Design of Binder-Free Slurry Electrodes for Lithium-Ion Batteries via Identification of Electronic and Ionic Transport Networks

Abstract

To achieve higher energy density in lithium-ion batteries and simplify electrode fabrication processes, the development of polymer-binder-free electrodes has attracted attention. In particular, slurry electrodes, in which the active materials and conductive additives are directly dispersed in an electrolyte, are promising to eliminate polymer binders and the drying step required in conventional electrode fabrication. However, the charge-transport mechanisms governing the electronic and ionic conduction in such binder-free slurry electrodes are insufficiently understood. In this study, the relationship between the slurry composition and charge-transport properties of binder-free electrodes composed of an active material, a conductive additive, and an electrolyte was systematically investigated. Slurries with different electrolyte contents were prepared and characterized by alternating-current impedance spectroscopy combined with distribution of relaxation times analysis. In addition, the electrochemical performance of half-cells and full cells containing the binder-free electrodes was evaluated. The impedance and distribution of relaxation times analyses revealed three distinct conduction regimes depending on the electrolyte content: electron-dominated conduction, mixed electronic / ionic conduction, and iondominated conduction. Notably, electronic and ionic conduction pathways were found to coexist at electrolyte contents of 30-50 wt%, indicating the formation of balanced charge-transport networks within the slurry structure. Although the optimized binder-free electrode exhibited performance degradation after several cycles in half-cells, stable cycling for more than 50 cycles was achieved in full cells. This suggests that the interfacial instability at the Li metal counter electrode may significantly contribute to the degradation observed in the half-cells.