A methodology for absolute environmental sustainability assessment of batteries: a comparative case study of sodium-ion and lithium-ion battery

Increasing global demand for Li-ion batteries driven by renewable energy transition and decarbonization targets have triggered associated sustainability concerns, including environmental impacts, material criticality, toxicity, and circularity. Sodium-ion batteries, though in the early stage of development and commercialization, are considered a promising alternative given their potential environmental and cost benefits. Assessing sustainability from an absolute sustainability perspective is particularly relevant for emerging technologies to avoid unintended impacts and track their implementation to stay within the planetary boundaries. This study presents a methodology for sustainability assessment of batteries, comparing environmental impacts (LCA results) with the allocated share to estimate absolute sustainability performance. The proposed methodology is illustrated using a comparative case study of a sodium-ion battery (NaNMC type) and a lithium-ion battery (LiNMC type). An economic allocation-based approach has been applied to determine the allocated shares. The high deviation in the sustainability ratio indicates poor performance of current battery production practices relative to planetary boundaries for climate change, abiotic resource depletion, and human toxicity impacts. The absolute sustainability performance is comparable for both batteries, with the highest difference in the case of human toxicity (non-cancer) and abiotic resource depletion. Given the high uncertainty and potential limitations of the economic-allocation-based sharing principle and the data sources, the estimated results require critical evaluation and further investigation (e.g., uncertainty and sensitivity analysis and comparative assessment with multiple sharing principles) for a robust assessment and more realistic interpretations. Potential advantages, challenges, and limitations of the applied methodology are addressed.