Large discharge capacities at high current rates for carbon-coated LiMnPO4 nanocrystalline cathodes

Nanocrystalline LiMnPO4 particles approximately 100 nm in size are synthesized for use as a cathode material using a hydrothermal method. Small charge transfer resistances (R-ct) measured using electrochemical impedance spectroscopy (EIS) indicate that the particles are effectively coated with the conductive C layer by pyrolyzing sucrose in an inert atmosphere. The cathode composed of nanocrystalline C-coated LiMnPO4 exhibits the largest specific capacities of 171 mAhg(-1) and 153 mAhg(-1) for the first cycle and 166 mAhg(-1) and 146 mAhg(-1) after 110 battery cycles at a rate of 0.05 C at 55 degrees C and 25 degrees C, respectively, with a degradation rate of 4 +/- 1% after 110 battery cycles. The specific capacities are 165 mAhg(-1) and 142 mAhg(-1) for the first cycle at 55 degrees C for the nanoparticles with high crystallinity, even at high discharging current of 0.5 C and 5C, respectively. Diffusion coefficients of Li+ in LiMnPO4 (the fully discharged state) and in MnPO4 (the fully charged state) are estimated to be 3.58 x 10(-16) and 4.99 x 10(-17) cm(2)s(-1), respectively, from EIS in the low frequency region. (C) 2013 Elsevier B.V. All rights reserved.