Bimetal selenide heterojunction composite material and preparation method thereof

Abstract

The invention provides a bimetallic selenide heterojunction composite material and a preparation method thereof. The preparation method comprises the following steps: by taking graphite as an anode, an inert carrier as a cathode and mixed molten salt containing a first metal source and a second metal source as electrolyte, heating and melting, adding selenium particles into the molten salt, electrolyzing in a protective atmosphere, taking out a cathode product after the electrolysis is finished, washing and drying, thereby obtaining the selenium-enriched graphite. The bimetallic selenide heterojunction composite material grown in the confinement of the carbon nano tube is obtained. The preparation method is simple, reduction and selenylation of the metal oxide and in-situ growth of the carbon nano tube are realized in the high-temperature molten salt electrolyte in the whole process, a large amount of water or organic solvent depended by a traditional hydrothermal / solvothermal method is not needed, and tedious steps such as repeated filtration, washing, drying and re-selenylation are also avoided; therefore, solvent consumption and waste liquid discharge are greatly reduced, the environmental burden is relieved, and the treatment cost is saved.

Description

Technical Field

[0001] This invention relates to the field of non-ferrous metallurgy technology, and more specifically, to a bimetallic selenide heterojunction composite material and its preparation method. Background Technology

[0002] Sodium resources are abundant and inexpensive in the Earth's crust and oceans, and sodium-ion batteries have similar working mechanisms and manufacturing processes to lithium-ion batteries, making them one of the most promising large-scale energy storage technologies.

[0003] In sodium-ion batteries, the anode material is a key factor determining its energy density, rate performance, and cycle stability. While widely studied carbon-based anode materials (such as hard carbon and soft carbon) possess good cycle stability, their specific capacity is limited, making it difficult to meet high energy density requirements. In contrast, transition metal selenides have attracted widespread attention in the anode field of sodium-ion batteries due to their high theoretical specific capacity and excellent electronic and ion conductivity. However, these materials exhibit significant volume expansion during charge and discharge, which can easily lead to electrode structure pulverization and damage to the conductive network. Furthermore, their low intrinsic conductivity and slow sodium-ion diffusion kinetics also limit their ability to achieve high-rate performance.

[0004] To address the aforementioned issues, researchers have proposed various modification strategies, including the preparation of metal selenide anode materials. Currently, metal selenide anode materials are mainly prepared using wet chemical methods such as hydrothermal or solvothermal methods. These methods typically rely on large solvent environments and long reaction times, involving repeated filtration, washing, and drying steps; further high-temperature carbonization of the precursor is required to achieve carbon composite. This not only leads to significant solvent consumption and wastewater discharge, causing environmental pressure, but also restricts the continuous and large-scale production of materials due to limited reaction equipment capacity and complex batch operation procedures. Summary of the Invention

[0005] In view of the shortcomings of the prior art, one of the objectives of this invention is to solve one or more problems existing in the prior art. For example, one objective of this invention is to provide a method for preparing bimetallic selenide heterojunction composite materials with a simplified process flow that avoids the use of large amounts of liquid solvents for the confined growth of carbon nanotubes.

[0006] The present invention provides a method for preparing a carbon nanotube confined growth bimetallic selenide heterostructure composite material, which may include the following steps: using graphite as the anode, an inert support as the cathode, and a mixed molten salt containing a first metal source and a second metal source as the electrolyte, heating and melting the mixture, adding selenium particles to the molten salt, electrolyzing under a protective atmosphere, and after electrolysis, removing the cathode product, washing, and drying to obtain the carbon nanotube confined growth bimetallic selenide heterostructure composite material.

[0007] Furthermore, the electrolysis temperature can be 650 ℃~850 ℃, and the electrolysis voltage can be 2.0 V~2.8 V.

[0008] Furthermore, the molar ratio of the first metal source to the second metal source can be 1:(1~4), and the mass ratio of the total mass of the first metal source and the second metal source to the mass of the selenium particles can be 1:(2~4).

[0009] Furthermore, the first metal source can be an iron source, which includes at least one of FeO, Fe2O3, and Fe3O4; the second metal source can be a cobalt source, a nickel source, a copper source, or a zinc source, wherein the cobalt source can be at least one of CoO, Co2O3, and Co3O4; the nickel source can be at least one of NiO, Ni2O3, and Ni3O4; the copper source can be at least one of CuO, Cu2O, and Cu4O3; and the zinc source can be ZnO.

[0010] Furthermore, the inert carrier can be carbon fiber paper or carbon cloth; the molten salt can be CaCl2-NaCl-CaO molten salt or CaCl2-NaCl-MgO molten salt.

[0011] Furthermore, bimetallic selenide heterostructures can be grown on the inner wall of carbon nanotubes and anchored on the outer wall of carbon nanotubes.

[0012] Another aspect of the present invention provides a carbon nanotube confined growth bimetallic selenide heterojunction composite material, wherein the composite material can be based on carbon nanotubes as a framework, with bimetallic selenide heterojunctions grown on the inner wall of the carbon nanotubes and anchored on the outer wall of the carbon nanotubes, wherein the bimetal is any one of cobalt, nickel, copper and zinc combined with iron.

[0013] Another aspect of the present invention provides a sodium battery anode, which may include the composite material prepared by the above-described method for preparing carbon nanotube confined growth bimetallic selenide heterojunction composite material.

[0014] Another aspect of the present invention provides a sodium battery, which may include the sodium battery negative electrode described above.

[0015] Compared with the prior art, the beneficial effects of the present invention include at least one of the following:

[0016] (1) The preparation method of the present invention is simple. The reduction, selenization and in-situ growth of metal oxides and carbon nanotubes are achieved in a high-temperature molten salt electrolyte throughout the process. It does not require a large amount of water or organic solvents as relied upon by the traditional hydrothermal / solventothermal method, and also avoids cumbersome steps such as multiple filtration, washing, drying and reselenization. This greatly reduces solvent consumption and waste liquid discharge, reduces environmental burden and saves treatment costs.

[0017] (2) This invention constructs a carbon nanotube conductive network and a bimetallic selenide heterojunction simultaneously on the surface of an inert carbon substrate through molten salt electrolysis-in-situ growth. Only a single reaction system and a single electrochemical operation are required to achieve a tight combination of the two. The interface structure is excellent and helps to promote the efficient transport of electrons and sodium ions.

[0018] (3) This invention utilizes the “cavity confinement + outer wall anchoring” effect of carbon nanotubes to make the bimetallic selenide heterojunctions distributed in a gradient inside and outside the carbon nanotubes. It not only buffers the volume change caused by sodium ion insertion / extraction through the flexible carbon layer, suppressing material pulverization and active phase shedding, but also improves conductivity and active site density through the synergistic effect of the hetero interface and bimetallic components, thereby enhancing rate performance and cycle stability while maintaining high specific capacity.

[0019] (4) The present invention uses the carbon-containing gas generated during the electrolysis process as a carbon source, and converts it into high-value-added carbon nanotubes in situ under the catalysis of metal nanoparticles, so as to realize the resource utilization of harmful gases; at the same time, the molten salt electrolyte can be recycled after salt replenishment and purification, further reducing the process cost and improving the green level of the whole process.

[0020] (5) The molten salt electrolysis process used in this invention is highly compatible with existing industrial electrolysis equipment. It is easy to increase production capacity by expanding the scale of the electrolysis cell or by connecting parallel units. Combined with the continuous feeding and discharging mechanism, it is expected to achieve continuous production, overcome the bottleneck of limited batch production and poor repeatability of the traditional hydrothermal / solventothermal method, and provide a feasible path for the large-scale preparation of high-performance anode materials.

[0021] (6) The full cell assembled with the carbon nanotube confined bimetallic selenide heterojunction prepared in this invention as the negative electrode and a commercial Na3V2(PO4)3@C positive electrode exhibits excellent electrochemical performance at 500 mA g. -1 After 100 cycles at current density, it still has a reversible capacity of approximately 241.3 mAh g⁻¹, with a capacity retention of 85.3%. Attached Figure Description

[0022] The above and other objects and features of the present invention will become clearer from the following description taken in conjunction with the accompanying drawings, in which:

[0023] Figure 1 The image shows the XRD pattern of the bimetallic selenide heterojunction composite material prepared by confined growth of carbon nanotubes in Example 1 of this invention.

[0024] Figure 2 This is a comparison diagram of the cathode before and after electrolysis in Example 1 of the present invention.

[0025] Figure 3SEM and TEM images of the bimetallic selenide heterostructure prepared by confined growth of carbon nanotubes in Example 1 of this invention.

[0026] Figure 4 The diagram shows the cycle performance of a full cell assembled with the carbon nanotube confined growth bimetallic selenide heterojunction composite material prepared in Example 1 as the negative electrode and a commercial Na3V2(PO4)3@C (NVP@C) positive electrode. Detailed Implementation

[0027] The bimetallic selenide heterojunction composite material and its preparation method according to the present invention will be described in detail below with reference to the accompanying drawings and exemplary embodiments.

[0028] Specifically, this invention achieves in-situ synchronous construction and gradient-confined growth of carbon nanotubes and bimetallic selenide heterojunctions through ingenious reaction pathway design. Specifically, the carbon source for the carbon nanotubes originates from carbon dioxide generated during electrolysis, which is produced by the reaction of oxygen ions generated from the electrolysis of the first and second metal sources with the anode graphite. The bimetallic selenide heterojunction, on the other hand, originates from metal ions generated from the electrolysis of the first and second metal sources in molten salt, which combine in situ with selenium ions diffused at high temperatures. It is worth noting that the metal ions released during heterojunction formation can further act as catalysts, promoting the nucleation and growth of carbon nanotubes, thereby constructing a tightly coupled "carbon nanotube-heterojunction" composite system. Throughout the electrolysis process, the growth of carbon nanotubes and the formation of the bimetallic selenide heterojunction occur simultaneously, exhibiting a unique "internal-external symbiotic" structure: the bimetallic selenide heterojunction is confined within the internal cavity of the carbon nanotube and simultaneously anchored to the outer wall of the carbon nanotube, forming a gradient-distributed confined growth morphology. This structure not only effectively utilizes the confinement effect and flexible support properties of carbon nanotubes to alleviate the volume change during the sodium ion insertion / extraction process, but also enhances conductivity and reactivity through the synergistic effect of heterogeneous interfaces and metal components, thereby improving the overall electrochemical stability and rate performance of the material.

[0029] The specific reaction mechanism is as follows:

[0030] (I) Electrochemical Reduction of Metal Oxides and Formation of Metal Ions. Oxides containing iron, cobalt, nickel, copper, or zinc undergo electrochemical reduction at the cathode, generating the corresponding metal or low-valence metal intermediates; simultaneously, some of the metal species dissolved in the molten salt are converted into M... 2+ / M + It exists in form, providing a metal source for subsequent selenization.

[0031] (ii) Carbon dioxide generation, capture and in situ growth of CNTs.

[0032] (1) In the molten salt electrolysis process of the present invention, the oxygen ions (O2) released by the metal oxide in the cathode region 2-The CO2 migrates towards the anode, where it undergoes an oxidation reaction to generate CO2 gas. The generated CO2 rapidly dissolves and reacts with basic oxides (such as CaO or MgO) in the molten salt to form dissolved carbonates (such as CaCO3 and MgCO3), thus achieving in-situ capture of CO2 and preventing its direct emission. This process can be represented as (using CaO as an example):

[0033] C (anode) + 2O 2− → CO2 + 4e − ;

[0034] CaO + CO2 ⇌ CaCO3.

[0035] (2) At the cathode potential of the present invention, the above-mentioned carbonate undergoes further electrochemical decomposition in the cathode region, on the one hand regenerating CaO (or MgO) and O. 2- This maintains the alkalinity and ionic balance of the molten salt system; on the other hand, it generates active carbon species or intermediates (such as Ca). x M, Ca x M y ), where Ca x M, Ca x M y These are alkaline earth metal-transition metal alloys or intermetallic compounds. The intermediates possess high carbon solubility and good carbon diffusion ability, making them key precursors for carbon nanotube nucleation and growth. This process can be represented as (using CaO as an example):

[0036] CaCO3 ⇌ Ca 2+ + CO3 2− ;

[0037] CO3 2− + 4e − → C (CNT) + 3O 2− ;

[0038] Total: CaCO3 + 4e − → Ca 2+ + C (CNT) + 3O 2− .

[0039] (3) At the same time, dissolved transition metal ions (such as Fe) in the molten salt 2+ Co 2+ Ni 2+ Cu 2+ Zn 2+The carbon nanoparticles (such as Mg2+) are gradually reduced on the cathode surface, generating nanoscale metal particles or forming localized Ca-M alloy phases with Ca. These metal nanoparticles / alloy phases act as "dissolution pools" for carbon, continuously dissolving carbon seeds obtained from carbonate decomposition. Furthermore, after reaching localized carbon supersaturation, graphitized carbon layers continuously precipitate from the surface or edges of the metal particles via a "carbon dissolution-diffusion-precipitation" process. Due to the combined effects of interfacial energy and curvature, the precipitated graphite layers tend to curl and grow directionally along one side of the metal particles, ultimately contributing to the formation of tubular carbon nanotubes with hollow structures.

[0040] (III) Construction and confinement effect of bimetallic selenide heterostructures. Metal ions near the cathode (such as Fe) 2+ Co 2+ Ni 2+ Cu 2+ Zn 2+ (etc.) and Se diffused from molten salt 2+ In-situ selenization reactions occur, preferentially forming corresponding metal selenide phases, such as FeSe, on the surface of newly formed metal nuclei. x CoSe x NiSe x CuSe x ZnSe x Under certain electric fields and concentration gradients, different metal selenide phases grow continuously or semi-continuously in space, forming bimetallic selenide heterojunctions with tightly contacted interfaces (such as FeSe / CoSe, FeSe / ZnSe, etc.), and are distributed along the gradient of the inner cavity and outer surface of carbon nanotubes, achieving a synergistic structural design of "inner confinement-outer anchoring". The geometric confinement of CNT channels and the synergy of the inner and outer interfaces enable the bimetallic selenide particle size to be controlled and the volume expansion to be limited, resulting in a more stable structure during charge and discharge. The charge redistribution and built-in electric field at the heterojunction interface help accelerate the growth of Na+. + Migration and electron transport are among the key reasons why the materials of this invention exhibit excellent overall performance in sodium-ion batteries.

[0041] This invention provides a method for preparing a bimetallic selenide heterostructure composite material grown in a confined space using carbon nanotubes. In some embodiments, the preparation method includes the following steps:

[0042] Step 1: Mix the first metal source and the second metal source with molten salt, and heat to dissolve the first metal source and the second metal source in the molten salt.

[0043] Step 2: Using graphite as the anode, an inert support as the cathode, and molten salt containing molten first and second metal sources as the electrolyte, selenium particles are fed into the molten salt and electrolyzed under a protective atmosphere to obtain the electrolysis products.

[0044] Step 3: The electrolysis product is then washed and dried to obtain a bimetallic selenide heterostructure composite material with confined carbon nanotube growth.

[0045] In some embodiments, the first metal source may be an iron source. The iron source may include at least one iron oxide such as FeO, Fe2O3, and Fe3O4.

[0046] In some embodiments, the second metal source can be a cobalt source, a nickel source, a copper source, or a zinc source. The cobalt source can be at least one of cobalt oxides such as CoO, Co2O3, and Co3O4. The nickel source can be at least one of nickel oxides such as NiO, Ni2O3, and Ni3O4; the copper source can be at least one of copper oxides such as CuO, Cu2O, and Cu4O3; and the zinc source can be a zinc oxide such as ZnO.

[0047] In some embodiments, the molten salt can be CaCl2-NaCl-CaO or CaCl2-NaCl-MgO. The CaO or MgO in the molten salt can serve not only as an oxygen ion carrier but also as a source of alkaline oxides to capture carbon dioxide generated during electrolysis. The molar ratio of the molten salt can be adjusted according to melting point and conductivity requirements; for example, the CaCl2:NaCl molar ratio can be (1-3):1, and the amount of CaO or MgO added can be 1 wt% to 5 wt% of the total mass of the molten salt. Of course, the molten salt of the present invention can also be other molten salts, such as CaCl2 molten salt or CaCl2-NaCl molten salt.

[0048] In some embodiments, the heating temperature for dissolving the first metal source and the second metal source in the molten salt can be 650 °C to 850 °C. For example, the heating temperature can be a combination of 700 °C to 800 °C, 720 °C to 780 °C, 735 °C to 755 °C, or higher. Of course, the melting temperature can be adjusted according to the solubility and electrochemical window of different metal oxides.

[0049] In some implementations, the inert carrier can be a carbon material such as carbon fiber paper or carbon cloth.

[0050] In some implementations, the electrolysis temperature can be from 650 °C to 850 °C. For example, the electrolysis temperature can be a combination of 660 °C to 830 °C, 685 °C to 805 °C, 712 °C to 755 °C, or higher. The electrolysis voltage can be from 2.0 V to 2.8 V. At an electrolysis voltage of 2.0 V to 2.8 V, the efficiency of metal oxide electroreduction, decomposition of intermediates such as CaCO3, and carbon nanotube formation can be balanced. For example, the electrolysis voltage can be a combination of 2.2 V to 2.7 V, 2.4 V to 2.6 V, or higher. The electrolysis time can be from 0.5 h to 5 h. For example, the electrolysis time can be a combination of 0.5 h to 5 h, 0.8 h to 4.6 h, 1.2 h to 4.2 h, 1.8 h to 3.5 h, 2.3 h to 3.1 h, or higher.

[0051] In some embodiments, the molar ratio of the first metal source to the second metal source can be 1:(1~4). Preferably, the molar ratio of the first metal source to the second metal source can be 1:1. A 1:1 molar ratio is beneficial for forming a compositionally balanced bimetallic selenide heterojunction.

[0052] The mass ratio of the total mass of the first metal source and the second metal source to the mass of the selenium particles can be 1:(2-4). For example, the mass ratio of the total mass of the first metal source and the second metal source to the mass of the selenium particles can be 1:3.

[0053] In some embodiments, the protective gas can be argon or nitrogen. The flow rate of the protective gas into the reaction system can be 50 ml / min to 200 ml / min. For example, the flow rate of the protective gas can be 80 ml / min to 180 ml / min, 100 ml / min to 165 ml / min, 125 ml / min to 140 ml / min, or a combination of the above ranges.

[0054] In some implementations, the selenium particles can be fed into the molten salt using tools such as alumina tubes to deliver them to the bottom of the molten salt. At an electrolysis temperature of 650 °C to 850 °C, the selenium particles melt and partially vaporize in the molten salt, forming a precipitate of Se. 2- The dominant selenium anion species diffuses towards the vicinity of the cathode under the influence of the electric field.

[0055] In some implementations, bimetallic selenide heterojunctions are grown on the inner wall of carbon nanotubes and anchored on the outer wall of carbon nanotubes.

[0056] Another aspect of the present invention provides a carbon nanotube confined growth bimetallic selenide heterostructure composite material. In some embodiments, the composite material can be based on a carbon nanotube framework, with bimetallic selenide heterostructures grown on the inner wall of the carbon nanotubes and anchored on the outer wall of the carbon nanotubes, wherein the bimetal is any one of cobalt, nickel, copper, and zinc combined with iron.

[0057] Another aspect of the present invention provides a sodium battery anode. In some embodiments, the sodium battery anode comprises the carbon nanotube-confined-growth bimetallic selenide heterojunction composite material described above. The resulting full cell assembled with the anode and a commercial Na3V2(PO4)3@C (NVP@C) cathode exhibits excellent sodium storage capacity and cycle stability.

[0058] Another aspect of the present invention provides a sodium battery. In some embodiments, the sodium-ion battery includes the aforementioned sodium-ion battery negative electrode.

[0059] To better understand the present invention, specific examples are provided below to further illustrate the content of the present invention, but the content of the present invention is not limited to the examples below.

[0060] Example 1

[0061] A method for preparing a carbon nanotube confined growth bimetallic selenide heterostructure composite material may include the following steps:

[0062] Step 1: At room temperature, weigh 0.49 g FeO and 0.51 g CoO and mix them with 350 g molten salt (containing 229.3 g CaCl2, 120.7 g NaCl and 3.5 g CaO), then heat to 750 °C to completely dissolve them, and obtain a secondary solution.

[0063] Step 2: Using a graphite rod as the anode, carbon fiber paper as the cathode, and a secondary solution as the electrolyte, 2g of selenium granules are fed to the bottom of the molten salt through an alumina tube with a hole on one side. Under an argon atmosphere (flow rate of 100ml / min), a cell voltage of 2.1V is applied, and electrolysis is carried out for 1.5h to obtain the electrolysis product.

[0064] Step 3: Wash the electrolysis product with deionized water to remove residual molten salt, and then keep it in a vacuum drying oven at 60 °C for 12 h to obtain a carbon nanotube confined growth bimetallic selenide heterostructure composite material.

[0065] The XRD pattern of the bimetallic selenide heterostructure composite material prepared in this embodiment, which is grown in a confined space with carbon nanotubes, is shown below. Figure 1 As shown in the figure, the composite material mainly contains FeSe2, CoSe2, and CNTs (carbon nanotubes). A comparison of the cathodes before and after electrolysis is shown below. Figure 2 As shown, where, Figure 2a is the cathode diagram before electrolysis. Figure 2 b is the cathode diagram after electrolysis.

[0066] The SEM and EDS images, TEM and EDS images of the carbon nanotube confined-growth bimetallic selenide heterostructure composite material prepared in this embodiment are shown below. Figure 3 As shown, where, Figure 3 a shows the SEM and EDS images of the carbon nanotube-confined bimetallic selenide heterostructure composite material; Figure 3 b shows the TEM and EDS images of the carbon nanotube-confined-grown bimetallic selenide heterostructure composite material. Figure 3 Image b is a magnified high-resolution TEM image of a bimetallic selenide heterostructure. From Figure 3 Figure a shows that the prepared carbon nanotube confined growth bimetallic selenide heterostructure composite material is mainly composed of carbon nanotubes and bimetallic selenide heterostructures; the SEM image corresponds to the EDS image ( Figure 3 (a1, a2, a3, a4). Image a1 shows the distribution of carbon (C), image a2 shows the distribution of fe (Fe), image a3 shows the distribution of co (Co), and image a4 shows the distribution of selenium (Se). The EDS images demonstrate that the bimetallic selenide heterostructure is anchored to the carbon nanotube. Figure 3 As shown in Figure b, the interior of the carbon nanotubes is also filled with bimetallic selenide heterostructures. Figure 3 The high-resolution TEM image (magnified view of the filler) in b shows a clear boundary between the bimetallic selenide heterostructure, namely the (111) crystal plane (0.51 nm) of FeSe2 and the (221) crystal plane (0.20 nm) of CoSe2; the corresponding EDS image of the TEM image ( Figure 3 (b1, b2, b3, b4), b1 is the distribution map of C element, b2 is the distribution map of Fe element, b3 is the distribution map of Co element, and b4 is the distribution map of Se element. The EDS images demonstrate that the bimetallic selenide heterostructure is confined within carbon nanotubes. Combined with... Figure 1 and Figure 3 This invention demonstrates that a carbon nanotube confined growth bimetallic selenide heterojunction composite material was prepared, in which the bimetallic selenide heterojunction is grown in a gradient confined space inside and outside the carbon nanotube framework. The bimetallic selenide heterojunction is confined inside the carbon nanotube and anchored outside the carbon nanotube, achieving an ingenious "internal and external symbiosis" structural design.

[0067] The full-cell cycle performance of the carbon nanotube confined-growth bimetallic selenide heterostructure composite material prepared in this embodiment, used as the negative electrode and assembled with a commercial Na3V2(PO4)3@C (NVP@C) positive electrode is shown in the figure below. Figure 4 As shown. From Figure 4 It can be seen that the full cell is at 500 mA g -1After 100 charge / discharge cycles at a certain rate, it still yields approximately 241.3 mAh g. -1 The reversible capacity has a capacity retention rate of 85.3%.

[0068] Example 2

[0069] A method for preparing a carbon nanotube confined growth bimetallic selenide heterostructure composite material may include the following steps:

[0070] Step 1: At room temperature, weigh 0.3g FeO and 0.7g Co2O3 and mix them with 350g molten salt (containing 229.3g CaCl2, 120.7g NaCl, and 3.5g CaO). Then heat the mixture to 850℃ to completely dissolve it, resulting in a secondary solution.

[0071] Step 2: Using a graphite rod as the anode, carbon cloth as the cathode, and a secondary solution as the electrolyte, 3g of selenium granules are fed to the bottom of the molten salt through an alumina tube with a hole on one side. Under an argon atmosphere (flow rate of 150ml / min), a cell voltage of 2.2V is applied, and electrolysis is carried out for 1 hour to obtain the electrolytic product.

[0072] Step 3: Wash the electrolysis product with deionized water to remove residual molten salt, and then keep it in a vacuum drying oven at 80 °C for 9 h to obtain a carbon nanotube confined growth bimetallic selenide heterostructure composite material.

[0073] Example 3

[0074] A method for preparing a carbon nanotube confined growth bimetallic selenide heterostructure composite material may include the following steps:

[0075] Step 1: At room temperature, weigh 0.49g Fe2O3 and 0.51g Ni2O3 and mix them with 350g molten salt (containing 229.3g CaCl2, 120.7g NaCl and 7g CaO), then heat to 800℃ to completely dissolve them and obtain a secondary solution.

[0076] Step 2: Using a graphite rod as the anode, carbon fiber paper as the cathode, and a secondary solution as the electrolyte, 4g of selenium granules are fed to the bottom of the molten salt through an alumina tube with a hole on one side. Under an argon atmosphere (flow rate of 100ml / min), a cell voltage of 2.0V is applied, and electrolysis is carried out for 2.5h to obtain the electrolysis product.

[0077] Step 3: Wash the electrolysis product with deionized water to remove residual molten salt, and then keep it in a vacuum drying oven at 80 °C for 12 h to obtain a carbon nanotube confined growth bimetallic selenide heterostructure composite material.

[0078] Example 4

[0079] A method for preparing a carbon nanotube confined growth bimetallic selenide heterostructure composite material may include the following steps:

[0080] Step 1: At room temperature, weigh 0.63g Co3O4 and 0.37g Cu2O and mix with 350g molten salt (containing 229.3g CaCl2, 120.7g NaCl and 10.5g CaO), then heat to 850℃ to completely dissolve it, and obtain a secondary solution.

[0081] Step 2: Using a graphite rod as the anode, carbon fiber paper as the cathode, and a secondary solution as the electrolyte, 2g of selenium granules are fed to the bottom of the molten salt through an alumina tube with a hole on one side. Under an argon atmosphere (flow rate of 200ml / min), a cell voltage of 2.3V is applied, and electrolysis is carried out for 1 hour to obtain the electrolysis product.

[0082] Step 3: Wash the electrolysis product with deionized water to remove residual molten salt, and then keep it in a vacuum drying oven at 70 °C for 10 h to obtain a carbon nanotube confined growth bimetallic selenide heterostructure composite material.

[0083] Example 5

[0084] A method for preparing a carbon nanotube confined growth bimetallic selenide heterostructure composite material may include the following steps:

[0085] Step 1: At room temperature, weigh 0.49 g CuO and 0.51 g ZnO and mix with 350 g molten salt (containing 229.3 g CaCl2, 120.7 g NaCl and 7 g CaO), then heat to 650 °C to completely dissolve them, and obtain a secondary solution.

[0086] Step 2: Using a graphite rod as the anode, carbon cloth as the cathode, and a secondary solution as the electrolyte, 5g of selenium granules are fed to the bottom of the molten salt through an alumina tube with a hole on one side. Under an argon atmosphere (flow rate of 150ml / min), a cell voltage of 2.4V is applied, and electrolysis is carried out for 1 hour to obtain the electrolytic product.

[0087] Step 3: Wash the electrolysis product with deionized water to remove residual molten salt, and then keep it in a vacuum drying oven at 60 °C for 12 h to obtain a carbon nanotube confined growth bimetallic selenide heterostructure composite material.

[0088] Although the invention has been described above in conjunction with exemplary embodiments, those skilled in the art will understand that various modifications and changes can be made to the exemplary embodiments of the invention without departing from the spirit and scope defined by the claims.

Claims

1. A method for preparing a carbon nanotube confined growth bimetallic selenide heterostructure composite material, characterized in that, Includes the following steps: Using graphite as the anode, an inert support as the cathode, and a mixed molten salt containing a first metal source and a second metal source as the electrolyte, selenium particles were added to the molten salt after heating and melting. Electrolysis was carried out under a protective atmosphere. After electrolysis, the cathode product was taken out, washed, and dried to obtain a carbon nanotube confined growth bimetallic selenide heterostructure composite material.

2. The method for preparing carbon nanotube confined growth bimetallic selenide heterostructure composite material according to claim 1, characterized in that, The electrolysis temperature is 650 ℃~850 ℃, and the electrolysis voltage is 2.0 V~2.8 V.

3. The method for preparing carbon nanotube confined growth bimetallic selenide heterostructure composite materials according to claim 1 or 2, characterized in that, The molar ratio of the first metal source to the second metal source is 1:(1~4), and the ratio of the total mass of the first metal source and the second metal source to the mass of the selenium particles is 1:(2~4).

4. The method for preparing carbon nanotube confined growth bimetallic selenide heterojunction composite materials according to claim 1 or 2, characterized in that, The first metal source is an iron source, which includes at least one of FeO, Fe2O3, and Fe3O4; the second metal source is a cobalt source, a nickel source, a copper source, or a zinc source, wherein the cobalt source is at least one of CoO, Co2O3, and Co3O4; the nickel source is at least one of NiO, Ni2O3, and Ni3O4; the copper source is at least one of CuO, Cu2O, and Cu4O3; and the zinc source is ZnO.

5. The method for preparing carbon nanotube confined growth bimetallic selenide heterostructure composite materials according to claim 1 or 2, characterized in that, The inert carrier is carbon fiber paper or carbon cloth; the molten salt is CaCl2-NaCl-CaO molten salt or CaCl2-NaCl-MgO molten salt.

6. The method for preparing carbon nanotube confined growth bimetallic selenide heterojunction composite materials according to claim 1 or 2, characterized in that, Bimetallic selenide heterojunctions grow on the inner wall of carbon nanotubes and are anchored on the outer wall of carbon nanotubes.

7. A composite material prepared by the method for preparing bimetallic selenide heterostructure composite materials with confined growth of carbon nanotubes according to any one of claims 1 to 6, characterized in that, Using carbon nanotubes as a framework, bimetallic selenide heterojunctions are grown on the inner wall of the carbon nanotubes and anchored on the outer wall of the carbon nanotubes. The bimetal is any one of cobalt, nickel, copper and zinc combined with iron.

8. A sodium battery negative electrode, characterized in that, The composite material prepared by the method for preparing carbon nanotube confined growth bimetallic selenide heterojunction composite material according to any one of claims 1 to 6, or the composite material according to claim 7.

9. A sodium battery, characterized in that, Includes the sodium battery negative electrode as described in claim 8.

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