Trifunctional\nElectrolyte Additive Hexadecyltrioctylammonium\nIodide for Lithium–Sulfur Batteries with Extended Cycle Life

Abstract

Lithium–sulfur\n(Li–S) battery with a very high theoretical\nenergy density (∼2500 Wh kg^–1) is a very\npromising alternative to the commercial lithium-ion battery as the\nnext-generation energy storage device. However, the Li–S battery\nsuffers from shuttle effect and Li dendrites growth due to the solubility\nof polysulfides in the electrolyte system and the inhomogeneous deposition\nof Li, resulting in short cycling life span, which is the major obstacle\nin its practical application. Herein, we report an additive, hexadecyltrioctylammonium\niodide (HTOA-I), in the conventional electrolyte system, which shows\ntrifunctional effect on extending Li–S battery cycle life.\nIt can not only help us to form a protective solid–electrolyte\ninterface (SEI) on the surface of Li anode so as to reduce the contact\nof polysulfides with Li but also hinder the shuttling of polysulfides\nto the Li anode due to the strong combination of large-sized HTOA⁺ with polysulfide anions (S<i>_n</i>^2–), which retard the migration of S<i>_n</i>^2– and cause homogeneous Li deposition\nowing to the large size and stronger trend of HTOA⁺ to\nbe absorbed on Li anode as well. A new method of phosphorescence analysis\nfor direct observation of polysulfides shuttling has been put forward\nfor the first time, which can be further developed in future studies.\nThe cell with the HTOA-I-added electrolyte system shows high cycling\nstability, retaining 83.4% of the initial capacity after 200 cycles\nat 1 A g^–1 and achieving 689 mAh g^–1 even after 1000 cycles. This cost-effective and facile approach\nwill not increase the complexity of the battery manufacturing process.\nCompared to other electrolyte additives, the additive in our work,\nHTOA-I, has better positive effects on extending cycle life. This\ntrifunctional electrolyte additive will inspire the design of other\nnew additives and further promote the development of Li–S batteries.