Uncovering Full‐Cell Cycling Morphology Through a Rechargeable Sodium Ion Battery Based on Tungsten Oxide and Sodium Prussian Blue Intercalation Chemistry

ABSTRACT Half‐cells have been employed to investigate the intrinsic electrochemical behavior of the cathode material, as the chemical potential of the alkali metal reference electrode remains relatively constant during discharge. However, in full cells, the discharge mechanism is anode‐dependent. Herein, a rechargeable nonaqueous sodium ion battery (SIB) is fabricated using tungsten trioxide (WO 3 ) nanopowder on a graphite substrate as the anode and a nickel‐hexacyanoferrate Prussian blue (PB) cathode to understand the dominant discharge mechanism. The battery cells are evaluated for reversibility and durability and exhibit reversible charge–discharge plateaus, confirming sodium‐ion intercalation/deintercalation in both electrodes. The sodium‐ion diffusion coefficient of 5.3 × 10 −13 cm 2 .s −1 calculated using electrochemical impedance spectroscopy (EIS) is consistent with a planar finite space diffusion mechanism. Cyclic voltammetry (CV) shows a broad reversible redox peak on the WO 3 anode, owing to its multiple valence states, also observed in potential versus differential capacitance (dQ/dV) and simulated density of states (DOS). The full cell demonstrates an open‐circuit voltage (OCV) of 2.2 V (charged), a discharge capacity of 79 mAh.g −1 at 0.1C rate, and retains 69% of its capacity after 500 cycles, indicating promising durability and reversibility for sodium‐ion storage. The charge carrier concentration (ccc), DOS, electrical and thermal conductivities, and chemical potential simulations for the charged and discharged phases, in both electrodes, reveal that the anode determines the shape of the discharge curve and the cathode the capacity of the cell. This study paves the way to predicting the behavior of a full cell, including cycling curve shape, process, dependencies, and thermal runaway.