New cathode materials for lithium-sulfur batteries constructed out of vertically aligned sulfur–graphene (S-G) nanowalls on electrically conductive substrates — delivering high capacity + rate performance — have been developed by researchers at Beihang University in China.
The new cathode materials allow for the fast diffusion of lithium ions + electrons as a result of the sulfur nanoparticles in each individual S-G nanowall being homogeneously anchored between the various graphene layers.
The new cathodes reportedly achieved (this is more for the technically minded readers here) a reversible capacity of 1261 mAh g–1 in the first cycle, and over 1210 mAh g–1 after 120 cycles with excellent cyclability and high-rate performance (more than 400 mAh g–1 at 8C, 13.36 A g–1). As it stands, this is currently the best demonstrated rate performance for sulfur-graphene cathodes — according to the researchers involved.
Green Car Congress provides more information on the methodology used by the researchers:
The Beihang team devised a simple electrochemical assembly strategy to achieve ordered sulfur−graphene nanowalls, which are controllably and vertically aligned onto the surface of electrically conductive substrates during the tunable cyclic voltammetry (CV) processes.
Sulfur nanoparticles were first anchored onto the surface of graphene (or reduced graphene oxides) via the reaction of Na2S with graphene oxide (GO). The team then conducted electrochemical assembly processes in a two electrode system with electrical conductive substrates (copper or nickel sheet) as the work electrode and a platinum sheet as contrast electrode. Controllable cyclic voltammetry processes were operated in the voltage range of -0.5 to 2V at a scanning rate of 50 mV s-1. Adjusting the scanning numbers results in vertically aligned S-G nanowalls with tunable thickness. The mass areal density of S-G nanowalls fabricated by CV scanning 10 cycles is 1.3 mg cm-2; increasing the CV scanning number to 15 and 20 increased the mass areal density to 1.8 and 2.2 mg cm-2, respectively.
For electrochemical measurement, the team assembled coin cells with the as-prepared S-G nanowalls directly using as electrode without any binder and conductive additive, Li metal as a counter electrode, a separator (Celgard 2300), and an electrolyte of 1 M LiTFSI in a mixture of 1,3-dioxolane (DOL), 1,2-dimethoxyethane (DMC) and tetraethylene glycol dimethyl ether (TEGDME) (volume ratio 5:4:1).
The researchers of course (predictably, not that that’s a bad thing) think that their new work will open up new routes to be taken with regard to the manufacture of assorted graphene-containing composites with unique structures “for catalysis, sensors, and energy storage and conversions.”
The new findings are outlined in a new paper published in the ACS journal Nano Letters.
Image Credit: Beihang University in China
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