For sodium‐ion batteries, two pressing issues concerning electrolytes are flammability and compatibility with hard carbon anode materials. Non‐flammable electrolytes that are sufficiently stable against hard carbon have—to the authors’ knowledge—previously only been obtained by either the use of high salt concentrations or additives. Herein, the authors present a simple, fluorine‐free, and flame‐retardant electrolyte which is compatible with hard carbon: 0.38 m sodium bis(oxalato)borate (NaBOB) in triethyl phosphate (TEP). A variety of techniques are employed to characterize the physical properties of the electrolyte, and to evaluate the electrochemical performance in full‐cell sodium‐ion batteries. The results reveal that the conductivity is sufficient for battery operation, no significant self‐discharge occurs, and a satisfactory passivation is enabled by the electrolyte. In fact, a mean discharge capacity of 107 ± 4 mAh g−1 is achieved at the 1005th cycle, using Prussian white cathodes and hard carbon anodes. Hence, the studied electrolyte is a promising candidate for use in sodium‐ion batteries.

Halogen‐Free and Flame‐Retardant Electrolyte for Sodium‐ion Batteries Apart from achieving a greater understanding of fluorine‐free electrolytes, it is essential to create safer electrolytes for the state‐of‐the‐art sodium‐ion batteries. In article number 2101135, Lars Olow Simon Colbin, Reza Younesi, and co‐workers demonstrate that using triethyl phosphate (TEP) with sodium bis(oxalato)borate (NaBOB) as the electrolyte will help to achieve this goal. Imagine if battery electrolytes could also help to fight fires, rather than fueling them—the case today.

Metallic bismuth is here studied as an anode material for sodium-ion batteries. The details of electrochemical redox reactions, rate performance and cycled life were investigated using relatively high mass loading...