Increasing Lithium Content Research Articles

Lithium Doping of MgAl2O4 and ZnAl2O4 Investigated by High-Resolution Solid State NMR

Lithium-doped spinels could function as solid state electrolytes in batteries in which all components have the spinel structure. In this study we prepared lithium-doped MgAl2O4 and ZnAl2O4. Advanced solid state 7Li, 25Mg, and 27Al NMR have been used to investigate the structure of these spinels and the structural changes that take place therein upon lithium doping. The spinel structure is well retained, although the amount of tetrahedral aluminum increases with increased lithium content. Using MQMAS experiments, the presence of two tetrahedral sites is discovered in both doped and undoped spinels. It is shown that the spinel structure of MgAl2O4 is heterogeneous, which leads to distributions in chemical shift and quadrupolar parameters. The heterogeneity is also shown in 25Mg spectra obtained with the quadrupolar Carr–Purcell–Meiboom–Gill (QCPMG) and sideband selective Double Frequency Sweep-QCPMG (ssDFS-QCPMG) pulse sequences. Lithium mobility is measured using static variable temperature 7Li NMR experim...

ReaxFF molecular dynamics simulations on lithiated sulfur cathode materials.

Sulfur is a very promising cathode material for rechargeable energy storage devices. However, sulfur cathodes undergo a noticeable volume variation upon cycling, which induces mechanical stress. In spite of intensive investigation of the electrochemical behavior of the lithiated sulfur compounds, their mechanical properties are not very well understood. In order to fill this gap, we developed a ReaxFF interatomic potential to describe Li-S interactions and performed molecular dynamics (MD) simulations to study the structural, mechanical, and kinetic behavior of the amorphous lithiated sulfur (a-LixS) compounds. We examined the effect of lithiation on material properties such as ultimate strength, yield strength, and Young's modulus. Our results suggest that with increasing lithium content, the strength of lithiated sulfur compounds improves, although this increment is not linear with lithiation. The diffusion coefficients of both lithium and sulfur were computed for the a-LixS system at various stages of Li-loading. A grand canonical Monte Carlo (GCMC) scheme was used to calculate the open circuit voltage profile during cell discharge. The Li-S binary phase diagram was constructed using genetic algorithm based tools. Overall, these simulation results provide insight into the behavior of sulfur based cathode materials that are needed for developing lithium-sulfur batteries.

Designing new lithium-excess cathode materials from percolation theory: nanohighways in Li(x)Ni(2-4x/3)Sb(x/3)O2.

Increasing lithium content is shown to be a successful strategy for designing new cathode materials. In layered Li(x)Ni(2-4x/3)Sb(x/3)O2 (x = 1.00-1.15), lithium excess improves both discharge capacity and capacity retention at 1C. Structural studies reveal a complex nanostructure pattern of Li-Sb and Ni-Sb ordering where the interface between these domains forms the correct local configuration for good lithium mobility. The <1 nm Li-Sb stripe domains and their interfaces thereby effectively act as nanohighways for lithium diffusion.

Multiscale analysis of prelithiated silicon nanowire for Li-ion battery

A diffusion induced stress (DIS) model based on the finite element method was used to analyze mechanical stress within a multiscale framework for silicon nanowire anodes designed for use in Li-ion batteries. With a prelithiated nanowire, the mechanical moduli of lithium silicide and the migration energy barriers of lithium were calculated by density functional theory method, while the diffusion constants for lithium silicide were obtained using kinetic Monte Carlo simulations. Unlike previous DIS analyses, this multiscale approach reveals a decreasing hoop stress with increasing lithium concentration. Furthermore, an increase in the diffusion coefficient with Li concentration was also found to be a much more significant factor than the reduction in the mechanical moduli, causing a prelithiated silicon anode to experience lower stress levels than pristine silicon. On the basis of this finding, it is concluded that prelithiation reduces the loss in cycling performance that typically occurs due largely to an excess of induced stress.

Molten Carbonate Composition Effects on Carbon Electro-Oxidation at a Solid Anode Interface

The electrochemical oxidation of graphite is investigated to determine the relative influence of the composition of a molten carbonate electrolyte on a solid anode. The binary eutectics of sodium, lithium and potassium carbonates were investigated as well as ternary mixtures including the eutectic and combinations of systematically varied lithium content. It was seen that the combination of cations included in the carbonate melt can influence the electrochemical performance of graphite with binary combinations performing better than ternary in all cases. Very little change in the mechanistic behavior was observed through tafel analysis; instead it is proposed that the observed kinetic effects are a combination of the catalytic role of all metal cations present as well as the intercalation of lithium into the solid graphite electrode. The effect of lithium intercalation is suggested to lead to a change in the graphite surface polarity which affects product gas bubble formation and dislodgement at the solid anode. Increased lithium concentration, and it is assumed intercalation, encourages smaller bubbles to form which are dislodged at a faster rate than surfaces with less lithium intercalation in the ternary electrolyte. A threshold lithium concentration is reached above approximately 65 % where the electrochemical behavior is significantly changed and bubble formation behavior is no longer observed.

Enthalpy of formation of Li1+xMn2−xO4 (0 < x < 0.1) spinel phases

The enthalpies of formation of Li1+xMn2−xO4 (0<x<0.1) spinel phases were measured using high temperature oxide solution calorimetry in a sodium molybdate solvent at 701°C. One commercially available LiMn2O4 powder and two Li1+xMn2−xO4 samples synthesized using the sol–gel method were used for the measurements. The enthalpies of formation of the spinels from the binary constituent oxides and from the elements become more exothermic with increasing lithium content and increasing average oxidation state of the manganese cation in the range 0<x<0.1. Additionally, the lithium-rich boundary of the Li1+xMn2−xO4 phase for 0<x<0.1 was re-investigated using differential thermal analysis combined with thermogravimetric analysis.

Mechanical behavior of electrochemically lithiated silicon

The time-independent and time-dependent mechanical behavior of electrochemically lithiated silicon was studied with nanoindentation. As indentation was performed with continuous stiffness measurements during loading and load-hold, new insight into the deformation behavior of lithiated silicon is furnished. Supporting other research, Young's modulus and the hardness of lithiated silicon are found to decline with increasing lithium content. However, the results of this study indicate that Young's modulus of the fully lithiated phase, at 41 GPa, is in fact somewhat larger than reported in some other studies. Nanoindentation creep experiments demonstrate that lithiated silicon creeps readily, with the observed viscoplastic flow governed by power law creep with large stress exponents (>20). Flow is thought to occur via local, shear-driven rearrangement at the scale of the Li15Si4 molecular unit volume. This research emphasizes the importance of incorporating viscoplasticity into lithiation/delithiation models. Additionally, more broadly, the work offers insight into nanoindentation creep methodology.

The Influence of Li on the Point Defect Structure of ZnO Varistor Ceramics

In this paper, the dielectric properties of ZnO-Bi2O3 based varistor ceramics doped with Li are investigated by Novocontrol wide band dielectric spectrometer. It is found that Lithium is an amphoteric impurity. If the content of Lithium is very low, It will enters into the interstitials and Lithium interstitial is formed as a donor. While with the increase of Lithium content, Zn is replaced with Li and Lithium substitution for Zinc as a acceptor is formed. If the content of Lithium increases further, Lithium interstitial is formed again with the redundant Lithium. Therefore, the concentrations of intrinsic point defects of Zinc interstitial and oxygen vacancy varies with the content of Lithium, which leads to the increase of Schottky barrier at grainboundary with Lithium.

Hard X-ray photoelectron spectroscopy of LixNi1-xO epitaxial thin films with a high lithium content.

The core-level and valence-band electronic structures of LixNi1-xO epitaxial thin films with x = 0, 0.27, and 0.48 were studied by hard X-ray photoelectron spectroscopy. A double peak structure, consisting of a main peak and a shoulder peak, and a satellite structure were observed in the Ni 2p3/2 core-level spectra. The intensity ratio of the shoulder to main peak in this double peak structure increased with increasing lithium content in LixNi1-xO. This lithium doping dependence of the Ni 2p3/2 core-level spectra was investigated using an extended cluster model, which included the Zhang-Rice (ZR) doublet bound states arising from a competition between O 2p - Ni 3d hybridization and the Ni on-site Coulomb interaction. The results indicated that the change in the intensity ratio in the main peak is because of a reduction in the ZR doublet bound states from lithium substitutions. This strongly suggests that holes compensating Li doping in LixNi1-xO are of primarily ZR character.

Structural, morphological and optical study of Li doped ZnO thin films on Si (100) substrate deposited by pulsed laser deposition

Structural, morphological and optical properties of Zn1−xLixO thin films grown on Si (100) substrates by pulsed laser deposition at different Li doping concentrations (x=0.0, 0.05, 0.07 and 0.09) are reported. The XRD spectra indicate the formation of single crystalline ZnO thin films preferentially grown along (002) crystallographic orientation with c-axis perpendicular to the substrate surface. FESEM analysis shows the average size of Zn1−xLixO nanostructures to decrease from 42 to 30nm and AFM analysis also shows the average size of Zn1−xLixO nanostructures to decrease from 30 to 05nm with increasing lithium concentrations from x=0 to 0.09. Moreover, Raman and Photoluminescence spectra also confirm the single-phase formation of ZnO thin films. A significant enhancement in optical band gap is found from 3.35 to 3.63eV by Li doping from x=0 to 0.09. It may be due to the increased carrier concentrations by Li doping that blocks the lowest states in the conduction band and results in the increase in band gap. The obtained Zn1−xLixO thin films with c-axis oriented along (002) plane are useful for device fabrication in broadband UV photo-detectors for high tunable wavelength resolution.

Lithium-Induced Phase Transitions in Lead-Free Bi0.5Na0.5TiO3 Based Ceramics

Lithium-substituted 0.95[0.94(Bi0.5Na(0.5–x)Lix)TiO3–0.06BaTiO3]–0.05CaTiO3 materials include the polar rhombohedral R3c and the weakly polar tetragonal P4bm phases. On increasing lithium content, the (R3c/P4bm) phase ratio decreased, while the rhombohedral and tetragonal lattice distortions remained the same. The temperature corresponding to the shoulder in the dielectric permittivity shows no clear shift with respect to lithium substitution because of the rhombohedral distortion remaining constant. Electrical poling produced an increase of the rhombohedral phase fraction together with a rise of the rhombohedral and tetragonal distortion. This confirmed the occurrence of a phase transition from the weakly polar to the polar phase during electrical poling. Four peaks found in the current–electric field (I–E) loops are related to reversible electric field induced transitions. By studying the temperature dependence of the current peaks in the I–E loops, it was found that the minimum temperature where these electric field induced transitions take place decreases with increasing lithium substitution.

The role of composition in the atomic structure, oxygen loss, and capacity of layered Li–Mn–Ni oxide cathodes

Lithium-rich layered Li[Li1/3−2x/3Mn2/3−x/3Nix]O2 (0 < x ≤ 1/2) oxide cathodes show promise as a potential candidate for Li-ion batteries due to their high capacity. However, the intricacies of the role of composition with increasing excess Li on the degree of oxygen loss during the first charge and the discharge capacity in subsequent cycles are not fully understood. With an aim to develop a better fundamental understanding, we present here an in-depth investigation of the Li[Li1/3−2x/3Mn2/3−x/3Nix]O2 (0 < x ≤ 1/2) series with a range of different excess lithium contents prepared by two different synthesis methods. The oxygen loss from the lattice during the first charge and the discharge capacity in subsequent cycles increase with increasing lithium content. In-depth analysis with a combination of X-ray diffraction, scanning electron microscopy (SEM), aberration-corrected scanning transmission electron microscopy (STEM), diffraction-STEM (D-STEM), and energy dispersive X-ray spectroscopy (EDS) reveals that the samples transition from an Rm structure to a C2/m structure with increasing lithium content and decreasing nickel to manganese ratio, for both the synthesis methods, indicating that the maximum oxygen loss and discharge capacity are achieved with a single C2/m phase. We further show that within a single particle, the cation layers of these materials can order on different {111} planes in the basic NaCl structure.

Potentiodynamic Tests of Magnesium Alloy AZ31 with Lithium Additive

The purpose of the study is to assess electrochemical corrosion resistance of magnesium alloy AZ31 with additives of 4.5, 7.5 and 15 % lithium in NaCl solutions. Corrosion tests were performed in solutions with concentration 0.01 2 M NaCl with application of electrochemical testing system VoltaLab®PGP201. Resistance to electrochemical corrosion was evaluated on the ground of registered anodic polarisation curves by means of potentiodynamic method. Results of performed tests show unequivocally deterioration of corrosion characteristics of the alloy together with increase of molar concentration of NaCl solution. As chloride ions concentration increases, decrease of corrosion potential and polarisation resistance, as well as increase of corrosion current density are observed. Deterioration of corrosion characteristics of AZ31 alloy was shown with the increase of lithium content. It must be highlighted that irrespective of molar concentration of NaCl solution, there is also presence of pitting corrosion in the tested alloy. It proves that magnesium alloy AZ31-Li is not resistant to that type of corrosion. Test results prove that it is necessary to apply protective films on elements made of magnesium alloy with lithium additive.

Structural, optical and electrical properties of undoped and Li-doped NiO thin films prepared by sol–gel spin coating method

Un-doped and lithium doped nickel oxide thin films have been prepared on glass substrates by the sol–gel spin coating technique using nickel acetate and lithium chloride as source materials. The thickness of the films was increased by increasing the number of layers successively deposited on the same substrate. The effect of the number of layers on the structural, optical and electrical properties of NiO thin films was studied. The results of investigations of the samples show that four is the most suitable number of layers of undoped NiO films with high optical transparency. Then, by using these optimized deposition parameters, lithium doped nickel oxide films are prepared. The surface morphology and crystalline structure of the thin films were investigated by atomic force microscopy and X-ray diffraction (XRD), respectively. A modification in the morphology of the films was observed while increasing the Li amount in the solution. XRD patterns show that the films are polycrystalline. The preferred orientations were evaluated from XRD data. The average transmittance of the NiO films in the visible region increases with the increase of Li concentration. The electrical measurements show that the resistance of the films decreases as the lithium content increases.

Structural, optical, and ferroelectric behavior of Zn1−xLixO (0⩽x⩽0.09) nanostructures

Abstract The present study reports structural, optical and ferroelectric behavior of lithium doped zinc oxide (Zn1−xLixO with x = 0.0, 0.05, 0.07 and 0.09) nanostructures synthesized by hydrothermal method. The XRD pattern indicates the pure phase formation of ZnO without any impurity and the particle size, calculated through XRD data, is found to decreases from 51 to 42 nm for samples with x = 0–0.09, respectively. FESEM images show that the size of Li doped ZnO nanostructures decreases with increasing lithium concentrations. Moreover, Raman and Photoluminescence spectra also confirm the wurtzite phase formation of ZnO. PL spectra show a blue shift in both UV and visible region as a result of doping. A significant enhancement in optical band are found to be 3.39–4.23 eV by Li doping due to increasing carrier concentration that blocks the lowest states in the conduction band and results the increase in band gap. Further, Li incorporation enhances the room temperature ferroelectric behavior and the maximum value of polarization (Pmax) increases from 8.973 to 19.394 μC/cm2 for x = 0–0.09, respectively.

Li Segregation Induces Structure and Strength Changes at the Amorphous Si/Cu Interface

The study of interfacial properties, especially of their change upon lithiation, is a fundamentally significant and challenging topic in designing heterogeneous nanostructured electrodes for lithium ion batteries. This issue becomes more intriguing for Si electrodes, whose ultrahigh capacity is accompanied by large volume expansion and mechanical stress, threatening with delamination of silicon from the metal current collector and failure of the electrode. Instead of inferring interfacial properties from experiments, in this work, we have combined density functional theory (DFT) and ab initio molecular dynamics (AIMD) calculations with time-of-flight secondary ion mass spectrometry (TOF-SIMS) measurements of the lithium depth profile, to study the effect of lithiation on the a-Si/Cu interface. Our results clearly demonstrate Li segregation at the lithiated a-Si/Cu interface (more than 20% compared to the bulk concentration). The segregation of Li is responsible for a small decrease (up to 16%) of the adhesion strength and a dramatic reduction (by one order of magnitude) of the sliding resistance of the fully lithiated a-Si/Cu interface. Our results suggest that this almost frictionless sliding stems from the change of the bonding nature at the interface with increasing lithium content, from directional covalent bonding to uniform metallic. These findings are an essential first step toward an in-depth understanding of the role of lithiation on the a-Si/Cu interface, which may contribute in the development of quantitative electrochemical mechanical models and the design of nonfracture-and-always-connected heterogeneous nanostructured Si electrodes.

Electronic Origin for the Phase Transition from Amorphous LixSi to Crystalline Li15Si4

Silicon has been widely explored as an anode material for lithium ion battery. Upon lithiation, silicon transforms to amorphous LixSi (a-LixSi) via electrochemical-driven solid-state amorphization. With increasing lithium concentration, a-LixSi transforms to crystalline Li15Si4 (c-Li15Si4). The mechanism of this crystallization process is not known. In this paper, we report the fundamental characteristics of the phase transition of a-LixSi to c-Li15Si4 using in situ scanning transmission electron microscopy, electron energy loss spectroscopy, and density function theory (DFT) calculation. We find that when the lithium concentration in a-LixSi reaches a critical value of x = 3.75, the a-Li3.75Si spontaneously and congruently transforms to c-Li15Si4 by a process that is solely controlled by the lithium concentration in the a-LixSi, involving neither large-scale atomic migration nor phase separation. DFT calculations indicate that c-Li15Si4 formation is favored over other possible crystalline phases due to the similarity in electronic structure with a-Li3.75Si.

Effect of Li doping on the magnetic and magnetocaloric properties of Pr0.5Sr0.5−xLixMnO3 (0≤x≤0.3)

The magnetic properties and magnetocaloric effect have been studied in Pr0.5Sr0.5−xLixMnO3 (0≤x≤0.3) prepared by conventional solid-state reaction. Magnetic measurements versus temperature revealed that the Curie temperature (TC) increased gradually with increasing lithium content (0.05≤x≤0.2); TC values are about 260 and 290K for x=0.05 and 0.2, respectively. But it shows abrupt drop in TC value for x=0.3 (TC=235K). Meanwhile, the paramagnetic–ferromagnetic (PM–FM) transition is second-order in x≤0.2, it changes into first order for x=0.3. However, the magnitude of the isothermal magnetic entropy (ΔSM) increased gradually. In a magnetic field change of 15.0kOe, the maximum ΔSM achieved around TC are −1.03, −1.05, −1.48, −2.17 and −2.64Jkg−1K−1 for x=0, 0.05, 0.1, 0.2and 0.3, respectively. Although ΔSM for x=0.2 is smaller compared to the composition x=0.3, the relative cooling capacity (RCP) 59.6Jkg−1 is similar compared with the value 59.8Jkg−1 for x=0.3. Addition of suitable TC makes it a desirable material for room temperature magnetic refrigeration.

Adipic Acid Assisted Sol-Gel Synthesis of Li1+x(Mn0.4Ni0.4Fe0.2)1-xO2(0 &gt; x &gt; 0.3) as Cathode Materials for Lithium Ion Batteries

Layered Li1+x(Mn0.4Ni0.4Fe0.2)1-xO2 (0 < x < 0.3) solid solutions were synthesized using solgel method with adipic acid as chelating agent. Structural and electrochemical properties of the prepared powders were examined by means of X-ray diffraction, Scanning electron microscopy and galvanostatic charge/discharge cycling. All powders had a phase-pure layered structure with R3m space group. The morphological studies confirmed that the size of the particles increased at higher x content. The charge-discharge profiles of the solid solution against lithium using 1 M LiPF6 in EC/DMC as electrolyte revealed that the discharge capacity increases with increasing lithium content at the 3a sites. Among the cells, Li1.2(Mn0.32Ni0.32Fe0.16)O2 (x = 0.2)/ Li + exhibits a good electrochemical property with maximum initial capacity of 160 mAhg �1 between 2-4.5 V at 0.1 mAcm �2 current density and the capacity retention after 25 cycles was 92%. Whereas, the cell fabricated with x = 0.3 sample showed continuous capacity fading due to the formation of spinel like structure during the subsequent cycling. The preparation of solid solutions based on LiNiO2-LiFeO2-Li2MnO3 has improved the properties of its end members.

Coupled mechano-diffusional driving forces for fracture in electrode materials

Li/Si undergoes significant softening in the form of rapid decreases in elastic modulus and yield stress as lithium concentration increases. To investigate how this lithiation-induced softening affects the fracture behavior of electrodes, we formulate a J-integral for coupled mechanical deformation and mass diffusion processes. This measure is used to analyze mechano-diffusional driving forces for fracture through simulations using a mixed finite element framework. Calculations show that under tensile loading, Li accumulates in front of crack tips, leading to an anti-shielding effect on the energy release rate. For a pre-cracked Li/Si thin-film electrode, it is found that the driving force for fracture is significantly lower when the electrode is operated at higher Li concentrations – a result of more effective stress relaxation via global yielding. The results indicate that operation at higher concentrations is an effective means to minimize failure of thin-film Li/Si alloy electrodes. A design map for avoiding failure is developed.