Modelling the bottom effect of electrochemical devices with large aspect ratios in α-MnO2 based Zn2+ pouch cells

Aqueous zinc-ion batteries (ZIBs) are promising for energy storage due to their high safety, but Zn 2+ distribution characters in cathodes remains poorly understood. In this study, we comprehensively map the overall Zn 2+ distribution profiles and reveal localized nonuniform distribution characteristics in a representative α-MnO 2 cathode. Two striking features of the nonuniform distribution are identified: the ‘bottom effect’ characterized by substantially higher Zn concentration at the electrode bottom, and ‘inactive areas’ where Zn concentration is extremely low. The bottom effect occurs only under specific initial electrode capacity and nonuniform discharging current-density distribution. Inactive areas are distinguished by the absence of Zn 4 (SO 4 ) (OH) 6 ·xH 2 O (ZSH) nanosheets on the surface, which probably results from poor wettability with the aqueous electrolyte due to lack of hydrophilic α-MnO 2 . This conceptual framework offers new insights for developing strategies to mitigate these issues and enhance electrode performance.