Morphology-controlled LiFePO4 cathodes by a simple polyol reaction for Li-ion batteries

LiFePO4 cathodes with secondary nanorod structures and nano-plate morphologies were synthesized by varying the reaction time in a polyol refluxing process without the use of any characteristic structure directing agents. The X-ray diffraction studies indicate the highly crystalline nature of the prepared samples. Electron microscopy investigations revealed the morphology of the samples after 1 to 16 h polyol reaction to be secondary nanorod bundles whereas the olivine sample recovered after 32 h polyol reaction displayed nano-plate morphology. The dimensions of the obtained samples varied from a few tens to a few hundred nanometers. When employed in a lithium test cell, the LiFePO4 cathodes reacted for 1, 4, 8, 16 and 32 h delivered discharge capacities of 161, 162, 171, 143 and 155 mAhg− 1, respectively, with a well-defined plateau at 3.4 V and impressive capacity retentions until 50 cycles. Interestingly, among the prepared electrodes, the LiFePO4 nanorod bundle cathode prepared under 1 h reaction time maintained the highest average reversible capacities of 123 and 103 mAhg− 1 at C-rates as high as 3.2 and 6.4 C. The crystal growth mechanism during the polyol refluxing method can be explained by the stages of precursor dissolution and nucleation, oriented crystal growth and alignment by self-assembly, aggregation and partial dissolution and complete re-crystallization.