Lithium-ion batteries are in our phones, computers, luggage, and even cars. Compared to fossil fuels, like oil and gas, rechargeable batteries like these are meant to be a more sustainable option, but lithium-ion batteries have a dark secret: not only are the elements used in these batteries, like cobalt and lithium, dwindling, but mining for these toxic metals can cause environmental damage. Not to mention, lithium-ion batteries themselves can quickly lose charging capacity after repeated use.
In search of a longer-lasting, more environmentally friendly alternative to these popular batteries, researchers have looked to organic materials instead. Previous studies have explored solutions such as synthetic polypeptides (i.e. proteins) to play the role of the battery's electrode, but a new study for York University has now looked at how a carbon-based organic molecule could work instead.
While these organic materials can face their own stability challenges, the York University team has demonstrated how a new molecule derived from organic materials can not only match lithium-ion batteries in terms of charge capacity but can outlast them in cycle recharges. All while overcoming cycle stability troubles associated with these organic approaches.
The study, published Thursday in the journal Batteries & Supercaps, explored how an electroactive, chemical compound, called phosphoryl-bridged viologens (or phosphaviologens) can be tethered to super tiny, carbon nanotube scaffolding to create an organic structure capable of replacing elements like cobalt in a lithium-ion battery. After fabricating this composite, the researchers set out to compare the effectiveness of their new battery to traditional models.
Co-author of the study and professor of chemistry at York University, Thomas Baumgartner, tells Inverse that what sets their approach apart is that instead of focusing on already existing building blocks, they are designing new ones.
"The goal is to create sustainable batteries."
"A lot of organic battery research around the world uses the same very few organic building blocks as active component," says Baumgartner. "For this technology to mature and expand further, new powerful electroactive molecules are required. This is what we do in my group - develop new building blocks. We had introduced a new building block a few years ago and how now further optimized it in the current work, to make the battery fabrication more efficient, which addresses the critical cost factor for this technology to become viable."
The researchers observed that a hybrid, lithium-phosphaviologens battery exhibited voltages equivalent to traditional lithium-ion battery, up to 3.5 volts, and continued to retain its performance after 500 charge/recharge cycles. For comparison, a typical lithium-ion battery's lifespan caps out at just 500 charging cycles.
With the promising results of this study, Baumgartner said in a statement that new composites like this could help make creating and recycling batteries in the future much easier and more sustainable.
"Organic electrode materials are considered to be extremely promising materials for sustainable batteries with high power capabilities," said Baumgartner. "Electrodes made with organic materials can make large-scale manufacturing, recycling or disposing of these elements more environmentally friendly. The goal is to create sustainable batteries that are stable and have equally as good if not better capacity."
However, Baumgartner also tells Inverse that these achievements don't mean that lithium-ion batteries themselves will totally disappear; just change.
"Our device is still a lithium-ion battery at its core, and that design still follows that of traditional batteries consisting of two electrodes - a positive and a negative one - separated by a charge transport medium," says Baumgartner. "In the foreseeable future, this will likely not change. What could change is the nature of both electrodes - with organic materials for both currently being explored, as well as finding alternatives for the charge transport medium (i.e. the Li-ions)."
That said, there are still a few wrinkles to iron out when it comes to perfecting their design before lithium-ion batteries are truly a thing of the past.
One such wrinkle is the resilience of their battery design at different temperatures. The authors report that the battery showed much more capacity loss at 5 degrees Celcius (41 degrees Fahrenheit) compared to higher temperatures during the trials of around 20 degrees Celcius (68 degrees Fahrenheit) after 500 cycles. The authors write that this decreased capacity could be the result of incomplete discharging at this temperature and cycle range.
Moving forward Baumgartner says his team hopes to further improve the capacity of these batteries even beyond that of a traditional lithium-ion battery, which he tells Inverse will involve overcoming a weight disadvantage these molecules have compared to traditional lithium-ion batteries.
"Many molecules are still too heavy for the amount of energy that can be stored in a given volume. That is what we are working on - making the materials better in storing more energy by also becoming lighter," says Baumgartner. "At this point, given the weight disadvantage, organic batteries would not provide enough power in such a small space required for a phone, for example. Application in a car is more realistic since there is arguably more space for the battery, but the added weight could be unreasonably high. Realistically, a lot more work needs to go into considerably improving the capacity of organic batteries before they can become commercially viable. But we are at least on the right track."
Abstract: The adoption of intermittent renewable power sources has placed battery technologies into the limelight, initiating a push to develop sustainable materials for energy storage that do not rely on rare or toxic elements. Organic electrode materials are made from abundant elements that are consumed in the biomass cycle, which can make large-scale manufacturing and recycling of these materials less detrimental to the environment. Herein, we explore how organic, electroactive phosphoryl-bridged viologens (phosphaviologens) can be composited with single-walled carbon nanotubes (SWCNTs) and used as organic electrodes composed of sustainable/abundant materials. To this end, we have functionalized phosphaviologens that exhibit two stable and reversible reductions with pendant pyrene moieties to interface them with carbon nanotubes. The anchoring of the redox active species on the surface of SWCNTs prevents electrode dissolution, and hybrid batteries with a high voltage (1.95–3.5 V) vs. Li/Li+ using phosphaviologens as the cathode remain stable past 500 charge/discharge cycles.