期刊
ADVANCED ENERGY MATERIALS
卷 11, 期 24, 页码 -出版社
WILEY-V C H VERLAG GMBH
DOI: 10.1002/aenm.202100700
关键词
hierarchy; ionic liquid; porous carbon; pulsed‐ field gradient NMR
类别
资金
- DFG [DV 58/2-2]
- Federal Ministry of Education and Research (BMBF) [03SF0498]
- Alexander von Humboldt Foundation
- HPC platform the Center for Information Services at TU Dresden
- Projekt DEAL
- High Performance Computing (ZIH) at TU Dresden
The article discusses a potentially critical feature in the design of supercapacitor electrodes, known as confinement-induced ion-solvent separation. Research shows that this effect can significantly slow down the migration speed of ions in pore networks. Explanations for the occurrence of this effect and ways to circumvent it are provided.
The rate of charging of supercapacitors depends on how quickly ions can reach and accommodate the surface of electrodes. Diffusivity, a parameter reflecting the speed of ions' migration, is believed to be crucial in designing supercapacitor electrodes. Herein, this belief is questioned, shedding light on a puzzling and potentially critical feature of ionic dynamics denoted as confinement-induced ion-solvent separation. This effect can lead to a strong slowdown of the ion mobility inside hierarchical pore networks. Explanations for when such an effect occurs and how it can be circumvented are provided. Furthermore, this microscopic picture of diffusion seen by NMR is bridged with the macroscopic charging behavior of supercapacitors investigated by impedance spectroscopy. Quantifying the average residence time of ions within carbon particles shows that the nanopore environment may not be the rate-limiting factor for the overall ion mobility and thus performance of a cell-as commonly expected. Combining direct diffusion studies performed with neat and solvated ionic liquids and those on organic electrolytes, the so far lacking criteria for the rational selection of electrolyte-carbon systems is developed and recommendations for the preparation of transport-optimized materials for supercapacitors to minimize ionic diffusion limitations are given.
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