2D-Channel-Forming Catechol-Based Polyphosphates as Solid Polymer Electrolytes and Their Microstructure-Assisted Li-Ion Conductivity

Abstract

Electrochemical energy storage devices are the much-required technology for potential applications in renewable energy systems from intermittent wind and solar sources and portable applications in electric vehicles. This paper describes the synthesis, characterization, and Li-ion conductivity of catechol-based copolymer of polyphosphates (P1–P4) for solid polymer electrolyte (SPE) applications in Li-ion batteries. The synthesized polymers are thermally stable with a high molecular weight and porous nature and their particles have a rodlike morphology. The Li-ion conductivity of one of the SPEs produced using P3 with 20 wt % of LiTFSI is 1.4 × 10–3 S cm–1 at 80 °C, while P1 having 40 wt % of LiTFSI shows the conductivity of 1.2 × 10–3 S cm–1 at 80 °C. The remaining polymers (P1–P4) show good conductivity at room temperature (∼10–4 S cm–1). The results demonstrate the highest Li-ion conductivity among those reported in the literature so far at 80 °C. The high conductivity achieved is attributed to the microstructure of polymer molecules dictated by the bulky and rigid groups as a co-monomer, which creates perpetual voids in the polymer matrices. Galvanostatic charge–discharge cycling studies on the coin cells fabricated using SPE1 exhibit constant overpotential values and stable cycling behavior for about 2000 cycles.