Unveiling a Hidden Conversion Pathway in CoSe₂ Anodes via Rationally Designed CNT-Interwoven Hollow Carbon...

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 CoSe₂, 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 (CoSe₂ → K_xCoSe₂ → Co + K₂Se), 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 Co₃Se₄ intermediate. Thermodynamic analysis via first-principles calculations confirms that this newly unearthed route effectively sequesters major strain during the initial CoSe₂ → Co₃Se₄ transition, thereby preserving the electrode's integrity throughout subsequent potassiation. In situ X-ray diffraction provides direct, real-time evidence of this stabilized Co₃Se₄ phase and its smooth evolution into K_xCo₃Se₄, 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.