Potassium metal has been considered as one of the ultimate anode for rechargeable potassium batteries because of its high theoretical capacity (686 mAh g^-1) and low electrode potential (~2.93 V vs. SHE). However, K metal is thermodynamically instable in aprotic electrolyte and uneven K plating usually leads to dendritic K metal deposition, resulting in low Coulombic efficiency and safety concerns.^1,2 In this study, we introduce potential strategy to stabilize the K metal anode via simple chemical interface control. The robust and ionically conductive passivation layer can be controllably designed by the spontaneous chemical reaction when a K metal foil kept in contact with a liquid phase potassium-polysulfide (0.05M K₂S₅ dissolved in DEGDME);³ this provides a strong guiding effect to form an electronically and ionically conductive solid electrolyte interphase (SEI) layer, enabling a dense K plating with dendrite-free morphology. The unique characteristics of the functionalized K-metal is fully evidenced by the Operando optical microscopy and phase field modeling in electrodeposition process. Under practical constraints (i.e. using lean electrolyte and thin polymer separator), the functionalized K-metal anode exhibits the ultra-long-term K plating-stripping cycles over 1200 h in a symmetrical cells and further highlights a practical applicability with high areal capacity and fast charging-discharging capability in full-cells using TiS₂ cathode.

References

1. U.-H. Kim, G.-T. Park, B.-K. Son, G. W. Nam, J. Liu, L.-Y. Kuo, P. Kaghazchi, C. S. Yoon and Y.-K. Sun, Nat. Energy, 2020, 5, 860.
2. J.-Y. Hwang, S.-T. Myung and Y.-K. Sun, Adv. Funct. Mater., 2018, 28, 1802938.
3. J.-Y. Hwang, H. M. Kim, C. S. Yoon and Y.-K. Sun, ACS Energy Lett., 2018, 3, 540-541.