Battery research into new materials for anodes, cathodes, and electrolytes brings news of breakthroughs almost daily. But there are few reports of research into the basic architecture of the battery. Perhaps that’s why a recent press release and scientific paper by a team at Cornell University is so interesting: It details a concept for a 3D, self-assembling battery with a gyroidal structure.
It’s not the first time that the Cornell University research group, led by Dr. Ulrich Wiesner, has published about the practical use of gyroidal structures. According to a 2016 Cornell press release, “The gyroid is a complex cubic structure based on a surface that divides space into two separate volumes that are interpenetrating and contain various spirals.”
3D on a Nanoscale
In an ordinary battery, the anode and cathode are more or less parallel to each other on either side of a non-conducting separator that also contains the electrolyte. If the components could be integrated into 3D architectures on the nanoscale, it has been suggested that batteries could be built with improved power capability. But traditional fabrication techniques haven’t allowed such architectures to be explored.
The idea from the Cornell group is to intertwine the components into a self-assembling, three-dimensional gyroid structure. The structure includes thousands of nanoscale micro-pores that are filled with the components needed to allow energy storage and delivery. The self-assembly refers to the ability of the gyroid structure to organize and grow based upon the arrangement of its nanoscale components.
Previous work from the same laboratory included a gyroidal solar cell and a gyroidal superconductor. Joerg Werner, lead author on the current work, was developing a self-assembling filtration membrane when he began to wonder if the same concept could be applied to a battery design.
The anode (grey, with minus sign), separator (green), and cathode (blue with plus sign) layers (not to scale) self-assemble into a 3D battery structure. Each layer is about 20 nanometers thick. The molecular structures of each layer is also presented. (Image source: Cornell University)
Anode and Cathode
According to the latest Cornell press release, “The gyroidal thin films of carbon—the battery anode, generated by block co-polymer self-assembly—featured thousands of periodic pores on the order of 40 nanometers wide. These pores were then coated with a 10 nanometer thick, electronically insulating but ion-conducting separator through electropolymerization, which by the very nature of the process produced a pinhole-free separation layer.”
The freedom of holes and porosity in the separator was considered crucial. Piercing of the separator can cause short circuits and fires in traditional battery designs. After adding the separator, the cathode material—made from sulfur—was added in an amount that didn’t quite fill the remaining pores. Sulfur doesn’t conduct electricity, so a layer of electronically conducting polymer was then deposited over the sulfur.
“This three-dimensional architecture basically eliminates all losses from dead volume in your device,” said Wiesner in the Cornell press release. “More importantly, shrinking the dimensions of these interpenetrated domains down to the nanoscale, as we did, gives you orders of magnitude higher power density. In other words, you can access the energy in much shorter times than what’s usually done with conventional battery architectures."
Proof of Concept
A proof-of-concept lithium ion sulfur battery was constructed, with a functional carbon anode intercalated with lithium ions and a sulfur cathode. They were separated by an ultrathin electrolyte phase. Each layer was less than 20 nanometers thick and extended throughout a macroscopic demonstration battery.
The good news is that the initial test battery did function. However, charging and discharging the battery resulted in volume changes in the sulfur that could not be accommodated by the electronically conducting polymer. The polymer eventually ripped apart and the battery no longer worked. It did, however, indicate a new and very different possible direction in battery architecture—one that deserves significantly more study.
Senior Editor Kevin Clemens has been writing about energy, automotive, and transportation topics for more than 30 years. He has masters degrees in Materials Engineering and Environmental Education and a doctorate degree in Mechanical Engineering, specializing in aerodynamics. He has set several world land speed records on electric motorcycles that he built in his workshop.
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