Fluorinated sodiophilic interphase for high-rate and low-temperature initially anode-free sodium battery

Abstract

Sodium-ion batteries are promising as next-generation energy storage batteries, while suffer from the limited energy density. Initially anode-free sodium batteries effectively alleviate this predicament, but they are primarily hindered by uneven plating/stripping behavior, especially at high rates and low temperatures. Herein, we propose a fluorinated sodiophilic interphase towards high-rate and low-temperature initially anode-free sodium batteries. Systemically comparison between various interphase reveals that Na-alloying-metal containing interphase with high Na adsorption energy and low lattice mismatch facilitates uniform spherical Na plating under high current densities. Besides that, the in-situ formed sodium fluoride strengthens the mechanical properties of the interphase and regulates Na deposition. The optimized BiF3-derived interphase enables stable Na plating/stripping for over 2800 hours with an average Coulombic efficiency of 99.90%, high-rate capability at 20 mA cm−2, and low-temperature adaptability at −30 °C. Coupled with Na4Fe3(PO4)2P2O7 positive electrode, initially anode-free full batteries deliver specific powers of 8257.5 W kg−1 at 25 °C and 486.9 W kg−1 at −30 °C (based on the mass of active materials). The assembled pouch-cell operate stably at a high rate of 7 C (1 C = 100 mA g−1). This work provides a strategic framework for advancing initially anode-free sodium battery technology.