Polymer-Sulfide Composite Solid State Electrolyte with Enhanced Interfacial Stability with Sodium Metal

Rechargeable sodium-ion batteries have received growing attention as promising alternatives to lithium-ion batteries for grid energy storage devices because of the abundance of Na resources as well as its high theoretical capacity of 1165 mAh g-1, and low electrochemical potential (-2.71 V vs. standard hydrogen electrode). However the safety issues still remain as the most critical challenges for its wide application. The rise of solid state electrolyte (SSE) with high Na-ion conductivity has brought about new opportunities for the development of sodium metal batteries. The recently reported Na-ion superior conductor Na3SbS4 (NSS) with a room temperature ionic conductivity of 1.2 mS cm-1 represents the highest Na-ion conductivity. However, NSS is unstable with Na metal and will decompose to Na2S upon cycling confirmed with synchrotron X-ray diffraction and XPS studies. The formation of Na2S leads to the increase of interfacial resistance and deteriorates the battery performance. To stabilize the interface between Na and electrolyte, we report a multilayer cellulose-supported PEO polymer(CPEO)/NSS electrolyte design which combines the high ionic conductivity of NSS and the high stability of CPEO layer, thus resulting in a stable electrochemical process of Na stripping/plating (Figure b). Symmetric cell with CPEO/NSS multilayer electrolyte demonstrate a stable areal specific resistance (ASR) of 2000 Ω cm2 for 130 cycles, while the battery with pristine NSS electrolyte shows an increasing ASR from 80 Ω cm2 to 4300 Ω cm2. The superior interfacial stability of multilayer electrolyte would be promising for designing all-solid-state sodium batteries. Figure 1