Negative electrode active material, preparation method therefor, secondary battery, and electric apparatus

Abstract

The present application relates to the field of lithium batteries, and provides a negative electrode active material, a preparation method therefor, a secondary battery, and an electric apparatus. The secondary battery comprises a negative electrode sheet, the negative electrode sheet comprising a negative electrode film layer, the negative electrode film layer comprising a negative electrode active material, the negative electrode active material comprising a carbon core and a nitrogen-doped porous carbon layer coated on a surface of the carbon core, wherein the nitrogen-doped porous carbon layer comprises pyrrolic nitrogen, pyridinic nitrogen, and mesopores; a volume percentage of the mesopores in a total pore volume of the negative electrode active material is 40% to 90%; a mass percentage of a total nitrogen content in the negative electrode active material is 0.4% to 3%; and a mass proportion of both pyrrolic nitrogen and pyridinic nitrogen in the total nitrogen content of the negative electrode active material is 30% to 80%. The secondary battery exhibits good fast-charging performance.

Description

Negative electrode active materials and their preparation methods, secondary batteries and electrical devices

[0001] Cross-references

[0002] This application claims priority to Chinese Patent Application No. 202510198804.5, filed on February 21, 2025, entitled “Negative Electrode Active Material and Preparation Method Thereof, Secondary Battery and Electrical Device”, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to the field of lithium battery technology, and in particular to a negative electrode active material and its preparation method, a secondary battery and an electrical device. Background Technology

[0004] In recent years, rechargeable batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and many other fields. As the application scope of batteries becomes increasingly wide, the performance requirements for rechargeable batteries are becoming increasingly stringent.

[0005] Currently, the fast-charging performance of rechargeable batteries still needs further improvement. Summary of the Invention

[0006] This application is made in view of the above-mentioned issues, and its purpose is to provide a negative electrode active material and its preparation method, a secondary battery and an electrical device, which can effectively improve the fast charging performance of the secondary battery.

[0007] The first aspect of this application provides a secondary battery including a negative electrode sheet, the negative electrode sheet including a negative electrode film layer.

[0008] The negative electrode film layer includes a negative electrode active material, which includes a carbon core and a nitrogen-doped porous carbon layer covering the surface of the carbon core. The nitrogen-doped porous carbon layer includes pyrrole nitrogen, pyridine nitrogen, and mesopores.

[0009] Among them, mesopores account for 40%-90% of the total pore volume of the negative electrode active material.

[0010] The total nitrogen content in the negative electrode active material accounts for 0.4%-3% by mass, and the combined mass of pyrrole nitrogen and pyridine nitrogen accounts for 30%-80% of the total nitrogen content in the negative electrode active material.

[0011] In the secondary battery provided in this application, the introduced negative electrode active material achieves both high mesoporous content and high nitrogen doping, and the high nitrogen doping mainly exists in the form of pyrrole nitrogen and pyridine nitrogen. Therefore, the high mesoporous content effectively improves the wettability of the negative electrode active material, allowing solvated lithium ions to reach the surface of the carbon core more efficiently. The high nitrogen doping enhances the adsorption capacity of the negative electrode active material for lithium ions, and the rich pyrrole nitrogen and pyridine nitrogen improve the desolvation rate of solvated lithium ions and the lithium ion diffusion rate. The combined effect of these three factors accelerates the kinetic process during the charging of the secondary battery and effectively improves the fast charging performance of the secondary battery.

[0012] In any embodiment, the contact angle of the negative electrode active material is 10°-38.5°.

[0013] The aforementioned negative electrode active material has a small contact angle with the electrolyte and good wettability, which is beneficial for improving the fast charging capability and cycle performance of secondary batteries.

[0014] In any embodiment, the nitrogen-doped porous carbon layer contains micropores and macropores, and the micropores, macropores, and mesopores are at least partially interconnected. The total volume of the micropores and macropores accounts for 10%-60% of the total pore volume of the negative electrode active material. By ensuring that the micropores, macropores, and mesopores are at least partially interconnected, and by controlling the total volume of the micropores and macropores to account for 10%-60% of the total pore volume of the negative electrode active material, the pore structure of the material can be effectively improved in conjunction with the mesopores. This is beneficial for improving the contact angle of the negative electrode active material, enhancing wettability, and improving the fast-charging performance of the battery.

[0015] In any embodiment, the mass percentage of pyrrole nitrogen in the total nitrogen content of the negative electrode active material is 12%-40%; and / or, the mass percentage of pyridine nitrogen in the total nitrogen content of the negative electrode active material is 15%-45%.

[0016] By controlling the content of pyrrole nitrogen and pyridine nitrogen within the aforementioned high range, it is beneficial to improve the desolvation rate of solvated lithium ions and the lithium ion diffusion rate, thereby enhancing the fast-charging performance of secondary batteries.

[0017] In any embodiment, the combined mass percentage of pyrrole nitrogen and pyridine nitrogen in the negative electrode active material is 0.3%-0.9%; and / or,

[0018] The mass percentage of pyrrole nitrogen in the negative electrode active material is 0.1%-0.4%; and / or,

[0019] The mass percentage of pyridine nitrogen in the negative electrode active material is 0.2%-0.5%.

[0020] By controlling the content of pyrrole nitrogen and pyridine nitrogen within the aforementioned high range, it is beneficial to improve the desolvation rate of solvated lithium ions and the lithium ion diffusion rate, thereby enhancing the fast-charging performance of secondary batteries.

[0021] In any embodiment, the nitrogen-doped porous carbon layer comprises graphitic nitrogen and nitrogen oxides; wherein the mass percentage of graphitic nitrogen in the total nitrogen content of the negative electrode active material is 10%-30%.

[0022] Controlling the mass percentage of graphite nitrogen in the total nitrogen content of the negative electrode active material within the above range is beneficial to make the total mass percentage of pyridine nitrogen and pyrrole nitrogen in the total nitrogen content 30%-70%, thereby improving the fast charging performance of the secondary battery.

[0023] In any embodiment, the negative electrode active material satisfies at least one of (a1)-(a6):

[0024] (a1) The volumetric particle size distribution Dv50 of the negative electrode active material is 7μm-22μm;

[0025] (a2) The specific surface area of ​​the negative electrode active material is 1.0 m². 2 / g-10.5m 2 / g;

[0026] (a3) The thickness of the nitrogen-doped porous carbon layer is ≤500 nm;

[0027] (a4) The carbon core includes at least one of artificial graphite and natural graphite;

[0028] (a5) Nitrogen-doped porous carbon layers include at least one of nitrogen-doped porous soft carbon layers and nitrogen-doped porous hard carbon layers.

[0029] Controlling the negative electrode active material to satisfy at least one of (a1)-(a5) is beneficial to improving the fast charging performance of secondary batteries.

[0030] In any embodiment, the carbon core comprises secondary particulate graphite, the secondary particulate graphite having a volumetric particle size distribution Dv50 of 9 μm-22 μm; or,

[0031] The carbon core consists of graphite single particles with a volumetric size distribution (Dv50) of 5 μm to 10 μm.

[0032] Secondary graphite particles have rich orientations but poor structural stability. Therefore, using secondary graphite particles within the above-mentioned particle size range as the carbon core is beneficial to improving the compaction density of the negative electrode sheet and to the core being wetted by the electrolyte, so that the secondary battery can achieve both better energy density and fast charging performance.

[0033] Graphite particles have a stable structure but poor wettability. Therefore, selecting particles with a particle size within the aforementioned small range is beneficial for improving cycle performance and fast charging performance of secondary batteries.

[0034] In any embodiment, the nitrogen-doped porous carbon layer is a nitrogen-doped porous soft carbon layer, and the negative electrode active material satisfies at least one of (b1)-(b2):

[0035] (b1) The specific surface area of ​​the negative electrode active material is 1.0 m². 2 / g-9.0m 2 / g;

[0036] (b2) The nitrogen-doped porous carbon layer contains micropores and mesopores, with the micropores and mesopores at least partially interconnected, the volume of the micropores accounting for 0-25% of the total pore volume, and / or the volume of the mesopores accounting for 63%-90% of the total pore volume.

[0037] Controlling the negative electrode active material composed of a carbon core coated with a nitrogen-doped porous soft carbon layer to satisfy at least one of (b1)-(b2) is beneficial to improving the wettability of the negative electrode active material, improving the fast charging performance and cycle performance of the battery.

[0038] In any embodiment, the nitrogen-doped porous carbon layer is a nitrogen-doped porous hard carbon layer, and the negative electrode active material satisfies at least one of (c1)-(c2):

[0039] (c1) The specific surface area of ​​the negative electrode active material is 4.0 m². 2 / g-10.5m 2 / g;

[0040] (c2) The nitrogen-doped porous carbon layer contains micropores and mesopores, with the micropores and mesopores at least partially interconnected. The volume of the micropores accounts for 25%-50% of the total pore volume, and / or the volume of the mesopores accounts for 40%-85% of the total pore volume. Controlling the negative electrode active material composed of a carbon core coated with a nitrogen-doped porous hard carbon layer to satisfy at least one of (c1)-(c2) is beneficial to improving the wettability of the negative electrode active material, improving the fast charging performance and cycle performance of the battery.

[0041] In any embodiment, the areal density of the negative electrode film is 100 mg / cm³. 2 -200mg / cm 2 ; and / or,

[0042] The compaction density of the negative electrode film is 1.3 g / cm³. 3 -1.8g / cm 3 ; and / or,

[0043] The porosity of the negative electrode film is 20%-35%.

[0044] Controlling the areal density of the negative electrode film within the aforementioned range facilitates lithium-ion diffusion within the film and effectively suppresses lithium plating, thereby improving the fast-charging and cycle performance of the secondary battery. Controlling the negative electrode film within the aforementioned higher compaction density range allows for improved energy density while maintaining fast-charging performance, facilitating high-rate charging. Controlling the porosity of the negative electrode film within the aforementioned range allows for more thorough electrolyte wetting during cycling, enhancing fast-charging and cycle performance and enabling high-rate charge / discharge.

[0045] In any embodiment, the negative electrode absorbs the E324 electrolyte at a rate of 0.5 mg / s. 1 / 2 ~4mg / s 1 / 2 .

[0046] The aforementioned negative electrode has a high liquid absorption rate, which can improve the wetting efficiency of the electrolyte on the negative electrode, improve the ion transport path, reduce the interface resistance, and improve the fast charging performance of the secondary battery.

[0047] A second aspect of this application also provides an electrical device comprising the secondary battery provided in the first aspect of this application.

[0048] A third aspect of this application also provides a negative electrode active material, which includes a carbon core and a nitrogen-doped porous carbon layer covering the surface of the carbon core, wherein the nitrogen-doped porous carbon layer includes pyrrole nitrogen, pyridine nitrogen, and mesopores.

[0049] Among them, mesopores account for 40%-90% of the total pore volume of the negative electrode active material.

[0050] The total nitrogen content in the negative electrode active material accounts for 0.4%-3% by mass, and the combined mass of pyrrole nitrogen and pyridine nitrogen accounts for 30%-80% of the total nitrogen content in the negative electrode active material.

[0051] Therefore, the negative electrode active material provided in this application achieves both high mesoporous content and high nitrogen doping, with the nitrogen doping mainly existing in the form of pyrrole nitrogen and pyridine nitrogen. Thus, the high mesoporous content effectively improves the wettability of the negative electrode active material, allowing solvated lithium ions to reach the surface of the carbon core more efficiently. The high nitrogen doping enhances the adsorption capacity of the negative electrode active material for lithium ions, and the rich pyrrole nitrogen and pyridine nitrogen content improves the desolvation rate of solvated lithium ions and the lithium ion diffusion rate. The combined effect of these three factors accelerates the kinetic process during the charging of the secondary battery and effectively improves the fast charging performance of the secondary battery.

[0052] In any embodiment, the negative electrode active material satisfies at least one of (d1)-(d5):

[0053] (d1) The volumetric particle size distribution Dv50 of the negative electrode active material is 7μm-22μm.

[0054] (d2) The specific surface area of ​​the negative electrode active material is 1.0 m². 2 / g-10.5m 2 / g.

[0055] (d3) The thickness of the nitrogen-doped porous carbon layer is ≤500nm.

[0056] (d4) The carbon core includes at least one of artificial graphite and natural graphite;

[0057] (d5) Nitrogen-doped porous carbon layers include at least one of nitrogen-doped porous soft carbon layers and nitrogen-doped porous hard carbon layers.

[0058] Controlling the negative electrode active material to satisfy at least one of (d1)-(d5) is beneficial to improving the fast charging performance of secondary batteries.

[0059] The fourth aspect of this application provides a method for preparing a negative electrode active material, comprising:

[0060] The high-nitrogen polymer and carbon core are mixed and then carbonized in an inert atmosphere.

[0061] Among them, the total nitrogen content in the high-nitrogen polymer is ≥0.8%, and the high-nitrogen polymer includes pyrrole nitrogen and pyridine nitrogen. The total mass ratio of pyrrole nitrogen and pyridine nitrogen in the total nitrogen content of the negative electrode active material is 40%-90%.

[0062] The preparation method provided in this application selects a high-nitrogen polymer rich in pyridine nitrogen and pyrrole nitrogen as the carbon and nitrogen sources, and mixes it directly with the carbon core and then carbonizes it. This facilitates the process by allowing some nitrogen from the high-nitrogen polymer to overflow and increase the mesopores of the negative electrode active material, while the remaining nitrogen is doped into the formed carbon layer and tends to form pyridine nitrogen and pyrrole nitrogen. The resulting negative electrode active material not only has a more uniform distribution of nitrogen doping and mesopores, but also simultaneously increases the mesopore content and nitrogen doping amount in the negative electrode active material. The nitrogen doping mainly exists in the form of pyrrole nitrogen and pyridine nitrogen. The high mesopore content effectively improves the wettability of the negative electrode active material, allowing solvated lithium ions to reach the surface of the carbon core more efficiently. The high nitrogen doping enhances the adsorption capacity of the negative electrode active material for lithium ions, and the richness of pyrrole nitrogen and pyridine nitrogen improves the desolvation rate of solvated lithium ions and the lithium ion diffusion rate. The combined effect of these three factors accelerates the kinetic process during the charging of the secondary battery and effectively improves the fast-charging performance of the secondary battery.

[0063] In any embodiment, the preparation method satisfies at least one of (e1)-(e3):

[0064] (e1) High-nitrogen polymers include at least one of high-nitrogen pitch and high-nitrogen copolymers.

[0065] (e2) The carbonization temperature is 700℃-1300℃ and the carbonization time is 6h-15h.

[0066] (e3) The mass ratio of high-nitrogen polymer to carbon core is 100:2-20.

[0067] By controlling the preparation method to satisfy at least one of (e1)-(e3), it is beneficial to prepare a negative electrode active material that achieves both high mesoporous content and high nitrogen doping, thereby improving the fast charging of secondary batteries.

[0068] In any embodiment, the high-nitrogen polymer is a high-nitrogen copolymer.

[0069] The nitrogen content in the high-nitrogen copolymer is 1%-5% by mass; and / or,

[0070] The carbonization temperature is 1000℃-1100℃; and / or,

[0071] High-nitrogen copolymers include acrylic acid-acrylonitrile copolymers.

[0072] When selecting a high-nitrogen polymer as a high-nitrogen copolymer, by controlling the nitrogen mass content and / or the holding temperature within the above range, it is beneficial for the high-nitrogen copolymer to carbonize and form a nitrogen-doped porous hard carbon coating layer that coats the surface of the carbon core. Combined with the holding time, the carbonization depth is kept within a suitable range, thus obtaining a negative electrode active material that achieves both high mesoporous content and high nitrogen doping, which is beneficial for improving the fast charging performance of the battery.

[0073] In any embodiment, the high-nitrogen polymer is high-nitrogen bitumen.

[0074] Among them, the nitrogen content in high-nitrogen asphalt is 0.8%-4% by mass; and / or,

[0075] The insulation temperature is 900℃-1300℃.

[0076] When high-nitrogen polymers are selected as high-nitrogen asphalt, by controlling the nitrogen mass content and / or the heat preservation temperature within the above range, it is beneficial for the high-nitrogen asphalt to carbonize and form a nitrogen-doped porous soft carbon coating layer that coats the surface of the carbon core. Combined with the heat preservation time, the carbonization depth is kept within a suitable range, so as to obtain a negative electrode active material that achieves both high mesoporous content and high nitrogen doping, which is beneficial to improving the fast charging performance of the battery. Attached Figure Description

[0077] Figure 1 is a schematic diagram of a secondary battery according to an embodiment of this application.

[0078] Figure 2 is an exploded view of a secondary battery according to an embodiment of this application shown in Figure 1.

[0079] Figure 3 is a schematic diagram of a battery module according to one embodiment of this application.

[0080] Figure 4 is a schematic diagram of a battery pack according to one embodiment of this application.

[0081] Figure 5 is an exploded view of the battery pack of one embodiment of this application shown in Figure 4.

[0082] Figure 6 is a schematic diagram of an electrical device using a secondary battery as a power source according to an embodiment of this application.

[0083] Explanation of reference numerals in the attached figures:

[0084] 1-Battery pack; 2-Upper housing; 3-Lower housing; 4-Battery module; 5-Battery cell; 51-Housing; 52-Electrode assembly; 53-Top cover assembly. Embodiments of the present invention

[0085] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the negative electrode active material, its preparation method, secondary battery, and power application device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0086] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0087] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0088] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0089] Unless otherwise specified, all steps of this application may be performed sequentially or randomly, preferably sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0090] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0091] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0092] As the application of rechargeable batteries becomes more and more widespread, people are facing serious challenges to their performance. Currently, the fast charging performance of rechargeable batteries still needs to be further improved.

[0093] The key to improving the fast charging capability of secondary batteries lies in improving the performance of the negative electrode active material and the negative electrode sheet. During the charging process of secondary batteries, taking carbon-coated graphite as an example, the electrode dynamics process usually includes the following steps: (1) diffusion of solvated lithium ions in the electrolyte; (2) solvated lithium ions reaching the surface of the graphite negative electrode begin to desolvate; (3) desolvated lithium ions pass through the solid electrolyte (SEI) film, through the carbon coating layer and are embedded in the graphite interlayer with charge transfer; (4) lithium ions diffuse inside the graphite particles.

[0094] Based on this, the first aspect of the present application provides a secondary battery, which includes a negative electrode sheet, and the negative electrode sheet includes a negative electrode film layer.

[0095] The negative electrode film layer includes a negative electrode active material, which includes a carbon core and a nitrogen-doped porous carbon layer covering the surface of the carbon core. The nitrogen-doped porous carbon layer includes pyrrole nitrogen, pyridine nitrogen, and mesopores.

[0096] Among them, mesopores account for 40%-90% of the total pore volume of the negative electrode active material.

[0097] The total nitrogen content in the negative electrode active material accounts for 0.4%-3% by mass, and the combined mass of pyrrole nitrogen and pyridine nitrogen accounts for 30%-80% of the total nitrogen content in the negative electrode active material.

[0098] Pyridine nitrogen and pyrrole nitrogen refer to the bonding methods of nitrogen atoms with the graphite lattice. Pyridine nitrogen refers to nitrogen atoms being bonded to two carbon atoms at the edge of the graphite surface, which provides a p electron to the conjugated π system, resulting in p doping. Pyrrole nitrogen refers to nitrogen atoms being bonded to two carbon atoms on the graphite surface to form a five-membered ring, which provides two p electrons to the conjugated π system, resulting in p doping.

[0099] In this application, the composition of pyrrole nitrogen and pyridine nitrogen, as well as their mass percentage in the total nitrogen content, can be characterized and confirmed using X-ray photoelectron spectroscopy (XPS). Specifically, the powder scraped from the surface of the negative electrode sheet is calcined to remove binders, conductive agents, etc., to obtain the negative electrode active material. X-ray photoelectron spectroscopy (XPS) is then performed using an X-ray source with Al target Kα radiation at hν of 1486.6 eV. The N1s peaks are split at 399.5 eV and 398.5 eV, and the area percentages of pyrrole nitrogen and pyridine nitrogen are calculated respectively. The pyrrole nitrogen area percentage represents the mass percentage of pyrrole nitrogen in the total nitrogen content of the negative electrode material, and the pyridine nitrogen area percentage represents the mass percentage of pyridine nitrogen groups in the total nitrogen content of the negative electrode material.

[0100] In this application, the method for testing the volume ratio of mesopores in the total pore volume of the negative electrode active material includes: calcining powder scraped from the surface of the negative electrode sheet to remove binders, conductive agents, etc., to obtain a negative electrode active material sample; placing the negative electrode active material sample in a gas adsorption analyzer at -196℃ to obtain isothermal adsorption-desorption curves. The volume of N2 gas at an adsorption relative pressure of 0.99 is equivalent to the total pore volume. Then, based on the volume distribution corresponding to different pore sizes within the micropore and mesopore ranges, the isothermal adsorption curves are analyzed using the Horvath-Kawazoe (HK) method to determine the proportion of mesopore volume to the total pore volume.

[0101] For anode active materials, based on pore size, mesopores with a pore size of 2nm ≤ 50nm are more conducive to the transport of solvated lithium ions than micropores. The content of mesopores is positively correlated with wettability. However, excessive content leads to poor mechanical properties and easily causes breakage, which deteriorates kinetic and cycling performance. Therefore, controlling the content of mesopores within the above range, based on the good mechanical properties of the nitrogen-doped carbon coating layer, not only provides more lithium ion insertion channels and shortens the lithium ion transport distance, but also provides multidimensional open permeation channels, enhancing the wettability of the electrolyte. This makes it easier for solvated lithium ions in the electrolyte to diffuse and transfer to the surface of graphite particles, allowing solvated lithium ions to reach the surface of the carbon core more efficiently and accelerating the liquid phase mass transfer step in the electrolyte phase.

[0102] The total nitrogen content in the negative electrode active material is controlled to be 0.4%-3% by mass, with pyrrole nitrogen and pyridine nitrogen accounting for 30%-80% of the total nitrogen content. High nitrogen doping enhances the adsorption capacity of the negative electrode active material for lithium ions. Furthermore, nitrogen doping rich in pyrrole nitrogen and pyridine nitrogen induces the formation of an electrolyte in the SEI during film formation, resulting in a higher inorganic SEI – lithium nitride (Li3N). This inorganic SEI has a higher adsorption energy than Li2CO3, making it easier for lithium ions to diffuse to the surface. Simultaneously, this type of inorganic SEI has a lower desolvation energy barrier, accelerating the reduction of lithium ion transport impedance in the coating layer and speeding up the desolvation step of solvated lithium ions. On the other hand, pyridine nitrogen and pyrrole nitrogen, due to the lone pair electrons in their heterocyclic nitrogen atoms, exhibit high reactivity in electrochemical and catalytic applications, enabling more efficient adsorption of lithium ions during charge and discharge, reducing the desolvation energy barrier, and lowering the lithium ion concentration. + Mass transfer resistance and improved lithium-ion diffusion capacity of the coating layer are reduced, accelerating the diffusion of desolvated lithium ions in the graphite coating layer.

[0103] Understandably, for the reasons mentioned above, if the total content of pyrrole nitrogen and pyridine nitrogen, or the total nitrogen content, is too low, the effect of improving the desolvation rate of solvated lithium ions and the lithium ion diffusion rate will be limited. If it is too high, it will lead to the thickening of the SEI, affecting the first efficiency of the secondary battery and the long-term performance of the secondary battery. Therefore, in this application, the mass ratio of the total nitrogen content in the negative electrode active material is controlled to be 0.4%-3%, and the mass ratio of pyrrole nitrogen and pyridine nitrogen in the total nitrogen content of the negative electrode active material is 30%-80%.

[0104] In summary, the secondary battery provided in this application introduces a negative electrode active material that achieves both high mesoporous content and high nitrogen doping. The high nitrogen doping mainly exists in the form of pyrrole nitrogen and pyridine nitrogen. Therefore, the high mesoporous content effectively improves the wettability of the negative electrode active material and shortens the lithium-ion transport distance. The high nitrogen doping enhances the adsorption capacity of the negative electrode active material for lithium ions. Furthermore, the rich pyrrole nitrogen and pyridine nitrogen content improves the lithium-ion diffusion rate, and the introduction of defect sites improves the wettability of the negative electrode active material. The combined effect of these three factors improves the wettability of the negative electrode active material and constructs a migration path that enables rapid lithium-ion transport, effectively enhancing the fast-charging performance of the secondary battery.

[0105] For example, the volume percentage of mesopores in the total pore volume of the negative electrode active material is any one of 40%, 45%, 50%, 55%, 60%, 65%, 70%, 80%, 85%, 90%, or between any two of these values.

[0106] For example, the total nitrogen content in the negative electrode active material is any one of 0.4%, 0.6%, 0.8%, 1.0%, 1.3%, 1.5%, 1.7%, 2.0%, 2.2%, 2.5%, 2.7%, or 3.0% by mass, or between any two of these values.

[0107] For example, the mass percentage of pyrrole nitrogen and pyridine nitrogen in the total nitrogen content of the negative electrode active material is any one of 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70% or between any two of these values.

[0108] In some embodiments, the contact angle of the negative electrode active material is 10°-38.5°.

[0109] In this application, the contact angle testing method includes: baking the powder to be tested in a forced-air oven at 65°C for 2 hours, then fixing it in an SDC-200 contact angle tester; adding 11µL of test electrolyte to the surface to test the contact angle, ensuring the droplet shape is stable, recording 100 photos and then selecting the 80th photo, using the tester's software SDC-200 to fit the contact angle as a single measurement value; in this application, the same sample is tested 6 times at different points, and 4 similar values ​​are selected for output to ensure the reliability of the test results.

[0110] The aforementioned negative electrode active material has a small contact angle with the electrolyte and good wettability, which is beneficial to improving the fast charging capability and cycle performance of secondary batteries.

[0111] For example, the contact angle of the negative electrode active material is any value of 10°, 12°, 15°, 17°, 20°, 23°, 25°, 28°, 30°, 32°, 35°, 38°, 38.5° or between any two values.

[0112] In some embodiments, the nitrogen-doped porous carbon layer contains micropores and macropores, and the micropores, macropores and mesopores are at least partially interconnected. The total volume of the micropores and macropores accounts for 10%-60% of the total pore volume of the negative electrode active material.

[0113] The method for determining the proportion of micropore and macropore volume to the total pore volume includes: placing the negative electrode active material sample in a gas adsorption analyzer at -196℃ to obtain isothermal adsorption-desorption curves. The volume of N2 gas at an adsorption relative pressure of 0.99 is equivalent to the total pore volume. Then, based on the volume distribution corresponding to the pore size within the micropore range, the proportion of micropore volume to the total pore volume is determined by analyzing the isothermal adsorption curves using the Horvath-Kawazoe (HK) method.

[0114] Based on pore size, micropores have a pore size < 2 nm, while macropores have a pore size > 50 nm.

[0115] By ensuring that micropores, macropores, and mesopores are at least partially interconnected, and by controlling the total volume of micropores and macropores to account for 10%-60% of the total pore volume of the negative electrode active material, the material can work together with mesopores to effectively improve the pore structure of the material. This is beneficial for improving the contact angle of the negative electrode active material, increasing wettability, and improving the battery's fast charging performance and cycle performance.

[0116] For example, the total volume of micropores and macropores in the total pore volume of the negative electrode active material is any one of 10%, 15%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, or between any two of these values.

[0117] In some embodiments, pyrrole nitrogen accounts for 12%-40% of the total nitrogen content of the negative electrode active material by mass; and / or, pyridine nitrogen accounts for 15%-45% of the total nitrogen content of the negative electrode active material by mass.

[0118] Controlling the mass percentage of pyrrole nitrogen and / or pyridine nitrogen in the total nitrogen content of the negative electrode active material to be within the aforementioned higher range is beneficial to improving the desolvation rate of solvated lithium ions and the lithium ion diffusion rate, thereby enhancing the fast-charging performance of the secondary battery.

[0119] For example, the mass percentage of pyrrole nitrogen in the total nitrogen content of the negative electrode active material is any one of 12%, 15%, 20%, 25%, 30%, 35%, or 40%, or between any two of these values.

[0120] For example, the mass percentage of pyridine nitrogen in the total nitrogen content of the negative electrode active material is any one of 15%, 20%, 25%, 30%, 35%, 40%, or 45%, or between any two of these values.

[0121] In some embodiments, the combined mass percentage of pyrrole nitrogen and pyridine nitrogen in the negative electrode active material is 0.3%-0.9%; and / or,

[0122] The mass percentage of pyrrole nitrogen in the negative electrode active material is 0.1%-0.4%; and / or,

[0123] The mass percentage of pyridine nitrogen in the negative electrode active material is 0.2%-0.5%.

[0124] By controlling the content of pyrrole nitrogen and pyridine nitrogen within the aforementioned high range, it is beneficial to improve the desolvation rate of solvated lithium ions and the lithium ion diffusion rate, thereby enhancing the fast-charging performance of secondary batteries.

[0125] For example, the mass percentage of pyrrole nitrogen and pyridine nitrogen in the negative electrode active material is any one of 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9% or between any two of these values.

[0126] For example, the mass percentage of pyrrole nitrogen in the negative electrode active material is any one of 0.1%, 0.2%, 0.3%, 0.4%, or between any two of these values.

[0127] For example, the mass percentage of pyridine nitrogen in the negative electrode active material is any one of 0.2%, 0.3%, 0.4%, 0.5%, or between any two of these values.

[0128] In some embodiments, the nitrogen-doped porous carbon layer includes graphitic nitrogen and nitrogen oxides; wherein the mass percentage of graphitic nitrogen in the total nitrogen content of the negative electrode active material is 10%-30%.

[0129] Graphite nitrogen refers to the bonding mode between nitrogen atoms and the graphite lattice. Graphite nitrogen refers to the situation where a nitrogen atom is bonded to three carbon atoms, which will provide an n electron to the conjugated π system, thus causing n doping of graphite.

[0130] In this application, the composition of graphite nitrogen and its mass percentage in the total nitrogen content can be characterized and confirmed using X-ray photoelectron spectroscopy (XPS). Specifically, the powder scraped from the surface of the negative electrode sheet is calcined to remove binders, conductive agents, etc., to obtain the negative electrode active material. X-ray photoelectron spectroscopy (XPS) is then used to test this material using an X-ray source with Al target Kα radiation at hν of 1486.6 eV. The N1s peak is fractionated at 401 eV, and the graphite nitrogen area percentage is calculated. This graphite nitrogen area percentage represents the mass percentage of graphite nitrogen in the total nitrogen content of the negative electrode material.

[0131] Graphite nitrogen refers to nitrogen atoms arranged in sp... 2The hybrid state exists in the six-membered ring structure. The introduction of graphite nitrogen into graphite or graphite-like coated materials can form an additional π-electron system, enhance the electron transport capability of the material, improve its conductivity, enhance the diffusion capability of electrons in the coating layer, and improve fast charging performance.

[0132] Controlling the mass percentage of graphite nitrogen in the total nitrogen content of the negative electrode active material within the above range can not only enhance conductivity, but also help to make the total mass percentage of pyridine nitrogen and pyrrole nitrogen in the total nitrogen content 30%-80%, thereby improving the fast charging performance of the secondary battery.

[0133] For example, the mass percentage of graphite nitrogen in the total nitrogen content of the negative electrode active material is any one of 10%, 12%, 15%, 17%, 20%, 22%, 25%, 27%, 30%, or between any two of these values.

[0134] In some embodiments, the negative electrode active material satisfies at least one of (a1)-(a5):

[0135] (a1) The volumetric particle size distribution Dv50 of the negative electrode active material is 7μm-22μm.

[0136] To determine the volumetric particle size distribution (Dv50) of the negative electrode active material, the powder scraped from the surface of the negative electrode sheet can be calcined to remove binders, conductive agents, etc., yielding the negative electrode active material as a sample for laser diffraction testing. The laser diffraction method utilizes a Malvern 2000 (MasterSizer2000) laser particle size analyzer, following the standard procedure GB / T19077-2016 / ISO13320:2009. The specific testing procedure is as follows: Take an appropriate amount of the sample to be tested (ensuring a sample concentration of 8-12% opacity), add 20 ml of deionized water, and simultaneously incubate for 5 minutes (53 kHz / 120 W) to ensure complete dispersion. Then, measure the sample according to the GB / T19077-2016 / ISO13320:2009 standard. It should be noted that when the negative electrode film is composed of this fast-charging negative electrode active material and graphite layered coating, the scraped thickness should not exceed the thickness of the surface layer.

[0137] The volume particle size distribution Dv50 of the negative electrode active material is within the above range, which is beneficial for the negative electrode sheet to maintain the porosity of the negative electrode film layer within the range of 20%-35% when under pressure. This can reduce the loss of energy density caused by excessive porosity and enable the battery to better balance energy density while having high fast charging performance.

[0138] For example, the volumetric particle size distribution Dv50 of the negative electrode active material is any value of 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, 21μm, 22μm or between any two values.

[0139] (a2) The specific surface area of ​​the negative electrode active material is 1.0 m². 2 / g-10.5m 2 / g.

[0140] Specific surface area test: The test method refers to the standard GB / T19587-2004 "Gas Adsorption BET Determination of Specific Surface Area of ​​Solid Substances". It can be understood that the test obtained here is the average specific surface area of ​​the negative electrode active material.

[0141] Controlling the specific surface area of ​​the negative electrode active material within the above range allows it to have a larger specific surface area, which is beneficial for adsorbing lithium ions and improving fast charging performance.

[0142] For example, the specific surface area of ​​the negative electrode active material is 1.0 m². 2 / g、2m 2 / g、3m 2 / g、4m 2 / g、5m 2 / g、6m 2 / g、7m 2 / g、8m 2 / g、9m 2 / g, 10.0m 2 / g, 10.5m 2 Any value in / g or between any two values.

[0143] (a3) The thickness of the nitrogen-doped porous carbon layer is ≤500nm.

[0144] The thickness of the nitrogen-doped porous carbon layer is a well-known concept in the art and can be measured using methods known in the art. For example, multiple measurements can be taken using transmission electron microscopy (TEM), such as testing 30 anode active materials, and the average thickness of the 30 anode active materials can be used as the thickness of the nitrogen-doped porous carbon layer; wherein, for each anode active material, the thickness of 10 sites at different locations is selected as the thickness of the nitrogen-doped porous carbon layer of that anode active material.

[0145] When the thickness of the nitrogen-doped porous carbon layer is within the above range, it can improve the overall conductivity and structural stability of the negative electrode active material, and also help to further enhance the shuttle migration speed of active lithium ions in the negative electrode film, thereby improving the fast charging performance of the battery.

[0146] For example, the thickness of the nitrogen-doped porous carbon layer is any one of 10 nm, 50 nm, 100 nm, 200 nm, 250 nm, 300 nm, 400 nm, 490 nm, or 499 nm, or between any two of these values.

[0147] (a4) The carbon core includes at least one of artificial graphite and natural graphite.

[0148] Taking the distinction between natural and artificial graphite in negative electrode active materials as a non-limiting example, natural and artificial graphite can be differentiated by the appearance and morphology of the particles. Further X-ray diffraction (XRD) analysis can be performed. In the XRD pattern, a very sharp and high-intensity characteristic peak near 2θ26.5° indicates natural graphite; a relatively broad and weak characteristic peak near 2θ26.5° indicates artificial graphite. Alternatively, Raman spectroscopy can be used for analysis, and hard carbon can be analyzed based on the characteristic peak information of carbon composition in the spectrum (such as the intensity ratio of the D peak to the G peak, ID / G). Both the D and G peaks are Raman characteristic peaks of carbon atom crystals. The D peak represents defects in the carbon atom crystal; the more defects, the greater the intensity of the D peak. The intensity of the D peak can reflect the content of amorphous (randomly stacked) regions. The G peak represents the in-plane stretching vibration of sp2 hybridization of carbon atoms; the intensity of the G peak can reflect the content of graphitized (layered structure) regions. As the degree of disorder of carbon atoms increases, the intensity ratio of the D peak to the G peak also increases. The difference in intensity between the D and G peaks in the Raman spectrum can also be used to distinguish between natural graphite and artificial graphite.

[0149] For example, the carbon core is artificial graphite.

[0150] Nitrogen-doped carbon-coated graphite obtained after surface coating has higher specific capacity and higher rate performance, which can further improve the energy density and fast charging performance of secondary batteries.

[0151] (a5) Nitrogen-doped porous carbon layers include at least one of nitrogen-doped porous soft carbon layers and nitrogen-doped porous hard carbon layers.

[0152] The nitrogen-doped porous carbon layer includes at least one of a nitrogen-doped porous soft carbon layer and a nitrogen-doped porous hard carbon layer, wherein the nitrogen-doped porous carbon layer is a nitrogen-doped porous soft carbon layer, the nitrogen-doped porous carbon layer is a nitrogen-doped porous hard carbon layer, or the nitrogen-doped porous carbon layer is a nitrogen-doped porous soft carbon layer and a nitrogen-doped porous hard carbon layer, wherein the nitrogen-doped porous soft carbon layer and the nitrogen-doped porous hard carbon layer are stacked, wherein the nitrogen-doped porous soft carbon layer may be located between the nitrogen-doped porous hard carbon layer and the carbon core, or the nitrogen-doped porous hard carbon layer may be located between the nitrogen-doped porous soft carbon layer and the carbon core.

[0153] For example, the nitrogen-doped porous carbon layer is a nitrogen-doped porous soft carbon layer or a nitrogen-doped porous hard carbon layer.

[0154] In some embodiments, the carbon core comprises secondary particulate graphite with a volumetric particle size distribution Dv50 of 9 μm-22 μm; or,

[0155] The carbon core consists of graphite single particles with a volumetric size distribution (Dv50) of 5 μm to 10 μm.

[0156] Secondary granular graphite refers to graphite obtained by mixing artificial graphite powder with a binder, followed by granulation, carbonization, and graphitization. Secondary granular graphite exhibits rich orientation but poor structural stability. Therefore, using secondary granular graphite within the aforementioned particle size range as the carbon core is beneficial for increasing the compaction density of the negative electrode sheet and for ensuring the core is wetted by the electrolyte, thus enabling the secondary battery to achieve both better energy density and fast-charging performance.

[0157] For example, the volumetric particle size distribution Dv50 of the secondary graphite particles is any value of 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 20μm, 22μm or between any two values.

[0158] A single graphite particle refers to a single graphite particle, which is a primary graphite particle. It has a stable structure but poor wettability. Therefore, selecting a particle size within the aforementioned small range is beneficial for improving cycle performance and fast charging performance of secondary batteries.

[0159] For example, the volumetric particle size distribution Dv50 of the graphite single particle is any value of 5μm, 6μm, 7μm, 8μm, 9μm, 10μm or between any two values.

[0160] In some embodiments, the nitrogen-doped porous carbon layer is a nitrogen-doped porous soft carbon layer, and the negative electrode active material satisfies at least one of (b1)-(b2):

[0161] (b1) The specific surface area of ​​the negative electrode active material is 1.0 m². 2 / g-9.0m 2 / g.

[0162] Within the aforementioned specific surface area range, the negative electrode active material composed of a carbon core coated with a nitrogen-doped porous soft carbon layer has better porosity, which is beneficial for improving the contact angle of the negative electrode active material, enhancing wettability, and improving the battery's fast charging performance and cycle performance.

[0163] For example, the specific surface area of ​​the negative electrode active material is 1.0 m². 2 / g、2m 2 / g、3m 2 / g、4m 2 / g、5m2 / g、6m 2 / g、7m 2 / g、8m 2 / g, 9.0m 2 Any value in / g or between any two values.

[0164] (b2) The nitrogen-doped porous carbon layer contains micropores and mesopores, with the micropores and mesopores at least partially interconnected, the volume of the micropores accounting for 0-25% of the total pore volume, and / or the volume of the mesopores accounting for 63%-90% of the total pore volume.

[0165] Controlling the volume of micropores to account for 0-25% of the total pore volume, and / or the volume of mesopores to account for 63%-90% of the total pore volume, is not only beneficial to improving the pore structure of nitrogen-doped porous soft carbon layers, but also beneficial to improving the contact angle of the negative electrode active material, improving wettability, improving battery fast charging performance and cycle performance. Moreover, the lower micropore content has a weaker effect on the deterioration of the first efficiency.

[0166] For example, the proportion of the volume of the micropores to the total pore volume is any one of 0, 1%, 3%, 5%, 7%, 10%, 12%, 15%, 17%, 20%, 22%, 25% or between any two values.

[0167] For example, the proportion of mesopore volume to total pore volume is any one of 63%, 65%, 68%, 70%, 73%, 75%, 77%, 80%, 82%, 85%, 87%, 90%, or between any two of these values.

[0168] In some embodiments, the nitrogen-doped porous carbon layer is a nitrogen-doped porous hard carbon layer, and the negative electrode active material satisfies at least one of (c1)-(c2):

[0169] (c1) The specific surface area of ​​the negative electrode active material is 4.0 m². 2 / g-10.5m 2 / g.

[0170] Within the aforementioned specific surface area range, the negative electrode active material composed of a carbon core coated with a nitrogen-doped porous hard carbon layer has better porosity, which is beneficial for improving the contact angle of the negative electrode active material, enhancing wettability, and improving the battery's fast charging performance and cycle performance.

[0171] For example, the specific surface area of ​​the negative electrode active material is 4m². 2 / g、5m 2 / g、6m 2 / g、7m 2 / g、8m 2 / g, 9.0m 2 / g, 10.0m2 / g, 10.5m 2 Any value in / g or between any two values.

[0172] (c2) The nitrogen-doped porous carbon layer contains micropores and mesopores, with the micropores and mesopores at least partially interconnected, the volume of the micropores accounting for 25%-50% of the total pore volume, and / or the volume of the mesopores accounting for 40%-85% of the total pore volume.

[0173] The volume of micropores accounts for 25%-50% of the total pore volume, and / or the volume of mesopores accounts for 40%-85% of the total pore volume. Improving the pore structure of nitrogen-doped porous hard carbon layers is beneficial to improving the contact angle of the negative electrode active material, increasing wettability, improving battery fast charging performance and cycle performance, and the lower micropore content has a weaker effect on the deterioration of the first efficiency.

[0174] For example, the volume of the micropores accounts for any one of 25%, 30%, 35%, 40%, 45%, 50% of the total pore volume, or between any two of these values.

[0175] For example, the proportion of mesopore volume to total pore volume is any one of 40%, 45%, 50%, 55%, 60%, 65%, 68%, 70%, 73%, 75%, 77%, 80% or between any two values.

[0176] In some embodiments, the areal density of the negative electrode film is 100 mg / cm³. 2 -200mg / cm 2 .

[0177] In this application, the areal density of the negative electrode film has a meaning known in the art and can be tested using methods known in the art. For example, take an electrode sheet that has been coated on one side and cold-pressed (if it is a double-coated electrode sheet, the film layer on one side can be wiped off first), cut it into a small circular piece with an area of ​​S1, weigh it, and record its weight as M1. Then wipe off the film layer of the weighed electrode sheet, weigh the current collector, and record it as M0. The areal density of the film layer = (M1-M0) / S1. To ensure the accuracy of the test results, multiple sets (e.g., 10 sets) of samples can be tested, and the average value can be calculated as the test result.

[0178] When the surface density of the negative electrode film is within the above range, it is beneficial for the diffusion of lithium ions in the negative electrode film and can effectively suppress lithium plating, thereby more effectively improving the fast charging performance and cycle performance of the secondary battery.

[0179] For example, the areal density of the negative electrode film is 100 mg / cm³. 2 110mg / cm 2 120mg / cm2 130mg / cm 2 140mg / cm 2 150mg / cm 2 160mg / cm 2 170mg / cm 2 180mg / cm 2 190mg / cm 2 200mg / cm 2 It can be any value in the range or any two values ​​in between.

[0180] In some embodiments, the compaction density of the negative electrode film is 1.3 g / cm³. 3 -1.8g / cm 3 .

[0181] The compaction density of the electrode sheet is a well-known concept in the art and can be tested using methods known in the art. The negative electrode sheet is removed from the lithium-ion battery, and a certain area of ​​the negative electrode sheet is taken. The mass and thickness of the negative electrode sheet and the negative current collector (after removing the negative electrode film) are measured respectively. The compaction density of the negative electrode sheet is calculated according to the following formula: Compaction density of the negative electrode sheet = (Mass of the negative electrode sheet - Mass of the negative current collector) / [(Thickness of the negative electrode sheet - Thickness of the negative current collector) × Area of ​​the negative electrode sheet].

[0182] The aforementioned negative electrode film layer has a high compaction density, which means that, in addition to having fast charging performance, the energy density of the secondary battery can be effectively improved, which is beneficial for high-rate charging.

[0183] For example, the compaction density of the negative electrode film is 1.3 g / cm³. 3 1.4g / cm 3 1.5g / cm 3 1.6g / cm 3 1.7g / cm 3 1.8g / cm 3 It can be any value in the range or any two values ​​in between.

[0184] In some implementations, the porosity of the negative electrode film is 20%-35%.

[0185] The porosity test method for the negative electrode film layer in this application includes: discharging the secondary battery to the discharge cutoff voltage and disassembling it to obtain the negative electrode sheet; immersing the negative electrode sheet in DMC (dimethyl carbonate), washing it with deionized water and ethanol, and drying the washed negative electrode sheet. The porosity of the positive electrode film layer is measured by a volumetric method, and the porosity of the negative electrode film layer is calculated by the volume of liquid immersed in the pores of the negative electrode film layer. The test steps are as follows: placing the negative electrode sheet sample in a graduated cylinder, adding n-butanol liquid to immerse the negative electrode sheet, and recording the volume V1 at this time. After standing for 6 hours, the above-mentioned n-butanol liquid is immersed in the negative electrode film layer, and the change in volume ΔV is read. The negative electrode sheet is removed, dried, and the negative electrode film layer is scraped off, and the volume of the negative electrode current collector is measured as V2. The porosity δ of the negative electrode film layer is calculated, where δ = ΔV / (V1 - V2).

[0186] Controlling the porosity of the negative electrode film to 20%-35% is beneficial for the negative electrode film to be more fully wetted by the electrolyte during cycling, which is beneficial for improving fast charging and cycling performance, and for achieving high-rate charging and discharging.

[0187] For example, the porosity of the negative electrode film layer is any value of 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, or 35%, or between any two values.

[0188] In some embodiments, the negative electrode has an absorption rate of 0.5 mg / s for the E324 electrolyte. 1 / 2 -4mg / s 1 / 2 .

[0189] The liquid absorption rate of the negative electrode sheet reflects its ability to wet in the electrolyte. In this application, the liquid absorption rate is tested by: disassembling the battery cell to remove the negative electrode sheet, drying the negative electrode sheet, cutting it into 20mm × 10mm sheets, measuring the sheet thickness as D, fixing it on a sample stage, and dripping E324 electrolyte while timing with a stopwatch; recording the weight increase and time; and calculating the liquid absorption rate of the electrode sheet based on the weight change over time. A higher liquid absorption rate indicates a faster wetting speed.

[0190] The E324 electrolyte comprises: a solvent consisting of ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) in a volume ratio of 1:3:6; a lithium salt of 1.0M LiPF6; and additives of 1% by mass of vinylene carbonate (VC) and 1% by mass of fluoroethylene carbonate (FEC).

[0191] The aforementioned negative electrode has a high liquid absorption rate, which can improve the wetting efficiency of the electrolyte on the negative electrode, improve the ion transport path, reduce the interface resistance, and improve the fast charging performance of the secondary battery.

[0192] For example, the negative electrode has an absorption rate of 0.5 mg / s for the E324 electrolyte. 1 / 2 1.0 mg / s 1 / 2 1.5mg / s 1 / 2 2.0 mg / s 1 / 2 2.5mg / s 1 / 2 3.0 mg / s 1 / 2 3.5mg / s 1 / 2 4.0 mg / s 1 / 2 It can be any value or any two values.

[0193] A second aspect of this application provides an electrical device that includes the secondary battery provided in the first aspect of this application.

[0194] The third aspect of this application provides a negative electrode active material, which includes a carbon core and a nitrogen-doped porous carbon layer covering the surface of the carbon core. The nitrogen-doped porous carbon layer includes pyrrole nitrogen, pyridine nitrogen, and mesopores.

[0195] Among them, mesopores account for 40%-90% of the total pore volume of the negative electrode active material;

[0196] The total nitrogen content in the negative electrode active material accounts for 0.4%-3% by mass, and the combined mass of pyrrole nitrogen and pyridine nitrogen accounts for 30%-80% of the total nitrogen content in the negative electrode active material.

[0197] For anode active materials, based on pore size, mesopores with a pore size of 2nm ≤ 50nm are more conducive to the transport of solvated lithium ions than micropores. The content of mesopores is positively correlated with wettability. However, excessive content leads to poor mechanical properties and is prone to breakage, which deteriorates kinetic and cycling performance. Therefore, controlling the content of mesopores within the above range provides not only more lithium ion insertion channels and shortens the lithium ion transport distance, but also multidimensional open permeation channels, enhancing the wettability of the electrolyte. This makes it easier for solvated lithium ions in the electrolyte to diffuse and transfer to the surface of graphite particles, allowing solvated lithium ions to reach the surface of the carbon core more efficiently and accelerating the liquid-phase mass transfer steps in the electrolyte phase.

[0198] The total nitrogen content in the negative electrode active material is controlled to be 0.4%-3% by mass, with pyrrole nitrogen and pyridine nitrogen accounting for 30%-80% of the total nitrogen content. High nitrogen doping enhances the adsorption capacity of the negative electrode active material for lithium ions. Furthermore, nitrogen doping rich in pyrrole nitrogen and pyridine nitrogen induces the formation of an SEI during film formation, resulting in more inorganic SEI-lithium nitride (Li3N). This inorganic SEI has a higher adsorption energy than Li2CO3, making it easier for lithium ions to diffuse to the surface. Simultaneously, this type of inorganic SEI has a lower desolvation energy barrier, accelerating the reduction of lithium ion transport impedance in the coating layer and speeding up the desolvation step of solvated lithium ions. On the other hand, pyridine nitrogen and pyrrole nitrogen, due to the lone pair electrons in their heterocyclic nitrogen atoms, exhibit high reactivity in electrochemical and catalytic applications, enabling more efficient adsorption of lithium ions during charge and discharge, reducing the desolvation energy barrier, and lowering the Li3N content. + Mass transfer resistance and improved lithium-ion diffusion capacity of the coating layer are reduced, accelerating the diffusion of desolvated lithium ions in the graphite coating layer.

[0199] Understandably, for the reasons mentioned above, if the total content of pyrrole nitrogen and pyridine nitrogen, or the total nitrogen content, is too low, the effect of improving the desolvation rate of solvated lithium ions and the lithium ion diffusion rate will be limited. If it is too high, it will lead to the thickening of the SEI, affecting the first efficiency of the secondary battery and the long-term performance of the secondary battery. Therefore, in this application, the mass ratio of the total nitrogen content in the negative electrode active material is controlled to be 0.4%-3%, and the mass ratio of pyrrole nitrogen and pyridine nitrogen in the total nitrogen content of the negative electrode active material is 30%-80%.

[0200] In summary, the negative electrode active material provided in this application achieves both high mesoporous content and high nitrogen doping, with the high nitrogen doping mainly existing in the form of pyrrole nitrogen and pyridine nitrogen. Therefore, the high mesoporous content effectively improves the wettability of the negative electrode active material and shortens the lithium-ion transport distance, the high nitrogen doping enhances the adsorption capacity of the negative electrode active material for lithium ions, and the rich pyrrole nitrogen and pyridine nitrogen improve the lithium-ion diffusion rate and introduce defect sites to improve the wettability of the negative electrode active material. The combined effect of these three factors improves the wettability of the negative electrode active material and constructs a migration path that enables rapid lithium-ion transport, effectively enhancing the fast-charging performance of the secondary battery.

[0201] For example, the volume percentage of mesopores in the total pore volume of the negative electrode active material is any one of 40%, 45%, 50%, 55%, 60%, 65%, 70%, 80%, 85%, 90%, or between any two of these values.

[0202] For example, the total nitrogen content in the negative electrode active material is any one of 0.4%, 0.6%, 0.8%, 1.0%, 1.3%, 1.5%, 1.7%, 2.0%, 2.2%, 2.5%, 2.7%, or 3.0% by mass, or between any two of these values.

[0203] For example, the mass percentage of pyrrole nitrogen and pyridine nitrogen in the total nitrogen content of the negative electrode active material is any one of 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70% or between any two of these values.

[0204] In some embodiments, the negative electrode active material satisfies at least one of (d1)-(d5):

[0205] (d1) The volumetric particle size distribution Dv50 of the negative electrode active material is 7μm-22μm.

[0206] The volume particle size distribution Dv50 of the negative electrode active material is within the above range, which is beneficial for the negative electrode sheet to maintain the porosity of the negative electrode film layer within the range of 20%-35% when under pressure. This can reduce the loss of energy density caused by excessive porosity and enable the battery to better balance energy density while having high fast charging performance.

[0207] For example, the volumetric particle size distribution Dv50 of the negative electrode active material is any value of 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, 21μm, 22μm or between any two values.

[0208] (d2) The specific surface area of ​​the negative electrode active material is 1.0 m². 2 / g-10.5m 2 / g.

[0209] Controlling the specific surface area of ​​the negative electrode active material within the above range allows it to have a larger specific surface area, which is beneficial for adsorbing lithium ions and improving fast charging performance.

[0210] For example, the specific surface area of ​​the negative electrode active material is 1.0 m². 2 / g、2m 2 / g、3m 2 / g、4m 2 / g、5m 2 / g、6m 2 / g、7m 2 / g、8m 2 / g、9m 2 / g, 10.0m 2 / g, 10.5m2 / g can be any value or any two values.

[0211] (d3) The thickness of the nitrogen-doped porous carbon layer is ≤500 nm;

[0212] When the thickness of the nitrogen-doped porous carbon layer is within the above range, it can improve the overall conductivity and structural stability of the negative electrode active material, and also help to further enhance the shuttle migration speed of active lithium ions in the negative electrode film, thereby improving the fast charging performance of the battery.

[0213] For example, the thickness of the nitrogen-doped porous carbon layer is any one of 10 nm, 50 nm, 100 nm, 200 nm, 300 nm, 400 nm, 490 nm, or 499 nm, or between any two of these values.

[0214] (d4) The carbon core includes at least one of artificial graphite and natural graphite.

[0215] Nitrogen-doped carbon-coated graphite obtained after surface coating has higher specific capacity and higher rate performance, which can further improve the energy density and fast charging performance of secondary batteries.

[0216] For example, the carbon core is artificial graphite.

[0217] Nitrogen-doped carbon-coated graphite obtained after surface coating has higher specific capacity and higher rate performance, which can further improve the energy density and fast charging performance of secondary batteries.

[0218] (d5) Nitrogen-doped porous carbon layers include at least one of nitrogen-doped porous soft carbon layers and nitrogen-doped porous hard carbon layers.

[0219] The nitrogen-doped porous carbon layer includes at least one of a nitrogen-doped porous soft carbon layer and a nitrogen-doped porous hard carbon layer, wherein the nitrogen-doped porous carbon layer is a nitrogen-doped porous soft carbon layer, the nitrogen-doped porous carbon layer is a nitrogen-doped porous hard carbon layer, or the nitrogen-doped porous carbon layer is a nitrogen-doped porous soft carbon layer and a nitrogen-doped porous hard carbon layer, wherein the nitrogen-doped porous soft carbon layer and the nitrogen-doped porous hard carbon layer are stacked, wherein the nitrogen-doped porous soft carbon layer may be located between the nitrogen-doped porous hard carbon layer and the carbon core, or the nitrogen-doped porous hard carbon layer may be located between the nitrogen-doped porous soft carbon layer and the carbon core.

[0220] The fourth aspect of this application provides a method for preparing a negative electrode active material, comprising:

[0221] The high-nitrogen polymer and carbon core are mixed and then carbonized in an inert atmosphere.

[0222] Among them, the total nitrogen content in the high-nitrogen polymer is ≥0.8%, and the high-nitrogen polymer includes pyrrole nitrogen and pyridine nitrogen. The total nitrogen content in the high-nitrogen polymer is 40%-90% by mass.

[0223] In this application, a high-nitrogen polymer is selected as both a carbon source and a nitrogen source. During the carbonization process, a nitrogen-doped carbon coating layer can be directly formed on the surface of the carbon core, which is beneficial for more uniform nitrogen doping and mesopore distribution.

[0224] In this application, by selecting a high-nitrogen polymer as both the carbon and nitrogen sources and controlling the total nitrogen content in the high-nitrogen polymer to be ≥0.8%, it is beneficial that some of the nitrogen in the high-nitrogen polymer decomposes and overflows during carbonization, creating pores in the formed carbon layer, such as mesopores and micropores. This is beneficial because the mesopores account for 40%-90% of the total pore volume of the negative electrode active material after carbonization, and the remaining nitrogen is doped in the carbon layer, which helps to achieve a total nitrogen content of 0.4%-3% by mass. At the same time, since pyrrole nitrogen and pyridine nitrogen together account for 40%-90% of the total nitrogen content in the high-nitrogen polymer, pyridine nitrogen and pyrrole nitrogen are more likely to be formed during carbonization, and the high content of pyridine nitrogen and pyrrole nitrogen in the carbon layer is beneficial because the total nitrogen content of pyrrole nitrogen and pyridine nitrogen together accounts for 30%-80% by mass.

[0225] In other words, the preparation method provided in this application selects a high-nitrogen polymer rich in pyridine nitrogen and pyrrole nitrogen as the carbon source and nitrogen source, and mixes it directly with the carbon core and then carbonizes it. This facilitates the process in which some nitrogen in the high-nitrogen polymer overflows to increase the mesopores of the negative electrode active material, while the remaining nitrogen is doped into the formed carbon layer and tends to form pyridine nitrogen and pyrrole nitrogen. The resulting negative electrode active material not only has a more uniform distribution of nitrogen doping and mesopores, but also simultaneously increases the mesopore content and nitrogen doping amount in the negative electrode active material. The nitrogen doping mainly exists in the form of pyrrole nitrogen and pyridine nitrogen. The high mesopore content effectively improves the wettability of the negative electrode active material, allowing solvated lithium ions to reach the surface of the carbon core more efficiently. The high nitrogen doping improves the adsorption capacity of the negative electrode active material for lithium ions, and the richness of pyrrole nitrogen and pyridine nitrogen improves the desolvation rate of solvated lithium ions and the lithium ion diffusion rate. The combined effect of these three factors accelerates the kinetic process during the charging of the secondary battery and effectively improves the fast charging performance of the secondary battery.

[0226] In some embodiments, the preparation method satisfies at least one of (e1)-(e3):

[0227] (e1) High-nitrogen polymers include at least one of high-nitrogen pitch and high-nitrogen copolymers;

[0228] Both the high-nitrogen asphalt and the high-nitrogen copolymer mentioned above can be used as nitrogen and carbon sources to prepare the above-mentioned negative electrode active materials.

[0229] High-nitrogen asphalt is mainly derived from petroleum asphalt, where the nitrogen compounds originate from natural heterocyclic nitrogen compounds in crude oil. During petroleum processing, these nitrogen compounds can be retained or further enriched to form high-nitrogen asphalt. For example, heavy petroleum asphalt is selected as a high-nitrogen asphalt, as it is the most common type of nitrogen-containing asphalt, directly derived from the crude oil refining process. Heavy petroleum asphalt contains various heterocyclic nitrogen compounds, such as pyridine, quinoline, indole, and their derivatives.

[0230] It should be noted that, in order to achieve a more uniform coating, when the high-nitrogen polymer is high-nitrogen asphalt, the two can be directly mixed. During the process of heating to the carbonization temperature, the high-nitrogen asphalt softens and coats the surface of the carbon core, and then carbonization is carried out at the carbonization temperature. When the high-nitrogen polymer is a high-nitrogen copolymer, the high-nitrogen copolymer can be dissolved in a solvent beforehand, mixed with the liquid phase of the carbon core, and then heated to the carbonization temperature for carbonization.

[0231] (e2) The carbonization temperature is 700℃-1300℃ and the carbonization time is 6h-15h.

[0232] The heat preservation time and temperature affect the carbonization depth. Controlling the carbonization temperature and time within the above range is beneficial in two ways: firstly, it ensures that enough nitrogen remains in the carbon layer after carbonization; secondly, it promotes the full carbonization of high-nitrogen polymers, reducing the impact of residual non-carbon elements and organic residues on the purity and long-term performance of the material. It also helps to form an ordered graphite structure, resulting in a finished product with good electrical conductivity and mechanical strength, as well as good pore structure and improved wettability.

[0233] For example, the carbonization temperature is any value of 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h or between any two values.

[0234] For example, the carbonization time is any value of 700°C, 750°C, 800°C, 850°C, 900°C, 950°C, 1000°C or between any two values.

[0235] Optionally, the temperature is increased to the carbonization temperature at a heating rate of 2℃ / min-20℃ / min.

[0236] For example, the heating rate is any value of 2℃ / min, 5℃ / min, 7℃ / min, 10℃ / min, 12℃ / min, 15℃ / min, 17℃ / min, 20℃ / min or between any two values.

[0237] (e3) The mass ratio of high-nitrogen polymer to carbon core is 100:2-20.

[0238] By using a mass ratio of high-nitrogen polymer to carbon core of 100:2-20, it is beneficial for the carbon coating layer to fully coat the surface of the carbon core, and avoid the carbon coating layer formed by carbonization being too thick, which would degrade the fast charging performance of the secondary battery.

[0239] For example, the mass ratio of the high-nitrogen polymer to the carbon core is any one of 100:2, 100:5, 100:7, 100:10, 100:12, 100:15, 100:17, 100:20 or between any two of these values.

[0240] In some embodiments, the high-nitrogen polymer is a high-nitrogen copolymer.

[0241] The nitrogen content in the high-nitrogen copolymer is 1%-5% by mass; and / or,

[0242] The carbonization temperature is 1000℃-1100℃; and / or,

[0243] High-nitrogen copolymers include acrylic acid-acrylonitrile copolymers.

[0244] Acrylic acid-acrylonitrile copolymers, through copolymerization of two or more monomers, can introduce more nitrogen, resulting in a high nitrogen content, which is beneficial for preparing the negative electrode active material of this application.

[0245] When selecting a high-nitrogen polymer as a high-nitrogen copolymer, by controlling the nitrogen mass content and / or the holding temperature within the above range, it is beneficial for the high-nitrogen copolymer to carbonize and form a nitrogen-doped porous hard carbon coating layer that coats the surface of the carbon core. Combined with the holding time, the carbonization depth is kept within a suitable range, thus obtaining a negative electrode active material that achieves both high mesoporous content and high nitrogen doping, which is beneficial for improving the fast charging performance of the battery.

[0246] For example, the insulation temperature is any value of 1000℃, 1010℃, 1020℃, 1030℃, 1040℃, 1050℃, 1060℃, 1070℃, 1080℃, 1090℃, 1100℃ or between any two values.

[0247] In some embodiments, the high-nitrogen polymer is high-nitrogen bitumen.

[0248] Among them, the nitrogen content in high-nitrogen asphalt is 0.8%-4% by mass; and / or,

[0249] The insulation temperature is 900℃-1300℃.

[0250] When high-nitrogen polymers are selected as high-nitrogen asphalt, by controlling the nitrogen mass content and / or the heat preservation temperature within the above range, it is beneficial for the high-nitrogen asphalt to carbonize and form a nitrogen-doped porous soft carbon coating layer that coats the surface of the carbon core. Combined with the heat preservation time, the carbonization depth is kept within a suitable range, so as to obtain a negative electrode active material that achieves both high mesoporous content and high nitrogen doping, which is beneficial to improving the fast charging performance of the battery.

[0251] For example, the nitrogen content in high-nitrogen asphalt is any one of 0.8%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, or 4.0%, or between any two of these values.

[0252] For example, the insulation temperature is any value of 700℃, 750℃, 800℃, 850℃, 900℃, 950℃, 1000℃ or between any two values.

[0253] In addition, the secondary battery, battery module, battery pack and power device of this application will be described below with appropriate reference to the accompanying drawings.

[0254] [Rechargeable Battery]

[0255] The second aspect of this application provides a secondary battery. This application does not particularly limit the type of secondary battery; for example, the secondary battery can be a lithium-ion battery, etc.

[0256] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0257] This application does not impose any particular restriction on the type of electrolyte, which can be selected according to actual needs. For example, the electrolyte can be selected from at least one of solid electrolytes and liquid electrolytes (i.e., electrolyte solutions). This applies to secondary batteries using electrolyte solutions, as well as some secondary batteries using solid electrolytes.

[0258] [Positive electrode plate]

[0259] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector.

[0260] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0261] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0262] In some embodiments, when the secondary battery is a lithium-ion battery, the positive electrode active material may be a positive electrode active material known in the art for lithium-ion batteries. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.8 Co 0.15 Al 0.05at least one of O2) and its modified compounds. Examples of the lithium phosphate with olivine structure may include, but are not limited to, lithium iron phosphate (such as LiFePO4 (which can also be abbreviated as LFP)), composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and composite material of lithium manganese iron phosphate and carbon.

[0263] In some embodiments, in order to further improve the energy density of the secondary battery, the positive electrode active material for the lithium ion battery may include a lithium transition metal oxide having the general formula Li a Ni b Co c M d O e A f and one or more of its modified compounds. 0.8 ≤ a ≤ 1.2, 0.5 ≤ b < 1, 0 < c < 1, 0 < d < 1, 1 ≤ e ≤ 2, 0 ≤ f ≤ 1, M is selected from one or more of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, and B, and A is selected from one or more of N, F, S, and Cl.

[0264] In some embodiments, by way of example, the positive electrode active material for the lithium ion battery may include LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (NCM523), LiNi 0.6 [[ID=三十二]]Co 0.2 Mn 0.2 O2 (NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811), LiNi<000"137>Co 0.15 Al 0.05 O2, LiFePO4, and LiMnPO4.

[0265] In the present application, the modified compounds of the above positive electrode active materials may be doping modification and / or surface coating modification of the positive electrode active materials.

[0266] As an optional technical solution of the present application, the polyanion-type compound may be Li 1+x Mn 1-y A y P 1-z "R zO4; where x is any value in the range of -0.100 to 0.100, y is any value in the range of 0.001 to 0.500, z is any value in the range of 0.001 to 0.100, A includes one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge, and R includes one or more elements selected from B, S, Si and N;

[0267] As an optional technical approach in this application, the polyanionic compound can be Li a A e Mn 1-f B f P 1-g C g O 4-n D n Wherein, A includes one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo, and W; B includes one or more elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb, and Ge; C includes one or more elements selected from B, S, Si, and N; D includes one or more elements selected from S, F, Cl, and Br; a is selected from the range of 0.9 to 1.1, e is selected from the range of 0.001 to 0.1, f is selected from the range of 0.001 to 0.5, g is selected from the range of 0.001 to 0.1, n is selected from the range of 0.001 to 0.1, and the second positive electrode active material is electrically neutral.

[0268] During the charging and discharging process of a battery, Li undergoes insertion / extraction and consumption, resulting in varying molar Li content at different discharge states. In the examples of cathode materials in this application, the molar Li content refers to the initial state of the material, i.e., the state before feeding. When the cathode material is applied to the battery system, the molar Li content changes after charge-discharge cycles.

[0269] In the examples of cathode materials in this application, the molar content of O is only a theoretical value. Oxygen release from the crystal lattice will cause changes in the molar content of oxygen, and the actual molar content of O will fluctuate.

[0270] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0271] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0272] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0273] [Negative electrode plate]

[0274] In some embodiments, the negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector.

[0275] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0276] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0277] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0278] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0279] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0280] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto a negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0281] [Electrolytes]

[0282] The electrolyte plays a role in conducting ions between the positive and negative electrode plates.

[0283] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0284] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0285] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0286] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0287] [Isolation membrane]

[0288] 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.

[0289] 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.

[0290] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0291] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0292] 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; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0293] In this application, a secondary battery can refer to a single battery cell, or it can refer to a single physical module comprising multiple battery cells to provide higher voltage and capacity, and it can take the form of a battery pack, battery module, etc.

[0294] This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 shows a square battery cell 5 as an example.

[0295] In some embodiments, referring to FIG2, the outer packaging may include a housing 51 and a top cover assembly 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the top cover assembly 53 can cover the opening to close the receiving cavity. The positive electrode sheet, negative electrode sheet, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 may be one or more, which can be selected by those skilled in the art according to specific practical needs.

[0296] In some implementations, individual battery cells can be assembled into a battery module. The number of individual battery cells contained in a battery module can be one or more, and the specific number can be selected by those skilled in the art based on the application and capacity of the battery module.

[0297] Figure 3 shows a battery module 4 as an example. Referring to Figure 3, in the battery module 4, multiple battery cells 5 can be arranged sequentially along the length of the battery module 4. Of course, they can also be arranged in any other manner. Furthermore, the multiple battery cells 5 can be fixed in place using fasteners.

[0298] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0299] 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 one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0300] Figures 4 and 5 show a battery pack 1 as an example. Referring to Figures 4 and 5, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper box 2 and a lower box 3, with the upper box 2 covering the lower box 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 box.

[0301] In addition, this application also provides an electrical device, which includes a secondary battery (at least one of a battery cell, battery module, or battery pack) provided in this application. The secondary battery can be used as a power source for the electrical device or as an energy storage unit of the electrical device. The electrical device may include, 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.

[0302] As an electrical device, you can choose individual battery cells, battery modules, or battery packs according to your usage requirements.

[0303] Figure 6 shows an example of an electrical device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0304] 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.

[0305] Example

[0306] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0307] Example 1

[0308] Negative electrode active materials

[0309] High-nitrogen asphalt and artificial graphite were mixed at a mass ratio of 10:1 and heated to 1050℃ in an argon atmosphere at a heating rate of 10℃ / min and held for 9 hours to obtain a negative electrode active material. The negative electrode active material includes an artificial graphite core and a nitrogen-doped porous carbon layer coated on its surface.

[0310] Among them, artificial graphite is secondary particle artificial graphite.

[0311] [Negative electrode plate]

[0312] The aforementioned negative electrode active material, thickener (carboxymethyl cellulose), binder (SBR), and conductive agent were mixed sequentially in a mass ratio of 97.3:1.2:0.8:0.7. This mixture was then combined with a solvent (deionized water) under vacuum stirring at specific parameters to prepare a negative electrode slurry. This slurry was then uniformly coated onto a copper foil used as a negative electrode current collector. After drying the coated current collector at room temperature, it was transferred to an oven for further drying. Following cold pressing and slitting, the negative electrode sheet was obtained. The single-sided areal density of the negative electrode film was 160 mg / cm³. 2 .

[0313]

Positive Electrode

[0314] The positive electrode active material NCM811(LiNi) 0.8 Co 0.1 Mn 0.1 O2), conductive agent (SuperP), binder (PVDF), etc. are mixed in a ratio of 96:2:2, solvent (NMP) is added, and the mixture is stirred under vacuum until the system becomes uniform and transparent to obtain a positive electrode slurry. The positive electrode slurry is uniformly coated onto the positive electrode current collector aluminum foil. The positive electrode current collector coated with the positive electrode slurry is dried at room temperature and then transferred to an oven for drying. After cold pressing and slitting, the positive electrode sheet is obtained.

[0315]

Isolation Film

[0316] A polyethylene film with a thickness of 12μm was selected.

[0317] Electrolyte

[0318] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1. Then, fully dried lithium salt LiPF6 was dissolved in the mixed organic solvent at a ratio of 1 mol / L to prepare an electrolyte.

[0319] Rechargeable batteries

[0320] The prepared positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrode. The electrode assembly is then wound up to obtain the electrode assembly. The electrode assembly is placed in the shell, baked, and then injected with electrolyte. After processes such as settling, hot and cold pressing, formation, aging, shaping, and capacity testing, a secondary battery is obtained.

[0321] Examples 2-16 and Comparative Examples 1-2

[0322] The main difference between the above embodiments and comparative examples lies in the negative electrode active material and the negative electrode sheet. The specific relevant parameters are shown in Table 1 and Table 2 below.

[0323] The only difference between Example 6 and Example 1 is that the artificial graphite selected in the preparation process is artificial graphite single particles. Due to the different selection of artificial graphite, the parameters of the prepared negative electrode active material change as shown in Table 1 and Table 2.

[0324] The only difference between Comparative Example 1 and Example 1 is that the total nitrogen content in the high-nitrogen precursor is only 0.40%, and the mass ratio of pyrrole nitrogen and pyridine nitrogen in the total nitrogen content of the high-nitrogen precursor is 74%, which leads to the changes in the parameters of the prepared negative electrode active material as shown in Table 1 and Table 2.

[0325] The only difference between Comparative Example 2 and Example 1 is that the parameters of the prepared negative electrode active material change as shown in Tables 1 and 2 because the mass percentage of pyrrole nitrogen and pyridine nitrogen in the total nitrogen content of the high nitrogen precursor is too small.

[0326] Table 1. Parameters for the differences between each embodiment and comparative example.

[0327]

[0328] Table 2. Parameters for the differences between each embodiment and comparative example.

[0329]

[0330] In addition, the secondary batteries prepared in the above embodiments and comparative examples were subjected to the following performance tests.

[0331] Fast charging performance test: The batteries of the above embodiments and comparative examples were charged and discharged for the first time at a current of 1C (i.e., the current value at which the theoretical capacity is completely discharged within 1 hour). Specifically, the batteries were charged at a constant current rate of 1C to a voltage of 4.4V at 35°C, then charged at a constant voltage rate to a current of ≤0.05C, left to stand for 5 minutes, and then discharged at a constant current rate of 0.33C to a voltage of 2.8V. The actual capacity was recorded as C0.

[0332] Then, the battery was sequentially charged at constant current rates of 1.0C0, 1.3C0, 1.5C0, 1.8C0, 2.0C0, 2.3C0, 2.5C0, 3.0C0, 3.5C0, 4C0, 4.5C0, and 5C0 until the full battery charging cutoff voltage of 4.4V or the negative terminal cutoff potential of 0V (whichever comes first). After each charging, the battery was discharged at 1C0 until the full battery discharge cutoff voltage of 2.8V. The negative terminal potentials corresponding to charging to 10%, 20%, 30%, ..., 80% SOC (State of Charge, where "SOC=0" indicates the battery is fully discharged and "SOC=100%" indicates the battery is fully charged) at different charging rates were recorded. The charging rates at different SOC states were plotted. The negative electrode potential curve, after linear fitting, yields the charging rate corresponding to a negative electrode potential of 0V under different SOC states. This charging rate is the charging window for that SOC state, denoted as C10%SOC, C20%SOC, C30%SOC, C40%SOC, C50%SOC, C60%SOC, C70%SOC, and C80%SOC. The charging time T, in minutes, is calculated using the formula (60 / C20%SOC + 60 / C30%SOC + 60 / C40%SOC + 60 / C50%SOC + 60 / C60%SOC + 60 / C70%SOC + 60 / C80%SOC) × 10%. The shorter this time, the better the battery's fast charging performance.

[0333] Fast charging cycle performance test: Step charge is performed at various SOC levels obtained from the fast charging performance test, specifically: C10% SOC CC to 10% SOC, C20% SOC CC to 20% SOC, C30% SOC CC to 30% SOC, C40% SOC CC to 40% SOC, C50% SOC CC to 50% SOC, C60% SOC CC to 60% SOC, C70% SOC CC to 70% SOC, C80% SOC CC to 80% SOC, 0.33C to 100% SOC, 0.33CDC to 2.5V. The number of cycles when fading to 80% SOH is recorded. Where C10% SOC represents the charging rate at 10% SOC, CC represents constant current charging, and DC represents...

[0334] The results are shown in Table 3.

[0335] Table 3: Performance test results of the examples and comparative examples

[0336]

[0337] According to Tables 1, 2 and 3, it can be seen that the secondary battery provided in this application embodiment has a low charging time from 10% SOC to 80% SOC and has good fast charging performance.

[0338] As can be seen from Example 1 and Comparative Example 1, the low nitrogen content in the precursor results in a low residual total nitrogen content in the prepared negative electrode active material and a small amount of overflow, leading to an excessively large contact angle of the negative electrode active material. This results in a long charging time for the secondary battery from 10% SOC to 80% SOC, a low number of cycles at 45°C and 80% SOH, and poor fast charging performance.

[0339] As can be seen from Example 2 and Comparative Example 2, the main reason is that the mass ratio of pyrrole nitrogen and pyridine nitrogen in the total nitrogen content of the negative electrode active material is too small, resulting in a long charging time for the secondary battery from 10% SOC to 80% SOC and poor fast charging performance.

[0340] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A secondary battery, wherein, Includes a negative electrode sheet, wherein the negative electrode sheet includes a negative electrode film layer; The negative electrode film layer includes a negative electrode active material, which includes a carbon core and a nitrogen-doped porous carbon layer covering the surface of the carbon core. The nitrogen-doped porous carbon layer includes pyrrole nitrogen, pyridine nitrogen, and mesopores. The mesopores account for 40%-90% of the total pore volume of the negative electrode active material. The total nitrogen content in the negative electrode active material accounts for 0.4%-3% by mass, and the pyrrole nitrogen and the pyridine nitrogen together account for 30%-80% of the total nitrogen content in the negative electrode active material by mass.

2. The secondary battery according to claim 1, wherein The contact angle of the negative electrode active material is 10°-38.5°.

3. The secondary battery according to claim 1 or 2, wherein The nitrogen-doped porous carbon layer contains micropores and macropores, and the micropores, macropores and mesopores are at least partially interconnected. The total volume of the micropores and macropores accounts for 10%-60% of the total pore volume of the negative electrode active material.

4. The secondary battery according to any one of claims 1 to 3, wherein The pyrrole nitrogen accounts for 12%-40% of the total nitrogen content of the negative electrode active material by mass; and / or, the pyridine nitrogen accounts for 15%-45% of the total nitrogen content of the negative electrode active material by mass.

5. The secondary battery according to any one of claims 1 to 4, wherein The pyrrole nitrogen and the pyridine nitrogen together account for 0.3%-0.9% of the mass of the negative electrode active material; and / or, The pyrrole nitrogen in the negative electrode active material accounts for 0.1%-0.4% by mass; and / or, The pyridine nitrogen in the negative electrode active material accounts for 0.2%-0.5% by mass.

6. The secondary battery according to any one of claims 1 to 5, wherein The nitrogen-doped porous carbon layer comprises graphitic nitrogen and nitrogen oxides; The graphite nitrogen accounts for 10%-30% of the total nitrogen content in the negative electrode active material by mass.

7. The secondary battery according to any one of claims 1-6, wherein, The negative electrode active material satisfies at least one of (a1)-(a5): (a1) The volumetric particle size distribution Dv50 of the negative electrode active material is 7μm-22μm; (a2) The specific surface area of ​​the negative electrode active material is 1.0 m². 2 / g-10.5m 2 / g; (a3) The thickness of the nitrogen-doped porous carbon layer is ≤500 nm; (a4) The carbon core includes at least one of artificial graphite and natural graphite; (a5) The nitrogen-doped porous carbon layer includes at least one of nitrogen-doped porous soft carbon layer and nitrogen-doped porous hard carbon layer.

8. The secondary battery according to any one of claims 1-7, wherein, The carbon core comprises secondary particulate graphite, wherein the volumetric particle size distribution Dv50 of the secondary particulate graphite is 9 μm-22 μm; or, The carbon core comprises graphite single particles, and the volumetric particle size distribution Dv50 of the graphite single particles is 5μm-10μm.

9. The negative electrode active material according to any one of claims 1-8, wherein, The nitrogen-doped porous carbon layer is a nitrogen-doped porous soft carbon layer, and the negative electrode active material satisfies at least one of (b1)-(b2): (b1) the specific surface area of the negative electrode active material is 1.0 m2 / g or more and 9.0 m2 / g or less 2 (g-9.0 m2 / g 2 (g; (b2) The nitrogen-doped porous carbon layer contains micropores and mesopores, wherein the micropores and the mesopores are at least partially interconnected, and the volume of the micropores accounts for 0-25% of the total pore volume, and / or the volume of the mesopores accounts for 63%-90% of the total pore volume.

10. The negative electrode active material according to any one of claims 1-9, wherein, The nitrogen-doped porous carbon layer is a nitrogen-doped porous hard carbon layer, and the negative electrode active material satisfies at least one of (c1)-(c3): (c1 ) the specific surface area of the negative electrode active material is 4.0 m2 / g to 10.5 m2 / g 2 / g to 10.5 m2 / g 2 / g; (c2) The nitrogen-doped porous carbon layer contains micropores and mesopores, wherein the micropores and the mesopores are at least partially interconnected, and the volume of the micropores accounts for 25%-50% of the total pore volume, and / or the volume of the mesopores accounts for 40%-85% of the total pore volume.

11. The secondary battery according to any one of claims 1-10, wherein, The single surface area density of the negative electrode film layer is 100 mg / cm 2 - 200 mg / cm 2 ; and / or, The compaction density of the negative electrode film layer is 1.3 g / cm 3 -1.8 g / cm 3 , and / or, The porosity of the negative electrode film is 20%-35%.

12. The secondary battery according to any one of claims 1-11, wherein, The negative electrode has an absorption rate of 0.5 mg / s for the E324 electrolyte. 1 / 2 -4mg / s 1 / 2 .

13. An electrical appliance, wherein, Includes the secondary battery as described in any one of claims 1-12.

14. A negative electrode active material, wherein, The negative electrode active material includes a carbon core and a nitrogen-doped porous carbon layer covering the surface of the carbon core, wherein the nitrogen-doped porous carbon layer includes pyrrole nitrogen, pyridine nitrogen, and mesopores. The mesopores account for 40%-90% of the total pore volume of the negative electrode active material. The total nitrogen content in the negative electrode active material accounts for 0.4%-3% by mass, and the pyrrole nitrogen and the pyridine nitrogen together account for 30%-80% of the total nitrogen content in the negative electrode active material by mass.

15. The negative electrode active material according to claim 14, wherein, The negative electrode active material satisfies at least one of (d1)-(d5): (d1) The volumetric particle size distribution Dv50 of the negative electrode active material is 7μm-22μm; (d2) The specific surface area of ​​the negative electrode active material is 1.0 m². 2 / g-10.5m 2 / g; (d3) The thickness of the nitrogen-doped porous carbon layer is ≤500 nm; (d4) The carbon core includes at least one of artificial graphite and natural graphite; (d5) The nitrogen-doped porous carbon layer includes at least one of nitrogen-doped porous soft carbon layer and nitrogen-doped porous hard carbon layer.

16. A method for preparing a negative electrode active material, wherein, include: The high-nitrogen polymer and carbon core are mixed and then carbonized in an inert atmosphere. The high-nitrogen polymer contains a total nitrogen content of ≥0.8%, and includes pyrrole nitrogen and pyridine nitrogen. The total nitrogen content of the high-nitrogen polymer by mass is 40%-90%.

17. The preparation method according to claim 16, wherein, The preparation method satisfies at least one of (e1)-(e3): (e1) The high-nitrogen polymer includes at least one of high-nitrogen pitch and high-nitrogen copolymer; (e2) The carbonization temperature is 700℃-1300℃, and the carbonization time is 6h-15h; (e3) The mass ratio of the high-nitrogen polymer to the carbon core is 100:2-20.

18. The preparation method according to claim 16 or 17, wherein, The high-nitrogen polymer is a high-nitrogen copolymer; Wherein, the nitrogen content in the high-nitrogen copolymer is 1%-5% by mass; and / or, The carbonization temperature is 1000℃-1100℃; and / or, The high-nitrogen copolymer includes an acrylic acid-acrylonitrile copolymer.

19. The preparation method according to claim 16 or 17, wherein, The high-nitrogen polymer is high-nitrogen asphalt; Wherein, the nitrogen content in the high-nitrogen asphalt is 0.8%-4% by mass; and / or, The carbonization temperature is 900℃-1300℃.

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