Preferentially engineering edge–nitrogen sites in porous hollow spheres for ultra–fast and reversible potassium storage

Abstract

Hard carbons have been regarded as potential anode materials for potassium ion batteries due to their superior merits of low cost, good chemical stability, and adjustable structure. However, hard carbons still suffer from the sluggish kinetics and large volume expansion during potassiation/depotassiation processes. Edge–nitrogen doping has been demonstrated an effective strategy to solve these issues. Currently, the low portion of edge–nitrogen sites restricts K+ adsorption ability of hard carbons. Herein, we preferentially engineer edge–nitrogen sites with a high portion of 85.6% in hollow porous carbon spheres, through structure engineering combined with dual doping. The as–developed anode materials possess unique interior void space and various nanoscale curvature, preferentially exposing rich edge–nitrogen sites. Additional phosphorus doping modulates valence bands of edge–nitrogen sites, advantageous for generating a large fraction of edge sites. The edge dominated nitrogen species confer strong K+ adsorption capability, thus contributing a rapid surface–controlled potassium adsorption process. Consequently, the as–prepared hollow porous N,P–codoped carbon spheres exhibit comparable reversible capacities, outstanding rate performance (193.0 mAh g−1 at 4 A g−1), and stable cycling ability (137.6 mAh g−1 at 2 A g−1 after 1500 cycles). Ex operando Raman, XRD and DFT calculations reveal the stable structure, reinforced K+ adsorption ability and modulated band structure. Our work provides an efficient path to engineer active edge sites in carbon materials and boost potassium storage.