posted on 2018-01-08, 00:00authored byJonas Scholz, Buğra Kayaalp, Anika C. Juhl, Daniel Clemens, Michael Fröba, Simone Mascotto
One
key aspect in the cathode chemistry of lithium–sulfur
(Li–S) batteries is the firm contact between elemental sulfur
and the conducting carbon host to ensure the occurrence of the reduction
reaction. In this respect, we study the retention of sulfur in the
model cathode material CMK-8 carbon loaded by 20 and 50 wt % in the
presence of solvents of different nature (D2O, d-THF, d-toluene) using small-angle neutron
scattering. Exploiting the contrast matching between carbon and these
liquids, the scattering of the sulfur phase is isolated and the amount
and distribution of sulfur in the pores is determined in precise and
direct fashion. The chord-length distribution (CLD) analysis shows
that sulfur is preserved in both meso- and micropores if D2O is used. In the case of d-THF, sulfur is found
in the micropores only, whereas complete removal from the pore network
occurs for wetting with d-toluene. This severe loss
in the presence of solvents similar to those used in Li–S batteries
(e.g., dioxolane, diglyme) is ascribed to their superior adhesion
on the carbon surface and, more importantly, indicates that only a
little amount of loaded sulfur is available for the electrochemical
reactions.