Direct Measurements of Effective Electronic Transport in Porous Li-Ion Electrodes

Abstract

An accurate assessment of the electronic conductivity of electrodes is necessary for understanding and optimizing battery performance. The bulk electronic conductivity of porous LiCoO 2 -based cathodes was measured as a function of porosity, pressure, carbon fraction, and the presence of an electrolyte. The measurements were performed by delamination of thin-film electrodes from their aluminum current collectors and by use of a four-line probe. FIB/SEM (focused ion beam/scanning electron microscope) imaging was used to correlate the electrode microstructure to electronic conductivity. The introduction of electrolyte to dry electrodes reduced electronic conductivity by around 60%.

Micro-Four-Line Probe to Measure Electronic Conductivity and Contact Resistance of Thin-Film Battery Electrodes

“…Tests could quantify the change in electronic conductivity when electrolyte is introduced into dry electrodes. 2,9 Tests could be performed to compare conductivity averages and variations between aged and cycled electrodes and corresponding pristine electrodes. The method could be adapted to measure localized ionic conductivity.…”

“…A 2-cm square section of Toda HE5050 electrode (see below for details) was delaminated from its current collector using the technique described in our prior work. 9 In particular, the film was adhered to a glass microscope slide with the aluminum layer facing up. Then the aluminum layer was removed with sequential application of gallium metal and of HCl solution.…”

“…Previously, our group has measured bulk electrode conductivity by delaminating the electrode film from its current collector, attaching it to an insulating support surface, and pressing against a macroscale four-line probe. 9 We note some prior work that purports to be able to deduce the contact resistance between the electrode film and the current collector.10,11 This is a potentially significant source of internal resistance in batteries, 12 and it can be difficult to quantify separately from other resistances.Our goal is to develop a rapid, accurate, and non-destructive method to measure these conductive properties. Recent work in a companion paper 1 has demonstrated that a four-line contact geometry with line spacing on the order of the film thickness is ideal.…”

Quantifying Tortuosity of Porous Li-Ion Battery Electrodes: Comparing Polarization-Interrupt and Blocking-Electrolyte Methods

“…Landesfeind et al simplified the blocking electrolyte TLM by neglecting electronic resistance because of its typical small magnitude in comparison to ionic resistance (a fact confirmed by our own experiments). 27,28 Knowing R ion based on this model, the effective conductivity can be determined based on the cross-sectional area of the cell (A), the thickness of the sample (l), and the intrinsic conductivity of the electrolyte (k int ):…”

Mathematical Model of Four-Line Probe to Determine Conductive Properties of Thin-Film Battery Electrodes

“…However, it is surprisingly difficult to accurately measure the electrical conductivity and contact resistance (between electrode and current collector) of these films. [4][5][6][7][8][9] This is because the contact resistance between probe and sample is high relative to the resistance of the sample, the sample is mechanically fragile, and the conductivity of the electrode film is confounded by the presence of a highly conductive adjacent metal layer (the current collector). The electrode film can be delaminated from the current collector in order to eliminate the last problem, 4 though it is more desirable to measure electrodes non-destructively as is proposed in this work.…”