The lithiation behaviour of sputtered molybdenum oxide thin films is reported. Results indicate that such films prepared and dry lithiated under certain conditions undergo reversible lithium insertion without exhibiting a significant optical property change in the solar spectral range. Hence, such films have potential for use in electrochromic (EC) systems as counter electrodes for lithium ion storage. An all-solid EC system was fabricated and studied for its optical switching behaviour using an amorphous tungsten oxide film as the base EC layer. Encouraging results were found relative to the application of such MoO3 films for lithium ion storage.