Hierarchical architecture composites of N-doped hollow polyhedra anchored on Ti3C2Tx nanosheets for advanced lithium-ion and sodium-ion capacitors

Abstract

Limited by the kinetic imbalance between the 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/Ti₃C₂T_x composite with synergistic effects as an anode for LIHCs and SIHCs. The prepared nitrogen-doped hollow polyhedron structured material possesses abundant mesopores, electrochemically active surface sites, and good mechanical robustness. The cavity structure serves as an ion buffer pool effectively mitigating the volume change and alleviating the aggregation of Ti₃C₂T_x lamellar materials, facilitating the penetration of electrolyte. Highly conductive Ti₃C₂T_x enhances the electrical conductivity of the metal–organic framework (MOF) derived materials, facilitates fast electron/ion transport, accelerates the reaction kinetics of the materials, and significantly reduces internal stresses to provide long-lasting cycling stability performance. Electrochemical results show that Co@NC/Ti₃C₂T_x composites exhibit ultra-high energy densities (187 W h kg⁻¹ and 128 W h kg⁻¹) at high power densities (∼154 W kg⁻¹) in LIHCs and SIHCs, respectively. In addition, they exhibit excellent cycling stability (90.1% and 86.2% capacity retention after 10 000 cycles at 2 A g⁻¹) and coulombic efficiency (∼100%). Impressively, the improved specific capacity, structural stability, electronic conductivity and effective ion buffering capacity of the composites in a novel combinatorial approach provide cutting-edge insights into developing high-performance LIHC/SIHC anode materials for a wide range of scientific and industrial applications.