Binder-free and carbon-free 3D porous air electrode for Li-O2 batteries with high efficiency, high capacity, and long life

Pt-Gd alloy polycrystalline thin film is deposited on 3D nickel foam by pulsed laser deposition method serving as a whole binder/carbon-free air electrode, showing great catalytic activity enhancement as an efficient bifunctional catalyst for the oxygen reduction and evolution reactions in lithium oxygen batteries. The porous structure can facilitate rapid O2 and electrolyte diffusion, as well as forming a continuous conductive network throughout the whole energy conversion process. It shows a favorable cycle performance in the full discharge/charge model, owing to the high catalytic activity of the Pt-Gd alloy composite and 3D porous nickel foam structure. Specially, excellent cycling performance under capacity limited mode is also demonstrated, in which the terminal discharge voltage is higher than 2.5 V and the terminal charge voltage is lower than 3.7 V after 100 cycles at a current density of 0.1 mA cm−2. Therefore, this electrocatalyst is a promising bifunctional electrocatalyst for lithium oxygen batteries and this depositing high-efficient electrocatalyst on porous substrate with polycrystalline thin film by pulsed laser deposition is also a promising technique in the future lithium oxygen batteries research

A germanium/single-walled carbon nanotube composite paper as a free-standing anode for lithium-ion batteries

Paper-like free-standing germanium (Ge) and single-walled carbon nanotube (SWCNT) composite anodes were synthesized by the vacuum filtration of Ge/SWCNT composites, which were prepared by a facile aqueous-based method. The samples were characterized by X-ray diffraction, field emission scanning electron microscopy, and transmission electron microscopy. Electrochemical measurements demonstrate that the Ge/SWCNT composite paper anode with the weight percentage of 32% Ge delivered a specific discharge capacity of 417 mA h g−1 after 40 cycles at a current density of 25 mA g−1, 117% higher than the pure SWCNT paper anode. The SWCNTs not only function as a flexible mechanical support for strain release, but also provide excellent electrically conducting channels, while the nanosized Ge particles contribute to improving the discharge capacity of the paper anode

Quantum Algorithm for Unsupervised Anomaly Detection

Anomaly detection, an important branch of machine learning, plays a critical role in fraud detection, health care, intrusion detection, military surveillance, etc. As one of the most commonly used unsupervised anomaly detection algorithms, the Local Outlier Factor algorithm (LOF algorithm) has been extensively studied. This algorithm contains three steps, i.e., determining the k-distance neighborhood for each data point x, computing the local reachability density of x, and calculating the local outlier factor of x to judge whether x is abnormal. The LOF algorithm is computationally expensive when processing big data sets. Here we present a quantum LOF algorithm consisting of three parts corresponding to the classical algorithm. Specifically, the k-distance neighborhood of x is determined by amplitude estimation and minimum search; the local reachability density of each data point is calculated in parallel based on the quantum multiply-adder; the local outlier factor of each data point is obtained in parallel using amplitude estimation. It is shown that our quantum algorithm achieves exponential speedup on the dimension of the data points and polynomial speedup on the number of data points compared to its classical counterpart. This work demonstrates the advantage of quantum computing in unsupervised anomaly detection

Development of novel materials for rechargeable lithium batteries

In the field of electrical energy storage, lithium ion batteries (LIBs) are considered as one of the most promising technologies due to their particularly higher energy density and longer shelf life, as well as they do not suffer from the serious memory effect problems that afflict Ni-MH batteries. Graphite and LiCoO2 are currently the most common commercial anode and cathode materials for the LIB, but they still suffer from low theoretical capacities of 372 mAh g-1 and 170 mAh g-1, respectively. Such low discharge capacity would be unable to satisfy the growing demand for large-scale potential lithium ion battery applications, such as electric vehicles (EVs), hybrid electric vehicles (HEVs), and stationary energy storage for solar and wind electrical energy generation. Therefore, the electrical performance of active electrode materials in rechargeable lithium ion batteries must continue to be improved. In this doctoral work, several promising materials for both anode and cathode electrodes were synthesized and combined with conductive polymer to further improve their electrochemical performance. These include LiV3O8-polyaniline, Germaniumpolypyrrole, and LiNi0.5Mn1.5O4-polypyrrole composites. Monodisperse porous Ni0.5Zn0.5Fe2O4 nanospheres are also successfully synthesized by the solvothermal method and their electrical performances as novel anode materials for LIB are investigated in detailed. In addition, another key aspect for the electrochemical performance of LIB is the stability of the electrolyte. The most widely used electrolyte for lithium ion batteries is LiPF6 dissolved in ethylene carbonate (EC), dimethyl carbonate (DMC) and diethyl carbonate (DEC). The battery performance may be limited, however, by the highly oxidizing conditions at high voltage (\u3e 4.5 V). Herein, room temperature ionic liquid was used as a new type of electrolyte for the high-voltage cathode material LiNi0.5Mn1.5O4, and the relationship between the electrolyte characteristics and the performance of Li/LiNi0.5Mn1.5O4 cells at the high potential of 5.1 V was studied in more detail. Anode materials for the LIBs Nano-Germanium/polypyrrole composite has been synthesized by a simpe chemical reduction method in aqueous solution. The Ge nanoparticles were directly coated on the surface of the polypyrrole. The morphology and structural properties of samples were determined by X-ray diffraction, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Thermogravimetric analysis was carried out to determine the polypyrrole content. The electrochemical properties of the samples have been investigated and their suitability as anode materials for the LIB was examined. The discharge capacity of the Ge nanoparticles in the Ge-polypyrrole composite was calculated as 1014 mAh g-1 after 50 cycles at the 0.2 C rate, which is much higher than that of pristine germanium (439 mAh g-1). The composite also demonstrates high specific discharge capacity at different current rates (1318, 1032, 661, and 460 mAh g-1 at 0.5, 1.0, 2.0, and 4.0 C, respectively). The superior electrochemical performance of Ge-polypyrrole composite could be attributed to the polypyrrole core, which provides an efficient transport pathway for electrons. SEM images of the electrodes have demonstrated that polypyrrole can also act as a conductive binder and alleviate the pulverization of electrode caused by the huge volume changes of the nanosized germanium particles during Li+ intercalation/deintercalation. Monodisperse porous Ni0.5Zn0.5Fe2O4 nanospheres have been successfully synthesized by the solvothermal method. The diameter of the nanospheres can be tuned by controlling the reactant concentration. Lower reactant concentration is favoured for the synthesis of mesoporous Ni0.5Zn0.5Fe2O4 nanospheres with higher surface area. The electrochemical results show that mesoporous Ni0.5Zn0.5Fe2O4 nanospheres exhibit high reversible specific capacity (1110 mAh g-1) for Li storage and high capacity retention, with 700 mAh g-1 retained up to 50 cycles. The excellent electrochemical properties could be attributed to the large surface area and mesoporous structure. The results suggest that Ni0.5Zn0.5Fe2O4 could be a promising high capacity anode material for lithium ion batteries. Cathode materials for the LIBs LiV3O8-polyaniline nanocomposites have been synthesized via chemical oxidative polymerization, directed by the anionic surfactant sodium dodecyl benzene sulfate. The polyaniline particles are uniformly coated on the LiV3O8 nanorods. The composite with 12 wt. % polyaniline retains a discharge capacity of 204 Ah kg-1 after 100 cycles and has better rate capability (175 Ah kg-1 at 2 C, and 145 Ah kg-1 at 4 C) than the bare LiV3O8 reference electrode in the potential range of 1.5-4.0 V. The polyaniline coating can buffer the electrode dissolution into the LiPF6 that occurs in LiV3O8 during cycling. The charge transfer resistance of the composite electrode is much lower than that of the bare LiV3O8 electrode, indicating that the polyaniline coating significantly increases the electrical conductivity between the LiV3O8 nanorods. Conductive polyaniline is also proven as a conductive binder which buffers the dissolution of LiV3O8 into the electrolyte and reduces the contact resistance among the nanorods, so the performance of the composite is significantly improved. Conductive polypyrrole-coated LiNi0.5Mn1.5O4 (LNMO) composites have been applied as another promising cathode materials in LIB, and their electrochemical properties are explored at both room and elevated temperature. The morphology, phase evolution, and chemical properties of the as-prepared samples were analyzed by means of X-ray powder diffraction, thermogravimetric analysis, Raman spectroscopy, and scanning and transmission electronic microscopy techniques. The composite with 5 wt. % polypyrrole coating shows discharge capacity retention of 92 % after 300 cycles and better rate capability than the bare LNMO electrode in the potential range of 3.5-4.9 V vs. Li/Li+ at room temperature. At elevated temperature, the cycling performance of the electrode made from LNMO-5 wt. % polypyrrole (PPy) is also remarkably stable (~91 % capacity retention after 100 cycles). It is revealed that the polypyrrole coating can suppress the dissolution of manganese in to the electrolyte which occurs during cycling. The charge transfer resistance of the composite electrode is much lower than that of the bare LNMO electrode after cycling, indicating that the polypyrrole coating significantly increases the electrical conductivity of the LNMO electrode. Polypyrrole can also work as an effective protective layer to suppress the electrolyte decomposition arising from undesirable reactions between the cathode electrode and the electrolyte on the surface of the active material at elevated temperature, leading to high coulombic efficiency. Ionic liquid electrolyte for the LIB Among the high voltage cathode materials, LiNi0.5Mn1.5O4 is of particular interest, with comparable capacity (around 140 Ah kg-1) to LiCoO2 and LiFePO4, and with much higher specific energy (658 Wh kg-1). The stability of the electrolyte is still a major concern, however, for the high voltage spinel cathode materials because the potential range is beyond the decomposition potential of conventional electrolyte (~4.7 V vs. Li/Li+). In this research work, a 5 V cathode material, LiNi0.5Mn1.5O4 nanoparticles, was prepared via the sol-gel method. The room temperature ionic liquid, 1 M lithium bis(trifluoromethysulfony)imide (LiTFSI) in N-butyl-N-methylpyrrolidinium bis(trifluoromethane-sulfonyl) imide (Py14TFSI), was used as electrolyte. The electrochemical performance shows that the LiNi0.5Mn1.5O4 nanoparticles with room temperature ionic liquid as electrolyte show comparable capacity to that of conventional electrolyte (1 M LiPF6 in EC: DEC = 1:2 (v/v)), with improved coulombic efficiency at the high voltage of 5.1 V

Development of new electrode materials for lithium battery

Lithium ion batteries are currently the best portable energy storage devices for the consumer electronics market. Large capacity, good cyclability, and no reaction with electrolytes are indispensable characteristics for lithium ion battery materials. In this Master’s research study, several materials were characterized and examined for possible applications as cathode or anode for rechargeable lithium-ion batteries. Among the cathode candidates, copper sulphur (CuS) and lithium trivanadate (LiV3O8) with polyaniline were studied. Tin with polypyrrol was also studied as an anode material candidate for use in rechargeable lithium-ion batteries. Tin nanoparticle/polypyrrole (nano-Sn/PPy) composite was prepared by chemically reducing and coating Sn nanoparticles onto the PPy surface. The composite shows much higher surface area than the pure nano-Sn reference sample, due to the porous higher surface area of PPy and the much smaller size of Sn in the nano-Sn/PPy composite than in the pure tin nanoparticle sample. Poly (vinylidene fluoride)(PVDF) and sodium carboxymethyl cellulose (CMC) were also used as binders, and the electrochemical performance was investigated. The electrochemical results show that both the capacity retention and the rate capability are in the same order of nano-Sn/PPy-CMC \u3e nano-Sn/PPy-PVDF \u3e nano-Sn-CMC \u3e nano-Sn-PVDF. Scanning electronic microscopy (SEM) and electrochemical impedance spectroscopy (EIS) results show that CMC can prevent the formation of cracks in electrodes during the charge-discharge process, despite the big volume changes, and the PPy in the composite can provide a conducting matrix and alleviate the agglomeration of Sn nanoparticles. The present results indicate that the nano-Sn/PPy composite could be suitable for the next generation of anode materials with relatively good capacity retention and rate capability. CuS nanoparticles, including nanoflakes, microspheres composed of nanoflakes, microflowers, and nanowires have been selectively synthesized by a facile hydrothermal method using CuSO4 and thiourea as precursors under different conditions. The morphology of CuS particles was affected by the following synthetic parameters: temperature, time, surfactant, pH value, solvent, and concentration of the two precursors. The synthesized CuS nanomaterials were characterized by X-ray diffraction, Brunauer-Emmett-Teller N2 adsorption, SEM, and energy-dispersive Xray spectroscopy. The electrochemical tests, including constant current charge discharge and cyclic voltammetry, show the specific capacities of the different morphologies, as well as their cycling stability. The nanowire electrode presented here has near theoretical specific capacity and relatively stable cycling performance. A composite, LiV3O8-polyaniline (PANi), suitable for lithium-ion battery cathodes, was synthesized by dispersing LiV3O8 and dissolving PANi powders in N-methyl-2-pyrrolidinone (NMP) followed by heating. Electrochemical impedance measurements showed that the polyaniline significantly decreased the charge-transfer resistance of LiV3O8 electrodes. Charge-discharge properties of composites as cathode materials for lithium-ion batteries were studied. The results indicated that PANi-LiV3O8 had higher discharge capacity and better cycling property. The PANi-LiV3O8 composite with 10 wt% polyaniline showed the best electro chemical performance, with a specific capacity of ~161 mAh g-1 retained after 55 cycles

Metallic state two-dimensional holey-structured Co3FeN nanosheets as stable and bifunctional electrocatalysts for zinc–air batteries

Exploring economically efficient electrocatalysts with robust bifunctional oxygen conversion catalytic activity and designing appropriate structures are essential to realize ideal zinc-Air batteries with high energy density and long lifespan. Two-dimensional metallic state Co3FeN nanosheets with a holey-structured architecture are designed and shown to exhibit enhanced catalytic properties owing to the complete exposure of the atoms in the large lateral surfaces and in the edges of pore areas, together with the lowest OH∗ adsorption energy on exposed surfaces due to bimetallic synergistic effects. Meanwhile, this porous architecture can not only accelerate electron transportation by its metallic state highly oriented crystallized structure, but also facilitate the diffusion of intermediates and gases. These edge-enriched 2D holey Co3FeN nanosheets exhibit enhanced catalytic activity towards reversible oxygen conversion. When employed in zinc-Air batteries, they exhibit a maximum power density of 108 mW cm-2 and cycle life up to 900 cycles with a low round-Trip voltage of 0.84 V. The Co3FeN nanosheets maintain a strong stable structure in an oxygen-rich electrochemical environment with a high-orientation crystalline texture during the whole cycling time. This work may provide a promising candidate to promote the further development of zinc-Air batteries

Porous AgPd-Pd composite nanotubes as highly efficient electrocatalysts for lithium-oxygen batteries

Porous AgPd-Pd composite nanotubes (NTs) are used as an efficient bifunctional catalyst for the oxygen reduction and evolution reactions in lithium-oxygen batteries. The porous NT structure can facilitate rapid O2 and electrolyte diffusion through the NTs and provide abundant catalytic sites, forming a continuous conductive network throughout the entire energy conversion process, with excellent cycling performance

High capacity and high rate capability of nanostructured CuFeO2 anode materials for lithium-ion batteries

Non-toxic, cheap, nanostructured ternary transition metal oxide CuFeO2 was synthesised using a simple sol–gel method at different temperatures. The effects of the processing temperature on the particle size and electrochemical performance of the nanostructured CuFeO2 were investigated. The electrochemical results show that the sample synthesised at 650 °C shows the best cycling performance, retaining a specific capacity of 475 mAh g−1 beyond 100 cycles, with a capacity fading of less than 0.33% per cycle. The electrode also exhibits good rate capability in the range of 0.5C–4C. At the high rate of 4C, the reversible capacity of CuFeO2 is around 170 mAh g−1. It is believed that the ternary transition metal oxide CuFeO2 is quite acceptable compared with other high performance nanostructured anode materials

Porous Ni0.5Zn0.5Fe2O4 nanospheres: synthesis, characterization, and application for lithium storage

Monodisperse porous Ni0.5Zn0.5Fe2O4 nanospheres have been successfully synthesized by the solvothermal method. The diameter of the nanospheres can be tuned by controlling the reactant concentration. Lower reactant concentration is favoured for the synthesis of mesoporous Ni0.5Zn0.5Fe2O4 nanospheres with higher surface area. The electrochemical results show that mesoporous Ni0.5Zn0.5Fe2O4 nanospheres exhibit high reversible specific capacity (1110 mAh g-1) for Li storage and high capacity retention, with 700 mAh g-1 retained up to 50 cycles. The excellent electrochemical properties could be attributed to the large surface area and mesoporous structure. The results suggest that Ni0.5Zn0.5Fe2O4 could be a promising high capacity anode material for lithium ion batteries