Lithium-sulfur battery is cost-effective and has a theoretical specific energy density of up to 2600 W·h·kg-1;moreover,the earth is rich in sulfur resources;therefore,it is considered a promising candidate for next-generation high-energy-density batteries.However,a few obstacles still persist in the process of commercialization,including the insulation of charge and discharge products,huge volume changes,flammable electrolytes,polysulfide"Shuttle Effect",and unstable lithium metal anode.Among these challenges,safety is a main concern in the process of commercialization.Batteries using sulfurized polyacrylonitrile(PAN/S)as positive electrode active material have substantial advantages in terms of lifespan and a wider selection of electrolytes.As lithium polysulfide dissolution has not been considered,phosphate-based electrolytes can be used in this system because they also have good nonflammable properties.Phosphate-based flame retardants or nonflammable solvents can capture combustion free radicals and have excellent flame retardant effects as main solvents and flame retardant additives.This study explores the application of high-concentration triethyl phosphate(TEP)and tri(2,2,2-trifluoroethyl)phosphate(TFP)electrolytes in Li-PAN/S batteries to improve battery safety for next-generation high-energy-density secondary batteries.We investigate the effect of TEP and TFP-based electrolytes on the stability of lithium metal negative and sulfur positive electrodes as well as interfacial reactions during battery cycling.Charge-discharge and Li deposition/stripping tests were conducted using a high-concentration electrolyte with a molar ratio of 1∶2 between LiFSI and TEP.The results reveal that the electrolyte can achieve a 99.6％S utilization at 0.1 Cand stable Li deposition/stripping performance.However,the high viscosity and limited ionic conductivity of electrolyte limit its battery performance under high-loading electrode and high-rate conditions.By conducting electrochemical tests on TEP and TFP-based electrolytes with different TTE dilution ratios,we found that the charge-discharge overpotential of TFP-based electrolytes was higher,making it difficult to stably cycle in Li/Cu half cells.Furthermore,TFP molecules formed an unstable interface layer on the Li metal surface,which deteriorates the cell performance.After diluting TEP-based electrolyte with TTE at a volume fraction of 1:2,excellent rate performance was achieved,with stable cycling of over 200 cycles at a rate of lC and ultimately maintaining a discharge specific capacity of 1038.1 mA·h·g-1.These results highlight the potential of high-concentration TEP as a promising candidate for safer and higher-performing Li-S batteries.
维普
万方数据