Evidence for bond-disproportionation in LiNiO2 from x-ray absorption spectroscopy
Abstract
The electronic structure of LiNiO2, a promising Li-ion battery cathode material, has remained a challenge to understand due to its highly covalent yet correlated nature. Here we elucidate the electronic structure in LiNiO2 and the related compound NaNiO2 using x-ray absorption spectra (XAS) and quantum many-body calculations. Notably, we use inverse partial fluorescence yield to correctly measure the Ni L-edge XAS, which is inaccurate using conventional methods. We show that the XAS are indicative of a strong Jahn-Teller effect in NaNiO2 and a bond disproportionated state in LiNiO2, supporting a theory of a high-entropy, glassy disproportionated state that stabilizes charging cycles in LiNiO2.
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