High Volumetric Quasi‐Solid‐State Sodium‐Ion Capacitor under High Mass Loading Conditions

Abstract The sodium‐ion capacitor (NIC) represents an important research approach to bridge the gap between batteries and capacitors, but is still limited by inferior energy behavior at high power, low volumetric performance, low electrode mass loading, and safety issues with conventional liquid electrolyte. Herein, a high‐performing, kinetically superior, and safer quasi‐solid‐state NIC utilizing the fast sodium storage in TiO 2 and rapid ion adsorption on a biomass‐derived porous carbon with a sodium‐ion conducting P(VDF‐HFP) gel polymer electrolyte is presented. Owing to high mass loading, low graphene content in TiO 2 , and by overcoming the diffusion‐limited sodium storage by surface limited storage enable the NIC to deliver an impressive volumetric energy of ≈89 Wh L −1 (94 Wh kg −1 ) based on total mass in both electrodes. Also, a remarkable power of ≈9.4 kW L −1 (10 kW kg −1 ) while retaining an energy of ≈28.7 Wh L −1 (30.6 Wh kg −1 ) is attained. Furthermore, the NIC shows a long‐term stability both at room temperature and high temperature (50 °C), outperforming conventional NICs. This research opens new opportunities for applications of high‐performing and safer NICs in next‐generation storage devices requiring high energy at high power with high safety.