Negative active material, method for manufacturing the same, negative electrode sheet, secondary battery, and electric device

Abstract

This application provides a negative electrode active material and its preparation method, a negative electrode sheet, a secondary battery, and an electrical device. The preparation method of the negative electrode active material includes: coating graphite particles with an amide polymer having a fused ring structure to form a coating layer, obtaining a precursor of the negative electrode active material; and graphitizing the precursor of the negative electrode active material to obtain the negative electrode active material. The beneficial effects of the embodiments of this application are: on the one hand, the amide polymer has a fused ring structure, which easily forms a graphite layered structure after graphitization; on the other hand, during the graphitization process, nitrogen atoms in the amide polymer are distributed in sp... 2 The method involves embedding the carbon lattice of the graphite layer structure to form a graphite nitrogen structure. The nitrogen atoms in the graphite nitrogen structure provide additional free electrons, which improves the conductivity of the coating layer and thus enhances the fast-charging performance of the negative electrode active material.

Description

Technical Field

[0001] This application belongs to the field of new energy technology, and in particular relates to a negative electrode active material and its preparation method, a negative electrode sheet, a secondary battery, and electrical equipment. Background Technology

[0002] In some related technologies, the negative electrode active material includes graphite particles and coatings, with the coatings improving the performance of the negative electrode active material.

[0003] However, coating the negative electrode active material will affect the battery's fast charging performance. Summary of the Invention

[0004] This application provides a method for preparing a negative electrode active material, aiming to solve the technical problem of how to improve the conductivity of the negative electrode active material and thus enhance fast charging performance.

[0005] In a first aspect, embodiments of this application provide a method for preparing a negative electrode active material, the method comprising: coating graphite particles with an amide polymer having a fused ring structure to form a coating layer, thereby obtaining the negative electrode active material precursor; and graphitizing the negative electrode active material precursor to obtain the negative electrode active material.

[0006] Optionally, in some embodiments of this application, the method for preparing the amide polymer with a fused ring structure includes: performing a condensation reaction between a diacid anhydride with a fused ring structure and an aromatic diamine to obtain an amide polymer with a fused ring structure.

[0007] Optionally, in some embodiments of this application, the dicarboxylic anhydride having a fused ring structure includes one or more of perylene tetracarboxylic dianhydride (PTCDA) and pyromellitic tetracarboxylic dianhydride (PMDA).

[0008] Optionally, in some embodiments of this application, the aromatic diamine includes one or more of 4,4'-diaminodiphenyl ether (ODA), p-phenylenediamine (PDA), terephthalamide (TA), and 1,5-diaminonaphthalene (NDA).

[0009] Optionally, in some embodiments of this application, the solid content of the amide polymer having a fused ring structure ranges from 15% to 25%.

[0010] Optionally, in some embodiments of this application, the carbon residue of the amide polymer having a fused ring structure ranges from 55% to 65%.

[0011] Optionally, in some embodiments of this application, the amount of the amide polymer with the fused ring structure added is positively correlated with the residual carbon content of the coating layer, wherein the residual carbon content of the coating layer ranges from 0.2% to 0.7%.

[0012] Optionally, in some embodiments of this application, the graphite particles are coated with an amide polymer having a fused ring structure to form a coating layer; the coating process includes one or more of liquid phase spray coating and liquid phase fusion coating.

[0013] Optionally, in some embodiments of this application, the low-temperature graphitization treatment of the negative electrode active material precursor includes: heating the negative electrode active material precursor at 80°C to 300°C for 3 to 5 hours, with a heating rate of 1°C / min to 2°C / min, and holding at each of the following temperature ranges for 30 minutes: 150°C to 200°C, 220°C to 250°C, and 250°C to 300°C; and / or, heating at 300°C to 600°C for 2 to 3.5 hours. The heating rate is 2°C / min to 5°C / min, and the temperature is maintained at 400°C to 500°C for 30 min; and / or, the temperature is maintained at 600°C to 1500°C for 3 h to 8 h, with a heating rate of 2°C / min to 5°C / min; and / or, the temperature is maintained at 1500°C to 1800°C for 2 h to 3.5 h, with a heating rate of 2°C / min to 5°C / min; and / or, the temperature is maintained at 1800°C to 2000°C for 2 h to 4 h.

[0014] Optionally, in some embodiments of this application, the method for preparing the graphite particles includes: mixing petroleum coke particles, a binder, and a solvent to obtain a suspension; drying the suspension under preset drying conditions to obtain a carbonization precursor; carbonizing the carbonization precursor under preset granulation and carbonization conditions to obtain a graphitized precursor; and graphitizing the graphitized precursor under preset graphitization conditions to obtain the graphite particles, wherein the binder forms a granulated layer after graphitization.

[0015] Optionally, in some embodiments of this application, the Dv50 value of the petroleum coke particles ranges from 7 μm to 11 μm.

[0016] Optionally, in some embodiments of this application, the solvent includes one or more of water and N-methylpyrrolidone.

[0017] Optionally, in some embodiments of this application, the solid content of the suspension is 20% to 30%.

[0018] Optionally, in some embodiments of this application, the adhesive includes one or more of asphalt, phenolic resin, or amide polymers having a fused ring structure.

[0019] Optionally, in some embodiments of this application, the solid content of the adhesive ranges from 15% to 25%.

[0020] Optionally, in some embodiments of this application, the carbon residue rate of the adhesive ranges from 55% to 65%.

[0021] Optionally, in some embodiments of this application, the amount of binder added is positively correlated with the residual carbon content of the graphite particles, wherein the residual carbon content of the binder ranges from 0.8% to 2.0%.

[0022] Optionally, in some embodiments of this application, the preset drying conditions include: at least spray drying, wherein the spray inlet air temperature ranges from 220°C to 280°C, and the outlet air temperature ranges from 100°C to 140°C.

[0023] Optionally, in some embodiments of this application, the preset granulation carbonization conditions include: granulation carbonization heating conditions of a heating rate of 1°C / min to 2°C / min from 200°C to 600°C, wherein the temperature is held at 400°C to 500°C for 1 hour; and / or, a heating rate of 1°C / min to 2°C / min from 600°C to 1000°C, wherein the temperature is held at 700°C to 800°C for 1 hour; and / or, a heating rate of 1°C / min to 2°C / min from 1000°C to 1250°C, wherein the temperature is held at 1150°C to 1250°C for 2 hours; Optionally, in some embodiments of this application, the preset graphitization conditions include: the protective gas for graphitization includes one or more of nitrogen or argon. Optionally, in some embodiments of this application, the preset graphitization conditions include: a heating rate of 2°C / min to 5°C / min; and / or, processing at 1300°C to 1800°C for 2 to 5 hours; And / or, treat at 1800°C to 2400°C for 2 to 5 hours, and hold at 2100°C to 2200°C for 2 hours; and / or, treat at 2400°C to 2800°C for 2 to 5 hours; and / or, treat at 2800°C to 3000°C for 1 hour, and hold at 3000°C for 3 hours.

[0024] Secondly, embodiments of this application also provide a negative electrode active material, including the negative electrode active material prepared by the aforementioned preparation method.

[0025] Thirdly, embodiments of this application also provide a negative electrode sheet, including the aforementioned negative electrode active material or the negative electrode active material prepared by the aforementioned preparation method.

[0026] In some embodiments of this application, the sphericity Sh (90%) of the negative electrode active material ranges from 0.90 to 0.96.

[0027] In some embodiments of this application, the nitrogen content of the coating layer ranges from 1.3% to 2.0%.

[0028] In some embodiments of this application, the particle size D50 of the negative electrode active material ranges from 13.1 μm to 23.5 μm.

[0029] In some embodiments of this application, the powder orientation degree I004 / I110 of the negative electrode active material ranges from 1.20 to 1.60.

[0030] In some embodiments of this application, the graphite interlayer spacing d002 of the negative electrode active material ranges from 0.3357 nm to 0.3376 nm.

[0031] Fourthly, embodiments of this application also provide a secondary battery, including the aforementioned negative electrode.

[0032] Fifthly, embodiments of this application also provide an electrical device, including the aforementioned secondary battery.

[0033] The beneficial effects of the embodiments of this application are as follows: amide polymers with fused ring structures, on the one hand, have fused ring structures, which easily form graphite layered structures after graphitization; on the other hand, during the graphitization process, nitrogen atoms in the amide polymer are distributed in sp... 2 The nitrogen atoms are embedded in the carbon lattice of the graphite layered structure to form a graphitic nitrogen structure. On one hand, nitrogen atoms are uniformly distributed within the graphite layered structure, inducing surrounding carbon atoms to form "Li" atoms through electron cloud shift. + Traps (weak adsorption sites) promote Li + Uniform distribution in the bulk phase reduces local concentration polarization and improves fast-charging performance. On the other hand, because the electronegativity of nitrogen (N) atoms in graphite is higher than that of carbon (C), it induces the electron cloud of surrounding C atoms to shift towards N, forming a local negatively charged region that attracts Li. + Adsorption, and the introduction of nitrogen into the graphite increases the spacing between the graphite layers, promoting Li adsorption. + Diffusion indirectly improves capacity utilization. Attached Figure Description

[0034] To more clearly illustrate the solutions in this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0035] Figure 1 These are the main preparation steps of the negative electrode active material in some embodiments of this application; Figure 2 This is a SEM image of the negative electrode active material of Example 1 of this application. Detailed Implementation

[0036] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application. In addition, it should be understood that the specific embodiments described herein are only for illustration and explanation of this application and are not intended to limit this application. In this application, unless otherwise stated, directional terms such as "upper" and "lower" generally refer to the upper and lower positions of the device in actual use or operation, specifically the drawing directions in the accompanying drawings; while "inner" and "outer" refer to the outline of the device.

[0037] like Figure 1 To address the technical problem of improving the conductivity of negative electrode active materials and thus enhancing fast charging performance, this application provides a method for preparing negative electrode active materials, the method comprising: S100: A coating layer is formed by coating graphite particles with an amide polymer having a fused ring structure to obtain a precursor of negative electrode active material.

[0038] S200: The negative electrode active material precursor is graphitized to obtain the negative electrode active material.

[0039] Understandably, on the one hand, amide polymers have a fused ring structure, which easily forms a graphitic layered structure after graphitization; on the other hand, during the graphitization process, nitrogen atoms in amide polymers are distributed in sp... 2 The method involves embedding the carbon lattice of the graphite layer structure to form a graphite nitrogen structure. The nitrogen atoms in the graphite nitrogen structure provide additional free electrons, which improves the conductivity of the coating layer and thus enhances the fast-charging performance of the negative electrode active material.

[0040] In some embodiments, a method for preparing an amide polymer having a fused ring structure includes: performing a condensation reaction between a diacid anhydride having a fused ring structure and an aromatic diamine to obtain an amide polymer having a fused ring structure.

[0041] It is understandable that a condensation reaction between a diacid anhydride with a fused ring structure and an aromatic diamine yields an amide polymer with a fused ring structure. After graphitization, the resulting amide polymer with a fused ring structure contains graphite nitrogen in the coating layer, forming an ordered lattice nitrogen, which is beneficial for improving the fast-charging performance of the battery. In this application, graphite nitrogen refers to nitrogen atoms arranged in sp... 2 Hybridization is incorporated into the carbon lattice of the graphite layered structure.

[0042] In some embodiments, the dicarboxylic anhydride having a fused ring structure includes one or more of perylene tetracarboxylic dianhydride (PTCDA) and pyromellitic tetracarboxylic dianhydride (PMDA).

[0043] In some embodiments, the aromatic diamine includes one or more of 4,4'-diaminodiphenyl ether (ODA), p-phenylenediamine (PDA), terephthalamide (TA), and 1,5-diaminonaphthalene (NDA).

[0044] It is understandable that amide polymers with fused ring structures, formed by the condensation of diacid anhydrides with aromatic diamines, can be used to coat graphite particles. This is beneficial for forming a coating layer with graphite nitrogen on the surface of the graphite particles, thereby improving the fast charging performance of the battery.

[0045] In some embodiments, the solid content of the amide polymer having a fused ring structure ranges from 15% to 25%.

[0046] In some embodiments, the carbon residue rate of the amide polymer with a fused ring structure ranges from 55% to 65%. Here, the carbon residue rate in this application refers to the percentage of residual carbon that remains unburned or decomposed after high-temperature thermal decomposition of the polymer material in an inert gas atmosphere (such as nitrogen), relative to the initial sample mass. The corresponding standard for carbon residue rate is ASTM D4530-25, "Standard Test Method for Determination of Carbon Residue (Micro Method)". The high-temperature decomposition temperature for testing carbon residue rate in this application is 1150 degrees Celsius.

[0047] In some embodiments, the amount of amide polymer with a fused ring structure added is positively correlated with the residual carbon content of the coating layer, wherein the residual carbon content of the coating layer ranges from 0.2% to 0.7%.

[0048] It is understood that the residual carbon content of amide polymers with fused ring structures can be any value or a range of any two values, such as 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, and 0.7%. This application uses an amide polymer with a fused ring structure as the substrate to form a coating layer. The ratio of the mass of the substrate to the graphite particles = residual carbon content of the coating layer / (solid content of the substrate). (Carbon residue rate of the attached material). The carbon residue rate of the coating layer is set according to actual needs. An increase in the carbon residue rate of the coating layer indicates an increase in the amount of amide polymer with a fused ring structure added to the surface of the graphite particles, an increase in the thickness of the coating layer, an increase in the disorder of the graphite coating layer, an increase in the lithium intercalation channel, a shortening of the lithium ion diffusion path, and thus an improvement in fast charging performance. However, when the carbon residue rate of the coating layer is greater than the range of this application, the particle size of the negative electrode active material is too large, and the coating layer thickness and surface defects are too large, resulting in increased transport resistance, deterioration of fast charging performance, and a decrease in capacity and an increase in expansion rate. When the coating layer is too thin, the coating layer on the graphite surface is uneven, the protection is insufficient, the interface is unstable, and the SEI film thickens and the risk of lithium plating is high during fast charging.

[0049] In some embodiments, graphite particles are coated with an amide polymer having a fused ring structure to form a coating layer; the coating process includes one or more of liquid phase spray coating and liquid phase fusion coating.

[0050] In some embodiments, the negative electrode active material precursor is subjected to low-temperature graphitization treatment, including: the negative electrode active material precursor is heated at 80°C to 300°C for 3 to 5 hours, the heating rate is 1°C / min to 2°C / min, and the temperature is held at 150°C, 250°C, and 300°C for 30 minutes in each stage.

[0051] It is understandable that during the time range of 80°C to 300°C, the precursor of the negative electrode active material undergoes imidization of the amide polymer with a fused ring structure, forming a five-membered imide ring.

[0052] In some embodiments, the time at 300°C to 600°C is 2h to 3.5h, the heating rate is 2°C / min to 5°C / min, and the temperature is held at 500°C for 30min.

[0053] Understandably, within the temperature range of 300°C to 600°C, the imine ring breaks, and the cyano group (-C≡N) inserts into the aromatic fragment, forming a pyridine nitrogen precursor.

[0054] In some embodiments, the time between 600°C and 1500°C is 3 h to 8 h, and the heating rate is 2°C / min to 5°C / min.

[0055] It is understandable that aromatic rings condense to form nano-graphite layered structures within the temperature range of 600°C to 1500°C.

[0056] In some embodiments, the time between 1500°C and 1800°C is 2 h to 3.5 h, and the heating rate is 2°C / min to 5°C / min.

[0057] It is understandable that within the temperature range of 1500°C to 1800°C, nitrogen atoms are embedded in the carbon lattice of the graphite layered structure to form graphite nitrogen, and the bond positions are rearranged to form ordered lattice nitrogen.

[0058] In some embodiments, the time at 1800°C to 2000°C is 2 hours to 4 hours.

[0059] It is understandable that within the temperature range of 1800°C to 2000°C, the lattice of the cladding layer stabilizes and the six-membered ring is reconstructed.

[0060] In some embodiments, the method for preparing graphite particles includes: Petroleum coke particles, binder, and solvent are mixed to obtain a suspension; The suspension was dried under preset drying conditions to obtain a carbonized precursor. The carbonization precursor is carbonized under preset granulation and carbonization conditions to obtain a graphitized precursor. Graphitization of a graphitization precursor under preset graphitization conditions yields graphite particles, wherein the binder is graphitized to form a granulation layer.

[0061] It should be noted that the petroleum coke particles in this application refer to petroleum coke particles with a Dv50 within a certain range formed after processing petroleum coke raw materials.

[0062] In some embodiments, the petroleum coke feedstock includes low-sulfur petroleum coke, such as one or more of calcined Anqing coke and Jinling coke.

[0063] In some embodiments, the Dv50 value of petroleum coke particles ranges from 7 μm to 11 μm.

[0064] In some embodiments, the solvent includes one or more of water and N-methylpyrrolidone.

[0065] It is understood that, for the binders listed in this application, apart from bitumen, water is used as a solvent when adjusting the solid content, and when bitumen is used as a solvent, N-methylpyrrolidone (NMP) is required as a solvent.

[0066] In some embodiments, the solid content of the suspension is 20% to 30%.

[0067] Understandably, the solid content of the suspension within the scope of this application is moderate, which facilitates the formation of negative electrode active materials with appropriate particle size during spray granulation, thus improving battery capacity. When the solid content of the suspension exceeds 40%, the suspension concentration is high, resulting in poor fluidity; and the graphite content per unit volume is high, leading to a larger D50 of the spherical negative electrode active material prepared during spray granulation. Conversely, when the solid content of the suspension is lower, below 20%, the graphite content per unit volume is low, resulting in a lower D50 of the spherical negative electrode active material prepared during spray granulation. Furthermore, due to the low binder concentration, the spherical particles have poor bonding strength and are easily broken, thus affecting battery capacity.

[0068] In some embodiments, the binder includes one or more of asphalt, phenolic resin, or amide polymer having a fused ring structure.

[0069] In some embodiments, the solid content of the adhesive ranges from 15% to 25%.

[0070] In some embodiments, the carbon residue of the adhesive ranges from 55% to 65%.

[0071] In some embodiments, the amount of binder added is positively correlated with the carbon residue of the graphite particles, wherein the carbon residue of the binder ranges from 0.8% to 2.0%.

[0072] Wherein, binder mass / petroleum coke particles = residual carbon content of granulation layer / (binder solid content) (Carbonator carbon residue rate). The carbon residue rate of the granulation layer is set according to actual needs.

[0073] It is understood that the residual carbon content of the granulation layer can be any value or a range of any two values, such as 0.8%, 1.0%, 1.2%, 1.6%, 1.8%, and 2.0%. The negative electrode active material, after being bonded with the binder of this application and graphitized to form graphite particles, and then coated with an adhering material, exhibits high sphericity, thus improving the expansion rate of the non-in-situ electrode.

[0074] In some embodiments, preset drying conditions include: at least spray drying, wherein the spray inlet air temperature ranges from 220°C to 280°C and the outlet air temperature ranges from 100°C to 140°C.

[0075] Understandably, suitable spray drying conditions facilitate moisture evaporation, shorten drying time, and allow for better control of the particle size of the anode active material, thereby increasing capacity. Higher spray drying temperatures lead to rapid evaporation of moisture from the droplet surface and faster formation of spherical graphite particles, resulting in a larger D50 for the spherical anode active material and a tendency to produce hollow, porous, and brittle particles with a wider particle size distribution. Conversely, lower spray drying temperatures result in slower evaporation of moisture from the droplet surface, slower formation of spherical graphite particles, and a tendency to produce smaller, denser particles with a generally narrower particle size distribution.

[0076] In some embodiments, preset granulation carbonization conditions include: granulation carbonization heating conditions of a heating rate of 1°C / min to 2°C / min from 200°C to 600°C, wherein the temperature is held at 500°C for 1 hour; and / or, a heating rate of 1°C / min to 2°C / min from 600°C to 1000°C, wherein the temperature is held at 800°C for 1 hour; and / or, a heating rate of 1°C / min to 2°C / min from 1000°C to 1250°C, wherein the temperature is held at 1250°C for 2 hours.

[0077] Understandably, in the granulation carbonization temperature range of 200°C to 600°C, adsorbed water and residual solvents evaporate, molecular chains and functional groups break down, producing small molecules such as H2O, CH4, and HCN, and releasing CO and CO2. If the temperature is too high, the main chain and small molecules are excessively released, resulting in the loss of key elements such as carbon and nitrogen; if the temperature is too low, water and residual solvents do not evaporate sufficiently, leading to a disordered structure. The heating rate at this stage is 1°C / min to 2°C / min, allowing sufficient time for small molecules to migrate and form stable CC crosslinks, promoting the growth of graphite-like microregions. When the temperature rises too quickly, small molecules are released explosively, creating pores and cracks, resulting in a large specific surface area and improved fast-charging performance, but the capacity is affected; if the heating rate is too slow, the development process is too long, costly, and inefficient.

[0078] The heating rate from 600°C to 1000°C is 1°C / min to 2°C / min. During the 1-hour holding period at 800°C, the binder transitions from polymer to amorphous carbon. Residual aromatic rings undergo dehydrogenation and condensation to form polycyclic aromatic hydrocarbon structures. Free radical reactions lead to cross-linking of the carbon skeleton, generating graphite-like microregions. Excessive temperature results in the loss of key elements such as carbon and nitrogen; excessively low temperature leads to disordered molecular chains. A heating rate of 1°C / min to 2°C / min in this stage favors free radical reactions that lead to carbon skeleton cross-linking and the generation of graphite-like microregions. Too rapid a heating rate causes a sudden surge in free radical concentration, but migration is hindered, resulting in localized disordered cross-linking; too slow a heating rate leads to excessively long development processes, high costs, and low efficiency.

[0079] The heating rate from 1000°C to 1250°C was 1°C / min to 2°C / min, with a holding time of 2 hours at 1250°C. During this stage, the carbon microcrystals became ordered, and the proportion of sp² hybrid carbon increased. Due to limitations of the carbonization furnace equipment, higher carbonization temperatures could not be achieved. When the temperature was too low during this stage, sp² hybrid carbon... 3 Multiple structures, sp 2 Limited structure leads to capacity loss. The heating rate at this stage is 1°C / min to 2°C / min, resulting in high orderliness, enrichment of carbon and nitrogen elements, high structural strength, and an increased proportion of sp² hybrid carbon. If the heating rate is too fast, the yield of low-carbon materials decreases, and carbon layer defects or cracks appear; if the heating rate is too slow, the development process becomes too long, costly, and inefficient.

[0080] In some embodiments, the preset graphitization conditions include: the protective gas for graphitization includes one or more of nitrogen or argon.

[0081] In some embodiments, preset graphitization conditions include: Heating rate of 2°C / min to 5°C / min; and / or, treatment at 1300°C to 1800°C for 2 to 5 hours; And / or, treat at 1800°C to 2400°C for 2 to 5 hours, and hold at 2200°C for 2 hours; and / or, treat at 2400°C to 2800°C for 2 to 5 hours; and / or, treat at 2800°C to 3000°C for 1 hour, and hold at 3000°C for 3 hours.

[0082] Understanding this process involves processing at 1300°C to 1800°C for 2 to 5 hours to further eliminate volatiles, gradually forming a layered graphite structure and increasing particle size. Excessive temperature at this stage disrupts the natural growth of graphite crystallites, leading to high structural disorder; conversely, insufficient temperature results in a high proportion of sp³ hybrid carbon. The optimal heating rate at this stage is 2°C / min to 5°C / min. Excessive heating will cause carbon layer distortion, resulting in a high proportion of sp³ hybrid carbon and a significantly increased specific surface area; insufficient heating leads to excessively long processing times, high costs, and low efficiency.

[0083] The process involves treating the graphite layers at 1800°C to 2400°C for 2 to 5 hours, followed by a 2200°C hold-up period. During this stage, elongated, graphite-stacked planar layers are formed. Excessive temperature disrupts the growth of graphite crystallites, leading to high structural disorder; conversely, insufficient temperature results in low graphitization. A heating rate of 2°C / min to 5°C / min during this stage promotes the ordering of the graphite crystal structure and increases the proportion of sp² hybridized carbon. Excessive heating rate distorts the carbon layers, resulting in a high proportion of sp³ hybridized carbon and a significantly increased specific surface area; conversely, a low heating rate leads to excessively long processing times, high costs, and low efficiency.

[0084] Processing at 2400°C to 2800°C for 2 to 5 hours allows the graphite layered structure to gradually grow and stack. Excessive temperature disrupts the growth pattern of graphite crystallites, leading to high structural disorder; excessively low temperature results in low graphitization. A heating rate of 2°C / min to 5°C / min during this stage promotes the ordering of the graphite crystal structure and increases the proportion of sp² hybrid carbon. Excessively high heating rates distort the carbon layers, resulting in a high proportion of sp³ hybrid carbon and a significantly increased specific surface area; conversely, excessively low rates lead to excessively long processing times, high costs, and low efficiency.

[0085] The graphite is treated at 2800°C to 3000°C for 1 hour, followed by a hold at 3000°C for 3 hours. During this stage, graphite recrystallizes, further increasing its graphitization degree. Due to equipment limitations, the graphitization temperature is generally limited to a maximum of 3000°C. If the temperature is too low at this stage, the graphitization of the graphite particles will be insufficient. The heating rate at this stage, ranging from 2°C / min to 5°C / min, is beneficial for the ordered structure of the graphite crystals and increases the proportion of sp² hybrid carbon. If the heating rate is too high, the carbon layers will be distorted, resulting in a high proportion of sp³ hybrid carbon and a significantly increased specific surface area; if the rate is too low, the recrystallization degree of graphite will be poor, and the graphitization degree will be low.

[0086] As a second aspect of this application, this application also provides a negative electrode active material, including a negative electrode active material prepared by the preparation method described above.

[0087] In some embodiments, the sphericity Sh (90%) of the negative electrode active material ranges from 0.90 to 1.0.

[0088] It is understandable that the sphericity Sh (90%) of the negative electrode active material can be any value or a range of any two values ​​from 0.90, 0.91, 0.92, 0.93, 0.94, 0.95, and 0.96. For example... Figure 2 As shown, the negative electrode active material exhibits good sphericity. A negative electrode active material with high sphericity has high isotropy and multiple lithium-intercalation end faces, providing more lithium-ion intercalation channels and thus improving fast-charging performance. Simultaneously, the high sphericity of the particles buffers volume changes, allowing stress to be released in all directions and improving the expansion rate.

[0089] In some embodiments, the nitrogen content of the coating layer ranges from 1.3% to 2.0%.

[0090] It is understandable that the nitrogen content of the coating layer refers to the ratio of nitrogen element to the total mass of the coating layer. The nitrogen content in the coating layer can be any value or a range of any two values ​​from 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, and 2.0%. Nitrogen element is present in the coating layer, and the nitrogen element exists mainly in the form of graphitic nitrogen.

[0091] In some embodiments, the particle size D50 of the negative electrode active material ranges from 13.1 μm to 23.5 μm.

[0092] Understandably, the particle size of the negative electrode active material can range from any value or any two values ​​within the ranges of 13.1, 13.8, 14, 14.5, 14.8, 15, 15.2, 15.4, 15.5, 15.8, 16.4, 16.5, 16.8, 17.6, 17.8, 18.8, 19.8, and 23.5. When the petroleum coke particles have a uniform particle size, increasing the particle size of the negative electrode active material can improve expansion and rate performance; however, when the particle size is too large, the processing performance becomes abnormal.

[0093] In some embodiments, the powder orientation degree I004 / I110 of the negative electrode active material ranges from 1.20 to 1.60. The powder orientation degree I004 / I110 can be any value or a range of any two values ​​from 1.20, 1.22, 1.22, 1.22, 1.26, 1.30, 1.31, 1.32, 1.34, 1.34, 1.35, 1.38, 1.40, 1.42, 1.44, 1.48, 1.50, 1.58, and 1.60.

[0094] It is understandable that the smaller the powder orientation degree I004 / I110, the higher the isotropy of the particles, the more lithium intercalation end faces, and the more lithium intercalation channels are provided for lithium ion intercalation, thereby improving fast charging performance; at the same time, the particles with higher sphericity buffer volume changes, so that stress is released in all directions, improving the expansion rate.

[0095] In some embodiments of this application, the graphite interlayer spacing d002 of the negative electrode active material ranges from 0.3357 nm to 0.3376 nm.

[0096] It is understandable that the graphite interlayer spacing d002 of the negative electrode active material can take any value or any two values ​​from 0.3357, 0.3358, 0.3359, 0.336, 0.3361, 0.3362, 0.3363, 0.3364, 0.3365, 0.3367, 0.3368, 0.337, and 0.3376.

[0097] In some embodiments of this application, the particle size distribution span value (D90-D10) / D50 of the negative electrode active material is <1.5.

[0098] In some embodiments of this application, the graphitization degree of the negative electrode active material is greater than 94%.

[0099] As a third aspect of this application, this application also provides a negative electrode sheet, including the negative electrode active material as described above.

[0100] As a fourth aspect of this application, this application also provides a secondary battery, including the negative electrode as described above.

[0101] As a fifth aspect of this application, this application also provides an electrical device, including a secondary battery as described above.

[0102] The present application will be further described below through specific embodiments. Unless otherwise specified, the experimental materials used in the embodiments can be purchased from conventional biochemical reagent companies.

[0103] Example 1 The graphite anode material is prepared according to the following steps: Step 1: The low-sulfur calcined Anqing petroleum coke raw material is processed by a coarse crusher, mechanical mill and shaping machine to obtain petroleum coke particles with a Dv50 of 8 microns.

[0104] Step 2: Take 1.5 kg of petroleum coke granules, weigh 218.75 g of binder (the binder is polyamic acid synthesized by PMDA:ODA=1:1, with a solid content of 16% and a carbon residue rate of 60%) according to the granulation layer residual carbon rate of 1.4%, add 5 kg of water according to the solid content of 30%, and place it in a double planetary mixer and stir at 1600 rpm for 1 hour to obtain a suspension.

[0105] Step 3: The suspension is transferred to the spray plate by a peristaltic pump. Under the strong centrifugal force of the centrifugal spray plate, the rotation speed is 13000 rpm, forming small droplets. The spray inlet air temperature is 240°C and the outlet air temperature is 120°C. The spherical carbonized precursor is obtained by instantaneous water evaporation and drying.

[0106] Step 4: The obtained carbonized precursor was carbonized in a roller kiln under a nitrogen atmosphere at a heating rate of 2°C / min for 3.5 hours, followed by a holding time at 500°C for 1 hour. Then, the temperature was increased to 2°C / min for 3.5 hours between 600°C and 1000°C, followed by a holding time at 800°C for 1 hour. Finally, the temperature was increased to 2°C / min for 2 hours between 1000°C and 1250°C, followed by a holding time at 1250°C for 2 hours, yielding the graphitized precursor.

[0107] Step 5: The obtained graphitized precursor is graphitized in a medium-frequency furnace under a nitrogen atmosphere at a heating rate of 5°C / min. The process is carried out at 1300°C to 1800°C for 2 hours, 1800°C to 2400°C for 5 hours, and then held at 2200°C for 2 hours. The process is carried out at 2400°C to 2800°C for 4 hours, 2800°C to 3000°C for 1 hour, and then held at 3000°C for 3 hours to obtain graphite particles.

[0108] Step 6: Take 1 kg of graphite particles, weigh 41.7 g of coating material (the binder is polyamic acid synthesized by PMDA:ODA=1:1, with a solid content of 16% and a carbon residue rate of 60%) according to the residual carbon rate of the coating layer of 0.4%, add 4 L of water according to the solid content of 25%, and place it in a planetary mixer and stir at 1600 rpm for 1 hour to obtain a suspension.

[0109] Step 7: Rapidly and instantaneously evaporate and dry the material at 220°C by spray drying to obtain the precursor of the negative electrode active material.

[0110] Step 8: The obtained negative electrode active material precursor is imidized in a protective atmosphere at 80℃ to 300℃ for 3.3h with a heating rate of 2℃ / min, and held at 150℃, 250℃, and 300℃ for 30 min each; then at 300℃ to 600℃ for 2h with a heating rate of 5℃ / min, and held at 500℃ for 30 min; then at 600℃ to 1500℃ for 3h with a heating rate of 5℃ / min; then at 1500℃ to 1800℃ for 3.5h with a heating rate of 2℃ / min; and finally at 1800℃ to 2000℃ for 4h to obtain the negative electrode active material.

[0111] In this embodiment, ODA (4.2 mol) was added to deionized water (8.4 kg), and a small amount of hydrochloric acid was added to adjust the pH to 2-3. The mixture was stirred until completely dissolved. PMDA (4.2 mol) was added to the ODA solution in batches (dropping rate 1 g / min), and the temperature was controlled at 40°C. Stirring was continued (40°C to 50°C, 6-12 hours) to induce polycondensation and generate polyamic acid. Triethylamine (TEA, 5 mol) was then added to form an aqueous polyimide slurry. The imidized solution was transferred to a vacuum degassing tank (-0.09 MPa, 25°C) to remove air bubbles. The solution was then filtered through a 1-5 μm filter membrane and stored at 5-10°C under sealed conditions.

[0112] In the embodiments of this application, the synthesis steps of polyamic acid in other embodiments or comparative examples are the same as those in this embodiment, only the raw materials are replaced accordingly.

[0113] Example 2 The difference between this embodiment and embodiment 1 is that the residual carbon rate of the coating layer in step 6 is 0.2%, and the amount of coating layer is adjusted accordingly.

[0114] Example 3 The difference between this embodiment and embodiment 1 is that the residual carbon rate of the coating layer in step 6 is 0.3%, and the amount of coating layer is adjusted accordingly.

[0115] Example 4 The difference between this embodiment and embodiment 1 is that the residual carbon rate of the coating layer in step 6 is 0.5%, and the amount of coating layer is adjusted accordingly.

[0116] Example 5 The difference between this embodiment and Embodiment 1 is that the residual carbon rate of the coating layer in step 6 is 0.6%, and the amount of coating layer is adjusted accordingly.

[0117] Example 6 The difference between this embodiment and embodiment 1 is that the residual carbon rate of the coating layer in step 6 is 0.7%, and the amount of coating layer is adjusted accordingly.

[0118] Example 7 The difference between this embodiment and embodiment 1 is that the residual carbon rate of the coating layer in step 6 is 1.0%, and the amount of coating layer is adjusted accordingly.

[0119] Example 8 The difference between this embodiment and embodiment 1 is that the residual carbon rate of the granulation layer in step 2 is 0.4%, and the amount of binder is adjusted accordingly.

[0120] Example 9 The difference between this embodiment and embodiment 1 is that the residual carbon rate of the granulation layer in step 2 is 0.8%, and the amount of binder is adjusted accordingly.

[0121] Example 10 The difference between this embodiment and embodiment 1 is that the residual carbon rate of the granulation layer in step 2 is 1.0%, and the amount of binder is adjusted accordingly.

[0122] Example 11 The difference between this embodiment and embodiment 1 is that the residual carbon rate of the granulation layer in step 2 is 1.2%, and the amount of binder is adjusted accordingly.

[0123] Example 12 The difference between this embodiment and embodiment 1 is that the residual carbon rate of the granulation layer in step 2 is 1.6%, and the amount of binder is adjusted accordingly.

[0124] Example 13 The difference between this embodiment and embodiment 1 is that the residual carbon rate of the granulation layer in step 2 is 1.8%, and the amount of binder is adjusted accordingly.

[0125] Example 14 The difference between this embodiment and embodiment 1 is that the residual carbon rate of the granulation layer in step 2 is 2.0%, and the amount of binder is adjusted accordingly.

[0126] Example 15 The difference between this embodiment and Embodiment 1 is that the residual carbon rate of the granulation layer in step 2 is 2.2%, and the amount of binder is adjusted accordingly.

[0127] Example 16 The difference between this embodiment and embodiment 1 is that the adhering substance in step 6 is polyamic acid prepared by PTCDA:TA=1:1.

[0128] Example 17 The difference between this embodiment and embodiment 1 is that the adhering substance in step 6 is polyamic acid prepared by PTCDA:NDA=1:1.

[0129] Example 18 The difference between this embodiment and Embodiment 1 is that the particle size of the petroleum coke particles in step 1 is 6 micrometers.

[0130] Example 19 The difference between this embodiment and Embodiment 1 is that the particle size of the petroleum coke particles in step 1 is 7 micrometers.

[0131] Example 20 The difference between this embodiment and Embodiment 1 is that the particle size of the petroleum coke particles in step 1 is 9 micrometers.

[0132] Example 21 The difference between this embodiment and Embodiment 1 is that the particle size of the petroleum coke particles in step 1 is 10 micrometers.

[0133] Example 22 The difference between this embodiment and Embodiment 1 is that the particle size of the petroleum coke particles in step 1 is 11 micrometers.

[0134] Example 23 The difference between this embodiment and Embodiment 1 is that the binder in step 2 is liquid asphalt YQ2 from Liaoning Aoyida New Material Co., Ltd., and the corresponding solvent is replaced with NMP.

[0135] Example 24 The difference between this embodiment and embodiment 1 is that the adhesive in step 2 is phenolic resin, specifically 7475 liquid resin from Jiangmen Kunyi Resin Materials Technology Co., Ltd.

[0136] Example 25 The difference between this embodiment and Embodiment 1 is that the adhesive in step 2 is a polyamic acid formed by CHDA:ODA=1:1, which does not contain a fused ring structure.

[0137] Example 26 The difference between this embodiment and Embodiment 1 is that the heating rate in step 8, which is between 80°C and 300°C, is 5°C / min.

[0138] Example 27 The difference between this embodiment and Embodiment 1 is that the heating rate in step 8, within the range of 300℃ to 600℃, is 5℃ / min.

[0139] Example 28 The difference between this embodiment and Embodiment 1 is that the heating rate in step 8, within the range of 600℃ to 1500℃, is 5℃ / min.

[0140] Example 29 The difference between this embodiment and embodiment 1 is that the highest temperature in step 8 is 1500℃, and the duration is the same.

[0141] Example 30 The difference between this embodiment and Embodiment 1 is that the highest temperature in step 8 is 1500℃, while the duration is the same.

[0142] Example 31 The difference between this embodiment and embodiment 1 is that the spray inlet temperature in step 3 is 300°C.

[0143] Example 32 The difference between this embodiment and embodiment 1 is that the spray inlet air temperature in step 3 is 200°C.

[0144] Example 33 The difference between this embodiment and embodiment 1 is that the spray outlet temperature in step 3 is 160°C.

[0145] Example 34 The difference between this embodiment and embodiment 1 is that the spray outlet temperature in step 3 is 90°C.

[0146] Example 35 The difference between this embodiment and Embodiment 1 is that the heating rate of the carbonization process in step 4 is 5°C / min.

[0147] Example 36 The difference between this embodiment and embodiment 1 is that no heat preservation was performed at 500℃ in step 4.

[0148] Example 37 The difference between this embodiment and embodiment 1 is that no heat preservation was performed at 1250℃ in step 4.

[0149] Example 38 The difference between this embodiment and embodiment 1 is that no heat preservation was performed at 2200℃ in step 5.

[0150] Example 39 The difference between this embodiment and Embodiment 1 is that no heat preservation was performed at 3000℃ in step 5.

[0151] Example 40 The difference between this embodiment and embodiment 1 is that step 5 does not involve high-temperature treatment at 2800°C to 3000°C.

[0152] Example 41 The difference between this embodiment and embodiment 1 is that the negative electrode active material precursor obtained in step 8 is subjected to carbonization treatment at a maximum temperature of 1250°C for 12 hours.

[0153] Comparative Example 1 The difference between this comparative example and Example 1 is that: no coating was performed in step 6, and the graphite particles obtained in step 5 were used as the negative electrode active material.

[0154] Comparative Example 2 The difference between this comparative example and Example 1 is that the raw material for the coating layer in step 6 is YQ2 asphalt.

[0155] Comparative Example 3 The difference between this comparative example and Example 1 is that the raw material for the coating layer in step 6 is 7475 phenolic resin.

[0156] Comparative Example 4 The difference between this comparative example and Example 1 is that the raw material for the coating layer in step 6 is polyacrylic acid.

[0157] Comparative Example 5 The difference between this comparative example and Example 1 is that the raw material for the coating layer in step 6 is polyamic acid formed by CHDA:ODA=1:1, which does not contain a fused ring structure.

[0158] Test methods for negative electrode active materials: Nitrogen content of the coating layer: obtained by EDS analysis of the coating layer.

[0159] Median particle size test method: The particle size distribution range is tested using a Malvern MS3000 laser particle size analyzer with wet sample injection.

[0160] Sphericity testing method: Sphericity was tested using a Malvern Panaco M4 automatic static image analyzer; Sh(90%) indicates that the cumulative mass distribution of particles smaller than this sphericity value is 90%; The method for testing the interlayer spacing d002 (nm) of graphite is as follows: The diffraction angle of the 002 crystal plane of graphite particles is obtained by X-ray diffraction (XRD) test and analysis. According to Bragg's equation: 2dsinθ=nλ (λ is the wavelength of the incident ray, and n is the diffraction order 1), the interlayer spacing d002 of the graphite material is calculated.

[0161] Powder orientation I004 / I110: The diffraction intensity of different 004 and 110 crystal planes is analyzed by X-ray diffraction (XRD). The powder orientation is the intensity ratio of the 004 / 110 crystal planes.

[0162] Preparation methods and specific testing methods for button batteries The manufacturing method of button batteries is as follows: The performance of the negative electrode materials in the examples and comparative examples was verified using a half-cell test method. The mixing ratio was: graphite:CMC:SP:SBR = 95:1.5:1.5:2. A suitable amount of water was added to form a slurry, which was then coated onto copper foil. The coated electrode was placed in a vacuum drying oven at 110℃ and dried for 4 hours. The electrolyte was 1 mol / L LiPF6, EC / DEC / DM = 1:1:1. A lithium metal sheet was used as the counter electrode, and a polypropylene microporous membrane was used as the separator. The cells were assembled into a battery.

[0163] The testing method for button batteries is as follows: Battery capacity characterization test: First, charge the battery with a constant current of 0.2C to 4.2V, then charge it with a constant voltage to 10mA, and then let it rest for 10 minutes. Then discharge it with a constant current of 0.2C to 2.7V, and let it rest for 10 minutes. Repeat this charge and discharge cycle 3 times to obtain the battery capacity.

[0164] Rate testing: The prepared coin cells are cycled 10 times each at 0.1C, 0.5C, 1C, 2C, and 0.1C. The 2C / 0.2C discharge capacity retention rate can be calculated by dividing the 2C discharge capacity by the 0.2C discharge capacity. In the table, "2C / 0.2C" represents the 2C / 0.2C discharge capacity retention rate.

[0165] Testing of in-situ electrode expansion rate: The thickness change of the electrode before and after 20 cycles is tested to obtain the in-situ expansion rate of the electrode.

[0166] The relevant experimental data, process parameters and test results are detailed in Tables 1 to 4.

[0167] Table 1. Raw material parameters of Examples 1 to 25 and Comparative Examples 1 to 5 of this application.

[0168] Table 2 Test results of Examples 1 to 25 of this application and Comparative Examples 1 to 5

[0169] Table 3 Process parameters for Examples 26 to 41

[0170] Table 4 Test results of Examples 26 to 41

[0171] By comparing Examples 1 to 7 with Comparative Example 1, it can be found that the residual carbon content of the coating layer is within the scope of this application. Examples 1 to 6 have better capacity, rate performance, and non-in-situ electrode expansion rate. Comparative Example 1, without coating, has a slightly improved capacity, but its rate performance is significantly reduced. The residual carbon content of the coating layer in Example 7 is too high, which is not conducive to the utilization of the graphite particle capacity. The reason is that the residual carbon content of the coating layer is within the scope of this application, which increases the disorder of the graphite surface layer, increases the lithium intercalation channels, shortens the lithium-ion diffusion path, and thus improves fast charging performance.

[0172] like Figure 2 As shown, this application uses an amide polymer with a fused ring structure as a binder and an amide polymer with a fused ring structure as an adhesive. After graphitization, a coating layer is formed, resulting in a negative electrode active material with good sphericity.

[0173] Comparing Examples 1 and 8 to 15 reveals that using an amide polymer with a fused ring structure as a binder results in better capacity, rate performance, and in-situ electrode expansion rate for Examples 1 and 7 to 13. Example 15 exhibits a small particle size, low granulation strength, poor isotropy, and a high in-situ electrode expansion rate. Example 8 has excessively large particle size and poor processing performance. This is because the negative electrode active material formed using an amide polymer with a fused ring structure has a moderate D50 and good sphericity, resulting in high isotropy and numerous lithium-intercalation faces, providing more lithium-intercalation channels and thus improving fast-charging performance. Simultaneously, the high sphericity of the particles buffers volume changes, allowing stress to be released in all directions, thus improving the expansion rate.

[0174] By comparing Examples 1 to 6 with Comparative Examples 2 to 5, it can be found that Comparative Examples 2 to 5 use other materials to form the coating layer. The powder orientation I004 / I110 of Examples 1 to 6 is lower than that of Comparative Examples 2 to 5, and the capacity is higher. This indicates that Examples 1 to 6 have higher isotropy than Comparative Examples 2 to 5. The possible reason is that the coating layer raw material in Examples 1 to 6 is an amide polymer with a fused ring structure, which has better binder properties. The prepared negative electrode material has high sphericity and high isotropy. Moreover, the amide polymer with a fused ring structure has a better degree of graphitization, and the negative electrode active material coating layer has a graphitic nitrogen structure after graphitization, which makes the battery capacity of Examples 1 to 6 better.

[0175] By comparing Examples 1, 9 to 14, and 23 to 25, it can be found that the powder orientation I004 / I110 and the expansion rate of the non-in-situ electrode in Examples 23 to 25 are higher than those in Examples 1 and 9 to 14, while the sphericity and capacity are lower. This is because the amide polymer with a fused ring structure has a planar conjugated structure, and the high sphericity and isotropy of the negative electrode active material result in the advantages of large capacity and multiple lithium-ion insertion / extraction channels, balancing rate performance and energy density, while also exhibiting low expansion characteristics.

[0176] By comparing Example 1 with Examples 26 to 28, it can be found that Example 26, at a heating rate of 5°C / min from 80°C to 300°C, has a lower rate performance, possibly because the imidization of polyamic acid is incomplete and volatilizes quickly at this stage. Example 27, at a heating rate of 5°C / min from 300°C to 600°C, experiences rapid volatilization due to the breakage of the imid ring, resulting in nitrogen loss. Example 28, with a heating rate of 5°C / min, also suffers from nitrogen loss, affecting its rate performance.

[0177] By comparing Example 1 with Examples 29 and 30, graphite particles were subjected to low-temperature graphitization after the coating layer was attached. When the low-temperature graphitization temperature was too low, graphitic nitrogen could not be generated, and pyridine nitrogen or pyrrole nitrogen was the main component, which had a significant impact on capacity. When the low-temperature graphitization temperature was too high, graphitic nitrogen was unstable, its content decreased, and its capacity performance declined.

[0178] By comparing Example 1 with Examples 31 to 34, it can be found that the inlet and outlet air temperatures of spray drying must be within the range specified in this application. The corresponding drying temperatures of Examples 31 and 33 are relatively high, resulting in excessively fast drying, hollow spherical graphite structures, poor bonding strength, and affecting the performance of battery capacity.

[0179] A comparison of Example 1 and Example 35 shows that the granulation carbonization heating rate of Example 35 was 5°C / min, which was too high, resulting in incomplete imidization. 3 It is predominantly a hybrid structure and has a low capacity.

[0180] A comparison of Example 1 and Example 36 reveals that in Example 36, the carbonization process for preparing graphite particles was not maintained at 500°C, resulting in incomplete imidization. 3 It is predominantly a hybrid structure and has a low capacity.

[0181] By comparing Example 1 with Examples 37 to 39, in the graphitization process of graphite particle preparation in Examples 37 to 39, the lattice structure had high disorder and low capacity when no heat preservation was performed at 1250℃, 2200℃ and 2200℃.

[0182] By comparing Example 1 and Example 40, Example 37, which was not subjected to high-temperature treatment at 2800°C to 3000°C, has a high degree of lattice disorder, low capacity, and large interlayer spacing.

[0183] By comparing Example 1 and Example 41, the coating layer only underwent carbonization treatment, resulting in an increased nitrogen content in the final coating layer. However, since the coating layer only underwent carbonization treatment, the amorphous carbon content in the coating layer of Example 41 was higher than that of Example 1. Therefore, the capacity of Example 1 was lower than that of Example 1.

[0184] In summary, embodiments 1 to 6 of this application improve rate performance by coating graphite particles with graphite nitrogen in the coating layer.

[0185] In embodiments 9 to 13 of this application, the sphericity of the negative electrode active material is high after the petroleum coke particles are bonded with the binder of this application and graphitized to form graphite particles, and after being coated with an attachment, which improves the expansion rate of the non-in-situ electrode.

[0186] The embodiments of this application have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this application. The description of the above embodiments is only for the purpose of helping to understand the method and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A method for preparing a negative electrode active material, characterized in that, The preparation method includes: Petroleum coke particles, binder, and solvent are mixed to obtain a suspension; The suspension was dried under preset drying conditions to obtain a carbonized precursor; The carbonization precursor is carbonized under preset granulation and carbonization conditions to obtain a graphitized precursor. The graphitization precursor is graphitized under preset graphitization conditions to obtain graphite particles. The graphite particles are coated with an amide polymer having a fused ring structure to form a coating layer, thereby obtaining a precursor for the negative electrode active material. The negative electrode active material precursor is graphitized to obtain the negative electrode active material. The binder is graphitized to form a granulated layer; the amount of binder added is positively correlated with the residual carbon content of the granulated layer, wherein the residual carbon content of the granulated layer ranges from 0.8% to 2.0%.

2. The preparation method according to claim 1, characterized in that, The method for preparing the amide polymer with a fused ring structure includes: A condensation reaction is carried out between a diacid anhydride with a fused ring structure and an aromatic diamine to obtain an amide polymer with a fused ring structure.

3. The preparation method according to claim 2, characterized in that, The dicarboxylic acid anhydride having a fused ring structure includes one or more of perylene tetracarboxylic dianhydride and pyromellitic tetracarboxylic dianhydride; And / or, the aromatic diamine includes one or more of 4,4'-diaminodiphenyl ether, p-phenylenediamine, terephthalamide, and 1,5-diaminonaphthalene; And / or, the solid content of the amide polymer having a fused ring structure ranges from 15% to 25%; And / or, the carbon residue of the amide polymer having a fused ring structure ranges from 55% to 65%; And / or, the amount of the amide polymer with the fused ring structure added is positively correlated with the residual carbon content of the coating layer, wherein the residual carbon content of the coating layer ranges from 0.2% to 0.7%.

4. The preparation method according to claim 1, characterized in that, In the step of coating graphite particles with an amide polymer having a fused ring structure to form a coating layer... The coating process includes one or more of liquid phase spray coating and liquid phase fusion coating.

5. The preparation method according to claim 4, characterized in that, The graphitization treatment of the negative electrode active material precursor includes: The negative electrode active material precursor is heated to 300°C for 3 to 5 hours at a temperature of 80°C to 300°C, with a heating rate of 1°C / min to 2°C / min, and is held at 150°C to 200°C, 220°C to 250°C, and 250°C to 300°C for 30 minutes in each temperature range. And / or, at 300°C to 600°C for 2 to 3.5 hours, at a heating rate of 2°C / min to 5°C / min, and at 400°C to 500°C for 30 minutes; And / or, the time between 600°C and 1500°C is 3 h to 8 h, and the heating rate is 2°C / min to 5°C / min; And / or, the time at 1500°C to 1800°C is 2 h to 3.5 h, and the heating rate is 2°C / min to 5°C / min; And / or, at 1800°C to 2000°C for 2 to 4 hours.

6. The preparation method according to claim 1, characterized in that, The Dv50 value of the petroleum coke particles ranges from 7 μm to 11 μm; And / or, the solvent includes one or more of water and N-methylpyrrolidone; And / or, the solid content of the suspension is 20% to 30%; And / or, the adhesive comprises one or more of asphalt, phenolic resin, or amide polymer having a fused ring structure; And / or, the solid content of the adhesive is in the range of 15% to 25%; And / or, the carbon residue of the adhesive is in the range of 55% to 65%.

7. The preparation method according to claim 1, characterized in that, The preset drying conditions include: at least spray drying, wherein the spray inlet air temperature ranges from 220°C to 280°C, and the outlet air temperature ranges from 100°C to 140°C. And / or, the preset granulation carbonization conditions include: granulation carbonization heating conditions of a heating rate of 1°C / min to 2°C / min from 200°C to 600°C, wherein the temperature is held at 400°C to 500°C for 1 hour; and / or, a heating rate of 1°C / min to 2°C / min from 600°C to 1000°C, wherein the temperature is held at 700°C to 800°C for 1 hour; and / or, a heating rate of 1°C / min to 2°C / min from 1000°C to 1250°C, wherein the temperature is held at 1150°C to 1250°C for 2 hours; And / or, the preset graphitization conditions include: the protective gas for graphitization includes one or more of nitrogen or argon; And / or, the preset graphitization conditions include: Heating rate of 2°C / min to 5°C / min; and / or, treatment at 1300°C to 1800°C for 2 to 5 hours; And / or, treat at 1800°C to 2400°C for 2 to 5 hours, and hold at 2100°C to 2200°C for 2 hours; and / or, treat at 2400°C to 2800°C for 2 to 5 hours; and / or, treat at 2800°C to 3000°C for 1 hour, and hold at 3000°C for 3 hours.

8. A negative electrode active material, characterized in that, This includes negative electrode active materials prepared by the preparation method according to any one of claims 1 to 7.

9. The negative electrode active material according to claim 8, characterized in that, The sphericity Sh (90%) of the negative electrode active material ranges from 0.90 to 0.96; And / or, the nitrogen content of the coating layer ranges from 1.3% to 2.0%; And / or, the particle size D50 of the negative electrode active material ranges from 13.1 μm to 23.5 μm; And / or, the powder orientation degree I004 / I110 of the negative electrode active material ranges from 1.20 to 1.60; And / or, the graphite interlayer spacing d002 of the negative electrode active material ranges from 0.3357 nm to 0.3376 nm.

10. A negative electrode sheet, characterized in that, Includes the negative electrode active material as described in claim 8 or 9.

11. A secondary battery, characterized in that, Includes the negative electrode sheet as described in claim 10.

12. An electrical appliance, characterized in that, Includes the secondary battery as described in claim 11.

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