  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 ($\rm Na$ and $\rm K$) to produce a mixed alkali honeycomb
layered oxide material, namely, $\rm NaKNi_2TeO_6$. Via transmission electron
microscopy measurements, we reveal the local atomic structural disorders
characterised by aperiodic stacking and incoherency in the alternating
arrangement of $\rm Na$ and $\rm K$ atoms. We also investigate the possibility
of mixed electrochemical transport and storage of $\rm Na$ and $\rm K$ ions in
$\rm NaKNi_2TeO_6$. In particular, we report an average discharge cell voltage
of about $4\, \rm V$ and a specific capacity of around $80\, \rm mAh\, g^{-1}$
at low specific currents (i.e., $< 10\, \rm mA\, g^{-1}$) when a $\rm
NaKNi_2TeO_6$-based positive electrode is combined with a room-temperature $\rm
NaK$ 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.
