A Valence Gradient Protective Layer for Dendrite‐Free and Highly Stable Lithium Metal Anodes

Abstract Li metal is the next‐generation anode material for high‐energy‐density Li‐ion batteries. Unfortunately, its practical application is hampered by drawbacks such as an unstable solid electrolyte interphase and undesirable Li dendrites. Herein, an Fe‐based protective layer with a valence gradient is constructed on Li anodes, which consists of an Fe 3+ /Fe 2+ ‐rich outer layer and an Fe 0 ‐containing inner layer. The protective layer not only isolates the underlying Li metal from the corrosive carbonate electrolyte, but also uniformly stores Li during plating and inhibits the growth of Li dendrites. The Li anode with the Fe‐based protective layer shows dendrite‐free Li plating/stripping behaviors; therefore, Li symmetric cells stably run for 1000 h at 1 mA cm ‐2 and 1 mA h cm ‐2 and even survive for 380 h at an ultra‐high capacity of 30 mA h cm ‐2 . With such a highly stable Li anode, LiFePO 4 cells operate steadily for 1600 and 1000 cycles at 1 and 5 C, respectively. High‐loading LiCoO 2 cells also present excellent cycling stability and rate capability, proving the advantages of the protective layer in Li anode protection.