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

Abstract

Despite the extensive commercial use of Li 1-x Ni 1-y-z Mn z Co y O 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 333 and NMC 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 −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) Cathodes having high energy and power density, adequate safety, excellent cycle life, and low cost are a critical need for Li-ion batteries to enable the commercialization of electric transportation and stationary storage.1 Towards this end, much previous research focused on the development of LiNi 1-x Co x O 2 (NC) 2-10 cathode due to its high capacity (∼275 mAh/g) and favorable operating cell voltage (4.3 V vs. Li/Li + ), which is within the voltage stability window of current liquid electrolytes, and lower cost than LiCoO 2 . Despite extensive optimization, e.g., with respect to the Ni/Co ratio, 2-10 NC suffers from poor structural stability during electrochemical cycling. 11Significant efforts were subsequently focused on improving structural stability and electrochemical performance by partial substitution Mn 12-17 (electrochemically inactive in this compound over the operating cell voltage window). Thus our objective in this work is to systematically characterize and interpret the transport properties of NMC 333 and NMC 523 . We use additive-free, single phase sintered samples in which the extrinsic effects due to binders, conductive additives, and particle microstructures that may be present in composite electrodes are avoided. Using electron blocking and ionic blocking cell configurations, respectively, and electrochemical impedance spectroscopy and DC polarization and depolarization techniques (see Table I), we deconvolute the electronic and ionic conductivities of NMC 333 and NMC 523 as a function of temperature and Li content, up to a lithium deficiency of x = 0.75, which corresponds to high charge voltages of 4.7 V and 4.8 V for NMC 333 and NMC 523 respectively. Our sample configuration permits measurement of single-phase properties up to delithiation levels (state-of-charge) where electrochemically-induced microfracture intrudes. Electronic conductivity was not apparently affected by these effects, whereas ionic transport shows an apparent increase beyond x = 0.50 which we attribute to fast transport paths created by microfracture. • C for 12 h in ambient atmosphere, preceded by h...

Effects of microstructure on fracture strength and conductivity of sintered NMC333

“…For all sintering temperatures below 1100°C, the electrical conductivity at room temperature was in the range 3.7 − 6.3 × 10 −4 S/cm, which agrees well with reported literature values for fully lithiated NMC333 . For the material sintered at 1100°C, an order of magnitude reduction in conductivity was observed.…”

“…In addition, while samples sintered below 1100°C shared similar activation energies (~0.26 eV), the samples prepared at 1100°C deviated with an observed increase in activation energy to 0.46 eV for sintering times of 1 and 10 hours. These values for activation energy are within the range reported for partially delithiated Li 0.9 Ni 0.33 Mn 0.33 Co 0.33 O 2 and fully lithiated NMC333, respectively (0.29‐0.48 eV) …”

“…R1 and R2 measurements were attributed to grain cores and grain boundaries, respectively. R1 and R2 were deconvoluted from the spectrum using capacitance values of 10 −10 F and 10 −7 F as previously reported for similar materials and mechanisms . The conductivity calculations were normalized by sample geometry.…”

“…Developed from the high voltage LiCoO 2 prototype, the LiN 1− x − y Co x Mn y O 2 cathode was optimized for reduced cost, increased capacity, and stabilized layered structure to yield LiNi 0.33 Mn 0.33 Co 0.33 O 2 (NMC333) . Optimization of the synthesis, calcination, material properties, and electrochemical performance has been extensively researched . Traditional battery architectures utilize small particles with high surface area for efficient active material utilization and high power density.…”

Galvanostatic Intermittent Titration and Performance Based Analysis of LiNi0.5Co0.2Mn0.3O2Cathode

“…Although the above results give reasonable macro trends for diffusivity variation with state of charge, the diffusivity magnitudes have wide variations depending on the active area definition used. Further diffusivity computations for NCM523 have been undertaken by Kong et al 24 (EIS), Xia et al 25 (EIS) and Amin et al 26 (EIS and GITT at multiple temperatures).…”