Microscopic observations of the formation, growth and shrinkage of lithium moss during electrodeposition and dissolution

• Videos of lithium electrodeposition and dissolution have been obtained.
• Li filaments can develop into bushes by growing at a broadening tip with defects.
• Dissolving Li from moss results in dead Li which can remain attached to the substrate.
• One non-tip growth mode is dead Li is pushed outside during further Li deposition.
• Li moss can grow by insertion of lithium metal into the metallic backbone.

Lithium electrodeposition and -dissolution in a commercial battery electrolyte (1 M LiPF6 in EC:DMC) has been studied in situ by light microscopy and ex situ by scanning electron microscopy (SEM). We describe the transition between lithium filaments, which are most likely whiskers, and lithium moss and report in detail on the growth of mossy lithium structures. In the case of mossy lithium, the deposition can occur at the tips or the base of the growing structure. However, the growth is not limited to these locations, but can also occur by insertion at further growth points distributed inside the mossy Li deposit. We show that two different growth modes have to be distinguished: the unusual non-tip-growth by lithium metal insertion into the metallic moss backbone, and the condition where the deposition at the top of the mossy structure is not possible anymore because it was electrically isolated from the current collector due to a previous lithium dissolution step. After a dissolution period causing insulation of Li (“dead Li”), whole moss remnants can get pushed outside by metal structures growing underneath.

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