Quantifying and Studying Electrolyte Pumping in Lithium-Ion Cells Using Rotational Inertia Measurements

Abstract

State-of-the-art cylindrical Li-ion cells can be susceptible to degradation in the form of accelerated inhomogeneous lithium plating on the negative electrode, which has recently been shown to be caused by an electrolyte motion-induced salt inhomogeneity in the electrolyte. Electrolyte motion is caused by the cyclic expansion and contraction of the electrode active materials at different states of charge, which displaces some of the electrolyte back and forth between the pores of the electrodes and the empty and inactive areas located at the ends of the cylindrical cell and in the core of the electrode winding. To study electrolyte motion, Rotational Inertia Measuring instruments have been developed, which are torsional oscillators that detect changes in the resonant frequency of a cylindrical cell as its mass distribution changes during cycling. Resonant frequency changes are used to calculate the amount of displaced electrolyte in relation to the state of charge of the cell. Rotational Inertia Measuring instruments are effective for studying electrolyte motion in a variety of cylindrical cell formats, with the goal of understanding and reducing the impact of electrolyte motion on cell degradation.