Rechargeable Na/Cl₂ and Li/Cl₂ batteries

Lithium-ion batteries (LIBs) are widely used in applications ranging from electric vehicles to wearable devices. Before the invention of secondary LIBs, the primary lithium-thionyl chloride (Li-SOCl₂) battery was developed in the 1970s using SOCl₂ as the catholyte, lithium metal as the anode and amorphous carbon as the cathode^1–7. This battery discharges by lithium oxidation and catholyte reduction to sulfur, sulfur dioxide and lithium chloride, is well known for its high energy density and is widely used in real-world applications; however, it has not been made rechargeable since its invention^8–13. Here we show that with a highly microporous carbon positive electrode, a starting electrolyte composed of aluminium chloride in SOCl₂ with fluoride-based additives, and either sodium or lithium as the negative electrode, we can produce a rechargeable Na/Cl₂ or Li/Cl₂ battery operating via redox between mainly Cl₂/Cl⁻ in the micropores of carbon and Na/Na⁺ or Li/Li⁺ redox on the sodium or lithium metal. The reversible Cl₂/NaCl or Cl₂/LiCl redox in the microporous carbon affords rechargeability at the positive electrode side and the thin alkali-fluoride-doped alkali-chloride solid electrolyte interface stabilizes the negative electrode, both are critical to secondary alkali-metal/Cl₂ batteries.