Suppression of Dendrite Formation with Porous and Conductive Carbon on Anode for Aqueous Zinc-Ion Hybrid Capacitors

Abstract

Electrochemical energy storage systems with high power and energy density have been drawing attention with the increasing demand for electric vehicles and portable electronics. However, rechargeable nonaqueous lithium-based energy storage system, which is the most widely-used type, is still limited with unsafety, resulting from its toxic organic electrolyte and flammability. Hence, zinc has been considered a strong candidate in rechargeable aqueous energy storage systems. With high theoretical capacity (823 mAh g−1) and low operating potential (−0.76 V vs. standard hydrogen electrode), Zinc-ion batteries show the highest energy density among all aqueous batteries at low cost. Moreover, to improve the low power density and short cycle life for batteries, Zinc-ion hybrid capacitors (ZICs) are introduced by combining the characterizations of both battery and supercapacitor.Despite the advantages of ZICs mentioned above, the instability during the charging and discharging process are unneglectable. Formation of dendrites due to uneven zinc electrostripping and electroplating process on zinc metal anode can cause internal short-circuit after they penetrate the separators of the batteries. Hydrogen generation also results in low Columbic efficiency. To enhance electrochemically stability for zinc metal anode, a zinc anode modification with porous reduced graphene oxide (rGO) is reported.Electrostatic Spray Deposition (ESD) is a technique through which liquid droplets of a precursor solution are accelerated by a high DC voltage to form aerosol and deposit on the heated substrate. By coating rGO with ESD on zinc anode, the study of how the morphology of coating affects the electrostripping and electroplating process can be discussed in detail. The modified materials were examined by scanning electron microscopy and electrochemical active surface area. The porous rGO coated zinc anode shows small voltage polarization and long cycle life. With porous rGO coated zinc anode, the charge distribution on the electrode can be optimized, and the porous structure can guide pathways for zinc ions. Furthermore, the zinc deposition is much uniform than bare zinc during cycling, which can be observed in several operando techniques, including transmission X-ray microscopy and optical microscopy.