Fluorinated Graphite (FG)-Modified Li–S Batteries with Superhigh Primary Specific Capacity and Improved Cycle Stability

Lithium–sulfur (Li–S) batteries have received extensive attention because of their high theoretical energy density and low cost. However, the low sulfur utilization and the shuttle effect of polysulfide cause low initial capacity and serious capacity decay. Herein, fluorinated graphite (FG) is introduced to the cathode to alleviate these issues. The results indicated that the FG could provide additional capacity during the first discharge process and increase the porosity and polarity of the cathode via in situ formation of lithium fluoride (LiF) nanocrystals, which can enhance the infiltration of electrolyte and polysulfide adsorption. As a result, the as-prepared cathode containing FG shows a high initial specific capacity of 1602 mA h g–1 and the reversible specific capacity is 650 mA h g–1 at 0.5C after 300 cycles. Moreover, its specific capacity remains at 860 mA h g–1 at 5C, which is 367% higher than that of the sample without FG. This paper provides a new strategy to improve the energy density and the cycle stability of Li–S batteries.