Tin modification of sodium manganese hexacyanoferrate as a superior cathode material for sodium ion batteries

Tin modified sodium manganese hexacyanoferrate, as a Prussian blue analogue, is studied as a cathode material for sodium ion batteries. By co-precipitation of Sn4+ during the synthesis process, the modified sodium manganese hexacyanoferrate materials crystallize with face-centered cubic structure with space group Fm3¯m, while the unmodified one possesses a rhombohedral structure with space group R3¯m. Compared to the unmodified material, the modified materials exhibit smaller particles with rougher surface, showing improved rate capability and cycling stability. The material modified by 10% Sn maintains 80.5% capacity after 100 cycles at 2 C (240 mA g−1) and delivers 53.4 mA h g−1 at 20 C. Both Fe and Mn take part in the redox reaction and the structural changes are reversible upon the initial Na+ extraction and insertion for both pristine and modified samples. For long-term cycling, the modified materials undergo less structural transformation than the pristine material that may lead to a better structural stability, and furthermore to enhanced cycling performance.