The lithium metal deposition was carried out in 2032-type coin-cells. Specifically, both the Li and Cu foils were punched to around 1.3 cm 2 disks. Cu was rinsed with deionized water and acetone prior to transferring to the Ar glove box for coin-cell assembly to remove surface contaminants. The electrolyte, 1 M LiPF6 in ethylene carbonate and diethylene carbonate (EC/DEC, v 1:1), was stored in argon-filled glove box (Vigor, oxygen <0.01 ppm, water <0.01 ppm). Lithium was mechanically sheared with a polyethylene scraper to remove the surface oxide and improve electrical connection to the stainless-steel coin cell. 60 μL of electrolytes were used in each cell for full wetting of both working and counter electrode surfaces. Li metal plating was carried out on a Biologic VMP3 system. A total capacity of 0.5 mAh cm -2 was deposited under a constant current of 2 mA cm -2 . The half-stripped cells were then discharge at the same current density for 0.25 mAh cm -2 . The cells were then disassembled immediately or rested for different time periods before disassembly to mimic various cell calendar aging scenarios. After cell disassembly, the deposited Li metal anode was rinsed with pure DEC solvent to remove residual salts, and then sonicated in DEC for 10 s to form a suspension of lithium dendrites in DEC. The lithium dendrites in suspension were then dropped onto the holey carbon grids (Quantifoil, R2/1). The TEM grids were then sealed in an airtight container, which was immediately submerged and crushed in liquid nitrogen to rapidly expose the sample to cryogen without air exposure and preserve the electrolyte and the electrode. The samples were then loaded into cryogenic sample storage boxes under liquid N2 and transferred into a larger liquid N2 dewar. For the aging experiments, the cycled cells were rested at open circuit voltage (OCV) for a designated period.