Improved Sodiation Additive and Its Nuances in the Performance Enhancement of Sodium-Ion Batteries.

The abundance of the available sodium sources has led to rapid progress in sodium-ion batteries (SIBs), making them potential candidates for immediate replacement of lithium-ion batteries (LIBs). However, commercialization of SIBs has been hampered by their fading efficiency due to the sodium consumed in the formation of solid-electrolyte interphase (SEI) when using hard carbon (HC) anodes. Herein, NaCO sodium salt is introduced as a highly efficient, cost-effective, and safe cathode sodiation additive. This sustainable sodium salt has an oxidation potential of ∼4.0 V vs Na/Na°, so it could be practically implemented into SIBs. Moreover, for the first time, we have also revealed by X-ray photoelectron spectroscopy (XPS) that in addition to the compensating Na ions spent in the SEI layer, the high specific capacity and capacity retention observed from electrochemical measurements are due to the formation of a thinner and more stable cathode-electrolyte interphase (CEI) on the P2-NaMnFeTiO while using such a cathode sodiation additive. Half-cell studies with P2-NaMnFeTiO cathodes show a 27% increase in the specific capacity (164 mAh g) with cathode sodiation additives. Full-cell studies with the HC anode show a 4 times increase in the specific capacity of P2-NaMnFeTiO. This work provides notable insights into and avenues toward the development of SIBs.