In the US, 62% of EV-hesitant consumers cite high battery repair costs as a barrier, while in the UK, 37% of motorists with no plans to buy an EV point to concerns over battery lifespan. External heat is an important factor in those concerns, with fears that hotter temperatures could shorten EVs’ viable lifespans.
Researchers and consumers have long known that lithium-ion batteries are sensitive to temperature, Haochi Wu, a postdoctoral researcher at Stanford University in California, told Professional Engineering in March this year. Speaking following the publication of research he led at the University of Michigan, in collaboration with Zhejiang University in China, Wu said that short-term effects are often observed on performance. Cold weather can limit a battery’s ability to discharge, for example, leading to concerns about EV performance during winter.
Heat could be an even more pressing issue. Lithium-ion batteries in hot climates in the US degrade three times faster than in more temperate areas, according to the research in Nature, which could lead to owners having to replace them more frequently. Wu pointed to the fate of the Nissan Leaf model in Phoenix, Arizona, in 2012, which suffered early battery failures after extreme high temperatures. Nissan bought back two vehicles, while independent testing found that affected cars had suffered measurable range reductions.
With both extreme cold and extreme heat potentially threatening to shorten battery lifetime, Wu and his colleagues set out to provide clarity over EVs’ ability to continue operating in a changing climate. While previous research focused on energy system engineering, analysis and optimisation, especially considering resilience to extreme weather events, this year’s paper covered durability – an important consideration for factors including EV market value and future demand for critical minerals from the EV industry.
“In our research, we just tried to answer a really important question – that is, will the projected future climate warming harm the longevity or the durability of EV batteries?” Wu said. To answer that question, Wu and his colleagues simulated urban EV driving patterns and battery temperatures, states of charge and charging rates by integrating EV driving and thermal management models. Those were combined with high-resolution climate data for 300 cities around the world to see how batteries would cope if global average temperatures rose by 2°C.
The storage characteristics of batteries are determined by chemical reactions inside, Wu said, with Arrhenius’ law stating that the rate of chemical reactions increases exponentially with temperature. The fear is that “this reaction is something harmful to the battery itself, so under the hotter climate, this reaction rate will be quickened, leading to premature capacity loss and increased internal resistance of the battery, and then finally leading to the short-term lifetime of the EV battery,” Wu said.
The researchers compared degradation models for batteries manufactured between 2010 and 2018 with those manufactured between 2019 and 2023, with the older batteries losing an average 8% of their life expectancy at higher temperatures. Newer ones lost just 3%, showing that recent technological improvements such as liquid cooling systems and advanced battery management software could be boosting longevity.
“The improvement in the modern commercial battery isn’t just a single breakthrough,” the lead author said. “It’s really the whole overall holistic engineering achievement. Over the past decade, we have seen great progress in many aspects – in materials, in chemistry design, in the packing design… and the overall system control working together to provide a better electric vehicle durability performance.”
The team did identify some specific trends, however, such as single cells with increased capacity. Previous cells might have held two ampere hours, while modern options can offer 10 times that capacity.
Another key trend is better pack design and internal battery design, Wu said: “Maybe they are just making fewer mistakes… There is a saying called ‘learn by doing’. So for the EV battery manufacturer, when they are producing more, they learn to avoid more mistakes.”
The research could provide potential buyers with assurance during a tricky period for EVs. New prime minister Andy Burnham has launched a consultation on the Zero Emission Vehicle (ZEV) Mandate, which could see the sales target of 80% by 2030 reduced to as little as 50%. The Society of Motor Manufacturers and Traders welcomed the consultation, saying that “regulatory targets are now running ahead of current consumer demand”.
Those consumers could be more likely to buy EVs if they can safely survive extreme heat, however. The Nature paper “addresses an important and timely question,” said external expert Dr Viet Nguyen-Tien from the London School of Economics. “By linking global climate projections with EV performance modelling... the study represents an important step towards understanding these issues.”
Wu added: “Our research could serve as a source that the durability of the battery has really improved a lot… In the future, battery lifetime will no longer be a bottleneck for the electric vehicle’s whole lifetime. This could, I think, increase some confidence for consumers when they are deciding to buy a car. Even in some moderately hot regions, they could have more confidence in EVs.”
Longer battery lifetime could also work in EVs’ favour when policymakers are calculating their overall carbon emissions, he added, reducing the perceived negative effect on the environment. Battery technology improvements can therefore “effectively double as an important climate adaptation strategy”, the authors said in a research briefing.
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