Blocks of molybdenum ditelluride: A high rate anode for sodium-ion battery and full cell prototype study

Abstract

Sodium-ion batteries (SIBs) are considered next-generation rechargeable batteries for grid-scale energy storage applications. This is because sodium is abundant in nature, and SIBs display electrochemical behavior that is similar to lithium-ion batteries (LIBs). Several high-performance sodium-rich cathode materials have been developed, which show excellent electrochemical performance. Nevertheless, the large-scale application of the ultimate metal-free sodium-ion battery that has a full cell configuration is hampered due to unavailability of reliable anode materials. We demonstrated a two-dimensional (2D), layered structured molybdenum di-telluride (MoTe2) as anode material in SIBs through this work. MoTe2 has been synthesized through a facile solid-state reaction route, and it has been used as an anode material without further surface modification or any conductive-coating carbon additives. Synchrotron X-ray diffraction (SXRD) and high-resolution scanning transmission electron microscopy (HRSTEM) confirm the hexagonal structure of MoTe2, which has the space group, P63/mmc. In a half-cell configuration (with respect to sodium metal), the MoTe2 electrode exhibits an initial specific capacity of 320 mA h g−1 at a current density of 1.0 A g−1, and it retains a high capacity of 270 mA h g−1 after 200 cycles. To detect the phase changes during sodiation/desodiation process and to explore the underlying sodium storage mechanism, SXRD, HRTEM with SAD, X-ray photoelectron spectrodcopy (XPS), X-ray absorption near edge structure (XANES) in ex situ mode along with in situ electrochemical impedance spectroscopy (EIS) and quantitative electrochemical kinetic calculations have been used. Further, a sodium-ion full cell is constructed by coupling the MoTe2 as anode and sodium vanadium phosphate Na3V2(PO4)3 (NVP) as cathode. The sodium-ion full cell retains 88% of its initial capacity after 150 cycles at a current density of 0.5 A g−1. Operating at an average potential of ~2 V, the full cell delivers a high energy density of 414 W h kg−1. The present study opens up a new direction to the anode materials for rechargeable sodium-ion batteries.