Unveiling the structure-activity relationship of hollow spindle-like α-Fe2O3 nanoparticles via phosphorus doping engineering for enhanced lithium storage

Abstract

The low-cost earth-abundant transition metal oxides (TMOs) reveal high-capacity as post‑carbon anodes towards Li-ion batteries (LIBs), however, their intrinsically low electroconductivity, sluggish Li-ion diffusion and undesirably large volume change during cycles, strictly hamper their practical applications. Doping heteroatoms and designing hollow structures is a facile strategy in improving electronic/ionic conductivity and buffering volume expansion, respectively. Herein, a design strategy of inner-outer phosphorus (P) doped hollow spindle-like α-Fe2O3 nanoparticles (NPs), is introduced, where hollow spindle-like α-Fe2O3 NPs endure volume change during Li-ion (de-)intercalation process while inner-outer P-doping induced phase transition of Fe2O3-to-Fe3O4 causes P-Fe3O4/Fe2O3 heterojunction to improve the ionic/electronic conductivity and Li-ion active sites owing to abundant oxygen vacancies. Significantly, calcination temperatures determined the P contents, where increasing temperature from 300 °C (1 wt% P) to 500 °C (29 wt% P) exhibits the emergence and disappearance of P-Fe3O4/Fe2O3 heterojunctions and the transition of hollow-to-solid structures, which thus improves and attenuates their electrochemical performances, electronic/ionic conductivity and reaction kinetics. Notably, 10 wt% P doped Fe2O3 (350 °C) anode exhibits the remarkable rate capacity and cycle stability. This work thus deciphers the structure-activity relationship of electrode materials and opens a new avenue to enhance the electrochemical performance of energy storage devices.