High Capacity Utilization of Li Metal Anodes by Application of Celgard Separator-Reinforced Ternary Polymer Electrolyte

Abstract

© The Author(s) 2019. PEO-based solid polymer electrolytes typically show limited capability for the suppression of Li metal dendrites, which is mainly attributed to their low mechanical strength. To tackle this issue, we improved the mechanical strength of a ternary solid polymer electrolyte (TSPE: PEO-LiTFSI-Pyr14TFSI) by integrating Celgard 2500 separator as a high modulus domain. The Celgard-reinforced TSPE (CgTSPE) presents a significantly higher elastic modulus (223 MPa) than TSPE (0.2 MPa) at 60°C, which in result leads to more lithium anode utilization. Specifically, the Columbic efficiency of Li electrodeposition/dissolution during cycling in Li|CgTSPE|Cu cells (≈90%) is distinctly higher than in Li|TSPE|Cu (≈30%). Furthermore, the cycling of Li||Li symmetric cells with CgTSPE displays an improved cycling stability, due to the presence of Celgard, in which high surface area lithium (HSAL), e.g., dendrite formation is suppressed. Operando electrochemical dilatometry (ECD) analysis as well as post mortem surface analysis with SEM reveal the formation of “dead lithium” and cavities under an areal capacity utilization of 5 mAh/cm2. It is also suggested by the cycling behavior of the Li||Li cell with high areal capacity utilization that lithium surface treatment is required to completely eliminate the formation of “dead lithium” and of cavities.