Doped Hard Carbon Nanotube Bundles for Superior Potassium Storage

Potassium-ion batteries (KIBs) have garnered significant attention as an economical energy storage solution driven by the growing demand for technologies that efficiently store renewable and surplus energy. Hard carbon (HC) stands out among anode materials due to its superior electrochemical performance, abundance of active sites, and larger interlayer spacing than conventional graphitic materials. This work reports the development of N/O-co-doped one-dimensional mesoporous HC nanotube bundles (N/O-HCNTB), synthesized using MnO2 nanowires as sacrificial templates, which were subsequently removed using an aqueous citric acid solution. The nanoscale hollow architecture of N/O-HCNTB enhances potassium-ion storage by boosting the availability of active sites and effectively accommodating volume fluctuations during cycling. The nanoscale bundled configuration addresses the loose packing limitation of multiwalled carbon nanotubes by forming a relatively dense electrode, thereby enhancing energy density. Therefore, the N/O-HCNTB demonstrates remarkable electrochemical performance as KIB anode materials, delivering an initial charge capacity of 427 mAh g–1 and maintaining 94.8% capacity retention after 200 cycles at 100 mA g–1. Furthermore, it also demonstrates good stability even under high-rate cycling conditions at 500 mA g–1, retaining a 395 mAh g–1 after 1000 cycles. This study underscores the potential of N/O-HCNTB, advancing its practical application in sustainable energy storage systems.