3D Vertical Arrays of Nanomaterials for Microscaled Energy Storage Devices

The ever-growing market of miniature and autonomous electronics has motivated an upsurge of interest in exploiting microscaled energy storage devices (MESDs) such as microbatteries and microsupercapacitors. To meet the burgeoning demand for energy, electrodes with high mass loading to synchronously raise areal energy and power are extensively pursued. Increasing the thickness of the conventional thin-film electrode to augment the areal loading is not a feasible approach, as it leads to elongated solid diffusion path, thereby limiting the power output of microdevices. This scenario is more unfavorable for solid-state microdevices because ion diffusion in solid electrolytes is more sluggish than in liquid electrolytes. To tackle such a dilemma, adoption of 3D array electrodes has been proposed to pave a new path for the design and development of MESDs. In comparison with 2D electrode geometries, the state-of-the-art designs of 3D vertical arrays have proved very effective in mitigating the manufacture and performance challenges related to MESDs. First of all, thick electrodes with high loading can be engineered while the nanoscale diffusion of ions is maintained, thus significantly enhancing areal energy without compromising the power output. Second, electrodes based on arrays grown on conductive substrates waive the addition of binders and conducting agents, thereby remarkably simplifying the fabrication procedures and reducing the processing cost. Third, the presence of organized channels in the electrode arrays not only accelerates ion diffusion, but also offers enough space to accommodate the electrode swelling upon energy storage. Fourth, 3D arrays possess large surface areas and massive reactive sties, enabling relatively homogeneous current distribution throughout the electrode surface. In the past few years, we have developed several techniques to design and produce 3D vertical electrode arrays for robust microenergy storage. Through 3D electrode design, substantial improvement in the energy and power within a given footprint area has been achieved. In this Account, we highlight such improvements and progresses in our groups as well as some critical advancements acquired in other teams. As research in this area is still at an early stage, the majority of the important progresses is embodied in the form of materials design and electrode fabrication. The remaining challenges and possible solutions are discussed, and insights for further research are also proposed.