Aqueous Lithium‐ion Battery LiTi 2 (PO 4 ) 3 /LiMn 2 O 4 with High Power and Energy Densities as well as Superior Cycling Stability**

Porous, highly crystalline Nasicon‐type phase LiTi 2 (PO 4 ) 3 has been prepared by a novel poly(vinyl alcohol)‐assisted sol–gel route and coated by a uniform and continuous nanometers‐thick carbon thin film using chemical vapor deposition technology. The as‐prepared LiTi 2 (PO 4 ) 3 exhibits excellent electrochemical performance both in organic and aqueous electrolytes, and especially shows good cycling stability in aqueous electrolytes. An aqueous lithium‐ion battery consisting of a combination of LiMn 2 O 4 cathode, LiTi 2 (PO 4 ) 3 anode, and a 1 M Li 2 SO 4 electrolyte has been constructed. The cell delivers a capacity of 40 mA h g –1 and a specific energy of 60 W h kg –1 with an output voltage of 1.5 V based on the total weight of the active electrode materials. It also exhibits an excellent cycling stability with a capacity retention of 82 % over 200 charge/discharge cycles, which is much better than any aqueous lithium‐ion battery reported.