Kinetic and Electrochemical Reaction Mechanism Investigations of Rodlike CoMoO₄ Anode Material for Sodium-Ion Batteries

Abstract

Sodium-ion batteries are considered the most promising power source for electrical energy storage systems because of the abundance of sodium and their significant cost advantages. However, high-performance electrode materials are required for their successful application. Herein, we report a monoclinic-type CoMoO₄ material which is synthesized by a simple solution method. An optimized calcination temperature with a high crystallinity and a rodlike morphology of the material are selected after analyzing the as-synthesized powder by temperature-dependent time-resolved X-ray diffraction. The CoMoO₄ rods exhibit initial discharge and charge capacities of 537 and 410 mA h g^-1, respectively, when used as an anode for sodium-ion batteries. The sodium diffusion coefficient in the bimetallic CoMoO₄ anode is measured using the galvanostatic intermittent titration technique and calculated in the range of 1.565 × 10^-15 to 4.447 × 10^-18 cm² s^-1 during the initial cycle. Further, the reaction mechanism is investigated using ex situ X-ray diffraction and X-ray absorption spectroscopy, and the obtained results suggest an amorphous-like structure and reduction/oxidation of Co and Mo during the sodium insertion/extraction process. Ex situ transmission electron microscopy and energy-dispersive spectroscopy images of the CoMoO₄ anode in fully discharged and recharged state reveal the rodlike morphology with homogenous element distribution.