Hybrid Aluminum‐Ion Capacitors for High‐Temperature Energy Storage: Commercial Viability and Performance Evaluation

Hybrid capacitors capable of stable operation at 85°C remain underdeveloped despite the demand for energy‐storage systems in electric vehicles, grid storage, aerospace systems, and other thermally demanding applications, where additional cooling increases system size and complexity. Conventional supercapacitors (SCs) and lithium‐ion capacitors (LICs) are constrained at elevated temperatures by organic‐electrolyte instability and interfacial degradation. Herein, we present a hybrid aluminum‐ion capacitor (AIC) using commercially available activated carbon (AC) as the cathode, aluminum foil as the anode, and an AlCl 3 /[EMIm]Cl ionic liquid electrolyte. At 25°C, the AIC delivered 14 mWh cm −3 at 81 mW cm −3 , approximately twice that of the AC‐based SC and comparable to that of an LIC. At 85°C, the energy density increased to 25.4 mWh cm −3 , 1.8 times the room‐temperature value, with performance comparable to that reported for SCs and an LIC developed for high‐temperature operation. This improvement is associated with increased ionic conductivity and temperature‐dependent changes in the charge‐storage behavior. Above 55°C, the capacitance increase is associated with an increased diffusion‐controlled contribution, which may include thermally facilitated ion transport within confined pores of the AC cathode and enhanced aluminum interfacial charge‐transfer kinetics. Structural and surface analyses indicated no significant degradation of the AC cathode or aluminum anode during high‐temperature operation. The AIC retains 83.5% of its initial capacitance after 10 000 cycles at 85°C, and pouch‐type cells power an LED at 25°C and 85°C. These findings demonstrate the potential of AICs based on commercially available electrode materials for thermally demanding energy‐storage applications.