The Decisive Role of Li₂O₂ Desorption for Oxygen Reduction Reaction in Li–O₂ Batteries

Abstract

Fundamental issues relevant to the oxygen reduction reaction (ORR) mechanism and reaction interface are ambiguous in Li−O 2 batteries. Herein, we utilized highly sensitive surface-enhanced Raman spectroscopy (SERS) to reveal the spontaneous desorption behavior of insoluble products of lithium peroxide (Li 2 O 2 ) from the electrode surface. Furthermore, the electrochemical ORR mechanism is elucidated at the electrode/Li 2 O 2 interface based on a dynamic equilibrium between the generation and desorption of Li 2 O 2 . The desorption of adsorbed Li 2 O 2 species (Li 2 O 2 *) is crucial to releasing surface sites and maintaining the electrochemical ORR process at the electrode substrate surface instead of the Li 2 O 2 / electrolyte interface. The proceeding of Li 2 O 2 * desorption can guarantee the stability of Li 2 O 2 * concentration and the discharge plateau in the galvanostatic ORR process. The suppression of Li 2 O 2 * desorption is proved to induce the termination of Li 2 O 2 * generation, which is accompanied by the growth of adsorbed lithium superoxide (LiO 2 *), leading to rapid potential attenuation.

Effect of alkali-metal cation on oxygen adsorption at Pt single-crystal electrodes in non-aqueous electrolytes

“…Bands at 1040 and 1310 cm −1 correspond to the methyl-group rocking modes in DMSO and that at 1420 cm −1 to n(S]O). [74][75][76] The bands associated with DMSO vibrations increase at −0.55 V, coinciding with the formation of O ) species is also indicated by the signicant increase in DMSO bands aer this point. Increased DMSO band intensity in the potential range where ORR occurs has not been observed for Na + , 24 probably due to DMSO less successfully competing for Pt sites with more strongly adsorbed NaO 2 , i.e., smaller cation-O 2 − complexes are more strongly adsorbed on the Pt(111) surface, while for larger cation-O 2 − complexes, adsorption is weaker, and they are readily desorbed back into solution.…”

Aprotic Lithium–Oxygen Batteries Based on Nonsolid Discharge Products

“…Particularly, a distinct potential located at approximately 2.87 V was found from the charge curve of Ir/AP-POP-catalyzed Li–O 2 batteries (Figure a); such a low charge plateau is different from the formation of LiO 2 in other reported studies. ,, Previous studies have manifested that the formation of these off-stoichiometric states with good electronic and ionic conductivity is favorable to the decomposition during the charge process. ,,− To gain greater insight into the generation of nonstoichiometric LiO 2 , gas-assisted focused ion beam time-of-flight secondary ion mass spectrometry (FIB-TOF-SIMS) was employed to explore the residual electrolyte on the separator surface . As shown in the mass spectra of Figure S41, the discharge electrolyte on the separator with Ir/AP-POP exhibits the peaks for the nonstoichiometric product Li 1– x O 2 ( m / Q = 38, 37, 35) compared with the discharge cathode with Ir/super p and without Ir/AP-POP. − Moreover, the clear depth profiles for Li + in Figure S42a demonstrated the presence of products for the samples after discharge. As the sputter depth increased, the intensity remained constant in the time range of 100–600 s. The normalized intensity of the Li + signal on the discharged separator is smaller than that on the discharged cathode with the Ir/super p and without the Ir/AP-POP, implying the generation of the nonstoichiometric product for Ir/AP-POP in the electrolyte.…”

Cathode Chemistries of Lithium–Oxygen Batteries in Nanoconfined Space

“…In principle, the growth of Li 2 O 2 films can take place at the interface either between Li 2 O 2 and the electrolyte or between the gCNT surface and Li 2 O 2 . In the former case, electrons continually pass through the as-formed Li 2 O 2 to reach the external surface of the Li 2 O 2 film, where O 2 molecules are continuously reduced to generate Li 2 O 2 (with the combination of Li + from the bulk electrolyte). , In the latter case, O 2 molecules are continuously transported to the vicinity of the gCNT surface to get reduced to form Li 2 O 2 that is in direct touch with the gCNT surface. − In this case, Li + supplementation might have been via a mobile point defect mechanism through the already formed Li 2 O 2 films . We note that the growth process of Li 2 O 2 seems to be highly sensitive to Li–O 2 cell components, such as electrolyte composition, additives, catalysts, etc.…”