Preparation And Characterization Of Novel Single Lithium-ion Conducting Block Copolymer Electrolytes Based On Poly[(4-Styrenesulfonyl)(Trifluoromethanesulfonyl)Imide] Anions

Soild polymer electrolytes (SPEs) have attracted much attention recently as safeelectrolytes for application in solvent-free lithium rechargeable batteries. However, thedevelopment of SPEs has been hampered by two issues: the inability to design a SPE thathas both a high ionic conductivity and good mechanical properties and the fact that themotion of lithium ions carries only a small fraction (1/5th) of the overall ionic current, whichleads during battery operation to the formation of a strong concentration gradient withdeleterious effects such as favoured dendritic growth and limited power delivery. Here wedescribe a new single-ion polymer electrolyte based on self-assembled polyanionic ABdiblock copolymers to finely tune mechanical properties, ionic conductivity and lithiumtransport number at the same time. In the present work, the AB block copolymer we createdis based on soft poly(ethylene glycol) methyl ether methacrylate monomer and lithium(p-styrenesulfonyl)(trifluoromethylsulfonyl)imide with high dissociation level.The paper consists of two parts as below:(1) Novel single-ion AB block copolymersPoly(POEM) b LiPSTFSI with four various molar ratios of oxyethylene unit to lithium ion(EO/Li+) were prepared by reversible addition-fragmentation chain transfer radicalpolymerization of lithium (p-styrenesulfonyl)(trifluoromethanesulfonyl)imide (LiSTFSI)with poly[poly(ethylene glycol) methyl ether methacrylate](Macro-CTA) asmacromolecular chain transfer agent. For comparision, the four corresponding blendedpolymer electrolytes (Poly(POEM)/LiPSTFSI) are also prepared and characterized.(2) Thestructures of the prepared polymers both are characterized by1H NMR,19F NMR and so on.The fundamental properties of these two types of lithium-ion conducting polymerelectrolytes are comparatively studied, in terms of molecular weight, phase transitions,thermal stability, XRD, ionic conductivities and lithium-ion transference numbers (tLi+). Theresults of the characterizations for these single-ion conductors were discussed. It turns outthat no microphase separation is observed in small angle X-ray Scattering, indicative ofcompatibility of the two segments. However, these novel single lithium-ion conducting blockcopolymer electrolytes have low glass transition (EO/Li+=17.1, Tg=-59.2oC), goodthermal stability (decomposition temperature, Td>260oC), high ambient-temperature ionic conductivity (EO/Li+=17.1, σ=3.75×106S/cm), high lithium-ion transference number(tLi+≈1) and a high degree of amorphous phase.