With the popularity of electric vehicles (EVs) rising, it’s increasingly important that the engineers involved in developing them understand how to meet marketplace needs. One way to do that is to improve the electric car battery life span. Relatedly, they must understand what factors impact EV battery life span. Knowing the specifics can help manufacturers give car owners tips to help their batteries last as long as possible.
Using Analysis and Simulation Tools
One common way to see how long EV batteries should last is to use advanced simulations to see how they’d hold up. In the U.S., researchers at the National Renewable Energy Laboratory (NREL) use the Battery Lifetime Analysis and Simulation Tool (BLAST) Suite. It combines electrical and thermal performance models with a battery degradation model.
Besides examining a range of batteries, these models assess other factors that could impact life span. Those include user interactions and the environment. The specialized BLAST-V interface provides information specifically about battery performance in electric cars. It includes yearlong travel statistics on more than 300 drivers and the charging infrastructure they use.
The NREL also has a lifetime predictive model that uses calendar and charge cycle-based models to anticipate how long a battery should last. In addition to testing a completed battery, the model can help engineers make development alterations to increase the life span of batteries. Suppose the model shows electrode stack stress would likely shorten how long the product lasts. Then, an engineering team could explore tweaks to reduce that adverse outcome.
Company Creates Digital Twin to Examine EV Battery Life Span
Silver Power Systems is a company based in the U.K. that specializes in battery analytics. It created a tool called the Real-time Electrical Digital Twin Operating Platform (REDTOP) to increase the likelihood of accurate battery life span predictions.
The data came from a nine-month, 500,000-kilometer trial of electric taxis and an electrically powered sports car. Each vehicle had an onboard Internet of Things (IoT) device that sent real-time battery health data to the cloud. The people involved in the project say the associated data shows current battery performance statistics but can also predict how those might change over time. As a result, they believe it is an accurate way to estimate electric car battery life span.
“This really is the holy grail,” said Peter Bishop, chief technology officer, Silver Power Systems. “Understanding how an electric vehicle’s battery is performing right now — and predicting how it will perform over the coming years — is absolutely critical for many sectors. But to date, there has been a lack of data, and predictive modeling has been largely lab-based.
“By combining a robust real-world trial with our EV-OPS machine-learning analytics capability through the REDTOP program, we have not only been able to unlock an unprecedented view of real-time battery performance and state of health, but also create the world’s most advanced digital twin enabling prediction of battery future life,” he continued.
The tool can also show differences between batteries. If manufacturers get access to that data, they might use it to show how the EVs they make stack up to competing options.
Determining if Retired Batteries Can Have Second Lives
People have raised ongoing concerns about the difficulties in recycling EV batteries. They point out that failing to account for these issues now will lead to electric vehicle power sources ending up in landfills earlier than many individuals might expect.
However, researchers proposed several ways to determine if an EV battery could have a safe and useful second life after refurbishment. They mentioned measuring the open-circuit voltage, capacity, and internal resistance. If batteries did not meet certain criteria associated with those examinations, they did not pass and could not get used in additional applications.
Additionally, they recommended using non-destructive methods to assess a battery’s remaining useful life (RUL). A couple of the proposed solutions were X-ray computed tomography neutron-scattering techniques. They can show the physical and chemical changes in a battery since it got used for the first time. Those methods can also indicate to what extent those changes happened.
Second-life applications for EV batteries don’t necessarily result in them ending up in other cars. In one collaboration between Audi and a power plant, 60 batteries from decommissioned development vehicles will provide about 4.5 megawatt-hours of electricity.
Examining the Benchmark for EV Battery Life
The electric vehicle industry performs several tests before batteries reach the market. Some shake tables can exert up to 60 kilonewtons of force, ensuring a battery can withstand vehicle vibrations. Regarding how long power sources last, the sector generally says that a battery has reached the end of its useful life when it loses 20%-30% of its original capacity.
However, researchers asserted that might not be a useful metric. They took a closer look at EV capacity fade and showed vehicles experiencing it could still often meet owners’ daily transportation needs.
The researchers referred to 159,844 travel itineraries of EV owners using their cars throughout the week. They then put that data in a simulator to learn how frequently batteries could continue meeting owners’ travel needs. One startling takeaway was that, even once batteries fell to 30% of their originally rated capacity, they still could handle the trips of 55% of drivers.
That takeaway could prove critical, especially since a more recent study revealed that battery capacity often drops much faster than expected. Every battery in an EV sold in the U.S. comes with a battery warranty. It states the power source must last for at least eight years or 100,000 miles.
However, a 2020 study involved using models to assess 220 capacity-fade scenarios. Like the investigation mentioned above, the team used real-world-trip data. In this case, it came from GPS data associated with 16,263 cars. They found that 41 models caused the cars’ battery capacity to drop below 80% of its original capacity in less than five years.
What Strategies Can Extend the EV Battery Life Span?
Companies are pursuing various aims to make it easier for EV owners to recharge when necessary. Jeep aims to add charging stations to trailheads in California and Utah. Other efforts center on helping people find functional charge points and report outages. Those things undoubtedly bring convenience, but investments should also relate to making batteries last progressively longer when possible.
While figuring out how to meet that daunting challenge, researchers have uncovered some helpful tips for making EV batteries last longer.
Ensure the Battery can Tolerate Fast-Charging Options
Engineers and others who work with electric cars express the estimated battery-charging time as the C-rate. 1C means it takes the cell an hour to get a full charge. Conversely, a 4C rate indicates it would theoretically take only 15 minutes for that to happen.
A researcher examined fast-charging mechanisms on battery life and found the life span impact depends on the type. The study concerned nickel manganese cobalt (NMC) and lithium iron phosphate (LFP) batteries. It indicated that fast-charging above 1C adversely affected the NMC battery life span. However, LFP batteries did not show the same degradation, even when charged at rates up to 4C.
The research also indicated that battery management systems can reduce the unwanted life span shortening during fast-charging, though. Thus, engineers don’t necessarily need to rule out options to replenish the power source faster. But, they need to accommodate potential adverse consequences.
Help Consumers Adopt Good Charging Habits
Some people may not immediately see the link between electric car battery life span and how often they fully charge the vehicle or let it drain. That’s why engineers should ideally be involved in making suggestions about how drivers should charge their batteries for best results.
The manuals that come with EV models often recommend that people only charge the battery to 80% and never deplete it. Occasional failures to follow that advice won’t likely cause significant life span drops. However, people should do their best to abide by what the manufacturers say.
Engineers should suggest that manufacturers clarify any built-in battery features that prevent people from making mistakes. For example, some batteries quit charging at 80% by design to stop the potential degradation. Telling consumers about that is an excellent way to educate them so that they don’t think they have defective cars.
Adjust Recommendations About Charging Before Long Periods of Disuse
Researchers have also looked at how keeping EVs parked for long periods could affect their overall life spans. Their findings indicated people should not park the vehicle with its battery at 80%, as is commonly suggested. Instead, the data showed that lifespan degradation was slowest with the capacity at 60% or less. In contrast, it was the most severe when the battery capacity was at 70%-80%.
Interestingly, degradation was the slowest on a depleted battery. However, it could lose 4%-8% of its capacity in a year if stored at 70%-80% capacity. The storage temperature also mattered, though. The conclusions indicated that keeping a car at 77°F halved the degradation rates. On the other hand, temperatures of 104°F caused short-circuiting in the battery.
Keeping the target audience in mind could guide future temperature recommendations. Some areas of the world rarely or never get above 100°F. In such places, a more user-friendly strategy could be to remind drivers to avoid storing their cars in extreme heat, clarifying that moderation is best.
EV Battery Life Span Knowledge Will Evolve
This overview shows some options for testing and lengthening electric car battery life spans. They’re certainly worth knowing about and could shape engineers’ future efforts. However, professionals working with electric car batteries should stay mindful of emerging research and adapt their methods to stay current as researchers learn more about this essential topic.