Negative active material, method for preparing the same, and secondary battery and electric device including the same

Abstract

The application provides a negative electrode active material and a preparation method thereof, and a secondary battery and an electric device comprising the same. The negative electrode active material comprises a carbon matrix and a filling material. The graphitization degree of the carbon matrix is less than or equal to 87%. The carbon matrix comprises a plurality of pore structures. At least a part of the filling material is located in the pore structures of the carbon matrix. The filling material comprises one or more of elements capable of alloying with Li. The negative electrode active material provided by the application can have high specific capacity, high initial coulombic efficiency, low volume expansion, high conductivity and good cycle stability.

Description

Technical Field

[0001] This application belongs to the field of battery technology, specifically relating to a negative electrode active material and its preparation method, as well as a secondary battery and power-consuming device containing the same. Background Technology

[0002] In recent years, secondary batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and many other fields. During the rapid development of secondary batteries, higher demands have been placed on their energy density. Carbon-based materials, represented by graphite, are the most commonly used negative electrode active materials in secondary batteries, but their capacity utilization is already close to their theoretical specific capacity. Non-carbon materials, such as silicon-based, tin-based, and germanium-based materials, have attracted widespread attention due to their high theoretical specific capacity; however, these negative electrode active materials generally suffer from large volume expansion, low initial coulombic efficiency, and / or poor conductivity. Summary of the Invention

[0003] The purpose of this application is to provide a negative electrode active material and its preparation method, as well as a secondary battery and power device containing the same, wherein the negative electrode active material can achieve high specific capacity, high initial coulombic efficiency, low volume expansion, high conductivity and good cycle stability.

[0004] The first aspect of this application provides a negative electrode active material, comprising a carbon matrix and a filler material, wherein the degree of graphitization of the carbon matrix is ​​less than or equal to 87%, the carbon matrix comprises a plurality of pore structures, at least a portion of the filler material is located in the pore structures of the carbon matrix, and the filler material comprises one or more elements capable of alloying with Li.

[0005] The inventors of this application discovered that by placing a filler material with high specific capacity within the porous structure of a carbon matrix with low graphitization (greater than 0 and less than or equal to 87%), the resulting negative electrode active material can achieve a balance of high specific capacity, high initial coulombic efficiency, low volume expansion, high conductivity, and good cycle stability. Furthermore, it enables the secondary battery to achieve a balance of high energy density, high initial coulombic efficiency, and long cycle life. The carbon matrix of this application has a graphitization degree of less than or equal to 87%, which, compared to carbon matrices obtained by creating pores with pore-forming agents, offers advantages in high conductivity and high initial coulombic efficiency. Compared to natural graphite, it offers advantages in low volume expansion and high cycle stability. Therefore, the negative electrode active material provided by this application can fully leverage the high specific capacity advantage of the filler material while compensating for the poor conductivity and low initial coulombic efficiency of the filler material. In addition, at least a portion of the filler material is located within the porous structure of the carbon matrix, thereby reducing the volume expansion of the filler material through the carbon matrix.

[0006] In any embodiment of this application, the degree of graphitization of the carbon matrix is ​​65%-87%. This is beneficial for the negative electrode active material to better balance high specific capacity, high initial coulombic efficiency, low volume expansion, high conductivity, and good cycle stability.

[0007] In any embodiment of this application, the element capable of alloying with Li includes one or more of silicon, tin, and germanium. This is advantageous for the negative electrode active material to have a high specific capacity.

[0008] In any embodiment of this application, the filler material includes one or more of silicon-based materials, tin-based materials, and germanium-based materials.

[0009] In any embodiment of this application, the silicon-based material includes one or more of elemental silicon, silicon oxide, silicon-carbon materials, silicon-nitrogen composites, and silicon alloys.

[0010] In any embodiment of this application, the tin-based material includes one or more of elemental tin, tin oxide, tin sulfide, tin phosphide, tin composite oxide, tin-carbon material, and tin alloy material.

[0011] In any embodiment of this application, the germanium-based material includes one or more of elemental germanium, germanium oxide, germanium carbon material, germanium alloy material, and germanate.

[0012] In any embodiment of this application, the filling material includes crystalline and / or amorphous filling materials, and optionally includes crystalline silicon-based materials and / or amorphous silicon-based materials. Silicon-based materials have the advantage of high specific capacity, which is beneficial for improving the energy density of secondary batteries.

[0013] In any embodiment of this application, the grain size of the crystalline filler material is ≤100nm, and can be selected as 2nm-50nm. When the crystalline filler material has a suitable grain size, it can improve the initial coulombic efficiency of the secondary battery while avoiding significant adverse effects on the cycle performance and storage performance of the secondary battery.

[0014] In any embodiment of this application, the filling material includes one or more of vapor-deposited silicon-based materials, tin-based materials, and germanium-based materials, and optionally includes vapor-deposited silicon-based materials.

[0015] In any embodiment of this application, in the X-ray diffraction pattern of the negative electrode active material measured by an X-ray diffractometer, the negative electrode active material includes a (002) crystal plane peak at 26.4° and a (111) crystal plane peak at 28.6°, and the ratio of the half-width at half-maximum (WHM) of the (002) crystal plane peak to the WHM of the (111) crystal plane peak is 0.2-50, optionally 0.2-20. By controlling the WHM of the (002) crystal plane peak and the WHM of the (111) crystal plane peak within a suitable range, the carbon matrix can have a suitable degree of graphitization, and the filler material can have a suitable grain size, thereby facilitating the negative electrode active material to achieve high specific capacity, high initial coulombic efficiency, low volume expansion, high conductivity, and good cycle stability.

[0016] In any embodiment of this application, at least a portion of the filler material is located within the porous structure of the carbon matrix, and there are voids between the filler material and the carbon matrix. When there are voids between the filler material and the carbon matrix, these voids can serve as spaces to accommodate the volume expansion of the filler material, thereby buffering the stress generated during the expansion process and further reducing the probability of particle breakage and pulverization.

[0017] In any embodiment of this application, the negative electrode active material further includes a coating layer located on at least a portion of the surface of the carbon matrix. The coating layer prevents direct contact between the filler material and the electrolyte, thereby reducing electrolyte side reactions, decreasing active ion consumption, and improving the cycle performance of the secondary battery. Simultaneously, it enhances the stability of the negative electrode slurry, preventing reactions between the filler material and solvents such as water, which would increase the processing difficulty of the negative electrode slurry. Furthermore, the coating layer also buffers the volume expansion of the filler material, which further improves the structural stability of the negative electrode active material and enhances the electrochemical performance of the secondary battery.

[0018] In any embodiment of this application, the coating layer comprises one or more of carbon materials, conductive polymers, metal oxides and metal sulfides, and optionally includes carbon materials.

[0019] In any embodiment of this application, the thickness of the coating layer is ≤100nm, and can be selected as 10nm-100nm. When the thickness of the coating layer is within the above range, the integrity of the coating layer is higher, which can more effectively avoid the contact between the filler material and the electrolyte, thereby helping to reduce electrolyte side reactions and enabling the negative electrode active material to achieve high specific capacity, high initial coulombic efficiency and low volume expansion.

[0020] In any embodiment of this application, the negative electrode active material includes carbon and elements capable of alloying with Li.

[0021] In any embodiment of this application, the mass percentage of carbon in the negative electrode active material is 20wt%-80wt%, and optionally 30wt%-70wt%.

[0022] In any embodiment of this application, the mass percentage of the element capable of alloying with Li in the negative electrode active material is 20wt%-80wt%, and optionally 30wt%-70wt%.

[0023] When the content of carbon and / or elements that can undergo alloying reactions with Li in the negative electrode active material is within the above range, it is beneficial for the negative electrode active material to achieve both high specific capacity and high conductivity.

[0024] In any embodiment of this application, the negative electrode active material further includes other elements, including one or more of oxygen, metal elements and nitrogen.

[0025] In any embodiment of this application, the sum of the mass percentages of the other elements in the negative electrode active material is less than or equal to 20 wt%, and optionally less than or equal to 10 wt%.

[0026] In any embodiment of this application, the initial coulombic efficiency of the carbon matrix is ​​≥75%, optionally 75%-87%. This is beneficial for improving the initial coulombic efficiency of the negative electrode active material.

[0027] In any embodiment of this application, the powder resistivity of the carbon matrix at a pressure of 16 MPa is ≤5 × 10⁻⁶. -2 Ω·cm, can be selected as ≤3.5×10 -2 Ω·cm. This is beneficial for improving the conductivity of the negative electrode active material.

[0028] In any embodiment of this application, the BET specific surface area of ​​the carbon matrix is ​​50 m². 2 / g-1000m 2 / g, optional 100m 2 / g-700m 2 / g. This is beneficial for the negative electrode active material to have a suitable BET specific surface area, thereby reducing the surface activity of the negative electrode active material, reducing interfacial side reactions, reducing SEI film formation consumption, and thus improving the first coulombic efficiency and cycle performance of the secondary battery.

[0029] In any embodiment of this application, the graphitization degree of the negative electrode active material is ≥65%, optionally 65%-87%. This allows the negative electrode active material to better balance high initial coulombic efficiency, high conductivity, and good cycle stability.

[0030] In any embodiment of this application, the initial coulombic efficiency of the negative electrode active material is ≥92%, optionally 92%-95%. This reduces the irreversible consumption of active ions and improves the capacity utilization characteristics and cycle performance of the secondary battery.

[0031] In any embodiment of this application, the volumetric particle size Dv50 of the negative electrode active material is 3μm-50μm, and can be selected as 5μm-20μm.

[0032] In any embodiment of this application, the volumetric particle size Dv90 of the negative electrode active material is ≤60μm, and can be selected as 20μm-50μm.

[0033] In any embodiment of this application, the diameter (Dv90-Dv10) / Dv50 of the negative electrode active material is 1.0-3.0, and can be selected as 1.0-2.0.

[0034] When at least one of the volumetric particle size Dv50, volumetric particle size Dv90, and particle size distribution (Dv90-Dv10) / Dv50 of the negative electrode active material is within the above range, it helps to reduce the surface activity of the negative electrode active material, reduce interfacial side reactions, reduce SEI film formation consumption, and also helps to improve the active ion and electron transport performance, thereby further improving the cycle performance of the secondary battery.

[0035] In any embodiment of this application, the BET specific surface area of ​​the negative electrode active material is 2m². 2 / g-100m 2 / g, optional 2m 2 / g-30m 2 / g. When the BET specific surface area of ​​the negative electrode active material is within the above range, it helps to reduce surface activity, reduce interfacial side reactions, and reduce SEI film formation consumption, thereby improving the first coulombic efficiency and cycle performance of the secondary battery.

[0036] In any embodiment of this application, the powder resistivity of the negative electrode active material at a pressure of 16 MPa is ≤5 × 10⁻⁶. -1 Ω·cm, can be ≤2×10 -1 Ω·cm. Therefore, the negative electrode active material exhibits good conductivity, which is beneficial for improving the cycle performance and rate performance of the secondary battery.

[0037] The second aspect of this application provides a method for preparing a negative electrode active material, comprising the following steps: Step 1, providing a carbon matrix with a graphitization degree of less than or equal to 87%, optionally 65%-87%, and including multiple pore structures; Step 2, dispersing a filler material into the pore structure of the carbon matrix to obtain the negative electrode active material, wherein the negative electrode active material includes a carbon matrix and a filler material, the carbon matrix includes multiple pore structures, at least a portion of the filler material is located in the pore structure of the carbon matrix, and the filler material includes one or more elements capable of alloying with Li, optionally, the elements capable of alloying with Li include one or more elements selected from silicon, tin, and germanium.

[0038] In any embodiment of this application, in step 1, the carbon matrix is ​​prepared by the following method: a carbon source comprising multiple porous structures is placed in a high-temperature furnace and graphitized at 1600℃-2400℃ under a protective gas atmosphere, and the carbon matrix is ​​obtained after the treatment. This yields a carbon matrix with a graphitization degree of less than or equal to 87%, optionally 65%-87%, and comprising multiple porous structures.

[0039] In any embodiment of this application, the heat treatment time for graphitization is 1h-12h.

[0040] In any embodiment of this application, the carbon source includes one or more selected from hard carbon, petroleum coke, pitch coke, biomass carbon, and resin carbon.

[0041] By graphitizing a carbon source with multiple porous structures at a certain temperature, the micropores in the carbon source can be reduced, improving the dispersion uniformity of subsequent filling materials. On the other hand, residual bonds on the surface of the carbon source can be removed, reducing the content of oxygen-containing functional groups in the carbon source and reducing electrolyte side reactions. This is beneficial to improving the initial coulombic efficiency, conductivity, and high-temperature performance of the obtained carbon matrix, thereby enabling the secondary battery to have good cycle performance.

[0042] In any embodiment of this application, in step 1, the initial coulombic efficiency of the carbon matrix is ​​≥75%, optionally 75%-87%.

[0043] In any embodiment of this application, in step 1, the powder resistivity of the carbon matrix at a pressure of 16 MPa is ≤5 × 10⁻⁶. -2 Ω·cm, can be selected as ≤3.5×10 -2 Ω·cm.

[0044] In any embodiment of this application, in step 1, the BET specific surface area of ​​the carbon matrix is ​​50 m². 2 / g-1000m 2 / g, optional 100m2 / g-700m 2 / g.

[0045] In any embodiment of this application, in step 1, the volumetric particle size Dv50 of the carbon matrix is ​​3μm-50μm, and can be selected as 5μm-20μm.

[0046] In any embodiment of this application, in step 2, the process of dispersing the filler material into the porous structure of the carbon matrix includes liquid phase deposition and vapor phase deposition, with vapor phase deposition being the preferred option. Compared to liquid phase deposition, vapor phase deposition is advantageous for better deposition and uniform dispersion of the filler material within the porous structure of the carbon matrix, and can avoid problems such as filler material agglomeration and / or excessive deposition on the carbon matrix surface. Furthermore, vapor phase deposition is a relatively mature technology and is easy to mass-produce industrially.

[0047] In any embodiment of this application, the vapor deposition process includes chemical vapor deposition and physical vapor deposition, and may be selected as chemical vapor deposition.

[0048] In any embodiment of this application, step 2, the step of dispersing the filler material into the porous structure of the carbon matrix, includes the following steps: placing the carbon matrix in a reactor, introducing a first mixed gas containing a source of elements capable of alloying with Li, and depositing at a first temperature T1 for a first time t1, thereby obtaining the negative electrode active material.

[0049] In any embodiment of this application, the first mixed gas includes the source of the element capable of alloying with Li and a protective gas. Optionally, the volume percentage of the source of the element capable of alloying with Li in the first mixed gas is 10%-50%.

[0050] In any embodiment of this application, the first mixed gas further includes a carbon source gas.

[0051] In any embodiment of this application, the volume ratio of the source of the element capable of alloying with Li to the carbon source gas is greater than or equal to 0.5:1, and can be selected as (2-10):1.

[0052] In any embodiment of this application, the volume percentage of the carbon source gas in the first mixed gas is ≤20%, and can be selected as 5%-20%.

[0053] In any embodiment of this application, the pressure inside the reactor is 200Pa-600Pa higher than atmospheric pressure.

[0054] In any embodiment of this application, the total gas flow rate of the first mixed gas is 0.5 L / min to 20 L / min.

[0055] In any embodiment of this application, the first temperature T1 is 400℃-1000℃.

[0056] In any embodiment of this application, the first time t1 is 1h-12h.

[0057] By adjusting at least one of the composition ratio of the first mixed gas, the total gas flow rate of the first mixed gas, the first temperature, and the first time to be within the above-mentioned range, it is beneficial to deposit the filling material in the porous structure of the carbon matrix, and it is also beneficial to adjust the crystallinity and / or grain size of the filling material within a suitable range.

[0058] In any embodiment of this application, the method further includes step 3: forming a coating layer on at least a portion of the surface of the negative electrode active material obtained in step 2, the coating layer comprising one or more of carbon materials, conductive polymers, metal oxides and metal sulfides.

[0059] In any embodiment of this application, the step of forming the coating layer includes the following steps: placing the negative electrode active material obtained in step 2 in a reactor, introducing a second mixed gas containing carbon source gas, and depositing it at a second temperature T2 for a second time t2, after which carbon-coated negative electrode active material is obtained.

[0060] In any embodiment of this application, the second mixed gas includes a carbon source gas and a protective gas. Optionally, the volume percentage V2 of the carbon source gas in the second mixed gas is 5%-50%.

[0061] In any embodiment of this application, the total gas flow rate of the second mixed gas is 0.5 L / min to 20 L / min.

[0062] In any embodiment of this application, the second temperature T2 is 700℃-850℃.

[0063] In any embodiment of this application, the second time t2 is 1h-6h.

[0064] In step 3, by adjusting at least one of the composition ratio of the second mixed gas, the total gas flow rate of the second mixed gas, the second temperature, and the second time to be within the above range, it is beneficial to form a coating layer of appropriate thickness and avoid the coating layer being too thick, which would reduce the specific capacity of the negative electrode active material.

[0065] A third aspect of this application provides a secondary battery, including a negative electrode sheet, wherein the negative electrode sheet comprises the negative electrode active material of the first aspect of this application or the negative electrode active material prepared by the method of the second aspect of this application.

[0066] The fourth aspect of this application provides an electrical device, including the secondary battery of the third aspect of this application.

[0067] The inventors of this application discovered that by placing a high-capacity filling material within the porous structure of a carbon matrix with low graphitization, the resulting negative electrode active material can achieve high capacity, high initial coulombic efficiency, low volume expansion, high conductivity, and good cycle stability. Furthermore, the secondary battery can achieve high energy density, high initial coulombic efficiency, and long cycle life. The power supply device of this application includes the secondary battery provided in this application and therefore possesses at least the same advantages as the aforementioned secondary battery. Attached Figure Description

[0068] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly described below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0069] Figure 1 This is a schematic diagram of one embodiment of the battery cell of this application.

[0070] Figure 2 This is an exploded view of one embodiment of the battery cell of this application.

[0071] Figure 3 This is a schematic diagram of one embodiment of the battery module of this application.

[0072] Figure 4 This is a schematic diagram of one embodiment of the battery pack of this application.

[0073] Figure 5 yes Figure 4 An exploded view of an embodiment of the battery pack shown.

[0074] Figure 6 This is a schematic diagram of one embodiment of an electrical device that uses a secondary battery as a power source, as described in this application.

[0075] The accompanying drawings are not necessarily drawn to scale. The reference numerals are explained as follows: 1 Battery pack, 2 Upper casing, 3 Lower casing, 4 Battery module, 5 Individual battery cell, 51 Housing, 52 Electrode assembly, 53 Cover plate. Detailed Implementation

[0076] The following detailed description, with appropriate reference to the accompanying drawings, discloses the negative electrode active material of this application, its preparation method, and embodiments of secondary batteries and power-consuming devices comprising the same. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0077] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0078] Unless otherwise specified, all embodiments and optional embodiments of this application may be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of this application.

[0079] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions, and such technical solutions shall be deemed to be included in the disclosure of this application.

[0080] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0081] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0082] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: 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).

[0083] Unless otherwise specified, in this application, the terms "first," "second," etc., are used to distinguish different objects, rather than to describe a specific order or primary / secondary relationship.

[0084] In this application, the terms "multiple", "several", "various", and "several types" refer to two or more kinds.

[0085] Unless otherwise stated, the terms used in this application have the common meanings as commonly understood by those skilled in the art.

[0086] Unless otherwise stated, the values ​​of the parameters mentioned in this application can be determined using various testing methods commonly used in the art, for example, according to the testing methods given in this application.

[0087] To meet the higher energy density requirements of rechargeable batteries, non-carbon materials, such as silicon-based, tin-based, and germanium-based materials, have attracted widespread attention due to their high theoretical specific capacity. Silicon has a theoretical specific capacity as high as 4200 mAh / g, tin has a theoretical specific capacity as high as 994 mAh / g, and germanium has a theoretical specific capacity as high as 1600 mAh / g, which can significantly improve the energy density of rechargeable batteries.

[0088] However, unlike the energy storage mechanism of graphite, non-carbon materials, such as silicon-based, tin-based, and germanium-based materials, store energy through alloying reactions with metals (e.g., lithium, sodium). This results in a significant volume effect during charge and discharge, easily causing particle breakage and pulverization, leading to pulverization of the negative electrode film. This makes it easy for the negative electrode film to lose electrical contact with the current collector, hindering the intercalation and deintercalation of active ions and significantly increasing irreversible capacity. Furthermore, the large volume effect causes repeated damage and reconstruction of the solid electrolyte interphase (SEI) film on the surface of the negative electrode active material particles, further increasing the irreversible consumption of active ions and ultimately affecting the capacity of the secondary battery. Simultaneously, as the charge and discharge process progresses, the SEI film on the surface of the negative electrode active material particles becomes thicker, resulting in a continuous increase in the impedance of the secondary battery. Moreover, the unstable SEI film on the surface of the negative electrode active material particles allows direct contact between the negative electrode active material and the electrolyte, further increasing interfacial side reactions and irreversible capacity.

[0089] Therefore, when the aforementioned non-carbon materials are used as negative electrode active materials, they typically suffer from drawbacks such as high irreversible capacity, low initial coulombic efficiency, and large volume expansion, resulting in significant actual capacity loss and poor cycle life in secondary batteries. Furthermore, silicon is a semiconductor material with low intrinsic conductivity and poor electrical conductivity, further deteriorating the electrochemical performance of secondary batteries.

[0090] In view of this, the inventors of this application have proposed a novel negative electrode active material through extensive research, which can take into account high specific capacity, high initial coulombic efficiency, low volume expansion, high conductivity and good cycle stability, and can also enable secondary batteries to take into account high energy density, high initial coulombic efficiency and long cycle life.

[0091] Negative electrode active materials

[0092] The first aspect of this application provides a negative electrode active material. The negative electrode active material includes a carbon matrix and a filler material. The degree of graphitization of the carbon matrix is ​​less than or equal to 87%. The carbon matrix includes a plurality of porous structures. At least a portion of the filler material is located within the porous structures of the carbon matrix. The filler material includes one or more elements capable of alloying with Li.

[0093] The filler material includes one or more elements that can undergo alloying reactions with Li, thereby contributing a higher capacity and compensating for the low capacity of the carbon matrix. However, it has a serious volume effect, which affects the performance of electrochemical properties.

[0094] In existing research, to overcome the drawback of large volume expansion of filler materials, current methods involve depositing them into carbon matrices or natural graphite with multiple porous structures using processes such as deposition. However, the carbon matrices with multiple porous structures currently used are mostly obtained by etching with pore-forming agents, such as alkaline solutions. The carbon matrix itself is non-graphitized carbon (or amorphous carbon), which results in drawbacks such as high irreversible capacity, low initial coulombic efficiency, and poor conductivity. Natural graphite, on the other hand, has a porous structure and can therefore be used as a substrate material for deposition, with the advantage of excellent conductivity. However, the irregular pore structure of natural graphite leads to poor uniformity of filler material dispersion. In addition, natural graphite also suffers from poor structural stability, large volume expansion, and poor cycling performance.

[0095] Therefore, the methods currently used cannot achieve a negative electrode active material that simultaneously possesses high specific capacity, high initial coulombic efficiency, low volume expansion, high conductivity, and good cycle stability.

[0096] The inventors of this application discovered that by placing a filler material with high specific capacity within the porous structure of a carbon matrix with low graphitization (greater than 0 and less than or equal to 87%), the resulting negative electrode active material can achieve a balance of high specific capacity, high initial coulombic efficiency, low volume expansion, high conductivity, and good cycle stability. Furthermore, it enables the secondary battery to achieve a balance of high energy density, high initial coulombic efficiency, and long cycle life. The carbon matrix of this application has a graphitization degree of less than or equal to 87%, which, compared to carbon matrices obtained by creating pores with pore-forming agents, offers advantages in high conductivity and high initial coulombic efficiency. Compared to natural graphite, it offers advantages in low volume expansion and high cycle stability. Therefore, the negative electrode active material provided by this application can fully utilize the high specific capacity advantage of the filler material while compensating for the poor conductivity and low initial coulombic efficiency of the filler material. In addition, at least a portion of the filler material is located within the porous structure of the carbon matrix, thereby reducing the volume expansion of the filler material through the carbon matrix.

[0097] In this application, the graphitization degree of the carbon matrix is ​​less than or equal to 87%, for example, less than or equal to 85%, less than or equal to 80%, less than or equal to 75%, or less than or equal to 70%. When the graphitization degree of the carbon matrix is ​​greater than 87%, the carbon matrix exhibits large volume expansion and poor structural stability during charge and discharge processes, thereby affecting the cycle stability and cycle life of the negative electrode active material. A lower graphitization degree of the carbon matrix improves its structural stability, which is beneficial for enhancing the cycle stability of the negative electrode active material and extending the cycle life of the secondary battery.

[0098] The inventors of this application further noted in their research that the graphitization degree of the carbon matrix should not be too low, as this results in poor initial coulombic efficiency and conductivity, thus making the improvement effect on the initial coulombic efficiency and conductivity of the negative electrode active material less significant. For example, the graphitization degree of the carbon matrix can also be greater than or equal to 10%, greater than or equal to 20%, greater than or equal to 30%, greater than or equal to 40%, greater than or equal to 45%, greater than or equal to 50%, greater than or equal to 55%, greater than or equal to 60%, or greater than or equal to 65%.

[0099] In some embodiments, the degree of graphitization of the carbon matrix may be 40%-87%, 50%-87%, 60%-87%, 65%-87%, 65%-85%, 65%-82%, or 65%-80%. This allows the negative electrode active material to better balance high specific capacity, high initial coulombic efficiency, low volume expansion, high conductivity, and good cycle stability.

[0100] In some embodiments, at least a portion of the filler material is located within the porous structure of the carbon matrix, and there are voids between the filler material and the carbon matrix. When there are voids between the filler material and the carbon matrix, these voids can serve as spaces to accommodate the volume expansion of the filler material, thereby buffering the stress generated during the expansion process and further reducing the probability of particle breakage and pulverization.

[0101] In some embodiments, the element capable of alloying with Li may optionally include one or more of silicon, tin, and germanium. This is advantageous for the negative electrode active material to have a high specific capacity.

[0102] In some embodiments, the filler material includes one or more of silicon-based materials, tin-based materials, and germanium-based materials, optionally including silicon-based materials.

[0103] In this application, the term "silicon-based material" refers to a compound containing silicon. In some embodiments, the silicon-based material may include one or more of elemental silicon, silicon oxide, silicon-carbon materials, silicon-nitrogen composites, and silicon alloys.

[0104] In this application, the term "tin-based material" refers to a compound containing the element tin. In some embodiments, the tin-based material may include one or more of elemental tin, tin oxides, tin sulfides, tin phosphides, tin composite oxides, tin-carbon materials, and tin alloy materials. Tin composite oxides refer to metal and / or non-metal oxides incorporating glassy phases into tin oxides.

[0105] In this application, the term "germanium-based material" refers to a compound containing the element germanium. In some embodiments, the germanium-based material may include one or more of elemental germanium, germanium oxide, germanium carbon material, germanium alloy material, and germanate.

[0106] In some embodiments, the filler material may include crystalline filler material and / or amorphous filler material.

[0107] In some embodiments, the filler material comprises crystalline silicon-based materials and / or amorphous silicon-based materials. Silicon-based materials have the advantage of high specific capacity, which is beneficial for improving the energy density of secondary batteries. Optionally, the filler material comprises crystalline elemental silicon and / or amorphous elemental silicon.

[0108] In some embodiments, the grain size of the crystalline filler material is ≤100nm, for example, it can be ≤80nm, ≤70nm, ≤60nm, ≤50nm, ≤40nm, ≤30nm, or ≤20nm. Optionally, the grain size of the crystalline filler material is 2nm-50nm, 2nm-40nm, 2nm-30nm, or 2nm-20nm.

[0109] Larger grain sizes in crystalline filler materials can improve the initial coulombic efficiency of a secondary battery, but are detrimental to its cycle performance and storage capacity. Therefore, when the crystalline filler material has a suitable grain size, it can improve the initial coulombic efficiency of the secondary battery while avoiding significant adverse effects on its cycle performance and storage capacity.

[0110] The grain size of crystalline filler materials is a term known in the art and can be determined using instruments and methods known in the art. For example, it can be tested and measured using a high-resolution transmission electron microscope (HRTEM).

[0111] In some embodiments, the filler material can be obtained through a vapor deposition process. For example, the filler material may include one or more of vapor-deposited silicon-based materials, tin-based materials, and germanium-based materials. Optionally, the filler material includes vapor-deposited silicon-based materials, and more preferably, the filler material includes vapor-deposited silicon. The vapor deposition process includes chemical vapor deposition and physical vapor deposition, and may be selected as chemical vapor deposition, such as thermochemical vapor deposition, plasma-enhanced chemical vapor deposition, or microwave plasma-assisted chemical vapor deposition. Compared with liquid phase deposition, vapor deposition is advantageous for better deposition and uniform dispersion of the filler material within the porous structure of the carbon matrix, and can avoid problems such as filler material agglomeration and / or excessive deposition on the carbon matrix surface. Furthermore, vapor deposition is a relatively mature technology and is easy to industrialize.

[0112] In some embodiments, in the X-ray diffraction pattern of the negative electrode active material measured by an X-ray diffractometer, the negative electrode active material includes a (002) crystal plane peak at 26.4° and a (111) crystal plane peak at 28.6°, and the ratio of the half-width at half-maximum (HWHM) of the (002) crystal plane peak to the HWHM of the (111) crystal plane peak is 0.2-50, for example, it can be a range consisting of 0.2, 0.5, 1, 2, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50 or any of the above values. Optionally, the ratio of the HWHM of the (002) crystal plane peak to the HWHM of the (111) crystal plane peak is 0.2-20.

[0113] The half-width at half maximum (WHM) of the (002) crystal plane peak and the half-width at half-maximum (WHM) of the (111) crystal plane peak can be determined by referring to JIS K 0131-1996. The crystal cell parameters can be calculated using an X-ray diffractometer (such as Bruker D8 Discover). The peak positions of C 002 and Si 111 of two parallel samples can be obtained by the centroid method. The test angle range can be 20°-80°.

[0114] The half-width at half-maximum (WHM) of the (002) crystal plane peak can characterize the integrity of the (002) crystal plane arrangement in the carbon matrix, while the half-width at half-maximum (WHM) of the (111) crystal plane peak can characterize the content of elemental silicon and the grain size of elemental silicon in the filler material. By controlling the WHM of the (002) crystal plane peak and the WHM of the (111) crystal plane peak within a suitable range, the carbon matrix can have a suitable degree of graphitization, and the filler material can have a suitable grain size. This is beneficial for the negative electrode active material to achieve high specific capacity, high initial coulombic efficiency, low volume expansion, high conductivity, and good cycle stability.

[0115] In some embodiments, the negative electrode active material further includes a coating layer located on at least a portion of the surface of the carbon matrix. The coating layer prevents direct contact between the filler material and the electrolyte, thereby reducing electrolyte side reactions, decreasing active ion consumption, and improving the cycle performance of the secondary battery. It also enhances the stability of the negative electrode slurry, preventing reactions between the filler material and solvents such as water, which would increase the processing difficulty of the negative electrode slurry. Furthermore, the coating layer buffers the volume expansion of the filler material, which further improves the structural stability of the negative electrode active material and enhances the electrochemical performance of the secondary battery.

[0116] In some embodiments, the coating layer may optionally comprise one or more of carbon materials, conductive polymers, metal oxides, and metal sulfides.

[0117] In some embodiments, the carbon material includes one or more of hard carbon, soft carbon, graphene, carbon fiber, and carbon nanotubes.

[0118] In some embodiments, the conductive polymer includes one or more of polyaniline, polypyrrole, and polythiophene.

[0119] In some embodiments, the metal oxide includes one or more of iron oxide, zinc oxide, tin oxide, copper oxide, and titanium oxide.

[0120] In some embodiments, the metal sulfide includes one or more of tin sulfide, molybdenum sulfide, titanium sulfide, iron sulfide, and copper sulfide.

[0121] In some embodiments, the coating layer comprises a carbon material. Thus, in addition to preventing direct contact between the filler material and the electrolyte and buffering the volume expansion of the filler material, the coating layer can also contribute to the capacity and improve the specific capacity of the negative electrode active material. Furthermore, when the coating layer includes a carbon material, it also helps to improve the conductivity of the filler material, especially silicon-based materials, thereby improving the capacity performance characteristics of the negative electrode active material.

[0122] In some embodiments, the thickness of the coating layer is ≤100 nm, optionally 10 nm-100 nm. When the coating layer thickness is within the above range, the integrity of the coating layer is higher, which can more effectively prevent the filler material from contacting the electrolyte, thereby helping to reduce electrolyte side reactions and enabling the negative electrode active material to achieve high specific capacity, high initial coulombic efficiency, and low volume expansion. When the coating layer thickness is greater than 100 nm, the integrity of the coating layer is better, but the brittleness increases, and it is more prone to breakage and pulverization during repeated charge and discharge; in addition, the specific capacity of the negative electrode active material decreases.

[0123] In some embodiments, the negative electrode active material includes carbon and elements capable of alloying with Li.

[0124] In some embodiments, the carbon content in the negative electrode active material is 20 wt% to 80 wt%, for example, it can be any range consisting of 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, 50 wt%, 55 wt%, 60 wt%, 65 wt%, 70 wt%, 75 wt%, 80 wt%, or more. Optionally, the carbon content in the negative electrode active material is 30 wt% to 70 wt%. The distribution area of ​​the carbon is not specifically limited, for example, it can be located in at least one of the carbon matrix, the filler material, and the coating layer.

[0125] In some embodiments, the mass percentage of the element capable of alloying with Li in the negative electrode active material is 20 wt%-80 wt%, for example, it can be any range consisting of 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, 50 wt%, 55 wt%, 60 wt%, 65 wt%, 70 wt%, 75 wt%, 80 wt%, or more. Optionally, the mass percentage of the element capable of alloying with Li in the negative electrode active material is 30 wt%-70 wt%. Optionally, the element capable of alloying with Li includes silicon.

[0126] When the content of carbon and / or elements that can undergo alloying reactions with Li in the negative electrode active material is within the above range, it is beneficial for the negative electrode active material to achieve both high specific capacity and high conductivity.

[0127] In some embodiments, the negative electrode active material includes carbon and elements capable of alloying with Li, as well as other elements, including one or more of oxygen, metallic elements, and nitrogen. The distribution area of ​​these other elements is not specifically limited; for example, they may be located in at least one of the coating layer, the filler material, and the carbon matrix.

[0128] In some embodiments, the sum of the mass percentages of the other elements in the negative electrode active material is optionally less than or equal to 20 wt%, more preferably less than or equal to 10 wt%, or less than or equal to 5 wt%.

[0129] In some embodiments, the initial coulombic efficiency of the carbon matrix is ​​≥75%, optionally 75%-87%. This is beneficial for improving the initial coulombic efficiency of the negative electrode active material.

[0130] In some embodiments, the powder resistivity of the carbon matrix at 16 MPa pressure is ≤5 × 10⁻⁶. -2 Ω·cm, can be selected as ≤3.5×10-2 Ω·cm. This is beneficial for improving the conductivity of the negative electrode active material.

[0131] In some embodiments, the BET specific surface area of ​​the carbon matrix is ​​50 m². 2 / g-1000m 2 / g, optional 100m 2 / g-700m 2 / g. This is beneficial for the negative electrode active material to have a suitable BET specific surface area, thereby reducing the surface activity of the negative electrode active material, reducing interfacial side reactions, reducing SEI film formation consumption, and thus improving the first coulombic efficiency and cycle performance of the secondary battery.

[0132] In some embodiments, the graphitization degree of the negative electrode active material is ≥65%, optionally 65%-87%. This allows the negative electrode active material to better balance high initial coulombic efficiency, high conductivity, and good cycle stability.

[0133] In some embodiments, the initial coulombic efficiency of the negative electrode active material is ≥92%, optionally 92%-95%. This reduces the irreversible consumption of active ions and improves the capacity utilization characteristics and cycle performance of the secondary battery.

[0134] In some embodiments, the volumetric particle size Dv50 of the negative electrode active material is 3μm-50μm, and can be selected as 5μm-20μm.

[0135] In some embodiments, the volumetric particle size Dv90 of the negative electrode active material is ≤60μm, and can be selected as 20μm-50μm.

[0136] In some embodiments, the diameter (Dv90-Dv10) / Dv50 of the negative electrode active material is 1.0-3.0, and can be selected as 1.0-2.0.

[0137] When at least one of the volumetric particle size Dv50, volumetric particle size Dv90, and particle size distribution (Dv90-Dv10) / Dv50 of the negative electrode active material is within the above range, it helps to reduce the surface activity of the negative electrode active material, reduce interfacial side reactions, reduce SEI film formation consumption, and also helps to improve the active ion and electron transport performance, thereby further improving the cycle performance of the secondary battery.

[0138] In some embodiments, the BET specific surface area of ​​the negative electrode active material is 2m². 2 / g-100m 2 / g, optional 2m 2 / g-30m 2 / g, 2m 2 / g-20m 2 / g. When the BET specific surface area of ​​the negative electrode active material is within the above range, it helps to reduce surface activity, reduce interfacial side reactions, and reduce SEI film formation consumption, thereby improving the first coulombic efficiency and cycle performance of the secondary battery.

[0139] In some embodiments, the powder resistivity of the negative electrode active material at 16 MPa pressure is ≤5 × 10⁻⁶. -1 Ω·cm, can be ≤2×10 -1 Ω·cm. Therefore, the negative electrode active material exhibits good conductivity, which is beneficial for improving the cycle performance and rate performance of the secondary battery.

[0140] In this application, the volumetric particle sizes Dv10, Dv50, and Dv90 of materials (e.g., negative electrode active materials, carbon matrix, etc.) have meanings known in the art, representing the particle sizes corresponding to a cumulative volume distribution percentage of 10%, 50%, and 90%, respectively, and can be determined using instruments and methods known in the art. For example, they can be conveniently determined using a laser particle size analyzer, referring to GB / T 19077-2016. The testing instrument can be a Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0141] In this application, the BET specific surface area of ​​materials (e.g., negative electrode active materials, carbon matrix, etc.) has a meaning known in the art and can be measured using instruments and methods known in the art. For example, it can be measured using the nitrogen adsorption specific surface area analysis method according to GB / T 19587-2017 and calculated using the BET (Brunauer Emmett Teller) method. The nitrogen adsorption specific surface area analysis can be performed using a TRISTAR II 3020 specific surface area and porosity analyzer from Micromeritics, USA.

[0142] In this application, the powder resistivity of materials (e.g., negative electrode active materials, carbon matrix, etc.) has a meaning known in the art and can be measured using instruments and methods known in the art. For example, a certain mass of powder sample can be placed in the feeding cup of a resistivity tester, a certain pressure can be applied, and then data can be manually collected and recorded to record the powder resistivity test results of the sample under different pressures. In this application, the test pressure can be 16 MPa.

[0143] In this application, the degree of graphitization of materials (e.g., negative electrode active materials, carbon matrix, etc.) has a meaning known in the art and can be measured using instruments and methods known in the art. For example, the interlayer spacing d of the (002) crystal plane can be obtained using an X-ray diffractometer (such as a Bruker D8 Discover) with reference to JIS K 0131-1996. 002Then, according to the formula g = (0.3440 - d) 002 The degree of graphitization of the material is calculated by 0.3440-0.3354)×100%.

[0144] In this application, the content of each element in the negative electrode active material can be determined using instruments and methods known in the art. For example, the carbon content can be tested according to GB / T 20123-2006 / ISO 15350:2000, and the testing instrument can be an HCS-140 infrared carbon-sulfur analyzer. The silicon content can be tested according to GB / T 20975.5-2020. The tin content in the negative electrode active material can be tested according to GB / T 20975.10-2020. The germanium content can be tested according to GB / T20127.6-2006.

[0145] Preparation method

[0146] The second aspect of this application provides a method for preparing a negative electrode active material, which can prepare the negative electrode active material of the first aspect of this application.

[0147] The method includes the following steps: Step 1, providing a carbon matrix with a graphitization degree of less than or equal to 87%, optionally 65%-87%, and including multiple porous structures; Step 2, dispersing a filler material into the porous structure of the carbon matrix to obtain a negative electrode active material, wherein the negative electrode active material includes a carbon matrix and a filler material, the carbon matrix includes multiple porous structures, at least a portion of the filler material is located in the porous structure of the carbon matrix, and the filler material includes one or more elements that can undergo alloying reactions with Li, optionally, the elements that can undergo alloying reactions with Li include one or more elements selected from silicon, tin, and germanium.

[0148] In some embodiments, in step 1, the carbon matrix is ​​prepared by placing a carbon source comprising multiple porous structures in a high-temperature furnace and performing graphitization treatment at 1600°C-2400°C under a protective gas atmosphere, thereby obtaining the carbon matrix. For example, the graphitization treatment can be performed within a range of 1600°C, 1700°C, 1800°C, 1900°C, 2000°C, 2100°C, 2200°C, 2300°C, 2400°C, or any combination thereof. This yields a carbon matrix with a graphitization degree of less than or equal to 87%, optionally 65%-87%, and comprising multiple porous structures.

[0149] When the graphitization temperature is too low, the resulting carbon matrix is ​​still non-graphitized carbon (or amorphous carbon), which has high irreversible capacity, low initial coulombic efficiency, and poor conductivity, thus affecting the initial coulombic efficiency and cycle performance of the secondary battery. When the graphitization temperature is too high, the resulting carbon matrix has large volume expansion and poor structural stability during charge and discharge, thus affecting the cycle stability of the negative electrode active material and the cycle performance of the secondary battery.

[0150] In some embodiments, the heating rate of the high-temperature furnace is optionally below 10°C / min, for example below 8°C / min or below 5°C / min.

[0151] In some embodiments, the heat treatment holding time for graphitization is optionally 1h-12h, for example, it can be a range of 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h or any of the above values.

[0152] In some embodiments, the carbon source may optionally include one or more selected from hard carbon, petroleum coke, pitch coke, biomass carbon, and resin carbon.

[0153] In some embodiments, the high-temperature furnace may optionally be a graphitization furnace, such as any one of a box-type graphitization furnace, an Atchison graphitization furnace, a continuous graphitization furnace, and an internally connected graphitization furnace.

[0154] In step 1, the carbon sources used to prepare the carbon matrix are diverse, abundant in nature, and inexpensive, and the preparation process of the carbon matrix is ​​simple. The carbon source comprising multiple pore structures can be directly obtained commercially or prepared according to methods known in the art, such as by etching with a pore-forming agent, such as an alkaline solution.

[0155] By graphitizing a carbon source with multiple porous structures at a certain temperature, the micropores in the carbon source can be reduced, improving the dispersion uniformity of subsequent filling materials. On the other hand, residual bonds on the surface of the carbon source can be removed, reducing the content of oxygen-containing functional groups in the carbon source and reducing electrolyte side reactions. This is beneficial to improving the initial coulombic efficiency, conductivity, and high-temperature performance of the obtained carbon matrix, thereby enabling the secondary battery to have good cycle performance.

[0156] In some embodiments, in step 1, the initial coulombic efficiency of the carbon matrix is ​​≥75%, optionally 75%-87%.

[0157] In some embodiments, in step 1, the powder resistivity of the carbon matrix at a pressure of 16 MPa is ≤5 × 10⁻⁶. -2 Ω·cm, can be selected as ≤3.5×10 -2 Ω·cm.

[0158] In some embodiments, in step 1, the BET specific surface area of ​​the carbon matrix is ​​50 m². 2 / g-1000m 2 / g, optional 100m 2 / g-700m 2 / g.

[0159] In some embodiments, in step 1, the volumetric particle size Dv50 of the carbon matrix is ​​3μm-50μm, and can be selected as 5μm-20μm.

[0160] In some embodiments, the process of dispersing the filler material into the porous structure of the carbon matrix in step 2 includes liquid phase deposition and vapor phase deposition, with vapor phase deposition being the preferred option. Compared to liquid phase deposition, vapor phase deposition is advantageous for better deposition and uniform dispersion of the filler material within the porous structure of the carbon matrix, and it avoids problems such as filler material agglomeration and / or excessive deposition on the carbon matrix surface. Furthermore, vapor phase deposition is a relatively mature technology and is easy to mass-produce industrially.

[0161] In some embodiments, the vapor deposition process may optionally include chemical vapor deposition and physical vapor deposition, and may more preferably be a chemical vapor deposition process, such as any one of thermochemical vapor deposition, plasma-enhanced chemical vapor deposition, and microwave plasma-assisted chemical vapor deposition.

[0162] In some embodiments, step 2, the step of dispersing the filler material into the porous structure of the carbon matrix, includes the following steps: placing the carbon matrix in a reactor, introducing a first mixed gas containing a source of elements capable of alloying with Li, and depositing at a first temperature T1 for a first time t1, thereby obtaining the negative electrode active material.

[0163] In some embodiments, the first mixed gas may optionally include a source of the element capable of alloying with Li and a protective gas.

[0164] In some embodiments, optionally, the volume percentage of the source of the element in the first mixture that can undergo an alloying reaction with Li is 10%-50%, for example, it can be any range consisting of 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50% or more.

[0165] In some embodiments, the first mixture may further include a carbon source gas.

[0166] In some embodiments, optionally, the volume ratio of the source of the element capable of alloying with Li to the carbon source gas is greater than or equal to 0.5:1, optionally (2-10):1. When the volume ratio of the source of the element capable of alloying with Li to the carbon source gas is within the above range, it is beneficial for the negative electrode active material to have a high specific capacity. If the volume ratio is too small, the resulting filler material has a high carbon content and a low content of the element capable of alloying with Li, which leads to a less significant improvement in the capacity of the negative electrode active material.

[0167] In some embodiments, the volume percentage of the carbon source gas in the first mixed gas is optionally ≤20%, more preferably 5%-20%. This is beneficial for the negative electrode active material to achieve both high specific capacity and high conductivity.

[0168] In some embodiments, the volume percentage of the protective gas in the first mixture is optionally 30%-90%, for example, it can be a range of any values ​​consisting of 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, or more.

[0169] In some embodiments, the total gas flow rate of the first mixed gas can be 0.5 L / min to 20 L / min. For example, it can be 1 L / min, 2 L / min, 3 L / min, 4 L / min, 5 L / min, 6 L / min, 7 L / min, 8 L / min, 9 L / min, 10 L / min, 12 L / min, 14 L / min, 16 L / min, 18 L / min, 20 L / min, or any range of the above values.

[0170] In some embodiments, the pressure inside the reactor can be a slightly positive pressure, for example, 200 Pa to 600 Pa higher than atmospheric pressure, which is beneficial for the smooth progress of the deposition process.

[0171] In some embodiments, the reactor includes, but is not limited to, any one of a deposition furnace, a rotary furnace, a tubular furnace, and a fluidized bed.

[0172] In some embodiments, the first temperature T1 may be 400℃-1000℃, for example, it may be a range consisting of 400℃, 450℃, 500℃, 550℃, 600℃, 650℃, 700℃, 750℃, 800℃, 850℃, 900℃, 950℃, 1000℃ or any value above.

[0173] In some embodiments, the first time t1 may be 1h-12h, for example, it may be a range of 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h or any of the above values.

[0174] In the vapor deposition process, by adjusting at least one of the composition ratio of the first mixed gas, the total gas flow rate of the first mixed gas, the first temperature, and the first time to be within the above-mentioned range, it is beneficial to deposit filling materials in the pore structure of the carbon matrix, and at the same time, it is also beneficial to adjust the crystallinity and / or grain size of the filling material to be within a suitable range.

[0175] In some embodiments, the method further includes step 3: forming a coating layer on at least a portion of the surface of the negative electrode active material obtained in step 2, the coating layer comprising one or more of carbon materials, conductive polymers, metal oxides and metal sulfides.

[0176] The method for forming a coating layer on at least a portion of the surface of the negative electrode active material obtained in step 2 is not specifically limited and can be selected according to the composition of the coating layer, for example, any one of solid phase coating, liquid phase coating or gas phase coating can be used.

[0177] In some embodiments, the step of forming the coating layer includes the following steps: mixing the negative electrode active material obtained in step 2 with the coating material and then performing a carbonization treatment. Optionally, the coating material includes one or more of asphalt (e.g., coal tar pitch, petroleum asphalt, etc.) and polymer materials. Optionally, the carbonization treatment temperature is 500℃-1000℃.

[0178] In some embodiments, the step of forming the coating layer includes the following steps: placing the negative electrode active material obtained in step 2 in a reactor, introducing a second mixed gas containing carbon source gas, and depositing it at a second temperature T2 for a second time t2, after which carbon-coated negative electrode active material is obtained.

[0179] In some embodiments, the second mixture includes a carbon source gas and a protective gas. Optionally, the volume percentage V2 of the carbon source gas in the second mixture is 5%-50%, for example, it can be any range consisting of 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50% or more.

[0180] In some embodiments, the total gas flow rate of the second mixture is 0.5 L / min to 20 L / min. For example, it can be 0.8 L / min, 1 L / min, 2 L / min, 3 L / min, 4 L / min, 5 L / min, 6 L / min, 7 L / min, 8 L / min, 9 L / min, 10 L / min, 12 L / min, 14 L / min, 16 L / min, 18 L / min, 20 L / min, or any range of the above values.

[0181] In some embodiments, the second temperature T2 is 700℃-850℃, for example, it can be a range consisting of 700℃, 710℃, 720℃, 730℃, 740℃, 750℃, 760℃, 770℃, 780℃, 790℃, 800℃, 810℃, 820℃, 830℃, 840℃, 850℃ or any of the above values.

[0182] In some embodiments, the second time t2 is 1h-6h, for example, it can be a range of 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h or any of the above values.

[0183] In step 3, by adjusting at least one of the composition ratio of the second mixed gas, the total gas flow rate of the second mixed gas, the second temperature, and the second time to be within the above range, it is beneficial to form a coating layer of appropriate thickness and avoid the coating layer being too thick, which would reduce the specific capacity of the negative electrode active material.

[0184] In this application, the term "protective gas" includes one or more of nitrogen and rare gases. Optionally, the rare gas may include one or more of argon, helium, etc.

[0185] In this application, the term "source of an element capable of alloying with Li" refers to a gas capable of forming the filler material of this application, which may include one or more of silicon source gas, tin source gas, and germanium source gas.

[0186] Silicon source gas refers to the gas capable of forming the silicon-based material of this application. Optionally, the silicon source gas includes, but is not limited to, silane (H4Si), silane (H6Si2), propane (H8Si3), silicon tetrachloride (Cl4Si), trichlorosilane (Cl3HSi), dichlorosilane (Cl2H2Si), chlorosilane (ClH3Si), silicon tetrafluoride (F4Si), trifluorosilane (F3HSi), difluorosilane (F2H2Si), fluorosilane (FH3Si), and hexachlorodisilane (Cl6Si). 2) Pentachlorodisilane (Cl5HSi2), tetrachlorodisilane (Cl4H2Si2, including 1,1,2,2-tetrachlorodisilane and 1,1,1,2-tetrachlorodisilane), trichlorodisilane (Cl3H3Si2, including 1,1,2-trichlorodisilane and 1,1,1-trichlorodisilane), dichlorodisilane (Cl2H4Si2, including 1,1-dichlorodisilane and 1,2-dichlorodisilane), monochlorodisilane (ClH5Si2), hexafluorodisilane (F6Si2), pentafluorodisilane (F... s One or more of the following: HSi2), 1,1,2,2-tetrafluorodisilane (F4H2Si2), 1,1,1-trifluorodisilane (F3H3Si2), difluorodisilane (F2H4Si2, including 1,1-difluorodisilane and 1,2-difluorodisilane), monofluorodisilane (FH5Si2), methylsilane, ethylsilane, dimethylsilane, trimethylsilane, tetramethylsilane, methyldisilane, dimethyldisilane, trimethyldisilane, tetramethyldisilane, hexamethylsilane, methyltrichlorosilane, methylchlorosilane, chloroethylsilane, dichlorodimethylsilane, and dichlorodiethylsilane.

[0187] Tin source gas refers to the gas capable of forming the tin-based material of this application. Optionally, the tin source gas includes, but is not limited to, one or more of stanzanol (H4Sn), Cl4Sn, Cl3HSn, Cl2H2Sn, ClH3Sn, F4Sn, F3HSn, F2H2Sn and FH3Sn.

[0188] The germanium source gas refers to the gas capable of forming the germanium-based material of this application. Optionally, the germanium source gas includes, but is not limited to, one or more of methanegermanium (H4Ge), Cl4Ge, and F4Ge.

[0189] In this application, "carbon source gas" refers to a gas capable of forming carbon materials. Optionally, the carbon source gas includes, but is not limited to, one or more of the following: methane, ethane, propane, isopropane, butane, isobutane, ethylene, propylene, butene, acetylene, chloroethane, fluoroethane, difluoroethane, chloromethane, fluoromethane, difluoromethane, trifluoromethane, vinyl chloride, vinyl fluoride, difluoroethylene, methylamine, formaldehyde, benzene, toluene, xylene, styrene, and phenol.

[0190] Unless otherwise specified, all raw materials and instruments used in the preparation method of this application can be obtained commercially.

[0191] Secondary batteries

[0192] The third aspect of this application provides a secondary battery.

[0193] The secondary battery mentioned in the embodiments or implementations of this application refers to a single physical module comprising one or more battery cells to provide higher voltage and capacity. For example, the secondary battery mentioned in this application may include battery cells, battery modules, or battery packs. A battery cell is the smallest unit constituting a secondary battery, capable of charging and discharging independently. This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. Figure 1 The example shown is a square-structured battery cell 5.

[0194] In some embodiments, a single battery cell includes an electrode assembly, and the single battery cell may also include an outer packaging. The electrode assembly is made from a positive electrode sheet, a negative electrode sheet, and a separator, etc., through a winding process and / or a stacking process, and the outer packaging is used to encapsulate the aforementioned electrode assembly. The outer packaging can be a rigid shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging can also be a flexible package, such as a pouch-type flexible package. The material of the flexible package can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0195] In some embodiments, such as Figure 2 As shown, the outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates enclosing a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 is used to cover the opening to close the receiving cavity. Electrode assemblies 52 are encapsulated in the receiving cavity. The number of electrode assemblies 52 contained in the battery cell 5 may be one or more, and can be adjusted as needed.

[0196] In some embodiments of this application, individual battery cells can be assembled into a battery module. The number of individual battery cells contained in a battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module. Figure 3 This is a schematic diagram of battery module 4 as an example. Figure 3 As shown, in battery module 4, multiple battery cells 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple battery cells 5 can be fixed in place using fasteners.

[0197] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0198] 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. Figure 4 and Figure 5 This is a schematic diagram of battery pack 1 as an example. Figure 4 and Figure 5 As shown, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3. The upper body 2 covers the lower body 3, forming a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0199] This application does not impose any particular restrictions on the type of secondary battery. For example, secondary batteries may include, but are not limited to, lithium-ion batteries, sodium-ion batteries, etc.

[0200] [Negative electrode plate]

[0201] In some embodiments, the negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector and comprising a negative electrode active material. For example, the negative current collector has two surfaces opposite each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative current collector.

[0202] In some embodiments, the negative electrode film layer comprises the negative electrode active material of the first aspect of the present application or the negative electrode active material prepared by the method described in the second aspect of the present application. This enables the secondary battery to achieve high energy density, high initial coulombic efficiency, and long cycle life. In some embodiments, the negative electrode film layer may further comprise other negative electrode active materials besides the aforementioned negative electrode active materials. In some embodiments, the other negative electrode active materials include, but are not limited to, one or more of natural graphite, artificial graphite, soft carbon, hard carbon, elemental silicon, silicon oxide, silicon-nitrogen composites, silicon alloy materials, elemental tin, tin oxide, tin alloy materials, and lithium titanate. This application is not limited to these materials, and other conventionally known materials that can be used as negative electrode active materials for secondary batteries may also be used.

[0203] In some embodiments, the negative electrode film layer may optionally include a negative electrode conductive agent. This application does not impose any particular limitation on the type of negative electrode conductive agent. As an example, the negative electrode conductive agent may include one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0204] In some embodiments, the negative electrode film layer may optionally include a negative electrode binder. This application does not impose any particular limitation on the type of negative electrode binder. As an example, the negative electrode binder may include one or more of the following: styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, waterborne acrylic resins (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0205] In some embodiments, the negative electrode film may optionally include other additives. As an example, other additives may include thickeners, such as sodium carboxymethyl cellulose (CMC-Na), PTC thermistor materials, etc.

[0206] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. As an example of the metal foil, copper foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include one or more of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymer material base layer may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0207] The negative electrode film layer is typically formed by coating a negative electrode slurry onto a negative electrode current collector, followed by drying and cold pressing. The negative electrode slurry is typically formed by dispersing a negative electrode active material, optional conductive agent, optional binder, and other optional additives in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP) or deionized water, but is not limited to these.

[0208] The negative electrode sheet does not exclude other additional functional layers besides the negative electrode film layer. For example, in some embodiments, the negative electrode sheet of this application may further include a conductive undercoat layer (e.g., composed of a conductive agent and an adhesive) sandwiched between the negative electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector; in some embodiments, the negative electrode sheet of this application may further include a protective layer covering the surface of the negative electrode film layer.

[0209] [Positive electrode plate]

[0210] In some embodiments, the positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector and comprising a positive electrode active material. For example, the positive current collector has two surfaces opposite each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0211] The positive electrode film layer includes a positive electrode active material, which may be a positive electrode active material known in the art for use in secondary batteries.

[0212] When the secondary battery of this application is a lithium-ion battery, the positive electrode active material may include 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 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 respective modified compounds. Examples of lithium-containing phosphates with an olivine structure may include 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 respective modified compounds. This application is not limited to these materials, and other conventionally known materials that can be used as positive electrode active materials for secondary batteries may also be used.

[0213] In some embodiments, to further improve the energy density of secondary batteries, the positive electrode active material for lithium-ion batteries may include materials with the general formula Li. a Ni b Co c M d O e A f One or more of lithium transition metal oxides and their modified compounds. 0.8≤a≤1.2, 0.5≤b<1, 0<c<1, 0<d<1, 1≤e≤2, 0≤f≤1, M includes one or more of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti and B, and A includes one or more of N, F, S and Cl.

[0214] As an example, positive electrode active materials for lithium-ion batteries may include LiCoO2, LiNiO2, LiMnO2, LiMn2O4, and LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2(NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM523), LiNi 0.6 Co0.2 Mn 0.2 O2(NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811), LiNi 0.85 Co 0.15 Al 0.05 One or more of O2, LiFePO4 and LiMnPO4.

[0215] When the secondary battery of this application is a sodium-ion battery, the positive electrode active material may include, but is not limited to, one or more of sodium-containing transition metal oxides, polyanionic materials (such as phosphates, fluorophosphates, pyrophosphates, sulfates, etc.), and Prussian blue materials.

[0216] As an example, positive electrode active materials for sodium-ion batteries may include NaFeO2, NaCoO2, NaCrO2, NaMnO2, NaNiO2, and NaNi 1 / 2 Ti 1 / 2 O2, NaNi 1 / 2 Mn 1 / 2 O2, Na 2 / 3 Fe 1 / 3 Mn 2 / 3 O2, NaNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, NaFePO4, NaMnPO4, NaCoPO4, Prussian blue materials and materials with the general formula X p M' q (PO4) r O x Y 3-x One or more of the materials. In the general formula X p M' q (PO4) r O x Y 3-x In the given condition, 0 < p ≤ 4, 0 < q ≤ 2, 1 ≤ r ≤ 3, 0 ≤ x ≤ 2, and X includes elements selected from H. + Li + Na + K + and NH4 + M' is one or more of the following, which can be a transition metal cation, selected from one or more of V, Ti, Mn, Fe, Co, Ni, Cu and Zn, and Y is a halide anion, selected from one or more of F, Cl and Br.

[0217] In this application, the modified compounds of the above-mentioned positive electrode active materials may be those that have undergone doping modification and / or surface coating modification of the positive electrode active materials.

[0218] In some embodiments, the positive electrode film may optionally include a positive electrode conductive agent. This application does not impose any particular limitation on the type of positive electrode conductive agent. As an example, the positive electrode conductive agent includes one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0219] In some embodiments, the positive electrode film layer may optionally include a positive electrode binder. This application does not impose any particular limitation on the type of positive electrode binder. As an example, the positive electrode binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins.

[0220] In some embodiments, the positive current collector may be a metal foil or a composite current collector. An example of the metal foil is aluminum foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base layer. An example of the metal material may be one or more of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. An example of the polymer base layer may be one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0221] The positive electrode film is typically formed by coating a positive electrode slurry onto a positive electrode current collector, followed by drying and cold pressing. The positive electrode slurry is typically formed by dispersing the positive electrode active material, optional conductive agent, optional binder, and any other components in a solvent and stirring until homogeneous. The solvent may be N-methylpyrrolidone (NMP), but is not limited to this.

[0222] [Electrolytes]

[0223] The electrolyte acts as a conductor of active ions between the positive and negative electrode plates. This application does not specifically limit the type of electrolyte; it can be selected according to requirements. For example, the electrolyte may include one or more selected from solid electrolytes and liquid electrolytes (i.e., electrolyte solutions).

[0224] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0225] When the secondary battery of this application is a lithium-ion battery, as an example, the electrolyte salt may include 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).

[0226] When the secondary battery of this application is a sodium-ion battery, particularly a sodium-ion secondary battery, the electrolyte salt may include one or more of the following: sodium hexafluorophosphate (NaPF6), sodium tetrafluoroborate (NaBF4), sodium perchlorate (NaClO4), sodium hexafluoroarsenate (NaAsF6), sodium bis(fluorosulfonyl)imide (NaFSI), sodium bis(trifluoromethanesulfonyl)imide (NaTFSI), sodium trifluoromethanesulfonate (NaTFS), sodium difluorooxalate borate (NaDFOB), sodium dioxalate borate (NaBOB), sodium difluorophosphate (NaPO2F2), sodium difluorodioxalate phosphate (NaDFOP), and sodium tetrafluorooxalate phosphate (NaTFOP).

[0227] The type of solvent is not specifically limited and can be selected according to actual needs. In some embodiments, as an example, the solvent may include one or more of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl 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).

[0228] In some embodiments, the electrolyte may optionally include additives. For example, the 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 power performance.

[0229] [Isolation membrane]

[0230] Secondary batteries using electrolytes, as well as some secondary batteries using solid electrolytes, also include a separator. The separator is disposed between the positive and negative electrodes, primarily serving to prevent short circuits between the positive and negative electrodes while allowing active ions to pass through. 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.

[0231] In some embodiments, the material of the separator may include one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film. When the separator is a multi-layer composite film, the materials of each layer may be the same or different.

[0232] [Preparation Method]

[0233] The method for preparing the secondary battery described in this application is well known. In some embodiments, a positive electrode, a separator, a negative electrode, and an electrolyte can be assembled to form a secondary battery. As an example, the positive electrode, separator, and negative electrode can be formed into an electrode assembly through a winding or stacking process. The electrode assembly is placed in an outer packaging, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping, a battery cell is obtained. Multiple battery cells can be further connected in series, parallel, or a combination thereof to form a battery module. Multiple battery modules can also be connected in series, parallel, or a combination thereof to form a battery pack. In some embodiments, multiple battery cells can also be directly assembled into a battery pack.

[0234] Electrical appliances

[0235] This application also provides an electrical device, which includes the secondary battery described in this application. The secondary battery can be used as a power source for the electrical device or as an energy storage unit. The electrical device can be, but is not limited to, mobile devices (e.g., mobile phones, tablets, 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.

[0236] The electrical device can select the specific type of secondary battery according to its usage requirements, such as a battery cell, battery module, or battery pack.

[0237] Figure 6 This is a schematic diagram illustrating an example of an electrical device. This device could be 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, a battery pack or battery module can be used as the power source.

[0238] Another example of an electrical device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a single battery cell as their power source.

[0239] Example

[0240] The following embodiments describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on mass, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0241] Example 1

[0242] (1) Preparation of negative electrode active materials

[0243] Step 1: Select 1 kg of commercially available porous biochar (BET surface area 1545 m²) 2 (The particle size distribution (Dv50) is approximately 6 μm, which can also be obtained by creating pores using a pore-forming agent.) The powder is placed in a graphitization furnace and graphitized at a rate of 5 °C / min to 2400 °C under nitrogen protection. It is then held at 2400 °C for 2 hours and cooled to room temperature. The resulting powder has a graphitization degree of 87%, an initial coulombic efficiency of 85%, and a powder resistivity of 5.5 × 10⁻⁶. -3 Ω·cm, BET specific surface area is 100m² 2 / g of carbon matrix.

[0244] Step 2: Place the above-mentioned carbon matrix as a substrate in a vapor deposition furnace and heat it to 500°C at a rate of 5°C / min. Introduce the first mixed gas according to the ratio of 20% silane + 80% nitrogen (volume ratio), with a total gas flow rate of 5L / min. The pressure in the reactor is 200Pa higher than atmospheric pressure. The deposition reaction is carried out for 8 hours.

[0245] Step 3: Turn off the first mixed gas, then raise the temperature to 800℃ at a rate of 5℃ / min, and introduce the second mixed gas according to 40% acetylene + 60% nitrogen (volume ratio), with a total gas flow rate of 0.8L / min. The deposition reaction is carried out for 2 hours. After the reaction is completed, the material is cooled, discharged, and passed through a 325-mesh sieve to obtain the negative electrode active material.

[0246] (2) Preparation of secondary batteries (full cells)

[0247] Preparation of negative electrode sheet: The negative electrode active material prepared above is mixed with conductive agent conductive carbon black and carbon nanotubes and binder polyacrylic acid at a mass ratio of 95:1.9:0.1:3. The mixture is then added to deionized water as a solvent and stirred under the action of a high-speed stirrer until the system is homogeneous, thereby obtaining a negative electrode slurry with a solid content of 45%. The negative electrode slurry is uniformly coated on the negative electrode current collector copper foil and dried at 85°C. After cold pressing, the negative electrode sheet is obtained.

[0248] Preparation of the positive electrode: The positive electrode active material LiNi... 0.8 Co 0.1 Mn 0.1 O2 (NCM811), conductive agent carbon black (Super P), and binder polyvinylidene fluoride (PVDF) are mixed thoroughly in an appropriate amount of solvent NMP at a mass ratio of 97:1:2 to form a uniform positive electrode slurry. The positive electrode slurry is then uniformly coated onto the surface of the positive electrode current collector aluminum foil, and after drying and cold pressing, a positive electrode sheet is obtained.

[0249] Preparation of electrolyte: Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed uniformly at a volume ratio of 20:20:60 as an organic solvent. LiPF6 was then dissolved in the organic solvent, and fluoroethylene carbonate (FEC) was added. The concentration of LiPF6 in the electrolyte was 1 mol / L, and the mass percentage of FEC was 5 wt%.

[0250] Preparation of the separator membrane: Celgard 2400 separator membrane was used.

[0251] Preparation of secondary batteries: The positive electrode, separator, and negative electrode are stacked and wound in sequence to obtain an electrode assembly; the electrode assembly is placed in an outer packaging, dried, and then injected with electrolyte. After vacuum sealing, standing, formation, and shaping, a secondary battery is obtained.

[0252] (3) Preparation of button cell (half cell)

[0253] The prepared negative electrode active material was mixed with conductive carbon black (conductive agent) and polyacrylic acid (binder) at a mass ratio of 8:1:1. The mixture was then added to deionized water and stirred under high speed until homogeneous, yielding a negative electrode slurry with a solid content of 45%. This slurry was uniformly coated onto a copper foil current collector and dried at 85°C. After cold pressing, the electrode sheet was obtained. A lithium metal sheet was used as the counter electrode, a Celgard 2400 separator was employed, and the same electrolyte as used in the secondary battery preparation was injected to assemble a coin cell.

[0254] Example 2-24

[0255] The preparation methods for secondary batteries and coin cells are similar to those in Example 1, except that the preparation process parameters of the negative electrode active material are adjusted, as detailed in Table 1.

[0256] Comparative Example 1

[0257] The preparation methods for secondary batteries and coin cells are similar to those in Example 1, except that amorphous carbon-coated crystalline silicon is used as the negative electrode active material, and the coating thickness is 80 nm.

[0258] Step 1: Provide crystalline silicon particles with a volumetric particle size Dv50 of 500 nm.

[0259] Step 2: Place the above-mentioned crystalline silicon particles into a rotary kiln, and introduce a mixed gas of 40% acetylene + 60% nitrogen (volume ratio) at a total gas flow rate of 0.8 L / min. Deposition reaction is carried out at 800℃ for 2 hours. After the reaction is completed, the material is cooled and discharged to obtain amorphous carbon-coated crystalline silicon material.

[0260] Comparative Example 2

[0261] The preparation methods for secondary batteries and coin cells are similar to those in Example 1, except that the preparation process parameters of the negative electrode active material are adjusted.

[0262] Step 1: Mechanically crush, classify, spheroidize, and purify the flake graphite to obtain natural spherical graphite.

[0263] Step 2: Select 1 kg of natural spherical graphite as a substrate and place it in a vapor deposition furnace. Heat the furnace to 500°C at a rate of 5°C / min. Introduce the first mixed gas, which consists of 20% silane and 80% nitrogen (by volume). The total gas flow rate is 5 L / min. The pressure inside the furnace is 200 Pa higher than atmospheric pressure. The deposition reaction lasts for 8 hours.

[0264] Step 3: Turn off the first mixed gas, then raise the temperature to 800℃ at a rate of 5℃ / min, and introduce the second mixed gas according to 40% acetylene + 60% nitrogen (volume ratio), with a total gas flow rate of 0.8L / min. The deposition reaction is carried out for 2 hours. After the reaction is completed, the material is cooled, discharged, and passed through a 325-mesh sieve to obtain the negative electrode active material.

[0265] Comparative Example 3

[0266] The preparation methods for secondary batteries and coin cells are similar to those in Example 1, except that the preparation process parameters of the negative electrode active material are adjusted, as detailed in Table 1.

[0267] Comparative Example 4

[0268] The preparation methods for secondary batteries and coin cells are similar to those in Example 1, except that the preparation process parameters of the negative electrode active material are adjusted.

[0269] Step 1: Select 1 kg of porous biomass carbon directly as the carbon matrix without graphitization.

[0270] Step 2: Place the above-mentioned carbon matrix as a substrate in a vapor deposition furnace and heat it to 500°C at a rate of 5°C / min. Introduce the first mixed gas according to the ratio of 20% silane + 80% nitrogen (volume ratio), with a total gas flow rate of 5L / min. The pressure in the reactor is 200Pa higher than atmospheric pressure. The deposition reaction is carried out for 8 hours.

[0271] Step 3: Turn off the first mixed gas, then raise the temperature to 800℃ at a rate of 5℃ / min, and introduce the second mixed gas according to 40% acetylene + 60% nitrogen (volume ratio), with a total gas flow rate of 0.8L / min. The deposition reaction is carried out for 2 hours. After the reaction is completed, the material is cooled, discharged, and passed through a 325-mesh sieve to obtain the negative electrode active material.

[0272] Test section

[0273] (1) Graphitization degree test of carbon matrix and negative electrode active material

[0274] Referring to JIS K 0131-1996, the interlayer spacing d of the (002) crystal plane was obtained using X-ray diffraction. 002 Then, according to the formula g = (0.3440 - d) 002 The degree of graphitization of the carbon matrix and the negative electrode active material is calculated by 100% / (0.3440-0.3354). A Bruker D8 Discover X-ray diffractometer can be used for testing.

[0275] (2) Initial coulombic efficiency test of carbon matrix

[0276] The carbon matrix prepared above was mixed with conductive carbon black (conductive agent) and polyacrylic acid (binder) at a mass ratio of 8:1:1 until homogeneous. This mixture was then added to deionized water and stirred under high speed until the system was homogeneous, yielding a negative electrode slurry with a solid content of 45%. The negative electrode slurry was uniformly coated onto a copper foil current collector and dried at 85°C. After cold pressing, the electrode sheet was obtained. A lithium metal sheet was used as the counter electrode, a Celgard 2400 separator was employed, and the same electrolyte as in Example 1 was injected to assemble a coin cell.

[0277] After the coin cells were left to stand for 4 hours, they were placed in the Blue Electric Test Chamber and discharged at a constant current of 0.05C to 5mV. After standing for 10 minutes, they were discharged at a constant current of 50μA to 5mV, and the total discharge capacity of the coin cells was recorded. Then, after the coin cells were left to stand for 10 minutes, they were charged at a constant current of 0.1C to 2.0V, and the charging capacity of the coin cells was recorded. The initial coulombic efficiency of the carbon matrix = charging capacity / total discharge capacity.

[0278] (3) Powder resistivity test of carbon matrix and negative electrode active material

[0279] A certain mass of carbon matrix and negative electrode active material powder samples are placed in the feeding cup of a resistivity tester, a certain pressure is applied, and then data is manually collected and recorded to record the powder resistivity test results under different pressures. In this application, the test pressure can be 16 MPa.

[0280] (4) Specific surface area test of carbon matrix

[0281] The nitrogen adsorption specific surface area analysis method was used in accordance with GB / T 19587-2017, and the specific surface area of ​​the carbon matrix was calculated using the BET (Brunauer Emmett Teller) method. The testing instrument used was a TRISTAR II 3020 specific surface area and porosity analyzer from Micromeritics, USA.

[0282] (5) Grain size test of filler material

[0283] Samples were taken from the middle region of the negative electrode active material particles using dual-beam focused ion beam transmission electron microscopy (DIB-SEM), and then the grain size of the filling material was measured using high-resolution transmission electron microscopy (HRTEM).

[0284] (6) Content test of each element in the negative electrode active material

[0285] The carbon content in the negative electrode active material is tested according to GB / T 20123-2006 / ISO 15350:2000, using an HCS-140 infrared carbon-sulfur analyzer. The silicon content in the negative electrode active material is tested according to GB / T 20975.5-2020. The tin content in the negative electrode active material is tested according to GB / T 20975.10-2020. The germanium content in the negative electrode active material is tested according to GB / T 20127.6-2006.

[0286] (7) X-ray diffraction pattern test of negative electrode active material

[0287] Referring to JIS K 0131-1996, the crystal cell parameters were calculated using an X-ray diffractometer. The centroid method was used to find the peak positions of C 002 and Si 111 in two parallel samples, with a test angle range of 20°-80°. From the X-ray diffraction pattern of the negative electrode active material, the full width at half maximum (FWHM) of the (002) crystal plane peak at 26.4° and the (111) crystal plane peak at 28.6° were obtained. A Bruker D8 Discover X-ray diffractometer was used for the testing.

[0288] (8) First coulombic efficiency test of negative electrode active material

[0289] After the coin cells prepared in the above embodiments and comparative examples were allowed to stand for 4 hours, they were placed in a blue electric test cabinet and discharged at a constant current of 0.05C to 5mV. After standing for 10 minutes, they were discharged at a constant current of 50μA to 5mV. The total discharge capacity of the coin cells was recorded as the lithium insertion capacity. Then, after the coin cells were allowed to stand for 10 minutes, they were charged at a constant current of 0.1C to 2V. The charging capacity of the coin cells was recorded as the lithium extraction capacity. The initial coulombic efficiency of the negative electrode active material = lithium extraction capacity / lithium insertion capacity.

[0290] (9) Cycle performance test of secondary batteries

[0291] At 25°C, the prepared secondary battery was fully charged at 0.5C and then fully discharged at 1C. This constitutes one charge-discharge cycle. The discharge capacity at this point is recorded as the initial discharge capacity. The secondary battery was then subjected to cyclic charge-discharge tests using the above method, and the discharge capacity after each cycle was recorded until the discharge capacity of the secondary battery decreased to 80% of the initial discharge capacity. The number of cycles at this point characterizes the cycle performance of the secondary battery. The higher the number of cycles, the better the cycle performance.

[0292] Table 1

[0293]

[0294]

[0295] The test results in Table 2 show that incorporating high-specific-capacity filler materials, such as silicon-based, tin-based, and germanium-based materials, into the porous structure of a carbon matrix with a graphitization degree of ≤87% enables the obtained negative electrode active material to achieve high specific capacity, high initial coulombic efficiency, high conductivity, and good cycle stability. This, in turn, allows the secondary battery to achieve high energy density, high initial coulombic efficiency, and long cycle life. Furthermore, the test results from Examples 1-7 also indicate that when the graphitization degree of the carbon matrix is ​​65%-87%, the prepared negative electrode active material exhibits better conductivity and a higher initial coulombic efficiency, reaching over 92%, and the secondary battery also possesses a longer cycle life.

[0296] In the negative electrode active material provided in this application, at least a portion of the filler material is located within the porous structure of the carbon matrix, thereby reducing the volume expansion of the filler material through the carbon matrix. Comparative Example 1 uses carbon-coated crystalline silicon as the negative electrode active material. Crystalline silicon exhibits a significant volume effect, while the surface carbon layer provides limited protection for the crystalline silicon. Furthermore, the carbon layer cracks after multiple charge-discharge cycles, leading to repeated damage and reconstruction of the SEI film, increasing the irreversible consumption of active ions. Moreover, with increasing charge-discharge cycles, the SEI film thickness continuously increases, consequently increasing the impedance of the secondary battery. Therefore, the secondary battery prepared in Comparative Example 1 exhibits very poor cycle performance.

[0297] Comparative Example 2 uses natural spherical graphite as the carbon matrix. Natural spherical graphite itself has a porous structure, which can be used as a substrate material for deposition and has the advantage of excellent conductivity. However, the pore structure of natural spherical graphite is irregular, which leads to poor uniformity of the dispersion of the filling material. In addition, natural spherical graphite also has the defects of poor structural stability and large volume expansion, which results in poor cycle performance of the secondary battery. It cannot achieve high energy density, high initial coulombic efficiency and long cycle life of the secondary battery.

[0298] In Comparative Example 3, when the temperature during the graphitization treatment of porous biomass carbon in step 1 is higher than 2400℃, and the graphitization of the obtained carbon matrix is ​​too high, the negative electrode active material prepared at this time has a large volume expansion and poor structural stability during the charge and discharge process. As a result, the cycle performance of the secondary battery is very poor, and the secondary battery cannot achieve high energy density, high initial coulombic efficiency and long cycle life.

[0299] Comparative Example 4 directly uses porous biomass carbon that has not undergone graphitization treatment as the carbon matrix. At this time, the carbon matrix is ​​non-graphitized carbon, which has the defects of high irreversible capacity, low initial coulombic efficiency and poor conductivity. The negative electrode active material prepared from it has low initial coulombic efficiency and very poor conductivity. Therefore, it is not possible for the secondary battery to achieve high energy density, high initial coulombic efficiency and long cycle life.

[0300] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

[0301]

[0302]

Claims

1. A negative electrode active material, comprising a carbon matrix and a filler material, wherein, The degree of graphitization of the carbon matrix is ​​40%-87%, the carbon matrix includes multiple porous structures, at least a portion of the filling material is located in the porous structures of the carbon matrix, and the filling material includes one or more elements that can undergo alloying reaction with Li, including one or more of silicon, tin and germanium.

2. The negative electrode active material according to claim 1, wherein, The degree of graphitization of the carbon matrix is ​​65%-87%.

3. The negative electrode active material according to claim 1 or 2, wherein, The filler material includes one or more of silicon-based materials, tin-based materials, and germanium-based materials.

4. The negative electrode active material according to claim 3, wherein, The silicon-based materials include one or more of elemental silicon, silicon oxide, silicon-carbon materials, silicon-nitrogen composites, and silicon alloys.

5. The negative electrode active material according to claim 3, wherein, The tin-based materials include one or more of elemental tin, tin oxides, tin sulfides, tin phosphides, tin composite oxides, tin-carbon materials, and tin alloy materials.

6. The negative electrode active material according to claim 3, wherein, The germanium-based materials include one or more of elemental germanium, germanium oxides, germanium carbon materials, germanium alloy materials, and germanates.

7. The negative electrode active material according to any one of claims 1-6, wherein, The filler material includes crystalline filler material and / or amorphous filler material.

8. The negative electrode active material according to claim 7, wherein, The filler material includes crystalline silicon-based materials and / or amorphous silicon-based materials.

9. The negative electrode active material according to claim 7, wherein, The grain size of the crystalline filler material is ≤100nm.

10. The negative electrode active material according to claim 9, wherein, The grain size of the crystalline filler material is 2nm-50nm.

11. The negative electrode active material according to any one of claims 1-10, wherein, The filler material includes one or more of the following: vapor-deposited silicon-based materials, tin-based materials, and germanium-based materials.

12. The negative electrode active material according to claim 11, wherein, The filling material includes vapor-deposited silicon-based materials.

13. The negative electrode active material according to any one of claims 1-12, wherein, In the X-ray diffraction pattern of the negative electrode active material measured by an X-ray diffractometer, the negative electrode active material includes a (002) crystal plane peak at 26.4° and a (111) crystal plane peak at 28.6°, and the ratio of the half-width at half maximum (WHM) of the (002) crystal plane peak to the half-width at half maximum (WHM) of the (111) crystal plane peak is 0.2-50.

14. The negative electrode active material according to claim 13, wherein, The ratio of the half-width at half maximum (WHM) of the (002) crystal plane peak to the half-width at half maximum (WHM) of the (111) crystal plane peak is 0.2-20.

15. The negative electrode active material according to any one of claims 1-14, wherein, At least a portion of the filler material is located within the porous structure of the carbon matrix, and there are voids between the filler material and the carbon matrix.

16. The negative electrode active material according to any one of claims 1-15, wherein, The negative electrode active material further includes a coating layer located on at least a portion of the surface of the carbon matrix.

17. The negative electrode active material according to claim 16, wherein, The coating layer includes one or more of carbon materials, conductive polymers, metal oxides, and metal sulfides.

18. The negative electrode active material according to claim 17, wherein, The coating layer comprises carbon material.

19. The negative electrode active material according to claim 16, wherein, The thickness of the coating layer is ≤100nm.

20. The negative electrode active material according to claim 19, wherein, The thickness of the coating layer is 10nm-100nm.

21. The negative electrode active material according to any one of claims 1-20, wherein, The negative electrode active material includes carbon, and the mass percentage of carbon in the negative electrode active material is 20wt%-80wt%.

22. The negative electrode active material according to claim 21, wherein, The negative electrode active material includes carbon, and the mass percentage of carbon in the negative electrode active material is 30wt%-70wt%.

23. The negative electrode active material according to claim 1, wherein, The mass percentage of the element in the negative electrode active material that can undergo an alloying reaction with Li is 20wt%-80wt%.

24. The negative electrode active material according to claim 23, wherein, The mass percentage of the element in the negative electrode active material that can undergo alloying reaction with Li is 30wt%-70wt%.

25. The negative electrode active material according to any one of claims 1-24, wherein, The negative electrode active material also includes other elements, including one or more of oxygen, metal elements and nitrogen.

26. The negative electrode active material according to claim 25, wherein, The sum of the mass percentages of the other elements in the negative electrode active material is less than or equal to 20 wt%.

27. The negative electrode active material according to claim 26, wherein, The sum of the mass percentages of the other elements in the negative electrode active material is less than or equal to 10 wt%.

28. The negative electrode active material according to any one of claims 1-27, wherein, The carbon matrix satisfies at least one of the following: (1) The initial coulombic efficiency of the carbon matrix is ​​≥75%; (2) The resistivity of the carbon matrix powder at 16 MPa pressure is ≤5×10⁻⁶. -2 Ω·cm; (3) The BET specific surface area of ​​the carbon matrix is ​​50 m². 2 / g-1000m 2 / g.

29. The negative electrode active material according to claim 28, wherein, The carbon matrix satisfies at least one of the following: (1) The initial coulombic efficiency of the carbon matrix is ​​75%-87%; (2) The resistivity of the carbon matrix powder at 16 MPa pressure is ≤3.5×10⁻⁶. -2 Ω·cm; (3) The BET specific surface area of ​​the carbon matrix is ​​100 m². 2 / g-700m 2 / g.

30. The negative electrode active material according to any one of claims 1-29, wherein, The negative electrode active material satisfies at least one of the following: (1) The degree of graphitization of the negative electrode active material is ≥65%; (2) The initial coulombic efficiency of the negative electrode active material is ≥92%; (3) The volumetric particle size Dv50 of the negative electrode active material is 3μm-50μm; (4) The volumetric particle size Dv90 of the negative electrode active material is ≤60μm; (5) The diameter spacing (Dv90-Dv10) / Dv50 of the negative electrode active material is 1.0-3.0; (6) The BET specific surface area of ​​the negative electrode active material is 2m². 2 / g-100m 2 / g; (7) The powder resistivity of the negative electrode active material at a pressure of 16 MPa is ≤5×10⁻⁶. -1 Ω·cm.

31. The negative electrode active material according to claim 30, wherein, The negative electrode active material satisfies at least one of the following: (1) The degree of graphitization of the negative electrode active material is 65%-87%; (2) The initial coulombic efficiency of the negative electrode active material is 92%-95%; (3) The volumetric particle size Dv50 of the negative electrode active material is 5μm-20μm; (4) The volumetric particle size Dv90 of the negative electrode active material is 20μm-50μm; (5) The diameter spacing (Dv90-Dv10) / Dv50 of the negative electrode active material is 1.0-2.0; (6) The BET specific surface area of ​​the negative electrode active material is 2m². 2 / g-30m 2 / g; (7) The powder resistivity of the negative electrode active material at a pressure of 16 MPa is ≤2×10⁻⁶. -1 Ω·cm.

32. A method for preparing a negative electrode active material, comprising the following steps: Step 1, providing a carbon matrix with a graphitization degree of 40%-87% and including a plurality of porous structures; Step 2, dispersing a filler material into the porous structure of the carbon matrix to obtain the negative electrode active material, wherein... The negative electrode active material includes a carbon matrix and a filler material. The carbon matrix includes a plurality of pore structures. At least a portion of the filler material is located in the pore structures of the carbon matrix. The filler material includes one or more elements that can undergo an alloying reaction with Li. The elements that can undergo an alloying reaction with Li include one or more elements selected from silicon, tin, and germanium.

33. The method according to claim 32, wherein, In step 1, the degree of graphitization of the carbon matrix is ​​65%-87%.

34. The method according to claim 32 or 33, wherein, In step 1, the carbon matrix is ​​prepared by the following method: a carbon source including multiple porous structures is placed in a high-temperature furnace and graphitized at 1600℃-2400℃ under a protective gas atmosphere, and the carbon matrix is ​​obtained after the process.

35. The method according to claim 34, wherein, The heat preservation time for the graphitization treatment is 1h-12h.

36. The method according to claim 34, wherein, The carbon source includes one or more selected from hard carbon, petroleum coke, pitch coke, biomass carbon, and resin carbon.

37. The method according to any one of claims 32-36, wherein, In step 1, the carbon matrix satisfies at least one of the following: (1) The initial coulombic efficiency of the carbon matrix is ​​≥75%; (2) The resistivity of the carbon matrix powder at 16 MPa pressure is ≤5×10⁻⁶. -2 Ω·cm; (3) The BET specific surface area of ​​the carbon matrix is ​​50 m². 2 / g-1000m 2 / g; (4) The volumetric particle size Dv50 of the carbon matrix is ​​3μm-50μm.

38. The method according to claim 37, wherein, In step 1, the carbon matrix satisfies at least one of the following: (1) The initial coulombic efficiency of the carbon matrix is ​​75%-87%; (2) The resistivity of the carbon matrix powder at 16 MPa pressure is ≤3.5×10⁻⁶. -2 Ω·cm; (3) The BET specific surface area of ​​the carbon matrix is ​​100 m². 2 / g-700m 2 / g; (4) The volumetric particle size Dv50 of the carbon matrix is ​​5μm-20μm.

39. The method according to any one of claims 32-38, wherein, In step 2, the process of dispersing the filler material into the porous structure of the carbon matrix includes either liquid phase deposition or vapor phase deposition.

40. The method according to claim 39, wherein, The process of dispersing filler material into the porous structure of the carbon matrix is ​​a vapor phase deposition process.

41. The method according to claim 40, wherein, The vapor deposition process includes either chemical vapor deposition or physical vapor deposition.

42. The method according to claim 41, wherein, The vapor deposition process is a chemical vapor deposition process.

43. The method according to any one of claims 39-42, wherein, In step 2, the step of dispersing the filler material into the porous structure of the carbon matrix includes the following steps: placing the carbon matrix in a reactor, introducing a first mixed gas containing a source of elements capable of alloying with Li, and depositing it at a first temperature T1 for a first time t1. After the deposition is completed, the negative electrode active material is obtained.

44. The method according to claim 43, wherein, The first mixed gas includes the source and protective gas of the element capable of alloying with Li.

45. The method according to claim 43, wherein, The volume percentage of the source of the element that can undergo an alloying reaction with Li in the first mixed gas is 10%-50%.

46. ​​The method according to claim 43, wherein, The pressure inside the reactor is 200Pa-600Pa higher than atmospheric pressure.

47. The method according to claim 43, wherein, The total gas flow rate of the first mixed gas is 0.5L / min-20L / min.

48. The method according to claim 43, wherein, The first temperature T1 is 400℃-1000℃.

49. The method according to claim 43, wherein, The first time t1 is 1h-12h.

50. The method according to any one of claims 43-49, wherein, The first mixture also includes a carbon source gas.

51. The method according to claim 50, wherein, The volume ratio of the source of the element capable of alloying with Li to the carbon source gas is greater than or equal to 0.5:

1.

52. The method according to claim 51, wherein, The volume ratio of the source of the element capable of alloying with Li to the carbon source gas is (2-10):

1.

53. The method according to claim 50, wherein, The volume percentage of the carbon source gas in the first mixture is ≤20%.

54. The method according to claim 53, wherein, The carbon source gas in the first mixture accounts for 5%-20% of the volume.

55. The method according to any one of claims 32-54, further comprising step 3: forming a coating layer on at least a portion of the surface of the negative electrode active material obtained in step 2, said coating layer comprising one or more of carbon materials, conductive polymers, metal oxides and metal sulfides.

56. The method according to claim 55, wherein, The steps for forming the coating layer include the following steps: placing the negative electrode active material obtained in step 2 into a reactor, introducing a second mixed gas containing carbon source gas, and depositing it at a second temperature T2 for a second time t2. After the deposition is completed, a carbon-coated negative electrode active material is obtained.

57. The method according to claim 56, wherein, The second mixture includes a carbon source gas and a protective gas.

58. The method according to claim 57, wherein, The volume percentage V2 of the carbon source gas in the second mixture is 5%-50%.

59. The method according to claim 56, wherein, The total gas flow rate of the second mixture is 0.5 L / min to 20 L / min.

60. The method of claim 56, wherein, The second temperature T2 is 700℃-850℃.

61. The method according to claim 56, wherein, The second time t2 is 1h-6h.

62. A secondary battery, comprising a negative electrode sheet, said negative electrode sheet comprising the negative electrode active material according to any one of claims 1-31 or the negative electrode active material prepared by the method according to any one of claims 32-61.

63. An electrical device comprising the secondary battery as described in claim 62.

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