Lithiated assemblies of metal chalcogenide nanowires

The nanoparticles based on either nickel-manganese oxide or carbon-coated LiNi0.5Mn1.5O4 are synthesized by flame spray pyrolysis technology with controlled particle sizes. The structural properties of nanoparticles are characterized by x-ray diffraction and high resolution electron microscopy. It is observed that the higher surface tension of precursors in the flame spray pyrolysis setup increases the particle sizes. The post annealing treatment significantly enhances the crystallinity of nanoparticles due to the favorable oxidation process and the structure conversion from NiMn2O4 to NiMnO3. In addition, the solid state reaction of as-prepared NiMn2O4 results in the LiNi0.5Mn1.5O4 nanoparticles which can be applied to cathode materials in Li-Ion batteries. The carbon-coated LiNi0.5Mn1.5O4 nanoparticles are also made by additional carbonization reaction. The control of surface tension of precursors in the flame spray pyrolysis process is expected to result in the small size of nanoparticles for cathode materials in high cyclic stability and high capacity Li-ion batteries.

Theoretical evaluation of high-energy lithium metal phosphate cathode materials in Li-ion batteries

Nickel-rich layered oxides with their large reversible capacity are considered to be some of the most promising cathode materials for high-energy Li-ion batteries. However, the fast decay of capaci...

In this paper, we report on the preparation of a Li2MnSiO4@C nanocomposite and its application as a high-capacity cathode material for rechargeable Li-ion batteries. Li2MnSiO4@C was synthesized via a hydrothermal-assisted solution route by using ascorbic acid as a carbon source and reductant. Based on the characterization by XRD, SEM, TEM, BET, elemental analysis and Raman analysis, it was found that the as-obtained homogenous Li2MnSiO4@C nanocomposite was composed of a Li2MnSiO4 core in a high-purity phase and a graphitized carbon shell. The electrochemical measurement results showed that Li2MnSiO4@C with an average particle size of 22.8 nm exhibited enhanced electrochemical properties, with initial discharge capacities of 281.5 mA h g−1 at 25 °C and 321.4 mA h g−1 at 45 °C, suggesting two lithium ions per formula unit.

Li-rich Li1 + x (Mn0.675Ni0.1625Co0.1625)1 − x O2 (x = 0.1, 0.2, 0.3, and 0.4) materials were prepared using MCO3 precursors through hydrothermal treatment with using urea as precipitator. X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and charge/discharge test are conducted to evaluate the physical and electrochemical properties of the spherical mesocrystal and resulting materials. Results show that the c/a ratio for the cathode material decreases and the layered structure deteriorates with increasing Li content. Li1.2Mn0.54Ni0.13Co0.13O2 (x = 0.2) exhibits the excellent electrochemical performance with an initial discharge capacity of 339 mAh g−1 at 20 mA g−1 and a capacity of 115 mAh g−1 at 400 mA g−1 after 50 cycles.

Cathode materials in Li-ion batteries, especially oxides, are still under intense investigation as electric vehicle and other demanding application require longer cycle life and higher energy density. V2O5 is an important cathode material for Li ion batteries enabling a stable reaction with lithium through a series of phase changes that are Coulombically efficient and reversible. V2O5 can be improved by modifying the physical structure as well as its crystalline structure or stoichiometry. These modifications include macroporous, interconnected networks or the oxide that enhanced stability and mitigate capacity fading under some conditions, as in context we show our recent development with 3DOM battery materials as a comparison to the data presented in this paper. Such improvements are investigated in this work through the development of a unique inverse opal ordered 3D macroporous of V2O5 by electrodeposition. We show the electrodeposition follows a diffusion limited growth mode to form 3D porous crystalline V2O5 after removal of the colloid self-assembled photonic crystal template. Structurally stable electrodeposited vanadium pentoxide inverse opal networks on FTO-coated glass are electrochemically tested as a function of C-Rate, i.e. the inverse of the time (in hours) it takes for the electrode fully discharges or charges (1C = 1/n hours). By selectively controlling whether the inverse opal network is open-worked or overfilled is also of focus in the galvanostatic cycling investigation. Electrochemical analysis shows lithium phase shifts with increasing C-rate in both open and overfilled network cases, which affect specific capacity retention in the electrode. Raman scattering and X-ray diffraction is used to investigate the change in each electrode as a function of C-rate, along with electron microscopy analysis to investigate the effect of C-rate on the structural changes to theV2O5 inverse opal network. Using chronoamperometry, we also show that the nature of the limited response in ordered porous cathodes materials at high rates is governed almost entirely by electronic conductivity, even with advantageous electrolyte access to the material surface.

Different strategies of introduction of lithium ions into nickel‑manganese‑cobalt carbonate resulting in LiNi0.6Mn0.2Co0.2O2 (NMC622) cathode material for Li-ion batteries

Two-dimensional covalent organic frameworks often π stack into crystalline solids that allow precise spatial positioning of molecular building blocks. Inspired by the hydrogen-bonded G-quadruplexes found frequently in guanine-rich DNA, here we show that this structural motif can be exploited to guide the self-assembly of naphthalene diimide and perylene diimide electron acceptors end-capped with two guanine electron donors into crystalline G-quadruplex-based organic frameworks, wherein the electron donors and acceptors form ordered, segregated π-stacked arrays. Time-resolved optical and electron paramagnetic resonance spectroscopies show that photogenerated holes and electrons in the frameworks have long lifetimes and display recombination kinetics typical of dissociated charge carriers. Moreover, the reduced acceptors form polarons in which the electron is shared over several molecules. The G-quadruplex frameworks also demonstrate potential as cathode materials in Li-ion batteries because of the favourable electron- and Li-ion-transporting capacity provided by the ordered rylene diimide arrays and G-quadruplex structures, respectively.

Manganese oxides from the compound family of layered birnessites have attracted interest for their use as cathode materials in Li-ion batteries, as supercapacitors, and as water oxidation catalysts. Furthermore, birnessites are also excellent precursors for low-temperature syntheses of manganese oxide-based materials such as LiMn2O4 (spinel and hollandite). Most syntheses leading to highly crystalline birnessites either require hydrothermal conditions for extended periods of time ranging from days to months or a high post-treatment temperature (400-500 °C). Here, we present a novel sol-gel synthesis route leading to the formation of highly crystalline birnessites within one hour without the need for any post-treatment to enhance crystallinity. Small birnessite crystals form virtually immediately upon mixing of the reactants, albeit initially of lower crystallinity. The size of the fully developed monoclinic birnessite platelets is in the micrometer-range with a thickness of about 20-50 nm. Under the studied conditions, the presence of Li+, Na+, and K+ is necessary for the formation of well-crystallized birnessites, and the crystal size can be tuned by variation of the synthesis time. This is suggested to be linked to an increase of the Na+ content in the birnessite with increasing synthesis time.

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Lithium-rich oxides LixNi0.25Co0.10Mn0.65O(3.4+x)/2 (x=1.6, 1.4, 1.2, 1.0, 0.8) were synthesized and characterized for their structural, morphological, and performance as cathode materials in Li-ion batteries. The baseline composition x=1.4 had been previously determined as having the best electrochemical performance due to its small primary particle size and homogeneous distribution of nano-domains consisting of (C2/m) and (R3¯m) phases. In this study, the Rietveld refinement results indicate the presence of two phases at high lithium levels (x=1.6 and 1.4): Li2MnO3 (C2/m) and Li M O2 ( M = Ni, Co, Mn) (R3¯m); the latter contains Ni2+ and Ni3+. At low lithium levels (x=1.2, 1.0, and 0.8) an additional spinel phase Li M 2O4 (Fd3¯m) emerges, which is known to affect the electrochemical performance of the oxide. Structural analysis reveals that the spinel phase contains mixed transition metals Ni, Co, and Mn as [Li+,Co2+][Ni2+,Co3+,Mn4+]2O4. A low lithium level is found to induce primary particle growth, as well as Co and Ni segregation within the secondary particles. These results are expected to contribute to material optimization and commercialization of lithium-rich oxide cathodes.

Among the Li-rich layered oxides Li2MnO3 has significant theoretical capacity as a cathode material for Li-ion batteries. Pristine Li2MnO3 generally has to be electrochemically activated in the first charge-discharge cycle which causes very low Coulombic efficiency and thus deteriorates its electrochemical properties. In this work, we show that low-temperature reduction can produce a large amount of structural defects such as oxygen vacancies, stacking faults, and orthorhombic LiMnO2 in Li2MnO3. The Rietveld refinement analysis shows that, after a reduction reaction with stearic acid at 340 °C for 8 h, pristine Li2MnO3 changes into a Li2MnO3-LiMnO2 (0.71/0.29) composite, and the monoclinic Li2MnO3 changes from Li2.04Mn0.96O3 in the pristine Li2MnO3 (P-Li2MnO3) to Li2.1Mn0.9O2.79 in the reduced Li2MnO3 (R-Li2MnO3), indicating the production of a large amount of oxygen vacancies in the R-Li2MnO3. High-resolution transmission electron microscope images show that a high density of stacking faults is also introduced by the low-temperature reduction. When measured as a cathode material for Li-ion batteries, R-Li2MnO3 shows much better electrochemical properties than P-Li2MnO3. For example, when charged-discharged galvanostatically at 20 mA·g-1 in a voltage window of 2.0-4.8 V, R-Li2MnO3 has Coulombic efficiency of 77.1% in the first charge-discharge cycle, with discharge capacities of 213.8 and 200.5 mA·h·g-1 in the 20th and 30th cycles, respectively. In contrast, under the same charge-discharge conditions, P-Li2MnO3 has Coulombic efficiency of 33.6% in the first charge-discharge cycle, with small discharge capacities of 80.5 and 69.8 mA·h·g-1 in the 20th and 30th cycles, respectively. These materials characterizations, and electrochemical measurements show that low-temperature reduction is one of the effective ways to enhance the performances of Li2MnO3 as a cathode material for Li-ion batteries.

In the past decades, research efforts on polyanion-type cathode materials by the scientific community intensified significantly. This paper reviews the latest advances in the exploration and development of polyanion-type compounds as high performance cathode materials for Li-ion batteries. It focuses on the synthesis, structure and physicochemical (especially electrochemical) properties of several classes of polyanion compounds. The relationship between composition–structure–performance of the novel electrode materials is also summarized and analyzed. The main approaches, achievements and challenges in this field are briefly commented and discussed.

A simple method to prepare NH4V3O8 nanorods as cathode material for Li-ion batteries

As a promising cathode material for Li-ion batteries(LIBs), Li-rich layered oxide (donated as LLO) has been deeply concerned because of the superior performance and high energy density, however, it’s still suffering from structure deterioration during cycling and the irreversible removal of Li+ in the initial cycle. Micron-sized spherical powders are mainly used as cathode materials due to the high tap density and volumetric energy density, through the spray-drying process can prepare the ideal morphology for LIBs. In this work, hierarchical nano/micro-sphere Li1.2Ni0.13Mn0.54Co0.13O2 composites were synthesized by a two-step spray-dry method by using acetate materials and citric acid as a chelating agent in different molar ratios (transition metal ions (TM): citric acid = 3:1 / 3:2 / 3:3). Adding the CA chelating agent is beneficial to uniform distribution transition metal ions, better structural stability and electrochemical performance of the as-prepared lithium-rich materials. As the results, the morphology of Li1.2Ni0.13Mn0.54Co0.13O2 is spherical and without aggregation occurred. The LLO with hierarchical nano/micro-sphere plays an important role in improving the coulombic efficiency in the first cycle and also enhance the capacity retention after cycling. After 3 cycles activation from 2~4.8V, the discharge capacities of the Li-rich composite samples with 3:1, 3:2, 3:3 ratios displayed 254mAh/g, 280mAh/g, and 267mAh/g, respectively. It was found that the discharge capacity of the LLO composite with the ratio = 3:2 shows the best electrochemical performance among samples. Keywords: Li-ion battery, Cathode material, Li-rich oxide, Spray-Dry, Hierarchical nano/micro-sphere