Yuji Mahara

Disordered rock‐salt (DRS) type active materials are highly significant because of their large reversible capacities, which are due to their unique Li ⁺ diffusion pathway and the redox capabilities of cationic transition metals (TMs) and anionic O ions. Loosely crystalline DRS materials have weak covalent bonds between TMs and O, increasing the O redox contribution and thereby enhancing their capacities. In this study, Mn‐based positive electrode materials with DRS structures are activated and stabilized by mechanochemical doping of nonmetallic elements P and B into interstitial sites. Synthesized Li _0.90 Mn _0.84 P _0.04 O ₂ (LMPO5) exhibits an initial discharge capacity of 346 mAh g ⁻¹ (1050 Wh kg ⁻¹ ) during charging/discharging. Li _0.91 Mn _0.83 B _0.10 O ₂ (LMBO5) has a moderately expanded lattice size, which facilitates high‐capacity retention during cycling (≈284 mAh g ⁻¹ at the 30th cycle). The structural properties of the synthesized active materials are extensively characterized. By introducing nonmetallic elements into the interstitial sites of Mn‐based materials, inexpensive, high‐capacity, and long‐cycling/calendar‐life Co/Ni‐free monometallic positive electrode materials may be further developed.

Si anodes have attracted considerable attention for their potential application in next-generation lithium-ion batteries because of their high specific capacity (Li₁₅Si₄, 3579 mAh g^-1) and elemental abundance. However, Si anodes have not yet been practically applied in lithium-ion batteries because the volume change associated with lithiation and delithiation degrades their capacity during cycling. Instead of considering the active material, we focused on the structural design and developed a scalable process for producing Si anodes with excellent cycle characteristics while precisely controlling the morphology. Al-Si alloy powders were prepared by gas atomization, and porous Si with a skeletal structure was prepared by leaching Al using HCl. Porous Si (p-Si₁₂, p-Si₁₉) prepared from Al₈₈Si₁₂ and Al₈₁Si₁₉ comprised resinous eutectic Si, and porous Si (p-Si₂₅) prepared from Al₇₅Si₂₅ comprised lumpy primary Si and resinous eutectic Si. The porosity of the Si anodes varied from 63% to 76%, depending on the Si composition. The p-Si₁₉ anode displayed the finest pore distribution (20-200 nm), excellent rate characteristics, a reversible discharge capacity of 1607 mAh g^-1 after 200 cycles at a rate of 0.1 C with a Coulombic efficiency of over 97%, and high stability. The performances of the p-Si₂₅ and p-Si₁₉ electrodes began to decrease after 250 and 850 cycles, respectively, with a constant-charge capacity of 1000 mAh g^-1 and at a rate of 0.2 C. In contrast, the p-Si₁₂ anode maintained its discharge capacity at 1000 mAh g^-1 for up to 1000 cycles without degradation. Therefore, the developed manufacturing process is expected to produce porous Si as an active material in lithium-ion batteries for high capacity and long life at an industrial scale.

In pursuit of high-capacity Mn-based oxides as positive electrode materials for lithium-ion batteries, the changes in the charge-discharge curve due to the spinel transition still stand in the way of the cycling stability. We found in this study that Li_1.12Mn_0.74O_1.60F_0.40 (LMOF05) positive electrodes with a loose-crystalline rock salt structure (LCRS), in which F is placed near Mn, show a stable and high capacity (300 mA h g^-1, 952 W h kg^-1) with little change in the charge-discharge curve. We demonstrated by F K-edge soft X-ray absorption spectroscopy and X-ray diffraction (XRD) that a part of F in the LCRS positive electrode forms F-Mn bonds. Operando XRD/X-ray absorption fine structure measurements revealed the lattice size and Mn surrounding environment during charge/discharge of F-containing LCRS positive electrodes (LMOF05), LCRS-LiMnO₂ (LMO), and a spinel-like Li_1.1Al_0.1Mn_1.8O₄ positive electrode (SPINEL). Micro- and macroscopic structural changes indicate how the introduction of F suppresses the local spinel transition in Mn-based positive electrodes. These findings should be an effective tool for applying Co-free positive electrode materials for lithium-ion batteries.

The front cover artwork for Issue 16/2018 is a collaboration between Nagoya University, ESICB Kyoto University, and JASRI (all in Japan). The image shows energy dispersive X‐rays illuminating a PdO nanoparticle reduced by methane. See the Communication itself at https://doi.org/10.1002/cctc.201800573.

The highly active species of Pd/Al₂O₃ catalysts for methane combustion was revealed by in situ time‐resolved dispersive X‐ray absorption fine structure (DXAFS) spectroscopy. By using CH₄ as a reduction agent, PdO in Pd/Al₂O₃ is reduced in a 2‐step model involving Pd⁰ nucleation and growth of Pd⁰ domain in a PdO particle. Kinetic analysis of the 2‐step model reduction of PdO nanoparticles leads to a suggestion that partial formation of Pd⁰ in a PdO particle accelerates methane combustion.

We report herein the first general catalytic system for the direct synthesis of N‐substituted γ‐ and δ‐lactams by reductive amination/cyclization of keto acids (including levulinic acid) with nitriles and H₂ under mild conditions (7 bar H₂, 110 °C, solvent free). The most effective catalyst, Pt and MoO_x co‐loaded TiO₂ (Pt‐MoO_x/TiO₂), shows a wide substrate scope, high turnover number (TON), and good reusability.

The particle size effect of Pd nanoparticles supported on alumina with various crystalline phases on methane combustion was investigated. Pd/θ, α‐Al₂O₃ with weak metal‐support interaction showed a volcano‐shaped dependence of the catalytic activity on the size of Pd particles, and the catalytic activity of the strongly interacted Pd/γ‐Al₂O₃ increased with the particle size. Based on a structural analysis of Pd nanoparticles using CO adsorption IR spectroscopy and spherical aberration‐corrected scanning/transmission electron microscopy, the dependence of catalytic activity on Pd particle size and the alumina crystalline phase was due to the fraction of step sites on Pd particle surface. The difference in fraction of the step site is derived from the particle shape, which varies not only with Pd particle size but also with the strength of metal–support interaction. Therefore, this interaction perturbs the particle size effect of Pd/Al₂O₃ for methane combustion.