Influence of Electrolytes on the Electronic Transfer in Electrode Materials: Ex- and In-Situ Dielectric Spectroscopy Study between 103 and 1010 Hz

Abstract

The fruitful contribution of Broadband Dielectric Spectroscopy (BDS) to study hierarchical materials applied to batteries electrodes has been previously shown [1-5]. The results demonstrate that the broadband dielectric spectroscopy technique is very sensitive to the different scales of the electrode architecture involved in the electronic transport, from interatomic distances to macroscopic sizes, as well as to the morphology at these scales, coarse or fine distribution of the constituents. When the frequency increases, different kinds of polarizations appear from interatomic distances to macroscopic sizes (Fig. 1) and give rise to dielectric relaxations in the following order: (a) space-charge polarization (low-frequency range) due to the interface sample/current collector; (b) polarization of clusters of particles (micronic scale) and (c) polarization of particles due to the existence of resistive junctions between them; d) electron transfers (nanometric or interatomic scale).The BDS measurement was up to now ex situ measurement, on dry electrode. They provide a fundamental insight into the conduction properties at all scales of the materials before being integrated in a real battery. An innovative device (measurement cell) has been developed to make synchronized BDS measurements and electrochemical cycling. The frequency range is about 103 - 1010 Hz. In this work, data acquisitions were made on dry electrode (LiNi1/3Co1/3Mn1/3O2 / Carbon black / PVdF) and then on the same electrode wetted with an electrolyte. Short- and long-range motions of ions are evidenced in the low-frequency region. At higher frequencies, the study shows for the first time the influence of the ions of the electrolyte on the transfer of the electronic charges (holes) in LiNi1/3Co1/3Mn1/3O2at the micronic scale. Acknowledgements Financial funding from CNRS, Université de Nantes, UMICORE, and the ANR program n° ANR-09-STOCK-E-02-01 is acknowledged.