G-quadruplex organic frameworks

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.

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.

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.

High-rate performance of a three-dimensional LiFePO4/graphene composite as cathode material for Li-ion batteries

Recycling the cathode materials of spent Li-ion batteries in a H-Shaped neutral water electrolysis cell

Investigation of various cobalt concentrations on LiV2O5 as cathode materials with tunable high rate capability and operating voltage in Li-ion batteries

Nickel-rich LiNi0.8Mn0.1Co0.1O2 (NMC811) is one of the most promising Li-ion battery cathode materials and has attracted the interest of the automotive industry. Nevertheless, storage conditions can affect its properties and performance. In this work, both NMC811 powder and electrodes were storage-aged for one year under room conditions. The aged powder was used to prepare electrodes, and the performance of these two aged samples was compared with reference fresh NMC811 electrodes in full Li-ion coin cells using graphite as a negative electrode. The cells were subjected to electrochemical as well as ante- and postmortem characterization. The performance of the electrodes from aged NM811 was beyond expectations: the cycling performance was high, and the power capability was the highest among the samples analyzed. Materials characterization revealed modifications in the crystal structure and the surface layer of the NMC811 during the storage and electrode processing steps. Differences between aged and fresh electrodes were explained by the formation of a resistive layer at the surface of the former. However, the ageing of NMC811 powder was significantly mitigated during the electrode processing step. These novel results are of interest to cell manufacturers for the widespread implementation of NMC811 as a state-of-the-art cathode material in Li-ion batteries.

Secondary Li-Ion batteries are considered as alternative to the combustion engine in automotive applications paving the way to electromobility. In a recent review, Andre et al. pointed out that in order to reach a driving range of 300 miles, the specific energy of today’s Li-ion batteries needs to be increased to ~250 Wh/kgcell, which corresponds to an improvement by a factor of almost 2.5 compared to today’s batteries.[1] To meet these targets, layered lithium nickel manganese cobalt oxides (LiNixMnyCozO2, NMC) are one of the most promising class of cathode materials.[1-3] Despite their very high theoretical capacity of ~275 mAh/gNMC, not all of the lithium can easily be extracted due to structural instabilities occurring at high states-of-charge (SOC).[4-6] Therefore, the accessible capacity is much lower than the theoretical one and is ~160 mAh/gNMC for LiNi1/3Mn1/3Co1/3O2 (NMC111) [6-8] when cycled up to 4.3 V vs. Li/Li+, which is insufficient to meet the required specific energy targets. With Ni-rich NMCs (Ni-content >> Mn- and Co-content), significantly higher specific capacities are accessible. In particular, 25% higher reversible capacities of up to ~200 mAh/gNMC were reported for LiNi0.8Mn0.1Co0.1O2 (NMC811) for the same upper cut-off voltage.[6, 7, 9] However, one major drawback of Ni-rich NMCs is their increased surface reactivity. Gauthier et al. rationalized this by an increasing nucleophilicity of the surface oxygen in layered LiMO2 (M = transition metals) from early to late transition metals, because the oxygen p-band is shifted to higher energies.[10] Therefore, the high Ni-content in NMC811 renders the surface oxygen chemically more reactive.[10-12] Upon storage at ambient air this surface reactivity can lead to the formation of carbonates and/or hydroxides via a reaction of CO2 and/or H2O with the NMC surface causing irreversible damage to the NMC material. In the present study, we analyze the impact of ambient air contact on NMC811 in comparison to NMC111. It will be shown that in contrast to NMC111, NMC811 is very sensitive when stored under ambient conditions and that the formation of surface impurities detrimentally affects the performance of both, NMC811/Li and NMC811/graphite cells. We will critically investigate the chemical nature of the formed surface species and present a simple method to quantify them. Finally, we will demonstrate that a proper handling of NMC811 is much more challenging compared to NMC111 and if the latter is to be replaced by NMC811, it is of primary importance to control the amounts of surface impurities on Ni-rich NMC cathode materials to allow for low impedance and good cycling stability.

With its good thermal stability, abundance in nature and benign environmental impact, LiFePO4 (LFP) cathode material is seen as one of the most promising candidate for the next generation of Li-ion batteries. Many synthetic routes have already been used for preparing LFP material, best known being solid state, sol-gel, hydrothermal, co-precipitation and microwave preparations. All of them are performed at moderate temperature and/or in a wide range of pressures. Melt process of LFP, advanced by Gauthier et al. in 2003[1], operates in the liquid phase above 1000⁰C and then benefits from increased reaction kinetics and from the thermodynamic stability of LFP in a mild reducing atmosphere. The melt synthesis allows the use of a wide range of simple raw materials as well as a possible purification strategy during the melt step or upon solidification, potentially enabling for usage of less pure non-expensive raw materials. In this work, thermodynamic considerations are first addressed for deep understanding of the Li-Fe-P-O systems. A model has recently been developed and is supported by experimental data. On this basis, recent experimental observations and progress on raw material selection (including direct use of iron ore concentrates) and systems will be reported. Eventually, melt-synthesis conditions and the latest results in controlling the purification of LiFePO4 from major phase impurities will also be covered. All these considerations allow the selection of the best conditions to prepare a high purity LiFePO4 by melt-process. This work is part of an Automotive Partnership of Canada supported program to develop and pilot the molten-synthesis process to make high purity C-LiFePO4with excellent electrochemical properties for using as a cathode material in Li-ion batteries for EVs and PHEVs application. [1] M. Gauthier, L. Gauthier, D. Lavoie, C. Michot, N. Ravet, US Patent 7,534,408 B2. (2003).

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