“Nano Reservoir” of Dual Energy Storage Mechanism for High-Performance Sodium Ion Capacitors

Transitioning the cathodic energy storage mechanism from a single electric double layer capacitor to a battery and capacitor dual type not only boosts the energy density of sodium ion capacitors (SICs) but also merges performance gaps between the battery and capacitor, giving rise to a broad range of applications. In this work, Na₃V₂(PO₄)₃ (NVP) is preconfigured in activated carbon (AC) as a “nano reservoir” of sodium ions and electrons to stimulate the synergy between the hybrid energy storage mechanisms, resulting in a more comprehensive electrochemical performance of the AC/NVP hybrid cathode than a pure AC or NVP cathode. The hybrid cathode of AC/NVP-90 exhibits superior specific capacities at low and high current densities over those of AC (133 vs 102 m Ah g^-1@0.05 A g^-1) and NVP (100 vs 35 m Ah g^-1@16 A g^-1). Meanwhile, the SICs composed of an AC/NVP hybrid cathode and a microsized bismuth (Bi) anode have a regulated energy/power density and cycle life metrics (∼218.6 Wh kg^-1/∼22.7 kW/∼14,000 cycles), which could provide specific guidance of energy-power-life output dependency at a specific working and expense condition. Therefore, this work demonstrates feasibility for broad practical development of sodium ion energy storage devices with bespoke performances.