Search

The application of solid-state electrolytes in Li batteries has been hampered by the occurrence of Li-dendrite-caused short circuits. To avoid cell failure, the electrolytes can only be stressed with rather low current densities, severely restricting their performance. Since grain size and pore distributions significantly affect dendrite growth in ceramic electrolytes like Li7 La3 Zr2 O12 and its variants, here we have proposed a "detour and buffer" strategy to bring the superiority of both coarse and fine grains into play. To validate the mechanism, a coarse/fine bimodal grain microstructure was obtained by seeding unpulverized large particles in the green body. The rearrangement of coarse grains and fine pores was fine-tuned through changing the ratio of pulverized and unpulverized powders. The optimized bimodal microstructure, obtained when the two powders are equally mixed, allowed, without extra interface decoration, cycling for over 2000 h as the current density was increased from 1.0 mA·cm-2 gradually up to 2.0 mA·cm-2 . The "detour and buffer" effects was confirmed from postmortem analysis. The complex grain boundaries formed by fine grains discourage the direct infiltration of Li. Simultaneously, the coarse grains further increase the tortuosity of the Li path. Our study sheds light on the microstructure optimization for the polycrystalline solid-state electrolytes. This article is protected by copyright. All rights reserved.

Laser shock peening (LSP), a surface modification technique, is promising to enhance the strength and wear resistance for Ni-based superalloys. To understand the strengthening mechanism in a laser shock peened Ni-based superalloy DZ417G, we utilize synchrotron poly- and monochromatic X-ray microdiffraction, as well as electron microscopy and microhardness to quantify the local microstructures and mechanical properties at various depths. In the 1.2-mm-deep hardened layer, the microhardness increases monotonically by ∼50% from the unaffected interior to the surface. Quantitative microdiffraction analysis shows that large amounts of dislocations are introduced by LSP. High densities of 7.1 × 1015 m−2 and 11.8 × 1015 m−2 are seen close to the peened surface for the γ- and γ′-phases, respectively, which are 5 and 20 times of those in the unaffected region. Different gradients of dislocation density are observed for the two phases from interior to surface, and their combined effect accounts well for the hardness increment. Due to the unaltered γ′-precipitates and chemical composition in the LSP affected zone, the large density of dislocations dominates the observed strengthening. Combined poly- and monochromatic X-ray microdiffraction allows quantifying the local microstructures of plastic deformation over a large sampling scale that can hardly be achieved using other materials characterization techniques.

Nanotwin structures in materials engender fascinating exotic properties. However, twinning usually alter the crystal orientation, resulting in random orientation and limited performances. Here, we report a well-aligned rutile TiO2 nanotwin film with superior preferential orientation than its isostructural substrate. By means of the synchrotron X-ray Laue nanodiffraction technique, the crystal orientation, twin boundaries, and deviatoric stresses of the film were quantitatively imaged at unprecedented spatial resolution to unravel the underlying mechanism of this anomalous alignment. Massive {101}-type rutile nanotwins were observed, and a crystallographic relationship of the heteroepitaxy was proposed. The rapid twinning and twin-controlled heteroepitaxy are responsible for the texture improvement. This work would open up opportunities for rational design of better twin-based functional materials, and implies the powerful capabilities of X-ray nanodiffraction technique for multidisciplinary applications.

Carbon-defect engineering in metal single-atom catalysts by simple and robust strategy, boosting their catalytic activity, and revealing the carbon defect-catalytic activity relationship are meaningful but challenging. Herein, we report a facile self-carbon-thermal-reduction strategy for carbon-defect engineering of single Fe-N4 sites in ZnO-Carbon nano-reactor, as efficient catalyst in Fenton-like reaction for degradation of phenol. The carbon vacancies are easily constructed adjacent to single Fe-N4 sites during synthesis, facilitating the formation of C-O bonding and lowering the energy barrier of rate-determining-step during degradation of phenol. Consequently, the catalyst Fe-NCv-900 with carbon vacancies exhibits a much improved activity than the Fe-NC-900 without abundant carbon vacancies, with 13.5 times improvement in the first-order rate constant of phenol degradation. The Fe-NCv-900 shows high activity (97% removal ratio of phenol in only 5 min), good recyclability and the wide-ranging pH universality (pH range 3-9). This work not only provides a rational strategy for improving the Fenton-like activity of metal single-atom catalysts, but also deepens the fundamental understanding on how periphery carbon environment affects the property and performance of metal-N4 sites. Designing carbon-defect engineering is significant for boosting the catalytic performance of metal single-atom sites catalysts. Herein, the authors report a self-carbon-thermal-reduction strategy for carbon defect engineering to boost the Fenton-like activity of single Fe-N4 sites. [ABSTRACT FROM AUTHOR]

X-ray nanodiffraction was used to measure the thermal stress of 10 µm nanotwinned Cu bumps in Cu/SiO2 hybrid structures at −55 °C, 27 °C, 100 °C, 150 °C, and 200 °C. Bonding can be achieved without externally applied compression. The X-ray beam size is about 100 nm in diameter. The Cu bump is dominated by (111) oriented nano-twins. Before the hybrid bonding, the thermal stress in Cu bumps is compressive and remains compressive after bonding. The average stress in the bonded Cu joint at 200 °C is as large as −169.1 MPa. In addition, using the strain data measured at various temperatures, one can calculate the effective thermal expansion coefficient (CTE) for the 10 µm Cu bumps confined by the SiO2 dielectrics. This study reports a useful approach on measuring the strain and stress in oriented metal bumps confined by SiO2 dielectrics. The results also provide a deeper understanding on the mechanism of hybrid bonding without externally applied compression. [ABSTRACT FROM AUTHOR]

Abstract: In-situ neutron powder diffraction was employed to investigate the structural evolution of the electrode materials in a commercial lithium-ion battery used for electric buses in Taiwan. The battery, containing a vanadium-added LiFePO4 cathode, does not exhibit a delayed phase transition between LiFePO4 (triphylite) and FePO4 (heterosite) suggesting that the delayed phase transition can be suppressed through the use of vanadium-added LiFePO4 cathodes, which also enhances the capacity and prolongs the cycle life of these batteries. Furthermore, we characterize the readily reversible structural change of the anode (Li x C6 where 0 < x ≦ 1) and correlate this to battery voltage. [Copyright &y& Elsevier]

The influences of adding vanadium to the structure evolution and electrochemical performance of LiFePO 4 are systematically investigated by in-situ X-ray powder diffraction and X-ray absorption near edge structure spectroscopy. The results indicate that the addition of a small amount of vanadium (less than at 1%) significantly reduces the formation of non-crystalline (highly disordered) triphylite and remnant heterosite phases in the cathode of battery especially at the rate capability higher than 0.5C. The cycle stability of LiFePO 4 cathode with vanadium additive after 80 cycles is improved by 14.9% compared to that without vanadium additive. Such an enhancement could be attributed to the ion diffusion kinetics being improved and inactive triphylite being reduced by the supervalent-vanadium additive in cathode during electrochemical redox cycles. [ABSTRACT FROM AUTHOR]