MeTFSI (Me = Li, Na) Solvation in Ethylene Carbonate and Fluorinated Ethylene Carbonate: A Molecular Dynamics Study

Classical and ab initio molecular dynamics (MD) simulations have been performed for electrolytes based on LiTFSI and NaTFSI solutions in ethylene carbonate and its mono- and difluoro derivatives. Differences between electrolytes with Li⁺ or Na⁺ ions and the effect of fluorination on the structure and transport properties have been analyzed. The observed differences are related to the strength of Me⁺-carbonate binding, which is weaker for the Na⁺ cation and/or fluorinated solvents. Infrared spectra have been computed from ab initio MD and density functional tight binding (DFTB) MD trajectories. The changes of vibrational frequencies have been related to the local structure of the electrolyte and to interactions between salt cations and solvent molecules. The frequency shifts obtained from the AIMD simulations agree with experimental data, whereas DFTB underestimates Na⁺-carbonate interactions.

A facile route to prepare mixed transition metal oxide yolk-shell microspheres for enhanced lithium storage

A coordination co-precipitation route followed by a calcination process was developed to prepare mixed transition metal oxide microspheres with a yolk-shell structure. ZnCo2O4, NiCo2O4, MnCo2O4, ZnMn2O4 and CoMn2O4 have been successfully fabricated, which demonstrates the universality of this route. As a promising anode for lithium-ion batteries (LIBs), ZnCo2O4 was investigated as a typical example, which showed a remarkable reversible capacity of 1063 mA h g-1 after 50 cycles at a current density of 200 mA g-1 and a good rate capability of 839 mA h g-1 after 200 cycles at a large current density of 900 mA g-1. This work shows the extensive potential of a general route for the synthesis of yolk-shell microspheres for next-generation energy conversion and storage devices.

Interfacial structure and electrochemical stability of electrolytes: methylene methanedisulfonate as an additive

The mechanism responsible for widening the electrochemical stability window of methylene methanedisulfonate (MMDS)-containing electrolytes compared to conventional carbonate electrolytes is suggested based on molecular dynamics (MD) simulations and density functional theory (DFT) calculations. We find that MMDS has a stronger reduction ability and higher affinity for the electrode surface than solvents, and these behaviors provide an important condition for priority decomposition of the additive. The addition of MMDS could reduce the probability of finding solvent-ion complexes at the electrolyte-electrode interface, which is especially beneficial for the stability of the solvent electrochemical window. This knowledge of the local electrolyte composition and structure at the surface plays a significant role in advancing our understanding of the relationships between interface structure and battery cycling performance, and expanding the operating windows of electrochemical devices.