Morphology Controled LiFePO4 Electrodes Via Polyol Refluxing for Enhanced Lithium-Ion Battery Performance

Abstract

In the synthesis of LiFePO4 cathodes with secondary nanorod structures and nano-plate morphologies, researchers utilized a polyol refluxing process. Notably, we achieved this without the use of characteristic structure directing agents. Through varying the reaction time, they were able to modulate the morphological characteristics of the synthesized samples.X-ray diffraction studies conducted on the prepared samples indicated a highly crystalline nature. This suggests that the synthesized cathodes possessed a robust and ordered atomic structure, which is crucial for their electrochemical performance.Electron microscopy investigations provided insights into the morphology of the samples obtained at different reaction times. Samples produced after 1 to 16 hours of polyol reaction exhibited secondary nanorod bundles. However, the sample recovered after 32 hours of polyol reaction displayed a distinct nano-plate morphology. These observations highlight the influence of reaction time on the final morphology of the synthesized cathodes.The dimensions of the obtained samples ranged from a few tens to a few hundred nanometers. This nano-scale size is advantageous for enhancing the electrode's surface area, which can facilitate rapid ion diffusion and electron transport during battery cycling.When employed in lithium test cells, the LiFePO4 cathodes synthesized for different durations delivered varying discharge capacities. Specifically, cathodes prepared under 1, 4, 8, 16, and 32 hours of reaction time exhibited discharge capacities of 161, 162, 171, 143, and 155 mAhg−1, respectively. Notably, all samples displayed a well-defined discharge plateau at 3.4 V, indicating stable electrochemical behavior during cycling.Remarkably, among the prepared electrodes, the LiFePO4 nanorod bundle cathode synthesized under 1 hour reaction time demonstrated the highest average reversible capacities. It maintained capacities of 123 and 103 mAhg−1 at C-rates as high as 3.2 and 6.4 C, respectively. This highlights the importance of reaction time in controlling the electrochemical performance of the synthesized cathodes.The crystal growth mechanism during the polyol refluxing method can be elucidated through several stages. These include precursor dissolution and nucleation, oriented crystal growth and alignment through self-assembly, aggregation, partial dissolution, and finally, complete re-crystallization. Understanding these mechanisms is essential for optimizing the synthesis process and tailoring the properties of LiFePO4 cathodes for various applications. Tarascon JM, Armand M. Issues and challenges facing rechargeable lithium batteries. Nature 2001;414:359–67Amatucci GG, Tarascon JM, Klein LC. CoO2, the end member of the LixCoO2 solid solution. J Electrochem Soc 1996;143:1114–23Ravet N, Chouinard Y, Magnan JF, Besner S, Gauthier M, Armand M. Electroactivity of natural and synthetic triphylite. J Power Sources 2001;97–98:503–7 Figure 1