It is a done deal that the combustion engine will sooner or later be replaced by the electric drive.

But whether the electric motor will really catch on as quickly as politicians and energy experts currently want is questionable.

A number of circumstances are likely to keep many drivers from making the switch.

There are the shorter ranges compared to a combustion engine, safety concerns, but above all the long time it takes at the charging station until an empty battery is fully charged again.

"Drivers want the shortest possible charging times, especially when they have to cover long distances for which one battery charge is not enough," says British battery researcher Clare Gray from the University of Oxford in Berlin.

Manfred Lindinger

Editor in the “Nature and Science” section.

  • Follow I follow

If the batteries are charged too quickly, the lithium ions will build up on the graphite anode. Lithium cannot be stored quickly enough in the spaces between the graphite layers. Instead, the alkali metal accumulates on the anode surface and begins to grow in an uncontrolled manner. With repeated charging, dendrites are formed. As with many battery researchers, these Christmas tree-like lithium crystals are Grey's biggest problem children. If the dendrites pierce the separator that separates the anode from the cathode, they come into contact with the negative electrode. A short circuit occurs. The liquid electrolyte can ignite, which often leads to an explosion of the battery. A burning battery is not that easy to extinguish. Another disadvantage: If the dendrites break off the graphite anode,they swim as dead lithium in the electrolyte. This leads to a loss of active lithium, which reduces the storage capacity of the battery. The electricity storage system ages faster and quickly becomes unusable.

The British battery researcher and her colleagues took a closer look at the processes involved in dendrite formation.

To do this, she had to develop a suitable method with which the lithium ions can be observed, in vivo, as it were, when the particles move back and forth between the electrodes during charging and discharging.

She took inspiration from medicine.

Magnetic resonance imaging (MRI) is used there to image tissue.

The process only works with atomic nuclei that have a magnetic moment.

These include the hydrogen nuclei, the protons, but also the atomic nuclei of lithium.

However, Gray had to develop a special high-frequency coil into which a battery can be clamped.

In addition, the frequency of the radiated signal had to be matched to the lithium cores rotating in a magnetic field.

The tricky inner workings of a battery

What worked for lithium was more difficult for oxygen and carbon, two elements found in large quantities in the electrolyte and other components of the battery.

Here, Gray's researchers had to fall back on isotopes of these elements, which they built into battery cells of various sizes.

In this way, they were able to explore the inner workings of test batteries during operation and track down short-lived connections that arise during charging and discharging and that play a role in the aging process of the battery.

Many substances have long since dissolved when the battery is dismantled.

Based on their observations, the researchers can take appropriate measures, for example to optimize the electrolyte and thus prevent undesirable reactions.

The uncontrolled formation of dendrites could also be prevented by passivating the graphite electrode with a special coating.

Batteries for stationary applications

In addition to safety and service life, Gray is interested in increasing the energy density of batteries, shortening charging times and reducing the manufacturing costs of a battery. Avoiding toxic and expensive raw materials is also on their agenda, as is the case with many battery researchers. This is where next-generation batteries come in, which use sodium or magnesium as the active material instead of lithium. But these batteries are too heavy for mobile applications, so they can be used for stationary energy storage.

Completely new battery variants are also very promising. Clare Gray has developed what is known as a lithium-air battery, which can boast an energy density that is up to ten times higher than that of lithium-ion batteries. This would make it an ideal electricity supplier, especially for electric cars. A lithium-air battery consists of an anode made of metallic lithium and a cathode made of porous carbon. Atmospheric oxygen serves as a reactant at the cathode. When electricity is drawn from the battery, the metal electrode releases lithium ions, which migrate through the electrolyte to the cathode. There, oxygen is reduced, which combines with the lithium ions to form lithium peroxide.

The redox flow battery is ideal for stationary applications.

The actual energy stores here are two liquid electrolytes that are pumped through a two-part electrochemical cell.

Because the electrolytes are stored in external tanks, flow batteries can store enormous amounts of electricity.

So far, many new battery types have been tested in pilot projects.

Despite the many advances that have been made at many research sites, Gray is reluctant to apply it in practice.

After all, the classic lithium-ion battery also has a few flaws that need to be addressed.