Femtosecond Laser‐Etched MXene Microsupercapacitors with Double‐Side Configuration via Arbitrary On‐ and Through‐Substrate Connections

Abstract The capacitance of microsupercapacitors (MSCs) can double if both sides of substrates are used to construct MSCs. Nevertheless, achieving electric connections of MSCs through substrates is a challenge due to the difficulty in precisely positioning each MSC couple that has two of the same MSCs units on two sides. In this work, taking advantage of the synchronous etching on both sides of transparent polyethylene terephthalate substrates by femtosecond laser pulses, a double‐sided configuration is attained with high precision in the alignment of back‐to‐back MSC couples and versatile double‐side MSCs are realized via arbitrary on‐ and through‐substrate connections of MXene MSC units. The MXene double‐side MSC fabricated by the series connection of 12 spiral pattern MXene MSC units with interdigital electrodes of 10 μm width interspace can output a large working voltage of 7.2 V. Additionally, femtosecond laser etching brings the transformation of MXene into titania near‐etched edges with a lateral distance less than 1 µm. Such a small laser‐affected area has little influence on the capacitive performance, which is one of advantages for femtosecond laser over conventional lasers. This research is valuable for one‐step manufacturing of highly integrated MSCs in the field of miniaturized energy storage systems.