Abstract

Cointercalation is a potential approach to influence the voltage and mobility with which cations insert in electrodes for energy storage devices. Combining a robust thermodynamic model with first-principles calculations, we present a detailed investigation revealing the important role of H₂O during ion intercalation in nanomaterials. We examine the scenario of Mg²⁺ and H₂O cointercalation in nanocrystalline Xerogel-V₂O₅, a potential cathode material to achieve energy density greater than Li-ion batteries. Water cointercalation in cathode materials could broadly impact an electrochemical system by influencing its voltages or causing passivation at the anode. The analysis of the stable phases of Mg-Xerogel V₂O₅ and voltages at different electrolytic conditions reveals a range of concentrations for Mg in the Xerogel and H₂O in the electrolyte where there is no thermodynamic driving force for H₂O to shuttle with Mg during electrochemical cycling. Also, we demonstrate that H₂O shuttling with the Mg²⁺ ions in wet electrolytes yields higher voltages than in dry electrolytes. The thermodynamic framework used to study water and Mg²⁺ cointercalation in this work opens the door for studying the general phenomenon of solvent cointercalation observed in other complex solvent–electrode pairs used in the Li- and Na-ion chemical spaces.