A 5V lithium secondary cell was fabricated using LiFe0.5Mn1.5O4 cathode material with all-solid-state design. As an additional approach to improve the battery performance of the all-solid-state secondary cell, a metal oxide-retaining layer was placed between the cathode material and solid electrolyte. The cathode material has an excellent cyclability in this cell design, since it just loses 5 and 18% of its initial capacity after 100 and 500 charge–discharge cycles, respectively.