A 2.6 V Flexible Supercapacitor Based on Al-MnO₂-Na₂SO₄//AC-KOH with High Specific Energy

In this work, we have synthesized Al-doped MnO 2 nanoparticles (Al-MnO 2 ) by rapid coprecipitation followed by hydrothermal and heat treatment. Al-MnO 2 shows a specific capacitance of 301.8 F g –1 at 1 A g –1 in a sample of 14% Al-MnO 2 -260 °C. The specific capacitance still remains at 206 F g –1 at 20 A g –1 . It also shows a good cycling stability with no capacitance degradation after 5000 cycles. More importantly, a new type of supercapacitor, Al-MnO 2 |PVA-Na 2 SO 4 //PVA-KOH|AC, has been designed using a Na 2 SO 4 -poly(vinyl alcohol)//cation exchange membrane//KOH-poly(vinyl alcohol)-based decoupled electrolyte. This device exhibits a specific capacitance of 68.9 F g –1 at 1 A g –1, corresponding to 64.7 Wh kg –1 at 1300 W kg –1 . It also delivers a good capacitance retention of ∼84% after 5000 cycles. The cell voltage is up to 2.6 V, which could light up a green light-emitting diode. The PVA-based decoupled gel electrolyte offers good processability to assemble flexible and foldable devices, which is important for mass production in manufacturing. These results clearly indicate that such high-voltage flexible supercapacitors with high specific energy are very promising in future wearable electronics.