Polar and Nonpolar Matrix Consisting of Twined Multiwalled Carbon Nanotube and High Nitrogen-Doped Porous Carbon Derived from Ionic Liquid for Stable Li-S Battery

Lithium-sulfur batteries are recognized as high energy density systems. However, due to the reproducibility of nonpolar S-8, polar polysulfide intermediates and the final Li2S during cycling, developing an effective matrix to reduce sulfur consumption in the cathode and improve the cycle stability is still challenging. Herein, a polar and nonpolar matrix consisting of twined multiwalled carbon nanotube (MWCNT) and high nitrogen-doped porous carbon is designed, in which the twined MWCNT could provide the nonpolar and physical bind, meanwhile, the N-enriched porous carbon derived from ionic liquid could provide polar and chemical anchoring. The composite is prepared by carbonizing the 1-ethyl-3-methylimidazolium dicyanamide (Emim-dca) ionic liquid, which is loaded on the intertwined MWCNT. The ionic-liquid-derived composite material shows more microporous and low-diameter mesoporous structures than intertwined MWCNT, and the nitrogen content reaches 7.42 At%. Assembled in lithium-sulfur batteries, the specific capacity of the battery reaches 1558.6 mAh g(-1) at the first cycle of 0.1 C. After the 300 times cycling at 1 C, the specific capacity still remains 614.34 mAh g(-1) and the attenuation is only 0.021% for each cycle. Moreover, the attenuation in the changing rate charge-discharge test is weaker than the pure intertwined MWCNT composite cathode.