LiCoPO4 and Li2CoSiO4 Nanoparticles Synthesis by Supercritical Fluid Process for Lithium Ion Battery Application

Wednesday, May 14, 2014
Grand Foyer, Lobby Level (Hilton Orlando Bonnet Creek)
M. K. Devaraju (Institute of Multidisciplinary Research for Advanced Materials, Tohoku University), Q. D. Truong (Tohoku University), and I. Honma (Institute of Multidisciplinary Research for Advanced Materials, Tohoku University)
In recent years, transition metal polyanionic compounds such as phosphates and silicates are considered as promising positive electrode materials for lithium-ion batteries. These members of the lithium metal polyanion family have been a major focus of research for reasons of high safety, low cost and low environmental impact. Among, metal phosphate cathode material, LiCoPO4 electrode materials have received considerable attention for the application in lithium secondary batteries due to its high stability, non toxicity, good charge/discharge capabilities and cheap cost. Recently, polyanion-containing frameworks are of great research interest in the area of lithium ion batteries, because, these materials can reversibly insert/extract two lithium ions per formula unit would help to increase the capacity and energy density. Regarding this, silicates with the general formula Li2MSiO4 (M=Mn, Fe and Co) have been considered as potential lithium insertion/ extraction cathodes. Among silicates, Li2CoSiO4 is an attractive cathode due to its high operating voltage. In this work, we have used supercritical fluid process for  the synthesis of LiCoPO4 and Li2CoSiO4 nanoparticles and are investigated for lithium ion battery applications. LiCoPO4 and Li2CoSiO4 nanoparticles were synthesized from LiOH.H2O/Lithum acetyl acetonate, CoCl3.6H2O/C4H6CoO4.4H2O and H3PO4/TEOS in molar ratio of 1:1:1 for LiCoPO4 and 4:1:1 for Li2CoSiO4 nanoparticles via supercritical fluid process. Cheap solvents such as water, ethanol and water-ethanol mixed solvents were used to prepare precursor solutions and reducing agents were also used in the synthesis. Supercritical synthesis was carried out at 400-450oC for about 5-10 min of reaction time. Then, the products were washed thoroughly in water and ethanol followed by vacuum dry for overnight. The as-synthesized LiCoPO4 and Li2CoSiO4 nanoparticles  showed 20-150 nm in diameter,  which was analysed by transmission electron microscopy (TEM). Further, LiCoPO4 and Li2CoSiO4 nanoparticles were systematically characterized using powder X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), scanning transmission electron microscopy (STEM), energy dispersive spectroscopy (EDS) and charge-discharge measurements. The discharge capacities of 80-110 mAhg-1 for LiCoPO4 nanoparticles and 40-110 mAhg-1 for Li2CoSiO4 nanoparticles were observed. The electrochemical property was measured by galvanostatic discharge method using 1M LiPF6 mixed in EC:DEC as electrolyte. The electrode was prepared using 10 wt% PTFE as binder. The weight ratio of active material:AB:PTFE are 80:10:10.