Effects of fluoroethylene carbonate additive on potassium metal anode

Fluoroethylene carbonate (FEC) is an excellent additive for Li and Na metal batteries by constructing a robust solid electrolyte interface (SEI). However, the effects of FEC in K metal batteries are still under debate. Herein, we observed that FEC addition into carbonate electrolytes with salts of KPF 6 and KFSI leads to deteriorate electrochemical performances. FEC increased overpotential and charge transfer resistance. Meanwhile, FEC increased oxidation stability and thus was helpful to expand voltage window of a cell. When FEC was added, gas evolution was suppressed. From X-ray photoelectron spectroscopy, we found that the electrochemical behavior and gas generation are highly related to KF-rich SEI. This study reveals that the FEC has both sides of coins for K metal batteries unlike the effect of FEC on Li metal.