Solution Processed NiO Nanoparticles towards High-Energy and High-Power Density Inkjet-Printed Supercapacitors

Name of the conference: Materials Research Society (MRS) Conference

Date of publication: 1- 6 December 2019

Abstract: The push towards self-powered electronics through energy harvesting, calls for the development of high-performance supercapacitors that can enable sustained, autonomous operation of electronic devices for applications such as wearable electronics, biomedical implants and internet-of-things. Low cost supercapacitors with high energy density can potentially work as stand-alone and maintenance-free power sources when combined with energy harvesters. Therefore, great efforts have been devoted to extend the energy density of these storage systems by using pseudocapacitive transition-metal oxides, which store energy by fast surface redox reactions, enhancing the storage ability of the system, while keeping the energy/cost ratio low. The limited electronic conductivity of most pseudocapacitive oxides leads to high electrode resistance and, consequently, lower power densities. As a result, pseudocapacitive devices with high energy density and high-rate handling ability remain a major challenge. Considering the pressing need for high-power and high-energy density storage devices through low-cost fabrication strategies, our work focuses on the fabrication and integration of high performance, fully solution processed, co-planar NiO micro-supercapacitors through inkjet printing. In this study, the phenomenon of electrical conductivity enhancement of NiO when the material is processed at the nanoscale, was exploited through a developed nanoparticle-based, inkjet-printable ink that was used to produce highly porous NiO electrodes that demonstrated up to 14 orders of magnitude higher electrical conductivity compared to single crystal NiO. To the best of our knowledge, this is the highest electrical conductivity for NiO film reported to date. The enhanced conductivity of the electrodes was reflected in the ultra-high charge/discharge rate handling ability of up to 50,000 mV·s-1 and the low relaxation time constant of just 30 ms of the devices, which is among the lowest achieved for any supercapacitors. A surfactant-based saturated magnesium perchlorate aqueous gel electrolyte with extended operating voltage window was developed to enable the operation of the devices up to 1.5 V. The devices showed remarkable areal and volumetric specific capacitances of up to 155 mF·cm-2 and 705 F·cm-3 at 5 mV·s-1 respectively, surpassing the best micro-supercapacitors known. The superior energy and power density of the devices bridges the gap between lithium-ion batteries and electrolytic capacitors, opening new exciting opportunities in the field of electrochemical energy storage and harvesting.