Search

A free-standing transparent film for sodium-ion conduction in PEO-based solid polymer electrolyte (additionally comprising NaClO4 and nano-sized TiO2) has been fabricated for use in Na-ion batteries by using a solution casting technique. The crystallinity of the solid polymer electrolyte and the interactions between PEO and the Na-ions is characterized by X-ray diffraction (XRD) and Fourier transformed infra-red (FTIR) spectra, which reveals the degree of Na+ ion solvation by PEO oxygen atoms (EO:Na). The ionic conductivities of the films are investigated by impedance analysis from 1 MHz to 1 Hz within the temperature range 303–363 K. A solid polymer electrolyte with anatomic ratio EO:Na = 20 exhibits a maximum ionic conductivity of 1.35 × 10−4 S cm−1, which increases to 2.62 × 10−4 S cm−1 by the addition of TiO2 (3.4 nm, 5 wt%) at temperature 60 °C. The performance of a Na2/3Co2/3Mn1/3O2 half cell with a polymer electrolyte is compared to a similar cell with a liquid electrolyte.

In this study, size effect of NiO particles has been studied as the anode material of lithium ion battery. It is found that NiO nanoparticles synthesized in confined space of ordered mesoporous silica behave anomalous high capacity and higher energy efficiency than sub-micro-sized NiO does. The higher energy efficiency is resulted from the reduction of the hysteresis loop between charge and discharge voltage plateaus, the main drawback of conversion reaction-based metal oxide anode materials. The interesting behavior is proposed to be the reversible formation/dissolution of solid electrolyte interphase (SEI) layers associated with 3-D porous, originally nanostructured NiO electrode that is able to remain stable during charge–discharge process.

Despite the intensive effort directed at the synthesis of anion exchange membranes (AEMs) only a few studies show enhanced ionic conductivity with simultaneous suppression of unfavourable mass transport and improved thermal and mechanical properties. Here we report an alkaline nanocomposite membrane based on fully exfoliated graphene nanosheets and poly(vinyl alcohol) (PVA) prepared by a simple blending process. The composite membrane shows improved ionic transport due to the homogeneous distribution of the graphene nanosheets which are able to form continuous, well-connected ionic channels. Significant enhancement of the ionic conductivity for the prepared graphene/PVA composite membranes is observed with a 0.7 wt% graphene loading resulting in a ∼126% improvement in ionic conductivity and a ∼55% reduction in methanol permeability. The resulting maximum power density obtained by incorporating the membrane in a cell is increased by ∼148%. A higher graphene loading (1.4 wt%) enhances the adhesion of the nanofiller–matrix, giving a ∼73% improvement in the tensile strength. This study provides a simple route to designing and fabricating advanced AEMs.

Effects caused by the morphology of mesoporous silica on the characterization of protic ionic liquid-based composite membranes for anhydrous proton exchange membrane applications are investigated. Two types of SBA15 materials with platelet and fiberlike morphologies are synthesized and incorporated into a mixture of polymerizable monomers together with an ionic liquid (IL) [1-butyl-3-methylimidazolium bis(trifluoromethane sulfone)imide (BMIm-TFSI)] to form new conducting membranes using an in situ photo crosslinking process. Incorporation of a defined amount of fiber-shaped SBA 15 and platelet 15 significantly increases the ionic conductivity to between two and three times that of a plain poly(methyl methacrylate) (PMMA)/IL membrane (2.3 mS cm −1 )a t 160

In this study, a novel mesoporous carbon-encapsulated NiO nanocomposite is proposed and demonstrated for Li-ion battery negative electrode. The nanostructure of the electrode composes of an ordered mesoporous CMK-3 as a 3D nanostructured current collector with micorporous channels for Li+ transportation. In addition, exclusive formation of NiO nanoparticles in the confined space of the ordered mesoporous carbon is achieved using the hydrophobic encapsulation route. The half-cell assembled with the synthesized NiO/CMK-3 nanocomposite is able to deliver a high charge capacity of 812 mAh g−1 at the first cycle at a C-rate of 1000 mA g−1 and retained throughout the test with only 0.236% decay per cycle. Even the C-rate as high as 3200 mA g−1, a charge capacity of 808 mAh g−1 contributed by the NiO nanoparticles in CMK-Ni is obtained, which shows excellent rate capability for NiO with utilization close to 100%. The result suggests fast kinetics of conversion reaction for NiO with Li+. It also indicates the blockage of the pore channels by NiO nanoparticles does not take place in the synthesized NiO/CMK-3.

In this study, the mechanism of enhanced performance of ZrO2-coated LiCoO2 especially at high potential range is systematically investigated. Firstly, when overcharging to 4.5 V (higher than 4.2 V, the normal cutoff charging potential), phase transformation from H1 to H2 takes place with less volume expansion for ZrO2-coated LiCoO2 (1.2% and 2.2% for as-received one). EIS analysis indicates the growth of interfacial impedance during charging/discharging can be effectively suppressed with ZrO2 coating on the LiCoO2 surface. It is demonstrated as well that cation mixing of the cycled LiCoO2 caused by re-intercalation of dissolved Co2+ is inhibited with the ZrO2 coating on the LiCoO2. Therefore the ZrO2-coated LiCoO2 shows great enhancement in the electrochemical properties with 85% capacity retention after 30 cycles from 3 to 4.5 V at a rate of 0.5C. Nevertheless, under the same evaluation process, the as-received LiCoO2 possesses only 21% capacity retention, which is resulted from the formation of polymeric layers by the electrolyte decomposition on its surface, the higher volumetric changes during charging/discharging and possible cation mixing by re-intercalation of the dissolved Co2+.

The synthesis of rod-like LiFePO 4 /C cathodes using template-free reverse micelle process is reported for high performance lithium batteries. We have demonstrated that the size of the primary particles could be controlled based on sintering temperature and sintering time and size of the large aggregates is adjustable based on the carbon content of the sample. Thermogravimetry and differential thermal analysis have been used to propose a possible mechanism for the formation rod-like LiFePO 4 /C cathode material. X-ray diffraction, scanning electron microscopy, impedance spectroscopy and charge–discharge measurements have been used to characterize the material. Electrochemical performance of rod-like LiFePO 4 /C cathode material offers higher initial capacity and excellent rate capability than that obtained by loose porous LiFePO 4 /C material due to unique rod-like composite material formed by primary nanoparticles. Hence, it can be suggested that that the rod-like nanostructured morphology improves structural stability, lithium ion diffusion and electronic conductivity of the LiFePO 4 /C composite material. The template-free reverse micelle process for the synthesis of the rod-like LiFePO 4 /C cathode material opens up a new route to synthesize lithium transition metal oxides with controlled morphologies for applications in high power lithium batteries.

Li1.02Ni0.5Mn1.5O4 spinel cathode materials were successfully synthesized by a citric acid-assisted sol–gel method. The structure and morphology of the materials have been examined by X-ray diffraction and scanning electron microscopy, respectively. Electrochemical properties of the materials were investigated using cyclic voltammetry and galvanostatic charge/discharge measurements at two different temperatures (25 and 55 °C) using lithium anode. The initial capacity and capacity retention are highly dependent on the particle size, particle size distribution, crystallinity and purity of the materials. The Li1.02Ni0.5Mn1.5O4 materials synthesized both at 800 and 850 °C have shown best electrochemical performance in terms of capacity and capacity retention between 3.5 and 4.9 V with a LiPF6 based electrolyte.

The local structure and oxidation states for both the precursors and the LiFePO 4 /C composite powders were investigated by X-ray absorption spectroscopy (XAS) to provide a deep insight into their formation mechanism. It was found that the local structure and oxidation states of the precursors and the synthesized LiFePO 4 /C powders as well as the electrochemical properties of the synthesized powders were strongly influenced by the R ratio ( R : molar ratio of citric acid to total metal ions). The oxidation states of iron ions of the precursors for R = 1 and 0.75 consist mainly of Fe(II) and traces of Fe(III). However, the oxidation state of iron ions of the precursor for R = 0.5 comprises mainly of Fe(III). The oxidation state of iron ions of all the synthesized powders is Fe(II). The structure of the precursors and the synthesized powders for R = 1 and 0.75 is more ordering than that for R = 0.5. It is in good agreement with the observation of the cation mixing obtained from the Riteveld analysis of the XRD data. The better the electrochemical performance is, the more ordering the structure or the less the cation mixing. However, the effect of the R values on the carbon content is also essential for the electrochemical properties of the synthesized LiFePO 4 /C composite powders. Increasing the carbon content leads to the increase in the electronic conductivity but impedes the Li + ion diffusion of the composite materials. Consequently, the powders synthesized at the optimal R ratio of 0.75 exhibited the highest initial capacity, about 150 mAh g −1 when cycled at 1/40 C rate at room temperature. The structural scheme of the precursors and the synthesized powders and the formation mechanism of the LiFePO 4 /C composite powders are also addressed in this work.

A modified synthesis process was developed based on co-precipitation method followed by spray drying process. In this process, a spherical shaped (Co1/3Ni1/3Mn1/3)(OH)2 precursor was synthesized by co-precipitation and pre-heated at 500 °C to form a high structural stability spinel (CoNiMn)O4 to maintain its shape for further processing. The spherical LiNi1/3Co1/3Mn1/3O2 was then prepared by spray drying process using spherical spinel (CoNiMn)O4. LiNi1/3Co1/3Mn1/3O2 powders were then modified by coating their surface with a uniform and nano-sized layer of ZrO2. The ZrO2-coated LiNi1/3Co1/3Mn1/3O2 material exhibited an improved rate capability and cycling stability under a high cut-off voltage of 4.5 V. X-ray diffraction (XRD) measurements revealed that the material had a well-ordered layered structure and Zr was not doped into the LiNi1/3Co1/3Mn1/3O2. Electrochemical impedance spectroscopy measurements showed that the coated material has stable cell resistance regardless of cycle number. The interrupt charging/discharging test indicated that the ZrO2 coating can suppress the polarization effects during the charging and discharging process. From these results, it is believed that the improved cycling performance of ZrO2-coated LiNi1/3Co1/3Mn1/3O2 is attributed to the ability of ZrO2 layer in preventing direct contact of the active material with the electrolyte resulting in a decrease of electrolyte decomposition reactions.

The synthesis and formation mechanism of the nano-sized Ce 0.8 Sm 0.2 O 1.9 particles prepared by a urea-based low-temperature hydrothermal process was investigated in this study. From ex situ X-ray diffraction and induced coupled plasma-atomic emission spectroscopy investigations, it was found that large quantities of cerium hydroxide co-precipitated with some samarium hydroxide at the initial stage of the hydrothermal process. The remaining Sm 3+ ions in the solutions were further hydrolyzed and deposited on the surface of the cerium hydroxide-rich precipitates to form a core–shell-like structure. During the hydrothermal process, the core–shell-like structure transformed to a single cubic fluorite phase which is due to the incorporation of the deposited samarium hydroxide into the cerium oxide-rich core. Further, the average grain size of the synthesized nanocrystalline Ce 0.8 Sm 0.2 O 1.9 was reduced with increasing the urea concentration in the solution. The density of the disk prepared with the synthesized Ce 0.8 Sm 0.2 O 1.9 powders was found to increase with a decrease in the grain size of Ce 0.8 Sm 0.2 O 1.9 . The existence of SO 4 2− anions in the SDC powders prepared at low-urea concentration may result in the SDC disks with low density due to their decomposition during sintering process.

Multi-scale dispersion involving dispersion of catalyst particles on carbon support as well as intra-particle dispersion within the particles of a ternary Pt-Ru-Ti/C catalyst has been demonstrated. The presence of TiO 2 can dramatically decreases the grain size of the obtained catalyst to about 1–2 nm when compared with similarly prepared Pt-Ru/C (3–4 nm) catalyst indicating that TiO 2 can enhance the dispersion of the catalyst particles on carbon support. The structure and distribution of the Pt-Ru-Ti/C catalyst nanoparticles has been studied from high angle annular dark-field (HAADF) images combining with energy-dispersive X-ray spectroscopy (EDX). The composition of the Pt–Ru–Ti/C was found to be 50:34:16 (Pt:Ru:Ti, at%). The role of TiO 2 in improving the intra-particle distribution has been investigated by X-ray absorption spectroscopy (XAS) at extended X-ray absorption fine structure region (EXAFS). The XAS parameters suggest that the Pt-Ru-Ti/C catalyst possess a structure in which the core is rich in Pt–Ru alloy and the shell is rich in Pt. In the shell, the Pt, Ru and TiO 2 species are distributed homogenously. As a result of the improved multi-scale dispersion, the Pt-Ru-Ti/C catalyst exhibited enhanced activity towards methanol oxidation when compared to the commercial E-TEK 30 Pt-Ru/C catalyst and shows nearly similar performance when compared to the commercial JM 30 Pt-Ru/C catalyst with promising applications in fuel cells.