Influence of Moisture on the Electrochemical Performance of Prelithiated Graphite/SiO_x Composite Anodes for Li-Ion Batteries

Prelithiation is widely recognized as a promising technology to enable the use of high capacity anode active materials such as silicon. Numerous prelithiation techniques have been proposed over the years, with a handful successfully undergoing pilot scale testing. Nevertheless, new challenges arise when moving from optimizing single processes to integrating them into the process chain. A major concern is the stability of prelithiated electrodes against moisture. In this study, we investigate the influence of industrially-relevant moisture levels on the electrochemical performance of prelithiated graphite/SiO_x composite anodes in 3-electrode half- and full-cells. We identify several indicators of electrode degradation such as an increase in open circuit potential, a decrease in graphite lithiation potential, and changes in specific charge/discharge capacity. The underlying degradation mechanisms are examined using electrochemical impedance spectroscopy, X-ray photoelectron spectroscopy, and time-of-flight secondary ion mass spectrometry, which show increased solid electrolyte interphase (SEI)-related interfacial resistances but no clear evidence of SEI degradation. Based on the experimental results, we define a process window for the stability of the investigated electrodes as a function of dew point and exposure time. Our results indicate an encouragingly high stability at dew points up to −40 °C for a realistic exposure time of 1 h.