Fatigue in 0.5Li2MnO3:0.5Li(Ni1/3Co1/3Mn1/3)O2 positive electrodes for lithium ion batteries

• Published in: Journal of power sources Vol. 325; pp. 391 - 403
• Main Authors: Riekehr, Lars, Liu, Jinlong, Schwarz, Björn, Sigel, Florian, Kerkamm, Ingo, Xia, Yongyao, Ehrenberg, Helmut
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.09.2016
• Subjects: Anionic charge compensation; Irreversible oxygen loss; Li-rich composites; Synchrotron XRD; TEM; Anionic charge compensation; TEM; Synchrotron XRD; Li-rich composites; Irreversible oxygen loss
• ISSN: 0378-7753; 1873-2755
• DOI: 10.1016/j.jpowsour.2016.06.014

Two different Li-rich nickel–cobalt–manganese-oxide (Li-rich NCM) active materials with the same nominal composition 0.5Li2MnO3:0.5Li(Ni1/3Co1/3Mn1/3)O2 but different pristine nano structure have been analyzed structurally and electrochemically in different cycling states. For structural characterization, transmission electron microscopy (TEM) and high resolution synchrotron powder diffraction (S-XRD) experiments were conducted. The changes in structure with increasing cycle number are correlated with characteristic features in the corresponding electrochemical dQ/dV-profiles that were obtained by galvanostatically cycling the two different active materials. The presented data demonstrates that structural changes upon cycling, e.g. LiMnO2 and spinel formation, strongly depend on the degree oxygen is involved in the reversible charge compensation for delithiation/lithiation. According to our data, firstly a twin-like environment with nanometer dimensions is formed within the R-3m matrix during the initial cycle, which then gradually transforms into a spinel-like structure with increasing cycle number. As another result, we can show that Li2MnO3 to LiMnO2 transformation is not directly dependent in the irreversible oxygen loss in the first cycle but more importantly on transition metal migration. A model is presented explaining the dependency of LiMnO2 and spinel formation on the ability of Li-rich active materials to include oxygen in the charge compensation process. •TEM nano structure analysis of cycled Li-rich NCM composite structures.•Synchrotron XRD of cycled Li-rich NCM composite structures.•Irreversible oxygen loss and LiMnO2 formation.•Reversible anionic redox activity and peroxide formation.•Nanotwin and spinel formation during initial cycle and subsequent cycling.