Confining Co_1.11Te₂ nanoparticles within mesoporous hollow carbon combination sphere for fast and ultralong sodium storage

Co_1.11Te₂ nanoparticles are in-situ uniformly grown within mesoporous hollow carbon combination sphere (MHCCS@Co_1.11Te₂) using a hard-template and spray drying process, solution impregnation and pyrolysis tellurization. Material characterizations reveal that Co_1.11Te₂, with a diameter of ∼ 20 nm, is attached to the internal walls of the unit spheres or embedded in the mesopore shells of the unit spheres, presenting a distinctive “ships-in-combination-bottles” nanoencapsulation structure. In sodium-ion half-cells, MHCCS@Co_1.11Te₂ exhibits excellent cycling stability, achieving reversible capacities of 257 mAh/g at 0.5 A/g after 250 cycles, 235 mAh/g at 1.0 A/g after 300 cycles and 161 mAh/g at 10.0 A/g after 1900 cycles. Electrochemical kinetic analyses and ex-situ characterizations reveal rapid electron/Na⁺ transport kinetics, prominent surface pseudocapacitive behavior, robust nanocomposite structure, and multi-step conversion reactions of sodium polytellurides. In sodium-ion full-cells, MHCCS@Co_1.11Te₂ still demonstrates stable cycling performance at 1.0 and 5.0 A/g and excellent rate capability. The superior electrochemical performance is associated with the nanoencapsulation structure based on mesoporous hollow carbon combination spheres, which promotes electron conduction and Na⁺ transport. The space-confined effect maintains the high electrochemical activity and cycling stability of Co_1.11Te₂.