Fig. 1

(a) Schematic of SEI formation on graphite anode[22]; (b) Thermodynamics of SEI formation on anode and cathode, where μe-,Anode and μe-,Cathode are the electrochemical potentials of the anode and cathode respectively, and the stability window of the electrolyte is the difference between the energies of LUMO and HOMO, expressed as Eg[30]; (c) Qualitative description of chain reactions during thermal runaway[5]"

Fig. 2

(a) Schematic of in-situ heating XPS; (b) Quantitative analysis of the XPS survey spectra, C 1s, O 1s, and F 1s spectra from the lithiated VGCF during the temperature rising from 25 ℃ to 300 ℃; (c) Cryo-TEM images of SEI on the lithiated VGCF at 25, 150, 200 ℃ and their corresponding elemental distribution of C (marked in red) and O (marked in green) based on EELS map scanning[34]"

Fig. 3

(a) In-situ XRD patterns of the lithiated graphite anode when heated from 25 to 280 ℃ at 2 ℃/min; (b) The influence of oxygen on the lithiated graphite anode at different temperatures during the DSC measurements; (c) In-situ monitoring the evolution of H2, CH3·, CH4, CO/C2H4, O2, and CO2 during heating of the lithiated graphite anode; (d) The quantitative analysis of the gas cumulative ratio at 100, 150, 200, and 250 ℃, respectively[39]"

Fig. 4

(a) Macroscopic and (b) microscopic mechanisms of lithium plating during Li+ intercalation into graphite[4]; (c) Effect of lithium plating on SEI[45]"

Fig. 5

AFM height images and their corresponding averaged cross-section of HOPG cycled in (a) Mn-free electrolyte and (b) Mn-containing electrolyte; (c) Mn distribution along the cross-sectional electrode when it was stored for one month after 5 cycles in Mn-containing electrolyte; (d) Schematic diagram of the effect of Mn2+ deposition on graphite anode[54]"

Fig. 6

Summary of SEI regulation strategies (a) regulating the composition of the electrolyte, such as adjusting the HOMO-LUMO of solvents[5]; (b) Incorporating additives into the anode facilitating the in-situ construction of SEI with high Li+ conductivity, such as sulfur element[57]; (c) Inorganic coating layer, such as MoO x -MoP x coated graphite[58]; (d) Organic coating layer, such as the polymer SEI that promotes the transport of Li+ between electrolyte and graphite anode[4, 59]"

Fig. 7

(a) DSC curves of the fully de-lithiated graphite anodes collected from the cells cycled in 1 mol/L LiPF6 EC/EMC (volume ratio 1∶2) electrolytes with/without mass fraction 2% VC/glycolide (GL00)/GL01 additives[61]; (b) High-resolution cryo-TEM image of the SEI formed in 1.8 mol/L LiFSI DOL electrolyte, and the inset shows the corresponding FFT pattern; (c) Corresponding schematic of the high-resolution cryo-TEM image; (d) Long cycling performance of LiFePO4||graphite pouch cells with two electrolytes, and the inset shows a photograph of the pouch cell[66]; (e) Diffusion activation energy of Li+ in SEI[67]"