Solid polymer electrolytes based on poly(lithium carboxylate) salts

Abstract

The ionic conductivity, lithium ion transference number, electrochemical stability, and thermal property of solid polymer electrolytes composed of poly(ethylene oxide) (PEO) and poly(lithium carboxylate)s, (poly(lithium acrylate) (Poly(Li-A)) or poly(lithium fumarate) (Poly(Li-F)), with and without BF 3 ·OEt 2 were investigated. The ionic conductivities of all solid polymer electrolytes were enhanced by one to two orders of magnitude with addition of BF 3 ·OEt 2 because the dissociation of lithium ion and carboxylate anion was promoted by the complexation with BF 3 . The lithium ion transference number in the solid polymer electrolytes based on poly (lithium carboxylate)s showed relatively high values of 0.41-0.70, due to the suppression of the transport of counter anion by the use of a polymeric anion. The solid polymer electrolytes with addition of BF 3 ·OEt 2 showed good electrochemical stability.

Ceramic and polymeric solid electrolytes for lithium-ion batteries

“…For example, the addition of polymers with carboxylic acid group, such as poly(acrylic acid) (PAA) and poly(methacrylic acid) (PMAA), leads to an increase in the conductivity of PEO [124]. The addition of PAA or other poly(lithium carboxylate)s can also increase the lithium-ion transport number by reducing the transport of anions [134]. The conductivity of such polymers can be improved with the addition of boron trifluoride etherate (BF 3 ·OEt 2 ), which promotes dissociation of the lithium cations and carboxylate anions.…”

Solid polymer electrolytes which contain tricoordinate boron for enhanced conductivity and transference numbers

“…A number of papers have been published where boron containing compounds were incorporated as low molecular weight additives 42,43 or boron species were imbedded in a polymer. 44 An example of the former case are plasticizers made of PEG-borate and PEG-aluminate esters which have shown good conductivity enhancements due to Lewis acidity of boron and aluminum, 42 but transference observed was small due to mobility of the plasticizers that could sequester anions. On the other hand, when poly(lithium carboxylate) (polymeric anion) was used, the addition of BF 3 $OEt 2 stimulated dissociation of Li salt, while the transport of anions was suppressed that resulted in transference numbers 0.41-0.70.…”

Electrolytes for high-energy lithium batteries

“…This mechanism leads to impractically low conductivities in these systems, though lithium transference is unity. Recently, mixed polymer systems of PEO and poly(lithium acrylate) salts were shown to have improved conductivity (10 -6 S/cm at room temperature and 10 -4 S/cm at elevated temperatures) in the presence of the additive BF 3 OEt 2 , which coordinates with the tethered carboxylate anion and promotes ion-pair dissociation (Itoh et al 2009). This study suggests that single ion-conducting conductors with high conductivity may be possible with improvements in anion coordinating additives.…”