Pore and doping engineering of carbon cathodes for high-performance Zn-ion capacitors

Abstract

Pore engineering emerges as a critical strategy for improving carbon cathodes in Zn-ion capacitors (ZICs). Nevertheless, harmonizing the ratios of various pore levels, including macropores, mesopores, and micropores, to concurrently achieve superior Zn storage capacity and sustained cyclic stability within ZICs represents an ongoing and intricate challenge. In this work, we propose a novel pore and doping engineering strategy for the carbon cathode, achieving N-doped ordered macro-/meso-/microporous carbon (denoted as N-Macro/Meso/Micro-C) via templating methods. In which, the ordered interconnected macropores can provide channels for rapid electrolyte diffusion, the mesopores can act as intermediaries, bridging the gap between the macropores and micropores, optimizing the ion transport pathways, and the micropores can provide abundant active sites for Zn-storage. Furthermore, the introduction of N atoms within carbon enhances Zn-ion affinity and stability. As expected, ZICs assembled with the N-Macro/Meso/Micro-C cathode exhibit remarkable performance, delivering a high Max. energy/power density of 143.14 Wh kg⁻¹/40.1 kW kg⁻¹. Remarkably, after 50,000 cycles, the ZICs can retain 88 % of their initial capacity, illustrating robust cyclability. These advancements are further validated in flexible Zn-ion micro capacitors, showing excellent performance under mechanical stress. The colloidal crystal template-based pore engineering design philosophy will provide direction for the development of the next generation of high-performance Zn-ion based devices.