Nanostructure engineering of cobalt-nickel glycerate (CoNi-G) spheres as anodes for constructing high-performance lithium-ion capacitors

Electrode materials with heterogeneous structure and favorable morphology can increase the contact with the electrolyte while accelerating the ion transport. Here, we prepared Co₂NiO₄/NiO solid spheres and CoNi₂S₄ hollow spheres by high-temperature calcined oxidation and solvent-thermal vulcanization, with cobalt-nickel glycerate (CoNi-G) solid spheres as precursors, respectively. The specific capacities of Co₂NiO₄/NiO and CoNi₂S₄ as anodes after 170 and 570 cycles at 0.1 A g⁻¹ are 1260.9 mAh g⁻¹ and 495.0 mAh g⁻¹ respectively, and even after 3000 cycles at 2 A g⁻¹, their specific capacities can reach 168.9 mAh g⁻¹ and 211.1 mAh g⁻¹ respectively. The initial specific capacities of both materials are higher, but the solid structure is more stable than the hollow structure. Density Functional Theory (DFT) calculations show that the constructed Co₂NiO₄/NiO heterojunction has reduced Li⁺ embedding formation energy and enhanced conductivity. Finally, the assembled Co₂NiO₄/NiO//AC and CoNi₂S₄//AC lithium-ion capacitors have maximum energy densities of 106.7 Wh kg⁻¹ and 73.6 Wh kg⁻¹ (at 205 W kg⁻¹ and 95 W kg⁻¹), and maximum power densities of 20.5 kW kg⁻¹ and 19.0 kW kg⁻¹ (at 10.8 Wh kg⁻¹ and 19.5 Wh kg⁻¹). Improved electrode structures via precursor treatments enhance lithium-ion capacitors performance, suggesting new avenues for material research.