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In this study, P2-type K 0.7 [Cr 0.85 Sb 0.15 ]O 2 (KCSO) is prepared via a solid-state route and its electrochemical properties are compared with those of P2-K 0.62 Na 0.08 [Cr 0.85 Sb 0.15 ]O 2 (IE-KCSO), which is prepared via an electrochemical ion-exchange of P2-Na 0.7 [Cr 0.85 Sb 0.15 ]O 2 . Despite the near-identical chemical compositions and crystallographic structures, the IE-KCSO demonstrates rate capability and cyclic stability that is distinctively better than those of KCSO when used as a cathode in potassium-ion batteries (KIBs). For example, while KCSO shows a significant reduction in discharge capacities at high rates (48 mAh•g −1 at 2C vs 70 mAh•g −1 at 0.1C), IE-KCSO retains substantial capacities at high rates (67 mAh•g −1 at 2C vs 78 mAh•g −1 at 0.1C). The cyclic stability of IE-KCSO is also superior, as it delivers 96% of initial capacity after 100 charge/discharge (C/D) cycles, in contrast to 76% retention for KCSO. This study confirms that the Na + ions remaining in IE-KCSO contribute to the fast K + diffusion and, thereby, to its superior rate capability. Smaller dimensional changes in IE-KCSO during C/D are also apparent and these result in better cyclic stability. This work suggests that preparing KIB cathode materials via an ion-exchange protocol is more efficient than direct synthesis, particularly when the latter creates difficulties in obtaining phase-pure target compounds.

In contrast to O3–NaCrO2, O3–Na0.8[Cr0.9Sb0.1]O2 shows reversibility when charged to 3.95 V and high-voltage charge/discharge features, which results in improvement of energy density.