Nanoarchitectonics for a long-life and robust Na-ion battery at low temperature with Prussian blue cathode and low-concentration electrolyte

Na-ion batteries are considered as promising battery systems for large-scale energy storage. Although Na-ion batteries exhibit enhanced low-temperature cycling performance compared with lithium-ion batteries, there is still a great challenge to overcome for practical low-temperature applications. In this work, we propose a low-performance Na-ion battery composed of FeNi co-doped Mn-based Prussian cathode (FeNi-MnHCF) and a low-concentration electrolyte (0.5 mol L−1) containing a small amount of 2,2,2-trifluoroethyl acetate (ETFA, 1 wt%). The introduction of ETFA could decrease the viscosity, increase ionic conductivity and change the solvation structure of the electrolyte at low temperature. ETFA could also participate in constructing a uniform, stable, and Na-ion conductive CEI layer, enabling rapid Na-ion transport and effective protection of FeNi-MnHCF. The cells with the ETFA-contained electrolyte and FeNi-MnHCF cathode exhibit excellent rate capability and long cycle life at low temperature. When being cycled at −20 °C, the cell with ETFA could retain 92.1 % of the capacity after 1120 cycles at 1 C. The cell could also show stable cycling after overcharge to 4.8 V or overdischarge to 1.2 V at −20 °C. This work sheds light on the design of long-life and robust Na-ion batteries for sustainable energy storage at low temperature.