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Smarter battery packs can give electric car batteries a longer life. The illustration shows a reconfigurable battery pack where all cells have their own switches, which are controlled by a battery management system (blue lines). A weak cell (dark) can be bypassed while the current (yellow) continues through the rest of the pack.
Illustration Credit: created by Albert Škegro, Chalmers University of Technology, Sweden, with the help of AI.
Scientific Frontline: Extended "At a Glance" Summary: Reconfigurable Battery Pack Architecture
The Core Concept: A reconfigurable battery pack is an energy storage system capable of dynamically altering the electrical connections between its individual cells as they age.
Key Distinction/Mechanism: Unlike conventional battery packs with fixed configurations where the weakest cell limits the overall performance of the system, a reconfigurable architecture utilizes switches and control systems to isolate and bypass deteriorated cells, allowing the pack to continue operating efficiently using its healthy cells.
Origin/History: The system-level models and impact assessments of this architecture were developed by researchers at Chalmers University of Technology, including Albert Škegro and Changfu Zou, in collaboration with industry partners like Zeekr Technology Europe, with findings published in Nature Communications and Nature Energy.
Major Frameworks/Components:
- Reconfigurable cell connections equipped with individual or grouped hardware switching mechanisms.
- Advanced battery management systems capable of actively monitoring cell health and redirecting current.
- Application models focusing on high-voltage electric vehicle integration.
Branch of Science: Electrical Engineering, Energy Storage Technology, and Automotive Engineering.
Future Application: Integration into commercial electric vehicles could theoretically extend battery lifetime by more than 20 percent and defer battery replacement by approximately 14 months under optimal conditions.
Why It Matters: By maximizing the usable capacity of a battery pack and adapting to uneven cell degradation over time, this technology lowers the total cost of ownership for consumers and improves the long-term sustainability of electric transportation.
In today’s electric vehicle batteries, the weakest cells can limit the lifetime of the entire battery pack, even when most of the cells are still performing well. Researchers at Chalmers University of Technology, together with industry partners, have investigated a battery architecture that can instead bypass cells that have deteriorated. In the models, the technology could extend battery lifetime by more than 20 percent under certain conditions. In a representative use case, it defers battery replacement by around 14 months while also reducing overall costs.
A battery pack in an electric vehicle consists of many interconnected battery cells. However, the cells are not identical. Differences arise during manufacturing and can become more pronounced as the battery is used and ages. Some cells therefore lose capacity faster than others.
In conventional battery packs, the cells are connected in a fixed configuration. This means that the weakest cell can set the limit for the entire battery pack.
The researchers compare this to a group of hikers tied together by a rope.
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| Albert Škegro Photo Credit: Malin Aronsson |
“They must all move at the pace of the slowest person and stop when that person stops, regardless of how much energy the others have left. With the architecture we have modeled, the battery can instead bypass the cell that is causing problems and continue using the remaining cells,” says Albert Škegro, a PhD student at the Department of Electrical Engineering, Chalmers.
The impact of cell-to-cell differences in practice was recently quantified in a separate study published in Nature Energy. In that study, Changfu Zou, professor at the Department of Electrical Engineering at Chalmers, together with researchers at Zeekr Technology Europe and universities in China, analyzed data from electric cars and buses. The results show how variations between individual cells affect battery pack performance and lifetime.
A battery that can adapt as cells age
In the new study, published in Nature Communications, Škegro, Zou, and their co-authors investigate a possible system-level solution: so-called reconfigurable battery packs.
Unlike a conventional battery pack, a reconfigurable pack can change the connections between its cells. Using switches and control systems, it can isolate a cell that has begun to limit the pack.
This makes it possible to utilize more of the capacity that is still available in the battery.
In the researchers’ models, the most fine-grained and idealized form of reconfiguration yields a potential lifetime extension of more than 20 percent for certain high-voltage vehicles.
However, the researchers emphasize that this figure represents a theoretical upper bound and does not necessarily indicate what today’s commercial systems can be expected to achieve. The model assumes that every individual cell can be controlled separately and that the system makes optimal use of this capability.
In practical designs, groups of cells are more likely to be controlled together. This requires less electronic hardware and is easier to implement, but also means that less of the theoretical benefit can be realized.
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| Changfu Zou Photo Credit: Chalmers, Tekniska Högskola |
“Reconfiguration is not an on-or-off choice. It is a spectrum. Where a manufacturer chooses to position itself on that spectrum determines how much of the potential benefit can be realized,” says Changfu Zou, professor at the Department of Electrical Engineering, Chalmers.
The researchers therefore do not give a single general figure for how much longer a commercial battery would last. Long-term studies in which battery packs using this architecture are followed throughout the entire lifetime of a vehicle are still lacking.
Battery replacement could be delayed by more than a year
To make the results more tangible, the researchers also analyzed a representative use case: an electric vehicle with an 80 kWh battery, driven 12,000 kilometers per year, with an expected vehicle lifetime of 18.8 years.
Under these assumptions, the new battery architecture defers battery replacement by around 14 months. The battery pack also retains a higher residual value when it is removed from the vehicle because it has undergone less degradation.
“For a private EV owner, this could mean postponing a battery replacement. For a vehicle fleet with hundreds of battery packs, delaying that cost by a year could translate into significant savings,” says Albert Škegro.
The outcome varies, however, depending on factors including battery size, annual mileage, and usage patterns.
Greatest potential in high-voltage vehicles
The benefits increase when more battery cells are connected in series. This makes the architecture particularly interesting for high-voltage vehicles, such as long-range electric cars and electric trucks.
The more cells that are connected in series, the greater the probability that one of them will age faster or develop problems. In a conventional battery pack, such a cell can limit the entire system. With the new architecture, that cell can instead be bypassed.
However, the results show that the benefits do not increase indefinitely as voltage rises. The gains increase substantially when moving from low-voltage systems to a 400-volt architecture, and continue to increase at higher voltages, but more slowly.
Prototypes exist, but no production vehicles yet
Reconfigurable battery technology is not a new field of research. Several automotive and battery companies have worked on different versions of the technology over the past decade.
The technology has also been used in stationary energy storage. In the automotive sector, experimental systems and demonstrators already exist. Volvo Cars, for example, has worked on its SmartCell concept, and a major vehicle manufacturer has begun real-world road testing of a passenger car prototype using a battery system based on this principle. However, there is not yet a mass-produced passenger car or truck on the market using the type of battery architecture examined in the study.
The new architecture can already be cost-effective
The new architecture requires more switches, connections, and advanced control systems, adding to the upfront cost of the battery pack. The researchers therefore carried out a comprehensive techno-economic analysis to determine whether the additional investment can be offset by longer battery life and higher residual value.
“The results show that the architecture can already be cost-effective under a wide range of real-world usage conditions. Based on a component-level analysis using automotive-grade hardware, the additional hardware would increase the total pack cost by approximately 9 percent. The analysis identifies a break-even threshold of around 12 percent, above which the architecture becomes less likely to provide an economic benefit over the vehicle’s lifetime,” says Changfu Zou.
The researchers also identified a combination of conditions under which the economic case is particularly robust: an additional upfront cost below roughly 7 percent, combined with an annual mileage below a threshold of 12,150 kilometers. For context, a privately owned passenger car in Sweden is driven an average of around 11,400 kilometers per year. Within those bounds, the architecture is cost-effective in at least 99.7 percent of the scenarios tested, despite variations in every other parameter.
The current cost estimate is based on component prices at prototype-scale volumes of 1,000 units. At the substantially higher volumes used in automotive production, component costs are expected to fall, bringing the technology closer to the region where the study finds the economic case to be particularly robust.
Sustainability gains beyond the vehicle
The researchers also identify potential sustainability benefits beyond simply keeping the battery in the vehicle for longer.
During manufacturing, considerable resources are devoted to testing and matching cells with similar characteristics. A battery capable of managing greater variation between its cells could reduce the need for such precise matching.
Once the battery is no longer used in the vehicle, the same capability could also make it easier to give the battery a second life, for example, in stationary energy storage. Because the system can identify and bypass weak cells, a larger proportion of the battery pack could be reused as a complete unit.
“A battery pack that is retired prematurely represents both wasted materials and wasted energy. Keeping battery packs in use for longer is therefore a sustainability argument even before the economics are considered,” says Albert Škegro.
Published in journal:
- Nature Communications
- Nature Energy
Title:
- System-level assessment of dynamic reconfiguration for lifetime and cost outcomes in electric vehicle battery packs
- Quantifying the impact of cell-to-cell inconsistency on electric vehicle battery degradation and utilization
Authors:
- Albert Škegro, Torsten Wik, Bo Bijlenga, Alexander Bessman, and Changfu Zou
- Litao Zhou, Xiaolei Bian, Yizhou Zhang, Zhenpo Wang, Zhongwei Chen, Zhiyu Mao, and Changfu Zou
Source/Credit: Chalmers University of Technology | Sandra Tavakoli
Edited by: Scientific Frontline
Reference Number: eng100826_01