An etched and reduced graphene oxide-coated FeS2 composite material and its preparation method

Abstract

This invention discloses an etched-reduced graphene oxide-coated FeS2 composite material and its preparation method. The composite material prepared by this invention features a double carbon layer coating. FeS2 nanoparticles with an amorphous carbon coating are coated with etched-reduced graphene oxide, which has a porous structure. This composite material exhibits excellent conductivity due to the introduction of the carbon layer, while the etched reduced graphene oxide surface has a porous structure, forming 3D channels, which is beneficial for Na+. + The composite material exhibits excellent electronic / ionic conductivity due to its efficient transport properties. Simultaneously, the double carbon layer effectively accommodates the volume changes of FeS2 during charge and discharge, effectively addressing the problem of rapid capacity decay caused by FeS2 expansion and pulverization during charging and discharging. This invention provides an etched-reduced graphene oxide-coated FeS2 composite material as a sodium-ion battery anode material, demonstrating excellent cycle life and rate performance. The preparation method provided by this invention effectively overcomes the shortcomings of FeS2 anode materials, improves their performance, and expands their application range.

Description

Technical Field

[0001] This invention relates to the field of energy materials technology, and in particular to an etched and reduced graphene oxide-coated FeS2 sodium ion anode material and its preparation method. Background Technology

[0002] Compared to lithium, sodium is far more abundant and cheaper on Earth, making sodium-ion batteries a more promising candidate for large-scale energy storage devices. FeS2, as a sodium-ion battery anode material, has a theoretical capacity of 894 mAh / g. However, during charge and discharge, FeS2 undergoes significant volume expansion (280%), and the resulting friction can even pulverize the FeS2 anode material, directly leading to rapid capacity decay during cycling. Furthermore, FeS2 has poor conductivity and slow ion diffusion, resulting in poor rate performance. Therefore, modifying FeS2 to address these problems is crucial for the commercial application of FeS2 anode materials.

[0003] Carbon materials have good electrical conductivity, especially reduced graphene oxide, which has excellent conductivity. Combining it with FeS2 can effectively solve the problem of poor conductivity of FeS2. By imparting FeS2 to a carbon layer, the carbon layer coating can effectively solve the problem of FeS2 particles pulverizing during recycling, and at the same time improve the conductivity of the negative electrode material.

[0004] The properties of a material are determined by its structure. How to improve the cycle performance and rate performance of FeS2 materials by introducing carbon materials to suppress the pulverization problem during the charging and discharging process of FeS2 through the structural design of composite materials remains a difficult problem for scientists to solve. Summary of the Invention

[0005] The purpose of this invention is to provide an etched and reduced graphene oxide-coated FeS2 composite material and its preparation method. The composite material provided by this invention exhibits excellent electronic / ionic conductivity. As a negative electrode material for sodium-ion batteries, it can effectively solve the problem of rapid capacity decay of FeS2 materials during charge and discharge, and can also significantly improve the rate performance of FeS2.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] A method for preparing an etched and reduced graphene oxide-coated FeS2 composite material is provided, comprising the following steps:

[0008] S1. Dissolve ferric chloride hexahydrate and sodium oleate in a mixed solution of ethanol, water and hexane, heat at 70°C for a certain time, take the upper organic layer, wash with water to obtain a solid substance;

[0009] S2. Dissolve the solid material obtained in step S1 and oleic acid in n-octadecane to form a mixed solution. Heat the mixed solution to 320°C and age it at this temperature for a certain time. After cooling to room temperature, add ethanol and centrifuge to obtain the surface-modified Fe3O4 solid reactant Fe3O4-OA.

[0010] S3. Disperse the Fe3O4-OA prepared in step S2 into water to obtain solution A. Add graphite oxide and dodecyltrimethylammonium bromide into water and disperse by ultrasonication to obtain solution B. Add solution A into solution B and stir for 1-3 hours. Separate the precipitate obtained from the reaction, wash with water and ethanol, and freeze dry to obtain solid Fe3O4-OA / GO.

[0011] S4. The solid material Fe3O4-OA / GO after freeze-drying in step S3 is transferred into a heating furnace and heated at 500°C for a certain time under Ar atmosphere to carbonize the oleic acid in Fe3O4-OA / GO and at the same time reduce the graphene oxide to obtain the reduced graphene oxide-coated Fe3O4 composite material Fe3O4@RGO.

[0012] S5. The Fe3O4@RGO obtained in step S4 was mixed and ground with sulfur powder, and then transferred to a heating furnace. The mixture was reacted at 400℃ for a certain time under an Ar atmosphere. After cooling, it was washed with carbon disulfide, ethanol and water in sequence, and then freeze-dried to obtain the reduced graphene oxide-coated FeS2 composite material FeS2@RGO.

[0013] S6. Disperse the FeS2@RGO obtained in step S5 into an H2O2 solution, react it in a reactor at 180°C for a certain time, cool it to separate the solid product, wash it with water, and freeze-dry it to obtain the etched and reduced graphene oxide-coated FeS2 composite material FeS2@HRGO.

[0014] Preferably, the mass ratio of ferric chloride hexahydrate and sodium oleate in step S1 is 0.15~0.6, the volume ratio of ethanol to water in the mixed solution is 0.5~2, and the volume ratio of ethanol to hexane is 0.8~3.

[0015] Preferably, the mixed solution is heated at 70°C for 2-6 hours in step S1.

[0016] Preferably, in the mixed solution described in step S2, the mass ratio of the solid substance to oleic acid is 0.3 to 1.5, and the mass ratio of the solid substance to n-octadecane is 0.01 to 0.05.

[0017] Preferably, the aging time in step S2 at 320°C is 0.15~1h.

[0018] Preferably, in step S3, the concentration of Fe3O4-OA in solution A is 3~15 g / L, the concentration of graphite oxide in solution B is 0.1~1.0 g / L, the concentration of dodecyltrimethylammonium bromide is 0.004~0.015 g / L, and the volume ratio of solution A to solution B is 0.3~1.2.

[0019] Preferably, the heating time at 500°C in step S4 is 1~5 hours.

[0020] More preferably, the heating time at 500°C in step S4 is 2-4 hours.

[0021] Preferably, the mass ratio of the reactant Fe3O4@RGO to sulfur powder in step S5 is 0.3~1.5.

[0022] Preferably, in step S5, the reaction time at 400°C under an Ar atmosphere is 1.5~4.5 h.

[0023] More preferably, in step S5, the reaction time at 400°C under an Ar atmosphere is 2-4 hours.

[0024] Preferably, the concentration of the H2O2 solution in step S6 is 3~10wt%, and the concentration of FeS2@RGO in the H2O2 solution is 10~50g / L.

[0025] More preferably, the concentration of the H2O2 solution in step S6 is 4~8wt%, and the concentration of FeS2@RGO in the H2O2 solution is 12~40 g / L.

[0026] Preferably, in step S6, the reaction time in the reactor is 3-7 hours at 180°C.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] (1) This invention proposes an etched reduced graphene oxide (RGO) coated FeS2 composite material. Compared with existing materials, this composite material has a significantly improved structure. The FeS2 surface has an amorphous carbon coating, which can, to a certain extent, suppress the problem of electrode material collapse and pulverization caused by the volume expansion and contraction of FeS2 during charging and discharging. In particular, the outer layer of reduced graphene oxide (RGO) has flexible, bendable, and stretchable characteristics, which can well contain the FeS2 whose volume changes continuously during use. Secondly, the etched RGO has pores on its surface. These mesopores form 3D continuous channels in the composite material, thereby greatly accelerating the Na+ process. +The diffusion and transport of these molecules can significantly improve the ionic conductivity of the material.

[0029] (2) The etched reduced graphene oxide-coated FeS2 composite material prepared in this invention introduces amorphous carbon and RGO. Since carbon materials have good electronic conductivity, especially RGO, the composite material has excellent electronic conductivity. At the same time, the composite material has good ionic conductivity. As a sodium ion anode material, the composite material exhibits excellent recycling performance and rate performance, which effectively solves the problems of rapid capacity decay and poor rate performance of FeS2 materials during use.

[0030] (3) The present invention can ultimately control and adjust the morphology and microstructure of the composite material by controlling parameters such as the ratio of added reagents. Attached Figure Description

[0031] Figure 1 These are (a) scanning electron microscope (SEM) images and (b) transmission electron microscope (TEM) images of the etched and reduced graphene oxide-coated FeS2 composite material prepared in Example 1 of this invention.

[0032] Figure 2 The graphs show (a) the charge-discharge cycle curves of the etched and reduced graphene oxide-coated FeS2 composite material prepared in Example 1 of this invention, under a current density of 0.1 A / g and a voltage range of 0.1~3.0 V for 200 cycles, and (b) the discharge curves at different current densities.

[0033] Figure 3 The curves show the capacity and coulombic efficiency changes of the etched and reduced graphene oxide-coated FeS2 composite material prepared in Example 1 of this invention after 1200 cycles at a current density of 5 A / g.

[0034] Figure 4 This invention relates to the etched and reduced graphene oxide-coated FeS2 composite material Na. + Schematic diagram of electron transport in composite materials (1 / 4 cross-section). Detailed Implementation

[0035] The present invention will be further described below with reference to specific embodiments. The following embodiments are for illustrative purposes only and should not be construed as limiting the scope of protection of the present invention. Unless otherwise specified, the raw materials and equipment used in the following embodiments are those conventionally used in the art.

[0036] Example 1

[0037] S1. Dissolve 10.8g of ferric chloride hexahydrate and 36.5g of sodium oleate in a mixed solution of ethanol, water and hexane (the mixed solution is composed of 80mL of ethanol, 60mL of deionized water and 140mL of hexane), heat the mixture at 70℃ for 4h, take the upper organic layer, wash it with water, and obtain the solid substance.

[0038] S2. Dissolve 3.6g of solid material and 5.7g of oleic acid obtained in step S1 in 200g of n-octadecane to form a mixed solution. Heat the mixed solution to 320℃ and age it at this temperature for 30min. After cooling to room temperature, add 500mL of ethanol and centrifuge to obtain the surface-modified Fe3O4 solid reactant Fe3O4-OA.

[0039] S3. Disperse 2g Fe3O4-OA in 300mL of deionized water to obtain solution A. Add 0.2g of graphite oxide to 500mL of deionized water and ultrasonically disperse for 1h. Then add 0.004g of dodecyltrimethylammonium bromide to obtain solution B. Add solution A to solution B and stir for 1h. Separate the precipitate obtained from the reaction, wash with water and ethanol, and freeze dry to obtain solid Fe3O4-OA / GO.

[0040] S4. The solid material Fe3O4-OA / GO after freeze-drying in step S3 is transferred into a tube furnace and heated at 500°C for 3 hours under Ar atmosphere to carbonize the oleic acid in Fe3O4-OA / GO and reduce the graphene oxide to obtain the reduced graphene oxide-coated Fe3O4 composite material Fe3O4@RGO.

[0041] S5. Mix and grind 2g Fe3O4@RGO and 3g sulfur powder, transfer to a heating furnace, react at 400℃ for 3h under Ar atmosphere, cool and wash with carbon disulfide, ethanol and water in sequence, and then freeze dry to obtain reduced graphene oxide coated FeS2 composite material FeS2@RGO.

[0042] S6. 4.5 g FeS2@RGO was dispersed in 200 mL H2O2 (5 wt%) solution and reacted in a reactor at 180 °C for 5 h. After cooling, the solid product was separated, washed with water, and freeze-dried to obtain the etched and reduced graphene oxide-coated FeS2 composite material FeS2@HRGO.

[0043] For the analysis of the test results, please refer to [link / reference]. Figures 1-4 :

[0044] Figure 1 These are (a) scanning electron microscope (SEM) images and (b) transmission electron microscope (TEM) images of the etched and reduced graphene oxide-coated FeS2 composite material prepared in Example 1 of this invention.

[0045] Figure 1 The scanning electron microscope image shows that FeS2 nanoparticles are coated with wrinkled reduced graphene oxide (RGO). The surface of the RGO is relatively rough, which is caused by H2O2 etching to form pores on the RGO surface. Figure 1 The transmission electron microscope image of b shows more clearly a layer of carbon deposited on the FeS2 surface (inside the coil). This carbon layer is amorphous, and its outermost layer is covered by RGO. Some small shaded areas on the RGO surface are pores formed after etching. BET surface area tests further confirm that these pores are approximately 10-30 nm in size, forming 3D continuous channels in the composite material, thus greatly accelerating the Na+ etching process. + The diffusion and transmission of [something].

[0046] Figure 2 The graphs show (a) the charge-discharge cycle curves of the etched and reduced graphene oxide-coated FeS2 composite material prepared in Example 1 of this invention at a current density of 0.1 A / g and a voltage range of 0.1 to 3.0 V for 200 cycles, and (b) the discharge curves at different current densities.

[0047] Figure 2 As shown in Figure a, the FeS2 composite material with etched and reduced graphene oxide coating prepared in this experiment has an initial discharge specific capacity of 592 mAh / g, a charge specific capacity of 474 mAh / g, and a discharge specific capacity of 409 mAh / g after 200 cycles. Figure 2 The composite material in b maintains a stable discharge specific capacity of 468 mAh / g at a current density of 0.1 A / g, and still reaches a high specific capacity of 233 mAh / g at a high current density of 10.0 A / g. After 70 cycles, when the current density returns to 0.1 A / g, its discharge specific capacity is 401 mAh / g.

[0048] Figure 3 The curves showing the specific capacity and coulombic efficiency changes of the etched and reduced graphene oxide-coated FeS2 composite material prepared in Example 1 of this invention after 1200 cycles at a current density of 5 A / g.

[0049] Figure 3 As shown in the figure, the initial discharge specific capacity of the composite material is 303 mAh / g. After 1200 cycles, the discharge specific capacity remains at 252 mAh / g. Compared to the initial discharge specific capacity, the capacity retention rate after 1200 cycles is 83.2%, and compared to the second discharge specific capacity (279 mAh / g), the capacity retention rate reaches 90.3%. The figure also shows that the capacity does not fluctuate significantly during the charge and discharge process and remains stable, fully demonstrating the excellent rate capability and cycle life of the composite material.

[0050] Figure 4 This invention relates to the etched and reduced graphene oxide-coated FeS2 composite material Na. + Schematic diagram of electron transport in composite materials (1 / 4 cross-section).

[0051] Figure 4 As can be seen, FeS2 nanoparticles, amorphous carbon coating, and etched-reduced graphene oxide together constitute 3DNa. + The conductive network channel, due to the excellent conductivity of amorphous carbon and reduced graphene oxide, also facilitates electron transport. At the same time, this structure can effectively encapsulate FeS2 nanoparticles, and its voids can perfectly accommodate the volume changes of FeS2 particles. Therefore, the composite material has excellent rate performance and recyclability.

[0052] Example 2

[0053] S1. Dissolve 10.8 g of ferric chloride hexahydrate and 36.5 g of sodium oleate in a mixed solution of ethanol, water and hexane (the mixed solution is composed of 70 mL of ethanol, 70 mL of deionized water and 140 mL of hexane), heat the mixture at 70 °C for 5 h, take the upper organic layer, wash it with water, and obtain the solid substance.

[0054] S2. Dissolve 3.6g of solid material and 5.7g of oleic acid obtained in step S1 in 200g of n-octadecane to form a mixed solution. Heat the mixed solution to 320℃ and age it at this temperature for 50min. After cooling to room temperature, add 500mL of ethanol and centrifuge to obtain the surface-modified Fe3O4 solid reactant Fe3O4-OA.

[0055] S3. Disperse 2.4g Fe3O4-OA in 300mL of deionized water to obtain solution A. Add 0.2g of graphite oxide to 500mL of deionized water and ultrasonically disperse for 1h. Then add 0.005g of dodecyltrimethylammonium bromide to obtain solution B. Add solution A to solution B and stir for 1h. Separate the precipitate obtained from the reaction, wash with water and ethanol, and freeze dry to obtain solid Fe3O4-OA / GO.

[0056] S4. The solid material Fe3O4-OA / GO after freeze-drying in step S3 is transferred into a tube furnace and heated at 500°C for 4 hours under Ar atmosphere to carbonize the oleic acid in Fe3O4-OA / GO and reduce the graphene oxide to obtain the reduced graphene oxide-coated Fe3O4 composite material Fe3O4@RGO.

[0057] S5. Mix and grind 2.4g Fe3O4@RGO and 3g sulfur powder, transfer to a heating furnace, react at 400℃ for 4h under Ar atmosphere, cool and wash with carbon disulfide, ethanol and water in sequence, and then freeze dry to obtain reduced graphene oxide coated FeS2 composite material FeS2@RGO.

[0058] S6. 4.5 g FeS2@RGO was dispersed in 200 mL H2O2 (8 wt%) solution and reacted in a reactor at 180 °C for 6 h. After cooling, the solid product was separated, washed with water, and freeze-dried to obtain the etched and reduced graphene oxide-coated FeS2 composite material FeS2@HRGO.

[0059] The etched and reduced graphene oxide-coated FeS2 composite material prepared in Example 2 had an initial discharge specific capacity of 301 mAh / g at a current density of 5 A / g. After 1200 cycles, the specific capacity of the material remained at 251 mAh / g. Compared with the initial discharge specific capacity, the specific capacity retention rate after 1200 cycles was 83.4%, and compared with the second discharge specific capacity (280 mAh / g), the capacity retention rate reached 89.6%.

[0060] Examples 3-6

[0061] The preparation methods for Examples 3-6 are basically the same as those for Example 1, with the following differences:

[0062] The difference between Example 3 and Example 1 is that in step S1, 8g of ferric chloride hexahydrate and 24g of sodium oleate are dissolved in a mixed solution of ethanol, water and hexane (the mixed solution is composed of 70mL of ethanol, 70mL of deionized water and 140mL of hexane), and the mixture is heated at 70°C for 4 hours. The upper organic layer is then taken and washed with water to obtain a solid substance.

[0063] The difference between Example 4 and Example 1 is that in step S2, 3g of solid material and 6g of oleic acid obtained in step S1 are dissolved in 150g of n-octadecane to form a mixed solution. The mixed solution is heated to 320℃ and aged at this temperature for 30min. After cooling to room temperature, 500mL of ethanol is added, and the surface-modified Fe3O4 solid reactant Fe3O4-OA is obtained by centrifugation.

[0064] Example 5 differs from Example 1 in that: in step S5, 2g of Fe3O4@RGO and 3g of sulfur powder are mixed and ground, transferred to a heating furnace, and reacted at 400℃ for 2 hours under an Ar atmosphere. After cooling, the mixture is washed successively with carbon disulfide, ethanol, and water, and then freeze-dried to obtain the reduced graphene oxide-coated FeS2 composite material FeS2@RGO.

[0065] The difference between Example 6 and Example 1 is that in step S6, 3g of FeS2@RGO is dispersed in 200mL of H2O2 (5wt%) solution, reacted in a reactor at 180℃ for 5h, and after cooling, the solid product is separated, washed with water, and freeze-dried to obtain the etched and reduced graphene oxide-coated FeS2 composite material FeS2@HRGO.

[0066] The etched-reduced graphene oxide-coated FeS2 composite materials prepared in Examples 3-6 exhibited initial discharge specific capacities of 299, 300, 305, and 302 mAh / g at a current density of 5 A / g, respectively. After 1200 cycles, the specific capacities remained at 249, 250, 245, and 248 mAh / g, respectively. Compared to the initial discharge specific capacity, the capacity retention rates after 1200 cycles were 83.3%, 83.3%, 80.3%, and 82.1%, respectively. Compared to their second discharge specific capacities, the capacity retention rates were 89.9%, 90.0%, 88.0%, and 89.2%, respectively. This demonstrates that the composite materials possess excellent rate performance and good cyclic performance.

Claims

1. A method for preparing an etched reduced graphene oxide-coated FeS2 composite material, characterized by The FeS2 nanoparticles with amorphous carbon coating on the surface are etched and reduced by graphene oxide, and the etched and reduced graphene oxide has a pore structure on the surface, which is prepared by the following steps: S1. Dissolve ferric chloride hexahydrate and sodium oleate in a mixed solution of ethanol, water and hexane, heat the solution at 70℃ for a certain time, take the upper organic layer, wash with water, and obtain a solid material; the mass ratio of ferric chloride hexahydrate to sodium oleate is 0.15-0.6, the volume ratio of ethanol to water in the mixed solution is 0.5-2, and the volume ratio of ethanol to hexane is 0.8-3; S2. Dissolve the solid material obtained in step S1 and oleic acid in n-octadecane to form a mixed solution, heat the mixed solution to 320℃, and age at this temperature for a certain time, then cool to room temperature and add ethanol to centrifuge to obtain the oleic acid surface modified Fe3O4 solid reactant Fe3O4-OA; in the mixed solution, the mass ratio of the solid material to oleic acid is 0.3-1.5, and the mass ratio of the solid material to n-octadecane is 0.01-0.05; S3. Disperse the Fe3O4-OA prepared in step S2 into water to obtain solution A, add graphene oxide and dodecyltrimethylammonium bromide to water and ultrasonically disperse to obtain solution B, add solution A to solution B, stir for 1-3h, separate the precipitate obtained in the reaction, wash with water and ethanol, and freeze-dry to obtain a solid material Fe3O4-OA / GO; the concentration of Fe3O4-OA in the A solution is 3-15g / L, the concentration of graphene oxide in the B solution is 0.1-1.0g / L, the concentration of dodecyltrimethylammonium bromide is 0.004-0.015g / L, and the volume ratio of A solution to B solution is 0.3-1.2; S4. Move the solid material Fe3O4-OA / GO after freeze-drying in step S3 into a heating furnace, heat at 500℃ under Ar atmosphere for a certain time, carbonize the oleic acid in Fe3O4-OA / GO, and reduce the graphene oxide to obtain a reduced graphene oxide coated Fe3O4 composite material Fe3O4@RGO; S5. Mix and grind the Fe3O4@RGO obtained in step S4 and sulfur powder, move into a heating furnace, react at 400℃ under Ar atmosphere for a certain time, wash with carbon disulfide, ethanol and water in sequence, and then freeze-dry to obtain a reduced graphene oxide coated FeS2 composite material FeS2@RGO; the mass ratio of the reactants Fe3O4@RGO and sulfur powder is 0.3-1.5; S6. Disperse the FeS2@RGO obtained in step S5 into an H2O2 solution, react in a reaction kettle at 180℃ for a certain time, separate the solid product after cooling, wash with water, and freeze-dry to obtain an etched and reduced graphene oxide coated FeS2 composite material FeS2@HRGO; the concentration of the H2O2 solution is 3-10wt%, and the concentration of FeS2@RGO in the H2O2 solution is 10-50g / L.

2. The method of claim 1, wherein the graphene-oxide-coated FeS2 composite is prepared by etching. The time for heating the mixed solution in step S1 at 70℃ is 2-6h.

3. The method of claim 1, wherein the method of preparing the etched reduced graphene oxide-coated FeS2 composite is characterized by, The time for aging in step S2 at 320℃ is 0.25-1h.

4. The method of claim 1, wherein the method of preparing the etched reduced graphene oxide-coated FeS2 composite is characterized by, The time for heating in step S4 at 500℃ is 1-5h.

5. The method of claim 1, wherein the method of preparing the etched reduced graphene oxide-coated FeS2 composite is characterized by, The time for reacting in step S5 at 400℃ under Ar atmosphere is 1.5-4.5h.

6. The method of claim 1, wherein the method of preparing the etched reduced graphene oxide-coated FeS2 composite is characterized by, The time for reacting in step S6 in a reaction kettle at 180℃ is 3-7h.

7. The etching reduced graphene oxide coated FeS2 composite material prepared by the preparation method according to any one of claims 1-6.

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