Valence evaluation of LiMnO2 and related battery materials by x-ray absorption spectroscopy

We present an x-ray absorption study of the oxidation states of transition-metal-ions of LiMnO2 and its related materials, widely used as cathodes in Li-ion batteries. The comparison between the obtained spectrum and the configuration-interaction cluster-model calculations showed that the Mn3+ in LiMnO2 is a mixture of the high-spin and low-spin states. We found that Li deficiencies occur in the case of Cr substitution, whereas there are no Li deficiencies in the case of Ni substitution. We conclude that the substitution of charge-transfer-type Ni or Cu is effective for LiMnO2 battery materials.