Durable Zn-ion hybrid capacitors using 3D printed carbon composites

Rechargeable Zn-ion hybrid capacitors (ZHCs) have gained considerable attention towards future energy storage applications owing to their non-flammable nature, high abundance of raw materials and remarkable energy storage performance. However, the uncontrolled growth of dendrites, interfacial corrosion of Zn anodes and limited mass loading of cathode materials, hinders their practical applicability. Herein, we demonstrate ZHCs with enhanced capacity and durability using a synergistic combination of a hybrid-ion electrolyte and a high-mass loading three-dimensionally (3D) printed graphene-carbon nanotube (Gr-C) cathode. The hybrid electrolyte composed of NaCl and ZnSO4, features higher ionic conductivity and lower pH compared with pristine ZnSO4, which enable uniform plating/stripping of Zn2+ ions on Zn anode, as demonstrated by in situ electrochemical and ex situ ToF-SIMs characterizations. Additionally, the multi-layered 3D Gr-C composite electrodes in ZHCs enable higher energy storage performance due to their porous architectures, high ion accessibility and dual-ion charge storage contributions. As a result, the 3D Gr-C//Zn cell unveiled a maximum capacity of 0.84 mA h cm(-2) at 3 mA cm(-2) with a high life cycle (78.7% at 20 mA cm(-2)) compared to the pristine electrolyte-based ZHCs (0.72 mA h cm(-2) and 14.8%). The rapid rate measurements that we propose along with benchmarked energy density (0.87 mW h cm(-2)) and power density (31.7 mW cm(-2)) of hybrid electrolyte-based 3D Gr-C//Zn, pave the way for the development of dendrite-free and highly durable 3D energy storage devices.

Automated summary

This study demonstrates the enhanced capacity and durability of rechargeable Zn-ion hybrid capacitors (ZHCs) using a hybrid-ion electrolyte and a high-mass loading three-dimensionally printed graphene-carbon nanotube (Gr-C) cathode. The hybrid electrolyte with higher ionic conductivity and lower pH enables uniform plating/stripping of Zn2+ ions on Zn anode, while the multi-layered 3D Gr-C composite electrodes contribute to higher energy storage performance. The proposed 3D Gr-C//Zn cell shows promising results in terms of capacity and cycle life, paving the way for dendrite-free and durable 3D energy storage devices.