Long Cycle Life Organic Polysulfide Catholyte for Rechargeable Lithium Batteries

Abstract

Abstract Organic compounds with active sites for lithiation can be used as electrode materials for lithium batteries. Their tunable structures allow a variety of materials to be made and investigated. Herein, a spectrum of dipyridyl polysulfides (Py2Sx, 3 ≤ x ≤ 8) is prepared in electrolyte by a one‐pot synthesis method from dipyridyl disulfide (Py2S2) and elemental sulfur. It renders up to seven dipyridyl polysulfides (i.e., Py2S3, Py2S4, Py2S5, Py2S6, Py2S7, and Py2S8) which show fully reversible electrochemical behavior in lithium batteries. In the discharge, the initial lithiation occurs at 2.45 V leading to the breakage of SαSβ bonds in Py2Sx and formation of lithium 2‐pyridinethiolate, in which lithium is coordinated in between N and S atoms. The left sulfur species act as elemental sulfur, showing two voltage plateaus at 2.3 and 2.1 V. The molecular dynamics simulations show the attraction between pyridyl groups and lithium polysulfides/sulfide via N···Li···S bonds, which enable good retention of soluble discharge products within electrodes and stable cycling performance. In the recharge, low‐order Py2Sx (e.g., Py2S3, Py2S4, and Py2S5) remain as the charged products. The mixture catholyte exhibits superlong cycle life at 1C rate with 1200 cycles and 70.5% capacity retention.

Keywords

• dipyridyl polysulfide
• lithium batteries
• molecular dynamic simulations
• organosulfide
• ultra performance liquid chromatographyquadrupole time‐of‐flight‐mass spectrometry (UPLC‐QTof‐MS)