Observing Li Nucleation at Li Metal-Solid Electrolyte Interface in All-Solid-State Batteries

TL;DR

This study uses advanced molecular dynamics simulations to reveal that lithium dendrite nucleation in all-solid-state batteries occurs within the solid-electrolyte interphase, driven by electronic structure changes that facilitate metallic lithium formation.

Contribution

It provides the first atomic-level insight into the initial nucleation sites and mechanisms of lithium dendrite formation at the anode/solid electrolyte interface in ASSLBs.

Findings

Li clusters form inside the SEI, about 1 nm from the anode/SEI boundary.

Decreased bandgap in SEI facilitates electronic conduction and Li reduction.

Understanding of dendrite nucleation sites aids in designing dendrite-inhibiting strategies.

Abstract

Benefiting from the significantly improved energy density and safety, all-solid-state lithium batteries (ASSLBs) are considered one of the most promising next-generation energy technologies. Their practical applications, however, are strongly impeded by the Li dendrite formation. Despite this recognized challenge, a comprehensive understanding of Li dendrite nucleation and formation mechanism remains elusive. In particular, the initial locations of Li dendrite formation are still ambiguous: do Li clusters form directly at the Li anode surface, or inside the bulk solid electrolyte (SE), or within the solid-electrolyte interphase (SEI)? Here, based on the deep-potential molecular dynamics simulations combined with enhanced sampling techniques, we investigate the atomic-level mechanism of Li cluster nucleation and formation at the Li anode/SE interface. We observe that an isolated Li cluster initially forms inside the SEI between the Li6PS5Cl SE and the Li metal anode, located ~1 nm away from the Li anode/SEI boundary. The local electronic structure of the spontaneously formed SEI is found to be a key factor enabling the Li cluster formation within SEI, in which a significantly decreased bandgap could facilitate electronic conduction through the SEI and reduce Li+ ions to metallic Li atoms therein. Our work therefore provides atomic-level insights into Li-dendrite nucleation at anode/SE interfaces in ASSLBs, and could guide future design for developing Li-dendrite-inhibiting strategies.