Negative electrode material and secondary battery

Abstract

The present application provides a negative electrode material and a secondary battery. The negative electrode material comprises graphite composite particles, a cross-section of each graphite composite particle being divided into an inner core region A and a near-surface region B, the near-surface region B being disposed around the periphery of the inner core region A, a pore filling rate of the inner core region A being a, and a pore filling rate of the near-surface region B being b, where 85%≤a / b≤99%, and b≥90%. The graphite composite particles in the negative electrode material provided by the present application have a high internal pore filling rate and a low specific surface area, and in particular, the near-surface region B has a higher pore filling rate. Even if the graphite composite particles are directly exposed to an electrolyte, the problem of performance deterioration is effectively ameliorated, thereby effectively improving initial Coulombic efficiency and interface transmission performance.

Description

Anode materials and secondary batteries

[0001] This application claims priority to Chinese patent application 202411804036.5, filed on December 9, 2024. The entire contents of the aforementioned Chinese patent application are incorporated herein by reference. Technical Field

[0002] This application relates to the field of battery materials technology, and more specifically, to a negative electrode material and a secondary battery. Background Technology

[0003] Secondary batteries possess advantages such as high specific capacity, high operating voltage, good safety, and no memory effect, and are widely used in electric vehicles, smartphones, laptops, and other fields. Currently, graphite anode materials still dominate in commercially available secondary batteries. Natural graphite is widely used due to its high charge / discharge capacity, low charge / discharge plateau, and low production cost. However, due to its high anisotropy and abundant surface defects, natural graphite has the following drawbacks as a secondary battery anode material: ① In propylene carbonate (PC)-based electrolytes, a large number of solvated lithium ions (Li... + ) Co-embedded in the graphite anode, leading to the exfoliation of the graphite layered structure. ②Li + Li only exists at the edge of the graphite end face + Transport activity, leading to Li + Low transfer efficiency and poor rate performance. ③ Graphite surface defects are highly active, easily reacting with Li during the initial lithium intercalation. + Irreversible side reactions occur, reducing the initial coulombic efficiency.

[0004] To improve the electrochemical performance of natural graphite, the mainstream approach is to use a crushing-spheroidizing technique to curl flake graphite into spherical graphite, followed by a further pitch coating-carbonization process to achieve uniform soft carbon coating. This method can effectively reduce the anisotropy of natural graphite, increase tap density, and improve interfacial stability. However, natural graphite still has many pores after these processes, making it difficult to coat and modify using conventional pitch mixing and carbonization processes. During cycling, electrolyte molecules gradually penetrate into the pores inside the graphite, reacting with the uncoated flake graphite and causing capacity loss in lithium batteries.

[0005] Some researchers have conducted studies on the preparation of modified natural graphite, using a method that includes: first, processing natural graphite in a shaping machine; then, mixing graphite and asphalt evenly in the shaping machine to obtain a mixture; next, subjecting the mixture to isostatic pressing to obtain an extruded body; finally, carbonizing the extruded body and then sieving it to obtain the final product. Although this method uses external pressure to force the asphalt into the pores of the graphite, the low fluidity of the asphalt and the poor pore filling of the graphite particles still lead to a deterioration in the performance of the secondary battery when directly exposed to the electrolyte. Summary of the Invention

[0006] The main objective of this application is to provide an anode material and a secondary battery to solve the problem that graphite anode materials in the prior art are difficult to achieve good specific capacity, initial coulombic efficiency and cycle stability.

[0007] To achieve the above objectives, according to a first aspect of this application, a negative electrode material is provided, the negative electrode material comprising graphite composite particles, the cross-section of which is divided into a core region A and a near-surface region B, the near-surface region B surrounding the periphery of the core region A, the pore filling rate of the core region A being a, the pore filling rate of the near-surface region B being b, and 85% ≤ a / b ≤ 99%, b ≥ 90%.

[0008] According to a second aspect of this application, a secondary battery is provided, which includes the negative electrode material provided in the first aspect of this application.

[0009] Applying the technical solution of this application, the pore filling rate b of the near-surface region B in the graphite composite particles of the negative electrode material provided by this application is ≥90%, and the pore filling rate a of the core region A and the pore filling rate b of the near-surface region B satisfy 85% ≤ a / b ≤ 99%. This results in a high internal pore filling rate and low specific surface area for the graphite composite particles, especially with a higher pore filling rate in the near-surface region B. This effectively mitigates performance degradation even when directly exposed to the electrolyte, thereby significantly improving the initial coulombic efficiency and interfacial transport performance. Conversely, if b < 90%, it indicates a low pore filling rate in the near-surface region B. When it comes into direct contact with the electrolyte, the contact area is too large, making it prone to side reactions and leading to a significant decrease in its electrochemical performance. When a / b < 85%, it indicates that even though the near-surface region B has fewer pores, the core region A has a low pore filling rate and more pores. When it comes into direct contact with a large amount of electrolyte, the contact area is too large, which can easily lead to side reactions, resulting in a significant decrease in the initial coulombic efficiency and cycle performance. When a / b > 99%, the lithium-ion diffusion performance is poor, and the specific capacity of the anode material is low. Attached Figure Description

[0010] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings:

[0011] Figure 1 is a schematic diagram of the structure of a secondary battery provided in an embodiment of this application during charging;

[0012] Figure 2 is a schematic diagram of the structure of a secondary battery provided in an embodiment of this application during discharge;

[0013] Figure 3 shows a scanning electron microscope image of the negative electrode material provided according to Embodiment 1 of this application.

[0014] The above figures include the following reference numerals:

[0015] 100. Electrode assembly; 101. Positive electrode; 102. Negative electrode; 103. Separator. Detailed Implementation

[0016] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present application will now be described in detail with reference to the embodiments.

[0017] As analyzed in the background section of this application, natural graphite is widely used due to its high charge / discharge capacity, low charge / discharge plateau, and low production cost. However, natural graphite contains numerous pores, and during cycling, electrolyte molecules gradually penetrate into these pores, causing performance degradation. To address this issue, this application provides a negative electrode material and a secondary battery.

[0018] In a first typical embodiment of this application, a negative electrode material is provided, comprising graphite composite particles. The cross-section of the graphite composite particles is divided into a core region A and a near-surface region B. The near-surface region B surrounds the periphery of the core region A, and the major axis L of the core region A is... a =1 / 2L1, minor axis L b =1 / 2L2, the porosity of the core region A is a, the porosity of the near-surface region B is b, 85%≤a / b≤99%, and b≥90%.

[0019] In this application, the graphite composite particles include a graphite core and an amorphous carbon coating layer located on at least a portion of the surface of the graphite core. Simultaneously, the pores of at least a portion of the graphite core are filled with amorphous carbon. The amorphous carbon can be distinguished by TEM observation.

[0020] In this application, the near-surface region B refers to the area outside the core region A in the cross-section of the graphite composite particle; the pore filling rate refers to (area of ​​the cross-section of the graphite composite particle - area of ​​pores in the cross-section of the graphite composite particle) / area of ​​the cross-section of the graphite composite particle.

[0021] In this application, the method for determining the core region and the near-surface region located on the periphery of the core region is as follows: A negative electrode material particle is selected, and a circular or elliptical region is selected on the core cross-section of the particle. The intersection of the transverse median and the longitudinal median of the core cross-section of a single particle is used as the center of the ellipse or circle. A circle is formed when the transverse median and the longitudinal median are equal. The major axis of the ellipse or circle is half the length of the transverse median, and the minor axis is half the length of the longitudinal median. The core cross-section is divided into the core region (A) and the near-surface region (B) by the outline of the ellipse. The transverse median is the longest horizontal diameter of the cross-section in the test interface. The longitudinal median is perpendicular to the transverse median and passes through the midpoint of the transverse median, intersecting with the edge of the material cross-section.

[0022] As shown in Figure 3, the inner side of the ellipse's outline is the core region (A), and the outer side of the ellipse's outline is the near-surface region (B).

[0023] By selecting the shape described above, the core region can be located at the center of the cross-section as much as possible, and can be clearly distinguished from the near-surface region, thereby more accurately testing the porosity ratio of the core region and the near-surface region.

[0024] The core region represents the average state of the internal region of the particle, while the near-surface region represents the average state of the peripheral region of the particle. In some embodiments, the core region is circular or elliptical, and its center is the intersection of the transverse median and the longitudinal median of the core section. The definition of the core region ensures that the analysis scope covers the central portion of the particle's core section.

[0025] The graphite composite particles in the negative electrode material provided in this application have a pore filling rate b ≥ 90% in the near-surface region B, and the pore filling rate a in the core region A and the pore filling rate b in the near-surface region B satisfy 85% ≤ a / b ≤ 99%. The graphite composite particles have a high internal pore filling rate and a low specific surface area, especially the near-surface region B, which has an even higher pore filling rate. This effectively mitigates performance degradation even when directly exposed to the electrolyte, thereby significantly improving the initial coulombic efficiency and interfacial transport performance. Conversely, if b < 90%, it indicates a low pore filling rate in the near-surface region B. When it comes into direct contact with the electrolyte, the contact area is too large, making it prone to side reactions and leading to a significant decrease in its electrochemical performance. When a / b < 85%, it means that even though the near-surface region B has fewer pores, the core region A has a lower pore filling rate and more pores. When it comes into direct contact with a large amount of electrolyte, the contact area is too large, which can easily lead to side reactions and cause a significant decrease in the initial coulombic efficiency and cycle performance. When a / b > 99%, the lithium-ion diffusion rate is low and the specific capacity of the anode material is low.

[0026] Furthermore, the negative electrode material provided in this application is filled with highly disordered carbon material, thus possessing excellent kinetic transport performance.

[0027] Specifically, but not limitingly, the ratio of the pore filling rate 'a' of the core region A to the pore filling rate 'b' of the near-surface region B in the graphite composite particles of the negative electrode material can be 85%, 88%, 90%, 92%, 95%, 98%, 99%, or any range of two values, or 85% ≤ a / b ≤ 90%, or 85% ≤ a / b ≤ 92%, or 90% ≤ a / b ≤ 99%. The pore filling rate of the near-surface region B can be 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or any range of two values, or b ≥ 92%, or b ≥ 94%, or b ≥ 96%.

[0028] In some embodiments, the pore filling rate α of the core region A in the graphite composite particles of the negative electrode material can be 82% to 98.5%, specifically, but not limitingly, α can be 90% to 98.5%, or α can be any value within the range of 82%, 84%, 86%, 88%, 90%, 92%, 94%, 96%, 98%, 98.5%, or any combination of the above values. Controlling the pore filling rate α of the core region A within the above range helps to improve the specific capacity and structural stability of the negative electrode material, thereby enhancing the overall electrochemical performance of the negative electrode material.

[0029] In some embodiments, the average pore size of the core region A is R1, and the average pore size of the near-surface region B is R2, where R1 > R2 and 1.1 < R1 / R2 < 4. This results in the average pore size of the near-surface region inside the graphite composite particle being smaller than the average pore size of the core region. Consequently, the near-surface region of the graphite composite particle has a higher density, which is more conducive to improving its stability, further mitigating performance degradation issues, and improving the first coulombic efficiency and interfacial transport performance. Furthermore, when 85% ≤ a / b ≤ 99%, b ≥ 90%, and 1.1 < R1 / R2 < 4, the internal pores of the graphite composite particle are even smaller. Even when it is in direct contact with a large amount of electrolyte, this further reduces the occurrence of side reactions, thereby further improving the capacity and first coulombic efficiency of the anode material.

[0030] In this application, R1 / R2 can be 1.15, 1.20, 1.25, 1.30, 1.35, 1.50, 1.80, 2.0, 2.5, 3.0, 3.9 or any two values ​​within a range, or 1.1 < R1 / R2 ≤ 1.50, or 1.1 < R1 / R2 ≤ 3.0, or 1.50 ≤ R1 / R2 ≤ 3.9, or 2.0 ≤ R1 / R2 < 4.

[0031] In some embodiments, R1 is 0.05 μm-0.65 μm; specifically, but not limitingly, R1 can be 0.1 μm-0.65 μm, or any value within the range of 0.09 μm, 0.1 μm, 0.18 μm, 0.2 μm, 0.25 μm, 0.3 μm, 0.35 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.65 μm, or any combination of two of the above values. Controlling R1 within the above range helps reduce the probability of side reactions and improve the cycle stability of the negative electrode material.

[0032] In some embodiments, R2 is 0.08 μm-0.25 μm; specifically, but not limitingly, R2 can be 0.1 μm-0.21 μm, or any value within the range of 0.08 μm, 0.1 μm, 0.12 μm, 0.14 μm, 0.16 μm, 0.18 μm, 0.20 μm, 0.21 μm, 0.23 μm, 0.25 μm, or any combination of two of the above values. Controlling R2 within the above range helps to improve the density of the negative electrode material, thereby helping to improve the energy density of the negative electrode material; in addition, controlling R2 within the above range also helps to improve the cycle stability of the negative electrode material.

[0033] In some embodiments, the average particle size of the negative electrode material is 4μm-25μm, such as 4μm, 5μm, 8μm, 10μm, 12μm, 15μm, 18μm, 20μm, 22μm, 25μm or any combination of two values. Controlling the average particle size of the negative electrode material within the above range is beneficial to improving the compaction density of the negative electrode sheet prepared by using it as a negative electrode material.

[0034] In some embodiments, the carbon content of the negative electrode material is ≥99wt% to further improve its conductivity and ion transport performance.

[0035] In some embodiments, the Raman spectrum of the negative electrode material contains a D peak and a G peak, and the peak intensity of the D peak is I. D The peak intensity of peak G is I G I D / I G The range is 0.3-0.9, such as 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.7, 0.75, 0.8, 0.85, 0.9 or any two values. This indicates that the negative electrode material has both a certain degree of graphitization (i.e., order) and an appropriate amount of disorder or defects, which is beneficial to the negative electrode material having excellent electrochemical performance.

[0036] In a second typical embodiment of this application, a method for preparing a negative electrode material is also provided. The method includes the following steps: Step S1, mixing natural graphite particles, organic conductive small molecule monomers and an initiator with water, wherein the organic small molecule monomers undergo polymerization under the initiation of the initiator to form a conductive polymer, and the conductive polymer is deposited into the inner and outer layers of the natural graphite particles to obtain a graphite polymer composite material; Step S2, subjecting the graphite polymer composite material to a first calcination treatment to obtain a graphite carbonization intermediate; Step S3, mixing the graphite carbonization intermediate with a soft carbon precursor and performing molding and pulverization treatment to obtain a negative electrode material precursor; Step S4, subjecting the negative electrode material precursor to a second calcination treatment to obtain a negative electrode material; wherein the negative electrode material includes graphite composite particles, the cross-section of the graphite composite particles is divided into a core region A and a near-surface region B, the near-surface region B surrounds the periphery of the core region A, the pore filling rate of the core region A is a, the pore filling rate of the near-surface region B is b, 85% ≤ a / b ≤ 99%, and b ≥ 90%.

[0037] The method for preparing the anode material provided in this application utilizes the good wettability in a liquid phase environment. A graphite carbonization intermediate is obtained through liquid-phase filling combined with a single calcination process. This intermediate is then mixed with a soft carbon precursor, and through molding and a second calcination, a target anode material with high density and good stability is obtained. This method also has advantages such as high practicality and applicability to natural graphite particles of different sizes.

[0038] Specifically, in the preparation method of the negative electrode material provided in this application, organic conductive small molecule monomers and initiators are mixed with natural graphite particles in water, allowing some of the organic conductive small molecule monomers to penetrate into the inner layer of the natural graphite particles. Then, under the action of the initiator, the organic conductive small molecule monomers undergo a polymerization reaction to form a conductive polymer. This conductive polymer is deposited onto the inner and outer layers of the natural graphite particles, respectively, to obtain a graphite polymer composite material. The graphite polymer composite material is then subjected to a first calcination treatment, allowing the conductive polymers in the inner and outer layers of the natural graphite particles to... The carbonized compound partially fills the inner layer of natural graphite particles and partially coats the outer layer of natural graphite particles to obtain a graphite carbonization intermediate. The graphite carbonization intermediate and a soft carbon precursor are then subjected to a molding process, in which part of the soft carbon precursor is pressed into the pores inside the graphite carbonization intermediate. After pulverization, a second calcination process is carried out to carbonize the soft carbon precursor into soft carbon, which partially fills the pores inside the graphite carbonization intermediate and partially coats the outside of the graphite carbonization intermediate. This achieves high pore filling and yields an anode material with further improved density and stability.

[0039] Furthermore, the negative electrode material provided in this application is used as a negative electrode active material in secondary batteries. Thanks to the high density and stability of the negative electrode material, the secondary battery has the characteristics of high initial coulombic efficiency and fast interfacial transport, exhibiting excellent electrochemical performance.

[0040] In step S1 above, the specific type of water is not limited. However, in order to avoid introducing impurities that may affect the electrochemical performance of the negative electrode material, the water is preferably any one or a mixture of deionized water, purified water, or distilled water.

[0041] To further promote the penetration of organic conductive small molecule monomers and initiators into the interior of natural graphite particles, in some embodiments, in step S1 above, natural graphite particles and water are first mixed, and the pH value is adjusted to 1-10 (e.g., 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, etc.). Then, organic conductive small molecule monomers are added and mixed, allowing more organic conductive small molecule monomers to enter the interior of natural graphite particles. Finally, an initiator is added, allowing the organic conductive small molecule monomers to undergo a polymerization reaction under the action of the initiator, forming a conductive polymer uniformly deposited in the inner and outer layers of natural graphite particles, filling the pores inside the natural graphite particles. The conductive polymer outside the natural graphite particles is wrapped around the outer layer of the natural graphite particles, resulting in a graphite polymer composite material, which further improves the electrical performance of the negative electrode material.

[0042] In some specific embodiments, the pH value of the mixed solution of natural graphite particles and water is adjusted to 1-10 using acidic or alkaline substances. Acidic substances include, but are not limited to, any one or more mixed acids selected from hydrochloric acid, sulfuric acid, phosphoric acid, and nitric acid; alkaline substances include, but are not limited to, any one or more mixtures selected from lithium hydroxide, sodium hydroxide, potassium hydroxide, sodium carbonate, and sodium bicarbonate.

[0043] In step S1 above, organic conductive small molecule monomers are converted into cationic free radicals in water. Similar cationic free radicals form dimers in a head-to-tail connection manner. The dimers continue to grow to form polymers with higher polymerization degree and are uniformly deposited on the inner and outer layers of natural graphite particles.

[0044] The initiators mentioned above are commonly used initiators in this field, including but not limited to any one or more of ammonium sulfate, hydrogen peroxide, ferric chloride, and aluminum chloride.

[0045] To further improve initiation efficiency, in some embodiments, the initiator is first prepared into an initiator solution, and then the initiator solution is added to a solution formed by natural graphite particles, water, and organic conductive small molecule monomers. Preferably, the molar concentration of the initiator solution is 0.1 mol / L-2 mol / L, such as 0.1 mol / L, 0.2 mol / L, 0.5 mol / L, 0.8 mol / L, 1.0 mol / L, 1.2 mol / L, 1.5 mol / L, 1.8 mol / L, 2 mol / L, or any range of two such values.

[0046] The specific type of the above-mentioned organic conductive small molecule monomer is not limited, but it is preferably an aniline compound, and more preferably any one or more of aniline, diphenylamine, phenylenediamine, triphenylamine, methylaniline, ethylaniline, and nitroaniline.

[0047] To further improve the efficiency of the polymerization reaction, the preferred polymerization temperature is 1℃-65℃, and the polymerization time is 1h-30h. Controlling the polymerization conditions within the above range is beneficial for the polymerization reaction to proceed fully, thereby improving polymerization efficiency and the uniformity of the molecular weight distribution of the conductive polymer.

[0048] The polymerization temperature can be 1℃, 2℃, 5℃, 8℃, 10℃, 15℃, 20℃, 25℃, 30℃, 35℃, 40℃, 50℃, 60℃, 65℃ or any range of two values; the polymerization time can be 1h, 2h, 3h, 5h, 8h, 10h, 12h, 15h, 18h, 20h, 25h, 30h or any range of two values.

[0049] To further improve the electrical performance of the anode material, in some embodiments, the mass ratio of natural graphite particles to organic conductive small molecule monomers is 100:(1-20), such as 100:1, 100:1.5, 100:2, 100:3, 100:5, 100:8, 100:10, 100:12, 100:15, 100:18, 100:20, or any range of two such values. Controlling the amount of organic conductive small molecule monomers within the above range helps to improve the overall electrochemical performance of the anode material.

[0050] To improve the efficiency of liquid phase filling, in some embodiments, the mass ratio of natural graphite particles to water is 100:(100-500), such as 100:100, 100:150, 100:200, 100:250, 100:300, 100:350, 100:400, 100:450, 100:500, or any range of two values.

[0051] To further improve the porosity of the negative electrode material, the average particle size of the natural graphite particles is preferably 4μm-22μm. Specifically, the average particle size of the natural graphite particles can be 4μm, 5μm, 8μm, 10μm, 15μm, 18μm, 20μm, 22μm, or any combination of two values.

[0052] In step S2 above, in order to further improve the carbonization efficiency of the conductive polymer, the preferred calcination temperature is 200℃-1500℃ and the calcination time is 1h-20h, so as to facilitate the carbonization of the conductive polymer to form hard carbon. Some of the hard carbon fills the pores inside the natural graphite particles, and some of the hard carbon coats the outside of the natural graphite particles, which in turn helps to improve the electrochemical performance of the prepared negative electrode material.

[0053] Typically, but not limitingly, the temperature for a single calcination can be 200℃, 250℃, 300℃, 400℃, 500℃, 600℃, 700℃, 800℃, 900℃, 1000℃, 1100℃, 1200℃, 1300℃, 1400℃, 1500℃ or any range of two values, and the time for a single calcination can be 1h, 2h, 5h, 8h, 10h, 12h, 15h, 18h, 20h or any range of two values.

[0054] To avoid introducing impurities during the primary calcination process that could affect the electrical performance of the negative electrode material, it is preferable to carry out the primary calcination under a protective atmosphere, such as nitrogen or argon.

[0055] In step S3 above, the soft carbon precursor is not limited. In order to further promote the soft carbon precursor to be pressed into the interior of the graphite carbonization intermediate, in some embodiments, the soft carbon is preferably any one or more of coal tar pitch, petroleum pitch, and mesophase pitch; in other embodiments, the softening point of the soft carbon precursor is preferably 60℃-300℃, such as 60℃, 70℃, 80℃, 90℃, 100℃, 120℃, 150℃, 180℃, 200℃ or any range of two values.

[0056] To further improve the electrochemical performance of the anode material, the preferred mass ratio of graphite carbonization intermediate to soft carbon precursor is 100:(4-20), such as 100:4, 100:5, 100:8, 100:10, 100:12, 100:15, 100:18, 100:20 or any range of two values.

[0057] To further promote uniform mixing of the graphite carbonization intermediate and the soft carbon precursor, the preferred mixing time is 10 min to 80 min. Specifically, the mixing time can be 10 min, 15 min, 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 60 min, 70 min, 80 min, or any combination of two values.

[0058] In step S3 above, the pressing process is a commonly used pressing process in the art. Any method that can press the soft carbon precursor into the graphite carbonization intermediate is acceptable. In order to improve the efficiency of the pressing process, it is preferred to use cold isostatic pressing or warm isostatic pressing.

[0059] To further improve the quality of the soft carbon precursor pressed into the graphite carbonization intermediate, the preferred pressing pressure is 20 MPa-300 MPa, and the holding time is 10 min-60 min. Controlling the pressing conditions within the above range helps to ensure that the soft carbon precursor fully fills the interior of the graphite carbonization intermediate, thereby helping to improve the initial coulombic efficiency of the subsequently prepared anode material. Specifically, the pressing pressure can be 20 MPa, 50 MPa, 80 MPa, 100 MPa, 120 MPa, 150 MPa, 180 MPa, 200 MPa, or any combination of two values, and the holding time can be 10 min, 15 min, 20 min, 25 min, 30 min, 40 min, 50 min, 60 min, or any combination of two values.

[0060] In step S3 above, a pulverization process is performed to obtain a negative electrode material precursor with a suitable particle size, which is then calcined a second time to obtain the desired negative electrode material.

[0061] To improve the preparation efficiency of the anode material, it is preferable that in step S4 above, the secondary calcination temperature is 500℃-3000℃ and the secondary calcination time is 1h-20h, so as to facilitate the carbonization of the soft carbon precursor to form soft carbon. Some of the soft carbon fills the pores inside the graphite particles, and some of the soft carbon coats the outside of the graphite particles, which in turn helps to improve the electrochemical performance of the prepared anode material.

[0062] Typically, but not limitingly, the temperature for the secondary calcination can be 500℃, 600℃, 700℃, 800℃, 900℃, 1000℃, 1100℃, 1200℃, 1300℃, 1400℃, 1500℃, 1800℃, 2000℃, 2200℃, 2500℃, 2800℃, 3000℃ or any range of two values, and the time for the primary calcination can be 1h, 2h, 5h, 8h, 10h, 12h, 15h, 18h, 20h or any range of two values.

[0063] To avoid introducing impurities during the secondary calcination process that could affect the electrical performance of the negative electrode material, it is preferable to carry out the secondary calcination under a protective atmosphere, such as nitrogen or argon.

[0064] In a third typical embodiment of this application, a secondary battery is also provided, which includes the negative electrode material provided in the first typical embodiment or the negative electrode material obtained by the preparation method provided in the second typical embodiment.

[0065] The secondary battery provided in this application uses the aforementioned negative electrode material as the negative electrode material. Benefiting from the high internal filling degree and highly disordered structure of the aforementioned negative electrode material, it has excellent first-time coulombic efficiency and interfacial transport dynamics performance, and has broad application prospects.

[0066] In some embodiments, the secondary battery includes a casing, an electrode assembly, and an electrolyte. Both the electrode assembly and the electrolyte are located within the casing.

[0067] The outer casing can be a packaging bag encapsulated with a sealing film (such as aluminum-plastic film), for example, a pouch battery. In other embodiments, it can also be a steel-cased battery, an aluminum-cased battery, etc.

[0068] Referring to Figures 1 and 2, the electrode assembly 100 includes a positive electrode 101, a negative electrode 102, and a separator 103, with the separator 103 disposed between the positive electrode 101 and the negative electrode 102. When an electrolyte (not shown) is present, during charging (referring to Figure 1), active ions (such as lithium ions) are extracted from the crystal lattice of the positive electrode material (such as a lithium-ion intercalated compound) of the positive electrode 101, pass through the separator 103 via the electrolyte, reach the negative electrode 102, and are inserted into the crystal lattice of the negative electrode material. During discharging (referring to Figure 2), active ions (such as lithium ions) are extracted from the crystal lattice of the negative electrode material of the negative electrode 102, pass through the separator 103 via the electrolyte, reach the positive electrode 101, and are inserted into the crystal lattice of the positive electrode material (such as a lithium-ion intercalated compound). Electrons are generated and travel from the negative electrode 102 to the positive electrode 101 via an external circuit. The reverse movement of these electrons forms a current, which can be used in electrical appliances.

[0069] In some embodiments, the electrode assembly 100 may be a stacked structure, which is formed by alternatingly stacking a positive electrode 101, a separator 103, and a negative electrode 102. In other embodiments, the electrode assembly 100 may also be a wound structure, which is formed by sequentially stacking and then winding the positive electrode 101, the separator 103, and the negative electrode 102.

[0070] Positive electrode film

[0071] The positive electrode 101 includes a positive current collector and a positive electrode material active layer disposed on at least one surface of the positive current collector. The positive current collector can be aluminum foil or nickel foil, or any composite current collector disclosed in the prior art, such as, but not limited to, current collectors formed by combining the aforementioned conductive foil and polymer substrate. The positive electrode material active layer includes a positive electrode active material, which includes a compound that reversibly inserts and extracts lithium ions (i.e., a lithiation intercalation compound). In some embodiments, the positive electrode active material may include a lithium transition metal composite oxide. This lithium transition metal composite oxide contains lithium and at least one element selected from cobalt, manganese, and nickel. In some embodiments, the positive electrode active material may include, but is not limited to, lithium cobalt oxide (LiCoO2), lithium nickel manganese cobalt ternary materials (NCM), lithium manganese oxide (LiMn2O4), and lithium nickel manganese oxide (LiNi). 0.5 Mn 1.5 At least one of lithium iron phosphate (LiFePO4) or lithium iron phosphate (LiFePO4).

[0072] The positive electrode material active layer also includes an adhesive for bonding the positive electrode active material particles to facilitate the formation of the film layer, and also to improve the bonding force between the positive electrode material active layer and the positive electrode current collector. In some embodiments, the adhesive may include, but is not limited to, at least one of polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon.

[0073] The positive electrode material active layer may further include a conductive material, which includes, but is not limited to, carbon-based materials, metal-based materials, conductive polymers, or any combination thereof. In some embodiments, carbon-based materials may include, but are not limited to, natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof. In some embodiments, metal-based materials may include, but are not limited to, metal powders or metal fibers, such as copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer may be a polyphenylene derivative.

[0074] negative electrode sheet

[0075] The negative electrode 102 includes a negative electrode current collector and an active layer of negative electrode material disposed on at least one surface of the negative electrode current collector. The negative electrode current collector can be at least one of copper foil, nickel foil, stainless steel foil, titanium foil or carbon-based current collector, or any composite current collector disclosed in the prior art, such as, but not limited to, a current collector formed by combining the aforementioned conductive foil and polymer substrate.

[0076] The active layer of the negative electrode material includes the negative electrode material, which includes graphite, silicon, etc.

[0077] The active layer of the negative electrode material also includes a binder to bond the negative electrode active material particles, thereby facilitating the formation of the film layer and improving the bonding force between the active layer of the negative electrode material and the negative electrode current collector. In some embodiments, the binder may include, but is not limited to, polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon, etc.

[0078] The active layer of the negative electrode material may further include a conductive material, which includes, but is not limited to, carbon-based materials, metal-based materials, conductive polymers, or any combination thereof. In some embodiments, carbon-based materials may include, but are not limited to, natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof. In some embodiments, metal-based materials may include, but are not limited to, metal powders or metal fibers, such as copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer may be a polyphenylene derivative.

[0079] Separating membrane

[0080] The separator 103 includes a membrane layer with a porous structure, and its material includes, but is not limited to, at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide, or aramid. For example, the separator 103 may be a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane, etc.

[0081] electrolytes

[0082] The electrolyte serves to conduct ions between the positive electrode 101 and the negative electrode 102. The electrolyte can be in one or more of the following states: gel, solid, and liquid. In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution conducts active ions between the positive electrode 101 and the negative electrode 102. In some embodiments, the electrolyte solution includes a lithium salt and an organic solvent. The lithium salt may be selected from, but is not limited to, lithium hexafluorophosphate (LiPF6). 6)One or more of the following lithium salts are used: lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), lithium perchlorate (LiClO4), lithium tetraphenylborate (LiB(C6H5)4), lithium methanesulfonate (LiCH3SO3), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis(trifluoromethanesulfonyl)imide (LiN(SO2CF3)2), lithium tris(trifluoromethanesulfonyl)methyl lithium (LiC(SO2CF3)3), lithium dioxarate borate (LiBOB), and lithium difluorophosphate (LiPO2F2). For example, LiPF6 is chosen as the lithium salt because it provides high ionic conductivity and improves cycling characteristics. The organic solvent can be a carbonate compound, a carboxylic acid ester compound, an ether compound, a nitrile compound, or others. Organic solvents or combinations thereof. Examples of carbonate compounds include, but are not limited to, diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), vinyl ethylene carbonate (VEC), fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, trifluoromethylethylene carbonate, or combinations thereof.

[0083] The beneficial effects of this application will be further illustrated below with reference to embodiments and comparative examples.

[0084] Example 1

[0085] This embodiment provides a negative electrode material, which is prepared according to the following steps:

[0086] (1) Take 30 kg of natural graphite particles (average particle size 6.670 μm) and mix them evenly with 45 L of deionized water. Add phosphoric acid solution to adjust the pH to 4, add 600 g of aniline monomer and stir thoroughly to form a mixture. Place the mixture in a 4℃ water bath and stir vigorously. At the same time, add 3.3 L (concentration 2 mol / L) of ammonium persulfate aqueous solution. After the mixture is finished, continue stirring for 10 h. After solid-liquid separation, graphite polymer composite material is obtained.

[0087] (2) Under a nitrogen atmosphere, the graphite polymer composite material was heated to 1250℃ and held for 4 hours for a calcination treatment to obtain a graphite carbonization intermediate.

[0088] (3) Take 25 kg of graphite carbonization intermediate and 2.89 kg of asphalt (softening point 250℃) and add them to the VC mixer and mix for 30 min. Then, perform isostatic pressing, adjust the pressure parameters to 90 MPa, and hold the pressure for 30 min. After completion, pulverize to obtain a negative electrode material precursor with an average particle size of 7.541 μm;

[0089] (4) The negative electrode material precursor is placed in a nitrogen atmosphere, heated to 1250℃ and kept at that temperature for 4 hours for secondary calcination to obtain the negative electrode material.

[0090] Example 2

[0091] This embodiment provides a negative electrode material, which is prepared according to the following steps:

[0092] (1) Take 30 kg of natural graphite particles (average particle size 6.670 μm) and mix them evenly with 45 L of deionized water. Add phosphoric acid solution to adjust the pH to 4, add 1200 g of aniline monomer, and stir thoroughly to form a mixture. Place the mixture in a 4℃ water bath and stir vigorously. At the same time, add 6.6 L (concentration 2 mol / L) of ammonium persulfate aqueous solution. After the mixture is finished, continue stirring for 10 h. After solid-liquid separation, graphite polymer composite material is obtained.

[0093] (2) Under a nitrogen atmosphere, the graphite polymer composite material was heated to 500°C and held for 4 hours for calcination to obtain a graphite carbonization intermediate.

[0094] (3) Take 25 kg of graphite carbonization intermediate and 2.89 kg of asphalt (softening point 250℃) and add them to the VC mixer and mix for 30 min. Then, perform isostatic pressing, adjust the pressure parameters to 90 MPa, and hold the pressure for 30 min. After completion, pulverize to obtain a negative electrode material precursor with an average particle size of 7.592 μm;

[0095] (4) The negative electrode material precursor is placed in a nitrogen atmosphere, heated to 1250℃ and kept at that temperature for 4 hours for secondary calcination to obtain the negative electrode material.

[0096] Example 3

[0097] This embodiment provides a negative electrode material, which is prepared according to the following steps:

[0098] (1) Take 30 kg of natural graphite particles (average particle size 6.670 μm) and mix them evenly with 45 L of deionized water. Add phosphoric acid solution to adjust the pH to 4, add 4800 g of aniline monomer, and stir thoroughly to form a mixture. Place the mixture in a 4℃ water bath and stir vigorously. At the same time, add 13.2 L (concentration 2 mol / L) of ammonium persulfate aqueous solution. After the mixture is finished, continue stirring for 10 h. After solid-liquid separation, graphite polymer composite material is obtained.

[0099] (2) Under a nitrogen atmosphere, the graphite polymer composite material was heated to 500°C and held for 4 hours for a calcination treatment to obtain a medium graphite carbonization intermediate.

[0100] (3) Take 25 kg of graphite carbonization intermediate and 2.89 kg of asphalt (softening point 250℃) and add them to the VC mixer and mix for 30 min. Then, perform isostatic pressing, adjust the pressure parameters to 90 MPa, and hold the pressure for 30 min. After completion, pulverize to obtain a negative electrode material precursor with an average particle size of 7.616 μm;

[0101] (4) The negative electrode material precursor is placed in a nitrogen atmosphere, heated to 1250℃ and kept at that temperature for 4 hours for secondary calcination to obtain the negative electrode material.

[0102] Example 4

[0103] This embodiment provides a negative electrode material, which is prepared according to the following steps:

[0104] (1) Take 30 kg of natural graphite particles (average particle size 6.670 μm) and mix them evenly with 45 L of deionized water. Add phosphoric acid solution to adjust the pH to 4, add 7500 g of aniline monomer, and stir thoroughly to form a mixture. Place the mixture in a 4℃ water bath and stir vigorously. At the same time, add 26.4 L (concentration 2 mol / L) of ammonium persulfate aqueous solution. After the mixture is finished, continue stirring for 10 h. After solid-liquid separation, graphite polymer composite material is obtained.

[0105] (2) Under a nitrogen atmosphere, the graphite polymer composite material was heated to 500°C and held for 4 hours for a calcination treatment to obtain a graphite carbonization intermediate.

[0106] (3) Take 25 kg of graphite carbonization intermediate and 2.89 kg of asphalt (softening point 250℃) and add them to the VC mixer and mix for 30 min. Then, perform isostatic pressing, adjust the pressure parameters to 90 MPa, and hold the pressure for 30 min. After completion, pulverize to obtain a negative electrode material precursor with an average particle size of 7.684 μm;

[0107] (4) The negative electrode material precursor is placed in a nitrogen atmosphere, heated to 1250℃ and kept at that temperature for 4 hours for a second calcination treatment to obtain the negative electrode material.

[0108] Example 5

[0109] This embodiment provides a negative electrode material, which is prepared according to the following steps:

[0110] (1) Take 30 kg of natural graphite particles (average particle size 6.670 μm) and mix them evenly with 30 L of deionized water. Add phosphoric acid solution to adjust the pH to 4, add 600 g of aniline monomer and stir thoroughly to form a mixture. Place the mixture in a 4 °C water bath and stir vigorously. At the same time, add 3.3 L (2 mol / L) of ammonium persulfate aqueous solution. After the mixture is finished, continue stirring for 10 h. After solid-liquid separation, graphite polymer composite material is obtained.

[0111] (2) Under a nitrogen atmosphere, the graphite polymer composite material was heated to 1250℃ and held for 4 hours for a calcination treatment to obtain a graphite carbonization intermediate.

[0112] (3) Take 25 kg of graphite carbonization intermediate and 2.89 kg of asphalt (softening point 250℃) and add them to the VC mixer and mix for 30 min. Then, perform isostatic pressing, adjust the pressure parameters to 90 MPa, and hold the pressure for 30 min. After completion, pulverize to obtain a negative electrode material precursor with an average particle size of 7.572 μm;

[0113] (4) The negative electrode material precursor is placed in a nitrogen atmosphere, heated to 1250℃ and kept at that temperature for 4 hours for a second calcination treatment to obtain the negative electrode material.

[0114] Example 6

[0115] This embodiment provides a negative electrode material, which is prepared according to the following steps:

[0116] (1) Take 30 kg of natural graphite particles (average particle size 6.670 μm) and mix them evenly with 60 L of deionized water. Add phosphoric acid solution to adjust the pH to 4, add 600 g of aniline monomer and stir thoroughly to form a mixture. Place the mixture in a 4 °C water bath and stir vigorously. At the same time, add 3.3 L (2 mol / L) of ammonium persulfate aqueous solution. After the mixture is finished, continue stirring for 10 h. After solid-liquid separation, graphite polymer composite material is obtained.

[0117] (2) Under a nitrogen atmosphere, the graphite polymer composite material was heated to 1250℃ and held for 4 hours for a calcination treatment to obtain a graphite carbonization intermediate.

[0118] (3) Take 25 kg of graphite carbonization intermediate and 2.89 kg of asphalt (softening point 250℃) and add them to the VC mixer and mix for 30 min. Then, perform isostatic pressing, adjust the pressure parameters to 90 MPa, and hold the pressure for 30 min. After completion, pulverize to obtain a negative electrode material precursor with an average particle size of 7.544 μm;

[0119] (4) The negative electrode material precursor is placed in a nitrogen atmosphere, heated to 1250℃ and kept at that temperature for 4 hours to obtain the negative electrode material.

[0120] Example 7

[0121] This embodiment provides a negative electrode material, which is prepared according to the following steps:

[0122] (1) Take 30 kg of natural graphite particles (average particle size 6.670 μm) and mix them evenly with 45 L of deionized water. Add phosphoric acid solution to adjust the pH to 4, add 600 g of aniline monomer, and stir thoroughly to form a mixture. Place the mixture in a 1 °C water bath and stir vigorously. At the same time, add 3.3 L (2 mol / L) of ammonium persulfate aqueous solution. After the mixture is finished, continue stirring for 10 h. After solid-liquid separation, graphite polymer composite material is obtained.

[0123] (2) Under a nitrogen atmosphere, the graphite polymer composite material was heated to 1250℃ and held for 4 hours for a calcination treatment to obtain a graphite carbonization intermediate.

[0124] (3) Take 25 kg of graphite carbonization intermediate and 2.89 kg of asphalt (softening point 250℃) and add them to the VC mixer and mix for 30 min. Then, perform isostatic pressing, adjust the pressure parameters to 90 MPa, and hold the pressure for 30 min. After completion, pulverize to obtain a negative electrode material precursor with an average particle size of 7.554 μm;

[0125] (4) The negative electrode material precursor is placed in a nitrogen atmosphere, heated to 1250℃ and kept at that temperature for 4 hours for secondary calcination to obtain the negative electrode material.

[0126] Example 8

[0127] This embodiment provides a negative electrode material, which is prepared according to the following steps:

[0128] (1) Take 30 kg of natural graphite particles (average particle size 6.670 μm) and mix them evenly with 45 L of deionized water. Add phosphoric acid solution to adjust the pH to 4, add 600 g of aniline monomer and stir thoroughly to form a mixture. Place the mixture in a 60 °C water bath and stir vigorously. At the same time, add 3.3 L (concentration 2 mol / L) of ammonium persulfate aqueous solution. After the mixture is finished, continue stirring for 10 h. After solid-liquid separation, graphite polymer composite material is obtained.

[0129] (2) Under a nitrogen atmosphere, the graphite polymer composite material was heated to 1250℃ and held for 4 hours for a calcination treatment to obtain a graphite carbonization intermediate.

[0130] (3) Take 25 kg of graphite carbonization intermediate and 2.89 kg of asphalt (softening point 250℃) and add them to the VC mixer and mix for 30 min. Then, perform isostatic pressing, adjust the pressure parameters to 90 MPa, and hold the pressure for 30 min. After completion, pulverize to obtain a negative electrode material precursor with an average particle size of 7.567 μm;

[0131] (4) The negative electrode material precursor is placed in a nitrogen atmosphere, heated to 1250℃ and kept at that temperature for 4 hours for a second calcination treatment to obtain the negative electrode material.

[0132] Example 9

[0133] This embodiment provides a negative electrode material, which is prepared according to the following steps:

[0134] (1) Take 30 kg of natural graphite particles (average particle size 6.670 μm) and mix them evenly with 45 L of deionized water. Add phosphoric acid solution to adjust the pH to 4, add 600 g of aniline monomer and stir thoroughly to form a mixture. Place the mixture in a 4℃ water bath and stir vigorously. At the same time, add 3.3 L (concentration 2 mol / L) of ammonium persulfate aqueous solution. After the mixture is finished, continue stirring for 10 h. After solid-liquid separation, graphite polymer composite material is obtained.

[0135] (2) Under a nitrogen atmosphere, the graphite composite material was heated to 1250℃ and held for 4 hours for a calcination treatment to obtain a graphite carbonization intermediate.

[0136] (3) Take 25 kg of graphite carbonization intermediate and 1.34 kg of asphalt (softening point 250℃) and add them to the VC mixer and mix for 30 min. Then, perform isostatic pressing, adjust the pressure parameters to 90 MPa, and hold the pressure for 30 min. After completion, pulverize to obtain a negative electrode material precursor with an average particle size of 7.326 μm;

[0137] (4) The precursor of the anode material is placed in a nitrogen atmosphere, heated to 1250℃ and kept at the temperature for 4 hours for secondary calcination to obtain a high tap density natural graphite anode material.

[0138] Example 10

[0139] This embodiment provides a negative electrode material, which is prepared according to the following steps:

[0140] (1) Take 30 kg of natural graphite particles (average particle size 6.670 μm) and mix them evenly with 45 L of deionized water. Add phosphoric acid solution to adjust the pH to 4, add 600 g of aniline monomer and stir thoroughly to form a mixture. Place the mixture in a 4℃ water bath and stir vigorously. At the same time, add 3.3 L (concentration 2 mol / L) of ammonium persulfate aqueous solution. After the mixture is finished, continue stirring for 10 h. After solid-liquid separation, graphite polymer composite material is obtained.

[0141] (2) Under a nitrogen atmosphere, the graphite polymer composite material was heated to 1250℃ and held for 4 hours for a calcination treatment to obtain a graphite carbonization intermediate.

[0142] (3) Take 25 kg of graphite carbonization intermediate and 4 kg of asphalt (softening point 250℃) and add them to the VC mixer and mix for 30 min. Then, perform isostatic pressing, adjust the pressure parameters to 90 MPa, and hold the pressure for 30 min. After completion, pulverize to obtain a negative electrode material precursor with an average particle size of 7.754 μm;

[0143] (4) The negative electrode material precursor is placed in a nitrogen atmosphere, heated to 1250℃ and kept at that temperature for 4 hours for a second calcination treatment to obtain the negative electrode material.

[0144] Example 11

[0145] This embodiment provides a negative electrode material, which is prepared according to the following steps:

[0146] (1) Take 30 kg of natural graphite particles (average particle size 6.670 μm) and mix them evenly with 45 L of deionized water. Add phosphoric acid solution to adjust the pH to 4, add 600 g of aniline monomer and stir thoroughly to form a mixture. Place the mixture in a 4℃ water bath and stir vigorously. At the same time, add 3.3 L (concentration 2 mol / L) of ammonium persulfate aqueous solution. After the mixture is finished, continue stirring for 10 h. After solid-liquid separation, graphite polymer composite material is obtained.

[0147] (2) Under a nitrogen atmosphere, the graphite polymer composite material was heated to 1250℃ and held for 4 hours for a calcination treatment to obtain a graphite carbonization intermediate.

[0148] (3) Take 25 kg of graphite carbonization intermediate and 2.89 kg of asphalt (softening point 250℃) and add them to the VC mixer and mix for 30 min. Then, perform isostatic pressing, adjust the pressure parameter to 30 MPa, and hold the pressure for 30 min. After completion, pulverize to obtain a negative electrode material precursor with an average particle size of 7.754 μm;

[0149] (4) The negative electrode material precursor is placed in a nitrogen atmosphere, heated to 1250℃ and kept at that temperature for 4 hours for a second calcination treatment to obtain the negative electrode material.

[0150] Example 12

[0151] This embodiment provides a negative electrode material, which is prepared according to the following steps:

[0152] (1) Take 30 kg of natural graphite particles (average particle size 6.670 μm) and mix them evenly with 45 L of deionized water. Add phosphoric acid solution to adjust the pH to 4, add 600 g of aniline monomer and stir thoroughly to form a mixture. Place the mixture in a 4℃ water bath and stir vigorously. At the same time, add 3.3 L (concentration 2 mol / L) of ammonium persulfate aqueous solution. After the mixture is finished, continue stirring for 10 h. After solid-liquid separation, graphite polymer composite material is obtained.

[0153] (2) Under a nitrogen atmosphere, the graphite polymer composite material was heated to 1250℃ and held for 4 hours for a calcination treatment to obtain a graphite carbonization intermediate.

[0154] (3) Take 25 kg of graphite carbonization intermediate and 2.89 kg of asphalt (softening point 250℃) and add them to the VC mixer and mix for 30 min. Then, perform isostatic pressing, adjust the pressure parameters to 150 MPa, and hold the pressure for 30 min. After completion, pulverize to obtain a negative electrode material precursor with an average particle size of 7.532 μm;

[0155] (4) The negative electrode material precursor is placed in a nitrogen atmosphere, heated to 1250℃ and kept at that temperature for 4 hours for a second calcination treatment to obtain the negative electrode material.

[0156] Example 13

[0157] This embodiment provides a negative electrode material, which is prepared according to the following steps:

[0158] (1) Take 30 kg of natural graphite particles (average particle size 6.670 μm) and mix them evenly with 45 L of deionized water. Add phosphoric acid solution to adjust the pH to 4, add 600 g of aniline monomer and stir thoroughly to form a mixture. Place the mixture in a 4℃ water bath and stir vigorously. At the same time, add 3.3 L (concentration 2 mol / L) of ammonium persulfate aqueous solution. After the mixture is finished, continue stirring for 10 h. After solid-liquid separation, graphite polymer composite material is obtained.

[0159] (2) Under a nitrogen atmosphere, the graphite polymer composite material was heated to 1250℃ and held for 4 hours for a calcination treatment to obtain a graphite carbonization intermediate.

[0160] (3) Take 25 kg of graphite carbonization intermediate and 2.89 kg of asphalt (softening point 250℃) and add them to the VC mixer and mix for 30 min. Then, perform isostatic pressing, adjust the pressure parameters to 90 MPa, and hold the pressure for 10 min. After completion, pulverize to obtain a negative electrode material precursor with an average particle size of 7.737 μm;

[0161] (4) The negative electrode material precursor is placed in a nitrogen atmosphere, heated to 1250℃ and kept at that temperature for 4 hours for a second calcination treatment to obtain the negative electrode material.

[0162] Example 14

[0163] This embodiment provides a negative electrode material, which is prepared according to the following steps:

[0164] (1) Take 30 kg of natural graphite particles (average particle size 6.670 μm) and mix them evenly with 45 L of deionized water. Add phosphoric acid solution to adjust the pH to 4, add 600 g of aniline monomer and stir thoroughly to form a mixture. Place the mixture in a 4℃ water bath and stir vigorously. At the same time, add 3.3 L (concentration 2 mol / L) of ammonium persulfate aqueous solution. After the mixture is finished, continue stirring for 10 h. After solid-liquid separation, graphite polymer composite material is obtained.

[0165] (2) Under a nitrogen atmosphere, the graphite polymer composite material was heated to 1250℃ and held for 4 hours for a calcination treatment to obtain a graphite carbonization intermediate.

[0166] (3) Take 25 kg of graphite carbonization intermediate and 2.89 kg of asphalt (softening point 250℃) and add them to the VC mixer and mix for 30 min. Then, perform isostatic pressing, adjust the pressure parameters to 90 MPa, and hold the pressure for 60 min. After completion, pulverize to obtain a negative electrode material precursor with an average particle size of 7.547 μm;

[0167] (4) The negative electrode material precursor is placed in a nitrogen atmosphere, heated to 1250℃ and kept at that temperature for 4 hours for a second calcination treatment to obtain the negative electrode material.

[0168] Example 15

[0169] This embodiment provides a negative electrode material. The difference between its preparation method and that of Embodiment 1 is that in step (1), the particle size of natural graphite is 4.174 μm.

[0170] Example 16

[0171] This embodiment provides a negative electrode material. The difference between its preparation method and that of Embodiment 1 is that in step (1), the particle size of natural graphite is 11.284 μm.

[0172] Example 17

[0173] This embodiment provides a negative electrode material. The difference between its preparation method and that of Embodiment 1 is that in step (1), the particle size of natural graphite is 17.852 μm.

[0174] Example 18

[0175] This embodiment provides a negative electrode material, which is prepared according to the following steps:

[0176] (1) Take 30 kg of natural graphite particles (average particle size 6.670 μm) and mix them evenly with 45 L of deionized water. Add phosphoric acid solution to adjust the pH to 4, add 300 g of aniline monomer and stir thoroughly to form a mixture. Place the above mixture in a 4℃ water bath and stir vigorously. At the same time, add 3.3 L (concentration 2 mol / L) of ammonium persulfate aqueous solution. After the mixture is finished, continue stirring for 10 h. After solid-liquid separation, graphite polymer composite material is obtained.

[0177] (2) Under a nitrogen atmosphere, the graphite polymer composite material was heated to 1250℃ and held for 4 hours for a calcination treatment to obtain a graphite carbonization intermediate.

[0178] (3) Take 25 kg of graphite carbonization intermediate and 5 kg of asphalt (softening point 250℃) and add them to the VC mixer and mix for 30 min. Then, perform isostatic pressing, adjust the pressure parameters to 90 MPa, and hold the pressure for 60 min. After completion, pulverize to obtain a negative electrode material precursor with an average particle size of 7.904 μm;

[0179] (4) The negative electrode material precursor is placed in a nitrogen atmosphere, heated to 1250℃ and kept at that temperature for 4 hours for a second calcination treatment to obtain the negative electrode material.

[0180] Example 19

[0181] This embodiment provides a negative electrode material. The difference between its preparation method and that of Example 1 is that in step (1), the amount of aniline monomer used is 300g.

[0182] Example 20

[0183] This embodiment provides a negative electrode material. The difference between its preparation method and that of Embodiment 1 is that in step (1), the amount of aniline monomer used is 6000g.

[0184] Example 21

[0185] This embodiment provides a negative electrode material. The difference between its preparation method and that of Embodiment 1 is that in step (3), the amount of asphalt used is 1.2 kg, and the pressure parameter is 20 MPa, with a pressure holding time of 60 min.

[0186] Example 22

[0187] This embodiment provides a negative electrode material. The difference between its preparation method and that of Embodiment 1 is that in step (3), the amount of asphalt used is 6 kg, and the pressure parameter is 200 MPa, and the pressure is maintained for 60 min.

[0188] Comparative Example 1

[0189] This comparative example provides a negative electrode material, which is prepared according to the following steps:

[0190] 25 kg of natural graphite particles (average particle size 6.670 μm) and 1.75 kg of petroleum asphalt (softening point 250℃) were added to a VC mixer and mixed for 30 min to obtain a mixture. The mixture was then subjected to isostatic pressing at 90 MPa for 30 min and pulverized to obtain a graphite precursor with an average particle size of 7.365 μm. The graphite precursor was then heated to 1250℃ under a nitrogen atmosphere and held at that temperature for 4 hours to obtain the graphite material.

[0191] Comparative Example 2

[0192] This comparative example provides a negative electrode material, which is prepared according to the following steps:

[0193] (1) Take 30 kg of natural graphite particles (average particle size 6.670 μm) and mix them evenly with 45 L of deionized water. Add phosphoric acid solution to adjust the pH to 11, add 600 g of aniline monomer, and stir thoroughly to form a mixture. Place the mixture in a 4℃ water bath and stir vigorously. At the same time, add 3.3 L (concentration 2 mol / L) of ammonium persulfate aqueous solution. After the mixture is finished, continue stirring for 10 h. After solid-liquid separation, graphite polymer composite material is obtained.

[0194] (2) Under a nitrogen atmosphere, the graphite polymer composite material was heated to 500°C and held for 4 hours for calcination to obtain a graphite carbonization intermediate.

[0195] (3) Take 25 kg of graphite carbonization intermediate and 2.89 kg of asphalt (softening point 250℃) and add them to the VC mixer and mix for 30 min. Then, perform isostatic pressing, adjust the pressure parameters to 90 MPa, and hold the pressure for 30 min. After completion, pulverize to obtain a negative electrode material precursor with an average particle size of 7.762 μm;

[0196] (4) The negative electrode material precursor is placed in a nitrogen atmosphere, heated to 400°C and kept at that temperature for 4 hours to obtain the negative electrode material.

[0197] Comparative Example 3

[0198] This comparative example provides a negative electrode material, which is prepared according to the following steps:

[0199] (1) Take 30 kg of natural graphite particles (average particle size 7.760 μm) and mix them evenly with 45 L of deionized water. Add phosphoric acid solution to adjust the pH to 4, add 600 g of aniline monomer, and stir thoroughly to form a mixture. Place the mixture in a 4℃ water bath and stir vigorously. At the same time, add 3.3 L (concentration 2 mol / L) of ammonium persulfate aqueous solution. After the mixture is finished, continue stirring for 30 min. After solid-liquid separation, graphite polymer composite material is obtained.

[0200] (2) Under a nitrogen atmosphere, the graphite polymer composite material was heated to 1250℃ and held for 4 hours for calcination to obtain a graphite carbonization intermediate.

[0201] (3) Take 25 kg of graphite carbonization intermediate and 2.89 kg of asphalt (softening point 250℃) and add them to the VC mixer and mix for 30 min. Then, perform isostatic pressing, adjust the pressure parameters to 90 MPa, and hold the pressure for 30 min. After completion, pulverize to obtain a negative electrode material precursor with an average particle size of 7.745 μm;

[0202] (4) The negative electrode material precursor is placed in a nitrogen atmosphere, heated to 1250℃ and kept at that temperature for 4 hours for secondary calcination to obtain the negative electrode material.

[0203] Comparative Example 4

[0204] This comparative example provides a negative electrode material, which is prepared according to the following steps:

[0205] (1) Take 30 kg of natural graphite particles (average particle size 6.670 μm) and mix them evenly with 45 L of deionized water. Add phosphoric acid solution to adjust the pH to 4, add 600 g of aniline monomer and stir thoroughly to form a mixture. Place the mixture in a 4℃ water bath and stir vigorously. At the same time, add 3.3 L (concentration 2 mol / L) of ammonium persulfate aqueous solution. After the mixture is finished, continue stirring for 10 h. After solid-liquid separation, graphite polymer composite material is obtained.

[0206] (2) Under a nitrogen atmosphere, the graphite polymer composite material was heated to 1250℃ and held for 4 hours for calcination to obtain a graphite carbonization intermediate.

[0207] (3) Take 25 kg of graphite carbonization intermediate and 8.75 kg of asphalt (softening point 250℃) and add them to the VC mixer and mix for 30 min. Then, perform isostatic pressing, adjust the pressure parameters to 90 MPa, and hold the pressure for 30 min. After completion, pulverize to obtain a negative electrode material precursor with an average particle size of 9.123 μm;

[0208] (4) The negative electrode material precursor is placed in a nitrogen atmosphere, heated to 1250℃ and kept at that temperature for 4 hours for secondary calcination to obtain the negative electrode material.

[0209] Comparative Example 5

[0210] This comparative example provides a negative electrode material whose preparation method differs from that of Example 1 in that the average particle size of the natural graphite particles is 17.852 μm, while the other components, amounts, and preparation methods are the same as those in Comparative Example 1.

[0211] Comparative Example 6

[0212] This comparative example provides a negative electrode material, the preparation method of which differs from that of Example 1 in that, in step (3), the amount of asphalt used is 0.2 kg.

[0213] Comparative Example 7

[0214] This comparative example provides a negative electrode material whose preparation method differs from that of Example 1 in that, in step (1), the amount of aniline monomer used is 100g.

[0215] Comparative Example 8

[0216] This comparative example provides a negative electrode material whose preparation method differs from that of Example 1 in that, in step (1), the amount of aniline monomer used is 7000g.

[0217] Comparative Example 9

[0218] This comparison provides a negative electrode material whose preparation method differs from that of Example 1 in that step (2) is omitted, and the graphite polymer composite material is directly used to replace the graphite carbonization intermediate in steps (3) and (4).

[0219] Performance testing

[0220] 1. Method for testing the surface morphology of negative electrode material particles: The microstructure of the surface of negative electrode material particles was observed using a HITACHI-S4800 scanning electron microscope. The steps are as follows: Affix conductive adhesive to the sample cup, evenly coat the sample onto the conductive adhesive, use a bulb syringe to blow away any loose sample, and then place the sample into the scanning electron microscope chamber for testing.

[0221] 2. Test methods for negative electrode material particles b, a / b, and R1 / R2:

[0222] The negative electrode material is ionized into argon ions (Ar) under high vacuum using an ion mill (HITACHI E3500) through an ion source. +Argon ions are then accelerated by a high-voltage electric field to bombard the sample surface with high energy, thereby removing the surface material and achieving the effects of grinding and polishing. The cross-section of the particles is observed under a high-magnification electron microscope (HITACHI S4800), with a magnification of 2.5kX to 9.0kX for each particle to ensure the cross-section shows a complete single particle.

[0223] Select at least 30 cross-sections of particles; take the intersection of the transverse median and the longitudinal median of the cross-section of a single particle's kernel as the center of an ellipse or circle (a circle when the transverse median and the longitudinal median are equal). The major axis of the ellipse or circle is 1 / 2 the length of the transverse median, and the minor axis is 1 / 2 the length of the longitudinal median. Divide the kernel cross-section into a kernel region (A) and a near-surface region (B) with the outline of the ellipse or circle as the boundary, as shown in Figure 3. The inner side of the outline of the ellipse or circle is the kernel region (A), and the outer side of the outline of the ellipse or circle is the near-surface region (B).

[0224] The aforementioned transverse median line is the longest horizontal diameter of the cut surface. The longitudinal median line is perpendicular to the transverse median line and passes through the midpoint of the transverse median line, intersecting with the edge of the material cut surface.

[0225] First, use image processing software such as Image Pro Plus, Image J, or Aztec Feature to calculate the pore area of ​​region A. The ratio of the pore area to the total area of ​​region A is defined as the porosity. Similarly, the porosity of region B is The fill rate of area A is The fill rate of area B is... Then, 30 cross-sectional images were generated for each sample, and the average a / b ratio was calculated. Image processing software such as Image Pro Plus, Image J, and Aztec Feature were used to calculate the average pore size R1 of region A and the average pore size R2 of region B. Then, 30 cross-sectional images were generated for each sample, and the average R1 / R2 ratio was calculated.

[0226] Taking Image Pro Plus as an example, the statistical process is illustrated as follows: 1) After opening Image Pro Plus software, open the electron microscope cross-sectional morphology image of a single particle by pressing File (F), Open (O), or Ctrl+O; 2) Perform scale calibration in Measure (M), Calibration (C), and Spatial Calibration Wizard; 3) Click Irregular AOI and draw the outline of a single particle in Trace mode; 4) Click Measure (M) and Count / Size and select Colors..., click Histogram Based, select the range of 0-255, click Count to fill the selected area, and click View and Statistics to record the area of ​​a single particle at Sum; 5) In RGB mode, use the extractor to extract the RGB values ​​of the pores, and then click Count to identify them; then click Draw / Merge Objects in Edit to select the unfilled pores, click OK after selection, and click View and Statistics to record the area value at Sum, which is the pore area of ​​a single particle; 6) Click Measure (M), Measure... Draw a line parallel to the ruler using the distance tool, and move this line segment to the selected area of ​​the AOI to obtain the horizontal median line (the maximum value of the line segment). Click Measure distance to draw a line segment with a length of 1 / 2 the horizontal median line starting from the endpoint. At the midpoint of the horizontal median line, draw a vertical median line perpendicular to the horizontal median line and intersecting the particle outline. 7) Using the center of the horizontal median line as the center of an ellipse, with the major axis of the ellipse being 1 / 2 the length of the horizontal median line and the minor axis being 1 / 2 the length of the short side of the vertical median line, first use Measure distance to mark the length range, and then use Elliptical AOI to draw an ellipse at the marked location as the core region. 8) Repeat steps 4) and 5) to calculate the area of ​​the core region and the pore area. 9) Calculate the near-surface area and pore area using the particle area, particle pore area, core region area, and pore area, and calculate the porosity of the core region of a single particle. Porosity of the near-surface region And the a / b ratio of the core region and the near-surface region; 10) Perform the above steps 1)-9) on 30 particles and calculate the average value.

[0227] 3. Test method for the average particle size D50 of the negative electrode material: The particle size distribution range of the graphite material was tested using a Malvern 3000 laser particle size analyzer. A dispersant (ethanol, pure water, and a low-foaming surfactant) and the test sample were placed in a 50 mL beaker, followed by the addition of a certain amount of pure water. The mixture was stirred thoroughly with a glass rod to ensure uniform dispersion. The pump speed was set to 2400 r / min–2500 r / min, and the frequency was 19.5 Hz for particle size analysis. D50 represents the particle size corresponding to a cumulative volume distribution percentage of 50% for a given sample.

[0228] 4. Test method for specific surface area of ​​negative electrode material: The specific surface area of ​​the material is tested using a Micron DX400 analyzer. The sample is loaded into a sample tube, and an isothermal jacket is used on the sample tube. The filler rod is placed inside the bubble tube, and the retaining ring and O-ring are attached to the bubble tube. The assembled sample bubble tube is then placed in the corresponding analytical station for testing. Under constant temperature and low temperature, the amount of nitrogen gas adsorbed on the solid surface at different relative pressures is measured. Based on the Brown-Nauer-Etter-Taylor adsorption theory and its formula (BET formula), the monolayer adsorption amount of the sample is calculated, thereby determining the specific surface area and pore size distribution data of the material.

[0229] 5. Raman I D / I G Test method: Raman scattering spectra were measured using a HORIBA-XPLORA laser confocal Raman spectrometer with a laser wavelength of 532 nm. Data were collected from 30 points for each sample, and peak fitting was performed on the scattering spectrum obtained at each point. The peak position of material D was at 1350±10 cm⁻¹. -1 The G peak is located at 1580±10cm. -1 After labeling peaks D and G, the intensity ratio of peak D to peak G is calculated, and the average of 30 data points is denoted as I. D / I G .

[0230] 6. Tap density test method: The tap density of the negative electrode material was tested using a Quanta Dual Autotap instrument. A 100 mL sample of the negative electrode material was placed in a graduated cylinder and mechanically vibrated 1000 times. The tap density of the negative electrode material was calculated based on the sample mass and the volume after tapping.

[0231] 7. Electrochemical Performance Testing Method: Using the negative electrode materials prepared in the examples and comparative examples, the negative electrode materials, carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) were dissolved in water at a mass ratio of 96.5:1.5:2, with the solid content controlled at 50 wt%. This solution was coated onto a copper foil current collector, vacuum dried, rolled, and stamped to obtain the negative electrode sheet. A lithium metal sheet was used as the counter electrode. Guotai Huarong LB5315C electrolyte was injected into an argon-filled glove box, and the cells were assembled into coin cells. Charge-discharge tests were conducted at a current density of 0.1C, within a charge-discharge range of 0.01V-1.5V, to obtain the initial reversible specific capacity, the first charge capacity, and the first discharge capacity. The initial coulombic efficiency was calculated as: first discharge capacity / first charge capacity.

[0232] 8. Expansion Performance Test: The electrode expansion rate was tested using the battery electrode thickness change measurement device and system disclosed in patent document CN209991940U. The negative electrode material, CMC, and SBR were uniformly mixed at a mass ratio of 96.5:1.5:2, with the solid content controlled at 50wt%, to obtain the negative electrode slurry. The negative electrode slurry was coated onto a copper foil current collector, and after vacuum drying and rolling, a compacted density of 1.60 g / cm³ was obtained. 3 The initial thickness d1 of the negative electrode sheet was tested. The positive electrode active material, lithium cobalt oxide, conductive carbon black, and PVDF were mixed uniformly at a mass ratio of 96.5:2:1.5 and coated onto aluminum foil (single-sided) to obtain the positive electrode sheet. The prepared positive and negative electrode sheets were injected into Guotai Huarong LB5315C electrolyte and placed into a self-made three-electrode testing device (using the battery disclosed in patent document CN209991940U) for testing. This three-electrode testing device can record the electrode thickness change in situ, and the electrode expansion rate can be calculated.

[0233] The following charge / discharge regime was used for testing: In the first week, the battery was charged at a constant rate of 0.01C for 30 minutes, then at a constant rate of 0.05C for 30 minutes, followed by a constant rate of 0.1C to 4.2V. Once the voltage reached the upper limit of 4.2V, constant voltage charging was implemented, with the current gradually decreasing to 0.01C to complete the charging process. The battery was then discharged at 0.1C to 3V. In the second week, the battery was charged at a constant rate of 0.2C to 4.2V; once the voltage reached 4.2V, the current gradually decreased to 0.01C. After the initial charge cycle, the battery was discharged at a constant rate of 0.2C to 3V. From cycle 3 to 20, it was charged at a constant rate of 0.5C to 4.2V. Once the voltage reached 4.2V, it was charged at a constant voltage, with the current decreasing to 0.01C to end the charging. Then, it was discharged at a constant rate of 0.5C to 3V. In the final half-cycle, it was charged at a constant rate of 0.5C to 4.2V. Once the voltage reached 4.2V, it was charged at a constant voltage, with the current decreasing to 0.01C to end the charging. The battery was then removed, and the thickness d2 of the negative electrode was measured after 20 cycles. The expansion rate was calculated using the formula: Electrode Expansion Rate = (d2 - d1) / d1 × 100%.

[0234] Note: The above samples refer to the negative electrode materials provided in the examples or comparative examples.

[0235] The a, b, a / b, R1, R2, R1 / R2, particle size D50, specific surface area, and Raman spectroscopy of the negative electrode materials provided in the above embodiments and comparative examples are as follows: D / I G The tap density is shown in Table 1 below.

[0236] Table 1

[0237] The initial reversible specific capacity, initial coulombic efficiency, and electrode expansion rate of the graphite materials provided in the above embodiments and comparative examples are shown in Table 2 below.

[0238] Table 2

[0239] As can be seen from the above description, the embodiments of this application achieve the following technical effects:

[0240] The negative electrode material provided in this application exhibits good electrochemical performance. As shown in Figure 3, the cross-sectional view of the material obtained in Example 1 is shown. The intersection of the longest and shortest lines in the cross-sectional view of a single negative electrode material is taken as the center of the ellipse, and the major and minor axes of the ellipse are respectively 1 / 2 the length of the median line of the longest line and 1 / 2 the length of the shortest line. The cross-section of the negative electrode material is divided into two parts: the elliptical area is the core region (A), and the remaining area is the near-surface region (B). The pore filling rate of region A is a = 91.69%, and the pore filling rate of region B is b = 96.29%, a / b = 95.22%. After statistically analyzing 30 cross-sectional views of Example 1, the average a / b ratio is 95.16%. Similarly, the average R1 / R2 ratio of Example 1 is calculated to be 2.77.

[0241] As shown in Examples 1-22, the pore filling rate b of the near-surface region B in the graphite composite particles of the negative electrode material of this application is ≥90%, and the pore filling rate a of the core region A and the pore filling rate b of the near-surface region B satisfy 85% ≤ a / b ≤ 99%. The internal pore filling rate of the graphite composite particles is high, especially the near-surface region B, which has a higher pore filling rate. This effectively improves the performance degradation problem even when directly exposed to the electrolyte, thereby effectively improving the first coulombic efficiency and interfacial transport performance. Furthermore, this negative electrode material exhibits excellent electrochemical performance when used as a negative electrode material for secondary batteries.

[0242] Furthermore, a comparison of Examples 1-17 and Examples 19-22 with Example 18 shows that the graphite composite particles in the negative electrode material provided in this application, while satisfying 85%≤a / b≤99% and b≥90%, also satisfy 1.1<R1 / R2<4 (the average pore size of the core region A is R1, the average pore size of the near-surface region B is R2, and R1>R2), can further increase the density of the near-surface region of the graphite composite particles, which is more conducive to improving its stability, further improving the performance degradation problem, and improving the first coulombic efficiency and interface transport performance.

[0243] Examples 1-4 show that as the aniline content increases during the preparation process, the internal pores of natural graphite become smaller, the pore filling rate increases, R1 / R2 decreases, a / b gradually increases, and the initial coulombic efficiency also increases.

[0244] Examples 5-6 show that the ratio of natural graphite to deionized water affects the uniformity of mixing. A higher ratio results in uneven polyaniline coating. A lower ratio generates a large amount of free polyaniline, leading to low pore filling rate in the core region, larger pores, increased R1 / R2, decreased a / b, and a higher specific surface area of ​​the negative electrode material.

[0245] Examples 7-8 show that when the reaction temperature is lowered, the aniline reaction is incomplete within the same reaction time; when the temperature is too high, aniline will generate a large number of free polyaniline particles. Both of these will result in low pore filling rate in the core region of natural graphite, larger internal pore size, larger R1 / R2, lower a / b, higher specific surface area, and slightly decreased electrochemical performance.

[0246] Examples 9-10 show that as the asphalt content increases, due to the large amount of asphalt filling the near-surface region, R1 / R2 increases, a / b decreases, and the specific surface area decreases, but the capacity decreases significantly to 356.4 mAh / g.

[0247] Examples 11-14 show that if the isostatic pressing pressure and molding time are too low, the asphalt cannot fully penetrate the internal pores of the graphite for filling, resulting in a reduced near-surface filling rate, larger internal pore size of the graphite, increased R1 / R2, decreased a / b, and reduced initial coulombic efficiency. While increasing the pressure and molding time results in material properties that are not significantly different from those in Example 1, it leads to energy waste and reduced preparation efficiency.

[0248] Examples 15-17 show that as the particle size increases, the filling effect of asphalt deteriorates, the filling rate in the near-surface region is higher than that in the core region, R1 / R2 increases, a / b decreases, and both the initial coulombic efficiency and capacity increase.

[0249] Compared with Examples 1-17 and 19-22, Example 18 shows that when a small amount of aniline and a large amount of asphalt are used as fillers, the core region filling rate is lower than that of the near-surface region, i.e., R1 / R2 is greater than 4. This will cause the first coulombic efficiency of the negative electrode material to be relatively lower than that of other examples, the expansion rate to be relatively higher than that of other examples, and the expansion rate of the electrode at 20 weeks to increase.

[0250] Examples 19-20 show that as the aniline content increases, the internal pores of natural graphite become smaller, the filling rate increases, R1 / R2 decreases, a / b gradually increases, and the initial coulombic efficiency also increases.

[0251] Examples 21-22 show that as the asphalt content increases, due to the large amount of asphalt filling the near-surface area, R1 / R2 increases, a / b decreases, the specific surface area decreases, but the capacity decreases.

[0252] Compared to Example 1, if the liquid phase filling is removed during the preparation process, the porosity of the near-surface region of graphite is higher than that of the core region, and the internal pore size is larger, with an a / b ratio of 83.23. This indicates that there are still large pores inside the graphite, resulting in an excessively high specific surface area. This leads to a significant decrease in the initial coulombic efficiency and cycle performance of the anode material. Furthermore, the introduction of nitrogen atoms into the polyaniline also contributes to pseudocapacitive properties, which can improve lithium storage capacity. Removing the liquid phase coating significantly reduces the capacity of the prepared anode material to 355.7 mAh / g.

[0253] Compared with Example 1, Comparative Example 2 changed the reaction conditions for liquid phase filling, resulting in poor filling effect of polyaniline core region, increased R1 / R2, lower a / b value, and significantly increased electrode expansion rate at 20 weeks.

[0254] Compared with Example 1, the liquid phase coating reaction time of Comparative Example 3 should not be too short, which will result in a low pore filling rate of graphite, an increased R1 / R2 ratio, and a lower a / b ratio of 83.68%. Among them, the amount of polyaniline filling is small, the capacity is significantly reduced by 354.2 mAh / g, and the initial coulombic efficiency is only 90.7%.

[0255] Compared with Example 1, Comparative Example 4 had an asphalt content exceeding the limit, and contained a large amount of soft carbon both inside and outside the graphite, resulting in a capacity reduction to 333.4 mAh / g and a decrease in the initial coulombic efficiency.

[0256] Compared with Example 1, if the liquid phase filling is removed in the preparation process, the pore filling rate of the near-surface region of graphite is much higher than that of the core region, R1 / R2 increases, and a / b decreases. Removing aniline will significantly reduce the capacity of the prepared negative electrode material to 360.7 mAh / g.

[0257] Compared with Example 1, when the bitumen content is too low, a large number of pores inside the graphite are not filled, and the filling rate is low both inside and outside. The b value is 86.25%, resulting in an excessively high specific surface area and a decrease in the initial coulombic efficiency.

[0258] Compared with Example 1, when the aniline content is too low, the graphite internal filling rate is too low, and the a / b ratio is 84.08%. When the aniline content is too high, a large amount of free aniline is prone to self-polymerization, generating aniline particles, which also results in a low aniline internal filling rate of graphite, with an a / b ratio of 84.26%, and a significant reduction in capacity.

[0259] Compared with Example 1, Comparative Example 9 was not carbonized after aniline coating, and the asphalt was not easily pressed into the internal pores of the graphite, resulting in low filling rates in both the near-surface and core regions of the graphite, with b being 88.14%, which significantly reduced the capacity.

[0260] The negative electrode material, the method for preparing the negative electrode material, and the secondary battery described above are merely preferred embodiments of this application and are not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A negative electrode material, characterized in that, The negative electrode material includes graphite composite particles. The cross-section of the graphite composite particles is divided into a core region A and a near-surface region B. The near-surface region B surrounds the periphery of the core region A. The pore filling rate of the core region A is a, and the pore filling rate of the near-surface region B is b, and 85% ≤ a / b ≤ 99%, b ≥ 90%.

2. The negative electrode material according to claim 1, characterized in that, At least one of the following conditions must be met: (1) a / b is any value within the range of 85%, 88%, 90%, 92%, 95%, 98%, 99% or any two of the above values; (2) 85% ≤ a / b ≤ 90%; (3) 85% ≤ a / b ≤ 92%; (4) 90% ≤ a / b ≤ 99%.

3. The negative electrode material according to claim 1, characterized in that, At least one of the following conditions must be met: (1) The value of b is any value within the range of 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or any two of the above values; (2)b≥92％； (3)b≥94％； (4)b≥96％。 4. The negative electrode material according to claim 1, characterized in that, At least one of the following conditions must be met: (1) The percentage of a is 82% to 98.5%; (2) The percentage of a is 90% to 98.5%; (3) The value of a is any value within the range of 82%, 84%, 86%, 88%, 90%, 92%, 94%, 96%, 98%, 98.5% or any two of the above values.

5. The negative electrode material according to claim 1, characterized in that, The average aperture of the core region A is R1, and the average aperture of the near-surface region B is R2, where R1 > R2 and 1.1 < R1 / R2 < 4.

6. The negative electrode material according to claim 5, characterized in that, At least one of the following conditions must be met: (1) R1 / R2 is any value in the range of 1.15, 1.20, 1.25, 1.30, 1.35, 1.50, 1.80, 2.0, 2.5, 3.0, 3.9 or any two of the above values; (2) 1.1 < R1 / R2 ≤ 1.50; (3) 1.1 < R1 / R2 ≤ 3.0; (4) 1.50≤R1 / R2≤3.9; (5) 2.0 ≤ R1 / R2 < 4.

7. The negative electrode material according to claim 5 or 6, characterized in that, At least one of the following conditions must be met: (1) The R1 is 0.05μm-0.65μm; (2) R1 is 0.1μm-0.65μm; (3) R1 is any value within the range of 0.09μm, 0.1μm, 0.18μm, 0.2μm, 0.25μm, 0.3μm, 0.35μm, 0.4μm, 0.5μm, 0.6μm, 0.65μm or any two of the above values.

8. The negative electrode material according to claim 5 or 6, characterized in that, At least one of the following conditions must be met: (1) The R2 is 0.08μm-0.25μm; (2) The R2 is 0.1μm-0.21μm; (3) R2 is any value within the range of 0.08μm, 0.1μm, 0.12μm, 0.14μm, 0.16μm, 0.18μm, 0.20μm, 0.21μm, 0.23μm, 0.25μm or any two of the above values.

9. The negative electrode material according to claim 1, characterized in that, The average particle size of the negative electrode material is 4μm-25μm.

10. The negative electrode material according to claim 1, characterized in that, The specific surface area of ​​the negative electrode material is 1.0 m². 2 / g-6.0m 2 / g.

11. The negative electrode material according to claim 1, characterized in that, The tap density of the negative electrode material is 0.7 g / cm³. 3 -1.3g / cm 3 .

12. The negative electrode material according to claim 1, characterized in that, The carbon content of the negative electrode material is ≥99wt%.

13. The negative electrode material according to any one of claims 1 to 6, characterized in that, The Raman spectrum of the negative electrode material contains D peaks and G peaks, and the peak intensity of the D peak is I. D The peak intensity of the G peak is I. G , and I D / I G It ranges from 0.3 to 0.

9.

14. A secondary battery, characterized in that, The secondary battery comprises the negative electrode material according to any one of claims 1 to 13.

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