Monday, April 13, 2015

Aluminum batteries might find application in hybrids and FCVs

New publications about battery breakthroughs appear regularly in the media. In practice however not much has changed in the field of battery technology in the last few years. Recently Stanford University came up with a new story.

This time the story is about the aluminum-ion battery. Stanford has developed such a battery that they present as very promising. Of course they are looking for investors to help further develop this technology into actual products.

The main difference with the commonly used lithium-ion battery is the use of aluminum instead of lithium.

Aluminum offers a number of advantages compared to lithium. Aluminum does not cause a fire hazard in case of incidents. Another important advantage is the shorter charge time: Stanford has succeeded in charging the battery in only a minute. Finally the battery has a much longer life time than lithium batteries. Standford's battery could withstand 7,500 cycles without capacity decay, where a typical lithium battery lasts about 1,000 cycles. Finally aluminum is also cheaper than lithium.

The major disadvantage of the aluminum is the lower voltage, about half the voltage of a lithium battery. That also leads to lower battery energy density. In other words: more batteries are needed to store the same amount of energy. That is a key disadvantage which disqualifies this battery for most of the popular applications of lithium batteries, such as mobile devices and electric vehicles.

Still there are applications where the advantages of this aluminum battery seem more important than the disadvantage. Stanford suggests using this battery for storage of excess electricity from sustainable energy sources such as wind and solar. In such a stationary application the size of the battery stack is much less relevant and life time is more crucial.

Hybrid vehicles
Although aluminum seems unsuitable for electric vehicles and plug-in hybrids, I do see opportunities for vehicle applications. Hybrid vehicles without a plug such as the Toyota Prius have a relatively small battery which can be charged and uncharged multiple times during a single trip. And it is crucial that the battery can be charged quickly as this is needed to store breaking energy. The life time of lithium batteries in hybrid vehicles is a major bottleneck. In Toyota's hybrid synergy drive system the potential capacity of the batteries is only used for a small amount in order to extend battery life. In Honda's IMA (Integrated Motor Assist) system it is even worse. Battery failure is one of the main reasons why the IMA system is unsuccessful on the market. Aluminum batteries might offer new opportunities for such hybrid systems.

Fuel Cell Vehicles 
Another type of vehicles that might see use of this type of batteries is the Fuel Cell Vehicle. FCVs are in fact hybrid vehicles which use a lithium-ion battery to store energy which can be used to improve response to the gas pedal. The battery is charged from breaking energy or when you let go of the gas pedal because the fuel cell doesn't stop producing power immediately. Just like ordinary hybrid vehicles, FCVs have relatively small capacity batteries that are typically charged and uncharged multiple times during a single trip.

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