Comparative Study of the Power Performance for Advanced Li-Ion Capacitors with Various Carbon Anodes

Lithium-ion Capacitors (LICs) have attracted much attention as a new power source due to its high energy density compared to conventional electric double-layer capacitors (EDLCs), and its high power density compared to batteries as well as having the long cycle life. Recently, some research work^1-2 in our group has been done on LICs. In this abstract, various carbon material anode electrode including hard carbon, soft carbon and graphite were studied and compared for the Li-ion Capacitors application.

To compare the hard carbon, soft carbon and graphite, three Li-ion capacitor full cells with these carbon electrodes were assembled to compare the power and cycle performance. Figure 1 presents the voltage profiles of the LIC full cells with various carbon electrodes. It can be seen that the swing potential of hard carbon and soft carbon anode electrodes is in a wider range than graphite electrodes. The swing potential range of hard carbon and soft carbon negative electrodes is 0.2-0.4 and 0.4-0.7 V vs. Li/Li⁺, respectively; which are above 0 V vs. Li/Li⁺ and can suppress the formation of lithium dendrites in anode to a large extent. On the other side, the potential plateau of graphite anode electrode is near 0 V vs. Li/Li⁺, which increases the possibility for lithium dendrites to form and short the LIC cells.

The LIC full cells with various carbon electrodes were also tested in Figure 2. This was done in order to compare the energy, power and cycle performance. It can be obviously observed from Figure 2(a) that LIC full cell with hard carbon electrode displays both higher energy density and higher power density than the cells with soft carbon and graphite. For the cycle performance as shown in Figure 2(b), after 1000 cycles, the LIC cell with hard carbon can retain up to 100% while the LIC cells with soft carbon and graphite only retain up to 80% and 78% of the initial discharge energy density, respectively. Based on the evaluation of the electrochemical properties including energy, power and cycle performance of the various carbon electrodes, it is concluded that hard carbon is the best option for negative electrode, as it displays a higher energy density, power density and longer cycle life implemented in two-electrode Li-ion capacitor systems.

References

1. W.J. Cao, J.P. Zheng, J. Power Sources, 213, 180 (2012).

2. W.J. Cao and J.P. Zheng, J. Electrochem. Soc. 160, A1572 (2013).