To replace conventional metal electrode, flexible carbon nanotube (CNT) sheet having excellent electrical properties is first applied as a current collector in all-solid-state lithium batteries, and its effect on the performance of all-solid-state lithium batteries are investigated. In the case of cells without the CNT sheet, gaps between the all-solid-state composite cathode and metal current collector (e.g., a conventional metal foil or coin cell) limits physical contacts which is not a trivial problem for the all-solid-state composite cathode. On the contrary, the CNT sheet makes intimate contact and provides a large interfacial contact area by filling the gaps. It is a great benefit in practical process viewpoint that this sufficient physical contact is achieved even without any polymeric binder. The greatly reduced interfacial contact resistance due to the intimate contact between the all-solid-state composite cathode and CNT sheet causes improvements in reversible capacity and high-rate discharge performance.