Preparation Method of Anemone-like CoSe2 Composite Material and Application in Anode of Sodium-ion Battery

Abstract

The present invention provides a preparation method of an anemone-shaped CoSe2 composite material and its application as a negative electrode of a sodium-ion battery. The method includes: by regulating hydrothermal synthesis conditions, preparing Co(CO3) 0.5 (OH)·0.11H2O anemone-shaped precursor, adding the precursor to a Tris buffer solution for ultrasonic dispersion, adding dopamine to the precursor solution and stirring at room temperature to obtain a black precipitate-like isolate; washing with deionized water and ethanol, and drying to obtain Co(CO3) 0.5 (OH)·0.11H2O@PDA; mixing the dried product and Se powder evenly, and performing selenization treatment to obtain a CoSe2@NC composite material with an anemone-like morphology. The CoSe2@NC composite material is used as a negative electrode material for sodium-ion batteries, and can still maintain a specific capacity of 214.6 mAh g ‑1 after cycling 100 times at a current density of 2 Ag ‑1 . The first Coulombic efficiency is as high as 93.93%. The excellent sodium storage performance of the composite material can be attributed to the unique anemone-like structure of the composite material. This structure can not only provide more active sites for sodium storage, but also effectively alleviate the volume expansion of the negative electrode material during charge and discharge.

Description

Technical Field

[0001] The present invention relates to the technical field of electrode materials, and particularly constructs a preparation method of an anemone-shaped CoSe2 composite material and its application as a negative electrode of a sodium-ion battery. Background Art

[0002] In recent years, due to the limited lithium resources and the high-performance requirements for new electrode materials, sodium-ion batteries with great development prospects have received extensive attention. However, the rapid capacity decay and unstable cycle rate performance during charge and discharge processes have hindered the large-scale development of sodium-ion batteries. Therefore, exploring suitable electrode materials has become an urgent problem to be solved. Among negative electrode materials, cobalt diselenide has a large atomic layer spacing, which can effectively improve the sodium storage capacity and is a promising sodium-ion negative electrode material. However, how to alleviate the volume expansion and structural pulverization of this material during electrochemical conversion has become the difficulty and focus of research. Yin prepared CoSe2 particles attached to carbon nanofibers, and tests showed that it had a relatively high specific capacity and significantly improved cycle stability. Different research groups have also demonstrated that N-doped CoSe2 composite materials can alleviate the capacity decay problem during long cycling. For example, Yang et al. demonstrated that the N-doped carbon framework composite material exhibited very low capacity decay in each cycle test, which was closely related to the strong binding energy between the N-doped carbon matrix and the CoSe2 particles providing sodium storage sites. Jo et al. synthesized graphene nanofibers (N-CNT / rGO / CoSe2 NF) in the shape of dandelion-like CoSe2 nanocrystals composite with N-CNTs through a multi-step heat treatment temperature design combined with an electrospinning preparation method. Its unique dandelion flower-like structure provides a more convenient and fast channel for the transport of sodium ions. Electrochemical tests at a high current density of 10 A / g showed that the reversible capacity of N-CNT / rGO / CoSe2 NF reached 264 mAh / g after 10,000 cycles, and a high discharge capacity retention rate of 89% could still be achieved after the 100th cycle. Zhao et al. designed a CoSe2 nanostructure (CoSe2@NC@TiO2) based on a co-embedded TiO2 coating layer of a nitrogen-doped carbon matrix using ZIF-67 as a precursor. The nanoparticles of CoSe2 in the nitrogen-doped carbon matrix accelerated the transport rate of sodium ions in the active material, and its electrochemical performance was tested at a current density of 0.1 A / g. Its initial charge and discharge capacity was 520 mAh / g, and after 200 cycles, the capacity retention rate was as high as 78%.

[0003] Therefore, when exploring the energy storage application of cobalt diselenide as the anode material for sodium-ion batteries, the first and most crucial challenge to be considered and overcome is how to effectively alleviate the volume expansion of the anode material during charge and discharge processes. In summary, some researchers have prepared CoSe2 composite materials with different structures through relatively complex synthesis processes. The present invention has prepared a composite material with a unique structure through process optimization, providing more active sites for sodium storage applications and being able to highly alleviate the volume expansion of the anode material during charge and discharge processes. Summary of the Invention

[0004] The present invention constructs a preparation method of a sea anemone-like CoSe2 composite material and its application as the anode for sodium-ion batteries, which can effectively solve the problems that occur in the above application process.

[0005] Aiming at the deficiencies such as capacity attenuation and low initial Coulomb efficiency in the prior art, the present invention provides a preparation method of a sea anemone-like CoSe2 composite material and its application as the anode for sodium-ion batteries. Through simple hydrothermal synthesis and controllable gas-phase selenization steps, a composite material with CoSe2 nanoparticles wrapped by a nitrogen-doped carbon layer is prepared, and it has a unique sea anemone-like morphology. When applied as the anode material for sodium-ion batteries, the initial Coulomb efficiency is as high as over 90%, the cycling performance at a relatively high current density is significantly improved, the charge transfer resistance is small, and overall it exhibits excellent electrochemical performance.

[0006] The present invention is realized as follows:

[0007] The present invention further provides a preparation method of a sea anemone-like CoSe2 composite material, comprising the following steps:

[0008] S1, by regulating the hydrothermal synthesis conditions, Co(CO3) 0.5 (OH)·0.11H2O precursor is prepared, and this precursor has a unique sea anemone-like morphology. Add the Co(CO3) 0.5 (OH)·0.11H2O precursor to a pH = 8.0 - 9.0 buffer solution containing Tris for ultrasonic dispersion, and then according to the mass ratio of Co(CO3) 0.5 (OH)·0.11H2O precursor to dopamine being 0.8 - 1.9:1, add dopamine to the solution and stir at room temperature for 8 - 20 h to obtain a black precipitate-like separation;

[0009] S2, wash the obtained black precipitate-like separation with deionized water and ethanol multiple times and then put it into an oven, and keep it at a constant temperature of 60°C - 80°C for 5 - 10 h to obtain Co(CO3) 0.5 (OH)·0.11H2O@PDA;

[0010] S3, Co(CO3)0.5 (OH)·0.11H2O@PDA and Se powder are mixed evenly according to a mass ratio of 1:2 - 5, placed in a tube furnace filled with Ar atmosphere, kept at a constant temperature of 350 - 450 °C for 2 - 6 h, with the heating rate controlled at 1 - 5 °C / min, and subjected to selenization treatment to finally obtain CoSe2@NC.

[0011] The present invention provides an application of a sea anemone-like CoSe2 composite material as the negative electrode of a sodium-ion battery. The active material of the negative electrode is a nitrogen-doped carbon-coated sea anemone-like CoSe2@NC composite material, and the particle size of the nitrogen-doped carbon-coated modified sea anemone-like CoSe2@NC composite material is 1 - 3 microns.

[0012] The beneficial effects of the present invention are as follows: The CoSe2 composite material of the present invention is prepared by a convenient and low-cost hydrothermal synthesis method and a highly controllable selenization process to obtain a CoSe2 material (CoSe2@NC) with a unique sea anemone-like structure. When this material is applied to the negative electrode of a sodium-ion battery, it exhibits excellent electrochemical performance, with the initial Coulombic efficiency as high as 93.93%. After 100 cycles at a current density of 2Ag -1 it can still maintain a specific capacity of 214.6 mAh g -1 The excellent performance of this composite material is inseparable from its unique sea anemone-like structure. This special structure not only provides more active sites for sodium storage applications, but also the nitrogen-doped carbon coating layer on the material surface effectively alleviates the volume expansion of the negative electrode material during charge and discharge, thus enabling the material to have more potential electrochemical performance for applications. Description of the Drawings

[0013] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for the embodiments. It should be understood that the following drawings only show some embodiments of the present invention, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, without creative efforts, other related drawings can also be obtained based on these drawings.

[0014] Figure 1 is the XRD characterization diagram of the Co(CO3) 0.5 (OH)·0.11H2O precursor provided by the embodiment of the present invention.

[0015] Figure 2 is the SEM diagram of the Co(CO3) 0.5 (OH)·0.11H2O precursor provided by the embodiment of the present invention.

[0016] Figure 3 is the Co(CO3) 0.5(OH)·0.11H2O@PDA SEM image.

[0017] Figure 4 It is the XRD characterization diagram of CoSe2@NC provided by the embodiment of the present invention.

[0018] Figure 5 It is the SEM image of CoSe2@NC provided by the embodiment of the present invention.

[0019] Figure 6 It is the CV test curve of CoSe2 provided by the embodiment of the present invention at a scanning rate of 0.1 mV s -1 and a voltage window of 0.01 - 3.0 V vs. (Na / Na + ).

[0020] Figure 7 It is the charge-discharge curve of the first cycle of the CoSe2 and CoSe2@NC electrode materials provided by the embodiment of the present invention at a voltage window of 0.01 - 3.0 V and a current density of 200 mA g -1 .

[0021] Figure 8 It is the cycling performance curve of CoSe2 and CoSe2@NC provided by the embodiment of the present invention cycled 100 times under the condition of a current density of 2 A g -1 .

[0022] Figure 9 It is the Nyquist spectrum of CoSe2 and CoSe2@NC after cycling provided by the embodiment of the present invention, and the inset is the fitted equivalent circuit diagram. Detailed implementation manners

[0023] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

[0024] In the description of the present invention, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0025] The embodiment of the present invention provides a method for preparing anemone-shaped CoSe2 composite material, comprising the following steps:

[0026] S1, Co(CO3) was prepared by adjusting the hydrothermal synthesis conditions 0.5 (OH)·0.11H2O precursor, which has a unique anemone-like morphology. 0.5 The (OH)·0.11H2O precursor was added to a buffer solution containing Tris at pH 8.0-9.0 and then ultrasonically dispersed. 0.5 The mass ratio of (OH)·0.11H2O precursor to dopamine is 0.8-1.9:1. The mass of added dopamine is closely related to the thickness of the nitrogen-doped carbon layer formed after vapor phase selenization. Too much dopamine will lead to a thicker nitrogen-doped carbon layer, thus affecting the cycle rate performance. Too little dopamine may result in failure of the nitrogen-doped carbon layer to be coated. Dopamine is added to the solution and stirred at room temperature for 8-20 hours to obtain a black precipitate-like separation.

[0027] S2, the black precipitate obtained above is washed several times with deionized water and ethanol, and then placed in an oven at a constant temperature of 60°C to 80°C for 5 to 10 hours to obtain Co(CO3) 0.5 (OH)·0.11H2O@PDA;

[0028] S3, Co(CO3) 0.5 (OH)·0.11H2O@PDA and Se powder are mixed evenly in a mass ratio of 1:2-5. Too little Se powder will lead to 0.5 (OH)·0.11H2O@PDA is not completely selenized; if too much is added, residual molten Se will be mixed in the target sample CoSe2@NC, which is difficult to remove completely; it is placed in a tube furnace filled with Ar atmosphere, kept at a constant temperature of 350-450℃ for 2-6h, and the heating rate is controlled at 1-5℃ / min for selenization treatment, and finally CoSe2@NC is obtained. The sample can be prevented from being oxidized in an inert atmosphere, and the anemone-like morphology of the composite material can be well maintained in this temperature range.

[0029] As a further improvement, in step S1, the Co(CO3) having a unique anemone-like morphology0.5 (OH)·0.11H2O precursor was obtained by the following method:

[0030] S11. A certain amount of cobalt acetate tetrahydrate was added to deionized water and stirred. After it was fully dissolved, urea was added and stirred until a uniform mixed solution was formed. Then it was transferred into a 50 ml reaction kettle, placed in an oven, and reacted at 100 °C for 5 h to obtain a precipitate. The precipitate was centrifugally washed with deionized water and alcohol for many times and then dried to obtain Co(CO3) with a unique sea anemone-like morphology. 0.5 (OH)·0.11H2O precursor, for use. Co(CO3) 0.5 The particle size and morphology of the (OH)·0.11H2O precursor can be adjusted by strictly controlling the parameter ratio of cobalt acetate tetrahydrate and urea. Preferably, in one embodiment, 1 g - 1.5 g of cobalt acetate tetrahydrate was added to 30 ml of deionized water. After it was fully dissolved, 1 g - 1.5 g of urea was added. After stirring to form a uniform mixed solution, it was transferred into a 50 ml reaction kettle, placed in an oven, and reacted under the condition of 100 °C - 120 °C for 5 h. The preferred addition amounts of cobalt acetate tetrahydrate and urea were 1:1. A large number of ratio experiments showed that when the addition amounts of cobalt acetate tetrahydrate and urea were 1:1, such as when the addition amount of cobalt acetate tetrahydrate in Example 1 was 1 g and the addition amount of urea was also 1 g, the formed composite material had a unique sea anemone-like morphology. For other ratios, such as when the addition amounts of cobalt acetate tetrahydrate and urea were 1:2, 1:4, 1:8, composite materials with a unique sea anemone-like morphology could not be formed; the temperature range was 100 °C - 120 °C. By controlling the amount of medicine added and the temperature, it was an important factor to obtain a composite material with a unique sea anemone-like morphology.

[0031] As a further improvement, in step S1, the pH of the Tris buffer solution was 8.4 - 8.6. A weakly alkaline buffer solution was more conducive to the subsequent self-polymerization process of PDA to coat on the surface of the Co(CO3) 0.5 (OH)·0.11H2O precursor.

[0032] As a further improvement, in step S1, the Co(CO3) 0.5 The step of adding dopamine to the solution containing the precursor and stirring at room temperature for 8 - 20 h with the mass ratio of the (OH)·0.11H2O precursor to dopamine being 0.8 - 1.9:1 includes:

[0033] The according to Co(CO3) 0.5(OH)·0.11H2O precursor and dopamine are in a mass ratio of 1.8:1. Dopamine is added to the precursor solution and continuously stirred at room temperature for 12 h. In step S2, the precipitate is washed several times with deionized water and ethanol, and then dried at 70 °C for 8 h to obtain Co(CO3) 0.5 (OH)·0.11H2O@PDA, for use;

[0034] As a further improvement, in step S3, the step of mixing Co(CO3) 0.5 (OH)·0.11H2O@PDA and Se powder in a mass ratio of 1:2 - 5, mixing evenly, placing in a tubular furnace filled with Ar atmosphere, and keeping at a constant temperature of 350 - 450 °C for 2 - 6 h with a heating rate controlled at 1 - 5 °C / min includes:

[0035] Mix Co(CO3) 0.5 (OH)·0.11H2O@PDA and Se in a mass ratio of 1:3, mixing evenly, placing in a tubular furnace filled with Ar atmosphere, and keeping at a constant temperature of 380 - 420 °C for 3.5 - 4.5 h with a heating rate controlled at 2 - 3 °C / min.

[0036] The embodiment of the present invention further provides an application of the anemone - shaped CoSe2 composite material as the negative electrode of a sodium - ion battery. The negative - electrode active material is a nitrogen - doped carbon - modified anemone - shaped CoSe2@NC composite material. By the foregoing steps, PDA is coated on the surface of the precursor to form Co(CO3) 0.5 (OH)·0.11H2O@PDA. After gas - phase selenization, the PDA coated on the surface is derived into a nitrogen - doped carbon layer, which is coated on the surface of CoSe2 nanoparticles to form a modification; the particle size of the nitrogen - doped carbon - modified anemone - shaped CoSe2@NC composite material is 1 - 3 microns. The particle sizes of the CoSe2@NC composite material particles observed under SEM are different, and the particle size is in the range of about 1 - 3 microns, referring to the particle size after doping and modification.

[0037] Example 1:

[0038] Add 1 g of cobalt acetate tetrahydrate to 30 ml of deionized water. After complete dissolution, add 1 g of urea, stir to form a homogeneous mixed solution, transfer it to a 50 - ml reaction kettle, place it in an oven, and react at 100 °C for 5 h. Wash the precipitate several times with deionized water and ethanol, and then dry to obtain Co(CO3) with a unique anemone - shaped morphology 0.5(OH)·0.11H2O precursor, set aside. Prepare 100mL of buffer solution containing Tris, adjust the pH value of the solution to 8.5 by controlling the amount of Tris added, accurately weigh 0.1g of the precursor and dissolve it in the buffer solution, ultrasonically disperse it for half an hour, and then add 55mg of dopamine (PDA) at a mass ratio of 1.8:1 between the precursor and dopamine, stir continuously for 12h in a constant temperature environment at 30℃, wash and centrifuge with deionized water and ethanol several times, and then put the precipitate obtained by centrifugation into a blast drying oven set at a set temperature, keep a constant temperature of 70℃ for 8h, and dry it to obtain Co(CO3) 0.5 (OH)·0.11H2O@PDA. The prepared Co(CO3) 0.5 (OH)·0.11H2O@PDA and Se powder were uniformly mixed in a mass ratio of 1:3, placed in a tubular furnace filled with Ar atmosphere, and kept at a constant temperature of 390°C for 4 h. The heating rate was controlled at 2°C / min to finally obtain a nitrogen-doped carbon-modified anemone-like CoSe2 composite material, namely CoSe2@NC composite material.

[0039] Comparative Example 1:

[0040] The comparative example is basically similar to the embodiment, but the difference is that the Co(CO3) without dopamine coating is 0.5 The (OH)·0.11H2O precursor and Se powder were uniformly mixed in a mass ratio of 1:3, placed in a tubular furnace filled with Ar atmosphere, and kept at a constant temperature of 390°C for 4h. The heating rate was controlled at 2°C / min. As a comparison, CoSe2 material was obtained.

[0041] Preparation and assembly of electrodes: The active material slurry consists of active material, conductive carbon (Super-P) and sodium carboxymethyl cellulose as a binder in a mass ratio of 7:2:1. The active material slurry is fully ground and coated on a copper foil collector to prepare a working electrode. After vacuum drying and rolling, it is cut into pieces. The diameter of the circular electrode piece is 12 mm. Pure metallic sodium sheet is used as the counter electrode. It is assembled into a button cell in a glove box filled with argon. The diaphragm model is Celgard2325.

[0042] Structural characterization: The material phase analysis and crystal structure analysis were performed using a Bruker-D8-Advance X-ray diffractometer (XRD), and the sample morphology and microstructure analysis were performed using a Hitachi High-Tech SU8000 series super-resolution field emission scanning electron microscope (SEM).

[0043] Electrochemical performance characterization: The electrochemical performance of the material was characterized by a constant current charge-discharge test using a Blue Electric Battery Test System (CT3002CA). The voltage window for the electrochemical test was fixed at 0.01 - 3 V. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were both carried out using a Shanghai Chenhua Electrochemical Workstation (CHI660D), and the selected scan rate was 0.1 mV s -1 , and the frequency range was 100 kHz - 0.1 Hz.

[0044] Structural characterization:

[0045] The crystal structure of the precursor Co(CO3) Figure 1 (OH)·0.11H2O was characterized by XRD( 0.5 ). The spectrum of the synthesized precursor was compared with the standard card of Co(CO3) 0.5 (OH)·0.11H2O, and it was found that the positions of all characteristic diffraction peaks corresponded to those of the standard card. SEM characterization showed( Figure 2 ) that the prepared precursor presented an anemone-like morphology, and its size was about 1 - 3 microns.

[0046] Experimental example 1:

[0047] To compare the phase structures of the original sample and the modified sample, first, the crystal structures of CoSe2 and CoSe2@NC composites were analyzed. The XRD spectra of the two are as shown in Figure 1 and 4 . Compared with the CoSe2 standard card, the characteristic diffraction peaks at various positions in the spectra could all be corresponded. The characteristic peaks at 30.4°, 34.2°, 37.6°, 43.7°, 46.4°, 51.7°, 54.2°, 56.4°, 58.8°, 63.4, 71.9°, 73.9°, 76.0° in the spectra corresponded to the (200), (210), (211), (220), (221), (311), (222), (230), (321), (400), (420), (421), (332) crystal planes in CoSe2 (PDF#09 - 0234) respectively, indicating that a pure-phase CoSe2 material was successfully prepared by a simple hydrothermal synthesis and a controllable gas-phase selenization method. In addition, a broad diffuse peak appeared near 20° in the XRD pattern of CoSe2@NC, confirming the existence of amorphous carbon in the CoSe2@NC composite.

[0048] Experimental example 2:

[0049] The morphological structure of the product. The SEM technique was used to study Co(CO3) 0.5 (OH)·0.11H2O, Co(CO3) 0.5(OH)·0.11H2O@PDA and CoSe2@NC composite materials were characterized morphologically. Figure 3 This is the SEM image of the precursor after coating with hydrochloric acid dopamine. Comparing Figure 1 it was found that the surface of the precursor became rough from smooth after dopamine coating, but the overall sea anemone-like morphology of the material was still maintained. Figure 5 This is Co(CO3) 0.5 This is the SEM image of (OH)·0.11H2O@PDA transformed into CoSe2@NC through controllable vapor-phase selenization. After carbonization, the material can still maintain the original sea anemone-like structure, fully indicating that the outer carbon layer plays a good stabilizing role in the overall structure, which is sufficient to relieve the volume change of the material to a large extent during the charge-discharge cycle, thus showing excellent cycle stability. At the same time, due to the doping of nitrogen element derived from dopamine, it is more conducive to increasing the wettability of the electrolyte during the contact between the composite material and the electrolyte, providing a large number of active sites for sodium storage and further accelerating the electron conduction rate of the material.

[0050] Electrochemical performance characterization:

[0051] The results of the above material structure and morphology characterization preliminarily confirmed that the CoSe2@NC composite material was successfully prepared by the simple hydrothermal synthesis and controllable vapor-phase selenization methods in this invention. In order to study the improvement of the sea anemone-like structure designed in this invention on the electrochemical performance of the material, in this experiment, the CoSe2@NC composite material was compared with CoSe2, and performance tests were carried out respectively under the same experimental conditions from several aspects such as cycle performance, constant current charge-discharge, and AC impedance, and the results were compared and analyzed. First, the cyclic voltammetry (CV) test method was used to analyze the electrochemical reaction process that occurred during the charge-discharge cycle of the composite material. Figure 6 This shows the CV curve of the CoSe2 composite material electrode tested under the scanning rate of 0.1 mV s -1 and the voltage window of 0.01 - 3.0 V vs. (Na / Na + ) conditions. On the initial CV cathodic scanning curve of the material, the peak at 1.04 V corresponds to Na +React with CoSe2 in the embedding material, converting into metallic Co and Na2Se, along with the decomposition of the electrolyte and the formation of the solid electrolyte interface (SEI). During the anodic scan, the peaks at 1.78 and 1.87 V correspond to the re-conversion of metallic Co nanocrystals and the Na2Se matrix to CoSe2. Starting from the second cycle, the reduction peak shifts towards a more positive potential. This is due to the significant volume expansion of the composite material during the first cycle of cycling, and the change in the internal structure leads to the shift of the reduction peak position. This is also a common phenomenon for transition metal compounds during sodium storage. In addition, it is found that the CV curves of the second and third cycles coincide well, and the polarization degree of the CoSe2 composite material is small, indicating that the impedance of the modified composite material is significantly reduced, which is beneficial for Na + to be rapidly inserted and extracted during the electrochemical reaction process, thus significantly improving the cycle stability of the material.

[0052] Experimental Example 3:

[0053] Due to the excellent electrochemical performance of the modified composite material, the constant current charge-discharge tests were carried out on CoSe2 and CoSe2@NC composite materials. Figure 7 Figure 1 is the first charge-discharge curves of CoSe2 and CoSe2@NC composite materials under the conditions of a voltage window of 0.01 - 3.0 V and a current density of 200 mA g -1 . After the first cycle, the discharge specific capacity of the CoSe2@NC composite material is 359.3 mAh g -1 , and the charge specific capacity is 337.7 mAh g -1 . After calculation, its first Coulombic efficiency is as high as 93.93%. Under the same test conditions, the first Coulombic efficiency of CoSe2 is only 45.83%, indicating that the nitrogen-doped carbon coating structure has a great improvement effect on the cycle stability of the composite material. At the same time, the ultra-high first Coulombic efficiency also indicates that a very stable SEI film is formed during the first cycle of the material.

[0054] Experimental Example 4:

[0055] The electrochemical performance of the composite material at a large current density was tested by cycling the modified and unmodified materials. Figure 8 Figure 2 is the performance graph of CoSe2 and CoSe2@NC composite materials cycled 100 times at a current density of 2 A g -1 . It can be found that after modification, the CoSe2@NC composite material can still maintain 214.6 mAh g -1specific capacity. However, the capacity of the unmodified CoSe2 material decays rapidly during cycling, and the specific capacity decays to nearly zero after 100 cycles. Combining with the fact that the CoSe2@NC composite material maintains a good sea anemone-like morphology in the SEM image, it can be shown that it has good structural stability. At the same time, the design of the nitrogen-doped carbon layer helps to alleviate the volume expansion during cycling and slow down the capacity decay rate. Through the above tests of the cycling performance, it is further confirmed that this unique sea anemone-like CoSe2@NC composite material with carbon layer coating has excellent cycling stability performance.

[0056] Experimental Example 5:

[0057] Effect of nitrogen-doped carbon layer on Na + diffusion kinetics. AC impedance tests were carried out on CoSe2 and CoSe2@NC composite materials in the frequency range of 100 kHz to 0.1 Hz. Figure 9 is the Nyquist plot of the electrode of the CoSe2@NC composite material after cycling tests. The small inset is the fitted equivalent circuit. It can be clearly seen that the Nyquist plots of the materials before and after modification are both composed of a typical semicircle in the high-frequency region and a straight line in the low-frequency region. Among them, the semicircle in the high-frequency region corresponds to the charge transfer resistance (R2), and the straight line in the low-frequency region is related to the Warburg impedance (W1) of Na + diffusion. The Nyquist plot was fitted into an equivalent circuit diagram for analysis. The charge transfer resistances (R2) of CoSe2 and CoSe2@NC materials are 473.7 Ω and 183.8 Ω respectively. This shows that after the material is coated with a nitrogen-doped carbon layer, the interfacial impedance has been significantly reduced, which is beneficial to promoting the transmission of internal electron charges of the material, thus showing more excellent electrochemical performance.

[0058] The above is only the preferred embodiment of the present invention and is not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A preparation method of an anemone-like CoSe2 composite material, characterized in that, It includes the following steps: S1. Prepare Co(CO₃)(OH)·0.11H₂O precursor by hydrothermal synthesis. Add the precursor to a buffer solution containing Tris and perform ultrasonic dispersion. Then, add dopamine to the solution at room temperature with a mass ratio of Co(CO₃)(OH)·0.11H₂O precursor to dopamine of 0.8 - 1.9:1 and stir to obtain a black precipitate-like isolate; 0.5 (OH)·0.11H2O precursor, add the precursor to a buffer solution containing Tris and perform ultrasonic dispersion. Then, in the solution, according to the mass ratio of Co(CO3) 0.5 (OH)·0.11H2O precursor to dopamine of 0.8 - 1.9:1, add dopamine and stir at room temperature to obtain a black precipitate-like isolate; S2. After washing the above-mentioned isolate with deionized water and ethanol and drying, Co(CO₃) 0.5 (OH)·0.11H₂O @PDA is obtained; S3. Mix Co(CO3) 0.5 (OH)·0.11H2O@PDA and Se powder evenly. Place the mixture in a tubular furnace filled with an Ar atmosphere and carry out selenization treatment at a constant temperature of 350 - 450 °C to finally obtain a CoSe2@NC composite material with an anemone-like morphology. The particle size of the anemone-like CoSe2@NC composite material modified with nitrogen-doped carbon is 1 - 3 microns; Co(CO3) 0.5 (OH)·0.11H2O precursor with a unique sea anemone-like morphology is obtained by the following method: 0.5 ​ S11. Add a certain amount of cobalt acetate tetrahydrate to deionized water and stir. After it is fully dissolved, add urea and stir until a homogeneous mixed solution is formed. Then transfer it to a 50 ml reaction kettle, put it into an oven, and react at 100 °C for 5 h to obtain a precipitate. Wash it by centrifugation with deionized water and alcohol for several times, and finally dry it to obtain a Co(CO3) 0.5 (OH)·0.11H2O precursor; The prepared sea anemone-like CoSe2 composite material is used as the negative electrode of a sodium-ion battery.

2. The preparation method of the sea anemone-like CoSe2 composite material according to claim 1, characterized in that, Step S1: Add the precursor to a pH = 8.0 - 9.0 buffer solution containing Tris and perform ultrasonic dispersion.

3. The preparation method of the sea anemone-like CoSe2 composite material according to claim 1, wherein, Step S1: Add dopamine to the solution and stir at room temperature for 8 - 20 h to obtain a black precipitate-like isolate.

4. The preparation method of the sea anemone-like CoSe2 composite material according to claim 1, characterized in that, Step S2: The black precipitate isolate obtained in Step S1 is washed multiple times with deionized water and ethanol and then placed in an oven. After maintaining a constant temperature of 60 °C to 80 °C for 5 to 10 h, Co(CO3) 0.5 (OH)·0.11H2O @PDA is obtained.

5. The preparation method of the sea anemone-like CoSe2 composite material according to claim 1, characterized in that, Step S3, mix Co(CO3) 0.5 (OH)·0.11H2O@PDA and Se powder evenly at a mass ratio of 1:2 to 5.

6. The preparation method of the sea anemone-like CoSe2 composite material according to claim 5, characterized in that, Step S3: Keep the temperature constant for 2 - 6 h, control the heating rate at 1 - 5 °C / min, perform selenization treatment, and finally obtain a sea anemone-like CoSe2@NC composite material.

7. Application of an anemone-like CoSe2 composite material as the negative electrode of a sodium-ion battery, characterized in that, The negative electrode active material of the negative electrode of the sodium-ion battery is the sea anemone-like CoSe2@NC composite material obtained by the preparation method described in any one of claims 1 - 6, and the particle size of the sea anemone-like CoSe2@NC composite material is 1 - 3 microns.

8. The negative electrode application of a sodium ion battery according to claim 7, characterized in that, The initial Coulombic efficiency of the negative electrode of the sodium-ion battery is as high as 93.93%, and it can still maintain a specific capacity of 214.6 mAh g -1 after 100 cycles at a current density of 2 A g -1 .

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