Difunctional block copolymer with ion solvating and crosslinking sites as solid polymer electrolyte for lithium batteries

Abstract

High conductivity, solid polymer electrolytes (sPE) are an enabling technology for safe, high energy-density lithium ion batteries. Unfortunately, polymer architectures with high ion conductivity are usually associated with poor mechanical properties. In this study, a difunctional block copolymer (DFBCP) which addresses the need has been synthesized and demonstrated. The first block, P(DBEA-co-MA), has tethered double bonds and can form a dense, crosslinked network upon UV irradiation to provide mechanical strength. The second block is a pendant type polyethylene glycol (PEG) moiety with low crystallization to provide ion solvation. The PEG moiety is confined on one side of the polymer and has high segmental motion, resulting in an adequate ionic conductivity, 0.6 mS/cm. The amorphous nature of PEG second block also ensures low interfacial resistance, <80 Ω∙cm2, and mechanical adaptability to electrode volumetric changes. The combined advantages of high conductivity, low interfacial resistance and good mechanical stability enable full cell durability, >1000 cycles at 2C in a Li–LiFePO4 battery.