Lithium-ion batteries play a vital role as sources of power for various electronic devices and even go as far as powering electric vehicles. The fact that electronic devices have become more prevalent in recent years has also meant that lithium-ion batteries have attracted significant attention because of their application in these devices. With this attention, comes the need to make the batteries more efficient by improving their components.
One of the vital components of a LIB is the separator. It is a crucial component because it has the following functions: First, it prevents direct contact between the positive and negative electrodes. Secondly it holds the liquid electrolyte in its pores to facilitate the transportation of lithium ions, and lastly, it acts as an electronic insulator. Whereas presently porous polyolefin membranes are commonly used to serve this purpose, they have shortcomings that limit the efficiency of lithium-ion batteries.
Scientists at Shanghai Jiao Tong University, Naiqiang Liang, Jianhua Fang, and Xiaoxia Guo embarked on a study to come up with an alternative to polyolefin membranes through the preparation of porous polybenzimidazole membranes. The approach taken by researchers in the preparation of these membranes involved the extraction of polyethylene glycol (PEG) from dry OPBI/PEG blend membranes using water. To do this, the researchers conducted an experiment that entailed a number of steps as follows; the acquisition of the necessary materials, the synthesis of OPBI (poly(2,2’-(p-oxydiphenylene)-5,5’-bibenzimidazole), preparation of porous OPBI membranes, and the preparation of cathodes. They then measured parameters including Porosity, Electrolyte Uptake and Ionic conductivity of the resultant polybenzimidazole membrane.
The results obtained from their experiment showed that the blend of OPBI and PEG membranes had good miscibility properties since it did not show any macroscopic phase separation. Since OPBI is completely insoluble in water whereas PEG is soluble in contrast, soaking the blended membranes in water principally removed the PEG component and replaced it with micropores. The results also showed that the formation of these micropores was affected by factors such as the weight content and molecular weight of the PEG.
The researchers further established that a proper molecular weight of the PEG and a high PEG content were essential for the formation of micropores and that the ratio of 1:5 (OPBI/PEG10000) was most ideal. The properties exhibited by the resultant polybenzimidazole membrane included a higher Electrolyte Uptake due to increased porosity and also a relatively higher ionic conductivity in comparison to less porous membranes.
The study thus led the researchers involved to a number of conclusions. They realized that; the use of water in the preparation of a series of OPBI microporous membranes by simply extracting PEG from dry OPBI/PEG blend membranes was indeed practical. The significance of the PEG weight and molecular fraction throughout this process also became evident. The polybenzimidazole membranes that were formed also had better qualities and therefore, the potential to make lithium-ion batteries more efficient and safer in comparison to the commonly used polyolefin membranes.
Liang, Naiqiang, Jianhua Fang, and Xiaoxia Guo. A simple approach for preparation of porous polybenzimidazole membranes as a promising separator for lithium ion batteries. Journal of Materials Chemistry A 5.29 (2017): 15087-15095.
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