1 research outputs found
Conductive Lewis Base Matrix to Recover the Missing Link of Li<sub>2</sub>S<sub>8</sub> during the Sulfur Redox Cycle in Li–S Battery
Sulfur and polysulfides play important
roles on the environment
and energy storage systems, especially in the recent hot area of high
energy density of lithium–sulfur (Li–S) batteries. However,
the further development of Li–S battery is still retarded by
the lack of complete mechanistic understanding of the sulfur redox
process. Herein we introduce a conductive Lewis base matrix which
has the ability to enhance the battery performance of Li–S
battery, via the understanding of the complicated sulfur redox chemistry
on the electrolyte/carbon interface by a combined in operando Raman
spectroscopy and density functional theory (DFT) method. The higher
polysulfides, Li<sub>2</sub>S<sub>8</sub>, is found to be missing
during the whole redox route, whereas the charging process of Li–S
battery is ended up with the Li<sub>2</sub>S<sub>6</sub>. DFT calculations
reveal that Li<sub>2</sub>S<sub>8</sub> accepts electrons more readily
than S<sub>8</sub> and Li<sub>2</sub>S<sub>6</sub> so that it is thermodynamically
and kinetically unstable. Meanwhile, the poor adsorption behavior
of Li<sub>2</sub>S<sub><i>n</i></sub> on carbon surface
further prevents the oxidization of Li<sub>2</sub>S<sub><i>n</i></sub> back to S<sub>8</sub> upon charging. Periodic DFT calculations
show that the N-doped carbon surface can serve as conductive Lewis
base “catalyst” matrix to enhance the adsorption energy
of Li<sub>2</sub>S<sub><i>n</i></sub> (<i>n</i> = 4–8). This approach allows the higher Li<sub>2</sub>S<sub><i>n</i></sub> to be further oxidized into S<sub>8</sub>, which is also confirmed by in operando Raman spectroscopy. By recovering
the missing link of Li<sub>2</sub>S<sub>8</sub> in the whole redox
route, a significant improvement of the S utilization and cycle stability
even at a high sulfur loading (70%, m/m) in the composite on a simple
super P carbon