- Second Century
- ✈️ Issue #12: Will this new battery enable electric aviation? 🔋⚡️
✈️ Issue #12: Will this new battery enable electric aviation? 🔋⚡️
The biggest drawback of Lithium-ion batteries for aviation purposes is their low energy density.
Fortunately, an alternative is being developed at the moment.
However, it has a downside as well.
Want to know more? Scroll some more ⬇️
👩✈️On the menu
Starter: The biggest obstacle
Main course: A solid solution?
Dessert: And there is more
The biggest obstacle
The biggest obstacle to get to zero-emission aviation is this:
How to store enough energy required for propulsion without negatively influencing the transport capabilities of the aircraft?
Fortunately, it is a problem that other modes of transportation, who are faced with sustainability issues like cars and ships, are facing as well. That means that finding a solution is done by more people than just those who are working in aviation. Especially the electric aircraft being developed today heavily rely on developments in battery technology for electric cars, mobile phones and laptops.
While almost all current battery driven devices and vehicles rely on lithium-ion (Li-ion) batteries, there is a good chance that these will become obsolete in the (near) future. Research centers all over the world are finding new ways to store energy for consumer electronics and vehicles. Li-ion batteries are facing some heavy competition.
🍲 Main course
A solid solution?
So, Li-ion batteries are overweight. For cars, being overweight is not a big problem, but it is a no go for aircraft. But what does being overweight look like when looking at the numbers?
An important number for batteries is the energy density. How much energy a battery can store per unit of weight. A number that is expressed in watt-hours per kilogram (Wh/kg). Current Li-ion batteries have an energy density of around 250-300 Wh/kg. Ten years ago it was about half of what it is now. And experts expect it to be at 400 Wh/kg in about four or five years.
That 400 Wh/kg is the number to watch when it comes to batteries. FlightGlobal calls it "The magic number that makes electric flight viable" By electric flight they mean Urban Air Mobility (UAM) in eVTOL aircraft. These aircraft don't need to consume that much energy because they only carry a small amount of people, about four or five, over a short distance of about 60-100 miles.
So, while these types of batteries will be fine for short eVTOL routes, for fixed wing aircraft it won't suffice. Dr James Robinson, a senior research fellow in chemical engineering at University College London, states that these type of aircraft will require “batteries that extend performance beyond the limits of Li-ion technology”.
Fortunately, a number of alternatives for Li-ion batteries are currently being developed. The type that looks the most promising for aviation applications is the solid state battery.
Whereas Li-ion batteries use a liquid to store the energy, solid state batteries use a solid material (hence the name). This type of battery is capable of delivering more energy while weighing less than current batteries, thereby improving the energy density. The NASA program Solid-state Architecture Batteries for Enhanced Rechargeability and Safety (SABERS) has demonstrated a solid state battery with an energy density of 500 Wh/kg. Almost twice as much as Lio-ion batteries.
An additional advantage is that the solid material is less prone to overheating than a liquid material which makes them less likely to catch on fire when malfunctioning. NASA’s tests have proven that solid state batteries can operate in temperatures close to twice as warm as Li-ion batteries can. Thinking of the battery problems the first series of Boeing 787 aircraft had and the fact you often cannot take battery devices in your hold luggage proves that this is a downside of the current batteries for aviation. This safety aspect could be a game changer when it comes to certification.
Not there yet
Unfortunately, solid state batteries are not yet capable enough to be placed in an electric aircraft. Looking at energy density, these new batteries crush their Li-ion counterparts. However, when it comes to charge and discharge rates, there is yet no battery type that can beat Lio-ion.
The charge rate indicates how quickly a battery can recharge. Translate that to aviation operations and you can state that it will take more time to charge an aircraft using a solid state battery. Making turnarounds longer and reducing the numbers of flights one aircraft can execute per day. Directly influencing the economic viability and operational flexibility.
The low discharge rate is potentially even worse. While a low charge rate only has a negative influence on the time it takes to charge, a low discharge rate has a direct negative effect on the performance of the aircraft. Everyone who has ever driven an electric car knows how quickly they can accelerate. This is because of the high discharge rate of the Li-ion battery that’s inside. That battery can release a large amount of energy in a short amount of time. Doing that limits the range, but it can safe you from a dangerous situation. For example, when a captain decides to make a go-around close to the runway, he or she wants the aircraft to climb as soon as possible. A solid state battery will take more time to get the engine to full power, thereby taking more time to execute the go-around.
NASA wouldn’t be NASA if they weren’t working on solving that problem. They state that “SABERS has experimented with innovative new materials yet to be used in batteries, which have produced significant progress in power discharge. During the past year, the team successfully increased their battery’s discharge rate by a factor of 10 – and then by another factor of 5 – inching researchers closer to their goal of powering a large vehicle."
It is not yet clear when solid state batteries are ready to replace Li-ion batteries. Because many materials are available to function as the solid in the battery, there are many materials to choose from. Improving the chance of finding one that is suitable for the job. However, it will take some time to figure out which one is best.
And there is more
There is a lot more going on in battery development than I am able to discuss in this issue. This video gives a good overview of other developments in battery technology. And as you will see, solid state technology is an integral part of several new technologies.