Crystal Domain Engineering of Ni-based Co-Free Layered Cathodes for High-Performance Li-Ion Batteries

Ni-based layered oxides (NCMs) are one of the crucial candidates for high-energy Li-ion batteries, but suffer from severe structural degradation owing to diverse irreversible phase transitions, especially when Co is removed. Addressing such intrinsic instabilities calls for creative bulk design strategies, wherein crystal domain engineering emerges as a compelling approach. In this research, we developed a simple one-step strategy based on crystal domain engineering to controllably integrate locally ordered Li-rich Li₂TMO₃ crystal domain, which is composed of LiNi_{6- x}Mn_x hexatomic-ring, into the NMs bulk lattice. By precisely controlling the lithium stoichiometry to obtain "twin domain" Ni-based cobalt-free lithium-rich layered oxides (Ni-LLOs) with a tunable lithium-rich functional unit. Benefiting from such crystal domain engineering, the optimal cathode material with competitive capacity (∼200 mAh g^-1) can deliver an excellent capacity retention of 90.59% after 600 cycles in pouch-type cells at 1 C. Further mechanistic investigation reveals that the intergrown Li₂TMO₃ crystal domain suppress the formation of H3 phase and mitigate lattice contraction through a pinning effect, while simultaneously alleviating Li/Ni cation mixing, thereby reducing the necessity for cobalt incorporation. Collectively, this work establishes crystal domain engineering as a versatile and powerful strategy for developing high-energy, long-lifespan cathode materials for next-generation high-performance lithium-ion batteries.