Lithium ion motion in a hybrid polymer: confirmation of a decoupled polyelectrolyte.

Ionic conductivity involving ion transport in polymer electrolytes has been a major focus of polymer battery research, and an important concept in understanding the mechanisms of ionic transport in polymers is the issue of the coupling between ion motion and the relaxation of the polymer segmental chain. This means that, in typical polymer electrolytes, ion transport is strongly coupled to the segmental motion of the polymer matrix. Therefore, significant conductivity is only observed above the glass-transition temperature of the system, resulting Vogel–Tammann–Fulcher behavior (VTF). Research into polymer electrolytes has focused largely on enhancing the flexibility of the polymer matrix in order to promote ionic mobility. This has met with success, but its disadvantage is that the conduction mechanism is dominated by ion–polymer interactions and the numbers of cations transported (vital for battery applications) can be very low. New materials with unconventional conduction mechanisms are clearly needed. However, a different class of polymer electrolytes has recently been reported, in which the ionic conductivity is not coupled to the segmental motion of the polymer chain, that is, in which the ions move independently of the viscous flow. The approach used in the development of the segmental motion-decoupled polymer is the synthesis of a hard polymer (e.g. , liquid-crystalline materials, polyesters, ordered polymers, and organic plastic crystals). These materials represent an alternative way to increase ionic conductivity in polymer electrolytes. In a previous paper, we described the synthesis, thermal properties, and good ionic conductivity (s=10 5 Wcm 1 at room temperature) of a single-phase hybrid polyeletrolyte (SPHP). Arrhenius behavior of the conductivity as a function of temperature was reported for the SPHP, suggesting that the ion motion is decoupled from the polymer segmental motion for temperatures above the glass-transition temperature Tg (about 79 8C). This single-phase hybrid polyelectrolyte (SPHP) was synthesized by a derivative in situ polymerizable method (a nonhydrolytic sol–gel process) based on the formation of a complex of Si and citric acid (CA) that was subsequently polymerized by means of a polyesterification reaction with ethylene glycol (EG). The material became ionically conductive when Li2CO3 was dissolved in the structure during its synthesis. A transparent, amorphous solid hybrid was obtained after elimination of the solvent. The main goal herein is to understand the motion of the Li ions in an SPHP from a microscopic standpoint, and to identify the active sites, that is, the counterions of the hybrid polyelectrolyte matrix.