Credit: Robert Hoetink - Fotolia
Lithium-ion batteries are all around us. They are popular in portable devices, such as smart phones, laptops, cameras and more. They are also common in electric vehicles and can even be found in aerospace applications. The reason for the proliferation is that lithium-ion batteries have a high energy density, a slow loss of charge and no "memory effect" - reduced effectiveness when batteries are not completely recharged.
However, when it comes to electric vehicles that are only powered by a battery, the energy density in lithium ion batteries still falls short. Such full electric vehicles currently have a top range of just 150 km before they need to be recharged.
"At present, the best technologies are lithium-ion batteries, but they are somewhat limited. The energy content can be increased by up to 50% but not much more than that," explains Stefano Passerini, a professor specialising in electrochemical energy storage at Germany's Helmholtz-Institute Ulm. He says new battery technologies and chemistries, known as next-generation batteries, are needed to make electric cars more viable.
And that was precisely the focus of the EU-funded LABOHR project, which Passerini coordinated when he was with Germany's Westf"alische Wilhelms-University M"unster. The project completed its work in March 2014.
The next-generation technology in question is the lithium-air battery (Li-air), which is both environmentally safe and requires no fossil fuels, says Passerini. Although originally proposed in the 1970s, materials technology had, at the time, not advanced enough to design and build anything remotely on the scale required to power a vehicle.
But the past few years have brought renewed interest as electric cars, buses, motorcycles and other forms of transport have finally begun to come into their own and researchers have been keen to find ways to overcome their limitations.
"There has been quite a lot of work on lithium-air batteries in recent years, but it has been focused on the fundamental science or has been limited to very small cells," notes Elie Paillard, a senior researcher in Passerini's group who is working on the technical and scientific challenges of lithium-air batteries within LABOHR.
Driven by powerful ambition
Even though no workable blueprint existed for a Li-air battery to power a vehicle, LABOHR set out to design a prototype for a battery that could not only propel a vehicle but radically increase its range.
The concept uses environmentally benign ionic liquid electrolytes and nano-structured electrodes. These harvest dry oxygen from the air during discharge and return the oxygen to the atmosphere when the battery is recharging. This design helps to avoid cathode clogging, a common problem with conventional batteries.
LABOHR focused on both design aspects and fundamental research. The project investigated the possibility of scaling up Li-air technology into a battery-pack for electric vehicles. It studied key technological issues, such as the stabilisation of the lithium-metal electrode and the development of porous carbons and catalysts for the air electrode.
"We came up with a design for a large battery system for cars and we also proved that the principle works on a large scale, but we don't have a prototype yet," says Passerini.
He adds: "If we can close the gap between the engineering and the chemistry, it will be possible to make a mid-size car like the Volkswagen Golf travel 500 km with one charge."
With the end of the project, the former project partners plan to work on getting to the prototype stage. Passerini notes that it would take about a decade before such a battery can be put into production.
Describing it as the "Holy Grail" for the automotive sector, Passerini says that interest from European industry in this technology is enormous. In addition to Volkswagen, which was involved in LABOHR, BMW is also very interested and is already financing related work by the team.
LABOHR's potential not only contributes to the EU's environmental, energy-efficiency and transportation objectives, it can help to advance its renewable energy policy goals.
"This kind of battery can also be used to store renewable energy, such as that generated by wind turbines," says Passerini. "But if we can be successful with electrical vehicles, then stationary applications like this will follow, as they are simpler systems."
