Trace water content in the electrolyte causes the degradation of LiPF, and the decomposed products further react with water to produce HF, which alters the surface of anode and cathode. As a result, the reaction of HF and the deposition of decomposed products on electrode surface cause significant capacity fading of cells. Avoiding these phenomena is crucial for lithium ion batteries. Considering the Lewis-base feature of the N-Si bond, 1-(trimethylsilyl)imidazole (1-TMSI) is proposed as a novel water scavenging electrolyte additive to suppress LiPF decomposition. The scavenging ability of 1-TMSI and beneficiary interfacial chemistry between the MCMB electrode and electrolyte are studied through a combination of experiments and density functional theory (DFT) calculations. NMR analysis indicated that LiPF decomposition by water was effectively suppressed in the presence of 0.2 vol % 1-TMSI. XPS surface analysis of MCMB electrode showed that the presence of 1-TMSI reduced deposition of ionic insulating products caused by LiPF decomposition. The results showed that the cells with 1-TMSI additive have better performance than the cell without 1-TMSI by facilitating the formation of solid-electrolyte interphase (SEI) layer with better ionic conductivity. It is hoped that the work can contribute to the understanding of SEI and the development of electrolyte additives for prolonged cycle life with improved performance.

No abstract

The role of ethylene sulfite (ES) as an electrolyte additive for lithium ion batteries is explained by investigating the one- and two-electron reductive decomposition of ES and (ES)Li(+)(PC)(n) (n = 0-2), both in vacuum and solvent, with the aid of high-level density functional theory calculations. The open-chain radical, which is formed as a result of reduction of ES in solvent without first being coordinated with Li(+), is further stabilized by a dissolved lithium ion. The resulting more stable intermediate releases a somewhat large amount of energy, which is utilized in the formation of a subsequent radical anion. On the basis of the study on the reductive decomposition of ES, (ES)Li(+)(PC), and (ES)Li(+)(PC)(2), the major products that are responsible for the formation of a protective solid electrolyte interphase film are Li(2)SO(3), (CH(2)OSO(2)Li)(2), CH(3)CH(OSO(2)Li)CH(2)OCO(2)Li, and ROSO(2)Li.

The capability to activate methane at mild temperature and facilitate all elementary reactions on the catalyst surface is a defining characteristic of an efficient catalyst especially for the direct conversion of methane to ethylene. In this work, theoretical calculations are performed to explore such catalytic characteristic of an IrO 2 (110) surface. The energetics and mechanism for methane dehydrogenation reactions, as well as C-C coupling reactions on the IrO 2 (110) surface, are investigated by using van der Waals-corrected density functional theory calculations. The results indicate that a non-local interaction significantly increases the binding energy of a CH 4 molecule with an IrO 2 (110) surface by 0.35 eV. Such an interaction facilitates a molecular-mediated mechanism for the first C-H bond cleavage with a low kinetic barrier of 0.3 eV which is likely to occur under mild temperature conditions. Among the dehydrogenation reactions of methane, CH 2 dissociation into CH has the highest activation energy of 1.19 eV, making CH 2 the most significant monomeric building block on the IrO 2 (110) surface. Based on the DFT calculations, the formation of ethylene could be feasible on the IrO 2 (110) surface via selective CH 4 dehydrogenation reactions to CH 2 and a barrierless self-coupling reaction of CH 2 species. The results provide an initial basis for understanding and designing an efficient catalyst for the direct conversion of methane to ethylene under mild temperature conditions.