As one of the landmark technologies, Li-ion batteries (LIBs) have reshaped our life in the 21stcentury, but molecular-level understanding about the mechanism underneath this young chemistry is still insufficient. Despite their deceptively simple appearances with just three active components (cathode and anode separated by electrolyte), the actual processes in LIBs involve complexities at all length-scales, from Li migration within electrode lattices or across crystalline boundaries and interfaces to the Li accommodation and dislocation at potentials far away from the thermodynamic equilibria of electrolytes. Among all, the interphases situated between electrodes and electrolytes remain the most elusive component in LIBs. Interphases form because no electrolyte component (salt anion, solvent molecules) could remain thermodynamically stable at the extreme potentials where electrodes in modern LIBs operate, and their chemical ingredients come from the sacrificial decompositions of electrolyte components. The presence of an interphase on electrodes ensures reversibility of Li intercalation chemistry in anode and cathode at extreme potentials and defines the cycle life, power and energy densities, and even safety of the eventual LIBs device. Despite such importance and numerous investigations dedicated in the past two decades, we still cannot explain why, nor predict whether, certain electrolyte solvents can form a protective interphase to support the reversible Li intercalation chemistries while others destroy the electrode structure. The most representative example is the long-standing "EC-PC Disparity" and the two interphasial extremities induced therefrom: differing by only one methyl substituent, ethylene carbonate (EC) forms almost ideal interphases on the graphitic anode, thus becoming the indispensable solvent in all LIBs manufactured today, while propylene carbonate (PC) does not form any protective interphase, leading to catastrophic exfoliation of the graphitic structure. With one after another hypotheses proposed but none satisfactorily rationalizing this disparity on the molecular level, this mystery has been puzzling the battery and electrochemistry community for decades. In this Account, we attempted to decipher this mystery by reviewing the key factors that govern the interaction between the graphitic structure and the solvated Li right before interphase formation. Combining DFT calculation and experiments, we identified the partial desolvation of the solvated Li at graphite edge sites as a critical step, in which the competitive solvation of Li by anion and solvent molecules dictates whether an electrolyte is destined to form a protective interphase. Applying this model to the knowledge of relative Li solvation energy and frontier molecular orbital energy gap, it becomes theoretically possible now to predict whether a new solvent or anion would form a complex with Li leading to desirable interphases. Such molecular-level understanding of interphasial processes provides guiding principles to the effort...

Fluoroalkylsilane treatment of super‐hydrophobic, aligned carbon nanotube films (see electron micrograph) prepared by pyrolysis of metal phthalocyanines results in the films having both super‐hydrophobic and super‐lipophobic properties, namely they are super‐“amphiphobic” surfaces.

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The design of artificial receptors for sulfate ions is of great interest because of the importance of sulfate ions in environmental and biological systems.[1] One of the applications of sulfate ion receptors is extraction of the sulfate ion from nitrate-rich mixtures in the remediation of nuclear waste. [2] Based on liquid-liquid anion exchange technology, extraction of sulfate ions from an aqueous to an organic phase was realized by using macrocyclic receptors.[ ) of the receptor were needed in this case to ensure applicable extraction. Hence, the extraction efficiency has yet to be improved for sulfate ion extractants. This aim is quite challenging because of the extremely large hydration energy of the sulfate ion (DG h = À1080 kJ mol À1 for SO 4 2À compared to À300 kJ mol À1 for NO 3 À ) [3] according to the Hofmeister series, [4] as well as the high nitrate/sulfate ratios present in the crude waste. To overcome the Hofmeister bias, which disfavors the separation of the extremely hydrophilic sulfate ion from water, the receptor must have both excellent affinity and selectivity for sulfate ions.In recent years, some receptors for sulfate ions have been synthesized by employing different binding groups (mostly NH moieties), such as protonated Schiff base macrocycles, [5] diindolylureas, [6] and an M 4 L 6 cage containing a bipyridinefunctionalized monourea; [7] these receptors bind the anion in the 1:1, 3:1 and 6:1 (host/guest) mode, respectively. The trenbased tripodal trisurea backbone (L 1 ; tren = tris(2-aminoethyl)amine) has also been found to encapsulate the sulfate ion in a 2:1 (host/guest) ratio. [8] Although saturated coordination (12 hydrogen bonds) for sulfate and phosphate ions has been achieved by these receptors, the complementarity for the ions is not optimal in most cases. Calculations have demonstrated that the optimal saturated coordination mode for sulfate ions is binding in a tetrahedral cavity with 12 hydrogen bonds along the edges. [9] In this regard, the ideal sulfate ion receptor would possess a complementary tetrahedral cavity surrounded by 12 optimally arranged binding sites.The chelate effect may also play an important role in the host-guest binding affinity because of the favorable contributions from both entropy and enthalpy. As a typical example of the chelate effect, the Co 2+ complex of the bidentate ligand 1,2-diaminoethane is 10 8 times more stable than that of the unidentate ligand ammonia.[10] Moreover, the hexadentate ligand ethylenediaminetetraacetic acid (EDTA) displays extremely high binding affinities toward most metal ions (for example, 10 14.3 m À1 for Fe 2+ and 10 16.3 m À1 for Co 2+ ).[11]Given the similarities between anion coordination and classical transition-metal coordination chemistry, [12] increasing the number of binding sites to achieve high chelate effects should be an effective way to improve the extraction efficiency of sulfate ion extractants.We have devoted our efforts to the synthesis of selective anion receptors based on the urea functionality. [8a...

A word in urea: A strategy of mimicking the scaffold and metal coordination behavior of oligo‐2,2′‐bipyridine ligands was used to obtain a triple anion helicate from a bis(biurea) receptor and phosphate ions. The successful assembly of the triple helical structure provides guidelines for the design of new anion ligands by taking advantage of the similarities of metal and anion coordination.