Low-heating Solid-state Reaction Research Articles

Facile synthesis of hydrotalcite and its thermal decomposition kinetics mechanism study with masterplots method

Abstract The hydrotalcite, Mg4Al2(OH)12CO3·3H2O, was synthesized via low-heating solid-state reaction at 80 °C. The thermal decomposition of Mg4Al2(OH)12CO3·3H2O experienced two stages. The apparent activation energy Ea was estimated with Vyazovkin procedure. The average values of Ea associated with the two stages were determined to be 110.9 ± 10.3, 140.3 ± 4.2 kJ mol−1, respectively, which the two stages are single-step kinetic processes. Masterplots and nonlinear methods were used to define the most probable reaction mechanisms of the two stages. The results show that the reaction mechanism functions of the two stages are as follows: (i) g(α) = (1 − α)−2 − 1, (ii) g(α) = (1 − α)−1/2 − 1, respectively. The values of pre-exponential factor A for the two stages were obtained on the basis of Ea and g(α). Besides, some thermodynamic functions (ΔS#, ΔH# and ΔG#) of the transition state complexes for the two stages were also calculated.

Preparation and electrochemical properties of LiFePO4/C nanoparticles using different organic carbon sources

Uniform LiFePO4/C particles were prepared by a fast, facile, and environmentally friendly microwave-assisted low-heating solid-state reaction using different organic carbon sources. The particles are very uniform and are 50–80 nm in size. The effects of the carbon sources on the microstructure and electrochemical properties of LiFePO4/C nanoparticles were investigated by X-ray diffraction, transmission electron microscopy, and electrochemical measurements. The results showed that the LiFePO4/C nanoparticles prepared from citric acid as carbon source, which has good crystallinity and a narrow particle size distribution, provided an initial discharge capacity of 112 mAh g−1 at 0.5 C with excellent capacity retention. These advantages, coupled with the simple and effective preparation method, render LiFePO4/C nanoparticles attractive for practical and large-scale applications.

Reaction mechanisms for 0.5Li2MnO3·0.5LiMn0.5Ni0.5O2 precursor prepared by low-heating solid state reaction

Lithium-excess manganese layered oxides, which are commonly described in chemical formula 0.5Li2MnO3·0.5LiMn0.5Ni0.5O2, were prepared by low-heating solid state reaction. The reaction mechanisms of synthesizing precursors, the decomposition mechanism, and intermediate materials in calcination were investigated by means of Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The major diffraction patterns of 0.5Li2MnO3·0.5LiMn0.5Ni0.5O2 powder calcinated at 720°C for 15 h are indexed to the hexagonal structure with a space group of 3 R\(\bar 3\)m, and the clear splits of doublets at (006)/(102) and (108)/(110) indicate that the sample adopts a well-layered structure. FESEM images show that the size of the agglomerated particles of the sample ranges from 100 to 300 nm.

Fe Content Effects on Electrochemical Properties of 0.3Li<sub>2</sub>MnO<sub>3</sub>•0.7LiMn<sub>x</sub>Ni<sub>x</sub>Fe<sub>(1-2x)/2</sub> O<sub>2</sub> Cathode Materials

The cathode materials 0.3Li2MnO3•0.7LiMnxNixFe(1-2x)/2O2(0.35≤x≤0.5) were synthesized via low-heating solid-state reaction method. The prepared samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), thermogravimetric analysis (TG) and differential thermal analysis (DTA), and their electrochemical performances were also investigated here. The FESEM images of samples revealed that the particle of Fe-substituted samples became smaller and size distribution got narrower compared with the materials without Fe-doping. The results showed that electrochemical properties of the material depended on the content of Fe. 0.3Li2MnO3• 0.7LiMn0.4 Ni0.4Fe2O2 maintained 99.5% of the reversible capacity after 60 cycles

Synthesis and electrochemical characteristics of xLi 2MnO 3·(1− x)Li-(Ni 1/3Co 1/3Mn 1/3)O 2 compounds

xLi 2MnO 3·(1− x)Li(Ni 1/3Co 1/3Mn 1/3)O 2 ( x=0.25, 0.40, 0.55) compounds were prepared by low-heating solid state reaction. In the voltage range of 2.70-4.35 V, the discharge capacity of the electrode decreased with the increase of x, with a better cyclability. However, when cycled between 2.7 and 4.6 V, the cathodes delivered much larger capacities and their capacities increased with the introduction of Li 2MnO 3. Moreover, it was found that the discharge capacity gradually increased with the cycle number. The reason for this phenomenon was discussed. It was found that the relatively low cut-off potential made the activation of the Li 2MnO 3 component in the compound a gradual process, which caused the increasing capacity.

Understanding the phenomenon of increasing capacity of layered 0.65Li[Li1/3Mn2/3]O2·0.35Li(Ni1/3Co1/3Mn1/3)O2

Abstract The layered 0.65Li[Li 1/3 Mn 2/3 ]O 2 ·0.35Li(Ni 1/3 Co 1/3 Mn 1/3 )O 2 solid solution was synthesized by low-heating solid-state reaction. When the sample was cycled between 2.5 V and 4.6 V at 0.5 C, a phenomenon that the capacity increased with the cycle number was observed. The synthesized electrode delivered 97 mAh/g in the first discharge and reached the maximum of 229 mAh/g in the 24th cycle. The d Q /d V curves showed that the increasing capacity resulted from the redox-reaction of Mn. Then the cells were tested in different voltage at different rates, revealing that the main reason of the growing Mn peak is the relatively low cut-off potential. The influence of current density on the increasing capacity was also studied.

Comparative study of layered 0.65Li[Li 1/3Mn 2/3]O 2·0.35LiMO 2 (M = Co, Ni 1/2Mn 1/2 and Ni 1/3Co 1/3Mn 1/3) cathode materials

The layered cathode materials 0.65Li[Li 1/3Mn 2/3]O 2·0.35LiMO 2 (M = Co, Ni 1/2Mn 1/2 and Ni 1/3Co 1/3Mn 1/3) were synthesized by a low-heating solid state reaction. The XRD results showed that the superlattice peaks became weaker as the Co content increased and the involvement of Co helped to reduce the cation mixing. When cycled between 2.5 and 4.4 V at 0.5 C, the Ni 1/2Mn 1/2 and Ni 1/3Co 1/3Mn 1/3 containing electrodes showed excellent cycle performances and their capacities increased with the introduction of cobalt. However, when the electrodes were cycled between 2.5 and 4.6 V at 0.5 C, their discharge capacities increased gradually with cycling to a maximum. As the amount of Co increases, the number of cycles that were required to reach the maximum capacity decreases. According to the d Q/d V curves it was found that the presence of cobalt ions in the structure could accelerate the irreversible reaction above 4.5 V. Furthermore, the presence of cobalt seems to lead to the deterioration of the high potential electrochemical performance of the materials.

Synthesis and electrochemical characterization of 5 V LiNi 1/2Mn 3/2O 4 cathode materials by low-heating solid-state reaction

LiNi 1/2Mn 3/2O 4 as a 5 V cathode material, was prepared by low heating solid-state reaction with heating the mixed precursors at 500, 600, 700 °C. X-ray diffraction patterns of the prepared samples are identified as the spinel structure with a space group of F d 3 ¯ m . Scanning electron microscope was used to study the morphology of the synthesized LiNi 1/2Mn 3/2O 4 powders. The charge–discharge curves of the samples synthesized by low-heating solid-state reaction appear a plateau at 4.7 V.

Studies on the low-heating solid-state reaction method to synthesize LiNi 1/3Co 1/3Mn 1/3O 2 cathode materials

The low-heating solid-state method has been adopted to synthesize LiNi 1/3Co 1/3Mn 1/3O 2 materials. The final product, with homogeneous phase and smooth crystals indicated by XRD and SEM results, can be synthesized at 700 °C, much lower than the synthesis temperatures of co-precipitation method. The reaction process and microstructure of precursor has been investigated by IR spectrum. By comparative studies with the mixture of CH 3COOLi and (Ni, Co, Mn)(C 2O 4), it is testified that the precursor is homogeneous, rather than a mixture. The decomposition process and the reaction energy have been studied to investigate the reaction mechanism of the precursor when heated at high temperature. The as-synthesized LiNi 1/3Co 1/3Mn 1/3O 2 exhibits excellent electrochemical properties, exhibiting initial specific capacity of 167 mAh g −1 with stable cyclic performance.

Simple synthesis of CuFe 2O 4 nanoparticles as gas-sensing materials

Semiconductive nanometer-size material CuFe 2O 4 was synthesized by a low-heating solid-state reaction of inorganic reagents of Cu(CH 3COO) 2·H 2O, Fe(NO 3) 3·9H 2O and NaOH. The process was a convenient, environment friendly, inexpensive and efficient preparation method for the CuFe 2O 4 nanomaterial. X-ray diffraction (XRD) was used to confirm the material structure and scanning electron microscopy (SEM) to depict the crystallite microstructure. Conductance responses of the nanocrystalline CuFe 2O 4 thick film were measured by exposing the film to reducing gases of ammonia (NH 3), acetone (CH 3COCH 3), hydrogen (H 2) and ethanol gas (C 2H 5OH). It was found that the sensor exhibited various sensing responses to these gases at different operating temperatures. Furthermore, the sensor exhibited a fast response and a good recovery.