MWCNT porous microspheres with an efficient 3D conductive network for high performance lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries are considered as a promising commercial alternative to lithium-ion batteries (LIBs) for next-generation battery systems. However, the practical application of Li-S batteries is hindered by several obstacles, such as the insulating nature of elemental sulfur and the high solubility of lithium polysulfide products. In this work, a new type of multi-walled carbon nanotube (MWCNT) microsphere was synthesized successfully and used as a carbon framework for the sulfur cathode of lithium sulfur batteries. Commercial aqueous-dispersed MWCNTs of low cost are easily accessible for the large-scale production of the carbon skeleton through a simple spray drying approach. The as-prepared carbon framework shows a porous microspherical architecture with the particle size of around several micrometers, and the MWCNTs in it are intertwined to construct a three-dimensional (3D) continuous electronic conductive network. For the sulfur cathode, the C/S microspheres (MS-C/S) were facilely prepared by a melt-diffusion method. The obtained MS-C/S electrode displays excellent cycling stability and rate capability. The electrode with a sulfur loading of 2.5 mg cm^-2 shows an initial discharge capacity of 983 mA h g^-1 and a stable capacity of 858 mA h g^-1 after 100 cycles at a current rate of 0.2C. Even when the current rate increases to 0.5C, a stable capacity of 806 mA h g^-1 is maintained over 100 cycles.