The Development of a Stabilized SEI Layer for Si-Containing Lithium Ion Battery Anodes

This project focuses on the development of new lithium ion battery (LIB) electrolyte/cathode combinations that enable stabilized solid electrolyte interphases (SEI) on Si- based materials. This effort focuses on negative electrodes combining synthetic graphite and Si- based materials, where Si contributes at least 30% of the reversible capacity of the electrode. This effort will result in significantly longer cycle life and calendar life for LIBs that feature Si- containing negative electrodes. Recent work has shown that the capacity fade seen in well-designed Si and Si-based negative electrodes is a consequence of an increase in surface area with cycling as the Si-based material expands and contracts. The increased surface area results in an increase in parasitic side reactions and accelerated electrolyte consumption. High precision calorimetry combined with high precision coulometry allows an early identification of the increasing parasitic thermal power that accompanies the increasing surface area. The volume changes of Si-based materials can be diluted but they cannot be suppressed. The path forward for truly enabling Si-based materials therefore lies in targeted electrolyte chemistry. Electrolyte constituents that lead to the formation of carbon dioxide (CO2) or CO2 precursors have recently been shown to be effective in extending the cycle life of Si. It is believed the presence of CO2, or readily reducible intermediates, leads to the formation of an inorganic carbonate Si SEI and has a remarkable effect on extending cycle life. Early results show this approach as being superior to fluoroethylene carbonate, the gold standard electrolyte solvent for Si. The strategy of this effort will be two-fold: 1) development of electrolyte components that can provide a sustainable level of CO2 or reducible intermediates in order to provide Si-containing electrodes capable of at least 1000 cycles and 2) engineering the cell positive electrode such that the positive electrode surface reactions lead to by-products that help stabilize the Si SEI. Early work in this area has been promising. Coulometrics, LLC will partner with Cyclikal, LLC to provide an excellent balance of cell assembly and cell testing capabilities with state-of-the-art microcalorimetry, which has proven successful in recent years in increasing the life of Si in LIBs. The combined team has excellent equipment, facilities, and 20 trained staff that have over 100 years of experience developing LIBs. Dr. Edward Buiel has over 25 years of experience as CTO of two advanced energy storage companies and now CEO of Coulometrics, LLC. Joe Turner has 15 years of LIB development experience and recently was R&D director of K2 Energy before joining Coulometrics. Dr. Larry Krause has over 30 years of industrial energy storage experience, especially relating to Si. The team also benefits from Coulometrics’ consulting business that has been profitable since 2008 and provides significant revenue to support this effort and any commercialization effort that may arise from this program.