Three-Dimensionally Structured Conversion Compound Electrodes for High Energy Density Lithium Batteries

Transition metal based conversion compounds have attracted extensive attention due to the possibility of multiple redox states enabling storage of more than one lithium per transition metal atom, resulting in much higher specific capacity than conventional intercalation compounds. However, conversion compound electrodes often suffer from poor power density and poor cyclability at least in part because of the intrinsically poor ionic and electronic conductivity of the materials. Addition of a conductive agent, usually carbon, improves cyclability significantly, but with a reduction of the overall capacity. Here, using a colloidal templating strategy, we three-dimensionally architecture and nanostructure conversion compound electrodes to overcome the sluggish kinetics. We focus on Fe₂O₃ nanoparticles as active materials. Bicontinuous Ni inverse opals formed via colloidal templating with pore size of about 500nm were used as the current collectors, and Fe₂O₃ nanoparticles (30-50nm) were electroplated onto this scaffold. By using a pulsed voltage deposition method, a uniform coating of nanoparticles on the Ni scaffold was realized. After optimizing the phase of the materials, cycling tests showed a good specific capacity (~1000mAh/g at 0.5C). The high-rate performance of the three-dimensional electrodes was impressive. At a rate of 20C, more than 400mAh/g capacity could still be delivered. The good capacity and cyclability of the three-dimensional electrodes was due to the combination of the porous electrode support structure and the nanostructured active phase which provided short pathways for both ions and electrons.