Article ID: 2018-0046
リチウムイオン電池(LIB)中の負極と電解液の界面に主に充電時に形成される被膜をSolid Electrolyte Interphase (SEI)と呼ぶ.このSEIの性質によってLIBの性能や安全性が大きく変化する.しかし,この界面過程のその場観察・オペランド観察実験はいまだに困難が多く,高精度な理論計算による微視的機構の解明に大きな期待が寄せられている.本稿では,特に密度汎関数理論をベースにした第一原理計算によるSEI研究の現状を,著者らの研究も含めて,概観し今後について展望する.
Schematic pictures of (a) charging and (b) discharging processes in Lithium Ion Battery (LIB). (c) Typical solvent and additive molecules (EC, VC, FEC), and decomposed products (Li2EDC, Li2DOB) in LIB electrolyte solution. The detail is explained in the text.
Microscopic picture of SEI formation processes at the first charging of LIB.
Schematic pictures of (a) first-principles cluster calculation with cluster boundary condition and typically polarizable continuum model for solvent effect, and (b) first-principles molecular dynamics calculation of solution states where all the atoms are explicitly treated and periodic boundary condition is applied. The pink, red, sky-blue and white spheres denote Li+, O, C, and H, respectively.
Products of reductive decompositions (RC) of EC solvent and VC additive in EC solvent. (a) [Li-O2CO-CH2-CH2]− by 1e− RC of EC, (b) Li+-CO32- & C2H4 by consecutive 2e− RC of EC, (c) CO & Li (OCH2)2 by concerted 2e− RC of EC, and (d) CO & Li (OCH)2 or Li (OCH)2− by 1e- or 2e− RC of VC.
Atomistic structures obtained in the equilibrium trajectories for (a) EC-derived SEI and (b) that with F−. (a) Li+-glue for the organic species and (b) F− -glue for the lithiated organic species are depicted.
Schematic explanations of (a) conventional surface deposit mechanism and (b) near-shore aggregation mechanism proposed by the present authors.
Peled model for SEI composition.
Schematic pictures of the properties of (a) Li2CO3, (b) Li2CO3/LiF interface, and (c) Li metal anode/Li2CO3/EC electrolyte interface.