Nanoporous core–shell–structured multi-wall carbon nanotube/graphene oxide nanoribbons as cathodes and protection layer for aqueous zinc-ion capacitors: Mechanism study of zinc dendrite suppression by in-situ transmission X-ray microscopy

Recently, owing to the increasing demand for wearable electronics, it is necessary to investigate flexible and highly safe energy storage devices. Commonly used energy storage devices, such as lithium-ion batteries and supercapacitors with organic electrolytes, may suffer from fire and explosion. Therefore, zinc-ion capacitors (ZICs) with nontoxic and nonflammable aqueous electrolytes have recently attracted considerable attention. In this study, high-surface-area nanoporous core-shell-structured multiwalled carbon nanotube@graphene oxide nanoribbon (NP-MWCNT@GONR) is used as the cathode material in aqueous ZICs for the first time. These ZICs exhibit a high energy density of 90 Wh kg⁻¹ at 95 W kg⁻¹ and a high power density of 19 kW kg⁻¹ at 31 Wh kg⁻¹. The cycling retention is 86.5% after 200 cycles; however, the device fails after 200 cycles owing to the formation of zinc dendrites on the anode. To suppress dendrite formation, NP-MWCNT@GONR-coated zinc anode and freeze-dried gel electrolyte are used, and the cycle life is extended beyond 2000 cycles. In-situ synchrotron transmission X-ray microscopy is performed during charging and discharging, which demonstrates that the gel electrolyte and the NP-MWCNT@GONR-coated zinc anode can effectively inhibit dendrite formation. This study reveals that ZICs with NP-MWCNT@GONR cathodes, NP-MWCNT@GONR-coated zinc anode, and gel electrolytes are highly safe energy storage devices for use in flexible and wearable electronics.