In this study, we investigate K ordering and its impact on K intercalation and storage capacity in graphite, bilayer and single-layer graphene through two-dimensional cluster expansion implemented in first-principles calculations with van der Waals corrections. For graphite, similar to the Li counterpart, K intercalation exhibits a multistage feature as the K concentration increases from C to KC. However, beyond KC, K atoms become crowded in graphite, resulting in a negative discharge voltage. For bilayer and single-layer graphene, a noticeable displacement of K from original hexagonal sites occurs at higher K concentrations compared to graphite. K intercalation in graphite after the initial segment (from C to KC) leads to an increase in interlayer distance, while in bilayer graphene causes much larger elongation in interlayer distance. The calculated overpotential for K intercalation on bilayer and single-layer graphene is found to be 0.17 and 0.13 V, respectively, which is lower than the overpotential (0.86 V) observed on graphite. The charge redistribution between K and carbon layers indicates that bilayer and single-layer graphene offer pseudo-capacitance, facilitating faster charge transfer and higher K capacity. The above observation suggests the graphene structures have a superior K-storage capacity compared to graphite.

中文翻译：

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通过二维簇扩展建模揭示石墨烯及其变体上的 K 插层


在这项研究中，我们通过范德华校正的第一性原理计算中实现的二维簇扩展，研究了 K 有序性及其对石墨、双层和单层石墨烯中 K 插层和存储容量的影响。对于石墨来说，与 Li 类似，随着 K 浓度从 C 增加到 KC，K 插层表现出多阶段特征。然而，超出 KC 后，K 原子会在石墨中变得拥挤，导致负放电电压。对于双层和单层石墨烯，与石墨相比，当 K 浓度较高时，K 会从原始六方位点发生明显位移。在石墨中初始段（从 C 到 KC）之后的 K 插层导致层间距离增加，而在双层石墨烯中则导致层间距离更大的伸长。双层和单层石墨烯上 K 插层的计算过电势分别为 0.17 和 0.13 V，低于在石墨上观察到的过电势 (0.86 V)。 K层和碳层之间的电荷重新分布表明双层和单层石墨烯提供赝电容，有利于更快的电荷转移和更高的K容量。上述观察结果表明，与石墨相比，石墨烯结构具有优异的储钾能力。