Cubic phase CoSe2 (at) graphene composite material and preparation method and application thereof

Abstract

The invention belongs to the technical field of synthesis of micro-nano composite materials, and particularly relates to a cubic phase CoSe2 (at) graphene composite material as well as a preparation method and application thereof. The preparation method comprises the following steps: S1, adding cobaltous sulfate heptahydrate and citric acid into an N, N-dimethylformamide solution to obtain a solution A, then adding graphene into the solution A, and carrying out ultrasonic treatment to form a dispersion liquid B; s2, adding Se powder into a hydrazine aqueous solution, and stirring to form a turbid liquid C; s3, pouring the dispersion liquid B into the turbid liquid C, stirring, and transferring into a reaction kettle for reaction; and S4, finally, sequentially carrying out centrifugal cleaning and drying on a product after the reaction to obtain the cubic phase CoSe2 / graphene composite material. According to the CoSe2 / graphene composite material prepared by the method, cubic-phase CoSe2 which is more beneficial to sodium ion intragranular diffusion can be obtained through liquid-phase synthesis, and due to the introduced graphene, on one hand, the overall conductivity of the composite material can be promoted, and on the other hand, the volume strain of the CoSe2 in the charging and discharging process can be inhibited.

Description

Technical Field

[0001] This invention belongs to the field of micro-nano composite material synthesis technology, and particularly relates to a cubic phase CoSe2@graphene composite material, its preparation method and application. Background Technology

[0002] Sodium-ion batteries, due to the high abundance of sodium in the Earth's crust, low cost, and high safety, have been considered an ideal alternative to lithium-ion batteries. However, their commercialization is limited by the development of high-performance positive and negative electrode materials. Negative electrode materials storing sodium face harsher electrochemical environments, such as significant electrode volume strain caused by crystal structure transformations and side reactions at low voltages. Currently, mainstream negative electrode materials are mainly carbon-based materials such as hard carbon and soft carbon, which generally suffer from low capacity and complex manufacturing processes. While some transition metal compounds, such as oxides and sulfides, have high theoretical specific capacities, they exhibit low reaction kinetics and energy densities, and large volume changes during charge and discharge, resulting in cycle performance far below commercial requirements.

[0003] Compared to transition metal oxides / sulfides, transition metal selenides have become a research hotspot due to their higher theoretical capacity and lower reaction energy barrier, but they also face some challenges. For example, the large volume change during sodium storage in metal selenides can cause electrode material pulverization, and their poor conductivity can also lead to electrode polarization. Furthermore, the intracrystalline diffusion of sodium ions varies in selenides with different crystal structures, making it impossible for the active material to undergo a reversible sodium storage reaction.

[0004] Therefore, there is an urgent need for a cubic phase CoSe2@graphene composite material, its preparation method, and its application to solve the above problems. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, this invention provides a cubic CoSe2@graphene composite material, its preparation method, and its applications. This invention obtains a cubic CoSe2 phase more conducive to the intracrystalline diffusion of sodium ions through a one-step liquid-phase synthesis, while also introducing graphene. This not only improves the overall conductivity of the composite material but also effectively mitigates the volume change of CoSe2 during electrochemical reactions.

[0006] To achieve one of the above objectives, the present invention adopts the following technical solution: A method for preparing a cubic phase CoSe2@graphene composite material includes the following steps: S1. Cobalt sulfate heptahydrate and citric acid are added to N,N-dimethylformamide (DMF) solvent to obtain solution A. Then, graphene is added to solution A and fully sonicated to form dispersion B. S2. Add Se powder to the hydrazine aqueous solution and stir thoroughly to form a suspension C; S3. Pour dispersion B into suspension C, stir thoroughly, and then transfer to a reaction vessel for high-temperature reaction. S4. Finally, the products after the reaction are centrifuged, washed and dried to obtain the CoSe2@graphene composite material.

[0007] Preferably, the molar ratio of cobalt sulfate heptahydrate to citric acid is 1:10.

[0008] Preferably, the molar concentration of cobalt sulfate heptahydrate in solution A is 0.03 mmol / mL. -1 The mass concentration of citric acid is 0.06 g / ml. -1 .

[0009] Preferably, the mass concentration of graphene in dispersion B is 2–10 mg / ml. -1 .

[0010] Preferably, the molar concentration of Se in suspension C is 0.06 mmol / ml. -1 The mass concentration of the hydrazine aqueous solution is 85%.

[0011] Preferably, in step S3, the volume ratio of dispersion B to suspension C is (2-3):1.

[0012] Preferably, in step S3, the reaction temperature is 180–200°C and the reaction time is 24–48 h.

[0013] Preferably, in step S4, the product is washed three times with DMF solution and water alternately, and then dried in an oven at 75-85°C.

[0014] To achieve the second objective mentioned above, the present invention provides a cubic CoSe2@graphene composite material, which is a black powder and the CoSe2 in the composite material has a layered cubic phase structure.

[0015] To achieve the third objective mentioned above, this invention provides the application of a cubic CoSe2@graphene composite material, which serves as the anode material for high-performance sodium-ion batteries, comprising the following steps: Cubic CoSe2@graphene composite material was uniformly mixed and dispersed with conductive carbon black and PVDF at a mass ratio of 8:1:1 in 400 μL of 1-methyl-2-pyrrolidone (NMP) to prepare sodium-ion battery anode material slurry.

[0016] The advantages of this invention are: (1) The CoSe2@graphene composite material prepared by the present invention can obtain a layered cubic phase structure of CoSe2 that is more conducive to the diffusion of sodium ions in the crystal through liquid phase synthesis, thereby improving the rate performance and long cycle performance of the material.

[0017] (2) In this invention, graphene can promote the overall conductivity of the composite material on the one hand, and suppress the volume change of CoSe2 on the other hand, while thinner graphene will not hinder the transport of sodium ions. At the same time, during the synthesis of CoSe2@graphene composite material, graphene also provides nucleation sites for the growth of cubic phase CoSe2, which is beneficial to obtaining smaller CoSe2 particles.

[0018] (3) The cubic CoSe2@graphene composite material prepared by this invention has a very simple synthesis process. It is synthesized in one step by liquid phase. The crystal structure of CoSe2 is a layered cubic phase structure with a stable three-dimensional structure and excellent ion / electron transport capability (its isotropic structure has uniform stress distribution during the volume expansion / contraction process of charging and discharging, and is not easy to pulverize, thus maintaining the integrity of the structure). This enhances the intracrystalline diffusion of sodium ions in cobalt selenide and promotes the rapid and reversible reaction of active materials. At the same time, after the cubic CoSe2 is prepared into a negative electrode material, the three-dimensional ion diffusion channels of its cubic phase allow sodium ions to migrate rapidly in the bulk phase of the material, thus maintaining a high capacity even at high current densities. The cubic CoSe2 itself is a metallic conductor with excellent electronic conductivity, which is beneficial for charge transport.

[0019] (4) Compared with graphene oxide, the graphene material used in this invention can reduce the synthesis cost of electrode materials, simplify the synthesis process, and is more conducive to commercial production. At the same time, the preparation method is simple and easy to operate, safe and pollution-free, and low in cost. Attached Figure Description

[0020] Figure 1 The images shown are FESEM images of the cubic CoSe2@graphene composite material prepared in Example 1 of this invention, where Figure (a) is a low-magnification FESEM image and Figure (b) is a high-magnification FESEM image.

[0021] Figure 2 The XRD diffraction pattern of the cubic CoSe2@graphene composite material prepared in Example 1 of this invention.

[0022] Figure 3 The image shows the electrochemical rate performance of the sodium-ion battery prepared using the cubic CoSe2@graphene composite material in Example 2 of this invention.

[0023] Figure 4The electrochemical cycling performance diagram of the sodium-ion battery prepared by cubic CoSe2@graphene composite material in Example 2 of this invention is shown.

[0024] Figure 5 Electrochemical rate performance of sodium-ion batteries with pure cubic CoSe2 phase.

[0025] Figure 6 Electrochemical cycling performance of a sodium-ion battery with pure cubic CoSe2 phase. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0027] Example 1

[0028] The preparation method of cubic phase CoSe2@graphene composite material includes the following steps: S1. Add 1 mmol of cobalt sulfate heptahydrate and 2 g of citric acid to 22 ml of DMF solution, and dissolve by sonication to obtain solution A. Then add 60 mg of graphene to solution A and sonicate thoroughly to form dispersion B. S2. Add 0.158 g of Se powder to 8 ml of 85% hydrazine aqueous solution to form suspension C; S3. Pour dispersion B into suspension C and stir thoroughly for 1 h, then transfer to a reaction vessel and react at 180 °C for 24 h. S4. After the product was naturally cooled, it was washed three times with DMF solution and water alternately and then dried in an oven at 80 °C for 24 h to obtain cubic phase CoSe2@graphene composite material.

[0029] Figure 1 The image shows the FESEM image of the cubic CoSe2@graphene composite material. Figure 1 It can be seen that the cubic CoSe2 exhibits star-shaped clusters and good dispersibility, while the cubic CoSe2 is coated with graphene sheets.

[0030] Figure 2 The image shows the XRD pattern of the cubic CoSe2@graphene composite material. XRD analysis reveals that the diffraction peaks of the synthesized CoSe2 correspond one-to-one with the crystal structure card (PDF#53-0449) and there are no other impurities, indicating that this CoSe2 has a layered cubic crystal structure.

[0031] Example 2

[0032] The negative electrode material for sodium-ion batteries includes the following steps: S1. The cubic phase CoSe2@graphene composite material prepared in Example 1 was uniformly mixed and dispersed with conductive carbon black and PVDF at a mass ratio of 8:1:1 in 400 μL of 1-methyl-2-pyrrolidone (NMP) to prepare a sodium-ion battery anode material slurry.

[0033] The performance testing of the negative electrode material for sodium-ion batteries includes the following steps: Sodium-ion battery negative electrode material slurry was uniformly coated onto a copper foil current collector using a 250 μm scraper and dried in a 60℃ vacuum drying oven for 24 h. The dried copper foil current collector was sliced ​​to form a 1.1 cm diameter circular electrode. A sodium foil sheet was used as the counter electrode, glass fiber as the separator, and a binary electrolyte. A 2032 button half-cell was assembled in an argon-filled glove box. The voltage ranges were tested at 0.5–3.0 V and 0.1–3.0 V, respectively. The results are as follows: Figure 3-4 As shown.

[0034] Figure 3 This is a rate performance graph of cubic CoSe2@graphene composite material as a negative electrode in the test voltage ranges of 0.5–3.0 V and 0.1–3.0 V. (Source: [Insert graphite here]) Figure 3 It can be seen that during the first 10 charge-discharge cycles, the specific capacity of the cubic CoSe2@graphene composite electrode decreased significantly in different voltage ranges. The main reason for this is likely that electrolyte decomposition and SEI film formation occurred in the electrode material, accompanied by some side reactions. In the voltage test range of 0.1–3.0 V, at current densities of 0.05, 0.1, 0.2, 0.5, 1.0, 1.5, 2.0, and 3.0 A / g, the specific capacities of the composite electrode reached 397.3, 310.4, 305.7, 296.3, 280.6, 263.5, 234.2, and 208.3 mAh / g, respectively, which are slightly higher than the specific capacities of 315.3, 292.1, 275.4, 263.5, 254.6, 230.2, and 169.5 mAh / g in the 0.05–3.0 V voltage range. When the current density returned to 0.1 A / g, the reversible specific capacity at test voltages of 0.1–3.0 V and 0.5–3.0 V recovered to 409.5 and 301.5 mAh / g, respectively, indicating that it has good reversibility when applied as an anode material for sodium-ion batteries.

[0035] Figure 4 This is a graph showing the cycling stability of a cubic CoSe2@graphene composite electrode at a current density of 2 A / g. Figure 4It can be seen that the cubic phase CoSe2@graphene composite material, as a negative electrode, exhibits good cycle stability under voltages of 0.5–3.0 V. After 2000 charge-discharge cycles, the specific capacity can still be maintained at 226.5 mAh / g, with a capacity retention rate of approximately 98.3%.

[0036] Figure 5-6 The results show the performance of pure-phase CoSe2 as a negative electrode material for sodium-ion batteries. The comparison reveals that, compared to pure-phase CoSe2, cubic-phase CoSe2@graphene composite material exhibits superior electrochemical sodium storage performance as a negative electrode material for sodium-ion batteries.

[0037] The above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a cubic phase CoSe2@graphene composite material, characterized in that, Includes the following steps: S1. Cobalt sulfate heptahydrate and citric acid are added to N,N-dimethylformamide solution to obtain solution A. Then, graphene is added to solution A and ultrasonically dispersed to form dispersion B. S2. Add Se powder to a hydrazine aqueous solution and stir to form a suspension C; S3. Pour dispersion B into suspension C, stir, and then transfer to a reaction vessel for reaction; S4. Finally, the products after the reaction are centrifuged, washed and dried to obtain the CoSe2@graphene composite material.

2. The method for preparing a cubic phase CoSe2@graphene composite material according to claim 1, characterized in that: The molar ratio of cobalt sulfate heptahydrate to citric acid is 1:

10.

3. The method for preparing a cubic phase CoSe2@graphene composite material according to claim 1, characterized in that: The molar concentration of cobalt sulfate heptahydrate in solution A is 0.03 mmol·ml. -1 The mass concentration of citric acid is 0.06 g / ml. -1 .

4. The method for preparing a cubic phase CoSe2@graphene composite material according to claim 1, characterized in that: The mass concentration of graphene in dispersion B is 2–10 mg / ml. -1 .

5. The method for preparing a cubic phase CoSe2@graphene composite material according to claim 1, characterized in that: The molar concentration of Se in suspension C is 0.06 mmol / mL. -1 .

6. The method for preparing a cubic phase CoSe2@graphene composite material according to claim 1, characterized in that: In step S3, the volume ratio of dispersion B to suspension C is (2-3):

1.

7. The method for preparing a cubic phase CoSe2@graphene composite material according to claim 1, characterized in that: In step S3, the reaction temperature is 180–200℃ and the reaction time is 24–48 h.

8. The method for preparing a cubic phase CoSe2@graphene composite material according to claim 1, characterized in that: In step S4, the product is washed three times with N,N-dimethylformamide solution and water alternately, and then dried in an oven at 75-85°C.

9. A composite material prepared by the method for preparing cubic phase CoSe2@graphene composite material according to any one of claims 1-8, characterized in that: The composite material is a black powder, and the CoSe2 in the composite material has a layered cubic phase crystal structure.

10. An application of the cubic phase CoSe2@graphene composite material as described in claim 9, characterized in that: This composite material serves as the negative electrode material for sodium-ion batteries.

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