Deciphering solid–electrolyte interface in cellulose-montmorillonite nanocomposites for sodium batteries

Abstract

Electrolytes and their interphases are critical for emerging battery chemistries such as metal–sulphur and metal–oxygen, especially in the case of solid electrolytes, which offer attractive energy storage possibilities but involve drastic phase transitions and structural challenges. Therefore, developing improved electrolytes and interphases is a key to achieving sustainable battery performance. Here, we introduce a novel polymer composite electrolyte utilising abundant montmorillonite and cellulose nanocrystals (CNC), creating a stable interphase with the Na metal and alleviating common degradation issues. For example, this electrolyte exhibits a stability window of 2.3–5.3 V and a transference number of ∼0.87, although its durability and performance need further improvement. FT-IR spectroscopy, XPS, and Raman spectroscopy provide valuable insights into the interfacial chemistry, as evidenced by a prominent hydroxyl stretching band associated with the CNC. While hydroxyl groups may compromise interfacial stability at the cathode, possibly causing cell degradation, they simultaneously enhance the sodium-ion mobility at the anode by facilitating favourable coordination with sodium metal. This dual function underscores the need for tuning functional groups in electrolyte design.