Carbon Wrapped Sulfur Cathode Materials for Rechargeable Batteries

Introduction:

 Currently available rechargeable Li-ion batteries based on spinal, layer and olivine crystal structures of Li (Mn, Ni, Co) O_x and related material systems, shows lower capacity and poor cycling characteristics. In addition, LiCoO₂ is expensive and environmentally unfriendly. Due to high volume and gravimetric energy density, rechargeable lithium batteries have become the dominant power source for portable electronic devices including cell phones and laptops. However, the energy and power densities of rechargeable lithium batteries require significant improvement in order to power electric vehicles¹. Lower specific capacities of cathode materials (~150mAh/g for layered oxides and ~170mAh/g for LiFePO₄) compared to those of the anode (370mAh/g for graphite and 4200mAh/g for Si) have been a limiting factor to the energy density of batteries. It is highly desirable to develop and optimize high capacity cathode materials for rechargeable lithium batteries.

Sulfur is a promising cathode material with a theoretical specific capacity of 1672mAh/g,² ~ 5 times higher than those of traditional cathode materials based on transition metal oxides or phosphates. Sulfur also possesses other advantages such as low cost and environmental friendly.

Experimental:

Here we present a rational design and synthesis of a novel carbon-sulfur composite material at low temperature. Sulfur particles are synthesized and wrapped by carbon black a simple assembly process. The phase formation behavior of the synthesized powder was investigated using X-ray diffraction, using Cu Kα radiation.  The morphology of the synthesized powder was investigated using a scanning electron microscopy (SEM), and transmission electron microscopy (TEM, Carl Zeiss Leo Omega 922 at 200 KeV).

Result:

The XRD patterns (Fig1.)  of all samples could be indexed to the orthorhombic space group based on the phase –pure ordered structure. Electrochemical properties will be study using cyclic Voltammetry, Charge-Discharge Curves, and Electrochemical Impedance  spectroscopy (EIS). These measurements are still in progress.

Fig1. X ray diffraction patterns of Sulfur-carbon composite (insert morphology image).

References:

1. Bruce, P. G.; Scrosati, B.; Tarascon, J. Angew. Chem. Int. Ed. 2008, 47, 2930-2946
2. Ellis, B. L.; Lee, K. T.; Nazar, L. F. Chem. Mater. 2010, 22, 691-714