Contact Resistance of Carbon–Li_x(Ni,Mn,Co)O₂ Interfaces

Abstract

Electronic resistance in lithium‐ion battery positive electrodes is typically attributed to the bulk resistance of the active material and the network resistance of the carbon additive. Expected overpotentials from these bulk components are minimal relative to that from charge‐transfer resistance. However, literature reports show that cell overpotentials are often much more sensitive to conductive additives than the expected level from bulk or percolating‐network transport. This discrepancy motivated a detailed examination of the contact resistance between the active material and conductive additive. The contact and bulk resistances are simultaneously measured using dense bar samples of lithium‐layered oxides (LixNi1 /3Mn1/3Co1/3O2 and LixNi0.5Mn0.3Co0.2O2) in contact with carbon black. It is found that the contact resistance dominates the overall electronic resistance when the length scale is smaller than millimeters; after correcting for contact effects, bulk conductivity of layered oxides is determined to be orders‐of‐magnitude higher than previously reported. In porous electrodes, it is found from three‐electrode electrochemical impedance spectroscopy that the carbon content most heavily influences the low‐frequency regime (≈0.01 Hz), as opposed to the high frequency (>103 Hz) regime expected from electronic percolating properties. Constriction effects within the layered oxide are identified as the dominant mechanism for contact resistance and its implication is investigated for porous electrodes.

Beyond Constant Current: Origin of Pulse-Induced Activation in Phase-Transforming Battery Electrodes

“…The voltage cutoffs were set at 2 and 4 V. Two-electrode tests were performed by an Arbin LBT20084 battery cycler or a Biologic BCS-805. Three-electrode cells were fabricated as detailed in Kuo et al Three-electrode measurements were performed using a Biologic MPG-2.…”

Improved lithium-ion battery cathode rate performance via carbon black functionalization

“…3d and e) is estimated as the voltage difference between NMC622 samples (CB, CB-OH (24 h), CB]O (72 h), and CB-COOH (20%) at 0.25C) with CB (at 0.05C), and thus is termed overpotential. 73 In Fig. 3c, the GCD curve of NMC622 with CB at 0.05C (discharge capacity ∼175 mA h g −1 ) is shown as reference.…”

“…The measured EIS spectra were averaged from three cells aer normalisation. 73,77 In Fig. 4a, Nyquist plots of CB and CB] O (72 h) cathodes are shown at different applied potentials during charging and discharging.…”

Morphology‐Dependent Influences on the Performance of Battery Cells with a Hierarchically Structured Positive Electrode**

“…Amin et al [28] found that the electronic conductivity of NMC111 varies between 10 À 6 S m À 1 and 10 0 S m À 1 depending on lithiation and temperature. Furthermore, results from Kuo et al [29] suggested that measuring the electronic conductivity of NMC111 is difficult and includes uncertainties. For this reason, we chose a range of 10 À 6 S m À 1 to 10 À 2 S m À 1 for studying the qualitative influence of electronic conductivity on the cell performance.…”