Kinetic Insights into Li x Ni 0.67 N (1.67 ≤ x ≤ 2.17), a quasi "Zero-Strain" Negative Electrode Material for Li-Ion Battery

The kinetics of the electrochemical lithium intercalation in the nitridonickelate Li x Ni 0.67 N (1.67 ≤ x ≤ 2.17) is investigated by electrochemical impedance spectroscopy during a full reduction-oxidation cycle in a two-electrode cell. The layered structure of this anode material delivers a reversible and stable specific capacity of 200 mAh g-1 over 100 cycles at C/10 near 0.5 V vs Li + /Li. The equivalent electric circuit simulation allows a full assignment of the impedance spectra, with different contributions including the SEI layers on each electrode, charge transfer and Li diffusion. The calculated lithium diffusion coefficient value of approximately 5×10 −9 cm 2 s −1 almost does not vary with the lithium content in Li x Ni 0.67 N (1.67 ≤ x ≤ 2.17). Conversely, the charge transfer resistance (R ct) is found to strongly depend on the depth of reduction to be maximum for the fully reduced electrode, with a totally reversible behavior during oxidation. The overall impedance of the cell remains stable upon long cycling, which indicates a good chemical stability of the SEI on Li x Ni 0.67 N as well as 2 remarkable structural and chemical stability of the nitridonickelate upon cycles. The present kinetic findings shed light on the remarkable "zero-strain" behavior of this negative electrode material presenting numerous Li vacancies.