Sulfur Nanocrystals Confined in Carbon Nanotube Network As a Binder-Free Electrode for High-Performance Lithium Sulfur Batteries

A binder-free nano sulfur–carbon nanotube composite material featured by clusters of sulfur nanocrystals anchored across the superaligned carbon nanotube (SACNT) matrix is fabricated via a facile solution-based method. The conductive SACNT matrix not only avoids self-aggregation and ensures dispersive distribution of the sulfur nanocrystals but also offers three-dimensional continuous electron pathway, provides sufficient porosity in the matrix to benefit electrolyte infiltration, confines the sulfur/polysulfides, and accommodates the volume variations of sulfur during cycling. The nanosized sulfur particles shorten lithium ion diffusion path, and the confinement of sulfur particles in the SACNT network guarantees the stability of structure and electrochemical performance of the composite. The nano S-SACNT composite cathode delivers an initial discharge capacity of 1071 mAh g^–1, a peak capacity of 1088 mAh g^–1, and capacity retention of 85% after 100 cycles with high Coulombic efficiency (∼100%) at 1 C. Moreover, at high current rates the nano S-SACNT composite displays impressive capacities of 1006 mAh g^–1 at 2 C, 960 mAh g^–1 at 5 C, and 879 mAh g^–1 at 10 C

Sulfur Embedded in a Mesoporous Carbon Nanotube Network as a Binder-Free Electrode for High-Performance Lithium–Sulfur Batteries

Sulfur-porous carbon nanotube (S-PCNT) composites are proposed as cathode materials for advanced lithium–sulfur (Li–S) batteries. Abundant mesopores are introduced to superaligned carbon nanotubes (SACNTs) through controlled oxidation in air to obtain porous carbon nanotubes (PCNTs). Compared to original SACNTs, improved dispersive behavior, enhanced conductivity, and higher mechanical strength are demonstrated in PCNTs. Meanwhile, high flexibility and sufficient intertube interaction are preserved in PCNTs to support binder-free and flexible electrodes. Additionally, several attractive features, including high surface area and abundant adsorption points on tubes, are introduced, which allow high sulfur loading, provide dual protection to sulfur cathode materials, and consequently alleviate the capacity fade especially during slow charge/discharge processes. When used as cathodes for Li–S batteries, a high sulfur loading of 60 wt % is achieved, with excellent reversible capacities of 866 and 526 mAh g^–1 based on the weights of sulfur and electrode, respectively, after 100 cycles at a slow charge/discharge rate of 0.1C, revealing efficient suppression of polysulfide dissolution. Even with a high sulfur loading of 70 wt %, the S-PCNT composite maintains capacities of 760 and 528 mAh g^–1 based on the weights of sulfur and electrode, respectively, after 100 cycles at 0.1C, outperforming the current state-of-the-art sulfur cathodes. Improved high-rate capability is also delivered by the S-PCNT composites, revealing their potentials as high-performance carbon–sulfur composite cathodes for Li–S batteries