Characterization of Electronic and Ionic Transport in Li[subscript 1-x]Ni[subscript 0.33]Mn[subscript 0.33]Co[subscript 0.33]O[subscript 2](NMC[subscript 333]) and Li[subscript 1-x]Ni[subscript 0.50]Mn[subscript 0.20]Co[subscript 0.30]O[subscript 2](NMC[subscript 523]) as a Function of Li Content

Abstract

Despite the extensive commercial use of Li[subscript 1-x]Ni[subscript 1-y-z ]Mn[subscript z]Co[subscript y]O[subscript 2](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 NMC[subscript 333] and NMC[subscript 523] 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 [superscript -7] Scm [superscript -1] to ∼10[superscript -2] Scm [superscript -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.