An understanding of the transport properties in nanocomposites, which are used as electrodes, is fundamental to improving their performance. These porous nanocomposites are made of an active semiconductor (AM) material, nanoscale carbon black (CB) and a polymer binder (B). The presence of a network of pores makes ion transfer easier when filled with electrolyte (EL). The carbon black is percolated to ensure better electronic transfer into the material. Electrode materials are hierarchical architectures because they are made up of agglomerates of CB and AM particles. The presence of AM / AM, CB / CB, CB / AM, EL / AM and EL / CB interfaces therefore induces limitations in the electronic transfer at all scales of the composite material. The tortuosity of the porous network also results in a limitation of the ion diffusion in the electrode. The existence of strong interactions between the liquid electrolyte (LiPF₆ in EC: DEC or EC: DMC) and the active material LiNi_xMn_yCo_zO₂ has been demonstrated [1, 2]. However, interactions at the CB / EL interface could not be studied due to the low amount of carbon black (slightly above the percolation threshold) in this first work. The active material is substituted here by an insulating compound, γAl2O3 in order to detect and highlight possible interactions between the electrolyte and the carbon black, the concentration of which has been varied [3]. The charge transports in composite electrodes are generally explained by considering the percolation and the tortuosity of the CB particles network for electrons on one hand, and of the pores network for ions on the other hand. The contributions of the different interfaces within composite electrodes are however scarcely studied.

Simultaneous measurement of ionic and electronic conductivities requires instrumentation that takes into account both the constraints imposed by the nature of the samples and the mobilities of mobile species (ions, electrons). In and ex situ dielectric spectroscopy makes it possible to fulfill this objective over a wide frequency band from 40 Hz to 10 GHz between 200 and 300 K. The compositions of these composites are similar to those of composite electrodes for lithium batteries. Only the carbon black content varies across its percolation threshold, which makes it possible to understand the interaction between carbon black and the liquid electrolyte in the pores of the composite. The architecture of the composites has been studied by FIB / SEM in order to establish a correlation with the electrical responses at different scales of the material [3]. When carbon black is percolated, the influence of the electrolyte is such that the electrons of the carbon black have greatly reduced mobility due to their Coulomb interaction with the cations (Li ⁺) of the electrolyte. This phenomenon is in turn correlated with an increase in the ionic mobility of the electrolyte in the pore network compared to the "free" electrolyte [3].

In this presentation, we will report our recent discoveries of the perturbations due to interfaces on electronic and ionic conductions within composite electrodes for Li-Ion batteries.

References

[1] K.A. Seid, J.C. Badot, C. Perca, O. Dubrunfaut , P. Soudan , D. Guyomard, B. Lestriez, An In Situ Multiscale Study of Ion and Electron Motion in a Lithium-Ion Battery Composite Electrode. Adv. Energy Mater., 5, 1400903 (2015).

[2] Influence of a Liquid Electrolyte on Electronic and Ionic Transfers in LiNi_0.5Mn_0.3Co_0.2O₂ / Poly(vinylidene fluoride-co-hexafluoropropylene) based Composite Material. J. Phys. Chem. C, 125, 17629-17646 (2021).

[3] E. Panabière, J.C. Badot, O. Dubrunfaut, A. Etiemble, B. Lestriez. Electronic and Ionic Dynamics Coupled at Solid-Liquid Electrolyte Interfaces in Porous Nanocomposites of Carbon Black, Poly(vinylidene fluoride), and γ-Alumina. J. Phys. Chem. C, 121, 8364-8377 (2017).