Revealing the chemical separated two-phase structure in lithium-manganese-rich cathode

Jiayi Wang; Xincheng Lei; Hao Meng; Pengxiang Ji; Tenglong Lu; Weijun Liang; Xiaozhi Liu; Sheng Meng; Lin Gu; Miao Liu; Xin Wang; Dong Su

doi:10.1093/nsr/nwaf202

Revealing the chemical separated two-phase structure in lithium-manganese-rich cathode

Natl Sci Rev. 2025 May 21;12(7):nwaf202. doi: 10.1093/nsr/nwaf202. eCollection 2025 Jul.

Authors

Jiayi Wang¹, Xincheng Lei^{2

3}, Hao Meng¹, Pengxiang Ji^{2

3}, Tenglong Lu², Weijun Liang⁴, Xiaozhi Liu², Sheng Meng^{2

3

4}, Lin Gu⁵, Miao Liu^{2

4

6}, Xin Wang¹, Dong Su^{2

3}

Affiliations

¹ Institute of Carbon Neutrality, Zhejiang Wanli University, Ningbo 315100, China.
² Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
³ School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China.
⁴ Songshan Lake Materials Laboratory, Dongguan 523808, China.
⁵ Beijing National Center for Electron Microscopy and Laboratory of Advanced Materials, Department of Materials Science and Engineering, Tsinghua University, Beijing 100084, China.
⁶ Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, China.

Abstract

Lithium-manganese-rich (LMR) oxides are regarded as one of the most promising cathode materials for next-generation batteries. However, their poor rate capability and performance degradation during cycling present significant challenges for practical applications. Understanding how to optimize their microscopic structures during synthesis may provide critical insights for enhancing their performance. In this work, we investigated the structural evolution during the solid-state sintering of Li_1.2Ni_0.2Mn_0.6O₂ from Li-/Mn-/Ni-carbonate precursors. Combining X-ray diffraction and transmission electron microscopy (TEM) techniques, we observed the nucleation of a nanoscaled solid-solution phase at 550°C, accompanied by secondary phases of spinel-like, layered and rock salt. At 800°C, a relatively pure solid-solution phase R3̅m is formed. Notably, we uncovered, for the first time, a phase transition from a solid-solution structure to a chemically separated two-phase structure when annealing the sample from 850°C to 900°C. Atomic resolution scanning-TEM (STEM) imaging clearly distinguished the C2/m phase from the R3̅m phase, separated by a coherent grain boundary, as confirmed by using STEM-energy-dispersion spectroscopy mapping. Our calculations indicate that the diffusion of Ni²⁺ induced by high-temperature activation plays a significant role in facilitating the phase separation. The relatively large chemically separated two-phase structure is expected to exhibit different performance characteristics compared with the previously reported nanosized two-phase structures, providing a new foundation for further improving high-energy-density LMR cathodes.

Keywords: Li-ion battery; ion migration; lithium-manganese-rich cathode; phase separation; solid solution; transmission electron microscopy.