(Invited) Inductive Effects to Control the Operating Voltage of Fast-Charging Molybdenum Oxide Anodes

Abstract

Batteries are essential to most modern technologies, as they provide a sustainable alternative to traditional energy sources. One area of active research is in identifying new battery materials made from plentiful elements to produce stable, high power and fast-charging batteries. A candidate for the next-generation anode material is molybdenum oxide, as it shows fast-charging capabilities, stability, and high capacity. The disadvantage of this material is that the expected power is relatively low, as the redox voltage for molybdenum is not optimized to the stability window of the liquid electrolyte. Using the inductive effect as a guiding principle, we suggest lowering the Mo+6/+5 redox voltage by adding a cation to the structure. The structural modification will influence the covalency of the metal-oxygen bond and will therefore allow lower ionization energy (IE) for the d-orbital electrons. To this aim, we compare the electrochemistry of Li2Mo4O13 and MoO3 as well as the IE and the Li diffusivity. The results show that the addition of Li lowers the voltage by 300 mV for Mo+5/+6 compared to MoO3 but does not reduce the Li diffusivity. The change in IE also supports our hypothesis that the Li reduces the polarity of the M-O bond. Additional electrochemical studies indicate limited capacity for Li2Mo4O13 compound, which is related to structural changes after the first lithiation process. Our results demonstrate the utility of exploring new systems with elevated redox voltage to better fit the electrolyte stability window and yield higher power.