In situ7Li and 133Cs nuclear magnetic resonance investigations on the role of Cs+ additive in lithium-metal deposition process

•Symmetric Li planar cells were fabricated for in situ7Li and 133Cs NMR.•Cs+ enhances the formation of aligned Li nanorods and reversibility of electrode.•In situ133Cs NMR indicates that Cs+ migrates to Li electrode during charge process.•A Li deposition model was proposed to explain these observations.

Cesium ion (Cs+) has been reported to be an effective electrolyte additive to suppress Li dendrite growth which prevents the application of lithium (Li) metal as an anode for rechargeable Li batteries. In this work, we investigated the effect of Cs+ additive on Li depositions using quantitative in situ7Li and 133Cs nuclear magnetic resonance (NMR) with planar symmetric Li cells. It's found that the addition of Cs+ can significantly enhance both the formation of well aligned Li nanorods and reversibility of the Li electrode. In situ133Cs NMR directly confirms that Cs+ migrates to Li electrode to form a positively charged electrostatic shield during the charging process. Much more electrochemical “active” Li was found in Li films deposited with Cs+ additive, while more electrochemical “dead” and thicker Li rods were identified in Li films deposited without Cs+. Combining the in situ and the previous ex-situ results, a Li deposition model has been proposed to explain these observations.