DFT reveals why Mo substitution enables multi-electron redox in Wadsley–Roth MoxW1−xNb12O33

Abstract

Transition metal oxide Wadsley-Roth (W-R) crystallographic shear compounds are promising alternatives to graphite for high-rate Li-ion battery applications, as fast charging can drive unsafe lithium metal plating on graphite anodes when Li⁺ ions deposit as metallic lithium rather than 2 intercalating into the graphite lattice. Despite this promise, fundamental materials chemistry questions remain regarding how to tune W-R structure and composition to achieve desirable electrochemical properties such as lower working potential, enhanced capacity, and improved cycle stability. Motivated by these questions, we systematically investigated a series of MoxW1−xNb12O33 compounds synthesized using two distinct thermal processing protocols to determine whether electrochemical trends associated with Mo substitution persist across materials prepared under different synthesis conditions. Differential capacity measurements revealed that Mo substitution introduces new electrochemically active states at more positive potentials and systematically increases capacity beyond values expected for single-electron redox. Both sample series exhibit the same systematic increase in capacity with increasing Mo content, indicating that Mo substitution rather than synthesis-induced disorder is the dominant factor governing the electrochemical trends. Electronic structure calculations predict that Mo occupying edge-sharing octahedral sites along crystallographic shear planes can support multi-electron redox and provide a plausible explanation for the experimentally observed capacity enhancement. Mo-rich samples exhibit greater capacity loss with additional cycling, possibly due to the inability of severely distorted Mo octahedra from "rocking" back and forth during lithiation/de-lithiation cycles. These findings identify Mo substitution as an effective strategy for enhancing multi-electron redox behavior in W-R anodes and provide guidance for future efforts aimed at controlling cation site occupancy and electrochemical performance.