Next generation of energy storage devices may largely benefit from fast and solid Li + ceramic electrolyte conductors to allow for safe and efficient batteries. For those applications, the ability of Li-oxides to engineer their interfaces and be processed as thin film and bulk structures and with high control over Lithiation and phases at low temperature is of essence to control performance. For a high longevity and cycle life internal interfaces such as space charges at grian boundaries drive reduction potentials for lithium. Through the presentation we take a fundamental look at the defect theory and local potentials of space charges at internal solid state interfaces, and study as proof of concept on the examples of various solid state Li+ conductors strategies to mitigate the space charge potentials, ultimately leading to increased critical current densities. At the end of the talk, we will look at the opposite strategy, namely novel amorphous solid state Li+ conductors, which are completely avoiding interfaces and gain a deeper understanding on their local bonding units and compositions.