A FeCo-Se@NiCo-PO₄ Electrode Designed by Hierarchical Strategy for Supercapacitors and NiCo//Bi Batteries

In this work, FeCo-Se and NiCo-PO₄ were electrodeposited on nickel foam (NF) successively to prepare a cathode material for asymmetric supercapacitors (ASCs) and NiCo//Bi batteries. FeCo-Se@NiCo-PO₄ combines the advantages of transition metal selenides (TMSs) and transition metal phosphates (TMPs). FeCo-Se electrodeposited in the underlying layer can facilitate electron transfer for higher conductivity. NiCo-PO₄ in the outer layer can facilitate OH^- ions diffusion because TMPs can be intercalated into ions readily and the outer robust P-O bond of TMPs can stabilize the structure. Precisely because the hierarchical structure maximizes the synergy between FeCo-Se and NiCo-PO₄, FeCo-Se@NiCo-PO₄ delivers a rapid electron/ion transfer capability and superior electrochemical performance. The FeCo-Se@NiCo-PO₄ exhibits a high specific capacitance of 2221.5 F g^-1 (888.6 C g^-1) at 1 A g^-1. Its aqueous ASC shows specific capacitance of 115.8 F g^-1 at 1 A g^-1 and all-solid-state ASC presents high reversibility. Its aqueous NiCo//Bi battery has superior durability of about 60% capacity retention and 98% Coulombic efficiency after 2300 cycles. And its all-solid-state NiCo//Bi battery possesses a higher energy density and power density.