A comparative study of polarization during the initial lithiation step in tungsten-oxide negative electrodes for lithium-ion batteries​

In this study, polarization behavior during initial lithiation step was comparatively investigated using a tungsten oxide (WO₃) and its reduced one (WO_3 − x). Ex-situ X-ray diffraction revealed that the overall lithiation process in WO₃ was mostly similar to that of WO_3 − x, which was associated with the typical conversion reaction of transition-metal oxide. In the WO_3 − x anode, however, insertional lithiation was initiated above 2 V vs. Li/Li⁺ and a following conversion reaction was observed, which was different charging behavior from WO₃ electrode. The severe polarization related with the conversion reaction was alleviated owing to the high electrical conductivity in the mixed-valance state of WO_3 − x. Furthermore, the different initial polarization in WO_3 − x anode resulted in the improvement of cycle performance and efficiency.​