High-energy-density batteries have been a long-standing target toward sustainability, but the energy density of state-of-the-art lithium-ion batteries is limited in part by the small capacity of the positive electrode materials. Although employing the additional oxygen-redox reaction of Li-excess transition-metal oxides is an attractive approach to increase the capacity, an atomic-level understanding of the reaction mechanism has not been established so far. Here, using bulk-sensitive resonant inelastic X-ray scattering spectroscopy combined with ab initio computations, we demonstrate the presence of a localized oxygen 2p orbital weakly hybridized with transition metal t_2g orbitals that was theoretically predicted to play a key role in oxygen-redox reactions. After oxygen oxidation, the hole in the oxygen 2p orbital is stabilized by the generation of either a (σ + π) multiorbital bond through strong π back-donation or peroxide O₂²⁻ through oxygen dimerization. The multiorbital bond formation with σ-accepting and π-donating transition metals can thus lead to reversible oxygen-redox reaction.

中文翻译：

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多轨道键的形成可稳定电池电极中的氧-氧化还原反应

高能量密度电池一直是实现可持续性的长期目标，但是现有技术的锂离子电池的能量密度在一定程度上受到正极材料小容量的限制。尽管采用过量的过量Li-过渡金属氧化物进行氧-氧化还原反应是提高容量的诱人方法，但到目前为止，尚未建立对反应机理的原子级理解。在这里，使用体敏共振非弹性X射线散射光谱与从头算相结合，我们证明了与过渡金属t _2g弱杂化的局域氧2p轨道的存在理论上预测的轨道在氧-氧化还原反应中起关键作用。氧氧化后，氧2p轨道中的空穴通过强π背供电产生（σ+π）多轨道键或通过氧二聚作用产生过氧化物O ₂ ^2-来稳定。因此，与具有σ受体和π供体的过渡金属形成的多轨道键可导致可逆的氧-氧化还原反应。