Synthesis of a cathode material $LiFePO_4$ for Li-ion batteries by spray pyrolysis and improvement of its electrochemical property

Abstract

$iFePO_4$ as a new promising cathode material for lithium-ion batteries has been developed because of economical and environmental advantages compared with currently used cathode materials such as $iCoO_2$. However, it was known that the low electrical conductivity is drawback of this material. In this thesis, $iFePO_4$ were prepared by the conventional spray pyrolysis varying the experimental conditions to find out the optimum condition for obtaining single phase of $LiFePO_4$. $H_2$ 5%/Ar mixed gas was used as a carrier gas for both spray pyrolysis and post-treatment to reduce $Fe^{3+}$ to $Fe^{2+}$ completely. Preparation temperature was fixed at 800℃ and prepared particles were post treated under different post-treatment conditions. To improve low electronic conductivity of $LiFePO_4$, sucrose as a carbon source was added directly into the precursor solutions and the effect of sucrose on the physical morphology and electrochemical properties of $LiFePO_4$ was studied. As maintaining reductive atmosphere throughout the process, $LiFePO_4$ was produced by the spray pyrolysis than by the solid state reaction method after post-treated at 750℃ for 4 hours. $LiFePO_4$ prepared by the spray pyrolysis showed similar discharge capacity to that prepare by the solid state reaction as 60~70mAh/g. Still low discharge capacity was increased by improving the intrinsically low electrical conductivity by adding sucrose as a carbon source, sucrose in this study. When sucrose was added to $LiFePO_4$, the recorded maximum capacity was 140mAh/g which is 2 times higher than pure one. Morphologies were also improved due to carbon incorporated in the particles.