Flexible electronic devices based on smart fabrics are generating a vast amount of interest and increasing efforts are being devoted to their development. In the next future, smart textiles will integrate diverse functions such as energy harvesting, human health monitoring and more. As a consequence, the development of flexible energy storage as a mean to power wearable devices has become ever more urgent.

Among the manufacturing techniques for flexible batteries and capacitors, inkjet printing has cemented itself as one of the most popular, mainly thanks to its versatility and simplicity. In this scenario, a great effort is being devoted towards research and development of innovative, more sustainable materials that satisfy the requirements for both printability and energy storage capabilities. [1] Prussian blue analogues (PBA) are a class of materials that have been studied extensively as cathodic materials for a wide variety of energy storage devices, such as Li-ion batteries, Na-ion batteries, Zn-ion batteries, and supercapacitors. [2] Their open framework structure allows reversible intercalation of hydrated cations, making them perfectly compatible with aqueous electrolytes. Thanks to this feature, along with their agile synthetic route, low cost and benign nature of their precursors, PBA are regarded as one of the most promising materials for future energy storage devices. [3]

Despite their increasing popularity, inkjet printing of PBA for flexible energy storage devices has not been reported yet. In this work, inkjet printing of PBA is proposed as a viable technique to manufacture flexible asymmetric supercapacitors with a Ti₃C₂ MXene anode. MXenes are a new class of 2D materials which have gained a lot of interest due to their metallic conductivity and exceptional water processability. While their use in symmetric capacitors has already been demonstrated, these devices tend to operate in a small potential window (≈ 500 mV) as to prevent unwanted MXene oxidation, which limits their specific power. [4] By coupling the MXene anode with a PBA cathode, it is therefore possible to extend the potential window of the device and consequently the power that can be delivered.

Prussian blue analogues powders are synthesized by the traditional co-precipitation route. Printable, water-based inks containing the PBA particles are then used to manufacture flexible electrodes on various substrates. Electrochemical characterization is carried out in custom, 3D printed, three electrodes cells, allowing for non-destructive testing of the printed electrodes. Finally, the electrochemical properties of the capacitors will be tested in aqueous electrolytes as well as with semi-solid electrolytes at rest and under mechanical deformation.

Bibliography

[1] K. H. Choi, D. B. Ahn, and S. Y. Lee, “Current Status and Challenges in Printed Batteries: Toward Form Factor-Free, Monolithic Integrated Power Sources,” ACS Energy Lett., vol. 3, no. 1, pp. 220–236, Jan. 2018.

[2] G. Du and H. Pang, “Recent advancements in Prussian blue analogues: Preparation and application in batteries,” Energy Storage Mater., vol. 36, pp. 387–408, Apr. 2021.

[3] B. Wang et al., “Prussian Blue Analogs for Rechargeable Batteries,” iScience, vol. 3, pp. 110–133, May 2018.

[4] D. Wen et al., “Inkjet Printing Transparent and Conductive MXene (Ti3C2Tx) Films: A Strategy for Flexible Energy Storage Devices,” ACS Appl. Mater. Interfaces, vol. 13, no. 15, pp. 17766–17780, Apr. 2021.