A comprehensive cradle-to-grave life cycle assessment of three representative lithium-ion stationary batteries targeting a 20-year bi-daily charge–discharge service

Abstract

Along with the harvesting of renewable energy sources to decrease the environmental footprint of the energy sector, energy storage systems appear as a relevant solution to ensure a reliable and flexible electricity supply network. Lithium-ion (Li-ion) batteries are so far, the most widespread operational electrochemical storage system. The aim of this study is to address the lack of comprehensive cradle-to-grave environmental impact evaluation for stationary Li-ion batteries. Three stationary Li-ion batteries are assessed here: a prototype lithium iron phosphate/graphite (LFP/G) battery and two alternatives (with nickel manganese cobalt (NMC) positive electrodes and graphite (G) or lithium titanate oxide (LTO) negative electrodes). Midpoint to endpoint environmental indicators are estimated and compared using the life cycle assessment methodology. With the help of literature data, the modelling includes all auxiliary equipment (container, power electronics, etc.) and considers end-of-life (EoL) processes that are as specific as possible for each component. The evaluation accounts for two full charge equivalent per day for a 20-year period. The endpoint analysis does not enable to determine which of the NMC/G and LFP/G batteries has the lesser environmental impacts. A more detailed examination of the midpoint indicators is essential for making a choice between the two, as both present pros and cons. However, for both endpoint and midpoint indicators, the NMC/LTO battery is less impactful than the other batteries, particularly for critical categories (human toxicity, freshwater ecotoxicity and eutrophication) as it does not need any pack replacement and contains less copper. Auxiliary equipment does not contribute significantly to most of the cradle-to-grave environmental indicators, except for steel container recycling, which induces human carcinogenic toxicity. In all other categories, the screened EoL processes indicated potential net negative impacts, especially through the recycling of lithium compounds in LFP and LTO electrodes with adapted processes. Recovering the aluminium cell containers and electrode foils from dismantled cells is also significantly beneficial. This work provides a consistent comparison between three different battery storage systems including all auxiliary components and all life cycle stages. Reliability of the findings hinges on the selected inventories and parameters’ assumptions, most of which are derived from the literature. Sensitivity analysis has shown the significance of certain parameters, such as the battery pack’s lifespan, in determining the least impactful battery. Primary data on the battery use phase (lifespan, round-trip efficiency, depth-of-discharge) as well as a more detailed modelling of both auxiliary equipment and EoL processes would provide a more accurate picture of the associated environmental impacts. Finally, to make a choice, other criteria such as economic aspects, pack safety or criticality risks of materials should be considered.

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