Predominant intercalation of H+ enables ultrahigh rate capability of oxygen deficient MoO3 for aqueous Al-ion batteries

Establishing conclusive proof of ion intercalation/deintercalation is challenging and critical to accurately assessing and optimizing the performance of aqueous aluminum-ion batteries (AAIBs). In this article, we develop oxygen-deficient α-MoO3 (denoted OD-MoO3-x) with an ultrahigh rate capability (97 mA h g−1 at 50 A g−1) for AAIBs. The fast kinetics of charge storage are not only due to interlayer expansion but also related to the charge storage mechanism. Through DFT calculations, in situ XRD, in situ Raman spectroscopy, in situ pH monitoring, ex situ TEM and ToF-SIMS, we identify and quantify the contribution of H+ intercalation to the total energy storage. The mechanism of the ultrahigh rate capability of OD-MoO3-x is established as the predominant H+ intercalation. Our study may shed some light on the electrode development of high-performance multivalent-ion batteries.