Novel Asymmetric Capacitors Using Intercalated Metal-Organic Framework Negative Electrodes

We propose a novel intercalated metal–organic framework (iMOF) electrode material, 2,6-naphthalene dicarboxylate dilithium (2,6-Naph(COOLi)₂) as a next-generation negative electrode material for advanced lithium-ion batteries or asymmetric capacitors.

This iMOF material exhibits an operating potential of 0.8 V (vs. Li/Li⁺) between those of graphitic carbon, operating at 0.1 V, and Li₄Ti₅O₁₂, operating at 1.55 V. Given the risks of an internal short circuit because of lithium metal deposition in the case of graphitic carbon electrodes and cell-voltage reduction in the case of high-operating-potential Li₄Ti₅O₁₂ electrodes, this iMOF material possibly represents an advantageous battery design. In addition, because Al can be used as a current collector for this iMOF negative electrode material, whose operating potential is more positive than the potential of the Li–Al alloy reaction (0.4 V), it can potentially be used as a negative electrode material in high-voltage bipolar batteries using only Al current collector.

The proposed electrode material has an organic-inorganic layered structure of p-stacked naphthalene and tetrahedral LiO₄ units (Figure 1(a)), and shows a reversible two-electron-transfer Li intercalation (220 mAh g^-1) at a flat potential of 0.8 V vs. Li/Li⁺ with a small polarization (Figure 1(b)). ^{1, 2} Detailed crystal structure analysis during Li intercalation of this material shows the layered framework to be maintained and its volume change is only 0.33%. This value is much lower than that of the conventional Li-intercalated electrode materials such as graphite (ca. 10%) and Li transition metal oxides (~ 10%). Furthermore, the proposed material exhibits improved regularity of p-stacked packing via self-organization induced by heat treatment under inert atmosphere; this improved packing led to an improvement of reversible capacity as well as to a reduction of internal resistance.³

We examined the device performance of novel asymmetric capacitors comprising the iMOF negative and activated carbon positive electrodes. In this presentation, the possibility of the iMOF as the negative electrodes for asymmetric capacitors will be discussed.

References

1.           N. Ogihara, Y. Kishida, T. Ohsuna, K. Miyamoto and N. Ohba, in Meeting Abstracts of 17th International Meeting on Lithium Batteries, p. 320 (2014).

2.           N. Ogihara, T. Yasuda, Y. Kishida, T. Ohsuna, K. Miyamoto and N. Ohba, Angew. Chem. Int. Ed., 53, 11467 (2014).

3.           T. Yasuda and N. Ogihara, Chem. Commun., 50, 11565 (2014).