Cathodic electrophoretic deposition (EPD) of two-dimensional colloidal Ni(OH)2 and NiO nanosheets on carbon fibers (CF) for binder-free structural solid-state hybrid supercapacitor

The exponential growth of the renewable energies field and the increase of portable electric vehicles (EVs) demand a new generation of multifunctional efficient electrochemical energy storage devices (EESDs). In this work, binder-free hybrid battery-like electrodes were prepared by cathodic electrophoretic deposition (EPD). One-step (synthesis and deposition) processing of β-Ni(OH)2 was developed avoiding a previous calcination step to form NiO. The redox reaction (RR) contribution to the electrochemical performance of the hybrid electrodes was enhanced without influencing the mechanical properties of the CF substrate. Moreover, the sintering of the coated-CF under a high-vacuum atmosphere and the controlled mass deposition (<0.1 mg·cm−2) demonstrated to enhance the synergic effect of the redox reactions, ion diffusion (NiO) and the electrochemical double layer (CF) contributions. Thus, the hybrid electrodes in a half-cell configuration achieved remarkably high capacitance values (1161 F·g−1 at 2 A·g−1), while hybrid electrodes in a symmetric structural hybrid solid-state supercapacitor (HSSS) with an ionic liquid/resin structural solid-electrolyte reached a capacitance of 9.8 mF·g−1, a power and energy density of 3.5 mW·kg−1 and 1 mWh·kg−1 respectively and good electrochemical stability with a Columbic efficiency of 75 % at 0.8 mA·g−1.