Selenium vacancy engineering in MoSe ₂ nanoflowers: unlocking high-rate and durable potassium storage through plasma-mediated defect activation

Rechargeable potassium-ion batteries (PIBs) have emerged as promising sustainable alternatives to lithium-ion systems. However, their practical application is limited by the scarcity of high-performance electrode materials that can effectively accommodate the relatively large size of K⁺ ions. Herein, we present a defect-engineering strategy aimed at activating the basal planes of MoSe₂ through the controlled introduction of selenium vacancies (V_Se-MoSe₂) using a plasma-mediated discharge etching process. The optimized vacancy concentrations substantially narrow the bandgap from 1.43 to 0.38 eV, enhance electronic conductivity, and generate multidimensional K⁺ ion diffusion pathways. Furthermore, the introduction of structural defects can significantly enhance the pseudocapacitive contribution of the V_Se-MoSe₂ electrode. <i>In situ</i> XRD, <i>ex situ</i> XPS/TEM, and DFT calculations collectively elucidate a highly reversible conversion mechanism for potassium storage, confirming the critical role of selenium vacancies in stabilizing the host structure and facilitating rapid K⁺ ion adsorption. Consequently, the optimal electrode exhibits a high reversible capacity of 286.2 mAh g^-1 at a current density of 1 A g^-1 after 100 cycles and maintains a capacity of 134.9 mAh g^-1 even at 5 A g^-1 after 300 cycles. This study highlights the transformative potential of precisely engineered defects in unlocking durable, high-rate potassium storage within layered transition metal dichalcogenides.