Behavior of Li Guest in KNb5O13 Host with One-Dimensional Tunnels and Multiple Interstitial Sites

Potassium niobium oxide (KNb5O13) exhibits multiple unoccupied interstitial sites in its crystal structure. In a lithiation/delithiation process, similar to 3.5 Li+ ions can be inserted/extracted into/from these sites above 1.0 V vs Li/Li+. Although there are two-dimensional tunnels in KNb5O13, the experiment demonstrates that only a-axis tunnels have access to the electrolyte for the lithiation/delithiation process. The one-dimensional tunnels connect to multiple off-axis sites (4c, 4d, and 8e), which results in a polarization hysteresis in the potential profile of the lithiation/delithiation process. Using experimental and calculation methods, the study explains the polarization hysteresis with a proposed lithiation/delithiation process in KNb5O13.