Kinetic insights into LixNi0.67N (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 LixNi0.67N (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 LixNi0.67N (1.67 ≤ x ≤ 2.17). Conversely, the charge transfer resistance (Rct) 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 LixNi0.67N as well as 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.