Unrevealing the Capacity Fading from Anode‐to‐Cathode Cross‐Talk in Prussian White Cathode

Abstract The rapid capacity fading of manganese‐based Prussian white (MnPW) is a significant challenge, hindering its practical application in sodium‐ion batteries. In regards to the capacity fading of MnPW, most of the research focuses on optimizing the structure of MnPW. In this work, it is surprisingly found that the capacity decay of MnPW is mainly caused by anode‐to‐cathode cross‐talk instead of the structural degradation of MnPW. This cross‐talk induces the formation of a thick ferrifluoride‐rich interface on the MnPW cathode, severely hindering ion transport and accelerating capacity fading. When activated carbon (AC) is employed as the counter electrode to mitigate this cross‐talk, the MnPW electrode can achieve a much higher capacity retention of 82.4% over 200 cycles than that matched with Na metal counter electrode (30.4% after 200 cycles). Furthermore, this strategy also works well for iron‐based Prussian white, achieving capacity retention of 80.0% after 1500 cycles, in contrast to 40.6% with Na metal counter electrode. These findings reveal the significant impact of anode‐to‐cathode cross‐talk for MnPW cathode and offer a promising path for the practical application of Prussian white in sodium‐ion batteries.