New lithium-ion conductors based on the NASICON structure

Lithium-ion conduction in mixed-metal phosphates, LiMVMIII(PO4)3 [MV=Nb, Ta; MIII=Al, Cr, Fe], possessing the rhombohedral (R3c) NASICON structure has been investigated. Among the phosphates investigated, LiTaAl(PO4)3 exhibits the highest conductivity, σ ≈ 1.0×10-2 S cm-1 at 350°C (Ea=0.47 eV), comparable to the conductivity of LiTi2(PO4)3. Unlike LiTi2(PO4)3 which contains lithium-reducible TiIV, LiTaAl(PO4)3 contains stable TaV and AlIII oxidation states and hence deserves further attention towards tailoring new lithium-ion conductors for application as electrolytes in solid state lithium batteries