Many decide against an electric car because they are put off by long charging times. Rapid progress in the development of new batteries could soon change that – but that would not solve all the problems.
electric cars being charged at a new charging station in braintree, england. Researchers are on the verge of developing batteries for electric cars that can be charged in ten minutes.
Electric cars are conquering the country: from january to july 2021, 367 electric cars were registered in germany, according to a report by the federal motor Transport Authority.905 electric vehicles registered. This is not only 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. As expected, the reasons for the purchase decision are primarily ecological – but in times of rising fuel prices and CO2 taxes, operating costs are also playing an increasingly important role.
But there are also aspects that make potential buyers give electric cars a wide berth. 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. However, in order to charge an electric car to 80 percent – the limit above which the charging speed is automatically reduced to prevent damage to the battery – you have to expect an average waiting time 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 speed up the charging process. To achieve this, work is underway to develop both new lithium-ion and solid-state batteries that can be charged more quickly – potentially in under 20 minutes – with greater stability.
In addition, scientists have developed a prototype lithium battery that, at least under laboratory conditions, can be half-charged in under three minutes – thousands of times without noticeable wear and tear. It could be the first market-ready battery to be fully charged in under ten minutes.
But for all the good news, the path 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 the wisdom and wisdom of spending so much energy on developing faster-charging batteries in light of the power grid.
Why lithium-ion cells explode?
The batteries used in today’s electric cars are made up of thousands of lithium-ion cells that can be charged 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 too hasty stacking of jenga blocks leads to an unstable structure. Similar problems arise if the lithium builds up too quickly in the anode.
Gallery: flown out, pulled in
At an extremely high charging speed, 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 rather than inside during rapid charging. This defective process is known as lithium plating, which drastically reduces the capacity of the battery. In addition, lithium deposits are formed in the form of shrub-like crystal structures known as dendrites. Once this process is started, the structures can grow through the electrolytes until they reach the cathode. A short circuit occurs, which causes the battery to catch fire or even explode.
"this is obviously a safety hazard," says peter slater, professor of materials chemistry at the university of birmingham in england.
Because of these potential hazards during fast charging, all batteries installed in electric cars have a charging speed limit that is set at the charge port of the car. The maximum power of the charging stations available in germany is currently 350 kilowatts. At such a charging station, the driver of an audi e-tron suv, for example, would theoretically be able to fully charge the 95 kWh battery of his vehicle in about 16 minutes. However, for safety reasons, the battery can only convert a maximum of 150 kilowatts of energy, so the actual charging time is around 40 minutes.
The battery of the future
The speed at which a battery is charged in everyday use is determined not only by the charging station and the way in which the battery’s energy consumption is reduced. Many other factors also have an influence: 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 an average of half an hour – the equivalent of a range of several hundred kilometers. Tesla car owners even have access to super-charging stations that can recharge the car in 15 minutes to the point where an additional range of over 320 kilometers is possible.
This is a good value, but in terms of time invested still no competition to 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 the development is the use of alternative anode materials, which should enable a faster and at the same time safer charging process. The British start-up 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, managing director of echion. echion’s prototype battery cell can be charged in six minutes, "with no negative impact on safety or lifespan," he said.
But the improved charging speed comes at a cost: niobium anodes store less energy per unit mass than conventional graphite anodes, resulting in a shorter range. However, manufacturers of electric cars prioritize energy-dense batteries that need to be charged less frequently and offer a long range – how quickly the battery charges must be subordinate to these aspects. For this reason, echion batteries are being used in other areas, such as energy storage 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 through solid electrolytes – often ceramics – rather than liquids. Unlike liquids, solid electrolytes are not flammable, which significantly reduces the safety risk. They will also be able to choose 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, technical director of solid power, it can be half charged in 15 minutes. For the version that will later be installed in electric cars, the aim is to achieve a charging time of 20 minutes for a complete charge. In addition, researchers are working on batteries with lithium metal anodes, which could 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.
However, current research suggests that the super-battery could be coming soon. A team led by xin li, a materials scientist at harvard university in massachusetts, has recently designed a solid-state lithium metal acu cell that uses multiple layers of different materials in its electrode to stop dendrites from forming. 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 a high charge capacity after 10 minutes.After only 20,000 charging and discharging processes, the battery will still have more than 80 percent of its capacity – current electric car batteries reach this level of wear after only 1.000 to 2.000 charging and discharging processes.
However, research in this area is still in its infancy. The team now needs to show that their prototype battery, which is the size of a coin, is suitable for use in vehicles and for mass production in a larger version. Xin li expects a commercial version of the battery to be ready for the market in about five years, "if nothing comes up.
Fast charging has limits
Even if electric vehicle batteries could be charged in under ten minutes, it is not clear whether this potential could be realized 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 private households. If everyone drove an electric car and wanted to charge it extremely quickly, the power grid could be stretched to its limits.
"the capacity of the power grid is an aspect that we absolutely must not neglect," says xin li. "it is important to know what demand can be served without the system breaking down."
"the challenge is to balance the demand for electricity at the charging stations with the needs of the general public – while also balancing convenience and price," says joshua buettner-garrett. According to him, the manufacturers of electric vehicles have already realized this. The goal is to make charging times of 20 to 30 minutes available for electric cars by the mid-2020s.