Research On The Nucleation Mechanism Of Sulfur Batteries And The Protection Of Lithium Negative Electrodes

Lithium–sulfur batteries with a high theoretical energy density(2600 Wh kg^-1) based on multi-electron redox reactions were strongly considered.The lithium disulfide/sulfide(Li₂S₂/Li₂S,denoted as Li₂S_1/2)precipitation is critical to achieve high sulfur utilization.However,the kinetic effect on Li₂S_1/2 precipitation in a working battery has been rarely investigated.And lithium metal anode of Lithium–sulfur batteries,which has extremely high theoretical specific capacity(3860 mA h g^-1)andlow reduction potential?-3.04 V vs standard hydrogen electrode?,has still severelyhindered by the growth of Li dendrites.Investigating Li₂S_1/2 deposition and regulating Li deposition are significant to improve the performance of lithium sulfur batteries.Based on the two issues above,this work includes two sections:Firstly,the current-density-dependent Li₂S_1/2 nucleation/growth was explored and such a dependence served as the guiding principle for the construction of high-sulfur-loading/content Li–S batteries.Generally,the Li₂S_1/2 nucleation density is proportional to two-third the power of the current density and the shift from a high to low current density alters the Li₂S_1/2 precipitation pathway from surface deposition to solution-mediated growth.The in-solution growth rate was found to be restricted by the mobilities of polysulfide intermediates and Li₂S_1/2 in conventional ether electrolytes.The rationalized guideline directed the design of a lightweight,high surface-area,and open-pore conductive framework for sulfur cathodes,which enabled an extremely high sulfur content of 93.4 wt%in the whole electrode and a high capacity(1269 mA h g^-1).The present work affords a kinetic understanding of the liquid–solid conversion in working Li–S batteries and optimization schemes for practical operation parameters.Secondly,trimethylene sulfate?TMS?additives were employed to suppress Li dendrites and promote the applications of an ultrathin Li anode.While applied in aworking battery with an ultrathin Li anode?33?m?,a high loading LiNi_0.5Co_0.2Mn_0.3O₂?NCM523?cathode(2.5 mA h cm^-2),and lean electrolytes(7.7 g A^-1h^-1),130 cycles was achieved in Li|NCM523 batteries with TMS additives compared with 60 cycles without additives.As disclosed by X-ray photoelectron spectroscopy,much sulfate components were detected in solid electrolyte interphase formed with TMS additives,affording to the improved uniformity of Li deposition.This work highlights the challenges from ultrathin Li in practical Li metal batteries and develops an effective electrolyte additive for emerging high-energy-density Li metal batteries.