A MoO3 / C co-coated micro-expanded microcrystalline graphite / Fe3O4 lithium ion battery negative electrode material and its preparation method and application

Abstract

The present invention discloses a MoO3 / C co-coated micro-expanded microcrystalline graphite / Fe3O4 lithium-ion battery negative electrode material, its preparation method, and application. These materials relate to the fields of new material preparation and new energy technologies. The method comprises preparing a micro-expanded microcrystalline graphite / Fe3O4 composite material using micro-expanded microcrystalline graphite as a matrix through a sol-gel method. Furthermore, the micro-expanded microcrystalline graphite / Fe3O4 composite material is then prepared using a liquid phase coating method by adjusting the amounts of ammonium molybdate and citric acid added, using the micro-expanded microcrystalline graphite / Fe3O4 composite material as a matrix. The composite material is then used as a negative electrode material for lithium-ion batteries. At a current density of 0.1 A / g, the coated material exhibits an initial discharge specific capacity of 987.3 mAh / g and an initial coulombic efficiency of 81.6%. Even after 100 cycles, the material maintains a discharge specific capacity of 853.2 mAh / g. This method significantly improves the reversible capacity and other lithium storage properties of high-purity microcrystalline graphite lithium-ion battery negative electrode materials, thereby enhancing the application potential and commercial value of microcrystalline graphite.

Description

Technical Field

[0001] The present invention belongs to the field of new material preparation and new energy technology, and specifically relates to a MoO3 / C co-coated micro-expanded microcrystalline graphite / Fe3O4 lithium ion battery negative electrode material, a preparation method thereof, and application in lithium ion batteries. Background Art

[0002] Currently, due to the inadequate development and utilization of microcrystalline graphite resources and limited investment in high-end technology development, the deep processing level of graphite products is relatively low, primarily remaining at the initial processing and simple handling of raw materials, resulting in a significant waste of mineral resources. Given its fine grains and isotropic structural properties, microcrystalline graphite exhibits enormous application potential in the field of novel lithium-ion power batteries. However, when used as a negative electrode material for lithium-ion batteries, microcrystalline graphite still faces the challenges of poor reversible specific capacity and rate performance. Oxidizing microcrystalline graphite to increase interlayer spacing and pore structure is an effective means of increasing lithium storage capacity. Compounding microcrystalline graphite with oxides of the conductive metal Fe can significantly increase lithium storage capacity. However, the metal oxide undergoes significant volume expansion during the de-lithiation / intercalation process, rendering the structure unstable. Summary of the Invention

[0003] In order to suppress the volume expansion of Fe3O4 during charging and discharging and improve the lithium storage capacity of microcrystalline graphite lithium ion battery negative electrode materials, the purpose of the present invention is to provide a MoO3 / C co-coated micro-expanded microcrystalline graphite / Fe3O4 lithium ion battery negative electrode material and its preparation method and application. With microcrystalline graphite as the core, micro-expanded microcrystalline graphite and nano-Fe3O4 are compounded, and the precursor is carbonized through a specific process to form a core-shell structure. This structure can not only increase the specific capacity of the lithium ion battery, but also effectively suppress the volume expansion of metal oxides and enhance the structure and cycle stability of the microcrystalline graphite negative electrode material.

[0004] To further achieve the above objectives, the present invention adopts the following technical solution: a method for preparing a MoO3 / C co-coated micro-expanded microcrystalline graphite / Fe3O4 lithium ion battery negative electrode material, comprising:

[0005] Micro-expanded microcrystalline graphite / Fe3O4 composite materials were prepared using the sol-gel method with micro-expanded microcrystalline graphite as the matrix.

[0006] Then, using the micro-expanded microcrystalline graphite / Fe3O4 composite material as the matrix, the liquid phase coating method was adopted to prepare MoO3 / C co-coated micro-expanded microcrystalline graphite / Fe3O4 composite material by changing the addition amount of ammonium molybdate and citric acid.

[0007] Optionally, the sol-gel method is used to prepare the micro-expanded microcrystalline graphite / Fe3O4 composite material, comprising the following steps:

[0008] Step (1): weigh 0.3-0.6 g of ferric nitrate, add 20-40 ml of deionized water, and sonicate for 30-40 min;

[0009] Step (2): add 0.1-0.4 g of citric acid, stir in a magnetic stirring water bath at 50-70°C, and add ammonia water dropwise until the solution is neutral;

[0010] Step (3): When the ferric nitrate and citrate mixed solution is in a colloidal state, 0.1 to 0.3 g of ultrasonically dispersed micro-expanded microcrystalline graphite is added, and heating and stirring are continued until the water is evaporated to dryness, thereby obtaining a composite material precursor;

[0011] Step (4): Place the prepared precursor into an Ar gas-protected tubular furnace, heat it to 300-400°C at a rate of 5-7°C / min, keep it warm for 1-2 hours, and cool it to room temperature to prepare micro-expanded microcrystalline graphite / Fe3O4 composite materials with different Fe3O4 mass fractions.

[0012] Furthermore, the microcrystalline graphite is micron-sized microcrystalline graphite with a slightly expanded edge of about 5 μm, and the Fe3O4 prepared in step (4) is nano-sized particles, and the two form a micro-nano composite structure.

[0013] Optionally, the liquid phase coating method, by changing the amount of ammonium molybdate and citric acid added, prepares a MoO3 / C co-coated micro-expanded microcrystalline graphite / Fe3O4 composite material, comprising the following steps:

[0014] Step (1): Weigh 0.5-2 g of micro-expanded microcrystalline graphite / Fe3O4 composite material, disperse it in 20-50 ml of anhydrous ethanol, and ultrasonicate it for 20-50 min;

[0015] Step (2): Weigh 0.2-0.8 g of ammonium molybdate and 0.0035-0.0087 g of citric acid, add 20-40 ml of deionized water, and sonicate until completely dissolved;

[0016] Step (3): stirring in a water bath at 60-90°C, adding the dispersed micro-expanded microcrystalline graphite / Fe3O4 composite material and continuing to stir until the water is evaporated;

[0017] Step (4): drying in a vacuum oven at 50-80°C;

[0018] Step (5): Place the prepared coating material into an Ar gas-protected tubular furnace, heat it to 200-460°C at a rate of 5-7°C / min, keep it warm for 1-2 hours, and cool it naturally to room temperature to obtain a MoO3 / C co-coated micro-expanded microcrystalline graphite / Fe3O4 composite material.

[0019] As described above, the MoO3 / C coating material and Fe3O4 prepared in step (5) are distributed in the form of microspheres on the surface and edge of the micro-expanded microcrystalline graphite.

[0020] A MoO3 / C co-coated micro-expanded microcrystalline graphite / Fe3O4 composite material prepared by the above-mentioned preparation method.

[0021] An application of the aforementioned micro-expanded microcrystalline graphite / Fe3O4 composite material in a negative electrode of a lithium-ion battery.

[0022] Application of the MoO3 / C co-coated micro-expanded microcrystalline graphite / Fe3O4 composite material prepared as described above in the negative electrode of a lithium-ion battery.

[0023] Technical advantages of the present invention:

[0024] (1) The present invention uses micro-expanded microcrystalline graphite as raw material and adopts the sol-gel method to prepare a micro-expanded microcrystalline graphite / Fe3O4 composite material. Since microcrystalline graphite has fine grains and isotropic properties, the number of lithium ion diffusion channels is increased, and the reversible lithium storage capacity is higher than that of flake graphite. In order to increase the lithium storage capacity, the use of micro-expanded microcrystalline graphite can increase the number of lithium ion pore channels. However, due to its small size, microcrystalline graphite is generally slightly oxidized at the edges. Therefore, using slightly oxidized microcrystalline graphite as the matrix, nano-sized Fe3O4 is mainly filled into the edge pores of the micro-expanded microcrystalline graphite to form a micro-nano structure. The two have a high degree of bonding and can form a stable lithium storage structure. The sol-gel method is an effective means of preparing micro-nano composite materials.

[0025] (2) The present invention uses micro-expanded microcrystalline graphite / Fe3O4 as raw materials and adopts a liquid phase coating method to prepare a MoO3 / C co-coated micro-expanded microcrystalline graphite / Fe3O4 composite material. Because Fe3O4 expands significantly during charging and discharging of lithium-ion batteries, a combination of MoO3 and C with high mechanical strength is used to coat the edges of the composite material, forming a core-shell structure with micro-expanded microcrystalline graphite / Fe3O4 as the core and the MoO3 / C composite material as the shell. This can suppress the volume expansion effect of the composite material and enhance the cycling stability of the lithium-ion battery. The liquid phase coating method promotes thorough mixing of the reactants, which is conducive to the formation of a uniformly coated core-shell structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is the microstructure morphology of the micro-expanded microcrystalline graphite / Fe3O4 composite material prepared in Example 1 of the present invention.

[0027] Figure 2 This is the microstructure morphology of the MoO3 / C co-coated micro-expanded microcrystalline graphite / Fe3O4 composite material prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0028] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0029] A method for preparing a MoO3 / C co-coated micro-expanded microcrystalline graphite / Fe3O4 lithium ion battery negative electrode material comprises the following steps:

[0030] (1) Weigh 0.3-0.6 g of ferric nitrate, add 20-40 ml of deionized water, and sonicate for 30-40 min;

[0031] (2) Add 0.1-0.4 g of citric acid, stir in a magnetic stirring water bath at 50-70 °C, and add ammonia water dropwise until the solution becomes neutral;

[0032] (3) When the ferric nitrate and citrate mixed solution is in a colloidal state, 0.1 to 0.3 g of ultrasonically dispersed microcrystalline graphite is added, and heating and stirring are continued until the water is evaporated to obtain a composite material precursor;

[0033] (4) placing the prepared precursor into an Ar gas-protected tubular furnace, heating it to 300-400°C at a rate of 5-7°C / min, keeping it at that temperature for 1-2 hours, and cooling it to room temperature to prepare micro-expanded microcrystalline graphite / Fe3O4 composite materials with different Fe3O4 mass fractions;

[0034] (5) Weigh 0.5-2 g of micro-expanded microcrystalline graphite / Fe3O4 composite material, disperse it in 20-50 ml of anhydrous ethanol, and sonicate for 20-50 min;

[0035] (6) Weigh 0.2-0.8 g of ammonium molybdate and 0.0035-0.0087 g of citric acid, add 20-40 ml of deionized water, and sonicate until completely dissolved;

[0036] (7) stirring in a water bath at 60-90° C., adding the micro-expanded microcrystalline graphite / Fe 3 O 4 composite material dispersed in step (5) and continuing to stir until the water is evaporated;

[0037] (8) Drying in a vacuum oven at 50-80°C;

[0038] (9) placing the prepared coating material in an Ar gas-protected tubular furnace, heating it to 200-460°C at a rate of 5-7°C / min, keeping it warm for 1-2 hours, and naturally cooling it to room temperature to obtain a MoO3 / C co-coated micro-expanded microcrystalline graphite / Fe3O4 composite material;

[0039] (10) Micro-expanded microcrystalline graphite / Fe3O4 composite materials and MoO3 / C co-coated micro-expanded microcrystalline graphite / Fe3O4 composite materials are used as negative electrode materials for lithium-ion batteries.

[0040] Example 1: Weigh 0.3 g of ferric nitrate, add 20 ml of deionized water, and ultrasonicate for 30 minutes; add 0.3 g of citric acid, stir in a 50°C magnetic stirring water bath, and add ammonia water dropwise until the solution is neutral; when the ferric nitrate and citric acid mixed solution is colloidal, add 0.1 g of ultrasonically dispersed microcrystalline graphite, continue heating and stirring until the water is evaporated, thereby obtaining a composite material precursor; the prepared precursor is placed in an Ar gas-protected tubular furnace, heated to 300°C at a rate of 5°C / min, kept warm for 1 hour, and cooled to room temperature, and the microcrystalline graphite / Fe3O4 composite materials with different Fe3O4 mass fractions are prepared by this sol-gel method as lithium-ion battery negative electrode materials;

[0041] Weigh 0.5g of micro-expanded microcrystalline graphite / Fe3O4 composite material, disperse it in 20ml of anhydrous ethanol, and ultrasonicate for 20min; weigh 0.5g of ammonium molybdate and 0.0036g of citric acid and add 20ml of deionized water, and ultrasonicate until completely dissolved; stir in a 60℃ water bath, then add the dispersed micro-expanded microcrystalline graphite / Fe3O4 composite material and continue stirring until the water is evaporated; dry in a vacuum oven at 50℃; place the prepared coating material in an Ar gas-protected tubular furnace, heat to 200℃ at a rate of 5℃ / min, keep warm for 1h, and naturally cool to room temperature. This liquid phase coating method is used to prepare MoO3 / C co-coated micro-expanded microcrystalline graphite / Fe3O4 composite material as a negative electrode material for lithium-ion batteries.

[0042] like Figure 1 As shown in the figure, the microstructure of the prepared micro-expanded microcrystalline graphite / Fe3O4 composite material is shown. White nano-Fe3O4 particles are distributed on the surface of the micron-oxidized microcrystalline graphite, especially on the boundary. Figure 2 As shown in the figure, the microstructure morphology of the MoO3 / C co-coated micro-expanded microcrystalline graphite / Fe3O4 composite material is prepared. After coating, the material boundary is smoother, and the holes and cracks on the surface and edge of the micro-expanded microcrystalline graphite / Fe3O4 are gradually covered by MoO3 / C microspheres.

[0043] Comparative Example 1: According to the sol-gel method in Example 1, 0.6 g of ferric nitrate and 0.3 g of citric acid were weighed, and the remaining operations were the same as in Example 1.

[0044] Comparative Example 2: According to the sol-gel method in Example 1, 0.3 g of ferric nitrate and 0.4 g of citric acid were weighed, and the remaining operations were the same as in Example 1.

[0045] Comparative Example 3: According to the sol-gel method in Example 1, 0.2 g of micro-expanded microcrystalline graphite was weighed, and the rest of the operation process was the same as in Example 1.

[0046] Comparative Example 4: According to the sol-gel method in Example 1, 0.3 g of micro-expanded microcrystalline graphite was weighed, and the rest of the operation process was the same as in Example 1.

[0047] Table 1 Electrochemical properties of micro-expanded microcrystalline graphite / Fe3O4 composites

[0048]

[0049] Table 2 Electrochemical properties of MoO3 / C co-coated micro-expanded microcrystalline graphite / Fe3O4 composites

[0050]

[0051]

[0052] Example 2: Weigh 0.6 g of ferric nitrate, add 40 ml of deionized water, and ultrasonicate for 40 min; add 0.2 g of citric acid, stir in a magnetic stirring water bath at 70 ° C, and add ammonia water dropwise until the solution is neutral; when the ferric nitrate and citric acid mixed solution is colloidal, add 0.3 g of ultrasonically dispersed microcrystalline graphite, continue heating and stirring until the water is evaporated, thereby obtaining a composite material precursor; put the prepared precursor into an Ar gas protected tubular furnace and heat at 6 ° C. min -1 The temperature was raised to 400℃ at a speed of 1000℃, kept at this temperature for 2 hours, and cooled to room temperature. Micro-expanded microcrystalline graphite / Fe3O4 composite materials with different Fe3O4 mass fractions were prepared by this sol-gel method as negative electrode materials for lithium-ion batteries.

[0053] Weigh 2g of micro-expanded microcrystalline graphite / Fe3O4 composite material, disperse it in 50ml of anhydrous ethanol, and ultrasonicate it for 30min; weigh 0.3g of ammonium molybdate and 0.0057g of citric acid, add them into 40ml of deionized water, and ultrasonicate them until they are completely dissolved; stir them in an 80℃ water bath, then add the dispersed micro-expanded microcrystalline graphite / Fe3O4 composite material and continue stirring until the water evaporates; dry it in a vacuum oven at 80℃; put the prepared coating material into an Ar gas-protected tubular furnace and heat it at 6℃·min -1 The temperature was raised to 400°C at a rate of 100°C, kept at this temperature for 2 hours, and naturally cooled to room temperature. The MoO3 / C co-coated micro-expanded microcrystalline graphite / Fe3O4 composite material was prepared by this liquid phase coating method as the negative electrode material of lithium-ion batteries.

[0054] Comparative Example 5: According to the sol-gel method in Example 2, 0.2 g of microcrystalline graphite was weighed, and according to the liquid phase coating method in Example 2, 1 g of the micro-expanded microcrystalline graphite / Fe3O4 composite material was weighed. The rest of the operation process was the same as in Example 2.

[0055] Comparative Example 6: According to the sol-gel method in Example 2, 0.1 g of microcrystalline graphite was weighed, and according to the liquid phase coating method in Example 2, 0.5 g of micro-expanded microcrystalline graphite / Fe3O4 composite material was weighed. The rest of the operation process was the same as in Example 2.

[0056] Comparative Example 7: According to the sol-gel method in Example 2, 0.3 g of ferric nitrate and 0.4 g of citric acid were weighed. According to the liquid phase coating method in Example 2, 0.5 g of ammonium molybdate and 0.0087 g of citric acid were weighed. The remaining operating procedures were the same as in Example 2.

[0057] Comparative Example 8: According to the sol-gel method in Example 2, 0.4 g of ferric nitrate and 0.3 g of citric acid were weighed. According to the liquid phase coating method in Example 2, 0.8 g of ammonium molybdate and 0.0035 g of citric acid were weighed. The remaining operating procedures were the same as in Example 2.

[0058] Table 3 Electrochemical properties of expanded microcrystalline graphite / Fe3O4 composites

[0059]

[0060] Table 4 Electrochemical properties of MoO3 / C co-coated micro-expanded microcrystalline graphite / Fe3O4 composites

[0061]

[0062] In the present invention, the lithium-ion battery test conditions are: using Shenzhen Xinweier BTS-5V / 2.2A battery testing equipment, a constant temperature of 25°C, and a test voltage range of 0.01 to 3V. As can be seen from Tables 1 to 4, the micro-expanded microcrystalline graphite / Fe3O4 composite material prepared by the sol-gel method as a negative electrode material for lithium-ion batteries has an initial discharge specific capacity of 860.3 mAh / g and an initial coulombic efficiency of 78.6% at a current density of 0.1 A / g. After 100 cycles, the composite material has a reversible specific capacity of 765.3 mAh / g and a capacity retention rate of 89.0%. The MoO3 / C co-coated micro-expanded microcrystalline graphite / Fe3O4 composite material prepared by the liquid phase coating method as a negative electrode material for lithium-ion batteries has an initial charge and discharge specific capacity of 987.3 mAh / g and an initial coulombic efficiency of 81.6% at a current density of 0.1 A / g. After 100 cycles, it still has a reversible specific capacity of 853.2 mAh / g and a capacity retention rate of 86.4%.

[0063] The above description is only a preferred embodiment of the present invention, which certainly cannot be used to limit the scope of rights of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and changes can be made without departing from the principles of the present invention. These improvements and changes are also considered to be within the scope of protection of the present invention.

Claims

1. A method for preparing a MoO3 / C co-coated micro-expanded microcrystalline graphite / Fe3O4 lithium ion battery negative electrode material, characterized in that: include: Micro-expanded microcrystalline graphite / Fe3O4 composite materials were prepared using the sol-gel method with micro-expanded microcrystalline graphite as the matrix. Then, the micro-expanded microcrystalline graphite / Fe3O4 composite material was used as the matrix and the MoO3 / C co-coated micro-expanded microcrystalline graphite / Fe3O4 composite material was prepared by liquid phase coating method by changing the addition amount of ammonium molybdate and citric acid. The microcrystalline graphite is micron-sized microcrystalline graphite with a slightly expanded edge of about 5 μm, and the Fe3O4 is nano-sized particles, and the two form a micro-nano composite structure.

2. The method for preparing the MoO3 / C co-coated micro-expanded microcrystalline graphite / Fe3O4 lithium ion battery negative electrode material according to claim 1, characterized in that the micro-expanded microcrystalline graphite / Fe3O4 composite material is prepared by a sol-gel method, comprising the following steps: Step (1): Weigh 0.3-0.6 g of ferric nitrate, add 20-40 ml of deionized water, and sonicate for 30-40 minutes; Step (2): add 0.1-0.4 g of citric acid, stir in a magnetic stirring water bath at 50-70°C, and add ammonia water dropwise until the solution is neutral; Step (3): When the ferric nitrate-citrate mixed solution is in a colloidal state, 0.1 to 0.3 g of ultrasonically dispersed microcrystalline graphite is added, and heating and stirring are continued until the water is evaporated to obtain a composite material precursor; Step (4): Place the prepared precursor into an Ar gas-protected tubular furnace, heat it to 300-400°C at a rate of 5-7°C / min, keep it warm for 1-2 hours, and cool it to room temperature to prepare micro-expanded microcrystalline graphite / Fe3O4 composite materials with different Fe3O4 mass fractions.

3. The method for preparing the MoO3 / C co-coated micro-expanded microcrystalline graphite / Fe3O4 lithium ion battery negative electrode material according to claim 1, characterized in that: The liquid phase coating method is to prepare a MoO3 / C co-coated micro-expanded microcrystalline graphite / Fe3O4 composite material by changing the addition amount of ammonium molybdate and citric acid, and comprises the following steps: Step (1): Weigh 0.5-2 g of micro-expanded microcrystalline graphite / Fe3O4 composite material, disperse it in 20-50 ml of anhydrous ethanol, and ultrasonicate it for 20-50 min; Step (2): Weigh 0.2-0.8 g of ammonium molybdate and 0.0035-0.0087 g of citric acid, add 20-40 ml of deionized water, and sonicate until completely dissolved; Step (3): Stir in a water bath at 60-90°C, then add the dispersed micro-expanded microcrystalline graphite / Fe3O4 composite material and continue stirring until the water evaporates; Step (4): drying in a vacuum oven at 50-80°C; Step (5): Place the prepared coating material into an Ar gas protected tubular furnace, heat it to 200-460°C at a rate of 5-7°C / min, keep it warm for 1-2 hours, and cool it naturally to room temperature to obtain a MoO3 / C co-coated micro-expanded microcrystalline graphite / Fe3O4 composite material.

4. The MoO3 / C co-coated micro-expanded microcrystalline graphite / Fe3O4 composite material prepared by the preparation method according to any one of claims 1 to 3.

5. Use of the MoO3 / C co-coated micro-expanded microcrystalline graphite / Fe3O4 composite material prepared as claimed in claim 4 in the negative electrode of a lithium ion battery.

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