Effect of the Heating Rate to Prevent the Generation of Iron Oxides during the Hydrothermal Synthesis of LiFePO 4

Nanomaterials (Basel). 2021 Sep 16;11(9):2412. doi: 10.3390/nano11092412.

Abstract

Lithium-ion batteries (LIBs) have gained much interest in recent years because of the increasing energy demand and the relentless progression of climate change. About 30% of the manufacturing cost for LIBs is spent on cathode materials, and its level of development is lower than the negative electrode, separator diaphragm and electrolyte, therefore becoming the "controlling step". Numerous cathodic materials have been employed, LiFePO4 being the most relevant one mainly because of its excellent performance, as well as its rated capacity (170 mA·h·g-1) and practical operating voltage (3.5 V vs. Li+/Li). Nevertheless, producing micro and nanoparticles with high purity levels, avoiding the formation of iron oxides, and reducing the operating cost are still some of the aspects still to be improved. In this work, we have applied two heating rates (slow and fast) to the same hydrothermal synthesis process with the main objective of obtaining, without any reducing agents, the purest possible LiFePO4 in the shortest time and with the lowest proportion of magnetite impurities. The reagents initially used were: FeSO4, H3PO4, and LiOH, and a crucial phenomenon has been observed in the temperature range between 130 and 150 °C, being verified with various techniques such as XRD and SEM.

Keywords: crystallinity and purity; heating rate; hydrothermal synthesis; lithium iron phosphate; morphology.