Extended Data Fig. 5: Reversible halide redox chemistry enabled by intercalation in graphite.
From: Aqueous Li-ion battery enabled by halogen conversion–intercalation chemistry in graphite
Galvanostatic charge and discharge profiles of different composite cathodes at a current density of 80 mA g−1 in WiBS gel electrolyte. a, LiBr–graphite (mass ratio of about 1:1) cathode in the potential range 3.20–4.62 V. Without the presence of Cl−, there were no further oxidation reactions of Br0 until the potential was raised to above 4.55 V versus Li/Li+, where Br0 was further irreversibly oxidized into BrO−. b, Composite of (LiBr)0.5(LiCl)0.5 and titanium nanopowder (mass ratio 1:20), showing a charge capacity of 85% of the theoretical value for halogen anion redox reactions and negligible discharge capacity. The higher overpotential might be due to the lack of carbon catalysis for the redox reactions. c, (LiBr)0.5(LiCl)0.5/graphitized carbon black (mass ratio 1:3). d, (LiBr)0.5(LiCl)0.5/active carbon (mass ratio 1:3). e, (LiBr)0.5(LiCl)0.5/KS4 (mass ratio 6:4). f, g, N2 absorption/desorption isotherm of a graphite (KS4) electrode (f) and an active-carbon electrode (g) with 5 wt% PTFE binder. The results indicate that, unlike active carbon, the graphite host cannot provide a large surface area and small size pores to store halogens by adsorption. h, Ex situ XRD intensity of LiBr/LiCl/active-carbon cathodes at fully charged and discharged states. After adsorbing halogen (Br2 and BrCl) during charging, a relatively strong peak appears in the (002) peak area, and (100) weakens. This might imply the reformation of randomly oriented small graphitic zones with the help of halogen integration, which indicates a minor contribution of intercalation-like behaviour to halogen storage into nano-graphitized grains.
