No abstract

Nanostructured LiMnO 2 integrated with Li 3 PO 4 was successfully synthesized by the mechanical milling route and examined as a new series of positive electrode materials for rechargeable lithium batteries. Although uniform mixing at the atomic scale between LiMnO 2 and Li 3 PO 4 was not anticipated because of the noncompatibility of crystal structures for both phases, our study reveals that phosphorus ions with excess lithium ions dissolve into nanosize crystalline LiMnO 2 as first evidenced by elemental mapping using STEM-EELS combined with total X-ray scattering, solid-state NMR spectroscopy, and a theoretical ab initio study. The integrated phase features a low-crystallinity metastable phase with a unique nanostructure; the phosphorus ion located at the tetrahedral site shares faces with adjacent lithium ions at slightly distorted octahedral sites. This phase delivers a large reversible capacity of ∼320 mA h g –1 as a high-energy positive electrode material in Li cells. The large reversible capacity originated from the contribution from the anionic redox of oxygen coupled with the cationic redox of Mn ions, as evidenced by operando soft XAS spectroscopy, and the superior reversibility of the anionic redox and the suppression of oxygen loss were also found by online electrochemical mass spectroscopy. The improved reversibility of the anionic redox originates from the presence of phosphorus ions associated with the suppression of oxygen dimerization, as supported by a theoretical study. From these results, the mechanistic foundations of nanostructured high-capacity positive electrode materials were established, and further chemical and physical optimization may lead to the development of next-generation electrochemical devices.

Dependence on lithium-ion batteries for automobile applications is rapidly increasing. The emerging use of anionic redox can boost the energy density of batteries, but the fundamental origin of anionic redox is still under debate. Moreover, to realize anionic redox, many reported electrode materials rely on manganese ions through π-type interactions with oxygen. Here, through a systematic experimental and theoretical study on a binary system of Li 3 NbO 4 −NiO, we demonstrate for the first time the unexpectedly large contribution of oxygen to charge compensation for electrochemical oxidation in Ni-based materials. In general, for Ni-based materials, e.g., LiNiO 2 , charge compensation is achieved mainly by Ni oxidation, with a lower contribution from oxygen. In contrast, for Li 3 NbO 4 −NiO, oxygen-based charge compensation is triggered by structural disordering and σ-type interactions with nickel ions, which are associated with a unique environment for oxygen, i.e., a linear Ni−O−Ni configuration in the disordered system. Reversible anionic redox with a small hysteretic behavior was achieved for LiNi 2/3 Nb 1/3 O 2 with a cation-disordered Li/Ni arrangement. Further Li enrichment in the structure destabilizes anionic redox and leads to irreversible oxygen loss due to the disappearance of the linear Ni−O−Ni configuration and the formation of unstable Ni ions with high oxidation states. On the basis of these results, we discuss the possibility of using σ-type interactions for anionic redox to design advanced electrode materials for highenergy lithium-ion batteries.

Li-excess electrode materials potentially boost the energy density of Li-ion batteries, but the origin of the instability of anionic redox in cation-disordered rocksalt material is still under debate. In this study, a binary system of Li 3 NbO 4 −CoO is targeted as electrode materials for lithium storage applications. In this binary system, stoichiometric LiCo 2/3 Nb 1/3 O 2 crystallizes into a rocksalt-type structure with partial ordering of Nb ions. Upon increase of the Li 3 NbO 4 fraction, cation ordering is lost, forming a cation-disordered rocksalt structure in Li-excess phases. Although Li-excess Li 4/3 Co 2/9 Nb 4/9 O 2 delivers a large reversible capacity as electrode materials, inferior cyclability and large voltage hysteresis for charge/discharge curves are noted. Irreversible structural changes in electrochemical cycles are also evidenced from results of in situ XRD measurements, suggesting that anionic redox is destabilized for Li 4/3 Co 2/9 Nb 4/9 O 2 . X-ray absorption spectroscopy reveals that partial stabilization of ligand holes as observed in SrCoO 3 is achieved for these oxides. Ligand holes are more effectively stabilized for Li 7/6 Co 4/9 Nb 7/18 O 2 with less Li-excess and Co-rich composition. Through systematic study of the binary system of Li 3 NbO 4 −CoO with different chemical compositions, factors affecting reversibility and irreversibility of anionic redox are further discussed.

Didymellaceae is a family of fungal species belonging to the order Pleosporales of coelomycetous fungi. 1 Human infections by coelomycetous fungi are rare and poorly characterized. 1 A 35-year-old Japanese woman was referred from the Department of Otorhinolaryngology of our hospital due to erythematous plaques on her nose that had developed within the past month. She had a history of acute lymphoblastic leukemia