Characterization and stability of sedimentary colloids in different ecology regions in Taihu Lake

Colloidal particles,heterogeneous mixture with various organic components and continuous molecular weight(MW)distribution,is omnipresent in lake sediments and substantially influence the retention,transportation,and fate of contaminants in lake ecosystem.We sampled and extracted sedimentary colloids from different ecology regions in Taihu Lake,Jiangsu,East China,in June 2020,and they were further separated into four different particle size ranges by tangent ultrafiltration,and the properties of colloids were studied in various methods,including zeta potential analysis,transmission electron micrograph images(TEM),Fourier transformation infrared(FTIR),and 3D fluorescence.Results show that the surface of the colloids is covered with organic macromolecular substances,such as humuslike substances and protein-like substances.There were significant differences in molecular weight and fraction content of colloids in the sediments from macrophyte-dominant(MD)area and algae-dominant(AD)area in the lake.Colloids from MD area are mainly composed of humic acid,protein,and fulvic acid;the content of fulvic acid is lower than that of humic acid and protein.The humic acid exists mainly in small molecular weight(10-100 kDa),protein exists in mainly large molecular weight colloids(0.45-1μm).Colloids from AD area are mainly composed of humic acid,and mainly distributed in the molecular weight(10 kDa-0.45μm).The presence of humic acid inhibits effectively the agglomeration of the colloids.Especially,the stability of colloids is closely related to the molecular weight,with low molecular weight from MD area show higher stability.The existence of humic acid in colloids increases the electrostatic repulsion between colloidal particles,which can effectively inhibit the agglomeration of colloids,thus enhancing the stability of colloids.Furthermore,both monovalent and divalent electrolytes enhance colloidal aggregation,and the low-molecular-weight(LMW)colloid fraction exhibits higher stability efficiency than the high-molecular-weight(HMW)colloidal.

Molecular dynamics simulations of the electric double layer capacitance of graphene electrodes in mono-valent aqueous electrolytes

Electrical double layer （EDL） capacitors based on recently emergent graphene materials have shown several folds performance improvement compared to conventional porous carbon materials, driving a wave of technology breakthrough in portable and renewable energy storage. Accordingly, much interest has been generated to pursue a comprehensive understanding of the fundamental yet elusive double layer structure at file electrode^electrolyte interface. In this paper, we carried out comprehensive molecular dynamics simulations to obtain a com- prehensive picture of how ion type, solvent properties, and charging conditions affect the EDL structure at the graphene electrode surface, and thereby its contribution to capacitance. We show that different symmetrical monovalent aqueous electrolytes M^X- （M~ = Na~, K~, Rb＋, and Cs＋; X- = F-, CI-, and I ） indeed have distinctive EDL structures. Larger ions, such as, Rb＊, Cs＊, C1, and I, undergo partial dehydration and penetrate through the first water layer next to the graphene electrode surfaces under charging. As such, the electrical potential distribution through the EDL strongly depends on the ion type. Interestingly, we further reveal that the water can play a critical role in determining the capacitance value. The change of dielectric constant of water in different electrolytes largely cancels out the variance in electric potential drop across the EDL of different ion type. Our simulation sheds new lights on how the interplay between solvent molecules and EDL structure cooperatively contributes to capacitance, which agrees with our experimental results well.

Instability of lithium bis(fluorosulfonyl)imide(LiFSI)–potassium bis(fluorosulfonyl)imide(KFSI) system with LiCoO_2 at high voltage

The cycling performance, impedance variation, and cathode surface evolution of the Li/LiCoO2 cell using Li FSI–KFSI molten salt electrolyte are reported. It is found that this battery shows poor cycling performance, with capacity retention of only about 67% after 20 cycles. It is essential to understand the origin of the instability. It is noticed that the polarization voltage and the impedance of the cell both increase slowly upon cycling. The structure and the properties of the pristine and the cycled LiCoO2 cathodes are investigated by x-ray diffraction（XRD）, scanning electron microscopy（SEM）, Raman spectroscopy, x-ray photoelectron spectroscopy（XPS）, and transmission electron microscopy（TEM）. It is found that the LiCoO2 particles are corroded by this molten salt electrolyte, and the decomposition by-product covers the surface of the LiCoO2 cathode after 20 cycles. Therefore, the surface side reaction explains the instability of the molten salt electrolyte with LiCoO2.

‘‘Soggy sand'' polymer composite nanofber membrane electrolytes for lithium ion batteries

A kind of octanol-modifded silica nanoparticle was fabricated and employed as a framework to form‘‘soggy sand’’electrolyte along with 1-butyl-3-methylimidazolium tetrafluoroborate.‘‘Soggy sand’’and poly（vinylidene fluoride-hexafluoropropylene）composite electrolyte membranes were electrospun for the frst time.The properties of this membrane electrolyte have been evaluated by the mechanical test and electrochemical test.The Young’s modulus increased by 275%from 6.8 MPa to 25.5 MPa and the electrical conductivity increased to 7.6 10à5S/cm at 290.15 K when compared to pristine P（VdF-HFP）membrane electrolyte.The conductivity is 3.1 10à4S/cm at 323.15 K.