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, MoSe₂, MoS₂, and MoO₂ were selected as model materials, guided by theoretical calculations, to investigate the K ion storage process. Through ex situ characterization, it was found that intercalation reactions preferentially occur in MoSe₂ and MoS₂, while an adsorption reaction preferentially occurs in MoO₂. This is because of the larger interlayer spacing and lower K ion intercalation barrier in MoSe₂ and MoS₂ than in MoO₂. 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 MoSe₂−rGO and MoS₂−rGO hybrids showed higher reversible capacities than the MoO₂−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.