Template-Free Hydroxyl-Induced Synthesis Of Three-Dimensional Ordered Structure Vanadium Disulfide And Its Sodium/Potassium Storage Properties

Large-scale storage of intermittent renewable clean energy is an important challenge in energy sector.Lithium ion batteries?LIB?are currently the most widely used high-efficiency energy storage devices.However,due to the limited lithium reserves of the earth's crust,the high cost of lithium-ion batteries has limited its application as a large-scale energy storage for renewable energy.In order to reduce energy storage costs,low-cost sodium ion batteries?SIB?and potassium ion batteries?KIB?have attracted widespread attention.However,because of the large size of and the sluggish kinetics Na ions and K ions,the anode material suitable for LIB is not necessarily suitable for SIB and KIB.The layered transition metal dichalcogenides?TMDs?have a graphite-like two-dimensional layered structure,which has a wider lattice spacing than graphite,providing transmission channels and more active sites for the Na⁺/K⁺/electrons,resulting in excellent sodium storage and potassium storage properties.However,the morphology of the commercially layered transition metal dichalcogenides are mostly disorderly stacked,resulting in a significant reduction in the area with the electrolyte,unable to transmit ions at high speed and efficiently.In this paper,we propose a method of using hydroxyl induction to synthesize TMD materials without using template agents.The effect of the type of alcohol on the morphology,crystal spacing and crystallinity of vanadium disulfide was systematically studied,and the performance of its electrochemical storage of sodium/potassium ions was systematically evaluated.The research results are as follows:?1?VS₂ spherical nano flowers:using propylene glycol as a solvent,without using any growth template,a simple alcohol solvothermal method was used to synthesize VS₂ spherical nano flowers?SNF-VS₂?with a three-dimensional porous ordered structure in one step.The nanoflower structure provides a stable structural framework for the insertion and extraction of Na⁺/K⁺,a shorter ion diffusion path,and a larger contact area with the electrolyte.In terms of sodium storage performance,SNF-VS₂ exhibits an excellent reversible specific capacity of 329 m Ah g^-1 at 0.2 A g^-1,and has an initial coulombic efficiency?ICE?of up to 88.52%.In terms of potassium storage performance,SNF-VS₂ shows a specific charge capacity of?556 m Ah g^-1 in the initial cycle,with an excellent initial coulombic efficiency of 74.09%,and shows a high reversible charging specific capacity of 383 m Ah g^-1 at 25 m A g^-1.The electrochemical properties of SNF-VS₂ nearly doubled compared to randomly stacked layered VS₂,which were synthesized using water as a solvent.?2?Mechanism of alcohol-solvothermal synthesis of VS₂:We systemtically explored the influence of the number of alcohol hydroxyl groups and the dielectric constant on the chemical properties and physical morphology of the final synthesized product in the VS₂ alcohol-solvothermal synthesis system,and tested the sodium and potassium storage properties of the synthesized product.The results show that when the dielectric constant of the alcohol solvent is lower than a certain value,the polarity is not enough to ionize ammonia to obtain an enough content of OH^-,the synthesis reaction of VS₂ cannot continue,and V₂O₃ is generated instead.The number of hydroxyl groups affects the final physical appearance of the sample.Ethylene glycol with two hydroxyl groups can provide more negatively charged oxygen to a specific crystal surface to reduce the surface energy.structure.The performance tests of sodium ion batteries and potassium ion batteries reflect the structural excellence of EG-VS₂.In a sodium ion battery,the EG-VS₂ electrode can maintain a high reversible specific capacity of 342 m Ah g^-1 after 300 cycles at a current density of 0.2 A g^-1.In potassium ion batteries,EG-VS₂ shows a reversible specific capacity of424 m Ah g^-1 at a current density of 25 m A g^-1.The research results show that the three-dimensional porous ordered vanadium disulfide prepared by the alcohol solvothermal method has a significantly higher capacity and better cycle performance than the disorderly stacked vanadium disulfide when used as a negative electrode material for sodium/potassium secondary batteries.Therefore,the alcohol induced design and synthesis of ordered three-dimensional nanostructures proposed in this paper is one of the simple and efficient synthesis methods to improve the sodium and potassium storage properties of TMDs anode materials.