Interfacial-engineering-enabled practical low-temperature sodium metal battery

Solid-state sodium (Na) batteries have received extensive attention as a promising alternative to room-temperature liquid electrolyte Na-ion batteries and high-temperature liquid electrode Na-S batteries because of safety concerns. However, the major issues for solid-state Na batteries are a high interfacial resistance between solid electrolytes and electrodes, and Na dendrite growth. Here we report that a yttria-stabilized zirconia (YSZ)-enhanced beta-alumina solid electrolyte (YSZ@BASE) has an extremely low interface impedance of 3.6 Omega cm(2) with the Na metal anode at 80 degrees C, and also exhibits an extremely high critical current density of similar to 7.0 mA cm(-2) compared with those of other Li- and Na-ion solid electrolytes reported so far. With a trace amount of eutectic NaFSI-KFSI molten salt at the electrolyte/cathode interface, a quasi-solid-state Na/YSZ@BASE/NaNi0.45Cu0.05Mn0.4Ti0.1O2 full cell achieves a high capacity of 110 mAh g(-1) witha Coulombic efficiency >99.99% and retains 73% of the cell capacity over 500 cycles at 4C and 80 degrees C. Extensive characterizations and theoretical calculations prove that the stable beta-NaAlO2-rich solid-electrolyte interphase and strong YSZ support matrix play a critical role in suppressing the Na dendrite as they maintain robust interfacial contacts, lower electronic conduction and prevent the continual reduction of BASE through oxygen-ion compensation.

Automated summary

This study reports a solid electrolyte YSZ@BASE which effectively reduces the interfacial impedance in solid-state sodium batteries and exhibits high critical current density with Na metal anode. By using a trace amount of NaFSI-KFSI molten salt, a high-capacity and cyclically stable full cell has been achieved.