Olivine-type nanoparticle for hybrid supercapacitors

Abstract

LiCoPO4 nanoparticles were precipitated from polyethylene glycol solution of lithium acetate, cobalt acetate, and ammonium dihydrogen phosphate by refluxing at 250 °C for 35 h. The resultant powder samples were heated at 800 °C for different time periods of 2 and 4 h to study the effect of annealing time on the growth of samples. The X-ray diffraction pattern of the obtained samples exhibited olivine phase. The scanning electron microscopic images of dried powder sample and samples heated at 800 °C for 2 and 4 h showed a homogenous orthorhombic morphology with a particle size of few nanometers range. For the first time, orthorhombic olivine was introduced as positive electrode for a hybrid electrochemical supercapacitor cell with carbon nanofoam as negative electrode in 1 M LiClO4 in ethylene carbonate and propylene carbonate (1:1 in volume) solution. A sloping voltage profile of 2 to 0 V is observed for all the three hybrid cells. From the impedance results, we inferred that LiCoPO4 nanoparticles synthesized by polyol process offers less resistance than lithium titanium oxide. According to the results of electrochemical testing for the first time, maximum power density of 192 W/kg at 11 Wh/kg energy density was obtained for LiCoPO4 nanoparticles annealed at 800 °C for 2 h. The dried sample and the sample heated at 800 °C for 2 and 4 h exhibited high capacitances of 5, 19, and 4 F/g, respectively, with an excellent rate capability over 1,000 cycles.