High-Capacity Rechargeable $Li/C{l}_2$ Batteries with Graphite Positive Electrodes

Abstract

Developing new types of high-capacity and high-energy density rechargeable battery is important to future generations of consumer electronics, electric vehicles, and mass energy storage applications. Recently we reported ~ 3.5 V sodium/chlorine $(Na/C{l}_2)$ and lithium/chlorine $(Li/C{l}_2)$ batteries with up to 1200 mAh $g^{-1}$ reversible capacity, using either a Na or Li metal as the negative electrode, an amorphous carbon nanosphere (aCNS) as the positive electrode, and aluminum chloride $(AlC{l}_3)$ dissolved in thionyl chloride $(SOC{l}_2)$ with fluoride-based additives as the electrolyte. The high surface area and large pore volume of aCNS in the positive electrode facilitated NaCl or LiCl deposition and trapping of $C{l}_2$ for reversible $NaCl/C{l}_2$ or $LiCl/C{l}_2$ 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 $Li/C{l}_2$ battery, attaining high battery performance after activation in carbon dioxide $(C{O}_2)$ 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/de-intercalation and exfoliation that generated sufficient pores for hosting $LiCl/C{l}_2$ redox. This work opens up widely available, low-cost graphitic materials for high-capacity alkali metal/$C{l}_2$ batteries. Lastly, we employed mass spectrometry to probe the $C{l}_2$ trapped in the graphitic positive electrode, shedding light into the $Li/C{l}_2$ battery operation.

37 pages, 16 figures, 1 table