Strategy for enhancement of magnesium ion diffusion in a vanadium tetra sulfide-layered structure for rechargeable magnesium batteries

A theoretically higher volumetric capacity, natural abundance, low cost, dendrite free and ecofriendly rechargeable magnesium battery system (RMBS) is considered to be a promising candidate device for future commercialization. However, low capabilities due to the sluggish diffusion kinetics due to the highly polarized Mg²⁺ ions of cathodic materials are hindering the potential application of such devices. Considering the key role of diffusive contribution, we conducted systematic research to enhance the diffusion contribution of Mg²⁺ ions in vanadium tetrasulfide (VS₄). Nanosized particles were synthesized to provide additional surface area for Mg²⁺ ions. The effects of sulfur vacancies due to nickel substitution in the VS₄-layered atomic structure were studied theoretically. Subsequently, it was confirmed experimentally that the layered atomic structure of VS₄ was further expanded and more stable vacancies were generated after nickel substitution. As a result, enhanced diffusion of Mg²⁺ up to 59.35% at 0.1 mV s⁻¹ exhibited improved cathodic performance enabling a high-performance RMBS. Moreover, these structural alterations exhibited improved electrochemical properties on a copper current collector, such as 5%Ni-VS₄, which displayed a remarkable discharge capacity of 477.9 mA h g⁻¹ at 100 mA g⁻¹ that was sustained for up to 1500 cycles at a current density of 500 mA g⁻¹. Hence, the proposed strategy is an effective way forward to develop an efficient VS₄ cathode for an RMBS.