Stable Na-organosulfide batteries enabled by an in-situ constructed protective interphase

Abstract

Sodium-organic battery is one of the most promising energy storage systems, due to the low-cost, earth-abundant Na and absence of transition metals. Organosulfide compounds through the breakage and reformation of SS bonds to achieve the redox process have emerged as high-capacity candidates for the family of organic cathodes. To understand the electrochemical properties, we investigate the three aromatic-based organosulfide compounds in which each benzene ring consists of different number of thiol groups, i.e., 4,4′-thiobisbenzenethiol (TBBT), 1,3-benzenedithiol (1,3-BDT), and 1,3,5-benzenetrithiol (BTT). It is revealed that BTT with three thiol groups can most strongly coordinate with Na cation and enter the solvation sheath. It promotes the uniform distribution of organosulfide in the anode|electrolyte interphase, effectively protecting the active Na from corrosion of polysulfides. Meanwhile, the massive NaF decomposed from concentrated NaPF6 salts renders the smooth plating of Na and avoids the repetitive exposure of fresh Na to the electrolyte. The synergism between the organosulfide and NaF-rich interphase enables the Na|BTT cell stable cycling for 200 times with the highest reversible capacity of 342.8 mAh/g and average Coulombic efficiency of 98.9 %. The work sheds light on rational design of molecular structures for high-performance Na-organic batteries.