Application And Research Of Organic Thiol In Lithium Metal Batteries

With the rapid development of renewable energy systems and intelligent electronic devices,there is an urgent need for rechargeable secondary batteries with high-energy-density and low-cost.In the past few decades,traditional lithium-ion batteries have dominated the entire battery field and have been successfully commercialized.However,it cannot meet the growing demand for high-energy-density energy storage systems due to its limited energy density.Lithium-sulfur(Li-S)/lithiumselenium(Li-Se)batteries have been widely studied due to its high energy density,which are considered as promising next-generation energy storage systems.Despite the exhilarating advantage,the practical implementation of Li-S/Li-Se batteries still face great challenges owing to the shuttle effect of soluble polysulfides/polyselenides and instability of the lithium anode interface,resulting in low utilization of active substances,serious self-discharge,fast capacity decay and inferior Coulombic efficiency.In view of this,a series of benzenedithiols(BDTs),namely 1,2-BDT,1,3-BDT,1,4-BDT,were investigated as electrolyte additives in order to address the challenges faced by Li-S batteries.Among them,the Li-S battey with 1,4-BDT achieves the best electrochemical performance,which is attributed to the different steric structure of 1,4BDT compared with the other two isomers.The two sulfhydryl groups(-SH)of 1,4BDT are in the para position,which make 1,4-BDT molecule difficult to selfpolymerize.Therefore,it is more effective to participate in electrochemical reactions on the both sulfur cathode and lithium anode.For example,1,4-BDT will polymerize with more sulfur atoms in the cathode to form sulfur-sulfur(S-S)bonds,which changes the inherent redox reaction pathway of traditional sulfur cathode and inhibits the shuttle effect of polysulfides.At the same time,a dense and stable solid-state electrolyte interface(SEI)is formed on the surface of lithium anode.Accordingly,the lithium/lithium(Li/Li)symmetric battery exhibits an ultra-low overpotential of 80 mV at a high current density of 5 mA cm-2,and work stably for 300 h.The Li-S cell with 1,4-BDT displays superior cycle performance at a C/5 rate,the cell with a high initial capacity of 1548.5 mAh g-1 and a reversible capacity of 1306.9 mAh g-1 after 200 cycles.In addition,The Li-S pouch cell with 1,4-BDT containing 2.8 g S8 exhibits an initial capacity of 2640 mAh and a capacity retention rate of 84.2%after 26 cycles at a C/10 rate.This work demonstrates that organodithiol compounds can be used as functional electrolyte additives and provides a new direction to design materials for advanced LiS batteries.Inspired by the former work,1,4-BDT is further studied as an organic redox mediator in Li-Se battery to regulate the distribution and activity of polyselenides.Polyselenides as intrinsic redox mediators in Li-Se battery,linking Se and Li2Se for redox reactions,which play a vital role in complex redox reactions.Unfortunately,the dissolution and shuttle effect of polyselenides resulting in inferior electrochemical performances.Therefore,adjusting the distribution and activity of polyselenides is an important strategy to improve the electrochemical performance of Li-Se batteries.The direct modification of polyselenides molecules is an attractive strategy compared with the extrinsic regulations such as physical constraint and chemical adsorption/catalysis.Here,1,4-BDT additive can be as a redox mediator to directly modify polyselenides.It can reversibly storage and release Se,which directly changes the redox reaction pathway of Se,accelerates the redox kinetics,improves the capacity and cycle stability of the Li-Se battery.Therefore,the Li-Se cell with 1,4-BDT delivers a high initial capacity of 626 mAh g-1 and a stable cycle of 700 cycles at 1 C.Moreover,the Li-Se battery with 1,4-BDT containing a high Se loading of 5.5 mg cm-2 and a low electrolyte/Se(E/Se)ratio of 10 μL mg-1 still achieves a capacity of 430.3mAh g-1 after 100 cycles.This work proves an effective redox regulation strategy and can inspire more exploration of organosulfur mediators in working batteries with the multi-phase and multi-electron transition.