Long life nanowire batteries possible

A STABILISED nanowire can extend the lifespan of a battery to hundreds of thousands of charging cycles and potentially lead to consumer product batteries that may never need replacing thanks to a Plexiglas-like gel that has been developed by researchers.

A research team from the University of California Irvine (UCI) has coated a gold nanowire in a manganese dioxide (MnO₂) shell, then encased the assembly in an electrolyte of the Poly(methyl methacrylate) (PMMA) gel.

The team do not yet fully understand the stabilisation mechanism; however, their hypothesis is that the gel plasticises the MnO₂ shell, thereby softening it and giving it enough flexibility to prevent brittle fracturing and separation of the MnO₂ from the gold nanowire current collector.

The team cycled the nanowire prototype up to 200,000 times over three months without detecting any loss of capacity or power and without fracturing any of the nanowires.

Being able to use nanowires in batteries would be advantageous as they are thousands of times thinner than a human hair and provides a large surface area for the storage and transfer of electrons on the electrode. They are also highly conductive.

With nanowires proving susceptible to cracking, they last only 5,000-7,000 charging cycles before being destroyed, which is unsuitable for use in today’s batteries. The team hope the gel-stabilised technology can eventually be integrated into commercial lithium batteries that would not need replacing.

Reginald Penner, chair and professor of chemistry at UCI, told The Chemical Engineer: “Nanowires are bulky, requiring space between them to function well. It is difficult to predict whether they will make the battery smaller - this will depend on whether clever engineers can improve the packaging. But they should definitely last longer.”

“Our immediate goal is to contribute to the science that still needs to be done. With some luck, in ten years we'll have nanowires in our [lithium ion] batteries and they'll be smaller than they are today,” he added.

The next step for the team will be to test the plasticising hypothesis by using nanoindenting to directly probe the mechanical properties of the MnO₂. The team are also investigating whether the stabilisation method from the PMMA gel can be used for other metal oxides, and if there is another gel that will have a greater stabilising effect than PMMA.

ACS Energy Letters, DOI: 10.1021/acsenergylett.6b00029