Influence of liquid electrolyte salt nature and concentration on tortuosity measurement of battery electrode

Abstract

The electrode tortuosity is the ratio between the effective conductivity of the Li ion in the electrolyte phase of the electrode thickness and the electrolyte conductivity. This is a critical parameter for high rate application, particularly in battery charge for the negative electrode and notably for fast charge challenge in the electric vehicles’ (EV) application. A common method to measure it at macroscopic level is the electrochemical impedance spectroscopy in a symmetric cell configuration in blocking conditions. Such conditions can be obtained using a non-intercalating cation with generally a large steric hindrance. In this study, the electrolyte salt nature and concentration influence on the tortuosity measurement is investigated. Several electrolyte salts are evaluated with different cations or anions, including the conventional LiPF₆ salt, considering different steric hindrance or affinity. A robust method is firstly developed by examining the effects of the temperature and the electrode porosity. Selecting an electrolyte concentration of 10 mM is an effective way to achieve tortuosity value with a precision lower than 0.15, approximately 3 % of the tortuosity of a conventional graphite electrode. Finally, the electrolyte salt nature does not affect the electrode tortuosity measurement as long as an acceptable capacitive behavior is obtained.