Cathode Materials Based On C/S Composite For High Performance Lithium-sulfur Batteries

The rational integration of conductive nanocarbon scaffolds and insulative sulfur is an efficient method to build composite cathodes for high performance lithium–sulfur batteries. Herein, carbon nanotubes(CNTs), nano-sized hollow graphene spheres(GSs) super-long carbon nanotubes(LCNTs) that possess robust mechanical properties, excellent electrical conductivities, and hierarchical porous structures were employed to fabricate carbon/sulfur composite cathode. The hollow GSs afforded close space to accommodate sulfur species, sustain the volume fluctuation during cycling, and retard the dissolution of polysulfides and parasitic shuttle. The carbon nanotubes possess robust mechanical properties and excellent electrical conductivites. The super-long carbon nanotubes possess excellent flexible and great conductive for electrons freely transport.In this work,the GS-S composite was firstly fabricated by co-heating process. The CNT/GS/S cathode was then fabricated by a normal coating method. A free-standing paper electrode was constructed by rational integration of high conductive super-long carbon nanotubes(CNTs) and nano-sized hollow graphene spheres(GS-S) through a room-Temperature solution-processable method for lithium–sulfur batteries. Both of them demonstrated that the integration of conductive nanocarbon as flexible scaffolds is an efficient and effective route toward flexible high-energy-density lithium–sulfur batteries.In addition, a family of electrodes with a real sulfur loading densities ranging from 0.32 to 4.77 mg cm-2 were fabricated to reveal the relationship between sulfur loading density and their electrochemical behavior. A high initial discharge capacity of 1288 m Ah gS-1(577 m Ah gC/S+PVDF-1, 84 m Ah gC/S+PVDF+Al-1) at 0.2 C was achieved with the sulfur loading amount of 0.32 mg cm-2. The as-obtained Li–S cell afforded the highest sulfur utilization compared to the other cells with different loading amount. A cell with an initial discharge capacity of 1215 m Ah gS-1(280 m Ah gC/S+PVDF-1, 547 m Ah gC/S+PVDF+Al-1) at 0.2 C was achieved with the sulfur loading amount increasing to 2.02 mg cm-2. When the sulfur loading amount was 3.77 mg cm-2, a high initial areal discharge capacity of 3.21 mg cm-2(864 m Ah gS-1) was achieved. The full demonstration of the high-energy-density electrodes is a key issue towards full utilization of sulfur in a lithium–sulfur cell.The CNTs acting as conductive scaffolds provided a robust electrochemical environment, high effective electron pathways and ion channels for the electrochemical process of Li–S batteries, which are promising candidates for the construction of high energy density Li–S batteries.