The Battery Pack May Soon Be Obsolete

The key to making an EV go is the battery pack that stores energy. Ever since the earliest EVs were developed in the late 19^th century, they have had a battery pack, but that component is starting to become obsolete. It’s important to note that batteries aren’t going away anytime soon, but the box that holds the cells certainly seems to be. Two early examples of this trend are the BYD Seal and the Tesla Model Ys built with 4680 cylindrical cells.

Until recently, the architecture of a typical EV battery was a box in a box. Cells are packed into a box that makes up a module. Then modules are packed into a larger box—the pack enclosure. Each of those boxes and the cell containers occupy physical space, and active cell material typically only accounts for about 30%-35% of a modular pack’s total volume.

A newer trend is the adoption of a cell-to-pack (C2P) architecture. In this layout, the modules are eliminated, and the cells are bonded together and installed directly into the enclosure. Our Next Energy’s Aries II battery pack uses lithium iron phosphate (LFP) cells in a C2P arrangement that is claimed to have a ratio of 75% active cell material by volume. This arrangement is still installed into the vehicle body in a similar fashion to modular packs, where the box is bolted to the floor or frame.

The next stage is to eliminate the pack enclosure entirely, since the enclosure and the floorpan of the vehicle body each take up some volume. In a way, Tesla has done this with the latest iteration of the Model Y. It technically still has a pack enclosure, but Tesla has eliminated the floor of the body. Components like seats and consoles that are normally fastened to the floor are actually bolted to the chassis battery, and the whole subassembly is inserted into the body shell and fastened from below.

This eliminates many components from both the battery system and the vehicle structure and has the potential to simplify assembly and reduce costs. Installing seats and other interior parts into vehicle bodies has always been challenging, and this new architecture opens up the potential to further automate these processes.

At the recent IAA Mobility Summit in Munich, Germany, Chinese automaker BYD showed off its new Seal electric sedan. The Seal utilizes what BYD calls a cell-to-body, or C2B, architecture for the battery. As with the Model Y, there is no separate pack enclosure. However, BYD’s Blade prismatic cells are bonded together into a block, inserted into a cavity in the bottom of the body, and sandwiched in place with the cooling plates and bottom cover.

The use of rectangular prismatic cells eliminates the space found between the cylindrical cells of the Tesla and has allowed BYD to get 82.5 kWh worth of LFP cells in a midsize sedan similar in size to the Hyundai Ioniq 6. That’s enough for more than 350 miles of range on the European WLTP (Worldwide Harmonised Light Vehicle Test Procedure) drive cycle. LFP cells have about 30% lower energy storage capacity than most nickel-cobalt cells like those used by Hyundai. However, the modular battery pack of the Ioniq 6 loses storage volume, for the reasons described above.

This shift away from modular battery packs and even separate pack enclosures should yield significant reduction in cost and help achieve the goal of more affordable EVs in the coming years. For more information about the EV battery market, including technology and design trends and market forecasts, check out Guidehouse Insights’ recent EV Batteries report.