Molecular insights into the electric double-layer structure at a polymer electrolyte-electrode interface
Molecular insights into the electric double-layer structure at a polymer electrolyte-electrode interface
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DOI：
10.1016/j.electacta.2023.142131
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发表时间：
2023-03-04
影响因子：
6.6
通讯作者：
Shen, Caiwei
中科院分区：
文献类型：
--
作者：
Asha, Aysha Siddika;Iroegbu, Justice Nkemakolam;Shen, Caiwei
基于聚合物电解质的双电层超级电容器（EDLC）越来越多地被研究用于柔性、可穿戴和多功能储能应用。尽管电极材料在聚合物电解质中表现出比在液体电解质中显着更低的EDL电容的现象已被广泛观察到，但尚未得到很好的研究和解释。在这里，我们提出了一种代表性聚合物电解质基双电层电容器的分子动力学模拟，首次揭示了这种聚合物电解质-电极界面的原子结构。在石墨烯电极之间模拟由聚环氧乙烷和高氯酸锂组成的聚合物电解质，并与具有相同锂盐的水性电解质体系进行比较。我们发现基于聚合物的系统在内亥姆霍兹层和外亥姆霍兹层中显示出独特的 EDL 结构，这在水性系统中是看不到的。统计分析和从头计算表明，差异主要来自离子、聚合物或水分子与石墨烯电极之间的不同相互作用强度。尽管存在这些差异，但根据不同 EDLC 的各种模拟电荷状态计算出的固有界面电容显示出非常接近的值。结合实验测量，我们得出结论，文献中报道的聚合物电解质电容降低的原因是电极和电解质之间的界面不良，通过适当的热处理可以显着改善这种界面。
Polymer electrolyte-based electric double-layer supercapacitors (EDLCs) have been increasingly studied for flexible, wearable, and multifunctional energy storage applications. Although the phenomenon that electrode materials present significantly lower EDL capacitances in polymer electrolytes than in liquid electrolytes has been widely observed, it has not been well studied and explained. Here we present the molecular dynamics simulation of a representative polymer electrolyte-based EDLC to reveal the atomic structure of such a polymer electrolyte-electrode interface for the first time. The polymer electrolyte composed of polyethylene oxide and lithium perchlorate is simulated between graphene electrodes and compared with an aqueous electrolyte-based system with the same lithium salt. We find that the polymer-based system shows unique EDL structures in the inner and outer Helmholtz layers that are not seen in the aqueous one. Statistical analyses along with ab initio calculations show that the disparities mainly come from the different interaction strengths between ions, poly-mer or water molecules, and graphene electrodes. Despite these disparities, the intrinsic interfacial capacitances calculated from various simulated charge states of different EDLCs show very close values. Combined with experimental measurements, we conclude that the reduced capacitances with polymer electrolytes reported in the literature come from the poor interface between electrode and electrolyte, which can be significantly improved through proper thermal treatments.