A novel amorphous cathode material Li_xM_yPO_z for all-solid-state thin-film lithium-ion battery has been developed. Since a non-annealing process is employed, a thin-film lithium-ion battery can be fabricated by direct deposition of materials onto thin plastic film. Li_xM_yPO_z is formed through sputter deposition of Li₃PO₄ and metal or metal oxide targets. We have tested several metal elements (M = Ni, Mn, Co, Cu, Ag), and LiNiPO showed a high capacity of 330 mAh g⁻¹ at 1C. In addition, a cell using this cathode material has demonstrated a high charge/discharge rate up to 30C.