Stable structure and pair distribution function analysis of 0.4Li2MnO3–0.6Li(Mn1/3Ni1/3Co1/3)O2 as cathode materials lithium ion secondary batteries during charge-discharge process using first-principle calculation and quantum beam

Abstract

In this study, first-principles calculations were conducted to identify a local structure model that replicates both the pristine state and the state of the electrode after five charge and discharge cycles at 25 and 60 °C. The material studied was 0.4Li₂MnO₃–0.6Li(Mn_1/3Ni_1/3Co_1/3)O₂, which is used as a Li-ion battery positive electrode. The stable structures obtained were compared with the pair distribution function G(r) derived from synchrotron X-ray total scattering measurements. Our calculated G(r) models are in good agreement with the observed G(r) values from these measurements. In the model that reproduces the stable structure during the fifth cycle charging at 25 and 60 °C, Li atoms in the transition metal (TM) layer, surrounded by Mn and not adjacent to Co, move toward the Li layer due to weak LiO bonding, partially creating vacancies. The coordination number of Mn near these vacancies in the TM layer changed during charging. During discharging, the model in which Li ions were locally coordinated away from the vacancies in the TM layer was stable. In the 25 °C-charging model, compared to the pristine model, less changes were observed in MnO bonds within the MnO₆ octahedra, which are most abundant in the TM layer. Furthermore, less distortion in the Mn-O₆ octahedra was observed, resulting in minimal changes to the host structure during charging and discharging. Therefore, compared to 60 °C, the cycle characteristics were evidently improved when charging and discharging at 25 °C.