In Situ-Formed Fe-Based Protective Layer for Dendrite-Free K Metal Anode

Constructing artificial SEI (ASEI) is an effective method to suppress dendrite growth and achieve a stable solid electrolyte interphase in a potassium metal anode. However, traditional methods for preparing ASEI still have some problems such as poor adhesion and inadequate/uneven reactions. These drawbacks significantly impede ion diffusion kinetics and the effectiveness of dendrite inhibition. In this study, an in situ reaction approach was introduced to fabricate a Fe-based protective layer on the surface of K via the spontaneous dynamic chemical reaction between Fe3O4 and K. The in situ-formed Fe-based artificial protective layer not only prevents the corrosion of the carbonate electrolyte, but also has high potassiophilicity and high ionic conductivity, which can reduce side reactions, regulate the uniform adsorption of K+, and improve the transport kinetics of K+, thus inhibiting the growth of potassium metal dendrites. With the Fe-based protective layer, the symmetric cell demonstrates a cycling stability exceeding 1700 h at 0.5 mA cm–2 and 0.5 mAh cm–2. Notably, it also exhibits a promising cycling stability and rate performance when paired with a Prussian blue (PB) cathode. This work offers insights into the development of protection layers for an advanced alkali metal anode.