Liquid-Crystalline MXene Inks Enable Stack-Free Thick Electrodes for High-Performance 3D-Printed Micro-Supercapacitors

The burgeoning development of portable electronics has stimulated an escalating need for miniaturized energy storage devices. On-chip microsupercapacitors (MSCs) offer high power density, excellent cycle stability, and enhanced safety features, making them attractive for portable electronics. The performance of these devices is strongly determined by the electrode material. Among various electrode material choices, MXenes are preferred due to their nanometer-thick layer structure, high conductivity, and redox-active surface. However, conventional electrode fabrication methods often lead to undesirable stacking of MXene nanosheets, which hinders ion transport and degrades the device performance. To tackle this challenge, we utilize MXene liquid crystal (MLC) to mitigate layer stacking and introduce a filtration method to produce a homogeneous, viscoelastic MLC ink, enabling the fabrication of thick electrodes by three-dimensional (3D) printing with controlled electrode properties, including nanosheet alignment, layer spacing, thickness, and device size. This technique yields stack-free, horizontally aligned MXene electrodes with thickness up to several hundred micrometers. The electrode architecture facilitates rapid ion transport, leading to MSCs with significantly higher energy and power densities (32.32 μWh cm^-2 and 8000 μW cm^-2, respectively) compared to those produced by traditional methods like inkjet printing, spray coating, and stamp printing. This technique holds promise for producing high-performance MSCs for diverse applications in wearable and flexible electronics.