Significantly Enhanced Electrochemical Redox for High‐Performance Electrochemical Capacitor via Active Ion‐Tunnel Oriented BaCoF4 Electrodes

Active plane and specific morphology with reduced particle sizes have long been considered a promising strategy to achieve superior electrochemical properties, but the active sites involved may not be sufficiently utilized or the surface atomic configurations may obscure the activity. Herein, a novel structural “active orientation” strategy is developed to overcome the aforementioned shortcomings and improve the efficiency at active sites. A transition‐metal fluoride BaCoF4 is well controlled to thin the dimensions along an active [31¯0] orientation through a sodium dodecyl benzene sulfonate assisted solution chemistry route. The active orientation facilitates the opening of the ionic pathways, for example, OH– in the electrolyte, to take full advantage of the redox activity of the electrochemically active Co2+/Co3+ cations in [31¯0]‐BaCoF4, resulting in significantly enhanced electrochemical redox performance. A high specific capacitance (692 F g−1 at 1 A g−1 in 6 m KOH electrolyte) is achieved owing to active‐tunnels orientation, ≈five‐fold higher compared to its bulk counterpart. Strikingly, the asymmetric electrochemical capacitor (AEC) fabricated with [31¯0]‐BaCoF4 and activated carbon exhibits an ultrahigh energy density of 147.7 Wh kg−1 at a power density of 1.025 kW kg−1 (also >100 Wh kg−1 at 5 kW kg−1), much higher than the majority of existing AEC systems. A novel structural “active orientation” strategy is developed to sufficiently utilize the active sites via controlling over the active ion tunnels in BaCoF4. The [31¯0]‐oriented BaCoF4 based asymmetric electrochemical capacitor (AEC) exhibits an ultrahigh energy density of 147.7 Wh kg−1 at 1.025 kW kg−1 that is superior to a majority of existing AEC systems.