Shedding light on rechargeable Na/Cl₂ battery.

Area of Science:

• Electrochemistry and Materials Science
• Advanced Energy Storage Solutions

Background:

• Growing demand for efficient energy storage necessitates novel rechargeable battery chemistries.
• Previous work established rechargeable sodium/chlorine (Na/Cl2) and lithium/chlorine (Li/Cl2) batteries using metal anodes and carbon cathodes.

Purpose of the Study:

• To elucidate the detailed reaction mechanisms within the amorphous carbon nanosphere (aCNS) positive electrode during Na/Cl2 battery operation.
• To investigate the structural and chemical transformations of the aCNS electrode during charge and discharge cycles.

Main Methods:

• X-ray photoelectron spectroscopy (XPS) to identify surface chemical species, including carbon-chlorine (C-Cl) bonds and trapped molecular chlorine (Cl2).
• Synchrotron X-ray diffraction (XRD) to analyze structural changes in the aCNS electrode, observing the development of graphitic ordering.
• Mass spectrometry to confirm the presence of Cl2 during the charging process.

Main Results:

• Charging a Na/Cl2 battery leads to the chlorination of the aCNS electrode, forming C-Cl bonds and infiltrating the porous structure with Cl2.
• The aCNS electrode undergoes reversible graphitic ordering upon charging and amorphization upon discharge, correlating with redox conversion.
• XPS and mass spectrometry confirmed the presence and reversibility of Cl2 species within the porous carbon electrode.

Conclusions:

• The rechargeable Na/Cl2 battery chemistry involves a redox conversion between NaCl and Cl2, coupled with reversible structural changes in the carbon electrode.
• The formation of C-Cl bonds and reversible graphitic ordering are key mechanisms enabling high cyclable capacity in these advanced batteries.
• This study provides critical insights into the fundamental processes governing the performance of chlorine-based rechargeable batteries.