Sulfur/Carbon Nanotube Composite Film as a Flexible Cathode for Lithium–Sulfur Batteries

A flexible composite film composed of carbon nanotubes (CNTs) and sulfur as the cathode for lithium–sulfur (Li–S) batteries is prepared by coating an ultrathin sulfur nanolayer on a preprepared CNT film through a simple two-step heating process. The sulfur–CNT composite film with an areal density of ∼5 mg cm–2 has a high sulfur content of 65 wt % and is tough enough to be directly employed as the cathode in Li–S cells without binders, conductive additives, and current collectors. The porous and film-like CNT matrices enormously improve the electrical conductivity of sulfur and offer 3D pathways for fast Li ion diffusion, while the strong covalent bonds formed between sulfur and CNTs ensure the stability of sulfur during charge/discharge. Consequently, the film electrode delivers an initial capacity of 1100 mA h g–1 and can retain a reversible capacity of 740 mA h g–1 after 100 charge/discharge cycles at 0.1 C. It also shows good rate capability that a reversible capacity of 520 mA h g–1 can be reached at the rate of 2 C. Moreover, the high sulfur content gives rise to a high energy density of ∼1200 W h kg–1 based on the total mass of the electrode.