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Synthesis and Electrochemical and Structural Investigations of Oxidatively Stable Li2MoO3 and xLi2MoO3·(1 – x)LiMO2 Composite Cathodes

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journal contribution
posted on 29.06.2018, 00:00 by Ethan C. Self, Lianfeng Zou, Ming-Jian Zhang, Richard Opfer, Rose E. Ruther, Gabriel M. Veith, Bohang Song, Chongmin Wang, Feng Wang, Ashfia Huq, Jagjit Nanda
The structural evolution of Li2MoO3 during electrochemical delithiation/lithiation is reported. Li2MoO3 undergoes an irreversible crystalline to amorphous transformation which starts during the first delithiation step and gradually proceeds throughout subsequent cycles. This observation is supported by complementary data obtained from X-ray diffraction (XRD), Raman spectroscopy, and transmission electron microscopy (TEM). The amorphization does not prevent reversible Li storage, and the Li2MoO3 cathodes exhibit initial capacities of 147 mAh/g (corresponding to 0.87 Li cycled per formula unit) at an average operating potential ∼2.5 V vs Li/Li+ with reasonably good cycling stability (81% capacity retention after 50 cycles). In-situ mass spectrometry studies reveal the amorphization of Li2MoO3 does not involve the release of oxygen gas even when charged to very positive potentials (i.e., 4.8 V vs Li/Li+). The Li storage properties and excellent oxidative stability of Li2MoO3 make it a promising candidate to improve the performance of traditional LiMO2 compounds in layered–layered composite cathodes with the general formula xLi2MoO3·(1 – x)­LiMO2. Multiple synthesis routes were explored to prepare composites with x = 0.10–0.15, and their structure was characterized using XRD and time-of-flight neutron diffraction. Preliminary characterization of these materials shows that Li2MoO3 improves the cycling stability of an NMC cathode, presumably by mitigating detrimental structural rearrangement at high states of charge.