Li2RuO3 (001) films with a lithium-rich layered rocksalt structure are epitaxially grown on a Al2O3(0001) substrate through pulsed laser deposition, followed by stacking of an amorphous Li3PO4 solid electrolyte. A half solid-state battery with a Li3PO4/Li2RuO3 cathode, liquid electrolyte, and lithium anode exhibits two redox peak pairs at 3.4 and 3.6 V, demonstrating lithium intercalation in the Li2RuO3 through the Li3PO4 solid electrolyte. All-solid-state batteries are fabricated by Li or In metal anode deposition on the Li3PO4/Li2RuO3. The Li/Li3PO4/Li2RuO3 cell delivers an initial discharge capacity of 101 mAh g−1, which does not fade significantly over 30 cycles. Furthermore, the Li2RuO3 rate capability is comparable to that of a liquid-type battery. Lithium-rich layered materials are available for use as cathodes in all-solid-state batteries.