Inverse Capacity Growth and Pocket Effect in SnS₂ Semifilled Carbon Nanotube Anode

SnS₂ with high theoretical capacity has been impeded from practical applications as the anode of lithium-ion (Li-ion) batteries due to its large volume expansion and fast capacity decay. A nanostructure of the SnS₂ semifilled carbon nanotube (SnS₂@CNT) has been realized by plasma-assisted fabrication of Sn semifilled CNT (Sn@CNT) followed by post-sulfurization. When serving as the anode of a Li-ion battery, SnS₂@CNT delivers an initial discharge capacity of 1258 mAh g^-1 at 0.3 A g^-1. Instead of capacity fading, SnS₂@CNT shows inverse capacity growth to 2733 mAh g^-1 after 470 cycles. The high-resolution transmission electron microscopy images show that the void in CNTs, after cycling, is fully filled with pulverized SnS₂ grains which have a shortened Li-ion diffusion path and enhanced surface area for interfacial redox reactions. In addition, the CNTs, like a pocket, confine the pulverized SnS₂, maintain the electric contact and structural integrity, and thus allow the electrodes to work safely under long cyclic loadings and extreme temperature conditions.