Chemical and spatial dual- confinement engineering for stable Na- S batteries with approximately 100% capacity retention

Sodium- sulfur (Na- S) batteries are attracting intensive attention due to the merits like high energy and low cost, while the poor stability of sulfur cathode limits the further development. Here, we report a chemical and spatial dual- confinement approach to improve the stability of Na- S batteries. It refers to covalently bond sulfur to carbon at forms of C- S/N- C=S bonds with high strength for locking sulfur. Meanwhile, sulfur is examined to be S1- S2 small species produced by thermally cutting S8 large molecules followed by sealing in the confined pores of carbon materials. Hence, the sulfur cathode achieves a good stability of maintaining a high- capacity retention of 97.64% after 1000 cycles. Experimental and theoretical results show that Na+ is hosted via a coordination structure (N center dot center dot center dot Na center dot center dot center dot S) without breaking the C- S bond, thus impeding the formation and dissolution of sodium polysulfide to ensure a good cycling stability. This work provides a promising method for addressing the S- triggered stability problem of Na- S batteries and other S- based batteries.