Operating-temperature Dependence of the Average and Electronic Structures of 0.4Li₂MnO₃–0.6Li(Mn_1/3Ni_1/3Co_1/3)O₂

We report the temperature dependence of the average structures of 0.4Li₂MnO₃–0.6LiMn_1/3Ni_1/3Co_1/3O₂ during the 5th discharge process, where the structures are characterized via neutron and synchrotron X-ray diffraction analyses. In the cycle tests at room temperature (25 °C) and high temperature (60 °C), the 0.4Li₂MnO₃–0.6LiMn_1/3Ni_1/3Co_1/3O₂ electrode delivered a high capacity of over 280 mAh/g in the 5th discharge process within the voltage range from 2.5 V to 4.8 V vs. Li/Li⁺ at the high temperature, which was greater than about 250 mAh/g at room temperature. However, the cycle characteristics during high-temperature operation were inferior to those during room temperature operation. To clarify the cause of the change in the electrode characteristics, electrodes were prepared in the pristine state, the 5th charge state, and the 5th discharge state and their average structural change was evaluated by Rietveld analysis. The Rietveld analysis showed that the distortion of parameter for the M–O₆ (M = transition metal) octahedra was larger for the samples cycled at 60 °C. A valence evaluation was also performed on the basis of the peak shifts in the Mn, Ni, and Co X-ray absorption near edge structure spectra. The results suggested that the temperature change for Mn greatly affected the distortion, especially at 60 °C. The aforementioned results revealed that changing the operating temperature led to a large change in the structure of 0.4Li₂MnO₃–0.6LiMn_1/3Ni_1/3Co_1/3O₂, mainly related to Mn, which might affect battery performance.