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

Abstract

Prelithiation of Si containing anodes has commonly been acknowledged as a potential solution to the challenge of the high irreversible lithium losses that still hinder the widespread adoption of this next-generation anode active material. However, upscaling and implementation in the process chain remain major hurdles for most proposed prelithiation processes. A significant part of this comes down to the high reactivity of prelithiation agents and prelithiated electrodes towards moisture. In industrial scale electrode production, dry rooms with dew point controlled atmospheres are already in use, but are a significant cost factor. Therefore, the compatibility of prelithiated electrodes with dry room conditions is a major factor for the implementation of prelithiation into existing production lines.In this work C/SiOx composite anodes are electrochemically prelithiated and subsequently subjected to industry relevant moisture levels. The influence of dew point and exposure time is examined. After exposure, the anodes are assembled into half-cells and their electrochemical performance during the first lithiation/delithiation cycle is analysed using a 3-electrode setup. The evaluation of the specific capacities and the potential curves provides information about the extent of the damage to the electrode. The results indicate a promising stability window for dew points of up to -40° C and realistic exposure times of up to one hour. Additional aging investigations in full cells against NMC622-based cathodes confirm these findings. Furthermore, electrochemical impedance spectroscopy, XPS and ToF-SIMS measurements are performed to elucidate the effect of moisture exposure on the solid electrolyte interface (SEI) composition. The results suggest the development of a double-layered SEI structure, where the first layer forms during prelithiation and is altered by moisture exposure, while the second layer forms on top of the first layer during formation. Figure 1