Seok Gwang Doo

Si/Ge Double-Layered Nanotube Array as a Lithium Ion Battery Anode

Problems related to tremendous volume changes associated with cycling and the low electron conductivity and ion diffusivity of Si represent major obstacles to its use in high-capacity anodes for lithium ion batteries. We have developed a group IVA based nanotube heterostructure array, consisting of a high-capacity Si inner layer and a highly conductive Ge outer layer, to yield both favorable mechanics and kinetics in battery applications. This type of Si/Ge double-layered nanotube array electrode exhibits improved electrochemical performances over the analogous homogeneous Si system, including stable capacity retention (85% after 50 cycles) and doubled capacity at a 3C rate. These results stem from reduced maximum hoop strain in the nanotubes, supported by theoretical mechanics modeling, and lowered activation energy barrier for Li diffusion. This electrode technology creates opportunities in the development of group IVA nanotube heterostructures for next generation lithium ion batteries.

Silicon nanowires with a carbon nanofiber branch as lithium-ion anode material

Si n nanowires (SiNWs)–carbon nanofibers (CNFs) branched structures with variation in carbon densities were synthesized. SiNWs with critical density of CNFs show the best electrochemical performance, which is attributed to increase in free volume around the SiNWs as well as a buffering role of the branched CNFs against large volumetric change during cycling.

Characterization of a thin, uniform coating on P2-type Na2/3Fe1/2Mn1/2O2 cathode material for sodium-ion batteries

A thin, uniform carbon coating on Na2/3Fe1/2Mn1/2O2 (NFMO) using 2,3-dihydroxynaphthalene (DN) was prepared. Pristine and DN-coated samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). An amorphous nanolayer coating of carbon is obtained on the surface of the layered pristine material. The 0.2 wt% DN-coated NFMO exhibits excellent electrochemical performance. An initial discharge capacity of 178 mA h g−1 was obtained at a C-rate of 0.1 C; this capacity is 20% higher than bare NFMO. Capacity retention (77.8% at the 50th cycle) is also maintained comparable to bare NFMO (77.7% at the 50th cycle). The thin and uniform carbon layer leads to improvement of charging and discharging kinetics and protects against direct contact between cathode and electrolyte.