Electromobility: when will charging be as fast as refueling??

Many decide against an electric car because long charging times deter them. Rapid progress in the development of new batteries could soon change that – but that would not solve all the problems.

electric cars will be charged at a new charging station in Braintree, England

Electric cars being charged at a new charging station in Braintree, England. Research is on the verge of developing batteries for electric cars that can be charged in ten minutes.

Electric cars are taking over the country: from January to July 2021, according to a report by the Federal Motor Transport Authority, 367.905 electric vehicles registered. Not only is this a high figure in itself, but the market share of registered electric cars also exceeded that of newly registered diesel vehicles (22.2 percent) for the first time in this period, at just under 22.6 percent. The reasons for the purchase decision are, as expected, primarily ecological – but in times of rising fuel prices and CO2 taxes, operating costs are also increasingly playing a role.

But there are also aspects that make potential buyers steer clear of electric cars. The argument of the long charging time is particularly decisive here. Drivers are used to filling up their cars at the gas pump in under five minutes. But to charge an electric car to 80 percent – the limit at which charging speed is automatically throttled to prevent damage to the battery – you have to expect an average wait of 30 minutes, depending on the size and condition of the battery, even at the fastest charging stations.

But there is hope: In the next five to ten years, it should be possible to significantly accelerate the charging process. To address this, work is underway to develop both new lithium-ion and solid-state batteries that can also be charged faster – potentially in under 20 minutes – with greater stability.

Scientists have also developed a prototype lithium battery that can be half-charged, at least under laboratory conditions, in under three minutes – and thousands of times without any noticeable wear and tear. It could become the first market-ready battery that is fully charged in under ten minutes.

But for all the good news, the road to an ultra-fast-charging electric vehicle battery that is both technologically feasible and affordable will not be without obstacles for science and engineering. Experts are already questioning whether it is really wise and right in terms of the power grids to spend so much energy on the development of faster-charging batteries.

Why do lithium-ion cells explode??

The batteries used in electric cars today are made up of thousands of lithium-ion cells that can be recharged thousands of times and store the charged energy. Each of these cells consists of two electrodes – a metal cathode and a graphite anode – separated by liquid electrolytes. As the battery charges, lithium ions flow through the liquid from the cathode to the anode. They pile up in the space between the graphite layers of the anode like the wooden blocks of a Jenga tower.

The speed at which the lithium ions move from the cathode to the anode determines how fast the battery charges. But stacking Jenga blocks on top of each other too hastily leads to an unstable structure. Similar problems arise when the lithium builds up too quickly in the anode.

Gallery: Flown out, pulled in

If the charging speed is extremely high, there is a risk that lithium batteries will overheat and be damaged over time. But it is even more serious if the lithium builds up on the surface of the anode instead of inside during rapid charging. This faulty process is called lithium plating, which drastically reduces the battery’s capacity. Lithium deposits are also forming in the form of shrub-like crystal structures called dendrites. Once this process is initiated, the structures can grow through the electrolytes until they reach the cathode. A short circuit occurs that causes the battery to catch fire or even explode.

“It’s obviously a safety hazard,” says Peter Slater, professor of materials chemistry at the University of Birmingham in England.

Because of these potential hazards of fast charging, all batteries installed in electric cars have a charging speed limit that is set at the car’s charge port. The maximum power of the charging columns available in Germany is currently 350 kilowatts. At such a charging point, for example, the driver of an Audi e-tron SUV would theoretically be able to fully charge his vehicle’s 95 kWh battery in about 16 minutes. But the battery can convert a maximum of 150 kilowatts of energy for safety reasons, so the actual charge time is about 40 minutes.

The battery of the future

Exactly how quickly a battery is charged in everyday use is determined not only by the charging station and the throttling of the battery’s energy consumption. Many other factors have an impact as well: the size of the battery, how full or empty the battery is at the time of charging – and even the weather. At the most modern charging stations, a battery can be charged to 80 percent within half an hour on average – the equivalent of a range of several hundred kilometers. Owners of Tesla vehicles even have access to super-charging stations that can charge the car in 15 minutes to the point where an additional range of over 320 kilometers is possible.

That’s a good value, but in terms of time invested, it still doesn’t compete with the few minutes it takes to fill up a car with an internal combustion engine. Anyone expecting such peak times from an electric car will inevitably have to wait for the next generation of batteries.

One idea being explored in development is the use of alternative anode materials to enable faster yet safer charging. British startup Echion Technologies, for example, has developed a niobium anode that inhibits lithium plating and dendrite formation. Batteries incorporating this material can be charged “as fast as you want,” according to Jean De La Verpilliere, Echion’s CEO. The prototype of Echion’s battery cell can be charged within six minutes, “without any negative impact on safety or durability.

But for improved charging speed, sacrifices have to be made elsewhere: Niobium anodes store less energy per unit mass than conventional graphite anodes, which results in a shorter range. However, electric car manufacturers are prioritizing energy-dense batteries that need to be charged less often and offer long range – how fast the battery charges must be subordinate to these aspects. For this reason, Echion batteries are being used in other areas, such as energy storage systems and power tools.

For the private car driver who wants faster charging performance, the currently emerging solid-state batteries could be a promising alternative. In them, the lithium ions flow not through liquid but through solid electrolytes – often ceramics. Unlike liquids, solid electrolytes are not flammable, which significantly reduces the safety risk. They also make it possible to select materials for the anode that are less prone to lithium plating and can therefore be charged more quickly.

Solid Power, a company developing solid-state batteries with financial support from the BMW Group and Ford, is working on a silicone anode battery cell. According to Joshua Buettner-Garrett, Solid Power’s technical director, it can be half charged within 15 minutes. For the version later installed in electric cars, the company is aiming for a charging time of 20 minutes for a full charge. In addition, the company is working on batteries with lithium metal anodes that can store up to ten times more energy per unit mass than graphite anodes.

In theory, the solid-state battery should have a particularly short charging time due to the lithium metal anodes. In practice, however, it has been shown that the susceptibility to dendrites is extremely high. Failures are not uncommon, especially at high charging speeds. Fast-charging lithium metal batteries are something of the Holy Grail of high-performance batteries in electric cars, but “we’re still in the middle of development,” says Joshua Buettner-Garrett.

Current research results, however, suggest that the super battery could soon be on the way. A team led by Xin Li, a materials scientist at Harvard University in Massachusetts, recently designed a solid-state lithium metal battery cell that uses multiple layers of different materials in its electrode to stop the formation of dendrites. In their study published in the journal Nature, the scientists describe the prototype of their battery: It can be fully charged within three minutes and still has 80 percent of its capacity even after 10.The battery still retains more than 80 percent of its capacity after more than 1,000 charging and discharging cycles – a level of wear and tear that is already reached after 1.000 to 2.000 loading and unloading operations.

But research in this area is still in its infancy. The team must now show that their battery, whose prototype is the size of a coin, is suitable for use in vehicles as well as for mass production in a larger version. Xin Li expects a commercial version of the battery to be ready for market in about five years, “if nothing comes up.”.

Fast charging has limits

Even if the batteries of electric vehicles could be charged in under ten minutes, it is not clear whether this potential could even be exploited in everyday life. With a voltage of 400 volts or more, today’s fast-charging stations already draw much more power from the grid than the 230-volt outlets found in homes. If everyone drove an electric car and wanted to charge it extremely quickly, this could push the power grid to its limits.

“The capacity of the power grid is one aspect we definitely can’t neglect,” says Xin Li. “It’s important to know what demand can be met without breaking down the system.”

“The challenge is to balance the demand for electricity at charging stations with the needs of the general public – while also balancing convenience and price,” says Joshua Buettner-Garrett. According to him, electric vehicle manufacturers have already realized that. The goal, he said, is to make charging times of 20 to 30 minutes available for electric cars in the mid-2020s.

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