Unveiling a Hidden Conversion Pathway in CoSe ₂ Anodes via Rationally Designed CNT‐Interwoven Hollow Carbon Microclusters for High‐Performance Potassium‐Ion Batteries

ABSTRACT The search for sustainable energy storage has positioned potassium‐ion batteries (PIBs) as a compelling alternative to lithium‐ion systems, yet the lack of robust anode materials remains a significant hurdle. Transition‐metal selenides, particularly CoSe ₂ , are attractive for their high theoretical capacity and fast kinetics, but they inevitably succumb to catastrophic structural failure. This degradation is rooted in the traditional stepwise insertion pathway (CoSe ₂ → K _x CoSe ₂ → Co + K ₂ Se), which triggers a relentless lattice expansion exceeding 250%. Herein, we report the rational design of CNT‐interwoven hollow carbon microclusters as a rigid nanoconfined host to modulate this reaction behavior. This specific architecture does more than buffer volume changes; it fundamentally steers the electrochemical behavior toward a previously hidden conversion‐insertion mechanism mediated by a Co ₃ Se ₄ intermediate. Thermodynamic analysis via first‐principles calculations confirms that this newly unearthed route effectively sequesters major strain during the initial CoSe ₂ → Co ₃ Se ₄ transition, thereby preserving the electrode's integrity throughout subsequent potassiation. In situ X‐ray diffraction provides direct, real‐time evidence of this stabilized Co ₃ Se ₄ phase and its smooth evolution into K _x Co ₃ Se ₄ , bypassing the destructive traditional landscape. Our findings underscore that meticulous structural tailoring can be a powerful tool to capture elusive intermediates and redefine reaction pathways for high‐endurance PIB anodes.