A Sodium-Ion Battery with the Diglyme Electrolyte: Graphite || Alumina-Coated Na_5/6[Ni_1/3Mn_1/6Fe_1/6Ti_1/3]O₂ Cell

High Resolution Image Download MS PowerPoint Slide Co-intercalation of sodium ions and glyme molecules enables the utilization of graphite as a negative electrode material for high-power sodium-ion batteries (SIBs). However, the electrolyte’s incompatibility with high-potential positive electrode materials hinders the development of high-performance SIBs. To address the capacity degradation caused by anodic side reactions with glyme electrolytes, an alumina-coated Na 5/6 [Ni 1/3 Mn 1/6 Fe 1/6 Ti 1/3 ]O 2 positive electrode material was synthesized. The alumina-coated material demonstrated a capacity retention of 93% and a Coulombic efficiency of >99% over 50 cycles in half-cells, significantly outperforming the uncoated material, which exhibited a 76% capacity retention and 92% Coulombic efficiency. The uncoated positive electrode material suffered from anodic decomposition of the electrolyte at the active material/electrolyte interface, leading to pitting corrosion and rock salt phase formation at the active material surface, thus increasing interface resistance and causing capacity decay. In contrast, the alumina coating effectively mitigated electrolyte decomposition and surface degradation, enabling stable battery operation. Utilizing the alumina-coated positive electrode, Na-ion full cells with a synthetic graphite negative electrode demonstrated far superior capacity retention compared to full cells with the uncoated material. Furthermore, these full cells maintained a discharge capacity of over 50 mA h g –1 (positive electrode) even at a very high current density of 1.27 A g –1 (10C), showcasing great potential for use in high-power applications.