Stretchable supercapacitors made with plasticine/graphene/CeNdNiO2 composite electrodes

Abstract

Mechanically strong, flexible and deformable supercapacitors (SCs) are of particular interest for the wearable electronics. Therefore, stretchable dual SCs composed of two single devices were fabricated and studied in this research. Soft SC electrodes were made of plasticine decorated with graphene microplates and had cylindrical shape. To enhance the capacitance of the devices, Ce0.8Nd0.1Ni0.1O2-δ (CNNO) particles were added as redox material in the SC electrodes. Electrochemical tests were performed for the single SCs made only with graphene electrodes and produced capacitances/energy-densities of 178–215 F g−1/24–30 W h kg−1. When the single graphene supercapacitors are connected in-series, a maximum specific capacitance/energy density of 370.9 F g−1/51.4 W h kg−1 is obtained. The single SCs made with CNNO particles had higher specific capacitances/energy-densities of 326–436 F g−1/45–61 W h kg−1. The SCs made with CNNO were connected in-series and in-parallel, producing specific capacitances/energy densities of 257.1 F g−1/35.7 W h kg−1 and 516 F g−1/71.7 W h kg−1, respectively. Thus, incorporating the CNNO particles to the SCs enhanced their capacitance by 51–144%. According to the CV curves, the current densities are increased from 6 to 15 A g−1 to 37 A g−1 when the single devices are connected in-parallel. If the single devices are connected in-series, the output voltages of the supercapacitors increased from 1 to 1.3 V. The devices were also subjected to stretching at 25% and the capacitance dropped by 90–96.5% because the electrodes were broken. However, the devices were unstretched and the capacitance was recovered by ≈ 40–60%. If those last devices are heated at 50 °C, the SC electrodes are totally repaired, and the capacitance is even 12–33% higher in comparison with the original capacitance for the non-stretched device. Additionally, absorbance, Raman and XPS analyses revealed the presence of oxygen vacancies, Ce3+/Ce4+, Nd0/Nd1+/Nd3+ and Ni0/Ni2+/Ni3+, which worked as redox centers for the charge storage. In summary, the results presented here demonstrate that our stretchable SC can operate in-series or in-parallel connection and their electrodes can be re-built after applying heat. The cost of those SCs is drastically reduced because they are made with plasticine and due to their flexibility and stretchability, they are good candidates for wearable applications, which require deformable devices.