researchers from empa, the swiss federal laboratories for materials science and technology in dubendorf, and the university of geneva (switzerland) have developed an initial prototype of a solid-state sodium battery that promises greater safety from thermal runaway and enhanced energy storage.
composition of the solid sodium battery. (empa)
according to a report from the university, the research team focused on solid-state batteries to improve changing efficiency and increase the storage capacity. the design gets rid of the typical liquid electrolyte used in lithium-ion batteries, which allows for the use of a metal anode.
“the researchers discovered that a boron-based substance, a closo-borane, enabled the sodium ions to circulate freely,” the article explained. “furthermore, since the closo-borane is an inorganic conductor, it removes the risk of the battery catching fire while recharging. it is a material, in other words, with numerous promising properties.”
the anode was made from solid metallic sodium and the cathode from a mixed sodium chromium oxide. to get the layers to mix with the new electrolyte, “researchers dissolved part of the battery electrolyte in a solvent before adding the sodium chromium oxide powder. once the solvent had evaporated, they stacked the cathode powder composite with the electrolyte and anode, compressing the various layers to form the battery.”
the prototype was stable up to three volts and 85 percent of the energy capacity was functional after 250 charge and discharge cycles. researchers insist that 1,200 cycles will be necessary before the battery can be commercialized and the battery also needs to be tested at room temperature.
the ongoing research was recently published in energy and environmental science. the report’s abstract said:
“we report on a particularly stable 3 v all-solid-state sodium–ion battery built using a closo-borate based electrolyte, namely na2(b12h12)0.5(b10h10)0.5.
“battery performance is enhanced through the creation of an intimate cathode–electrolyte interface resulting in reversible and stable cycling with a capacity of 85 ma h g−1 at c/20 and 80 ma h g−1 at c/5 with more than 90% capacity retention after 20 cycles at c/20 and 85% after 250 cycles at c/5.
“we also discuss the effect of cycling outside the electrochemical stability window and show that electrolyte decomposition leads to faster though not critical capacity fading.
“our results demonstrate that owing to their high stability and conductivity closo-borate based electrolytes could play a significant role in the development of a competitive all-solid-state sodium–ion battery technology.”