KMn _7.6 Co _0.4 O ₁₆ nano-rod clusters with a high discharge specific capacity as cathode materials for potassium-ion batteries

Cryptomelane-type KMn ₈ O ₁₆ with a unique tunnel structure is a suitable cathode for potassium-ion batteries. In this work, KMn ₈ O ₁₆ clusters of nano-rods are synthesized by a facile and template-free hydrothermal method. Electrochemical characterization has been carried out, and the results show that the KMn ₈ O ₁₆ nano-rods exhibit high discharge capacity but a poor cycling performance, which are attributed to the unique but unstable tunnel structure. Therefore, a cobalt doping strategy is developed to enhance the structural stability. The results show that there are no changes in the crystal structure and morphology after Co doping, while higher specific capacity and better cycling stability are achieved. Among all the doped samples, KMn _7.6 Co _0.4 O ₁₆ exhibits the best electrochemical properties with high initial discharge capacities (246 mA h g ^-1 at a current density of 10 mA g ^-1 and 174 mA h g ^-1 at a current density of 100 mA g ^-1 in the 1.5-4.0 V range). The results show that Co doping efficiently enhances its structural stability.