Adjusting the yolk–shell structure of carbon spheres to boost the capacitive K+ storage ability

Abstract

Carbon materials continue to be a focus of rapid innovative application in potassium-ion batteries (KIBs) owing to their abundant resources. However, K⁺ storage of carbon electrodes is limited by the intercalation chemistry which brings a large structural change and sluggish potassiation kinetics. In this work, we synthesized a series of hierarchical porous yolk–shell carbon sphere (HYCS) materials through an extended Stöber reaction. By controlling the concentration of tetraethyl orthosilicate (TEOS), their morphologies, including pore volume, specific surface area and yolk ratios, can be well adjusted. Quantitative analysis reveals that these adjusted materials show enhanced capacitive behavior, which leads to fast reaction kinetics and enhanced K⁺ adsorption capability. Furthermore, the capacitance contribution can be controlled through adjusting the yolk–shell nanostructures. The optimized sample with the largest pore volume (1.47 cm³ g⁻¹) and the highest specific surface area (703.1 cm² g⁻¹) possesses the best rate performance with capacities of 314 and 121 mA h g⁻¹ at 50 and 5000 mA g⁻¹, respectively. These achievements signify that structural adjustment is an effective approach for constructing high-performance K⁺ storage materials.