Improved electrochemical performances of lithium-oxygen batteries with tungsten carbide-coated cathode

The electrochemical properties of lithium-oxygen batteries are improved by coating a tungsten carbide layer onto an oxygen cathode. Tungsten carbide (WC) coating is conducted by physical vapor deposition. The uniform deposition of WC onto the cathode is confirmed by scanning electron microscopy, field-emission transmission electron microscopy and electron probe microanalysis. The discharge-recharge voltage gap of the cell with a WC-coated electrode is estimated to be 0.88 V, which is 700 mV smaller than that of an electrode without the WC coating at 100 mA g^-1_carbon. The overpotentials of the WC-coated electrode remain unchanged even after the 10^th cycles, while that of the uncoated electrode gradually increases. In addition, the WC-coated electrode exhibits a stable voltage profile, even at a current density of 200 mA g^-1_carbon. The observed improvement in cell performance can be attributed to the catalytic property and high electrical conductivity of WC. The enhanced electrochemical properties of cells are examined by impedance analysis and SEM.