Starch-based hard carbon composite graphite negative electrode material and preparation method and application thereof

Abstract

The present application relates to the technical field of battery negative electrode material, and particularly relates to a starch-based hard carbon composite graphite negative electrode material, a preparation method and application thereof. The starch-based hard carbon composite graphite negative electrode material is obtained by mixing and fully grinding expanded graphite and esterified starch and then carbonizing. The starch-based hard carbon composite graphite material realizes large-capacity storage of lithium ions through the synergistic effect of biomass hard carbon and graphite, and promotes the reaction kinetics. The starch-based hard carbon composite graphite negative electrode material prepared by the present application exhibits large lithium ion storage capacity and good charge / discharge rate in a wide potential window. In addition, the capacity retention rate can still be above 90% after 100 cycles in the cycle test. The material realizes a technical breakthrough of high capacity and high rate performance in the lithium ion battery negative electrode.

Description

Technical Field

[0001] This invention relates to the field of battery anode material technology, and in particular to a starch-based hard carbon composite graphite anode material, its preparation method, and its application. Background Technology

[0002] Hard carbon, due to its stable structure, excellent electrical conductivity, and ease of processing, is one of the most promising anode materials for lithium-ion batteries. It also exhibits excellent cycle performance at high current densities, making it a popular choice for lithium-ion battery anode materials. Starch, as a low-cost, readily available, and environmentally friendly biomass hard carbon, has been widely researched and applied. Among all biomass precursors, starch, as a precursor, offers the highest degree of control over the microstructure and properties of the final hard carbon. Compared to other biomass precursors, starch exhibits a pristine natural spherical morphology, making it a highly advantageous candidate material for preparing spherical carbon materials. However, direct carbonization of starch easily leads to the breakage of starch spheres and low compaction density. Therefore, it is necessary to provide a method that can both maintain the spherical morphology of starch and improve its lithium storage performance. During heat treatment, the introduction of crosslinking agents promotes the effective connection of aromatic units within the starch. This highly crosslinked nanostructure not only maintains the good spherical morphology of the final hard carbon but also... The research and development of crosslinking agents bring a bright prospect for the application of starch in lithium-ion battery anodes.

[0003] In existing technologies, maleic anhydride is often used as a crosslinking agent. However, maleic anhydride crosslinking agents have high raw material costs and cannot improve the limited specific capacity of biomass hard carbon. Moreover, directly using hard carbon as a lithium-ion anode material has the problem of volume expansion caused by the destruction of the starch macromolecular structure during high-temperature carbonization. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing technologies by proposing a starch-based hard carbon composite graphite anode material, its preparation method, and its applications. This material exhibits good electronic conductivity, high lithium storage capacity, small volume change, large specific surface area, and uniform particle size, resulting in excellent rate capability and cycle performance.

[0005] The present invention discloses a method for preparing a starch-based hard carbon composite graphite anode material, wherein expanded graphite is mixed with esterified starch and thoroughly ground, and then carbonized to obtain the starch-based hard carbon composite graphite anode material.

[0006] Furthermore, the mass ratio of the expanded graphite to the esterified starch is 1:1 to 30.

[0007] Furthermore, the carbonization temperature is 900-1300℃, and the carbonization time is 1-8 hours.

[0008] Furthermore, the heating rate for carbonization is 1–10 °C / min.

[0009] Furthermore, the preparation method of esterified starch is as follows: corn starch is vacuum dried and then subjected to a hydrothermal reaction with melamine to obtain esterified starch.

[0010] Furthermore, the mass ratio of corn starch to melamine is 4:1.

[0011] Furthermore, the hydrothermal reaction temperature is 50–150°C.

[0012] Furthermore, the expandable graphite is heated to 600°C in a muffle furnace at a rate of 20–30°C / min, held at that temperature for 0.5–3 hours, and then cooled down to obtain the expanded graphite.

[0013] A starch-based hard carbon composite graphite anode material prepared by the method described above.

[0014] Application of a starch-based hard carbon composite graphite anode material as described above in lithium batteries.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] (1) The cross-linked spherical structure of esterified starch promotes Li + The ML-1100 anode achieves rapid and efficient lithium transport, and by using melamine as a crosslinking agent, nitrogen doping is achieved to provide additional active sites, enhancing lithium storage capacity. Furthermore, the ML-1100 anode exhibits a wide operating potential (0–3V vs Li / Li). + Its capacitance characteristics enable the achievement of high reversible capacitance.

[0017] (2) The composite material prepared by the present invention has uniform particles, the spherical structure of corn starch remains stable and interconnected after esterification, and graphite is uniformly composited on the surface of the spherical structure.

[0018] Graphite composites further enrich lithium storage methods and capabilities. Lithium ions begin to embed within graphite layers when the voltage is below 0.25V, forming graphite interlayer compounds of different orders. There are three lithium storage methods for graphite materials: interlayer lithium storage, end-face lithium storage, and surface lithium storage, among which the graphite interlayer provides the main lithium storage space.

[0019] (3) The starch-based hard carbon and graphite composite material achieves high-capacity lithium-ion storage through the synergistic effect of biomass hard carbon and graphite, while also promoting reaction kinetics. The starch-based hard carbon composite graphite anode material prepared in this invention exhibits a wide potential window (relative to Li / Li). + It exhibits a large lithium-ion storage capacity (423.7 mAh g) within the range of 0–3V. -1It exhibits good charge / discharge rates. Furthermore, during cycling tests, the low polarization and minimal morphological changes of the negative electrode contribute to its electrochemical stability, with capacity retention exceeding 90% after 100 cycles. This material represents a technological breakthrough in achieving high capacity and high rate performance in lithium-ion battery anodes.

[0020] (4) The material has good electronic conductivity, high lithium storage capacity, small volume change, large specific surface area, and uniform particles, and has excellent rate and cycle performance. Attached Figure Description

[0021] Figure 1 This is a SEM image of the starch-based hard carbon composite graphite anode material prepared in Example 4.

[0022] Figure 2 The images show the XRD patterns of the starch-based hard carbon composite graphite anode materials prepared in Examples 1, 4, and 6.

[0023] Figure 3 The battery assembled from the starch-based hard carbon composite graphite anode material prepared in Example 4 of this invention operates at a low current density of 25 mAg. -1 The following is a charge / discharge curve.

[0024] Figure 4 The battery assembled from the starch-based hard carbon composite graphite anode material prepared in Example 4 of this invention operates at a low current density of 25 mAg. -1 The following is a graph showing the performance of GCD.

[0025] Figure 5 The batteries assembled from the starch-based hard carbon composite graphite anode materials prepared in Examples 1-6 of this invention operate at a current density of 0.1 Ag. -1 The following is a comparison chart of the cycle performance.

[0026] Figure 6 Batteries assembled from the materials prepared in Comparative Examples 1-4 of this invention were tested at a current density of 0.1 Ag. -1 The following is a graph showing the cyclic performance.

[0027] Figure 7 Batteries assembled from the materials prepared in Comparative Examples 1-4 of this invention were tested at a current density of 25 mAg. -1 A comparison of the galvanostatic intermittent titration (GITT) curves and the calculated diffusion coefficient D during lithiation and delithiation processes.

[0028] Figure 8 Batteries assembled from the materials prepared in Example 3, Comparative Examples 2 and 4 of this invention were tested at a current density of 25 mAg. -1A comparison of the galvanostatic intermittent titration (GITT) curves and the calculated diffusion coefficient D during lithiation and delithiation processes.

[0029] Figure 9 The batteries assembled from the negative electrode materials prepared in Comparative Examples 2 and 5 of this invention operate at a low current density of 25 mA g. -1 The following is a charge / discharge curve. Detailed Implementation

[0030] The following are specific embodiments of the present invention, which are described in conjunction with the accompanying drawings. However, the present invention is not limited to these embodiments.

[0031] <Example 1>

[0032] S1. Pretreatment of starch-based raw materials: Take a certain amount of corn starch and put it into a container. Place the container containing soluble starch into a vacuum drying oven and dry it at 50-100℃ for 24 hours. Then take out the container and add it into a reaction vessel at a mass ratio of starch to melamine of 4:1. Dry powder hydrothermal treatment is carried out at 50-150℃ to obtain the precursor material. Then, it is crushed to obtain precursor particles with a particle size of 40-500 mesh.

[0033] S2, Composite Graphite: Expandable graphite was heated to 600℃ in a muffle furnace at a rate of 20-30℃ / min and held at that temperature for 0.5h. After cooling, the expanded graphite was collected. The expanded graphite was mixed with the esterified starch prepared in S1 and ground thoroughly. The mass ratio of esterified starch to expanded graphite was 1:1. The resulting granular mixture was collected.

[0034] S3, Carbonization: Under the protection of argon atmosphere, the precursor particles obtained in S1 are heated to 1100℃ at 1-2℃ / min, held at the temperature for 2h, and then cooled to room temperature in the furnace to obtain starch-based hard carbon composite graphite anode material.

[0035] S4. Negative electrode preparation: The above-mentioned starch-based hard carbon composite graphite negative electrode material is used as the negative electrode active material to prepare the negative electrode sheet. The negative electrode material is uniformly ground with conductive agent and binder in a mass ratio of 8:1:1, and then mixed with N-methylpyrrolidone to prepare a negative electrode slurry. The slurry is coated on the current collector and placed in a vacuum oven at 100°C for 10 hours. After drying, it is cut into round negative electrode sheets.

[0036] S5. Half-cell assembly: Lithium sheet is used as the counter electrode. The electrolyte is prepared by 1.0 mol LiPF6 in a solution of ethylene carbonate, diethyl carbonate and dimethyl carbonate (EC / DEC / DMC, v / v / v = 1:1:1). The starch-based negative electrode sheet is assembled into a button cell in a glove box under an argon atmosphere.

[0037] <Example 2>

[0038] S1. Pretreatment of starch-based raw materials: Take a certain amount of corn starch and put it into a container. Place the container containing soluble starch into a vacuum drying oven and dry it at 50-100℃ for 24 hours. Then take out the container and add it into a reaction vessel at a mass ratio of starch to melamine of 4:1. Dry powder hydrothermal treatment is carried out at 50-150℃ to obtain the precursor material. Then, it is crushed to obtain precursor particles with a particle size of 40-500 mesh.

[0039] S2, Composite Graphite: Expandable graphite was heated to 600℃ in a muffle furnace at a rate of 0-10℃ / min and held at that temperature for 0.5h. After cooling, the expanded graphite was collected. The expanded graphite was mixed with the esterified starch prepared in S1 and ground thoroughly. The mass ratio of esterified starch to expanded graphite was 5:1. A granular mixture was collected.

[0040] S3, Carbonization: Under the protection of argon atmosphere, the precursor particles obtained in S1 are heated to 1100℃ at a rate of 1-2℃ / min, held at that temperature for 2h, and then cooled to room temperature in the furnace to obtain starch-based hard carbon composite graphite anode material.

[0041] S4. Negative electrode preparation: The above-mentioned starch-based hard carbon composite graphite negative electrode material is used as the negative electrode active material to prepare the negative electrode sheet. The negative electrode material is uniformly ground with conductive agent and binder in a mass ratio of 8:1:1, and then mixed with N-methylpyrrolidone to prepare a negative electrode slurry. The slurry is coated on the current collector and placed in a vacuum oven at 100°C for 10 hours. After drying, it is cut into round negative electrode sheets.

[0042] S5. Half-cell assembly: Lithium sheet is used as the counter electrode. The electrolyte is prepared by 1.0 mol LiPF6 in a solution of ethylene carbonate, diethyl carbonate and dimethyl carbonate (EC / DEC / DMC, v / v / v = 1:1:1). The starch-based negative electrode sheet is assembled into a button cell in a glove box under an argon atmosphere.

[0043] <Example 3>

[0044] S1. Pretreatment of starch-based raw materials: Take a certain amount of corn starch and put it into a container. Place the container containing soluble starch into a vacuum drying oven and dry it at 50-100℃ for 24 hours. Then take out the container and add it into a reaction vessel at a mass ratio of starch to melamine of 4:1. Dry powder hydrothermal treatment is carried out at 50-150℃ to obtain the precursor material. Then, it is crushed to obtain precursor particles with a particle size of 40-500 mesh.

[0045] S2, Composite Graphite: Expandable graphite was heated to 600℃ in a muffle furnace at a rate of 20-30℃ / min and held at that temperature for 0.5h. After cooling, the expanded graphite was collected. The expanded graphite was mixed with the esterified starch prepared in S1 and ground thoroughly. The mass ratio of esterified starch to expanded graphite was 10:1. The resulting granular mixture was collected.

[0046] S3, Carbonization: Under the protection of argon atmosphere, the precursor particles obtained in S1 are heated to 1100℃ at a rate of 1-2℃ / min, held at that temperature for 2h, and then cooled to room temperature in the furnace to obtain starch-based hard carbon composite graphite anode material.

[0047] S4. Negative electrode preparation: The above-mentioned starch-based hard carbon composite graphite negative electrode material is used as the negative electrode active material to prepare the negative electrode sheet. The negative electrode material is uniformly ground with conductive agent and binder in a mass ratio of 8:1:1, and then mixed with N-methylpyrrolidone to prepare a negative electrode slurry. The slurry is coated on the current collector and placed in a vacuum oven at 100°C for 10 hours. After drying, it is cut into round negative electrode sheets.

[0048] S5. Half-cell assembly: Lithium sheet is used as the counter electrode. The electrolyte is prepared by 1.0 mol LiPF6 in a solution of ethylene carbonate, diethyl carbonate and dimethyl carbonate (EC / DEC / DMC, v / v / v = 1:1:1). The starch-based negative electrode sheet is assembled into a button cell in a glove box under an argon atmosphere.

[0049] The dual transition metals selected in Examples 1, 2, and 3 are iron / cobalt, nickel / cobalt, and iron / manganese, respectively, and the selected organic ligand reagents are fumaric acid, benzoic acid, and oxalic acid, respectively.

[0050] <Example 4>

[0051] S1. Pretreatment of starch-based raw materials: Take a certain amount of corn starch and put it into a container. Place the container containing soluble starch into a vacuum drying oven and dry it at 50-100℃ for 24 hours. Then take out the container and add it into a reaction vessel at a mass ratio of starch to melamine of 4:1. Dry powder hydrothermal treatment is carried out at 50-150℃ to obtain the precursor material. Then, it is crushed to obtain precursor particles with a particle size of 40-500 mesh.

[0052] S2, Composite Graphite: Expandable graphite was heated to 600℃ in a muffle furnace at a rate of 20-30℃ / min and held at that temperature for 0.5h. After cooling, the expanded graphite was collected. The expanded graphite was mixed with the esterified starch prepared in S1 and ground thoroughly. The mass ratio of esterified starch to expanded graphite was 15:1. A granular mixture was collected.

[0053] S3, Carbonization: Under the protection of argon atmosphere, the precursor particles obtained in S1 are heated to 1100℃ at a rate of 1-2℃ / min, held at the temperature for 2h, and then cooled to room temperature in the furnace to obtain starch-based hard carbon composite graphite anode material.

[0054] S4. Negative electrode preparation: The above-mentioned starch-based hard carbon composite graphite negative electrode material is used as the negative electrode active material to prepare the negative electrode sheet. The negative electrode material is uniformly ground with conductive agent and binder in a mass ratio of 8:1:1, and then mixed with N-methylpyrrolidone to prepare a negative electrode slurry. The slurry is coated on the current collector and placed in a vacuum oven at 100°C for 10 hours. After drying, it is cut into round negative electrode sheets.

[0055] S5. Half-cell assembly: Lithium sheet is used as the counter electrode. The electrolyte is prepared by 1.0 mol LiPF6 in a solution of ethylene carbonate, diethyl carbonate and dimethyl carbonate (EC / DEC / DMC, v / v / v = 1:1:1). The starch-based negative electrode sheet is assembled into a button cell in a glove box under an argon atmosphere.

[0056] <Example 5>

[0057] S1. Pretreatment of starch-based raw materials: Take a certain amount of corn starch and put it into a container. Place the container containing soluble starch into a vacuum drying oven and dry it at 50-100℃ for 24 hours. Then take out the container and add it into a reaction vessel at a mass ratio of starch to melamine of 4:1. Dry powder hydrothermal treatment is carried out at 50-150℃ to obtain the precursor material. Then, it is crushed to obtain precursor particles with a particle size of 40-500 mesh.

[0058] S2, Composite Graphite: Expandable graphite was heated to 600℃ in a muffle furnace at a rate of 20-30℃ / min and held at that temperature for 0.5h. After cooling, the expanded graphite was collected. The expanded graphite was mixed with the esterified starch prepared in S1 and ground thoroughly. The mass ratio of esterified starch to expanded graphite was 20:1. The resulting granular mixture was collected.

[0059] S3, Carbonization: Under the protection of argon atmosphere, the precursor particles obtained in S1 are heated to 1100℃ at a rate of 1-2℃ / min, held at the temperature for 2h, and then cooled to room temperature in the furnace to obtain starch-based hard carbon composite graphite anode material.

[0060] S4. Negative electrode preparation: The above-mentioned starch-based hard carbon composite graphite negative electrode material is used as the negative electrode active material to prepare the negative electrode sheet. The negative electrode material is uniformly ground with conductive agent and binder in a mass ratio of 8:1:1, and then mixed with N-methylpyrrolidone to prepare a negative electrode slurry. The slurry is coated on the current collector and placed in a vacuum oven at 100°C for 10 hours. After drying, it is cut into round negative electrode sheets.

[0061] S5. Half-cell assembly: Lithium sheet is used as the counter electrode. The electrolyte is prepared by 1.0 mol LiPF6 in a solution of ethylene carbonate, diethyl carbonate and dimethyl carbonate (EC / DEC / DMC, v / v / v = 1:1:1). The starch-based negative electrode sheet is assembled into a button cell in a glove box under an argon atmosphere.

[0062] <Example 6>

[0063] S1. Pretreatment of starch-based raw materials: Take a certain amount of corn starch and put it into a container. Place the container containing soluble starch into a vacuum drying oven and dry it at 50-100℃ for 24 hours. Then take out the container and add it into a reaction vessel at a mass ratio of starch to melamine of 4:1. Dry powder hydrothermal treatment is carried out at 50-150℃ to obtain the precursor material. Then, it is crushed to obtain precursor particles with a particle size of 40-500 mesh.

[0064] S2, Composite Graphite: Expandable graphite was heated to 600℃ in a muffle furnace at a rate of 20-30℃ / min and held at that temperature for 0.5h. After cooling, the expanded graphite was collected. The expanded graphite was mixed with the esterified starch prepared in S1 and ground thoroughly. The mass ratio of esterified starch to expanded graphite was 30:1. The resulting granular mixture was collected.

[0065] S3, Carbonization: Under the protection of argon atmosphere, the precursor particles obtained in S1 are heated to 1100℃ at a rate of 1-2℃ / min, held at the temperature for 2h, and then cooled to room temperature in the furnace to obtain starch-based hard carbon composite graphite anode material.

[0066] S4. Negative electrode preparation: The above-mentioned starch-based hard carbon composite graphite negative electrode material is used as the negative electrode active material to prepare the negative electrode sheet. The negative electrode material is uniformly ground with conductive agent and binder in a mass ratio of 8:1:1, and then mixed with N-methylpyrrolidone to prepare a negative electrode slurry. The slurry is coated on the current collector and placed in a vacuum oven at 100°C for 10 hours. After drying, it is cut into round negative electrode sheets.

[0067] S5. Half-cell assembly: Lithium sheet is used as the counter electrode. The electrolyte is prepared by 1.0 mol LiPF6 in a solution of ethylene carbonate, diethyl carbonate and dimethyl carbonate (EC / DEC / DMC, v / v / v = 1:1:1). The starch-based negative electrode sheet is assembled into a button cell in a glove box under an argon atmosphere.

[0068] <Comparative Example 1>

[0069] S1. Pretreatment of starch-based raw materials: Take a certain amount of corn starch and put it into a container. Place the container containing soluble starch into a vacuum drying oven and dry it at 50-100℃ for 24 hours. Then take out the container and add it into a reaction vessel at a mass ratio of starch to melamine of 4:1. Dry powder hydrothermal treatment is carried out at 50-150℃ to obtain the precursor material. Then, it is crushed to obtain precursor particles with a particle size of 40-500 mesh.

[0070] S2, Carbonization: Under the protection of argon atmosphere, the precursor particles obtained in S1 are heated to 900℃ at a rate of 1-2℃ / min, held at that temperature for 2h, and then cooled to room temperature in the furnace to obtain starch-based hard carbon anode material.

[0071] S3. Preparation of negative electrode: The above-mentioned starch-based hard carbon negative electrode material is used as the negative electrode active material to prepare the negative electrode sheet. The negative electrode material is uniformly ground with conductive agent and binder in a mass ratio of 8:1:1, and then mixed with N-methylpyrrolidone to prepare a negative electrode slurry. The slurry is coated on the current collector and placed in a vacuum oven at 100°C for 10 hours. After drying, it is cut into round negative electrode sheets.

[0072] S4. Half-cell assembly: Lithium sheet is used as the counter electrode. The electrolyte is prepared by 1.0 mol LiPF6 in a solution of ethylene carbonate, diethyl carbonate and dimethyl carbonate (EC / DEC / DMC, v / v / v = 1:1:1). The starch-based negative electrode sheet is assembled into a button cell in a glove box under an argon atmosphere.

[0073] <Comparative Example 2>

[0074] S1. Pretreatment of starch-based raw materials: Take a certain amount of corn starch and put it into a container. Place the container containing soluble starch into a vacuum drying oven and dry it at 50-100℃ for 24 hours. Then take out the container and add it into a reaction vessel at a mass ratio of starch to melamine of 4:1. Dry powder hydrothermal treatment is carried out at 50-150℃ to obtain the precursor material. Then, it is crushed to obtain precursor particles with a particle size of 40-500 mesh.

[0075] S2, Carbonization: Under the protection of argon atmosphere, the precursor particles obtained in S1 are heated to 1100℃ at a rate of 1-2℃ / min, held at the temperature for 2h, and then cooled to room temperature in the furnace to obtain starch-based hard carbon anode material.

[0076] S3. Preparation of negative electrode: The above-mentioned starch-based hard carbon negative electrode material is used as the negative electrode active material to prepare the negative electrode sheet. The negative electrode material is uniformly ground with conductive agent and binder in a mass ratio of 8:1:1, and then mixed with N-methylpyrrolidone to prepare a negative electrode slurry. The slurry is coated on the current collector and placed in a vacuum oven at 100°C for 10 hours. After drying, it is cut into round negative electrode sheets.

[0077] S4. Half-cell assembly: Lithium sheet is used as the counter electrode. The electrolyte is prepared by 1.0 mol LiPF6 in a solution of ethylene carbonate, diethyl carbonate and dimethyl carbonate (EC / DEC / DMC, v / v / v = 1:1:1). The starch-based negative electrode sheet is assembled into a button cell in a glove box under an argon atmosphere.

[0078] <Comparative Example 3>

[0079] S1. Pretreatment of starch-based raw materials: Take a certain amount of corn starch and put it into a container. Place the container containing soluble starch into a vacuum drying oven and dry it at 50-100℃ for 24 hours. Then take out the container and add it into a reaction vessel at a mass ratio of starch to melamine of 4:1. Dry powder hydrothermal treatment is carried out at 50-150℃ to obtain the precursor material. Then, it is crushed to obtain precursor particles with a particle size of 40-500 mesh.

[0080] S2, Carbonization: Under the protection of argon atmosphere, the precursor particles obtained in S1 are heated to 1300℃ at a rate of 1-2℃ / min, held at that temperature for 2h, and then cooled to room temperature in the furnace to obtain starch-based hard carbon anode material.

[0081] S3. Preparation of negative electrode: The above-mentioned starch-based hard carbon negative electrode material is used as the negative electrode active material to prepare the negative electrode sheet. The negative electrode material is uniformly ground with conductive agent and binder in a mass ratio of 8:1:1, and then mixed with N-methylpyrrolidone to prepare a negative electrode slurry. The slurry is coated on the current collector and placed in a vacuum oven at 100°C for 10 hours. After drying, it is cut into round negative electrode sheets.

[0082] S4. Half-cell assembly: Lithium sheet is used as the counter electrode. The electrolyte is prepared by 1.0 mol LiPF6 in a solution of ethylene carbonate, diethyl carbonate and dimethyl carbonate (EC / DEC / DMC, v / v / v = 1:1:1). The starch-based negative electrode sheet is assembled into a button cell in a glove box under an argon atmosphere.

[0083] <Comparative Example 4>

[0084] S1. Pretreatment of starch-based raw materials: Take a certain amount of corn starch and put it into a container. Place the container containing soluble starch into a vacuum drying oven and dry it at 50-100℃ for 24 hours. Then take out the container and add it into a reaction vessel at a mass ratio of starch to maleic anhydride of 5:1. Dry powder hydrothermal treatment is carried out at 50-150℃ to obtain the precursor material. Then, it is crushed to obtain precursor particles with a particle size of 40-500 mesh.

[0085] S2, Carbonization: Under the protection of argon atmosphere, the precursor particles obtained in S1 are heated to 1100℃ at a rate of 1-2℃ / min, held at the temperature for 2h, and then cooled to room temperature in the furnace to obtain starch-based hard carbon anode material.

[0086] S3. Preparation of negative electrode: The above-mentioned starch-based hard carbon negative electrode material is used as the negative electrode active material to prepare the negative electrode sheet. The negative electrode material is uniformly ground with conductive agent and binder in a mass ratio of 8:1:1, and then mixed with N-methylpyrrolidone to prepare a negative electrode slurry. The slurry is coated on the current collector and placed in a vacuum oven at 100°C for 10 hours. After drying, it is cut into round negative electrode sheets.

[0087] S4. Half-cell assembly: Lithium sheet is used as the counter electrode. The electrolyte is prepared by 1.0 mol LiPF6 in a solution of ethylene carbonate, diethyl carbonate and dimethyl carbonate (EC / DEC / DMC, v / v / v = 1:1:1). The starch-based negative electrode sheet is assembled into a button cell in a glove box under an argon atmosphere.

[0088] <Comparative Example 5>

[0089] S1. Negative electrode preparation: Commercial graphite material is used as the negative electrode active material to prepare the negative electrode sheet. The negative electrode material is uniformly ground with conductive agent and binder in a mass ratio of 8:1:1, and then mixed with N-methylpyrrolidone to obtain a negative electrode slurry. The slurry is coated on the current collector and placed in a vacuum oven at 100°C for 10 hours. After drying, it is cut into circular negative electrode sheets.

[0090] S2. Half-cell assembly: Lithium sheet is used as the counter electrode. The electrolyte is prepared by 1.0 mol LiPF6 in a solution of ethylene carbonate, diethyl carbonate and dimethyl carbonate (EC / DEC / DMC, v / v / v = 1:1:1). The starch-based negative electrode sheet is assembled into a button cell in a glove box under an argon atmosphere.

[0091] Figure 1 This is a SEM image of the starch-based hard carbon composite graphite anode material prepared in Example 4. From... Figure 1 It can be seen that graphite is uniformly coated on the surface of spherical hard carbon. Due to the introduction of melamine crosslinking agent, the spherical structure of starch is maintained during the high-temperature carbonization process.

[0092] Figure 2 The images show the XRD patterns of the starch-based hard carbon composite graphite anode materials prepared in Examples 1, 4, and 6. Figure 2 It can be seen that as the proportion of composite graphite increases, the intensity of the (002) peak increases accordingly, and the degree of graphitization of the material continues to increase.

[0093] Figure 3The battery assembled from the starch-based hard carbon composite graphite anode material prepared in Example 4 of this invention operates at a low current density of 25 mA g. -1 The charge-discharge curves are shown below. The starch-based hard carbon composite graphite anode material prepared in Example 4 has a specific capacity as high as 425.6 mAh g. -1 .

[0094] Figure 4 This is a GCD performance diagram of a battery assembled from the starch-based hard carbon composite graphite anode material prepared in Example 4 of this invention. From... Figure 4 It can be seen that the starch-based hard carbon composite graphite anode material has excellent rate performance at 1A g. -1 It still has 142.8mAh g. -1 The high specific capacity is attributed to the excellent kinetic properties and abundant lithium storage sites of the graphite-coated spherical structure.

[0095] Figure 5 The batteries assembled from the starch-based hard carbon composite graphite anode materials prepared in Examples 1-6 of this invention operate at a current density of 0.1 A g. -1 The following is a comparison chart of the loop performance. From... Figure 5 It can be seen that among the graphite and starch precursor samples with different proportions, the electrochemical performance is best when the mass ratio of esterified starch to expanded graphite is 15:1.

[0096] Figure 6 Batteries assembled from the materials prepared in Comparative Examples 1-4 of this invention were tested at a current density of 0.1 Ag. -1 The following is a graph showing the cycle performance. From... Figure 6 It can be seen that the introduction of melamine crosslinking agent effectively improved the lithium storage capacity of esterified starch, and the carbonization effect at 1100℃ was the best compared with other carbonization temperatures.

[0097] Figure 7 Batteries assembled from the materials prepared in Comparative Examples 1-4 of this invention were tested at a current density of 25 mAg. -1 A comparison of the galvanostatic intermittent titration (GITT) curves and the calculated diffusion coefficient D during lithiation and delithiation processes. From Figure 7 It can be seen that Comparative Example 2 has the highest diffusion coefficient, indicating that the introduction of melamine gives esterified starch more active sites, which is more conducive to lithium ion storage.

[0098] Figure 8 Batteries assembled from the materials prepared in Example 3, Comparative Examples 2 and 4 of this invention were tested at a current density of 25 mAg. -1 A comparison of the galvanostatic intermittent titration (GITT) curves and the calculated diffusion coefficient D during lithiation and delithiation processes. From Figure 8It can be seen that Example 3 has the highest diffusion coefficient, and the starch-based hard carbon composite graphite has more active sites, which is more conducive to lithium ion storage.

[0099] Figure 9 The batteries assembled from the negative electrode materials prepared in Comparative Examples 2 and 5 of this invention operate at a low current density of 25 mA g. -1 The charge / discharge curves below. From Figure 9 It can be seen that graphite anode materials exhibit a significant plateau capacity, while hard carbon anode materials are dominated by slope capacity, corresponding to their different lithium storage mechanisms. From Figure 3 and Figure 9 It can be seen that the specific capacity of the anode material prepared in Example 4 is higher than that of the anode materials prepared in Comparative Examples 2 and 5. The starch-based hard carbon composite graphite yields an anode material with high lithium storage capacity.

[0100] For any points not covered above, existing technologies shall apply.

[0101] Although specific embodiments of the present invention have been described in detail by way of examples, those skilled in the art should understand that the above examples are for illustrative purposes only and are not intended to limit the scope of the invention. Those skilled in the art can make various modifications or additions to the described specific embodiments or use similar methods to replace them, without departing from the direction of the invention or exceeding the scope defined by the appended claims. Those skilled in the art should understand that any modifications, equivalent substitutions, improvements, etc., made to the above embodiments based on the technical essence of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a starch-based hard carbon composite graphite anode material, characterized in that: Expanded graphite was mixed with esterified starch and then thoroughly ground before carbonization to obtain the starch-based hard carbon composite graphite anode material. The mass ratio of expanded graphite to esterified starch is 1:1 to 30; The carbonization temperature is 900-1300℃, and the carbonization time is 1-8 hours. The heating rate for carbonization is 1–10 °C / min; The preparation method of esterified starch is as follows: corn starch is vacuum dried and then hydrothermally reacted with melamine to obtain esterified starch. The hydrothermal reaction temperature is 50-150℃. The spherical structure of corn starch remains stable and interconnected after esterification, with graphite uniformly composited on the surface of the spherical structure.

2. The preparation method according to claim 1, characterized in that: The mass ratio of corn starch to melamine is 4:

1.

3. The preparation method according to claim 1, characterized in that: Expandable graphite was heated to 600°C in a muffle furnace at a rate of 20–30°C / min, held at that temperature for 0.5–3 h, and then cooled to obtain the expanded graphite.

4. A starch-based hard carbon composite graphite anode material prepared by the preparation method according to any one of claims 1-3.

5. The application of the starch-based hard carbon composite graphite anode material as described in claim 4 in lithium batteries.

Images