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Solvent- and Anion-Dependent Li+-O2- Coupling Strength and Implications on the Thermodynamics and Kinetics of Li-O2 Batteries
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DOI：10.1021/acs.jpcc.9b09968.png)
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Abstract
En 中文
Lithium-oxygen (Li-O-2) batteries offer considerably higher gravimetric energy density than commercial Li-ion batteries (up to three times) but suffer from poor power, cycle life, and round-trip efficiency. Tuning the thermodynamics and pathway of the oxygen reduction reaction (ORR) in aprotic electrolytes can be used to enhance the Li-O-2 battery rate and discharge capacity. In this work, we present a systematic study on the role of the solvent and anion on the thermodynamics and kinetics of Li+ORR, from which we propose a unified descriptor for its pathway and kinetics. First, by thoroughly characterizing the solvation environment of Li+ ions using Raman spectroscopy, Li-7 NMR, ionic conductivity, and viscosity measurements, we observe increasing Li+-anion interactions with increasing anion DN in low DN solvents such as 1,2-dimethoxy-ethane and acetonitrile but minimal Lr-anion interactions in the higher DN dimethyl sulfoxide. Next, by determining the electrolyte-dependent Li+/Li, TBA(+),O-2/TBA(+)-O-2, and Li+,O-2 /Li+-O-2-redox potentials versus the solvent-invariant Me(10)Fc reference potential, we show that stronger combined solvation of Li+ and O-2- ions leads to weaker Li+-O-2 coupling. Finally, using rotating ring disk electrode measurements, we show that weaker is Li+-O-2 coupling in electrolytes with strong combined solvation leads to an increased generation of soluble Li+-O-2-type species and faster overall kinetics during Li+ORR.
Keywords:
OXYGEN REDUCTION REACTIONS
DIMETHYL-SULFOXIDE
ELECTROCHEMICAL REDUCTION
IONIC SOLVATION
CHEMICAL-SHIFTS
LITHIUM-SALTS
O-2 REDUCTION
REDOX COUPLE
SODIUM-IONS
IN-SITU
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