Pristine Cell Research Articles

Study of LiNi0.6Co0.2Mn0.2O2 Coated with Li2ZrO3 Nanolayers in All-Solid-State Lithium Ion Batteries

The Li2ZrO3 nanolayer was coated over LiNi0.6Co0.2Mn0.2O2 cathode material (NCM) to produce all-solid-state lithium ion batteries and their enhanced electrochemical properties were determined. To relieve interfacial resistance resulting from insufficient contact, a Li2ZrO3 nanolayer is a suitable cathode coating agent because it can block corrosive species and decrease contact loss, along with elimination of the space-charge layer. All-solid-state cells using Li2ZrO3-coated NCM material showed higher capacity than pristine NCM. X-ray diffraction patterns showed the same peak separations and lattice parameters as pristine material. Scanning electron microscopy and transmission electron microscopy images obtained with electron dispersive spectroscopy mapping confirmed homogeneous coating with a uniformly thick Li2ZrO3 layer of around 5 nm. X-ray photoelectron spectroscopy revealed that the surface of NCM had two different O1s peaks, with a Zr–O peak, and Ni, Co, Mn, and Zr peaks. Electrochemical studies on pristine and Li2ZrO3-coated NCM materials were conducted using electrochemical impedance spectroscopy with galvanostatic cycle performances by constructing an all-solid-state cell. The impedance spectra showed relieved interfacial resistance with low polarization as coating agent was added. Notably, the 4 wt.% Li2ZrO3-coated NCM exhibited capacity retention of 81% at a current density of 0.12 mA/cm2 after 30 cycles, while that of the pristine cell hadunstable cycle performance and a low capacity retention of 69 percent. Thus, the Li2ZrO3-coated NCM material exhibited potential for all-solid-state batteries requiring high power or stable application.

Fast and Controllable Prelithiation of Hard Carbon Anodes for Lithium-Ion Batteries.

Hard carbon has been extensively investigated as anode materials for high-energy lithium-ion batteries owing to its high capacity, long cycle life, good rate capability, and low cost of production. However, it suffers from a large irreversible capacity and thus low initial coulombic efficiency (ICE), which hinders its commercial use. Here, we developed a fast and controllable prelithiation method based on a chemical reaction using a lithium-containing reagent (1 M lithium biphenylide dissolved in tetrahydrofuran). The prelithiation extent can be easily controlled by tuning the reaction time. An SEI layer is formed during chemical prelithiation, and the ICE of prelithiated hard carbon in half-cell format can be increased to ∼106% in 30 s. When matched with a LiNi1/3Co1/3Mn1/3O2 cathode, the full cell with the prelithiated hard carbon anode exhibits a much improved ICE (90.2 vs 75%) and cycling performance than those of the pristine full cell. This facile prelithiation method is proved to be a practical solution for the commercial application of hard carbon materials.

Application of porous biomass carbon materials in vanadium redox flow battery

Porous nano biomass carbon was synthesized by one-step method using scaphium scaphigerum as carbon source and was employed as negative catalyst for vanadium redox flow battery. Potassium ferrate was used to realize synchronous etching, introducing oxygen-containing groups and graphitization of scaphium scaphigerum to obtain porous, oxygen-rich, high-graphization carbon materials (SS-K/Fe). Compared with traditional two-step method, one-step method has advantages of low-time requirement, high efficiency and no pollution. The prepared SS-K/Fe sample has abundant microporous structure, high degree of graphitization and many oxygen-containing groups. The electrochemical test results show that the prepared carbon-based materials exhibit superior electrocatalytic capability for V2+/V3+ redox reaction. The electrode process can be accelerated from three steps including ion diffusion, electrochemical reaction and electron transfer processes, which are due to the enhancement of wetting performance and electrical conductivity, and an increase of effective catalytic area. Compared with pristine cell, the SS-K/Fe modified cell can improve the energy efficiency by 6.2% at the current density of 50 mA cm−2. This method is expected to realize low cost, green and renewable porous carbon materials for future energy storage systems.

Ultra-Tiny Sb-Doped SnO2 Nanoparticles as a Superior Catalyst for Vanadium Redox Reactions

Herein, ultra-tiny Sb-doped SnO2 nanoparticles were prepared using co-precipitation as superior catalyst for vanadium redox reactions. Different concentrations of Sb in range of 2%, 5%, and 10% were doped in lattice structure of SnO2. The size of nanoparticles decreased, as doping concentration increased. Sb doping also decreased the crystallinity of SnO2, producing structural defects. It is notable that Sb-doped SnO2 showed greatly improved conductivity. However, excessive Sb doping reduced conductivity of SnO2. Sb-doped SnO2 exhibited better electrocatalysis for V3+/V2+ and VO2+/VO2+ reactions. It benefits from Sb-doped SnO2 with smaller size, more structural defects, and higher conductivity, increasing active sites and electron transfer rate for vanadium redox reactions. SnO2/Sb-5% showed the best electrocatalysis. SnO2/Sb-5% was used to modify graphite felt, such that it had better electrochemical performance for vanadium redox reactions. A cell using SnO2/Sb-5% improved electrolyte usage and discharge capacity retention at 50 mA cm−2 for 50 cycles. SnO2/Sb-5% also efficiently reduced electrochemical polarization of cell. The cell using SnO2/Sb-5% had higher energy efficiency compared to pristine cell. At 150 mA cm−2, the energy efficiency of modified cell increased by 9.2% compared with pristine cell (57.3%). Therefore, Sb-doped SnO2 can be used as a promising catalyst for vanadium redox reactions.

Novel 2D porous carbon nanosheet derived from biomass: Ultrahigh porosity and excellent performances toward V2+/V3+ redox reaction for vanadium redox flow battery

In this paper, biomass-derived carbon-based nanosheet from a kind of domestic waste (fish scales) has been successfully prepared as catalysts with high electrocatalytic activity for V2+/V3+ couple of vanadium redox flow battery (VRFB) using hydrothermal, lyophilization, and carbonization treatments. KOH is employed as template and activator, which results in nanosheet structure, ultrahigh porosity, and introduction of oxygen-containing groups. The obtained catalyst (FSC-K) exhibits the advantages of large surface area, many active sites and excellent wettability. FSC-K can effectively reduce electrochemical polarization of electrode reaction and accelerate mass transfer of active species. The cell using FSC-K demonstrates a high energy storage efficiency. Compared with pristine cell, the discharge capacity of FSC-K modified cell is 67.2 mA h at 150 mA cm−2, increased by 18 mA h, and the corresponding energy efficiency reaches 63.8%, enhanced by 7.9%. The capacity retention of FSC-K modified cell keeps 83.1% after 50 cycles at 75 mA cm−2, 16.7% larger than that for pristine cell. This work reveals that the electrocatalyst for V2+/V3+ couple obtained from biomass is significant for improving the comprehensive energy storage performance of VRFB.

Interfacial Engineering through Chloride-Functionalized Self-Assembled Monolayers for High-Performance Perovskite Solar Cells.

The family of organic-inorganic hybrid perovskite (OIHPs) materials is one of the most promising for very high-efficiency photovoltaic solar cell application. In the present work, the effect of a series of self-assembled monolayers placed at the TiO2-perovskite junction, on the functioning of triple cation perovskite solar cells has been investigated. We show that employing 4-chlorobenzoic acid leads to the marked boosting of the solar cell performances. The starting pristine cell had a power conversion efficiency (PCE) of 20.3% and the chemical engineering permitted to reach a PCE up to 21.35%. Our experimental study completed by density functional theory calculations and modeling show that this progress is due to the reduction of interfacial states, to the improvement of the quality of the OIHP material and to the structural continuity between TiO2 and the OIHP. Especially, we demonstrate that the interfacial chemical interactions are important to consider in the design of highly efficient devices.

Caloric restriction maintains stem cells through niche and regulates stem cell aging.

The functional loss of adult stem cells is a major cause of aging and age-related diseases. Changes in the stem cell niche, increased energy metabolic rate, and accumulation of cell damage severely affect the function and regenerative capacity of stem cells. Reducing the cellular damage and maintaining a pristine stem cell niche by regulating the energy metabolic pathways could be ideal for the proper functioning of stem cells and tissue homeostasis. Numerous studies point out that caloric restriction (CR) has beneficiary effects on stem cell maintenance and tissue regeneration. Recent researches indicate the preventive nature of calorie restriction in stem cells by modulating the stem cell niche through the reduction of energy metabolism and eventually decrease stem cell damage. In this review, we have focused on the general stimuli of stem cell aging, particularly the energy metabolism as an intrinsic influence and stem cell niche as an extrinsic influence in different adult stem cells. Further, we discussed the mechanism behind CR in different adult stem cells and their niche. Finally, we conclude on how CR can enhance the stem cell function and tissue homeostasis through the stem cells niche.

(Invited) A Leaf-Inspired Photon Management Scheme for Graphene/Silicon Solar Cells

Graphene/silicon (Gr/Si) Schottky junction solar cells have attracted much attention due to the ease and low cost of fabrication, along with the lucrative properties of high electron mobility, transparency and mechanical flexibility of graphene as a transparent conducting electrode.1 Utilizing its inherent mechanical flexibility, graphene can be integrated with thin flexible crystalline Si substrates opening up a new regime of applications in flexible and wearable electronics. Reducing Si absorber thickness below 50 um offers advantages of reduced material cost, along with mechanical flexibility and light weight.2 But Si at such thicknesses suffers from low photon absorption in the solar spectrum. To compensate for the low light absorption in such thin substrates, light management schemes become essential. Light trapping in Gr/Si solar cells is enabled by engineering the Si surface to form nanopillars, nanowires etc., which decreases the reflection loss and allows more light to couple in to the Si substrate. The structured Si absorber increases surface area and surface recombination, which is detrimental to the solar cell efficiency. Thus, it is imperative to use a light-trapping scheme devoid of Si structuring to enhance the photo-conversion efficiency. We present an all-dielectric light-trapping scheme on planar Gr/Si Schottky junction solar cells with the use of bottom layer of titania spheres and top layer of silica spheres.3 An optimal Si thickness coupled with an optimized light-trapping scheme leads to efficient electron-photon harvesting. The photo-conversion efficiency of a 20 um thick nanosphere-decorated Gr/Si solar cell improves to 9%, which is 1.3x higher than the pristine cell’s PCE of 7%. FDTD simulations are performed for optimizing the diameter of nanoparticles in each of the layers. The ratio of size of nanoparticles in the top to bottom layer plays a crucial role in advanced light management. An optimized structure of silica spheres, having diameter larger than that of titania spheres, suppresses reflection over wide angles of incidence and increases absorption in active Si layer over AM1.5G solar spectrum. The non-absorbing dielectric spheres can be easily realized by the well-known Stober technique. Additionally, the photovoltaic characteristic of the laminated solar cell shows negligible change after several bending cycles having bend radius ranging from 5 mm to 10 mm. After continuous bending and straightening, the ultra-thin solar cell can retain its performance, revealing the excellent stability and flexibility of the device. Such simple, low-cost light trapping schemes are universal in nature, devoid of recombination losses and are potentially viable for any solar cell technology. References 1 B Li, et al. Adv. Mater. 22, 2743 (2010). 2 K E Petersen, Proc. IEEE 70, 420 (1982). 3 S. Das, et al. Nano Energy 58, 47 (2019).

Electrocatalytic activity of MnO2 nanosheet array-decorated carbon paper as superior negative electrode for vanadium redox flow batteries

An in-situ and controllable redox deposition method has been applied to prepare binder-free MnO2 nanosheet array-decorated carbon paper as negative electrode for vanadium redox flow batteries (VRFB). Electrochemical performance of electrode depends on amount and uniform distribution of MnO2 on carbon paper, which were controlled by solution pH, KMnO4 concentration, and deposition time. Modified carbon paper (CPA-05-30) with a uniform MnO2 nanosheet coating layer was obtained in 0.05 M KMnO4 + 0.5 M H2SO4 solution for 30 min. CPA-05-30 presents the most excellent electrocatalytic performance for V3+/V2+ redox reaction. On CPA-05-30, charge transfer and diffusion processes for V3+/V2+ redox reaction are accelerated as a result of MnO2 nanosheet with high catalytic activity and excellent hydrophilcity. Therefore, loading MnO2 on carbon paper improves electrochemical activity V3+/V2+ redox reaction. Moreover, in charge-discharge test, the cell using CPA-05-30 as negative electrode shows higher discharge capacity and better capacity retention at 50 mA cm−2 for 50 cycles in comparison with pristine cell. It indicates that MnO2 nanosheet can efficiently increase electrolyte utilization. At 100 mA cm−2, energy efficiency of the cell using CPA-05-30 is 66.4%, which is 6.0% higher than that of pristine cell. MnO2 nanosheet decorated carbon paper shows excellent electrochemical properties for energy storage application, which evidences its potential application in VRFB.

MAPbI3 Incorporated with Carboxyl Group Chelated Titania for Planar Perovskite Solar Cells in Low-Temperature Process.

Low-temperature, solution-processed, highly efficient hybrid organic/inorganic perovskite planar heterojunction solar cells were fabricated by incorporating reactive crystalline titania (h-TAc) into MAPbI3 layers. The h-TAc was prepared by the sol-gel reaction at low temperature followed by solvothermal treatment. The photoelectrical properties of the solar cells with h-TAc were analyzed. The incorporation with 0.85-wt% h-TAc showed the highest power conversion efficiency (PCE, 15.9%), increasing 69% compared to the pristine cell. The enhancement arose from large-grained microstructures, leading to a low rate of charge recombination. The carboxyl groups chelated on the surface of h-TAc revealed a strong attraction to lead ions, which are significantly helpful to MAPbI3 crystal growth.

ZrO2 nanoparticle embedded carbon nanofibers by electrospinning technique as advanced negative electrode materials for vanadium redox flow battery

ZrO2 nanoparticle decorated carbon nanofibers (ZrO2/CNF) were explored by electrospinning technique with ZrOCl2·8H2O and polyacrilonitrile (PAN) as precursors, and were considered as negative electrode for vanadium redox flow battery (VRFB). It is found that the ZrO2 nanoparticle uniformly embedded in the CNF not only increases the disorder of CNF, but also improves the catalytic activity of CNF, further resulting in good electrochemical activity. Specially, the sample with proper content of ZrO2 (CNFZrO2-18) shows superior electrochemical activity for the negative couple for VRFB. Furthermore, the charge-discharge tests verify that CNFZrO2-18 can enhance performance of cell. At 100 mA cm−2, the discharge capacity and energy efficiency of the cell with CNFZrO2-18 arrive at 91.5 mA h and 73.3%, 8.7% and 8.3% more than those of pristine cell, respectively. After charging and discharging for 50 cycles at 80 mA cm−2, the cell exhibits outstanding stability with initial discharge capacity retention of 95.0%. The high electrochemical performance of ZrO2/CNF mainly comes from the good electrocatalytic properties of ZrO2 and in situ decoration for CNF by electrospinning technique.

Amino acid salt-driven planar hybrid perovskite solar cells with enhanced humidity stability

While hybrid perovskites have great potential as light-absorbing materials, they suffer from moisture-induced instability. Herein, we added the amino acid iodide salt-based molecular crosslinker p-aminobenzoic acid (PABA∙HI) to a perovskite precursor solution to enhance the humidity stability. The rigid molecular structure of PABA∙HI played an important role in determining the crystal orientation, trap density, and photovoltaic performance of the perovskite solar cells (PVSCs). PABA∙HI can effectively interact with the Pb-I framework via hydrogen bonds, enhancing the crosslinking efficiency compared with freely rotating flexible molecular crosslinkers. Kelvin probe force microscopy in conjunction with Raman analysis confirmed the presence of PABA∙HI at the grain boundaries; thus, stable quasi-two-dimensional perovskite existed along the grain boundaries, passivating the grain boundaries and improving the moisture stability. The PABA∙HI-added PVSCs having a power-conversion efficiency (PCE) of 17.4% retained 91% of their initial PCE when stored for 312 h at a relative humidity of 75% at 25 °C, whereas a pristine cell with a PCE of 16.4% only retained 37% of its initial value. Our findings clearly indicate that the amino acid salt as a rigid molecular crosslinker improved not only the photovoltaic performance but also the stability against moisture.

(Keynote) Developing Safe Sodium-Ion Battery Technology for Stationary Storage Applications

Sodium-ion batteries (NIBs) have been emerging as one of the most promising candidates for stationary storage applications such as telecommunication towers, micro-grids etc., mainly because Na is one of the most abundant elements on the Earth’s crust.1,2 NIB operating at ambient temperature is expected to be durable, safe and inexpensive. Regardless of the relatively lower energy density of NIBs, they can be effectively employed for stationary applications, where the weight and footprint requirements are not severe.3 However, identifying appropriate anode, cathode, electrolyte, as well as the combination of these three components have always been challenging to develop robust NIB.4,5 In this talk, we will present investigation of the storage performance, thermal stability6 and SEI layers of four notable anodes, viz., hard carbon, graphite, TiO2 and Na2Ti3O7 7 using ether-based non-flammable electrolyte: 1M NaBF4 in tetraglyme and compare with the results obtained with commonly used carbonate-based electrolyte: 1M NaClO4 in EC:PC. We report better storage performance with higher first cycle coulombic efficiency of above anodes tested against metallic Na using ether-based electrolyte compared to carbonate-based electrolytes. Thermal studies, ATR-FTIR and impedance spectroscopy recorded at fully sodiated and fully desodiated states of these four anodes further confirm that a more stabilized SEI is formed by ether-based electrolyte. Above studies further suggests that the ether-based electrolyte is much safer for NIBs compared to carbonate-based electrolytes such as 1M NaClO4 in EC:PC. For the cathode, Na3V2(PO4)3 (NVP) was chosen due to a high redox potential of 3.37 V vs. Na/Na+. By employing a highly scalable synthesis procedure8 two types of NVP are prepared: pristine NVP and modified NVP by aliovalent doping. Sodium storage performances (specific capacity, rate performance and cycle life) of modified NVP outperforms the pristine NVP. The observed superior storage performance in modified NVP is attributed to enhanced activity of vanadium (V3+ to V4+ and V4+ to V5+)9 as confirmed by XPS studies and higher chemical diffusion coefficient. We also present storage performance, XPS studies, measurement of heat loss and internal resistance of 18650-type non-flammable NIB cells made using NVP (pristine- and modified- NVP) vs. HC with 1M NaBF4 in tetraglyme as electrolyte. The 18650 cell of pristine NVP vs. HC shows low energy density (47 Wh.kg− 1), moderate rate performance and poor cyclability. On the other hand, the 18650 cell of modified NVP vs. HC exhibits improved energy density (60 Wh.kg− 1) and enhanced rate and cyclic performances. Further, we report lesser heat generation in modified NVP vs. HC cell compared to pristine NVP vs. HC cell. Corresponding internal resistance of these 18650 cells measured at different depths of discharge (DoD) and temperature intervals reveal improved chemical diffusion coefficient, and substantial reduction in charge transfer resistance of the modified NVP vs. HC cell caused by aliovalent doping of NVP. The work presented here for introducing a safe NIB technology for stationary storage application is an illustration of R&D with a long value chain: scale-up production of cathode materials, commercial type cell fabrication, investigation of storage performance, estimation of heat generation, quantification of heat loss in terms of internal resistance. This translational R&D at NUS thus bridges academics and industries.

Coral-like perovskite nanostructures for enhanced light-harvesting and accelerated charge extraction in perovskite solar cells

A novel coral-like perovskite nanostructured layer was grown on a compact perovskite foundation layer by the facile surface modification with dimethylformamide/isopropanol (DMF/IPA) as co-solvent. Surface morphological characterizations with SEM and XRD analyses revealed a growing mechanism of the new morphology, which was composed of the perovskite decomposition and recrystallization, excessive-PbI2 extraction, and sequential formation of coral-like nanostructured perovskite layer. The coral-like perovskite nanostructures resulted in significant light scattering, enhancing the light-harvesting efficiency, and thus augmenting the photocurrent density. Moreover, the geometric configuration of the perovksite solar cells was changed from planar to bulk heterojunction, which results in the acceleration of charge separation and extraction due to the high surface area at the interface between the obtained perovskite and hole-transport layers. The optimal perovskite solar cell exhibited an impressive power conversion efficiency (PCE) of 19.47%, as compared to that of the pristine cell (17.19%).

Enhanced electro-optical properties in titanium silicon oxide nanoparticle doped nematic liquid crystal system

We demonstrated the doping effects of titanium silicon oxide (TiSiO4) nanoparticles (NPs) on the characteristics of liquid crystal (LC) system. Simply by adding TiSiO4 to the LC medium, the electro-optical (EO) characteristics of LC cells can be improved. The EO characteristics were improved by increasing the doping concentration. However, it was confirmed that if the doping concentration was too high, the EO characteristics would be deteriorated due to interference with the LC behavior. In addition, TiSiO4 NPs dispersed in the LC mixture captured impurity ions and exhibited hysteresis-free voltage-transmittance (V–T) characteristics. The TiSiO4 NPs doped LC cells also showed higher thermal stability than a pristine LC cell. These results suggest that TiSiO4 NPs doped into an LC system could benefit not only the display industry but also other industrial fields requiring high-performance EO characteristics.

Preparation of Carbon Nanosheet by Molten Salt Route and Its Application in Catalyzing VO2+/VO2+ Redox Reaction

Carbon nanosheets were synthesized by facile molten salt route using glucose as carbon source, and employed as positive electrocatalyst for vanadium redox flow battery (VRFB). Two kinds of carbon nanosheets were obtained at glucose/salt mass ratio of 1:10 (CNS-10) and 1:100 (CNS-100), respectively. Compared with CNS-10, CNS-100 with graphene-like structure has crumpled shape and large surface area. Electrochemical measurements verify that as-prepared carbon nanosheets exhibit good electrocatalytic properties to VO2+/VO2+ redox reaction, and CNS-100 demonstrates the best performance. Excellent electrocatalytic performance of CNS-100 mainly comes from large specific area, crumpled shape and enhanced carbonization degree. These features favor the increase of reaction place, active site, and electrical conductivity, respectively, further accelerating the electrochemical kinetic process of VO2+/VO2+ redox reaction. The cell using CNS-100 as positive catalyst displays superior electrochemical performance. Higher discharge capacity and capacity retention can be achieved in the cell using CNS-100. Moreover, utilization of CNS-100 can lead to energy efficiency increase of 5.3% compared with pristine cell at 50 mA cm−2. Low-cost, high-performance, and graphene-like nanosheet obtained by molten salt route offers a broad application prospect for VRFB.

Biomass-Derived Porous Graphitic Carbon with Excellent Electrocatalytic Performances for Vanadium Redox Reactions

Biomass-derived carbon materials have attracted more and more attention in energy storage field owing to their diversity, low price and environmental friendliness. In this paper, porous graphitic carbon derived from biomass was obtained as bifunctional electrocatalyst for vanadium redox reaction by hydrothermal treatment for scaphium scaphigerum and following FeCl3 treatment. FeCl3 activated electrocatalyst (BDC-Fe) is characterized by nanoscale, large specific surface area (615.6 m2 g−1), and high graphitization degree. Compared with hydrothermal carbon (BDC-H) and hydrothermal/carbonized carbon (BDC-C), BDC-Fe demonstrates superior electrocatalytic performance for V2+/V3+ and VO2+/VO2+ redox reactions. The introduction of BDC-Fe can accelerate the charge transfer and mass transfer processes for electrode reaction, which can effectively reduce the electrochemical polarization of electrode reaction. The energy storage performance was evaluated by charge-discharge tests. The cell using BDC-Fe shows excellent electrochemical performance. At 100 mA cm−2, the discharge capacity and energy efficiency of the cell using BDC-Fe are 81.82 mA h and 67.5%, respectively, 21.8 mA h and 4.5% higher than those of pristine cell. Our study reveals that low-cost, porous, and graphitic carbon from biomass by FeCl3 activation as bifunctional electrocatalyst demonstrates a promising prospect in vanadium redox flow battery.

Rapid surface kinetics enhancement via flash light sintering for low-temperature solid oxide fuel cells

“Samaria-doped ceria (SDC), with exceptional electrochemical catalyzing characteristics, is a promising material for the operating temperature of solid oxide fuel cells (SOFC). Despite its extraordinary electrochemical reactivity, its chemical unstable behavior in terms of reduction phenomenon has made its application to SOFC electrolyte challenging. In regard to the defect chemistry, however, this instability can enhance the oxygen incorporation rate at the surface of the electrolyte. Here, we report a rapid surface treating method for SDC thin films via flash light sintering, which revealed an outstanding crystallinity development with nano-grains and increment of mobile dopant cation-induced oxygen vacancies within few milliseconds. We demonstrated that the flash light sintering-induced rapid development of crystallinity and reduction of ceria increases oxygen reducing surface kinetics, leading to an improvement in the oxygen incorporation rate of the cathodic reaction in SOFCs. The performance of SOFC sintered by flash light indicated more than two-folds enhancement comparing the pristine cell.”

Electrospun nitrogen-doped carbon nanofiber as negative electrode for vanadium redox flow battery

Carbon nanofiber (CNF) was developed via electrospinning technique with polyacrylonitrile as precursor. Nitrogen-doped carbon nanofiber (NCNF), synthesized by liquid phase dispersion and carbonization processes with urea at 800–1000 °C, were investigated as negative electrode for vanadium redox flow battery (VRFB). Morphology and structure of CNF and NCNF were systematically investigated by SEM, Raman, XPS, etc. The morphology of CNF is not changed by nitrogen doping. However, nitrogen doping can lead to marked enhancement of surface defect and hydrophilicity. Electrochemical test results show that NCNF treated at 900 °C (CNF-N9) exhibits the best electrochemical performance. The excellent energy storage performance of the cell is obtained by using CNF-N9. Discharge capacity of cell for CNF-N9 arrives at 98.0 mA h, 30.0 mA h higher than that of the pristine cell at 90 mA cm−2. And energy efficiency of the cell using CNF-N9 increases by 6.3% compared with pristine cell. Outstanding performances of CNF-N9 come from the increase of surface defect and the improvement of hydrophilicity and conductivity resulting from nitrogen doping, further promoting the electron and mass transfer between vanadium ion and electrode.

Metal Oxide Interlayer for Long-Lived Lithium-Selenium Batteries.

A lithium-selenium (Li-Se)-alkali activated carbon hybrid cell with a tungsten oxide interlayer is implemented for the first time. The Se hybrid at a Se loading of 70 % in the full Li-Se cell delivers a large reversible capacity of 625 mA h gSe -1 , in comparison with 505.8 mA h gSe -1 achieved for the pristine Se cell. This clearly shows the advantage of the carbon in improving the capacity of the Li-Se cell. A tungsten oxide interlayer is drop-cast over the battery separator to further circumvent the issues of polyselenide dissolution and shuttle, which cause severe capacity fading. The oxide layer conducts Li ions, as evidenced from the Li-ion diffusion coefficient of 4.2×10-9 cm2 s-1 , and simultaneously blocks the polyselenide crossover, as it is impermeable to polyselenides, thereby reducing the capacity fading with cycling. The outcome of this unique approach is reflected in the reversible capacities of 808 and 510 mA h gSe -1 achieved for the Li-oxide@separator/Se-alkali activated carbon cell before and after 100 cycles, respectively, thus demonstrating that carbon and oxide can efficiently restrict the capacity fading and improve the performances of Li-Se cells.