UC San Diego

The transition to a low-carbon economy relies heavily on lithium-ion batteries (LIBs), which power electric vehicles (EVs), consumer electronics, and renewable energy storage. Despite significant advancements in LIBs, sustainable end-of-life management and efficient recycling methods are critical for reducing environmental impact and resource consumption. A direct recycling method using hydrothermal treatment in a Li-containing solution has successfully regenerated degraded lithium manganese oxide (LMO) cathodes, restoring their high capacity and long cycling stability while minimizing the environmental footprint compared to traditional pyrometallurgical and hydrometallurgical processes. However, discrepancies among cathode chemistries present challenges, particularly in high-voltage spinel-type materials such as LiNi0.5Mn1.5O4, where structural instabilities, defect formation, and Li/Mn disordering contribute to sluggish Li+ transport and irreversible capacity loss. A defect engineering strategy inducing twin boundaries and preferred grain orientation has been employed to enhance Li+ diffusion and cycling stability.Another strategy is upcycling cathode materials into high end cathodes beyond its virgin performance. Here, we report an efficient upcycling method, converting spent polycrystalline LiNi0.33Co0.33Mn0.33O2 (NCM111) up to single-crystal LiNi0.8Co0.1Mn0.1O2 (NCM811) with lean input of precursors. Systematical investigation of the microstructure evolution in the upcycling process revealed an Ostwald ripening phenomenon during particle transformation. Optimizing sintering temperature and reaction time results in single-crystal particles showing uniform Ni element distribution and valence state, clean surface, and tunable sizes. Despite these advances in recycling and upcycling, LIBs still suffer from performance limitations under extreme fast-charging (XFC) conditions. Charging at high-rate leads to lithium plating, unfavorable solid electrolyte interphase (SEI) formation, and solvent co-intercalation, ultimately degrading cycle life. These failure modes primarily stem from the inadequacies of conventional electrolytes; however, using an ester-based electrolyte has significantly improved capacity retention. Addressing both sustainable battery recycling and performance degradation under XFC is crucial for advancing next-generation LIBs, ensuring long-term efficiency, and promoting a circular economy for energy storage solutions. Overall, this thesis explores the aforementioned strategies, providing fundamental insights and guidance for the rational design of highly efficient recycling and upcycling methodology and innovative electrolytes. By bridging sustainability with performance optimization, this work paves the way for more durable, efficient, and environmentally responsible energy storage solutions.