Effect of drying on the polyaniline-coated Prussian white cathode material for sodium-ion batteries

Abstract

Sodium iron hexacyanoferrate Prussian white (PW) is a commercially available cathode material for sodium-ion batteries. However, the structure of the hexacyanoferrate contains water, and the electrochemical performance of the PW strongly depends on the dehydration level of the material. Moreover, PW electrodes show a rapid capacity decrease, which is argued to be related with interfacial chemical reactions. A protective coating may be applied to suppress or completely prevent such reactions. In this work, we coated μm-sized PW particles with polyaniline (PANI) shell and investigated the effect of drying at increased temperature on PW@PANI material. The PW@PANI material exhibits a discharge capacity of 89.1 mAh g⁻¹ at 85 mA g⁻¹ with a capacity retention of 78.4 % over 500 cycles. PW@PANI electrode dried at 140 °C demonstrates a stable capacity of up to ≈ 97 mAh g⁻¹ during first 200 cycles at 85 mA g⁻¹, however, its capacity retention over 500 cycles is lower compared to the non-dried PW@PANI electrode. Drying PW@PANI electrodes at 180°C leads to a rapid capacity decrease. For the first time, a comparative study of the PW powder soaked with HCl acid solution used in the synthesis of PW@PANI has been performed and its stable long-term electrochemical performance has been observed.