Hewettite ZnV₆ O₁₆  ⋅ 8H₂ O with Remarkably Stable Layers and Ultralarge Interlayer Spacing for High-Performance...

Aqueous Zn-ion batteries (ZIBs) are promising candidates for grid-scale energy storage because of their intrinsic safety, low-cost and high energy-intensity. Vanadium-based materials are widely used as the cathode of ZIBs, especially A₂ V₆ O₁₆  ⋅ nH₂ O (AVO, A=NH₄ ⁺ , Na, K). However, AVO suffers from serious dissolution, phase transformation and narrow gallery spacing (∼3 Å), leading to poor cycling stability and rate capability. Herein, we unveiled the root cause of the performance degradation in the AVO cathode and therefore developed a new high-performance cathode of ZnV₆ O₁₆  ⋅ 8H₂ O (ZVO) for ZIB. Through a method of ion exchange induced phase transformation, AVO was converted to hewettite ZVO with larger gallery spacing (∼6 Å) and more stable V₆ O₁₆ layers. ZVO cathode thus constructed delivers a high capacity of 365 and 170 mAh g^-1 at 0.5 and 15 A g^-1 , while 86 % and 70 % of its capacity are retained at 0.5 A g^-1 after 300 cycles and at 15 A g^-1 after 10000 cycles, substantially better than conventional AVO.