Hybrid lithium-ion capacitors with asymmetric graphene electrodes†
The dramatically increased demand for electric devices such as electric vehicles and consumer electronics prompted us to explore new ideas in fabricating novel energy storage devices. In this work, we designed, constructed, and studied an asymmetric hybrid lithium-ion capacitor (LIC) by combining an electric double-layer capacitor cathode and a lithium-ion battery anode. Both electrodes were made of a single-wall carbon nanotube and graphene (SG) composite to reduce restacking of the graphene nanosheets, to improve the energy storage capacity, and to improve the electrical conductivity of the electrodes. One of the electrodes was pre-lithiated electrochemically. After pre-lithiation, the lithiated-SG (Li-SG) electrode showed excellent capacity in lithium intercalation and de-intercalation and was used as the anode of the LIC device. The advantage of the hybrid LIC with asymmetric graphene electrodes is that it maximizes the operable voltage between the two electrodes, thus increasing the energy density of the device. The hybrid LIC fabricated in this work exhibited an energy density of 222 W h kg−1 at a power density of 410 W kg−1.