Electrospun polymer membrane activated with room temperature ionic liquid: Novel polymer electrolytes for lithium batteries

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Original entry by A.J. Kumar, APPHY 225 Fall 2009

Reference

Gouri Cheruvally, Jae-Kwang Kim, Jae-Won Choi, Jou-Hyeon Ahn, Yong-Jo Shin, James Manuel, Prasanth Raghavan, Ki-Won Kim, Hyo-Jun Ahn, Doo Seong Choi, Choong Eui Song. Journal of Power Sources 172 (2007) 863–869

Keywords

Polymer electrolyte; Electrospinning; Porous membrane; Room temperature ionic liquid; Lithium batteries

Summary

In this article, the authors describe a specific polymer electrolyte that they have fabricated and incorporated into a lithium ion battery. Through the use of PE gels, they note marked improvement in operation temperatures and in overall efficiency of the battery, reaching over 80% of the theoretical capacity. The authors choose to use poly(vinylidene fluoride-co-hexafluoropropylene) {P(VdF-HFP)} because of its thermal and chemical stability and it's affinity for electrolytes. Most current batteries use molecular solvents for electrolytes but there is increased motivation to find alternatives as these pose safety and environmental risks. Room temperature ionic liquids (RTIL) are non-flammable and non-volatile molten salts with low melting temperatures. RTILs are hence a preferred candidate in new batteries. In this study, the authors use 1-butyl-3-methylimidazolium (BMI)-based RTILs, BMITFSI and BMIBF4. The polymer electrolyte was created by first electrospinnig a P(VdF-HFP) membrane and then activating it by incorporating the RTILs, BMITFSI or BMIBF4.

PEM surface.jpg

The authors then characterized the topology of the membrane as well as it's ionic uptake and ionic conductivity. They then incorporated the PEs into a Li/LiFePO4 cell to measure the performance of such a battery. Both types of BMI's produced cells with capacities over 80% at <math>25^o</math> C of the theoretical capacity for LiFePO4, a huge improvement over previous attempts with different PEs that only reached 32%. This shows that electrospun polymer membranes are good candidates for PEs in novel lithium batteries.

This shows that the batteries operate well after multiple cycles.

Soft Matter Connection

These types of batteries are known as lithium metal polymer batteries (LMPBs). These are of great interest because compared to current lithium-ion batteries, they are lighter, safer, and have more flexibility in design. The use of polymer membranes to actualize a suitable LMPB shows how soft matter and polymer science can be of great interest in energy. Given the current focus on energy technologies and global warming, soft matter may offer novel solutions to these pressing issues.