Anyone who has a portable device — including smartphones, tablets, laptops, smartwatches and fitness trackers — is obviously familiar with a lithium-ion (Li-ion) battery because most (if not all) of these devices are powered by this kind of battery. We’ve been okay with the rechargeable for a while, but as lithium-ion batteries are now close to reaching their maximum storage capacity (in other words, battery life can’t be extended any more), and with the horror stories about phone batteries that explode or burn, the search is on for an alternative battery that can meet our demands better and safer.
So far, the best bet is lithium-sulfur (Li-S) batteries. These batteries don’t just have an energy capacity that’s much higher than Li-ions, they’re quite light and are cheap to make too (because sulfur is abundant and inexpensive).
On the downside, however, Li-S batteries suffer from what’s referred to as ‘poor cycling stability’. This means that after a few charge and discharge cycles, its electrodes break down, reducing the cell’s capacity and making the battery unstable. To make Li-S batteries the new king of batteries, this problem will have to be addressed first.
Thankfully, researchers at the Yale University are claiming they may have the potential solution — an ultra-thin protective coating that can prolong the life and enhance the efficiency of Li-S batteries. The material they developed — a dendrimer-graphene oxide composite film — can supposedly be applied to any sulfur cathode. A cathode is a battery’s positive terminal while an anode is its negative terminal.
To come up with their composite film, the team simulated how different materials would react to molecules in the cathode. The ‘winning combination’ turned out to be graphene and dendrimer. Specifically, it was graphene oxide’s strength and the dendrimer molecule’s ability to confine lithium polysulfides that seemed to work.
At a thickness of about 90 nanometers, the dendrimer-graphene oxide gel-like mixture can easily be used to coat sulfur electrodes. The dendrimer kept the lithium compounds together, preventing them from leaking out and degrading the cell, while the strength of the graphene kept the film intact. The result is a longer life cycle and performance that remained efficient.
As Professor Hailiang Wang, one of the lead authors of the study, said in a statement they released: “The developed film is so thin and light it will not affect the overall size or weight of the battery, and thus it will function without compromising the energy and power density of the device.”
The new material is not just easy to prepare. It’s also composed of materials that are commercially available, making it cheap and relatively easily to scale up. The first hurdle has been overcome, and the team is now working on ways to further improve the performance of Li-S batteries.
The study was recently published in the journal Proceedings of the National Academy of Sciences.