Hollow carbon fibers with balanced graphitization and defects for extremely fast-charging potassium storage

Extremely fast-charging and long-life span are critical yet challenging for the development of cost-effective and sustainable potassium-ion batteries (PIBs) due to the sluggish kinetics and rapid capacity decay of graphite anodes caused by the large radius of K ions (1.38 Å). To tackle this issue, here a new type of nitrogen-doped graphitic carbon tubes (NGCTs) is reported via a ZrO₂-templated chemical vapor deposition (CVD) approach. The carbon interlayer spacing, crystallite size, and N-configurations in NGCTs are controlled by adjusting the CVD temperature (800, 900, 1000 °C). The optimized NGCT-900 sample well balances the graphitic domains and structural defects, thus enabling fast K⁺ insertion/extraction below 1 V (vs. K⁺/K). These tubular carbon membranes achieve exceptional K⁺-storage performance including high K⁺-storage capacities of 404 mAh g⁻¹ at 0.1 A g⁻¹, ultrafast charging at 50 A g⁻¹ and a super-long cycle life of up to 6,000 cycles. Ex-situ XRD, in-situ Raman, and GITT analyses reveal a synergistic K⁺-adsorption-intercalation mechanism. Further comparison with S or P heteroatoms underscores the significance of N-doping in enhancing reversible K⁺ intercalation into graphitic domains and boosting surface adsorption capacity. The fabricated NGCT-900//KxNi0.33Mn0.67O₂ PIB (1.2~3.2 V) provides both a high-energy density of 187 Wh kg⁻¹ (comparable to graphite//LiFePO₄ LIBs) and a high-power density of 2200 W kg⁻¹ at 123 Wh kg⁻¹. This study establishes a carbon anode design strategy for advanced potassium storage.