3 years ago

Manipulating Adsorption–Insertion Mechanisms in Nanostructured Carbon Materials for High-Efficiency Sodium Ion Storage

Manipulating Adsorption–Insertion Mechanisms in Nanostructured Carbon Materials for High-Efficiency Sodium Ion Storage
Maria L. Sushko, Jun Liu, Xinmiao Liang, Yuyan Shao, Yuliang Cao, Mengyu Yan, Jiwen Feng, Liqiang Mai, Hanxi Yang, Xinping Ai, Lifen Xiao, Shen Qiu, Kee Sung Han
Hard carbon is one of the most promising anode materials for sodium-ion batteries, but the low Coulombic efficiency is still a key barrier. In this paper, a series of nanostructured hard carbon materials with controlled architectures is synthesized. Using a combination of in situ X-ray diffraction mapping, ex situ nuclear magnetic resonance (NMR), electron paramagnetic resonance, electrochemical techniques, and simulations, an “adsorption–intercalation” mechanism is established for Na ion storage. During the initial stages of Na insertion, Na ions adsorb on the defect sites of hard carbon with a wide adsorption energy distribution, producing a sloping voltage profile. In the second stage, Na ions intercalate into graphitic layers with suitable spacing to form NaC x compounds similar to the Li ion intercalation process in graphite, producing a flat low voltage plateau. The cation intercalation with a flat voltage plateau should be enhanced and the sloping region should be avoided. Guided by this knowledge, nonporous hard carbon material has been developed which has achieved high reversible capacity and Coulombic efficiency to fulfill practical application. An “adsorption–intercalation” (A–I) mechanism is established for Na ion storage by using a combination of in situ X-ray diffraction mapping, ex situ electron paramagnetic resonance, electrochemical techniques, and simulations. The “A–I” mechanism means that Na ions adsorb on the defect sites of hard carbon producing a sloping voltage profile and subsequently intercalate into graphitic layers producing a flat low voltage plateau in the second stage.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/aenm.201700403

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