The Road to Extreme Fast Charging

The ultimate goal for electric vehicles is to offer the same driving experience as gas-powered vehicles, with zero emissions. That means sufficient driving range for long-distance travel. Is that even possible given the realities of the nation’s existing electrical grid?

The driving range of electric vehicles is becoming less of an issue as they surpass 200 miles or greater, approaching the distance between fill-ups of some internal combustion engine vehicles…or maybe the bladder capacity of their drivers. However, the time it takes to recharge an EV is still a negative attribute.

Generally, EVs charge at a fairly slow rate. A 240-volt Level 2 home or public charger will charge a Chevy Bolt from depleted to full in about 4 1/2 hours, providing a range of about 238 miles. That’s a far cry from 5 minutes to fill a gas tank. It’s significantly slower when charging a Bolt with a Level 1 charger using a household’s standard 120-volt power since this adds only about 4 miles an hour!

Of course, charging companies and automakers are working together to expand the small-but-growing network of fast chargers in key areas of the country, allowing EVs to gain up to 90 miles of charge in around 30 minutes. Tesla claims that its Supercharger stations being upgraded to Version 3 can charge a Tesla Model 3 Long Range at the rate of about 15 miles a minute, or 225 miles in just over 15 minutes under best conditions.

If current technology EVs become popular for mid- to long-range travel, gasoline stations, truck stops, and public charging stations equipped with Level 2 and even somewhat faster chargers run the very real risk of becoming parking lots.

Photo: EVgo

When it comes to charging EVs, charging times come down to kilowatts available. The best Tesla V3 charger is rated at 250 kilowatts peak charge rate. Now, much research is being done here and in other countries on what is called Extreme Fast Charging (XFC) involving charge rates of 350-400 kilowatts or more. The U.S. Department of Energy is sponsoring several projects aimed at reducing battery pack costs, increasing range, and reducing charging times.

There are several challenges for XFCs. First, when lithium-ion (Li-ion) batteries are fast charged, they can deteriorate and overheat. Tesla already limits the number of fast charges by its standard Superchargers because of battery degradation, and that’s only at 120-150 kilowatts. Also, when kilowatt charging rates increase voltage and/or amperage increases, which can have a detrimental effect on cables and electronics.

This begs the question: Is the current electrical infrastructure capable of supporting widespread use of EVs? Then, the larger question is whether the infrastructure is capable of handling XFC with charging rates of 350 kilowatts or more. This is most critical in urban areas with large numbers of EVs and in rural areas with limited electric infrastructure.

The answer is no. Modern grid infrastructures are not designed to supply electricity at a 350+ kilowatt rate, so costly grid upgrades would be required. Additionally, communities would be disrupted when new cables and substations have to be installed. There would be a need for costly and time-consuming environmental studies.

One approach being is XFC technology being developed by Zap&Go in the UK and Charlotte, North Carolina. The heart of Zap&Go’s XFC is carbon-ion (C-Ion) energy storage cells using nanostructured carbons and ionic liquid-based electrolytes. C-Ion cells provide higher energy densities than conventional supercapacitors with charging rates 10 times faster than current superchargers. Supercapacitors and superchargers are several technologies being considered for XFCs.

According to Zap&Go, the C-Ion cells do not overheat and since they do not use lithium, cobalt, or any materials that can catch fire, there is no fire danger. Plus, they can be recycled at the end of their life, which is about 30 years. Zap&Go’s business model would use its chargers to store electric energy at night and at off-peak times, so the current grid could still be used. Electrical energy would be stored in underground reservoirs similar to how gasoline and diesel fuels are now stored at filling stations. EVs would then be charged from the stored energy, not directly from the grid, in about the same time it takes to refuel with gasoline.

The fastest charging would work best if C-Ion cell batteries are installed in an EV, replacing Li-ion batteries. EVs with Li-ion batteries could also be charged, but not as quickly. Alternatively, on-board XFC cells could be charged in about five minutes, then they would charge an EV’s Li-ion batteries at a slower rate while the vehicle is driven, thereby preserving the life of the Li-ion battery. The downside is that this would add weight, consume more room, and add complexity. Zap&Go plans to set up a network of 500 ultrafast-charge charging points at filling stations across the UK.

General Motors is partnering with Delta Electronics, DOE, and others to develop XFSs using solid-state transformer technology. Providing up to 400 kilowatts of power, the system would let properly equipped electric vehicles add 180 miles of range in about 10 minutes. Since the average American drives less than 30 miles a day, a single charge could provide a week’s worth of driving.

The extreme charging time issue might be partly solved by something already available: Plug-in hybrid electric vehicles (PHEVs). As governments around the world consider banning or restricting new gasoline vehicles in favor of electric vehicles, they should not exclude PHEVs. Perhaps PHEVs could be designed so their internal combustion engines could not operate until their batteries were depleted, or their navigation system determines where they could legally operate on electric or combustion power.