Catalytic Co-N-C hollow nanocages as separator coating layer for lithium-sulfur batterys

Abstract

Despite the large theoretical mass/volume energy density, the shuttle effect of lithium-sulfur batteries greatly hinders its practical application. In order to inhibit the shuttle of polysulfide and accelerate its conversion rate. Here, a metal-doped carbon nanocage material for battery coating layer is proposed, which includes externally grown long graphitized carbon nanotubes and Co-N doped shell. Coating this multifunctional carbon material on a commercial separator can dramatically improve the performance of Li-S batteries using a high sulfur areal loading cathode. The metal Co doping and N active sites can increase the chemical adsorption capacity of polysulfides while accelerating redox kinetics. The hollow structure and epitaxially grown carbon nanotubes are beneficial to electrolyte penetration and lithium ion migration. Therefore, Li-S battery using the modified Co-N-C coating layer displayed both promising cycle performance and rate capability. In order to promote the commercial application of coated separators, all electrochemical performance tests are performed on the cathodes which possess sulfur areal density larger than 3 mg cm−2. In particular, the specific discharge capacity of the Li-S coin cell using the modified Co-N-C nanocage coating layer maintains 725 mAh g−1 after 200 charging/discharging cycles, and the capacity retention rate can reach 88%. Especially, while the sulfur mass areal loading increased to 4.7 mg cm−2, the battery can still cycle stably for more than 400 cycles at 1C.