Voltage-driven evolution of lithium nanoparticle morphology and SEI precursors

Abstract

Lithium metal anodes offer unmatched theoretical capacity amongst candidate battery materials, yet their commercial viability remains limited by uncontrolled dendrite growth and solid electrolyte interphase (SEI) formation. Whilst recent work has established that applied voltage controls lithium morphology through potential-dependent surface tension, how voltage determines which electrolyte decomposition products preferentially bind to those evolving surfaces remains unexplored. Here, we employ grand canonical density functional theory with implicit solvation to systematically examine how F⁻, O²⁻, and CO₃²⁻ compete for binding sites across thirteen crystallographic orientations spanning an electrochemically relevant potential window (−1.75 to +1.0 V vs. Li/Li⁺). Our calculations reveal systematic morphological transitions with decreasing potential: {311} dominates exclusively at +1.0 V, {320} emerges at intermediate potentials, and {110} progressively increases from 30% at −1.0 V to complete dominance at −1.75 V, yielding a rhombic dodecahedron consistent with ultrafast electrodeposition experiments. Competitive adsorption on the thermodynamically dominant surface at each voltage establishes a clear hierarchy: carbonate binding exceeds fluoride by 1.75–2.42 eV throughout the reducing potentials relevant to lithium deposition (−0.5 to −1.75 V), whilst fluoride achieves thermodynamic preference only under oxidising conditions (+1.0 V on {311}). The coupling between morphology and chemistry emerges through surface-dependent site availability—{110} and {311} present 3-fold hollow sites whilst {320} offers 4-fold configurations—which alters binding geometries as voltage drives morphological transitions. These findings rationalise the ubiquitous presence of Li₂CO₃ in experimental SEI characterisation and suggest that achieving LiF-rich interfaces requires kinetic strategies that bypass thermodynamic equilibrium. Our results establish that applied voltage functions as a thermodynamic selector, simultaneously shaping both the structure and composition of the lithium–electrolyte interface.