Li Migration Research Articles

Differentiating Contributions to “Ion Transfer” Barrier from Interphasial Resistance and Li+ Desolvation at Electrolyte/Graphite Interface

Efforts were made to differentiate the contributions to the so-called "ion transfer" barrier at the electrolyte/graphite junction from two distinct processes: (1) desolvation of Li(+) before it enters graphene interlayer and (2) the subsequent migration of bare Li(+) through the ad hoc interphase. By leveraging a scenario where no substantial interphase was formed on Li(+) intercalation hosts, we were able to quantify the distribution of "ion transfer" activation energy between these two interfacial processes and hence identify the desolvation process of Li(+) as the major energy-consuming step. The result confirmed the earlier belief that the rate-determining step in the charging of a graphitic anode in Li(+) intercalation chemistry relates to the stripping of solvation sheath of Li(+), which is closely interwoven with the interphasial resistance to Li(+) migration.

Lithium Insertion and Transport in the TiO2−B Anode Material: A Computational Study

TiO2−B is a highly promising anode material for rechargeable lithium batteries. Computational studies based on density functional theory (DFT) have been carried out on this material focusing on key issues relating to lithium insertion sites and lithium diffusion paths. Our simulation model shows good reproduction of the observed crystal structure of TiO2−B. Electronic structure calculations suggest that the lowest energy lithium site is a slightly off-center position in the b-axis channel for low lithium concentration (x < 0.125 for LixTiO2−B). Our calculated cell voltages are compatible with values from electrochemical measurements. Low Li migration energies are found for pathways along the b-axis channel and the [001] c-axis direction, suggesting significant Li ion mobility in this anode material.

Mo−S−I Nanowires: A Promising Anode Material for Lithium-Ion Batteries. A First-Principles Study

One of the important issues in the development of new li-ion battery technologies is to seek electrode materials with higher energy densities and a charge-discharge. using the principles calculations based on density functional theory, we systematically study the lithium interaction with the recently reported inorganic mo(12)s(9)i(9) nanowires. eleven initial li positions are optimized to identify the rich energetically preferable sites for li adsorption in the nanowire at the sulfur bridge planes and on the nanowire between dressing s and i atoms, the charge density and the electronic band structure are calculated to investigate die li-host physics, using the climbing image nudged elastic band method, we obtain that the diffusion barrier for li migration into the mo(12)s(9)i(9) nanowire is 0.86 ev, which is far lower than that of li diffusion into the carbon nanotube through the sidewall (about 10 ev [meunier et al. phys. rev. lett. 2002, 88, 075506]). these results indicate that the mo(12)s(9)i(9) nanowire will be a promising candidate material for anodes in li-ion battery application.

First-principles study of lattice dynamics of LiFePO 4

Lattice dynamics of lithium iron orthophosphate (LiFePO 4) isostructural with olivine have been investigated using the first-principles calculations taking into account the on-site Coulomb interaction within the GGA + U scheme. Born effective charge tensors, phonon frequencies at the Brillouin zone center and phonon dispersion curves are calculated and analyzed. The Born effective charge tensors exhibit anisotropy, which gives a convincing evidence for the one-dimensional Li migration tunnel along the [010] direction in LiFePO 4, which has been proposed by other theoretical calculations and experimental observation. The calculated phonon frequencies at the Γ point of the Brillouin zone show good agreement with the available experimental observations.

Arrangement of La and vacancies in La2/3TiO3 predicted by first-principles density functional calculation with cluster expansion and Monte Carlo simulation

High ionic conductivity of lithium in LixLa(2-x)/3TiO3 with A-site deficient type perovskite structure has attracted considerable attention owing to both the range of practical usage (e.g., all-ceramics Li secondary batteries) and the fundamental fascination of fast lithium ion transport in crystalline solids. In present paper, we investigated the arrangement of La and vacancies in La2/3TiO3 by means of first-principles computations combined with cluster expansion approach, since it has caused a difficulty of atomistic level discussion due to numerous freedoms of configuration. The computational results predicted the alternate La concentrated and diluted layers stacking along c-axis, which agreed with the previous structural analyses. In addition, La cluster formation within ab plane is indicated. Using predicted La/vacancy arrangement, we demonstrated to calculate the Li migration path and energy profiles during Li jump by nudged elastic band method, which showed diagonal pathways to avoid passing A-site center.

Defect Control and Lithium-Ion Conducting Properties of Layered Perovskite Oxides Li&lt;sub&gt;2&lt;/sub&gt;SrTa&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;7&lt;/sub&gt;

Lithium-ion conducting properties were investigated for a layered perovskite oxide Li2SrTa2O7 (LST) and defect-controlled LST, synthesized via solid state reactions. The ionic conductivities of A-site solid solutions Li2[Sr-(La2/3□1/3)-(La1/2Li1/2)]Ta2O7 (□ denotes vacancy.) suggested that lithium ions migrate in the Li-layer. The conductivity of Li-deficient (Li2-z□z)(LazSr1-z)Ta2O7 increased dramatically from 4.2 × 10-6 S cm-1 (z = 0, LST) to 1.6 × 10-3 S cm-1 (z = 0.2) at 400°C with increasing Li-vacancy concentration. This result obviously indicates that the conductivity of LST originate from the Li migration through vacancies in the Li-layer.

Lithium Battery Materials LiMPO4 (M = Mn, Fe, Co, and Ni): Insights into Defect Association, Transport Mechanisms, and Doping Behavior

The defect chemistry, doping behavior, and ion migration in olivine-type materials LiMPO4 (M = Mn, Fe, Co, and N) are investigated by atomistic simulation techniques. The most favorable intrinsic defect type is found to be the cation antisite defect, in which Li and M ions exchange positions. Li migration is found to occur preferentially down [010] channels, following a curved trajectory. Defect association or binding energies for pair clusters composed of combinations of lithium vacancies, antisite cations, and small polaron species are investigated. Migration energies for divalent antisite cations on Li sites suggest that such defects would impede Li diffusion in LiMPO4 to varying degrees. Calculation of dopant substitution energies for cations with charges +1 to +5 indicate that supervalent doping (e.g., Ga3+, Ti4+, Nb5+) on either Li or M sites is energetically unfavorable and does not result in a large increase in electronic (small polaron) species.

Intercalation processes and diffusion paths of lithium ions in spinel-type structuredLi1+xTi2O4: Density functional theory study

Intercalation processes and corresponding diffusion paths of Li ions into spinel-type structured ${\mathrm{Li}}_{1+x}{\mathrm{Ti}}_{2}{\mathrm{O}}_{4}$ $(0\ensuremath{\leqslant}x\ensuremath{\leqslant}0.375)$ are systematically studied by means of periodic density functional theory calculations for different compositions and arrangements. An analysis of the site preference for intercalation processes is carried out, while energy barriers for the diffusion paths have been computed in detail. Our results indicate that the Li insertion is thermodynamically favorable at octahedral sites $16c$ in the studied composition range, and Li migration from tetrahedral sites $8a$ to octahedral sites $16c$ stabilizes the structure and becomes favorable for compositions $x\ensuremath{\geqslant}0.25$. Diffusion paths from less stable arrangements involving Li migrations between tetrahedral and octahedral sites exhibit the lowest energy barrier since the corresponding trajectories and energy profiles take place across a triangle made by three neighboring oxygen anions without structural modification. Theoretical and experimental diffusion coefficients are in reasonable agreement.

The mechanism of Li-ion transport in the garnet Li5La3Nb2O12

We present a detailed study on the exact location and dynamics of Li ions in the garnet-type material Li(5)La(3)Nb(2)O(12) employing advanced solid state NMR strategies. Applying temperature-dependent (7)Li-NMR, (6)Li-MAS-NMR, (6)Li-{(7)Li}-CPMAS-NMR, (6)Li-{(7)Li}-CPMAS-REDOR-NMR as well as 2D-(6)Li-{(7)Li}-CPMAS-Exchange-NMR spectroscopy, we were able to quantify the distribution of the Li cations among the various possible sites within the garnet-type structure and to identify intrinsic details of Li migration. The results indicate a sensitive dependence of the distribution of Li cations among the tetrahedral and octahedral sites on the temperature of the final annealing process. This distribution profoundly affects the mobility of the Li cations within the garnet-type framework structure. Extended Li mobility at ambient temperature is only possible if the majority of the Li cations is accommodated in the octahedral sites, as observed for the sample annealed at 900 degrees C. Octahedrally-coordinated Li cations could be identified as the mobile Li species, whereas the tetrahedral sites seem to act as a trap for the Li cations, rendering the tetrahedrally-coordinated Li cations immobile on the time scale of the NMR experiments.

Factors that affect Li mobility in layered lithium transition metal oxides

The diffusion constant of Li in electrode materials is a key aspect of the rate capability of rechargeable Li batteries. The factors that affect Li mobility in layered lithium transition metal oxides are systematically studied in this paper by means of first-principles calculations. In close packed oxides octahedral ions diffuse by migrating through intermediate tetrahedral sites. Our results indicate that the activation barrier for Li hopping is strongly affected by the size of the tetrahedral site and the electrostatic interaction between ${\mathrm{Li}}^{+}$ in that site and the cation in the octahedron that shares a face with it. The size of the tetrahedral site is determined by the $c$-lattice parameter which has a remarkably strong effect on the activation barrier for Li migration. The effect of other factors such as cation mixing and doping with nontransition metal ions can be interpreted quantitatively in terms of the size and electrostatic effect. A general strategy to design high rate electrode materials is discussed.

Atomic-Scale Investigation of Defects, Dopants, and Lithium Transport in the LiFePO4 Olivine-Type Battery Material

Key issues relating to intrinsic defects, dopant incorporation, and lithium ion migration in the LiFePO4 electrode material have been investigated using well-established atomistic modeling techniques. Our simulation model shows good reproduction of the observed olivine-type structure of LiFePO4. The most favorable intrinsic defect is the Li−Fe “anti-site” pair in which a Li ion (on the M1 site) and an Fe ion (on the M2 site) are interchanged. This type of anti-site defect or “intersite exchange” has been observed in olivine silicates. The lowest Li migration energy is found for the pathway along the [010] channel, with a nonlinear, curved trajectory between adjacent Li sites. Trends in dopant substitution energetics of a range of cations with charges varying from +2 to +5 are also examined. Low favorable energies are found only for divalent dopants on the Fe site (such as Mn), which is in accord with experimental work. Our results suggest that, on energetic grounds, LiFePO4 is not tolerant to aliovalent d...

Electrochemical impedance study of Li-ion insertion into the raw acid-oxidized carbon nanotubes

Electrochemical impedance spectroscopy (EIS) was applied for the raw acid-oxidized multiwall carbon nanotubes during Li-ion insertion with the electrolyte of 1M LiPF 6 in EC and DMC. Impedance spectroscopy consists of two separated arcs in the high and intermediate range frequency. The high frequency arc is attributed to Li migration within the surface films and the medium frequency arc is associated with the charge transfer. Obtained spectra were analyzed with an equivalent circuit model. Kinetic parameters such as the charge transfer resistance, film resistance, diffusion coefficient and exchange current were evaluated. The contribution of the film to the measured impedance response is discussed.

Migrants and Housing Investments: Theory and Evidence from Nigeria

The dominance of housing may reflect limitations in the menu of investment choices available to migrants in the country of origin. In many developing countries individuals face relatively few savings opportunities where productive assets (such as land farm assets) are associated with high risks and/or low rates of return. Housing investments offer unique advantages in that they are durable highly visible and associated with low risk and monitoring requirements. However there are some important drawbacks associated with housing investments. In particular where resale and rental markets for housing are not well developed migrants housing assets may be relatively illiquid and irreversible. In the next section I provide some background on general patterns of investment behavior among migrants. Here the evidence on housing investments is discussed for a rich set of migrant sending and receiving countries. In Section III I develop the conceptual framework for understanding migrants housing investment decisions. Section IV provides a description of the data sources. Section V outlines the empirical strategy. In Section VI I discuss the empirical findings. Section VII presents conclusions. (excerpt)

The effect of mixed Mn valences on Li migration in LiMn2O4 spinel: A molecular dynamics study

Previous molecular dynamics (MD) simulations have shown that, with good choice of potential shapes and parameters, the structure and properties of stoichiometric LiMn2O4 can be reproduced to good accuracy. In particular, the experimentally observed self-diffusion of Li ions was shown to occur only for a discrete, mixed Mn valence model. Here, those MD studies have been extended, demonstrating that periodically switching the Mn valence states, reflecting an electron hopping model, greatly facilitates the Li ion self-diffusion. The interaction is mediated by the O atoms, which coordinate both cations and temporarily adopt local distortions based on the three coordinating Mn valences. Although the O atoms continue to vibrate harmonically about a displaced mean, permitting the Li atoms to migrate, the time and spatial average remains that of the ideal spinel with distributed Li.

Effects of B-site ion (M) substitution on the ionic conductivity of (Li 3 xLa 2/3− x) 1+ y/2 (M yTi 1− y)O 3 (M=Al, Cr)

Effect on the ionic conductivity of B-site ion (M) substitution in (Li 3 x La 2/3− x ) 1+ y/2 M y Ti 1− y O 3 (M=Al, Cr) has been investigated. It has been found that partial substitution of smaller Al 3+ for Ti 4+ is effective to enhance the ionic conductivity of Li 3 x La 2/3− x TiO 3. At 300 K, the maximum bulk conductivity of (1.58±0.01)×10 −3 S cm −1 is observed from the composition of (Li 0.39La 0.54) 1− y/2 Al y Ti 1− y O 3 with y=0.02 ( x=0.13), that is the highest yet reported for known perovskite solutions at room temperature. The conductivity enhancement is interpreted as being due to the substitution-induced bond-strength change rather than due to bottleneck size change for Li migration, TiO 6-octahedron tilting or A-site cation ordering.

Surface structural change of ZnO-coated LiNi 0.5Mn 1.5O 4 spinel as 5 V cathode materials at elevated temperatures

LiNi 0.5Mn 1.5O 4 powder was synthesized via sol–gel method and coated with ZnO in order to test the electrochemical cyclability of the material as a cathode for the secondary Li battery in the 5 V range at 55 °C. The ZnO-coated LiNi 0.5Mn 1.5O 4 powder nearly maintained its initial capacity of 137 mA h g −1 after 50 cycles whereas the uncoated powder was able to retain no more than 10% of the initial capacity after 30 cycles. TEM analysis of the cycled cathodes suggests that the formation of the graphitic surface phase, hindering the Li migration, may be responsible for the rapid capacity loss of the uncoated material while no such phase was observed on the surface of the ZnO coated LiNi 0.5Mn 1.5O 4 powder.

Molecular dynamics simulations of cathode/glass interface behavior: effect of orientation on phase transformation, Li migration, and interface relaxation

The molecular dynamics (MD) computer simulation technique has been used to study electrolyte/cathode interfaces formed in Li-based thin film oxide solid state ionic devices at the atomistic level. The solid electrolytes are lithium silicate glasses while the cathodes are V 2O 5 or WO 3 crystals. The work presented in this paper will focus on the behavior at the glass/V 2O 5 interface. The MD simulation technique has been successfully used to simulate a variety of silicate glasses and glass surfaces, with results consistent with a variety of experimental data. The simulations of the vanadia crystal reproduce the experimental crystal structures, vibrational frequency, and the appropriate phase transition of V 2O 5 as Li ions enter the crystal. The simulations have also shown that Li transport into the crystal is affected by the orientation of the crystal at the interface as well as by surface roughness. While the crystal oriented with the (001) planes parallel to the crystal/glass interface shows the appropriate phase transition to the δ-LiV 2O 5 phase as Li ions enter the crystal, the work presented here shows that the crystal oriented with the (100) planes parallel to the interface does not transform. The difference is attributed to the effect of interface bonding between the ions in the first crystal layer and those in the glass surface. The simulations show a relaxation occurring in a lithium metasilicate glass electrolyte but not in a lithium disilicate electrolyte. In addition, relaxation at the interface between a roughened glass surface and the crystal creates a distortion in the crystal planes in immediate contact with the glass that creates an induced strain in the crystal.

Mössbauer and Infrared Study of Heat-Treated Nontronite

AbstractThe Mössbauer and infrared spectra of Li- and Rb-saturated nontronites from Washington, USA (SWa-1), heat treated at different temperatures, were measured. The Mössbauer results show that diffusion of Li+ into the 2:1 layer by heat treatment at 250-300°C does not affect the magnetic hyperfine interactions of the octahedral iron centers. In contrast, significant changes were observed by calcination at temperatures &gt;300°C for Li-saturated nontronites. The main features of the Mössbauer spectra recorded at different temperatures reveal superparamagnetic behavior with a blocking temperature of ~5 K. The superparamagnetic behavior is related to small magnetic domains created by partially broken Fe-O-Fe bonds upon heat treatment. The infrared spectra of Li-rich nontronite, heat treated at 300°C, show changes attributed to Li migration into the hexagonal cavities. Heating to higher temperatures, produced changes in the spectra of the Li- and Rb-saturated nontronites owing to the dehydroxylation of the layer structure. The dehydroxylation process begins with the loss of OH groups in the FeOHFe bridges and is completed with the disruption of the Al-O bonds at &gt;600°C.

Lithium depth profiling in thin electrochromic WO3 films

Li profiles in sol-gel prepared electrochromic WO3 thin films have been characterized using three different techniques: neutron depth profiling (NDP), secondary ion mass spectrometry (SIMS), and elastic recoil detection (ERD). The results have been evaluated with respect to their concentration sensitivity and depth resolution. NDP and SIMS led to comparable results in terms of the shape of the profiles. The NDP results were quantified by using a calibration sample. NDP has the advantage that it is a quantitative nondestructive technique while SIMS has a very high sensitivity and depth resolution. Another advantage of NDP is that there is very little risk of neutron-induced Li migration during the measurement because of the very low energy of the incoming thermal neutrons. ERD was found to have a limited depth resolution, attributable to deterioration of the sample as a result of ion bombardment. However, the absolute amount of Li can be very accurately quantified with this technique.

Vacancy clustering in quenched Al-Li solid solution alloys studied by Doppler broadening spectroscopy

The clustering of vacancies in severely quenched Al-Li solid solution alloys, with Li content between 230 and 2760 ppm, has been studied using Doppler broadening spectroscopy. The alloy samples were initially annealed at 873 K in dry air or dry, pure nitrogen. The onset temperature for vacancy clustering in samples initially annealed in air was found to be , lower than for the nitrogen-annealed samples. This result is consistent with the migration of divacancies, formed as a result of the significant increase in vacancy concentration caused by Li migration to, and oxidation at, the surfaces of samples annealed in air. Li-vacancy binding may also contribute, to a lesser extent, to the retardation of vacancy migration in the nitrogen-annealed samples. No dependence on Li content was seen in the results for the two sets of samples.