Capacitance Improvement of Semiconductor Electrode By LbL Modification

Abstract

In the last decades, supercapacitors have been considered as one of the most promising energy storage devices due to their large power density and their long cycle life. Carbon and binder-free technologies have been recently proposed based on the consolidation of semiconductor nanostructures to use as device electrodes [1, 2] due to its wider mechanical and thermal stability. Among oxide films, NiO has been intensively investigated in supercapacitors based on their high theoretical specific capacity values (2584 F/g), high chemical stability, ready availability and lower cost. Electrodes requirements of a supercapacitor, and consequently their delivered capacitance, are largely dependent on the microstructure characteristics. In particular, it strongly depends on the increase of the active surface area avoiding electronic conductivity fall. In fact, a well-connected mesoporous structure, with a high and narrow pore size distribution exhibits greatly improved electrochemical performance. The processing of those ceramic films through inexpensive and ecofriendly powder technologies is challenging. Among different approaches, the use of the colloidal techniques allows nanostructures tailoring, strengthening the control over the specific final properties. In this work, colloidal routes have been explored to improve the electrochemical response of a pseudocapacitor electrode based on a NiO nanostructure consolidated at low temperature (325°C) [3]. At this time, we have considered the surface modification of Ni(OH)2 nanoplatelets synthesized by ultrasound through the addition of polyelectrolytes to the suspension. The formation of different layers with polycationic and polyanionic electrolytes was studied. Polyethylenimine (PEI) and Polyacrylic Acid (PAA) were used as polyelectrolytes to form a Layer by Layer system. As a result the modified Ni(OH)2 nanoplatelets were stabilized in suspension and shaped by Electrophoretic Deposition (EPD) on Ni substrates, for later sinterization of films which were electrochemically tested. [1] D.-H. Ha, M.A. Islam and R.D. Robinson, Binder-free and carbon-free nanoparticle batteries: A method for nanoparticle electrodes without polymeric binders or carbon black, Nano Lett .12, 2012, 5122–5130. [2] S.Cabanas-Polo, Z. González, A.J. Sanchez-Herencia, B.Ferrari, A.Caballero, L.Hernan and J.Morales. Cyclability of binder-free β-Ni(OH)2 anodes shapes by EPD for Li-ion batteries, J. Eu. Cer. Soc., 35, 2015, 573-584 [3] Z. González, B.Ferrari, A.J. Sanchez-Herencia, , A.Caballero and J.Morales. A One-Step and Binder-Free Method to CoatStructures with NiO nanoplatelets. Influence of the Particle Packing in Supercapacitor Electrodes. J. Electrochem. Soc.