Mixed alkali-ion transport and storage in atomic-disordered honeycomb layered NaKNi2TeO6

T Masese and Y Miyazaki and J Rizell and GM Kanyolo and CY Chen and H Ubukata and K Kubota and K Sau and T Ikeshoji and ZD Huang and K Yoshii and T Takahashi and M Ito and H Senoh and J Hwang and A Alshehabi and K Matsumoto and T Matsunaga and K Fujii and M Yashima and M Shikano and C Tassel and H Kageyama and Y Uchimoto and R Hagiwara and T Saito, NATURE COMMUNICATIONS, 12, 4660 (2021).

DOI: 10.1038/s41467-021-24694-5

Honeycomb layered oxides constitute an emerging class of materials that show interesting physicochemical and electrochemical properties. However, the development of these materials is still limited. Here, we report the combined use of alkali atoms (Na and K) to produce a mixed- alkali honeycomb layered oxide material, namely, NaKNi2TeO6. Via transmission electron microscopy measurements, we reveal the local atomic structural disorders characterised by aperiodic stacking and incoherency in the alternating arrangement of Na and K atoms. We also investigate the possibility of mixed electrochemical transport and storage of Na+ and K+ ions in NaKNi2TeO6. In particular, we report an average discharge cell voltage of about 4V and a specific capacity of around 80 mAh g(-1) at low specific currents (i.e., <10mAg(-1)) when a NaKNi2TeO6-based positive electrode is combined with a room-temperature NaK liquid alloy negative electrode using an ionic liquid-based electrolyte solution. These results represent a step towards the use of tailored cathode active materials for "dendrite-free" electrochemical energy storage systems exploiting room-temperature liquid alkali metal alloy materials. Honeycomb layered oxides are an emerging class of materials with peculiar physicochemical properties. Here, the authors report the synthesis and electrochemical energy storage characterisations of a mixed-alkali honeycomb layered oxide material capable of storing Na and K ions simultaneously.

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