Flexible potassium-ion batteries enabled by encapsulating hollow NiSe/SnSe nanocubes within freestanding N-doped carbon nanofibers

• Foldable electrodes featuring hollow NiSe/SnSe nanocubes confined in carbon nanofibers are designed for PIBs . • A novel selenization method is introduced for fabricating free-standing electrodes. • The designed anode exhibits impressive initial Coulombic efficiency, rate capability and cyclability at high mass loadings. • The K-ion pouch cell delivers excellent performance under periodic bending conditions. 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. Flexible and freestanding H NiSe/SnSe@NC anodes exhibit high initial Coulombic efficiencies, exceptional rate capacities, and extended cycling stabilities, even at high mass loadings. Leveraging its sophisticated composition and structure, a high-capacity and long-life foldable potassium-ion batteries can be realized.