Fig. 1

(a) Critical issues in lithium metal anode; (b) Desirable Characteristics of the SEI; (c) Representative developments of surface pretreatment engineering strategies for lithium metal anodes"

Fig. 2

(a) Finite element analysis of different surface patterns on LMA[25]; (b) Schematic of the fabrication of the Li/Li22Sn5 nanocomposite foil[42]; (c) Schematic illustration of the fabrication process; (d), (e) Top-view SEM images; (f) Corresponding EDS mappings of the thin Li/LiZn@Cu anode[43]"

Fig. 3

(a) The bent ESM and corresponding paper cranes folded with it (inset), inset is photograph of the collected eggshells, (b) Li growth on TESM-modified Cu foil, (c) Cryo-TEM image of the deposited Li with TESM[27], (d) Schematic illustration and digital pictures capturing the formation of the ICE resulting from the reaction between the PAP and Li, (e) In-situ TEM images during mechanical experiments and electrochemical experiments, (f) The performance of Li symmetric cells under high current density, (g) The cryo-TEM images of SEI of deposited Li with ICE[29], (h) Flow chart of the fabrication of PVDF-HFP by template etching[62]"

Fig. 4

(a) Structural design and mechanism diagram of DSP-n featuring high toughness, self-healing capabilities, and stretchability, (b), (c) Top view and cross-section SEM images of DSIPI@Li anodes after cycling[66], (d) Schematic illustration of the diffusion behaviour of lithium ions through different polymer interphases[64], (e) Design of in situ photocontrolled free radical polymerization for PH@HF layer fabrication[69], (f) Fabrication of BPPL on Li metal via a slurry-casting & UV-cured polymerization process, (g) SEM image and photographs of the as-synthesized BPPL with excellent flexibility[70]"

Fig. 5

(a) Schematic of lithium metal anodes with and without HFA treatment[78], (b) Schematic illustration of the preparation procedure of COF@Li, (c) The Li deposition behavior on the bare Li metal anode and COF@Li layer[79], (d) Schematic illustration of advanced SEI formed by CF3Si(CH3)3(F3), (e) SEM image and EDX element mapping of F3-Li, (f) Depth XPS profiles of SEI of F3-Li and bare Li [80], (g) Schematic illustration showing the fabrication of MF x @PVDF on Li surface, (h) SEM image and Cryo-TEM images of Li deposits on Cu grid with a MgF2@PVDF layer[81], (i) Prolonged cycling performance of Li||LiFePO4 cells with and without a MgF2@PVDF layer"

Fig. 6

(a) Typical force-indentation curves and schematic diagrams of polished Li at different voltages[88], (b) Schematic illustration of the construction of the LiF- FOM on the surface of LMA under a high-voltage electric field, (c) Cycling stability of symmetrical cells with B-Li and LiF-FOM/Li, (d,e) The cryo-TEM image and EDS mapping of the LiF-FOM layer after Li deposition, (f) Diffusion barrier energy of Li+ on the different organic-inorganic hybrid component[33], (g) Schematic illustration of the construction of the ECH layer on the surface of the LMA and the possible formation mechanism of ECH700-Li[91]"

Fig. 7

(a) Brief description of the apparatus of magnetron sputtering and schematic illustration of the principle of magnetron sputtering[94], (b) Schematic diagrams of the growth of uniform and thin Bi film on lithium substrate by evaporating Bi metal precursor[95], (c) Optical photographs of bare Li and Bi-coated Li foils after exposed in air, (d) Schematics of selective ALD LiF deposition on h-BN, (e) SEM characterization of 50 cycles of ALD LiF deposition on continuous h-BN, (f) SEM characterization of 50 cycles of ALD LiF deposition on the edge of h-BN[96], (g) Schematic illustration of the swollen-soft-scaffold strategy to reinforce the native SEI layer of Li metal anode, (h) Cross-sectional FIB-SEM image of Li metal coated by 100 nm of pDMAMS layer. Scale bar, 500 nm, (i), (j) Top-down SEM images of bare Li and 100 nm pDMAMS-Li. Scale bar, 20 µm[97]"

Fig. 8

(a) A schematic illustrates that the fluoropolymer, CYTOP, gradually decomposes and releases pure F2 gas upon heating, which reacts with Li metal to form a uniform and compact LiF coating, (b) Cross-sectional FIB-SEM and TEM images of LiF-coated Li metal[110], (c) Reactions of methoxysilane and ethoxysilane catalyzed by LiOH, (d) formation of an organic-inorganic coating layer on LMA[116], (e) Schematic illustration of the plasma discharge mechanism and the formation of artificial LiF and Li2C2[39], (f) Schematic illustration of artificial LiF/h-BN hybrid SEI-formation process for SPE-based LMBs by CF4-plasma surface modification treatment[117]"

Fig. 9

(a) Basic characterization tools for characterizing the structure and components of SEI layers; (b) Multi-perspective comparison of the potential for commercial application of SEI layers prepared by the three main methods"