Highly Active and Stable Li 2 S-Cu Nanocomposite Cathodes Enabled by Kinetically Favored Displacement Interconversion between Cu 2 S and Li 2 S.

The high activation barrier, inferior rate performance, and short cycling life severely constrain the practical applications of the high-capacity Li 2 S cathode. Herein, we fabricate a Li 2 S-Cu nanocomposite with a drastically reduced activation potential, fast rate capability, and extraordinary cycling stability even under a practically relevant areal capacity of 2.96 mAh cm -2 . Detailed experimental investigations aided by theoretical calculations indicate that instead of converting to S 8 via troublesome soluble lithium polysulfides, Li 2 S is thermodynamically and kinetically more favorable to react with Cu by the displacement reaction, which alters the redox couple from Li 2 S/S to Cu/Cu 2 S, leading to the excellent electrochemical performance. Moreover, the stability of the composite is demonstrated in the full-cell configuration consisting of commercial graphite anodes. This work provides an innovative and effective approach to realize highly activated and stable Li 2 S cathode materials.