Garnet Electrolytes with Ultralow Interfacial Resistance by SnS₂ Coating for Dendrite-Free all-Solid-State Batteries

Garnet-based solid electrolytes are highly attractive because of their excellent ionic conductivity and electrochemical stability toward Li metal anodes. However, poor interfacial contact between the garnet electrolyte and electrode leads to a high interfacial impedance, and the resulting inhomogeneous interfacial current distribution expedites the growth of Li dendrites. Here, we propose a practical method to assemble dendrite-free solid-state batteries by coating SnS2 onto Li6.5La3Zr1.5Ta0.5O12 (LLZTO) pellets. The SnS2 layer promotes wettability, homogenizes the space electric field at the interface by an in situ conversion reaction, and can also be used as an excellent electrode. Using this method, we decreased the garnet/Li interfacial impedance to an ultralow extent of ∼17 Ω/cm2, while increasing the critical current density to 1.2 mA/cm2. The Li/LLZTO@SnS2/SnS2 solid-state battery delivers a low interfacial impedance of ∼72 Ω/cm2, a high capacity of ∼717 mAh/g, and excellent cycling stability and rate performance. We believe that the understanding and manipulation strategy of the SnS2 coating layer will shed light on designing an excellent garnet/Li interface and assembling novel all-solid-state batteries.