W₇Nb₄O₃₁ Nanorods with a Mixed Crystal Structure: A Very Fast‐ and Stable‐Charging Anode Material for Aqueous Lithium‐Ion Batteries

Abstract

Aqueous lithium‐ion batteries (ALIBs) have attracted extensive interest since the safety problems of traditional lithium‐ion batteries are waived. Although the energy density of ALIBs is improved, their rate capability and power density are still poor due to the slow Li+ diffusivity of the existing anode materials, and their cyclic stability is also poor. Here, W7Nb4O31 nanorods with very fast‐ and stable‐charging capability are explored as a new anode material for ALIBs for the first time. This material owns different tetragonal tungsten bronze (TTB) structures together with 4 × 4 ReO3‐type blocks confined by TTB matrices, allowing abundant pentagonal and quadrangular tunnels for Li+ transport. These large‐sized tunnels combine with the large interlayer spacing (≈3.95 Å) not only lead to extremely fast Li+ diffusivity but also small unit‐cell volume variations (maximum 2.1%) during lithiation/delithiation, thereby enabling the LiMn2O4//W7Nb4O31 full cell to possess excellent rate capability with a 50C versus 1C capacity ratio of 68.3%, ultrahigh power density of 9854 W kg–1, and superior cyclic stability with capacity retention of 89.7/66.7/72.0% at 1C/5C/50C over 1000/10 000/10 000 cycles. This comprehensive study demonstrates that the W7Nb4O31 nanorods are highly promising for fast‐ and stable‐charging ALIBs.