10.1016/j.colsurfa.2012.08.033
Fabrication of conductive polymer-coated sulfur composite cathode materials based on layer-by-layer assembly for rechargeable lithium-sulfur batteries
Polyethyleneimine (PEI, Mw 50-100 kDa), poly(allylamine hydrochloride) (PAH) (Mw 70 kDa), poly(styrenesulfonate sodium salt) (PSS) (Mw 70 kDa), gultaraldehyde (GA) and the water-soluble polypyrrole (PPY) (5 wt% in water) doped with organic acid were purchased from Sigma-Aldrich. The aniline monomer was used with further purification by decompressed distillation and then stored at 0-5 degC. The water used in all experiments was prepared in a three-stage Millipore Milli-Q Plus 185 purification system and had a resistivity higher than 18.2 MΩ cm. 
Sulfur particles were separately dispersed in PEI solution (1 mg/mL in 0.5 M NaCl) and allowed to adsorb for 30 min. Then excess polyelectrolytes were removed by centrifugation and three times washing with 0.5 M NaCl. Subsequently the above suspensions were alternately dispersed in PAH and PSS solution (2 mg/mL in 0.5 M NaCl) for another 30 min, followed by three times washing in 0.5 M NaCl. After the assembly of a desired number of PAH/PSS layer, the coated particles were then dispersed in 5% glutaraldehyde (GA) aqueous solution for 30 min. Finally these sample suspensions were incubated at the high temperature for 20 min. 
In a typical procedure, the prepared polymer-coated sulfur particles aqueous dispersion was added into the aniline monomer solution mixed with 1 M hydrochloric acid (HCl) under stirring. After 30 min, the equivalent number of moles of 22.8 wt% aqueous ammonium persulphate (APS) solution (with respect to aniline) was slowly added, followed by an oxidative polymerization at 0-3 degC. The reaction was carried out for 24 h. The resultant green solid, PANI/polymer-coated sulfur particles, were obtained by centrifugation and washed with water and ethanol thoroughly to remove excess ions and monomers. The procedure was repeated to increase the PANI content. The final product was dried under vacuum at ambient temperature for 24 h. The whole experiments were performed under the nitrogen atmosphere. The conductive polypyrrole (PPY) shells were prepared through a electrostatic interaction of the negatively charged PPY on the positively charged outer shell of (PAH/PSS)n/PAH-coated sulfur particles. The resultant gray solid was dried for further characterization and testing.
Polyethyleneimine (PEI
Mw
50-100 kDa
kDa
poly(allylamine hydrochloride) (PAH)
Mw
70 kDa
kDa
poly(styrenesulfonate sodium salt) (PSS)
Mw
70 kDa
kDa
water-soluble polypyrrole (PPY)
in water
5 wt%
wt%
aniline monomer
stored
0-5 degC
degC
water
resistivity
higher than 18.2 MΩ cm
MΩ cm
solution
PEI
1 mg/mL
mg/mL
solution
NaCl
0.5 M
M
Sulfur particles were separately dispersed in PEI solution
adsorb
30 min
min
NaCl
0.5 M
M
NaCl
washing
three times
times
PAH and PSS solution
2 mg/mL
mg/mL
PAH and PSS solution
NaCl
0.5 M
M
NaCl
0.5 M
M
suspensions
washing
three times
times
suspensions
dispersed
30 min
min
glutaraldehyde (GA) aqueous solution
5%
%
coated particles
dispersed
30 min
min
sample suspensions
incubated
20 min
min
hydrochloric acid (HCl)
1 M
M
aqueous ammonium persulphate (APS) solution
slowly added
30 min
min
aqueous ammonium persulphate (APS) solution
slowly added
22.8 wt%
wt%
oxidative polymerization
0-3 degC
degC
reaction
carried out
24 h
h
final product
dried
24 h
h