Biobatteries: Taking battery technology to the next level

February 2, 2015 |

biobatteryThere’s a good chance that the electric battery of the future will have biobased aspects to them — or may even be powered by a biofuel. How’s that again? The Digest investigates.

If you’ve been following the long-standing competition between electric and fuel-powered cars, you’ll know the basics. That electric motors have better efficiency than internal combustion engines, but electric cars have short ranges because batteries lack the energy density of liquid fuels, are heavy, and expensive, and take a long time to re-charge.

The current favorite among advanced battery technologies is the lithium-ion battery, which can produce a real-world range just north of 200 miles for a Tesla S sedan, but the Tesla S checks in at 4600-4900 pounds, and costs between $70,000 and $100,000.

So, we have a ways to go before all-electrics dominate car sales.

The biobased pathway to batteries with 3x today’s top efficiency

One battery technology that may prove a game-changer is a lithium-air battery. Going back to the theory of the battery, you get electron current flow because at the positive end of a battery you are creating free electrons through reduction, and they are flowing out of the negative end through oxidation. No need to go through the specifics — just focus on oxidation, meaning you need oxygen, which batteries usually are loaded with. And oxygen adds weight.

Hence the lithium-air battery. Acts in many ways like a Li-ion battery, only it draws its oxygen from the air. Hence it weighs less, and is more efficient. Up to 3X what a Li-ion battery can achieve — that’s the promise seen in the labs.

Solving challenges in lithium-air, limitations in Li-ion

The biobased angle in this? Bio is solving three daunting challenges in making lithium-air a reality — stability, rate of discharge and recharge, and the cost of manufacturing.

The technology employed is not entirely unlike the process by which an sea-based organism builds a shell. From clams to abalone, they have a metabolic process by which they extract calcium from seawater, and use the calcium to accumulate a pattered structure.

A team led by Angela Belcher at MIT — who had a previous technological breakthrough that is currently at the heart of Siluria’s technology, to mention one — uses a modified virus known as M13, which extracts manganese from water and accumulates manganese oxide into an 80 nanomater-wide structure known as a nanowire, which can carry a current.

As you know, shells have a rough texture on the outside and a large surface area because of that texture, and M13’s nanowires have the same qualities. Bottom line, that dramatically increases the charge and discharge rate — and M13 works under normal room tempetature conditions. Plus, they are more stable than nanowires produced through chemical instead of an organic process.

The biobased pathway to 10X efficiency

Far beyond what lithium-air batteries can achieve, there are the efficiencies possible with fuel cells. Now, the typical fuel cell uses stored hydrogen, and in the process of mixing it with oxygen drawn from the air, produces water and an electron flow. It’s just about Nirvana when it comes to engine efficiency and green appeal, because you have electric motor efficiencies and the only emission is water.

But there’s the problem of hydrogen. It’s difficult to store very much of it in a confined space, it’s explosive, and it’s generally produced at economical rates only from petroleum. Whoops, there goes range, stability and green appeal. But help is on the way.

The solution is the organic world’s favorite energy source. You guessed it, sugar. Yes, glucose. It’s far more energy dense than hydrogen on a joules/cc basis, it’s stable, widely available and green.

Now, how do you get electric flow from sugar? That’s where fuel cell technology comes in.

A team at Virginia Tech recently demonstrated a small-scale practical system that works as a fuel cell that uses enzymes to extract electricity from glucose. In all, 13 enzymes, and an air intake. The headlines from a report in Nature Communications are:

24 electrons per glucose unit of maltodextrin…a maximum power output of 0.8 mW cm−2 and a maximum current density of 6 mA cm−2, which are far higher than the values for systems based on immobilized enzymes…Enzymatic fuel cells containing a 15% (wt/v) maltodextrin solution have an energy-storage density of 596 Ah kg−1. which is one order of magnitude higher than that of lithium-ion batteries.

The Bottom Line

As seen in the chart below, the energy densities far outstrip li-ion technologies, and only methanol fuel cells are showing a higher energy density. So, you have methanol or sugar as a pathway to producing on-board electricity for a future generation of vehicles.


Now, isn’t that an elegant solution? After all, the dirty secret of electric cars is that, since they generally charge up in location dependent on natural gas or coal for power gen, they are really a highly-efficient from of natgas or coal-powered vehicle. It’s not going to be all that renewable until there’s a lot more renewable power generation in the mix.

It’s early days. We haven’t seen costs yet, at scale — or a manufacturing process developed. Or outputs that would run a car. Let’s call it “early, early, early days”.

But for now, here’s the green outcome — producing electricity from sugars. Which in turn can be produced as a low-cost, energy-dense storage material from CO2, sunlight and water. As companies like Proterro are now demonstrating using bacteria to do the work, or as Mother Nature does every day with sugarcane, corn, grasses and the like.

That would be energy-efficient, emissions-negative, and really cool.

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