  In the quest of finding novel and efficient batteries, a great interest has
raised in K-based honeycomb layer oxide materials both for their fundamental
properties and potential applications. A key issue in the realization of
efficient batteries based on such compounds, is to understand the K-ion
diffusion mechanism. However, investigation of potassium-ion (K$^+$) dynamics
in materials using magneto-spin properties has so far been challenging, due to
its inherently weak nuclear magnetic moment, in contrast to other alkali ions
such as lithium and sodium. Spin-polarised muons, having a high gyromagnetic
ratio, make the muon spin rotation and relaxation ($\mu$+SR) technique ideal
for probing ions dynamics in weak magneto-spin moment materials. Here we report
the magnetic properties and K+ dynamics in honeycomb layered oxide material of
the K$_2$Ni$_2$TeO$_6$ using $\mu$+SR measurements. Our low-temperature
$\mu$+SR results together with, with complementary magnetic susceptibility,
find an antiferromagnetic transition at 26 K. Further $\mu$+SR studies
performed at higher temperatures reveal that potassium ions (K$^+$) become
mobile above 250 K and the activation energy for the diffusion process is Ea =
121(13) meV. This is the first time that K+ dynamics in potassium-based battery
materials has been measured using $\mu$+SR. Finally our results also indicate
an interesting possibility that K-ion self diffusion occurs predominantly at
the surface of the powder particles. This opens future possibilities for
improving ion diffusion and device performance using nano-structuring.
