A mechanochemical synthesis of submicron-sized Li2S and a mesoporous Li2S/C hybrid for high performance lithium/sulfur battery cathodes

Abstract

Lithium sulfide, Li₂S, is a promising cathode material for lithium–sulfur batteries (LSBs), with a high theoretical capacity of 1166 mA h g⁻¹. However, it suffers from low cycling stability, low-rate capability and high initial activation potential. In addition, commercially available Li₂S is of high cost and of large size, over ten microns, which further exacerbate its shortcomings as a sulfur cathode. Exploring new approaches to fabricate small-sized Li₂S of low cost and to achieve Li₂S cathodes of high electrochemical performance is highly desired. This work reports a novel mechanochemical method for synthesizing Li₂S of high purity and submicron size by ball-milling LiH with sulfur in an Ar atmosphere at room temperature. By further milling the as-synthesized Li₂S with polyacrylonitrile (PAN) followed by carbonization of PAN at 1000 °C, a Li₂S/C hybrid with nano-sized Li₂S embedded in a mesoporous carbon matrix is achieved. The hybrid with Li₂S as high as 74 wt% shows a high initial capacity of 971 mA h g⁻¹ at 0.1C and retains a capacity of 570 mA h g⁻¹ after 200 cycles as a cathode material for LSBs. A capacity of 610 mA h g⁻¹ is obtained at 1C. The synthesis method of Li₂S is facile, environmentally benign, and of high output and low cost. The present work opens a new route for the scalable fabrication of submicron-sized Li₂S and for the development of high performance Li₂S-based cathodes.