Potassium iodide as a low-cost cathode material for efficient potassium-ion storage

Potassium-ion batteries (KIBs) are attractive electrochemical energy storage technologies because of their low cost and high energy density . Currently, the reported cathode candidates for KIBs are all limited to the intercalation-type materials. The working principles of these materials all involve the repeated intercalation-deintercalation of bulky K-ions in the ionically-bonded rigid frameworks, which often results in sluggish reaction kinetics, irreversible structural deformation, and poor cycling stability. Here, a low-cost conversion-type material, potassium iodide (KI), is proposed as a promising cathode candidate for KIBs. It is revealed that the depotassiation-potassiation of KI proceeds via a dissolution-precipitation reaction process involving the highly soluble KI 3 intermediate, leading to the shuttle effect and capacity decay. Susequently, a simple strategy combining electrolyte modulation with separator modification is adopted to effectively enhance the electrochemical performance of KI, leading to an impressive capacity retention of 95.5% after 550 cycles. The present study may shed some light on further exploration of high-performance electrode materials based on dissolution-precipitation reaction mechanism for the emerging KIBs.