Methyl propionate-dominant electrolyte for enhanced kinetics and low-temperature performance of Prussian blue analogue-based rechargeable sodium-ion batteries

Abstract

The design of the electrolyte is an essential factor in enhancing fast ion-transport kinetics and overall stability in sodium-ion batteries (SIBs). Herein, we report a methyl propionate-based electrolyte with 10% fluoroethylene carbonate (MPF) that significantly outperforms a conventional ethylene carbonate-based electrolyte (ECDF) for Prussian blue analogue (PBA) cathodes. The MPF electrolyte demonstrates exceptional low-temperature ionic conductivity (5.8 mS cm⁻¹ at −20 °C) and an expanded electrochemical stability window of 5.6 V. Kinetic analysis via GITT reveals Na⁺ diffusion coefficients an order of magnitude higher than those of ECDF. Consequently, the PBA|MPF|Na cells exhibit an exceptional rate capability, retaining 96.87% of their capacity at 10C (normalized to 1C). Furthermore, excellent low-temperature performance is demonstrated at −20 °C, with capacity retention of 86.68% after 300 cycles at 1C. The MPF-based cell forms a thinner and fluorine-rich cathode–electrolyte interphase (CEI), reducing interfacial resistance in comparison to ECDF. A full coin cell delivers high reversible capacities (155 mA h g⁻¹) and a pouch cell demonstrates stable operation, maintaining 78% capacity retention after 200 cycles at 1C with near-unity coulombic efficiency. These findings highlight the key role of electrolyte design in enabling high-performance, wide-temperature, and long-life SIBs suitable for practical applications.