Interface-Engineering for All-Oxide Solid-State Batteries

Introduced in the 1990’s, Lithium ion batteries have become the main power source for many portable and stationary applications due to their high energy and power densities. Even so, research is ongoing to further enhance these properties, as well as making them safer and more environmentally friendly. LiMn2O4 cathode is known as a promising material due to its 3D Lithium pathways for diffusion and ability to intercalate a second lithium-ion at 3 V. However, it suffers from capacity fade and poor cycle performance due to Mn-dissolution and a Jahn-teller distortion. A model to study the lithiation mechanisms is needed, therefore, highly controlled thin films are made. By growing thin films on different oriented Nb:SrTiO3 substrates, the crystal orientation of LiMn2O4 is controlled, enabling a unique insight into the relation between electrochemistry, interface, and crystal directionality. By using Electrochemical Impedance Spectroscopy (EIS) the electrochemical behavior of the battery cell is modeled to get more in-depth knowledge of each component within the cell. High discharging rates with good energy capacity and good cyclability are achieved, demonstrating enhanced cycle life without excessive capacity fading as compared to previous polycrystalline studies.Cycling the 3 V plateau of Li2Mn2O4 shows stable capacity with negligible fade, indicating the extra capacity at the 3 V plateau can be utilized effectively. Furthermore, it can rejuvenate capacity loss at the 4 V plateau.Li3xLa2/3-xTiO3 electrolyte thin films are synthesized, but exhibit TiOx impurities most likely due to lithium deficiencies. Combining the solid electrolyte with the LiMn2O4 cathode a nanocomposite can be obtained. However, this then suffers from an insulating electrolyte layer preventing connection to the current collector, limiting charge-discharge behavior. Finally, an all-oxide full solid-state thin film battery was synthesized by combining the LiMn2O4-cathode and Li3xLa2/3-xTiO3-electrolyte with the anode Li4Ti5O12. Poor growth of the electrolyte, combined with shorts, prevented electrochemical performance. Further investigation and optimization on the growth of the Li3xLa2/3-xTiO3-electrolyte is required. This research demonstrates the scientific potential for epitaxial ceramic battery model systems, which new insights allow using a wider potential range for LixMn2O4 increasing the capacity almost twofold while achieving extensive lifetimes.