Impact of Hysteresis on Calendar Aging Mechanisms on Three-Electrode Cells With Silicon-Rich Anodes

Abstract

One promising strategy to increase the energy density of lithium-ion batteries is to increase the silicon (Si) content in the anode. However, an increasing amount of Si is a challenge for lifetime and diagnosis, as it suffers from high volume expansion and strong voltage hysteresis. While cyclic aging dominates current research, calendar aging remains still comparatively underexplored. Therefore, we present calendar aging results of Si-rich three-electrode lab cells, focusing on voltage hysteresis, loss of active material, and electrode-specific aging. We utilize OCV and float current analysis to assign electrode-specific aging. Both methods have shown promising results for pure graphite cells and are here transferred to cells with 69wt% Si combined with NCA cathode. The tests are conducted at the target state-of-charge/voltage, approached from both charge and discharge directions. We found no loss of anode-active material in the cells, but strong voltage hysteresis. As assigning the anode voltage time-series data to the OCV curve was not possible, anode aging was calculated indirectly from cathode aging and loss of lithium inventory. Anode and cathode aging increased with electrode potential, full-cell voltage, and SOC; however, no parameter exhibited a significantly strong correlation due to the limited accuracy of the reference electrode.