Li-ion batteries (LIBs) are becoming the technology of choice in many applications such as mobile electronics, electric/hybrid vehicles, and storage of renewable energy. However, their safety and energy/power density is yet to be improved. Improved resistance against hazards such as thermal runaway and fire/explosion are the immediate rewards for inclusion of a solid electrolyte in solid state LIBs. There are very good prospects to make solid electrolytes competitive to their liquid counterparts. This is supported by recent demonstration of solid composite electrolytes, e.g. [Tan2016], of which the performance closely follows those of the liquid ones.