Engineered nitrogen-doped hollow carbon nanospheres adhered by carbon nanotubes for capacitive potassium-ion storage

The CNTs-NHCSs consist of externally connected nitrogen-doped hollow carbon spheres, which provide accommodation space for potassium ions and buffer the volume expansion caused by K + insertion via its inner cavity, and graphitized structure of CNTs acts as skeleton for facilitating electron transport synergistically. The unique designed structure plays a critical role in enhancing the electrochemical performance of the CNTs-NHCSs electrode. • Hollow carbon spheres interconnected by carbon nanotube were engineered via a facile esterification reaction. • The introduction of carbon nanotube enhances rate capability of the CNTs-NHCSs electrode. • The potassium storage mechanism of CNTs-NHCSs is discussed. Hollow carbon materials are promising candidates when evaluated as anode for potassium ion batteries (PIBs) due to high capacity, available pore structure, excellent surface properties and unique structural for buffering the destructive volume expansion. However, the unsatisfactory electrical conductivity and structural stability caused by amorphous carbon structure hinder its further practical application of accommodating potassium ions. Herein, nitrogen-doped hollow carbon nanospheres (NHCSs) are synthesized by using acetone discriminatively dissolving the interior part of 3-aminophenol-formaldehyde resin nanospheres and then interconnected with carbon nanotubes (CNTs) to prepare the CNTs-NHCSs composite as advanced anode for PIBs. Owing to the long-range order graphitized structure introduced by CNTs and unique cavity structure provided by NHCSs, the integrity of the connection between NHCSs and CNTs can be confirmed to boost electron transport and buffer volume changing synergistically. Accordingly, the CNTs-NHCSs electrode delivers high reversible capacity of 228 and 165.2 mAh g −1 over 100 cycles at 100 mA g −1 and 1000 cycles at 1000 mA g −1 respectively, indicating superior reversible potassium storage capacity and excellent rate capability. The successful construction of advanced CNTs-NHCSs composite in this work provides a new avenue in structural design and function optimization for the development of PIBs electrode materials.