Revealing the mechanisms behind transient whisker suppression by LiNO3 in anode-free lithium metal batteries

Abstract

The electrolyte additive, lithium nitrate (LiNO3), is widely recognized for suppressing dendritic lithium growth in anode-free lithium metal batteries, yet its stabilizing effect is transient, and the mechanistic origin of this limitation has remained unresolved. Here, we uncover the origin of this behavior through a comprehensive analysis driven by artifact/damage-free direct cryogenic transmission electron microscopy, which enabled one of the most chemically specific and morphologically intuitive visualizations to date of intact solid-electrolyte interphases (SEIs) and lithium growth. Contrary to conventional interpretations centered on nitrogen-rich or single-component SEIs, we reveal that LiNO3 rapidly generates lithium hydroxide (LiOH) and lithium oxide (Li2O) rich interphases, whose complementary functions—ionic transport through LiOH and mechanical robustness from Li2O—synergistically suppress whisker nucleation and favor compact, particle-like growth. Over the extended plating, however, depletion of these species in combination with crystallographically favored orientations drives the particle-to-whisker transition, explaining why the effectiveness of LiNO3 is inherently limited. This direct mechanistic visualization resolves a long-standing ambiguity regarding the transient efficacy of LiNO3 and reframes its function from a nitrogen-driven mechanism to a synergistic dual oxygen-interphase framework. Beyond mechanistic clarification, these findings establish that continuous regeneration of LiOH and Li2O is essential for stable lithium deposition, offering a design principle for the development of durable electrolytes in high-performance anode-free lithium metal batteries.