Regulating anion chemistry with F-containing bonds enable superior potassium ions storage in hard carbon

The high reactivity of potassium metal and the large potassium ion radius lead to increased side reactions and poor stability at the electrode/electrolyte interface. Constructing a stable electrode/electrolyte interface is essential to develop high-performance potassium ion storage devices. Herein, we propose an anion chemistry strategy to enhance interfacial stability by modulating the F-containing bonds in electrolyte potassium salts. Compared to C-F and P-F bonds, the experimental results, together with theoretical calculations, revealed that the S-F bonds are more likely to break to facilitate the formation of dense, robust, stable and KF-rich SEI films with high ionic conductivity. Meanwhile, the electrochemical impedance spectroscopy reveals the unique role of S-F-containing potassium bis(fluorosulfonyl)imide (K((FSO2)2N), KFSI) electrolytes in stabilizing potassium metal, which inhibits electrolyte decomposition and potassium dendrite formation. The synergistic stabilization of electrode and potassium metal by KFSI electrolyte effectively boosts the Coulomb efficiency, rate capability (4.7 and 1.8 times higher than those obtained with P-F and C-F-containing electrolytes) and cycling performance (capacity retentions of 80.4%, 1.4% and 47.7% for S-F, P-F and C-F-containing electrolytes after 1000 cycles at 1 A g-1, respectively) of hard carbon anode. This work reveals the importance of anion chemistry in regulating interfacial properties and provides a valuable insight into the rational design of interfacial chemistry.

Automated summary

This study proposes an anion chemistry strategy to enhance interfacial stability by modulating the F-containing bonds in electrolyte potassium salts. The results show that S-F bonds are more likely to break and form dense, robust, stable and KF-rich SEI films with high ionic conductivity, which effectively stabilizes potassium metal.