Na ion battery electrode property of graphene-like molecules synthesized by fusing treatment of polycyclic aromatic hydrocarbons

摘要

In the past two decades, lithium ion batteries (LIBs) have been widely used as energy storage devices for several small electronic hardwares such as mobile phones, lap-top computers and so on because of the high energy density of LIBs. Recently it has become possible to use LIBs for large machines (e.g. electric vehicles). For such purpose, we need much more lithium metal resources. However, since the geographical distribution of lithium resources is limited, we would face a cost problem. Sodium ion battery (SIB) is of great interest to realize lithium-free energy storage. So far, SIB negative electrode properties of several kinds of carbon materials have been studied. Dahn et'al. [1] reported that sodium ions are likely to be inserted in the turbostratic structure and micropore space of porous carbons and to be attracted by hydrogen atoms of hydrocarbons. However, detailed intercalation mechanism has not been clarified yet. In order to investigate the mechanism, we need a systematic series of carbon samples in which the above-mentioned structural factors can be controlled and determined experimentally. Here, we prepared carbon materials by fusing treatments of two kinds of polycyclic aromatic hydrocarbons (PAH): coronene and pentacene. They have shown to be graphene-like molecules produced by thermal polymerization. We can control the polymerization degree of the fused PAHs by changing the heat treatment conditions. [2, 3] Using the structure controlled carbon sample, we investigated the sodium ion intercalation mechanism. We evaluated the sodium ion storage site by using the fused PAHs, and examined the relationship between the storage site and the amount of sodium ions stored electrochemically.