Compensating Sodium Ions and Regulating Interface Chemistry through a High-Capacity Organic Salt for Practical Na-Ion...

Area of Science:

• Electrochemistry
• Materials Science
• Energy Storage

Background:

• Sodium-ion batteries offer a low-cost, safe alternative to lithium-ion batteries.
• Irreversible sodium loss in initial cycles hinders their capacity and stability.
• Cathode additives can compensate for sodium loss and improve battery performance.

Purpose of the Study:

• To introduce sodium squarate (NCO) as a cathode additive for sodium-ion batteries.
• To investigate NCO's role in sodium compensation and interfacial regulation.
• To enhance the performance of Prussian white (PW) cathodes in sodium-ion full cells.

Main Methods:

• Incorporation of sodium squarate (NCO) into Prussian white (PW) cathodes.
• Electrochemical testing of PW-NCO cathodes in sodium-ion full cells (PW-NCO||HC).
• Analysis of cathode-electrolyte interphase (CEI) and solid electrolyte interphase (SEI) formation.

Main Results:

• NCO decomposition during charging releases Na+ ions, compensating for irreversible loss.
• Formation of a stable, carbonate-rich CEI on the cathode and SEI on the anode (enriched with NaF).
• PW-10% NCO||HC full cells showed a discharge capacity of 100 mAh g-1 (vs. 53 mAh g-1 for pristine PW).
• A multilayer pouch cell achieved 80.1% capacity retention after 100 cycles.

Conclusions:

• Sodium squarate (NCO) is an effective cathode additive for sodium-ion batteries.
• NCO promotes beneficial interfacial modifications, enhancing stability and capacity.
• This strategy offers a viable route for improving sodium-ion full cell performance.