Specific heats of ternary oxides in the Li–U(VI)–O System

Seven ternary oxides; Li₄UO₅, Li₂UO₄, Li₂₂U₁₈O₆₅, Li₂U_1.75O_6.25, Li₂U₂O₇, Li₂U₃O₁₀ and Li₂U₆O₁₉ in the system Li–U(VI)–O were prepared by solid-state reaction route and characterized by X-ray diffraction method. Specific heats of these compounds were measured by differential scanning calorimetry in the temperature range from 300 to 860 K. The specific heats show a decreasing trend with increase in UO₃(s) content in these lithium uranates. However, the specific heat per gram atom shows an increasing trend with decrease in number of oxygen atoms in the formula unit.     

Vibrational spectroscopic and X-ray diffraction study of crystalline phases in the Li2O-SiO2 system

xLi₂O · (100 ? x)SiO₂ phases, where x = 20, 25, 33, 40, 50, 55, and 60 mol % (hereinafter, Li20, Li25, Li33, Li40, Li50, Li55, and Li60) were crystallized from melts, and their qualitative composition was determined by X-ray diffraction. The Li₆Si₂O₇ phase was established to precipitate during the crystallization of the melt containing 60 mol % Li₂O, thus enabling us to locate characteristic bands in the IR and Raman spectra of lithium pyrosilicate.     

Graphene-supported cobalt nanoparticles used to activate SiO2-based anode for lithium-ion batteries

Although SiO₂-based anode is a strong competitor to supersede graphite anode for lithium-ion batteries, it still has problems such as low electrochemical activity, enormous loss of active lithium, and serious volume expansion. In order to solve these problems, we used a graphene network loaded with cobalt metal nanoparticles (rGO–Co) to coat SiO₂ porous hollow spheres (SiO₂@rGO–Co). The construction of porous hollow structure and graphene network can shorten the lithium-ion (Li⁺) diffusion distance and enhance the conductivity of the composite, which improves the electrochemical activity of SiO₂ effectively. They also alleviate the volume expansion of the anode in the cycling process. Moreover, nano-scale cobalt metal particles dispersed on graphene catalyze the conversion reaction of SiO₂ and activate the locked Li⁺ in Li₂O through a reversible reaction, which improves the charge and discharge capacity of the anode. The capacity of SiO₂@rGO–Co reaches 370.4 mAh/g after 100 cycles at 0.1 A/g, which is 6.19 times the capacity of pure SiO₂ (59.8 mAh/g) under the same circumstance. What is more, its structure also exhibits excellent cycle stability, with a volume expansion rate of only 13.0% after 100 cycles at a current density of 0.1 A/g.     

Electrochemical reduction of nano-SiO2 in hard carbon as anode material for lithium ion batteries

A composite of silica (SiO₂) and hard carbon was prepared by hydrothermal reaction. Special attention was paid to the characterization of the possible electrochemical reduction of nano-SiO₂ in the composite. Evidence by solid-state nuclear magnetic resonance (NMR) and X-ray photoelectron spectroscopy (XPS) and high lithium storage capacity of the composite prove the electrochemical reduction of nano-SiO₂ and the formation of Li₄SiO₄ and Li₂O as well as Si in the first-discharge. The reversible lithium storage capacity of the nano-SiO₂ is as high as 1675 mAh/g.     

Electrode reactions of manganese oxides for secondary lithium batteries

Nanorods of MnO₂, Mn₃O₄, Mn₂O₃ and MnO are synthesized by hydrothermal reactions and subsequent annealing. It is shown that though different oxides experience distinct phase transition processes in the initial discharge, metallic Mn and Li₂O are the end products of discharge, while MnO is the end product of recharge for all these oxides between 0.0 and 3.0 V vs. Li⁺/Li. Of these 4 manganese oxides, MnO is believed the most promising anode material for lithium ion batteries while MnO₂ is the most promising cathode material for secondary lithium batteries.     

Surfactant-assisted hydrothermal crystallization of nanostructured lithium metasilicate (Li2SiO3) hollow spheres: II—Textural analysis and CO2-H2O sorption evaluation

In a previous work, the synthesis and structural-microstructural characterization of different nanocrystalline lithium metasilicate (Li₂SiO₃) samples were performed. Then, in this work, initially, a textural analysis was performed over the same samples. Li₂SiO₃ samples prepared with a non-ionic surfactant (TRITON X-114) presented the best textural properties. Therefore, this sample was selected to evaluate its water vapor (H₂O) and carbon dioxide (CO₂) sorption properties. Sorption experiments were performed at low temperatures (30-80 °C) in presence of water vapor using N₂ or CO₂ as carrier gases. Results clearly evidenced that CO₂ sorption on these materials is highly improved by H₂O vapor, and of course, textural properties enhanced the H₂O-CO₂ sorption efficiency, in comparison with the solid-state reference sample.     

Thermal properties of oxide glasses

A criterion based on the length of induction period of crystallization was used to study the effect of added CoO and NiO oxides on the thermal stability of Li₂O·2SiO₂ glass system against crystallization. It was found out that the thermal stability of studied glasses against crystallization is Li₂O·2SiO₂ < Li₂O·2SiO₂·0.1CoO < Li₂O·2SiO₂·0.1NiO. The addition of CoO and NiO oxides to Li₂O·2SiO₂ glass system increases its thermal stability. These results coincide with the order determined by stability criteria based on the characteristic temperatures.     

Effect of the high pressure on the structure and intercalation properties of lithium-nickel-manganese oxides

Lithium-nickel-manganese oxides (Li_1+x(Ni_1/2Mn_1/2)_1−xO₂, x=0 and 0.2), having different cationic distributions and an oxidation state of Ni varying from 2+ to 3+, were formed under a high-pressure (3 GPa). The structure and cationic distribution in these oxides were examined by powder X-ray diffraction, infrared (IR) and electron paramagnetic resonance (EPR) in X-band (9.23 GHz) and at higher frequencies (95 and 285 GHz). Under a high pressure, a solid-state reaction between NiMnO₃ and Li₂O yields LiNi_0.5Mn_0.5O₂ with a disordered rock-salt type structure. The paramagnetic ions stabilized in this oxide are mainly Ni²⁺ and Mn⁴⁺ together with Mn³⁺ (about 10%). The replacement of Li₂O by Li₂O₂ permits increasing the oxidation state of Ni ions in lithium-nickel-manganese oxides. The higher oxidation state of Ni ions favours the stabilization of the layered modification, where the Ni-to-Mn ratio is preserved: Li(Li_0.2Ni_0.4Mn_0.4)O₂. The paramagnetic ions stabilized in the layered oxide are mainly Ni³⁺ and Mn⁴⁺ ions. The disordered and ordered phases display different intercalation properties in respect of lithium. The changes in local Ni,Mn-environment during the electrochemical reaction are discussed on the basis of EPR and IR spectroscopy.     

The structure of Li3.4Si0.7S0.3O4 by powder neutron diffraction

The structure of Li_4?2xSi_1?xS_xO₄ (x ≈ 0.32) has been determined from neutron powder diffraction studies at room temperature, 350, and 700°C. This compound, which is a member of the series of ionic-conducting solid solutions formed between Li₄SiO₄ and Li₂SO₄, is isostructural with Li₃PO₄. The space group is Pmnb, with a = 6.1701(1), b = 10.6550(2), c = 5.0175(1)Å at room temperature. The distribution of lithium ions suggests the occurrence of a defect cluster in which the inclusion of an interstitial lithium ion causes displacements of the adjacent lithium ions of the normal Li₃PO₄ structure. There appears to be little variation of the structure with temperature.     

The preparation,characterization, and thermal behaviour of some lithium aluminum oxides: Li3AlO3 and Li5AlO4

The purpose of this research was to study the best conditions for the synthesis of the double oxides Li₅AlO₄ and Li₃AlO₃ in the solid state starting from the simple oxides, and to determine their heats of formation. Li₅AlO₄ was obtained from Li₂O₂ or Li₂O and γ-Al₂O₃ in a Li/Al molar ratio of 5∶1, and was characterized by X-ray methods. Lithium orthoaluminate, Li₃AlO₃, was obtained from Li₂O₂ and γ-Al₂O₃ in a molar ratio 3∶1. The postulated formula, Li₃AlO₃, was confirmed by chemical analysis. The temperature ranges in which the compounds are stable were established by the DTA method, and were found to be very limited for Li₃AlO₃ (400–430°) but greater for Li₅AlO₄ (440 — more than 600°). The heats of formation of Li₅AlO₄ and Li₃A10₃, also determined by means of the DTA method, were found to be ?552.3 ± 0.8 kcal/mole and ?416.8 ± 2 kcal/mole, respectively.     

Mechanism of the thermal decomposition of nitrates from graphite furnace mass spectrometry studies

A basically new mechanism of the thermal decomposition of solids is proposed to explain the mass spectral observations of gaseous molecules of CoO, CuO, Cu₂O, NiO, PbO and Mg(OH)₂ during the low-temperature decomposition of the anhydrous and hydrated nitrates of these metals. The mechanism consists of two stages: congruent gasification of all reaction products irrespective of their saturated vapor pressure and subsequent condensation of the low-volatility species (oxides and hydroxides). The partial pressures of these species at the appearance temperatures calculated from this theory for the first stage of the process (1–50 mPa) are in agreement with the detection limits of the quadrupole mass spectrometers used in these experiments. The proposed mechanism is supported by other available data obtained by thermal analysis.     

In-Situ Constructing A Heterogeneous Layer on Lithium Metal Anodes for Dendrite-Free Lithium Deposition and High Li-ion Flux

Constructing efficient artificial solid electrolyte interface (SEI) film is extremely vital for the practical application of lithium metal batteries. Herein, a dense artificial SEI film, in which lithiophilic Zn/Li_xZn_y are uniformly but nonconsecutively dispersed in the consecutive Li⁺-conductors of Li_xSiO_y, Li₂O and LiOH, is constructed via the in situ reaction of layered zinc silicate nanosheets and Li. The consecutive Li⁺-conductors can promote the desolvation process of solvated-Li⁺ and regulate the transfer of lithium ions. The nonconsecutive lithiophilic metals are polarized by the internal electric field to boost the transfer of lithium ions, and lower the nucleation barrier. Therefore, a low polarization of ≈50 mV for 750 h at 2.0 mA cm⁻² in symmetric cells, and a high capacity retention of 99.2 % in full cells with a high lithium iron phosphate areal loading of ≈13 mg cm⁻² are achieved. This work offers new sights to develop advanced alkali metal anodes for efficient energy storage.     

Loss of metallicity in metal rich lithium oxide clusters

Mixed lithium-lithium oxide aggregates are experimentally obtained from unimolecular evaporative cascades starting at metal rich Li _p ⁺ (Li₂O)_n species and ending with the stoichiometric limit Li⁺(Li₂O)_n, for several sizes of the oxide part (Li₂O)_n with 0 ≤ n ≤ 8. The results show evidence of the vanishing of the properties of the quantum metallic droplet i.e. shell closing and odd-even alternation, portrayed in the dissociation energy, with increasing size of the oxide component. The competition between monomer and dimer lithium evaporation from the heated metal rich Li _p ⁺ (Li₂O)_n species points out the influence of the perturbation induced by the oxide component on the mixed metal oxide clusters.     

The chemical changes occurring upon cycling of a SnO2 negative electrode for lithium ion cell: In situ Mössbauer investigation

Electrochemical reduction of a SnO₂ electrode for a lithium ion cell is known to result in formation of Li_4.4Sn alloy+2Li₂O. In order to determine to which extent such an electrode can be considered as reversible, we studied the electrochemical oxidation of a previously reduced SnO₂ electrode, using in situ ¹¹⁹Sn Mössbauer spectroscopy. Contrary to what could be expected, the first step does not consist in extraction of lithium from Li_4.4Sn for β-Sn to be obtained. In fact, simple lithium extraction proceeds only down to the Li_1.4Sn composition. Further oxidation (second step) involves formation of unusual species (Sn(0) and oxygen-surrounded Sn(II), both probably in interaction with Li₂O). Then (third step), red SnO-like Sn(II) species are formed, along with some Sn(IV). Especially during the second and third steps, the working electrode is far from thermodynamic equilibrium despite the low oxidation rate. This non-equilibrium behavior is probably related to the ultrafine particle size resulting from electrochemical grinding.     

Solid-state synthesis and heat capacity measurements of ceramic compounds LiAlSiO4, LiAlSi2O6, LiAlSi3O8, and LiAlSi4O10

Number of lithium-based oxide ceramics in Li–Al–Si–O system were synthesized by solid-state reaction route using Li₂CO₃, Al₂O₃, and SiO₂. The progress of the reaction was monitored using thermogravimetry. A model-free approach was employed to fit the temperature versus mass loss data. Heat capacities were measured as a function of temperature using differential scanning calorimetry. Variation of lithium/silicon ratio resulted in change in heat capacity and average crystallite size in each compound.     

Saturated Vapor Pressure Over Melts of the Binary System NaNO2-KNO3

The partial pressures of sodium nitrite and potassium nitrate over melts of the binary system NaNO₂-KNO₃ were measured at 798, 823, and 848 K. Negative deviations of the vapor pressure from Raoult's law, which decrease with increasing temperature, are established. Coefficients A and B of the Clausius-Clapeyron equation, partial molar heats of vaporization, activity and activity coefficient are calculated as functions of composition for potassium nitrate.     

Threshold photoionization behaviour of (Li2O)Lin clusters produced by a laser vaporization source

We report on the production of small and medium size lithium and lithium oxide clusters by a laser vaporization cluster source. The isotopomeric distribution of natural lithium allowed to identify Li_kO clusters as the most abundant components in the mass spectrum. Photoionization efficiency curves of Li_kO clusters with photon energies from 3.4 to 4.7 eV were measured for 8 ≤ k ≤ 27. Using linear extrapolation of the increase in photoionization efficiency with photon energy, ionization potentials were extracted. With the chemical bond of the O^2- anion to two Li atoms, leaving n = k-2 valence electrons in the (Li₂O)Li_n clusters, clear shell closure effects are present at n = 8 and n = 20.     

Enhanced carbon dioxide adsorption performance and kinetic study of K and Al co-doped Li4SiO4

Effective K and Al incorporation in Li₄SiO₄ leads to the broadened adsorption temperature range and enhanced carbon dioxide adsorption performance.     

Comparative analysis of the state of lithium and sodium atoms in water clusters

Structures and energetic characteristics of Li(H₂O) _n and Li⁺(H₂O) _n clusters with n = 1–6, 19, and 27 determined in the second order of the Møller-Plesset perturbation theory with 6–31++G(d,p) basis set are analyzed. The electron density redistribution, which takes place upon the electron addition to a Li⁺(H₂O) _n cluster, is found to be provided by hydrogen-bonded water molecules: initially almost neutral molecules, which are most distant from lithium, become negatively charged. The calculated energies of the electron capture by Li⁺(H₂O) _n clusters are approximated with the appropriate electrostatic model, and estimates of the lithium ionization energy in water clusters of various sizes are found. Similar estimates obtained earlier for sodium are made more accurate.     

Effects of Solid Electrolyte Interphase Components on the Reduction of LiFSI over Lithium Metal

The use of a lithium metal anode still presents a challenging chemistry and engineering problem that holds back next generation lithium battery technology. One of the issues facing lithium metal is the presence of the solid electrolyte interphase (SEI) layer that forms on the electrode creating a variety of chemical species that change the properties of the electrode and is closely related to the formation and growth of lithium dendrites. In order to advance the scientific progress of lithium metal more must be understood about the fundamentals of the SEI. One property of the SEI that is particularly critical is the passivating behavior of the different SEI components. This property is critical to the continued formation of SEI and stability of the electrolyte and electrode. Here we report the investigation of the passivation behavior of Li₂O, Li₂CO_3, LiF and LiOH with the lithium salt LiFSI. We used large computational chemistry models that are able to capture the lithium/SEI interface as well as the SEI/electrolyte interface. We determined that LiF and Li₂CO₃ are the most passivating of the SEI layers, followed by LiOH and Li₂O. These results match previous studies of other Li salts and provide further examination of LiFSI reduction.