Hybrid Aluminum-Ion Capacitor with High Energy Density and Long-Term Durability


 Hybrid capacitors have been extensively investigated owing to their potential applications in advanced devices to satisfy the requirements of high-energy, high-power, and extended cycle life. With the aim of significantly improving the performance of such devices, we propose a novel hybrid aluminum-ion capacitor (AIC) utilizing pore-size-controlled activated carbon as the cathode, Al foil as the anode, and an AlCl3-based ionic liquid as the electrolyte. The AIC exhibits high gravimetric and volumetric energy densities (51 W h kg−1 and 28 mW h cm−3, respectively), exceeding those of electrochemical double-layer capacitors and comparable to those of Li-ion capacitors. The hybrid device also exhibits a long-term cycle life, with a capacitance retention of 97.9 % after 10,000 cycles, and a coulombic efficiency of 97.6–99.9 % over a specific current range of 0.1–5.0 A g−1. Therefore, high-performance AICs, obtained by optimizing the electrode materials have the potential to be cost-effective and safe, with high-energy and power density.