Energy storage systems (ESS) have gained great attentions recently for grid-scale applications. Among various types of batteries, Na-beta alumina batteries (NBBs), which are based on a β"-Al₂O₃ solid electrolyte (BASE) and a molten sodium anode, have been considered as a promising technology due to their high energy density, high efficiency, and good cycle life. Two types of NBBs, sodium sulfur (Na-S) and sodium-metal halide (Na-MH) batteries, have been investigated and commercialized in the past. Despite of being considered as a relatively new and less popular technology compared to Na-S batteries, Na-MH battery can provide several advantages over a Na-S battery including lower operating temperature (280^oC for Na-MH vs. 350^oC for Na-S), safe cell-failure mode, higher output voltage and safe assembly in the discharged state without preloading metallic sodium in the anode.

Our Na-MH battery researches in PNNL are primarily focused on developing advanced planar-type Na-MH batteries operated at temperatures below 200^oC. It was found that lowering operating temperature helps to retain the long-term stability and higher energy density by slowing down materials degradation. Lowering operating temperature also provides opportunities to deploy conventional high temperature polymers as sealing materials, which can greatly reduce cell manufacturing costs. In this presentation, we will present the important correlation between cathode formula and battery performances, and will discuss about the design and testing results of larger planar cells aiming practical applications.