An oxygen vacancy-rich ZnO layer on garnet electrolyte enables dendrite-free solid state lithium metal batteries

The huge interfacial resistance caused by Li₂CO₃ on garnet (LLZO) electrolyte and the lithium-dendrite growth through garnet greatly hinder the development of solid-state batteries (SSBs). Here, both the problems are simultaneously addressed through a general strategy of engineering garnet pellet with a layer of ZnO with oxygen vacancies (O_V-ZnO). The O_V-ZnO not only protects LLZO from being exposed to wet air, but also reacts spontaneously with lithium-metal to in-situ form an ionic conducting Li_xZnO interphase. The as-formed interphase improves the Li/LLZO contact, reduces the huge interface resistance caused by Li₂CO₃, suppresses the lithium-dendrite growth, and promotes the lithium transport between LLZO and Li-metal. As a result, an Li/Li symmetric cell with O_V-ZnO coated LLZO pellet shows a low area specific resistance of 55 Ω cm², a stable plating/stripping process for 200 h at a current density of 0.1 mA cm⁻², and a record-high critical current density of 1.4 mA cm⁻² ever reported at room temperature. Moreover, this approach of coating metal oxide with oxygen vacancies on garnet electrolytes has been extended to other metal oxides, such as copper oxide (O_V-CuO), titanium dioxide (O_V-TiO₂) and indium oxide (O_V-In₂O₃).