Binary Eutectic Fluoride Salts Modification Enhancing Structural Stability of Layered Oxide Cathodes for Na-ion Batteries

Abstract

Na-ion batteries (NIBs) have garnered significant attention due to the abundance and low cost of sodium resources, yet the limited capacity and poor stability of cathodes remain bottlenecks for practical use. This study proposes an innovative binary LiF-CaF₂ eutectic molten salt (BEMS) modification strategy, enabling atomic-level uniform selective ion doping and fluoride interface modification of O3-type NaNi_1/3Fe_1/3Mn_1/3O₂ (NFM) via a single-step sintering process. This synergistic modification significantly simplifies the phase transition pathway from the O3 to P3 phase during Na⁺ extraction and intercalation, increasing the structural stability of the O3 phase and mitigating structural and interfacial side reactions at high voltage and rates. The modified 2%BEMS@NFM exhibits higher reversible capacity, excellent rate performance, and stable cycling capability (achieving an 82% capacity retention after 1000 cycles at 1 C in full cell). Structural analyses reveal that BEMS modification reduces the unit cell volume change during phase transitions, improving interfacial stability. This study provides novel insights and effective methods for developing high-performance and stable layered oxide cathodes for NIBs.