Improved Cycling Stability of Polypyrrole Coated NaTi2(PO4)3 As an Aqueous Na-Ion Anode

Aqueous sodium ion batteries offer an economic method for large-scale energy storage demanded by current sources of renewable energy. Although NASICON type NaTi₂(PO₄)₃ is an attractive anode material with high capacity and a low redox potential allowing for high voltage cells, it suffers from considerable capacity fade when cycled slowly and deeply. In this work polypyrrole has been introduced as a coating for NaTi₂(PO₄)₃ through a high-energy ball-milling process. When too thick of a coating was applied no redox reactions from the NaTi₂(PO₄)₃  were visible due to the poor Na⁺ diffusion through the polypyrrole. The as coated composites containing 5wt% polypyrrole showed much better capacity retention compared to the uncoated material, retaining 57% of the initial discharge capacity after 50 cycles compared to the uncoated material retaining only 10% of the initial discharge capacity.