Experimental Visualization and the Mechanism of Current‐Collector Geometry Effects on Ion Distribution and Device Longevity

For electrochemical devices, electrode performances are fundamentally linked to cations' distribution. While simulations and modelling have revealed that current-collector geometry induces uneven current and charge distributions, and partial aging, experimental evidence, intrinsic mechanisms and solutions have remained unexplored. Herein, the 3D distribution of inserted ions in transition-metal-oxide cathodes and its ubiquitous bottom effect (i.e., accumulation of trapped cations at the bottom area far from the pole ear and the induced bottom aging) induced by the size effect of current collectors is depicted. Uneven distribution of embedded ions, accumulation of trapped cations, and bottom aging are experimentally visualized. An "end reflection model" is proposed and verified by designing the current collector with an extra-wide bottom or with a tiny blank at the bottom. Notably, these two designs solved the bottom effect and doubled the electrodes' cyclic life. This finding represents a milestone in the current-collector-geometry study and open new insights for regulating ion distribution.