How Accounting Choices Swing the Carbon Footprint of Battery Cells

The race to electrify transport in Europe runs on lithium-ion batteries, and it is increasingly policed by numbers. Under the European Union’s Batteries Regulation 2023/1542, manufacturers of electric vehicle and rechargeable industrial batteries will soon be legally required to calculate and declare the carbon footprint of every battery they sell. That sounds like a straightforward exercise in environmental accounting, but a new study from Technische Universität Braunschweig shows just how fragile the numbers can be. Published in the Journal of Industrial Ecology, the research demonstrates that two technical decisions buried deep inside the calculation rules—how data are aggregated in time and space, and how so-called multifunctionality is handled—can shift the reported climate impact of a single battery cell by meaningful margins, without the battery itself changing at all.

The stakes are considerable. The regulation mandates that the carbon footprint method align with the Product Environmental Footprint Category Rules for rechargeable batteries, and it authorises the European Commission to fix the details through Delegated Acts. A draft of the Delegated Act for electric vehicle batteries was released for public consultation in April 2024 and is still being refined. Because every manufacturer will have to follow the same standardised method, any ambiguity in that method translates directly into numbers that cannot be fairly compared across companies. The Braunschweig team, led by Jana Husmann, Johanna Holsten, Gabriela Ventura Silva and Christoph Herrmann, set out to find precisely where those ambiguities bite hardest, using a simulation-based case study of a 100 MWh battery cell production plant in Germany.

Battery cell production is an energy-hungry, multi-stage affair. It begins with mixing dry powders—active materials, carbon black, binders—with solvent, then coating the slurry onto foil substrates, drying and calendering the coated electrodes, and cutting them to size. The anodes and cathodes are then assembled into cells through packaging, final drying, contacting, electrolyte filling and tempering, all inside conditioned dry rooms whose humidity control alone demands enormous amounts of energy. The chain ends with formation, the charging and discharging that activates each cell’s electrochemistry. Because primary data from large-scale plants are rarely accessible, the researchers built a dynamic process chain simulation combining agent-based and discrete event approaches, capturing material and energy flows, machine behaviour, scrap rates and even the fluctuating energy demand of the dry room over time. The functional unit was a single battery cell of 33.3 Wh nominal capacity produced in Germany in 2023, assessed with the EF v3.1 method for climate change.

The first methodological minefield the study explores is multifunctionality—the situation where a single process delivers more than one product or service. For years, battery cell production was treated as a single-function process: it makes cells, full stop. But with the regulation’s mandatory recycled content targets and the industry’s circular economy ambitions, former waste streams are acquiring economic value. Non-functional cells rejected in final testing and scrap electrodes from coating and cutting steps are increasingly attractive feedstocks for recyclers, not least because electrodes can be directly recycled before the electrolyte is ever added. Once those waste flows become products in their own right, the environmental burdens of production must somehow be divided between the good cells and the scrap.

The researchers tested several ways of drawing that dividing line. The cut-off approach simply lets the waste leave the production system without any impacts attached; whoever recycles it and uses the secondary material carries the recycling burden. The circular footprint formula, or CFF, favoured by the PEFCR, splits burdens and benefits of recycling between the battery being recycled and the one made with recycled content, governed by parameters such as recycled content, recycling rate and material quality. The draft Delegated Act adds a special variant, the CFF PS, tailored to production scrap recycling. Finally, classical allocation based on mass or economic value distributes upstream production impacts between cells and scrap. The baseline result with cut-off was 6.3 kilograms of CO2-equivalent per cell. Between cut-off, CFF and CFF PS, impacts differed by less than one percent—but full allocation pushed the figure roughly six percent higher, because the waste cells and electrodes, which account for about eight percent of production impacts under the other approaches, no longer carried their share.

That six percent swing may sound modest, but multiplied across gigawatt-hours of production and scrutinised against regulatory thresholds, it matters enormously for comparability. The authors also found that allocation creates a deeper modelling problem: if recycled scrap re-enters production and is recycled again, the impacts assigned to materials change with every recycling loop, requiring detailed tracking and tracing of materials that is currently not feasible. Statistical modelling of how materials circulate could estimate these effects, but the researchers argue that any such approach would need standardised rules for documentation to keep companies comparable. Economic allocation, meanwhile, is largely ruled out in practice, since the guidelines permit it only when the value of final cells or electrodes is ten times that of the waste—unlikely given that both share identical production processes and costs.

The team’s recommendation is pointed: treat production scrap exactly like end-of-life batteries, and preferably use the cut-off approach. Their reasoning is consistency. The CFF, they argue, is complex, mixes product and material perspectives, leaves room for interpretation in its parameters, and would likely be applied inconsistently by different practitioners. More strikingly, they identified a substantive flaw: the default recycling processes in the draft Delegated Act do not recover lithium, even though the EU Batteries Regulation sets explicit targets for lithium recycling rates and recycled content. The cut-off approach, by contrast, is simpler, needs less data, and aligns with the many battery and cross-industry guidelines that already favour it. Only the CFF captures both recycled content and recycling rate, but the authors note that regulatory compliance on those targets will most likely be demonstrated through certificates and tools such as the battery passport, not through the carbon footprint calculation itself.

The second axis of the study concerns data aggregation, and here the findings are equally consequential. When the researchers varied temporal aggregation—averaging production data over a month, a day, or an hour of March 2023—they found that daily and hourly figures deviated from the monthly baseline by around plus or minus ten percent. The variation stems from processing energy, dry room energy demand, and the number of scrap cells produced in each period, all of which fluctuate with weather, electricity mix and production rhythm. Monthly or yearly averages smooth out these outliers and best represent long-term conditions, making them suitable for official reporting. Hourly and daily resolution, however, is what engineers need to spot inefficiencies, plan production, and integrate renewable energy sources—insights that vanish entirely in an annual average.

Spatial aggregation told a different story. Whether data were collected machine by machine, by factory area, or for the whole plant, the total climate impact per cell barely changed. What changed dramatically was the ability to locate hotspots. Machine-level data revealed that dry room energy and cathode dry mixing are major contributors; area-level data could only point to broad sections like cell production; factory-level data reduced the analysis to materials, energy and scrap. Since the regulation aims not just at reporting but at continuous improvement of carbon footprints, recycling rates and recycled content, the authors warn that a standard focused solely on reporting would squander LCA’s engineering potential. They propose that the methodology could require finer data collection internally without mandating public disclosure at that resolution.

On the question of how the mandatory one-year data collection period should be defined—calendar year or rolling year backwards from production—the study offers a concrete compromise: a rolling average updated monthly. For cells produced in March 2026, for example, the average of data from March 2025 to February 2026 would apply. This preserves the robustness of a full-year basis and comparability between companies, while incentivising detailed data collection and reflecting decarbonisation efforts, supplier changes and process improvements far more quickly than a fixed calendar year. Taken together, the study’s message is clear: before Europe’s battery carbon footprint rules are finalised, regulators must resolve how multifunctionality is handled, clarify the data collection period, and decide whether the CFF’s complexity is fit for large-scale implementation—or whether the humbler cut-off approach, and a method that serves engineering as well as reporting, would serve the energy transition better.

Subject of Research: Life cycle assessment methodology for battery cell production under the EU Batteries Regulation

Article Title: Life cycle assessment of battery cell production in the context of the European Union batteries regulation: the influence of data aggregation and multifunctionality handling

Article References: Husmann, J., Holsten, J., Ventura Silva, G., & Herrmann, C. (2026). Life cycle assessment of battery cell production in the context of the European Union batteries regulation: the influence of data aggregation and multifunctionality handling. Journal of Industrial Ecology. https://doi.org/10.1007/s44498-026-00169-y

Image Credits: AI Generated

DOI: 10.1007/s44498-026-00169-y

Keywords: life cycle assessment, battery cell production, EU Batteries Regulation, carbon footprint, multifunctionality, data aggregation, circular footprint formula, cut-off approach, recycling, lithium-ion batteries, production scrap, industrial ecology