Chemically tailored hollow Co@N-doped carbon nanoboxes with dual-phase synergy for high-energy and long-life lithium-ion capacitors

Abstract

Hollow-structured materials have gained considerable attention for their potential in alleviating the volume expansion of electrode materials; however, their controllable synthesis remains a critical challenge. This research presents a simple method for the synthesis of hollow Co@C composites through the derivatization of ZIF-67 via a chemical etching-coordination process and subsequent pyrolysis. The resulting nitrogen-doped carbon nanocubes exhibit a unique hollow structure with highly dispersed cobalt nanoparticles integrated into mesoporous carbon walls (denoted as H-Co@NCs). This structure mitigates volume expansion, ensures stable electrical contact, and offers numerous active sites, facilitating the storage and diffusion of lithium ions. The H-Co@NCs anode displays an impressive reversible capacity of 734.4 mAh g⁻¹ at 0.1 A g⁻¹ and notable cycling stability, maintaining 270 mAh g⁻¹ after 1000 cycles at 2 A g⁻¹. The assembled lithium-ion capacitor (LIC) with H-Co@NCs as the anode and activated carbon as the cathode achieves a high energy density of 151.3 Wh kg⁻¹ and a power density of 35.9 kW kg⁻¹, retaining over 88.4 % capacity after 40,000 cycles. This research presents a viable strategy for creating advanced energy storage materials to balance power and energy density for practical LIC applications.