Nucleation and Growth Controlled Polyol Synthesis of Size-Focused Nanocrystalline LiFePO4 Cathode for High Performance Li-Ion Batteries

Mono-dispersed and densely packed, LiFePO4 cathodes with high rate performance versus lithium were synthesized using a two-step polyol process. The particle-size distribution and packing density of LiFePO4 nanoparticles were fine-tuned via separation of the nucleation and particle growth processes in the polyol medium by varying reaction time and temperature. Precisely, the LiFePO4 samples were synthesized by heating the reaction mixtures at 200 degrees C for various reaction times (0, 1, 3 and 6 h) to facilitate nucleation and thereafter the solution temperature was raised and maintained at 320 degrees C to facilitate the crystal growth process. XRD studies confirmed the formation of olivine phase in all the samples. The FE-SEM, FE-TEM and particle-size distribution studies illustrate that the particle-size of olivine nanocrystals may be tuned to approximately 200 nm by controlling the aging time at 200 degrees C or in other words separating the nucleation and crystal growth process. The olivine cathodes synthesized by maintaining 3-6 h aging time demonstrate improved discharge capacities and cycle performances in comparison to those of the remaining samples. In particular, the 6 h olivine cathode registered average discharge capacities of 130, 87 and 64 mAh/g at 5 C, 10 C and 15.7 C current rates respectively. (C) 2014 The Electrochemical Society. All rights reserved.