Hierarchical Architecture of N-Doped Hollow Polyhedrons Anchored on Ti3c2tx Nanosheets for Advanced Lithium-Ion and Sodium-Ion Capacitors

Abstract

Limited by the kinetic imbalance between cathode and anode, combined with anode crushing caused by ion insertion/extraction, it is difficult to realize the simultaneous acquisition of high power/energy density of capacitors, which significantly limits the development of lithium/sodium ion hybrid capacitors (LIHCs/SIHCs). Here, we report a Co@NC/Ti3C2Tx composite with synergistic effects and as an anode for LIHC and SIHC. The prepared nitrogen-doped hollow polyhedron structured material possesses abundant mesopores, surface electrochemically active sites, and good mechanical robustness. The cavity structure serves as an ion buffer pool effectively mitigating the volume change and alleviating the aggregation of Ti3C2Tx lamellar materials, facilitating the penetration of electrolyte. Highly conductive Ti3C2Tx enhances the electrical conductivity of the Metal-organic framework (MOF) derived materials facilitate fast electron/ion transport, accelerate the reaction kinetics of the materials, and significantly reduce internal stresses to provide long-lasting cycling stability performance. Electrochemical results show that Co@NC/Ti3C2Tx composites exhibit ultra-high energy densities (187 Wh/kg and 128 Wh/kg) at high power densities (~154 W/kg) in LIHC and SIHC, respectively. In addition, they exhibit excellent cycling stability (90.1% and 86.2% capacity retention after 10000 cycles at 2A/g) and Coulombic efficiency (~100%). Impressively, the novel means of material compositing significantly improves the specific capacity and structural stability of the materials with high electronic conductivity and effective ion buffering, which provides unique insights into the development of LIHC/SIHC anode materials.

Keywords: Lithium-ion/Sodium-ion Hybrid Capacitors, N-doped hollow polyhedron, Ti3C2Tx, Synergistic effect