Rechargeable potassium-ion batteries are appealing candidates for next-generation energy storage devices not only owing to their projected low-cost but also to the high voltage that can be attained.[1-3] Honeycomb layered oxide cathode materials show high voltage and facilitate reversible potassium-ion extraction and insertion (K+ (de)intercalation) at decent capacities. This makes them promising cathode candidates that can be matched to suitable anode materials to design a high-voltage (high-energy density) battery.[4-6] It is crucial to investigate the reaction mechanism of electrode materials in order to understand the structural changes accompanying reversible (de)intercalation of the large K+ that lead to unique staircase-like voltage profiles. Honeycomb layered oxides such as K2Ni2TeO6 facilitate reversible K+ (de)intercalation at high voltages with staircase-like profiles. In this presentation, we will highlight the reaction mechanism of K2Ni2TeO6, based mainly on X-ray diffraction studies.AcknowledgementThis work was conducted under the support of Japan Prize Foundation, National Institute of Advanced Industrial Science and Technology (AIST) and the Japan Society for the Promotion of Science (JSPS KAKENHI Grant Numbers 19K15685).References T. Hosaka, K. Kubota, A. S. Hameed and S. Komaba, Chem. Rev. (2020). https://doi.org/10.1021/acs.chemrev.9b00463 T. Masese, K. Yoshii, Y. Yamaguchi, T. Okumura, Z.-D. Huang, M. Kato, K. Kubota, J. Furutani, Y. Orikasa, H. Senoh, H. Sakaebe and M. Shikano, Nat. Commun., 9, 3823 (2018).K. Yoshii, T. Masese, M. Kato, K. Kubota, H. Senoh and M. Shikano, ChemElectroChem, 6, 3901 (2019).T. Masese, K. Yoshii, M. Kato, K. Kubota, Z.-D. Huang, H. Senoh and M. Shikano, Chem. Commun., 55, 985 (2019).G. M. Kanyolo and T. Masese, chemRxiv,11961123 (2020). https://doi.org/10.26434/chemrxiv.11961123.v1 submittedG. M. Kanyolo, T. Masese, J. Rizell et al., Honeycomb Layered Oxides: Structure, Energy Storage, Transport, Topology and Relevant Insights. arXiv, 2003.03555 [cond-mat.mtrl-sci] (2020). https://arxiv.org/abs/2003.03555 submitted