Improving lithium-sulfur battery performance with lignin reinforced MWCNT protection layer

Multi-walled carbon nanotube (MWCNT) protection layers have previously been used to trap polysulfides and suppress the shuttle effect in lithium sulfur (Li-S) batteries, leading to significant performance improvement. While the MWCNT is inherently highly conductive and mechanically strong, the cost can be significant and in turn hampered wider application of MWCNT protection layers. Here, we employed lignin, a byproduct during high-quality bleached paper manufacturing, to replace a portion of MWCNT in the protection layer to reduce cost and enhance surface properties of pristine MWCNT protection layers. We found that the protection layer with 25 wt% lignin leads to the best overall electrochemical performance of Li-S batteries during charging/discharging at 0.5 degrees C and 1C rate (1C = 1,675 mA g(-1)) among various weight-ratios of lignin/MWCNT, and a low decay rate (0.20% per cycle) and high initial capacity (1342 mA g(-1) and 1437 mA g(-1) for 1C and 0.5C, respectively) are demonstrated. Besides, Li-S cells with 25 wt% lignin/MWCNT composite protection layer also exhibited great rate capability, of which the specific capacities at 0.1C, 0.5C, 1C, and 2C were 1150, 913, 824, and 637 mAh g(-1), respectively. The enhanced electrochemical stability and performance of Li-S batteries can be attributed to strengthened polysulfide trapping and improved lithium ion transport with lignin reinforced MWCNT protection layers. We showcased an economic approach to extend cycle life and improve rate capability of Li-S batteries.