The Concept of Effective Porosity in the Discharge Rate Performance of High-Density Positive Electrodes for Automotive Application

Abstract

The discharge rate performance of NMC532-based electrodes designed for EV application were measured between 0 and 40°C and were compared to the predictions of the electrolyte limited penetration depth model [Gallagher et al., J. Electrochem. Soc. 163, A138 (2016)], also called diffusion limited current density model [Heubner et al., J. Power Sources 419, 119 (2019)]. To support this analysis, we took into account the actual microstructure of the electrodes, previously characterized by FIB/SEM tomography, and their measured and/or simulated transport properties. We show that the performance of NMC532 electrodes, even with a low carbon content below the percolation threshold, are not limited by electrons transport through the electrode due to the high intrinsic conductivity of this active material. At 40°C, the swelling of the PVdF by the electrolyte solvents penalizes performance, especially as the binder content is high. Above all, the current density at which a brutal decrease in capacity occurs is well predicted by the model, although by reducing the porosity to its percolated micrometer sized fraction. This is in good agreement with the numerical simulations of the ionic transport properties.

Influence of a Liquid Electrolyte on Electronic and Ionic Transfers in a LiNi0.5Mn0.3Co0.2O2/Poly(vinylidene Fluoride-co-hexafluoropropylene)-Based Composite Material

“… 3 ≈ 63) because of a higher NMC content in N0b. The P4 relaxation (particle polarization) is well fitted by a CC-function with a relaxation frequency  4 = 6.4×10 9 Hz, a parameter  4 = 0.08 and a dielectric strength  4 = 1.1 at room temperature (Supporting Information S1, Table 1 and Fig. S11).…”

“…P2bs and P2s originate from interfacial capacities due to adsorbed EC dipoles at the PVdF/NMC interface and on the free NMC surface, respectively. At the other end of the spectrum, the high frequency relaxation P5 has a characteristic frequency  5  6×10 9 Hz and a dielectric strength  5  10 at room temperature. This relaxation is too intense to be attributed to NMC particle polarization whose strength is of the order of unity (Table 1).…”

Electrode Design for MnO2-Based Aqueous Electrochemical Capacitors: Influence of Porosity and Mass Loading

“…The usefulness of the calendering process is emphasized since it significantly helps to decrease this discrepancy between low- and high-mass loading when porosity is decreased down to 50%. It can be noted that unlike batteries, for which porosities as low as 20% have been measured [ 44 ], electrochemical capacitors require a certain level of porosity to mitigate ionic conductivity and electronic conductivity.…”

Continuous Processing of Cathode Slurry by Extrusion for Lithium‐Ion Batteries

“…[4] According to Tambio et al, mostly pores in the size range above 60 nm, so-called micrometric porosity, are important for the ion diffusion. [29] In this case, pore size distribution was determined in the range of 10 nm to 10 μm by mercury intrusion. Figure 8 shows the pore diameter distribution of the electrodes manufactured with different recipes.…”

“…[17] Tambio et al found that the micrometric pores, which are at least 60 nm in size and are included in the size range mentioned previously, are essential for sufficient ion diffusion. [29] Therefore, better electrochemical results can be expected. The geometric mean diameter influences mainly the modal value of the large peak at 2 μm: The lower the geometric mean diameter, the lower is the modal value.…”