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

Metal chloride-intercalated graphite with excellent conductivity and a large interlayer spacing is highly desired for use in sodium ion batteries. However, halogen vapor is usually indispensable in initiating the intercalation process, which makes equipment design and experiments challenging. In this work, SO₂Cl₂ was used as a chlorine generator to intensify the intercalation of BiCl₃ into graphite (BiCl₃-GICs), which avoided the potential risks, such as Cl₂ leakage, in traditional methods. The operational efficiency in the experiment was also improved. After the reaction of SO₂Cl₂, BiCl₃, and graphite at 200 ^oC for 20 h, the synthesized BiCl₃-GICs had a large interlayer spacing (1.26 nm) and a high amount of BiCl₃ intercalation (42%), which gave SIBs a high specific capacity of 213 mAh g⁻¹ at 1 A g⁻¹ and an excellent rate performance (170 mAh g⁻¹ at 5 A g⁻¹). In-situ Raman spectra revealed that the electronic interaction between graphite and intercalated BiCl₃ is weakened during the first discharge, which is favorable for sodium storage. This work broadly enables the increased intercalation of other metal chloride-intercalated graphites, offering possibilities for developing advanced energy storage devices.