Selection of Polymer Segment Species Matters for Electrolyte Properties and Performance in Lithium Metal Batteries

Abstract

Control of homogeneous lithium deposition governs prospects of advanced cell development and practical applications of high-energy-density lithium metal batteries. Polymer electrolytes are thus explored and employed to mitigate the growth of high-surface-area lithium species while enhancing the reversibility of the lithium reservoir upon cell cycling. Herein, an in-depth understanding of the distribution of membrane properties and lithium deposition behavior affected by the selection of polymer segment species is derived. It is demonstrated that severely localized lithium deposits featuring needle-like morphologies may be readily observed when electrostatic fields (or partial charges) and the amount of Li+ coordinators of the primary and secondary polymer segment species appear rather dissimilar, leading to a sudden cell failure at early stages of cell operation. In comparison, employment of optimized copolymer electrolytes enables superior cell performance at 1C even with thicker cathodes (6.3 mg cm–2). Additionally, the improvement of cell-cycling stability due to enhancement of similarity of dipole moments and partial charge distributions among copolymer segments are also demonstrated for different polymer systems, contributing to avoidance of undesired lithium protrusions, also reflecting a viable concept for the design of future copolymer electrolytes.