Uncovering Lithium Iron Metaphosphate as a Cathode Material Through Organophosphate Assisted One-Pot Synthesis

Abstract

Metaphosphate–based polyanionic compounds represent an underexplored class of cathode materials for lithium–ion batteries, despite their rigid framework chemistry and intrinsic safety advantages. Herein, we report the first systematic investigation of lithium iron metaphosphate (LiFe(PO3)3) as a lithium–ion battery cathode material, demonstrating its controlled synthesis, crystal structure evolution, carbon integration, and intrinsic electrochemical behavior. A facile one–pot strategy is developed to synthesize carbon–supported LiFe(PO3)3 nanoparticles by employing LiFeO2 as the metal source and phosphonic acid as a dual phosphate and carbon precursor. This process enables in–situ carbonization and the formation of size–controllable orthorhombic LiFe(PO3)3 uniformly anchored on conductive carbon nanosheets. In contrast to the common emphasis on nano–sizing, we show that increased crystallite size can mitigate Li+ cross grain–boundary diffusion, thereby contributing to improved electrochemical performance. This work establishes LiFe(PO3)3 as a previously unexplored polyanionic Li–insertion host and provides a pioneering study for further exploration of metaphosphate–based cathode chemistries.