(In)Coherent-bond-networks in Ni-rich layered oxides for durable lithium-ion batteries

An intriguing “coherent-bond-network” effect is suggested here for mitigating anisotropic lattice variations inducing micro-cracks, for durable Ni-rich layered cathodes based on Li[Ni_10/12Co_1/12Mn_1/12]O₂ (NCM) and Li[Ni_10/12Co_1/12Ti_1/12]O₂ (NCT) oxide models in lithium-ion batteries (LIBs). Upon charging, the c and a lattice strains for NCT are lower than those for NCM, implying that mechanical failures are mitigated in the former. Considering that Ni ions are a major component in compensating for the charge imbalance caused by Li deintercalation, the Ni–O bond populations in the deeply charged state reveal a uniform bond network in NCT, relative to the conventional Ni-rich cathode with NiO₆ distortion. For deeper insights, the O–O edge populations are calculated for the two oxide models, and the discretized values over the entire crystal framework are observed for NCM, whereas delocalization is shown in NCT. These results underpin the Ti-induced “coherent-bond-network” that smoothly connects the MO₆ octahedral network upon charging for Ni-rich layered oxides, where M denotes a transition metal. In addition, the oxide-model-dependent (in)coherent-bond-networks are consistently identified for the Li–O bond populations of NCT and NCM, and insights into the chemical stiffness of the Ti–O bond reinforces the structural origin of the uniform octahedral environment. The structural concept based on an in-depth understanding of the Ni-rich layered models not only accounts for the fundamental origin of the Ti-doping effect on the anisotropic lattice change but also provides a local-structure-related point of view in restraining the formation of micro-cracks for durable high-energy–density LIBs.