Electrochemical properties of nano-sized LiNi1/3Co1/3Mn1/3O2 powders in the range from 56 to 101 nm prepared by flame spray pyrolysis

Nano-sized LiNi_1/3Co_1/3Mn_1/3O₂ powders in the range from 56 to 101 nm with hexagonal α-NaFeO₂ structures are prepared directly by flame spray pyrolysis. Post-treatment of the powders at 700 °C increases their crystallinity and mean particle sizes. The intensity ratios of the powders’ (0 0 3) and (1 0 4) peaks in the XRD patterns prepared from spray solutions with lithium excesses of 10, 15 and 20% of the stoichiometric amount are 0.83, 1.25 and 1.25, respectively. The powder prepared with 15% excess lithium results in the highest initial discharge capacity of 174 mAh g⁻¹ when post-treated at 700 °C. The discharge capacity of the powder post-treated at 800 °C decreases from 168 to 120 mAh g⁻¹ after 30 cycles.     

Electrochemical properties of facile emulsified LiV3O8 materials

LiV₃O₈ cathode materials are post-treated by a special emulsion method (termed “EM”) and then calcinated at different temperatures. The experimental results show that the structure of these oxides is different from LiV₃O₈ prepared by the solid-state reaction (acronym “STATE”) route, although their starting materials are identical. The EM product prepared at 500 °C exhibits a better electrochemical behavior than its counterpart prepared by traditional methods (STATE) or by EM at other temperatures. Its initial discharge capacity is 305 mAh g⁻¹, and it still maintains 250.2 mAh g⁻¹ after 100 cycles at 0.2 C at the voltage range of 1.8–4.0 V vs. Li/Li⁺.     

Preparation of LiFePO4/C composite powders by ultrasonic spray pyrolysis followed by heat treatment and their electrochemical properties

LiFePO₄ powders could be successfully prepared from a precursor solution, which was composed of Li(HCOO)·H₂O, FeCl₂·4H₂O and H₃PO₄ stoichiometrically dissolved in distilled water, by ultrasonic spray pyrolysis at 500 °C followed by heat treatment at sintering temperatures ranging from 500 to 800 °C in N₂ + 3% H₂ gas atmosphere. Raman spectroscopy revealed that α-Fe₂O₃ thin layers were formed on the surface of as-prepared LiFePO₄ powders during spray pyrolysis, and they disappeared after sintering above 600 °C. The LiFePO₄ powders prepared at 500 °C and then sintered at 600 °C exhibited a first discharge capacity of 100 mAh g⁻¹ at a 0.1 C charge-discharge rate. To improve the electrochemical properties of the LiFePO₄ powders, LiFePO₄/C composite powders with various amounts of citric acid added were prepared by the present method. The LiFePO₄/C (1.87 wt.%) composite powders prepared at 500 °C and then sintered at 800 °C exhibited first-discharge capacities of 140 mAh g⁻¹ at 0.1 C and 84 mAh g⁻¹ at 5 C with excellent cycle performance. In this study, the optimum amount of carbon for the LiFePO₄/C composite powders was 1.87 wt.%. From the cyclic voltammetry (CV) and AC impedance spectroscopy measurements, the effects of carbon addition on the electrochemical properties of LiFePO₄ powders were also discussed.     

CTAB-assisted sol-gel synthesis of Li4Ti5O12 and its performance as anode material for Li-ion batteries

A simple CTAB-assisted sol-gel technique for synthesizing nano-sized Li₄Ti₅O₁₂ with promising electrochemical performance as anode material for lithium ion battery is reported. The structural and morphological properties are investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The electrochemical performance of both samples (with and without CTAB) calcined at 800 °C is evaluated using Swagelok™ cells by galvanostatic charge/discharge cycling at room temperature. The XRD pattern for sample prepared in presence of CTAB and calcined at 800 °C shows high-purity cubic-spinel Li₄Ti₅O₁₂ phase (JCPDS # 26-1198). Nanosized-Li₄Ti₅O₁₂ calcined at 800 °C in presence of CTAB exhibits promising cycling performance with initial discharge capacity of 174 mAh g⁻¹ (∼100% of theoretical capacity) and sustains a capacity value of 164 mAh g⁻¹ beyond 30 cycles. By contrast, the sample prepared in absence of CTAB under identical reaction conditions exhibits initial discharge capacity of 140 mAh g⁻¹ (80% of theoretical capacity) that fades to 110 mAh g⁻¹ after 30 cycles.     

Electrochemical properties of 0.3Li2MnO3·0.7LiNi0.5Mn0.5O2 composite cathode powders prepared by large-scale spray pyrolysis

0.3Li₂MnO₃·0.7LiNi_0.5Mn_0.5O₂ composite cathode powders with a mixed-layer crystal structure comprising Li₂MnO₃ and LiNi_0.5Mn_0.5O₂ phases are prepared by spray pyrolysis. The composition of the cathode powders is found to be Li_1.19Ni_0.39Mn_0.61O₂ by ICP analysis. At a constant current density of 30 mA g^?1, the initial discharge capacities of the composite cathode powders post-treated at 700, 750, 800, and 850 °C are 177, 202, 215, and 212 mAh g^?1, respectively. The discharge capacity of the composite cathode powders post-treated at 800 °C decreases from 215 mAh g^?1 to 205 mAh g^?1 by the 40th cycle, in which the capacity retention is 95%. The first cycle has a low Coulombic efficiency of 75%. However, in the subsequent cycles, the Coulombic efficiency is retained at nearly 100%. The dQ/dV curves show that Mn exists as Mn⁴⁺ in the sample. The Mn⁴⁺ ions in the cathode powders become increasingly active as the cycle number increases and participate in the electrochemical reaction.     

Microstructure and electrical conductivity of LaNi0.6Fe0.4O3 prepared by combustion synthesis routes

The continuing development of new materials suitable for solid oxide fuel cells operating at about 650-800 °C is of great interest in recent days. The present investigation deals with the development of a perovskite composition-LaNi_0.6Fe_0.4O₃ (LNF)-prepared following two combustion synthesis routes: citrate-gel (LNC) and urea (LNU). The powders were sintered over a wide temperature range (900-1400 °C) and sintering behavior for LNC and LNU was compared. The thermal expansion coefficient (TEC), electrical and microstructural characteristics of LNF was thoroughly investigated. Electrical conductivities were found to be one and a half times higher than that of most commonly used cathode material, La(Sr)MnO₃. Moreover, the TEC value of LNF was found to be ≈11.4×10⁻⁶ K⁻¹ at 800 °C. The study opens up a possibility of using LNF as a promising cell component for SOFC.     

Preparation of porous SnO2 helical nanotubes and SnO2 sheets

We report a surfactant-free chemical solution route for synthesizing one-dimensional porous SnO₂ helical nanotubes templated by helical carbon nanotubes and two-dimensional SnO₂ sheets templated by graphite sheets. Transmission electron microscopy, X-ray diffraction, cyclic voltammetry, and galvanostatic discharge–charge analysis are used to characterize the SnO₂ samples. The unique nanostructure and morphology make them promising anode materials for lithium-ion batteries. Both the SnO₂ with the tubular structure and the sheet structure shows small initial irreversible capacity loss of 3.2% and 2.2%, respectively. The SnO₂ helical nanotubes show a specific discharge capacity of above 800 mAh g⁻¹ after 10 charge and discharge cycles, exceeding the theoretical capacity of 781 mAh g⁻¹ for SnO₂. The nanotubes remain a specific discharge capacity of 439 mAh g⁻¹ after 30 cycles, which is better than that of SnO₂ sheets (323 mAh g⁻¹).     

Conductive polyaniline capped Fe2O3 composite anode for high rate lithium ion batteries

A composite of Fe₂O₃ capped by conductive polyaniline (PANI) was synthesized by a facile two-step method through combining homogeneous Fe₂O₃ suspension prepared by a hydrothermal method and in-situ polymerization of aniline. As anode material for lithium ion batteries, the Fe₂O₃/PANI composite manifests very large discharge capacities of 1635 mAh g⁻¹, 1480 mAh g⁻¹ at large currents of 1.0 and 2.0 A g⁻¹ (1C and 2C), respectively, as well as good cycling performance and rate capacity. The enhancement of electrochemical performance is attributed to the improved electrical conductivity and effective ion transportation of the composite electrode, in that, PANI keeps the Fe₂O₃ nanorods uniformly connected and offers conductive contact between the electrolyte and the active electrode materials.     

High rate performance of novel cathode material Li1.33Ni1/3Co1/3Mn1/3O2 for lithium ion batteries

Li_1.33Ni_1/3Co_1/3Mn_1/3O₂ with highly ordered structure has been successfully synthesized via a simple co-precipitation process. Charge–discharge tests showed that the initial discharge capacities are 153.0 mAh g⁻¹ and 128.9 mAh g⁻¹ at 5 C (1000 mA g⁻¹) and 10 C (2000 mA g⁻¹) between 2.5 and 4.5 V, respectively. The average full-charge time of this material is less than 12 min at 5 C and 6 min at 10 C. The electrode material composed of the prepared showed a better cyclability. The excellent high rate performance is attributed to the improved ordered layered structure and the electrical conductivity. The excess Li shorten Li⁺ diffusion distance between these submicron and nano-scaled particles. The results show that Li_1.33Ni_1/3Co_1/3Mn_1/3O₂ cathode material has potential application in lithium ion batteries.     

Low-temperature sintering characteristics of nano-sized BaNd2Ti5O14 and Bi2O3–B2O3–ZnO–SiO2 glass powders prepared by gas-phase reactions

Nano-sized BaNd₂Ti₅O₁₄ (BNT) powders were prepared by spray pyrolysis from solutions containing ethylenediaminetetraacetic acid and citric acid. Treatment at temperatures ≥900 °C and subsequent milling resulted in nanoparticle powders with orthorhombic crystal structures. The mean particle size of the powder post-treated at 1000 °C was 160 nm. Nano-sized Bi₂O₃–B₂O₃–ZnO–SiO₂ glass powder with 33 nm average particle size was prepared by flame spray pyrolysis and used as a sintering agent for the BNT. BNT pellets sintered at 1100 °C without the glass had porous structures and fine grain sizes. Those similarly sintered with the glass had denser structures and larger grains.     

Preparation and characteristics of nanostructured MnO2/MWCNTs using microwave irradiation method

Ball-nanostructured MnO₂/MWCNTs composite was successfully prepared by microwave irradiation. The surface morphology and structures of the composite were examined by scanning electron microscope and X-ray diffraction. Multi-walled carbon nanotubes play a role as sustainment to inhibit MnO₂ nanoplates from collapsing into nanorods. The electrochemical studies indicated that the composite had ideal capacitive performance and high specific capacitances of 298 F g^− 1, 213 F g^− 1 and 198 F g^− 1 at the current density of 2 mA·cm^− 2, 10 mA·cm^− 2 and 20 mA·cm^− 2, respectively. The formation mechanism of nanostructured MnO₂/MWCNTs and the electrochemical behaviour of composites were discussed in detail.     

Fabrication and lithium intercalation properties of epitaxial Li2RuO3 thin films

Lithium intercalation in a lithium excess layered material Li₂RuO₃ was investigated using two-dimensional model electrodes with a restricted reaction plane of (002). Li₂RuO₃ films were synthesized on Al₂O₃(0001) substrate by a pulsed laser deposition, and X-ray diffraction measurements confirmed epitaxial growth of Li₂RuO₃(002). Electrochemical characterization using cyclic voltammetry and charge/discharge measurements indicated electrochemical reactions with a discharge capacity of 200 mAh g^− 1 for the film deposited at 400 °C followed by post-annealing at 550 °C. The electrochemical activity on the (002) plane indicated three-dimensional lithium diffusion in the two-dimensional layered rocksalt structure through the lithium sites in the transition metal layer.     

One-step hydrothermal synthesis of Li<Subscript>2</Subscript>FeSiO<Subscript>4</Subscript>/C composites as lithium-ion battery cathode materials

Li₂FeSiO₄/C composites were one-step synthesized under hydrothermal conditions at 200 °C for 72 h using glucose as carbon source. By adjusting the quantity of added glucose, we obtained varied Li₂FeSiO₄/C composites with different size and morphology. A series of electrochemical tests demonstrate that the Li₂FeSiO₄/C nanoparticles with diameters about 20 nm have higher discharge capacity, and slower capacity fading in comparison with Li₂FeSiO₄ and other Li₂FeSiO₄/C composites. Li₂FeSiO₄/C nanoparticles deliver a discharge capacity of 136 mAh g⁻¹ at 0.2 C, and after 100 cycles, the discharge capacity remains 96.1%. Furthermore, Li₂FeSiO₄/C nanoparticles also exhibit an excellent rate capability with a capacity of about 80 mAh g⁻¹ at 10 C.     

High energy density lithium ion batteries using Li2.6Co0.4 − xCuxN (anode) and Cu0.04V2O5 (cathode) electrode materials

Li_2.6Co_0.4 - xCu_xN (x = 0, 0.15) anode materials were prepared by conventional solid state reaction. Between both materials, Li_2.6Co_0.25Cu_0.15N exhibited better capacity retention than that of Li_2.6Co_0.4N. According to electrochemical impedance spectroscopy, the better cycling behavior of Li_2.6Co_0.25Cu_0.15N has been attributed to the improvement in interfacial compatibility between the electrode and electrolyte interface. A possible explanation to this was given. Li_2.6Co_0.4 - xCu_xN/Cu_0.04V₂O₅ full-cells were assembled to investigate the reliability of Li_2.6Co_0.4 - xCu_xN anode materials in practical applications. The Li_2.6Co_0.25Cu_0.15N/Cu_0.04V₂O₅ cell delivered a specific capacity of 260 mA h g^− 1, and a specific energy of 505.7 mW h g^− 1, which was much higher than that of C/LiCoO₂ lithium ion batteries.     

Organic phosphoric sources for syntheses of Li3V2(PO4)3/C via improved rheological phase reaction

Li₃V₂(PO₄)₃/C is synthesized by an improved rheological phase method using Hydroxy Ethylidene-1,1-Diphosphonic Acid (HEDP) as organic phosphoric sources. The phosphoric sources with carbon chains can inhibit the grain growth of Li₃V₂(PO₄)₃ particles. X-ray powder diffraction pattern shows that the obtained Li₃V₂(PO₄)₃/C sample is monoclinic phase. Transmission electron microscope results show that the thickness of carbon layer is about 10 nm. The form of residual carbon is confirmed by Raman spectroscopy. The Li₃V₂(PO₄)₃/C sample prepared by 1-Hydroxy Ethylidene-1,1-Diphosphonic Acid (HEDP) displays the initial discharge capacity of 158 mAh g^− 1 and keeps 130 mAh g^− 1 after 100 cycles at 1 C rate. The improved rheological phase reaction method can be used for synthesis of Li₃V₂(PO₄)₃ cathode material and other polyanion materials.     

Preparation and electrochemical performance of LiFePO4/C composite with network connections of nano-carbon wires

LiFePO₄/C composite with network connections of nano-carbon wires was successfully prepared by using polyvinyl alcohol as carbon source. The composite was characterized by X-ray diffraction and transmission electron microscopic, and its electrochemical performance was investigated by galvanostatic charge and discharge tests. The experimental results show that LiFePO₄ grains are tightly connected by the network of nano-carbon wires. Moreover LiFePO₄/C composite exhibits high capacity of 168 mAh g⁻¹ applied 15 mA g⁻¹ current density (C/10), excellent cyclic ability and rate capability. When 1500 mA g⁻¹ current density (10C) was applied, the high discharge capacity of 129 mAh g⁻¹ has been obtained at room temperature.     

Crystallite structure,microstructure, dielectric,and piezoelectric properties of (Pb1.06−xBax)(Nb0.94Ti0.06)2O6 piezoelectric ceramics prepared using calcined powders with different phases

In an attempt to obtain dense lead metaniobate-based ceramics with improved dielectric and piezoelectric properties, the (Pb_1.06−xBa_x)(Nb_0.94Ti_0.06)₂O₆ (x = 0, 0.04, 0.08, 0.12) piezoelectric ceramics were prepared separately from the two kinds of calcined powders, i.e., the powders with the rhombohedral phase and orthorhombic phase. For obtaining the calcined powders with the different phases, two different calcination temperatures of 900 °C and 1250 °C were chosen. The calcined powders were characterized using X-ray diffraction, scanning electron microscope, laser particle size analyzer and differential scanning calorimetry. Effects of the phase structures of the calcined powders on crystallite structure, microstructure, dielectric and piezoelectric properties of the ceramics were studied in detail. The lattice parameters and grain size of the ceramics are related to the phase structures of the calcined powders. The doping of Ba²⁺ has an influence on the dielectric and piezoelectric properties of the ceramics. The ceramics with x = 0.08 fabricated from the calcined powders with the orthorhombic phase demonstrate the optimum dielectric and piezoelectric properties.     

MgO-templated porous carbons-based CO2 adsorbents produced by KOH activation

Nanoporous (styrene–divinylbenzene)-based ion exchange resin-based carbons (MPCs) were prepared by MgO-templating synthesis and activated by KOH. MPCs were prepared from a (styrene–divinylbenzene)-based ion exchange resin by the carbonization of a mixture with Mg gluconate at 900 °C. And then, the prepared MPCs were treated with KOH at KOH/MPCs ratios ranging from 0.5 to 4 at 800 °C. Low KOH/MPCs ratios (KOH/MPCs ratio = 1) tended to favor the formation of micropores, whereas higher KOH/MPCs (KOH/MPCs ratio = 4) led to the formation of mesopores. The treated MPCs with a KOH/MPCs ratio = 1 exhibited the best CO₂ adsorption value of 266 mg g⁻¹ at 1 bar. However, the treated MPCs with a KOH/MPCs ratio = 3 exhibited the best CO₂ adsorption value of 1385 mg g⁻¹ at 30 bar. This result indicated that the CO₂ adsorption capacity of nanoporous carbons attributed to the mesopore volume fraction at higher pressure.     

Phenol-formaldehyde resin-assisted synthesis of pure porous Li4Ti5O12 for rate capability improvement

Porous Li₄Ti₅O₁₂ has been synthesized via a simple template method using phenol-formaldehyde resin as template. SEM, TEM, XRD, nitrogen adsorption, galvanostatic charge-discharge, and ac impedance tests are used to characterize the appearance, structure, and electrochemical performance of the samples. The micrometer-scale crystal particles exhibit rough surface, large specific surface area, porous structure, and superior electrochemical performance. The initial discharge specific capacity is 167 mAh g⁻¹ under 0.2 C discharge rate, when the rate increases to 2.0 C, the capacity still retains to 112 mAh g⁻¹, exhibiting excellent rate capability.     

Effect of rhodium substitution on the electrochemical performance of LiFePO4/C

The effect of rhodium (Rh) substitution on the electrochemical properties of LiFePO₄/C cathode materials was studied. The results of electrochemical measurement show that Rh substitution can improve the rate capability of LiFePO₄/C. However, heavy Rh substitution causes a discharge capacity loss. The LiFe_0.975Rh_0.025PO₄/C sample shows an excellent high rate performance and its discharge capacity at a 10 C rate is 117.0 mAh g⁻¹ with a discharge voltage plateau of 3.31–3.0 V versus Li/Li⁺. LiFe_0.975Rh_0.025PO₄/C also shows a noticeably better cycling life at high temperature than LiFePO₄/C. It still remains a capacity of 135.4 mAh g⁻¹ at the 300th cycle at 55 °C under a 1 C rate, which is 82.0% of its initial capacity.