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LiI-promoted LiOH formation in Li-O 2 batteries with wet ether electrolytes has been investigated by Raman, nuclear magnetic resonance spectroscopy, operando pressure tests, and molecular dynamics simulations. We find that LiOH formation is a synergistic effect involving both H 2 O and LiI additives, whereas with either alone Li 2 O 2 forms. LiOH is generated via a nominal four-electron oxygen reduction reaction, the hydrogen coming from H 2 O and the oxygen from both O 2 and H 2 O, and with fewer side reactions than typically associated with Li 2 O 2 formation; the presence of fewer parasitic reactions is attributed to the proton donor role of water, which can coordinate to O 2 − and the higher chemical stability of LiOH. Iodide plays a catalytic role in decomposing H 2 O 2 /HO 2 − and thereby promoting LiOH formation, its efficacy being highly dependent on the water concentration. This iodide catalysis becomes retarded at high water contents due to the formation of large water-solvated clusters, and Li 2 O 2 forms again.

This work reports a simple and energy-saving strategy for selective synthesis of water-soluble and organic-soluble carbon dots at room temperature.

Hydrous materials are ubiquitous in the natural environment and efforts have previously been made to investigate the structures and dynamics of hydrated surfaces for their key roles in various chemical and physical applications, with the help of theoretical modelling and microscopy techniques. However, an overall atomic-scale understanding of the water-solid interface, including the effect of water on surface ions, is still lacking. Herein, we employ ceria nanorods with different amounts of water as an example and demonstrate a new approach to explore the water-surface interactions by using solid-state NMR in combination with density functional theory. NMR shifts and relaxation time analysis provide detailed local structure of oxygen ions and the nature of water motion on the surface: the amount of molecularly adsorbed water decreases rapidly with increasing temperature (from room temperature to 150 °C), whereas hydroxyl groups are stable up to 150 °C; dynamic water molecules are found to instantaneously coordinate to the surface oxygen ions. The applicability of dynamic nuclear polarization for selective detection of surface oxygen species is also compared to conventional NMR with surface selective-labeling: the optimal method depends on the feasibility of enrichment and the concentration of protons in the sample. These results provide new insight into the interfacial structure of hydrated oxide nanostructures which is important for relevant applications.

CAS [KGCX2-YW-806, KJCX2-YW-H21, 2009AA05Z108, 2010CB631304]; US Department of Energy, Office of Science, Office of Basic Energy Sciences [DE-AC02-06CH11357

The ion transportation mechanism in a high-concentration solution remains unclear due to the complexity of the strong ion–ion/ion–solvent interaction, resulting in the invalidation of most ionic conducting theories based on diluted solutions. Here, a superconcentrated electrolyte (water-in-salt) is investigated by multiple experimental techniques, including advanced tools (NMR, synchrotron X-ray diffraction, and spallation neutron scattering), combined with molecular dynamics (MD) simulation to draw out its unique microstructure and uncover its intrinsic relationship with the ionic transportation. Based on the results, we firstly proposed the ionic transport model for the water-in-salt electrolyte, where the solid-like nano-anion clusters construct a superfluid framework and the lithium ion is able to move freely like in an ionic atmosphere. Our model gives a unified explanation to the unique phenomena previously discovered in water-in-salt electrolytes, including the decoupling of conductivity–viscosity and the nanophase separation between the anion and water. Our findings on the microstructure of the super-high-concentrated electrolyte and the involved unique Li-conducting mechanism can fill in the gap between a solid-state conductor and a dilute liquid electrolytic solution.

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