A negative electrode active material and its preparation method, a secondary battery and an electrical device thereof

Abstract

This application relates to a negative electrode active material comprising a core structure and a shell structure disposed on the surface of the core structure. Both the core and shell structures have pores, and the average pore diameter of the pores in the shell structure is larger than that of the pores in the core structure. The negative electrode active material of this application can maintain excellent kinetic performance under high compaction density conditions. When this negative electrode active material is used in a battery, it can improve the battery's energy density and achieve fast charging. This application also relates to a method for preparing the above-mentioned negative electrode active material, a secondary battery, and an electrical device.

Description

Technical Field

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

[0002] Rechargeable batteries are now widely used in pure electric vehicles, hybrid electric vehicles, smart grids, and other fields. With the continuous development of the new energy industry, customers are placing higher demands on the use of rechargeable batteries.

[0003] Currently, research on anode active materials focuses primarily on improving their energy density. Compacted density is one of the reference indicators for energy density. Existing anode active materials cannot simultaneously maintain excellent kinetic performance under high compacted density conditions. Summary of the Invention

[0004] In view of the problems existing in the background art, this application provides a negative electrode active material that can maintain excellent kinetic performance under high compaction density conditions.

[0005] The negative electrode active material provided in the first aspect of this application includes a core structure and a shell structure disposed on the surface of the core structure. Both the core structure and the shell structure have pores, and the average pore diameter of the pores in the shell structure is larger than the average pore diameter of the pores in the core structure.

[0006] In the technical solution of this application embodiment, by wrapping a core structure with a smaller average pore size around a shell structure with a larger average pore size, the negative electrode active material possesses a gradient pore structure. This pore structure design can shorten the lithium ion transport path, reduce the time required for lithium ions to reach the graphite surface, and give the negative electrode active material excellent kinetic performance, thereby improving the wettability of the electrolyte to the negative electrode active material. Furthermore, the negative electrode active material with a gradient pore structure also has a high compaction density. Therefore, this negative electrode active material can maintain excellent kinetic performance even under high compaction density conditions. When this negative electrode active material is used in a battery, it can improve the battery's energy density and achieve fast charging.

[0007] In some embodiments, according to the first aspect, a first example of the first aspect is proposed, wherein the average pore diameter of the pores in the shell structure is denoted as D1, and the average pore diameter of the pores in the core structure is denoted as D2, then D1 / D2≥4; optionally, 20≤D1 / D2≤50.

[0008] When D1 / D2 satisfies the above relationship, it helps to shorten the lithium ion transport path, reduce the time required for lithium ions to reach the graphite surface, enable the negative electrode active material to have excellent kinetic performance, improve the wettability of the electrolyte to the negative electrode active material, and at the same time ensure a high compaction density.

[0009] In some embodiments, according to the first aspect, a second example of the first aspect is provided, wherein the average pore diameter of the pores in the shell structure is 100 nm to 1000 nm, optionally 200 nm to 500 nm; and / or, the average pore diameter of the pores in the core structure is 10 nm to 100 nm, optionally 20 nm to 50 nm.

[0010] Optimizing the average pore size of the shell and core structures can improve the kinetic performance of the anode active material while ensuring a high compaction density. An excessively large average pore size leads to energy density loss in the anode active material; an excessively small average pore size results in insufficient electrolyte capacity, making the electrolyte more easily squeezed out during charging and discharging, leading to poor wettability and consequently deteriorating kinetic performance.

[0011] In some embodiments, according to the first aspect, a third example of the first aspect is proposed, wherein the thickness of the shell structure is denoted as d, and the volume average particle size Dv50 of the negative electrode active material is denoted as D, then the negative electrode active material satisfies: d≥0.1D, that is, d≥1um; optionally, the negative electrode active material satisfies: 0.1D≤d≤0.3D.

[0012] Optimizing the relationship between shell structure thickness and negative electrode active material particle size can further improve the kinetic performance of the negative electrode active material, shorten the lithium-ion transport path, and reduce the time required for lithium ions to reach the graphite surface. If the shell structure thickness is too large, the negative electrode active material accommodates more electrolyte, reducing the lithium-ion transport path but resulting in energy density loss; if the shell structure thickness is too small, the lithium-ion transport path is too long, leading to poorer kinetics.

[0013] In some embodiments, according to the first aspect, a fourth example of the first aspect is provided, wherein the interlayer spacing d002 of the shell structure is greater than the interlayer spacing d002 of the core structure. Optionally, the interlayer spacing d002 of the core structure is 0.3355 nm to 0.3365 nm, or optionally 0.3355 nm to 0.3360 nm. Optionally, the interlayer spacing d002 of the shell structure is 0.3500 nm to 0.3800 nm, or optionally 0.3600 nm to 0.3700 nm.

[0014] Optimizing the interlayer spacing d002 of the shell and core structures can improve the kinetics of the anode material and increase the compaction density. If the interlayer spacing d002 is too large, the anode active material is more difficult to compact; if the interlayer spacing d002 is too small, lithium-ion transport is slower and the kinetics deteriorate.

[0015] In some embodiments, according to the first aspect, a fifth example of the first aspect is proposed, defining the pore size distribution P as (Pn90-Pn10) / Pn50, where Pn10 represents the pore size corresponding to the cumulative distribution percentage of the number of pores reaching 10%, Pn50 represents the pore size corresponding to the cumulative distribution percentage of the number of pores reaching 50%, and Pn90 represents the pore size corresponding to the cumulative distribution percentage of the number of pores reaching 90%. The pore size distribution of the shell structure is denoted as P1, satisfying P1≤0.7, optionally P1 is 0.4~0.6; and / or, the pore size distribution of the core structure is denoted as P2, satisfying P2≤0.6, optionally P2 is 0.3~0.5.

[0016] Optimizing the pore size distribution of the shell and core structures can further improve the kinetic performance of the anode active material, shorten the lithium-ion transport path, and reduce the time required for lithium ions to reach the graphite surface. A smaller pore size distribution coefficient indicates more uniform porosity, a more uniform lithium insertion / extraction state in the anode active material, and better kinetic performance.

[0017] In some embodiments, according to the first aspect, a sixth example of the first aspect is proposed, wherein the porosity of the negative electrode active material is 60% to 80%, optionally 60% to 70%.

[0018] If the porosity is too high, the compaction density of the negative electrode active material will be lower; if the porosity is too low, the kinetic performance of the negative electrode active material will be worse.

[0019] In some embodiments, according to the first aspect, a seventh example of the first aspect is provided, wherein the compaction density of the negative electrode active material after being pressed under a pressure of 2000 kgf is 1.6–2.0 g / cm³. 3 The concentration can be selected as 1.7–1.9 g / cm³. 3 .

[0020] Within the above-mentioned range, the compaction density of the negative electrode active material can also ensure fast charging performance.

[0021] In some embodiments, according to the first aspect, an eighth example of the first aspect is provided, wherein the specific surface area of ​​the negative electrode active material is 20–100 m². 2 / g, which can be selected as 20-50m 2 / g.

[0022] Maintaining the specific surface area of ​​the negative electrode active material within the aforementioned range is beneficial for improving battery capacity, reducing impedance, and increasing battery charge / discharge rates. Excessive specific surface area leads to more side reactions and a shorter battery lifespan; conversely, insufficient specific surface area reduces lithium-ion transport pathways, making it difficult to guarantee kinetic performance.

[0023] In some embodiments, according to the first aspect, a ninth example of the first aspect is proposed, wherein the reversible specific capacity of the negative electrode active material is ≥355mAh / g, and optionally, the reversible specific capacity is ≥360mAh / g.

[0024] By optimizing the compaction density and pore structure of the negative electrode active material, the electrolyte can still migrate quickly to the graphite surface under high compaction density conditions, resulting in less electrolyte polarization and a corresponding increase in reversible specific capacity, thereby improving the cycle performance of the battery.

[0025] In some embodiments, according to the first aspect, a tenth example of the first aspect is proposed, wherein the volume average particle size Dv50 of the negative electrode active material is 10 to 30 μm, and optionally 15 to 25 μm.

[0026] Optimizing the average particle size of the negative electrode active material is beneficial for improving compaction density and the wettability of the electrolyte to the negative electrode active material. A smaller average particle size means more exposed surface area, allowing lithium ions to reach the material surface more quickly and improving kinetic performance, but at the cost of decreased compaction density. Conversely, an excessively large average particle size can lead to bridging during slurry production, causing filtration difficulties and lengthening the lithium ion transport path, resulting in poorer kinetic performance.

[0027] In some embodiments, according to the first aspect, an eleventh example of the first aspect is provided, wherein the particle size distribution of the negative electrode active material is 0.8≤(Dv90-Dv10) / Dv50≤1.8, and optionally 1.2≤(Dv90-Dv10) / Dv50≤1.5.

[0028] Optimizing the particle size distribution of the negative electrode active material is beneficial for improving compaction density and the wettability of the electrolyte to the negative electrode active material. An excessively narrow particle size distribution leads to unsuitable particle size gradation, resulting in poor tap density and compaction density; an excessively wide particle size distribution increases the tortuosity of the electrode layers, reduces porosity, and consequently deteriorates kinetic performance.

[0029] In some embodiments, according to the first aspect, a twelfth example of the first aspect is provided, wherein the negative electrode active material includes magnetic impurities. The magnetic impurities include at least one selected from Fe, Ni, Cr, and Zn. Optionally, the content of the magnetic impurities is less than or equal to 1000 ppm.

[0030] Ensuring that the content of magnetic impurities in the negative electrode active material is within the above range is beneficial to reducing self-discharge and safety risks.

[0031] In some embodiments, according to the first aspect, a thirteenth example of the first aspect is proposed, wherein the negative electrode active material satisfies any one of the following conditions (1)-(4):

[0032] (1) The shell structure is hard carbon, and the core structure is soft carbon;

[0033] (2) The shell structure is soft carbon, and the core structure is hard carbon;

[0034] (3) The shell structure is graphite and the core structure is hard carbon;

[0035] (4) The shell structure is hard carbon and the core structure is graphite.

[0036] Optimizing the raw materials used to form the shell and core structures facilitates the formation of gradient pore structures, thereby improving the electrolyte wettability of the negative electrode active material and increasing its compaction density.

[0037] A second aspect of this application provides a method for preparing a negative electrode active material, comprising the following steps:

[0038] The first carbon precursor, catalyst 1 and dispersant 1 are mixed and then calcined to obtain substance A;

[0039] Substance A, catalyst 2, dispersant 2, and the second carbon precursor were mixed and calcined to obtain substance B;

[0040] Substance B is subjected to heat treatment to obtain the negative electrode active material;

[0041] The negative electrode active material includes a core structure and a shell structure disposed on the surface of the core structure. Both the core structure and the shell structure have pores, and the average pore diameter of the pores in the shell structure is larger than the average pore diameter of the pores in the core structure.

[0042] In the technical solution of this application embodiment, a negative electrode active material is obtained by using a first carbon precursor and a second carbon precursor as raw materials, followed by calcination and heat treatment. This material exhibits excellent kinetic properties even under high compaction density conditions. This method is simple to operate, highly repeatable, and beneficial for large-scale industrial production.

[0043] In some embodiments, according to the second aspect, a first example of the second aspect is provided, wherein the first carbon precursor includes at least one of coal tar, coal pitch, petroleum residue, and petroleum pitch.

[0044] In some embodiments, according to the second aspect, a second example of the second aspect is provided, wherein the second carbon precursor includes at least one of water-soluble phenolic resin, glucose, and sucrose.

[0045] Optimizing the types of raw materials used to form the shell and core structures can help improve the electrolyte wettability of the negative electrode active material and increase its compaction density.

[0046] In some embodiments, according to the second aspect, a third example of the second aspect is proposed, wherein the preparation method satisfies at least one of the following conditions (1)-(4): (1) catalyst 1 includes at least one of ferrocene and ferric acetylacetonate; (2) catalyst 2 includes at least one of ferric chloride, ferrous chloride, ferric nitrate, ferrous nitrate, ferric sulfate, ferrous sulfate, and ferric citrate; (3) dispersant 1 includes at least one of isooctane, xylene, ethyl acetate, cyclohexanone, tetrachloroethylene, tetrahydrofuran, and benzyl alcohol; (4) dispersant 2 includes at least one of water, ethanol, ethylene glycol, glycerol, and oxalic acid.

[0047] By optimizing the types of catalyst 1, catalyst 2, dispersant 1, and dispersant 2, it is beneficial to promote the formation of anode active materials with gradient structures. Specifically, catalyst 1 and catalyst 2 can promote the complete cell development of the anode active material under lower temperature conditions, ensuring that the battery has high reversible specific capacity and good cycle performance. Furthermore, optimizing the types of catalyst 1, catalyst 2, dispersant 1, and dispersant 2 helps to reduce the requirements for reaction conditions. Compared with the conventional synthesis conditions of 3000℃, the energy consumption cost of the preparation method in this application is reduced. In addition, the dispersant helps to uniformly disperse the catalyst and carbon precursor, forming a homogeneous system.

[0048] In some embodiments, according to the second aspect, a fourth example of the second aspect is proposed, wherein the particle size of catalyst 1 is 20 nm to 200 nm, optionally 40 nm to 100 nm; and / or, the particle size of catalyst 2 is 0.2 μm to 2 μm, optionally 0.4 μm to 1 μm.

[0049] Optimizing the particle size of catalyst 1 and catalyst 2 helps to control the average pore size of the core and shell structures. The larger the particle size of catalyst 1 and catalyst 2, the larger the average pore size of the core and shell structures in the resulting negative electrode active material, and vice versa.

[0050] In some embodiments, according to the second aspect, a fifth example of the second aspect is provided, wherein the mass ratio of the first carbon precursor to the second carbon precursor is 9:1 to 1:1, optionally 9:1 to 7:3; and / or, the mass ratio of catalyst 1 to the first carbon precursor is (0.1 to 1):1, optionally (0.2 to 0.5):1; and / or, the mass ratio of catalyst 2 to the second carbon precursor is (0.3 to 1):1, optionally (0.4 to 0.7):1.

[0051] Optimizing the mass ratio of the first and second carbon fluxes helps ensure that the active material has high energy density and kinetics. An excessively high mass ratio will result in an overly high proportion of the core structure in the negative electrode active material, leading to poor porosity, reduced electrolyte wettability, and consequently, deteriorated kinetics. Conversely, an excessively low mass ratio will result in an excessively low proportion of the core structure in the negative electrode active material, resulting in lower energy density.

[0052] Optimizing the amounts of catalyst 1 and catalyst 2 helps control the average pore size of the core and shell structures. A higher proportion of catalyst 1 and catalyst 2 results in a larger average pore size of the core and shell structures in the obtained negative electrode active material, and vice versa.

[0053] In some embodiments, according to the second aspect, a sixth example of the second aspect is provided, wherein the mass ratio of dispersant 1 to the first carbon precursor is (0.5 to 5):1, optionally (1 to 3):1; and / or, the mass ratio of dispersant 2 to the second carbon precursor is (1 to 5):1, optionally (2 to 4):1.

[0054] Optimizing the dosage of dispersant 1 and dispersant 2 helps control the average pore size of the core and shell structures. The higher the proportion of dispersant 1 and dispersant 2 added, the more uniform the average pore size of the core and shell structures in the resulting negative electrode active material.

[0055] In some embodiments, according to the second aspect, a seventh example of the second aspect is provided, wherein in the step of preparing substance A, the calcination temperature is 600-800°C, optionally 700-800°C; and / or, in the step of preparing substance A, the calcination time is 0.5-5h, optionally 1h-2h.

[0056] Optimizing the calcination temperature in this step helps control the average pore size of the core structure. The higher the calcination temperature, the smaller the average pore size of the core structure in the resulting negative electrode active material.

[0057] The longer the first carbon precursor is calcined, the more completely the dispersant 1 volatilizes, the more partially the catalyst 1 decomposes, and the smaller the average pore size of the core structure in the resulting negative electrode active material.

[0058] In some embodiments, according to the second aspect, an eighth example of the second aspect is provided, wherein in the step of preparing substance B, the calcination temperature is 800–1000°C, optionally 800–900°C; and / or, in the step of preparing substance B, the calcination time is 2–5 h, optionally 2–3 h.

[0059] Optimizing the calcination temperature in this step helps control the average pore size of the shell structure. The higher the calcination temperature, the smaller the average pore size of the shell structure in the resulting negative electrode active material.

[0060] The longer the second carbon precursor is calcined, the more completely the dispersant 2 volatilizes, the more partially the catalyst 2 decomposes, and the smaller the average pore size of the shell structure in the resulting negative electrode active material.

[0061] In some embodiments, according to the second aspect, a ninth example of the second aspect is provided, wherein the heat treatment temperature is 1800–2800°C, optionally 2000–2500°C; and / or the heat treatment time is 2–7 days, optionally 3–5 days.

[0062] Optimizing the heat treatment temperature helps control the average pore size of the core and shell structures. Higher heat treatment temperatures lead to greater catalyst volatility, resulting in smaller average pore sizes in the core and shell structures of the obtained anode active material.

[0063] As the heat treatment time increases, the average pore size of the core and shell structures gradually decreases. When the heat treatment time increases to a certain extent, the carbon structure becomes basically stable, and the pore size structure no longer changes.

[0064] In some embodiments, according to the second aspect, a tenth example of the second aspect is proposed, wherein after obtaining substance A, substance A is pulverized; and / or, after obtaining substance B, substance B is pulverized; and / or, after obtaining the negative electrode active material, it is sieved.

[0065] Crushing and / or sieving can help reduce particle adhesion caused by heat treatment and achieve the target particle size.

[0066] A third aspect of this application provides a secondary battery, including a negative electrode. The negative electrode includes the negative electrode active material described in the first aspect of this application or the negative electrode active material obtained according to the preparation method described in the second aspect of this application.

[0067] In the technical solutions of this application embodiment, since the negative electrode active material of the first aspect of this application or the negative electrode active material obtained according to the preparation method of the second aspect of this application is used, the secondary battery of this application has improved energy density and can achieve fast charging.

[0068] A fourth aspect of this application provides an electrical device including the secondary battery described in the third aspect of this application.

[0069] In the technical solutions of this application embodiment, since the negative electrode active material of the first aspect of this application or the negative electrode active material obtained according to the preparation method of the second aspect of this application is used, the power device of this application has improved energy density and can achieve fast charging.

[0070] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application, it can be implemented according to the contents of the specification. In order to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0071] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0072] Figure 1 This is a schematic diagram of one embodiment of a secondary battery.

[0073] Figure 2 yes Figure 1 The exploded diagram.

[0074] Figure 3 This is a schematic diagram of one embodiment of the battery module.

[0075] Figure 4 This is a schematic diagram of one embodiment of the battery pack.

[0076] Figure 5 yes Figure 4 The exploded diagram.

[0077] Figure 6 This is a schematic diagram of one embodiment of a device that uses a secondary battery as a power source.

[0078] Figure 7 This is a schematic diagram of the structure of the negative electrode active material prepared in Example 1 of this application.

[0079] Figure 8 This is a cross-sectional TEM image of the negative electrode active material prepared in Example 1 of this application. Detailed Implementation

[0080] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0081] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The terms "comprising" and "having," and any variations thereof, in the specification, claims, and foregoing description of the drawings, are intended to cover non-exclusive inclusion.

[0082] For simplicity, this paper only explicitly discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form an undefined range; and any lower limit can be combined with other lower limits to form an undefined range, just as any upper limit can be combined with any other upper limit to form an undefined range. Furthermore, although not explicitly stated, every point or individual value between the endpoints of a range is included within that range. Therefore, each point or individual value can serve as its own lower or upper limit and be combined with any other point or individual value, or with other lower or upper limits, to form an undefined range.

[0083] In this description, it should be noted that, unless otherwise stated, "above" and "below" include the stated number, and "multiple" in "one or more" means two or more (including two).

[0084] In the description of the embodiments of this application, the term "and / or" is merely a description of the relationship between related objects, indicating that there can be three relationships. For example, A and / or B can mean: A exists, A and B exist simultaneously, and B exists.

[0085] In the description of the embodiments of this application, unless otherwise expressly specified and limited, technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0086] The foregoing description of this invention is not intended to describe every disclosed embodiment or implementation. Instead, the following description provides more specific examples of exemplary embodiments. Throughout the application, guidance is provided through a series of embodiments that can be used in various combinations. The examples listed are merely representative and should not be construed as exhaustive.

[0087] Rechargeable batteries are now widely used in pure electric vehicles, hybrid electric vehicles, smart grids, and other fields. With the continuous development of the new energy industry, customers are placing higher demands on rechargeable batteries. Currently, research on negative electrode active materials focuses more on how to improve their energy density. Compacted density is one of the reference indicators for energy density. Existing negative electrode active materials cannot maintain excellent kinetic performance under high compacted density conditions.

[0088] To address the aforementioned issues, the inventors, through in-depth research, designed a negative electrode active material. By encapsulating a core structure with a smaller average pore size around a shell structure with a larger average pore size, the negative electrode active material possesses a gradient pore structure. Lithium ions are first intercalated in the portion of the negative electrode active material closest to the electrolyte, and later in the portion farther from the electrolyte. This gradient pore structure matches the concentration distribution of lithium ions on the negative electrode sheet, shortening the lithium ion transport path and reducing the time required for lithium ions to reach the graphite surface. This results in excellent kinetic performance and improved wettability of the negative electrode active material by the electrolyte. Furthermore, the negative electrode active material with the gradient pore structure also exhibits high compaction density. Therefore, this negative electrode active material can maintain excellent kinetic performance even under high compaction density conditions. When this negative electrode active material is used in batteries, it can improve the battery's energy density and achieve fast charging.

[0089] The technical solutions described in the embodiments of this application are applicable to negative electrode active materials, and also to the preparation process of negative electrode active materials, secondary batteries using negative electrode active materials, and electrical devices using secondary batteries.

[0090] In a first aspect, according to some embodiments of this application, this application provides a negative electrode active material. It includes a core structure and a shell structure disposed on the surface of the core structure. Both the core structure and the shell structure have pores, and the average pore diameter of the pores in the shell structure is larger than the average pore diameter of the pores in the core structure.

[0091] In some embodiments, the average pore diameter in the shell structure is denoted as D1, and the average pore diameter in the core structure is denoted as D2, then D1 / D2≥4; optionally, 20≤D1 / D2≤50.

[0092] When D1 / D2 satisfies the above relationship, it helps to shorten the lithium ion transport path, reduce the time required for lithium ions to reach the graphite surface, enable the negative electrode active material to have excellent kinetic performance, improve the wettability of the electrolyte to the negative electrode active material, and at the same time ensure a high compaction density.

[0093] In some specific embodiments, D1 / D2 may be, for example, 4, 10, 15, 20, 25, 30, 35, 40, 45, or 50. D1 / D2 can be within a numerical range formed by using any two of the values ​​listed above as endpoints.

[0094] In some embodiments, the average pore size of the pores in the shell structure is 100 nm to 1000 nm, optionally 200 nm to 500 nm; and / or, the average pore size of the pores in the core structure is 10 nm to 100 nm, optionally 20 nm to 50 nm.

[0095] Optimizing the average pore size of the shell and core structures can improve the kinetic performance and increase the compaction density of the anode active material. An excessively large average pore size leads to energy density loss in the anode active material; an excessively small average pore size results in insufficient electrolyte capacity, making the electrolyte more easily squeezed out during charging and discharging, leading to poor wettability and consequently deteriorating kinetic performance.

[0096] In some specific embodiments, the average pore diameter of the holes in the shell structure may be, for example, 110 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, 550 nm, 600 nm, 650 nm, 700 nm, 750 nm, 800 nm, 850 nm, 900 nm, 950 nm, or 1 μm. The average pore diameter of the holes in the shell structure can be within a numerical range formed by using any two of the values ​​listed above as endpoints. For example, the average pore diameter of the holes in the shell structure may be 110 nm to 500 nm, 200 nm to 500 nm, or 500 nm to 1 μm.

[0097] In some specific embodiments, the average pore size in the core structure can be, for example, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, 85 nm, 90 nm, 95 nm, or 100 nm. Optionally, the average pore size in the core structure can be 10–50 nm, 20–50 nm, or 50 nm–100 nm. The average pore size in the core structure can be within a numerical range formed by using any two of the values ​​listed above as endpoints.

[0098] In some embodiments, the thickness of the shell structure is denoted as d, and the volume average particle size Dv50 of the negative electrode active material is denoted as D. Then the negative electrode active material satisfies: d≥0.1D, that is, d≥1um; optionally, the negative electrode active material satisfies: 0.1D≤d≤0.3D.

[0099] Optimizing the relationship between shell structure thickness and negative electrode active material particle size can further improve the kinetic performance of the negative electrode active material, shorten the lithium-ion transport path, and reduce the time required for lithium ions to reach the graphite surface. If the shell structure thickness is too large, the negative electrode active material accommodates more electrolyte, reducing the lithium-ion transport path but resulting in energy density loss; if the shell structure thickness is too small, the lithium-ion transport path is too long, leading to poorer kinetics.

[0100] In some specific embodiments, d may be equal to, for example, 0.1D, 0.2D, 0.3D, 0.4D, or 0.5D. Optionally, 0.1D ≤ d ≤ 0.3D. d can be within a numerical range formed by any two of the values ​​listed above as endpoints.

[0101] In some embodiments, according to the first aspect, a fourth example of the first aspect is provided, wherein the interlayer spacing d002 of the shell structure is greater than the interlayer spacing d002 of the core structure. Optionally, the interlayer spacing d002 of the core structure is 0.3355 nm to 0.3365 nm, and optionally 0.3355 nm to 0.3360 nm. Optionally, the interlayer spacing d002 of the shell structure is 0.3500 nm to 0.3800 nm, and optionally 0.3600 nm to 0.3700 nm.

[0102] Optimizing the interlayer spacing d002 of the shell and core structures can improve the kinetics of the anode material and increase the compaction density. If the interlayer spacing d002 is too large, the anode active material is more difficult to compact; if the interlayer spacing d002 is too small, lithium-ion transport is slower and the kinetics deteriorate.

[0103] In some specific embodiments, the interlayer spacing d002 of the shell structure can be, for example, 0.3355 nm, 0.3356 nm, 0.3357 nm, 0.3358 nm, 0.3359 nm, 0.3360 nm, 0.3361 nm, 0.3362 nm, 0.3363 nm, 0.3364 nm, or 0.3365 nm. Optionally, the interlayer spacing d002 of the shell structure can be 0.3355–0.3360 nm or 0.3360–0.3365 nm. The interlayer spacing d002 of the shell structure can be within a numerical range formed by using any two of the values ​​listed above as endpoints.

[0104] In some specific embodiments, the interlayer spacing d002 of the core structure can be, for example, 0.3500 nm, 0.3550 nm, 0.3600 nm, 0.3650 nm, 0.3700 nm, 0.3750 nm, or 0.3800 nm. Optionally, the interlayer spacing d002 of the core structure can be 0.3600–0.3700 nm or 0.3700–0.3800 nm. The interlayer spacing d002 of the core structure can be within a numerical range formed by using any two of the values ​​listed above as endpoints.

[0105] In some embodiments, the pore size distribution P is defined as (Pn90-Pn10) / Pn50, where Pn10 represents the pore size corresponding to a cumulative distribution percentage of pores reaching 10%, Pn50 represents the pore size corresponding to a cumulative distribution percentage of pores reaching 50%, and Pn90 represents the pore size corresponding to a cumulative distribution percentage of pores reaching 90%. The pore size distribution of the shell structure is denoted as P1, satisfying P1≤0.7, and optionally, P1 is 0.4 to 0.6; and / or, the pore size distribution of the core structure is denoted as P2, satisfying P2≤0.6, and optionally, P2 is 0.3 to 0.5.

[0106] Optimizing the pore size distribution of the shell and core structures can further improve the kinetic performance of the anode active material, shorten the lithium-ion transport path, and reduce the time required for lithium ions to reach the graphite surface. A smaller pore size distribution coefficient indicates more uniform porosity, a more uniform lithium insertion / extraction state in the anode active material, and better kinetic performance.

[0107] In some specific embodiments, P1 may be, for example, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, or 0.7. Optionally, P1 may be 0.4 to 0.6, 0.1 to 0.4, or 0.2 to 0.5. P1 can be within a numerical range formed by using any two of the values ​​listed above as endpoints.

[0108] In some specific embodiments, P2 may be, for example, 0.1, 0.2, 0.3, 0.4, 0.5, or 0.6. Optionally, P2 may be 0.3 to 0.5, 0.1 to 0.3, or 0.2 to 0.4. P2 can be within the numerical range formed by any two of the values ​​listed above as endpoints.

[0109] In some embodiments, the porosity of the negative electrode active material is 60%–80%, optionally 60%–70%.

[0110] Optimizing the porosity of the negative electrode active material can improve its kinetic properties and increase its compaction density. Excessive porosity results in lower compaction density, while insufficient porosity leads to poorer kinetic properties.

[0111] In some specific embodiments, the porosity of the negative electrode active material may be, for example, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, or 80%. Optionally, the porosity of the negative electrode active material may be 60%–70% or 70%–80%. The porosity of the negative electrode active material may be within a numerical range formed by using any two of the values ​​listed above as endpoints.

[0112] In some embodiments, the compacted density of the negative electrode active material after being pressed under a pressure of 2000 kgf is 1.6–2.0 g / cm³. 3 The concentration can be selected as 1.7–1.9 g / cm³. 3 .

[0113] The compaction density of the negative electrode active material is within the above range, which can also ensure fast charging performance.

[0114] In some specific embodiments, the compaction density of the negative electrode active material after being pressed under a pressure of 2000 kgf can be, for example, 1.6 g / cm³. 3 1.7g / cm 3 1.8g / cm 3 1.9g / cm 3 Or 2.0g / cm 3 The compaction density can be within a range defined by any two of the values ​​listed above as endpoints.

[0115] In some embodiments, the specific surface area of ​​the negative electrode active material is 20–100 m². 2 / g, which can be selected as 20-50m 2 / g.

[0116] Maintaining the specific surface area of ​​the negative electrode active material within the aforementioned range is beneficial for improving battery capacity, reducing impedance, and increasing battery charge / discharge rates. Excessive specific surface area leads to more side reactions and a shorter battery lifespan; conversely, insufficient specific surface area reduces lithium-ion transport pathways, making it difficult to guarantee kinetic performance.

[0117] In some specific embodiments, the specific surface area of ​​the negative electrode active material may be, for example, 20 m². 2 / g、25m 2 / g、30m 2 / g、35m 2 / g、40m 2 / g、45m 2 / g, 50m 2 / g、55m 2 / g、60m 2 / g、65m 2 / g、70m 2 / g、75m 2 / g、80m 2 / g、85m 2 / g、90m 2 / g、95m 2 / g or 100m 2 / g. Optionally, the specific surface area of ​​the negative electrode active material can be 20–50 m² / g. 2 / g, 30~70m 2 / g or 50m2 / g~100m 2 / g. The specific surface area of ​​the negative electrode active material can be within the range formed by taking any two of the values ​​listed above as endpoints.

[0118] In some embodiments, the reversible specific capacity of the negative electrode active material is ≥355mAh / g, and optionally, the reversible specific capacity is ≥360mAh / g.

[0119] By optimizing the compaction density and pore structure of the negative electrode active material, the electrolyte can still migrate quickly to the graphite surface under high compaction density conditions, resulting in less electrolyte polarization and a corresponding increase in reversible specific capacity, thereby improving the cycle performance of the battery.

[0120] In some specific embodiments, the reversible specific capacity of the negative electrode active material may be, for example, 355 mAh / g, 356 mAh / g, 357 mAh / g, 358 mAh / g, 359 mAh / g, 360 mAh / g, 365 mAh / g, 370 mAh / g, or 375 mAh / g. The reversible specific capacity of the negative electrode active material can be within a numerical range formed by using any two of the values ​​listed above as endpoints.

[0121] In some embodiments, the volume average particle size Dv50 of the negative electrode active material is 10–30 μm, and can be selected as 15–25 μm.

[0122] Optimizing the average particle size of the negative electrode active material is beneficial for improving compaction density and the wettability of the electrolyte to the negative electrode active material. A smaller average particle size means more exposed surface area, allowing lithium ions to reach the material surface more quickly and improving kinetic performance, but at the cost of decreased compaction density. Conversely, an excessively large average particle size can lead to bridging during slurry production, causing filtration difficulties and lengthening the lithium ion transport path, resulting in poorer kinetic performance.

[0123] In some specific embodiments, the volume average particle size Dv50 of the negative electrode active material can be, for example, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 25 μm, 26 μm, 27 μm, 28 μm, 29 μm, or 30 μm. Optionally, the volume average particle size Dv50 of the negative electrode active material can be 15–25 μm, 10–20 μm, or 20–30 μm. The volume average particle size Dv50 of the negative electrode active material can be within a numerical range formed by using any two of the values ​​listed above as endpoints.

[0124] In some embodiments, the particle size distribution of the negative electrode active material is 0.8≤(Dv90-Dv10) / Dv50≤1.8, and optionally 1.2≤(Dv90-Dv10) / Dv50≤1.5.

[0125] Optimizing the particle size distribution of the negative electrode active material is beneficial for improving the compaction density and the wettability of the electrolyte to the negative electrode active material. An excessively narrow particle size distribution leads to a mismatch in particle size distribution, resulting in poorer tap density and compaction density; an excessively wide particle size distribution increases the tortuosity of the electrode layers, reduces porosity, and consequently deteriorates the kinetic performance.

[0126] In some specific embodiments, the particle size distribution (Dv90-Dv10) / Dv50 of the negative electrode active material can be equal to 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, or 1.8. The particle size distribution (Dv90-Dv10) / Dv50 of the negative electrode active material can be within a numerical range formed by using any two of the values ​​listed above as endpoints.

[0127] In some embodiments, the negative electrode active material includes magnetic impurities. These magnetic impurities primarily originate from the raw materials, raw material calcination, catalyst 1, and catalyst 2. The magnetic impurities include at least one of Fe, Ni, Cr, and Zn. The content of the magnetic impurities is less than or equal to 1000 ppm, for example, less than or equal to 500 ppm.

[0128] Keeping the magnetic impurities in the negative electrode active material within the above-mentioned range helps to reduce self-discharge and safety risks.

[0129] In some embodiments, the negative electrode active material satisfies the condition that the shell structure is hard carbon and the core structure is soft carbon.

[0130] In some embodiments, the negative electrode active material satisfies the condition that the shell structure is soft carbon and the core structure is hard carbon.

[0131] In some embodiments, the negative electrode active material satisfies the condition that the shell structure is graphite and the core structure is hard carbon.

[0132] In some embodiments, the negative electrode active material satisfies the condition that the shell structure is hard carbon and the core structure is graphite.

[0133] Optimizing the raw materials used to form the shell and core structures facilitates the formation of a gradient pore structure, thereby improving the electrolyte wettability of the negative electrode active material and increasing its compaction density. Preferably, the negative electrode active material satisfies the condition that the shell structure is soft carbon and the core structure is hard carbon.

[0134] A second aspect of this application provides a method for preparing a negative electrode active material, comprising the following steps:

[0135] The first carbon precursor, catalyst 1 and dispersant 1 are mixed and then calcined to obtain substance A;

[0136] Substance A, catalyst 2, dispersant 2, and the second carbon precursor were mixed and calcined to obtain substance B;

[0137] Substance B is subjected to heat treatment to obtain the negative electrode active material provided in the first aspect of this application.

[0138] In the technical solution of this application embodiment, a negative electrode active material is obtained by using a first carbon precursor, a second carbon precursor, and a specific catalyst as raw materials, followed by calcination and heat treatment. This material exhibits excellent kinetic performance even under high compaction density conditions. This method is simple to operate, highly repeatable, and beneficial for large-scale industrial production.

[0139] In some embodiments, the first carbon precursor includes at least one of coal tar, coal pitch, petroleum residue, and petroleum pitch.

[0140] In some embodiments, the second carbon precursor includes at least one of water-soluble phenolic resin, glucose, and sucrose.

[0141] Optimizing the types of raw materials used to form the shell and core structures can help improve the electrolyte wettability of the negative electrode active material and increase its compaction density.

[0142] In some embodiments, catalyst 1 includes at least one of ferrocene and ferric acetylacetonate.

[0143] In some embodiments, catalyst 2 includes at least one of ferric chloride, ferrous chloride, ferric nitrate, ferrous nitrate, ferrous sulfate, ferrous sulfate, and ferric citrate.

[0144] In some embodiments, dispersant 1 includes at least one of isooctane, xylene, ethyl acetate, cyclohexanone, tetrachloroethylene, tetrahydrofuran, and benzyl alcohol.

[0145] In some embodiments, the dispersant 2 includes at least one of water, ethanol, ethylene glycol, glycerol, and oxalic acid.

[0146] By optimizing the types of catalyst 1, catalyst 2, dispersant 1, and dispersant 2, it is beneficial to promote the formation of anode active materials with gradient structures. Specifically, catalyst 1 and catalyst 2 can promote the complete cell development of the anode active material under lower temperature conditions, ensuring that the battery has high reversible specific capacity and good cycle performance. Furthermore, optimizing the types of catalyst 1, catalyst 2, dispersant 1, and dispersant 2 helps to reduce the requirements for reaction conditions. Compared with the conventional synthesis conditions of 3000℃, the energy consumption cost of the preparation method in this application is reduced. In addition, the dispersant helps to uniformly disperse the catalyst and carbon precursor, forming a homogeneous system.

[0147] In some embodiments, the particle size of catalyst 1 is 20 nm to 200 nm, and can be selected as 40 nm to 100 nm.

[0148] In some embodiments, the particle size of catalyst 2 is 0.2 μm to 2 μm, and can be selected as 0.4 μm to 1 μm.

[0149] Optimizing the particle size of catalyst 1 and catalyst 2 helps to control the average pore size of the core and shell structures. The larger the particle size of catalyst 1 and catalyst 2, the larger the average pore size of the core and shell structures in the resulting negative electrode active material, and vice versa.

[0150] In some specific embodiments, the particle size of catalyst 1 may be, for example, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, 160 nm, 170 nm, 180 nm, 190 nm, or 200 nm. Optionally, the particle size of catalyst 1 may be 20–100 nm, 40–100 nm, or 100–200 nm. The particle size of catalyst 1 may be within a numerical range formed by using any two of the values ​​listed above as endpoints.

[0151] In some specific embodiments, the particle size of catalyst 2 may be, for example, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, or 2 μm. Optionally, the particle size of catalyst 2 may be 0.2–1 μm, 0.4–1 μm, or 1 μm–2 μm. The particle size of catalyst 2 may be within a numerical range formed by using any two of the values ​​listed above as endpoints.

[0152] In some embodiments, the mass ratio of the first carbon precursor to the second carbon precursor is 9:1 to 1:1, and can be selected as 9:1 to 7:3.

[0153] In some embodiments, the mass ratio of catalyst 1 to the first carbon precursor is (0.1 to 1):1, and may be (0.2 to 0.5):1.

[0154] In some embodiments, the mass ratio of catalyst 2 to the second carbon precursor is (0.3-1):1, and can be (0.4-0.7):1.

[0155] Optimizing the mass ratio of the first and second carbon fluxes helps ensure that the active material has high energy density and kinetics. An excessively high mass ratio will result in an overly high proportion of the core structure in the negative electrode active material, leading to poor porosity, reduced electrolyte wettability, and consequently, deteriorated kinetics. Conversely, an excessively low mass ratio will result in an excessively low proportion of the core structure in the negative electrode active material, resulting in lower energy density.

[0156] Optimizing the amounts of catalyst 1 and catalyst 2 helps control the average pore size of the core and shell structures. A higher proportion of catalyst 1 and catalyst 2 results in a larger average pore size of the core and shell structures in the obtained negative electrode active material, and vice versa.

[0157] In some specific embodiments, the mass ratio of the first carbon precursor to the second carbon precursor may be, for example, 9:1, 8:1, 7:1, 6:1, 5:1, 9:2, 4:1, 7:2, 3:1, 7:3, 2:1, 7:5, or 1:1. The mass ratio of the first carbon precursor to the second carbon precursor can be within a numerical range formed by taking any two of the values ​​listed above as endpoints.

[0158] In some specific embodiments, the mass ratio of catalyst 1 to the first carbon precursor may be, for example, 0.1:1, 0.2:1, 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, or 1:1, and may be selected as (0.1-1):1 or (0.2-0.5):1. The mass ratio of catalyst 1 to the first carbon precursor may be within a numerical range formed by taking any two of the values ​​listed above as endpoints.

[0159] In some specific embodiments, the mass ratio of catalyst 2 to the second carbon precursor can be, for example, 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, or 1:1, and can be selected as (0.3 to 1.0):1 or (0.4 to 0.7):1. The mass ratio of catalyst 2 to the second carbon precursor can be within a numerical range formed by taking any two of the values ​​listed above as endpoints.

[0160] In some embodiments, the mass ratio of dispersant 1 to the first carbon precursor is (0.5-5):1, and can be selected as (1-3):1.

[0161] In some embodiments, the mass ratio of dispersant 2 to the second carbon precursor is (1-5):1, and can be selected as (2-4):1.

[0162] Optimizing the dosage of dispersant 1 and dispersant 2 helps control the average pore size of the core and shell structures. The higher the proportion of dispersant 1 and dispersant 2 added, the more uniform the average pore size of the core and shell structures in the resulting negative electrode active material.

[0163] In some specific embodiments, the mass ratio of dispersant 1 to the first carbon precursor can be, for example, 0.5:1, 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, or 5:1, and can be selected as (0.5-2):1, (2-5):1, or (1-3):1. The mass ratio of dispersant 1 to the first carbon precursor can be within a numerical range formed by taking any two of the values ​​listed above as endpoints.

[0164] In some specific embodiments, the mass ratio of dispersant 2 to the second carbon precursor can be, for example, 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, or 5:1, and can be selected as (1-2):1, (2-4):1, or (1-3):1. The mass ratio of dispersant 2 to the second carbon precursor can be within a numerical range formed by taking any two of the values ​​listed above as endpoints.

[0165] In some embodiments, in the step of preparing substance A, the calcination temperature is 600–800°C, and optionally 700–800°C.

[0166] In some embodiments, in the step of preparing substance A, the calcination time is 0.5 to 5 hours, and can be selected as 1 hour to 2 hours.

[0167] Optimizing the calcination temperature in this step helps control the average pore size of the core structure. The higher the calcination temperature, the smaller the average pore size of the core structure in the resulting negative electrode active material.

[0168] The longer the first carbon precursor is calcined, the more completely the dispersant 1 volatilizes, the more partially the catalyst 1 decomposes, and the smaller the average pore size of the core structure in the resulting negative electrode active material.

[0169] In some specific embodiments, the calcination temperature in the step of preparing substance A can be, for example, 600°C, 650°C, 700°C, 750°C, or 800°C. The calcination temperature can be within a numerical range formed by using any two of the values ​​listed above as endpoints.

[0170] In some specific embodiments, the calcination time in the step of preparing substance A can be, for example, 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, or 5h. The calcination time can be within a numerical range formed by using any two of the values ​​listed above as endpoints.

[0171] In some embodiments, in the step of preparing substance B, the calcination temperature is 800–1000°C, and optionally 800–900°C.

[0172] In some embodiments, in the step of preparing substance B, the calcination time is 2 to 5 hours, optionally 2 to 3 hours.

[0173] Optimizing the calcination temperature in this step helps control the average pore size of the shell structure. The higher the calcination temperature, the smaller the average pore size of the shell structure in the resulting negative electrode active material.

[0174] The longer the second carbon precursor is calcined, the more completely the dispersant 2 volatilizes, the more partially the catalyst 2 decomposes, and the smaller the average pore size of the shell structure in the resulting negative electrode active material.

[0175] In some specific embodiments, the calcination temperature in the step of preparing substance B can be, for example, 800°C, 850°C, 900°C, 950°C, or 1000°C. The calcination temperature can be within a numerical range formed by using any two of the values ​​listed above as endpoints.

[0176] In some specific embodiments, the calcination time in the step of preparing substance B can be, for example, 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, or 5h. The calcination time can be within a numerical range formed by using any two of the values ​​listed above as endpoints.

[0177] In some embodiments, the heat treatment temperature is 1800–2800°C, and optionally 2000–2500°C.

[0178] In some embodiments, the heat treatment time is 2 to 7 days, optionally 3 to 5 days.

[0179] Optimizing the heat treatment temperature helps control the average pore size of the core and shell structures. Higher heat treatment temperatures lead to greater catalyst volatility, resulting in smaller average pore sizes in the core and shell structures of the obtained anode active material.

[0180] As the heat treatment time increases, the average pore size of the core and shell structures gradually decreases. When the heat treatment time increases to a certain extent, the carbon structure becomes basically stable, and the pore size structure no longer changes.

[0181] In some specific embodiments, the heat treatment temperature may be, for example, 1800°C, 1900°C, 2000°C, 2100°C, 2200°C, 2300°C, 2400°C, 2500°C, 2600°C, 2700°C, or 2800°C. The heat treatment temperature may be within a numerical range formed by using any two of the values ​​listed above as endpoints.

[0182] In some specific embodiments, the heat treatment time may be, for example, 2 days, 2.5 days, 3 days, 3.5 days, 4 days, 4.5 days, 5 days, 5.5 days, 6 days, 6.5 days, or 7 days. The heat treatment time can be within a numerical range formed by using any two of the values ​​listed above as endpoints.

[0183] In some embodiments, according to the second aspect, a tenth example of the second aspect is proposed, wherein after obtaining substance A, substance A is pulverized; and / or, after obtaining substance B, substance B is pulverized; and / or, after obtaining the negative electrode active material, it is sieved.

[0184] Crushing and / or sieving can help reduce particle adhesion caused by heat treatment and achieve the target particle size.

[0185] In some specific embodiments, after obtaining substance A, substance A is pulverized to an average particle size Dv50 of 8 μm to 27 μm, optionally 12 μm to 22 μm. For example, substance A is pulverized to an average particle size Dv50 of 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 25 μm, 26 μm, or 27 μm. The average particle size Dv50 of pulverized substance A can be within a numerical range formed by using any two of the values ​​listed above as endpoints.

[0186] In some specific embodiments, after obtaining substance B, substance B is pulverized to an average particle size Dv50 of 12µm to 32µm, optionally 17µm to 27µm. For example, substance B is pulverized to an average particle size Dv50 of 12µm, 13µm, 14µm, 15µm, 16µm, 17µm, 18µm, 19µm, 20µm, 21µm, 22µm, 23µm, 24µm, 25µm, 26µm, 27µm, 28µm, 29µm, 30µm, 31µm, or 32µm. The average particle size Dv50 of pulverized substance B can be within a numerical range formed by using any two of the values ​​listed above as endpoints.

[0187] In some specific embodiments, after obtaining the negative electrode active material, it is sieved to a Dv50 of 10µm to 30µm, optionally 15µm to 25µm. For example, the Dv50 is sieved to 10µm, 11µm, 12µm, 13µm, 14µm, 15µm, 16µm, 17µm, 18µm, 19µm, 20µm, 21µm, 22µm, 23µm, 24µm, 25µm, 26µm, 27µm, 28µm, 29µm, or 30µm. The sieved Dv50 can be within the range formed by any two of the values ​​listed above as endpoints.

[0188] In some embodiments, the heat treatment may be performed in a graphitization furnace.

[0189] In some embodiments, after heat treatment, the resulting negative electrode active material is allowed to cool naturally.

[0190] A third aspect of this application provides a secondary battery, including a negative electrode. The negative electrode includes the negative electrode active material described in the first aspect of this application or the negative electrode active material obtained according to the preparation method described in the second aspect of this application.

[0191] In the technical solutions of this application embodiment, since the negative electrode active material of the first aspect of this application or the negative electrode active material obtained according to the preparation method of the second aspect of this application is used, the secondary battery of this application has improved energy density and can achieve fast charging.

[0192] [Rechargeable Battery]

[0193] A rechargeable battery is a battery that can be recharged after it has been discharged, allowing the active materials to be reactivated and the battery to continue to be used.

[0194] Typically, a secondary battery includes a positive electrode, a negative electrode, a separator, and an electrolyte. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The separator, positioned between the positive and negative electrodes, serves as a barrier. The electrolyte, located between the positive and negative electrodes, conducts ions.

[0195] [Negative electrode plate]

[0196] In a secondary battery, the negative electrode typically includes a negative current collector and a negative electrode film layer disposed on the negative current collector, wherein the negative electrode film layer includes the negative electrode active material provided in this application.

[0197] The negative electrode current collector can be a conventional metal foil or a composite current collector (for example, a metal material can be disposed on a polymer substrate to form a composite current collector). As an example, the negative electrode current collector can be a copper foil.

[0198] The negative electrode film layer may also optionally include binders, conductive agents, and other optional additives.

[0199] As an example, the conductive agent can be one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0200] As an example, the adhesive may be one or more of styrene-butadiene rubber (SBR), water-based acrylic resin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), polyvinyl alcohol (PVA), and polyvinyl butyral (PVB).

[0201] As an example, other optional additives may be thickeners and dispersants (such as sodium carboxymethyl cellulose CMC-Na), PTC thermistor materials, etc.

[0202] [Positive electrode plate]

[0203] In a secondary battery, the positive electrode typically includes a positive current collector and a positive electrode film layer disposed on the positive current collector, the positive electrode film layer including a positive active material.

[0204] The positive electrode current collector can be a conventional metal foil or a composite current collector (a composite current collector can be formed by setting metal material on a polymer substrate). As an example, the positive electrode current collector can be aluminum foil.

[0205] The specific type of positive electrode active material is not limited. Any active material known in the art that can be used as the positive electrode of a secondary battery can be used. Those skilled in the art can select according to actual needs.

[0206] As an example, the positive electrode active material may include, but is not limited to, one or more of lithium transition metal oxides, lithium-containing phosphates with an olivine structure, and their respective modified compounds. Examples of lithium transition metal oxides may include, but are not limited to, one or more of lithium cobalt oxides, lithium nickel oxides, lithium manganese oxides, lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, lithium nickel cobalt manganese oxides, lithium nickel cobalt aluminum oxides, and their modified compounds. Examples of lithium-containing phosphates with an olivine structure may include, but are not limited to, one or more of lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, lithium manganese iron phosphate and carbon composites, and their modified compounds. All of these materials are commercially available.

[0207] In some embodiments, the modifying compounds for the above-mentioned materials may be those used for doping modification and / or surface coating modification of the materials.

[0208] The positive electrode film layer may also optionally include binders, conductive agents, and other optional additives.

[0209] As an example, the conductive agent can be one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, Super P(SP), graphene, and carbon nanofibers.

[0210] As an example, the adhesive may be one or more of styrene-butadiene rubber (SBR), water-based acrylic resin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), polyacrylic acid (PAA), carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), and polyvinyl butyral (PVB).

[0211] [Isolation membrane]

[0212] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0213] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0214] Electrolyte

[0215] A secondary battery may include an electrolyte, which acts as a conductor of ions between the positive and negative electrodes. The electrolyte may include an electrolyte salt and a solvent.

[0216] As an example, the electrolyte salt may be selected from one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0217] As an example, the solvent may be selected from one or more of ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0218] In some embodiments, the electrolyte also includes additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and additives that improve battery low-temperature performance.

[0219] In some embodiments, the secondary battery of this application is a lithium-ion secondary battery.

[0220] Secondary batteries can be prepared according to conventional methods in the field, such as winding (or stacking) the positive electrode, separator, and negative electrode in sequence, so that the separator is placed between the positive electrode and the negative electrode to play a role in isolation, thus obtaining a battery cell. The battery cell is placed in an outer package, electrolyte is injected and the package is sealed to obtain a secondary battery.

[0221] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. Figure 1 This is an example of a square-structured secondary battery 5.

[0222] In some embodiments, the secondary battery may include an outer packaging. The outer packaging is used to encapsulate the positive electrode, the negative electrode, and the electrolyte.

[0223] In some embodiments, refer to Figure 2 The outer packaging may include a shell 51 and a cover 53. The shell 51 may include a bottom plate and side plates connected to the bottom plate, the bottom plate and side plates forming a receiving cavity. The shell 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed on the opening to close the receiving cavity.

[0224] The positive electrode, negative electrode, and separator can be formed into an electrode assembly 52 by a winding or stacking process. The electrode assembly 52 is encapsulated in the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 can contain one or more electrode assemblies 52, which can be adjusted according to requirements.

[0225] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0226] In some embodiments, secondary batteries can be assembled into battery modules, and the number of secondary batteries contained in a battery module can be multiple, the specific number of which can be adjusted according to the application and capacity of the battery module.

[0227] Figure 3 This is an example of a battery module 4. In battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other way. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0228] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0229] 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.

[0230] Figure 4 and Figure 5 This is an example of a battery pack 1. The battery pack 1 may include a battery compartment and multiple battery modules 4 disposed within the battery compartment. The battery compartment includes an upper housing 2 and a lower housing 3, with the upper housing 2 covering the lower housing 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery compartment.

[0231] [Electrical appliances]

[0232] This application also provides an electrical device comprising at least one of the aforementioned secondary battery, battery module, and battery pack. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device or as an energy storage unit for the device. The electrical device can be, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0233] Electrical devices can be equipped with secondary batteries, battery modules, or battery packs depending on their usage requirements.

[0234] Figure 6 This is an example device. The 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 in its secondary batteries, a battery pack or battery module can be used.

[0235] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0236] Because the negative electrode active material of the first aspect of this application or the negative electrode active material obtained according to the preparation method of the second aspect of this application is used, the electrical device of this application has improved energy density and can achieve fast charging.

[0237] The beneficial effects of this application are further illustrated below with reference to the embodiments.

[0238] Example

[0239] To make the technical problems, technical solutions, and beneficial effects solved by this application clearer, the following will provide a more detailed description in conjunction with the embodiments and accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit this application or its applications. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this application.

[0240] All materials used in the embodiments of this application are commercially available.

[0241] Preparation of negative electrode active materials

[0242] Example 1

[0243] Coal tar, catalyst 1 acetylacetone iron (particle size 40 nm), and ethyl acetate were mixed evenly at a mass ratio of 1:0.2:1 and calcined at 700℃ for 1 h. After pulverizing to an average particle size Dv50 of 20 μm, substance A was obtained. Substance A was then impregnated in an aqueous solution of phenolic resin (phenolic resin:coal tar mass ratio 7:2) containing 300 nm ferric chloride, where the phenolic resin:ferric chloride:water mass ratio was 1:0.3:2. The mixture was calcined at 800℃ for 2 h and pulverized to an average particle size Dv50 of 27 μm to obtain substance B. Substance B was heat-treated at 2000℃ for 5 days in a graphitization furnace. After natural cooling, it was sieved to an average particle size Dv50 of 25 μm to obtain a negative electrode active material with a gradient pore structure. A schematic diagram of the structure of this negative electrode active material is shown below. Figure 7 As shown. A cross-sectional TEM image of the negative electrode active material is shown below. Figure 8 As shown.

[0244] Example 2-21

[0245] Examples 2-21 are performed according to the method described in Example 1, except that the parameters listed in Table 1 below are different from those in Example 1.

[0246] Comparative Examples 1-4

[0247] The method described in Example 8 is followed, except that the parameters listed in Table 1 below are different from those in Example 8.

[0248] Comparative Example 5

[0249] Coal tar was calcined at 700℃ for 1 hour, pulverized to an average particle size Dv50 of 20 μm, and then heat-treated at 3000℃ for 7 days in a graphitization furnace. After natural cooling, the calcined material was sieved to remove large, adherent particles until the average particle size Dv50 was 20 μm, yielding substance A. Substance A was mixed with petroleum asphalt at a ratio of 20:1 and calcined at 1100℃ for 2 hours to obtain substance B, which is the negative electrode active material.

[0250] Table 1

[0251]

[0252]

[0253]

[0254]

[0255]

[0256]

[0257] Using the negative electrode active materials prepared in the above examples and comparative examples, half-cells and secondary cells were prepared according to the general preparation method described below.

[0258] Preparation of half-cell

[0259] The prepared negative electrode active material, conductive agent Super P, and binder (PVDF) were mixed with solvent NMP (N-methylpyrrolidone) at a mass ratio of 91.6:1.8:6.6 and stirred until homogeneous. The mixture was then coated onto a 6 μm copper foil and vacuum dried at 120 °C for 12 h to prepare a negative electrode sheet. The sheet was then rolled on a roller press until the compacted density reached 1.5 g / cm³. 3 The negative electrode is punched into a small disc, which is the working electrode. A lithium sheet is used as the counter electrode, and a 12μm polypropylene film is used as the separator. LiPF6 solute is dissolved in ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) (1:1:1) solvent to form the electrolyte. The mixture is assembled into a CR2032 button cell to form a half cell.

[0260] Preparation of secondary batteries

[0261] LiNi, the positive electrode active material 0.8 Mn 0.1 Co 0.1 O2, conductive carbon black, and PVDF were mixed at a weight ratio of 96:2.5:1.5. An appropriate amount of N-methylpyrrolidone was added, and the mixture was stirred until homogeneous to obtain a positive electrode slurry. The positive electrode slurry was coated onto aluminum foil and dried to obtain a positive electrode sheet. The loading of the positive electrode active material on the positive electrode sheet was 0.02 g / cm³. 2 .

[0262] The prepared negative electrode active material was mixed with conductive carbon black, sodium carboxymethyl cellulose, and styrene-butadiene rubber in a weight ratio of 96.5:0.8:1.2:1.5. An appropriate amount of deionized water was added, and the mixture was stirred until homogeneous to obtain a negative electrode slurry. The negative electrode slurry was coated onto a 6 μm copper foil and dried to obtain a negative electrode sheet. The loading of the negative electrode active material on the negative electrode sheet was 0.012 g / cm³. 2 .

[0263] Ethyl carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1. LiPF6 was then uniformly dissolved in this solution to obtain the electrolyte. The concentration of LiPF6 in the electrolyte was 1 mol / L.

[0264] Using a polypropylene film as the separator, the prepared positive electrode, separator, and negative electrode are arranged in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The mixture is then wound into shape and packaged in an aluminum-plastic bag. Electrolyte is injected, and after encapsulation, capacity is determined to produce a secondary battery.

[0265] Characterization and testing of negative electrode active materials

[0266] 1. Reversible specific capacity testing of negative electrode active materials

[0267] After the above half-cell was placed at 25℃ for 6 hours, it was successively discharged at a constant current rate of 0.05C (1C is the theoretical current required to fully charge the battery in 1 hour) to 5.0mV, 50μA to 5.0mV, and 10μA to 5.0mV. After resting for 10 minutes, it was charged at a constant current rate of 0.1C to 2.0V. The constant current charging capacity was recorded as the reversible specific capacity of the negative electrode active material. The test results are shown in Table 2 below.

[0268] 2. Average pore size test of pores in the shell structure of negative electrode active materials

[0269] Referring to the test method of transmission electron microscopy analysis in JY / T0581-2020, a transmission electron microscope (JOELJEM-2100 Plus) was used to select n1≥20 particles, and n2≥20 selected areas (1um*9um) were made for the shell structure of each particle. The size of the pores in the selected areas was measured, and the average pore diameter was calculated through statistical analysis. The test results are shown in Table 2 below.

[0270] 3. Measurement of the average pore size in the core structure of negative electrode active materials

[0271] Following the testing method of transmission electron microscopy analysis in JY / T0581-2020, a transmission electron microscope (JOELJEM-2100 Plus) was used to select n1≥20 particles. For each particle, a selected area (1µm*9µm) with n2≥20 particles was created for its core structure. The pore size within the selected area was measured, and the average pore size was calculated through statistical analysis. The test results are shown in Table 2 below.

[0272] 4. Thickness test of the shell structure of the negative electrode active material

[0273] Referring to the test method of transmission electron microscopy analysis in JY / T0581-2020, a transmission electron microscope (such as JOEL JEM-2100 Plus) was used to select n1≥20 particles, and a selected area (1um*9um) with n2≥20 was made for the shell structure of each particle. The thickness of the selected area was measured. The test results are shown in Table 2 below.

[0274] 5. Volume average particle size (Dv50) test of negative electrode active material

[0275] Referring to GB / T 19077-2016 Particle Size Analysis by Laser Diffraction, the volume distribution average particle size Dv50 of the negative electrode active material was measured using a Mastersizer 3000 laser particle size analyzer. Dv50 represents the particle size corresponding to a cumulative volume distribution percentage of 50%. The test results are shown in Table 2 below.

[0276] 6. Pore size distribution of the shell structure of the negative electrode active material (P1 test)

[0277] Referring to the test method of transmission electron microscopy analysis in JY / T0581-2020, a transmission electron microscope (JOELJEM-2100 Plus) was used to select n1≥20 particles. For each particle's shell structure, n2≥20 selected areas (1µm*9µm in size) were created. The pore size within the selected areas was measured, and the pore size distribution P1 was obtained through statistical analysis. The pore size distribution P1 is calculated as (Pn90-Pn10) / Pn50, where Pn10 represents the pore size corresponding to a cumulative percentage distribution of pores reaching 10%, Pn50 represents the pore size corresponding to a cumulative percentage distribution of pores reaching 50%, and Pn90 represents the pore size corresponding to a cumulative percentage distribution of pores reaching 90%. The test results are shown in Table 2 below.

[0278] 7. P2 test of pore size distribution of the core structure of the negative electrode active material

[0279] Referring to the test method of transmission electron microscopy analysis in JY / T0581-2020, a transmission electron microscope (JOELJEM-2100 Plus) was used to select n1≥20 particles, and a selected area (size 1um*9um) of n2≥20 was made for the core structure of each particle. The size of the pores in the selected area was measured, and the pore size distribution P2 was obtained through statistical analysis. The pore size distribution P2 is (Pn90-Pn10) / nP50, where Pn10 represents the pore size corresponding to the cumulative distribution percentage of the number of pores reaching 10%, Pn50 represents the pore size corresponding to the cumulative distribution percentage of the number of pores reaching 50%, and Pn90 represents the pore size corresponding to the cumulative distribution percentage of the number of pores reaching 90%. The test results are shown in Table 2 below.

[0280] 8. Porosity testing of negative electrode active materials

[0281] The porosity of the negative electrode active material was tested according to the true density method in GB / T 24586-2009. The test results are shown in Table 2 below.

[0282] 9. Measurement of interlayer spacing d002 of the shell structure of the negative electrode active material

[0283] Following the testing method of transmission electron microscopy analysis in JY / T0581-2020, a transmission electron microscope (JOELJEM-2100 Plus) was used to select n1≥20 particles. For each particle, a selected area (1µm*9µm) with n2≥20 particles was created for its shell structure. The size of the lattice fringes within the selected area was measured, and the interplanar spacing d002 was obtained through statistical analysis. The test results are shown in Table 2 below.

[0284] 10. Measurement of interlayer spacing d002 of the core structure of negative electrode active materials

[0285] Following the testing method of transmission electron microscopy analysis in JY / T0581-2020, a transmission electron microscope (JOELJEM-2100 Plus) was used to select n1≥20 particles. For each particle, a selected area (1µm*9µm) with n2≥20 particles was created for its core structure. The size of the lattice fringes within the selected area was measured, and the interplanar spacing d002 was obtained through statistical analysis. The test results are shown in Table 2 below.

[0286] 11. Compacted density test of negative electrode active material after being pressed under a pressure of 2000 kgf

[0287] The compacted density of the powder was tested according to GB / T 24533-2009, the compaction density test method. The test results are shown in Table 2 below.

[0288] 12. Specific surface area test of negative electrode active materials

[0289] The specific surface area of ​​the powder was measured according to the BET method for gas adsorption in GB / T 19587-2004. The test results are shown in Table 2 below.

[0290] 13. Particle size distribution test of negative electrode active material

[0291] Referring to GB / T 19077-2016 Particle Size Analysis by Laser Diffraction, the volume distribution particle sizes Dv10, Dv50, and Dv90 of the negative electrode active material were measured using a Mastersizer 3000 laser particle size analyzer. Dv10 represents the particle size corresponding to a cumulative volume distribution percentage of 10%, Dv50 represents the particle size corresponding to a cumulative volume distribution percentage of 50%, and Dv90 represents the particle size corresponding to a cumulative volume distribution percentage of 90%. The test results are shown in Table 2 below.

[0292] 14. Testing of the types and contents of magnetic impurities in negative electrode active materials

[0293] The contents of Fe, Ni, Cr, and Zn were determined according to EPA 6010D-2014 Elemental Analysis - Inductively Coupled Plasma Emission Spectrometry. The test results are shown in Table 2 below.

[0294] Table 2

[0295]

[0296]

[0297]

[0298]

[0299]

[0300] Electrical performance characterization of secondary batteries

[0301] 1. Fast charging performance test:

[0302] The secondary batteries prepared in each embodiment and comparative example were placed at room temperature (25°C) and charged to 4.25V using a constant current rate of 0.33C. Then, they were charged to 0.05C using a constant voltage rate, allowed to rest for 5 minutes, and then discharged to 2.5V using a constant current rate of 0.33C. The constant current discharge capacity was recorded as the initial capacity C0. The batteries were then sequentially charged to 4.25V (full cell potential) or 0mV (negative electrode cutoff potential) using constant current rates of 0.5C0, 1C0, 1.5C0, 2C0, 2.5C0, 3C0, and 3.5C0 (reaching either condition indicates completion of charging). After each charging, the batteries were discharged to 2.5V using a constant current rate of 0.33C0. At 10% SOC (State of Charge), the corresponding negative electrode potential at different charging rates was recorded. Rate-negative electrode potential curves at different SOCs were plotted, and linear fitting was performed to obtain the charging rate corresponding to a negative electrode potential of 0mV at different SOCs, denoted as CX (x = 2~8). The charging time T (min) for the secondary battery to charge from 10% SOC to 80% SOC is calculated using the formula (1 / C2+1 / C3+1 / C4+1 / C5+1 / C6+1 / C7+1 / C8)×0.1×60. A shorter time indicates better fast-charging performance. The test results are shown in Table 3 below.

[0303] 2. Ultimate compaction density test of negative electrode sheet:

[0304] The negative electrode sheets prepared in each embodiment and comparative example were placed on a roller press for rolling experiments. The roller gap and rolling pressure were adjusted until the electrode sheet could not be pressed down or the edge burst. The thickness of the electrode sheet was measured with a micrometer along the direction perpendicular to the rolling direction, and 12 thicknesses were recorded and the average value was taken as h1 (um). The rolled electrode sheet was then punched to 1540.25 mm using a punching machine. 2Small circular pieces were collected and weighed on a 0.1% balance. The average weight of 12 small circular pieces was recorded as M1 (g). Copper foil without the negative electrode active material was taken, and its thickness was measured with a micrometer. The average thickness of 12 measured thicknesses was recorded as h0 (µm). The foil was then punched to a thickness of 1540.25 mm using a punching machine. 2 Take small round pieces and weigh them on a 0.1% balance. Record the average weight of the 12 pieces, which is M0 (g). According to the formula (M1-M0) / 1540.25*(h1-h0)*10 6 The ultimate compaction density of the negative electrode was calculated. A higher value indicates a higher energy density of the battery. The test results are shown in Table 3 below.

[0305] Table 3

[0306]

[0307]

[0308] As shown in Tables 2 and 3, the ultimate compaction density of the negative electrode sheet containing the negative electrode active material of this application is comparable to that of the negative electrode sheets in Comparative Examples 1-5. However, at such a high compaction density, the charging time of the secondary battery of this application is significantly lower than that of the secondary batteries corresponding to Comparative Examples 1-5. This demonstrates that the negative electrode active material of this application can maintain excellent kinetic performance under high compaction density conditions, thus achieving the goal of rapid battery charging.

[0309] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A negative electrode active material, characterized in that, The negative electrode active material includes a core structure and a shell structure disposed on the surface of the core structure. Both the core structure and the shell structure have pores, and the average pore diameter of the pores in the shell structure is greater than the average pore diameter of the pores in the core structure. The average pore diameter of the pores in the shell structure is 200 nm to 1000 nm. The average pore diameter of the pores in the shell structure is denoted as D1, and the average pore diameter of the pores in the core structure is denoted as D2. Then, 5 ≤ D1 / D2 ≤ 50.

2. The negative electrode active material according to claim 1, characterized in that, 20≤D1 / D2≤50.

3. The negative electrode active material according to claim 1, characterized in that, The average pore diameter in the shell structure is 200 nm to 500 nm; and / or, The average pore size in the core structure is 10 nm to 100 nm.

4. The negative electrode active material according to claim 1, characterized in that, The average pore size in the core structure is 20 nm to 50 nm.

5. The negative electrode active material according to claim 1, characterized in that, Let the thickness of the shell structure be d, and let the volume average particle size Dv50 of the negative electrode active material be D. Then the negative electrode active material satisfies: d≥0.1D.

6. The negative electrode active material according to claim 1, characterized in that, The thickness of the shell structure is denoted as d, where d ≥ 1 μm.

7. The negative electrode active material according to claim 5, characterized in that, The negative electrode active material satisfies: 0.1D ≤ d ≤ 0.3D.

8. The negative electrode active material according to claim 1, characterized in that, The interlayer spacing of the shell structure d 002 is greater than the interlayer spacing of the crystal planes of the core structure. d 002.

9. The negative electrode active material according to claim 1, characterized in that, The interlayer spacing of the core structure d 002 is 0.3355nm~0.3365nm.

10. The negative electrode active material according to claim 1, characterized in that, The interlayer spacing of the core structure d 002 is 0.3355nm~0.3360nm.

11. The negative electrode active material according to claim 1, characterized in that, The interlayer spacing of the shell structure d 002 is 0.3500nm~0.3800nm.

12. The negative electrode active material according to claim 1, characterized in that, The interlayer spacing of the shell structure d 002 is 0.3600nm~0.3700nm.

13. The negative electrode active material according to claim 1, characterized in that, The pore size distribution P is defined as (Pn90 - Pn10) / Pn50, where Pn10 represents the pore size corresponding to a cumulative distribution percentage of pores reaching 10%, Pn50 represents the pore size corresponding to a cumulative distribution percentage of pores reaching 50%, and Pn90 represents the pore size corresponding to a cumulative distribution percentage of pores reaching 90%. in, The pore size distribution of the shell structure is denoted as P1, satisfying P1≤0.7; and / or, The pore size distribution of the nuclear structure is denoted as P2, which satisfies P2≤0.

6.

14. The negative electrode active material according to claim 13, characterized in that, P1 is 0.4~0.

6.

15. The negative electrode active material according to claim 13, characterized in that, P2 is 0.3~0.

5.

16. The negative electrode active material according to claim 1, characterized in that, The porosity of the negative electrode active material is 60%~80%.

17. The negative electrode active material according to claim 1, characterized in that, The porosity of the negative electrode active material is 60%~70%.

18. The negative electrode active material according to claim 1, characterized in that, The compacted density of the negative electrode active material after being pressed under a pressure of 2000 kgf is 1.6~2.0 g / cm³. 3 .

19. The negative electrode active material according to claim 1, characterized in that, The compacted density of the negative electrode active material after being pressed under a pressure of 2000 kgf is 1.7~1.9 g / cm³. 3 .

20. The negative electrode active material according to claim 1, characterized in that, The specific surface area of ​​the negative electrode active material is 20~100m². 2 / g.

21. The negative electrode active material according to claim 1, characterized in that, The specific surface area of ​​the negative electrode active material is 20~50m². 2 / g.

22. The negative electrode active material according to claim 1, characterized in that, The reversible specific capacity of the negative electrode active material is ≥ 355 mAh / g.

23. The negative electrode active material according to claim 1, characterized in that, The reversible specific capacity of the negative electrode active material is ≥ 360 mAh / g.

24. The negative electrode active material according to claim 1, characterized in that, The volume average particle size Dv50 of the negative electrode active material is 10μm~30μm.

25. The negative electrode active material according to claim 1, characterized in that, The volume average particle size Dv50 of the negative electrode active material is 15μm~25μm.

26. The negative electrode active material according to claim 1, characterized in that, The particle size distribution of the negative electrode active material is 0.8 ≤ (Dv90-Dv10) / Dv50 ≤ 1.

8.

27. The negative electrode active material according to claim 1, characterized in that, The particle size distribution of the negative electrode active material is 1.2 ≤ (Dv90-Dv10) / Dv50 ≤ 1.

5.

28. The negative electrode active material according to claim 1, characterized in that, The negative electrode active material includes magnetic impurities, which include at least one of Fe, Ni, Cr, and Zn.

29. The negative electrode active material according to claim 28, characterized in that, The content of the magnetic impurities is less than or equal to 1000 ppm.

30. The negative electrode active material according to any one of claims 1 to 29, characterized in that, The negative electrode active material satisfies any one of the following conditions (1)-(4): (1) The shell structure is hard carbon, and the core structure is soft carbon; (2) The shell structure is soft carbon, and the core structure is hard carbon; (3) The shell structure is graphite and the core structure is hard carbon; (4) The shell structure is hard carbon and the core structure is graphite.

31. The method for preparing the negative electrode active material according to any one of claims 1 to 30, characterized in that, Includes the following steps: The first carbon precursor, catalyst 1 and dispersant 1 are mixed and then calcined to obtain substance A; The substance A, catalyst 2, dispersant 2, and second carbon precursor are mixed and then calcined to obtain substance B; The substance B is subjected to heat treatment to obtain a negative electrode active material; The negative electrode active material includes a core structure and a shell structure disposed on the surface of the core structure. Both the core structure and the shell structure have pores, and the ratio of the average pore diameter in the shell structure to the average pore diameter in the core structure is greater than or equal to 5 and less than or equal to 50.

32. The preparation method according to claim 31, characterized in that, The first carbon precursor includes at least one of coal tar, coal pitch, petroleum residue, and petroleum pitch.

33. The preparation method according to claim 31, characterized in that, The second carbon precursor includes at least one of water-soluble phenolic resin, glucose, and sucrose.

34. The preparation method according to claim 31, characterized in that, The preparation method satisfies at least one of the following conditions (1)-(4): (1) The catalyst 1 includes at least one of ferrocene and ferric acetylacetone; (2) The catalyst 2 includes at least one of ferric chloride, ferrous chloride, ferric nitrate, ferrous nitrate, ferric sulfate, ferrous sulfate, and ferric citrate; (3) The dispersant 1 includes at least one of isooctane, xylene, ethyl acetate, cyclohexanone, tetrachloroethylene, tetrahydrofuran, and benzyl alcohol; (4) The dispersant 2 includes at least one of water, ethanol, ethylene glycol, glycerol and oxalic acid.

35. The preparation method according to claim 31, characterized in that, The particle size of catalyst 1 is 20 nm to 200 nm; and / or the particle size of catalyst 2 is 0.2 μm to 2 μm.

36. The preparation method according to claim 31, characterized in that, The particle size of catalyst 1 is 40 nm to 100 nm.

37. The preparation method according to claim 31, characterized in that, The particle size of the catalyst 2 is 0.4 μm to 1 μm.

38. The preparation method according to claim 31, characterized in that, The mass ratio of the first carbon precursor to the second precursor is 9:1 to 1:1; and / or, The mass ratio of catalyst 1 to the first carbon precursor is (0.1~1):1; and / or, The mass ratio of catalyst 2 to the second carbon precursor is (0.3~1):

1.

39. The preparation method according to claim 38, characterized in that, The mass ratio of the first carbon precursor to the second precursor is 9:1 to 7:

3.

40. The preparation method according to claim 38, characterized in that, The mass ratio of catalyst 1 to the first carbon precursor is (0.2~0.5):

1.

41. The preparation method according to claim 38, characterized in that, The mass ratio of catalyst 2 to the second carbon precursor is (0.4~0.7):

1.

42. The preparation method according to claim 31, characterized in that, The mass ratio of the dispersant 1 to the first carbon precursor is (0.5~5):1; and / or, The mass ratio of the dispersant 2 to the second carbon precursor is (1~5):

1.

43. The preparation method according to claim 42, characterized in that, The mass ratio of the dispersant 1 to the first carbon precursor is (1~3):

1.

44. The preparation method according to claim 42, characterized in that, The mass ratio of the dispersant 2 to the second carbon precursor is (2~4):

1.

45. The preparation method according to claim 41, characterized in that, In the step of preparing substance A, the calcination temperature is 600~800℃; and / or, In the step of preparing substance A, the calcination time is 0.5~5h.

46. ​​The preparation method according to claim 45, characterized in that, In the step of preparing substance A, the calcination temperature is 700~800℃.

47. The preparation method according to claim 45, characterized in that, In the step of preparing substance A, the calcination time is 1h to 2h.

48. The preparation method according to claim 31, characterized in that, In the step of preparing substance B, the calcination temperature is 800~1000℃; and / or, In the step of preparing substance B, the calcination time is 2-5 hours.

49. The preparation method according to claim 48, characterized in that, In the step of preparing substance B, the calcination temperature is 800~900℃.

50. The preparation method according to claim 48, characterized in that, In the step of preparing substance B, the calcination time is 2-3 hours.

51. The preparation method according to claim 31, characterized in that, The heat treatment temperature is 1800~2800℃; and / or, The heat treatment time is 2 to 7 days.

52. The preparation method according to claim 51, characterized in that, The heat treatment temperature is 2000~2500℃.

53. The preparation method according to claim 51, characterized in that, The heat treatment time is 3 to 5 days.

54. The preparation method according to claim 31, characterized in that, After obtaining substance A, substance A is pulverized; and / or, After obtaining substance B, substance B is pulverized; and / or, After obtaining the negative electrode active material, it is sieved.

55. A secondary battery, comprising a negative electrode, characterized in that, The negative electrode sheet comprises the negative electrode active material according to any one of claims 1-30 or the negative electrode active material obtained by the preparation method according to any one of claims 31-54.

56. An electrical device, characterized in that, Includes the secondary battery as described in claim 55.

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