Hard@Soft Integrated Morning Glory Like Porous Carbon as a Cathode for a High-Energy Lithium Ion Capacitor

A lithium ion capacitor (LIC) is a hybrid energy storage device that combines the energy storage mechanism of lithium ion batteries and supercapacitors and presents their complementary features. However, imbalances of the capacity and kinetics between cathode and anode still remain challenges. Herein, to address the issue of low capacity in the cathode, we constructed a morning glory like porous material crimped from an opening sandwich structure consisting of a hard carbon inner layer and soft carbon outer layer, by coating graphene oxide containing flaky phenolic resin with coal tar pitch followed by carbonization and activation. Both the hard@soft carbon integrated design and the reduced graphene oxide network cocontributed to a favorable electrical conductivity and a developed microporosity. To deal with the sluggish kinetics limitation of the anode, a structure-optimized MnO@C electrode prepared by pore creation of CO₂ from an MnCO₃@polydopamine precursor was chosen due to its excellent rate performance. The LIC with this configuration can deliver a maximum energy density of 117.6 Wh kg^-1 and an favorable capacity retention of 76% after 3000 cycles at 2050 W kg^-1. Furthermore, the energy density of 27.8 Wh kg^-1 can still be delivered even at a high power density of 10250 W kg^-1. In general, this well-designed hybrid capacitor has a potential to make up the gap between lithium ion batteries and supercapacitors.