Failure mechanisms and remedy of an ultrathin Zn metal anode in pouch cells

Zinc (Zn) metal anodes have attracted much attention for their use in aqueous Zn batteries. However, their electrochemical behavior and failure mechanisms under practical conditions remain unclear, and their cycling performance is far from the target for practical use. Here, we have developed a failure mechanism map of ultrathin Zn metal anodes in practical large (49 cm²) pouch cells and divided it into three zones, i.e., polarization, short-circuiting, and transition between the two. The correlation between failure mode and depth of discharge was revealed. Moreover, to improve the durability of large Zn anodes, a molecular interfacial layer was designed to produce compact epitaxial growth of Zn. Consequently, practical Zn||I₂ pouch cells with modified Zn anodes had a high capacity (∼1,200 mAh) and cycling stability (∼600 cycles), which is the record-stable Ah-level full cell reported so far. This work provides both fundamental and practical insights for accelerating the use of Zn batteries.