Shedding light on rechargeable Na/Cl <sub>2</sub> battery
Guanzhou Zhu, Peng Liang, Cheng‐Liang Huang, Shu‐Chi Wu, Cheng-Chia Huang, Yuan‐Yao Li, Shi‐Kai Jiang, Wei‐Hsiang Huang, Jiachen Li, Feifei Wang, Bing‐Joe Hwang, Hongjie Dai
Abstract
Advancing new ideas of rechargeable batteries represents an important path to meeting the ever-increasing energy storage needs. Recently, we showed rechargeable sodium/chlorine (Na/Cl 2 ) (or lithium/chlorine Li/Cl 2 ) batteries that used a Na (or Li) metal negative electrode, a microporous amorphous carbon nanosphere (aCNS) positive electrode, and an electrolyte containing dissolved aluminum chloride and fluoride additives in thionyl chloride [G. Zhu et al. , Nature 596 , 525–530 (2021) and G. Zhu et al. , J. Am. Chem. Soc. 144 , 22505–22513 (2022)]. The main battery redox reaction involved conversion between NaCl and Cl 2 trapped in the carbon positive electrode, delivering a cyclable capacity of up to 1,200 mAh g −1 (based on positive electrode mass) at a ~3.5 V discharge voltage [G. Zhu et al. , Nature 596 , 525–530 (2021) and G. Zhu et al. , J. Am. Chem. Soc. 144 , 22505–22513 (2022)]. Here, we identified by X-ray photoelectron spectroscopy (XPS) that upon charging a Na/Cl 2 battery, chlorination of carbon in the positive electrode occurred to form carbon-chlorine (C-Cl) accompanied by molecular Cl 2 infiltrating the porous aCNS, consistent with Cl 2 probed by mass spectrometry. Synchrotron X-ray diffraction observed the development of graphitic ordering in the initially amorphous aCNS under battery charging when the carbon matrix was oxidized/chlorinated and infiltrated with Cl 2 . The C-Cl, Cl 2 species and graphitic ordering were reversible upon discharge, accompanied by NaCl formation. The results revealed redox conversion between NaCl and Cl 2 , reversible graphitic ordering/amorphourization of carbon through battery charge/discharge, and probed trapped Cl 2 in porous carbon by XPS.