Sulfonyl chloride-intensified metal chloride intercalation towards graphite for efficient sodium storage

Metal chloride-intercalated graphite with excellent conductivity and large layer spacing is highly desired for applications in sodium ion batteries. However, halogen vapor is usually indispensable to initiate the intercalation process, which pose great challenges to experiment and equipment. In this work, SO2Cl2 was innovatively used as chlorine generator to intensify the intercalation process of BiCl3 towards graphite (BiCl3-GICs), which avoided potential risks such as Cl2 leakage in traditional methods. Additionally, the operational efficiency in experiment is effectively improved. After reacting SO2Cl2, BiCl3, and graphite at 200 oC for 20 h, the as-synthesized BiCl3-GICs delivered a large interlayer spacing (1.26 nm) and a high amount of BiCl3 intercalation (42%), which endows SIBs with high specific capacity of 213 mAh g−1 at 1 A g−1 and fantastic rate performance (170 mAh g−1 at 5 A g−1). Moreover, the in-situ Raman spectra revealed that electronic interaction between graphite and intercalated BiCl3 is weakened during the first discharge, which is favorable for the sodium storage. This work broadly enables the intercalation intensification process of other metal chloride-intercalated graphite, offering possibilities for developing advanced energy storage devices.