Observation of anisotropic microstructural changes during cycling in LiNi0.5Co0.2Mn0.3O2 cathode material

• Published in: Journal of power sources 2015-02, Vol.275, p.99-105
• Main Authors: Kuriyama, Hiromichi, Saruwatari, Hidesato, Satake, Hideki, Shima, Amika, Uesugi, Fumihiko, Tanaka, Hiroki, Ushirogouchi, Tooru
• Format: Article
• Language: English
• Subjects: Cathode; Electron energy-loss spectroscopy; Li ion secondary battery; Microstructural changes; Transmission electron microscopy
• ISSN: 0378-7753; 1873-2755
• DOI: 10.1016/j.jpowsour.2014.10.197

Microstructural changes in LiNi0.5Co0.2Mn0.3O2 cathode material after charge/discharge cycles were investigated by transmission electron microscopy and electron energy loss-spectroscopy. The microstructure on the surface of the cycled primary particles of LiNi0.5Co0.2Mn0.3O2 changed from an ordered rock-salt structure into a metal monoxide-type rock-salt structure, and this was accompanied by reduction of the oxidation states of the transition metal ions, especially the Mn4+ ions. It should be noted that the (0001) surface of the primary particles remained intact after the cycling test. These results indicate that the degradation mechanism of LiNi0.5Co0.2Mn0.3O2 is different from that of other LiNiO2-based cathode materials previously reported. Tailoring the transition metal ion content ratios is expected to give LiNi1−x−yCoxMnyO2 various levels of surface stability. •The microstructural changes of LiNi0.5Mn0.2Co0.3O2 during cycling are coupled with the reduction of Mn4+ and Co3+ions.•The anisotropic structural transformation was found in (hki0) surface regions of LiNi0.5Mn0.2Co0.3O2.•The TEM and EELS analysis demonstrated that LiNi0.5Co0.2Mn0.3O2 is a promising cathode material with long cycle life.