First exploration of LiFe(HPO3)2 as an anode material for Li-ion batteries

Abstract

In the search for novel negative electrode materials for Li-ion batteries (LiBs), this work is the first to explore the electrochemical behavior of lithium iron phosphite LiFe(HPO₃)₂ (LFPi) and its composites with reduced graphene oxide (rGO) (LFPi/rGO) as potential anodes. LFPi offers a three-dimensional framework with high phase purity and thermal stability, as confirmed by structural, spectroscopic and thermal characterizations. Electrochemical tests reveal a conversion-type mechanism primarily involving the redox activity of iron Fe³⁺, Fe²⁺/Fe⁰ systems. LFPi pristine delivers a reversible capacity of 210 mAh/g after 50 cycles at rate. The incorporation of rGO into LFPi through a two-step hydrothermal method significantly improves the electric conductivity of anode, which in turn enhances the anode's electrochemical performance and Li-ion diffusion. The optimized LFPi/rGO reaches 340 mAh/g after 50 cycles, with a lithium-ion diffusion coefficient of 4.18 × 10⁻¹⁰ cm²/s, twice that of pristine LFPi. This work demonstrates the potential of LFPi as anode and extends the landscape of phosphite-based materials for next-generation Li-ion batteries.