Phosphorus/nitrogen co-doped hollow carbon fibers enabling high-rate potassium storage

Abstract

Potassium-ion hybrid capacitors (PIHCs) reconcile the advantages of batteries and supercapacitors, exhibiting both good energy density and high-power density. However, the low-rate performance and poor cycle stability of battery-type anodes hinder their practical application. Herein, phosphorus/nitrogen co-doped hollow carbon fibers (P-HCNFs) are prepared by a facile template method. The stable grape-like structure with continuous and interconnected cavity structure is an ideal scaffold for shortening the ion transport and relieving volume expansion, while the introduction of P atoms and intrinsic N atoms can create abundant extrinsic/intrinsic defects and additional active sites, reducing the K⁺ diffusion barrier and improving the capacitive-controlled capacity. The P-HCNFs delivers a high specific capacity of 310 mAh·g⁻¹ at 0.1 A·g⁻¹ with remarkable ultra-high-rate performance (140 mAh·g⁻¹ at 50 A·g⁻¹) and retains an impressive capacity retention of 87% after 10,000 cycles at 10 A·g⁻¹. As expected, the as-assembled PIHCs present a high energy density (115.8 Wh·kg⁻¹ at 378.0 W·kg⁻¹) and excellent capacity retention of 91% after 20,000 cycles. This work not only shows great potential for utilizing heteroatom-doping and structural design strategies to boost potassium storage, but also paves the way for advancing the practicality of high-energy PIHCs devices.

Graphical abstract

摘要

钾离子混合电容器 （PIHCs） 综合了二次离子电池和超级电容器的优点， 表现出良好的能量密度和功率密度。然而，电池型负极的低倍率性能和较差的循环稳定性阻碍了其实际应用。在此，通过简单的模板方法制备了磷/氮共掺空心碳纤维 （P-HCNFs）。 稳定的葡萄状结构具有连续和相互连接的空腔结构，有利于缩短离子传输距离和缓解体积膨胀，而P原子和内在N原子的引入可以创造丰富的外在/内在缺陷和额外的活性位点， 减少K⁺扩散障碍，提高电容贡献比容量。 P-HCNFs在0.1 A·g⁻¹时提供了310 mAh·g⁻¹的高比容量， 具有显著的超高倍率性能 （50 A·g⁻¹时为140 mAh·g⁻¹）, 并且在10 A·g⁻¹时循环10000次后保持了87%的惊人容量。另外， 组装的PIHCs呈现出高能量密度 （在378.0 W·kg⁻¹时为115.8 Wh·kg⁻¹）， 并在20000次循环后保持91%的出色容量。 这项工作不仅显示了利用杂原子掺杂和结构设计策略来提高储钾的巨大潜力， 而且还为推进高性能PIHCs器件的实用化铺平了道路。