posted on 2021-04-15, 10:55authored bySiyuan Gao, Fan Xia, Bomin Li, Iddrisu B. Abdul Razak, Yuzi Liu, Ke Lu, Dennis E. Brown, Rongyue Wang, Yingwen Cheng
The
practical deployment of advanced Li–S batteries is severely
constrained by the uncontrollable lithium polysulfide conversion under
realistic conditions. Although a plethora of advanced sulfur hosts
and electrocatalysts have been examined, the fundamental mechanisms
are still elusive and predictive design approaches have not yet been
established. Here, we examined a series of well-defined Fe–N–C
sulfur hosts with systematically varied and strongly coupled Fe3C and Fe electrocatalysts, prepared by one-step pyrolysis
of a novel Fex[Fe(CN)6]y/polypyrrole composite at different temperatures.
We revealed the key roles of Fe3C and metallic Fe on modulating
polysulfide conversion, in that the polar Fe3C strongly
adsorbs polysulfide whereas the Fe particles catalyze fast polysulfide
conversion. We then highlight the superior performance of the rational
host with strongly coupled Fe3C and Fe on mesoporous Fe–N–C
host on promoting nearly complete polysulfide conversion, especially
for the challenging short-chain Li2S4 conversion
to Li2S. The electrodeposited Li2S on this host
was extremely reactive and can be readily charged back to S with minimal
activation overpotential. Overall, Li–S batteries equipped
with the novel sulfur host delivered a high specific capacity of 1350
mAh g–1 at 0.1C with a capacity retention of 96%
after 200 cycles. This work provides new insights on the functional
mechanism of advanced sulfur hosts, which could eventually translate
into new design principles for practical Li–S batteries.