Molecular Simulations of the Microstructure Evolution of Solid Electrolyte Interphase during Cyclic...

Area of Science:

• Materials Science
• Electrochemistry
• Computational Chemistry

Background:

• Lithium (Li) metal is a leading anode material for next-generation batteries due to its high capacity and low reduction potential.
• Uncontrolled lithium dendrite growth during cycling causes low efficiency and safety concerns, necessitating a deeper understanding of its formation mechanism.

Purpose of the Study:

• To investigate the formation and evolution of solid electrolyte interphase (SEI) films during lithium-metal anode cycling.
• To understand the early-stage mechanism of lithium dendrite growth under varying electrolyte compositions and anode morphologies.

Main Methods:

• Reactive molecular dynamics (MD) simulations combined with the electrochemical dynamics with implicit degrees of freedom (EChemDID) method.
• Simulations were conducted in two dimensions, exploring different electrolyte compositions and initial surface morphologies.

Main Results:

• Inhomogeneous lithium reduction, forming "hotspots," was identified as the primary initiator for dendrite growth, irrespective of electrolyte or morphology.
• Fluorine-containing electrolyte additives effectively reduced anode roughening by forming dense SEI layers and suppressing electrolyte decomposition.
• Lithium ions traverse the SEI layer through low-density pathways to reduction hotspots, promoting uneven deposition and dendrite propagation.

Conclusions:

• The study provides atomistic insights into the initial stages of lithium dendrite growth during cyclic loading.
• Findings offer guidance for designing artificial SEI layers and electrolytes to enhance the longevity and capacity of lithium-metal batteries.