size Dv50 of the negative active material is 3 ⁇ m to 10 ⁇ m;
  • the volume average particle size Dv50 of the negative active material is 5 ⁇ m to 7 ⁇ m.
  • the thickness of the first coating layer is 1.5nm ⁇ 50nm;
  • the thickness of the first coating layer is 1.5 nm to 20 nm.
  • the mass ratio of the SiO x to the core material is 0.5% to 5%
  • the mass ratio of the SiOx to the core material is 0.5% to 2%.
  • the thickness of the second coating layer is 1 nm to 50 nm;
  • the thickness of the second coating layer is 3 nm to 10 nm.
  • the mass content of the fluorocarbon material is not higher than 0.5%
  • the mass content of the fluorocarbon material is 0.05% to 0.15%.
  • the mass content of fluorine element in the fluorocarbon material is no more than 15%;
  • the mass content of fluorine element in the fluorocarbon material is 5% to 12.5%.
  • the silicon-based material is selected from at least one of silicon, silicon carbon, silicon nitrogen and silicon metal alloy.
  • a second aspect of the present application provides a method for preparing the negative active material of the first aspect, including the following steps:
  • step S2 Use acid solution to perform an in-situ chemical reaction on the product obtained in step S1 to form a silicic acid layer;
  • step S3 Coat at least part of the surface of the silicic acid layer of the product obtained in step S2 to form the second coating layer;
  • step S4 The product obtained in step S3 is subjected to vacuum heat treatment, so that the silicic acid layer forms a first coating layer containing SiO x .
  • the alkali solution includes an alkali metal hydroxide, an organic solvent and water, and the organic solvent can dissolve the alkali metal hydroxide; in the alkali solution, the quality of the water is 0.5% to 5% of the mass of the alkali metal hydroxide.
  • the organic solvent in (a) includes at least one of ethanol and glycerin.
  • the alkali metal hydroxide is selected from at least one of sodium hydroxide, potassium hydroxide, rubidium hydroxide and cesium hydroxide.
  • the acid liquid is selected from at least one of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid and acetic acid.
  • step S3 includes the following steps:
  • step S2 The product obtained in step S2 is placed in the carbon fluoride nanomaterial dispersion, mixed, the liquid phase is removed, and dried.
  • the temperature of the vacuum heat treatment is 120-180°C;
  • the temperature of the vacuum heat treatment is 150°C to 180°C.
  • a third aspect of the present application provides a secondary battery, which includes a negative electrode sheet that includes the negative active material as in the first aspect of the present application or includes a negative active material prepared according to the preparation method of the second aspect of the present application. Material.
  • a fourth aspect of the present application provides a battery module, including the secondary battery of the third aspect of the present application.
  • a fifth aspect of the present application provides a battery pack, including the battery module of the fourth aspect of the present application.
  • a sixth aspect of the present application provides an electrical device, which includes at least one of the secondary battery according to the third aspect of the present application, the battery module of the fourth aspect of the present application, and the battery pack of the fifth aspect of the present application. A sort of.
  • Figure 1 is a schematic cross-sectional structural diagram of an embodiment of the negative active material of the present application.
  • FIG. 2 is a schematic diagram of the preparation process of the negative active material according to an example of the present application.
  • FIG. 3 is a schematic diagram of an embodiment of a secondary battery.
  • FIG. 4 is an exploded view of FIG. 3 .
  • Figure 5 is a schematic diagram of an embodiment of a battery module.
  • Figure 6 is a schematic diagram of an embodiment of a battery pack.
  • FIG. 7 is an exploded view of FIG. 6 .
  • FIG. 8 is a schematic diagram of an embodiment of a device in which a secondary battery is used as a power source.
  • any lower limit can be combined with any upper limit to form an unexpressed range; and any lower limit can be combined with other lower limits to form an unexpressed range, and likewise any upper limit can be combined with any other upper limit to form an unexpressed range.
  • each individually disclosed point or single value may itself serve as a lower or upper limit in combination with any other point or single value or with other lower or upper limits to form a range not expressly recited.
  • Silicon-based materials are commonly used negative electrode active materials. However, they have serious volume expansion problems after multiple cycles, resulting in poor cycle performance. Technicians have discovered that modifying fluorocarbon materials such as fluorinated carbon nanotubes on the surface of silicon-based materials can regulate the solid electrolyte membrane (SEI) formed on the surface of silicon-based materials while inhibiting the expansion of the silicon anode.
  • SEI solid electrolyte membrane
  • the fluorine in the fluorocarbon material participates in the formation of SEI rich in lithium fluoride (LiF) and carbon nanotubes co-embedded. LiF has high interfacial energy and lithium ion conductivity. It is an important component of SEI, so it is beneficial to the migration and diffusion of lithium ions.
  • SEI has electronic insulation and ionic conductivity, which can prevent further reduction and decomposition of electrolyte on the surface of silicon-based materials.
  • the fluorocarbon material embedded in the SEI can act as a stress relief layer, inhibiting the expansion of the negative electrode during charge and discharge, increasing the toughness of the SEI, and avoiding the growth of unstable SEI.
  • the current general methods for modifying fluorocarbon materials such as fluorinated carbon nanotubes on the surface of silicon-based materials include direct coating methods, such as ball milling and conventional mechanical mixing methods. Directly coating fluorocarbons on the surface of silicon-based materials Material. There are also methods that use binders to bond fluorocarbon materials to silicon negative electrodes.
  • the former uses coating to coat fluorocarbon materials, but the coating effect is not ideal. There is a problem that some fluorocarbon materials are in a free state and cannot be effectively coated, which reduces the utilization efficiency of fluorocarbon materials; at the same time, it is difficult to The problem of controlling the presence, uniformity and content of fluorocarbon materials on the surface of silicon-based materials.
  • the fluorocarbon material coated with silicon-based materials formed by conventional mechanical methods has poor bonding force between the fluorocarbon material and the silicon anode. This is because the surface structure of fluorocarbon materials such as fluorocarbon nanotubes is super common. The yoke ⁇ bond cannot form strong chemical adsorption with the surface of the silicon anode.
  • the ball milling method can increase the binding force between fluorocarbon materials and silicon-based materials, it may also destroy the structure and morphology of fluorocarbon materials and silicon-based materials.
  • the latter uses a binder method. Although it can increase the bonding force between the fluorocarbon material and the surface of the silicon-based material, too much binder will affect the properties of SEI, increase the content of organic salts in SEI, and reduce lithium ion migration. and diffusion, and at the same time reduce the proportion of silicon-based materials, causing the problem of low battery energy density.
  • this application provides negative active materials and preparation methods thereof.
  • the prepared negative active material will be introduced in detail below in conjunction with the preparation method.
  • the negative active material includes a core material, a first coating layer and a second coating layer.
  • the core material includes a silicon-based material
  • the first cladding layer is located on at least part of the surface of the core material
  • the first cladding layer contains SiO x , 1 ⁇ x ⁇ 2
  • the second cladding layer is located on at least part of the first cladding layer Ostensibly
  • the second cladding layer includes a fluorocarbon material.
  • a specific two-layer coating layer is formed on the surface of a specific core material, wherein the first coating layer includes SiOx and the second coating layer includes fluorocarbon material.
  • the SiOx precursor (silicic acid) is first formed in the first coating layer.
  • F-CNTs fluorocarbon material
  • SEI silicon oxide solid electrolyte interface
  • SiOx and lithium will generate electrochemically inert substances Li 2 O and Li 4 SiO 4 , which together with the fluoride carbon material inhibit the core material. Volume expansion. In this way, the rebound rate of the negative electrode plate of the secondary battery can be reduced, and the service life of the secondary battery and the cycle performance of the battery can be improved.
  • the fluorinated carbon material is selected from at least one of fluorinated graphene, fluorinated fullerene, fluorinated single-walled carbon nanotubes, and fluorinated multi-walled carbon nanotubes.
  • the fluorinated carbon material is selected from fluorinated carbon nanotubes, and the fluorinated carbon nanotubes include at least one of fluorinated multi-walled carbon nanotubes and fluorinated multi-walled carbon nanotubes.
  • the silicon-based material is selected from at least one of silicon, silicon carbon, silicon nitrogen and silicon metal alloy.
  • silicon carbon is also called silicon carbon alloy.
  • Silicon metal alloy refers to an alloy formed by silicon and metal elements, including but not limited to at least one of silicon-aluminum alloy, silicon-magnesium alloy, etc.
  • the silicon-based material may exist in the form of particles, and may be at least one selected from the group consisting of silicon particles, silicon carbon particles, silicon nitrogen particles and silicon metal alloy particles.
  • the embodiment of the present application also provides a method for preparing the above-mentioned negative active material, including the following steps S1-S4.
  • step S2 The product obtained in step S1 is subjected to in-situ chemical reaction with acid solution to form a silicic acid layer;
  • step S3 Coating the product obtained in step S2 with the silicic acid layer to form the second coating layer;
  • step S4 The product obtained in step S3 is subjected to vacuum heat treatment, so that the silicic acid layer forms a first coating layer containing SiO x .
  • the negative active material of the present application can be prepared using the above preparation method.
  • steps S1 and S2 at least part of the surface of the core material is modified into H 2 SiO x (silicon) which has an adsorption effect on the fluorocarbon material. acid layer), and at the same time, the fluorine atoms in the fluorocarbon material form strong hydrogen bonds with the H 2 SiO x on the surface of the core material, thereby controllably coating the fluorocarbon material evenly on the H 2 SiO x surface of the core material, so The utilization efficiency of fluorocarbon materials is improved.
  • vacuum heat treatment is performed so that the silicate layer forms a first coating layer containing SiOx .
  • SiOx and lithium will generate electrochemical inert substances Li 2 O and Li 4 SiO 4 , can buffer the volume expansion of the core material, thereby ensuring the cycle performance of the secondary battery using it; on the other hand, it can also avoid the problem of unstable secondary battery performance caused by H 2 SiO x being unstable and easily absorbing water. It can also reduce the proton content in the negative active material and reduce the gas production of the secondary battery. At the same time, the activation energy of lithium insertion can be reduced, thereby reducing the interface lithium ion migration resistance.
  • the fluorocarbon material can be coated on the surface of the negative active material to form a LiF-rich SEI.
  • the fluorocarbon material can serve as a rivet point for LiF, limiting the growth of LiF grains. , producing more grain boundaries, which can increase the lithium ion migration rate, thereby improving the internal resistance, cycle performance and low-temperature performance of secondary batteries using the above-mentioned negative electrode active materials.
  • the fluorocarbon material is reduced to form carbon nanomaterials, which are embedded in the SEI film to increase the toughness and mechanical strength of the SEI film. Therefore, the volume expansion of the negative active material can be effectively suppressed, thereby reducing the rebound rate of the negative electrode piece of the secondary battery using the above negative active material; and improving the service life and cycle performance of the battery.
  • the above-mentioned preparation method of the negative active material of the present application does not require the use of binders, and ensures uniform coating of fluorocarbon materials, improving fluorination.
  • the utilization efficiency of carbon materials and the problem of reducing the proportion of silicon-based materials caused by the introduction of binders can effectively ensure the specific capacity of negative active materials and the energy density of secondary batteries using them.
  • the preparation method of the above-mentioned negative active material has good universality and simple operability, has low preparation cost, is easy to promote, and is suitable for industrial large-scale production.
  • first coating layer may cover the entire surface of the core material, or may only cover part of the surface of the core material.
  • the second coating layer may cover the entire surface of the first coating layer, or may only cover part of the surface of the first coating layer.
  • the negative active material 6 includes a core material 61 , a first coating layer 62 and a second coating layer 63 .
  • the first coating layer 62 covers the core material 61 . on the entire surface of the material.
  • the second coating layer 63 covers the entire surface of the core material.
  • the core material 61 is selected from at least one of silicon, silicon carbon, silicon nitrogen and silicon metal alloy.
  • the above-mentioned silicon is elemental silicon, and SiO x in the first cladding layer 62 includes but is not limited to at least one of silicon monoxide and silicon dioxide. Further, the first cladding layer 62 is a silicon oxide layer.
  • the second coating layer 63 is a fluorinated carbon nanotube layer.
  • the volume average particle size Dv50 of the negative active material is 3 ⁇ m to 10 ⁇ m; optionally, the volume average particle size Dv50 of the negative active material is 5 ⁇ m to 7 ⁇ m.
  • the volume average particle size Dv50 refers to: in the particle size distribution curve, the particle size corresponding to when the volume cumulative particle size distribution number of the particles reaches 50%. Its physical meaning is that 50% of the particles have a particle size smaller (or larger) than it. .
  • the volume average particle size Dv50 can be measured using methods known in the art. As an example, Dv50 can be easily measured using a laser particle size analyzer, such as the Mastersizer 2000E laser particle size analyzer of Malvern Instruments Co., Ltd. in the United Kingdom, referring to the GB/T 19077-2016 particle size distribution laser diffraction method.
  • the thickness of the first cladding layer is 1.5nm to 50nm, such as 1.5nm, 2nm, 3nm, 4nm, 5nm, 10nm, 15nm, 20nm, 25nm, 30nm, 40nm, 45nm, 50nm; optional
  • the thickness of the first cladding layer is 1.5 nm to 20 nm; further optionally, the thickness of the first cladding layer is 5 nm to 15 nm.
  • the mass ratio of SiO x to the core material is 3 to 5%; optionally, the mass ratio of SiO x to the core material is 0 to 20%.
  • the thickness of the second cladding layer is 1 nm to 50 nm; optionally, the thickness of the second cladding layer is 3 nm to 10 nm.
  • the mass content of the fluorocarbon material is no more than 0.5%, such as 0.05% to 0.5%.
  • the mass content of the fluorocarbon material is 0.05% to 0.15%.
  • Controlling the mass content of the fluorocarbon material in the negative active material ensures the mass proportion of the core material in the negative active material to ensure that the secondary battery using it has good energy density, and on the other hand, avoids the loss of fluorocarbon material The mass content is too high, which leads to excessive consumption of electrolyte and is not conducive to the improvement of electrochemical performance.
  • the fluorine element in the fluorocarbon material accounts for no more than 15% by mass.
  • the mass content of the fluorine element in the fluorocarbon material is 5% to 12.5%.
  • Controlling the mass content of the fluorine element in the fluorocarbon material used within the above-given range can better meet the demand for uniform coating of the fluorocarbon material, and the fluorocarbon material can be embedded into the surface of the negative active material to form a rich SEI containing LiF increases the toughness and mechanical strength of the SEI film, effectively suppresses the volume expansion of the negative active material and increases its lithium ion migration rate, thereby improving the cycle performance of secondary batteries using the negative active material.
  • fluorocarbon materials can be purchased from the market or made at home.
  • the fluorinated carbon material is fluorinated carbon nanotubes
  • the fluorinated carbon nanotubes can be prepared by plasma methods. Using CF 4 plasma as raw material, the reaction adjustment such as treatment time and temperature is adjusted to prepare carbon nanotubes with different fluorine contents. Fluorinated carbon nanotubes maintain a one-dimensional carbon nanotube-like structure and are connected to a large number of F on their surface. F forms CF bonds with the carbon on the surface of the carbon nanotube.
  • the alkali solution includes alkali metal hydroxide, organic solvent and water.
  • the organic solvent can dissolve alkali metal hydroxide.
  • the mass ratio of water to alkali metal hydroxide is 0.5% to 5%. Since the reaction between the alkali metal hydroxide and the silicon in the core material needs to be completed with the participation of water, and the alkali metal silicate formed is soluble in water, the preparation method of the present application controls the alkali solution to use an organic solvent as the solvent.
  • the degree of reaction in step S1 is controlled to avoid excess water causing the alkali metal silicate formed by the reaction to dissolve in excess water, and at the same time Since the reaction solvent is an organic solvent, and the alkali metal silicate is difficult to dissolve or is insoluble in the organic solvent, the formed alkali metal silicate coating is deposited on the surface of the core material, and is then etched in situ on the surface of the core material to form A first cladding layer containing an alkali metal silicate.
  • the mass content of water in the above-mentioned alkali solution is 0.5% to 5%.
  • step S1 the molar mass of the core material and the water in the alkali solution is controlled to be equal or excessive, and the alkali metal hydroxide in the alkali solution is controlled to be in excess relative to the water, which can then be controlled by controlling the water content in step S1.
  • the degree of reaction thereby controls the thickness of the alkali metal silicate formed and the ratio of the alkali metal silicate to the remaining core material.
  • step S1 the molar masses of the core material and the water in the alkali solution are controlled to be equal, and the alkali metal hydroxide in the alkali solution is controlled to be in excess relative to the water; after the reaction in step S1 is completed, filter the solid and proceed to step S2. .
  • alkali metal hydroxide is selected from at least one selected from the group consisting of sodium hydroxide, potassium hydroxide, rubidium hydroxide and cesium hydroxide.
  • the organic solvent includes at least one of ethanol and glycerin.
  • Step S1 can be performed at normal temperature, and the reaction temperature can be controlled not to be higher than the temperature of the organic solvent and the boiling point of water.
  • alkali solution there is no special requirement for the concentration of alkali metal hydroxide.
  • an organic solvent is added to dissolve the alkali metal hydroxide, and the final preparation is The concentration of the obtained alkali solution does not exceed the concentration that it can achieve in the saturated state.
  • the acid solution is selected from at least one of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid and acetic acid.
  • the product obtained in step S2 is treated with an acid solution, so that the silicate layer on the surface of the product is converted into H 2 SiO x (silicic acid) in the acid solution and deposited on the surface of the core material.
  • step S3 includes the following steps: mixing the product obtained in step S2 into a fluorocarbon material dispersion, removing the liquid phase, and drying. Since the surface of the product obtained in step S2 contains H 2 SiO x (silicic acid), it can form strong hydrogen bonds with the fluorine element in the fluorocarbon material. This not only ensures uniform coating of the fluorocarbon material, but also The coating degree is controllable, reducing the presence of free fluorocarbon materials in the product, and improving the utilization efficiency of fluorocarbon materials.
  • the temperature of the vacuum heat treatment is 120-180°C; optionally, the temperature of the vacuum heat treatment is 150-180°C.
  • silicate is decomposed and converted into silicon oxide SiOx.
  • the vacuum heat treatment time is 2 hours.
  • the core material is silicon particles
  • the fluorocarbon material is fluorocarbon nanotubes
  • the alkali metal is sodium hydroxide
  • the acid solution is hydrochloric acid.
  • Step S1 forms ultra-thin Na 2 SiO x on the silicon surface.
  • Step S2 converts Na 2 SiO x into H 2 SiO x .
  • Step S3 coats the H 2 SiO x surface.
  • Fluorinated carbon nanotubes are formed, and in step S4, H 2 SiO x is decomposed to form SiO x to obtain a negative active material.
  • the negative active material includes silicon and a SiO x layer and a fluorinated carbon nanotube layer sequentially coated on the surface of the silicon.
  • the reaction equation involved in this preparation method is as follows:
  • step S1 Si+2NaOH+H 2 O ⁇ Na 2 SiO x +2H 2 ⁇ (1);
  • step S2 Na 2 SiO x +2HCl ⁇ 2NaCl+H 2 SiO x ⁇ (2);
  • Step S4 Silicic acid decomposition equation in step S4: H 2 SiO x ⁇ SiO x +H 2 O (3).
  • Secondary batteries refer to batteries that can be recharged to activate active materials and continue to be used after the battery is discharged.
  • a secondary battery typically includes a positive electrode plate, a negative electrode plate, a separator and an electrolyte.
  • active ions are inserted and detached back and forth between the positive and negative electrodes.
  • the isolation film is arranged between the positive electrode piece and the negative electrode piece to play the role of isolation.
  • the electrolyte plays a role in conducting ions between the positive and negative electrodes.
  • the negative electrode sheet usually includes a negative electrode current collector and a negative electrode film layer disposed on the negative electrode current collector.
  • the negative electrode film layer includes the negative electrode active material provided above in this application.
  • the negative electrode film layer may also include at least one of the following materials: graphite, soft carbon, hard carbon, tin-based materials, lithium titanate, etc.
  • the tin-based material may be selected from at least one of elemental tin, tin oxide compounds and tin alloys.
  • Graphite includes but is not limited to artificial graphite and natural graphite.
  • the negative electrode film layer of the present application may also contain one or more of the above materials.
  • the negative electrode film layer further includes graphite, and the mass of the negative electrode active material is no more than 30% of the mass of graphite; optionally, the mass of the negative electrode active material is 5% to 25% of the mass of graphite. In this way, the energy density and cycle performance requirements of the secondary battery can be better met by using graphite together with the negative active material of the silicon-based core material covered by the first coating layer and the second coating layer.
  • the negative electrode current collector can be a conventional metal foil or a composite current collector (for example, a metal material can be placed on a polymer substrate to form a composite current collector).
  • the negative electrode current collector may be copper foil.
  • the negative electrode film layer also optionally includes binders, conductive agents and other optional auxiliaries.
  • the conductive agent may be one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.
  • the binder can be styrene-butadiene rubber (SBR), water-based acrylic resin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer One or more of (EVA), polyvinyl alcohol (PVA) and polyvinyl butyral (PVB).
  • SBR styrene-butadiene rubber
  • PVDF polyvinylidene fluoride
  • PTFE polytetrafluoroethylene
  • EVA ethylene-vinyl acetate copolymer
  • EVA polyvinyl alcohol
  • PVB polyvinyl butyral
  • additives may be thickening and dispersing agents (such as carboxymethyl cellulose sodium CMC-Na), PTC thermistor materials, etc.
  • the positive electrode sheet usually includes a positive electrode current collector and a positive electrode film layer disposed on the positive electrode current collector.
  • the positive electrode film layer includes a positive electrode active material.
  • the positive electrode current collector can be a conventional metal foil or a composite current collector (metal materials can be placed on a polymer substrate to form a composite current collector).
  • the positive electrode current collector may be aluminum foil.
  • the specific type of the positive active material is not limited. Active materials known in the art that can be used for the positive electrode of secondary batteries can be used, and those skilled in the art can select according to actual needs.
  • the cathode active material may include, but is not limited to, one or more of lithium transition metal oxides, lithium-containing phosphates with an olivine structure, and their respective modified compounds.
  • lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide One or more of lithium nickel cobalt aluminum oxide and its modified compounds.
  • lithium-containing phosphates with an olivine structure may include, but are not limited to, lithium iron phosphate, composites of lithium iron phosphate and carbon, lithium manganese phosphate, composites of lithium manganese phosphate and carbon, lithium iron manganese phosphate, lithium iron manganese phosphate One or more of the composite materials with carbon and its modified compounds. These materials are commercially available.
  • the modified compounds of each of the above materials may be doping modifications and/or surface coating modifications of the materials.
  • the positive electrode film layer also optionally includes binders, conductive agents and other optional auxiliaries.
  • the conductive agent can be one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, Super P(SP), graphene and carbon nanofibers.
  • the binder can be styrene-butadiene rubber (SBR), water-based acrylic resin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer One or more of (EVA), polyacrylic acid (PAA), carboxymethylcellulose (CMC), polyvinyl alcohol (PVA) and polyvinyl butyral (PVB).
  • SBR styrene-butadiene rubber
  • PVDF polyvinylidene fluoride
  • PTFE polytetrafluoroethylene
  • EVA ethylene-vinyl acetate copolymer
  • PAA polyacrylic acid
  • CMC carboxymethylcellulose
  • PVA polyvinyl alcohol
  • PVB polyvinyl butyral
  • the secondary battery further includes a separator film.
  • a separator film There is no particular restriction on the type of isolation membrane in this application. Any well-known porous structure isolation membrane with good chemical stability and mechanical stability can be used.
  • the material of the isolation membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride.
  • the isolation film can be a single-layer film or a multi-layer composite film, with no special restrictions. When the isolation film is a multi-layer composite film, the materials of each layer can be the same or different, and there is no particular limitation.
  • the secondary battery may include an electrolyte that serves to conduct ions between a positive electrode and a negative electrode.
  • the electrolyte solution may include electrolyte salts and solvents.
  • the electrolyte salt may be selected from lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium perchlorate (LiClO 4 ), lithium hexafluoroarsenate (LiAsF 6 ), lithium bisfluorosulfonyl imide ( LiFSI), lithium bistrifluoromethanesulfonimide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluoromethanesulfonate borate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorophosphate (LiPO 2 F 2 ), one or more of lithium difluorodioxalate phosphate (LiDFOP) and lithium tetrafluorooxalate phosphate (LiTFOP).
  • LiFSI lithium bisfluorosulfonyl imide
  • LiTFSI lithium bis
  • the solvent may be selected from ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), carbonic acid Dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), One or more of ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS) and diethyl sulf
  • additives are also included in the electrolyte.
  • additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain properties of the battery, such as additives that improve the overcharge performance of the battery, additives that improve the high-temperature performance of the battery, and additives that improve the low-temperature performance of the battery. Additives etc.
  • the secondary battery of the present application is a lithium-ion secondary battery.
  • the secondary battery can be prepared according to conventional methods in the art, for example, the positive electrode sheet, the separator film, and the negative electrode sheet are wound (or stacked) in order, so that the separator film is between the positive electrode sheet and the negative electrode sheet for isolation. function to obtain the battery core, place the battery core in the outer package, inject the electrolyte and seal it to obtain a secondary battery.
  • FIG. 3 shows an example of a square-structured secondary battery 5 .
  • the secondary battery may include an outer packaging.
  • the outer packaging is used to package the positive electrode pieces, negative electrode pieces and electrolyte.
  • the outer package may include a housing 51 and a cover 53 .
  • the housing 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose a receiving cavity.
  • the housing 51 has an opening communicating with the accommodation cavity, and the cover plate 53 can cover the opening to close the accommodation cavity.
  • the positive electrode piece, the negative electrode piece and the isolation film can be formed into the electrode assembly 52 through a winding process or a lamination process.
  • the electrode assembly 52 is packaged in the containing cavity.
  • the electrolyte soaks into the electrode assembly 52 .
  • the number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and can be adjusted according to needs.
  • the outer packaging of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc.
  • the outer packaging of the secondary battery may also be a soft bag, such as a bag-type soft bag.
  • the soft bag may be made of plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), and the like.
  • secondary batteries can be assembled into battery modules, and the number of secondary batteries contained in the battery module can be multiple. The specific number can be adjusted according to the application and capacity of the battery module.
  • FIG. 5 is a battery module 4 as an example.
  • a plurality of secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4 .
  • the plurality of secondary batteries 5 can be fixed by fasteners.
  • the battery module 4 may further include a housing having a receiving space in which a plurality of secondary batteries 5 are received.
  • the above-mentioned battery modules can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.
  • the battery pack 1 may include a battery box and a plurality of battery modules 4 arranged in the battery box.
  • the battery box includes an upper box 2 and a lower box 3 .
  • the upper box 2 can be covered with the lower box 3 and form a closed space for accommodating the battery module 4 .
  • Multiple battery modules 4 can be arranged in the battery box in any manner.
  • the present application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack.
  • the secondary battery, battery module or battery pack may be used as a power source for the device or as an energy storage unit for the device.
  • the device may be, but is not limited to, a mobile device (such as a mobile phone, a laptop, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, or an electric golf ball). vehicles, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.
  • the device can select secondary batteries, battery modules or battery packs according to its usage requirements.
  • FIG 8 is an electrical device as an example.
  • the electric device 7 is a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, or the like.
  • battery packs or battery modules can be used.
  • the device may be a mobile phone, a tablet, a laptop, etc.
  • the device is usually required to be thin and light, and a secondary battery can be used as a power source.
  • carbon nanotubes with different fluorine contents are prepared.
  • the carbon nanotubes maintain a tubular structure and are connected to a large number of CF bonds on their surface.
  • the plasma power is 40W
  • the flow rate of CF 4 is 40sccm at 60Pa (sccm standard liter per minute flow value)
  • the control processing time is 60s
  • the temperature is room temperature (25°C), to obtain fluorinated fluoride with a fluorine content of 5%.
  • Carbon nanotube F-CNTs-a control the processing time to 180s and the temperature to room temperature (25°C) to obtain fluorinated carbon nanotubes F-CNTs-b with a fluorine content of 10%; control the processing time to 360s and the temperature to At room temperature (25°C), fluorinated carbon nanotubes F-CNTs-c with a fluorine content of 12.5% were obtained; by controlling the processing time to 600s and the temperature at room temperature (25°C), fluorinated carbon with a fluorine content of 15% was obtained.
  • Nanotube F-CNTs-d control the processing time to 180s and the temperature to room temperature (25°C) to obtain fluorinated carbon nanotubes F-CNTs-b with a fluorine content of 10%; control the processing time to 360s and the temperature to At room temperature (25°C), fluorinated carbon nanotubes F-CNTs-c with a fluorine content of 12.5% were obtained; by controlling the processing time to 600s and the temperature at room
  • the alkali solution includes alkali metal hydroxide, organic solvent and water.
  • the alkali metal hydroxide is in excess relative to water.
  • the water mass content accounts for 1.2% of the organic solvent system.
  • the organic solvent is glycerol, and then the alkali metal hydroxide is prepared.
  • a saturated solution, the water content in the alkali solution is 1wt%.
  • the core material is silicon particles, and the molar ratio of silicon particles to water is 20. The silicon particles are dispersed in the above-mentioned alkali solution and stirred vigorously at 70°C for 10 minutes.
  • step S2 The product obtained in step S1 is subjected to an in-situ chemical reaction using an acid solution to form a silicic acid layer.
  • the acid solution is hydrochloric acid with a mass content of 10%.
  • the solid obtained in step S1 was immersed in the acid solution and stirred for 10 min.
  • step S3 The product obtained in step S2 is coated with the silicic acid layer to form a second coating layer. Specifically, the solid obtained in step S2 is directly added to the dispersion of fluorinated carbon nanotubes (F-CNTs-a, F-CNTs-b, F-CNTs-c, F-CNTs-d), stirred vigorously, and then passed Centrifuge at low speed to obtain silicon material coated with fluorinated carbon nanotubes. Dry in oven.
  • fluorinated carbon nanotubes F-CNTs-a, F-CNTs-b, F-CNTs-c, F-CNTs-d
  • step S4 The product obtained in step S3 is subjected to vacuum heat treatment, so that the silicic acid layer forms a first coating layer containing SiOx.
  • Vacuum heat treatment was carried out in a vacuum drying oven. The temperature of vacuum heat treatment was 160°C and the time was 24 hours.
  • the thickness of the first cladding layer and the second cladding layer, the SiOx mass of the first cladding layer, and the mass of the fluorinated carbon nanotubes of the second cladding layer were measured using a parallel measurement method.
  • the specific process is as follows:
  • steps S1 to S2 are carried out in parallel, and then the product obtained in step S2 is directly subjected to the above-mentioned S4, and the thickness of the coating layer of the obtained product is measured using an electron microscope, which is the thickness H1 of the first coating layer.
  • the mass difference M02-M01 before and after coating is the mass M0 of the first coating layer. Therefore, the number of moles of oxygen contained in the first coating layer is M0/16, and the SiOx in the first cladding layer mainly exists in the form of silicon monoxide and silicon dioxide, that is, the quality of silicon oxide in the first cladding layer is between M0/16 ⁇ 44 ⁇ M0/16 ⁇ 60 between, take the middle value.
  • M03-M02 is the mass of the fluorinated carbon nanotubes of the second coating layer.
  • Comparative Examples 1 to 3 are as follows.
  • the negative active material in Comparative Example 1 was the silicon particles used in step S1 without any treatment.
  • Comparative Example 2 is basically the same as Example 1. The difference is that without the step of coating with fluorinated carbon nanotubes, it is equivalent to directly forming a SiO x layer on the surface of the silicon particles, which does not contain a second coating layer.
  • Comparative Example 3 is basically the same as Example 1. The difference is that without the vacuum heat treatment in step S4, it is equivalent to forming a first coating layer of a silicate layer and forming a second coating layer on the silicate layer.
  • Preparation of the positive electrode sheet Combine the positive active material LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811), the binder polyvinylidene fluoride (PVDF), and the conductive agent acetylene black in a mass ratio of 97%:1.5%:1.5 % is dissolved in the solvent N-methylpyrrolidone (NMP), stir thoroughly and mix evenly to prepare a positive electrode slurry; the positive electrode slurry is evenly coated on the positive electrode current collector aluminum foil, and then dried, cold pressed, and cut. Get the positive electrode piece.
  • NMP N-methylpyrrolidone
  • the negative active materials artificial graphite, binder styrene-butadiene rubber (SBR), binder polyacrylic acid (PAA), dispersant (CMC-Na) and conductive carbon black (Super- P, SP) and carbon nanotubes (CNT) are fully stirred and mixed in an appropriate amount of deionized water at a weight ratio of 10%: 85%: 2%: 1%: 1%: 0.7%: 0.3% to prepare a negative electrode slurry. ;
  • the negative electrode slurry is coated on the current collector copper foil through coating equipment, and then dried, cold pressed, and cut to obtain negative electrode pieces.
  • Isolation film Polyethylene film (PE) with a thickness of 12 ⁇ m is used as the isolation film.
  • the first charge and discharge efficiency is the capacity ratio between the first charge and discharge of the secondary battery, referred to as the first efficiency.
  • the specific test process is as follows:
  • K value test K value refers to the voltage drop of the battery per unit time. Its numerical value can reflect the size of the secondary battery capacity. The greater the capacity, the greater the K value. The smaller the capacity, the smaller the K value.
  • the specific test methods are as follows:
  • Capacity retention rate at low temperature (%) D0 (-20°C)/D 0 (25°C) ⁇ 100%.
  • Mass energy density (Wh/Kg) discharge capacity (Wh) ⁇ U/lithium-ion secondary battery cell mass (Kg).
  • SiO -CNTs stands for
  • F-CNTs-a, F-CNTs-b, and F-CNTs-c prepared above with different fluorine contents is used.
  • the negative electrode sheet made of the negative electrode active material of the present application can improve the first efficiency, low temperature performance, energy density and cycle performance of the secondary battery.

Abstract

一种负极活性材料及其制备方法、二次电池及用电装置。其中，负极活性材料（6）包括：内核材料（61），包括硅基材料；第一包覆层（62），位于内核材料（61）的至少部分表面上，第一包覆层（62）包含SiO x，1＜x＜2；及第二包覆层（63），位于第一包覆层（62）的至少部分表面上，第二包覆层（63）包括氟化碳材料。

Description

负极活性材料及其制备方法、二次电池、电池模组、电池包及用电装置 技术领域
本申请属于二次电池技术领域，具体涉及一种负极活性材料及其制备方法、二次电池、电池模组、电池包及用电装置。
背景技术
二次电池因具有重量轻、无污染、无记忆效应等突出特点，被广泛应用于各类消费类电子产品和电动车辆中。随着新能源行业的不断发展，客户对二次电池提出了更高的使用需求。
硅基材料作为负极活性材料，因具有较高的容量被广泛关注，但是硅基材料存在严重的体积效应，充电过程中会产生巨大的体积膨胀，故而在充放电过程中，硅基材料极表面难以形成稳定的SEI膜，从而导致二次电池的容量衰减较快，进而导致二次电池的循环性能很差。
发明内容
鉴于背景技术中存在的技术问题，本申请提供一种负极活性材料及其制备方法、二次电池及用电装置，旨在使含有其的二次电池具有较好的循环性能。
为了实现上述目的，本申请的第一方面提供一种负极活性材料，包括：
内核材料，包括硅基材料；
第一包覆层，位于所述内核材料的至少部分表面上，所述第一包覆层包含SiO x，1≤x＜2；及
第二包覆层，位于所述第一包覆层的至少部分表面上，所述第二包覆层包括氟化碳材料。
相对于现有技术，本申请至少包括如下所述的有益效果：
本申请的负极活性材料，将特定的内核材料表面形成特定的两层包覆层，其中，第一包覆层包含SiOx，第二包覆层包括氟化碳材料。在制备时，第一包覆层中先形成SiOx的前驱体(硅酸)，一方面可提高氟化碳材料(F-CNTs)包覆稳定性和均匀性，从而充分发挥出氟化碳材料调控氧化硅固态电解质界面(SEI)的作用，另一方面，在充放电过程中，SiOx与锂会生成电化学惰性物质Li 2O和Li 4SiO 4，和氟化碳材料共同抑制内核 材料的体积膨胀。如此，可以降低二次电池的负极极片反弹率，提高二次电池的使用寿命及电池的循环性能。
在本申请任意实施例中，所述氟化碳材料选自氟化石墨烯、氟化富勒烯、氟化单壁碳纳米管、氟化多壁碳纳米管中的至少一种。
在本申请任意实施方式中，所述负极活性材料的体积平均粒径Dv50为3μm～10μm；
可选地，所述负极活性材料的体积平均粒径Dv50为5μm～7μm。
在本申请任意实施方式中，所述第一包覆层的厚度为1.5nm～50nm；
可选地，所述第一包覆层的厚度为1.5nm～20nm。
在本申请任意实施方式中，所述SiO x与所述内核材料的质量比为0.5％～5％；
可选地，所述SiOx与所述内核材料的质量比为0.5％～2％。
在本申请任意实施方式中，所述第二包覆层的厚度为1nm～50nm；
可选地，所述第二包覆层的厚度为3nm～10nm。
在本申请任意实施方式中，基于所述负极活性材料的质量，所述氟化碳材料的质量含量不高于0.5％；
可选地，基于所述负极活性材料的质量，所述氟化碳材料的质量含量为0.05％～0.15％。
在本申请任意实施方式中，基于所述氟化碳材料的质量，所述氟化碳材料中的氟元素所占的质量含量不高于15％；
可选地，基于所述氟化碳材料的质量，所述氟化碳材料中的氟元素所占的质量含量为5％～12.5％。
在本申请任意实施例中，所述硅基材料选自硅、硅碳、硅氮和硅金属合金中的至少一种。
本申请的第二方面提供一种第一方面的负极活性材料的制备方法，包括如下步骤：
S1：在所述内核材料的至少部分表面采用碱液进行原位化学刻蚀形成硅酸盐层；
S2：将步骤S1所得产物采用酸液进行原位化学反应形成硅酸层；
S3：在步骤S2所得产物的所述硅酸层的至少部分表面包覆形成所述第二包覆层；及
S4：将步骤S3所得产物进行真空热处理，以使所述硅酸层形成含有SiO x的第一包覆层。
在本申请任意实施方式中，所述碱液包括碱金属氢氧化物、有机溶剂及水，所述有机溶剂能够溶解碱金属氢氧化物；在所述碱液中，所述水的质量为所述碱金属氢氧化物的质量的0.5％～5％。
在本申请任意实施方式中，(a)所述有机溶剂包括乙醇和甘油中的至少一种。
在本申请任意实施方式中，所述碱金属氢氧化物选自氢氧化钠、氢氧化钾、氢氧化铷及氢氧化铯中的至少一种。
在本申请任意实施方式中，所述酸液选自盐酸、硫酸、硝酸、磷酸及醋酸中的至少一种。
在本申请任意实施方式中，步骤S3包括如下步骤：
将步骤S2所得产物置于氟化碳纳材料分散液中混合，除去液相，干燥。
在本申请任意实施方式中，所述真空热处理的温度为120～180℃；
可选地，所述真空热处理的温度为150℃～180℃。
本申请的第三方面提供一种二次电池，其包括负极极片，所述负极极片包括如本申请第一方面的负极活性材料或包括根据本申请第二方面的制备方法制备的负极活性材料。
本申请的第四方面提供一种电池模组，包含本申请的第三方面的二次电池。
本申请的第五方面提供一种电池包，包含本申请的第四方面的电池模组。
本申请的第六方面提供一种用电装置，其包括根据本申请第三方面的二次电池、如本申请的第四方面的电池模组和本申请的第五方面的电池包中的至少一种。
附图说明
为了更清楚地说明本申请的技术方案，下面将对本申请中所使用的附图作简单介绍。显而易见地，下面所描述的附图仅仅是本申请的一些实施方式，对于本领域普通技术人员来讲，在不付出创造性劳动的前提下，还可以根据附图获得其他的附图。
图1是本申请负极活性材料的一实施方式的截面结构示意图。
图2为本申请一示例的负极活性材料的制备流程示意图。
图3是二次电池的一实施方式的示意图。
图4是图3的分解图。
图5是电池模块的一实施方式的示意图。
图6是电池包的一实施方式的示意图。
图7是图6的分解图。
图8是二次电池用作电源的装置的一实施方式的示意图。
附图标记说明：
1、电池包；2、上箱体；3、下箱体；4、电池模块；5、二次电池；51、壳体；52、电极组件；53、盖板；6、负极活性材料；61、内核材料；62、第一包覆层；63、第二包覆层；7、用电装置。
具体实施方式
下面结合具体实施方式，进一步阐述本申请。应理解，这些具体实施方式仅用于说明本申请而不用于限制本申请的范围。
为了简明，本文仅具体地公开了一些数值范围。然而，任意下限可以与任意上限组合形成未明确记载的范围；以及任意下限可以与其它下限组合形成未明确记载的范围，同样任意上限可以与任意其它上限组合形成未明确记载的范围。此外，每个单独公开的点或单个数值自身可以作为下限或上限与任意其它点或单个数值组合或与其它下限或上限组合形成未明确记载的范围。
在本文的描述中，需要说明的是，除非另有说明，“以上”、“以下”为包括本数，“一种或几种”中“几种”的含义是两种及两种以上。
在本文的描述中，除非另有说明，术语“或(or)”是包括性的。也就是说，短语“A或(or)B”表示“A，B，或A和B两者”。更具体地，以下任一条件均满足条件“A或B”：A为真(或存在)并且B为假(或不存在)；A为假(或不存在)而B为真(或存在)；或A和B都为真(或存在)。除非另有说明，本申请中使用的术语具有本领域技术人员通常所理解的公知含义。除非另有说明，本申请中提到的各参数的数值可以用本领域常用的各种测量方法进行测量(例如，可以按照在本申请的实施例中给出的方法进行测试)。
硅基材料是常用的负极活性材料，然而其在多次循环后，有严重的体积膨胀较大的问题，导致循环性能较差。技术人员发现，在硅基材料表面修饰氟化碳纳米管等氟化碳材料，可以调控硅基材料的表面形成的固态电解质膜(SEI)，同时抑制硅负极膨胀。在化成阶段或者充放电过程中，氟化碳材料中的氟参与形成富含氟化锂(LiF)和碳纳米管共嵌的SEI，氟化锂具有较高的界面能和锂离子电导率，是SEI中重要的组成部分，故 而有利于锂离子的迁移和扩散。SEI具有电子绝缘性而离子导电性，可以阻止电解液在硅基材料表面的进一步还原分解。此外，氟化碳材料嵌入到SEI，可充当应力缓释层，抑制充放电中负极的膨胀，增加SEI的韧性，避免了不稳定的SEI的生长。
然而目前在硅基材料表面修饰氟化碳纳米管等氟化碳材料的一般方法包括有直接包覆法，例如球磨法和常规机械混合法等，在硅基材料表面上直接包覆氟化碳材料。此外还有一些方法是使用粘结剂将氟化碳材料粘结在硅负极上。
前者采取包覆的方式包覆氟化碳材料，包覆效果不理想，存在部分氟化碳材料呈现游离状态，不能有效包覆的问题，降低了氟化碳材料的利用效率；同时还存在难以控制氟化碳材料在硅基材料表面的存在状态、均匀性和含量的问题。常规的机械法形成的氟化碳材料包覆硅基材料，其氟化碳材料和硅负极之间的结合力差，这是因为由于氟化碳纳米管等氟化碳材料表面结构是超共轭π键，与硅负极表面无法形成强的化学吸附。球磨法虽然能够增加氟化碳材料与硅基材料的结合力，也可能破坏氟化碳材料与硅基材料的结构和形貌状态。后者采用粘结剂的方法，虽然能够增加氟化碳材料与硅基材料表面的结合力，然而过多的粘结剂会影响SEI的性质，增加SEI中有机盐的成分，降低锂离子迁移和扩散，并同时降低了硅基材料的占比，造成电池能量密度较低的问题。
基于此，本申请提供的负极活性材料及其制备方法。下面将结合制备方法对制得的负极活性材料进行详细的介绍。
该负极活性材料包括内核材料、第一包覆层及第二包覆层。内核材料包括硅基材料，第一包覆层位于内核材料的至少部分表面上，第一包覆层包含SiO x，1≤x＜2；第二包覆层位于第一包覆层的至少部分表面上，第二包覆层包括氟化碳材料。
本申请的负极活性材料，将特定的内核材料表面形成特定的两层包覆层，其中，第一包覆层包含SiOx，第二包覆层包括氟化碳材料。在制备时，第一包覆层中先形成SiOx的前驱体(硅酸)，一方面可提高氟化碳材料(F-CNTs)包覆稳定性和均匀性，从而充分发挥出氟化碳材料调控氧化硅固态电解质界面(SEI)的作用，另一方面，在充放电过程中，SiOx与锂会生成电化学惰性物质Li 2O和Li 4SiO 4，和氟化碳材料共同抑制内核材料的体积膨胀。如此，可以降低二次电池的负极极片反弹率，提高二次电池的使用寿命及电池的循环性能。
在本申请任意实施例中，氟化碳材料选自氟化石墨烯、氟化富勒烯、氟化单壁碳纳米管、氟化多壁碳纳米管中的至少一种。
在本申请任意实施例中，氟化碳材料选自氟化碳纳米管，氟化碳纳米管包括氟化多壁碳纳米管及氟化多壁碳纳米管中的至少一种。
在本申请任意实施例中，硅基材料选自硅、硅碳、硅氮和硅金属合金中的至少一种。
其中，硅碳也称为硅碳合金。硅金属合金是指硅与金属元素形成的合金，包括但不限于硅铝合金、硅镁合金等中的至少一种。
在本申请任意实施例中，上述硅基材料可颗粒的形式存在，选自硅颗粒、硅碳颗粒、硅氮颗粒和硅金属合金颗粒中的至少一种。
本申请实施方式还提供了一种上述的负极活性材料的制备方法，包括如下步骤S1-S4。
S1：在所述内核材料的至少部分表面采用碱液进行原位化学刻蚀形成硅酸盐层；
S2：在步骤S1所得产物采用酸液进行原位化学反应形成硅酸层；
S3：在步骤S2所得产物的硅酸层包覆形成所述第二包覆层；及
S4：将步骤S3所得产物进行真空热处理，以使所述硅酸层形成含有SiO x的第一包覆层。
不希望限于任何理论，本申请的负极活性材料可采用上述制备方法制得，通过步骤S1和S2将内核材料的至少部分表面改性为对氟化碳材料具有吸附作用的H 2SiO x(硅酸层)，同时氟化碳材料中氟原子与内核材料表面的H 2SiO x形成强氢键作用，从而可控地将氟化碳材料均匀包覆在内核材料的H 2SiO x表面，如此提高了氟化碳材料的利用效率。而在包覆第二包覆层之后进行真空热处理，以使硅酸层形成含有SiO x的第一包覆层，一方面，SiOx与锂会生成电化学惰性物质Li 2O和Li 4SiO 4，可起到缓冲内核材料的体积膨胀的作用，从而保证应用其的二次电池的循环性能；另一方面还可避免H 2SiO x不稳定且易吸水造成二次电池性能不稳定的问题，且还能降低负极活性材料中的质子含量，降低二次电池的产气。同时，可以降低嵌锂的活化能，从而减少界面锂离子迁移阻抗。
此外，在二次电池的化成阶段，氟化碳材料能够包覆到负极活性材料表面形成富含LiF的SEI，氟化碳材料可作为LiF的铆钉点，对LiF晶粒的生长产生限域作用，产生更多的晶界，进而可提升其锂离子迁移速率，从而改善了应用上述负极活性材料的二次电池的内阻、循环性能和低温性能。同时，氟化碳材料被还原形成碳纳米材料，嵌入到SEI膜中从而增加SEI膜的韧性及机械强度。因此能够有效地抑制负极活性材料的体积膨胀，从而降低了应用上述负极活性材料的二次电池的负极极片反弹率；改善了使用寿命及电 池的循环性能。
相比于上述传统的在硅基材料表面修饰氟化碳材料的方法，本申请上述负极活性材料的制备方法无需使用粘结剂，且保证了氟化碳材料的均匀包覆，提高了氟化碳材料的利用效率，同时不会存在引入粘结剂导致硅基材料的占比降低的问题，可以有效保证负极活性材料的比容量和应用其的二次电池的能量密度。
上述负极活性材料的制备方法具有良好的普适性和简易的操作性，制备成本低，易于推广，适合于工业化大生产。
可理解，第一包覆层可以包覆在内核材料的全部表面上，也可以只包覆在内核材料的部分表面上。第二包覆层可以包覆在第一包覆层的全部表面上，也可以只包覆在第一包覆层的部分表面上。
如图1所示，在如图1所示的具体示例中，负极活性材料6包括内核材料61、第一包覆层62及第二包覆层63，第一包覆层62包覆在内核材料的全部表面上。第二包覆层63包覆在内核材料的全部表面上。
进一步地，内核材料61选自硅、硅碳、硅氮和硅金属合金中的至少一种。
可理解，上述硅是单质硅，第一包覆层62中的SiO x，包括但不限于一氧化硅和二氧化硅中的至少一种。进一步地，第一包覆层62为氧化硅层。
进一步地，第二包覆层63为氟化碳纳米管层。
在其中一些实施例中，负极活性材料的体积平均粒径Dv50为3μm～10μm；可选地，负极活性材料的体积平均粒径Dv50为5μm～7μm。
其中，体积平均粒径Dv50指：在粒度分布曲线中，颗粒的体积累计粒度分布数达到50％时所对应的粒径，它的物理意义是粒径小于(或大于)它的颗粒占50％。体积平均粒径Dv50可以采用本领域已知的方法测试。作为示例，Dv50可以参照GB/T 19077-2016粒度分布激光衍射法，采用激光粒度分析仪方便地测定，如英国马尔文仪器有限公司的Mastersizer 2000E型激光粒度分析仪。
在其中一些实施例中，第一包覆层的厚度为1.5nm～50nm，例如1.5nm、2nm、3nm、4nm、5nm、10nm、15nm、20nm、25nm、30nm、40nm、45nm、50nm；可选地，第一包覆层的厚度为1.5nm～20nm；进一步可选地，第一包覆层的厚度为5nm～15nm。通过控制第一包覆层的厚度在纳米级别且在上述给定范围，在满足使氟化碳材料均匀包覆在内核材料表面的需求的同时，可以尽可能提高负极活性材料中内核材料的质量占比， 保证应用其的二次电池具有良好的能量密度。
在其中一些实施例中，SiO x与内核材料的质量比为3～5％；可选地，SiO x与内核材料的质量比为0～20％。通过控制SiO x与内核材料的质量比在上述给定范围，可以控制负极活性材料中硅基材料的组成和比例，进而保证应用其的二次电池具有良好的能量密度。
在其中一些实施例中，第二包覆层的厚度为1nm～50nm；可选地，第二包覆层的厚度为3nm～10nm。在其中一些实施例中，基于负极活性材料的质量，氟化碳材料的质量含量不高于0.5％，例如0.05％～0.5％。可选地，基于负极活性材料的质量，氟化碳材料的质量含量为0.05％～0.15％。控制负极活性材料中氟化碳材料的质量含量，一方面保证负极活性材料中内核材料的质量占比，以满足应用其的二次电池具有良好的能量密度，另一方面避免氟化碳材料的质量含量过高，导致电解液消耗过量进而不利于电化学性能的提升。
在其中一些实施例中，基于氟化碳材料的质量，氟化碳材料中的氟元素所占的质量含量不高于15％。可选地，基于氟化碳材料的质量，氟化碳材料中的氟元素所占的质量含量为5％～12.5％。控制采用的氟化碳材料中的氟元素所占的质量含量在上述给定范围，可以更好地满足氟化碳材料均匀包覆的需求，以及氟化碳材料嵌入到负极活性材料表面形成富含LiF的SEI，从而增加SEI膜的韧性及机械强度，有效地抑制负极活性材料的体积膨胀及提升其锂离子迁移速率的需求，进而提升应用该负极活性材料的二次电池的循环性能。
可理解，氟化碳材料可通过市场购获得，也可以通过自制获得。在一些示例中，氟化碳材料为氟化碳纳米管，氟化碳纳米管可通过等离子法制备。以CF 4等离子体为原料，调节处理时间和温度等反应调节，制备不同含氟量的碳纳米管。氟化碳纳米管维持了一维的碳纳米管状结构，且在其表面连接大量的F，F与碳纳米管表面的碳形成C-F键。
在其中一些实施例中，上述制备方法的步骤S1中，碱液包括碱金属氢氧化物、有机溶剂及水。其中的有机溶剂能够溶解碱金属氢氧化物。在碱液中，水的质量与碱金属氢氧化物的比值为0.5％～5％。由于碱金属氢氧化物与内核材料中硅的反应需在水的参与下完成，且形成的碱金属硅酸盐可溶于水，因此本申请的制备方法控制碱液以有机溶剂为溶剂，用于溶解金属氢氧化物，并通过控制碱液中水的加入量为上述痕量范围内，进而控制步骤S1的反应程度，避免水过量导致反应形成的碱金属硅酸盐溶于过量水中， 同时由于反应溶剂为有机溶剂，而碱金属硅酸盐难溶或不溶于有机溶剂，进而促使形成的碱金属硅酸盐包覆沉积在内核材料的表面，进而在内核材料的表面原位刻蚀形成含有碱金属硅酸盐的第一包覆层。
在其中一些实施例中，上述碱液中，水的质量含量为0.5％～5％。
进一步地，在步骤S1中控制内核材料和碱液中的水的摩尔质量相当或过量，并控制碱液中的碱金属氢氧化物相对于水过量，进而可而通过控制步骤S1中水含量控制反应程度，进而控制形成的碱金属硅酸盐的厚度及碱金属硅酸盐与剩余的内核材料的比例。
优选地，在步骤S1中控制内核材料和碱液中的水的摩尔质量相当，并控制碱液中的碱金属氢氧化物相对于水过量；在步骤S1反应结束之后，过滤取固体进行步骤S2。
进一步地，碱金属氢氧化物选自氢氧化钠、氢氧化钾、氢氧化铷及氢氧化铯中的至少一种。
进一步地，有机溶剂包括乙醇和甘油中的至少一种。步骤S1在常温下即可进行，控制反应温度不高于有机溶剂的温度和水沸点即可。
进一步地，上述碱液中，对碱金属氢氧化物的浓度没有特别的要求，在确认碱金属氢氧化物和水的用量比例的情况下，加入有机溶剂作为溶解碱金属氢氧化物，最终制得的碱液的浓度不超过其能达到的饱和状态的浓度即可。
在其中一些实施例中，酸液选自盐酸、硫酸、硝酸、磷酸及醋酸中的至少一种。如此，采用酸液对步骤S2所得产物进行处理，以使产物表面的硅酸盐层在酸液中转化为H 2SiO x(硅酸)沉积在内核材料的表面。
在其中一些实施例中，步骤S3包括如下步骤：将步骤S2所得产物置于氟化碳材料分散液中混合，除去液相，干燥。由于步骤S2所得产物的表面含有H 2SiO x(硅酸)，其能够与氟化碳材料中的氟元素形成强氢键，如此不仅保证了氟化碳材料的均匀包覆，并同时其包覆程度可控，减少产物中游离态氟化碳材料的存在，提高了氟化碳材料的利用效率。
在其中一些实施例中，步骤S4中，真空热处理的温度为120～180℃；可选地，真空热处理的温度为150℃～180℃。在真空热处理的条件下，硅酸盐分解转化为氧化硅SiOx。进一步地，步骤S4中，真空热处理的时间为2h。
在一具体示例中，以内核材料为硅颗粒、氟化碳材料为氟化碳纳米管、碱金属为氢氧化钠、酸液为盐酸作为示例。上述制备方法的反应过程如图3所示，步骤S1在硅表 面形成超薄的Na 2SiO x，步骤S2将Na 2SiO x转化为H 2SiO x，步骤S3在H 2SiO x表面包覆形成氟化碳纳米管，步骤S4将H 2SiO x分解形成SiO x，得到负极活性材料。该负极活性材料包括硅及依次包覆在硅表面的SiO x层和氟化碳纳米管层。该制备方法所涉及的反应方程式如下所示：
步骤S1的刻蚀反应方程式为：Si+2NaOH+H 2O→Na 2SiO x+2H 2↑(1)；
步骤S2的反应方程式：Na 2SiO x+2HCl→2NaCl+H 2SiO x↓(2)；
步骤S4的硅酸分解方程式：H 2SiO x→SiO x+H 2O(3)。
上述原料未特别说明的均可以通过市购获得。
二次电池
二次电池，是指在电池放电后可通过充电的方式使活性材料激活而继续使用的电池。
通常情况下，二次电池包括正极极片、负极极片、隔离膜及电解质。在电池充放电过程中，活性离子在正极极片和负极极片之间往返嵌入和脱出。隔离膜设置在正极极片和负极极片之间，起到隔离的作用。电解质在正极极片和负极极片之间起到传导离子的作用。
负极极片
在二次电池中，所述负极极片通常包括负极集流体及设置在负极集流体上的负极膜层，所述负极膜层包括本申请上述提供的负极活性材料。
在其中一些实施例中，负极膜层除了包括上述的负极活性材料，还可包括以下材料中的至少一种：石墨、软炭、硬炭、锡基材料和钛酸锂等。所述锡基材料可选自单质锡、锡氧化合物以及锡合金中的至少一种。石墨包括但不限于人造石墨、天然石墨。本申请的负极膜层在含有上述的第一包覆层和第二包覆层包覆的负极活性材料之外，还可同时含有上述材料中的一种或多种。
在其中一些实施例中，负极膜层还包括石墨，负极活性材料的质量不高于石墨的质量的30％；可选地，负极活性材料的质量为石墨的质量的5％～25％。如此通过石墨和上述的第一包覆层和第二包覆层包覆的硅基的内核材料的负极活性材料共同使用，可以更好地满足二次电池的能量密度和循环性能的需求。
所述负极集流体可以采用常规金属箔片或复合集流体(例如可以将金属材料设置在高分子基材上形成复合集流体)。作为示例，负极集流体可以采用铜箔。
所述负极膜层通常还可选地包括粘结剂、导电剂和其他可选助剂。
作为示例，导电剂可以为超导碳、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯及碳纳米纤维中一种或几种。
作为示例，粘结剂可以为丁苯橡胶(SBR)、水性丙烯酸树脂(water-based acrylic resin)、聚偏二氟乙烯(PVDF)、聚四氟乙烯(PTFE)、乙烯-醋酸乙烯酯共聚物(EVA)、聚乙烯醇(PVA)及聚乙烯醇缩丁醛(PVB)中的一种或几种。
作为示例，其他可选助剂可以是增稠及分散剂(例如羧甲基纤维素钠CMC-Na)、PTC热敏电阻材料等。
正极极片
在二次电池中，所述正极极片通常包括正极集流体及设置在正极集流体上的正极膜层，所述正极膜层包括正极活性材料。
所述正极集流体可以采用常规金属箔片或复合集流体(可以将金属材料设置在高分子基材上形成复合集流体)。作为示例，正极集流体可以采用铝箔。
所述正极活性材料的具体种类不做限制，可以采用本领域已知的能够用于二次电池正极的活性材料，本领域技术人员可以根据实际需求进行选择。
作为示例，所述正极活性材料可以包括，但不限于，锂过渡金属氧化物，橄榄石结构的含锂磷酸盐及其各自的改性化合物中的一种或几种。锂过渡金属氧化物的示例可包括但不限于锂钴氧化物、锂镍氧化物、锂锰氧化物、锂镍钴氧化物、锂锰钴氧化物、锂镍锰氧化物、锂镍钴锰氧化物、锂镍钴铝氧化物及其改性化合物中的一种或几种。橄榄石结构的含锂磷酸盐的示例可包括但不限于磷酸铁锂、磷酸铁锂与碳的复合材料、磷酸锰锂、磷酸锰锂与碳的复合材料、磷酸锰铁锂、磷酸锰铁锂与碳的复合材料及其改性化合物中的一种或几种。这些材料均可以通过商业途径获得。
在一些实施方式中，上述各材料的改性化合物可以是对材料进行掺杂改性和/或表面包覆改性。
所述正极膜层通常还可选地包括粘结剂、导电剂和其他可选助剂。
作为示例，导电剂可以为超导碳、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、Super P(SP)、石墨烯及碳纳米纤维中一种或几种。
作为示例，粘结剂可以为丁苯橡胶(SBR)、水性丙烯酸树脂(water-based acrylic resin)、聚偏二氟乙烯(PVDF)、聚四氟乙烯(PTFE)、乙烯-醋酸乙烯酯共聚物(EVA)、聚丙烯酸(PAA)、羧甲基纤维素(CMC)、聚乙烯醇(PVA)及聚乙烯醇缩丁醛(PVB) 中的一种或几种。
隔离膜
在一些实施方式中，二次电池中还包括隔离膜。本申请对隔离膜的种类没有特别的限制，可以选用任意公知的具有良好的化学稳定性和机械稳定性的多孔结构隔离膜。
在一些实施方式中，隔离膜的材质可选自玻璃纤维、无纺布、聚乙烯、聚丙烯及聚偏二氟乙烯中的至少一种。隔离膜可以是单层薄膜，也可以是多层复合薄膜，没有特别限制。在隔离膜为多层复合薄膜时，各层的材料可以相同或不同，没有特别限制。
电解液
二次电池可以包括电解液，电解液在正极和负极之间起到传导离子的作用。所述电解液可以包括电解质盐和溶剂。
作为示例，电解质盐可选自六氟磷酸锂(LiPF 6)、四氟硼酸锂(LiBF 4)、高氯酸锂(LiClO 4)、六氟砷酸锂(LiAsF 6)、双氟磺酰亚胺锂(LiFSI)、双三氟甲磺酰亚胺锂(LiTFSI)、三氟甲磺酸锂(LiTFS)、二氟草酸硼酸锂(LiDFOB)、二草酸硼酸锂(LiBOB)、二氟磷酸锂(LiPO 2F 2)、二氟二草酸磷酸锂(LiDFOP)及四氟草酸磷酸锂(LiTFOP)中的一种或几种。
作为示例，所述溶剂可选自碳酸亚乙酯(EC)、碳酸亚丙酯(PC)、碳酸甲乙酯(EMC)、碳酸二乙酯(DEC)、碳酸二甲酯(DMC)、碳酸二丙酯(DPC)、碳酸甲丙酯(MPC)、碳酸乙丙酯(EPC)、碳酸亚丁酯(BC)、氟代碳酸亚乙酯(FEC)、甲酸甲酯(MF)、乙酸甲酯(MA)、乙酸乙酯(EA)、乙酸丙酯(PA)、丙酸甲酯(MP)、丙酸乙酯(EP)、丙酸丙酯(PP)、丁酸甲酯(MB)、丁酸乙酯(EB)、1,4-丁内酯(GBL)、环丁砜(SF)、二甲砜(MSM)、甲乙砜(EMS)及二乙砜(ESE)中的一种或几种。
在一些实施方式中，电解液中还包括添加剂。例如添加剂可以包括负极成膜添加剂，也可以包括正极成膜添加剂，还可以包括能够改善电池某些性能的添加剂，例如改善电池过充性能的添加剂、改善电池高温性能的添加剂、改善电池低温性能的添加剂等。
在一些实施方式中，本申请的二次电池为锂离子二次电池。
可以按照本领域常规方法制备二次电池，例如将正极极片、隔离膜、负极极片按顺序卷绕(或叠片)，使隔离膜处于正极极片与负极极片之间起到隔离的作用，得到电芯，将电芯置于外包装中，注入电解液并封口，得到二次电池。
本申请实施例对二次电池的形状没有特别的限制，其可以是圆柱形、方形或其他任意的形状。如图3是作为一个示例的方形结构的二次电池5。
在一些实施例中，二次电池可包括外包装。该外包装用于封装正极极片、负极极片和电解液。
在一些实施例中，参照图4，外包装可包括壳体51和盖板53。其中，壳体51可包括底板和连接于底板上的侧板，底板和侧板围合形成容纳腔。壳体51具有与容纳腔连通的开口，盖板53能够盖设于所述开口，以封闭所述容纳腔。
正极极片、负极极片和隔离膜可经卷绕工艺或叠片工艺形成电极组件52。电极组件52封装于所述容纳腔。电解液浸润于电极组件52中。二次电池5所含电极组件52的数量可以为一个或多个，可根据需求来调节。
在一些实施例中，二次电池的外包装可以是硬壳，例如硬塑料壳、铝壳、钢壳等。二次电池的外包装也可以是软包，例如袋式软包。软包的材质可以是塑料，如可包括聚丙烯(PP)、聚对苯二甲酸丁二醇酯(PBT)、聚丁二酸丁二醇酯(PBS)等中的一种或几种。
在一些实施例中，二次电池可以组装成电池模块，电池模块所含二次电池的数量可以为多个，具体数量可根据电池模块的应用和容量来调节。
图5是作为一个示例的电池模块4。在电池模块4中，多个二次电池5可以是沿电池模块4的长度方向依次排列设置。当然，也可以按照其他任意的方式进行排布。进一步可以通过紧固件将该多个二次电池5进行固定。
可选地，电池模块4还可以包括具有容纳空间的外壳，多个二次电池5容纳于该容纳空间。
在一些实施例中，上述电池模块还可以组装成电池包，电池包所含电池模块的数量可以根据电池包的应用和容量进行调节。
图6和图7是作为一个示例的电池包1。在电池包1中可以包括电池箱和设置于电池箱中的多个电池模块4。电池箱包括上箱体2和下箱体3，上箱体2能够盖设于下箱体3，并形成用于容纳电池模块4的封闭空间。多个电池模块4可以按照任意的方式排布于电池箱中。
用电装置
本申请还提供一种用电装置，所述用电装置包括所述的二次电池、电池模块、或电 池包中的至少一种。所述二次电池、电池模块或电池包可以用作所述装置的电源，也可以作为所述装置的能量存储单元。所述装置可以但不限于是移动设备(例如手机、笔记本电脑等)、电动车辆(例如纯电动车、混合动力电动车、插电式混合动力电动车、电动自行车、电动踏板车、电动高尔夫球车、电动卡车等)、电气列车、船舶及卫星、储能系统等。
所述装置可以根据其使用需求来选择二次电池、电池模块或电池包。
图8是作为一个示例的用电装置。该用电装置7为纯电动车、混合动力电动车、或插电式混合动力电动车等。为了满足该装置对二次电池的高功率和高能量密度的需求，可以采用电池包或电池模块。
作为另一个示例的装置可以是手机、平板电脑、笔记本电脑等。该装置通常要求轻薄化，可以采用二次电池作为电源。
以下结合实施例进一步说明本申请的有益效果。
实施例
为了使本申请所解决的技术问题、技术方案及有益效果更加清楚，以下将结合实施例和附图进行进一步详细说明。显然，所描述的实施例仅仅是本申请一部分实施例，而不是全部的实施例。以下对至少一个示例性实施例的描述实际上仅仅是说明性的，决不作为对本申请及其应用的任何限制。基于本申请中的实施例，本领域普通技术人员在没有付出创造性劳动前提下所获得的所有其他实施例都属于本申请保护的范围。
本申请的实施例中所用的材料均可以通过商购获得。
一、负极活性材料的制备
1)等离子法制备氟化碳纳米管
以CF 4等离子体为原料，调节处理时间和温度等反应调节，制备不同含氟量的碳纳米管，碳纳米管维持管状结构，并在其表面连接大量C-F键。
其中，等离子体功率为40W，CF 4的流速在60Pa为40sccm(sccm标准公升每分钟流量值)，控制处理时间为60s，温度为室温(25℃)，得到含氟质量为5％的氟化碳纳米管F-CNTs-a；控制处理时间为180s，温度为室温(25℃)，得到含氟质量为10％的氟化碳纳米管F-CNTs-b；控制处理时间为360s，温度为室温(25℃)，得到含氟质量为12.5％的氟化碳纳米管F-CNTs-c；控制处理时间为600s，温度为室温(25℃)，得到含 氟质量为15％的氟化碳纳米管F-CNTs-d。
2)负极活性材料的制备
实施例1负极活性材料的制备。
S1：在内核材料的至少部分表面采用碱液进行原位化学刻蚀形成硅酸盐层。其中碱液包括碱金属氢氧化物、有机溶剂及水，其中碱金属氢氧化物相对于水是过量的，水质量含量占有机溶剂体系1.2％，有机溶剂为甘油，然后配置碱金属氢氧化物的饱和溶液，碱液中的水含量为1wt％。具体地，内核材料为硅颗粒，硅颗粒与水的摩尔数比值为20，将硅颗粒分散在上述碱液中并于70℃温度下剧烈搅拌10min。
S2：将步骤S1所得产物采用酸液进行原位化学反应形成硅酸层。酸液为质量含量在10％的盐酸。具体地，将步骤S1所得固体浸渍到酸液中，搅拌10min。
S3：在步骤S2所得产物的硅酸层包覆形成第二包覆层。具体地，将步骤S2所得固体直接添加到氟化碳纳米管(F-CNTs-a、F-CNTs-b、F-CNTs-c、F-CNTs-d)分散液中，剧烈搅拌，然后通过低速离心，得到氟化碳纳米管包覆的硅材料。在烘箱内干燥。
通过重复上述步骤，可以在硅负极材料上包覆不同量的氟化碳纳米管。
S4：将步骤S3所得产物进行真空热处理，以使硅酸层形成含有SiOx的第一包覆层。真空热处理在真空干燥箱中进行，真空热处理的温度为160℃，时间为24h。
其中，第一包覆层和第二包覆层的厚度、第一包覆层SiOx质量及第二包覆层的氟化碳纳米管的质量采用平行测定法，具体过程如下：
平行进行上述S1～S2的步骤，然后将步骤S2所得产物直接进行上述S4，采用电镜对得到的产物的包覆层的厚度进行测量，即为第一包覆层的厚度H1。
并用天平称量包覆前后的质量，分别记为M0和M02，覆前后的质量差M02-M01，即为第一包覆层的质量M0，因此第一包覆层含有的氧的摩尔数为M0/16，而第一包覆层中的SiOx主要以一氧化硅和二氧化硅的形式存在，即第一包覆层中的氧化硅质量在M0/16×44～M0/16×60之间，取中间值。
然后采用电镜对上述S1～S4制得的负极活性材料的包覆层厚度进行标定，记为H21，则第二包覆层的厚度H2＝H21-H1。
同时用天平称量上述S1～S4制得的负极活性材料的质量M03，则M03-M02即为第二包覆层的氟化碳纳米管的质量。
各实施例和对比例的负极活性材料按照上述制备方法制得，具体的工艺参数如表1 所示。
各实施例之间基本相同，不同之处在于：表1所示的参数。
其中，对比例1～3具体如下所述。
对比例1
对比例1的负极活性材料为步骤S1所采用的硅颗粒，不做任何处理。
对比例2
对比例2与实施例1基本相同，区别在于，不经过氟化碳纳米管包覆的步骤，相当于在硅颗粒的表面直接形成SiO x层，其不含有第二包覆层。
对比例3
对比例3与实施例1基本相同，区别在于，不经过步骤S4的真空热处理，相当于形成的第一包覆层为硅酸层，在硅酸层上形成第二包覆层。
二、电池的制备
1、正极极片的制备：将正极活性材料LiNi 0.8Co 0.1Mn 0.1O 2(NCM811)、粘结剂聚偏氟乙烯(PVDF)、导电剂乙炔黑按照质量比为97％:1.5％:1.5％溶于溶剂N-甲基吡咯烷酮(NMP)中，充分搅拌混合均匀后制备成正极浆料；将正极浆料均匀涂覆在正极集流体铝箔上，之后经过烘干、冷压、分切，得到正极极片。
2、负极极片的制备：
将上述各实施例和对比例制备的负极活性材料、人造石墨、粘结剂丁苯橡胶(SBR)、粘结剂聚丙烯酸(PAA)、分散剂(CMC-Na)以及导电炭黑(Super-P，SP)、碳纳米管(CNT)按10％：85％：2％：1％：1％：0.7％：0.3％的重量比在适量的去离子水中充分搅拌混合，制备成负极浆料；通过涂布设备，将负极浆料涂敷在集流体铜箔上，之后经过烘干、冷压、分切，得到负极极片。
3、隔离膜：以厚度为12μm的聚乙烯膜(PE)作为隔离膜。
4、电解液的制备：将碳酸亚乙酯(EC)、碳酸甲乙酯(EMC)、碳酸二乙酯(DEC)按体积比1:1:1混合，然后将LiPF 6均匀溶解在上述溶液中，得到电解液。该电解液中，LiPF 6的浓度为1mol/L。
5、二次电池的制备：将上述正极极片、隔离膜、负极极片按顺序堆叠并卷绕，得到电极组件；将电极组件放入外包装中，加入上述制备的电解液，经封装、静置、化成、老化等工序后，得到二次电池。
三、性能测试
1、将上述制得的各二次电池首次充放电效率测试
首次充放电效率即二次电池首次充电和放电的容量比值，简称首效，具体测试过程如下：
在25℃下，将上述电池0.2C的倍率恒流充电1小时，记为IGC0；然后以0.1C倍率放电至2.0V，记为AGD0；静置5分钟；再将上述二次电池以0.5C倍率充电到3.65V，记为AGC0；静置5分钟；然后以0.1C放电至2.5V，记为AGD1；其中C0为ICC0-AGD0+AGC0；D0为AGD1；首效计算方式为D0/C0。
2、K值测试：K值指的是单位时间内的电池的电压降，其数值大小可反映二次电池容量的大小，容量越大，K值越大，容量越小，K值越小，具体测试方法如下：
以0.2C的倍率下将上述制得的二次电池充电到3.0V，静置5min。测试开路电压V1；静置48h；测试开路电压V2；K值＝(V1-V2)/48。
3、循环性能
在25℃下，将上述二次电池以0.5C倍率充电到3.65V后恒压充电至电流低于0.05C，然后使用1C倍率放电至2.5V，以这种满充满放的形式进行循环测试，直至锂离子电池的放电容量衰减至初始容量的80％，记录此时的循环圈数。
4、电池低温(-20℃)容量保持率
在25℃下，将上述电池0.2C的倍率恒流充电1小时；然后以0.1C倍率放电至2.0V；静置5分钟；再将上述二次电池以0.5C倍率充电到3.65V；静置5分钟；然后以0.1C放电至2.5V，记为D0(25℃)；在25℃下，将上述电池0.2C的倍率恒流充电1小时；然后以0.1C倍率放电至2.0V；静置5分钟；再将上述二次电池以0.5C倍率充电到3.65V；静置5分钟；将充满电的电池移动至-20℃，然后以0.1C放电至2.5V，记为D0(-20℃)
低温的容量保持率(％)＝D0(-20℃)/D 0(25℃)×100％。
5、电池内阻先将电池以1/3C满充至3.65V；静置30min，记录此时电压V0；然后以4C恒流(电流记作I)放电30s，记录此时电压V1；DCR放电(30s)＝∣Vo-V1∣/I
6、能量密度
在25℃下以0.33C恒流标准充电到3.65V，静置5min，以0.05C恒压充电至3.65V，静置10min后，0.33C放电至2.5V，记录其放电容量和平均放电电压U，随后计算放 电时的质量能量密度。
质量能量密度(Wh/Kg)＝放电容量(Wh)×U/锂离子二次电池单体质量(Kg)。
上述制得的各二次电池的参数及性能测试结果如下表1所示。
表1中SiO X：内核材料是指上述制得的负极活性材料中SiOx与内核材料的质量比；F-CNTs％是指在制得的负极活性材料中氟化碳纳米管的质量含量；F-CNTs代表是
采用的是上述制得的不同氟含量的F-CNTs-a、F-CNT-b、F-CNTs-c中的一种。
表1
Figure PCTCN2022117986-appb-000001
Figure PCTCN2022117986-appb-000002
“/”表示不进行该步骤或不存在该参数。
由表1及表2的各实施例和对比例可知，采用本申请的负极活性材料制得的负极片，可以提高二次电池的首效、低温性能、能量密度及循环性能。
以上所述，仅为本申请的具体实施方式，但本申请的保护范围并不局限于此，任何熟悉本技术领域的技术人员在本申请揭露的技术范围内，可轻易想到各种等效的修改或替换，这些修改或替换都应涵盖在本申请的保护范围之内。因此，本申请的保护范围应以权利要求的保护范围为准。

Claims (20)

  1. 一种负极活性材料，包括：
    内核材料，包括硅基材料；
    第一包覆层，位于所述内核材料的至少部分表面上，所述第一包覆层包含SiO x，1≤x＜2；及
    第二包覆层，位于所述第一包覆层的至少部分表面上，所述第二包覆层包括氟化碳材料。
  2. 如权利要求1所述的负极活性材料，其中，所述氟化碳材料选自氟化石墨烯、氟化富勒烯、氟化单壁碳纳米管、氟化多壁碳纳米管中的至少一种。
  3. 如权利要求1至2任一项所述的负极活性材料，其中，所述负极活性材料的体积平均粒径Dv50为3μm～10μm；
    可选地，所述负极活性材料的体积平均粒径Dv50为5μm～7μm。
  4. 如权利要求1至3任一项所述的负极活性材料，其中，所述第一包覆层的厚度为1.5nm～50nm；
    可选地，所述第一包覆层的厚度为1.5nm～20nm。
  5. 如权利要求1至4任一项所述的负极活性材料，其中，所述SiO x与所述内核材料的质量比为0.5％～5％；
    可选地，所述SiO x与所述内核材料的质量比为0.5％～2％。
  6. 如权利要求1至5任一项所述的负极活性材料，其中，所述第二包覆层的厚度为1nm～50nm；
    可选地，所述第二包覆层的厚度为3nm～10nm。
  7. 如权利要求1至6任一项所述的负极活性材料，其中，基于所述负极活性材料的质量，所述氟化碳材料的质量含量不高于0.5％；
    可选地，基于所述负极活性材料的质量，所述氟化碳材料的质量含量为0.05％～0.15％。
  8. 如权利要求1至7任一项所述的负极活性材料，其中，基于所述氟化碳材料的质量，所述氟化碳材料中的氟元素所占的质量含量不高于15％；
    可选地，基于所述氟化碳材料的质量，所述氟化碳材料中的氟元素所占的质量含量 为5％～12.5％。
  9. 如权利要求1至8任一项所述的负极活性材料，其中，所述硅基材料选自硅、硅碳、硅氮和硅金属合金中的至少一种。
  10. 一种权利要求1至9任一项所述的负极活性材料的制备方法，包括如下步骤：
    S1：在所述内核材料的至少部分表面采用碱液进行原位化学刻蚀形成硅酸盐层；
    S2：将步骤S1所得产物采用酸液进行原位化学反应形成硅酸层；
    S3：在步骤S2所得产物的所述硅酸层的至少部分表面包覆形成所述第二包覆层；及
    S4：将步骤S3所得产物进行真空热处理，以使所述硅酸层形成含有SiO x的第一包覆层。
  11. 如权利要求10所述的制备方法，其中，所述碱液包括碱金属氢氧化物、有机溶剂及水，所述有机溶剂能够溶解碱金属氢氧化物；在所述碱液中，所述水的质量为所述碱金属氢氧化物的质量的0.5％～5％。
  12. 如权利要求11所述的制备方法，其中，所述有机溶剂包括乙醇和甘油中的至少一种。
  13. 如权利要求11所述的制备方法，其中，所述碱金属氢氧化物选自氢氧化钠、氢氧化钾、氢氧化铷及氢氧化铯中的至少一种。
  14. 如权利要求10至13任一项所述的制备方法，其中，所述酸液选自盐酸、硫酸、硝酸、磷酸及醋酸中的至少一种。
  15. 如权利要求10至14任一项所述的制备方法，其中，步骤S3包括如下步骤：
    将步骤S2所得产物置于氟化碳材料分散液中混合，除去液相，干燥。
  16. 如权利要求10至15任一项所述的制备方法，其中，所述真空热处理的温度为120～180℃；
    可选地，所述真空热处理的温度为150℃～180℃。
  17. 一种二次电池，包括负极极片，所述负极极片包括如权利要求1至9任一项所述的负极活性材料或者包括如权利要求10至16任一项所述的方法制备的负极活性材料。
  18. 一种电池模组，其特征在于，包含如权利要求17所述的二次电池。
  19. 一种电池包，其特征在于，包含如权利要求18所述的电池模组。
  20. 一种用电装置，包括如权利要求17所述的二次电池、如权利要求18所述的电池 模组和如权利要求19所述的电池包中的至少一种。
PCT/CN2022/117986 2022-09-09 2022-09-09 负极活性材料及其制备方法、二次电池、电池模组、电池包及用电装置 WO2024050799A1 (zh)

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* Cited by examiner, † Cited by third party
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JP2006097123A (ja) * 2004-02-24 2006-04-13 Hitachi Metals Ltd 金属微粒子およびその製造方法ならびに磁気ビーズ
CN109167032A (zh) * 2018-08-21 2019-01-08 浙江大学 一种纳米硅基复合材料及其制备方法和应用
CN109728259A (zh) * 2017-10-30 2019-05-07 华为技术有限公司 一种硅基复合负极材料及其制备方法和储能器件
CN112234174A (zh) * 2020-10-14 2021-01-15 江西壹金新能源科技有限公司 一种锂离子电池负极材料及其制备方法
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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2006097123A (ja) * 2004-02-24 2006-04-13 Hitachi Metals Ltd 金属微粒子およびその製造方法ならびに磁気ビーズ
CN109728259A (zh) * 2017-10-30 2019-05-07 华为技术有限公司 一种硅基复合负极材料及其制备方法和储能器件
CN109167032A (zh) * 2018-08-21 2019-01-08 浙江大学 一种纳米硅基复合材料及其制备方法和应用
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