Na Superionic Conductor-Type TiNb(PO4)3 Anode with High Energy Density and Long Cycle Life Enables Aqueous Alkaline-Ion Batteries.

High energy density aqueous alkaline-ion batteries have drawn significant attention because of their intrinsic high security and low cost. As suitable anode materials with satisfying capacity and proper operating potential in an aqueous electrolyte are limited, it is of urgent need to find candidate materials to build aqueous alkaline-ion batteries for practical applications. For the first time, highly crystalline Na superionic conductor-type phase TiNb(PO4)3 (TNPO) was explored as an alkali-ion intercalation host in the aqueous battery technology. The TNPO material manifests a high specific capacity of 94 mA h g-1 at 5 C rate together with superior cyclic stability and remarkable rate capacity in aqueous electrolytes, which is assigned to its super stable three-dimensional tunnel structure. Furthermore, the aqueous lithium-ion battery based on the TNPO anode and LiMn2O4 (LMO) cathode delivers a high specific energy of 121 W h kg-1 and a specific power of 189 W kg-1 with a voltage output of 2.1 V, while it exhibits excellent cycling performance (82% capacity retention after 1000 times at 5 C rate). The remarkable overall electrochemical performances of the TNPO anode have clearly suggested that TNPO can be used as a promising electrode material of aqueous alkali-ion batteries with high energy density and long cycle life for energy storage in future.