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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 Li₃NbO₄–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., LiNiO₂, charge compensation is achieved mainly by Ni oxidation, with a lower contribution from oxygen. In contrast, for Li₃NbO₄–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 LiNi₂/₃Nb₁/₃O₂ 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 high-energy lithium-ion batteries., 酸素が反応に寄与するニッケル系電池材料 高エネルギー密度リチウム電池実現に期待 --新規不規則岩塩型ニッケル系材料開発と次世代蓄電池への応用--. 京都大学プレスリリース. 2022-05-24.

We investigated the influence of the deposition rate on structural and magnetic properties of inverse-spinel ferrimagnet NiCo₂O₄ epitaxial films grown by pulsed laser deposition. While films' lattice constants are insensitive to the deposition rate, saturation magnetization, and perpendicular magnetic anisotropy for the film grown with a high deposition rate are reduced. These results imply that growing NiCo₂O₄ films with a high deposition rate leads to occupations of the tetrahedral site by Ni, although Ni ideally occupies only the octahedral site. Controlling the deposition rate and modulating the cation distribution is the key for tuning the magnetic properties in NiCo₂O₄ films.

We carried out x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) spectroscopy and investigated cation valence states and spin and orbital magnetic moments in the inverse-spinel ferrimagnet Ni$_{1-x}$Co$_{2+y}$O$_{4-z}$ (NCO) epitaxial films with the perpendicular magnetic anisotropy. We show that the oxygen pressure P$_{O2}$ during the film growth by pulsed laser deposition influences not only the cation stoichiometry (site-occupation) but also the cation valence state. Our XAS results show that the Ni in the O$_{h}$-site is in the intermediate valence state between +2 and +3, Ni$^{(2+\delta)+}$ (0

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Heterostructured thin films differing either in their structure, composition, or in both have shown novel magnetic, superconducting, ferroelectric, or electromechanical responses. In the case of ferroelectrics, multilayers or superlattices have displayed enhanced polarization, high dielectric permittivity and in some instances, entirely new structural phases. These observations have been accounted for on the basis of electric-field-induced coupling, epitaxial strain, and specific polar interactions between the interfacial layers. As most ferroelectrics have a strong non-negligible ferroelastic self-strain associated with their phase transformation, an aspect that should be equally fascinating is that of the elastic interactions between such multilayers. The interactions lead to the formation of ferroelastic domains, arranged in the form of periodalternating lamellae in order to relax the excess elastic energy. When these lamellae are of the same phase but of different crystallographic orientations, they are generally referred to as ‘‘twins’’. The ferroelastic-domain-wall (extrinsic) contribution to the dielectric, piezoelectric, and elastic properties of ferroelectrics is indeed quite significant in the case of bulk ceramics and single-crystals, and this can be several times larger than the intrinsic lattice piezoresponse. In the case of ferroelectric thin films, the issue of movement of ferroelastic domains is not without debate. Earlier experimental studies proposed that the ferroelastic ‘‘herringbone’’ pattern in thin films demonstrated very limited (if any) ability to move under external stress or electric field. This has been contradicted in more recent experiments on polycrystalline films. Nevertheless, gross quantitative enhancement has been reported only under special conditions, such as films patterned into