title: Role of Structural H2O in Intercalation Electrodes: The Case of Mg in Nanocrystalline Xerogel-V2O5.
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 Mg(2+) 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 Mg(2+) ions in wet electrolytes yields higher voltages than in dry electrolytes. The thermodynamic framework used to study water and Mg(2+) 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.
authors.affiliation: Department of Materials Science and Engineering, Massachusetts Institute of Technology , Cambridge, Massachusetts 02139, United States.|Materials Science Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
authors.forename: Gopalakrishnan
authors.initials: G
authors.lastname: Sai Gautam
authors.affiliation: Department of Materials Science and Engineering, Massachusetts Institute of Technology , Cambridge, Massachusetts 02139, United States.|Materials Science Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
authors.forename: Pieremanuele
authors.initials: P
authors.lastname: Canepa
authors.affiliation: Department of Materials Science and Engineering, Massachusetts Institute of Technology , Cambridge, Massachusetts 02139, United States.
authors.forename: William Davidson
authors.initials: WD
authors.lastname: Richards
authors.affiliation: Department of Materials Science and Engineering, Massachusetts Institute of Technology , Cambridge, Massachusetts 02139, United States.
authors.forename: Rahul
authors.initials: R
authors.lastname: Malik
authors.affiliation: Materials Science Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.|Department of Materials Science and Engineering, University of California , Berkeley, California 94720, United States.
authors.forename: Gerbrand
authors.initials: G
authors.lastname: Ceder
keywords: Solvent cointercalation; charge screening; crystal water; first-principles; magnesium batteries; phase diagram