Solid-state 3D micro-supercapacitors based on ionogel electrolyte: Influence of adding lithium and sodium salts to the ionic liquid

The ever-increasing interest in miniaturized Internet of Things devices and embedded electronics has given rise to a host of inquiries surrounding the need for safe, high performance energy storage devices. Solid-state 3D micro-supercapacitors based on ionogels provide a promising response to many of these pressing questions. Herein, leakage-free solid-state-like 3D micro-supercapacitors incorporating lithium and sodium salts added to 1-Ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide-based ionogels were investigated. The resulting micro-supercapacitors containing these lithium and sodium ions displayed energy densities of 10.2 and 9.5 µWh.cm−2 at power densities of 1.1 and 1.0 mW.cm−2, respectively. In those devoid of these alkaline ions, however, the energy density reached a mere 3 µWh.cm−2 at the same power density, thereby validating the proposed strategy. The 3D interdigitated MnO2 // MnO2 micro-supercapacitors were cycled 50 000 times at 1.75 mA.cm−2 with good capacitance retention (∼ 85 %). While performing under high temperatures (100°C), there was no evidence of electrolyte degradation, capacitance fading or electrolyte leakage.