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EV Makers Consider Structural Batteries

Sam Abuelsamid
Jul 20, 2021

Charging station for electric vehicle

While battery swapping for EVs has seen a resurgence of interest in the past couple years, not every automaker seems to be onboard with the idea. It’s not necessarily that they think swapping is a fundamentally bad concept but that they are balancing different priorities. A key aspect of engineering is evaluating the compromises that must inevitably be made to find the best solution, and for most potential EV drivers, range is at or near the top of their consideration list.

Since even the most advanced batteries expected to become available in the next decade still fall short of liquid fuels in energy density and replenishment time, reducing the need for charging is critical. Doing so requires increasing the vehicle’s available range. EVs are already energy efficient, so further enhancement will have limits.

Stuffing more kilowatt-hours into the battery pack is also a potential solution. Improved battery chemistries certainly help, and if solid-state batteries eventually come to market, they can be another step forward. There is another answer as well: increasing the density of cells in the battery pack. Current battery packs are comprised of cells packaged into modules that are then arranged into the full pack. Each module is typically a metal box containing from a dozen to several hundred cells, depending on the cell format, and the pack has an internal structure to contain the modules. This structure and module boxes make up some of the volume in the pack.

EV Makers Come Up with Solutions

In September 2020, Tesla held a battery presentation for investors where it outlined a concept for a structural battery pack using its new, larger 4680 cylindrical cells. In late June 2021, Volvo hosted an online technical presentation where it discussed a similar concept. Unlike Tesla, Volvo uses prismatic can cells. For its structural battery, the company plans to glue these cells together into one large block and then sandwich the whole thing between two metal plates. This structure would then form the floor of future EVs.

Volvo claims this approach would enable a more than 20% improvement in volumetric energy density in its next-generation batteries. Like Tesla, it also claims that this would improve the rigidity of the overall vehicle structure. This is important for safety, but it also contributes to improved ride and handling by providing a more stable platform to attach the suspension to.

Structural Batteries Present New Challenges

The downside of a structural battery pack is that it potentially becomes non-serviceable. With current pack designs, individual modules can be replaced and serviced if there are defective cells. When hundreds or thousands of cells are glued together, any problem may mean scrapping the whole pack. It also offers less flexibility for use in second-life battery applications.

However, during its presentation, Volvo stated that the improving quality of cells was a factor in enabling movement toward structural batteries. The cells must be consistently high quality or else the potential scrappage rates may make these new batteries too expensive. So far, neither Tesla nor Volvo have given a specific timeline for plans to launch structural batteries, but Tesla has hinted at using this approach for its upcoming Cybertruck. Volvos with structural packs probably won’t arrive before mid-decade.

One truism since the start of the automotive age is that there is no perfect solution for every application. Some vehicles in some markets will no doubt continue with swappable batteries while others will probably retain modular packs. It will be fascinating to see if the structural pack becomes a truly viable option.