A Composite Solid Polymer Electrolyte Containing Poly(propylene Carbonate) and Li1.5Al0.5Ge1.5(PO4)3 for All-Solid-State Li-Ion Batteries

Abstract

During last ~30 years, lithium-ion batteries (LIBs) have been improved significantly in aspects of energy density and cyclability. In spite of several advantages of LIBs, the conventional LIBs still have suffered from the issues related to organic based electrolytes, such as leakage, volatility, flammability, and lithium dendrite formation through porous separator leading to internal short circuits. A solution is to replace the organic liquid electrolyte with suitable composite solid polymer electrolyte (CSPE). Poly(ethylene oxide) (PEO) based electrolytes are the most studied solid polymer electrolyte (SPE). However, narrow potential window, poor mechanical strength, low lithium transference number, and insufficient ionic conductivity are the major issues to be addressed in case of PEO. In contrast, poly(propylene carbonate) (PPC) has attracted tremendous attention as an alternative owing to its higher ionic conductivity, better lithium transference number, and wide potential window. The weak mechanical strength of PPC membranes is the main bottle neck to be addressed before it sees the limelight of practical application. Incorporation of a ceramic filler into PPC polymer is one of the promising way to improve the ionic conductivity as well as the mechanical strength of SPE. Among the ceramic fillers, NASICON type Li1.5Al0.5Ge1.5(PO4)3 (LAGP) possesses good stability to moisture, thermal stability, and electrochemical stability. In this work, we have studied the effects of LAGP incorporation in PPC matrix on the physical and electrochemical properties of CSPE for all-solid-state LIBs. The formation of LAGP phase was analyzed by XRD, SEM, and TEM. Furthermore, the thermal stability of prepared CSPE was evaluated using DSC and TGA. The CSPE exhibited higher ionic conductivity and mechanical strength compared with pure PPC, leading to improvement in electrochemical properties of all-solid-state lithium ion batteries composed of Li/CSPE/LiNi0.6Co0.2Mn0.2O2 (NCM622).