Interface optimization strategy for high reliability MIM-type aluminum electrolytic capacitors

Metal-insulator–metal aluminium electrolytic capacitors (MIM-AECs) combines high capacity-density and high breakdown field strength of solid AECs with high frequency responsibility, wide working temperature window and waterproof properties of MIM nanocapacitors. However, diffusion and defects at multilevel interfaces hinder the development of high-breakdown, high-reliability devices. Herein, we successfully fabricated highly reliable MIM-AECs with ultra-high breakdown field strength (6.5 MV/cm) and low leakage current (1.1 × 10^-8 A/cm², four orders of magnitude lower than previously reported). This was achieved by introducing a buffer layer ALD-Al₂O₃ at the cathode/dielectric (SnO₂/AAO) interface and passivating defective sites at the SnO₂/Al₂O₃/AAO multi-interface. The buffer layer effectively inhibits Sn atom diffusion at the SnO₂/AAO interface, thereby ensuring a high breakdown field strength for the dielectric layer AAO. Simultaneously, oxygen plasma activation combined with H₂O vapor treatment introduces –OH active sites, leading to a high-quality MIM interface with reduced defects. Additionally, the device utilizes ALD technology for high SnO₂ cathode coverage on the porous dielectric/anode, resulting in high energy density (1.41 µWh/cm²) and power density (17.5 W/cm²), low tan δ (1.7 %), a phase angle of −89.7°, as well as wide temperature (−60 °C ∼ 326 °C) and humidity resistance (100 % RH). It also exhibits excellent circuit filtering under 1 V-8 V and charging/discharging performance. This work presents an important step for high-reliability MIM-AECs towards practical applications for energy storage systems in harsh environments.