With an estimated 16-million electric vehicles (EVs) on the world’s roads – 6.6 million of which were sold in 2021 alone – motorists are clearly embracing electrification and the many benefits it brings in increasing numbers.
EV owners love their vehicles. Not only are they environmentally friendly and fun to drive, but they are also cheaper to run than similarly sized fossil-fuelled cars.
At the same time, as with any nascent technology, EVs face several challenges – amongst these, limited range and lengthy charge times top the list of drivers’ concerns.
Image credit: StoreDot
Shifting towards high charge rates
In addressing these concerns, often cited as factors impeding EV uptake, manufacturers have steadily been increasing the power at which vehicles can charge, with infrastructure providers similarly rolling out high-powered DC fast-chargers to support this progress.
For instance, according to a 2021 IHS Markit report, merely 3 percent of BEV models in 2015 could charge at 100 kW or higher. Today, this picture has changed significantly, with popular EVs from brands such as Opel, Ford, and VW all capable of charging above 100 kW. Hyundai, Kia, Tesla, Audi, Porsche, BMW, and Jaguar Land Rover are even rated to charge at peaks over 200 kW.
There are, however, several caveats, to fast- or more precisely extreme fast-charging. Amongst these is the ability of a battery to safely accept the high charge rates without compromising the lifespan or negatively impacting the battery’s State of Health (SoH) – a measure of battery degradation over time.
Trading fast-charging for the battery’s SoH
According to cars.com, even if the EV is capable of Level-3 DC fast charging it is best not done often to prevent premature battery capacity loss.
To put this in context: a study of 6,300 fleet and consumer EVs by telematics company, Geotab, found that EV battery health across the 21 models in the trial degraded by about 2.3 percent per year. Under ideal climate and charging conditions, this improved to 1.6 percent degragation per year.
The results showed that the use of DC rapid chargers, even as low as 50 kW, had a significant impact on the SoH of the battery - particularly where the EV operated in a hot climate (defined as five days a year over 27°C/81°F). Under these conditions rapid-charging the battery more than three times a month reduced the average SoH to about 80 percent over 48 months, compared to 90 percent for an EV that had never been rapid-charged. Limiting rapid charging to less than three times a month improved the SoH outlook of the battery to approximately 85 percent.
To extend an EV battery’s SoH many manufacturers recommend drivers only use DC fast-charge stations when needed, instead recommending users opt for AC home/ slow charging for daily recharging.
Whilst this might be good advice for prolonging an EV battery pack’s life, drivers that do not have access to home chargers, such as the growing number of inner-city EV-owners, may have no other choice but to always charge at a public DC fast-charger.
Consequently, it is increasingly important that manufacturers develop charging systems, and in particular battery packs, that are capable of safe extreme fast charging without negatively impacting the life or SoH of the battery.
Safe fast-charging without affecting the battery’s SoH
Currently, the typical EV with a nominal battery capacity of 60 kWh is capable of adding 100 miles of range in a little under 17 minutes of high-powered DC fast-charging – this, largely dictated by current Li-ion battery technology that limits the charge rate to about 2C. StoreDot’s extremely fast charging (XFC) battery, on the other hand, is capable of charging to 80% in 10 minutes, reducing the time to charge for 100 miles of range to 5 minutes. This without impacting the SoH and therefore the longevity of the battery.
100 miles charged in 5 minutes, anytime, every time
The XFC battery has achieved over 1250 contiuous and consecutive extreme fast-charging cycles at a charge rate more than three times higher than most current LiBs before reaching SoH of 80 percent. Even after 1700 cycles, well beyond the accepted industry norm, StoreDot’s batteries maintain 70 percent of the original capacity, making them highly effective in second life usage for less dynamic applications such as energy storage and grid load balancing systems. Even before the battery is considered for second life EV users have the confidence that their vehicles will last for many thousands of miles.
What is more, the XFC battery has a constant charging curve, so where conventional LiBs typically reduce the charge rate when the battery reaches about 40 percent SoC, StoreDot’s XFC cells allow a constant rate across the entire fast charge range. This means that at any SoC the time to charge for 100 miles – or range replenishing speed - remains constant in the XFC.
This flat charging curve means that drivers are able to better plan their trips, knowing that irrespective of the battery’s SoC at any given point, the time to replenish 100 miles will remain constant. This also holds true for the entire charging event, where the time to add 100 miles would normally increase significantly as the battery’s SoC goes beyond about 50 percent, the XFC battery’s C-rate remains constant.
The impact of fast charging is not only of interest to the driver. With OEMs looking to extend battery warranties based on a guaranteed state of health within a given mileage, it is imperative that manufacturers ‘future-proof’ their batteries by taking into consideration the rollout of higher-powered charging infrastructure and the consumer’s use thereof.
What is more, as more EV batteries reach their ‘first’ end-of-life the SoH will play an increasingly important role as they are repurposed for applications such as grid storage systems for renewable energy, or peak shaving power demand.
Summary
At the end of the day, even though battery deterioration and a decline in the state of health over the lifetime of the battery-electric vehicle are unavoidable, drivers shouldn’t have to sacrifice battery health for convenient daily use. They should be able to charge their vehicles at any charge point, including high-powered DC fast chargers, without worry that they will negatively impact the battery’s state of health.
In addition, as EVs increasingly become a commodity designed to support the driver’s busy lifestyle, charging-related route planning should not dictate travel plans. A driver should be able to confidently charge at a consistenly high rate, regardless of how full the battery is when they arrive at the charging station.
