# Iodine-Doped Hollow Carbon Nanocages without Templates Strategy for Boosting Zinc-Ion Storage by Nucleophilicity

## TL;DR

A new method creates iodine-doped carbon nanocages to improve zinc-ion storage in energy systems.

## Contribution

A template-free strategy for making iodine-doped carbon nanocages that enhance zinc-ion storage through nucleophilicity.

## Key findings

- Iodine-doped carbon nanocages achieved a high capacity of 134.2 mAh/g at 1 A/g.
- The nanocages delivered an energy density of 114.1 Wh/kg and a power density of 42.5 kW/kg.
- I3− anions showed stronger bonding with Zn2+ than I5− anions in the nanocages.

## Abstract

Zn-ion hybrid supercapacitors (ZHCs) combining merits of battery-type and capacitive electrodes are considered to be a prospective candidate in energy storage systems. Tailor-made carbon cathodes with high zincophilicity and abundant physi/chemisorption sites are critical but it remains a great challenge to achieve both features by a sustainable means. Herein, a hydrogen-bonding interaction-guided self-assembly strategy is presented to prepare iodine-doped carbon nanocages without templates for boosting zinc-ion storage by nucleophilicity. The biomass ellagic acid contains extensional hydroxy and acyloxy groups with electron-donating ability, which interact with melamine and ammonium iodide to form organic supermolecules. The organic supermolecules further self-assemble into a nanocage-like structure with cavities under hydrothermal processes via hydrogen-bonding and π-π stacking. The carbon nanocages as ZHCs cathodes enable the high approachability of zincophilic sites and low ion migration resistance resulting from the interconnected conductive network and nanoscale architecture. The experimental analyses and theoretical simulations reveal the pivotal role of iodine dopants. The I5−/I3− doping anions in carbon cathodes have a nucleophilicity to preferentially adsorb the Zn2+ cation by the formation of C+-I5−-Zn2+ and C+-I3−-Zn2+. Of these, the C+-I3− shows stronger bonding with Zn2+ than C+-I5−. As a result, the iodine-doped carbon nanocages produced via this template-free strategy deliver a high capacity of 134.2 mAh/g at 1 A/g and a maximum energy and power density of 114.1 Wh/kg and 42.5 kW/kg.