Enhanced sodium ion storage in Prussian blue cathode material through nickel doping
Prussian blue (PB) is an promising and cost-effective materials for sodium ion batteries (SIBs) because it possesses fast diffusion channels for Na ion migration and features a two-electron redox reaction mechanism that offers a high theoretical capacity of 170 mAh/g. However, it is difficult to attain the full discharge capacity of PB in SIBs by the low-spin Fe2+/Fe3+ redox couple. In the present study, we found that doping PB with Ni ions (1-10%) resulted in enhanced electrochemical storage capacity and facilitated fast Na ion diffusion during discharge. Specifically, PB doped with 3% Ni ions showed a discharge capacity of 117 mAh/g, within which approximately 50 mAh/g was attributed to the low-spin Fe2+C6/Fe3+C6 redox couples. Despite that a gap remains to attain the full storage capacity of PB, this research sheds light on how substituting transition metal ions affects its electrochemical performance.