Band Diagram Framework for Materials Development in Cation Intercalation Batteries

The next generation of batteries may employ ionic liquid or solid electrolytes with stability windows of more than 6 volts, and migrate from lithium ion chemistries to more earth-abundant cations such as sodium, potassium, or magnesium ions. In this work we revisit known lithium ion battery cathode materials to gain insight into the requisite properties for electrode materials in next-generation batteries, with particular emphasis on spinel lithium manganese oxide (LiMn₂O₄).  LiMn₂O₄ is a common cathode material for lithium ion batteries, with a very fast charge-discharge rate. We employ periodic quantum mechanical calculations to theoretically evaluate the charge storage properties of spinel MnO₂ with intercalated Li⁺ as well as other cations. The equilibrium electrochemical potentials for a cation intercalation host (e.g. spinel MnO₂) are evaluated within an electronic structure and band diagram framework. We highlight the accuracy and predictive power of this theoretical framework by comparison with experimental results and provide insights for  materials development.  In general, the work function and electronic structure of a cation host material determine the equilibrium potential(s) for charge-transfer in the intercalated compound.