Comprehensive Understanding of Reduction Mechanisms of Ethylene Sulfite in EC-Based Lithium-Ion Batteries

The reliable electrolyte additives are critically important to satisfy the rapidly increasing demand for electrical energy storage with safety, low cost, long life, and high-energy/power density. As an effective electrolyte additive, ethylene sulfite (ES) is widely used in lithium-ion batteries to improve their cycling performance at low temperature. However, its working mechanism, particularly in ethylene carbonate (EC)-based electrolyte, is still elusive. Here, we present a comprehensive theoretical study of the reduction mechanism of ES in EC-based electrolyte with the ring-opening reaction followed by dimerization reaction and/or the second-electron reduction path. The effects of participation of cosolvents such as diethyl carbonate (DMC), ethyl methyl carbonate (EMC), and dimethyl sulfite (DMS) on the ring-opening reaction process of ES were also carefully investigated. Based on our calculation results, the reactivity order of the clusters (ES)Li+(M) (M = EC, PC, VC, DMC, DMS, and EMC) is shown as follows: (ES)Li+(VC) (4.09 × 1055 s–1) > (ES)Li+(PC) (9.21 × 1047 s–1) > Li+(ES) (8.47 × 1047 s–1) > (ES)Li+(EC) (7.07 × 1047 s–1) > (ES)Li+(DMS) (3.11 × 1043 s–1) > (ES)Li+(EMC) (1.91 × 1041 s–1) > (ES)Li+(DMC) (2.48 × 1037 s–1). The implication of our calculation results on the formation of SEI on the graphite is also discussed.