Solid state synthesis of LiFePO₄/C: Using low cost materials

Cathode materials have been the most important components of the Li-ion secondary battery research because they generally determine the capacity and safety of Li-ion battery (LIB). In order to decrease the cost of LIBs, main efforts are devoted to the cost reduction of the electrode materials. As a consequence, low cost raw materials are considered for cost reduction. Iron (III) phosphate has recently gained interest as a compatible source of both iron and phosphate in the field of LIB. It is prepared by a precipitation technique from aqueous solution. The starting material is Fe(NO₃)₃ • 9H₂O, in this study, which is one of the cheapest iron sources for LiFePO₄ cathode preparation. The olivine-type LiFePO₄/C composites are synthesized by a solid state reaction process using pre-milled Li₂CO₃ and pre-synthesized amorphous FePO₄ • xH₂O powders. The pre-synthesized FePO₄ • xH₂O powders are mixed with pre-milled lithium carbonate and glucose (8 wt.%) using either water or alcohol solvent sequentially via ball-mill process. The main purpose of the present study is to investigate Fe(NO₃)₃ • 9H₂O as a source material and explore the effect of precursor mixing solvent, if any, on the microstructure and electrochemical property of LiFePO₄ cathode materials. The structural characteristics of LiFePO₄/C composites are examined by XRD, SEM and TEM. To investigate the mixing solvent effect on the electrochemical property in LiFePO₄/C composites, a Li[LiPF₆ (ethylene carbonate + dimethyl carbonate)] LiFePO₄/C model cell is used. It is demonstrated that the LiFePO₄/C synthesize by using alcohol solvent exhibits the better electrochemical performance than that of water one. The reason of such kind of behavior is explicated by their corresponding TEM micrographs.