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

In this work, FeCo-Se and NiCo-PO 4 were electrodeposited on nickel foam (NF) successively to prepare a cathode material for asymmetric supercapacitors (ASCs) and NiCo//Bi batteries. FeCo-Se@NiCo-PO 4 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-PO 4 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-PO 4, FeCo-Se@NiCo-PO 4 delivers a rapid electron/ion transfer capability and superior electrochemical performance. The FeCo-Se@NiCo-PO 4 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.