Fig. 3. Soaking and electrochemical lithium plating experiments.

(A to C) Schematic and SEM of HCS electrodes soaked and dried in 1 M LiPF₆/EC/DEC electrolyte and saturated NaCl/H₂O solution. Blue arrows highlight the location of NaCl precipitation. (D to F) Schematic and SEM of ALD Al₂O₃/HCS electrodes soaked and dried in 1 M LiPF₆/EC/DEC electrolyte or saturated NaCl/H₂O solution. (H to J) Schematic and SEM of HCS electrodes after electrochemical lithium plating in LiPF₆/EC/DEC electrolyte. Red circles highlight the locations of plated lithium inside and outside HCS. (K to M) Schematic and SEM of ALD Al₂O₃/HCS electrodes after electrochemical lithium plating in LiPF₆/EC/DEC electrolyte. Red circle highlights the location of plated lithium inside ALD Al₂O₃/HCS. All electrodes were cut open using FIB for viewing. SEM images were taken with a sample rotation angle of 52°.