Ultra-stable lithium plating/stripping in garnet-based lithium-metal batteries enabled by a SnO₂ nanolayer

Owing to its high ionic conductivity (10⁻⁴ - 10⁻³ S cm⁻¹), excellent stability toward lithium and a wide electrochemical window, the garnet-type solid-state electrolyte has been regarded as one of the most promising solutions to the viability of lithium metal-based batteries. However, the poor interfacial contact between the garnet and the lithium metal leads to an ultrahigh interfacial resistance (∼1000 Ω cm²) and uneven current distribution. In this work, the issue is effectively addressed by coating the garnet pellet with a SnO₂ nanolayer. Attributed to the lithiation reaction between the lithium metal and SnO₂, an ion-conducting interlayer is generated automatically between the garnet and lithium metal, which reduces their interfacial resistance from 1019 to 153 Ω cm². A Li | SnO₂-garnet | Li symmetric cell is then built and achieves a stable lithium plating/stripping for more than 900 h at 0.2 mA cm⁻² without short circuit. Moreover, in a Li | SnO₂-garnet | LiFePO₄ full battery test, the SnO₂ nanolayer enables the full battery to be stably operated for over 100 cycles at 0.3 C with a capacity retention of 98.6%, whereas the control group using bare garnet is unable to work at this high rate.