Size Effect of Organosulfur and In Situ Formed Oligomers Enables High‐Utilization Na–Organosulfur Batteries

Organosulfurs are promising cathode materials for rechargeable metal batteries due to their high capacities, diverse structures, and electrochemical properties. Herein, the electrochemical behavior of three organosulfur compounds, i.e., 4,4'-thiobisbenzenethiol (TBBT), 1,4-benzenedithiol (1,4-BDT), and diphenyl disulfide (DPDS), is revealed in room-temperature rechargeable sodium (Na) batteries, which show significantly improved performances when sodiated Nafion membranes are used. Large oligomers of organosulfur can be formed during charging, and they are readily blocked by the nanosized ion-conducting clusters in the Nafion membrane. In addition, large organosulfur monomers can also be blocked. Only 5.4% of TBBT diffuses through the Nafion membrane after 800 h. The Na|TBBT cell sustains 77% of the theoretical capacity after 300 cycles (2420 h). Moreover, the Na|TBBT redox flow cell shows promising rechargeability. Due to the medium molecular size, the organosulfur oligomers are expected to provide a new avenue to develop high-capacity chalcogen cathodes, besides inorganic S and S-containing polymers.