Li-ion capacitors employ capacitive positive electrodes from electrochemical capacitors (ECs) and intercalation negative electrodes from Li-ion batteries (LIBs), bridging the performance gap between ECs and LIBs. However, the low capacity of capacitive positive electrodes limits the energy density of the Li-ion capacitors. Incorporating pseudocapacitance (surface redox reaction) into the carbon materials is a promising strategy to enhance the capacity of the carbon-based positive electrodes. We have been investigating the redox reactions of various organic materials with Li- and Na-ions for hybrid capacitor applications. We have revealed that the organic electrodes, which are prepared from pyrene derivatives,¹ hydrothermally synthesized carbon from glucose,² and polymerized dopamine,³ have redox reactions with Li- and (or) Na- ions. In this study, we further reveal that the organic electrodes can store high capacities in both Li- and Na-cells in the high voltage region by utilizing the redox reactions between oxygen functional groups and metal ions. Finally, we demonstrate the high-performance Li-ion capacitors by combining the organic positive electrode and high-energy battery negative electrode.

References

1. J. C. Bachman, R. Kavian, D. J. Graham, D. Y. Kim, S. Noda, D. G. Nocera, Y. Shao-Horn and S. W. Lee, Nature Communications, 6:7040 (2015).

2. T. Y. Liu, R. Kavian, Z. M. Chen, S. S. Cruz, S. Noda and S. W. Lee, Nanoscale, 8, 3671 (2016).

3. T. Liu, K. C. Kim, B. Lee, Z. Chen, S. Noda, S. S. Jang and S. W. Lee, Energy & Environmental Science, 10, 205 (2017).