All-solid-state lithium polymer secondary battery with LiNi0.5Mn1.5O4 by mixing of Li3PO4

5 V-class all-solid-state lithium polymer secondary batteries were prepared by the mixing of solid inorganic electrolyte (SIE, Li3PO4) with LiNi0.5Mn1.5O4 powder. The discharge capacity exhibited >120 and >550 mWh g−1 at the operation temperature of 333 K. We also prepared a lithium-metal-free battery by using copper current collector at the anode, and exhibit the similar discharge capacity. Our demonstration indicates the marked improvement in the energy density of lithium polymer batteries through a simple preparation, which leads to the manufacture of large-scaled batteries.