BiOI Nanopaper As a High-Capacity, Long-Life and Insertion-Type Anode for a Flexible Quasi-Solid-State Zn-Ion Battery

The development of intercalation anodes with high capacity is key to promote the progress of "rocking-chair" Zn-ion batteries (ZIBs). Here, layered BiOI is considered as a promising electrode in ZIBs due to its large interlayer distance (0.976 nm) and low Zn²⁺ diffusion barrier (0.57 eV) obtained by density functional theory, and a free-standing BiOI nanopaper is designed. The process and mechanism of Zn(H₂O)²⁺ insertion in BiOI are proved by ex situ X-ray diffraction, Raman, and X-ray photoelectron spectroscopy. The suitable potential (0.6 V vs Zn/Zn²⁺), high reversible capacity (253 mAh g^-1), good rate performance (171 mAh g^-1 at 10 A g^-1), long cyclic life (113 mAh g^-1 after 5000 cycles at 5 A g^-1), and dendrite-free operation of BiOI nanopaper prove its potential as a superior anode. When it is coupled with Mn₃O₄ cathode, the quasi-solid-state battery exhibits a high initial capacity of 149 mAh g^-1 (for anode) and a good capacity retention of 70 mAh g^-1 after 400 cycles. The self-assembled flexible battery also shows stable charge-discharge during the cyclic test. This work shows the feasibility of BiOX anode for dendrite-free ZIBs.