High-load Ti3C2 MXene cathode through surface modification for degradable aqueous zinc-ion micro-supercapacitors with excellent energy density and anti-self-discharge

Micro Zn-ion supercapacitors (MZSCs) with excellent power density and safety are considered the most promising micro-energy storage devices. However, the energy density per unit area of these devices is insufficient to meet the requirements for portable/wearable electronics. Furthermore, traditional energy storage devices produce a large amount of e-waste, causing serious environmental hazards. To solve these problems, degradable MZSCs are proposed based on high-load surface-modified MXene (O-Ti3C2 MXene) cathodes and Zn/carbon nanotube (CNT) anodes. Owing to the advantages of their three-dimensional interconnected microstructures and abundant oxygen-rich functional groups, the thick O-Ti3C2 MXene electrodes show high rate performances and excellent Zn2+ diffusion kinetics. Therefore, MZSCs exhibit an extremely high energy density (384.90 μWh cm−2 at 0.30 mW cm−2) and power density (6.0 mW cm−2 at 126.84 μWh cm−2) and are degradable. More importantly, because of the strong adsorption capacity of the O-Ti3C2 MXene cathode for SO42− and the redox reaction of Zn/Zn2+ in the Zn/CNT anode, MZSCs have an extremely low self-discharge rate (1.92 mV h−1). This research is expected to provide a promising direction for next-generation, high-performance, anti-self-discharge and degradable devices.