Sodium metal halide (Na-MH) batteries present tremendous opportunities for grid scale energy storage applications. In this work, we describe an advanced Na-MH battery operating at 190 °C using a bi-layer (thin dense/thick porous layers) β″-alumina solid-state electrolyte (BASE). The novel design of the bi-layer BASE promotes high Na-ion transportation by reducing the Na+ ion path length. The excellent battery performances are achieved with a stable capacity retention of 350 W h/kg up to >350 cycles (∼6 months). Moreover, owing to the thin dense layer of BASE, the round trip energy efficiency (or discharging energy density) of the tested battery shows an ∼8% increase compared to that of state of the art Na-MH battery reported in the literature. Results from this work clearly demonstrate that advanced Na-MH batteries using bi-layer BASEs can have significant impacts on improving battery performances at lower operating temperatures, and further stretch its feasibility in stationary energy storage applications.