Comprehensive Enhancement of Nanostructured Lithium-Ion Battery Cathode Materials via Conformal Graphene Dispersion.

Efficient energy storage systems based on lithium-ion batteries represent a critical technology across many sectors including consumer electronics, electrified transportation, and a smart grid accommodating intermittent renewable energy sources. Nanostructured electrode materials present compelling opportunities for high-performance lithium-ion batteries, but inherent problems related to the high surface area to volume ratios at the nanometer-scale have impeded their adoption for commercial applications. Here, we demonstrate a materials and processing platform that realizes high-performance nanostructured lithium manganese oxide (nano-LMO) spinel cathodes with conformal graphene coatings as a conductive additive. The resulting nanostructured composite cathodes concurrently resolve multiple problems that have plagued nanoparticle-based lithium-ion battery electrodes including low packing density, high additive content, and poor cycling stability. Moreover, this strategy enhances the intrinsic advantages of nano-LMO, resulting in extraordinary rate capability and low temperature performance. With 75% capacity retention at a 20C cycling rate at room temperature and nearly full capacity retention at -20 °C, this work advances lithium-ion battery technology into unprecedented regimes of operation.

Possibility of High Ionic Conductivity and High Fracture Toughness in All-Dislocation-Ceramics.

Based on the results of numerical calculations as well as those of some related experiments which are reviewed in the present paper, it is suggested that solid electrolytes filled with appropriate dislocations, which is called all-dislocation-ceramics, are expected to have considerably higher ionic conductivity and higher fracture toughness than those of normal solid electrolytes. Higher ionic conductivity is due to the huge ionic conductivity along dislocations where the formation energy of vacancies is considerably lower than that in the bulk solid. Furthermore, in all-dislocation- ceramics, dendrite formation could be avoided. Higher fracture toughness is due to enhanced emissions of dislocations from a crack tip by pre-existing dislocations, which causes shielding of a crack tip, energy dissipation due to plastic deformation and heating, and crack-tip blunting. All-dislocation-ceramics may be useful for all-solid-state batteries.

Effect of Stirring on Particle Shape and Size in Hydrothermal Synthesis of LiCoO2.

Lithium cobalt oxide (LCO) is a highly significant material for the positive electrodes of lithium-ion batteries. Due to the correlation between crystal morphology and electrochemical performance in the layered rock-salt structure, LCO with crystal morphology exhibiting anisotropy demonstrates superior charge-discharge characteristics. In this study, various morphologies of LCO were synthesized via hydrothermal synthesis using a plate-like precursor. Under conditions without agitation, a hexagonal plate-like LCO was synthesized, while a spherical LCO was obtained with agitation during synthesis. The particle morphology was investigated by using X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Furthermore, in the performance evaluation of positive electrode materials for lithium-ion batteries, the hexagonal plate-like LCO exhibited a larger charge-discharge capacity compared to the spherical LCO.

Interferometric phase shift compensation technique for high-power, tiled-aperture coherent beam combination.

We propose a simple coherent beam combining technique for applications in high-power multichannel laser amplifier systems with tiled aperture design. Using a photodiode pair coupled with piezo-actuator mirrors, we demonstrated robust beam combining bandwidth (~1 KHz) and root mean-square deviation (~λ/25) for two beam channels. We estimate that the performance of this technique can be further enhanced in terms of operational bandwidth and phase locking accuracy. It is not limited by single beam power or channel number restrictions, does not require optical phase retrieval algorithms, or calibrations, and can be integrated into various master oscillator power amplifier architectures.

Theoretical upper limit of dislocation density in slightly-ductile single-crystal ceramics.

Upper limit of dislocation density without fracture is numerically calculated for slightly- ductile single-crystal ceramics for which the Griffith criterion for fracture and the Bailey-Hirsch type relationship between applied stress and the dislocation density are nearly valid simultaneously in order to obtain useful information to improve functional, electrical, and mechanical properties of ceramics by the introduction of appropriate dislocations. Two models of fracture as a function of dislocation density are constructed; simple model and probability model. If the diameter of pre-existing microcracks is sufficiently small, the dislocation density could be as high as the crystallographic limit (~10^18 m^-2). Even if the typical diameter of pre-existing microcracks is not so small, there is some probability that the dislocation density could be as high as the crystallographic limit if the number of microcracks in the specimen is very small. Accordingly, the increase in ionic conductivity by several orders of magnitude without dendrite formation by introducing appropriate dislocations into single-crystal solid electrolytes with the dislocation density higher than about 10^17 m^-2 theoretically predicted by the authors may be practically possible.

Densification of a NASICON-Type LATP Electrolyte Sheet by a Cold-Sintering Process.

A NASICON-type Li1.3Al0.3Ti1.7(PO4)3 (LATP) electrolyte sheet for all-solid-state batteries was fabricated by a cold sintering process (CSP). The microstructure of the LATP sheet was controlled to improve the wettability which is an essential factor in CSP. The porous sheets of LATP were prepared by calcination the green sheets to remove the organic components and form the porous structure. By the CSP using the porous sheets, the densification of grain boundary was observed and further densified with increasing reaction time. The total conductivity of the prepared LATP sheet was improved from 3.0 × 10-6 S/cm to 3.0 × 10-4 S/cm due to the formation of necks between the particles at the grain boundary.