Ionically conducting polyether composites

Abstract

Ionic conductivity in polymer-salt electrolytes occurs in the amorphous regions of the complex. Poly(ethy1ene oxide) (PEO) is the best polyether for complexing salts. Unfortunately, it is partially crystalline at ambient temperatures. With inorganic (i.e., alumina) or organic (i.e., poly(acry1amide) (PAAM)) fillers the crystallization of PEO is inhibited and the room temperature conductivity is enhanced in these mixed phase systems by over two orders of magnitude (to -lo4 Slcm) above the base PEOsalt system (<lo4 Slcm). Even adding PAAM to an initially amorphous system (oxymethylene-linked PEO-LiC104) increases the room temperature conductivity by 2 to 3 times. Various alkali metal salts (Li, Na) and NH4SCN are used with a-Al,03, 0-A1,03, PAAM' and poly(N,Nf-dimethyl acrylamide) as fillers. The aluminas stiffen the complex and increase Tg. The addition of the organic fillers lowers T,, as is to be preferred. It is suggested that changes in the conductivity with changes in salt and filler concentration are due to changes in the ultrastructure and morphology and are the result of an equilibrium between various Lewis acid -Lewis base reactions. Qualified success has been achieved in modelling ionic conductivity in these composite electrolyte systems using an effective medium approach. In this approach it has been assumed that the main conductivity enhancement takes place in thin amorphous layers of the polyether that coat the dispersed polyacrylamide particles separated in a microphase. In the best complexes this layer is identified by a second T,.Key words: polyethers, composites, ionic conductivity, phase structure, Lewis acids and bases.Resume : La conductivitC ionique des Clectrolytes de la forme sel de polymbres se produit dans les rCgions amorphes du complexe. Le poly(oxyde d'Cthylkne) (ccPE0~) est le meilleur Cther pour la complexation des sels. En prksence de garnitures inorganiques (par exemple, de I'alumine) ou organique (par exemple, le poly(acry1amide) (PAAM)), la cristallisation du aPEO), est inhibk; dans ces systbmes de phases mixtes, la conductivitC i la tempCrature ambiante est de deux ordres de grandeur plus ClevCe (rehausske i environ lo4 Slcm) que celle du systkme de base ccPEOn-sel (<lo4 Slcm). M&me l'addition de PAAM i un systkme initialement amorphe (ecPE0~-LICI04 liC par de l'oxymtthylkne) provoque une augmentation (par des facteurs de deux i trois) de la conductivitC i la tempkrature ambiante. Divers sels de mCtaux alcalins (Li, Na), de meme que la NH4SCN, peuvent &tre utilisks comme garnitures de concert avec de I'm-Al,O,, du 0-A1,03, du PAAM et du poly (N,N'-dimtthyl acrylamide). Les alumines solidifent le complexe et augmentent la valeur de Tg. Comme on peut l'espkrer, I'addition de garnitures organiques diminue la valeur de T,. I1 a kt6 suggCrk que les changements dans la conductivitC associks B des changements dans la concentration en sel et en garniture sont dus i des changements dans l'ultrastructure et la morphologie et qu'ils sont le rksultat d'un Cquilibre entre diverses ...

Review on composite polymer electrolytes for lithium batteries

“…Since PEO is known as a Lewis base and Li þ cation as a Lewis acid the phenomena occurring in composite electrolyte were explained in terms of equilibria between various Lewis acide base reactions occurring in the composite electrolyte systems. The same group [93] also substantiated that the ionic conductivity occurs only in the amorphous phase of the polymeresalt electrolyte system. The authors found in a system composed of both organic (polyacrylamide) and inorganic (Al 2 O 3 ) fillers that the inorganic filler increases the glass transition temperature and on contrary, organic filler reduces the glass transition temperature.…”

A review of polymer electrolytes: fundamental, approaches and applications

“…composite polymer electrolytes (CPEs The CPEs offer some interesting features, for instance, good flexibility, high thermal stability, good interfacial contact and high ionic conductivity by enhancing ion mobility [16,32]. The electronic and ionic conductivities of CPEs depend on the characteristics of particles used, including the particles size, porosity, concentration, surface area and the interaction between the particles and the polymer matrices [63][64][65]. The enhanced electrochemical and mechanical properties of CPEs are important for their technological application in electrochemical devices.…”

Functionalized mesoporous silica MCM-41 in poly(ethylene oxide)-based polymer electrolytes: NMR and conductivity studies

“…Previous studies have shown that the ionic conduction of CPEs depends on the characteristics of the particles used, such as size, porosity, surface area and functionality, concentration, and on the interaction between the particles and the polymer [23][24][25]. To clarify these issues, one should consider tailoring structural modifications by selecting inorganic fillers having appropriate chemical properties and by maximizing their surface area.…”