The development of advanced batteries that have a higher energy density for current lithium-ion and beyond lithium-ion battery relies not only on the identification of new chemistries (e.g., a compatible combination of cathode, anode and non-aqueous electrolyte), but also mechanistic understanding of cathode performance during charge-discharge processes. For these reasons we focus on model thin film systems, which provide controllable geometry, orientation and surface roughness. Using pulsed laser deposition, we have grown lithium-based (e.g., LiMn₂O₄) and magnesium based (MgMn₂O₄) oxide thin films. Using these model systems, we have explored the electrochemical performance of these materials as new battery cathodes, as well as the intercalation mechanism of cations, namely Mg²⁺ and Li⁺, at the electrode/electrolyte interfaces. For example, the cubic phase of MgMn₂O₄ (MMO_C) can only be found in powder form at high temperature (> 950 °C) or high pressure (> 15.6 GPa), but is stabilized as thin films, which exhibited reversible Mg²⁺ insertion and extraction in non-aqueous electrolyte such as Mg(TFSI)₂ in diglyme with associated changes in bulk film structure and Mn-oxidation states. Using in situ X-ray reflectivity we have observed the film structural changes during charge-discharge processes. Our thin film model system studies provide a platform for material design and mechanistic understanding for lithium and beyond lithium-ion batteries.

This work was supported by the Joint Center for Energy Storage Research (JCESR) through the Office of Basic Energy Sciences (BES), U.S. Department of Energy (DOE).