Design and Development of Highly Active Cathodes for Metal-Sulfur Batteries

The lightweight rechargeable batteries with high energy density have received increasing attention in recent years, due to the demand from the rapid development of transportation and grid applications. Among these candidates, rechargeable metal−sulfur (M-S) batteries represent one of the most attractive electrochemical systems because of the high theoretical capacity (1672 mAhg-1) of the sulfur, low cost, and non-toxicity. Nevertheless, it has some challenges that are impeding their practical application, such as low Coulombic efficiency (CE) and poor cycling life. The low electronic conductivity of sulfur will result in the poor CE; the huge volume change of sulfur and the “shuttle effect” of polysulfides can lead to rapid capacity decay and poor cycling life. In this doctoral thesis, three different kinds of S- or M2Sx-based cathode materials, including Li2S carbon composites, freestanding S cathodes, and single-atom Fe carbon composites, are synthesized to develop high electrochemical performance M–S batteries. For the first work, we applied Li2S as cathode to overcome the large volume expansion in the process of electrochemical lithiation, and overcome the safety issues related to the Li anode. We designed a practical and facile in-situ method to synthesis C/Li2S composites and described well-distributed cobalt nanoparticles on nanoporous carbon matrix to accelerate lithium ion diffusion in an intrinsically ionic insulating Li2S cathode. The Co@C/Li2S showed a low energy barrier and delivered a high reversible capacity of 303 mAh g−1 after 380 cycles with a high mass loading of 3 mg cm−2 Li2S.