Stabilizing Lithium Metal Anode and Conversion Cathode Interphases for High Energy Density Batteries

Lithium metal batteries offer great promise for higher energy density, but are presently limited by significant side reactions, poor quality deposition, and the potential to form hazardous dendrites. This is especially true when paired with conversion cathodes, which could potentially result in cells with specific energy > 700 Wh/kg. In this presentation, recent advances made toward high energy full cells will be discussed. A particular emphasis will be placed on the electrode-electrolyte interphases that form in these devices in high performance localized high concentration electrolytes (LHCE). Specifically, we employ electron paramagnetic resonance (EPR) spectroscopy to identify radical intermediates and operando surface enhanced IR absorption (SEIRA) spectroscopy to clarify electrolyte reduction/oxidation mechanisms. Operando SEIRA provides detailed information about the organic components of the solid electrolyte interphase (SEI) and cathode electrolyte interphase (CEI) on lithium metal anodes and FeF2 cathodes respectively. Common SEI components from high Coulombic efficiency fluorinated electrolytes are identified and mechanisms will be discussed in the context of moving toward more environmentally friendly fluorine-free electrolytes. Furthermore, strategies to stabilize FeF2 conversion cathodes through interphase modification to produce more mechanically robust composite electrodes and improve cycling stability will be discussed. With the understanding developed through this holistic approach, we provide new insight into electrolytes and the formation of interphase components that promote stable cycling of lithium metal- FeF2 full cells.