Addressing Irreversibility and Structural Distortion in WS₂ Inorganic Fullerene-Like Nanoparticles: Effects of Voltage Cutoff Experiments in Beyond Li⁺-Ion Storage Applications

Large interlayer spacing beneficially allows Na⁺- and K⁺-ion storage in transition-metal dichalcogenide (TMD)-based electrodes, but side reactions and volume change, which pulverize the TMD crystalline structure, are persistent challenges for the utilization of these materials in next-generation devices. This study first determines whether irreversibility due to structural distortion, which results in poor cycling stability, is also apparent in the case of inorganic fullerene-like (IF) tungsten disulfide (WS₂) nanocages (WS₂IF). To address these problems, this study proposes upper and lower voltage cutoff experiments to limit specific reactions in Na⁺/WS₂IF and K⁺/WS₂IF half-cells. Three-dimensional (3D) differential capacity curves and derived surface plots highlight the continuation of reversible reactions when a high upper cutoff technique is applied, thereby indirectly suggesting restricted structural dissolution. This resulted in improved capacity retention with stable performance and a higher Coulombic efficiency, laying the ground for the use of TMD-based materials beyond Li⁺-ion storage devices.