Research and development of a new type of magnesium battery material based on VS4 one dimensional atomic chain

Rechargeable magnesium battery is considered to be one of the most attractive candidate devices for large-scale and sustainable electrochemical energy storage Magnesium metal has the advantages of high theoretical bulk energy density (3833 mahcm-3), abundant natural reserves and no dendrite deposition during charging However, there is a strong interaction between the strongly polarized divalent Mg 2 + ions and the lattice of the positive material, which will hinder the dynamics of Mg 2 + ions' embedding / disengaging and diffusion in the lattice of the material Therefore, it is a challenging problem to find the anode materials with fast kinetics, high capacity and long cycle life, which can be used for reversible intercalation of Mg 2 + Recently, the mesoscopic energy materials research team led by Jin Zhong and Liu Jie, Key Laboratory of mesoscopic chemistry Ministry of education, School of chemistry and chemical engineering, Nanjing University, worked closely with Ma Jing research group of Institute of theory and computational chemistry, Nanjing University, to design and prepare high-resolution branching vs 4 with special one-dimensional atomic chain structure It can be used as a new cathode material of Mg battery with high reversible capacity, excellent rate performance and cycle stability (Fig 1) This work was recently published in advanced materials (DOI: 10.1002 / ADMA 201802563) under the title of "highly branched vs 4 nanodrivers with one dimensional chain structure as a promising method material for long-cycling magnesium batteries" Figure 1 electrochemical performance of magnesium battery with branched vs 4 nanostructure a s positive material: (a) CV Curve, sweep rate of 0.2 MV S-1; (b) discharge charge curve; (c) cycle performance at current density of 100 Ma g-1; (d) discharge charge curve and (E) rate performance from 50 to 500 mA g-1; (f) current density of 500 mA g-1 Long cycle test for MA-1 (source: Advanced Materials) vs 4 nanostructures can be attributed to their unique one-dimensional atomic chain structure for their excellent magnesium storage performance The alignment of these vs 4 chains is the same The weak van der Waals force binding between each chain makes the linear open channel in vs 4 material favorable for Mg 2 + migration / diffusion The interaction between vs 4 and Mg 2 + is also weak S 22 dimer can provide a large number of active sites, so it can store a large number of Mg 2 + ions In order to elucidate the mechanism of reversible mg / de mg in vs 4, the researchers calculated by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Raman spectroscopy (Raman) and density functional theory (DFT) under different Mg 2 + ion embedded states, The transport / diffusion characteristics of Mg 2 + and the special internal redox behavior in vs 4 are analyzed in detail (Fig 2 and Fig 3) It is found by experimental characterization that the process of Mg 2 + implantation and desorption in vs 4 is accompanied by the reversible change of valence states of V and S atoms After the first discharge, a Mg ion embedded structure with Mg 0.84 vs 4 composition was formed During the subsequent charge discharge cycle, the composition of the electrode material changed reversibly from mg 0.24 vs 4 to Mg 0.84 vs 4 The reaction process can be expressed as: vs 4 + 0.24mg 2 + + 0.48e - → mg 0.24 vs 4 (1) mg 0.24 vs 4 + 0.6mg 2 + + 1.2e- A kind of Mg 0.84 vs 4 (2) Fig 2 studies the process of Mg ion insertion / removal in branched vs 4 nanostructures: (A-C) high resolution XPS spectra in the initial state, after the first discharge and after the first charge: (a) V 2p, (b) S 2p, (c) mg 2p (d) At the current density of 100mA g-1, the discharge charge curves of the first and second cycles are marked as 1-9, indicating different discharge charge states In these States, (E) XRD and (f) Raman spectra of electrode materials are collected The peaks of the "C" mark come from carbon paper, which is a collecting fluid (source: Advanced Materials) Figure 3 DFT calculation and schematic diagram illustrate the reversible embedding / disengaging behavior of Mg 2 + in vs 4 electrode materials (a) The relative formation energy calculated by DFT for mgxvs 4 (x from 1 / 8 to 7 / 8) cells with different Mg 2 + ion ratios (b) DFT calculated the charge density distribution (isovalue = 0.5) of mgxvs 4 (x = 0, 2 / 8 and 7 / 8) (c) According to the experimental results, the schematic diagram of reversible insertion / removal of Mg 2 + from vs 4 in the process of discharge / charging is obtained (source: Advanced Materials) the simulation results also show that there are many possible embedding sites in the formation of mgxvs 4 (x from 1 / 8 to 7 / 8) by embedding Mg 2 + ions in vs 4, which is thermodynamically advantageous With the increase of Mg content x, there is an "inverted volcano" curve, reaching a low energy point at x = 5 / 8, which is consistent with the experimental results Due to the above unique electrochemical properties of vs 4, the electrode materials based on branched vs 4 nanostructures show excellent Mg 2 + performance, with a reversible capacity of 251 MAH g-1 at 100 Ma g-1 and good cycle stability After 800 cycles at a large current density of 500 mA g-1, the capacity remains at 74 MAH g-1 The research work has been supported by national key R & D plan, National Natural Science Fund, Jiangsu Natural Science Fund, Jiangsu entrepreneurship and innovation talent plan and basic research business fees of central universities.