Fabrication of Cubic and Porous Carbon Cages with In-Situ-Grown Carbon Nanotube Networks and Cobalt Phosphide for High-Capacity and Stable Lithium–Sulfur Batteries

Lithium–sulfur (Li–S) batteries have attracted considerable attention due to their high specific capacity, low cost, and eco-friendly raw material. However, the insulating property of sulfur and dissolution of lithium polysulfides (LiPSs) lead to rapid capacity decay and low Coulombic efficiency. In this work, we smartly synthesized a composite material as the host material of active S by a facile one-step pyrolysis method. It was composed of in-situ-grown carbon nanotubes (CNTs) and CoP particles inside the porous carbon cages (denoted as CoP-CNT@C). The CNT networks in porous carbon cages can improve the conductivity of the cathode, while the CoP particles are capable of enhancing the adsorption of LiPSs, thereby effectively mitigating the "shuttle effect". Moreover, the porous structure of the carbon cages could effectively store the elemental sulfur. As a matter of fact, the Li–S battery based on the CoP-CNT@C/S cathode exhibited an ultrahigh initial specific capacity of 1456.8 mAh g–1 at 0.1C and superior performance (663.3 mAh g–1) at a high current rate of 3C. It is worth mentioning that a capacity of 473.9 mAh g–1 has been retained after 750 cycles tested at 0.5C, indicating the outstanding stability of the Li–S battery based on the CoP-CNT@C/S cathode. Overall, the CoP-CNT@C composite prepared is promising for the application of Li–S batteries as the host material.