Ionic-Conducting and Robust Multilayered Solid Electrolyte Interphases for Greatly Improved Rate and Cycling Capabilities of Sodium Ion Full Cells

The energy storage performance of sodium-ion batteries has been greatly improved by pairing ether-based electrolytes with high-capacity alloy-type anodes. However, the origin of this performance improvement by a unique electrode/electrolyte interface has yet to be explored. To understand such results, herein, the deterministic and distinct interfacial chemistries and solid electrolyte interphase (SEI) layers in both the ether- and ester-based electrolytes are described, as verified by post mortem, in-depth X-ray photoelectron spectroscopy, and electron energy loss spectroscopy analyses, employing a hierarchical Bi/C composite anode as the model system. In the ether-based electrolyte, fast sodium-ion storage kinetics and structural integrity are achieved due to the highly ionic-conducting and robust multi-layered SEI consisting of an inner dense bismuth-containing inorganic and outer polyether layer. No drastic capacity decay is observed over 1000 cycles and high capacity retention of 89% is achieved, increasing rates from 0.1 to 10 A g(-1). The benefit of this SEI is confirmed to demonstrate a high energy density of 162 Wh kg(-1)in a full-cell and a high areal capacity of 3.3 mAh cm(-2)even at a high mass loading of 11 mg cm(-2), which is nearly equivalent to the loading of commercial lithium-ion battery anodes.