Hollow carbon fibers with balanced graphitization and defects for extremely fast-charging potassium storage
Qian Yu, Xiaojun Shi, Taoqiu Zhang, Yi Zhao, Jun Jin, Rui Wang, Yansheng Gong, Huanwen Wang
Abstract
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 <em>via</em> a ZrO<sub>2</sub>-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<sup>+</sup> insertion/extraction below 1 V (vs. K<sup>+</sup>/K). These tubular carbon membranes achieve exceptional K<sup>+</sup>-storage performance including high K<sup>+</sup>-storage capacities of 404 mAh g<sup>−1</sup> at 0.1 A g<sup>−1</sup>, ultrafast charging at 50 A g<sup>−1</sup> and a super-long cycle life of up to 6,000 cycles. <em>Ex-situ</em> XRD, <em>in-situ </em>Raman, and GITT analyses reveal a synergistic K<sup>+</sup>-adsorption-intercalation mechanism. Further comparison with S or P heteroatoms underscores the significance of N-doping in enhancing reversible K<sup>+</sup> intercalation into graphitic domains and boosting surface adsorption capacity. The fabricated NGCT-900//K<sub>x</sub>Ni<sub>0.33</sub>Mn<sub>0.67</sub>O<sub>2</sub> PIB (1.2~3.2 V) provides both a high-energy density of 187 Wh kg<sup>−1</sup> (comparable to graphite//LiFePO<sub>4</sub> LIBs) and a high-power density of 2200 W kg<sup>−1</sup> at 123 Wh kg<sup>−1</sup>. This study establishes a carbon anode design strategy for advanced potassium storage.