Large-scale fabrication of re duce d graphene oxide-sulfur composite films for flexible lithium-sulfur batteries

The rapid development of flexible electronic devices requires the design of flexible energy-storage devices. Lithium-sulfur(Li-S) batteries are attracting much interest due to their high energy density. Therefore, flexible Li-S batteries with high areal capacity are desired. Herein, we fabricated freestanding reduced graphene oxide-sulfur(RGO@S) composite films with a cross-linked structure using a blade coating technique, followed by a subsequent chemical reduction. The porous cross-linked structure endows the composite films with excellent electrochemical performance. The batteries based on RGO@S composite films could exhibit a high discharge capacity of 1381 m Ah/g at 0.1 C and excellent cycle stability. Furthermore, the freestanding composite film possesses excellent conductivity and high mechanical strength. Therefore, they can be used as the cathodes of flexible Li-S batteries. As a proof of concept, soft-packaged Li-S batteries were assembled and remained stable electrochemical performance under different bending states.

Iron and lead ion adsorption by microbial flocculants in synthetic wastewater and their related carbonate formation

Although microbial treatments of heavy metal ions in wastewater have been studied, the removal of these metals through incorporation into carbonate minerals has rarely been reported. To investigate the removal of Fe^3＋ and Pb^2＋, two representative metals in wastewater, through the precipitation of carbonate minerals by a microbial flocculant （MBF） produced by Bacillus mucilaginosus. MBF was added to synthetic wastewater containing different Fe^3＋ and Pb^2＋ concentrations, and the extent of flocculation was analyzed. CO2 was bubbled into the mixture of MBF and Fe^3＋/Pb^2＋ to initiate the reaction. The solid substrates were analyzed via X-ray diffraction, transmission electron microscopy and energy dispersive spectroscopy. The results showed that the removal efficiency decreased and the MBF adsorption capacity for metals increased with increasing heavy metal concentration. In the system containing MBF, metals （Fe^3＋ and Pb^2＋）, and CO2, the concentrated metals adsorbed onto the MBF combined with the dissolved CO2, resulting in oversaturation of metal carbonate minerals to form iron carbonate and lead carbonates. These results may be used in designing a method in which microbes can be utilized to combine CO2 with wastewater heavy metals to form carbonates, with the aim of mitigating environmental problems.

An anti-freezing and anti-drying multifunctional gel electrolyte for flexible aqueous zinc-ion batteries

Aqueous zinc-ion batteries(ZIBs)have attracted immense attention for flexible energy storage devices due to their high safety and low cost.However,conventional flexible aqueous ZIBs will undergo severe capacity loss at subzero temperature due to the inevitably freeze of electrolytes.In addition,under large bending or stretching strains,the encapsulation of devices would be damaged,which causes the evaporation of water in electrolytes and results in device failure.Herein,an anti-freezing and anti-drying gel electrolyte based on polyacrylamide(PAM)and glycerol(Gly)is developed.The strong hydrogen-bonding interactions between PAM or Gly and water molecules not only avoid the crystallization of the gel electrolyte at low temperatures,but also constrain the free water and restrict its evaporation.Therefore,such gel electrolyte displays a high ionic conductivity of 9.65×10^(−5)S cm^(−1)at−40℃.Furthermore,it can restrict the dehydration process when the electrolyte is exposed to ambient environment.The flexible ZIBs based on such gel electrolyte exhibit excellent electrochemical performance at−40℃and the devices without encapsulation retain 98%of their initial capacity in ambient condition after 30 days.This work provides a route to design anti-freezing and anti-drying gel electrolytes for aqueous energy storage devices.

Sulfur nanoparticles encapsulated in reduced graphene oxide nanotubes for flexible lithium-sulfur batteries

Rapid development of flexible electronic devices is promoting the design of flexible energy-storage devices. Lithium-sulfur （Li-S） batteries are considered as promising candidates for high energy density energy-storage devices. Therefore, flexible Li-S batteries are desired. In this study, we fabricated composite films of freestanding reduced graphene oxide nanotubes wrapped sulfur nanoparticles （RGONTs@S） by pressing RGONTs@S composite foams, which were synthesized by combining cold quenching with freeze-drying and a subsequent reduction process. These RGONTs@S composite films can serve as self-supporting cathodes for Li-S batteries without additional binders and conductive agents. Their interconnected tubular structure allows easy electron transport throughout the network and helps to confine the polysulfides produced during the charge/ discharge process. As a result, the RGONTs@S composite films exhibited a high initial specific capacity, remarkable cycling stabilit36 and excellent rate capability. More importantly, the RGONTs@S composite films can serve as electrodes in flexible Li-S batteries. As a proof of concept, soft-packaged Li-S batteries were assembled using these electrodes and they displayed stable electrochemical performance at different bending states.

Smart supercapacitors from materials to devices

The recent development in smart electronic devices has increased the demand for supercapacitors to integrate with other different functions.Recently,many research efforts have been made to fabricate smart components of supercapacitors and to construct them into novel device configurations.In this mini review,we summarize recent progress in smart supercapacitors with the functions of self-healing,shape memory,electrochromism,and photodetection,including the design of electrode materials,the optimization of the configuration,and working mechanism.Furthermore,the perspective and challenges for the development of smart supercapacitors are also discussed deeply.

Bimetal-organic frameworks derived Co/N-doped carbons for lithium-sulfur batteries

Lithium-sulfur(Li-S) batteries have received extensive attention due to their high theoretical specific energy density.However,the utilization of sulfur is seriously reduced by the shuttle effect of lithium polysulfides and the low conductivity of sulfur and lithium sulfide(Li2S).Herein,we introduced bimetalorganic frameworks(Co/Zn-ZIF) derived cobalt and nitrogen-doped carbons(Co/N-C) into Li-S batteries through host design and sepa rator modification.The Co/N-C in Li-S batteries effectively limits the shuttle effect through simultaneously serving as polysulfide traps and chemical catalyst.As a result,the Li-S batteries deliver a high reversible capacity of 1614.5 mAh/g and superior long-term cycling stability with a negligible capacity decay of only 0.04% per cycle after 1000 cycles.Furthermore,they have a high area capacity of 5.5 mAh/cm2.

Soil total organic carbon/total nitrogen ratio as a key driver deterministically shapes diazotrophic community assemblages during the succession of biological soil crusts

The diazotrophic community in biological soil crusts(biocrusts)is the key supplier of nitrogen in dryland.To date,there is still limited information on how biocrust development influences the succession of diazotrophic community,and what are the most important factors mediating diazotrophic communities during biocrust succession.Using the high throughput nifH amplicon sequencing,the diazotrophs in soils at different developmental stages of biocrust were comparatively studied.The results evidenced the decreases of TOC/TN ratio and pH value with biocrust development.Nostoc and Scytonema were the most dominant diazotrophic genera at all biocrust stages,while Azospirillum and Bradyrhizobium were abundant only in bare soil.Diazotrophic co-occurrence networks tended to be less complex and less connected with biocrust succession.The soil TOC/TN ratio was the most dominant factor mediating diazotrophic diversity,community composition and assembly processes,while diazotrophic-diversity and NO3–-N/NH4+-N ratio were positively correlated with the nitrogenase activity during biocrust succession.This study provided novel understandings of nitrogen fixation and succession patterns of diazotrophic community,by showing the effects of biocrust succession on diazotrophic diversity,community composition,community assembly and co-occurrence networks,and recognizing TOC/TN ratio as the most dominant factor mediating diazotrophs during biocrust succession.

Activated carbon felts with exfoliated graphene nanosheets for flexible all-solid-state supercapacitors

The recent development of portable electronics promotes the growing demand for flexible energy storage devices. Supercapacitors are promising candidates due to their high power density. Therefore, flexible supercapacitors are desired. Here, the porous activated carbon felts(ACFs) with exfoliated graphene nanosheets and rich oxygen-containing groups were fabricated by a facile thermal treatment strategy.Such ACFs can act as the flexible electrodes of all-solid-state supercapacitors directly without the use of binder and conductive materials. They exhibit excellent electrochemical properties, such as high specific areal capacitance, superior rate ability and long-term cycling stability. Moreover, the fabricated flexible all-solid-state supercapacitors based on ACFs deliver stable electrochemical performance under different bending states.

Mechanical analysis of flexible integrated energy storage devices under bending by the finite element method

Although a great deal of studies focus on the design of flexible energy storage devices(ESDs),their mechanical behaviors under bending states are still not sufficiently investigated,and the understanding of the corresponding structural conversion therefore still lags behind.Here,we systematically and thoroughly investigated the mechanical behaviors of flexible all-in-one ESDs under bending deformation by the finite element method.The influences of thicknesses,Young’s moduli and Poisson’s ratios of electrodes and electrolyte were taken into account.Visualized and quantified results including displacement,strain energy,von Mises stress,and tensile,compressive,and interfacial shear stress are demonstrated and analyzed.Based on these results,significant conclusions are drawn for the design of flexible integrated ESDs with robust mechanical properties.This work will provide guidance for the design of ESDs with high flexibility.