Strongly Bonded Cfx@S Composite Assisting the Long-Cycle Stability of Li-S Battery

Abstract

Lithium-sulfur battery (LSB) has attracted extensive attention due to its high theoretical capacity. Nevertheless, the "shuttle effect" of polysulfide leads to low sulfur utilization and short cycle life. Herein, CFx@S composites strongly bonded by C=S have been prepared. The research shows that CFx in the composite will preferentially discharge to form F-doped carbon (F@C) conductive network and LiF, which improve the electronic and ionic conductivity, separately. Numerous polar sites on F@C cooperates with polar LiF to adsorb polysulfide effectively, and then inhibit the "shuttle effect". The F@C conductive network is firm and the structural stability can be further enhanced by the attached LiF, which can alleviate the volume expansion of S during the charge/discharge cycles. Profiting by the above-mentioned merits, the as-prepared 10-CFx@S composite with a sulfur content as high as 87.6% manifests excellent rate performance and outstanding cycle stability. The initial capacity of 10-CFx@S is 573 mAh g-1 at a high current of 1600 mAh g-1, and the capacity is retained as 334 mAh g-1 after 800 cycles, with an average capacity decay of 0.052% per cycle. This research supplies a simple and effective method to promote the performance of LSB.

Keywords: Lithium-sulfur battery, Graphite fluoride, Shuttle effect, Cyclic stability