Interlayer expansion of kinetically grown molybdenum oxide for Mg batteries with enhanced energy density

Abstract

The state-of-the-art lithium-ion batteries (LIBs) enabled electric vehicles (EVs) and energy storage systems (ESS), but their limited energy density has driven research into alternative “post-LIBs.” Multivalent (MV)-ion intercalation chemistry holds potential for multiplying the theoretical energy density of rechargeable batteries while utilizing the well-established intercalation hosts for LIBs. However, the higher charge density of MV-ions leads to substantial hindrances in interfacial and bulk diffusion kinetics in oxide hosts, which are at the forefront of cathode development due to their highest redox potential and largest theoretical capacity among the chalcogenides. In this study, we engineer the crystal structure of molybdenum trioxide (MoO₃), a representative layered oxide host in magnesium-ion (Mg²⁺ as a representative MV-ion) batteries, by introducing organic pillars to expand the interlayer spacing to 12.3 Å, i.e., 180 % of pristine MoO₃. At the same time, we induced the kinetic growth of the primary particles to reduce the diffusion path lengths to 5.8 % of commercial bulk MoO₃. The in-situ inter-layer expansion and kinetic growth strategies work synergistically to enhance the interfacial and intrinsic bulk diffusion kinetics, resulting in a material with a significantly increased specific capacity of 352 mAh/g as a cathode for magnesium-ion batteries, which provides 2.2 times larger capacity than the pristine MoO₃. This synergetic strategy of engineering multiscale microstructures may open a new avenue for the facilitation of various MV-ions’ intercalation into the layered oxides that provide higher energy density.