Ni-rich layered cathodes have been used in commercial Li-ion batteries because of their high capacity and low cost. However, they suffer from crack formation at the grain boundaries owing to heterogeneous large volume changes during the reactions. To improve their performance, a comprehensive understanding of the grain architecture, Li transport pathways, and phase transitions is essential. Here, we show the correlations between these factors using in situ transmission electron microscopy. The results show that Li ions are extracted through tortuous paths connecting the Li-containing a-b planes in the crystals. Moreover, the grain boundary resistance depends not only on the misorientations of the neighboring grains. Even twins with misorientation angles of 70° are not decisive factors in Li movement. We also show the existence of two-phase separation in single crystals between two hexagonal phases during fast charging. These results provide valuable information for determining the optimal grain architecture and for material design, helping enhance high capacity and high stability.

Influences of composition deviation from stoichiometry and heat treatment on crystal phases and Q factor in Ba(Zn 1/3 Nb 2/3 )O 3 (BZN) were studied. The structural order and the crystal phases strongly depended on the slight composition deviation from stoichiometric BZN. The maximum Q factor was obtained at the vicinity of the stoichiometric BZN. In the other regions, non-stoichiometric disordered BZN or ordered BZN with secondary phase were formed, and their Q factors were found to be low. For the stoichiometric BZN, the order-disorder phase transition occurred between 1300 and 1400 • C. The crystal-structural ordering of the stoichiometric BZN was improved by post-annealing at below its transition temperature, conserving the density and the grain size. However, no significant Q factor improvement was found. The Q factor of the stoichiometric BZN strongly depends on the density and grain size not on the crystalstructural order. These results suggest that the ceramic microstructure such as the pore and grain boundary, the secondary phase and lattice defect caused by non-stoichiometry affect the variation of the Q factor in BZN system than the crystal-structural ordering.

Understanding the electrochemical reactions taking place in composite electrodes during cell cycling is essential for improving the performance of all-solid-state batteries. However, comprehensive in situ monitoring of Li distribution, along with measurement of the evolution of degradation, is challenging because of the limitations of the characterization techniques commonly used. This study demonstrates the observation of Li distribution and degradation in composite cathodes consisting of LiNi 0.8 Co 0.15 Al 0.05 O 2 (NCA) and 75Li 2 S•25P 2 S 5 (LPS) during cell operation using operando time-of-flight secondary ion mass spectrometry. The evolution of the nonuniform reaction of NCA particles during charge and discharge cycles was successfully visualized by mapping fragments containing Li. Furthermore, degradation of the NCA/LPS interface was investigated by mapping PO x − and SO x − fragments, which are related to the solid electrolyte interphase. We found that during the charge−discharge cycle and application of a high-voltage stress to the composite electrodes, the PO 2 − and PO 3 − fragments increased monotonically, whereas the SO 3 − fragment exhibited a reversible increase−decrease behavior, implying the existence of a redox-active component at the NCA/LPS interface. The demonstrated technique provides insights into both the optimized structures of composite electrodes and the underlying mechanisms of interfacial degradation at active material/solid electrolyte interfaces.

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Organic field-effect transistors (OFETs) having an active channel of solution-processed 2,7-dioctyl[1]benzothieno [3,2-b][1]benzothiophene (C 8 − BTBT) were investigated by Kelvin-probe force microscopy (KFM). We found step-like potential distributions in a channel region, suggesting that the interlayer resistance between the conjugated BTBT core layers is quite high and each conjugated layer is electrically isolated from one another by insulating alkyl chain layers. We also found a noticeable positive charging in the channel region especially at the step edges after the device operation. The observed charging was explained by long-lived positive charges on the trap sites, and the trap density at the step edge was estimated to be on the order of 10 11 cm −2 . The KFM measurements suggest that the device performance of the staggered C 8 −BTBT OFETs could deteriorate due to the considerably high access resistance, which stems from the high interlayer resistance and/or by the site-specific charge trapping at the contact/semiconductor interface which originates from step edge structures.