TiO₆ as a Compensatory Structural Unit in Co-Free, High-Ni Layered Oxide for Durable Lithium-Ion Batteries

High-Ni layered oxides are among the most promising cathode materials for lithium-ion batteries (LIBs) due to their high capacity. However, the reliance on Co, a scarce, expensive, and geographically constrained element, poses challenges to sustainability and large-scale deployment. In this study, Ti is investigated as a cost-effective and earth-abundant substitute for Co in LiNi_1-xTi_xO₂ (LNTO, x = 0.07 and 0.14), synthesized via a scalable co-precipitation method. EXAFS analyses indicate that no obvious Jahn-Teller distortion is observed in LNTO-1, while DFT calculations suggest that Ti substitution modulates the Ni─O electronic interaction and helps reduce the driving force for cooperative Jahn-Teller distortion within the interconnected NiO₆ framework. In addition, it suppresses the detrimental H2-H3 phase transition and reduces internal mechanical stress during cycling. EXAFS and NEXAFS analyses further reveal that TiO₆ octahedra act as compensatory structural units that accommodate lattice strain in both bulk and surface regions, thereby stabilizing the rhombohedral framework. As a result, the optimized LNTO-1 (x = 0.07) delivers a high initial discharge capacity of 197.5 mAh g^{- 1} at 0.05 C and retains 80% capacity after 431 cycles at 0.5 C. This work provides strategic insights for the design of sustainable, high-performance cobalt-free Ni-rich cathodes for next-generation LIBs.