Tohoku University research has resulted in a hybrid electrolyte that is both more stable while also retaining excellent conductivity. This should provide a safer polymeric solid electrolyte for Li-ion batteries with a myriad of applications.
The research group’s paper, “Increasing the ionic conductivity and lithium-ion transport of photo-cross-linked polymer with hexagonal arranged porous film hybrids,” has been published in the free access journal iScience.
Lithium-ion batteries (LIBs) are one of the most used batteries that support the modern information technology society, including smartphones and EVs. LIBs are repeatedly charged and discharged by Li-ions passing back and forth between the positive and negative electrodes, with the Li-ion electrolyte acting as a passageway for the ions. Normally, organic electrolytes such as liquid ethylene carbonate (EC) and their gels have been used as the Li-ion electrolyte due to their voltage resistance and ionic conductivity. However, as the liquids and gels are flammable, a switch to safer polymeric solid electrolytes is preferable.
Polymeric solid electrolytes such as polyethylene glycol (PEG) have been proposed as impact-resistant Li-ion electrolytes. However, PEG-based polymer electrolytes crystallize near room temperature, resulting in a significant drop in Li-ion conductivity to around 10-6 S/cm at room temperature.
To solve this problem, the research group invented a new type of polymeric solid electrolyte by combining a porous polymer membrane with pores of several microns and a photo-cross-linkable polyethylene glycol PEG-based polymer electrolyte.
The polymeric solid electrolyte realized a wide potential window (4.7 V), a high Li-ion conductivity in the 10-4 S/cm class, which is equivalent to a liquid and sufficient for practical use, and a high Li-ion transference number (0.39).
Li-ions transferring in the electrolyte move in various directions due to natural diffusion. The distance is several µm to 10 µm and does not always move linearly between electrodes, which is one of the reasons for the decrease in ionic conductivity. In the present study, therefore, the performance of photo-cross-linked PEG-based solid polymer electrolytes was improved by constructing them with micron-sized porous membranes.
This polymeric solid electrolyte not only shows high performance as an electrolyte but is also expected to be effective in deterring the formation of Li dendrites (dendritic crystals), which can cause ignition, due to the inclusion of a porous membrane. Through the realization of safe, high-performance LIBs, this achievement will contribute to the realization of a sustainable energy supply, which is the seventh goal of the Sustainable Development Goals.
This might be the tech that really sets off lithium ion from the oncoming competing battery chemistries. While we’re pretty safe using lithium ion in small single batteries for cell phones and even laptops, larger ones in bunches as in cars and busses have offered some spectacular fires, way too often. Curiously, they also seem to ignite themselves when surviving a hurricane, albeit likely having been soaked in salt water.
There is a high probability that competing chemistries will have problems maturing too.
If this solid electrolyte can scale up for manufacturing at low cost and offer a much safer lithium ion battery, that would be quite an improvement. Let hope it scales up at a really low cost.
By Brian Westenhaus via New Energy and Fuel
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