Design and study N-doped 3D hollow sphere MXene with different nano curvatures as anodes for high-performance lithium-ion capacitors

• N-doped 3D hollow sphere MXene electrode materials with different pore sizes were prepared by sacrificing MF templates of different sizes. • The smaller the pore size of the 3D hollow sphere structure MXene, the greater the surface nano curvature, the stronger the interface electric field, and the better the electrochemical performance. • 300MF-8MXene composite exhibits excellent electrochemical performance when utilized as an anode material for LIC (a maximum energy density of 81.3 Wh kg −1 , and even at a higher power density of 7.2 kW kg −1 , it still exhibits an excellent energy density of 22.7 Wh kg −1 ). Transition metal carbon/nitrogen compound (MXene) materials are considered promising candidate materials for lithium-ion storage. Although various porous MXene electrodes have been constructed, the effect of nano curvature on the lithium storage performance of MXene has been rarely studied. This article reports the preparation of porous MXene materials with varying surface nano curvatures using melamine formaldehyde (MF) spheres of different diameters (150, 300, 800, 1400, 2000 nm) by calcination to remove templates. Surprisingly, when the MXene hollow spheres have the maximum nano curvature (template size of 300 nm), the interface electric field strength is much higher than others, providing the highest specific capacity of 414 mAh g −1 at 1 A g −1 . Due to the formation of a strong local electrostatic field near the MXene hollow sphere anode, a nearly heterojunction structure is formed between the electrode surface and the electrolyte. Under the influence of the space charge area and the built-in electric field, the ion diffusion rate and electron transfer rate are improved, which helps to overcome the unbalanced electrode dynamics in lithium ion capacitors (LICs) and achieve higher power performance. The device exhibits a maximum energy density of 81.3 Wh kg −1 and a maximum power density of 7200 W kg −1 . This work demonstrates the potential of MXene two-dimensional materials in energy storage applications and provides insightful guidance for designing porous electrodes for LICs anodes.