Enhanced energy storage performance of NiCo-LDH nanosheets decorated on biomass-derived carbon microtubes from natural poplar catkins for advanced hybrid supercapacitors

Nickel-cobalt layered double hydroxides (NiCo-LDHs) are promising electrode materials for hybrid supercapacitors (HSCs) due to their high theoretical charge storage capacity and excellent reversibility. However, their practical application is limited by low electrical conductivity and a tendency to agglomerate, which suppress their electrochemical performance. To address these challenges, NiCo-LDH NSs/CMT-PC composite electrode material is synthesized via a hydrothermal method. This composite integrates NiCo-LDH nanosheets (NiCo-LDH NSs) as a coating and carbon micro-tubes derived from poplar catkins (CMT-PC) with a high specific surface area as the framework. In a three-electrode system, the NiCo-LDH NSs/CMT-PC electrode demonstrated a specific capacity of 228.4 mAh g^-1 (1644.5 F g^-1, 822.2 C g^-1) at a current density of 1 A g^-1, and maintained a specific capacity of 101.7 mAh g^-1 (732.2 F g^-1, 366.1 C g^-1) even at 30 A g^-1. After 5000 cycles, the material exhibited excellent stability, retaining 96.5% of its capacity, with a decrease from 193.6 mAh g^-1 to 186.9 mAh g^-1. To explore its practical application in HSCs, we assembled NiCo-LDH NSs/CMT-PC//AC HSCs, using the NiCo-LDH NSs/CMT-PC as the positive electrode and activated carbon (AC) as the negative electrode. The assembled device exhibited a specific capacity of 88.3 mAh g^-1 at 1 A g^-1 and an energy density of 72.2 Wh kg^-1 at a power density of 508.6 W kg^-1. Impressively, after 9000 cycles at 3 A g^-1, the specific capacity increased from 64.2 mAh g^-1 to 66.5 mAh g^-1, demonstrating exceptional cycling stability and suitability for practical applications.