Optimizing the Silicon Anode Interfacial Stability to Achieve HighEnergy, Fast Charge Lithium-Ion Electric Vehicle Batteries at Scale

The integration of silicon anodes in Li-ion batteries can increase the energy density of the battery by around 30-50%, enabling advances in critical sectors with federal and commercial interest, such as electric vehicles or modular energy sources. However, to achieve higher power, the charge rate of a Li-ion battery must be increased, which is currently limited to avoid plating of lithium metal onto graphite for safety and cycle life concerns. By utilizing silicon dominant anodes, GDI is able to correct and mitigate safety and performance concerns for lithium plating at high rates, as there is reserve capacity for alloying any excess lithium atoms generated. General statement of how this problem is being addressed: Graphite is the main limiting factor when considering Li-ion charging speed, energy density, and safety. Lithium plating on graphite is the cause of many grid storage and EV fires. Understanding this, GDI is optimizing the Silicon anode interfacial stability to achieve high energy, fast charge Li-ion EV batteries at scale. In order to be cost-effective and efficient, our research efforts have xplored approaches to create silicon dominant Li-ion anodes through roll-to-roll plasma enhanced chemical vapor deposition (PECVD) processes, the same type of processes utilized in solar technologies. What was done in Phase I? Phase I research improved the interfacial stability of GDI’s silicon anode with electrolyte developments and molecular layer deposition (MLD) coatings on the anode surface. Initial testing was done in half cells to assess cycle life improvements and calendar life testing was done to specifically analyze interface stability. In half cells, when cycling at 2.2mAh/cm2, a greater than 400 cycle boost was seen in the best electrolyte relative to a standard DOE silicon electrolyte. The MLD coatings showed an improvement in formation efficiency, indicative of an improvement in interfacial stability, and also increased cycle life. Calendar testing was done based on NREL protocol, with a voltage hold and the current response was measured which correlates to anode SEI stability. Calendar testing revealed that GDI’s untreated silicon anode has excellent stability, bolstered by its inherent lower surface area. When compared to a commercial silicon-carbon composite, GDI’s silicon anode, with or without the MLD coatings, was advantaged in calendar life testing. What is planned for the Phase II project? In Phase II, GDI will focus on further improvements to the interfacial stability of the anode, with further MLD developments and electrolyte optimization. GDI would also investigate full cell architectures, as transition metal migration from the cathodes can yield undesirable anode impacts. This could be mitigated by surface engineering of the anode. The MLD treatment can be further optimized in 1) thickness, as only two thicknesses were explored during phase 1, and 2) via chemical composition, with potential for multi-layer approaches.