Intercalation-Induced Conversion Reactions Give High-Capacity Potassium Storage.

Potassium ion batteries (PIBs) have shown great potential as a next-generation electrochemical energy storage system, due to the natural abundance of potassium and the relatively low redox potential of K ions. To accommodate the large ionic radius of K ions, conversion-type electrode materials are regarded as suitable candidates for K ion storage. However, the triggering mechanism of a conversion reaction in most anode materials of PIBs is unclear, which limits their further development. To reveal the mechanism, in this work, MoSe, MoS, and MoO were selected as model materials, guided by theoretical calculations, to investigate the K ion storage process. Through characterization, it was found that intercalation reactions preferentially occur in MoSe and MoS, while an adsorption reaction preferentially occurs in MoO. This is because of the larger interlayer spacing and lower K ion intercalation barrier in MoSe and MoS than in MoO. The preferential intercalation reactions are able to induce a further conversion reaction by reducing the reaction barrier, thereby realizing high K ion storage capacities. As a result, the MoSe-rGO and MoS-rGO hybrids showed higher reversible capacities than the MoO-rGO hybrid. By demonstrating a relationship between intercalation and the conversion reaction and understanding the mechanism, guidance is provided for selecting the electrode materials to obtain PIBs with high performance.