Ultrafine TiO₂ Nanoparticle Supported Nitrogen-Rich Graphitic Porous Carbon as an Efficient Anode Material for Potassium-Ion Batteries

Potassium-ion batteries (KIBs) have attracted enormous attention as a next-generation energy storage system due to their low cost, fast ionic conductivity within electrolytes, and high operating voltage. However, developing suitable electrode materials to guarantee high-energy output and structural stability to ensure long cycling performance remains a critical challenge. Herein, anatase TiO₂ nanoparticles are encapsulated in nitrogen-rich graphitic carbon (TiO₂@NGC) with hierarchical pores and high surface area (250 m² g⁻¹) using the Ti-based metal–organic framework NH₂-MIL-125 (Ti₈O₈(OH)₄(NH₂-bdc)₆ with NH₂-bdc²⁻ = 2-amino-1,4-benzenedicarboxylate) as a sacrificial template. Serving as the anode material in a K-ion half-cell, TiO₂@NGC delivers a high capacity of 228 mA h g⁻¹ with remarkable cycling performance (negligible loss over 2000 cycles with more than 98% Coulombic efficiency). The charge-storing mechanism is underpinned using ex situ characterization techniques such as ex situ X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis. It is revealed that the original TiO₂ phase gets transformed to the anorthic Ti₇O₁₃ and monoclinic K₂Ti₄O₉ phase after the first charge/discharge cycle, which further initiates the charge storage process via the conversion reactions.