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

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.