Lithium (Li) metal has been considered as a very promising anode material for next-generation batteries because of its low electronegativity (-3.04 V), low gravimetric density (0.53 g cc^-1) and ultrahigh specific capacity (3860 mAh g^-1). The recent simulations forecast that the rechargeable Li metal batteries (LMBs) coupled with the conventional transient metal oxide cathodes and the Li metal anode can deliver a high gravimetric energy density of up to 500 Wh kg^-1.[1] However, major challenges including low Coulombic efficiency (CE), short cycle life, and safety concerns have plagued the practical applications of Li metal as anode in recharge batteries.[2]

Here we present a simple approach to suppress dendritic Li metal growth by introducing a multifunctional Janus-faced separator. This separator is designed by coating metallic copper (Cu) thin film (CuTF) onto one side surface of conventional polyethylene (PE) membrane via simple sputtering technique. The CuTF of the obtained Janus separator (PE/CuTF) plays a crucial role of an additional conducting agent for facile Li metal deposition/stripping. Furthermore, its electrically conductive nature can guide the backside plating of Li metal and electrochemical Li metal merging, resulting in less dendritic Li metal deposition (Figure 1). The lifetime of Li metal anode is enhanced by preventing short circuit failures even under extensive Li metal deposition. LMBs with the PE/CuTF separator exhibit stable cycling performances and enhanced CE during extended cycles. Moreover, the CuTF coating can suppress the thermal shrinkage of the polymer separators and enable a current collector-less cell configuration for high energy density.

1. K.G. Gallagher, S. Goebel, T. Greszler, M. Mathias, W. Oelerich, D. Eroglu, V. Srinivasan, Energy Environ. Sci. 7, 1555 (2014).
2. Xu, J. Wang, F. Ding, X. Chen, E. Nasybulin, Y. Zhang, J.-G. Zhang, Energy Environ. Sci. 7, 513 (2014).

Figure 1. Proposed working principle on Li dendrite suppression by using Janus-faced separator; (A) conventional PE separator and (B) Cu metal thin film (CuTF) coated Janus (PE/CuTF) separator.