Journal Article Delithiation/lithiation behavior of LiNi<inf>0.5</inf>Mn<inf>1.5</inf>O<inf>4</inf> studied by in situ and ex situ <sup>6,7</sup>Li NMR spectroscopy

Shimoda, Keiji  ,  Murakami, Miwa  ,  Komatsu, Hideyuki  ,  Arai, Hajime  ,  Uchimoto, Yoshiharu  ,  Ogumi, Zempachi

119 ( 24 )  , pp.13472 - 13480 , 2015-05-27 , American Chemical Society
Delithiation and lithiation behaviors of ordered spinel LiNi<inf>0.5</inf>Mn<inf>1.5</inf>O<inf>4</inf> and disordered spinel LiNi<inf>0.4</inf>Mn<inf>1.6</inf>O<inf>4</inf> were investigated by using in situ (in operando) <sup>7</sup>Li NMR and ex situ <sup>6</sup>Li MAS NMR spectroscopy. The in situ <sup>7</sup>Li monitoring of the ordered spinel revealed a clear appearance and subsequent disappearance of a new signal from the well-defined phase Li<inf>0.5</inf>Ni<inf>0.5</inf>Mn<inf>1.5</inf>O<inf>4</inf>, suggesting the two-phase reaction processes among Li<inf>1.0</inf>Ni<inf>0.5</inf>Mn<inf>1.5</inf>O<inf>4</inf>, Li<inf>0.5</inf>Ni<inf>0.5</inf>Mn<inf>1.5</inf>O<inf>4</inf>, and Li<inf>0.0</inf>Ni<inf>0.5</inf>Mn<inf>1.5</inf>O<inf>4</inf>. Also, for the disordered spinel, Li<inf>0.5</inf>Ni<inf>0.4</inf>Mn<inf>1.6</inf>O<inf>4</inf> was identified with a broad distribution in Li environment. High-resolution <sup>6</sup>Li MAS NMR spectra were also acquired for the delithiated and lithiated samples to understand the detailed local structure around Li ions. We suggested that the nominal Li-free phase Li<inf>0.0</inf>Ni<inf>0.5</inf>Mn<inf>1.5</inf>O<inf>4</inf> can accommodate a small amount of Li ions in its structure. The tetragonal phases Li<inf>2.0</inf>Ni<inf>0.5</inf>Mn<inf>1.5</inf>O<inf>4</inf> and Li<inf>2.0</inf>Ni<inf>0.4</inf>Mn<inf>1.6</inf>O<inf>4</inf>, which occurred when the cell was discharged down to 2.0 V, were very different in the Li environment from each other. It is found that <sup>6, 7</sup>Li NMR is highly sensitive not only to the Ni/Mn ordering in LiNi<inf>0.5</inf>Mn<inf>1.5</inf>O<inf>4</inf> but also to the valence changes of Ni and Mn on charge-discharge process.

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