Ultra-fast charging systems to rival fossil-fuel refuelling times
Economist
A row of electric vehicles (EVs) plugged into chargers while their drivers patiently wait for their batteries to be charged have become a familiar sight at many service stations. While some of the newest EVs can charge in as little as 20 minutes, many take much longer. But some EV drivers may be back on the road much more quickly. Companies are developing ultra-fast charging systems that can recharge a battery in nearly the same time it takes to refuel a fossil-fuel car. Fast charging could eliminate the last hurdles to widespread EV adoption.
Such a system will be unveiled in Paris on April 8 by China’s BYD, the world’s largest electric vehicle manufacturer. It consists of a powerful 1,500-kilowatt (kW) drive-through charger that resembles a large bridge with charging cables descending from it. When installed in BYD’s new premium model Denza Z9GT, the car’s 122 kilowatt-hour (kWh) “Blade Battery” capacity can be increased from 10 percent to 70 percent in five minutes. The vehicle can be fully charged in nine minutes.
Charging an EV battery requires a charger that will convert alternating current from the grid into direct current, the kind that batteries use. A charger inside cars can perform slow charging overnight when plugged into a home electrical outlet. For fast installations a much more powerful kit is required. This is found in public fast chargers that convert power directly from the grid, bypassing the charger in the car. This allows more power to be pumped into the battery faster.
However, there is a limit to the charging speed of the lithium-ion battery, which is widely used in electric vehicles. When the battery is installed, charged particles called lithium ions move from the cathode to the anode, where they are squirreled away and stored. When the battery is discharged, the ions migrate back. The challenge is that as the charge rate increases, bottlenecks form in the flow of ions, especially towards the anode. This creates a resistance that produces damaging heat.
BYD says the Blade Battery uses cathodes and anodes designed at the molecular level to allow ions to flow more easily. This is done in part by using thin battery components that reduce internal resistance. For these batteries to reach their potential, BYD will need to install powerful 1500kW chargers at service stations, where most existing fast chargers operate at 100-350kW. BYD aims to install its large chargers around the world and expects to have 20,000 in operation in China by the end of the year.
Nyobolt, an energy storage company out of the University of Cambridge in Britain, has taken a less scary approach to the same problem. The 35 kWh battery it installs in a lightweight sports car can be charged from 10 percent capacity to 80 percent in less than five minutes when plugged into an existing 350 kW fast charger. Although the capacity of the battery is small by today’s standards, the light weight of the vehicle means it can provide a range of approximately 250 km. The company can also produce larger versions.
Like BYD, Nyobolt overcomes the problem of internal resistance by redesigning the electrodes. Their anodes are made of a special form of niobium-tungsten oxide, which increases the charge rate by allowing ions to enter and exit much faster.
Nyobolt already supplies batteries equipped with these anodes for use in data centers that require fast-charging batteries to smooth out large fluctuations in power demand. The company also recently signed a deal with Symbotic, an American company, to equip its warehouse robots with fast-charging batteries, allowing the bots to spend more time working. Nyobolt is in talks with several vehicle manufacturers about the use of its batteries.
These increases in speed come at a cost. One consequence of fast charging is that the additional load on batteries can cause them to lose capacity faster than with normal charging. Engineers are also trying to overcome this problem. Sai Shivareddy, Nyobolt’s boss and co-founder, says its batteries have been tested with more than 4,000 fast charging cycles, which is the equivalent of a car traveling nearly a million kilometers while retaining more than 80 percent of its capacity. BYD says its battery will also have greater durability. Regardless, the opportunity to relax with a coffee or nap while your EV charges may soon be a thing of the past.
Economist
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