Pristine Interface between Lithium Lanthanum Zirconate and Lithium Manganese Oxide by Pulsed Laser Deposition

Abstract Solid state lithium‐ion batteries have garnered increasing interest in recent years due to several potential advantages over liquid‐electrolyte based systems. The possibility of integrating the lithium garnet oxide, Li_6.75La₃Zr_1.75Ta_0.25O₁₂ (LLZTO), with the high voltage cathode, spinel Li_xMn₂O₄ (LMO), is evaluated here. Thin film bilayer structures are prepared by pulsed laser deposition on MgO (001) substrates and characterized by x‐ray diffraction and transmission electron microscopy. The LLZTO is grown by an alternating layer‐by‐layer deposition of LLZTO and Li₃N and subsequently annealed for several hours at 575 °C to promote crystallinity. Growth of crystalline LMO with a pristine interface to LLZTO is achieved by gentle heat treatment (500 °C) to remove surface carbonate from the electrolyte and by cathode growth at a low temperature of 250 °C. Higher temperature depositions (330 – 450 °C) result in reaction between the two materials and the appearance of Li₂MnO₃, which may be in part due to the presence of excess lithium in the electrolyte layer. Because fully lithiated LiMn₂O₄ has a voltage of ≈3.7 V versus Li+/Li, the observation of a well‐defined interface, free of impurity phases and with no interdiffusion of elements, indicates LLZTO is stable to at least 3.7 V.