Résumé
The permittivity and conductivity of a porous composite consisting of a mixture of a lithium-ion battery electrode material, LiNi0.5Mn0.3Co0.2O2 (NMC532), and a polymeric binder, poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP), were simultaneously measured by broadband dielectric spectroscopy (BDS). The composite was either dry or wetted with a conventional battery electrolyte [LP30, LiPF6 in ethylene carbonate/dimethylcarbonate (EC/DMC)] or a mixture of electrolytic solvents (EC/DMC). The experimental results show that the electronic conductivity of NMC532 was much higher than that obtained with LiNi0.33Mn0.33Co0.33O2 (NMC333). In addition, a strong influence of liquids was evidenced. Dipolar species (in particular, EC dipoles) and ions (in particular, PF6– in LP30) considerably increased the surface conductivity of NMC532 clusters, leading to a facilitated electronic transfer from one cluster to another. The effective ionic conductivity was measured and compared to the ionic conductivity of the electrolyte to express the tortuosity factor of this composite electrode.