Fast-Charging Single-Crystalline O3-NaNi1/3Fe1/3Mn1/3O2 via Molten Salt Synthesis for Sodium-Ion Batteries

Abstract

O3-type cathodes in sodium-ion batteries (SIBs) are the most promising cathodes with higher sodium content and energy density than the P2-type cathodes. Along with standard battery performance metrics, fast-charging cathodes with high-rate kinetics and cycle stability are crucial for advancement in SIB technologies. The single-crystalline materials show improved cycling stability, and when combined with particle size control, result in high-rate performing and long cycle life cathodes. Herein, we report a molten salt-synthesized single-crystalline O3-NaNi_1/3Fe_1/3Mn_1/3O₂ (NFM) cathode with control over particle size/distribution through optimized molten salt ratios. The NFM cathode obtained from a 40:1 salt ratio shows rate capabilities of 102@1C, 93@2C, 75@5C (1C = 240 mAh g⁻¹), improving fast-charging kinetics. NFM showed impressive cycling stability at 68% retention after 200 cycles at 1C, 83% at 2C, and 76% at 5C after 100 cycles. This work offers a simple molten-salt synthesis for ∼1–2 µm-sized single-crystalline particles to achieve good rate capabilities through effective charge transfers and high ionic diffusion kinetics, which holds the future promise for fast charging and durable SIBs.