Theoretical studies of the reduction of cyclic esters on the anode interface of lithium batteries

SEI film with a stable structure and uniform morphology is important for lithium ion battery and Li metal battery. Density functional theory (DFT) theory comparative study on the reduction mechanism of cyclic esters are carried out to deeply analyze the formation, composition, structure, reactivity and stability of SEI film. The reaction activation energy, gibbs free energies, enthalpies and structures of the transition states are calculated. It is demonstrated that ethylene carbonate (EC), propylene carbonate (PC) and vinylene carbonate (VC) could be reduced to form organic species of LiOCH₂CH₂OLi, LiOCH₂(CH3)CHOLi and LiOCHCHOLi respectively, meanwhile release CO gases through two-electron mechanism, the reduction also can produce organic SEI components through one-electron reduction mechanism; the priority of the one-electron and two-electron reductions is in order of VC > EC > PC. The formation of Li₂CO₃ by two-electron reduction mechanism is more favorable in order of EC > PC > VC. Furthermore, the two-electron reduction for sulfites ethylene sulfite (ES) and 1,3-propylene sulfite (PS) to form Li₂SO₃ is harder than carbonates of EC, PC and VC, but the one-electron reduction decomposition of ES and PS binding with Li⁺ is easier than the carbonates esters, indicating that ES and PS are prior to form organic SEI film compared with carbonate esters.