Fig. 1

Electrochemical reactions involved in the charging and discharging process of lithium-sulfur batteries[24]"

Fig. 2

The main problems of lithium sulfur battery and in situ characterization technology"

Fig. 3

(a) A schematic illustration of the in situ Raman cell and laser focus point during Raman spectra collection; (b) In situ Raman results during discharge with the N, S-HGF catalytic electrode[25]"

Fig. 4

(a) Schematic illustration of the electrochemical device set up for a real-time TEM observation of an electrochemical lithiation of nanoconfined S cathodes; (b) Diagram of sample preparation process for a single S-CNT reaction vessel; (c)Selected images of the sample evolution during a typical lithiation process: (1)—(3) TEM images captured during lithiation of S nanoconfined in a CNT reaction vessel and (4)—(6) their corresponding EDP patterns; (1) and (4) correspond to the sample before the initiation and (3) and (6) after the completion of the electrochemical reaction. The darker area appearing at the bottom left corner of the CNT in (3) is a contaminant[26]"

Fig. 5

(a) A scheme showing the setup of the solid cell implemented with a MEMS heating device for in situ TEM observation; (b)Scheme showing the reaction mechanism of the lithiation/delithiation of a S@CNT cathode, (1) Lithiation at 30 ℃, (2) lithiation at 100 ℃, (3) delithiation at 30 ℃, and (4) delithiation at 300 ℃[27]"

Fig. 6

(a) Relative intensity ratios of S8 and Li2S x compounds with the battery cathode during the discharge process together with the corresponding voltage diagram of the Li-S cell[28]; (b) RXES spectra of Li2S x standards excited at the pre-edge resonance; (c) Operando sulfur RXES spectra at 2470.7 eV excitation energy from a Li-S battery recorded at three points at the beginning of the discharge process. A linear combination fit using measured reference spectra is used to determine the relative amount of sulfur and Li2S x spectral components. The corresponding XANES spectra are added on top for comparison[28]"

Fig. 7

(a) Schematic representation of the in operando ATR FTIR spectro-electrochemical cell; (b) Illustration of the IR beam reflected through the ATR crystal,absorbed by the electrolyte in a porous cathode; (c) The polysutfide order and concentratien after every charge cycle, and (d) capacity fading over 7 discharge/charge cycles[29]; (e) Battery window for Raman spectroscopy and schematic diagram thereof (f) [30]"

Fig. 8

(a) Schematic diagram and voltage distribution diagram of the battery using TFEE; (b)Molecular structures and electrochemical characterization[31]; (c) Schematic diagram of working mechanism of a typical lithium battery with gel polymer electrolyte; (d)Functional diagram of PVDF/PSPEG GPE in lithium sulfur battery[34]; (e) 7Li and 17O NMR spectra for different electrolytes Proposed solvent-dependent sulfur reduction reaction pathways[35]"

Fig. 9

(a)In situX ray photoelectron spectroscopy (XPS) and chemical imaging(left)； ab initio molecular dynamics (AIMD) computational modeling(right); Cartoon representation of SEI layer growth mechanism based on the combined XPS and computational result (bottom); (b) Core level S 2p XPS spectra of the Li-electrolyte interfacial region with subsequent charge/discharge cycles; (c) Evolution of various sulfur based species over charge/discharge cycles based on atomic concentration derived from S 2p peak areas; (d) The ratio between terminal sulfide and bridging sulfur atoms (SB0/ST1–) along with the disulfide and sulfide ratio (S2–/S1–) derived from S 2p peak areas; (e) Molecular structure of lithium polysulfide Li2S6 (top) and TFSI anion (bottom) with chemical labels used in the XPS analysis[40]"

Fig. 10

(a) Cylindrical micro battery, fitted into the in situ NMR probe; (b) Stacked plot of the in situ7Li NMR spectra in a functioning Li-S cell vs time during discharge/charge; (c) Major peaks of interest within the range of -260 to 300 ppm extracted at different times by fitting the spectra[41]; (d) Solid species formation upon cycling；(e) Soluble species at around -0.16 ppm evolution with time[42]"

Table 1

Advantages and limitations of in situ characterization techniques"