Development
of advanced carbon cathode support with the ability
to accommodate high sulfur (S) content as well as effective confinement
of the sulfur species during charge–discharge is of great importance
for sustenance of Li–S battery. A facile poly(vinylpyrrolidone)-assisted
solvothermal method is reported here to prepare Mg–1,4-benzenedicarboxylate
metal organic framework (MOF) from which mesoporous carbon is derived
by thermal treatment, where the hexagonal sheetlike morphology of
the parent MOF is retained. Existence of abundant pores of size 4
and 9 nm extended in three dimensions with zigzag mazelike channels
helps trapping of S in the carbon matrix through capillary effect,
resulting in high S loading. When tested as a cathode for lithium–sulfur
battery, a reversible specific capacity of 1184 mAh g
–1
could be achieved at 0.02 C. As evidenced by X-ray photoelectron
spectroscopy, in situ generated Mg in the carbon structure enhances
the conductivity, whereas MgO provides support to S immobilization
through chemical interactions between Mg and sulfur species for surface
polarity compensation, restricting the dissolution of polysulfide
into the electrolyte, the main cause for the “shuttle phenomenon”
and consequent capacity fading. The developed cathode shows good electrochemical
stability with reversible capacities of 602 and 328 mAh g
–1
at 0.5 and 1.0 C, respectively, with retentions of 64 and 67% after
200 cycles. The simple MOF-derived strategy adopted here would help
design new carbon materials for Li–S cathode support.
Spherically shaped MOF-derived CeO2@C shows a superior performance as a lithium-ion battery anode with high specific capacity, rate performance and cycling stability.
Effective trapping of polysulfides within the carbon cathode host strongly depends on intrinsic C-S interactions. We report herein a systematic study of the influence of S-loading process on C-S interactions in MWCNT/S composites prepared by three commonly used industry-friendly methods, namely, mechanical solidstate mixing, infiltration method from a solution of S in CS 2 , and chemical deposition by disproportionation reaction of sodium sulfide and sodium thiosulfate. FESEM and TEM studies reveal strikingly different morphologies of the resulting MWCNT/S composites. XPS and Raman studies indicate different extents of recovery of π bonds in MWCNT due to varying degrees of C-S interfacial interactions in the composites. Furthermore, it is found that the C/O atomic ratio in the composites plays a crucial role: the higher the C/O value the better is the S-confinement. These subtle physical changes induced by C-S interactions in the composites can be related to electrochemical performance when tested in Li-S coin cells. It is found that the best results (high initial capacity of 1143 mAh g −1 and better capacity retention) could be achieved when the solution infiltration method was used for S-loading. This conclusion is further validated by using activated carbon as S-host.
Two 4-methyl-2,6-diformylphenol based compounds with pyridylamine have been established as chemosensors for pH. The probes are able to differentiate between normal cells and cancer cells.
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