The secret of the battery, which is to end the waiting at the charging station, is about as fine as a hair and weighs as much as a penny piece. American researchers have equipped rechargeable batteries with thin foils made of nickel, thus giving them a long-awaited feature: they can be recharged to 80 percent in just ten minutes. With the technology of filling the electricity storage in electric cars could go in the future almost as fast as today refueling at the pump.
So far, the lack of reach is one of the main reasons why electric cars do not prevail on German roads. Because the battery is empty, drivers have to take a longer compulsory break. Even with new models, it usually takes at least half an hour before the battery is sufficiently filled for the next three hundred kilometers. The worry of not arriving at the destination with an electric car has even been reflected in a new word: "range anxiety".
The fact that the charging times are so long is due to the complex chemistry of the lithium-ion cells that are currently used in all electric cars. When such a battery is charged, lithium carriers are deposited in an electrode, a layer of carbon. When unloading, they are retrieved from there again.
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Particularly important component of the invention: a battery heater
However, the faster the battery is charged, the greater the risk that the charge carriers adhere to the surface of the electrode and form a metallic layer there. This not only reduces the power of the cell continuously, in the worst case can cause a short circuit and destroy the battery.
The novel battery bypasses the problem with a trick: a built-in heater. Before the actual charging process, the researchers allow current to flow through the thin nickel foils of their lithium-ion battery, thereby raising the temperature inside to up to 60 degrees Celsius. Within ten minutes, they then pump an enormous amount of energy into the cell. The heat prevents an unwanted lithium layer from forming.
So far, engineers are actually trying to avoid such high temperatures in batteries by any means. Because the heat stimulates unwanted chemical reactions and can decompose certain substances in the cell. However, because the US researchers led by Chao-Yang Wang of Pennsylvania State University only heated their batteries for a few minutes, the side effects were limited.
Measurements showed that even after 2500 charging cycles, their high-energy battery could still store more than 90 percent of the charge as at the beginning. This clearly exceeds the requirements that manufacturers typically place on a battery for an e-car.
Different techniques compete for the title Wunderakku
The scientists from Pennsylvania are not the only ones working on the fast charging of batteries. Other researchers are improving the recipes of the electrolyte, the liquid part of the cell, or experimenting with new materials for the negative electrode. By adding small amounts of silicon, researchers were able to significantly reduce the formation of the dangerous lithium metal layer. Which technology will prevail in the end is therefore not yet settled.
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So far, the US scientists have tested their novel battery with the nickel foil only in the laboratory - under ideal conditions. The experimental data shows, for example, that they allowed their batteries to cool down for ten minutes after fast-charging before re-discharging them - increasing the waiting time to 20 minutes. For a commercial use, the engineers also have to prove that the technology works reliably even on a large scale, when - as in an e-car - many cells are connected to form a battery pack.
Quite fast, the range anxiety will not disappear.
