It is empirically expected that K + would be extracted from the PBA framework after initial deintercalation, and Na + would gradually replace K + in following intercalation processes, which essentially transforms a K-PBA cathode to a Na-PBA cathode. Such kind of Na + -K + exchange has been reported, where 50% K in a KMnFe-PBA (M = Mn) cathode was substituted by Na after 30 cycles in a NIB cell. In contrast, no significant Na + -K + exchange was observed in the initial cycles of a KFeFe-PBA (M = Fe) cathode, but the result of longterm cycles remained unknown. Noting that theoretical simulations have demonstrated the strong dependence of cation intercalation in the PBA framework on the ionic radii of the cations, and K + intercalation took place at a higher voltage compared with Na + intercalation in the same PBA framework, thus potentially providing higher energy density. To this end, it is crucial to regulate cation intercalation mechanism of a hybrid NIB cell in a way that maximizes K + intercalation and minimizes Na + intercalation in a K-PBA cathode, even though the Na concentration in the electrolyte is several folder higher than the K concentration in the K-PBA cathode.