Uncovering lithium iron metaphosphate as a cathode material through organophosphate-assisted one-pot synthesis.

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.