PNNL

Abstract

Batteries using lithium (Li) metal as anode are considered promising energy storage systems because of their high specific energy densities. The crucial bottlenecks for Li-metal anode are Li dendrites growth and side reactions with electrolyte inducing low Coulombic efficiency (CE) and short cycle life. Vinylene carbonate (VC), as an effective electrolyte additive in Li-ion batteries, has been noticed to significantly enhance the CE, while the origin of such an additive remains unclear. Here we use cryo-TEM imaging combing with EDS elemental and EELS electronic structure analyses to reveal the role of VC additive. We discovered that the electrochemically deposited Li metal (EDLi) in VC-containing electrolyte is slightly oxidized with the SEI being a nanoscale-mosaic like structure comprised of organic species, Li2O and Li2CO3; while the EDLi formed in VC-free electrolyte is featured by a combination of fully oxidized Li with Li2O SEI layer and pure Li metal with multilayer nano-structured SEI. These results highlight the possible tuning of crucial structural and chemical features of EDLi and SEI through additives and consequently direct correlation with electrochemical performance, providing valuable guidelines to rational selection, design and synthesis of additives for new battery chemistries.