Enhanced capacitance and rate capability of graphene/polypyrrole composite as electrode material for supercapacitors

Graphene and polypyrrole composite (PPy/GNS) is synthesized via in situ polymerization of pyrrole monomer in the presence of graphene under acid conditions. The structure and morphology of the composite are characterized by X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectrometer (FTIR), X-rays photoelectron spectroscopy (XPS) and transmission electron microscope (TEM). It is found that a uniform composite is formed with polypyrrole being homogeneously surrounded by graphene nanosheets (GNS). The composite is a promising candidate for supercapacitors to have higher specific capacitance, better rate capability and cycling stability than those of pure polypyrrole. The specific capacitance of PPy/GNS composite based on the three-electrode cell configuration is as high as 482 F g⁻¹ at a current density of 0.5 A g⁻¹. After 1000 cycles, the attenuation of the specific capacitance is less than 5%, indicating that composite has excellent cycling performance.     

Sulphur-reduced graphene oxide composite with improved electrochemical performance for supercapacitor applications

In this research, carbon nanorods/fibers materials were successfully synthesized from sulphur-reduced graphene oxide (RGO-S) composite by using an improved Hummers' method. Morphological, structural, compositional and textural characterization of the composite material were obtained via scanning electron microscope (SEM), energy dispersive x-ray spectroscopy (EDX), transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS), respectively. The electrochemical performance of the composite sample as a promising supercapacitor electrode revealed a peak specific capacity of 113.8 mAh g⁻¹ at 0.5 A g⁻¹ estimated via GCD curves in 6 M KOH aqueous electrolyte. The half-cell could retain a columbic efficiency of about 98.7% with a corresponding energy efficiency of about 98.5% over 2000 constant charge/discharge cycle at a specific current of 5 A g⁻¹. Remarkably, an assembled hybrid device with carbonized iron cations (C-FP) and the RGO-S composite delivered high energy and power densities of 35.2 Wh kg⁻¹ and 375 W kg⁻¹ at 0.5 A g⁻¹ within a 1.5 V operating potential, respectively. A good cycling stability performance with an energy efficiency of 99% was observed for the device for up to 10,000 cycling at a specific current of 3 A g⁻¹.     

Diphenyloctyl phosphate as a flame-retardant additive in electrolyte for Li-ion batteries

The use of diphenyloctyl phosphate (DPOF) as a flame-retardant additive in liquid electrolyte for Li-ion batteries is investigated. Mesocarbon microbeads (MCMB) and LiCoO₂ are used as the anode and cathode materials, respectively. Cyclic voltammetry (CV), differential scanning calorimetry (DSC), electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM) are used for the analyses. The cell with DPOF shows better electrochemical cell performance than that without DPOF in initial charge/discharge and rate performance tests. In cycling tests, a cell with DPOF-containing electrolyte exhibited better discharge capacity and capacity retention than that of the DPOF-free electrolyte after cycling. These results confirm the viability of using DPOF as a flame-retardant additive for improving the cell performance and thermal stability of electrolytes for Li-ion batteries.     

Effect of FePO4 coating on electrochemical and safety performance of LiCoO2 as cathode material for Li-ion batteries

LiCoO₂ was surface modified by a coprecipitation method followed by a high-temperature treatment in air. FePO₄-coated LiCoO₂ was characterized with various techniques such as X-ray diffraction (XRD), auger electron spectroscopy (AES), field emission scanning electron microscope (FE-SEM), energy dispersive spectroscopy (EDS), transmission electron microscope (TEM), electrochemical impedance spectroscopy (EIS), 3 C overcharge and hot-box safety experiments. For the 14500R-type cell, under a high charge cutoff voltage of 4.3 and 4.4 V, 3 wt.% FePO₄-coated LiCoO₂ exhibits good electrochemical properties with initial discharge specific capacities of 146 and 155 mAh g⁻¹ and capacity retention ratios of 88.7 and 82.5% after 400 cycles, respectively. Moreover, the anti-overcharge and thermal safety performance of LiCoO₂ is greatly enhanced. These improvements are attributed to the FePO₄ coating layer that hinders interaction between LiCoO₂ and electrolyte and stabilizes the structure of LiCoO₂. The FePO₄-coated LiCoO₂ could be a high performance cathode material for lithium-ion battery.     

Supercapacitive behaviors of activated mesocarbon microbeads coated with polyaniline

The polyaniline/activated mesocarbon microbeads (PANI/ACMB) composites are prepared by in situ chemical oxidation polymerization. Fourier infrared spectroscopy (FTIR), scanning electron microscope (SEM) and transmission electron microscope (TEM) have been utilized to characterize the structure and morphology of PANI/ACMB composites. It has been found that PANI is uniformly deposited on the surface of the ACMB to form the leechee-like morphology. The supercapacitive behaviors of the PANI/ACMB composites are investigated with cyclic voltammetry (CV), galvanostatic charge/discharge and cycle life measurements. The results obtained from cyclic voltammograms show that the composites have a maximum specific capacitance of 433.75 F g⁻¹. Moreover, the electrochemical performance of the coin supercapacitor used PANI/ACMB composites as electrode active material represents both high specific capacitance and excellent cycle stability, indicating that the PANI/ACMB composites will be a kind of potential electrode active materials with excellent specific capacitance and enhanced cycle life for application in high performance supercapacitors.     

LiNi1/3Mn1/3Co1/3O2 with morphology optimized for novel concept of 3D Li accumulator

An array of LiNi_1/3Mn_1/3Co_1/3O₂ (NMC 111) samples with a hollow-sphere morphology enabling the use of binder-free, millimeter-thick electrodes in a battery are prepared by a combination of ball milling, hydrothermal treatment and calcination. Materials are studied by powder X-ray diffraction, nitrogen adsorption measurements, X-ray fluorescence analysis, and scanning electron microscopy. Their electrochemical performance for Li⁺ extraction/insertion is tested by cyclic voltammetry and galvanostatic chronopotentiometry on thin-film electrodes. Optimized materials, prepared by mechanical and thermal treatment with surface areas of 7 to 10 m² g⁻¹, provide charge capacity values of 141 to 156 mAh g⁻¹. The concentration of the crystalline phase in NMC 111 materials with a hollow-sphere morphology is found to be the decisive parameter for their galvanostatic cycling stability. Hollow spheres with well-developed NMC nanocrystals and a low concentration of amorphous phase in the walls, exhibiting excellent cycling stability and charge capacity in thin-film electrodes are incorporated into a NMC/graphite 3D-battery module. This 122 Ah/451 Wh 3D-battery provides 78% of theoretical capacity and 73% of theoretical energy after 10 formatting cycles. Additionally, the battery prototype exhibits stable performance over more than 200 cycles at C/10 rate. A series of analogous 3D Li accumulators, currently assembled and tested in a pilot plant, represent the first step toward large-scale production of novel 3D Li accumulator.     

Study on preparation and electrochemical properties of biomass-derived spherical activated carbon

以生物质风化煤系腐殖酸（LHA）为炭质前驱体,通过溶剂蒸发和KOH活化方法制备了球形活性炭。使用扫描电子显微镜（SEM）、N2物理吸脱附仪等手段对球形活性炭形貌和孔道结构进行了表征;还将活性炭组装成扣式电容器,进行了充放电容量、循环伏安特性和交流阻抗行为等电化学性能测试。结果表明：所制备的球形活性炭具有良好的球形度,通过少量碱活化后球形活性炭BET表面积为2034 m2/g、总孔容为1.24 cm3/g、平均孔径为2.38 nm。同时,以球形活性炭作为电极材料应用于水系超级电容器后显示了优异的电化学性能,比电容可达到319 F/g,在进行10000次充放电后,比电容保持率为98.9%。此外,球形活性炭相比于颗粒活性炭具有更好的导电性,也展现了更加优异的倍率性能和循环性能。因此说明LHA基球形活性炭是一种有潜在优势的超级电容器材料。     

Fabrication and properties of macroporous tin–cobalt alloy film electrodes for lithium-ion batteries

The Sn-based intermetallic compounds possess a high specific energy density, but their most important challenge to be used as anodes in lithium ion batteries consists in the mechanical fatigue caused by volume change during lithium intercalation and extraction processes. The current paper presents a facile procedure to prepare macroporous Sn–Co alloy film electrode through a colloidal crystal template method together with electroplating on a Ni-coated Cu sheet substrate. The structure and electrochemical properties of the macroporous Sn–Co alloy films were examined by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and galvanostatic cycling. The results illustrated that the macroporous Sn–Co alloy film electrode can deliver a reversible capacity as high as 610 mAh g⁻¹ up to 75th cycle. In comparison with the Sn–Co alloy film directly deposited on Ni-coated Cu sheet substrate, the macroporous structure of the Sn–Co alloy electrode prepared by the present procedure has enhanced significantly the capacity and the cyclic performance. It has demonstrated that the macroporous structure has played an important role, in addition to the alloying effect, to overcome the effect of volume expansion during charge/discharge cycling of Sn-based alloy anodes.     

Comparison of the surface changes on cathode during long term storage testing of high energy density cylindrical lithium-ion cells

Nickel-based oxide cathode material taking out from lithium-ion cell after storage for 2 years at 45 °C is analyzed by electron energy-loss spectroscopy in a scanning transmission electron microscope (STEM-EELS) and the result of STEM-EELS is compared with cobalt-based oxide cathode material which is treated as same manor as nickel-based oxide cathode material. The Ni-L_2,3 energy-loss near-edge structure (ELNES) spectra of nickel-based oxide cathode material show peak positions similar to original material before storage. This result indicates that nickel-based oxide material has no significant change in the surface structure. On the other hand, a remarkable shift to low energy is observed in the Co-L_2,3 ELNES spectra of the cobalt-based oxide cathode material after storage. The cycle test at 60 °C under the conditions of aggressive driving cycle (US06) mode for the nickel-based oxide cathode/graphite cell is also carried out. It is clear that cycle performance of the nickel-based oxide cathode/graphite cell is dependent on the depth of discharge (DOD).     

Enhanced properties of LiFePO4/C cathode materials co-doped with V and F ions via high-temperature ball milling route

V and F ions co-doped LiFePO₄/C (LFP-VF) cathode material is prepared via high-temperature ball milling route. Effects of V and F ions co-doped on the structure, morphology and electrochemical property of LiFePO₄ are investigated in this work, and some analysis of X-ray diffraction, scanning electron microscope, transmission electron microscope, charge-discharge tests, electrochemical impedance spectroscopy and cyclic voltammetry are employed. The results confirm that prepared LFP-VF exhibits excellent electrochemical property. The specific capacities are 165.7 (0.1 C), 154.9 (1.0 C) and 124.9 (10 C) mAhg⁻¹. Moreover, over 500 cycles at 1.0 C-rate, the discharge capacity is 148.2 mAhg⁻¹ with a capacity retention rate of 95.7%. Experimental results indicate that the electrochemical performance of LiFePO₄ can be greatly enhanced by co-doping with V and F ions.     

Preparation and electrochemical properties of indium- and sulfur-doped LiMnO2 with orthorhombic structure as cathode materials

The indium- and sulfur-doped LiMnO₂ samples with orthorhombic structure as cathode materials for Li-ion batteries are synthesized via hydrothermal method. The microstructure and composition of the samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), inductively coupled plasma atom emission spectroscopy (ICP-AES), and X-ray photoelectron spectroscopy (XPS) analysis. It is shown that these samples with the orthorhombic structure have irregular shapes with a grain size of about 100–200 nm. The electrochemical performance of these samples as cathode materials was studied by galvanostatic method. All doped materials can offer improved cycling stability and high rate discharge ability as compared with the un-doped Li_0.99MnO₂. Moreover, dual In/S doping can slow down the capacity decay to a great extent, although the transformation to spinel occurs undesirably for all the doped samples during electrochemical cycling.     

High electrochemical performance of PANI/CdO nanocomposite based on graphene oxide as a hybrid electrode materials for supercapacitor application

In the last decade, the production of clean and sustainable energy sources for energy storage purposes have grown dramatically due to the population growth and increasing demand for energy in the world. In this regard, supercapacitors have proved to be promising candidates in energy storage applications. Therefore, in this study, polyaniline/cadmium oxide/graphene oxide (PANI/CdO/GO) nanocomposite was prepared by co-precipitation method to evaluate the electrochemical performance. The structural and surface properties, morphology and particle size distribution were analyzed by XRD diffraction spectroscopy (XRD), field emission scanning electron microscope (FESEM), transmission electron microscope (TEM), N₂ adsorption-desorption, and Fourier transform infrared spectroscopy (FT-IR). Furthermore, the synthesized nanocomposite was applied as an active electrode material and its performance was investigated by cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and electrochemical impedance spectroscopy (EIS) in terms of energy storage. The results of these tests confirmed that PANI/CdO/GO nanocomposite provides great electrochemical behavior, including specific capacity of 647 F g^?1, energy density of 116.6 W h kg^?1, power density of 388 W kg^?1 compared to the other electrode. According to the stability test, the initial capacity maintenance was about 82% after 500 charge-discharge cycles, which indicated relatively good electrochemical stability. Moreover, the impedance spectroscopy studies showed that the nanocomposite possessed much lower internal strength and charge transfer reaction resistance in comparison to the other synthesized materials. Based on these results, it was found that the prepared nanocomposite has a good performance in the field of energy storage.     

Synthesis and application in solar cell of poly(3-octylthiophene)/cadmium sulfide nanocomposite

A conducting polymer composite, poly(3-octylthiophene)/cadmium sulfide (POT/CdS) was first synthesized. Transmission electron microscope (TEM) and scanning electron microscope (SEM) depict the morphology of the samples, defining that CdS was successfully coated by poly(3-octylthiophene) molecules. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and infrared spectroscopy (IR) show that there is a chemical interaction in the composite. The energy gap of the POT/CdS composite is lower at 0.824 eV, which also shows that the optical performance of the new material is far superior to POT or CdS separately, by ultraviolet-visible spectra (UV-vis). Solar cell was sensitized by POT/CdS. A solar-to-electric energy conversion efficiency of 0.581% was attained with the system. The results show that POT/CdS nanocomposites are promising materials with excellent performance characteristics in photoelectric applications.     

Sulfur/alumina/polypyrrole ternary hybrid material as cathode for lithium-sulfur batteries

Recently, lithium-sulfur batteries (LSBs) have received extensive attention due to its high energy density of 2600 Wh kg^?1. At the same time, sulfur is earth-abundant, economical and non-poisonous. Nevertheless, the poor electrochemical performance restricts its commercial application, including the inferior cycling stability caused by the significant dissolution of lithium polysulfides and the low specific capacity because of the poor electrical conductivity of sulfur. In this work, we adopt a simple and amicable process to prepare sulfur/alumina/polypyrrole (S/Al₂O₃/PPy) ternary hybrid material to overcome these defects. In this strategy, each composition of the ternary hybrid material plays an essential role in cathode: alumina and PPy can provide strong adsorption for the dissolved intermediate polysulfides. Meanwhile, PPy also works as a conductive and flexible additive to expedite electron transport, and is coated on the surface of the as-prepared SAl₂O₃ composite by in situ chemical polymerization. The sulfur is encapsulated uniformly and perfectively by the two components, which is confirmed by field emission scanning electron microscope. The ternary hybrid material manifests good electrochemical performance as expected, and displays high initial discharge capacity of 1088 mA h g^?1 and a discharge capacity of 730 mA h g^?1 after 100 cycles at a current density of 200 mA g^?1. Besides, S/Al₂O₃/PPy also shows good rate capability. The synergy between alumina and PPy is the decisive factor, which gives rise to good electrochemical performance of cathode for high-performance LSBs.     

Carbon-coated MoO3 nanobelts as anode materials for lithium-ion batteries

MoO₃ nanobelts are synthesized by a simple hydrothermal route followed by carbon coating. The effects of the carbon coating on the nanobelts are investigated by Raman spectroscopy, X-ray diffraction (XRD), scanning electron microscope (SEM) with an energy dispersive spectrometer (EDS), a transmission electron microscope (TEM), and galvanostatic cycling. As observed from the TEM and SEM images, the C-MoO₃ nanobelts have a diameter of 150 nm and a length of 5-8 μm. In the electrochemical results, the C-MoO₃ nanobelts exhibit excellent cycling stability after being cycled at a current rate of 0.1 C, maintaining their capacity at 1064 mAh g⁻¹ after 50 cycles. These results are better than those for a bare MoO₃ nanobelt electrode. The excellent electrochemical performance of the C-MoO₃ nanobelts can be attributed to the effects of the carbon coating which stabilizes the structure of the MoO₃, enhances the ionic/electrical conductivity, and moreover, can serve as a buffering agent to absorb the volume expansion during the Li⁺ intercalation process.     

Highly active cluster structure manganese-based metal organic frameworks (Mn-MOFs) like corals in the sea synthesized by facile solvothermal method as gas electrode catalyst for lithium-oxygen batteries

Lithium-oxygen batteries are promising energy storage systems for electric vehicles owing to their very high specific capacity. In all of their components, the catalysts in the air electrode have a profound influence on its electrochemical performances, especially cycle life and specific energy. In this paper, a type of cluster structure manganese-based metal organic frameworks (Mn-MOFs) material is synthesized by facile solvothermal method. Through X-ray diffraction (XRD), scanning electron microscope (SEM), and Raman spectrum tests, it shows that the Mn-MOFs materials with the 1.3:1 molar ratio (Mn: p-phthalic acid) have high crystallinity and orientation and show obvious cluster structure like corals in the sea. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) tests demonstrate that this MOFs material as the gas electrode catalyst has more excellent reversibility and the oxidation process. Furthermore, the air electrode has quick electronic and lithium ion transfer rate. In addition, the lithium-oxygen batteries with this Mn-based MOFs material as the air electrode catalyst have longer cycle life. After 35 times charge and discharge cycles, the specific discharge capacity can still be maintained over 500 mAh·g⁻¹, and it has the much higher discharge voltage platform.     

Promoting Si-graphite composite anodes with SWCNT additives for half and NCM811 full lithium ion batteries and assessment criteria from an industrial perspective

Single wall carbon nanotube (SWCNT) additives were formulated into µm-Si-graphite composite electrodes and tested in both half cells and full cells with high nickel cathodes. The critical role of small amount of SWCNT addition (0.2 wt%) was found for significantly improving delithiation capacity, first cycle coulombic efficiency (FCE), and capacity retention. Particularly, Si (10 wt%)-graphite electrode exhibits 560 mAh/g delithiation capacity and 92% FCE at 0.2 C during the first charge-discharge cycle, and 91% capacity retention after 50 cycles (0.5 C) in a half cell. Scanning electron microscope (SEM) was used to illustrate the electrode morphology, compositions and promoting function of the SWCNT additives. In addition, full cells assembled with high nickel-NCM811 cathodes and µm-Si-graphite composite anodes were evaluated for the consistence between half and full cell performance, and the consideration for potential commercial application. Finally, criteria to assess Si-containing anodes are proposed and discussed from an industrial perspective.     

Characterization of CoB–silica nanochains hydrogen storage composite prepared by in-situ reduction

The CoB–silica nanochains hydrogen storage composite was prepared by in-situ reduction of cobalt salt on the surface of amine-modified silica nanospheres. The structure and morphology of the sample were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The valence state of atoms was characterized by X-ray photoelectron spectroscopy (XPS). The electrochemical properties of the sample were also investigated. The results demonstrated that the CoB–silica nanochains hydrogen storage composite possessed amorphous nanochains structure by a series of nanospheres connecting in one-dimension. In addition, the material as electroactive negative electrodes showed high reversible discharge capacity (about 500 mAh/g in the first cycle) and good cycling stability. A properly electrochemical reaction mechanism was constructed primarily.     

Cycle life performance of lithium-ion pouch cells

Cycle life studies have been done on lithium-ion pouch cell with LiCoO₂ as cathode and meso-carbon micro-beads (MCMB) as anode at five different temperatures. By using the rate capability tests done at the same temperature as that of cycling and the half cell studies done on the fresh and cycled individual electrodes, the stoichiometric windows of individual electrodes at the beginning and at the end of cycling have been estimated. By analyzing these estimates along with the X-ray diffraction studies and half cell studies on cycled cathodes, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and half cell studies on cycled anodes, possible causes of increased capacity fade with increasing temperature were found to be the anode active material loss, probably due to a solvent/salt reduction reaction on the anode. Lithium deposition on the anode also has been identified as a possible side reaction during later stages of cycling at 35 and 45 °C.     

Stearic acid/polymethylmethacrylate composite as form-stable phase change materials for latent heat thermal energy storage

The aim of this research is to prepare of a novel form-stable composite phase change material (PCM) for the latent heat thermal energy storage (LHTES) in buildings, passive solar space heating or functional fluid by entrapping of SA into PMMA cell through ultraviolet curing dispersion polymerization. The composite PCM was characterized using scanning electron microscope (SEM) and Fourier transformation infrared (FT-IR) analysis technique. The results show that the form-stable microencapsulated PCM with core/shell structure was formed and the maximum encapsulated proportion of SA in the composite was 51.8 wt.% without melted PCM seepage from the composite. In the shape stabilized microencapsulated PCM, the polymer acts as supporting material to form the microcapsule cell preventing the leakage of PCM from the composite and the SA acts as a PCM encapsulated in the cell of PMMA resin. The oxygen atom of carbonyl group of skeleton is interacted with the hydrogen atom of hydroxyl group of SA. Thermal properties, thermal reliability and heat storage/release performance of the composite PCM were determined by differential scanning calorimetry (DSC), FT-IR and thermal cycling test analysis. The melting and freezing temperatures and the latent heats of the composite PCM were measured as 60.4 °C, 50.6 °C and 92.1 J/g, 95.9 J/g, respectively. The results of DSC, FT-IR and thermal cycling test are all show that the thermal reliability of the composite PCM has an imperceptible change. This conclusion indicates that the composite has a good thermal and chemical stability.