Deciphering the Dynamic Processes at the Electrode-Electrolyte Interface for Stable Deposition of Lithium.

Realization of lithium-metal (Li) batteries is plagued by the dendritic deposition of Li leading to internal short-circuit and low Coulombic efficiency. The Li-deposition process largely depends on the liquid electrolyte that reacts with the Li metal and forms a solid electrolyte interphase (SEI) layer with diverse chemical and physical properties. Moreover, the electrolyte possesses characteristic ion transport behaviors and directly affects the deposition kinetics at the electrode surface. As a result, the convolution of interfacial, ion transport, and kinetic effects of an electrolyte obscures the understanding of Li deposition in Li-metal batteries. Herein, the dynamic processes and the interfacial properties of Li-metal electrodes are precisely delineated in representative ether electrolytes. It is found that a combination of homogeneous SEI and slow deposition kinetics produces layer-by-layer epitaxial growth of Li. In contrast, the dendritic growth of Li is observed when the SEI is inhomogeneous and the reaction rate is fast. Nevertheless, it is shown that a homogeneous SEI is not a prerequisite in suppressing Li dendrites when the adverse effect of an unfavorable SEI can be subdued by proper kinetic tuning at the interface. Furthermore, an otherwise kinetically unstable electrolyte can also be made compatible with the Li-metal electrode when covered with a properly designed SEI. This delineation of the roles of SEI and deposition kinetics gives deep insight into designing efficient electrolytes in Li-metal batteries.

Raman spectroscopic study of ZnO/NiO nanocomposites based on spatial correlation model.

The effect of nickel concentration has been investigated in ZnO/NiO nanocomposites synthesized using the co-precipitation method. The X-ray diffraction and TEM measurements confirm the distinct phase of NiO in the ZnO/NiO samples. Furthermore, the Raman study shows the sharp modes at 99 cm-1 and 438 cm-1 corresponding to E(low) 2, E(high) 2 of hexagonal wurtzite ZnO structure and, 1080 cm-1 associated to the two-phonon (2P) mode of NiO, respectively. We also compared the effect of Ni concentration on the formation of ZnO/NiO by analyzing Ehigh 2 Raman mode of ZnO with the help of spatial correlation model. The correlation lengths, broadening and asymmetry ratio obtained from the fitting showed good agreement with the experimental results.

Controlling atomic joints between carbon nanotubes by electric current.

Using a transmission electron microscope and a nanomanipulator, we explored the early head-to-head coalescence of two capped carbon nanotubes (CNTs) under induction of electric current. We measured detaching forces for coalesced CNTs, showing discrete identifiable values attributable to van der Waals interaction, single sp2-like bonds, and double sp3-like bonds by comparing them with forces obtained using molecular dynamics simulations. Our results underscore the feasibility of atomically controlled junctions of CNTs tuned by the amount of the electrical current.