Operando Characterization of Active Surface Area and Passivation Effects on Sulfur-Carbon Composites for Lithium-Sulfur Batteries

• Sulfur electrodes for lithium-sulfur batteries necessarily contain a conductive additive,typically carbon, to enable the electrochemical reactions, since sulfur and the dischargeproduct, Li2S, are insulators. Consequently, the full passivation of carbon, by depositionof sulfur and/or Li2S, would necessarily produce the death of the battery. However, herewe demonstrate that for high-performance lithium-sulfur batteries operated under leanelectrolyte conditions (electrolyte to sulfur ratio of 6 µL mgS-1 in Li-S coin cells), theextent of passivation of carbon is not severe enough to limit performance. This is shownby performing impedance measurements of fully charged lithium-sulfur batteries, fromwhich we demonstrate that we can evaluate the specific surface area of carbon, and wefind that the capacity fade with cycling is not due to a decrease in the electrochemicallyactive specific surface area of carbon. These results show that introducing a higher sur-face area carbon in the sulfur electrode formulation is not needed to prevent passivation,and that the focus of lithium-sulfur development should be directed towards other is-sues, such as mitigating undesirable reactions at the lithium electrode and achievingrobust sulfur electrode structures enabling fast transport of electrolyte species and, thus,more homogeneous reactions.

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NATURVETENSKAP  -- Kemi -- Oorganisk kemi (hsv//swe)

NATURAL SCIENCES  -- Chemical Sciences -- Inorganic Chemistry (hsv//eng)

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