Synthesis of LiFePO<Subscript>4</Subscript> nanoparticles and electrochemical studies at full-cell level

LiFePO₄ nanoparticles have been successfully obtained by a solid-phase synthesis method using nanoscaled FePO₄ as starting materials. Three-electrode system using as-prepared LiFePO₄ as cathode was assembled to monitor the variation of voltage and impedance in the anode or cathode. The pouch-typed cells with prepared LiFePO₄ were assembled to investigate electrochemical performance at level of full-cell. The results show that the assembled pouch-typed full-cells present higher power density and favorable cycle life.     

Synthesis and electrochemical properties of Li-rich Li[Ni<Subscript>0.5</Subscript>Co<Subscript>0.2</Subscript>Mn<Subscript>0.3</Subscript>]O<Subscript>2</Subscript> for pouch-typed cell

Layered transition metal oxide LiNi _x Co _y MnzO₂ cathode materials with different Li amount were successfully synthesized via co-precipitation method. Monodispersed Li[Ni_0.5Co_0.2Mn_0.3]O₂ and Li-rich Li_1.1[Ni_0.5Co_0.2Mn_0.3]O₂ spherical agglomeration consisted of secondary particles, which is favorable for the higher tap-density of materials, can be easily obtained. The pouch-typed cells with obtained materials were assembled to investigate electrochemical performance at level of full-cell. The results show that the assembled pouch-typed full-cells with Li-rich sample present higher capacity, better rate capability and cycle life.     

Graphite and Solvothermally Synthesized LiFePO<Subscript>4</Subscript>/Graphene Electrode for Soft-Packed Cell

Well-crystallized and nano-sized LiFePO₄/graphene composite have been successfully synthesized by in-situ disperse graphene oxide (GO) in precursor via a rapid microwave-solvothermal process at 200°C within 10 min. In spite of the low synthesis temperature, the structural and morphological properties of as-prepared composites are of high specific capacity, an excellent high rate capability, and stable cycling performance. In comparison with LiFePO₄/grahite soft-packed full-cell, the assembled soft-packed full-cell with solvothermally synthesized LiFePO₄/graphene composite and graphite electrode show better cycle performances prepared at higher temperature.     

Synthesis of LiFePO<Subscript>4</Subscript> by In Situ Polymerization Restriction Method for Pouch-Typed Cell

We report a two-step approach to synthesize nanosized LiFePO₄C composite by an in situ polymerization restriction method. First step, the Fe₂O₃@polyaniline is fabricated with in situ polymerization method. Secondly, the as-obtained Fe₂O₃ coated with polyaniline is mixed with LiH₂PO₄, followed by carbothermal reduction process. The outer polyaniline shell coating Fe₂O₃ can restrict the aggregation of particles and serves as carbon-containing precursor. The studies of electrochemical performances were carried out at full cell level. The results show that the assembled pouch-typed full-cells with as-obtained LiFePO₄ present excellent rate capability and cycle life.     

Electochemical characteristics of LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript>/Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript> battery with conducting polymeric binder

Lithium-ion battery based on LiMn₂O₄/Li₄Ti₅O₁₂ materials was assembled for the first time. The cathode and anode of this battery are prepared with the aqueous combined binder poly-3,4-ethylenedioxythiophene: polystyrene sulfonate/carboxymethylcellulose (without polyvinylidene fluoride). The capacity of the LiMn₂O₄/Li₄Ti₅O₁₂ battery was found to be 75 mA h g^–1 at 0.1 C and 55 mA h g^–1 at 1 C. A 95% capacity was retained after 100 charge-discharge cycles. The batteries demonstrated a high Coulombic efficiency close to 100%. Scanning electron microscopy demonstrated that using the conducting binder poly-3,4-ethylenedioxythiophene: polystyrene sulfonate/carboxymethylcellulose provides formation of dense compact layers of electrode materials with good adhesion to the substrate. The electrode structure remains maintained after 100 charge-discharge cycles.     

Aging property for LiFePO<Subscript>4</Subscript>/graphite cell with different temperature and DODs

In this paper, we fabricated 1.7 A h soft-packed cells using commercial-grade LiFePO₄ and manmade graphite as the active materials for the cathode and anode, respectively. It has been shown that the cycle performances of assembled soft-packed full-cell were still temperature-dependent. An accelerated mechanism of the operating temperature to reformation/repairing of SEI layer have been established, which greatly consumes active lithium during cycling, therefore causes fast capacity loss at elevated temperatures. At same time, cycle property for LiFePO₄/graphite cell with different depth of discharge (DOD) levels and ranges. It has been shown that DOD level has very little effect on capacity fade for cell lifecycle; but for DOD range, obvious influence was observed on capacity fade, which is due to the sensitivity of SOC during the storage of the cell.     

Highly stable asymmetric supercapacitors based on Ni(OH)<Subscript>2</Subscript> deposited on electro-etched carbon paper

Herein, we introduce the application of nickel hydroxide nanosheets on the electro-etched carbon fiber (ECF) formed via a direct electrodeposition, for fabrication of asymmetric supercapacitor. To confirm the practical applicability of prepared Ni(OH)₂–ECF, an asymmetric device was assembled using Ni(OH)₂–ECF in combination with an activated carbon (AC) electrode. Our results showed a substantial cycling stability (96% capacitance retention after 10000 cycles) and considerable rate capability at large discharge currents (60% capacitance retention at 8 A g^??1) for this asymmetric supercapacitor that may have originated from the good contact between Ni(OH)₂ and ECF. A maximum specific capacitance of 88.1 F g^??1 was achieved for Ni(OH)₂–ECF//AC/CF device and showed considerable rate capability at large discharge currents (60% capacitance retention at 8 A g^??1). The results of this study suggest the Ni(OH)₂–ECF electrode is an excellent material for fabrication of supercapacitor electrodes.     

Influence of the Conditions for Preparing LaPO<Subscript>4</Subscript>-Based Materials with Inclusions of the LaP<Subscript>3</Subscript>O<Subscript>9</Subscript> Phase on Their Thermal and Mechanical Properties

A material based on lanthanum orthophosphate LaPO₄ with inclusion of particles of lanthanum metaphosphate LaP³O₉ was synthesized. The influence of the process parameters of the synthesis on the structure and properties of the material was determined. Heat treatment of the coprecipitated lanthanum phosphates at 700°C leads to the formation of a nanopowder with the LaPO₄crystallite size of approximately 17 nm. Heat treatment of the nanopowder at temperatures from 1100 to 1500°C yields compact materials based on the LaPO₄–LaP₃O₉ system. The heat treatment of the nanopowder at 1100°C leads to a sharp decrease in the porosity of the material (to ~5%) at insignificant grain growth (200–400 nm); under these conditions, the thermal conductivity [λ(25°C) = 3.2 W m–1 K^–1], microhardness [Hv(25°C) = 4.6 ± 0.4 GPa], Young’s modulus [E(25°C) = 132 ± 9 GPa], and cracking resistance [K_1c(25°C) = 1.6 ± 0.1 MPa m^1/2] pass through maxima. The thermal expansion coefficient of the material depends on the heat treatment conditions only slightly and amounts to (8.2 ± 0.2) × 10^–6 K^–1.     

The Effect of Particle Size on the Processes of Charging and Discharging of the LiFe<Subscript>0.97</Subscript>Ni<Subscript>0.03</Subscript>PO<Subscript>4</Subscript>/C/Ag Cathode Material

Olivine-structured LiFe_0.97Ni_0.03PO₄/C/Ag nanomaterials of varying dispersibility are prepared by using sol–gel synthesis with subsequent milling. The materials are certified using X-ray diffraction analysis, scanning electron microscopy, low-temperature nitrogen adsorption, and electrochemical testing under the lithium-ion battery operating conditions. The LiFe_0.97Ni_0.03PO₄/C/Ag cathode material primary particles’ size was shown to decrease, under the intensifying of ball-milling, from 42 to 31 nm, while the material’s specific surface area increased from 48 to 65 m²/g. The discharge capacity, under slow charging–discharging (C/8), approached a theoretical one for all materials under study. It was found that under fast charging–discharging (6 C and 30 C) the discharge capacity is inversely proportional to the particles’ mean size. The discharge capacity under the 6 С current came to 75, 94, 97, and 106 mA h/g for the initial material and that milled at a rotation velocity of 300, 500, and 700 rpm, respectively. An increase in the lithium diffusion coefficient upon the samples’ intense milling is noted.     

Effects of Mg,Al Co-doping into Mn site on electrochemical performance of LiNi<Subscript>0.5</Subscript>Co<Subscript>0.2</Subscript>Mn<Subscript>0.3</Subscript>O<Subscript>2</Subscript>

In order to study the influence of multiple ions doping into single-site on the structure and electrochemical properties of Ni-rich layered-structure cathode material LiNi_0.5Co_0.2Mn_0.3O₂, the coprecipitation of hydroxides was applied to synthesize Mg, Al co-doped cathode material LiNi_0.5Co_0.2Mn_0.3–x Mg_1/2x Al_1/2x O₂ (x = 0.00, 0.01, 0.02, 0.04) in this paper. Morphology and structure, kinetic parameter, impedance and electrochemical performance of the material were respectively characterized by SEM, XRD, CV, EIS and galvanostatic charge/discharge test. The results of comprehensive analysis showed that the properties of material were improved obviously when the amount of doping was 0.02. At this amount of doping, the corresponding material has smaller cation mixing, higher hexagonal ordering of layered-structure, larger Li⁺ ion diffusion coefficients which are 2.444 × 10^–10 and 4.186 × 10^–10 cm² s^–1 for Li+ intercalation and deintercalation respectively, smaller impedance which is 33.93 Ω, higher specific capacity of first-discharge which is 168.01 mA h g^–1 and higher capacity retention rate which is up to 95.06% after 20 cycles at 0.5 C (100 mA g^–1).     

Voltammetric determination of vitamin B<Subscript>6</Subscript> (pyridoxine) at a graphite screen-printed electrode modified with graphene oxide/Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@SiO<Subscript>2</Subscript> nanocomposite

The preparation and study of electrochemical properties of a graphite screen-printed electrode (SPE) modified with the GO/Fe₃O₄@SiO₂ (GO is graphene oxide) nanocomposites are described. The morphologies of the GO/Fe₃O₄@SiO₂ nanocomposites were examined by scanning electron microscopy. The electrochemical oxidation of vitamin B₆ (pyridoxine) on SPE modified with the GO/Fe₃O₄@SiO₂ nanocomposite was investigated by cyclic voltammetry, differential pulse voltammetry, and chronoamperometry. Under optimum conditions (pH 7.0), the vitamin B₆ oxidation at the surface of the modified SPE occurs at a potential about 190 mV less positive than that at the unmodified SPE. A linear voltammetric response for vitamin B₆ was obtained in the concentration range 1.0?10 ⁶—9.0?10 ⁴ mol L^–1 with a detection limit of 5.2?10 ⁷ mol L^–1 using differential pulse voltammetry. The developed sensor was also successfully applied for determination of trace level of vitamin B₆ in both the standard vitamin B₆ sample and biological samples (urine).     

Performance and characterisation of CeO<Subscript>2</Subscript>-TiO<Subscript>2</Subscript>-WO<Subscript>3</Subscript> catalysts for selective catalytic reduction of NO with NH<Subscript>3</Subscript>

Ce-Ti-W-O _x catalysts were prepared and applied to the NH₃-selective catalytic reduction (SCR) reaction. The experimental results showed that the Ce-Ti-W-O _x catalyst prepared by the hydrothermal method exhibited higher NO conversion than those synthesised via the sol-gel and impregnating methods, while the optimal content of WO₃ and molar ratio of Ce/Ti were 20 mass % and 4: 6, respectively. Under these conditions, the catalyst exhibited the highest level of catalytic activity (the NO conversion reached values higher than 90 %) across a wide temperature range of 225–450°C, with a range of gas hourly space velocity (GHSV) of 40000–140000 h^?1. The catalyst also exhibited good resistance to H₂O and SO₂. The influences of morphology, phase structure, and surface properties on the catalytic performance were investigated by N₂ adsorption-desorption measurement, XRD, XPS, H₂-TPR, and SEM. It was found that the high efficiency of NO removal was due to the large BET surface area, the amorphous surface species, the change to element valence states, and the strong interaction between Ce, Ti, and W.     

Synthesis and electrochemical performance of the Li-rich cathode material Li<Subscript>1.17</Subscript>Ni<Subscript>0.12</Subscript>Co<Subscript>0.13</Subscript>Mn<Subscript>0.58</Subscript>O<Subscript>2</Subscript> for lithium-ion batteries

Lithium-riched cathode material for lithium-ion batteries, Li_1.17Ni_0.12Co_0.13Mn_0.58O₂, was synthesized via crystallization from a solution of metal acetates, followed by a thermal treatment of the material obtained as a powder. The phase, elemental, and granulometric compositions of the material were examined, as well as the morphology of the powder particles obtained. The discharge capacity of the material in relation to the charging voltage was found from the results of electrochemical tests, and endurance tests were performed. The discharge capacity upon 85 charge/discharge cycles at voltages in the range 2.8–4.8 and a current of 0.1C was about 180 mA h g^–1.     

Improvement of the electrochemical properties of a LiNi<Subscript>0.5</Subscript>Mn<Subscript>1.5</Subscript>O<Subscript>4</Subscript> cathode material formed by a new solid-state synthesis method

In order to avoid the shortcomings of large particle size and poor uniformity of material synthesized by the traditional solid-state method, this paper utilizes a simple improvement of calcination process (i.e., calcination–milling–recalcination) based on the traditional solid-state synthesis to successfully prepare a large number of well-distributed, micrometer-sized, spherical secondary LiNi_0.5Mn_1.5O₄ particles. Each particle is composed of nano- and/or sub-micrometer-sized grains. Results of the electrochemical performance tests show that the material exhibits a remarkable cycle performance and rate capability compared with that obtained from traditional synthesis method; the spherical LiNi_0.5Mn_1.5O₄ particles can deliver a large capacity of 135.8 mAh g^?1 at a 1 C discharge rate with a high retention of 77 % after 741 cycles and a good capacity of 105.9 mAh g^?1 at 10 C. Cyclic voltammetry measurements confirm that the significantly improved electrochemical properties are due to enhanced electronic conductivity and lithium-ion diffusion coefficient resulting from the optimized morphology and particle size. This improved method is more suitable for mass production.     

From nickel oxalate dihydrate microcubes to NiS<Subscript>2</Subscript> nanocubes for high performance supercapacitors

In this study, NiS₂ nanocubes were successfully synthesized by a novel facile solvothermal method using NiC₂O₄·2H₂O microstructures and used as an electrode for high-performance supercapacitors. The electrochemical properties of the prepared NiS₂ electrode were studied using galvanostatic charge–discharge analysis, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) studies. Its maximum specific capacitance was 2077 F g^?1 at a constant current density of about 0.65 A g^?1. Further, the EIS results confirmed the pseudocapacitive nature of the NiS₂ electrode. The experimental results suggested that the NiS₂ electro-active material demonstrates excellent electrochemical performance with high specific capacitance, low resistance, and excellent cycling stability.     

Decay of H<Subscript>2</Subscript>O<Subscript>2</Subscript> under the action of the colloidal catalyst based on iron(III) oxides in a neutral medium

The catalytic activity of the colloidal catalyst based on iron(III) hydroxide was studied in the decomposition of H₂O₂ in a neutral medium (pH 6.7). A colloidal micellar solution of iron(III) hydroxide after preparation was kept at 19–20 °С for 2 or 20 h without additives or with C₂H₅OH additives. The decomposition of H₂O₂ under the action of the colloidal catalyst (20 h) proceeds via the first-order reaction with the decay rate constant k_d = 1.26?10^–4 s^–1, whereas the decay rate of the first-order reaction is k_d = 0.77?10^–4 s^–1 for the colloidal catalyst (2 h) prepared in the presence of C₂H₅OH.     

Natural graphite enhanced the electrochemical performance of Li<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> cathode material for lithium ion batteries

Natural graphite treated by mechanical activation can be directly applied to the preparation of Li₃V₂(PO₄)₃. The carbon-coated Li₃V₂(PO₄)₃ with monoclinic structure was successfully synthesized by using natural graphite as carbon source and reducing agent. The amount of activated graphite is optimized by X-ray diffraction, scanning electron microscope, transmission electron microscope, Raman spectrum, galvanostatic charge/discharge measurements, cyclic voltammetry, and electrochemical impedance spectroscopy tests. Our results show that Li₃V₂(PO₄)₃ (LVP)-10G exhibits the highest initial discharge capacity of 189 mAh g^?1 at 0.1 C and 162.9 mAh g^?1 at 1 C in the voltage range of 3.0–4.8 V. Therefore, natural graphite is a promising carbon source for LVP cathode material in lithium ion batteries.     

Preparation and characterization of LiFePO<Subscript>4</Subscript> from NH<Subscript>4</Subscript>FePO<Subscript>4</Subscript>·H<Subscript>2</Subscript>O under different microwave heating conditions

Olivine-type LiFePO₄ is a very promising polyanion-type cathode material for lithium-ion batteries. In this work, LiFePO₄ with high specificity capacity is obtained from a novel precursor NH₄FePO₄·H₂O via microwave processing. The grains grow up in the duration of sintering until they reach the decomposition temperature. The apparent conductivity of the samples rises rapidly with the irradiation time and influences the electrochemical performance of the material greatly at high current density. As a result, the LiFePO₄ cathode material obtained with a sintering time of 15 min has good electrochemical performance. Between 2.5 and 4.2 V versus Li, a reversible capacity is as high as 156 mAh g⁻¹ at 0.05 C.     

Preparation and electrochemical performance of nano-structured Li<Subscript>2</Subscript>Mn<Subscript>4</Subscript>O<Subscript>9</Subscript> for supercapacitor

Nano-structured spinel Li₂Mn₄O₉ powder was prepared via a combustion method with hydrated lithium acetate (LiAc·2H₂O), manganese acetate (MnAc₂·4H₂O), and oxalic acid (C₂H₂O₄·2H₂O) as raw materials, followed by calcination of the precursor at 300 °C. The sample was characterized by X-ray diffraction, scanning electron microscope, and energy-dispersive X-ray spectroscopy techniques. Electrochemical performance of the nano-Li₂Mn₄O₉ material was studied using cyclic voltammetry, ac impedance, and galvanostatic charge/discharge methods in 2 mol L⁻¹ LiNO₃ aqueous electrolyte. The results indicated that the nano-Li₂Mn₄O₉ material exhibited excellent electrochemical performance in terms of specific capacity, cycle life, and charge/discharge stability, as evidenced by the charge/discharge results. For example, specific capacitance of the single Li₂Mn₄O₉ electrode reached 407 F g⁻¹ at the scan rates of 5 mV s⁻¹. The capacitor, which is composed of activated carbon negative electrode and Li₂Mn₄O₉ positive electrode, also exhibits an excellent cycling performance in potential range of 0–1.6 V and keeps over 98% of the maximum capacitance even after 4,000 cycles.     

Electrochemical properties of spinel Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript> nanoparticles prepared via a low-temperature solid route

Spinel phase Li₄Ti₅O₁₂ (s-LTO) with an average primary particle size of 150 nm was synthesised via a solid state route by calcining a precursor mixture at 600 °C. The precursor was prepared from a stoichiometric mixture of TiO₂ nanoparticles and an ethanolic solution of Li acetate and activated by ball-milling. Effects of the calcination temperature and atmosphere are examined in relation to the coexistence of impurity phases by X-ray diffraction and ⁶Li MAS NMR. The charge capacity of s-LTO, determined from cyclic voltammogram at a scan rate of 0.1 mV/s, was 142 mAh/g. The capacity of our optimised material is superior to that of commercially available spinel (a-LTO), despite the considerably smaller BET-specific surface area of the former. The superior properties of our material were also demonstrated by galvanostatic charging/discharging. From these observations, we conclude that the presented low-temperature solid state synthesis route provides LTO with improved electrochemical performance.