Dendrite-Free Zn-Ion Energy Storage Using Hybrid Electrolyte and 3D Printed Electrodes

The rapid growth of miniaturized and customized electronics has initiated constant drive towards efficient energy storage systems, featuring high safety, cost-effective fabrication, and innovative design. Among the various energy storage devices, eco-benign zinc (Zn)-ion capacitors with natural abundancy, intrinsic safety, high electrochemical performance, and great compatibility, has nowadays been widely conceded as the most promising power supply for various portable electronic devices. Nevertheless, the formation of Zn dendrites and unsatisfactory cycling lifetime ascribed by the localized electric field/undesired side reactions on Zn led to an internal short-circuit and dimnished electrochemical perforformance. Various methods have been designed to inhibit the Zn dendrite formation, which include surface modification and electrolyte optimization. Additionally, compared to the planar/thin film cathodes, design of three-dimensional (3D) electrodes with large surface area could be a promising approach to increase energy density of the Zn-ion capacitor. Recently, Direct Ink Writing (DIW) based 3D printing technology is emerging as a novel platform for the scalable development of 3D architectured electrodes for high-performance energy storage devices. The 3D printed porous electrodes holds several advantages, including large surface area and can be printable in customized shapes within small footprint areas. Herein, we designed DIW-based 3D printed graphene-carbon nanotubes (Gr-C) electrodes as cathode and hybrid electrolyte for high-energy density and dendrite-free Zn-ion capacitors. The hybrid electrolyte provides two key beneficial features on the anode and cathode, which are: a dynamic electrostatic shield layer and a pH regulating effect which reduces the irreversible side reactions and dendrites. In addition, the high surface area and the good electrical conductivity of the 3D printed 6L Gr-C cathode enable a dual-ion electrochemical mechanism with the hybrid electrolyte, which leads to a maximum capacity of 0.84 mAh cm^-2 and energy density of 0.87 mWh cm^-2 with good cycling stability. The rate performance of the 3D Gr-C//Zn cells are also evaluated using advanced electrochemical methods. This work demonstrates a pathway towards the cost-effective development of efficient electrolytes and highly conductive 3D electrodes for sustainable energy storage devices.