基于增大碳层间距和增强电容行为的协同效应提升碳材料储钾性能

Enlarged interlayer spacing and enhanced capacitive behavior of a carbon anode for superior potassium storage

本文通过简易高效的碳化工艺,构建了一种具有大碳层间距(0.407 nm)、高比表面积(681.15 m2 g-1)以及丰富电化学活性位点的N/S共掺杂碳材料(NSC)用作钾离子电池负极材料.研究结果发现,基于增大碳层间距和增强电容行为的协同效应, NSC表现出了较高的储钾容量(在0.1和0.5 A g-1电流密度下,可逆容量分别为302.8和206.7 mA h g-1)和优异的长循环稳定性(在2 A g-1电流密度下循环600圈之后,可逆容量能够保持在105.2 mA h g-1).同时,通过与单一硫掺杂碳材料(SC)和商用硬碳(HC)材料的储钾性能对比,作者发现单一硫原子掺杂尽管能够最大限度地增大碳层间距、提升储钾容量,但也会加剧碳材料结构的不稳定性,导致较差的循环性能和倍率性能.因此,作者强调了氮原子的引入不仅能够增强碳材料的导电性和电容吸附行为,而且有助于保持碳材料微观结构的稳定性.

Potassium-ion batteries(PIBs) hold great potential as an alternative to lithium-ion batteries due to the abundant reserves of potassium and similar redox potentials of K+/K and Li+/Li. Unfortunately, PIBs with carbonaceous electrodes present sluggish kinetics, resulting in unsatisfactory cycling stability and poor rate capability. Herein, we demonstrate that the synergistic effects of the enlarged interlayer spacing and enhanced capacitive behavior induced by the co-doping of nitrogen and sulfur atoms into a carbon structure(NSC) can improve its potassium storage capability. Based on the capacitive contribution calculations, electrochemical impedance spectroscopy, the galvanostatic intermittent titration technique, and density functional theory results, the NSC electrode is found to exhibit favorable electronic conductivity,enhanced capacitive adsorption behavior, and fast K+ ion diffusion kinetics. Additionally, a series of exsitu characterizations demonstrate that NSC exhibits superior structural stability during the(de)potassiation process. As a result, NSC displays a high reversible capacity of 302.8 mAh g-1 at 0.1 Ag-1 and a stable capacity of 105.2 m Ahg-1 even at 2 Ag-1 after 600 cycles. This work may offer new insight into the effects of the heteroatom doping of carbon materials on their potassium storage properties and facilitate their application in PIBs.