Chemical composition and formation mechanisms in the cathode-electrolyte interface layer of lithium manganese oxide batteries from reactive force field （ReaxFF） based molecular dynamics

Lithium manganese oxide （LiMn2O4） is a principal cathode material for high power and high energy density electrochemical storage on account of its low cost, non-toxicity, and ease of preparation relative to other cathode materials. However, there are well-documented problems with capacity fade of lithium ion batteries containing LiMn2O4. Experimental observations indicate that the manganese content of the electrolyte increases as an electrochemical cell containing LiMn2O4 ages, suggesting that active material loss by dissolution of divalent manganese from the LiMn2O4 surface is the primary reason for reduced cell life in LiMn2O4 batteries. To improve the retention of manganese in the active material, it is key to understand the reactions that occur at the cathode surface. Although a thin layer of electrolyte decomposition products is known to form at the cathode surface, the speciation and reaction mechanisms of Mn^2＋ in this interface layer are not yet well understood. To bridge this knowledge gap, reactive force field （ReaxFF） based molecular dynamics was applied to investigate the reactions occurring at the LiMn2O4 cathode surface and the mechanisms that lead to manganese dissolution. The ReaxFFMD simulations reveal that the cathode-electrolyte interface layer is composed of oxida- tion products of electrolyte solvent molecules including aldehydes, esters, alcohols, polycarbonates, and organic radicals. The oxidation reaction pathways for the electro- lyre solvent molecules involve the formation of surface hydroxyl species that react with exposed manganese atoms on the cathode surface. The presence of hydrogen fluoride （HF） induces formation of inorganic metal fluorides and surface hydroxyl species. Reaction products predicted by ReaxFF-based MD are in agreement with experimentally identified cathode-electrolyte interface compounds. An overall cathode-electrolyte interface reaction scheme is proposed based on the molecular simulation results.

Molecular recognition of sulfonatocalixarene with organic cations at the self-assembled interface：a thermodynamic investigation

A microcalorimetric study on molecular recognition of p-sulfonatocalix[4]arene derivatives at selfassembled interface in comparison with in bulk water was performed,inspired by the dramatic change in physicochemical characteristics from bulk water to interface.A total of six cationic molecules were screened as model guests,including ammonium（NH_4~＋）,guanidinium（Gdm~＋）.N,N＇-dimethyl-1,4-diazabicyclo[2.2.2]octane（DMDABCO^（2＋））,tropylium（Tpm~＋）,N-methyl pyridinium（N-mPY＊） and methyl viologen（MV^（2＋））.The complexation with NH_4~＋.Gdm~＋ and DMDABCO2＊ is pronouncedly enhanced when the recognition process moved from bulk water to interface,whereas the complexation stabilities with Tpm~＋,N-mPY~＋ and MV2＊ increase slightly or even decrease to some extent.A more interesting phenomenon arises from the NH_4~＋/Gdm~＋ pair that the thermodynamic origin at interface differs definitely from each other although with similar association constants.The results were discussed in terms of differential driving forces,electrostatic,hydrogen bond as well as π-stacking interactions,originating from the unique physicochemical features of interfaces,mainly the polarity and dielectric constant.

Modeling nanoscale ice adhesion

Anti-icing is crucial for numerous instruments and devices in low temperature circum- stance. One of the approaches in anti-icing is to reduce ice adhesion strength, seeking spontaneous de-icing processes by natural forces of gravity or by winds. In order to enable tai- lored surface icephobicity design, research requires a good theoretical understanding of the atomistic interacting mechanisms between water/ice molecules and their adhering substrates. Herein, this work focuses on using atomistic modeling and molecular dynamics simulation to build a nanosized ice-cube adhering onto silicon surface, with different contact modes of solid-solid and solid-liquid-solid patterns. This study provides atomistic models for probing nanoscale ice adhesion mechanics and theoretical platforms for explaining experimental results.