Negative active material, method for manufacturing the same, secondary battery, battery module, battery pack, and electric device

Abstract

A negative electrode active material and its preparation method, a secondary battery, and an electrical device thereof are disclosed. The negative electrode active material (6) comprises: a core material (61), including a silicon-based material; and a first coating layer (62) located on at least a portion of the surface of the core material (61), the first coating layer (62) comprising SiO₂. x , 1 < x < 2; and a second coating layer (63) located on at least a portion of the surface of the first coating layer (62), the second coating layer (63) comprising a fluorocarbon material.

Description

Technical Field

[0001] This application belongs to the field of secondary battery technology, specifically relating to a negative electrode active material and its preparation method, a secondary battery, a battery module, a battery pack, and an electrical device. Background Technology

[0002] Rechargeable 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 are placing higher demands on the use of rechargeable batteries.

[0003] Silicon-based materials have attracted widespread attention as negative electrode active materials due to their high capacity. However, silicon-based materials suffer from severe volume effects, resulting in huge volume expansion during charging. Consequently, it is difficult to form a stable SEI film on the surface of silicon-based materials during charging and discharging, leading to rapid capacity decay of secondary batteries and poor cycle performance. Summary of the Invention

[0004] In view of the technical problems existing in the background art, this application provides a negative electrode active material and its preparation method, a secondary battery and an electrical device, aiming to enable the secondary battery containing the material to have better cycle performance.

[0005] To achieve the above objectives, a first aspect of this application provides a negative electrode active material, comprising:

[0006] Core materials, including silicon-based materials;

[0007] A first coating layer is located on at least a portion of the surface of the core material, and the first coating layer comprises SiO₂. x , 1≤x<2; and

[0008] A second coating layer is located on at least a portion of the surface of the first coating layer, and the second coating layer comprises a fluorocarbon material.

[0009] Compared with the prior art, this application includes at least the following beneficial effects:

[0010] The negative electrode active material of this application involves forming two specific coating layers on the surface of a core material. The first coating layer contains SiOx, and the second coating layer contains fluorinated carbon material. During preparation, a SiOx precursor (silicic acid) is first formed in the first coating layer. This improves the coating stability and uniformity of the fluorinated carbon material (F-CNTs), thereby fully leveraging the role of the fluorinated carbon material in regulating the silicon oxide solid electrolyte interface (SEI). Furthermore, during charge and discharge, SiOx reacts with lithium to form electrochemically inert substances Li₂O and Li₄SiO₄, which, together with the fluorinated carbon material, suppress the volume expansion of the core material. This reduces the negative electrode rebound rate of the secondary battery, improving its lifespan and cycle performance.

[0011] In any embodiment of this application, 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.

[0012] In any embodiment of this application, the volume average particle size Dv50 of the negative electrode active material is 3 μm to 10 μm;

[0013] Optionally, the volume average particle size Dv50 of the negative electrode active material is 5 μm to 7 μm.

[0014] In any embodiment of this application, the thickness of the first coating layer is 1.5 nm to 50 nm;

[0015] Optionally, the thickness of the first coating layer is 1.5 nm to 20 nm.

[0016] In any embodiment of this application, the SiO x The mass ratio of the core material to the core material is 0.5% to 5%;

[0017] Optionally, the mass ratio of SiOx to the core material is 0.5% to 2%.

[0018] In any embodiment of this application, the thickness of the second coating layer is 1 nm to 50 nm;

[0019] Optionally, the thickness of the second coating layer is 3 nm to 10 nm.

[0020] In any embodiment of this application, the mass content of the fluorinated carbon material is no higher than 0.5% based on the mass of the negative electrode active material;

[0021] Optionally, the mass content of the fluorinated carbon material is 0.05% to 0.15% based on the mass of the negative electrode active material.

[0022] In any embodiment of this application, based on the mass of the fluorocarbon material, the mass content of fluorine in the fluorocarbon material is not higher than 15%;

[0023] Optionally, based on the mass of the fluorocarbon material, the mass content of fluorine in the fluorocarbon material is 5% to 12.5%.

[0024] In any embodiment of this application, the silicon-based material is selected from at least one of silicon, silicon-carbon, silicon-nitrogen, and silicon metal alloys.

[0025] A second aspect of this application provides a method for preparing the negative electrode active material of the first aspect, comprising the following steps:

[0026] S1: An in-situ chemical etching of at least a portion of the surface of the core material is performed using an alkaline solution to form a silicate layer;

[0027] S2: The product obtained in step S1 is subjected to an in-situ chemical reaction with acid to form a silica layer.

[0028] S3: At least a portion of the surface of the silica layer of the product obtained in step S2 is coated to form the second coating layer; and

[0029] S4: The product obtained in step S3 is subjected to vacuum heat treatment to form a silica layer containing SiO2. x The first coating layer.

[0030] In any embodiment of this application, the alkaline solution comprises an alkali metal hydroxide, an organic solvent, and water, wherein the organic solvent is capable of dissolving the alkali metal hydroxide; and in the alkaline solution, the mass of the water is 0.5% to 5% of the mass of the alkali metal hydroxide.

[0031] In any embodiment of this application, (a) the organic solvent includes at least one of ethanol and glycerol.

[0032] In any embodiment of this application, the alkali metal hydroxide is selected from at least one of sodium hydroxide, potassium hydroxide, rubidium hydroxide, and cesium hydroxide.

[0033] In any embodiment of this application, the acid solution is selected from at least one of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, and acetic acid.

[0034] In any embodiment of this application, step S3 includes the following steps:

[0035] The product obtained in step S2 was mixed in a fluorinated carbon nanomaterial dispersion, the liquid phase was removed, and the mixture was dried.

[0036] In any embodiment of this application, the temperature of the vacuum heat treatment is 120–180°C;

[0037] Optionally, the temperature of the vacuum heat treatment is 150℃~180℃.

[0038] A third aspect of this application provides a secondary battery comprising a negative electrode, said negative electrode comprising a negative electrode active material as described in the first aspect of this application or comprising a negative electrode active material prepared according to the preparation method of the second aspect of this application.

[0039] A fourth aspect of this application provides a battery module that includes the secondary battery of the third aspect of this application.

[0040] The fifth aspect of this application provides a battery pack that includes the battery module of the fourth aspect of this application.

[0041] A sixth aspect of this application provides an electrical device comprising at least one of a secondary battery according to a third aspect of this application, a battery module according to a fourth aspect of this application, and a battery pack according to a fifth aspect of this application. Attached Figure Description

[0042] To more clearly illustrate the technical solution of this application, the accompanying drawings used in this application will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without any creative effort.

[0043] Figure 1 This is a cross-sectional structural schematic diagram of one embodiment of the negative electrode active material of this application.

[0044] Figure 2 This is a schematic diagram of the preparation process of an example negative electrode active material according to this application.

[0045] Figure 3 This is a schematic diagram of one embodiment of a secondary battery.

[0046] Figure 4 yes Figure 3 The exploded diagram.

[0047] Figure 5 This is a schematic diagram of one embodiment of the battery module.

[0048] Figure 6 This is a schematic diagram of one embodiment of the battery pack.

[0049] Figure 7 yes Figure 6 The exploded diagram.

[0050] Figure 8 This is a schematic diagram of one embodiment of a device that uses a secondary battery as a power source.

[0051] Explanation of reference numerals in the attached figures:

[0052] 1. Battery pack; 2. Upper casing; 3. Lower casing; 4. Battery module; 5. Secondary battery; 51. Housing; 52. Electrode assembly; 53. Cover plate; 6. Negative electrode active material; 61. Core material; 62. First coating layer; 63. Second coating layer; 7. Electrical device. Detailed Implementation

[0053] The present application will be further described below with reference to specific embodiments. It should be understood that these specific embodiments are for illustrative purposes only and are not intended to limit the scope of the present application.

[0054] For the sake of brevity, this article only discloses some specific numerical ranges. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, just as any upper limit can be combined with any other upper limit to form an unspecified range. Furthermore, each individually disclosed point or single value can itself serve as a lower or upper limit and be combined with any other point or single value or with other lower or upper limits to form an unspecified range.

[0055] In the description of this article, it should be noted that, unless otherwise stated, "above" and "below" include the number itself, and "several" in "one or more" means two or more.

[0056] In this description, unless otherwise stated, the term "or" is inclusive. That is, the phrase "A or (or) B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied if any of the following conditions are met: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist). Unless otherwise stated, the terms used in this application have their commonly known meanings as understood by those skilled in the art. Unless otherwise stated, the numerical values ​​of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art (e.g., they can be tested according to the methods given in the embodiments of this application).

[0057] Silicon-based materials are commonly used anode active materials; however, they suffer from significant volume expansion after repeated cycles, leading to poor cycle performance. Technicians have discovered that modifying the surface of silicon-based materials with fluorinated carbon nanotubes or other fluorinated carbon materials can regulate the solid electrolyte interphase (SEI) film formed on the silicon surface, while simultaneously suppressing silicon anode expansion. During the formation stage or charge / discharge process, fluorine in the fluorinated carbon material participates in the formation of an SEI rich in lithium fluoride (LiF) and carbon nanotubes. Lithium fluoride, with its high interfacial energy and lithium-ion conductivity, is an important component of the SEI, thus facilitating lithium-ion migration and diffusion. The SEI possesses electronic insulation and ionic conductivity, preventing further reduction and decomposition of the electrolyte on the silicon-based material surface. Furthermore, the embedding of fluorinated carbon materials into the SEI acts as a stress-relieving layer, suppressing anode expansion during charge / discharge, increasing SEI toughness, and preventing the growth of unstable SEI.

[0058] However, current common methods for modifying silicon-based materials with fluorinated carbon nanotubes and other fluorinated carbon materials include direct coating methods, such as ball milling and conventional mechanical mixing, which directly coat the silicon-based material surface with fluorinated carbon materials. Other methods involve using binders to bond the fluorinated carbon materials to the silicon anode.

[0059] The former method, coating fluorocarbon materials, has unsatisfactory coating effects. Some fluorocarbon material remains in a free state, failing to be effectively coated, thus reducing the utilization efficiency of the fluorocarbon material. Furthermore, it is difficult to control the presence, uniformity, and content of the fluorocarbon material on the silicon-based material surface. Conventional mechanical methods of coating silicon-based materials with fluorocarbon materials result in poor adhesion between the fluorocarbon material and the silicon anode. This is because the surface structure of fluorocarbon materials, such as fluorocarbon nanotubes, consists of hyperconjugated π bonds, which cannot form strong chemical adsorption with the silicon anode surface. While ball milling can increase the adhesion between the fluorocarbon material and the silicon-based material, it may also damage the structure and morphology of both materials. The latter method, using binders, can increase the adhesion between the fluorocarbon material and the silicon-based material surface; however, excessive binder can affect the properties of the SEI (Sediment Injection Layer), increasing the organic salt content in the SEI, reducing lithium-ion migration and diffusion, and simultaneously decreasing the proportion of silicon-based material, leading to lower battery energy density.

[0060] Based on this, this application provides a negative electrode active material and its preparation method. The prepared negative electrode active material will be described in detail below in conjunction with the preparation method.

[0061] The negative electrode active material includes a core material, a first coating layer, and a second coating layer. The core material includes a silicon-based material, and the first coating layer is located on at least a portion of the surface of the core material, comprising SiO₂. x, 1≤x<2; the second coating layer is located on at least a portion of the surface of the first coating layer, and the second coating layer comprises a fluorocarbon material.

[0062] The negative electrode active material of this application involves forming two specific coating layers on the surface of a core material. The first coating layer contains SiOx, and the second coating layer contains fluorinated carbon material. During preparation, a SiOx precursor (silicic acid) is first formed in the first coating layer. This improves the coating stability and uniformity of the fluorinated carbon material (F-CNTs), thereby fully leveraging the role of the fluorinated carbon material in regulating the silicon oxide solid electrolyte interface (SEI). Furthermore, during charge and discharge, SiOx reacts with lithium to form electrochemically inert substances Li₂O and Li₄SiO₄, which, together with the fluorinated carbon material, suppress the volume expansion of the core material. This reduces the negative electrode rebound rate of the secondary battery, improving its lifespan and cycle performance.

[0063] In any embodiment of this application, 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.

[0064] In any embodiment of this application, the fluorinated carbon material is selected from fluorinated carbon nanotubes, which include at least one of fluorinated multi-walled carbon nanotubes and fluorinated multi-walled carbon nanotubes.

[0065] In any embodiment of this application, the silicon-based material is selected from at least one of silicon, silicon-carbon, silicon-nitrogen, and silicon metal alloys.

[0066] Silicon-carbon is also known as silicon-carbon alloy. Silicon metal alloys refer to alloys formed by silicon and metallic elements, including but not limited to at least one of silicon-aluminum alloys and silicon-magnesium alloys.

[0067] In any embodiment of this application, the silicon-based material may exist in the form of particles, selected from at least one of silicon particles, silicon-carbon particles, silicon-nitrogen particles, and silicon metal alloy particles.

[0068] This application also provides a method for preparing the above-mentioned negative electrode active material, including the following steps S1-S4.

[0069] S1: An in-situ chemical etching of at least a portion of the surface of the core material is performed using an alkaline solution to form a silicate layer;

[0070] S2: The product obtained in step S1 is subjected to an in-situ chemical reaction with acid to form a silica layer;

[0071] S3: The silica layer of the product obtained in step S2 is coated to form the second coating layer; and

[0072] S4: The product obtained in step S3 is subjected to vacuum heat treatment to form a silica layer containing SiO2. x The first coating layer.

[0073] Not wishing to be limited to any particular theory, the negative electrode active material of this application can be prepared using the above-described preparation method, wherein at least a portion of the surface of the core material is modified into H2SiO, which has an adsorption effect on fluorinated carbon materials, through steps S1 and S2. x (Silicic acid layer), while fluorine atoms in the fluorinated carbon material react with H2SiO on the surface of the core material. x Strong hydrogen bonds are formed, allowing for the controllable and uniform coating of fluorinated carbon materials onto the H2SiO core material. x This improves the utilization efficiency of fluorinated carbon materials by coating the surface. After applying the second coating layer, vacuum heat treatment is performed to form a silicate layer containing SiO₂. x The first coating layer serves two purposes. First, SiOx reacts with lithium to form electrochemically inert substances Li2O and Li4SiO4, which can buffer the volume expansion of the core material, thus ensuring the cycle performance of the secondary battery using it. Second, it can also prevent H2SiO from being absorbed. x It is unstable and prone to absorbing water, which causes performance instability in secondary batteries. It can also reduce the proton content in the negative electrode active material, thus reducing gas production in the secondary battery. Simultaneously, it can lower the activation energy for lithium intercalation, thereby reducing interfacial lithium-ion migration resistance.

[0074] Furthermore, during the formation stage of the secondary battery, fluorinated carbon materials can coat the surface of the negative electrode active material to form a LiF-rich SEI. The fluorinated carbon material acts as a anchor point for LiF, confining the growth of LiF grains and generating more grain boundaries, thereby increasing the lithium-ion migration rate. This improves the internal resistance, cycle performance, and low-temperature performance of the secondary battery using the aforementioned negative electrode active material. Simultaneously, the fluorinated carbon material is reduced to form carbon nanomaterials, which are embedded in the SEI film, increasing its toughness and mechanical strength. Therefore, it effectively suppresses the volume expansion of the negative electrode active material, thereby reducing the negative electrode rebound rate of the secondary battery using this material and improving its lifespan and cycle performance.

[0075] Compared to the traditional method of modifying silicon-based materials with fluorinated carbon materials, the preparation method of the negative electrode active material in this application does not require the use of binders, and ensures uniform coating of fluorinated carbon materials, thereby improving the utilization efficiency of fluorinated carbon materials. At the same time, it avoids the problem of reducing the proportion of silicon-based materials due to the introduction of binders, and can effectively ensure the specific capacity of the negative electrode active material and the energy density of the secondary battery using it.

[0076] The above-mentioned method for preparing negative electrode active materials has good universality and simple operation, low preparation cost, and is easy to promote, making it suitable for large-scale industrial production.

[0077] It is understandable that the first coating layer may cover the entire surface of the core material or only a portion of the core material's surface. The second coating layer may cover the entire surface of the first coating layer or only a portion of the first coating layer's surface.

[0078] like Figure 1 As shown, in Figure 1 In the specific example shown, the negative electrode 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 entire surface of the core material. The second coating layer 63 covers the entire surface of the core material.

[0079] Furthermore, the core material 61 is selected from at least one of silicon, silicon-carbon, silicon-nitrogen, and silicon metal alloys.

[0080] It is understandable that the silicon mentioned above is elemental silicon, and the SiO in the first coating layer 62 is... x This includes, but is not limited to, at least one of silicon monoxide and silicon dioxide. Further, the first coating layer 62 is a silicon oxide layer.

[0081] Furthermore, the second coating layer 63 is a fluorinated carbon nanotube layer.

[0082] In some embodiments, the volume average particle size Dv50 of the negative electrode active material is 3 μm to 10 μm; optionally, the volume average particle size Dv50 of the negative electrode active material is 5 μm to 7 μm.

[0083] The volume average particle size (Dv50) refers to the particle size at which the cumulative volumetric particle size distribution reaches 50% in the particle size distribution curve. Physically, it means that 50% of the particles are smaller (or larger) than this value. The volume average particle size (Dv50) can be measured using methods known in the art. For example, Dv50 can be conveniently determined using a laser particle size analyzer, such as the Mastersizer 2000E laser particle size analyzer from Malvern Instruments Ltd., UK, according to GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method.

[0084] In some embodiments, the thickness of the first coating layer is 1.5 nm to 50 nm, for example, 1.5 nm, 2 nm, 3 nm, 4 nm, 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 40 nm, 45 nm, or 50 nm; optionally, the thickness of the first coating layer is 1.5 nm to 20 nm; more preferably, the thickness of the first coating layer is 5 nm to 15 nm. By controlling the thickness of the first coating layer to be at the nanometer level and within the given range, while meeting the requirement of uniformly coating the fluorinated carbon material on the surface of the core material, the mass ratio of the core material in the negative electrode active material can be increased as much as possible, ensuring that the secondary battery using it has good energy density.

[0085] In some embodiments, SiO x The mass ratio of SiO to the core material is 3-5%; optionally, SiO x The mass ratio of SiO to the core material is 0–20%. This is achieved by controlling the SiO content. x By controlling the mass ratio of silicon-based materials to core materials within the given range, the composition and proportion of silicon-based materials in the negative electrode active material can be controlled, thereby ensuring that the secondary battery using it has good energy density.

[0086] In some embodiments, the thickness of the second coating layer is 1 nm to 50 nm; optionally, the thickness of the second coating layer is 3 nm to 10 nm. In some embodiments, the mass content of the fluorinated carbon material is not higher than 0.5% based on the mass of the negative electrode active material, for example, 0.05% to 0.5%. Optionally, the mass content of the fluorinated carbon material is 0.05% to 0.15% based on the mass of the negative electrode active material. Controlling the mass content of the fluorinated carbon material in the negative electrode active material ensures the mass ratio of the core material in the negative electrode active material to meet the requirement that the secondary battery using it has good energy density, while avoiding excessive mass content of the fluorinated carbon material, which would lead to excessive electrolyte consumption and thus be detrimental to the improvement of electrochemical performance.

[0087] In some embodiments, the fluorine content in the fluorinated carbon material is no more than 15% by mass, based on the mass of the fluorinated carbon material. Optionally, the fluorine content in the fluorinated carbon material is 5% to 12.5% ​​by mass, based on the mass of the fluorinated carbon material. Controlling the fluorine content in the fluorinated carbon material within the given range can better meet the requirements for uniform coating of the fluorinated carbon material and the formation of a LiF-rich SEI by embedding the fluorinated carbon material into the surface of the negative electrode active material. This increases the toughness and mechanical strength of the SEI film, effectively suppresses the volume expansion of the negative electrode active material, and improves its lithium-ion migration rate, thereby enhancing the cycle performance of the secondary battery using this negative electrode active material.

[0088] Understandably, fluorinated carbon materials can be obtained commercially or synthesized in-house. In some examples, the fluorinated carbon material is fluorinated carbon nanotubes, which can be prepared via plasma methods. Using CF4 plasma as a raw material, carbon nanotubes with varying fluorine contents are prepared by adjusting reaction conditions such as processing time and temperature. The fluorinated carbon nanotubes maintain a one-dimensional carbon nanotube structure and have a large number of fluorine atoms bonded to their surface, forming CF bonds with the carbon atoms on the nanotube surface.

[0089] In some embodiments, in step S1 of the above preparation method, the alkaline solution includes an alkali metal hydroxide, an organic solvent, and water. The organic solvent is capable of dissolving the alkali metal hydroxide. In the alkaline solution, the mass ratio of water to alkali metal hydroxide is 0.5% to 5%. Since the reaction between the alkali metal hydroxide and silicon in the core material requires the participation of water, and the formed alkali metal silicate is soluble in water, the preparation method of this application controls the use of an organic solvent as the solvent to dissolve the metal hydroxide. By controlling the amount of water added to the alkaline solution to the above-mentioned trace amount range, the degree of reaction in step S1 is controlled, avoiding excessive water that would cause the formed alkali metal silicate to dissolve in excess water. At the same time, since the reaction solvent is an organic solvent, and alkali metal silicates are difficult or insoluble in organic solvents, the formed alkali metal silicate is deposited on the surface of the core material, thereby forming a first coating layer containing alkali metal silicate by in-situ etching on the surface of the core material.

[0090] In some embodiments, the water content in the above-mentioned alkaline solution is 0.5% to 5% by mass.

[0091] Furthermore, in step S1, the molar mass of the core material and the water in the alkaline solution is controlled to be equal or excessive, and the alkali metal hydroxide in the alkaline solution is controlled to be excessive relative to the water. Thus, the degree of reaction can be controlled by controlling the water content in step S1, thereby controlling the thickness of the formed alkali metal silicate and the ratio of the alkali metal silicate to the remaining core material.

[0092] Preferably, in step S1, the molar mass of the core material and the water in the alkaline solution are controlled to be equal, and the alkali metal hydroxide in the alkaline solution is controlled to be in excess relative to the water; after the reaction in step S1 is completed, the solid is filtered and taken for step S2.

[0093] Furthermore, the alkali metal hydroxide is selected from at least one of sodium hydroxide, potassium hydroxide, rubidium hydroxide, and cesium hydroxide.

[0094] Furthermore, the organic solvent includes at least one of ethanol and glycerol. Step S1 can be carried out at room temperature, provided that the reaction temperature does not exceed the temperature of the organic solvent and the boiling point of water.

[0095] Furthermore, there are no special requirements for the concentration of the alkali metal hydroxide in the above-mentioned alkaline solution. As long as the ratio of alkali metal hydroxide to water is confirmed, an organic solvent is added to dissolve the alkali metal hydroxide, and the concentration of the final alkaline solution does not exceed the concentration of its saturation state.

[0096] In some embodiments, the acid is selected from at least one of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, and acetic acid. Thus, the product obtained in step S2 is treated with the acid to convert the silicate layer on the product surface into H₂SiO in the acid. x (Silicic acid) is deposited on the surface of the core material.

[0097] In some embodiments, step S3 includes the following steps: mixing the product obtained in step S2 in a fluorocarbon material dispersion, removing the liquid phase, and drying. Because the surface of the product obtained in step S2 contains H2SiO... x (Silicic acid) can form strong hydrogen bonds with fluorine in fluorinated carbon materials. This not only ensures the uniform coating of fluorinated carbon materials, but also makes the coating degree controllable, reducing the presence of free fluorinated carbon materials in the product and improving the utilization efficiency of fluorinated carbon materials.

[0098] In some embodiments, in step S4, the temperature of the vacuum heat treatment is 120–180°C; optionally, the temperature of the vacuum heat treatment is 150°C–180°C. Under the conditions of vacuum heat treatment, silicate decomposes into silicon oxide (SiOx). Further, in step S4, the vacuum heat treatment time is 2 hours.

[0099] In a specific example, silicon particles are used as the core material, fluorinated carbon nanotubes are used as the fluorinated carbon material, sodium hydroxide is used as the alkali metal, and hydrochloric acid is used as the acid solution. The reaction process of the above preparation method is as follows: Figure 3 As shown, step S1 forms an ultrathin Na2SiO layer on the silicon surface. x Step S2 will use Na2SiO x Converted to H2SiO x Step S3 in H2SiO x Surface coating to form fluorinated carbon nanotubes, step S4 to H2SiO x Decomposition to form SiO x A negative electrode active material is obtained. This negative electrode active material comprises silicon and SiO₂ sequentially coated on the silicon surface. x The preparation method involves a layer of fluorinated carbon nanotubes and a layer of fluorinated carbon nanotubes. The reaction equations involved in this preparation method are shown below:

[0100] The etching reaction equation for step S1 is: Si + 2NaOH + H₂O → Na₂SiO x +2H2↑(1);

[0101] The reaction equation for step S2 is: Na₂SiO₂ x +2HCl→2NaCl+H2SiO x ↓(2);

[0102] The decomposition equation of silicic acid in step S4 is: H₂SiO₂ x →SiO x +H2O(3).

[0103] Unless otherwise specified, all of the above-mentioned raw materials can be obtained through commercial purchase.

[0104] Secondary batteries

[0105] A rechargeable battery is a battery that can be recharged after it has been discharged, allowing the active materials to be reactivated and the battery to continue to be used.

[0106] Typically, a secondary battery includes a positive electrode, a negative electrode, a separator, and an electrolyte. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The separator, positioned between the positive and negative electrodes, serves as a barrier. The electrolyte, located between the positive and negative electrodes, conducts ions.

[0107] Negative electrode sheet

[0108] In a secondary battery, the negative electrode typically includes a negative current collector and a negative electrode film layer disposed on the negative current collector, wherein the negative electrode film layer includes the negative electrode active material provided in this application.

[0109] In some embodiments, the negative electrode film layer, in addition to the aforementioned negative electrode active material, may also include at least one of the following materials: graphite, soft carbon, hard carbon, tin-based materials, and lithium titanate. 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 this application, in addition to containing the aforementioned negative electrode active material coated by the first and second coating layers, may also simultaneously contain one or more of the aforementioned materials.

[0110] In some embodiments, 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; alternatively, the mass of the negative electrode active material is 5% to 25% of the mass of graphite. Thus, by using graphite and the silicon-based core material coated by the aforementioned first and second coating layers together as the negative electrode active material, the energy density and cycle performance requirements of secondary batteries can be better met.

[0111] The negative electrode current collector can be a conventional metal foil or a composite current collector (for example, a metal material can be disposed on a polymer substrate to form a composite current collector). As an example, the negative electrode current collector can be a copper foil.

[0112] The negative electrode film layer may also optionally include binders, conductive agents, and other optional additives.

[0113] As an example, the conductive agent can be one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0114] As an example, the adhesive may be one or more of styrene-butadiene rubber (SBR), water-based acrylic resin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), polyvinyl alcohol (PVA), and polyvinyl butyral (PVB).

[0115] As an example, other optional additives may be thickeners and dispersants (such as sodium carboxymethyl cellulose CMC-Na), PTC thermistor materials, etc.

[0116] Positive electrode sheet

[0117] In a secondary battery, the positive electrode typically includes a positive current collector and a positive electrode film layer disposed on the positive current collector, the positive electrode film layer including a positive active material.

[0118] The positive electrode current collector can be a conventional metal foil or a composite current collector (a composite current collector can be formed by setting metal material on a polymer substrate). As an example, the positive electrode current collector can be aluminum foil.

[0119] The specific type of positive electrode active material is not limited. Any active material known in the art that can be used as the positive electrode of a secondary battery can be used. Those skilled in the art can select according to actual needs.

[0120] As an example, the positive electrode 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. Examples of lithium transition metal oxides may include, but are not limited to, one or more of lithium cobalt oxides, lithium nickel oxides, lithium manganese oxides, lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, lithium nickel cobalt manganese oxides, lithium nickel cobalt aluminum oxides, and their modified compounds. Examples of lithium-containing phosphates with an olivine structure may include, but are not limited to, one or more of lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, lithium manganese iron phosphate and carbon composites, and their modified compounds. All of these materials are commercially available.

[0121] In some embodiments, the modifying compounds for the above-mentioned materials may be those used for doping modification and / or surface coating modification of the materials.

[0122] The positive electrode film layer may also optionally include binders, conductive agents, and other optional additives.

[0123] As an example, 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.

[0124] As an example, the adhesive may be one or more of styrene-butadiene rubber (SBR), water-based acrylic resin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), polyacrylic acid (PAA), carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), and polyvinyl butyral (PVB).

[0125] Separating membrane

[0126] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0127] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0128] electrolyte

[0129] A secondary battery may include an electrolyte, which acts as a conductor of ions between the positive and negative electrodes. The electrolyte may include an electrolyte salt and a solvent.

[0130] As an example, the electrolyte salt may be selected from one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0131] As an example, the solvent may be selected from one or more of ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl 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), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0132] In some embodiments, the electrolyte also includes additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and additives that improve battery low-temperature performance.

[0133] In some embodiments, the secondary battery of this application is a lithium-ion secondary battery.

[0134] Secondary batteries can be prepared according to conventional methods in the field, such as winding (or stacking) the positive electrode, separator, and negative electrode in sequence, so that the separator is placed between the positive electrode and the negative electrode to play a role in isolation, thus obtaining a battery cell. The battery cell is placed in an outer package, electrolyte is injected and the package is sealed to obtain a secondary battery.

[0135] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. Figure 3 This is an example of a square-structured secondary battery 5.

[0136] In some embodiments, the secondary battery may include an outer packaging. This outer packaging is used to encapsulate the positive electrode, the negative electrode, and the electrolyte.

[0137] In some embodiments, refer to Figure 4 The outer packaging may include a shell 51 and a cover 53. The shell 51 may include a bottom plate and side plates connected to the bottom plate, the bottom plate and side plates forming a receiving cavity. The shell 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed on the opening to close the receiving cavity.

[0138] The positive electrode, negative electrode, and separator can be formed into an electrode assembly 52 by a winding or stacking process. The electrode assembly 52 is encapsulated in the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 can contain one or more electrode assemblies 52, which can be adjusted according to requirements.

[0139] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0140] In some embodiments, secondary batteries can be assembled into battery modules, and the number of secondary batteries contained in a battery module can be multiple, the specific number of which can be adjusted according to the application and capacity of the battery module.

[0141] Figure 5 This is an example of a battery module 4. In battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other way. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0142] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0143] In some embodiments, the battery modules described above 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.

[0144] Figure 6 and Figure 7 This is an example of a battery pack 1. The battery pack 1 may include a battery compartment and multiple battery modules 4 disposed within the battery compartment. The battery compartment includes an upper housing 2 and a lower housing 3, with the upper housing 2 covering the lower housing 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery compartment.

[0145] Electrical appliances

[0146] This application also provides an electrical device, which includes at least one of the aforementioned secondary battery, battery module, or battery pack. The secondary battery, battery module, or battery pack can be used as a power source for the device or as an energy storage unit for the device. The device can be, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0147] The device can be configured to use a secondary battery, battery module, or battery pack, depending on its usage requirements.

[0148] Figure 8 This is an example of an electrical device. This electrical device 7 is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the device's requirements for high power and high energy density of the secondary battery, a battery pack or battery module can be used.

[0149] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0150] The beneficial effects of this application are further illustrated below with reference to the embodiments.

[0151] Example

[0152] To make the technical problems, technical solutions, and beneficial effects solved by this application clearer, the following will provide a more detailed description in conjunction with the embodiments and accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit this application or its applications. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this application.

[0153] All materials used in the embodiments of this application are commercially available.

[0154] I. Preparation of negative electrode active materials

[0155] 1) Preparation of fluorinated carbon nanotubes by plasma method

[0156] Using CF4 plasma as raw material, carbon nanotubes with different fluorine contents were prepared by adjusting the reaction time and temperature. The carbon nanotubes maintained a tubular structure and had a large number of CF bonds attached to their surface.

[0157] The plasma power was 40W, the CF4 flow rate was 40 sccm (standard liters per minute flow rate) at 60 Pa, the processing time was controlled at 60 s, and the temperature was room temperature (25℃) to obtain fluorinated carbon nanotubes F-CNTs-a with a fluorine mass content of 5%; the processing time was controlled at 180 s and the temperature was room temperature (25℃) to obtain fluorinated carbon nanotubes F-CNTs-b with a fluorine mass content of 10%; the processing time was controlled at 360 s and the temperature was room temperature (25℃) to obtain fluorinated carbon nanotubes F-CNTs-c with a fluorine mass content of 12.5%; and the processing time was controlled at 600 s and the temperature was room temperature (25℃) to obtain fluorinated carbon nanotubes F-CNTs-d with a fluorine mass content of 15%.

[0158] 2) Preparation of negative electrode active materials

[0159] Example 1: Preparation of negative electrode active material.

[0160] S1: An in-situ chemical etching process using an alkaline solution is employed to form a silicate layer on at least a portion of the surface of the core material. The alkaline solution comprises an alkali metal hydroxide, an organic solvent, and water, wherein the alkali metal hydroxide is in excess relative to water, and the water content is 1.2% of the organic solvent system. The organic solvent is glycerol. A saturated solution of the alkali metal hydroxide is then prepared, with a water content of 1 wt%. Specifically, the core material is silicon particles, with a silicon particle to water molar ratio of 20. The silicon particles are dispersed in the aforementioned alkaline solution and vigorously stirred at 70°C for 10 minutes.

[0161] S2: The product obtained in step S1 is subjected to an in-situ chemical reaction using an acid solution to form a silica layer. The acid solution is hydrochloric acid with a mass content of 10%. Specifically, the solid obtained in step S1 is immersed in the acid solution and stirred for 10 minutes.

[0162] S3: The silica layer of the product obtained in step S2 is coated to form a second coating layer. Specifically, the solid obtained in step S2 is directly added to a dispersion of fluorinated carbon nanotubes (F-CNTs-a, F-CNTs-b, F-CNTs-c, F-CNTs-d), stirred vigorously, and then centrifuged at low speed to obtain silicon material coated with fluorinated carbon nanotubes. It is then dried in an oven.

[0163] By repeating the above steps, different amounts of fluorinated carbon nanotubes can be coated onto silicon anode materials.

[0164] S4: The product obtained in step S3 is subjected to vacuum heat treatment to form a first coating layer containing SiOx in the silica layer. The vacuum heat treatment is carried out in a vacuum drying oven at a temperature of 160°C for 24 hours.

[0165] The thicknesses of the first and second coating layers, the mass of SiOx in the first coating layer, and the mass of the fluorinated carbon nanotubes in the second coating layer were determined using a parallel measurement method, the specific process of which is as follows:

[0166] The steps S1 to S2 are performed in parallel. Then, the product obtained in step S2 is directly subjected to step S4. The thickness of the coating layer of the obtained product is measured by electron microscopy, which is the thickness H1 of the first coating layer.

[0167] The mass before and after coating was measured using a balance and recorded as M0 and M02 respectively. The mass difference before and after coating, M02-M01, is the mass of the first coating layer, M0. Therefore, the number of moles of oxygen contained in the first coating layer is M0 / 16. The SiOx in the first coating layer mainly exists in the form of silicon monoxide and silicon dioxide. That is, the mass of silicon oxide in the first coating layer is between M0 / 16×44 and M0 / 16×60, and the middle value is taken.

[0168] Then, the thickness of the coating layer of the negative electrode active material prepared by S1 to S4 is calibrated by electron microscopy and denoted as H21. The thickness of the second coating layer is H2 = H21 - H1.

[0169] At the same time, the mass M03 of the negative electrode active material prepared by S1 to S4 is weighed using a balance. Then, M03-M02 is the mass of the fluorinated carbon nanotubes of the second coating layer.

[0170] The negative electrode active materials of each embodiment and comparative example were prepared according to the above preparation method, and the specific process parameters are shown in Table 1.

[0171] The embodiments are basically the same, except for the parameters shown in Table 1.

[0172] Comparative Examples 1 to 3 are described in detail below.

[0173] Comparative Example 1

[0174] The negative electrode active material in Comparative Example 1 is the silicon particle used in step S1, without any treatment.

[0175] Comparative Example 2

[0176] Comparative Example 2 is basically the same as Example 1, except that it does not involve the fluorinated carbon nanotube coating step, which is equivalent to directly forming SiO on the surface of silicon particles. x The layer does not contain a second covering layer.

[0177] Comparative Example 3

[0178] Comparative Example 3 is basically the same as Example 1, except that it does not undergo the vacuum heat treatment in step S4, which is equivalent to forming a first coating layer of silica, and then forming a second coating layer on the silica layer.

[0179] II. Battery Preparation

[0180] 1. Preparation of the positive electrode sheet: The positive electrode active material LiNi is prepared... 0.8 Co 0.1 Mn 0.1 O2 (NCM811), binder polyvinylidene fluoride (PVDF), and conductive agent acetylene black are dissolved in solvent N-methylpyrrolidone (NMP) at a mass ratio of 97%:1.5%:1.5% and thoroughly mixed to prepare a positive electrode slurry. The positive electrode slurry is then uniformly coated onto the positive electrode current collector aluminum foil, followed by drying, cold pressing, and slitting to obtain the positive electrode sheet.

[0181] 2. Preparation of the negative electrode sheet:

[0182] The negative electrode active material, artificial graphite, styrene-butadiene rubber (SBR) binder, polyacrylic acid (PAA) binder, dispersant (CMC-Na), conductive carbon black (Super-P, SP), and carbon nanotubes (CNT) prepared in the above embodiments and comparative examples are thoroughly 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 then coated onto the current collector copper foil using a coating device, and then dried, cold-pressed, and slit to obtain the negative electrode sheet.

[0183] 3. Separating membrane: A polyethylene film (PE) with a thickness of 12μm is used as the separating membrane.

[0184] 4. Preparation of electrolyte: Ethyl carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1. LiPF6 was then uniformly dissolved in the mixture to obtain the electrolyte. The concentration of LiPF6 in this electrolyte was 1 mol / L.

[0185] 5. Preparation of secondary battery: The above positive electrode sheet, separator and negative electrode sheet are stacked and wound in sequence to obtain electrode assembly; the electrode assembly is placed in outer packaging, the electrolyte prepared above is added, and after processes such as encapsulation, standing, formation and aging, a secondary battery is obtained.

[0186] III. Performance Testing

[0187] 1. Test the initial charge-discharge efficiency of each of the secondary batteries prepared above.

[0188] The initial charge-discharge efficiency, also known as the capacity ratio of a secondary battery during its first charge and discharge, is as follows:

[0189] At 25°C, the battery is charged at a constant current rate of 0.2C for 1 hour, denoted as IGC0; then discharged at a rate of 0.1C to 2.0V, denoted as AGD0; left to stand for 5 minutes; then the secondary battery is charged at a rate of 0.5C to 3.65V, denoted as AGC0; left to stand for 5 minutes; then discharged at a rate of 0.1C to 2.5V, denoted as AGD1; where C0 is IGC0-AGD0+AGC0; D0 is AGD1; the first-efficiency calculation method is D0 / C0.

[0190] 2. K-value test: The K-value refers to the voltage drop of the battery per unit time. Its value reflects the capacity of the secondary battery. The larger the capacity, the larger the K-value, and the smaller the capacity, the smaller the K-value. The specific test method is as follows:

[0191] The secondary battery prepared above was charged to 3.0V at a rate of 0.2C and left to stand for 5 minutes. The open circuit voltage V1 was tested; the battery was left to stand for 48 hours; the open circuit voltage V2 was tested; the K value was (V1-V2) / 48.

[0192] 3. Cyclic performance

[0193] At 25°C, the above-mentioned secondary battery was charged to 3.65V at a rate of 0.5C, then charged at a constant voltage until the current was below 0.05C, and then discharged to 2.5V at a rate of 1C. This full charge and discharge cycle test was carried out until the discharge capacity of the lithium-ion battery decayed to 80% of the initial capacity, and the number of cycles at this time was recorded.

[0194] 4. Battery capacity retention at low temperature (-20℃)

[0195] At 25°C, the battery was charged at a constant current rate of 0.2C for 1 hour; then discharged at a rate of 0.1C to 2.0V; left to stand for 5 minutes; then charged at a rate of 0.5C to 3.65V; left to stand for 5 minutes; then discharged at a rate of 0.1C to 2.5V, recorded as D0(25°C); at 25°C, the battery was charged at a constant current rate of 0.2C for 1 hour; then discharged at a rate of 0.1C to 2.0V; left to stand for 5 minutes; then charged at a rate of 0.5C to 3.65V; left to stand for 5 minutes; the fully charged battery was moved to -20°C and then discharged at a rate of 0.1C to 2.5V, recorded as D0(-20°C). The capacity retention rate at low temperature (%) = D0(-20°C) / D0(25°C) × 100%.

[0196] 5. Battery internal resistance: First, fully charge the battery at 1 / 3C to 3.65V; let it stand for 30 minutes and record the voltage V0 at this time; then discharge it at a constant current of 4C (current denoted as I) for 30 seconds and record the voltage V1 at this time; DCR discharge (30s) = |Vo - V1| / I

[0197] 6. Energy density

[0198] At 25℃, it was charged to 3.65V at a constant current of 0.33C, allowed to stand for 5 minutes, charged to 3.65V at a constant voltage of 0.05C, allowed to stand for 10 minutes, and then discharged to 2.5V at 0.33C. Its discharge capacity and average discharge voltage U were recorded, and then the mass energy density during discharge was calculated.

[0199] Mass energy density (Wh / Kg) = Discharge capacity (Wh) × U / Mass of lithium-ion secondary battery cell (Kg).

[0200] The parameters and performance test results of the various secondary batteries prepared above are shown in Table 1 below.

[0201] In Table 1, SiOx: core material refers to the mass ratio of SiOx to core material in the prepared negative electrode active material; F-CNTs% refers to the mass content of fluorinated carbon nanotubes in the prepared negative electrode active material; F-CNTs represents...

[0202] The method used is one of the F-CNTs-a, F-CNT-b, and F-CNTs-c with different fluorine contents obtained above.

[0203] Table 1

[0204]

[0205]

[0206] The ' / ' sign indicates that the step is not performed or that the parameter does not exist.

[0207] As can be seen from the embodiments and comparative examples in Tables 1 and 2, the negative electrode sheet made using the negative electrode active material of this application can improve the first efficiency, low temperature performance, energy density and cycle performance of secondary batteries.

[0208] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and these modifications or substitutions should all be covered within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A negative electrode active material, comprising: Core materials, including silicon-based materials; A first coating layer is located on at least a portion of the surface of the core material, and the first coating layer comprises SiO₂. x , 1 ≤ x < 2; and A second coating layer is located on at least a portion of the surface of the first coating layer, and the second coating layer comprises a fluorocarbon material.

2. The negative electrode active material as described in claim 1, wherein, 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.

3. The negative electrode active material according to any one of claims 1 to 2, wherein, The volume average particle size Dv50 of the negative electrode active material is 3μm~10μm.

4. The negative electrode active material as described in claim 3, wherein, The volume average particle size Dv50 of the negative electrode active material is 5μm~7μm.

5. The negative electrode active material according to any one of claims 1 to 2, 4, wherein, The thickness of the first coating layer is 1.5nm~50nm.

6. The negative electrode active material as described in claim 5, wherein, The thickness of the first coating layer is 1.5nm~20nm.

7. The negative electrode active material according to any one of claims 1 to 2, 4, and 6, wherein, The SiO x The mass ratio of the material to the core material is 0.5% to 5%.

8. The negative electrode active material as described in claim 7, wherein, The SiO x The mass ratio of the material to the core material is 0.5% to 2%.

9. The negative electrode active material according to any one of claims 1 to 2, 4, 6, and 8, wherein, The thickness of the second coating layer is 1 nm to 50 nm.

10. The negative electrode active material as described in claim 9, wherein, The thickness of the second coating layer is 3 nm to 10 nm.

11. The negative electrode active material according to any one of claims 1 to 2, 4, 6, 8, and 10, wherein, Based on the mass of the negative electrode active material, the mass content of the fluorinated carbon material is no higher than 0.5%.

12. The negative electrode active material as described in claim 11, wherein, Based on the mass of the negative electrode active material, the mass content of the fluorinated carbon material is 0.05%~0.15%.

13. The negative electrode active material according to any one of claims 1 to 2, 4, 6, 8, 10, and 12, wherein, Based on the mass of the fluorocarbon material, the mass content of fluorine in the fluorocarbon material is no more than 15%.

14. The negative electrode active material as described in claim 13, wherein, Based on the mass of the fluorinated carbon material, the mass content of fluorine in the fluorinated carbon material is 5% to 12.5%.

15. The negative electrode active material according to any one of claims 1 to 2, 4, 6, 8, 10, 12, and 14, wherein, The silicon-based material is selected from at least one of silicon, silicon-carbon, silicon-nitrogen, and silicon metal alloys.

16. A method for preparing the negative electrode active material according to any one of claims 1 to 15, comprising the following steps: S1: An in-situ chemical etching of at least a portion of the surface of the core material is performed using an alkaline solution to form a silicate layer; S2: The product obtained in step S1 is subjected to an in-situ chemical reaction with acid to form a silica layer. S3: At least a portion of the surface of the silica layer of the product obtained in step S2 is coated to form the second coating layer; and S4: The product obtained in step S3 is subjected to vacuum heat treatment to form a silica layer containing SiO2. x The first coating layer.

17. The preparation method according to claim 16, wherein, The alkaline solution comprises an alkali metal hydroxide, an organic solvent, and water, wherein the organic solvent is capable of dissolving the alkali metal hydroxide; and the mass of the water in the alkaline solution is 0.5% to 5% of the mass of the alkali metal hydroxide.

18. The preparation method according to claim 17, wherein, The organic solvent includes at least one of ethanol and glycerol.

19. The preparation method according to claim 17, wherein, The alkali metal hydroxide is selected from at least one of sodium hydroxide, potassium hydroxide, rubidium hydroxide, and cesium hydroxide.

20. The preparation method according to any one of claims 16 to 19, wherein, The acid solution is selected from at least one of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, and acetic acid.

21. The preparation method according to any one of claims 16 to 19, wherein, Step S3 includes the following steps: The product obtained in step S2 is mixed in a fluorocarbon material dispersion, the liquid phase is removed, and the mixture is dried.

22. The preparation method according to any one of claims 16 to 19, wherein, The temperature of the vacuum heat treatment is 120~180℃.

23. The preparation method according to claim 22, wherein, The temperature of the vacuum heat treatment is 150℃~180℃.

24. A secondary battery, comprising a negative electrode sheet, said negative electrode sheet comprising a negative electrode active material as described in any one of claims 1 to 15 or comprising a negative electrode active material prepared by the method as described in any one of claims 16 to 23.

25. A battery module, characterized in that, It includes the secondary battery as described in claim 24.

26. A battery pack, characterized in that, It includes the battery module as described in claim 25.

27. An electrical device comprising at least one of the secondary battery as claimed in claim 24, the battery module as claimed in claim 25, and the battery pack as claimed in claim 26.

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