Characterization of Electronic and Ionic Transport in Li_1-xNi_0.33Mn_0.33Co_0.33O₂(NMC₃₃₃) and Li_1-xNi_0.50Mn_0.20Co_0.30O₂(NMC₅₂₃) as a Function of Li Content

Despite the extensive commercial use of Li_1-xNi_1-y-zMn_zCo_yO₂ (NMC) as the positive electrode in Li-ion batteries, and its long research history, its fundamental transport properties are poorly understood. These properties are crucial for designing high energy density and high power Li-ion batteries. Here, the transport properties of NMC₃₃₃ and NMC₅₂₃ are investigated using impedance spectroscopy and DC polarization and depolarization techniques. The electronic conductivity is found to increase with decreasing Li-content (increasing state-of-charge) from ∼10⁻⁷ Scm⁻¹ to ∼10⁻² Scm⁻¹ over Li concentrations x = 0.00 to 0.75, corresponding to an upper charge voltage of 4.8 V with respect to Li/Li⁺. The lithium ion diffusivity is at least one order of magnitude lower, and decreases with increasing x to at x = ∼0.5. The ionic conductivity and diffusivity obtained from the two measurements techniques (EIS and DC) are in good agreement, and chemical diffusion is limited by lithium transport over a wide state-of-charge range.

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Published in: Journal of The Electrochemical Society
License: https://creativecommons.org/licenses/by-nc-nd/4.0/ 
See article on publisher's website: https://dx.doi.org/10.1149/2.0131608jes