ZIF-derived nitrogen-doped carbon/silicon composites for asymmetric lithium-ion capacitors

Lithium-ion capacitors (LICs) are attracting interest as energy storage devices that bridge the gap between batteries and supercapacitors, offering both high energy and power density. However, the challenge lies in developing electrode materials that can combine high capacity with long-term stability. Silicon, despite its high theoretical capacity, suffers from severe volume changes during cycling, while traditional carbon materials are stable but often lack sufficient capacity. Herein, a ZIF-8-derived nitrogen-doped porous carbon (NPC) framework was employed as a conductive scaffold to stabilize silicon nanoparticles (Si NPs) for high-capacity anodes. Si NPs were incorporated into the porous NPC network via solvothermal treatment and anchored by subsequent pyrolysis, producing an NPC/Si composite in which NPC serves as the N-doped carbon matrix and a continuous electron pathway. In the NPC/Si anode composite, the micropore-dominated porosity and mechanical flexibility of NPC provide ion-accessible voids to buffer silicon volume expansion upon lithiation and sustain a robust carbon–silicon contact during cycling, nitrogen doping enhances electronic conductivity and interfacial affinity, and silicon contributes high lithium-storage capacity. These features together enable enhancing electrode stability and capacity retention. The NPC/Si anode electrode with 8.7% silicon content delivered 1053 mAh g −1 at 0.1 A g −1 and sustained 230 mAh g −1 after 1000 cycles at 5 A g −1 . When paired with a high-power ZIF-8-derived NPC-900 capacitive cathode, the NPC-800/Si-8.7||NPC-900 LIC device delivered 244 Wh kg −1 at 395.8 W kg −1 and maintained 71.5 Wh kg −1 at 5789.5 W kg −1 . It retained 80% of its capacity after 5000 cycles, after which the capacity gradually declined to ∼70% with 15,000 cycles. This dual utilization of ZIF-8-derived carbon is a promising way to develop high-energy LIC systems with long-term cyclability.