Rechargeable Li/Cl₂ Battery Down to -80 °C

Low temperature rechargeable batteries are important to life in cold climates, polar/deep-sea expeditions, and space explorations. Here, this work reports 3.5-4 V rechargeable lithium/chlorine (Li/Cl₂ ) batteries operating down to -80 °C, employing Li metal negative electrode, a novel carbon dioxide (CO₂ ) activated porous carbon (KJCO₂ ) as the positive electrode, and a high ionic conductivity (≈5-20 mS cm^-1 from -80 °C to room-temperature) electrolyte comprised of aluminum chloride (AlCl₃ ), lithium chloride (LiCl), and lithium bis(fluorosulfonyl)imide (LiFSI) in low-melting-point (-104.5 °C) thionyl chloride (SOCl₂ ). Between room-temperature and -80 °C, the Li/Cl₂ battery delivers up to ≈29 100-4500 mAh g^-1 first discharge capacity (based on carbon mass) and a 1200-5000 mAh g^-1 reversible capacity over up to 130 charge-discharge cycles. Mass spectrometry and X-ray photoelectron spectroscopy probe Cl₂ trapped in the porous carbon upon LiCl electro-oxidation during charging. At -80 °C, Cl₂ /SCl₂ /S₂ Cl₂ generated by electro-oxidation in the charging step are trapped in porous KJCO₂ carbon, allowing for reversible reduction to afford a high discharge voltage plateau near ≈4 V with up to ≈1000 mAh g^-1 capacity for SCl₂ /S₂ Cl₂ reduction and up to ≈4000 mAh g^-1 capacity at ≈3.1 V plateau for Cl₂ reduction.