Reimagining the Circular Economy in Hydrometallurgical Recycling of Lithium-Ion Batteries: The Hidden Bottleneck of Na2SO4

The rapid expansion of lithium-ion batteries (LIBs) has intensified the need for critical mineral recycling, with an emphasis on improving economic efficiency and material circularity. Currently, hydrometallurgical processing is the dominant industrial-scale method, valued for its high recovery rates of valuable metals such as lithium, cobalt, and nickel. However, the established hydrometallurgical route for LIB recycling involves a two-step process of H 2 SO 4 leaching, followed by NaOH precipitation, which inevitably generates large quantities of Na 2 SO 4 as a byproduct. This perspective paper argues that the generation and management of Na 2 SO 4 are hidden bottlenecks in scaling up industrial LIB recycling, fundamentally threatening the economic viability and environmental sustainability of large-scale hydrometallurgical LIB recycling. Addressing this challenge requires a shift toward more advanced techniques such as electrochemical salt splitting and byproduct valorization pathways. Supportive policies are essential for enabling a truly circular battery recycling economy.