Generating Short-Chain Sulfur Suitable for Efficient Sodium-Sulfur Batteries via Atomic Copper Sites on a N,O-Codoped Carbon Composite

Sodium-sulfur batteries have attracted attention due to their high energy capacities and low costs, but the dissolution of sodium polysulfides still severely affects their cycle life, limiting their real-world applications. Herein, a stable sulfur host is reported, based on a N,O-codoped carbon composite derived from a bimetallic Cu-Zn metal-organic framework, which ensures high sulfur loading (67 wt%). Most importantly, this composite also includes single-atom copper catalysts, with a high Cu loading of 8.03 wt%. Solid-state nuclear magnetic resonance, synchrotron X-ray absorption spectroscopy, and single-crystal X-ray diffraction analysis show that single atoms of Cu are coordinated with two N and two O atoms within the produced composite material. Those copper sites can weaken S-S bonds in the S-8 ring structure, and thus are able to catalyze the formation of short-chain sulfur molecules in even larger-size pores. In addition, Cu atoms facilitate the conversion between the short-chain sulfur and Na2S. As a result, when the produced sulfur-loaded carbon framework containing the atomic Cu catalyst is used as a cathode for sodium-sulfur batteries, it exhibits superior capacity of 776 mAh g(-1) with a high sulfur utilization (1158 mAh g(s)(-1) normalized with sulfur content) after 100 cycles at 0.1 A g(-1), and an excellent rate performance of 483 mAh g(-1) (720 mAh gs(-1)) at 5 A g(-1).

Automated summary

A stable sulfur host with single-atom copper catalysts derived from a bimetallic Cu-Zn metal-organic framework is reported, which significantly improves the performance of sulfur-loaded carbon framework used as a cathode in sodium-sulfur batteries, exhibiting superior capacity and rate performance.