2 research outputs found
Role of Structural H<sub>2</sub>O in Intercalation Electrodes: The Case of Mg in Nanocrystalline Xerogel‑V<sub>2</sub>O<sub>5</sub>
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 H<sub>2</sub>O during ion intercalation
in nanomaterials. We examine the scenario of Mg<sup>2+</sup> and H<sub>2</sub>O cointercalation in nanocrystalline Xerogel-V<sub>2</sub>O<sub>5</sub>, 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 V<sub>2</sub>O<sub>5</sub> and voltages
at different electrolytic conditions reveals a range of concentrations
for Mg in the Xerogel and H<sub>2</sub>O in the electrolyte where
there is no thermodynamic driving force for H<sub>2</sub>O to shuttle
with Mg during electrochemical cycling. Also, we demonstrate that
H<sub>2</sub>O shuttling with the Mg<sup>2+</sup> ions in wet electrolytes
yields higher voltages than in dry electrolytes. The thermodynamic
framework used to study water and Mg<sup>2+</sup> 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
Materials Design Rules for Multivalent Ion Mobility in Intercalation Structures
The diffusion of ions in solid materials
plays an important role
in many aspects of materials science such as the geological evolution
of minerals, materials synthesis, and in device performance across
several technologies. For example, the realization of multivalent
(MV) batteries, which offer a realistic route to superseding the electrochemical
performance of Li-ion batteries, hinges on the discovery of host materials
that possess adequate mobility of the MV intercalant to support reasonable
charge and discharge times. This has proven especially challenging,
motivating the current investigation of ion mobility (Li<sup>+</sup>, Mg<sup>2+</sup>, Zn<sup>2+</sup>, Ca<sup>2+</sup>, and Al<sup>3+</sup>) in spinel Mn<sub>2</sub>O<sub>4</sub>, olivine FePO<sub>4</sub>, layered NiO<sub>2</sub>, and orthorhombic δ-V<sub>2</sub>O<sub>5</sub>. In this study, we not only quantitatively assess these
structures as candidate cathode materials, but also isolate the chemical
and structural descriptors that govern MV diffusion. Our finding that
matching the intercalant site preference to the diffusion path topology
of the host structure controls mobility more than any other factor
leads to practical and implementable guidelines to find fast-diffusing
MV ion conductors