Reservoir Free Na SSBs Enabled by NaSICON Separators and Na Metal Oxyhalide Electrolytes

Reservoir-free sodium-based solid-state batteries (SSB) have gained significant attention as a promising alternative for next generation batteries that rely on low-cost and earth-abundant resources. However, their adoption has been hindered by the limited stability of anode-electrolyte, cathode-catholyte interfaces and their high interfacial resistances.
This talk will focus on interfacing Na_3.4Zr₂Si_2.4P_0.6O₁₂ (NaSICON; synthesized with a relative density of > 95% and an ionic conductivity of ~ 3.5 mS/cm) with recently discovered oxyhalide based Na catholytes - specifically NaTaOCl₄ (NTOC) and NaAlCl_4-2xO_x (NAOC) - and a variety of Na-metal oxide cathode materials for anode free Na SSBs. On the anode side alone, we will present data showing that relatively thick Na metal anodes can be electroplated and stripped onto a current collector in situ without degrading the NaSICON. Stable sodium plating was achieved at moderate current densities with a constant areal capacity of about 3 mAh/cm2 and 1.2 MPa stack pressure, showing good reversibility after ~ 800 hours of plating and stripping.
An in-depth investigation will be also presented on the behavior of the critical interfaces in the cells, combining techniques such as electrochemical impedance spectroscopy and Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS).