A strategy for designing low-cost, environment-friendly, high energy and power density sodium-ion full cells: Effect of extrinsic pseudocapacitance

Abstract In this work, we demonstrate the advantage of introducing extrinsic pseudocapacitance behavior in the active material for designing low-cost, high energy, and power density sodium-ion full cells. Here, tin and antimony based alloy nanopowder is synthesized via microwave assisted hydrothermal process (MAHP) for use as a negative electrode. Ex-situ x-ray diffraction studies reveal that the alloy nanopowder stores Na+ via a diffusion-controlled alloying mechanism. Extrinsic pseudocapacitance behavior is subsequently introduced by sandwiching the alloy nanopowder between nitrogen doped reduced graphene oxide nanosheets via MAHP. When coupled with a diffusion-controlled positive electrode comprising of an iron-based prussian blue analog, the resulting full cell demonstrates a high energy density of 262.5 Wh kg−1 at 1C rate with 85.7% capacity retention at the end of 100 cycles. Detailed cyclic voltammetry and electrochemical impedance studies provide insight into the effect of extrinsic pseudocapacitance in improving the electrochemical performance of the full cell.