Tailoring iron phosphate precursors via microcrystallization for high-performance lithium iron phosphate cathodes in lithium-ion batteries

Abstract

The lithium iron phosphate (LiFePO₄; LFP) cathode is gaining prominence owing to its exceptional electrochemical performance, thermal stability, and cost-effectiveness. The properties of the iron phosphate precursor considerably influence the performance of the LFP cathode. Consequently, we established that a microcrystallization process under varied pH conditions leads to a smaller, more uniform and highly crystalline precursor of FePO₄·2H₂O, in contrast to the amorphous FePO₄·xH₂O obtained prior to microcrystallization. This microcrystallization process also effectively removes undesired impurities that lead to metallic iron in the LFP cathode. Notably, LFP synthesized using a precursor microcrystallized at pH 2.6 shows superior physicochemical properties, including higher crystallinity, reduced lattice defects, and improved cycling stability and rate capability. These findings demonstrate that microcrystallizing FePO₄·xH₂O into FePO₄·2H₂O under controlled pH and temperature conditions effectively improves the crystal structure of LFP, thereby contributing to enhanced electrochemical performance for advanced Li-ion batteries.