Synthesis and Characterization of a New Class of Monolithium Salts for PEO-Based Solid Polymer Electrolyte Systems

Abstract

Lithium ion conducting polymer electrolytes have significant potential in the field of secondary lithium batteries, including display and sensor devices. We report here a new class of lithium sulfonimide salts for use in lithium-ion battery electrolytes. These salts, prepared by a two- to three- step synthetic strategy from inexpensive and readily available starting materials, were characterized by 1H-NMR, FTIR and elemental analysis. The thermal properties of the salts were determined by thermogravimetric analysis and showed stabilities up to 300ºC. Earlier studies demonstrated that the ionic conductivity of solid polymer electrolytes could be improved by use of a borate ester plasticizer. In order to optimize conductivity, solid polymer electrolyte films were prepared by incorporating this plasticizer with each of the new salts in a PEO matrix. We observed that the Li:O ratio of 1:20 exhibits maximum ionic conductivity (2.05x10-6 S/cm at 30ºC for the salt ALT01). A trend of decreasing conductivity with increasing size of the anionic moiety was also noted. It was found that 1 g of plasticizer can be loaded in a film containing 1 g of PEO without deterioration of mechanical properties. An improved ionic conductivity of 3.82x10-5 S/cm at 30ºC was observed. The films also exhibited good thermal and electrochemical stabilities. Glass transition temperature of the films were determined using differential scanning calorimetry.