An improved synthesis of iron phosphate as a precursor to synthesize lithium iron phosphate

Abstract

Two different kinds of $$\hbox {FePO}_{4}$$ : amorphous $$\hbox {FePO}_{4}$$ and crystalline $$\hbox {FePO}_{4}$$ , were synthesized as a precursor to synthesize $$\hbox {LiFePO}_{4}/\hbox {C}$$ . The crystalline $$\hbox {FePO}_{4}$$ was obtained by treating amorphous $$\hbox {FePO}_{4}$$ with phosphoric acid refluxing. Inductively coupled plasma-atomic emission spectrometry was used to evaluate the impurity content. The obtained materials were characterized by chemical analysis, scanning electron microscopy and X-ray diffraction. The results showed that the performance of $$\hbox {LiFePO}_{4}/\hbox {C}$$ synthesized by crystalline $$\hbox {FePO}_{4}$$ is significantly better than when $$\hbox {LiFePO}_{4}/\hbox {C}$$ is synthesized from amorphous $$\hbox {FePO}_{4}$$ . The capacity retention and capacity fade of $$\hbox {LiFePO}_{4}/\hbox {C}$$ synthesized from crystalline $$\hbox {FePO}_{4}$$ was 70.9% at $$-\,20{^{\circ }}\hbox {C}$$ and 0.012% per cycle after 150 cycles at 1C, respectively. The better performance from using crystalline precursor resulted from a more uniform powder with fewer crystalline defects and impurities.