Last week, we talked about lithium-ion battery electrodes being created from cheap natural mushrooms. Well, this time around, a research team (led by Dr. Da Deng) at Wayne State University in Detroit, has done one better – by actually utilizing harmful algal blooms (HABs) for creating battery electrodes with the high performance factor. In fact, in August, a bevy of these HABs managed to poison an entire water system in Toledo, Ohio; thus leading to the scarcity of drinking water for over 500,000 residents around the area. Fortunately, a few scientists did their best to salvage some of these toxic specimens from the lake. And now, after months of experimentation, they have demonstrated that when HABs are heated at very high temperatures (700-1000 degrees Centigrade) in argon gas, the algae can be transformed into what is known as ‘hard carbon’. This hard carbon in turn can be used for cheaply made, high-performance electrodes for sodium-ion (Na-ion) batteries.

In essence, the researchers have showcased their ‘trash-to-treasure’ approach with seemingly all round benefits. One of such advantages lies with the very nascent scope of Na-ion battery technology. To that end, the primary challenge in contriving a Na-ion battery pertains to finding a feasible electrode material, as opposed to conventional graphite used in Li-ion batteries. This is because Na ions are larger in their dimensions – which makes it problematic to fit into graphite structure. On the other hand, hard carbon demonstrates a more undulating structure with more number of defects, thus making it conducive to the bigger Na ions.

Now, in terms of modern scope, most of the world’s hard carbon is currently derived from petroleum. But this is the very first time that scientists were able to derive hard carbon from HABs (that entailed blue-green algae). Suffice it to say, this breakthrough is ‘greener’ than the regular processes, which is further complemented by the abundance and low-cost growth patterns of HABs. As for the process of creating the Na-ion battery electrodes, the scientists made use of 80 percent hard carbon (derived from HABs), 10 percent carbon black (for better conductivity) and the remaining percentage binder. And after the composite was dried, the resultant material was reformed into coin cells that were integrated with sodium foil as the counter electrode.

When translated to numbers, initial testing showed that the electrodes had a healthy first cycle capacity of up to 440 mAh/g. However, this figure irreversibly plunged after the primary cycle, thus amounting to a reduced capacity of 230 mAh/g from the second cycle. The good news is, the hard carbon electrodes tended to retain this capacity for numerous cycles afterwards. Moreover, the researchers are also tinkering with some modes in the heating process that can rather enhance the performance factor (including capacity and stability) of the Na-ion battery electrode.

And interestingly, beyond the green technology and effective performances, it is the core practicality of the Na-ion battery technology that can be prove to be more crucial in the near-future. In that regard, the scientists pointed out how Li-ion batteries accounted for an average cost of $410 per kWh in 2014, which starkly contrasts with the regular retail price of electricity (in United States) of 10 cents per kWh. On the other hand, sodium is more abundant than lithium, thus alluding to far cheaper prices for Na ion battery-generated electricity. We should also note how this (still nascent) technology deals with the HAB predicament in freshwater lakes. As Deng made it clear (as told to Phys) –

Harmful algal blooms, caused by cyanobacteria (or so called ‘blue-green algae’), severely threaten humans, livestock, and wildlife, leading to illness and sometimes even death. The Toledo water crisis in 2014 caused by HABs in Lake Erie is a vivid example of their powerful and destructive impact. The existing technologies to mitigate HABs are considered a ‘passive’ technology and have certain limitations. It would significantly and broadly impact our society and environment if alternative technologies could be developed to convert the HABs into functional high-value products.

The study was originally published in Environmental Science & Technology.

Credit: Da Deng, Wayne State University

Source: TechXplore