Reduced graphene oxide encapsulated MnO microspheres as an anode for high-rate lithium ion capacitors

Developing an anode material with high-rate Li⁺ intercalation and stable charge/discharge platform is important for achieving high performance lithium ion capacitors (LICs). Reduced graphene oxide (rGO)-encapsulated MnO microspheres (~2 μm) are obtained by a simple process including solvothermal and calcination techniques. The material contains a large number of mesopores (~2.8 nm diameter). The MnO/rGO has a favorable cycling stability (846 mAh g⁻¹ at 0.1 A g⁻¹ after 110 cycles) and an outstanding rate performance (207 mAh g⁻¹ at 6.4 A g⁻¹). Kinetic analysis reveals that a pseudocapacitive contribution plays a dominant role for the energy storage. The improvement in the pseudocapacitive behavior is ascribed to the fact that the uniform rGO coating on the MnO provides continuous pathways for electron transport, and the mesoporous structure provides numerous migration paths for Li-ions. Furthermore, MnO/rGO//activated carbon (AC) LICs have a high energy density of 98 Wh kg⁻¹ at a relatively high power density of 10350 W kg⁻¹, and have a capacity retention of 71% after 5 000 cycles at 1.6 A g⁻¹. These outstanding results indicate that the enhanced Li⁺ intercalation of the anode offsets the kinetic imbalance between the two electrodes.