Flexible Potassium-Ion Batteries Enabled by Encapsulating Hollow NiSe/SnSe Nanocubes within Freestanding N-doped Carbon Nanofibers

Self-supporting electrode materials are instrumental in accelerating the development of flexible potassium-ion batteries (PIBs). However, the challenge lies in designing self-supporting materials with sophisticated structures and compositions to overcome the sluggish kinetics and volume effect caused by the large size of potassium ions during K-storage. In this work, we present novel flexible anodes synthesized by confining hollow NiSe/SnSe nanocubes within nitrogen-doped carbon nanofibers (H-NiSe/SnSe@NC). Leveraging its unique organization and composition, the H-NiSe/SnSe@NC anode exhibits impressive initial Coulombic efficiency, excellent rate capability, and exceptional cyclability, even at high mass loadings, outperforming most reported PIBs anodes. Utilizing in-situ XRD and ex-situ TEM techniques, we elucidate the mechanism responsible for its high capacity and gain insights into the K-storage behavior and reaction kinetics through diverse electrochemical measurements. First-principles calculations further clarify the underlying mechanism by which the designed heterostructured anode enhances the adsorption/diffusion of K-ions. Additionally, we integrate this novel anode into full cells, achieving high energy density and extended cycling life. Remarkably, the pouch cell we fabricated delivers high reversible capacity and cyclability even under periodic bending conditions, highlighting its superiority for flexible devices. This research showcases the significance of designing and fabricating advanced self-supporting electrodes for flexible PIBs applications.