context: The plating and stripping behaviors of the LiF@Po–Li electrodes are observed by SEM after the Li deposition of 1 mA h cm−2 at a current density of 0.5 mA cm−2 with an EC/DEC:3/7, 1.3 M LiPF6, and 5 wt% FEC electrolyte (Fig. 3). All the electrochemical experiments are performed with carbonate-based electrolytes. It has been well known that the ether-based electrolytes, especially the DME/DOL system, exhibit better electrochemical properties compared to carbonate-based electrolytes in LMBs thanks to their stable SEI layer formation and more freedom to choose additives. However, the ether-based electrolyte is not suitable for various commercial cathode material due to its instability above 4.0 V vs. Li/Li+. In this regard, carbonated-based electrolytes should be explored for their electrochemical properties in upcoming high energy density LMBs. The electrodes are washed with dimethyl carbonate (DMC) to remove residual salts before SEM observation. The Li metal plated on the bare Li electrode shows a mossy, porous and dendritic morphology with an 11.8 μm thickness and 59% porosity (Fig. 3a, b and ESI Note 1†). In contrast, the Li metal plated on the LiF@Po–Li electrode exhibits a smooth and film-like morphology with significantly reduced porosity (Fig. 3c, d and S7†). The cross-sectional view of the LiF@Po–Li electrode after plating clearly shows that a 6.8 μm-thick dense Li film is deposited on the LiF@Po–Li electrode with 28% porosity (Fig. 3d). The stripping behavior is also monitored. As shown in Fig. 3e and f, the bare Li electrode has high-density craters with sizes ranging from 10 μm to 50 μm after the Li stripping. This non-uniform surface morphology is attributed to the localized current density caused by the inhomogeneous SEI layer. In contrast, the LiF@Po–Li electrode has a smooth and conformal surface without noticeable holes over a large area after Li stripping (Fig. 3g and h). This improvement in plating and stripping behaviors of Li is attributed to the LiF@Po protective layer, which enables a uniform Li ion concentration and current density over the Li electrode by suppressing the electrolyte decomposition.
answer:  5 wt% FEC