A process simulation study on the impact of electrochemical discharge on the circularity of lithium-ion batteries using new multi-dimensional indicators†

Spent lithium-ion batteries (LIBs) contain residual energy, which might be hazardous during storage, transportation, and recycling. Therefore, it is essential to either deactivate or discharge LIBs prior to any mechanical processing step. As recycling is a key activity to transform from a linear economy into a circular one, the evaluation of a discharge step from the perspective of circular economy (CE) is essential but remains largely unexplored. In this work, battery discharge systems using three different Na⁺-based aqueous solutions (i.e., NaCl, Na₂SO₄, and Na₂CO₃) were modelled with HSC® process simulation software. The resulting mass and energy flows were interpreted using a novel methodology involving multidimensional circularity parameters (i.e., statistical entropy, exergy, and exentropy). Statistical entropy only evaluates the concentrating action of different components in a system, without discriminating whether the produced streams are in a usable chemical form or irreversibly changed. Thus, a weighting factor for irreversible transformations was implemented for statistical entropy analysis. Exergy analysis revealed that the discharge systems do not significantly destroy energy, although it was unexpectedly revealed that corrosion aids in exergy preservation by producing highly concentrated hydrogen from the water splitting reaction. To further reconcile the preservation of energy and materials, the recently developed exentropy (χ) analysis was used. Na₂CO₃ was identified as the most promising electrolyte (χ = 0.066) compared to NaCl (χ = −0.055) and Na₂SO₄ (χ = −0.106), providing for the first time a parametrized basis to the idea that electrochemical discharge systems with strong corrosion are inefficient from the perspective of circularity.