Electrochemical Investigations of Sulfur-Decorated Organic Materials as Cathodes for Alkali Batteries.

Alkali metal-sulfur batteries (particularly, lithium/sodium- sulfur (Li/Na-S)) have attracted much attention because of their high energy density, the natural abundance of sulfur, and environmental friendliness. However, Li/Na-S batteries still face big challenges, such as limited cycle life, poor conductivity, large volume changes, and the "shuttle effect" caused by the high solubility of Li/Na-polysulfides. Herein, novel organosulfur-containing materials, i.e., bis(4-hydroxy-2,2,6,6-tetramethylpiperidin-1-yl)disulfide (BiTEMPS-OH) and 2,4-thiophene/arene copolymer (TAC) are proposed as cathode materials for Li and Na batteries. BiTEMPS-OH shows an initial discharge/charge capacity of 353/192 mAh g-1 and a capacity of 62 mAh g-1 after 200 cycles at 100 mA g-1 in ether-based Li-ion electrolyte. Meanwhile, TAC has an initial discharge/charge capacity of 270/248 mAh g-1 and better cycling performance (106 mAh g-1 after 200 cycles) than BiTEMPS-OH in the same electrolyte. However, the rate capability of TAC is limited by the slow diffusion of Li-ions. Both materials show inferior electrochemical performances in Na battery cells compared to the Li analogs. X-ray powder diffraction reveals that BiTEMPS-OH loses its crystalline structure permanently upon cycling in Li battery cells. X-ray photoelectron spectroscopy demonstrates the cleavage and partially reversible formation of S-S bonds in BiTEMPS-OH and the formation/decomposition of thick solid electrolyte interphase on the electrode surface of TAC.

Constructing Hollow Microcubes SnS2 as Negative Electrode for Sodium-ion and Potassium-ion Batteries.

Sodium/potassium-ion batteries (NIBs and KIBs) are considered the most promising candidates for lithium-ion batteries in energy storage fields. Tin sulfide (SnS2) is regarded as an attractive negative candidate for NIBs and KIBs thanks to its superior power density, high-rate performance and natural richness. Nevertheless, the slow dynamics, the enormous volume change and the decomposition of polysulfide intermediates limit its practical application. Herein, microcubes SnS2 were prepared through sacrificial MnCO3 template-assisted and a facile solvothermal reaction strategy and their performance was investigated in Na and K-based cells. The unique hollow cubic structure and well-confined SnS2 nanosheets play an important role in Na+/K+ rapid kinetic and alleviating volume change. The effect of the carbon additives (Super P/C65) on the electrochemical properties were investigated thoroughly. The in operando and ex-situ characterization provide a piece of direct evidence to clarify the storage mechanism of such conversion-alloying type negative electrode materials.

Study of the Lithium Storage Mechanism of N-Doped Carbon-Modified Cu2 S Electrodes for Lithium-Ion Batteries.

Owing to their high specific capacity and abundant reserve, Cux S compounds are promising electrode materials for lithium-ion batteries (LIBs). Carbon compositing could stabilize the Cux S structure and repress capacity fading during the electrochemical cycling, but the corresponding Li+ storage mechanism and stabilization effect should be further clarified. In this study, nanoscale Cu2 S was synthesized by CuS co-precipitation and thermal reduction with polyelectrolytes. High-temperature synchrotron radiation diffraction was used to monitor the thermal reduction process. During the first cycle, the conversion mechanism upon lithium storage in the Cu2 S/carbon was elucidated by operando synchrotron radiation diffraction and in situ X-ray absorption spectroscopy. The N-doped carbon-composited Cu2 S (Cu2 S/C) exhibits an initial discharge capacity of 425 mAh g-1 at 0.1 A g-1 , with a higher, long-term capacity of 523 mAh g-1 at 0.1 A g-1 after 200 cycles; in contrast, the bare CuS electrode exhibits 123 mAh g-1 after 200 cycles. Multiple-scan cyclic voltammetry proves that extra Li+ storage can mainly be ascribed to the contribution of the capacitive storage.

Influence of oxygen distribution on the Li-ion conductivity in oxy-sulfide glasses - taking a closer look.

Lithium thiophosphates are a promising class of solid electrolyte (SE) materials for all-solid-state batteries (ASSBs) due to their high Li-ion conductivity. Yet, the practical application of lithium thiophosphates is hindered by their chemical instability, which remains a prevalent challenge in the field. Oxygen substitution has been discussed in the literature as a promising strategy to enhance stability. Nevertheless, the lack of understanding of the role of synthesis strategy on the resulting structure-property relationship makes it difficult to predict and control the material's behaviour, limiting our ability to fully utilize oxygen substitution as a viable solution. Here, we show that not only the total oxygen content but also the oxygen distribution within the material affects the ion conductivity. By carefully analysing the local structure of oxy-sulfide glasses, we find that few highly oxygenated structural units like [PO4]3- and [PO3S]3- are more detrimental to the ionic conductivity than a larger amount of less substituted units like [POS3]3-. Further, we demonstrate how the oxygen distribution is connected to the synthesis in high-energy ball milling by comparing two different sets of precursor materials. The results may explain the deviations in the past literature. The findings should be transferable to other Li-thiophosphate materials and enable more directed design of new materials.

Investigation of SnS2 -rGO Sandwich Structures as Negative Electrode for Sodium-Ion and Potassium-Ion Batteries.

Sodium-ion and potassium-ion batteries (NIBs and KIBs) are considered promising alternatives to replace lithium-ion batteries (LIBs) in energy storage applications due to the natural abundance and low cost of Na and K. Nevertheless, a critical challenge is that the large size of Na+ /K+ leads to a huge volume change of the hosting material during electrochemical cycling, resulting in rapid capacity decay. Among negative candidates for alkali-metal-ion batteries, SnS2 is attractive due to the competitively high specific capacity, low redox potential and high abundance. Porous few-layer SnS2 nanosheets are in situ grown on reduced graphene oxide, forming a SnS2 -rGO sandwich structure via strong C-O-Sn bonds. This nano-scaled sandwich structure not only shortens Na+ /K+ and electron transport pathways but also accommodates volume expansion, thereby enabling high and stable electrochemical cycling performance of SnS2 -rGO. This work explores the influence of different conductive carbons (Super P and C65) on the SnS2 -rGO electrode. In addition, the effects of the electrolyte additive fluoroethylene carbonate (FEC) on the electrochemical performance in NIBs and KIBs is evaluated. This work provides guidelines for optimized electrode structure design, electrolyte additives and carbon additives for the realization of better NIBs and KIBs.

Elucidating the Mechanism of Li Insertion into Fe1-xS/Carbon via In Operando Synchrotron Studies.

The detailed understanding of kinetic and phase dynamics taking place in lithium-ion batteries (LIBs) is crucial for optimizing their properties. It was previously reported that Fe1-xS/C nanocomposites display a superior performance as anode materials in LIBs. However, the underlying lithium storage mechanism was not entirely understood during the 1st cycle. In this work, in operando synchrotron techniques are used to track lithium storage mechanisms during the 1st (de)-lithiation process in the Fe1-xS/C nanocomposite. The combination of in operando techniques enables the uncovering of the phase fraction alternations and crystal structural variations on different length-scales. Additionally, the investigation of kinetic processes, morphological changes, and internal resistance dynamics is discussed. These results reveal that the phase transition of Fe1-xS → Li2Fe1-xS2 → Fe0 + Li2S occurs during the 1st lithiation process. The redox reaction of Fe2+ + 2e- ⇌ Fe0 and the Fe K-edge X-ray absorption spectroscopy (XAS) transformation process are confirmed by in operando XAS. During the 1st de-lithiation process, Fe0 and Li2S convert to Li2-yFe1-xS2 and Li+ is extracted from Li2S to form Li2-yS. The phase transition from Li2S to Li2-yS is not detected in previous reports. After the 1st de-lithiation process, amorphous lithiated iron sulfide nanoparticles are embedded within the remaining Li2S matrix.

Linear alkylbenzenes in riverine runoff of the Pearl River Delta (China) and their application as anthropogenic molecular markers in coastal environments.

The average concentrations of SigmaLABs (sum of C10-C13-LABs) in runoff samples collected from the eight major riverine outlets of the Pearl River Delta (PRD) of China ranged from 1.4 to 6124 ng/L in the dissolved phase and from 0.01 to 11.4 microg/g dry weight in the particulate phase during March 2005-February 2006. The annual riverine flux of SigmaLABs from the PRD to the coastal ocean was estimated at approximately 14 tons/yr. The inventories of SigmaLABs in agricultural lands of Guangdong Province ranged from 313 to 1825 kg/yr. The early and late rice fields were the major sink of LABs, accounting for approximately 68% of total LABs inventory in agricultural lands. The social-economically estimated annual discharge of LABs from household detergents in the PRD was approximately 696 tons/yr, more than an order of magnitude higher than that estimated from field measurements (about 14 tons/yr), which was attributed to several factors.

Occurrence and phase distribution of polycyclic aromatic hydrocarbons in riverine runoff of the Pearl River Delta, China.

The occurrence and phase distribution of polycyclic aromatic hydrocarbons (PAHs) in waters at the eight riverine outlets of the Pearl River Delta (China) were examined based on a monthly sampling program from March 2005 to February 2006. The total concentrations of PAHs in the aqueous phase and suspended particulate matter (SPM) combined ranged from 55.5 to 522 ng/L, at the mid level of the global values in rivers and estuaries. No clear temporal and spatial trends of PAH concentrations were found. However, the concentrations of PAHs associated with SPM coincided with the monthly precipitation of Guangzhou, indicating the importance of atmospheric deposition. The PAHs found in the region were likely derived from a combined pyrolytic and petrogenic origin, as suggested by the molecular indices of PAHs. Normalized partition coefficient (K(oc)) between water and SPM was correlated with octanol-water partition coefficient (K(ow)) to understand the environmental behavior of PAHs.

Riverine inputs of total organic carbon and suspended particulate matter from the Pearl River Delta to the coastal ocean off South China.

A total of 1008 samples were collected from the eight major riverine runoff outlets in the Pearl River Delta (PRD) during 2005-2006 to estimate the fluxes of total organic carbon (TOC) to the coastal ocean off South China. The average dissolved organic carbon (DOC) concentration was 1.67 mg/L with a range of 1.38-2.13 mg/L. Concentrations of particulate organic carbon (POC) ranged from 2.66-4.12% of total suspended particulate matter (SPM). The fluxes of TOC and SPM from the PRD via the eight outlets were 9.2 x 10(5) and 2.5 x 10(7)tons/yr, respectively. Temporal variations in POC and DOC were observed at all outlets due to the large variability in runoff levels because of the seasonality of rainfall, and the riverine discharge amount was an important factor controlling TOC flux. The net contribution of organic carbon from the PRD to the coastal ocean represented approximately 0.1-0.2% of total organic carbon transported by rivers worldwide.

Impact of anthropogenic activities on urban stream water quality: a case study in Guangzhou, China.

Anthropogenic activities are increasingly impacting the quality of urban surface water, particularly in regions undergoing intensive urbanization, such as Guangzhou of South China with a large urban stream network. To examine such impacts, we conducted field sampling on December 24, 2010, May 24, 2011, and August 28, 2011, representative of the low-, normal-, and high-flow periods, respectively. The first sampling was timed immediately after the closing of the 16th Asian Games (November 12-27, 2010) and the 10th Asian Para Games (December 12-19, 2010) held in Guangzhou. Assessments based on a pollution index method showed that the urban streams under investigation were extremely polluted, with direct discharge of untreated domestic sewage identified as the main pollution contributor. In addition, stream water quality around urban villages with high population densities was worse than that within business districts away from the urban villages. Pollution control measures implemented in preparation for the Asian Games were effective for urban streams within the business districts, but less effective for those adjacent to the urban villages. However, short-term efforts may not be able to achieve sustainable urban water quality improvements. In the case of Guangzhou, minimizing or even eliminating direct point-source inputs to the urban streams is perhaps the best option.

Occurrence, phase distribution, and mass loadings of benzothiazoles in riverine runoff of the Pearl River Delta, China.

A set of six benzothiazoles was determined in riverine runoff samples of the Pearl River Delta (PRD) collected monthly from March 2005 to February 2006. The concentrations of total benzothiazoles ranged from 220 to 611 ng/L, with benzothiazole (BT) being the most prominent (82%), followed by 2-methylthiobenzothiazole (MBT),thianaphthene (TN), and triphenylene (TP). The annual fluxes ofTN, BT, MBT, dibenzothiophene (DBT), 2-(4-morpholinyl)benzothiazole (24MoBT), and TP from the PRD to the coastal ocean were 1.94, 65.1, 10.1,0.63, 0.18, and 0.89 tons/yr, summing to yield an annual flux of 79 tons/yr for total benzothiazoles. In the PRD, approximately 1.1 x 10(5) tons of rubber are estimated to be released into the environment each year. This corresponds to the annual fluxes of 13 tons/yr for BT and 0.4 tons/yr for 24MoBT from tire particles. The annual fluxes of BT from scrap tires from Japan, Korea, Brazil, the European Union, the United States, and China were 99, 21, 36, 270, 328, and 120 tons/yr, respectively. The fluxes of 24MoBT from the same countries were 3.0, 0.5, 1.1, 8.4, 10.3, and 3.8 tons/ yr, respectively. These results indicated that tire-wear particles and scrap tires are the dominant sources of benzothiazoles in the environment. By comparison, Asia may be the major contributor to the global input of benzothiazoles from auto tires in the coming years. Overall, the six benzothiazoles under investigation appeared to be suitable tracers of pollutant inputs to surface runoff within the PRD aquatic system. In addition, 24MoBT seemed more appropriate than BT to trace tire rubber residues and therefore can be a good indicator of economic development and urbanization in a specific region.

Assessment of sampling designs to measure riverine fluxes from the Pearl River Delta, China to the South China Sea.

The Pearl River Delta (PRD), located in South China and adjacent to the South China Sea, is comprised of a complicated hydrological system; therefore, it was a great challenge to sample adequately to measure fluxes of organic and inorganic materials to the coastal ocean. In this study, several sampling designs, including five-point (the number of sampling points along the river cross-section and three samples collected at the upper, middle, and bottom parts at each vertical line), three-point (at the middle and two other profiles), one-point (at the middle profile), and single-point (upper, middle, or bottom sub-sampling point at the middle profile) methods, were assessed using total organic carbon (TOC) and suspended particulate matter (SPM) as the measurables. Statistical analysis showed that the three- and five-point designs were consistent with one another for TOC measurements (p > 0.05). The three- and one-point sampling methods also yielded similar TOC results (95% of the differences within 10%). Single-point sampling yielded considerably larger errors than the three- and one-point designs, relative to the results from the five-point design, but sampling at the middle sub-point from the middle profile of a river achieved a relatively smaller error than sampling at the upper or bottom sub-point. Comparison of the sampling frequencies of 12 times a year, four times a year, and twice a year indicated that the frequency of twice a year was sufficient to acquire representative TOC data, but larger sample size and higher sampling frequency were deemed necessary to characterize SPM.

Polycyclic aromatic hydrocarbons in riverine runoff of the Pearl River Delta (China): concentrations, fluxes, and fate.

On the basis of a monthly sampling effort from March 2005 to February 2006, the total concentrations of the sums of 27 and 15 polycyclic aromatic hydrocarbons (defined as sigma27PAHs and sigma15PAHs, respectively) in riverine runoff of the Pearl River Delta (PRD), China, and associated fluxes were determined. No clear temporal and spatial trends of PAH concentrations were found at all eight riverine runoff outlets where the samples were collected. The annual fluxes of sigma27PAHs and sigma15PAHs from the PRD to the coastal ocean were 60.2 and 33.9 metric tons, respectively. Assuming that riverine flux was positively related to the regional emission of PAHs, the annual riverine fluxes from five major rivers in China to the global oceans were estimated, which are quite significant relative to other major rivers of the world. On the basis of mass balance considerations, approximately 87% of sigma15PAHs inputting to the Pearl River Estuary and northern South China Sea was derived from riverine runoff from the PRD. In addition, approcimately 22.3 metric tons of sigma15PAHs annually outflow to open seas, which is equivalent to a concentration of 0.34 pg/L in the global oceans if the PAHs are evenly distributed in the upper 200 m of the water column. A comparison with the global background level of PAHs indicated that approximately 0.4% of PAHs in the open oceans may have been contributed by 1-year discharge from the PRD.