Lithium ion batteries (LIB) can feature reactive anodes that operate at low potentials, such as lithium metal or silicon, passivated by solid electrolyte interphase (SEI) films. SEI is known to evolve over time as cycling proceeds. In this modeling work, we focus on the stability of two main SEI components, lithium carbonate (Li 2 CO 3 ) and lithium ethylene dicarbonate (LEDC). Both components are electrochemically stable but thermodynamically unstable near the equilibrium Li + /Li(s) potential. Interfacial reactions represent one way to trigger the intrinsic thermodynamic instability. Both Li 2 CO 3 and LEDC are predicted to exhibit exothermic reactions on lithium metal surfaces, and the barriers are sufficiently low to permit reactions on battery operation time scales. LEDC also readily decomposes on high Li-content Li x Si surfaces. Our studies suggest that the innermost SEI layer on lithium metal surfaces should be a thin layer of Li 2 O -the only thermodynamically and kinetically stable component (in the absence of a fluoride source).This work should also be relevant to inadvertant lithium plating during battery cycling, and SEI evolution on Li x Si surfaces.
Water and oxygen electrochemistry lies at the heart of interfacial processes controlling energy transformations in fuel cells, electrolyzers, and batteries. Here, by comparing results for the ORR obtained in alkaline aqueous media to those obtained in ultra-dry organic electrolytes with known amounts of H 2 O added intentionally, we propose a new rationale in which water itself plays an important role in determining the reaction kinetics. This effect derives from the formation of HO ad ···H 2 O (aqueous solutions) and LiO 2 ···H 2 O (organic solvents) complexes that place water in a configurationally favorable position for proton transfer to weakly adsorbed intermediates. We also find that even at low concentrations (<10 ppm), water acts simultaneously as a promoter and as a catalyst in the production of Li 2 O 2 , regenerating itself through a sequence of steps that include the formation and recombination of H + and OH -. We conclude that although the binding energy between metal surfaces and oxygen intermediates is an important descriptor in electrocatalysis, understanding the role of water as a proton-donor reactant may explain many anomalous features in electrocatalysis at metal-liquid interfaces.
Lithium metal anodes are critical enablers for high energy density next generation batteries, but they suffer from poor morphology control and parasitic reactions. Recent experiments have shown that an external packing force on Li metal batteries with liquid electrolytes extends their lifetimes by inhibiting the growth of dendritic structures during Li deposition. However, the mechanisms by which pressure affects dendrite formation and growth have not been fully elucidated. For
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