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 LiNi1-xTixO2 (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.