CAREER: Identifying reaction mechanisms for the formation of stable interphases in lithium metal batteries

Northwestern University, Evanston IL

Investigators

Abstract

Electrochemical energy storage devices are critical for transitioning the global energy economy away from fossil fuels used in transportation and energy generation. Metallic lithium anodes offer an avenue to reduce cost and increase adoptions by increasing energy density compared to state-of-the-art graphite and silicon containing anodes, yet challenges around stable cycling and safety remain. The roots of these challenges lie at the interface between the electrode and the liquid electrolyte, where a solid electrolyte interphase (SEI) forms because of (electro)chemical breakdown of the electrolyte solvent and salt molecules. Li metal electrodes are designed to operate well beyond the thermodynamic stability windows of useful electrolytes and long-term cycling can only be enabled by kinetic stabilization of the electrode-electrolyte interface. This research program will identify the electrolyte reaction mechanisms that underpin SEI formation in high Coulombic efficiency electrolytes and use this fundamental understanding to design and evaluate new fluorine free electrolytes. This research program will be closely coupled with educational and outreach activities. The project will design and implement a Sustainability Ambassadors program which will be a cohort-based program for one-on-one mentoring with Northwestern University undergraduate students and Chicago Public School high school students. The stabilization of Li metal electrodeposition in lithium-ion batteries is one of the largest outstanding challenges in energy storage research today. The central hypothesis of this CAREER project is that with an improved fundamental understanding of SEI formation reactions, new electrolytes can be precisely engineered to enable reversible Li metal cycling by promoting desirable SEI reactions and suppressing undesirable pathways. To better understand SEI formation reactions, this project will focus on the following objectives: 1) identifying the structure and role of radical inorganic and organic electrolyte decomposition products, 2) in situ monitoring of SEI growth and aging, and 3) study of reaction mechanisms in fluorine-free electrolytes designed to promote desirable SEI forming reactions. The research will use carefully designed ex situ electron paramagnetic resonance (EPR) experiments and advanced in situ characterization tools will provide new understanding to the field regarding electrolyte decomposition pathways and key mechanisms that improve Li metal cycling efficiency. The insights developed here will allow for a more systematic approach to be taken when designing F-free electrolyte materials for Li metal batteries and may also prove useful for other metal anode battery chemistries such as sodium, magnesium, calcium, and zinc. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.