Stabilizing the Na/Beta-Al2O3 interface with mixed ionic-electronic conductor towards room-temperature solid-state sodium metal battery

Beta-Al2O3, an inorganic solid electrolyte with high thermal stability and competitive ionic conductivity, is considered as the safe and efficient candidate for solid-state sodium metal batteries (SSMBs). The exhausting interfacial trouble between Beta-Al2O3 solid electrolyte and Na metal become the stumbling blocks of Beta-Al2O3 solid electrolyte applying at room-temperature. Herein, we demonstrate an efficient strategy by in-situ construction of mixed ionic-electronic (MIE) conductive layer (Na–Sn alloy and Na2S) to engineer intimate Na/Beta-Al2O3-MIE interface via spontaneous conversion-alloying reaction between Na and SnS2. Given by the modified MIE layer, the interfacial resistance is dramatically reduced from 3600 to 126 Ω cm2. The Na symmetrical battery with a high critical current density of 0.9 mA cm−2 and it can stably cycle for 2650 h at 0.3 mA cm−2 with a low overpotential of 25 mV at room temperature. By incorporating ameliorative interface into SSMB, the Na3V2(PO4)3|Beta-Al2O3-MIE|Na harvests 103.6 mA h g−1 at 0.5 C after 250 cycles (97.4% capacity retention). This work rolled out an effective strategy for constructing stable Na/Beta-Al2O3 interface to realize room-temperature SSMBs.