SBIR-STTR Award

GDI’s has shown that by integrating its silicon anodes it can enable 400Wh/kg, 950 Wh/L cells that are capable of 3.2C 15 minute charging, and can eliminate Li plating by utilizing a pure binder free Si anode that does not utilize carbon or binders which can catalyze Li plating and capacity restricting the Si anode to always provide Si excess for the Li to alloy with. Finally GDI has shown that at GW production scale the cost of the battery drops below $100/kWh. The intention of this grant work is to combine electrolyte optimization work done by GDI along with artificial surface layers deposited by the University of Michigan to form ideal surfaces for electrolyte decomposition thus tuning the interface both from the surface but also from the electrolyte. This project will promote the decomposition of thin and stable SEI layers which will both extend the cycle and calendar life while enabling fast charging to make it appropriate for automotive applications. With the combination of both surface stabilization strategies it is intended to create a synergistic solution by tuning the end terminations of the Si interface and optimize against known electrolyte additives. During this grant GDI will optimize the electrolyte and anode coating in order to hit the cycle life targets in small representative 200 mAh full pouch cells. GDI will make the initial learnings in coin cell formats and then translate these to multi-layer pouch cells to test under commercially representative samples.

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.