Re-chargeable Li ion batteries play a key role in modern consumer electronics and may have an important part to play as energy storage devices in a low carbon economy of the future. Typical modern devices consist of solid state electrodes and an organic liquid electrolyte which is chosen for its high ionic conductivity and high electrical resistivity, but this component is flammable and presents a risk of fire or explosion, which is a particular handicap to the development of larger devices. The development of all solid-state batteries is therefore desirable but is dependent on the discovery of new solid state electrolyte materials with high Li-ion conductivity and low electronic conductivity. Here we will use neutrons to locate lithium within these materials something which cannot be done with X-rays.