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Na2Ti3O7/C prepared by a simple acrylamide-assisted sol–gel method shows promising electro-chemical performance as an anode material for sodium-ion batteries. It maintains ca. 100 mAh·g−1 capacity after 100 cycles at 0.1C rate. What's more, it displays about 206.4, 181.2, 151.8, 129.0, 100.3, and 63.4 mAh g−1 at 0.1, 0.2, 0.5, 1, 2, and 5 C current rate, respectively. A capacity of 156.4 mAh·g−1 is recovered when the current density is back to 0.2 C. Density functional theory (DFT) together with molecular dynamics (MD) is used to reveal the Na+ intercalation and diffusion mechanism. Theoretical calculation shows highly active Na+ migration on the b–c planes, with a minimal 0.22 eV energy barrier and the highest diffusion coefficient of 3.8 × 10−7 cm2 s−1 along the b-axis, at the fully charged state. The high vitality of Na+ is maintained until the intercalation level x is more than 0.5. After that, the mobility of Na+ is greatly prohibited, leading to an energy barrier of more than 0.7 eV and a diffusion coefficient within the range 10−14–10−15 cm2 s−1 at the fully discharged state of Na4Ti3O7. The formation energy convex hull determined by means of cluster expansion enables the calculation of voltage profile and the variation of cell parameters, which reveals the low strain (< 1%) feature during the battery cycles. The calculation of electronic structure also reveals an insulator–metal transition upon the sodiation of the Na2Ti3O7 material. [ABSTRACT FROM AUTHOR]

During the first cycle of lithium-ion batteries, a passivation layer is formed on the surface of electrode due to electrolyte decomposition, which is called solid electrolyte interface (SEI). In this study, the evolution of LiFePO4 cathode surface and components of SEI layer are investigated in different states by high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy. The results suggest that SEI layer is mainly formed during the first cycle and remains stable in the following cycles. Furthermore, SEI layer can be divided into two parts, and components of these two parts are different. The outer layer that is near to electrolyte is composed of organic components, and the inner layer that is near to active material is composed of inorganic components. Taken together, the study reveals SEI layer formation process on LiFePO4 cathode surface, which is of significance for understanding the influence of SEI layer on electrochemical performance. [ABSTRACT FROM AUTHOR]

In this work, the atomistic simulation method based on Pedone model is applied to observe the concerted motion of lithium-ions in the perfect lattice of possible Li9Cr3(P2O7)3(PO4)2 cathode material. The simulation is carried out at a series of increasingly elevated temperatures in a super cell containing 27 unit cells. The superimposed Li+ trajectory at all timeframes offers an intuitive, reliable image of the Li+ migration in the crystal lattice. It reveals that lithium-ion propagates in a–b plane in an isotropic way and the propagation along the c axis is negligible. A typical lithium-ion migration path along the a or b axis can be described as migrating consecutively in the repeated sequence of Li1, Li3, Li1, and Li2. The energy barrier of Li9Cr3(P2O7)3(PO4)2 cathode material is about 0.345 eV and the estimated lithium-ion diffusion coefficients at room temperature are estimated at ca. 1.96 × 10−9 cm2 s−1. Compared with those intensively investigated cathode materials for lithium-ion batteries, which are normally considered to be highly potential or already in practical use, the lithium-ion conduction in the crystal grain for Li9Cr3(P2O7)3(PO4)2 cathode material is comparable or even superior. Therefore, the Li+ mobility is sufficiently high to exhibit good performances as a cathode material for lithium-ion batteries. More researches concerning the preparation, phase transformation, doping, surface modification, and the characterization of electro-chemical performance are urgently needed. [ABSTRACT FROM AUTHOR]

Aqueous magnesium ion batteries have been identified as potential electrochemical energy storage system due to their similar electrochemical properties to lithium, safety, high abundance, and low cost. Here, micron-sized Na0.7MnO2.05 is prepared by a facile sol-gel method used for cathode material in aqueous magnesium ion batteries. XRD, XPS, SEM, TEM, and EDS were used to test the composition, structure, and morphology of Na0.7MnO2.05. Na0.7MnO2.05 material is electro-chemical active although the intercalation/deintercalation is much difficult for Mg2+. The reversible specific capacities of the Na0.7MnO2.05 cathode material are estimated to be ca. 40, 35, 22, and 13 mAh·g−1 at the current density of 1 C, 2 C, 5 C, and 10 C, respectively. When the current density comes back to 1 C, the charge capacities recover to 40 mAh·g−1. Furthermore, EIS and GITT measured show that the diffusion coefficient of Mg2+ ion in lattice of Na0.7MnO2.05 varies from 2.17 × 10−11 cm2·s−1 to 7.81 × 10−11 cm2·s−1 in charge process and changes from 6.34 × 10−12 cm2·s−1 to 7.14 × 10−11 cm2·s−1 in discharge process. [ABSTRACT FROM AUTHOR]

C/FeOF/FeF3 nanocomposite was synthesized by a facile in situ partial oxidation method. High-resolution transmission electron microscopy (HR-TEM) showed a special texture comprised of interpenetrating nanodomains of FeOF and FeF3. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements revealed that the introduction of nanodomain FeOF enhanced both the electronic and ionic conductivity of the composite material. Therefore, the improvement of electron and lithium-ion dynamics resulted in the significant enhancement of the electrochemical performances of the material at ambient temperature. At a current density of 20 mA g−1 within potential range 1.5-4.5 V, the specific capacities of the first ten circles were maintained at about 400 mAh g−1. This material also exhibited excellent cycling capacity retention capability especially for high C rates. When the current density further increased to 100 and 200 mA g−1, a steady capacity of 80 and 60 mAh g−1 was observed, respectively. Furthermore, nearly no capacity loss was observed for the followed cycles. The discharge platforms based on intercalation and conversion reaction were also heightened by about 0.4 V, which increased the contribution of high voltage capacities. Compared to C/FeF3, C/FeOF/FeF3 is showing more of capacitive behavior, which also contributes to the high specific capacity delivered and is believed to be closely related to the enlarged nanodomain interfaces between two electrochemical active materials. An expansion-cracking-oxidation mechanism was proposed to explain the formation of this interpenetrating nanodomains of FeOF and FeF3. [ABSTRACT FROM AUTHOR]

Time-dependent elementary polarizations of FeF·3HO/C cathode material were quantitatively investigated in dc polarization in order to determine the key factors that comprise the total polarization. The measurement of electrochemical impedance spectrum at a given state of charge and the subsequent least square fitting of its equivalent circuit allow the calculation of elementary contributions of individual kinetic step to the total polarization. The profiles of the calculations were well consistent with those of experiments based on the same states of charge, and the elementary contributions could be differentiated successfully which reveal that the solid-state diffusion process makes the largest contribution to the total polarization after 2.5 s discharge beginning with open-circuit voltage (OCV) level 3.5 V. The results may be helpful for the design of batteries of better performance with FeF cathode. [ABSTRACT FROM AUTHOR]

The LiVPOF as cathode material for lithium-ion batteries was synthesized through two steps of solid-state reactions and investigated by ex situ Fourier transform infrared (FTIR) spectroscopy for the initial charge and discharge cycle. The characterization of the effect on the structure of the LiVPOF in the process of lithium-ion insertion/extraction at a molecular level by ex situ FTIR spectroscopy is helpful for the mechanism research for lithium-ion insertion/extraction and the improvement of the performance of lithium-ion batteries. In the process of the initial cycle, new bands of VPOF appear in the charge and the featured bands of LiVPOF reappear in the discharge. In this paper, ex situ FTIR spectra indicates that the structure of the LiVPOF in the process of lithium-ion insertion/extraction is almost not affected, which clearly states that the LiVPOF possesses stable structure as cathode material. Consequently, the LiVPOF might be expected as a potential cathode replacement for commercial lithium-ion batteries. [ABSTRACT FROM AUTHOR]

Nasicon-type solid electrolyte LiAlZnTiPO was prepared by citric acid-assisted acrylamide polymerisation gel method. X-ray diffraction pattern showed that the introduction of Zn in the parent matrix LiAlTiPO made it easier to get high-purity rhombohedral structure (space group $$ R\overline 3 C $$) LiAlZnTiPO without the evidence of impurity secondary phase. The Li kinetics were investigated by complex impedance in bulk pellet and ionic conductivity in battery-type composite cathode, respectively. Grain-interior resistance measured by galvanostatic intermittent titration technique, potential step chronoamperometry, and AC impedance spectroscopy at 20 °C varies in the range 1.2-1.95 × 10 S cm, which is in good agreement with that obtained by complex impedance method 1.5 × 10 S cm. [ABSTRACT FROM AUTHOR]

Layered lithium ion battery cathode material LiNiCoMnO with uniform particle size of about 6 μm was synthesized by a spray pyrolysis method. Infrared and X-ray diffraction analyses show that the pyrolysis at 1,000 °C for 2 s in the tube furnace eliminates nearly all the organic components but is still not enough for the complete crystallization of LiNiCoMnO materials. Therefore, further annealing at 850 °C is needed. The prepared LiNiCoMnO cathode materials show excellent electrochemical performances. By increasing the C-rates, the cell shows discharge capacities of 159.3, 148.2, 133.7, and 125.7 mAh g at 0.1, 0.2, 0.5, and 1C rates, respectively. Only 2.1 mAh g capacity loss is observed when back to 0.1C rate. Moreover, LiNiCoMnO cathode retains 96, 97.7, 97.1, 94.5, and 97.1 % of its initial discharge capacities after 20 cycles at 0.1, 0.2, 0.5, 1, and back to 0.1C rates, respectively. More than 97 % coulombic efficiencies are observed at all the current densities in 20 cycles. [ABSTRACT FROM AUTHOR]

Layered lithium ion battery cathode material LiNiCoMnO with a uniform particle size of about 6 μm was synthesized by a spray pyrolysis method. The lithium ion diffusion kinetics in LiNiCoMnO composite cathode were systematically studied by the ratio of potentio-charge capacity to galvano-charge capacity method, galvanostatic intermittent titration technique, electrochemical impedance spectroscopy, and potential step chronoamperometry methods. The variations of lithium ion diffusion coefficients obtained by the four methods show a close similarity. They vary in the range of 10 to 10 cm s, with a maximum at 4.1- to 4.2-V voltage level. [ABSTRACT FROM AUTHOR]

The thermal stabilities of hard carbon spherule (HCS), artificial graphite (AG), and natural graphite (NG) were investigated by thermo-gravimetric differential scanning calorimetry (TG-DSC). After lithiation, AG shows the lowest onset exothermic temperature. However, all there materials exhibit similar onset temperatures for thermal reactions after ten cycles. It is obvious that the thermal behaviors of solid electrolyte interphase (SEI) film for HCS and AG change gradually with the electrochemical cycling. In contrast, the thermal stability of the surface film on NG is maintained during repeated lithium ion insertion/extraction. Because of their different Li storage behaviors, their thermal reactivities with electrolyte are quite different from each other. Especially for HCS, it shows several successive and different exothermic peaks at the 1st and 11th lithiated states, while both AG and NG display similar thermal reactivity before and after repeated cycles. In summary, it is found that thermal properties of SEI layer and lithium in lithiated carbonaceous materials for all three samples have different impacts on the whole thermal behaviors of electrode. [ABSTRACT FROM AUTHOR]