Ultrafine Ni(OH)₂ nanoplatelets grown on 3D graphene hydrogel fabricated by electrochemical exfoliation for high-performance battery-type asymmetric supercapacitor applications

Rechargeable energy storage systems with merits of durable, powerful, and inexpensive are urgently desired along with the rapid development in portable electronics and electric vehicles. Herein, a facile electrochemical method is employed to prepare a free-standing exfoliated graphite (EG) electrode with significantly enhanced surface area and pore volume. Then a binder-free composite electrode is fabricated by a double-phase (DP) electrochemical deposition of vertical arrays of Ni(OH)₂ throughout the EG hydrogel electrode in an organic electrolyte. The obtained composite, Ni(OH)₂@EG-DP, exhibits battery-type capacitive behavior and much higher capacity than its counterparts fabricated either by single-phase electrochemical deposition or with non-exfoliated graphite foil. Ni(OH)₂@EG-DP also exhibits remarkable rate capability and cycling stability, due to the well-dispersed ultrathin Ni(OH)₂ nanoplatelets and the graphene-like expanded gallery of EG, enabling the efficient transportation of both electrons and ions. When coupling with an active carbon anode, the assembled asymmetric supercapacitor shows 84.5% capacity retention after 20000 cycles at 8 A g⁻¹, and a high energy density of 34.7 Wh kg⁻¹ at the power density of 15 kW kg⁻¹. This work opens an avenue towards the efficient construction of free-standing three-dimensional (3D) conductive substrates and high-performance 3D hybrid electrodes using electrochemistry.