Cobalt anti-MXenes as Promising Anode Materials for Sodium-ion Batteries

The current electric vehicle market is entirely dominated by lithium-ion batteries (LIBs). However, due to the limited and unequal distribution of LIB raw materials on earth, there is a continuous effort to design alternate storage devices. Among the alternatives to LIBs, sodium-ion batteries (NIBs) are at the forefront because sodium resources are ubiquitous worldwide and virtually inexhaustible. However, one of the major drawbacks of the NIBs is their low specific charge capacity. Since the specific charge capacity of a cell can be improved by increasing the specific charge capacity of the anode material, there is a constant effort to find suitable anode materials. Recent studies suggested that cobalt-boride (CoB) anti-MXene material (a newly discovered two-dimensional material) can yield superior specific charge capacities for LIBs than traditional graphite-based anodes. Inspired by these findings, in this work, we considered six cobalt-based anti-MXene materials (Co-anti-MXenes), namely, CoAs, CoB, CoP, CoS, CoSe, and CoSi, and examined their competency as anode materials for NIBs. Our findings suggest that Co-anti-MXenes possess superior specific charge capacities (~ 390–590 mAh/g) than many well-studied anode materials like MoS2 (146 mAh/g), Cr2C (276 mAh/g), expanded graphite (284 mAh/g), etc. Moreover, their greater affinity (-0.55 to -1.16 eV) to Na atoms, along with reasonably small diffusion energy barriers (0.32 to 0.59 eV) and low average sodiation voltages (0.2 to 0.64 V), suggest that these Co-anti-MXenes can serve as excellent anode materials for NIBs.