Abstract Even though the use of solid-state electrolytes for all-solid-state lithium battery applications has been a topic of great interest, an optimal material for this purpose has not been found. On the basis of the fact that ionic liquids are solidified at oxide particle surfaces and become quasi-solid materials, we previously fabricated a new lithium-ion-conducting solid electrolyte material comprising silica nano-particles and an ionic liquid that exhibited high ion conductivity comparable to the bulk ionic liquid. In the current study, this electrolyte was applied in the fabrication of an all-solid-state lithium secondary battery cell, by using three-dimensional structural cathode mixing the solid electrolyte and a cathode material (LiCoO2). The most important feature of the newly developed cell is that it was fabricated using thick films. There are no prior reports of all-solid-state secondary batteries employing thick films that exhibit high capacity. In this design, all of the cathode active materials could make contact with the electrolyte and the electron-conducting material despite the all-solid-state nature of the device. As a result, we have succeeded in the fabrication of an all-solid-state lithium secondary battery exhibiting high capacity of 126mAhg−1, nearly equal to theoretical capacity 138mAhg−1, despite the use of a micrometer order thick-film device. This study paves the way for the application of a new approach to the all-solid-state lithium secondary battery design.