Enhanced performance of flexible asymmetric supercapacitors via furnace and atmospheric-pressure plasma jet treatments of lithium manganese oxide and reduced graphene oxide

Abstract

Asymmetric supercapacitors (ASCs), compared to symmetric supercapacitors (SSCs), exhibit a higher operating voltage and greater energy density, thereby playing a significant role in energy storage. In this study, screen printing was utilized to separately deposit slurries of reduced graphene oxide (rGO) and LiCl–Mn(NO₃)₂·4H₂O onto a carbon cloth substrate. The electrodes were then treated using a furnace and nitrogen atmospheric pressure plasma jet (APPJ) to convert LiCl–Mn(NO₃)₂·4H₂O into LiMn₂O₄. Subsequently, the rGO electrode, LiMn₂O₄ electrode, and PVA-Li₂SO₄ gel electrolyte were combined to form rGO/LiMn₂O₄ flexible ASC. The results of electrochemical measurement showed that the ASCs treated with a combination of furnace and APPJ exhibited better performance compared to those treated with APPJ alone. At a charging/discharging current of 4 mA, the areal capacitance of ASC treated with APPJ is 5 times higher than that of the untreated sample. Furthermore, the areal capacitance after combined furnace and APPJ treatments is improved by 7.5 times compared to the untreated sample. This improvement is likely due to the more uniform and prolonged heating provided by the furnace, allowing the pastes to more completely be converted into LiMn₂O₄ and coat the carbon cloth fibers more evenly. Bending tests and stability tests were also conducted. The results showed that the ASCs treated with both the furnace and APPJ exhibited excellent performance under different curvatures. After 3000 charge-discharge cycles, the retention rate was 94.5 %. This study discovered an effective method for converting metals into metal oxides. Moreover, it demonstrates excellent retention rates during bending and stability tests.