Solid-state lithium metal batteries have emerged as a promising technology for electric vehicles due to their high specific energy and safety potential. Instability at metal–electrolyte interface, however, remains a significant challenge in both cell fabrication and operation. During fabrication, adequate fabrication pressure is required to promote close contact, but this pressure can cause Li deformation and penetration into the electrolyte, resuting in poor battery performance. Additionally during cycling, stripping-induced void formation and contact loss at the Li–electrolyte interface induce high local current and readily trigger cell short circuit.
Here, we present a strategy for addressing this problem by incorporating 10 atom.% Mg into Li. During cell fabrication, unlike pure Li which obeys Voce hardening law and allows unconstrained deformation, Li_0.9Mg_0.1follows the Swift hardening law and strengthens with strain under compression stress. Because of the constrained deformation of Li_0.9Mg_0.1, intimate contact with solid electrolyte is possible even at high fabriation pressure. Moreover, Li-Mg alloy suppress void growth and enables metal–electrolyte contact in successive stripping process. Using operando scanning electron microscopy, we demonstrate that voids coalesce into a single gap at the Li–electrolyte interface, whereas large voids spontaneously split into smaller voids and collapse to retrieve interfacial contact in Li-Mg anode. Density function theory calculations show strong Mg-S interaction leads to Mg accumulation at the sulfide electrolyte interface, repels vacancies away, and mitigates void formation. The superior interface stability of Li-Mg alloy enables a higher critical current density and full cell performance at high current density, high areal capacity, and long cycle life. Overall, our findings underscores the signficance of understanding Li metal mechanical properties and interfacial chemistry to improve solid-state battery performance.

Yan Yao

University of Houston

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