A method for preparing nitrogen-doped carbon tube-wrapped metal nitride electrode material

Abstract

The invention discloses a preparation method of a nitrogen-doped carbon tube-wrapped metal nitride electrode material, wherein a metal salt and urea are dissolved in deionized water to obtain a metal salt solution and a urea solution respectively; the urea solution is added to the metal salt solution, and after magnetic stirring, a hydrothermal reaction is carried out in a reactor to obtain a powder, which is washed, filtered, and dried to obtain a precursor; the precursor and a nitrogen source are mixed, and after a tubular furnace is evacuated, a hydrogen-argon mixed gas is introduced, the temperature is raised and kept, and the nitrogen-doped carbon tube-wrapped metal nitride electrode material is obtained. The preparation method forms a composite electrode by compounding metal nitride particles with a nitrogen-doped carbon tube structure, significantly enhancing the electronic conductivity and polarity of the carbon material, enhancing the adsorption capacity for LiPSs, and accelerating the reaction kinetics process; effectively avoiding agglomeration, maintaining good stability after long-term circulation, and the hollow structure of the nitrogen-doped carbon tube can slow down the volume effect during the charge and discharge process, and achieve excellent performance. It has broad application prospects in the field of energy storage.

Description

Technical Field

[0001] The invention belongs to the technical field of electrode materials and relates to a method for preparing a nitrogen-doped carbon tube-wrapped metal nitride electrode material. Background Art

[0002] High-energy storage devices are used for energy storage and redistribution. Among many energy storage devices, lithium-sulfur batteries have the advantages of high theoretical specific capacity (1675 mAh / g), low cost, and environmental friendliness, and are considered to be one of the most promising next-generation energy storage systems. However, the practical development of lithium-sulfur batteries is still restricted by many factors, especially the shuttle effect caused by soluble lithium polysulfides (LiPSs) and the slow reaction kinetics during charging and discharging.

[0003] In recent years, the electrocatalytic sulfur host materials that synergistically adsorb LiPSs and catalyze their redox reactions have been developed to inhibit the shuttle effect of LiPSs and improve their reaction kinetics, thereby improving the electrochemical performance of the battery. Metal nitrides are a typical interstitial compound, with nitrogen atoms located in the gaps between metal dense packings. Theoretical calculations and analysis show that metal nitrides have conductivity comparable to that of metals, which undoubtedly provides an excellent solution for the rapid conversion of LiPSs. However, in actual use, the preparation process of metal nitrides is often complicated, and in most cases dangerous ammonia is required, which poses new challenges to the low-cost, safe, and large-scale preparation of metal nitrides. At the same time, metal nitride particles are easy to agglomerate, resulting in poor stability of metal nitrides (100-cycle capacity retention rate <50%), poor rate performance (<50%), and (first-cycle specific capacity is less than 1000mAh / g). Summary of the invention

[0004] The purpose of the present invention is to provide a method for preparing a nitrogen-doped carbon tube-wrapped metal nitride electrode material to improve the stability of the metal nitride.

[0005] To achieve the above object, the technical solution adopted by the present invention is: a method for preparing a nitrogen-doped carbon tube-wrapped metal nitride electrode material, which is carried out according to the following steps:

[0006] 1) Take metal salt and urea separately in a molar ratio of 1:1;

[0007] Dissolve the metal salt in deionized water at a ratio of 1 mmol of the metal salt to 5 to 50 mL of deionized water to obtain a metal salt solution;

[0008] The metal salt is cobalt nitrate, cobalt chloride, cobalt sulfate, cobalt acetate, nickel nitrate, nickel chloride, nickel sulfate, nickel acetate, ferric nitrate, ferric chloride, ferric sulfate or ferric acetate.

[0009] Dissolve urea in deionized water at a ratio of 1 mmol of urea to 5-50 mL of deionized water to obtain a urea solution;

[0010] 2) adding the urea solution to the metal salt solution, stirring magnetically for 1 to 5 hours at a temperature of 10 to 40°C, and mixing thoroughly to obtain a mixed solution;

[0011] 3) placing the mixed solution in a reactor lined with polytetrafluoroethylene, and performing a hydrothermal reaction at 90-150°C for 4-12 hours to obtain a powder, washing the powder with deionized water for 3 times, and drying the powder at 50-100°C for 4-12 hours to obtain a precursor;

[0012] 4) Precursors and nitrogen sources are taken at a mass ratio of 1:0.1-5, mixed, and placed in a tube furnace. After evacuation, a hydrogen-argon mixed gas is introduced, and the temperature is increased to 200-800°C at a heating rate of 1-10°C / min, kept at this temperature for 1-4 hours, and naturally cooled to room temperature to obtain nitrogen-doped carbon tube-wrapped metal nitride electrode materials.

[0013] The nitrogen source is melamine, dicyandiamide, urea, biuret, polyvinyl pyrrolidone, ammonium carbonate or ammonium bicarbonate.

[0014] The hydrogen-argon mixed gas is composed of hydrogen and argon in a volume ratio of 1:5 to 10.

[0015] The preparation method of the present invention uses the carbon source atmosphere and ammonia generated by the high-temperature decomposition of nitrogen-containing organic matter as the source, and at the same time, the precursor is converted into a metal nitride in situ, and the nano-sized metal nitride particles are wrapped in nitrogen-doped carbon tubes to form a composite structure. The problem of metal nitride particles being easy to agglomerate, resulting in poor stability, poor rate performance, and low first-cycle specific capacity of metal nitrides is solved, thereby solving the problem of slow reaction kinetics, blocked charge transfer, and poor coulomb efficiency of metal nitride nanoparticles in lithium-sulfur batteries, thereby deteriorating performance. At the same time, compared with simple carbon material coating, nitrogen doping can significantly enhance the electronic conductivity and polarity of carbon materials, enhance their adsorption capacity for LiPSs, and accelerate the reaction kinetics process. To this end, the preparation method of the present invention utilizes a metal salt solution to perform a hydrothermal reaction to prepare a precursor, and adopts a method of nitriding and carbonizing nitrogen-containing organic matter, while the precursor is in situ converted into a metal nitride, it is coated in a nitrogen-doped carbon tube, and the carbon tube coating layer can enhance the conductivity, buffer the volume change, avoid the agglomeration of metal nitride particles, shorten the ion transmission path, and achieve excellent rate performance and cycle stability.

[0016] The preparation method of the present invention mainly solves the problems of poor stability, electron conduction, low polarity, weak adsorption of LiPSs, and lack of active sites on the surface of the sulfur host material in the lithium-sulfur battery. The metal nitride electrode material is wrapped with nitrogen-doped carbon tubes through the in-situ nitridation and carbonization method of nitrogen-containing organic matter. The conductivity of the sulfur host material is effectively improved, the LiPSs conversion kinetics are accelerated, the surface active sites of the sulfur host material are optimized, and the adsorption capacity of LiPSs is enhanced. The high conductivity and structural stability of the nitrogen-doped carbon nanotubes promote the transmission of electrons and ions while ensuring the excellent stability of the sulfur host material. The nano-sized metal nitride can effectively alleviate the volume change during the charge and discharge process. Multiple aspects work together to achieve excellent performance.

[0017] The nitrogen-doped carbon tube-wrapped metal nitride electrode material prepared by the preparation method of the present invention is used for preparing lithium-sulfur batteries.

[0018] The preparation method of the present invention has the following advantages:

[0019] 1. Metal nitride particles are combined with nitrogen-doped carbon tube structures to form a composite electrode. While the carbon tube coating improves the stability, nitrogen doping can significantly enhance the electronic conductivity and polarity of the carbon material, enhance its adsorption capacity for LiPSs, and accelerate the reaction kinetics. This mainly solves the problems of slow reaction kinetics of metal nitride nanoparticles in lithium-sulfur batteries, hindered charge transfer, and poor coulombic efficiency, which in turn deteriorates performance.

[0020] 2. Metal nitride particles are nanoparticles. On the one hand, the volume change of nanosized particles is small during the electrochemical process, which is conducive to improving stability; on the other hand, the larger specific surface area of ​​nanosized particles provides more active sites during the electrochemical process, effectively shortening the diffusion path of ions.

[0021] 3. The precursor is prepared by a hydrothermal reaction method, and the precursor is directly converted into a nitrogen-doped carbon tube-wrapped metal nitride particle electrode after calcination. Compared with the metal nitride obtained by calcination under existing ammonia conditions, it has the advantages of simple preparation method, low cost, no ammonia in the synthesis process, and high safety. The lithium-sulfur battery made of the electrode material prepared by the preparation method of the present invention has excellent performance, and the actual specific capacity reaches 1125 mAh / g. After 100 cycles at a current density of 0.2C, the specific capacity can reach 676 mAh / g.

[0022] 4. The prepared electrode material effectively improves the utilization rate of active materials, has excellent conductivity, polarity and stability, and can be used as an ideal lithium-sulfur battery electrode material. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a scanned image of the electrode material obtained in Example 1.

[0024] Figure 2 This is a transmission image of the electrode material obtained in Example 1.

[0025] Figure 3 This is a high-resolution transmission image of the electrode material obtained in Example 1.

[0026] Figure 4 It is the charge and discharge curve diagram of the electrode material obtained in Example 1.

[0027] Figure 5 It is a cycle stability curve diagram of the electrode material prepared in Example 1 at a current density of 0.2C. DETAILED DESCRIPTION

[0028] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0029] Example 1

[0030] 1 mmol of cobalt chloride was dissolved in 30 mL of deionized water to obtain a cobalt chloride solution; 1 mmol of urea was dissolved in 40 mL of deionized water to obtain a urea solution; the urea solution was added to the cobalt chloride solution, and magnetic stirring was performed at 30°C for 2 hours to fully mix to obtain a mixed solution; the mixed solution was placed in a reactor with a polytetrafluoroethylene liner, and hydrothermally reacted at 120°C for 12 hours to obtain a powder, and the powder was washed with deionized water and filtered for multiple times, and then dried at 80°C for 12 hours to obtain a precursor; the precursor and melamine were mixed in a mass ratio of 1:1, placed in a tube furnace, evacuated, and a hydrogen-argon mixed gas (composed of hydrogen and argon in a volume ratio of 1:10) was introduced, and the temperature was increased to 600°C at a heating rate of 4°C / min, kept warm for 2 hours, and naturally cooled to room temperature to obtain a nitrogen-doped carbon tube-wrapped metal nitride electrode material.

[0031] Example 1: The scanning image of the electrode material obtained is as follows: Figure 1 .Depend on Figure 1 It can be seen that the metal nitride is wrapped in nitrogen-doped carbon tubes, and the average diameter of the carbon tubes is about 500 nm.

[0032] Figure 2 is a transmission image of the electrode material prepared in Example 1; Figure 2 It can be seen that the metal nitride nanoparticles are well distributed around the carbon tube wall. At the same time, there is no obvious aggregation of metal nitride crystals on the wall, which also verifies the high dispersibility of metal nitride to a certain extent.

[0033] Figure 3 is a high-resolution transmission image of the electrode material prepared in Example 1; Figure 3 It can be seen that the lattice spacing of 0.25nm belongs to metal nitride (CoN), and the lattice spacing of 0.32nm belongs to carbon nanotube (CNT).

[0034] The electrode material prepared in Example 1 was used as an electrode to assemble a lithium-sulfur battery, and the electrochemical performance was measured. Figure 4 The charge and discharge curves shown in the figure (current density is 0.2C, 0.5C, 1C, 2C respectively). It can be seen that the electrode material of nitrogen-doped carbon tube wrapped metal nitride composite can significantly improve the specific capacity as an electrode. When the current density is 0.2C, the highest specific capacity can reach 1125 mAh / g; when the current density is 2 C, the specific capacity can still reach 601 mAh / g, and the rate performance can reach 53.4%.

[0035] Figure 5 The figure is a cycle stability curve of the electrode material prepared in Example 1 at a current density of 0.2C. The cycle stability test shows that after 100 cycles at a current density of 0.2C, the discharge specific capacity can reach 676 mAh / g, the discharge specific capacity and the charge specific capacity are almost overlapped, and the average coulombic efficiency is close to 100%, proving that the electrode material prepared by the preparation method of the present invention has excellent stability.

[0036] Example 2

[0037] 1 mmol nickel nitrate was dissolved in 5 mL deionized water to obtain a nickel nitrate solution; 1 mmol urea was dissolved in 50 mL deionized water to obtain a urea solution; the urea solution was added to the nickel nitrate solution, magnetically stirred at 10°C for 5 hours, and fully mixed to obtain a mixed solution; the mixed solution was placed in a reactor with a polytetrafluoroethylene liner, and hydrothermally reacted at 90°C for 8 hours to obtain a powder, and the powder was washed with deionized water and filtered for multiple times, and then dried at 50°C for 4 hours to obtain a precursor; the precursor and ammonium carbonate were mixed in a mass ratio of 1:0.1, placed in a tubular furnace, evacuated, and a hydrogen-argon mixed gas (composed of hydrogen and argon in a volume ratio of 1:5) was introduced, and the temperature was increased to 200°C at a heating rate of 1°C / min, kept warm for 4 hours, and naturally cooled to room temperature to obtain a nitrogen-doped carbon tube-wrapped metal nitride electrode material.

[0038] The cycle stability test shows that after 100 cycles at a current density of 0.2C, the specific capacity can reach 742 mAh / g, proving that the electrode material prepared by the preparation method of the present invention has excellent stability.

[0039] Example 3

[0040] 1 mmol of ferric acetate was dissolved in 50 mL of deionized water to obtain a ferric acetate solution; 1 mmol of urea was dissolved in 40 mL of deionized water to obtain a urea solution; the urea solution was added to the ferric acetate solution, magnetically stirred at 40°C for 3 hours, and fully mixed to obtain a mixed solution; the mixed solution was placed in a reactor with a polytetrafluoroethylene liner, and hydrothermally reacted at 150°C for 4 hours to obtain a powder, and the powder was washed with deionized water and filtered for multiple times, and then dried at 100°C for 8 hours to obtain a precursor; the precursor and polyvinyl pyrrolidone were mixed in a mass ratio of 1:5, placed in a tube furnace, evacuated, and a hydrogen-argon mixed gas (composed of hydrogen and argon in a volume ratio of 1:7) was introduced, and the temperature was increased to 800°C at a heating rate of 10°C / min, kept warm for 1 hour, and naturally cooled to room temperature to obtain a nitrogen-doped carbon tube-wrapped metal nitride electrode material.

[0041] The cycle stability test shows that after 100 cycles at a current density of 0.2C, the specific capacity can reach 705 mAh / g, which proves that the electrode material prepared by the preparation method of the present invention has excellent stability.

Claims

1. A method for preparing a nitrogen-doped carbon tube-wrapped metal nitride electrode material, characterized in that: The preparation method is carried out according to the following steps: 1) Take metal salt and urea separately in a molar ratio of 1:1; Dissolve the metal salt in deionized water at a ratio of 1 mmol of the metal salt to 5 to 50 mL of deionized water to obtain a metal salt solution; Dissolve urea in deionized water at a ratio of 1 mmol of urea to 5-50 mL of deionized water to obtain a urea solution; The metal salt is cobalt nitrate, cobalt chloride, cobalt sulfate, cobalt acetate, nickel nitrate, nickel chloride, nickel sulfate, nickel acetate, ferric nitrate, ferric chloride, ferric sulfate or ferric acetate; 2) Add urea solution to metal salt solution and stir magnetically to obtain a mixed solution; 3) The mixed solution is placed in a reactor with a polytetrafluoroethylene liner, and subjected to hydrothermal reaction at 90-150°C for 4-12 hours to obtain a powder, which is then washed with deionized water, filtered, and dried to obtain a precursor; 4) Precursors and nitrogen sources are taken at a mass ratio of 1:0.1-5, mixed, placed in a tube furnace, evacuated, introduced with hydrogen-argon mixed gas, heated to 200-800°C, kept warm for 1-4 hours, and naturally cooled to room temperature to obtain nitrogen-doped carbon tube-wrapped metal nitride electrode materials; The nitrogen source is melamine, dicyandiamide, urea, biuret or polyvinyl pyrrolidone.

2. The method for preparing the nitrogen-doped carbon tube-wrapped metal nitride electrode material according to claim 1, characterized in that: In the step 2), magnetic stirring is performed at a temperature of 10 to 40° C. for 1 to 5 hours.

3. The method for preparing the nitrogen-doped carbon tube-wrapped metal nitride electrode material according to claim 1, characterized in that: In the step 3), after washing with deionized water and filtering, the mixture is dried at 50 to 100° C. for 4 to 12 hours.

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