Method for preparing W / Se vacancy coexisting magnesium battery positive electrode material WSe2 based on vacancy solid solution principle

Abstract

The invention discloses a method for preparing a W / Se vacancy coexisting magnesium battery positive electrode material WSe2 based on a vacancy solid solution principle, and belongs to the technical field of battery materials. The preparation method comprises the following steps: ultrasonically dispersing tungsten powder and selenium powder in absolute ethyl alcohol according to a molar ratio of 1: 2.1, drying, putting a mixture into a tubular furnace, calcining for 2 hours at 800 DEG C in an argon atmosphere, and cooling along with the furnace to obtain WSe2; the obtained WSe2 and selenium powder are placed in a tube furnace heating area, the selenium powder is located at the upstream of airflow, calcination is conducted for 1 h at the temperature of 400 DEG C in the argon / hydrogen mixed atmosphere, and W / Se vacancy coexisting WSe2 is obtained after furnace cooling. Based on a vacancy solid solution principle, a simple calcination method is adopted, and coexistence of W vacancies and Se vacancies and a synergistic effect of the W vacancies and the Se vacancies are realized in a WSe2 structure, so that the magnesium storage specific capacity is increased, rapid diffusion of magnesium ions is promoted, and the electrochemical performance of the magnesium battery is improved. The magnesium battery assembled by the composite material has high specific capacity, excellent cycling stability and rate capability, and has a wide application prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of battery materials, and in particular to a method for preparing WSe2, a magnesium battery positive electrode material with coexisting W / Se vacancies, based on the vacancy solid solution principle. Background Art

[0002] Magnesium metal has the advantages of low cost, high specific capacity, low reduction potential and low dendrite formation. Therefore, magnesium batteries using magnesium metal as the negative electrode have attracted widespread attention. However, the charge imbalance during the embedding and extraction of multivalent ions in the positive electrode material leads to problems such as low specific capacity, poor cycle stability, unsatisfactory rate performance and slow migration kinetics of magnesium batteries. This greatly limits the development of magnesium batteries. In this case, it is necessary to explore the design and preparation methods of reasonable positive electrode materials to improve the electrochemical performance of rechargeable magnesium batteries.

[0003] Vacancy engineering is a simple and commonly used design strategy for cathode materials, which can effectively regulate the electronic properties of cathode materials and modify the surface properties of cathode materials, thereby enhancing their electrochemical performance without changing the intrinsic structural properties of cathode materials. Anion vacancies can effectively improve the surface chemical properties of cathode materials, thereby enhancing the conductivity of cathode materials, regulating the diffusion channels of magnesium ions and increasing active sites (reference: Interior-Confined Vacancy in Potassium Manganese Hexacyanoferrate for Ultra-Stable Potassium-Ion Batteries, Advanced Materials, 2024, 2310428). In addition, cation vacancies, as a type of vacancy, can also reduce the electrostatic interaction between magnesium ions and the cation lattice of cathode materials, thereby effectively reducing the diffusion barrier of magnesium ions. Therefore, when anion vacancies and cation vacancies are introduced simultaneously in the positive electrode material, the advantages of anion and cation vacancies can be fully utilized, thereby fully improving the magnesium storage performance of the positive electrode material (reference: Improved ions storage performance for various batteries: Anatase TiO2 with high-concentration of Ti vacancies, Materials Chemistry and Physics, 2023, 301, 127591). For the introduction of anion vacancies, anions can be removed from the structure by being reduced, while the introduction of cation vacancies is more difficult, and the introduction of anion vacancies and cation vacancies in the structure at the same time faces huge challenges. According to the vacancy solid solution principle, in a compound-based solid solution, when one of the components of the compound is dissolved into the compound, vacancies are formed at certain atomic positions of the other component. Therefore, by introducing another component in a superstoichiometric amount during the preparation of the compound, it is possible to effectively construct cation vacancies. Based on the above principles, it can be seen that in the process of constructing positive electrode materials, by introducing an atmosphere of superstoichiometric another component and under the support of a reducing atmosphere, it is possible to simultaneously introduce anion vacancies and cation vacancies into the structure. This has rarely been reported for the construction of positive electrode materials for magnesium batteries to improve their magnesium storage performance.

[0004] In summary, based on the principle of vacancy solid solution, the present invention adopts calcination method in an argon / hydrogen mixed atmosphere and an atmosphere of excess selenium powder to simultaneously construct W vacancies and Se vacancies in the WSe2 structure, and applies them to positive electrode materials of magnesium batteries, and studies their electrochemical properties. The electrochemical performance test results show that, thanks to the synergistic effect of W vacancies and Se vacancies, WSe2 with coexistence of W / Se vacancies exhibits excellent electrochemical cycle performance and rate performance, and at 50 mA g -1 At a current density of 1.5 MW, the specific capacity of WSe2 can be stably maintained at 140 mAh g -1 About, and when the current density reaches 1000mA g -1 It shows good rate performance, and during 2700 cycles, the specific capacity retention rate reaches 96%, which is of great significance for the development of new magnesium battery positive electrode materials. Summary of the invention

[0005] The purpose of the present invention is to provide a preparation method for simultaneously introducing anion / cation vacancies, and in particular to provide a method for preparing W / Se vacancies coexisting as a magnesium battery positive electrode material WSe2 based on the vacancy solid solution principle, and to explore the application of W / Se vacancies coexisting WSe2 as a positive electrode material in magnesium batteries. Under the synergistic effect of W vacancies and Se vacancies, the W / Se vacancies coexisting WSe2 prepared by this method exhibits good cycle stability and high rate performance.

[0006] To achieve the above-mentioned purpose of the invention, the process of preparing W / Se vacancy coexisting magnesium battery positive electrode material WSe2 based on the vacancy solid solution principle provided by the present invention comprises the following steps:

[0007] 1. Weigh tungsten powder and selenium powder in a molar ratio of 1:2.1, put them into anhydrous ethanol and ultrasonically disperse them for 2 hours;

[0008] 2. Collect the mixture by centrifugation and dry it in a drying oven at 60°C for 12 hours;

[0009] 3. Place the dried mixture in the heating zone of a tube furnace and calcine at 800°C for 2 h under an argon atmosphere, and then cool the furnace to obtain WSe2;

[0010] 4. Place the obtained WSe2 and selenium powder in two porcelain boats respectively, place the selenium powder upstream in the heating zone of a tubular furnace, calcine at 400°C for 1h in an argon / hydrogen mixed atmosphere, and obtain WSe2 with coexisting W / Se vacancies after cooling in the furnace.

[0011] The present invention also provides an application of WSe2 with coexisting W / Se vacancies as a positive electrode material for a magnesium battery. The WSe2 with coexisting W / Se vacancies is made into a positive electrode sheet and assembled into a button battery with a metal magnesium negative electrode material, a glass fiber separator and an APC-THF electrolyte. After the assembled battery is left to stand for 24 hours, an electrochemical performance test is performed on a CT2001A battery program-controlled tester. The test voltage window is 0.2 to 2.1 V and the current density is 50 to 1000 mA g -1 .

[0012] The advantages of the WSe2 magnesium battery positive electrode material with coexistence of W / Se vacancies provided by the present invention are:

[0013] 1. The preparation method based on the vacancy solid solution principle of the present invention is used to prepare WSe2 with coexistence of W / Se vacancies, and used as the positive electrode material of magnesium battery;

[0014] 2. The synergistic effect of W and Se vacancies in WSe2 prepared by the present invention can improve its electrochemical performance as a positive electrode material in a magnesium battery. The presence of Se vacancies can expose more active sites, promote WSe2 to adsorb more magnesium ions, and improve specific capacity. W vacancies can reduce the electrostatic repulsion between magnesium ions and the W lattice in the positive electrode material to promote the rapid diffusion of magnesium ions and improve its rate performance.

[0015] 3. The WSe2 prepared by the present invention with coexisting W / Se vacancies is used as the positive electrode material of magnesium battery, which shows excellent electrochemical performance: at 50 mA g -1 At a current density of 1.5 %, the specific capacity remains stable at 140 mAh g -1 When the current density reaches 1000mA g -1 It showed good rate performance, and the specific capacity retention rate reached 97.6% during 2700 cycles.

[0016] The concept, structure and technical effects of the present invention are further described below in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the following specific embodiments, they are used to explain the present invention but do not constitute a limitation of the present invention. In the accompanying drawings:

[0018] Figure 1 The XRD diagram of the WSe2 magnesium battery positive electrode material with coexisting W / Se vacancies obtained in the embodiment;

[0019] Figure 2 This is a HRTEM image of the WSe2 magnesium battery positive electrode material with coexisting W / Se vacancies obtained in the example;

[0020] Figure 3 This is the EPR spectrum of the WSe2 magnesium battery positive electrode material with coexisting W / Se vacancies obtained in the example;

[0021] Figure 4 The cycle performance curve and rate performance curve of the WSe2 magnesium battery positive electrode material with coexisting W / Se vacancies obtained in the embodiment;

[0022] Figure 5 The cycle performance curve of the WSe2 magnesium battery positive electrode material with coexisting W / Se vacancies obtained in the embodiment at a high current density; DETAILED DESCRIPTION

[0023] The present invention is further described in detail below with reference to specific examples, but these examples do not limit the scope of the present invention in any way.

[0024] Example

[0025] Tungsten powder and selenium powder were weighed separately according to the molar ratio of 1:2.1, added to anhydrous ethanol and ultrasonically dispersed for 2 hours, the mixture was collected by centrifugation, and dried in a drying oven at a temperature of 60°C for 12 hours; the dried mixture was placed in the heating zone of a tubular furnace, calcined at 800°C for 2 hours under an argon atmosphere, and WSe2 was obtained after cooling with the furnace. Subsequently, the prepared WSe2 and selenium powder were placed in different porcelain boats respectively and placed in the heating zone of a tubular furnace. The porcelain boat containing selenium powder was placed in the upstream area of ​​the airflow, and the porcelain boat containing WSe2 was placed in the downstream area of ​​the airflow. In a mixed atmosphere of argon / hydrogen, calcined at 400°C for 1 hour, and WSe2 with coexistence of W / Se vacancies was obtained after cooling with the furnace.

[0026] XRD results ( Figure 1 ) can be observed the diffraction peak of WSe2, proving that the method of the present invention can be used to prepare WSe2 without changing the physical phase of WSe2. Figure 2 ) can be clearly observed in many discontinuous lattice fringes, indicating that there are a large number of vacancies in the WSe2 structure. Figure 3 ) Two signal peaks can be clearly observed at g = 2.002 and g = 1.979, which correspond to Se vacancies and W vacancies respectively, indicating that a large number of vacancies in the WSe2 structure are composed of both W vacancies and Se vacancies.

[0027] The synthesized WSe2 powder with coexisting W / Se vacancies was used as the positive electrode active material, and was uniformly mixed with carbon black and binder (polyvinylidene fluoride PVDF) at a mass ratio of 6:3:1, and then the organic solvent 1-methyl-2-pyrrolidone was added and ground to a viscous state. The slurry was coated on the conductive current collector carbon paper with an I-shaped coater and then placed in a 60°C oven for drying for 12 hours. The dried electrode sheet was cut into a disc with a diameter of 12 mm using a cutting machine as the positive electrode of the magnesium battery. The 0.1 mm thick magnesium foil was sandpapered to remove the oxide layer on the surface, and was cut into a disc with a diameter of 16 mm using a cutting machine as the negative electrode of the magnesium battery, and a glass fiber filter membrane was used as a diaphragm, and 0.4 M APC / THF was used as the electrolyte, and button cells were assembled in a glove box with an argon atmosphere. After the assembled button cell was left to stand for 24 h, the electrochemical performance was tested on a CT2001A battery programmable tester with a test voltage window of 0.2 to 2.1 V and a current density of 50 to 1000 mA g -1 .

[0028] From the instruction manual Figure 4 and Figure 5 It can be seen that the W / Se vacancy coexistence WSe2 product is 50mA g -1 At a current density of 1.34 W, the specific capacity is maintained at 140 mAh g during the cycle. -1 At the same time, WSe2 with coexistence of W / Se vacancies is -1 Gradually increase to 500mA g -1 When the specific capacity is 145.5mAh g -1 Change to 54.8mAh g -1 , and when the current density drops back to 50 mA g -1 When -1 , showing excellent rate performance ( Figure 4 ). At 1000mA g -1 At a current density of 1.3 Å, WSe2 with coexisting W / Se vacancies can be cycled for 2700 times, and the capacity retention rate can reach 97.6% ( Figure 5 ).

Claims

1. A method for preparing WSe2, a magnesium battery positive electrode material with coexistence of W / Se vacancies, based on the vacancy solid solution principle, characterized in that: The preparation process is as follows: Tungsten powder and selenium powder were weighed respectively in a molar ratio of 1:2.1, ultrasonically dispersed in anhydrous ethanol for 2 hours, the mixture was collected by centrifugation and placed in a tubular furnace, calcined at 800°C for 2 hours under argon atmosphere, and cooled in the furnace to obtain WSe2; the obtained WSe2 and selenium powder were respectively placed in two porcelain boats, which were placed in the heating zone of the tubular furnace, with the selenium powder placed upstream of the gas, and calcined at 400°C for 1 hour under a mixed atmosphere of argon / hydrogen, and cooled in the furnace to obtain WSe2 with coexistence of W / Se vacancies. The obtained W / Se vacancy coexisting WSe2 was used as the positive electrode material to assemble a button-type magnesium battery. The voltage window of the electrochemical performance test was 0.2-2.1V, and the current density was 50-1000mAg -1 .

2. The method of preparing W / Se vacancy coexisting magnesium battery positive electrode material WSe2 based on the vacancy solid solution principle according to claim 1, characterized in that: Under the synergistic effect of W and Se vacancies, the adsorption active sites of magnesium ions can be increased, the diffusion of magnesium ions can be promoted, and the structural stability during the magnesium storage process can be maintained.

3. The method of preparing W / Se vacancy coexisting magnesium battery positive electrode material WSe2 based on the vacancy solid solution principle according to claim 1, characterized in that: The specific capacity of the prepared positive electrode material used in magnesium batteries is 140 mAh g -1 Around 1000mAg -1 The cycle life is 2700 cycles at the current density and has good rate performance.

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