Constructing 0D / 2D / 3D defects in WO3 / MoO2 for magnesium ion battery cathode materials

Abstract

The invention discloses the construction of 0D / 2D / 3D defects in WO3 / MoO2 and its application in magnesium ion battery positive electrode materials, belonging to the technical field of battery materials. Sodium tungstate dihydrate and sodium molybdate dihydrate are configured into an aqueous solution with a concentration of 0.2M in a molar ratio of 3:1, and then mixed evenly with a 0.3M glucose aqueous solution, 1M hydrochloric acid is added dropwise, the pH value of the mixed solution is adjusted to 2, and the mixture is hydrothermally heated at 200°C for 8h in a reactor; then, the mixture is washed with deionized water and ethanol for 3 times, dried, and the positive electrode material WO3 / MoO2 of the magnesium ion battery is obtained. The invention realizes the simultaneous construction of 0D / 2D / 3D structural defects in WO3 / MoO2 by a one-step hydrothermal method, exposes more active sites, improves the diffusion rate of magnesium ions while ensuring structural stability, and thus improves the electrochemical performance of the magnesium ion battery. The magnesium ion battery assembled by the method has high specific capacity, excellent cycle stability and rate capability, and has broad application prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of battery materials, and in particular to the construction of 0D / 2D / 3D defects in WO3 / MoO2 and their application in positive electrode materials for magnesium ion batteries. Background Art

[0002] In recent years, magnesium-ion batteries, which use magnesium metal as the negative electrode material, have developed rapidly and are expected to become the next generation of ion batteries. However, due to the low exposure of the active sites of magnesium ions and the serious structural damage of the positive electrode materials during the charge and discharge process, magnesium-ion batteries face problems such as low specific capacity, poor reaction kinetics, and cycle instability, which limits the further development of magnesium-ion batteries. Therefore, it is still a very challenging task to modify the positive electrode materials of magnesium-ion batteries to improve their electrochemical performance. Among the various modification strategies, defect engineering and the construction of amorphous structures can be used to modify positive electrode materials, which is a very meaningful work to promote the development of magnesium-ion batteries.

[0003] Crystal defects can provide more active sites for active materials, accelerate ion transfer and stabilize the structure. Defects are mainly divided into point defects (0D), line defects (1D), surface defects (2D) and body defects (3D). Rich vacancies, as typical 0D structural defects, reduce the activation energy of electrochemical reactions of electrochemically active species, and have abundant localized electrons, which can be used as functional sites to modify electrode materials (see literature: Atomic-scale unveiling of multiphase evolution during hydrated Zn-ion insertion in vanadium oxide, Byeon et al. Nat. Commun., 2021, 12, 4599). 2D surface defects are usually established by constructing heterojunctions, which are composed of various materials. It is well known that when semiconductor materials with different band gap structures come into contact with each other, electrons on the 2D defect heterointerface will flow unidirectionally, thereby forming a built-in electric field on the 2D defect heterointerface, accelerating the migration dynamics of ions (see reference: Boosted Charge Transfer in SnS / SnO2 Heterostructures: Toward High Rate Capability for Sodium-Ion Batteries, Zheng et al. Angew Chem. Int. Ed., 2016, 55, 3408-3413). Since magnesium ions tend to be adsorbed in negative charge accumulation areas, a so-called "ion pool" is generated, thereby increasing the specific capacity of magnesium ion batteries (see reference: Constructing CoO / Co3S4 HeterostructuresEmbedded in N-doped Carbon Frameworks for High-Performance Sodium-Ion Batteries, Adv. Funct. Mater., 2019, 29, 1901925). In addition to 0D and 2D structural defects, the reduction of active material crystallinity and even 3D bulk defects caused by disordered atomic arrangement in the amorphous phase can be exploited to optimize active sites, structural stability, and diffusion kinetics.Compared with crystalline materials with intrinsic anisotropy, although amorphous atoms have the characteristics of long-range random arrangement of atoms, a large number of oriented random bonds and unsaturated electronic configurations, which make the material have greater elastic contraction and higher tensile strength, the van der Waals force connecting the structure is weak, which will cause the amorphous layer to peel off, resulting in structural distortion or even collapse (see reference: 2D amorphous-MoO3-x@Ti3C2-MXene non-van der Waalsheterostructures as anode materials for lithium-ion batteries, Nano Energy, 2021, 86, 106139). Therefore, combining the amorphous structure with the crystal structure, that is, reducing the crystallinity of the crystal structure, can simultaneously maintain the advantages of the crystal and amorphous structures, and ensure the rapid and stable diffusion of magnesium ions while maintaining structural stability. However, there are few reports on the synergistic effect of multidimensional defects (0D / 2D / 3D) in the structure of positive electrode materials to improve the electrochemical performance of ion batteries.

[0004] The present invention constructs 0D / 2D / 3D defects in WO3 / MoO2 by a one-step hydrothermal method and applies them to positive electrode materials of magnesium ion batteries to study their electrochemical properties. The electrochemical performance test results show that under the synergistic effect of 0D / 2D / 3D structural defects, WO3 / MoO2 exhibits excellent electrochemical cycle performance and rate performance. -1 At a current density of 1.34 W / m, after 600 cycles, the specific capacity of WO3 / MoO2 can be stably maintained at 112.8 mAh g -1 About, and when the current density reaches 1A g -1 It shows good rate performance, which is of great significance for the development of new magnesium ion battery positive electrode materials. Summary of the invention

[0005] The purpose of the present invention is to provide a positive electrode material for a magnesium ion battery, in particular to provide 0D / 2D / 3D defects constructed in WO3 / MoO2 for application in a positive electrode material for a magnesium ion battery, and to explore its application in magnesium ion batteries. Under the synergistic effect of 0D / 2D / 3D defects, WO3 / MoO2 exhibits good cycle stability and high rate performance.

[0006] To achieve the above-mentioned purpose of the invention, the preparation process of constructing 0D / 2D / 3D defects in WO3 / MoO2 for magnesium ion battery positive electrode material provided by the present invention comprises the following steps:

[0007] 1. Sodium tungstate dihydrate and sodium molybdate dihydrate were weighed in a molar ratio of 3:1, respectively, and an aqueous solution with a concentration of 0.2M was prepared. The mixture was magnetically stirred at room temperature until completely dissolved to obtain solution A;

[0008] 2. Prepare a 0.3M glucose aqueous solution and stir it magnetically at room temperature until it is completely dissolved to obtain solution B;

[0009] 3. Pour solution B into solution A and continue magnetic stirring at room temperature until the two solutions are completely mixed;

[0010] 4. While magnetically stirring, add 1M hydrochloric acid dropwise to the mixed solution to adjust the pH value of the mixed solution to 2;

[0011] 5. Transfer the fully mixed mixed solution to a 100 ml reactor for hydrothermal reaction at a temperature of 200°C for 8 hours. After the reaction is completed, cool the mixture to room temperature.

[0012] 6. Wash with deionized water and anhydrous ethanol three times respectively, collect the precipitate by centrifugation, and dry the precipitate in a drying oven at a drying temperature of 60°C for 12 hours to obtain a WO3 / MoO2 composite.

[0013] The present invention also provides the use of WO3 / MoO2 as a positive electrode material for a magnesium ion battery. The WO3 / MoO2 is made into a positive electrode sheet and assembled into a button cell 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 0.2-2.1V and the current density is 0.05-1A g -1 .

[0014] The advantages of the WO3 / MoO2 magnesium ion battery positive electrode material provided by the present invention are:

[0015] 1. The present invention is used to simultaneously construct multi-dimensional structural defects (0D / 2D / 3D) in WO3 / MoO2 and used as a positive electrode material for magnesium ion batteries;

[0016] 2. The WO3 / MoO2 magnesium ion battery positive electrode material with 0D / 2D / 3D structural defects prepared by the present invention improves the conductivity of WO3 / MoO2 due to the synergistic effect of the structural defects of oxygen-rich vacancies (0D), heterogeneous interfaces (2D) and reduced crystallinity (3D), generates an ion pool that can adsorb a large amount of magnesium ions, provides a fast channel for the diffusion of magnesium ions, and maintains a stable structure, which is beneficial to improving the electrochemical performance of the magnesium ion battery.

[0017] 3. The WO3 / MoO2 prepared by the present invention as the positive electrode material of magnesium ion battery exhibits excellent electrochemical performance: at 0.05A g -1 A long cycle life of 600 cycles was achieved at a current density of 1.37 W / m and a specific capacity of 112.8 mAh g -1 and when the current density reaches 1A g -1 It shows good rate performance.

[0018] 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

[0019] 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:

[0020] Figure 1 The XRD diagram of the WO3 / MoO2 magnesium ion battery positive electrode material obtained in the embodiment;

[0021] Figure 2 This is a HRTEM photo of the WO3 / MoO2 magnesium ion battery positive electrode material obtained in the example;

[0022] Figure 3 This is the EPR image of the WO3 / MoO2 magnesium ion battery positive electrode material obtained in the embodiment;

[0023] Figure 4 This is the W high-resolution XPS spectrum of the WO3 / MoO2 magnesium ion battery positive electrode material obtained in the embodiment;

[0024] Figure 5 This is the Mo high-resolution XPS spectrum of the WO3 / MoO2 magnesium ion battery positive electrode material obtained in the example;

[0025] Figure 6 The cycle performance curve and rate performance curve of the WO3 / MoO2 magnesium ion battery positive electrode material obtained in the embodiment; DETAILED DESCRIPTION

[0026] 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.

[0027] Example

[0028] Constructing 0D / 2D / 3D defects in WO3 / MoO2 for magnesium ion battery cathode materials

[0029] Weigh 0.9895g of sodium tungstate dihydrate and 0.2420g of sodium molybdate dihydrate, dissolve the two drugs in 20ml of deionized water, and stir them thoroughly at room temperature until they are completely dissolved to obtain solution A; at the same time, weigh 1.1895g of glucose and dissolve it in 20ml of deionized water, stir them thoroughly at room temperature until they are completely dissolved to obtain solution B; mix solution B and solution A thoroughly, and then add 1M hydrochloric acid solution drop by drop during magnetic stirring until the pH value of the solution is adjusted to 2. Transfer the fully mixed mixed solution to a 100ml reactor for hydrothermal reaction at a temperature of 200°C and a reaction time of 8h. After the reaction is completed, cool it to room temperature with the furnace; wash it with deionized water and anhydrous ethanol three times respectively, collect the product by centrifugation, and dry the obtained product in a drying oven at a temperature of 60°C and a drying time of 12h to obtain WO3 / MoO2 rich in 0D / 2D / 3D defects.

[0030] In the XRD results ( Figure 1 ) can be observed that the diffraction peaks of WO3 / MoO2 can correspond to monoclinic WO3 and monoclinic MoO2 respectively, which can preliminarily prove the successful construction of WO3 / MoO2 composite after hydrothermal reaction. In addition, broadened diffraction peaks can be clearly observed in XRD, indicating that the crystallinity of WO3 / MoO2 decreases. In the HRTEM image ( Figure 2 ) can be observed in two places, and the interplanar spacings are 0.2nm and 0.18nm, corresponding to the (132) crystal plane of monoclinic WO3 and the (-301) crystal plane of monoclinic MoO2, respectively, which further proves the successful construction of the WO3 / MoO2 complex. In addition, discontinuous parts can be observed in the lattice fringes, which can preliminarily infer the formation of abundant oxygen vacancies (0D defects), and the lattice fringes are relatively blurred, which reflects the information consistent with the wide diffraction peaks in the XRD results, which can explain its poor crystallinity (3D defects). At the same time, it can be observed that the two different crystal planes are in direct contact, forming a clear interface between WO3 and MoO2, and producing a heterogeneous interface (2D defects). The EPR spectrum of WO3 / MoO2 ( Figure 3 ) shows a strong signal peak at g = 2.004, indicating that there are abundant O vacancies in WO3 / MoO2, further proving that 0D defects are successfully constructed in WO3 / MoO2. High-resolution XPS spectrum of W ( Figure 4 ) shows that W has both +5 and +6 valence states, where the presence of +5 valence W indicates the presence of O vacancies. The high-resolution XPS spectrum of Mo ( Figure 5 ) simultaneously shows the +3 and +4 valence states, among which the presence of +3 Mo also indicates the existence of O vacancies, further proving that 0D defects are successfully constructed in WO3 / MoO2.

[0031] The synthesized WO3 / MoO2 powder was used as the positive electrode active material, and was evenly mixed with carbon black and a binder (polyvinylidene fluoride PVDF) in 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 ion 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 ion 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 0.05 to 1 A g -1 .

[0032] The electrochemical properties of the obtained product WO3 / MoO2 are shown in the attached manual. Figure 6 , at 0.05A g -1 At a current density of 1.3 2.0 Å, WO3 / MoO2 achieved 600 cycles, and the specific capacity was maintained at 112.8 mAh g during the cycle. -1 At the same time, WO3 / MoO2 has a current density of 0.05A g -1 Gradually increase to 1A g -1 When the specific capacity is 118.3 mAh g -1 Change to 52.4mAh g -1 , and when the current density drops to 0.05A g -1 When -1 , showing excellent rate performance.

Claims

1. Construction of 0D / 2D / 3D defects in WO3 / MoO2 for magnesium ion battery positive electrode materials, characterized in that: The preparation process is as follows: Weigh sodium tungstate dihydrate and sodium molybdate dihydrate in a molar ratio of 3:1, prepare an aqueous solution with a concentration of 0.2M, and continue magnetic stirring until completely dissolved; prepare an aqueous glucose solution with a concentration of 0.3M, and magnetically stir at room temperature until completely dissolved; mix the above two solutions, and under the condition of magnetic stirring, add 1M hydrochloric acid drop by drop to adjust the pH value of the mixed solution to 2; transfer the mixed solution to a reactor for hydrothermal reaction at a reaction temperature of 200°C and a reaction time of 8h, and cool with the furnace after the reaction is completed; wash with deionized water and anhydrous ethanol for 3 times respectively, collect the product by centrifugation, and dry the obtained product to obtain a WO3 / MoO2 positive electrode material having oxygen-rich vacancies 0D, heterogeneous interfaces 2D and reduced crystallinity 3D; The obtained WO3 / MoO2 was used as the positive electrode material to assemble a button-type magnesium ion battery. The voltage window of the electrochemical performance test was 0.2-2.1V, and the current density was 0.05-1A. -1 .

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