Electrochemical response of carbon doped LiFePO4 olivine nanoparticles: Cobalt doping and temperature calcination effects

Abstract

We report the preparation of carbon-coated cobalt-doped olivine nanoparticles (LiFe 1-x Co x PO 4 /C) by the citrate gel precursor combustion method at different calcination temperatures. This work reveals side effects of cobalt doping, and temperature calcination in the structure, carbon coating characteristics and electrochemical performance of olivine nanoparticles. First, we report the effects of active material/carbon ratio and surface load of active material on the electrochemical properties by evaluating discharge capacity values, reversibility and faradaic efficiency. Once cathode preparation conditions were optimised, information on relevant parameters such as diffusion coefficient of lithium ions can be obtained from the analysis of electrochemical results. Values of diffusion kinetic parameters determined from cyclic voltammetry were compared with those obtained from electrochemical impedance spectroscopy. Optimal electrochemical responses were observed from electrodes prepared with a 75% of active material and surface loads of 2 mg. cm −2 . Since all samples presents a similar crystalline size domain, we can conclude that differences in electrochemical performance can be attributed to the amount and structural features of the carbonaceous coating of the olivine crystals, despite of the fact that we are dealing we a very complex system when considering the cathode preparation.