Reducing Interfacial Resistance between Garnet‐Structured Solid‐State Electrolyte and Li‐Metal Anode by a Germanium Layer

Substantial efforts are underway to develop all‐solid‐state Li batteries (SSLiBs) toward high safety, high power density, and high energy density. Garnet‐structured solid‐state electrolyte exhibits great promise for SSLiBs owing to its high Li‐ion conductivity, wide potential window, and sufficient thermal/chemical stability. A major challenge of garnet is that the contact between the garnet and the Li‐metal anodes is poor due to the rigidity of the garnet, which leads to limited active sites and large interfacial resistance. This study proposes a new methodology for reducing the garnet/Li‐metal interfacial resistance by depositing a thin germanium (Ge) (20 nm) layer on garnet. By applying this approach, the garnet/Li‐metal interfacial resistance decreases from ≈900 to ≈115 Ω cm 2 due to an alloying reaction between the Li metal and the Ge. In agreement with experiments, first‐principles calculation confirms the good stability and improved wetting at the interface between the lithiated Ge layer and garnet. In this way, this unique Ge modification technique enables a stable cycling performance of a full cell of lithium metal, garnet electrolyte, and LiFePO 4 cathode at room temperature.