A Study of Composite Solid Electrolytes: The Effect of Inorganic Additives on the Polyethylene Oxide-Sodium Metal Interface

High electrolyte-electrode interface stability is essential for solid state batteries to avoid side reactions that form interphases and voids, leading to loss of contact and increased impedance. Such detrimental situations increase overvoltage, reduce cycling efficiency, and shorten battery cycle life. While composite solid electrolytes were studied extensively, the effect of inorganic additives in the polymer matrix on the electrolyte-anode interface remains unclear. Here, solid electrolyte was studied for batteries with sodium metal anode based on polyethylene oxide (PEO) polymeric matrix containing ceramic additive. Extensive electrochemical analyses under both AC and DC conditions were performed, and chemical reactions between sodium metal and the PEO matrix, which produce interphases at the electrode-electrolyte interface, were investigated. Addition of sodium beta aluminate in the matrix appears to mitigate these reactions, removing a major obstacle on the way to effective all-solid-state rechargeable sodium batteries.