Published on December 19th, 2014 | by Tina Casey8
Two Nifty Little Nanoscale Lifts For Energy Storage
December 19th, 2014 by Tina Casey
Just when you thought the world was ready to move beyond lithium batteries, along comes a new discovery that shows how much more juice we can squeeze out of the technology. On the other hand, lithium has been the gold standard for energy storage in a slew of clean tech fields including electric vehicles and large-scale stationary batteries, but it’s beginning to bump up against some competition from other areas.
By other areas we mean sodium batteries. You thought I was going to say fuel cells, right?.
Advanced Energy Storage: Use The Force!
First, let’s take a look at some nano-news in the lithium-ion energy storage field. The item that caught our eye deserves a group hug from all you taxpayers out there, because it comes out of our Oak Ridge National Laboratory.
This is one of those surprise discoveries where you set out to do one thing, and you accidentally discover something else that’s much more exciting.
The research team was trying to measure the properties of polymerized ionic liquid thin films, a highly conductive material with a “unique” structure that has promising applications for lithium batteries and solar cells.
An ionic liquid refers to a salt in liquid state. Through polymerization into the mix (polymers refer to materials composed of similar molecules, typically in a long chain), and now you’re cooking with gas.
To measure the conductivity of polymerized ionic liquid, the team dusted off their trusty atomic force microscope. That’s not entirely a new thing, since the gizmo is commonly used to study non-conductive polymers, and to produce patterns in them.
The team didn’t expect the pattern thing to happen, but it did. The microscope bored nanoscale holes in the material.
That’s exciting because this kind of nanoscale lithography is becoming common in clean tech manufacturing and other nanoscale fields, but not at quite such a tiny scale. What you’re looking at is the potential for fabricating smaller, more powerful batteries while putting less energy into the manufacturing process.
The team also found that the process used far less energy to make patterns on their conductive material, compared to the same process used on non-conductive polymers.
The difference is that when applied to a non-conductive material, the holes are formed by highly localized heating. The team’s material, in contrast, kind of self-assembled its own holes when negative ions migrated to the positively charged tip of the microscope.
Here’s the next step according to study co-author Vera Bocharova:
Right now the size of the formed features is in the range of 100 nanometers, but it’s not the limit. We believe it’s possible to change the experimental setup to advance to lower scales.
If you want to see the details, look for “Controlled Nanopatterning of a Polymerized Ionic Liquid in a Strong Electric Field.”
Don’t Look Back…
As Satchel Paige famously said, “Don’t look back. Something might be gaining on you.” Obviously he was telling lithium batteries to watch out for sodium batteries, in this case enhanced by a form of graphene.
For those of you new to the topic, we have tirelessly described graphene as the nanomaterial of the new millennium for its practically limitless clean tech applications, including next generation solar cells as well as lithium electric vehicle batteries and other forms of advanced energy storage.
Graphene refers to a sheet of carbon just one atom thick. It possess Superman-style strength and unique — and powerful — conductive properties, but it is difficult to fabricate and work with.
That’s where graphene oxide comes in. It’s a “defective” form of graphene that functions as an insulator. However, when it is heated it can become a conductor or semiconductor.
An engineering team at Kansas State University took a look at the behavior of sheets of graphene oxide “paper” when used as electrodes in sodium-ion and lithium-ion batteries. Here’s the money quote from c-author Gurpreet Singh:
Most lithium electrode materials for sodium batteries cannot even last for more than a few tens of charge and discharge cycles because sodium is much larger than lithium and causes enormous volume changes and damage to the host material. This design is unique because the distance between individual graphene layers is large enough to allow fast insertion and extraction of the sodium ions, thanks to the oxygen and hydrogen atoms that prevent sheets from restacking.
Specifically, the study showed that the graphene oxide paper sheets withstood more than 1,000 charge/discharge cycles. That’s a big improvement over past experience with lithium electrode materials for sodium batteries, where the cycling can be counted in tens.
Not to worry, lithium-ion. Singh foresees that sodium batteries will find a place in large scale stationary energy storage, not so much in mobile energy storage for electric vehicles.
But, you never know…