Cathode-Anode Interactions in Layered Oxide/Sn Alloy Sodium-Ion Pouch Cells at High Temperature and Voltage

Replacing hard carbon with Sn anodes in sodium-ion batteries (SIBs) significantly enhances volumetric energy density, promising compact solutions for grid energy storage, but their limited lifetime remains a hurdle for long-lasting, high-energy-density systems. This study investigates cathode-anode interactions in Na 0.97 Ca 0.03 [Mn 0.37 Fe 0.32 Ni 0.22 Zn 0.09 ]O 2 (NCMFNZO)/Sn pouch cells using a 1 m NaPF 6 in tetraethylene glycol dimethyl ether electrolyte at 40 °C to understand cell failure mechanisms. Employing pouch bag experiments, electrochemical impedance spectroscopy, scanning electron microscopy, and gas evolution measurements, we reveal the cathode as the primary gas generation source, with the sodiated Sn anode mitigating gas accumulation in full cells. After 500 h storage at 4.0 V without cathode-anode interactions, the cathode retains morphological stability, while the Sn anode becomes porous and expanded, with both exhibiting increased charge transfer resistance. These findings indicate resistive electrode/electrolyte interphase formation without cathode-anode interactions, emphasizing the need for interphase optimization to improve SIB durability.