MnO2 Inks for the Fabrication of Supercapacitor Electrodes

The gap between electronics and users is becoming narrower as the portable electronics comes to wearable. As such, power supply, including storage devices, comes to wearable too. In addition to power and energy, specific characteristics are required for integration: lightweight, thickness, safety, washability, flexibility... and eventually hypoallergenic or biocompatibility. Facing these specifications, integration of storage devices such as Li-ion batteries or supercapacitors in clothes remains an exiting challenge. Supercapacitors based on pseudocapacitive metal oxide -based electrodes operated in neutral aqueous electrolytes could fit most of these requirements. The context of this study is the development of supercapacitor electrodes based on the deposition of MnO₂ onto flexible current collectors. Although various approaches have been investigated for the fabrication of high-performance flexible supercapacitors, they have to consider various material/device characteristics including intrinsic flexibility, mechanical integrity of the current collector/electroactive material assemble and retention of the electrochemical performances under stress. The material deposition onto flexible substrates can be carried out by electrodeposition, spin coating, spray or inkjet deposition [1]. Many surfactants have been used such as sodium dodecyl sulfate, Triton X100 or Caffeic acid, for the formulation of the complex MnO₂ particle suspensions required for the fabrication of homogeneous and performing electrodes by these latter techniques.

Figure: Cyclic voltammograms of Mn-oxide/free (a), Mn-oxide/SDS (b), Mn-oxide/CA (c), and Mn-oxide/TX100 (d) at a scan rate of 5 mV.s^-1 in 1M Na₂SO₄ aqueous electrolyte.

To enhance the rheological characteristics of the prepared inks, we have considered the use of these surfactants at the preliminary stages of the synthesis of MnO₂ particles by wet chemistry. The present study focuses on the impact of three different surfactants used for the synthesis by co-precipitation of MnO₂ on the (electro)chemical characteristics of the prepared powders. It also describes various approaches for the fabrication of supercapacitor electrodes based on these MnO₂ powders.

[1] J. Keskinen, E. Sivonen, S. Jussila, M. Bergelin, M. Johansson, A. Vaari, M. Smolander, Electrochimica Acta 85 (2012) 302-306