Oxygen Vacancies in Low‐Positive Thermal Expansion Al ₂ W ₃ O ₁₂ ‐Based Electrodes for Lithium‐Ion Batteries

A few members of the flexible open‐framework A 2 M 3 O 12 ceramics, sometimes deliberately containing oxygen vacancies (OVs), have been investigated for photocatalytic applications and for uses requiring high thermal shock resistance, owing to their negative or near‐zero thermal expansion. In some other relevant crystal structures, OVs have been reported to enhance charge storage capacity, rate performance, and Li + diffusion in lithium‐ion batteries (LIBs). In this study, the electrochemical properties of Al 2 W 3 O 12 ‐based electrodes with and without OVs have been compared when used as anode materials for LIBs. Extrinsic OVs were introduced into Al 2 W 3 O 12 , which served as the active material by the treatment in a hydrogen atmosphere, and their presence was confirmed by electron paramagnetic resonance. Despite these modifications, the OV‐containing electrode delivered a discharge capacity of 110 mAh g −1 at the 100 th cycle, which was lower than that of the electrode without OVs (133 mAh g −1 at the same cycle). Contrary to the expectations based on previous studies of other relevant LIB electrode materials, Al 2 W 3 O 12 with OVs exhibited inferior electrochemical performance. Structural and morphological analyses revealed rapid amorphization of the extremely flexible open‐framework structure in OV‐rich Al 2 W 3 O 12 during the initial lithiation cycles, which likely accounts for the absence of a beneficial effect of OVs on the specific capacity.