Controlled synthesis of hierarchical porous carbons with different morphologies and their application for potassium and lithium ion batteries

Abstract

Activated carbon is an ideal candidate as an anode material for rechargeable metal-ion batteries. However, the synthesis of highly porous and heteroatom-doped carbons with high yields and controlled morphologies is a grand challenge. Herein, heteroatom nitrogen-doped (in situ) hierarchical porous activated carbons with interconnected macro/meso/micropores and controlled morphologies were prepared from bio wastes using a facile synthesis technique. The surface morphology, pore distribution and crystal structure of the synthesized carbons were thoroughly investigated for various KOH etching times. Experimental results revealed that different morphologies i.e. 3-dimensional interconnected structures, nanosheets, and nanospheres, were achieved with significant pores and specific surface areas. Synthesized carbons were tested for potassium and lithium-ion storage. PIBs exhibited a maximum reversible capacity of 526 mA h g⁻¹ at 20 mA g⁻¹ and an excellent cycling performance (retaining 212 mA h g⁻¹ after 150 cycles at 20 mA g⁻¹) with N-doped active carbon nanospheres. Whereas, the reversible capacity of 1394 mA h g⁻¹ at 50 mA g⁻¹ with an excellent cycling performance (retaining 536 mA h g⁻¹ after 500 cycles at 500 mA g⁻¹) was delivered by N-doped active carbon nanospheres against Li⁺/Li. Furthermore, cyclic voltammetry and electrochemical impedance spectroscopy were employed to quantify the guest ion storage mechanisms and diffusion coefficients. The excellent electrochemistries of the synthesized carbons are attributed to their hierarchical porous structure, which provides micro reaction chambers, and modified chemical structures owing to heteroatom (nitrogen) doping. We hope that these findings will encourage chemical scientists to explore porous carbons from bio wastes.