Erik Wu1,Darren Tan1
Unigrid Inc.1
UNIGRID Battery aims to develop a sodium solid-state battery (Na SSBs) for stationary storage applications such as residential and grid storage. Na SSBs have been touted to offer improved safety (from the use of nonflammable solid-state electrolytes, or SSEs), lowered costs due to the use of abundant sodium-based materials, and higher performance, potentially culminating in a device with long life and high volumetric energy density. In recent years, the development of new SSEs for Na SSBs, such as halides and closo-borates, have advanced high-performance Na SSB chemistries closer to feasibility. However, each of these materials have their own drawbacks; the halides typically have lower sodium ion conductivity and are unstable with the anode, and the closo-borates are primarily cost-prohibitive and are less stable with cathodes. Thus, a single electrolyte with high Na ion conductivity, low costs, and stability with both electrodes remains elusive. Here, we report a new, thermally robust halide with a conductivity of 1 x 10<sup>-3</sup> S/cm at room temperature, at least an order of magnitude increase compared to previously reported Na-conducting halides. The halide is employed as a catholyte and cycling is demonstrated in a bilayer Na SSB configuration with superior rate performance.