High-Capacity Rechargeable Li/Cl₂ Batteries with Graphite Positive Electrodes

Developing new types of high-capacity and high-energy density rechargeable batteries is important to future generations of consumer electronics, electric vehicles, and mass energy storage applications. Recently, we reported ∼3.5 V sodium/chlorine (Na/Cl₂) and lithium/chlorine (Li/Cl₂) batteries with up to 1200 mAh g^-1 reversible capacity, using either a Na or a Li metal as the negative electrode, an amorphous carbon nanosphere (aCNS) as the positive electrode, and aluminum chloride (AlCl₃) dissolved in thionyl chloride (SOCl₂) with fluoride-based additives as the electrolyte [Zhu et al., Nature, 2021, 596 (7873), 525-530]. The high surface area and large pore volume of aCNS in the positive electrode facilitated NaCl or LiCl deposition and trapping of Cl₂ for reversible NaCl/Cl₂ or LiCl/Cl₂ redox reactions and battery discharge/charge cycling. Here, we report an initially low surface area/porosity graphite (DGr) material as the positive electrode in a Li/Cl₂ battery, attaining high battery performance after activation in carbon dioxide (CO₂) at 1000 °C (DGr_ac) with the first discharge capacity ∼1910 mAh g^-1 and a cycling capacity up to 1200 mAh g^-1. Ex situ Raman spectroscopy and X-ray diffraction (XRD) revealed the evolution of graphite over battery cycling, including intercalation/deintercalation and exfoliation that generated sufficient pores for hosting LiCl/Cl₂ redox. This work opens up widely available, low-cost graphitic materials for high-capacity alkali metal/Cl₂ batteries. Lastly, we employed mass spectrometry to probe the Cl₂ trapped in the graphitic positive electrode, shedding light into the Li/Cl₂ battery operation.