Lithium- and Manganese-Rich layered oxides (LMRs) are one of the promising candidates of positive electrode materials for the advanced LIB due to their high reversible capacities. The chemical formula is often described as xLi₂MnO₃•(1–x)LiMO₂ that consists of Li₂MnO₃- and LiMO₂-rich nano-domains. The LMR-based electrodes show a voltage plateau at ca. 4.5 V in the initial charge process, which leads to an irreversible capacity. This plateau is understood to appear for the activation of Li₂MnO₃.[1,2] This activation process is not thoroughly understood yet and the elucidation of this reaction would lead to the practical use of this material. Some groups have reported that the charge compensation on the delithiation from Li₂MnO₃ is associated with the oxidation of oxide ion including O₂release from the structure.[3,4] The present work focuses on clarifying the structural changes taking place inside LMR bulk at the initial delithiation (charge) using SR-X ray diffraction, STEM, and solid-state NMR.[5]

SR-XRD profiles showed that all the diffraction intensities were gradually decreased and broadened during the initial charge up to 4.8 V, which indicated that the initial delithiation caused the change to highly disordered material. The high-resolution ⁶Li MAS NMR spectra showed that Li⁺ was monotonously extracted from both the Li and TM layers. EELS mapping by STEM suggested that the Li⁺extraction from the sample of 50% SOC occurred in a biphasic manner inside a single particle. The lattice structures of the active material after charge-discharge cycle was also examined on samples at the 20^th discharged and 21^stcharged states.

This work was supported by the Research and Development Initiative for Scientific Innovation of New Generation Batteries (RISING) and the Research and Development Initiative for Scientific Innovation of New Generation Batteries II (RISING II) projects from the New Energy and Industrial Technology Development Organization (NEDO), Japan.

[1] Thackeray et al., J. Mater. Chem., 2007, 17, 3112.

[2] Yu & Zhou, J. Phys. Chem. Lett., 2013, 4, 1268.

[3] Yu et al., J. Electrochem. Soc., 2009, 156, A417.

[4] Oishi et al., J. Mater. Chem. A, 2016, 4, 9293.

[5] Shimoda et al., J. Mater. Chem. A, 2017, 5, 6695.