Seun Lee

Stable high-areal-capacity nanoarchitectured germanium anodes on three-dimensional current collectors for Li ion microbatteries

It is of great significance to improve the areal capacity of Li ion microbatteries in pursuit of high-end medical and RFID products and technologies. Here, we investigated germanium (Ge) nanoarray electrodes with high mass loading, directly anchored on three-dimensional (3D) copper (Cu) nanonet current collectors (Ge-na/Cu NNs). These nanoarchitectured electrodes showed superior areal capacity (>2 mA h cm−2) and usable lifetime at a current density of 1 mA cm−2 over 140 cycles. In addition, an excellent rate capability of 1.25 mA h cm−2 (calculated gravimetric capacity of 685 mA h g−1) at a current density of 5 mA cm−2 could be achieved using these synergistically fabricated Ge-na/Cu NN electrodes, making them potential electrodes for Li ion microbatteries with large energy and power densities.

Fe-based hybrid electrocatalysts for nonaqueous lithium-oxygen batteries

Lithium–oxygen batteries promise high energy densities, but are confronted with challenges, such as high overpotentials and sudden death during discharge–charge cycling, because the oxygen electrode is covered with the insulating discharge product, Li2O2. Here, we synthesized low–cost Fe–based nanocomposites via an electrical wire pulse process, as a hybrid electrocatalyst for the oxygen electrode of Li–O2 batteries. Fe3O4-Fe nanohybrids–containing electrodes exhibited a high discharge capacity (13,890 mA h gc−1 at a current density of 500 mA gc−1), long cycle stability (100 cycles at a current rate of 500 mA gc−1 and fixed capacity regime of 1,000 mA h gc−1), and low overpotential (1.39 V at 40 cycles). This superior performance resulted from the good electrical conductivity of the Fe metal nanoparticles during discharge–charge cycling, which could enhance the oxygen reduction reaction and oxygen evolution reaction activities. We have demonstrated the increased electrical conductivity of the Fe3O4-Fe nanohybrids using electrochemical impedance spectroscopy.