Effects of the Pd₃Co nanoparticles-additive on the redox shuttle reaction in rechargeable Li-S batteries

A lithium-sulfur (Li-S) battery system with bimetallic electrode additive, which limit the dissolution of intermediate lithium polysulfides, is studied. Palladium-cobalt (Pd₃Co) nanoparticles are successfully employed as redox promoters in Li-S cells. These cells show high capacity retention and excellent Coulombic efficiency, which are attributed to the fast charge transfer of Pd₃Co. Characterization of the Pd₃Co nanoparticles isperformed via high-resolution transmission electron microscopy, fast Fourier transform analysis, energy-dispersive X-ray, and X-ray diffraction. At 0.1 C-rate, the initial discharge and charge capacities of the Pd₃Co-sulfur electrodes are 1.24 and 1.36 times higher than those of the bare sulfur electrodes. During the first discharge cycle, the overpotential of the Pd₃Co electrode (100 mV) is much lower than that of the bare sulfur cell (190 mV). After 200 cycles at 1.0 C-rate, the Pd₃Co-sulfur electrodes deliver a discharge capacity of 544 mAh g^-1 a high Coulombic efficiency (99.6%). Moreover, the capacity retention of Pd₃Co cells is 83.9%. The inductively coupled plasma-atomic emission spectroscopy and X-ray photoelectron spectroscopy data demonstrate that the Pd₃Co nanoparticles can suppress the dissolution of lithium polysulfides and the shuttle effect. These results indicate that the reaction kinetics of the sulfur electrodes is enhanced by the Pd₃Co nanoparticles.