Expanded microcrystalline graphite / Fe2O3 / SnO2 lithium ion battery micro-nano negative electrode material as well as preparation method and application thereof

Abstract

The invention discloses an expanded microcrystalline graphite / Fe2O3 / SnO2 lithium ion battery micro-nano negative electrode material as well as a preparation method and application thereof, and relates to the technical field of new material preparation and new energy. Comprising the following steps: by taking high-purity microcrystalline graphite as a raw material, preparing expanded microcrystalline graphite by adopting an oxidation method and an inert atmosphere heat treatment method, then preparing an expanded microcrystalline graphite / Fe2O3 composite material by adopting a water bath method and an air atmosphere heat treatment method I, and then preparing the expanded microcrystalline graphite / Fe2O3 / SnO2 composite material by adopting a hydrothermal method and the air atmosphere heat treatment method I for the negative electrode of the lithium ion battery. The ternary composite material has the first specific discharge capacity of 1539.9 mAh / g under the current density of 0.1 A / g, the first coulombic efficiency is 70.1%, and the ternary composite material still has the specific discharge capacity of 1003.2 mAh / g after 100 cycles. The expansion effect of the high-purity microcrystalline graphite is remarkable, the lithium storage capacity and the cycling stability of the lithium ion battery negative electrode material are remarkably improved by selecting and adding the nano metal oxide, and a new thought and a new method are provided for developing the high-performance lithium ion battery negative electrode material.

Description

Technical Field

[0001] The invention belongs to the field of new material preparation and new energy technology, and specifically relates to an expanded microcrystalline graphite / Fe 2 O 3 / SnO 2 Lithium-ion battery micro-nano negative electrode material, preparation method thereof and application in lithium-ion batteries. Background Art

[0002] Microcrystalline graphite has abundant reserves and structural characteristics such as small size and isotropy. It is used in negative electrode materials for lithium-ion batteries, and its theoretical lithium storage capacity is higher than that of commercial flake graphite. However, compared with negative electrode materials such as Si / C, the lithium storage capacity of microcrystalline graphite is low, and the first coulomb efficiency is not high due to the formation of SEI film. Therefore, it is an urgent problem to try to use various modification methods to improve the lithium storage performance of microcrystalline graphite.

[0003] It is an effective method to increase the pore structure and lithium storage space of microcrystalline graphite by oxidation treatment. However, microcrystalline graphite is small in size, and generally has defects at the boundary and slight volume expansion due to etching. It is difficult to expand the overall volume of microcrystalline graphite. Metal oxide composite is also an effective means to increase the lithium storage capacity, but its volume expansion effect cannot be ignored, so it is particularly important to select a suitable metal oxide. Summary of the invention

[0004] In order to improve the lithium storage performance of microcrystalline graphite lithium ion battery negative electrode materials, the present invention provides an expanded microcrystalline graphite / Fe 2 O 3 / SnO 2 Lithium-ion battery micro-nano negative electrode material and its preparation method and application. High-purity microcrystalline graphite is expanded and then mixed with Fe 2 O 3 and SnO 2 The combination of nanomaterials and the addition of the two can give full play to the synergistic effect of nano-sized particles and micron-sized microcrystalline graphite, and effectively inhibit the volume expansion of metal oxides.

[0005] To further achieve the above purpose, the present invention adopts the following technical solution: an expanded microcrystalline graphite / Fe 2 O 3 / SnO 2 The method for preparing a lithium-ion battery micro-nano negative electrode material comprises the following steps:

[0006] Firstly, high-purity microcrystalline graphite is used as raw material to prepare expanded microcrystalline graphite by oxidation method and inert atmosphere heat treatment method;

[0007] Secondly, the expanded microcrystalline graphite / Fe was prepared by water bath method and air atmosphere heat treatment method I.2 O 3 Composite materials;

[0008] Finally, the expanded microcrystalline graphite / Fe was prepared by hydrothermal method and air atmosphere heat treatment method II. 2 O 3 / SnO 2 Composite materials.

[0009] Optionally, the method of preparing expanded microcrystalline graphite using high-purity microcrystalline graphite as raw material by oxidation method and inert atmosphere heat treatment method comprises the following steps:

[0010] Step (1): In an ice water bath, add 1-10 g of high-purity microcrystalline graphite into a beaker containing 50-100 mL of concentrated sulfuric acid, then add 50-100 mL of potassium permanganate, and stir for 30-60 min;

[0011] Step (2): After continuing to stir in a water bath at 20 to 50° C. for 10 to 40 minutes, add deionized water for dilution. When the temperature no longer rises, add an appropriate amount of hydrogen peroxide until no bubbles are generated;

[0012] Step (3): After standing for a period of time, high-speed centrifugation is performed and the mixture is washed with deionized water to a neutral state;

[0013] Step (4): drying the obtained product in a forced air oven at 30-80°C;

[0014] Step (5): Preparing expanded microcrystalline graphite by heating at 600-900° C. for 5-20 min in an inert atmosphere.

[0015] From the above, it can be seen that the expansion effect on the surface and boundary of the expanded microcrystalline graphite is significant.

[0016] Optionally, the water bath method and air atmosphere heat treatment method I are used to prepare expanded microcrystalline graphite / Fe 2 O 3 The composite material comprises the following steps:

[0017] Step (1): Weigh 0.1-0.5 g of expanded microcrystalline graphite and 0.01-0.5 g of FeCl 3 6H 2 O is placed in a beaker and ultrasonicated for 20 to 50 minutes;

[0018] Step (2): Stir in a water bath at 60-90°C for 3-6 hours, let stand for a while and then filter;

[0019] Step (3): placing the obtained product in a 40-80° C. forced air drying oven for 3-8 hours;

[0020] Step (4): Heat in air at 200-800°C for 1-2h to prepare different Fe 2 O 3 Mass fraction of expanded microcrystalline graphite / Fe 2 O 3 Composite materials.

[0021] From above, Fe 2 O 3 The nanoparticles are distributed in the pore structure on the surface and edge of expanded microcrystalline graphite.

[0022] Optionally, the hydrothermal method and air atmosphere heat treatment method II are used to prepare expanded microcrystalline graphite / Fe 2 O 3 / SnO 2 The composite material comprises the following steps:

[0023] Step (1): Weigh 0.1-1 g of SnCl 2 ·2H 2 O is dissolved in 10-20 mL of concentrated sulfuric acid and stirred magnetically until completely dissolved;

[0024] Step (2): weigh 0.01-0.5 g of L-ascorbic acid and dissolve it in 10-20 mL of deionized water;

[0025] Step (3): SnCl 2 The solution was added dropwise to the aqueous solution of L-ascorbic acid, stirred magnetically for 10 to 30 minutes, and then 0.1 to 0.5 g of expanded microcrystalline graphite / Fe was added. 2 O 3 Composite materials, stir for 10 to 40 minutes;

[0026] Step (4): reacting in a reaction kettle at 100-200° C. for 1-3 h, extracting the black precipitate with a centrifuge, washing with deionized water until neutral, and drying in a forced air drying oven at 50-80° C. for 1-3 h;

[0027] Step (5): The obtained material is kept at 300-700°C in air for 1-2 hours to prepare expanded microcrystalline graphite / Fe with different contents. 2 O 3 / SnO 2 Composite materials.

[0028] From above, Fe 2 O 3 and SnO 2 The nanoparticles are distributed on the surface and interlayers of the expanded microcrystalline graphite to form a micro-nano composite structure.

[0029] Expanded microcrystalline graphite / Fe prepared by the aforementioned preparation method 2 O 3 / SnO 2 Composite materials.

[0030] A kind of expanded microcrystalline graphite / Fe 2 O 3 / SnO 2 Application of composite materials in lithium-ion battery anode.

[0031] Compared with the prior art, the technical advantages of the present invention are:

[0032] (1) Due to the small size of microcrystalline graphite, oxidation treatment can only achieve a small volume expansion. The present invention uses high-purity microcrystalline graphite as raw material, adopts oxidation method and inert atmosphere heat treatment method, and the volume of the prepared expanded microcrystalline graphite is significantly expanded, and the pore structure is increased, which is conducive to increasing lithium storage vacancies and improving lithium storage capacity.

[0033] (2) Adding metal oxides to the negative electrode materials of lithium-ion batteries is a method to increase the lithium storage capacity. However, the metal oxides are prone to volume expansion during the lithium removal / insertion process, which reduces the cycle stability of the composite material. The composite material prepared by the present invention has a micro-nano structure through a water bath method and an air atmosphere heat treatment method. Due to the porous structure of the expanded microcrystalline graphite, it is conducive to embedding nano-metal oxide particles therein, which is Fe 2 O 3 and SnO 2 The volume expansion provides a slow-release space, giving full play to the synergistic effect of the micro-nanostructure and improving the electrochemical stability of the composite material.

[0034] (3) The raw materials used in the present invention are low in cost and simple in synthesis process, which significantly improves the electrochemical performance of the negative electrode material of lithium-ion batteries, expands the application scope of the abundant mineral resources (microcrystalline graphite), and improves the commercial value of microcrystalline graphite. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a microstructural morphology diagram of the expanded microcrystalline graphite prepared in Example 1 of the present invention.

[0036] Figure 2 The expanded microcrystalline graphite / Fe prepared in Example 1 of the present invention 2 O 3 / SnO 2 Microstructure morphology of the composite material. DETAILED DESCRIPTION

[0037] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. 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 creative work are within the scope of protection of the present invention.

[0038] A kind of expanded microcrystalline graphite / Fe 2 O 3 / SnO 2 The method for preparing a lithium-ion battery micro-nano negative electrode material comprises the following steps:

[0039] (1) In an ice water bath, add 1-10 g of high-purity microcrystalline graphite into a beaker containing 50-100 mL of concentrated sulfuric acid, then add 50-100 mL of potassium permanganate and stir for 30-60 min;

[0040] (2) After continuing to stir in a water bath at 20 to 50°C for 10 to 40 minutes, add deionized water for dilution. When the temperature no longer rises, add an appropriate amount of hydrogen peroxide until no bubbles are generated;

[0041] (3) After standing for a period of time, high-speed centrifugation is performed and the mixture is washed with deionized water to become neutral;

[0042] (4) drying the obtained product in a forced air oven at 30 to 80° C.;

[0043] (5) Preparing expanded microcrystalline graphite by keeping the temperature at 600-900° C. for 5-20 min in an inert atmosphere;

[0044] (6) Weigh 0.1-0.5 g of expanded microcrystalline graphite and 0.01-0.5 g of FeCl 3 6H 2 O is placed in a beaker and ultrasonicated for 20 to 50 minutes;

[0045] (7) Stir in a water bath at 60-90°C for 3-6 hours, let stand for a while and then filter;

[0046] (8) placing the obtained product in a 40-80° C. forced air drying oven for 3-8 hours;

[0047] (9) Heat the mixture at 200-800℃ in air for 1-2h to prepare different Fe 2 O 3 Mass fraction of expanded microcrystalline graphite / Fe 2 O 3 Composite materials;

[0048] (10) Weigh 0.1-1 g of SnCl 2 ·2H2 O is dissolved in 10-20 mL of concentrated sulfuric acid and stirred magnetically until completely dissolved;

[0049] (11) Weigh 0.01-0.5 g of L-ascorbic acid and dissolve it in 10-20 mL of deionized water;

[0050] (12) SnCl 2 The solution was added dropwise to the aqueous solution of L-ascorbic acid, stirred magnetically for 10 to 30 minutes, and then 0.1 to 0.5 g of expanded microcrystalline graphite / Fe was added. 2 O 3 Composite materials, stir for 10 to 40 minutes;

[0051] (13) reacting in a reaction kettle at 100-200° C. for 1-3 h, extracting the black precipitate with a centrifuge, washing with deionized water until neutral, and drying in a forced air drying oven at 50-80° C. for 1-3 h;

[0052] (14) The obtained material was kept at 300-700 °C in air for 1-2 h to prepare expanded microcrystalline graphite / Fe with different contents 2 O 3 / SnO 2 Composite materials;

[0053] (15) Preparation of expanded microcrystalline graphite / Fe 2 O 3 / SnO 2 The composite material is used as a negative electrode in lithium-ion batteries.

[0054] Example 1: In an ice-water bath, 5 g of high-purity microcrystalline graphite was added to a beaker containing 80 mL of concentrated sulfuric acid, and then 50 mL of potassium permanganate was added and stirred for 50 min; after continuing to stir in a 50°C water bath for 30 min, deionized water was added for dilution, and when the temperature no longer rose, an appropriate amount of hydrogen peroxide was added until no bubbles were generated; after standing for a period of time, high-speed centrifugation was performed, and the product was washed with deionized water to become neutral; the obtained product was dried in a 60°C blast oven; and the product was kept warm at 800°C in an inert atmosphere for 15 min, and expanded microcrystalline graphite was prepared by oxidation method and inert atmosphere heat treatment method.

[0055] Weigh 0.3 g of expanded microcrystalline graphite and 0.2 g of FeCl 3 6H 2 O was placed in a beaker and ultrasonicated for 30 minutes; stirred in a 70℃ water bath for 5 hours, and filtered after standing for a period of time; the obtained product was placed in a 60℃ forced air drying oven for 5 hours; kept at 500℃ in air for 1.5 hours, and different Fe 2 O 3 Mass fraction of expanded microcrystalline graphite / Fe 2 O3 Composite materials.

[0056] Weigh 0.5 g of SnCl 2 ·2H 2 O was dissolved in 15 mL of concentrated sulfuric acid and stirred magnetically until completely dissolved; 0.3 g of L-ascorbic acid was weighed and dissolved in 15 mL of deionized water; SnCl 2 The solution was added dropwise to the aqueous solution of L-ascorbic acid, stirred magnetically for 20 min, and then 0.3 g of expanded microcrystalline graphite / Fe 2 O 3 The composite material was stirred for 30 minutes; reacted in a reactor at 150°C for 2 hours, the black precipitate was extracted by a centrifuge, washed with deionized water until neutral, and dried in a blast drying oven at 60°C for 2 hours; the obtained material was kept at 500°C in air for 2 hours, and different contents of expanded microcrystalline graphite / Fe were prepared by hydrothermal method and air atmosphere heat treatment method II. 2 O 3 / SnO 2 Composite materials; prepared expanded microcrystalline graphite / Fe 2 O 3 / SnO 2 The composite material is used as a negative electrode in lithium-ion batteries.

[0057] like Figure 1 As shown in Figure 2, the overall volume of microcrystalline graphite expands and presents a porous structure. Figure 2 As shown, Fe 2 O 3 and SnO 2 The nanoparticles are tightly combined and distributed on the surface and interlayers of micron-sized expanded microcrystalline graphite.

[0058] The electrochemical performance test method of the composite material is: using Shenzhen Xinweier BTS-5V / 2.2A battery testing equipment, constant temperature 25°C, and test voltage range of 0.01~3V.

[0059] Comparative Example 1: According to the water bath method in Example 1, 10 g of high-purity microcrystalline graphite was weighed, and the rest of the operation process was the same as Example 1.

[0060] Comparative Example 2: According to the inert atmosphere heat treatment method in Example 1, the heat treatment temperature is 600°C, and the remaining operating procedures are the same as Example 1.

[0061] Table 1 Expanded microcrystalline graphite / Fe 2 O 3 / SnO 2 Electrochemical performance of composite materials I

[0062]

[0063]

[0064] Example 2: In an ice-water bath, 1 g of high-purity microcrystalline graphite was added to a beaker containing 50 mL of concentrated sulfuric acid, and then 50 mL of potassium permanganate was added and stirred for 30 min; after continuing to stir in a 20°C water bath for 20 min, deionized water was added for dilution, and when the temperature no longer rose, an appropriate amount of hydrogen peroxide was added until no bubbles were generated; after standing for a period of time, high-speed centrifugation was performed, and the product was washed with deionized water to become neutral; the obtained product was dried in a 60°C blast oven; and the product was kept warm at 700°C in an inert atmosphere for 5 min, and expanded microcrystalline graphite was prepared by oxidation method and inert atmosphere heat treatment method.

[0065] Weigh 0.1 g of expanded microcrystalline graphite and 0.01 g of FeCl 3 6H 2 O was placed in a beaker and ultrasonicated for 30 minutes; stirred in a 60℃ water bath for 3 hours, and filtered after standing for a period of time; the obtained product was placed in a 50℃ forced air drying oven for 3 hours; kept at 300℃ in air for 1 hour, and different Fe 2 O 3 Mass fraction of expanded microcrystalline graphite / Fe 2 O 3 Composite materials.

[0066] Weigh 0.2 g of SnCl 2 ·2H 2 O was dissolved in 10 mL of concentrated sulfuric acid and stirred magnetically until completely dissolved; 0.03 g of L-ascorbic acid was weighed and dissolved in 10 mL of deionized water; SnCl 2 The solution was added dropwise to the aqueous solution of L-ascorbic acid, stirred magnetically for 10 min, and then 0.2 g of expanded microcrystalline graphite / Fe 2 O 3 The composite material was stirred for 10 min; reacted in a reactor at 100 ° C for 1 h, the black precipitate was extracted by a centrifuge, washed with deionized water until neutral, and dried in a blast drying oven at 50 ° C for 1 h; the obtained material was kept at 300 ° C in air for 2 h, and different contents of expanded microcrystalline graphite / Fe were prepared by hydrothermal method and air atmosphere heat treatment method II. 2 O 3 / SnO 2 Composite materials; prepared expanded microcrystalline graphite / Fe 2 O 3 / SnO 2 The composite material is used as a negative electrode in lithium-ion batteries.

[0067] The electrochemical performance test method of the composite material is: using Shenzhen Xinweier BTS-5V / 2.2A battery testing equipment, constant temperature 25°C, and test voltage range of 0.01~3V.

[0068] Comparative Example 3: According to the water bath method in Example 2, 0.8 g of expanded microcrystalline graphite was weighed, and FeCl 3 6H 2 Weigh 0.5 g of O, and perform the remaining operations as in Example 2.

[0069] Comparative Example 4: According to the air atmosphere heat treatment method I in Example 2, the insulation temperature in air is 800°C, and the rest of the operation process is the same as Example 2.

[0070] Table 2 Expanded microcrystalline graphite / Fe 2 O 3 / SnO 2 Electrochemical properties of composite materials II

[0071]

[0072] Example 3: In an ice-water bath, 10 g of high-purity microcrystalline graphite was added to a beaker containing 100 mL of concentrated sulfuric acid, and then 100 mL of potassium permanganate was added and stirred for 60 min; after continuing to stir in a 50°C water bath for 40 min, deionized water was added for dilution, and when the temperature no longer rose, an appropriate amount of hydrogen peroxide was added until no bubbles were generated; after standing for a period of time, high-speed centrifugation was performed, and the product was washed with deionized water to become neutral; the resulting product was dried in a blast oven at 80°C; and the product was kept warm at 900°C in an inert atmosphere for 20 min, and expanded microcrystalline graphite was prepared by oxidation method and inert atmosphere heat treatment method.

[0073] Weigh 0.5 g of expanded microcrystalline graphite and 0.5 g of FeCl 3 6H 2 O was placed in a beaker and ultrasonicated for 50 minutes; stirred in a 90℃ water bath for 6 hours, and filtered after standing for a period of time; the obtained product was placed in an 80℃ forced air drying oven for 8 hours; kept at 800℃ in air for 2 hours, and different Fe 2 O 3 Mass fraction of expanded microcrystalline graphite / Fe 2 O 3 Composite materials.

[0074] Weigh 1g of SnCl 2 ·2H 2 O was dissolved in 20 mL of concentrated sulfuric acid and stirred magnetically until completely dissolved; 0.5 g of L-ascorbic acid was weighed and dissolved in 20 mL of deionized water; SnCl 2 The solution was added dropwise to the aqueous solution of L-ascorbic acid, stirred magnetically for 30 min, and then 0.5 g of expanded microcrystalline graphite / Fe 2 O 3The composite material was stirred for 40 minutes; reacted in a reactor at 200°C for 3 hours, the black precipitate was extracted with a centrifuge, washed with deionized water until neutral, and dried in a blast drying oven at 80°C for 3 hours; the obtained material was kept at 700°C in air for 2 hours, and different contents of expanded microcrystalline graphite / Fe were prepared by hydrothermal method and air atmosphere heat treatment method II. 2 O 3 / SnO 2 Composite materials; prepared expanded microcrystalline graphite / Fe 2 O 3 / SnO 2 The composite material is used as a negative electrode in lithium-ion batteries.

[0075] The electrochemical performance test method of the composite material is: using Shenzhen Xinweier BTS-5V / 2.2A battery testing equipment, constant temperature 25°C, and test voltage range of 0.01~3V.

[0076] Comparative Example 5: According to the hydrothermal method in Example 3, SnCl 2 ·2H 2 Weigh 0.3 g of O, and perform the remaining operations as in Example 3.

[0077] Comparative Example 6: Expanded microcrystalline graphite / Fe according to the hydrothermal method in Example 3 2 O 3 0.3 g of the composite material was weighed, and the rest of the operation process was the same as in Example 3.

[0078] Comparative Example 7: According to the air atmosphere heat treatment method II in Example 3, the insulation temperature in air is 600°C, and the rest of the operation process is the same as Example 3.

[0079] Table 3 Expanded microcrystalline graphite / Fe 2 O 3 / SnO 2 Electrochemical properties of composite materials III

[0080]

[0081] Application effects of the present invention:

[0082] (1) Expanded microcrystalline graphite / Fe prepared by oxidation method and inert atmosphere heat treatment method, water bath method and air atmosphere heat treatment method I, hydrothermal method and air atmosphere heat treatment method II 2 O 3 / SnO 2 As negative electrode material for lithium-ion batteries, microcrystalline graphite exhibits overall volume expansion and significantly increased porosity.

[0083] (2) The first charge and discharge specific capacity of the ternary composite material is 1539.9 mAh / g, the first coulombic efficiency is 70.1%, and after 100 cycles, it still has a reversible specific capacity of 1003.2 mAh / g, and the capacity retention rate is 62.9%.

[0084] (3) The synergistic effect of micro-nanostructures can effectively inhibit the volume expansion of metal oxides while increasing the lithium storage capacity.

[0085] The above 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 principle of the present invention, and these improvements and changes are also regarded as the protection scope of the present invention.

Claims

1. A method for preparing expanded microcrystalline graphite / Fe2O3 / SnO2 lithium ion battery micro-nano negative electrode material, characterized in that: The following steps are involved: Firstly, high-purity microcrystalline graphite is used as raw material to prepare expanded microcrystalline graphite by oxidation method and inert atmosphere heat treatment method; Secondly, the expanded microcrystalline graphite / Fe2O3 composites were prepared by water bath method and air atmosphere heat treatment method I; Finally, expanded microcrystalline graphite / Fe2O3 / SnO2 composites were prepared by hydrothermal method and air atmosphere heat treatment method II.

2. The method for preparing the expanded microcrystalline graphite / Fe2O3 / SnO2 lithium ion battery micro-nano negative electrode material according to claim 1, characterized in that: The method of preparing expanded microcrystalline graphite by using high-purity microcrystalline graphite as raw material and adopting oxidation method and inert atmosphere heat treatment method comprises the following steps: Step (1): In an ice water bath, add 1-10 g of high-purity microcrystalline graphite into a beaker containing 50-100 mL of concentrated sulfuric acid, then add 50-100 mL of potassium permanganate, and stir for 30-60 min; Step (2): After continuing to stir in a water bath at 20 to 50° C. for 10 to 40 minutes, add deionized water for dilution. When the temperature no longer rises, add an appropriate amount of hydrogen peroxide until no bubbles are generated; Step (3): After standing for a period of time, high-speed centrifugation is performed and the mixture is washed with deionized water to a neutral state; Step (4): drying the obtained product in a forced air oven at 30-80°C; Step (5): Preparing expanded microcrystalline graphite by heating at 600-900° C. for 5-20 min in an inert atmosphere.

3. The method for preparing the expanded microcrystalline graphite / Fe2O3 / SnO2 lithium ion battery micro-nano negative electrode material according to claim 1, characterized in that: The method of preparing the expanded microcrystalline graphite / Fe2O3 composite material by using a water bath method and an air atmosphere heat treatment method I comprises the following steps: Step (1): weigh 0.1-0.5 g of expanded microcrystalline graphite and 0.01-0.5 g of FeCl3·6H2O into a beaker and ultrasonicate for 20-50 min; Step (2): Stir in a water bath at 60-90°C for 3-6 hours, let stand for a while and then filter; Step (3): placing the obtained product in a 40-80° C. forced air drying oven for 3-8 hours; Step (4): heat the mixture at 200-800°C in air for 1-2 hours to prepare expanded microcrystalline graphite / Fe2O3 composite materials with different Fe2O3 mass fractions.

4. The method for preparing the expanded microcrystalline graphite / Fe2O3 / SnO2 lithium ion battery micro-nano negative electrode material according to claim 1, characterized in that: The method of preparing the expanded microcrystalline graphite / Fe2O3 / SnO2 composite material by using the hydrothermal method and the air atmosphere heat treatment method II comprises the following steps: Step (1): weigh 0.1-1 g of SnCl2·2H2O and dissolve it in 10-20 mL of concentrated sulfuric acid, and stir magnetically until it is completely dissolved; Step (2): weigh 0.01-0.5 g of L-ascorbic acid and dissolve it in 10-20 mL of deionized water; Step (3): adding the SnCl2 solution dropwise to the aqueous solution of L-ascorbic acid, stirring magnetically for 10 to 30 minutes, then adding 0.1 to 0.5 g of expanded microcrystalline graphite / Fe2O3 composite material, and stirring for 10 to 40 minutes; Step (4): reacting in a reaction kettle at 100-200° C. for 1-3 h, extracting the black precipitate with a centrifuge, washing with deionized water until neutral, and drying in a forced air drying oven at 50-80° C. for 1-3 h; Step (5): The obtained material is kept at 300-700° C. in air for 1-2 hours to prepare expanded microcrystalline graphite / Fe2O3 / SnO2 composite materials with different contents.

5. An expanded microcrystalline graphite / Fe2O3 / SnO2 composite material prepared by the preparation method according to any one of claims 1 to 4.

6. Use of the expanded microcrystalline graphite / Fe2O3 / SnO2 composite material as claimed in claim 5 in the negative electrode of a lithium ion battery.

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