The ionic conductivity of polymer-based solid electrolyte has been enhanced by more than 3 full orders of magnitude by researchers at Stanford University, through the use of ceramic nanowire fillers, according to a recent press release from the university. The new ceramic-nanowire-filled composite polymer electrolyte also possesses a better (enlarged) electrochemical window of stability. (It might be obvious to some here, but just to be clear, an improvement of 3 orders of magnitude is a considerably greater one than when something is increased 3 times over — it’s actually an increase of ~1,000 times.)
This improvement opens the way toward the design of solid ion electrolytes with superior performance as compared against conventional electrolytes, according to the researchers involved.
A bit of background — solid-state electrolytes have many potential advantages (improved safety performance, better electrochemical stability, etc) as compared against conventional liquid electrolytes, but there are barriers in the way of their wider use. The low mobility of lithium ions in solid electrolytes is probably the primary limitation/barrier in that regard, which is exactly what the new work from the Stanford researchers addresses.
Here are some of the specifics of the work coming via the new research paper:
In contrast, dispersing ceramic particles in polymer matrix increases ionic conductivity effectively, meanwhile improving electrochemical stability and mechanical strength. The addition of these ceramic particle fillers is believed to hinder the polymer crystallization or to contribute highly conductive interface layers between polymer and ceramic.
The ceramic fillers are generally divided into two categories: inactive fillers that are not involved in lithium ion conduction process (eg, Al2O3 SiO2) and active ones that participate in lithium ion transport (eg, Li3N and Li1.3Al0.3Ti1.7(PO4)3. Nanoscale ceramic fillers have large specific surface area and can enhance the ionic conductivity drastically. Most research has emphasized ceramic nanoparticles, whereas little attention has been given to one-dimensional ceramic fillers. Here we explore nanowire fillers and demonstrate significant improvement of ionic conductivity and electrochemical stability.
To be specific here, the researchers fabricated Li0.33La0.557TiO3 (LLTO) nanowires and dispersed them into PAN-LiClO4 polymer without any additional additives — at concentrations of between 5−20 wt %.
Out of the various concentrations tested, the composite electrolyte with 15 wt % nanowires was shown to possess the peak recorded conductivity — of 2.4 × 10−4 S cm−1 at room temperature. This is roughly 3 orders of magnitude higher than that of PAN-LiClO4 without any fillers — a huge improvement, in other words.
According to the researchers, the improvements are the result of the ceramic nanowires — as you can probably guess — acting as a conductive network within the wider polymer matrix. More or less a highway system, to put an analogy on it.
The new findings were just detailed in a paper published in the ACS journal Nano Letters.
Image by Kristoferb, via Wiki Commons
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