First-Principles Study On The Formation And Growth Of Solid Electrolyte Interphase In Lithium-ion Batteries

Along with economic progress and the large use of fossil fuels,serious environmental pollution and energy depletion have been caused.In order to reduce the pollution during the use of fossil fuels,human beings are actively developing renewable energy sources.Rechargeable batteries can effectively store electrical energy in chemical form,so they are indispensable for efficient use of renewable energy.Lithium-ion batteries?LIB?have indisputably dominated the electrochemical energy storage?EES?market.It is well accepted that the stability,safety,and lifetime of rechargeable lithium ion batteries significantly closely relate to the characteristics of the solid electrolyte interphase?SEI?between the electrolyte and anode surface.The solid electrolyte interphase?SEI?between the anode surface and the electrolyte of lithium ion batteries?LIB?has been considered to be the most important,yet the least understood issue of LIB.To make further effort in this aspect,a density functional theory?DFT?B3PW91/6-311++G?d,p?together with implicit solvent model and the transition state theory were used to,for the first time,comprehensively explore the electroreduction mechanism of a novel additive,4-chloromethyl-1,3,2dioxathiolane-2-oxide?CMDO?,and a few other solvents and additives such as ethylene carbonate?EC?,propylene carbonate?PC?,dimethyl carbonate?DMC?,fluoroethylene carbonate?FEC?,and even ethylene sulfite?ES?for a comparison.The one-electron reduction potential of Li⁺coordinated compounds Li⁺?X?for forming decomposition precursors[c-Li⁺(X^·-)]decreases in the following sequence CMDO?2.3-2.5V vs Li⁺/Li??ES?2.4 V?>FEC?0.8V V?>EC?0.57 V?>PC?0.55 V?>DMC?0.43 V?,implying that CMDO is reduced prior to other solvents or additives in the mixture.Although the ring opening of[c-Li⁺(CMDO^·-)]is the least kinetically favorable,reflected by the highest energy barrier?E_a?:CMDO?22.1-26.2 kcal/mol??ES?26.8?>FEC?16.0?>PC?12.2?>EC?11.0?>DMC?11.0?,CMDO still shows the highest overall reaction rate constant(?10⁵⁹s^-1)for forming opening ring radical[o-Li⁺(CMDO^·-)].In addition,the termination reaction of[o-Li⁺(CMDO^·-)]for forming Li Cl is thermodynamically more favorable than that of Li₂SO₃,not to mention the path of organic disulfite?Li SO₃?₂-R,which supports the experiment fact that for halogen containing additives Li F or Li Cl is predominant over all other halogen containing species of the SEI layer.Moreover,the hybrid model by including a second solvation shell of Li⁺via a supercluster[?CMDO?Li⁺?PC?₂]?PC?₉and the implicit solvent model?SMD?brings about a reduction potential??1.7 V?in an excellent agreement with the experimental reduction peak.