Ultrafine edge-split copper oxide nanoneedles for high-energy, fast-charging lithium-ion capacitors

Developing lithium-ion capacitors (LICs) that simultaneously deliver high energy and power densities without compromising cycle life remains a critical challenge for next-generation energy storage systems. Herein, we report ultrafine copper oxide (CuO) nanoneedle anodes directly grown on copper foil current collectors via a synergistic double nano-structuring strategy. First, Cu nanopillars (∼160 nm in diameter) are self-assembled on Cu foil through a galvanic displacement reaction. These pillars are subsequently transformed into edge-split Cu(OH)₂ nanoneedles as thin as ∼30 nm by ammonia-assisted electro-oxidation in an aqueous electrolyte. A subsequent annealing step dehydrates the Cu(OH)₂, yielding CuO nanoneedles endowed with abundant nanopores (1.5–8 nm) and a high specific surface area of 59.71 m² g⁻¹. This hierarchically porous, ultrafine architecture markedly enhances electrochemical kinetics. As a result, the CuO nanoneedle anodes exhibit excellent rate capability and cycling stability, delivering specific capacities of 973 mAh g⁻¹ at 0.2 A g⁻¹ and 663 mAh g⁻¹ at 5 A g⁻¹. When paired with activated carbon cathodes, the LIC devices demonstrate outstanding rate performance, achieving an energy density of 110.1 Wh kg⁻¹ at 2C and retaining ∼40 % of their capacity at an ultrafast rate of 60C. This facile fabrication route for ultrafine CuO electrode is expected to offer a promising pathway toward advanced energy storage applications.