Science Feature: A Salty Battery
A Salty Battery
'Who Killed the Electric Car?' asks a 2006 documentary film, proposing a sort of "crime" that most of us probably didn't even know had been committed. The culprit, according to the film, was equal parts Big-Oil conspiracy, and old-fashioned, change-resistant, consumerist, American sensibilities.
First off, let me just say that reports of the electric car's demise were greatly exaggerated. The movie focused on just one model, General Motors' EV1, which was manufactured between 1996 and 1999. For various reasons explored in the film, the EV1 never really caught on. So complete was its failure that nearly all of the EV1 units that had been manufactured--over a thousand of them--were recovered by GM and destroyed. There are of course other electric cars being manufactured today, but the strange tragedy of the EV1 highlights a problem that just won't go away. I'm talking about batteries.
There are a lot of different types of batteries, but they all function on the same basic principle. Electrically charged atoms--called ions--want to form stable molecular bonds with oppositely charged ions, just like the north and south poles of magnets want to stick together. Batteries usually consist of some kind of reactive chemical--an acid or alkali metal--that has either a positive or negative electrical charge. (If you want to go all Chemistry 101 here, the charge is determined by the number of electrons; if there are more electrons than protons in the atom, it has a negative charge, and wants to plug that extra electron into an element with a positive charge). Batteries provide current when those ions attempt to move around and form those connections.
It might be convenient to think of a rechargeable battery the same way we think of a gas tank--when it runs out of charge, we plug it in and fill it up with electricity--but that's a little misleading. It's really much more akin to winding an old fashioned clock. The clock has a spring that stores the potential energy--our energy as we twist the winding key--and as that spring uncoils, it pushes the clockwork gears until all of the energy stored in spring-tension form is gone. We can wind the clock up again, and store more energy in the spring, but every time we do that, the metal in the spring gets a little weaker.
A fully charged battery has a lot of stored ions. When an electrical circuit is closed, those ions seek out oppositely charged particles in the neighboring part of the battery cell and it's that transfer of polarized charges that results in current. The ions aren't leaving the battery; rather, they're just kind of bumping the electrons in the copper wire that forms the circuit, much the same way that energy passes through the balls in the middle of a Newton's Cradle toy.
When enough of those ions have found a new home in the reactive material, the battery has no more energy left to give. Charging the battery up reverses the process by forcing the ions out of the reactive material, where they'd prefer to be, and back into their agitated and reactive state. Since the ions really don't want to go back, this process requires time and a lot of energy, may create quite a bit of heat (which is energy lost) and depending on the type of battery, may release some potentially hazardous gases. The process will also permanently destabilize the battery components over time, which is why even rechargeable batteries wear out eventually. Commercially available rapid charging devices, which can have your electric car ready to drive in about half an hour, will wear the batteries out even faster. That means unlike a gas-powered car, which can run for years with only minor preventative maintenance, the average electric car will have to have its battery--the most important and expensive part of the car--replaced as often as once a year.
There's another weighty problem that limits the effectiveness of electric cars: batteries are heavy.
A twelve-volt car battery weighs about forty pounds, and all it really does is store electrical power for getting the engine to start, or running a few accessories when the engine is off. Leave the lights on when the car isn't running, and your battery will be dead in a few hours. An electric car needs a lot more battery power, so the car has to carry around a lot of battery weight, which in turn requires even more power to keep the thing moving. It's a vicious circle.
The first EV1 units to roll off the assembly line weighed in at about 3,000 pounds, lighter than a gas-powered vehicle, true, but most of that was battery weight, and those batteries gave the car a range of only about 60 miles, which made it somewhat useful as a commuter vehicle, but didn't allow the kind of freedom to drive that Americans have come to know and love. Later battery advancements for the second generation EV1 increased that range to about 160 miles, and cut almost half a ton off the weight, but that still doesn't come close to matching the range of the average car with a full tank of gas. And whereas you can top off a gas tank in just a few minutes and get back on the road, recharging an electric car requires plugging-in and waiting. The Gen 2 battery needed to charge from 1-3 hours to reach operational status.
Fortunately, the growing demand for portable consumer electronics has resulted in a new Renaissance of battery technology. We still use the old disposable zinc-acid type battery for a few things, but we are now seeing rechargeable batteries--utilizing exotic alkali metals like cadmium and lithium--that are lighter, recharge faster, and last longer. All of these advances will not only keep the electric car alive, but very probably make it the preferred transportation alternative in years to come.
It was just such a battery innovation that got me thinking about this subject. In June, scientist at the University of Maryland announced that they had created a battery out of tin, sodium, and wood.
Yes, you read that correctly--a battery made of wood and salt.
Actually, the wooden component is an incredibly thin layer of cellulose--one-thousandth the thickness of a piece of paper--completely enveloped in tin. Sodium--which is chemically one-half of table salt--is the medium for holding the charge. While lithium is more efficient at storing ions than sodium, it is also harder to come by--read: expensive--and perhaps even more troubling, hard to dispose of safely. Sodium, in its elemental form, can be pretty hazardous stuff too--it can make more than just your blood pressure explode--but we have it in abundance, which makes it a very affordable alternative to lithium for building high capacity batteries--the kind we need for electric cars. The wood and sodium battery also seems more durable than lithium-ion batteries, not only in terms of how many times it can be recharged, but also in withstanding temperature extremes and physical shock.
What's encouraging about this news is that it shows how scientists and innovators are actively addressing issues that have for too long held us in a state of inertia when it comes to technological advancement. We've held back from cutting our ties to what are basically Steam-era technologies because the practical considerations just seemed too daunting. 'Electric cars are too slow, they don't go far enough, they take too long to recharge... ', 'Rechargeable batteries? They're expensive, they wear out, and then what are you supposed to do with them? You can't just throw them in the trash...', 'Solar power isn't practical because there's no effective way to store power for use when the sun isn't shining...'
Will the wood-sodium battery change all that? It's too soon to say for sure, but it's definitely another step in the right direction.
Sean Ellis is the author of several thriller and adventure novels. He is a veteran of Operation Enduring Freedom, and has a Bachelor of Science degree in Natural Resources Policy from Oregon State University. Sean is also a member of the International Thriller Writers organization. He currently resides in Arizona, where he divides his time between writing, adventure sports, and trying to figure out how to save the world.