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Solvation structures formed by ions and solvent molecules at solid/electrolyte interfaces affect the energy storage performance of electrochemical devices, such as lithium-ion batteries. In this study, the molecular-scale solvation structures of an electrolyte, a solution of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in propylene carbonate (PC) at the electrolyte–mica interface, were measured using frequency-modulation atomic force microscopy (FM-AFM). The spacing of the characteristic force oscillation in the force versus distance curves increased with increasing ion concentration, suggesting an increase in the effective size of molecules at the interface. Molecular dynamics simulations showed that the effective size of molecular assemblies, namely, solvated ions formed at the interface, increased with increasing ion concentrations, which was consistent with the experimental results. Knowledge of molecular-scale structures of solid/electrolyte interfaces obtained by a combination of FM-AFM and molecular dynamics simulations is important in the design of electrolytes for future energy devices and in improving their properties., リチウムイオンが溶媒や負イオンに包まれている様子を可視化！ --リチウムイオン電池用電解質の固液界面における溶媒和構造の可視化--. 京都大学プレスリリース. 2022-12-22.

A fundamental understanding of lithiation dynamics in composite electrodes is essential for the development of all-solid-state batteries with high capacity and rate capability. However, a comprehensive methodology to monitor the time evolution of lithiation in a composite electrode has not been fully established because of the limitations of the characterization techniques currently employed. In this study, we demonstrate the visualization of the transient distribution of Li in composite graphite anodes during cell operation using operando time-of-flight secondary ion mass spectrometry. Selective detection of Li in the graphite electrode was successfully achieved by mapping the Li- fragment rather than the conventional mapping of positive Li-containing fragments. The results revealed the formation of a Li concentration gradient during charging, indicating that the reaction of the composite electrode is limited by the diffusion of Li ions inside the graphite. The demonstrated technique is expected to facilitate the investigation of the underlying lithiation mechanisms of composite electrodes in operating cells.

Organic-inorganic hybrid materials (OIHMs), such as methylammonium lead triiodide (MAPbI3), have a wide composition space because of the various potential combinations of organic molecules and inorganic cages. However, for unknown OHIMs, it is difficult to predict what kind of crystal structure will be stable without any experimental data. In this work, we report an efficient scheme for predicting crystal structures and phase diagrams of MA-Pb-I systems from first-principles calculations and genetic algorithms. In our scheme, OIHMs are divided into organic molecules and inorganic clusters. A pseudobinary phase diagram of MAI-PbI2 was obtained by predicting structures at each composition. These results indicated that only MAPbI3 and MA2PbI4 are stable phases, consistent with the experiments. In addition, the electronic and optical properties of the predicted structures were calculated and the solar cell performance was evaluated. Thus, our method allowed us to search for unknown OIHMs without any experimental data.

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 LiNi0.8Co0.15Al0.05O2 (NCA) and 75Li2S·25P2S5 (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 POx- and SOx- 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 PO2- and PO3- fragments increased monotonically, whereas the SO3- 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.

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.

A fundamental understanding of lithiation dynamics in composite electrodes is essential for the development of all-solid-state batteries with high capacity and rate capability. However, a comprehensive methodology to monitor the time evolution of lithiation in a composite electrode has not been fully established because of the limitations of the characterization techniques currently employed. In this study, we demonstrate the visualization of the transient distribution of Li in composite graphite anodes during cell operation using

When two different materials come into contact, mobile carriers redistribute at the interface according to their potential difference. Such a charge redistribution is also expected at the interface between electrodes and solid electrolytes. The redistributed ions significantly affect the ion conduction through the interface. Thus, it is essential to determine the actual distribution of the ionic carriers and their potential to improve ion conduction. We succeeded in visualizing the ionic and potential profiles in the charge redistribution layer, or space-charge layer (SCL), formed at the interface between a Cu electrode and Li-conductive solid electrolyte using phase-shifting electron holography and spatially resolved electron energy-loss spectroscopy. These electron microscopy techniques clearly showed the Li-ionic SCL, which dropped by 1.3 V within a distance of 10 nm from the interface. These techniques could contribute to the development of next-generation electrochemical devices.

Organic-inorganic hybrid materials (OIHMs), such as methylammonium lead triiodide (MAPbI

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

Total scattering measurements enable understanding of the structural disorder in crystalline materials by Fourier transformation of the total structure factor, S(Q), where Q is the magnitude of the scattering vector. In this work, the direct calculation of total scattering from a crystalline structural model is proposed. To calculate the total scattering intensity, a suitable Q-broadening function for the diffraction profile is needed because the intensity and the width depend on the optical parameters of the diffraction apparatus, such as the X-ray energy resolution and divergence, and the intrinsic parameters. X-ray total scattering measurements for CeO2 powder were performed at beamline BL04B2 of the SPring-8 synchrotron radiation facility in Japan for comparison with the calculated S(Q) under various optical conditions. The evaluated Q-broadening function was comparable to the full width at half-maximum of the Bragg peaks in the experimental total scattering pattern. The proposed calculation method correctly accounts for parameters with Q dependence such as the atomic form factor and resolution function, enables estimation of the total scattering factor, and facilitates determination of the reduced pair distribution function for both crystalline and amorphous materials.

All-solid-state lithium-ion batteries (LIBs) are one of the promising candidates to overcome some issues of conventional LIBs with liquid electrolytes. However, high interfacial resistance of Li-ion transfer at the electrode/solid electrolyte limits their performance. Thus, it is important to clarify interfacial phenomena in a nanometer scale. Here, we present a new method to dynamically observe the Li-ion distribution and Co-ion electronic states in a LiCoO2 cathode of the all-solid-state LIB during charge and discharge reactions using operando scanning transmission electron microscopy (STEM) and electron energy-loss spectroscopy (EELS). By applying a hyperspectral image analysis of non-negative matrix factorization (NMF) to the STEM-EELS, we succeeded in clearly observing the quantitative Li-ion distribution in the operando condition. We found from the operando observation with NMF that the Li ions did not uniformly extract/insert during the charge/discharge reactions, and the activity of the electroche...