Computational study of spinel ZnM₂O₄ as a cathode material for Zn-ion batteries

Multivalent metal-ion batteries offer a revolutionary solution for large-scale energy storage, utilizing abundant aluminum, zinc, calcium, and magnesium to create cost-effective batteries. The challenge is to develop innovative positive electrode materials that can efficiently transport these ions with an improved diffusion mechanism. In our study, we delve into the atomistic simulation of spinel-structured materials using first-principles calculations and classical molecular dynamic simulations (CMDs). Two promising spinel compounds, ZnM₂O₄, where M represents the transition metal redox elements Mn and Ni, have been theoretically predicted as promising cathode materials for zinc-ion batteries (ZIBs). Their potential in battery technology is explored by precisely calculating fundamental properties such as intercalation–deintercalation voltage, theoretical specific capacity, and ionic dynamics. Zn²⁺ ions are stabilized during diffusion by the Mn³⁺/Mn⁴⁺ redox pair, improving overall electrochemical performance. However, the Ni³⁺/Ni⁴⁺ pair finds it challenging to stabilize Zn²⁺, leading to greater voltages but less effective ionic diffusion, a notable distinction that opens up new possibilities for Mn-based materials. CMDs allow us to simulate ionic behavior at various temperatures, revealing how thermal vibrations and lattice dynamics influence ionic migration. Through these simulations, we investigate the diffusion kinetics of Zn²⁺ ions in these materials, discovering that ZnMn₂O₄ exhibits superior diffusion kinetics compared to ZnNi₂O₄. Our findings highlight that the combination of MD simulations and defect engineering provides a powerful toolkit for predicting and enhancing the performance of battery materials. Strategically lowering the energy barriers improves the intercalation properties of spinel compounds, paving the way for efficient multivalent metal-ion batteries.