Development of a prelithiation method on cell stack level for implementing silicon anodes
FacultiesFakultät für Naturwissenschaften
InstitutionsZentrum für Sonnenenergie- und Wasserstoff-Forschung Baden-Württemberg (ZSW)
One key factor for the breakthrough of electric mobility are high energy lithium ion batteries. One approach to increase energy density is replacing the commonly used active materials by alternatives. Silicon is seen as the most promising next-generation anode material due to its high theoretical capacity, low discharge potential and abundance. High periodic volume change and high irreversible lithium consumption make the implementation of silicon very challenging. Prelithiation is inevitable to prevent consumption of lithium and therewith waste of valuable cathode material in full cells. So far, commercially available cells contain silicon as an additive in maximum amounts of 5 wt.% and practically no safe and scalable prelithiation method exists. This thesis presents and veriﬁes a holistic concept addressing main diﬃculties for commercialization of anodes with high silicon contents. The 3D-structured current collector is a central element in this work, deﬁning the innovative electrode design and paving the way for a new lithium permeable cell concept. Scientiﬁc understanding of the lithiation and aging mechanism of micrometric silicon materials is gained. By including a prelithiation step, capacity losses are buﬀered and implementation of silicon anodes into eﬃcient high energy density full cells is enabled. With this, the overarching goal of this thesis is the development of a scalable prelithiation method conducted on already assembled cell stacks. After technical development of lithium permeable silicon anodes, parameters and eﬀects of the prelithiation concept are studied. Characterization of silicon anodes and examination of stabilizing eﬀects are performed by studying underlying lithiation mechanisms with the help of model approaches, evaluation of electrochemical data and electron microscopy. Simultaneous prelithiation of stacked silicon anodes in assembled cells is veriﬁed and inﬂuences on lithium distribution are examined. Applying the innovative electrode concept and prelithiation, cycling stability of full cells with high Si-content anodes (60 wt.%) could be increased from <100 cycles to up to 400 cycles before reaching end-of-life (80% capacity retention). The successful transfer of the developed prelithiation method into stacked pouch cells is demonstrated.
Subject HeadingsSilicone [GND]
Lithium ion batteries [LCSH]
Electron mobility [LCSH]