Novel silicon/silica/carbon (Si/SiO 2 /C) composite nanofibers were synthesized by electrospinning and subsequent heat-treatment of a mixture of Si nanoparticles, sol-gel tetraethyl orthosilicate solution, and aqueous polyvinyl alcohol solution. These Si/SiO 2 /C nanofiber composites were also coated with amorphous carbon by chemical vapor deposition (CVD) technique. The CVD carboncoated nanofiber composites formed freestanding, conductive nonwoven mats that were used directly as binder-free anodes in lithium-ion batteries. Results indicated that the SiO 2 component of the composite anodes provided sufficient buffer function to accommodate the volume expansion of the Si nanoparticles and the CVD amorphous carbon coating helped maintain the Si nanoparticles within the carbon nanofiber matrix during repetitive charging and discharging processes. Electrochemical performance tests showed that the capacity retention of CVD carbon-coated Si/SiO 2 /C nanofiber composites was greater than 91% and the corresponding coulombic efficiency was 97.4% at the 50th cycle. Electrochemical energy storage has been demonstrated as one of the most promising technologies for different applications such as grid storage, electric vehicles, and portable electronic devices.1-3 Because of their superior properties, including high energy density, good cycle life and good power performance, lithium-ion batteries are considered as the most preferred rechargeable battery technology in recent years.4-6 The development of high-capacity electrode materials for high-energy lithium-ion batteries is critically important for technological improvements on portable electronics and electric vehicles that use lithium-ion batteries as the power source. 7,8 Current commercial lithium-ion batteries use graphitic materials in the anode. However, graphitic anode materials cannot meet the capacity requirements of future portable electronics because of their low specific capacity of 372 mAh g −1 . 7,9,10 Lithium storage capacities of alloy-type anodes, such as silicon (Si), tin, germanium, etc., are much higher than that of commercially-used intercalation-type graphite anodes. Among all alloy-type anodes, Si has the highest theoretical capacity of 4200 mAh g −1 , making it the best candidate for next-generation high-energy lithium-ion batteries.11-13 However, the insertion of lithium ions into Si during cycling induces large volumetric change (up to 400%), which causes intense pulverization of active Si material, loss of electrical contact between Si and carbon conductor, and unstable solid electrolyte interphase (SEI) formation on the Si surface.14-16 These drawbacks bring together the performance degradation of active Si material during repetitive lithiation and de-lithiation processes. 17,18 To eliminate the aforementioned drawbacks, Si-based composite anodes have been widely investigated. Among them, Si/carbon (Si/C) composites have drawn great attention, which can potentially combine the advantageous properties of Si (high capacity) and C (excellent electr...
In the present study, a novel, wearable textile based microfluidic device was developed that provides a non-invasive, rapid, semi-quantitative detection of the lactate level in simulated sweat solution. The potential application was envisioned to be a biosensor that can monitor an athlete’s physical status during exercise. A photolithography technique was used for the fabrication of hydrophilic micro channels and reservoirs surrounded by hydrophobic barriers made from SU-8 negative photoresist. The reservoirs were functionalized by co-immobilization of lactate oxidase (LOX) and horseradish peroxidase (POX) enzymes. LOX uses L-(+)-Lactic acid as substrate and produces H2O2 which is a POX substrate. Then, POX oxidases H2O2 in the presence of 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) diammonium salt (ABTS) and results in color formation. The studies showed that excess amount of analyte presence resulted in analyte inhibition. It was also shown that analyte pH and temperature were effective on the color formation. For effective results, analyte pH and temperature should be ≥5℃ and 25–30℃, respectively. Lower pH and higher temperature values resulted in a decrease in the enzyme activity. The textile based biosensor system could make a semi-quantitative visual detection to differentiate between the normal (<5 mM) and high (≥5 mM) lactate level: while a high lactate level led to a denser purple color formation, normal levels led to a light purple formation and a green color started to be observed.
Polymeric coating on the separator with effective polysulfides diffusion inhibition can provide intimate contact between intermediate polysulfides and conductive layer of separator for high-energy lithium-sulfur (Li-S) batteries. Herein, polyacrylonitrile-poly (1,5-diaminoanthraquinone) (PAN/PDAAQ) and PAN-potassium functionalized graphene (PAN/K-FGF) nanofibers are synthesized via electrospinning method and act as effective separators for Li-S batteries to minimize polysulfides diffusion toward the anode. PAN/K-FGF coated separator shows capacity retention of 768 mAh g −1 after 100 cycles at 1C. The capacity maintains at 419 mAh g −1 after 500 cycles. PAN/PDAAQ nanofibers are coated on glass fiber separator functions as physical and chemical barrier for polysulfides diffusion. Therefore, the cell with PAN/PDAAQ coating on the separator demonstrates capacity retention of 881 mAh g −1 after 100 cycles at 1C and small capacity decay rate of 0.11% per cycle resulted in 800 cycles at 1C. PAN/PDAAQ could define as an ideal separator material for Li-S batteries.
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