In Situ TEM Studies of Sodium Polysulfides Electrochemistry in High Temperature Na-S Nanobatteries

Area of Science:

• Electrochemistry
• Materials Science
• Energy Storage

Background:

• Polysulfide formation limits discharge capacity in high-temperature sodium-sulfur (HT-Na-S) batteries.
• Direct imaging of polysulfides is challenging, hindering a full understanding of their electrochemistry.
• Current commercial HT-Na-S batteries achieve only one-third of their theoretical capacity.

Purpose of the Study:

• To investigate the real-time formation and evolution of polysulfides during HT-Na-S battery cycling.
• To understand the electrochemical reactions governing polysulfide behavior at high temperatures.
• To explore strategies for enhancing the capacity and cyclability of HT-Na-S batteries.

Main Methods:

• In situ transmission electron microscopy (TEM) combined with a microelectromechanical systems (MEMS) heating device.
• Real-time observation of electrochemical reactions within HT-Na-S batteries.
• Introduction of nanovoids into sulfur cathodes to buffer volume changes and improve ion diffusion.

Main Results:

• Real-time visualization of transient polysulfide formation and evolution during cycling.
• Demonstration of reversible polysulfide transformation (sulfur to Na₂S) during charge/discharge at high temperatures.
• Achieved full discharge to Na₂S in sulfur cathodes with nanovoids at 300°C, overcoming conventional Na₂S₂ limitation.
• Observed swift and highly reversible electrochemical reactions with nanovoid-modified cathodes.

Conclusions:

• In situ TEM provides critical insights into polysulfide electrochemistry in HT-Na-S batteries.
• Nanovoid engineering of sulfur cathodes significantly boosts discharge capacity and reversibility.
• These findings offer strategies for developing advanced HT-Na-S batteries for large-scale energy storage.