Controlling Electrochemical Lithium Deposition and Sulfur Reduction Mechanism through Liquid Electrolytes

Lithium metal anode has been regarded as the "Holy Grail" of next-generation battery technologies. In order to stabilize the electrodeposited Li metal for safe and high energy batteries, highly concentrated electrolytes (solvate electrolytes) have been proposed to suppress the formation of Li dendritic structure and polysulfide dissolution in lithium-sulfur (Li-S) batteries. (1-5) In this talk, we use in situ transmission X-ray microscopy (TXM) to study the effect of solvate electrolyte on Li plating/stripping process. In situ TXM images show that electrodeposited Li particles with uniform density are formed in solvate electrolyte during initial plating process. The effect of solvate electrolyte on the mechanism of Li growth is studied in detail. Additionally, in situ spectroscopy including Raman and X-ray spectroscopy (X-ray diffraction and X-ray absorption spectroscopy) are used to investigate sulfur reaction mechanism and the interaction between polysulfide and solvate electrolyte. We found that the sulfur species formed in the solvate electrolyte are different from the sulfur species formed in conventional DOL/DME electrolyte. These results suggest that solvate electrolyte changes both polysulfide solubility and sulfur reaction mechanism. We next propose different solvate electrolytes with low polysulfide solubility and high stability toward Li metal to enhance the capacity retention of Li-S batteries. References: [1] L. Suo et al., Nat. Commun. 2013, 4, 1481. [2] K. Dokko et al., J. Electrochem. Soc. 2013, 160, A1304. [3] M. Cuisinier et al., Energy Environ. Sci., 2014, 7, 2697. [4] Y. Yamada et al., J. Electrochem. Soc. 2015, 162 (14), A2406. [5] L. Cheng et al., ACS Energy Lett. 2016, 1, 503.