New lithium-ion conductors based on the NASICON structure

Lithium-ion conduction in mixed-metal phosphates, LiMVM III (PO 4 ) 3 [MV=Nb, Ta; M III =Al, Cr, Fe], possessing the rhombohedral (Rc) NASICON structure has been investigated. Among the phosphates investigated, LiTaAl(PO 4 ) 3 exhibits the highest conductivity, σ≈1.0×10 –2 S cm –1 at 350 °C (E a =0.47 eV), comparable to the conductivity of LiTi 2 (PO 4 ) 3 . Unlike LiTi 2 (PO 4 ) 3 which contains lithium-reducible Ti IV , LiTaAl(PO 4 ) 3 contains stable TaV and Al III oxidation states and hence deserves further attention towards tailoring new lithium-ion conductors for application as electrolytes in solid state lithium batteries.