Visualization of sulfur cathodes in Li-S batteries

With the dramatic increase of energy applications, the development of novel high performance energy storage systems with energy densities surpassing those of state-of-the-art lithium ion batteries (“beyond lithium” ion batteries) has become more urgent.

Among those systems, lithium sulfur batteries are one of the most attractive candidates, because elemental sulfur has a high theoretical capacity of 1,672 mAh g-1, is abundant, inexpensive and environmentally benign. However, there are several challenges hindering the practical deployment of Li-S batteries. One of the main challenges is that the polysulfide intermediates, formed during the battery operation, are soluble in the electrolyte, which causes the dissolution and reformation of the active sulfur species on the cathodes during the running of the batteries, making the reaction mechanisms highly complex. A recent work has been published in the Energy and Environmental Science, titled “Direct visualization of sulfur cathodes: new insights into Li-S batteries via operando X-ray based methods”, launching a breakthrough unraveling the mysteries in the reaction mechanisms in Li-S batteries, with the X-ray techniques from Cornell High Energy Synchrotron Source (CHESS). The team was led by Prof. Hector D. Abruña and Prof. Joel D. Brock, with their group members, Dr. Seung-Ho Yu and Dr. Xin Huang, and CHESS staff scientist Rong Huang.

In their work, the evolution of the morphology and crystal structure of the sulfur cathodes was measured during the operation of Li-S batteries via X-ray imaging and diffraction. The dissolution and reformation of sulfur clusters was clearly visualized: the sulfur clusters are totally dissolved during the discharge, and reformed near the end of the charge. Both the size of lithium sulfides and sulfur formed during discharge and charge, respectively, are strongly dependent on the operation conditions. At higher current density, both the sulfur and lithium sulfide tend to form smaller clusters with more uniform distribution. At lower temperature, the formed lithium sulfide also forms smaller clusters. Their results provide the new platform for further unraveling the reaction mechanisms in Li-S batteries.

Movie: (left top) Voltage profile, (left bottom) operando X-ray diffraction pattern and (right) images from operando X-ray imaging of a sulfur electrode during the discharge of Li-S battery.

Reference:

Yu, S.-H.; Huang, X.; Schwarz, K.; Huang, R.; Arias, T. A.; Brock, J. D.; Abruña, H. D., Direct visualization of sulfur cathodes: new insights into Li-S batteries via operando X-ray based methods. Energy & Environmental Science, 2018,11, 202-210, DOI: 10.1039/C7EE02874A.