Hierarchical NiO/NiCo ₂ O ₄ Hollow Fuzzy Balls for High-Efficiency All-Solid-State Hybrid Pseudocapacitors

Amid the escalating requisites of global energy consumption, there is a pressing need for the advancement of scalable, efficient, and high-performance energy storage systems with high power sources for long-lasting cycling conditions; herein, a cationic surfactant-assisted kinetic growth strategy is employed to design NiO/NiCo 2 O 4 with a hierarchical hollow fuzzy ball microstructure, high BET surface area (88 m 2 g –1 ), and greater pore (bimodal) volume (0.31 cm 3 g –1 ), for integration in an all-solid-state hybrid pseudocapacitor (ASSHPC) device. The unique microstructural architecture and electrochemical attributes of the NiO/NiCo 2 O 4 material, including excellent redox reversibility, enhanced redox electroactive sites, negligible potential drop, predominant faradaic charge storage, lowly impeded diffusion resistance (0.22 Ω), low charge transfer resistance (0.46 Ω), and efficient OH – diffusion in its unique hollow fuzzy ball matrix, has led to its integration (as a positive electrode material) in a hybrid pseudocapacitor device with a sandwiched PVA–KOH electrolytic separator and N-rGO as the negative electrode material. The integrated NiO/NiCo 2 O 4 ||N-rGO ASSHPC device demonstrates excellent pseudocapacitive charge storage performance, including hybrid charge storage (combination of surface and diffusion-controlled mechanisms), insignificant ohmic potential loss under elevated current operations, excellent specific and rate-adaptive capacity/capacitance, high Ragone efficiency (maximum energy density of 22 Wh kg –1 and specific power of 4957 W kg –1 ), and 98.8% retention of its specific capacitance after 14,000 repeated charge–discharge cycles. The remarkable performance of the ASSHPC device is attributable to the presence of Ni- and Co-based mixed oxides that supplement abundant redox-active sites through the hollow fuzzy ball microstructure of the material, which becomes a pool for efficient electrolyte ion diffusion. The high electronic conductivity (of N-rGO) and ionic permeability (of PVA–KOH polymeric gel electrolyte) further increase the overall charge storage. The presented approach paves the way for advancement in positive electrode materials for the development of highly Ragone-efficient and durable pseudocapacitor devices tailored for integration into next-generation portable electronic architectures.