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.