Rathnayake R M N M, Duignan Timothy T, Searles Debra J, Zhao X S
School of Chemical Engineering, The University of Queensland, St Lucia, Brisbane 4072, Australia.
Centre for Theoretical and Computational Molecular Science, Australian Institute for Bioengineering and Nanotechnology, The University of Queensland, Brisbane, QLD 4072, Australia and School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, QLD 4072, Australia.
Phys Chem Chem Phys. 2021 Feb 4;23(4):3063-3070. doi: 10.1039/d0cp06134d.
Expanded graphite (EG) has been shown to be able to store a significant amount of sodium ions. Understanding the alkali metal ion storage in EG is of importance for improving EG electrode performance. In this work, the effect of interlayer distance of pure EG on sodium ion storage was investigated using the density functional theory calculation method. EG structure models with interlayer distances ranging from 3.4 Å to 10.0 Å were simulated. It was found that EG can store a fairly large amount of sodium ions through an intercalation mechanism without any contributions from the co-intercalation mechanism or adsorption mechanism if the interlayer distance is larger than 4.4 Å and smaller than 6.0 Å. It was also found that an interlayer distance of 6.0 Å gives strong binding energy of sodium ions with EG forming thermodynamically stable sodium-graphite intercalation compound (Na-GIC). However, when the interlayer distance becomes larger than 6.0 Å, the binding energy between sodium ions and EG becomes weaker. Computational results have also shown that the enthalpy of formation of the Na-GIC of EG is energetically more favourable when the interlayer distance is increased. An optimal d-spacing of EG for sodium ion storage was identified in this work. These findings provide atomistic insights into sodium ion storage in EG, providing guidelines for the design of graphite-based anode materials for sodium-ion batteries.
膨胀石墨（EG）已被证明能够存储大量的钠离子。了解EG中碱金属离子的存储对于提高EG电极性能至关重要。在这项工作中，使用密度泛函理论计算方法研究了纯EG层间距对钠离子存储的影响。模拟了层间距范围从3.4 Å到10.0 Å的EG结构模型。研究发现，如果层间距大于4.4 Å且小于6.0 Å，EG可以通过嵌入机制存储相当数量的钠离子，而无需共嵌入机制或吸附机制的任何贡献。还发现层间距为6.0 Å时，钠离子与EG具有很强的结合能，形成热力学稳定的钠-石墨插层化合物（Na-GIC）。然而，当层间距大于6.0 Å时，钠离子与EG之间的结合能变弱。计算结果还表明，当层间距增加时，EG的Na-GIC形成焓在能量上更有利。这项工作确定了EG用于钠离子存储的最佳d间距。这些发现为EG中钠离子存储提供了原子层面的见解，为钠离子电池石墨基负极材料的设计提供了指导。
