Developing high-power Li||S batteries via transition metal/carbon nanocomposite electrocatalyst engineering

Abstract

The activity of electrocatalysts for the sulfur reduction reaction (SRR) can be represented using volcano plots, which describe specific thermodynamic trends. However, a kinetic trend that describes the SRR at high current rates is not yet available, limiting our understanding of kinetics variations and hindering the development of high-power Li||S batteries. Here, using Le Chatelier's principle as a guideline, we establish an SRR kinetic trend that correlates polysulfide concentrations with kinetic currents. Synchrotron X-ray adsorption spectroscopy measurements and molecular orbital computations reveal the role of orbital occupancy in transition metal-based catalysts in determining polysulfide concentrations and thus SRR kinetic predictions. Using the kinetic trend, we design a nanocomposite electrocatalyst that comprises a carbon material and CoZn clusters. When the electrocatalyst is used in a sulfur-based positive electrode (5 mg cm^-2 of S loading), the corresponding Li||S coin cell (with an electrolyte:S mass ratio of 4.8) can be cycled for 1,000 cycles at 8 C (that is, 13.4 A g_S^-1, based on the mass of sulfur) and 25 °C. This cell demonstrates a discharge capacity retention of about 75% (final discharge capacity of 500 mAh g_S^-1) corresponding to an initial specific power of 26,120 W kg_S^-1 and specific energy of 1,306 Wh kg_S^-1.