Sodium halide solid state electrolyte of Na 3 YBr 6 with low activation energy.

Halide solid-state electrolytes (SSEs) are considered promising candidates for practical applications in all-solid-state batteries (ASSBs), due to their outstanding high voltage stability and compatibility with electrode materials. However, Na + halide SSEs suffer from low ionic conductivity and high activation energy, which limit their applications in sodium all-solid-state batteries. Here, sodium yttrium bromide solid-state electrolytes (Na 3 YBr 6 ) with a low activation energy of 0.15 eV is prepared via solid state reaction. Structure characterization using X-ray diffraction reveals a monoclinic structure ( P 2 1 / c ) of Na 3 YBr 6 . First principle calculations reveal that the low migration activation energy comes from the larger size and vibration of Br - anions, both of which expand the Na + ion migration channel and reduce its activation energy. The electrochemical window of Na 3 YBr 6 is determined to be 1.43 to 3.35 V vs. Na/Na + , which is slightly narrower than chlorides. This work indicates bromides are a good catholyte candidate for sodium all solid-state batteries, due to their low ion migration activation energy and relatively high oxidation stability.