Our recent blog post compared the environment, economic, and convenience benefits of a very clean, very efficient internal combustion engine with an electric vehicle. This post dives into more detail about the problems of using battery to store energy, particularly for transportation.
In short, batteries are very big, heavy, and expensive compared to gasoline (or diesel, or methanol or biodiesel, or ethanol or other liquid hydrocarbons ) stored in a typical automotive fuel tank.
The article, Has the Battery Bubble Burst, by Fred Schlachter of the American Physical Society sums up the problem:
- Gravimetric power density: Batteries weigh more than 150 times as much gasoline for the same amount of stored energy, 0.3 MJ / kg to 47.5 MJ / kg. Weight is the enemy of vehicle efficiency, and a heavy battery compounds weight gain as the size of motors, supports, and suspension grow as well.
- Volumetric power density: Batteries take up more than 80 times as much space as gasoline, 04 MJ / L to 34.6 MJ / L.
In other words, because batteries have about 100 times less energy density than gasoline, EV vehicles all face severe weight and range disadvantages.
Another problem referred to by Dr. Schlachter is the very high cost of batteries. It is difficult to nail down precise numbers, but this article cites an industry insider and expert as saying it unlikely battery costs will drop below $200/kWh before the end of the decade. If this is the case, the $17,000+ cost of the 85 kWh battery in the Tesla S would, by itself, buy a nice, brand new car.
Moore’s Law for Battery?
We are used to seeing rapid improvements in the price and performance of electronic devices. Why isn’t that happening in batteries? Quoting from the IEEE article:
The essential answer is that electrons do not take up space in a processor, so their size does not limit processing capacity; limits are given by lithographic constraints. Ions in a battery, however, do take up space, and potentials are dictated by the thermodynamics of the relevant chemical reactions, so there only can be significant improvements in battery capacity by changing to a different chemistry.
The challenge of creating a better battery chemistry is very difficult. A battery must be: safe, light, small, cost-effective, disposable (or recyclable), and able to withstand thousands of recharging events while maintaining utility.
Yet another problem for batteries
The resources required to manufacture batteries may not be sustainable. This IEEE article points out that given the world reserves of lithium (28 million tons), the amount of lithium per electric vehicle (20 kg), and the number of car sold each year (60 million) we have enough lithium for only 23 years of an all-electric fleet. The authors note, “Even taking into account the possibility of lithium recycling, the competition for lithium in other applications would escalate price.”
This article in Environmental Science & Technology notes that the high demand electric vehicles place on rare earth elements dysprosium (Dy) and neodymium (Nd) “may result in large and disproportionate increases in demand for these two elements.”
I do not want to sound like a technology skeptic. Perhaps all these problems will be solved, and batteries will become small, light, cost-effective, and sustainable. It is important to note, though, that there is no solution in sight that solves even one of those problems. Meanwhile, we have a practical alternative that has already been largely proven and can achieve our goals of affordable, sustainable, clean transportation.
We are so familiar and comfortable with the internal combustion engine we sometimes lose sight of what amazing machines they are. The gasoline in a fully fueled car has about the same energy content as a thousand sticks of dynamite. The internal combustion engine safely uses this fuel, creating 50 controlled explosions per second, operating reliably for years and hundreds of thousands of miles. They operate at extremes of hot and cold temperature and at high elevation. They are so clean that emissions are now hard to distinguish from ambient air. They are made out of common materials, and therefore are so affordable that over 60,000,000 families each year buy a new one.
Perhaps most remarkable of all is that the Achates Power engine is much more efficient than the highly evolved conventional engines we take for granted today.