Professor Bilal El-Zahab and doctoral students, Meer Safa, Amir Chamaani, and Neha Chawla from Florida International University (FIU) developed a free-standing gel polymer electrolyte (GPE) and evaluated its thermal and electrochemical properties in order to ascertain the overall performance of their synthesis in lithium battery applications. The new findings appeared in peer-reviewed journal, Electrochimica Acta.
The gel polymer electrolyte comprised of a pyrrolidinium-based polymeric ionic liquid (PIL), an imidazolium based ionic liquid [EMIM][TFSI], and the lithium salt [LiTFSI]. They compared two electrolytes: the gel polymer electrolyte and ionic liquid electrolyte to investigate stability and compatibility with lithium metal electrode using various electrochemical characterization techniques, including electrochemical impedance spectroscopy with further determination of their rate performance in a cell with LiFePO4 cathode at room temperature.
Thermogravimetric analyses showed the prepared gel polymer electrolyte had a high thermal stability. The pair of polymeric ionic liquid and ionic liquid inside the gel polymeric electrolyte which contains ionic liquid and lithium salt content (LiTFSI) of about 80wt.% led to an improved ionic conductivity of approximately 3.35 mS×cm-1 when measured at 25°C using electrochemical impedance spectroscopy.
The most notable improvement using the FIU team’s new gel polymer electrolyte was its improved cathodic limit and widened electrochemical stability window. The improved cathodic limit to below the plating potential of lithium made this gel polymer electrolyte a preferred choice in Li/LiFePO4 cells. Moreover, the gel polymer electrolyte also showed higher lithium-ion transference number compared to the ionic liquid electrolyte indicating higher chemical affinity. This affinity was demonstrated using in Li/Li symmetrical cell that immensely outperformed the ionic liquid electrolyte.
The cyclic charge-discharge rate when observed at 40 cycles and 22°C showed that the gel polymer electrolyte batteries had a higher discharge capacity at higher C-rates compared to ionic liquid cells. The authors attribute this improved performance to the improved electrochemical and interfacial stability, and the increased Lithium transference number. The gel polymer electrolyte developed by the authors is an exciting development that can serve effectively as an electrolytic conductor with other lithium-ion electrodes.
Meer Safa, Amir Chamaani, Neha Chawla, Bilal El-Zahab. Polymeric Ionic Liquid Gel Electrolyte for Room Temperature Lithium Battery Applications, Electrochimica Acta 213 (2016) 587-593.
Mechanical and Materials Engineering Department, Florida International University, Miami, Florida 33174, USA
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