Electronic state analysis of Li2RuO3 positive electrode for lithium ion secondary battery

An investigation was made on the electronic structure of 4d transition metal layered oxide material of Li2RuO3 using X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS). The intensity of O K pre-edge peak increased for Li ion extracted samples, suggesting increased ligand holes. The Ru 3d XPS spectrum suggested the variation of local structure around Ru ions by extraction of Li ions. We conclude that the delithiation from Li2RuO3 is charge-compensated by O anions, and that the creation of the ligand holes reorganizes electronic structures composed of highly hybridized Ru 4d and O 2p orbitals

Revisiting Cationic Doping Impacts in Ni-Rich Cathodes

As a promising cathode material for high-energy-density Li-ion batteries, Ni-rich layered oxide cathode active materials deliver high specific capacity. However, their electrochemical performance degrades rapidly upon charge/discharge cycles probably due to electrochemical/thermochemical instabilities. While cationic doping in the transition-metal site has been regarded as an effective strategy to enhance the electrochemical performance, the true impact of cation doping is not well understood. To quantitatively assess the impact of cationic doping, in this work, the electrochemical performance and lattice oxygen stability of LiNi0.82Co0.18O2, isovalent Al3+-doped LiNi0.82Co0.15Al0.03O2, and high-valent Ti4+-doped LiNi0.82Co0.15Ti0.03O2 were investigated. Despite significant improvements in electrochemical performance by Al3+ and Ti4+ doping, it was revealed that these cation dopings had no discernible effect on the lattice oxygen stability. Such information suggests that the electrochemical enhancement by Al3+/Ti4+ doping is not attributed to the stabilization of lattice oxygen. This work highlights the importance of independent and quantitative experimental evaluations on kinetic electrochemical properties and thermodynamic stability of lattice oxygen to establish rational guidelines for doping strategy toward high-energy-density and reliable cathode-active materials

Unexpectedly Large Contribution of Oxygen to Charge Compensation Triggered by Structural Disordering: Detailed Experimental and Theoretical Study on a Li₃NbO₄–NiO Binary System

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.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