Regulating the Nanosize Effect of LiCoO₂ for High-Performance Battery-Supercapacitor Hybrid Devices

The nanosize effect in nanostructured electrode materials is significant for boosting rate performance; however, it brings about low capacity, low Coulombic efficiency, and poor stability. In this work, 2D atomically thin (001)-oriented single-crystalline LCO (SC-LCO) nanosheets with longer Li⁺ intercalation distance and a surface dominated with (001) planes are constructed to regulate the nanosize effect. The SC-LCO not only owns large plateau region capacity even at high rate (194 mAh g^–1 at 1C and 111 mAh g^–1 at 50C) but also realizes remarkable improvement in the initial Coulombic efficiency (92% at 1C) and cycling stability (83% capacity retention for 500 cycles). The battery-supercapacitor hybrid devices (BSHDs) assembled with kinetics and capacity doubly matched SC-LCO and mesoporous TiNb₂O₇ nanosheets offer high energy density (244 Wh kg^–1 @ 693 W kg^–1) and power density (15 kW kg^–1 @ 151 Wh kg^–1). Further, pouch-type full cells are assembled, demonstrating the enormous applicability of this strategy.