Using Polypyrrole Coating to Improve Cycling Stability of NaTi₂(PO₄)₃as an Aqueous Na-Ion Anode

Aqueous alkali - ion batteries offer an economical method for large-scale energy storage demanded by current sources of renewable energy. Although NASICON-type NaTi 2 (PO 4 ) 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 NaTi 2 (PO 4 ) 3 through a high-energy ballmilling process. When an excessive coating was applied, no redox reactions from the NaTi 2 (PO 4 ) 3 were visible due to the poor Na + diffusion through the polypyrrole. However, the as-coated composites containing 5 wt% 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, which retained only 10% of the initial discharge capacity. It is concluded that coating NaTi 2 (PO 4 ) 3 with conducting polymers can be an effective strategy for promoting battery lifetime.