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This paper presents the molecular dynamics simulation of 1 mol kg−1 LiPF6 in a binary solvent of ethylene carbonate (EC) and dimethylcarbonate, which is a representative electrolyte solution for lithium-ion batteries. The simulation successfully reproduced the diffusion coefficient, ionic conductivity, and shear viscosity as functions of EC content at 300 K, which had been experimentally determined in our previous study. The Yukawa potential was adopted to model intercharge interactions to reduce computational costs, which consequently allowed us to precisely calculate the conductivity and viscosity by directly integrating time-correlation functions without explicitly modeling the molecular polarization. Breaking down microscopic current correlation functions into components revealed that, whereas the cation–anion attractive interaction dominantly impedes the conduction when the EC content is low, it is the cation–cation and anion–anion repulsive interactions that reduce the conductivity at a high EC content. An analysis of the pressure correlations revealed that all components positively contribute to the viscosity in the binary solvent without the electrolyte. On the other hand, negative terms are observed in five out of six cross correlations in the presence of the electrolyte, implying that these correlations negatively contribute to the shear stress and entropy production, both of which are net positive. [ABSTRACT FROM AUTHOR]

The lithiation mechanism of electrode materials is important for understanding the basic reactions in Li-ion batteries. In particular, zero-strain materials have garnered interest owing to their stable charge–discharge performances. In this study, we investigated the atomistic phase transition mechanism of spinel Li4Ti5O12, a well-known zero-strain material, using high-resolution transmission electron microscopy. A single-crystalline Li4Ti5O12 (100) specimen was prepared and observed in situ at a lattice resolution under electron-beam-assisted lithiation. The lattice fringes originating from the Li plane of the spinel crystal were anisotropically altered during phase transition, suggesting the asymmetrical site shifting of Li atoms during lithiation. This spontaneous symmetry-breaking mechanism for the phase transition is considered essential for the lithiation of spinel lattice. [ABSTRACT FROM AUTHOR]

Based on experimental data, we optimized the potential parameters for the classical molecular dynamics simulation to reproduce the volume and ionic conductivity of the molten alkali-metal carbonates A2CO3 where A = Li, Na, K, Rb, and Cs at T/K = 1223 and ambient pressure. The force field was then applied to the binary mixtures (Li1−xCsx)2CO3 and (Li1−xKx)2CO3. In (Li1−xCsx)2CO3, the diffusion coefficient DCs exceeds DLi at x > 0.6, testifying to the Chemla effect. The net ionic conductivity was broken down into the contributions from the velocity auto- and cross-correlations of each ionic species. The significant negative deviation of the real conductivity of (Li1−xCsx)2CO3 from the one estimated by the Nernst-Einstein (NE) relation is clearly explained by the contribution from the cross correlations; specifically, the cross term between Li+and CO 3 2 − , which is negative at x = 0, significantly shifts to the positive side when x increases, which is dominantly responsible for dampening the conductivity from the NE conductivity. A similar behavior was observed in (Li1−xKx)2CO3 with a less pronounced manner than in (Li1−xCsx)2CO3. These observations corroborate the precedent studies pointing to the trapping of Li+ by the anion when a lithium salt is mixed with another salt of which the cation size is greater than that of Li+. [ABSTRACT FROM AUTHOR]