UC Irvine

The unprecedented growth in demand for lithium-ion batteries (LIBs) has intensified supply constraints on critical minerals (Ni and Co) and driven the accumulation of end-of-life battery waste, motivating sustainable waste-management strategies and the development of next-generation cathodes that simultaneously offer high electrochemical performance, stability, low cost, and material sustainability. This thesis addresses the current challenges in cathode materials and the trade-offs among these requirements through two complementary approaches: the upcycling of spent Ni-rich cathodes, and the compositional design of Ni-lean, Co-free layered oxide cathodes. The upcycling strategy focuses on retrieving value from recycled Ni-rich cathode material, LiNi0.8Mn0.1Co0.1O2 (NMC811), from battery waste and then upgrading it into a high-performance cathode via thermal regeneration and synergistic material engineering that combines multielement doping and single-crystal engineering. While both single-crystal engineering and multielement doping individually improve stability, their integration during regeneration of fragmented recycled NMC811 remains elusive. This work shows that high-valence dopants (Nb, Mo, Ta, Ti) preferentially segregate at grain boundaries due to limited solid solubility and lattice mismatch, inhibiting grain coalescence and single-crystal formation. Guided by this mechanistic behavior, this work develops a two-step strategy that decouples particle reconstruction from doping to enable a multielement-doped single-crystalline LiNi0.76Mn0.095Co0.095Nb0.02Mo0.02Ta0.01O2 (UP811) that delivers ~210 mAh g-1 with 90.7% capacity retention after 100 cycles, outperforming conventional single-crystalline LiNi0.8Mn0.1Co0.1O2 (SC811) that delivers similar capacity but only 81.9% retention. In parallel, this work addresses the limitations in conventional low-Ni layered cathode compositions by developing a family of Ni-lean, Co-free cathodes (30–40% Ni) achieving near-complete utilization of the Ni2+→ Ni3+→ Ni4+ redox couple through compositional tuning, enabling reversible capacities of near 200 mAh g-1 at as low as 30% Ni, comparable to Ni-rich cathodes, while demonstrating exceptional cycling stability of >90% capacity retention after 2,000 cycles in single-layer pouch cells. Furthermore, this work identifies 30% Ni as the practical lower threshold for sustaining high capacity without heavily relying on oxygen redox and ~10% Fe substitution for Ni as the upper limit for compensating capacity within this compositional space. Building on the mechanistic and compositional design principles from these two experiments, ongoing work extends the cathode design strategies to Co-free lithium- and manganese-rich (LMR) cathodes, which offer additional capacity through anionic oxygen redox but remain limited by voltage decay and oxygen instability. This work aims to establish composition–structure–performance relationships guiding the design of Co-free LMR chemistries. Together, these findings establish mechanistic and compositional design principles for reducing Ni and eliminating Co in next-generation cathode materials, supporting a sustainable battery supply chain while delivering high electrochemical performance and exceptional cycle life.