On the Origin of the Pre-plasticizer Effect of the Composite Electrode for Lithium Batteries

A Multiscale Description of the Electronic Transport within the Hierarchical Architecture of a Composite Electrode for Lithium Batteries

“…The binder/CB mixture forms a continuous 3D network that connects the surface of Li 1.2 V 3 O 8 particles, [13,15,40] Figure 1b and c. EC þ PC, which is added during the composite electrode preparation and remains in the dried film after the volatile solvent evaporation, forms a miscible blend with PMMA, with a glass transition temperature of 8 8C (at the PMMA/ (EC þ PC) composition studied here). [33] Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) give insufficient information about the electrode architecture with respect to the electrical properties for several reasons.…”

“…It was previously observed, for dilute Li 1.1 V 3 O 8 or CB dispersions without the PMMA binder, that the dispersion state switches from flocculated to well-dispersed for both types of particles when EC þ PC is added to the tetrahydrofuran solvent (THF). [15] The highly polar EC þ PC molecules dissolved into THF increase the dielectric constant of the solvent and then slightly raise the strength of the electrostatic repulsive forces. In a low dielectric solvent, the repulsive electrostatic forces are weak due to the low concentration of ionized species, but operate over long distances www.afm-journal.de due to the low ionic strength.…”

“…[48,49] In dilute dispersions, this situation can lead to well-dispersed particles, as observed previously for Li 1.1 V 3 O 8 and CB in THF/EC þ PC. [15] In real undiluted electrode slurries, however, the shortest interparticle distances favour collisions between the particles and their flocculation when the shear is stopped (at rest), as observed by rheological studies and optical microscopy, Figure 2b and c. However, the occurrence of long-range repulsive electrostatic forces, as flocculation decreases the number of free particles, allows a fraction of them to remain isolated, as observed in the electrode slurries that contain EC þ PC, Figure 2d, leading to a more homogeneous morphology on the whole. Flocculation is due to the van der Waals attraction, which is, however, weakened due to the steric repulsion induced by the PMMA chains that adsorb at the surface of the particles and form an elastic-like shell around them, preventing them from approaching too close.…”

“…Thus, s dc does not relate directly to the real electronic wiring of the active material particles and hardly correlates with the electrochemical performance of the composite electrode. [13][14][15] The extraction of electronic conductivities and interfacial resistances at all (macro-, micro-and nano-) scales is essential in order to further optimize electrode overall performance and, thus, to allow the smart and rational optimization of lithium battery performance.…”

“…The composite electrodes studied here were thoroughly characterized in our previous work. [13,15,[30][31][32][33][34][35] They are based on the lithium trivanadate (Li 1.1 V 3 O 8 ) active material, which offers a high theoretical capacity of 330 mA h g À1 and has been investigated as a promising positive electrode AM. [36][37][38][39] Various composite electrodes have been prepared in which the surrounding of the same Li 1.1 V 3 O 8 is changed by pre-plasticizing the poly(methylmethacrylate) (PMMA) binder with ethylene carbonate (EC) and propylene carbonate (PC).…”