Investigation of oxygen reduction chemistry in ether and carbonate based electrolytes for Li–O2 batteries

Clear description on the O2 reduction chemistry in aprotic media during discharge in Li–O2 batteries is critical to the development of nonaqueous Li–O2 batteries. Understanding the solvent's role in the discharge process would conduce to choose appropriate electrolyte for nonaqueous Li–O2 batteries. The electrodeposits in dimethoxyethane (DME) and the mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) were characterized by ex situ Raman spectra, X-ray diffraction patterns (XRD) and X-ray photoelectron spectroscopy (XPS). Change between the fresh and discharged DME electrolyte also had been examined by FTIR. All results showed that the mixture of EC and DEC are easily undergoing the decomposition to form Li2CO3 and CH3CH2OCO2Li in the presence of O2 reduction species such as superoxide ion. Although DME-based electrolyte demonstrated much higher discharge capacity and seemed to be more stable to O2 reduction species, it also decomposed after a long time exposed to O2 because of the formation of peroxide. The main discharge products in DME electrolyte were Li2O2 crystalline and amorphous Li2CO3. Continuous consumption of solvents caused both carbonate and ether-based electrolytes incompetence for the nonaqueous Li–O2 batteries.