In recent years, the EV market has been moving towards greater system integration, with technologies like cell-to-body and cell-to-chassis designs. These, however, can be harder to dismantle and/or remove from vehicles.

New EU regulations, approved in June this year will set out battery requirements, including a 'Battery Passport' and recovery of certain materials and covering the entire life cycle of a battery from the mined materials to their recycling at end of life.

To lessen the impact of initial manufacturing, there are requirements for more recycled content in the batteries but also targets for how much lithium (50% by 2027, 80% by 2031) and cobalt, copper, lead, and nickel (90% by 2027 and 95% by 2031) must be recovered from waste batteries.

Cell-to-pack batteries are designed such that a battery pack is no longer segmented into several modules. Instead, all of the cells are stacked directly together to reduce unnecessary materials and weight, improve energy density, simplify manufacturing, and reduce costs. According to IDTechEx research, the average cell-to-pack battery exhibits a 20% increase in its gravimetric cell-to-pack ratio (how much of the pack's weight is taken up by the cells). Cell-to-body or cell-to-chassis makes the battery pack a structural component of the vehicles structure, leading to greater integration and reducing the vehicle's overall weight. Manufacturer, BYD, for example, is already deploying cell-to-pack systems in large numbers and cell-to-chassis designs becoming more common from the likes of Tesla with its 4680 pack.

Despite having less parts in the battery pack, cell-to-pack designs typically use structural adhesives or encapsulating foams that can make dismantling a pack difficult. The standard approach in the event of a fault would be to replace the battery pack entirely. If the adhesives or encapsulants used can be dissolved with a solvent without damaging the cells too much, then this could make recycling much simpler. Cell-to-chassis batteries can make removal of the pack from the vehicle a more arduous task, making a recycler's job much more difficult.

The EU regulations do not state anything about the internal structure of the battery pack (e.g., module structure, cell separators, adhesives). One method of recycling is to crush/grind the battery which is then sieved to separate large and smaller particles, with the latter containing the valuable electrode materials. The black mass is then processed using hydrometallurgy to recover the lithium, cobalt and nickel in the form of battery-grade metal salts. Ideally, this process would start with just the cells so that the resulting black mass has a higher percentage of the critical metals. Some have placed entire modules into the grinder and it is possible to process an entire pack, but in that case, the design of the battery means little at end of life. The designer could take the short term benefits of a lower cost and easier to manufacture battery pack but that would make the later stages of extraction more difficult.

In addition to recycling, there is also the opportunity for EV batteries to be used in second-life applications, for example, as stationary energy storage. IDTechEx's report on second-life EV batteries has found that its market will reach US$7 billion by 2033. This bypasses the need in the short term to recycle a battery, and most second-life battery players are opting to integrate batteries at pack-level to avoid complex and timely disassembly to cell-level procedures.

There would still be a requirement to remove the pack from the vehicle. If the pack forms a structural part of the vehicle, then this would increase disassembly times, making second-life repurposing a more expensive process. Hypothetically, if a remanufacturer were to disassemble to cell-level to make use of the best-performing cells in the second-life battery, a cell-to-pack design (which is not cell-to-chassis) could decrease disassembly times and reduce remanufacturing costs.

Cell-to-pack designs are going away. If anything, the trend of greater vehicle integration is likely to continue, thanks to the reduced manufacturing costs and higher energy density. Although EV battery packs are generally lasting longer than many initially expected, as more EV packs start to hit end of life, the difficulty and effort of recycling large quantities of highly integrated battery packs may become apparent. Designers may have to consider this more carefully, especially as the targets for recovery of critical materials become more stringent.

IDTechEx has investigated the impact of cell-to-pack/cell-to-chassis on various materials used in the battery, including fire protection materials and thermal interface materials. Its report, "Materials for Electric Vehicle Battery Cells and Packs 2023-2033", covers the deployed and announced cell-to-pack and cell-to-body designs, and how this will impact the intensity of various materials and components, including steel, aluminium, copper, composites, thermal interface materials, fire protection materials, electrical insulation, cold plates, and coolant hoses. The report also looks at the materials used with the cells, such as lithium, cobalt, nickel, manganese, electrolyte, iron, phosphorous, binders, casings, carbon black, silicon, and separators, which are discussed with demand forecasts from 2023-2033.

Dr James Edmondson is Principal Technology Analyst at IDTechEx