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Abstract
We demonstrate the feasibility of using a combination of alkali
atoms (Na and K) to develop a robust mixed-alkali honeycomb layered oxide NaKNi2TeO6.
Through a series of atomic-resolution transmission electron microscopy in
multiple zone axes, we reveal for the first time the local atomic structural
disorders characterised by aperiodic stackings and incoherency in the
alternating arrangement of Na and K atoms. Our findings indicate great
structural versatility that renders NaKNi2TeO6 an ideal
platform for investigating other fascinating properties such as mixed ionic
transport and intriguing electromagnetic and quantum phenomena amongst honeycomb
layered oxides. Finally, we unveil the possibility of inducing mixed Na- and
K-ion transport electrochemistry of NaKNi2TeO6 at high
voltages (~ 4V), thus epitomising it as a competent cathode candidate for the
emerging dendrite-free batteries based on NaK liquid metal alloy as anodes. The
results not only betoken a new avenue for developing functional materials with
fascinating crystal versatility, but also prefigure a new age of
‘dendrite-free’ energy storage system designs that rely on mixed-cation
electrochemistry.
