Pliable Embedded-Type Paper Electrode of Hollow Metal Oxide@Porous Graphene with Abnormal but Superior Rate Capability for Lithium-Ion Storage

To improve the electrochemical performance of pliable graphene/metal oxide composite papers, a new kind of embedded-type MO@PG paper electrode including Fe2O3@PG and CuO@PG was designed and prepared by simple filtration and controllable oxidation. MO@PG paper electrodes have special structures in which hollow metal–oxide nanoparticles are embedded in the pores of porous graphene films and connected with the edges of the graphene to produce a strong interfacial interaction. Benefiting from this unique structure, the MO@PG paper electrodes for LIBs exhibit higher specific capacities and better cyclic stability and rate performance. In particular, the MO@PG electrodes show an interestingly abnormal rate performance in that the specific capacity increases with the current density from 50 to 500 mA g–1, which should be attributed to Li-ion storage in graphene films being mainly controlled by diffusion, while electrochemical reactions of Fe2O3 are mainly controlled by Faradaic capacitance. At a higher current density, the Li-ion diffusion in the graphene layers is largely suppressed, so the graphene films can play well the role of a conductive network, and the activity of the Fe2O3 will be clearly enhanced. In addition, the MO@PG paper electrodes also show higher specific capacity and superior long-term cyclic ability at very high rates: for Fe2O3@PG, 741, 249, and 141 mA h g–1 at the rates of 10, 30, and 50 A g–1 after 10000 cycles, respectively; and for CuO@PG, 980, 314, and 168 mA h g–1 at the rates of 10, 50, and 100 A g–1 after 10000 cycles, respectively). The strategy for embedded-type MO@PG paper electrodes provides a direction for the design of flexible electrode materials with both high power density and energy density.