Influence of pH-induced particle-size modulation on the electrochemical performance of spinel ZnFe2O4 anodes for lithium-ion batteries

Abstract

This study synthesizes ZnFe₂O₄ spinel via a co-precipitation method using ZnCl₂ and Fe(NO₃)₃·9H₂O as precursors, and the reaction pH is adjusted to 10, 11, and 12 to regulate the particle-size evolution. Based on the thermal analysis of the precursors, the resulting products inform the selection of the optimal calcination temperature for spinel formation (750 °C); the resulting samples are denoted as ZFO_pH 10, ZFO_pH 11, and ZFO_pH 12. Comparative analysis of the pH-regulated samples reveals that pH strongly influences the particle size and key electrochemical properties, including Li⁺-storage performance, cycling stability, and electrical conductivity. X-ray diffraction (XRD) analyses confirm that all samples predominantly comprise well-crystallized ZnFe₂O₄ without detectable secondary phases within the XRD detection limit. Notably, ZFO_pH 11 exhibits an average particle size of approximately 37 nm, which is considerably smaller than the approximately 42 nm particles observed in ZFO_pH 10. Consequently, the ZFO_pH 11 electrode delivers a high initial charge capacity of 992.78 mAh g⁻¹ and maintains a capacity of approximately 910.84 mAh g⁻¹ after 60 cycles at 0.1 A g⁻¹. These results demonstrate that pH adjustment is an effective strategy for tuning particle size and crystallinity, thereby enhancing electrochemical performance. Among the synthesized materials, ZFO_pH 11 demonstrates strong potential as an anode material for lithium-ion batteries owing to its favorable combination of particle size, crystallinity, and phase purity.