On the back of a 43 percent increase in electric vehicle (EV) sales in 2021, the 2.18 million EVs sold in Q2 2022 shows just how quickly consumers are warming to battery electric vehicles. However, some prospective buyers remain hesitant. One reason for this, often cited in consumer surveys, is the time it takes to charge the EV’s battery.
While drivers today are accustomed to filling a gas tank in less than five minutes, EVs, depending on the size and specifications of the battery and charging system, it could take longer than 30 minutes to charge at the fastest charging stations. Several factors influence this time: The capacity of the battery pack, the voltage at which the battery can be charged, and the power of the charger, being but a few.
For this reason, it is becoming popular to define the charge in terms of the time it takes to charge x-miles of range – typically quoted as x minutes per 100 miles. Whilst this is certainly more practical than quoting time to replenish a percentage of the battery’s capacity, it still does not tell the whole story.
Lithium-ion EV batteries typically cannot utilize the maximum power available at all SoC
Unlike fuelling an internal combustion engine powered vehicle, that irrespective of the amount of fuel in the tank can take on fuel at a constant flow-rate, the power at which most EVs charge is reduced as the battery’s state-of-charge (SoC) rises.
As can be seen in the diagram above, even EVs such as the Porsche Taycan, Tesla Model 3, and Mercedes EQS, acclaimed for their fast charging capabilities, significantly reduce the power delivered by the charging station as the SoC increases. This is largely dictated by the battery chemistry and design, and is a safety precaution to protect the battery from overheating and premature aging, amongst other undesirable effects.
For instance, in a practical test conducted by "Out of Spec Reviews” and reported on by “InsideEVs”, the peak charging power of the Mercedes EQS 450 tested at a 350 kW fast charger capable of delivering 500A was 202-203 kW at about 29 percent SoC. From this point charging power gradually decreased to about 100 kW at 80 percent SoC. After that, the decrease accelerated, reaching about 40 kW before the battery was charged to 90 percent SoC.
For the consumer, the reduction in charging power as the SoC increases translates into a seemingly inconsistent and often unexpected increase in the time it takes to ‘top up’ range when in a hurry or planning a road trip.
Thus, with the EQS consuming about 308 Wh/mile, when evaluated over the EPA combined drive cycle, a driver could add about 11 miles of range in 1 minute with the battery at 29 percent SoC. However, should the vehicle require charging with the battery at 80 percent SoC, the driver would only be able to add about 5 miles range per minute of charge-time – or about twice as long than when the battery’s SoC is at 29 percent.
This is particularly important for drivers planning a long trip along routes where the fast-charging infrastructure is not yet fully developed trying optimize charging rate by arriving to charging stations with low SoC – in such a case, travel time could be significantly extended or the driver could even be left stranded with an empty battery. Both situations adding to “range anxiety.”
The solution to lengthy and SoC-dependent charge times is already available in the form of StoreDot’s Extreme Fast Charging (XFC) EV battery. By utilizing the highest power at any state of charge – as can be seen in the chart above - the XFC reduces charging times by up to 50 percent. Such high performance battery pack will of course require system level design to balance all components including current carrying elements, Battery Management System, Thermal Management System and others.
StoreDot’s XFC utilizes maximum power to charge 100 miles in 5 minutes every time
Developed to overcome potential EV owners’ “range anxiety”, StoreDot’s extreme fast charging EV batteries can charge to 80 percent SoC in under 10 minutes, and importantly add 100 miles of range in under 5 minutes – at any SoC of the battery.
Not only does StoreDot’s silicon-dominant XFC technology offer the driver a true linear charging experience across the SoC range, but it does this without compromising the lifespan of the battery. Under extreme fast charging conditions, the XFC has already achieved over 1200cycles, exceeding the industry benchmark of 1000.
Conclusion: Utilizing the highest power available, charge times will continue to drop
Whereas the design and chemistry of the battery pack play an important role in determining the time to charge the battery safely, external factors such as the output power of the charge-station and the current-carrying capacity of the charging-cable and plug, also play a critical role.
In the US, the Department of Energy wants to lower charging times to less than 15 minutes by 2028. To achieve this it proposes to increase the charging output to 400 kW at most of the public charging stations.
The International Council on Clean Transportation estimates that by 2030, 27 percent of DC fast chargers in the US will be able to charge at up to 350 kW.
However, according to a report by “Mobility Foresights” on the EV fast charger market, as of Oct 2020 there were only ~230,000 DC fast chargers installed globally. The number of ultra-fast chargers capable of charging at >350kW numbered less than 2,000, or a mere 1 percent of the total.
So with the number of vehicles capable of fast charging at 350 kW and higher, and as the fast charging infrastructure is yet to support the ever-increasing demand for power outputs, the role of the battery in utilizing these power increases to reduce charge times becomes even more important.
With its silicon-dominant extreme fast charging EV battery technology, StoreDot has plotted out a future utilizing the power increases to continue reducing the time to charge at any SoC, thereby easing consumers’ range anxiety.
Whilst there is no doubt EVs have come a long way in meeting consumer needs, in the short to medium term car owners who have grown up expecting to fill a fuel tank in five minutes demand a similar experience when charging an EV battery.
At the same time EV owners intuitively expect the car to deliver a linear, or uniform, charging performance, whereas in reality the vehicle is only able to charge at the peak rate at specific points during the charge cycle.
To achieve this and ease range anxiety manufacturers will have to step up the development of extreme fast charging batteries capable of utilizing the maximum power available at any battery state of charge. Silicon Anode technology such as the one from StoreDot delivers an unparalleled charging experience in which the vehicle is charged in minutes as opposed to hours, thus eliminating the number one barrier of adoption of electric vehicles – range and charging anxiety.
