Fig. 1

(a) A schematic view of micro-scale all-solid-state Li-O2 battery assembled in the ESEM chamber[14]; (b) Product morphology observed during the discharge process[14]; (c) Growth process of a spherical particle during the discharge process. Yellow arrows indicate that the spherical particle grew up at TPI[14];(d) Decomposition process of the spherical particle during the charge process. Red arrows indicate the position where the particle decomposed[14]"

Fig. 2

Time-sequential STEM images showing the full charge process at the glassy carbon electrode. The dashed black lines indicate the surface of carbon electrode. The solid and dashed arrows with different colors indicate the decomposition kinetics of specific Li2O2 particles. The dashed red arrows at 296 s indicate the deactivated Li2O2 particles[20]"

Fig. 3

Time sequential HAADF-STEM images showing the dissolution of Li2O2 catalyzed by RuO2+TTF during the OER[23]"

Fig. 4

In-situ AFM images of the HOPG surface at (a) OCP, (b) 2 V, and (c) 4.8 V[33]"

Fig. 5

(a) Temperature dependent insitu XPS spectra of Li2O2 pellet in C 1s, O1s, Li 1s regions[34]; (b) Temperature dependent insitu XPS spectra of Li2O pellet in C 1s, O 1s, Li 1s regions[34]"

Fig. 6

(a) Insitu XRD patterns of Li2O2 during charge. The left image is the charging curve. The two images on the right are the enlarged XRD patterns[35]; (b) Insitu XRD patterns of Li2O during charge. The left image is the charging curve. The two images on the right are the enlarged XRD patterns[35]; (c) Left: the residual Li2O2 ratios for the electrodes with the same amount of different electrocatalysts (MNT, 0.5% Ru/MNT, 2% Ru/MNT and home-made Ru nano particles) after charging for 15 h at a constant current density; right: the operando SR-PXD patterns of an electrode with 2% Ru/MNT collected every 30 min during charging for 15 h at a constant current density[35]"

Fig. 7

In-situ FTIR spectra with external reflection configuration obtained on Cu electrode in (a) deoxygenated and (b) oxygenated 0.1 mol/L LiClO4-DMSO electrolytes, respectively[39]. The dashed lines represent the appearance/change of FT-IR peaks at various potentials. The “◇” represents peaks of DMSO solvent"

Fig. 8

Characterization of discharging process by in-situ Raman spectroscopy for Li-O2 battery[40]"

Fig. 9

(a) Heterodyne-detected (HD) and (b) homodyne-detected SFG spectra measured at glyme-air interface[41]"

Fig. 10

Design of a lithium-oxygen cell for in-situ NMR experiment[42]: (a) Schematic drawing and model of the double-compartment cylindrical cell and (b) Photograph and model of the cell mounted on the NMR probehead; (c) NMR line-fitting of the operando spectra at t = 2 h (beginning of discharge), 18 h (end of the first discharge) and 40 h (end of first charge) reveals the spectral evolution at the different cycling periods[42]"

Fig. 11

Charging curve of Li2O2 in an in-situ EPR cell with 0.5 mol/L LiTFSI in diglyme containing 0.1 mol/L 4-oxo-TEMP as a spin trap under an argon atmosphere; inset: previous discharge in a standard cell under an oxygen atmosphere (left) and in-situ EPR spectra, recorded at the different charging potentials(right)[43]"

Fig. 12

On-line electrochemical mass spectrometry analysis system[46]"

Fig. 13

Gas evolution during charge (a) without the redox mediator and (b) with 10 mmol/L TEMPO. (c) Amount of by-product in the cathode during charge without the redox mediator or with 10 mmol/L TEMPO[48]"

Fig. 14

(a)The charging profiles of Li-O2 cells with the VC electrode[49]; (b)?OEMS O2 evolution analysis of Li-O2 cells with the VC electrode[49]; (c)?The charging profiles of Li-O2 cells with the Ru/VC electrode[49]; (d)?OEMS O2 evolution analysis of Li-O2 cells with the Ru/VC electrode[49]"