Lithium Ion Conducting Block Copolymers: Conductivity and Battery Performance

Abstract

Polymeric solid electrolytes are an enabling technology for an all solid-state lithium battery using an intercalation or metal anode. In this study, random and block copolymers with polar functional groups were characterized for use in lithium batteries. The focus of this talk is on the lithium ion conductivity and structure-property relationship of the solid polymer electrolyte. The block copolymer is synthesized by sequential raft polymerization of different monomers. The first block is poly(acrylate) or poly(styrene), which is imparts sufficient mechanical properties to the polymer. The second block is poly(carbonate) (PC) or polyethylene glycol (PEG) to solvate the lithium ions. Nano-phase separation occurs when the polymer is cast due to differences in polarity between the two blocks. Lithium salts and plasticizer are included in the polymer mixture. The interconnected polycarbonate phase provides ion conducting channels for lithium ion conduction. The mechanical properties of the solid polymer electrolyte are also improved by creating a crosslinking network. Experimentally, a series of block co-polymers with different molecular weight and block ratio have been synthesized. The chemical structure of the block co-polymers was characterized by NMR and gel permeation chromatography. The nano-phase separation is confirmed by small angle scattering spectroscopy. Li ion conductivity was measured by electrochemical impedance spectroscopy (EIS). The battery performance was tested with Li metal anode and LiFePO4 cathode. The relationship between polymer structure, nano-phase separation and membrane performance will be discussed in this talk.