Structural and electrochemical study on Li(Li1/3Ti5/3)O4 anode material for lithium ion batteries

Chemical and electrochemical studies have shown that various titanium oxides can incorporate lithium in different ratios. Other compounds with a spinel-type structure and corresponding to the spinel oxides LiTi₂O₄ and Li₄Ti₅O₁₂ have been evaluated in rechargeable lithium cells with promising features. The spinel Li[Li_1/3Ti_5/3]O₄ [1–5] compound is a very appealing electrode material for lithium ion batteries. The lithium insertion-deinsertion process occurs with a minimal variation of the cubic unit cell and this assures high stability which may reflect into long cyclability. In addition, the diffusion coefficient of lithium is of the order of 10⁻⁸ cm²s⁻¹ [5] and this suggests fast kinetics which may reflect in high power capabilities. In this work we report a study on the kinetics and the structural properties of the Li[Li_1/3Ti_5/3]O₄ intercalation electrode carried out by: cyclic voltammetry, galvanostatic cycling and in-situ X-ray diffraction. The electrochemical characterization shows that the Li[Li_1/3Ti_5/3]O₄ electrode cycles around 1.56 V vs. Li with a capacity of the order of 130 mAhg⁻¹ which approaches the maximum value of 175 mAhg⁻¹ corresponding to the insertion of 1 equivalent per formula unit. The delivered capacity remains constant for hundred cycles confirming the stability of the host structure upon the repeated Li insertion-deinsertion process. This high structural stability has been confirmed by in situ Energy Dispersion X-ray analysis. Paper presented at the 7th Euroconference on Ionics, Calcatoggio, Corsica, France, Oct. 1–7, 2000.     

Ionic Pathways in Li13Si4 investigated by 6Li and 7Li solid state NMR experiments

Local environments and dynamics of lithium ions in the binary lithium silicide Li₁₃Si₄ have been studied by ⁶Li MAS-NMR, ⁷Li spin-lattice relaxation time and site-resolved ⁷Li 2D exchange NMR measurements as a function of mixing time. Variable temperature experiments result in distinct differences in activation energies characterizing the transfer rates between the different lithium sites. Based on this information, a comprehensive picture of the preferred ionic transfer pathways in this silicide has been developed. With respect to local mobility, the results of the present study suggests the ordering Li6/Li7>Li5>Li1>Li4 >Li2/Li3. Mobility within the z=0.5 plane is distinctly higher than within the z=0 plane, and the ionic transfer between the planes is most facile via Li1/Li5 exchange. The lithium ionic mobility can be rationalized on the basis of the type of the coordinating silicide anions and the lithium-lithium distances within the structure. Lithium ions strongly interacting with the isolated Si⁴⁻ anions have distinctly lower mobility than those the coordination of which is dominated by Si₂⁶⁻ dumbbells.     

Raman spectroscopic studies of LixSiy compounds

The phase diagram of the Li–Si system contains several phases with Li and Si in well defined ratios. So far, only the Raman spectrum of LiSi has been reported. In this work, we present experimental Raman scattering results for the crystalline lithium silicide phases Li₁₂Si₇, Li₇Si₃, Li₁₃Si₄, and Li₂₁Si₅/Li₂₂Si₅, which show clearly distinguishable Raman modes. The experimental results are compared with theoretical data obtained by density functional theory calculations. Copyright © 2013 John Wiley & Sons, Ltd.     

Determination of the diffusion coefficient of lithium ions in nano-Si

The diffusion coefficients of lithium ions (D_Li⁺) in nano-Si were determined by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic intermittent titration technique (GITT). D_Li⁺ values are estimated to be ~ 10^? 12 cm² s^? 1 and exhibit a “W” type varying with the lithium concentration in silicon. Two minimum regions of D_Li⁺ (at Li_2.1 ± 0.2Si and Li_3.2 ± 0.2Si) are found, which probably result from two amorphous compositions (a-Li₇Si₃ and a-Li₁₃Si₄). Besides the two minimum regions, one maximum D_Li⁺ is observed at Li₁₅Si₄, corresponding to the crystallization of highly lithiated amorphous Li_xSi.     

Structural reinvestigation of Li3FeN2: Evidence of cationic disorder through XRD,solid-state NMR and Mössbauer spectroscopy

A significant cationic disorder is evidenced on Li₃FeN₂ prepared through solid-state reaction under controlled atmosphere. This derivative anti fluorite type structure (orthorhombic, space group Ibam, a=4.870(1) Å, b=9.652(1) Å and c=4.789(1) Å), solved first through single crystal X-ray diffraction [7], is usually described by Li⁺ and Fe⁺³ ordered distribution in tetrahedral sites formed by the nitrogen network, leading to [FeN_4/2]³⁻ edge-sharing tetrahedral chains. From ⁷Li/⁶Li Nuclear Magnetic Resonance spectroscopy, ⁵⁷Fe Mössbauer spectroscopy and powder X-ray and neutron diffraction, we demonstrate that about 4% of lithium sites are filled by iron and about 11% of iron sites are occupied by Li, which can explain the discrepancy within the Gudat's model observed on larger scale solid-state synthesis samples.     

Electrochemical behavior of Li intercalation processes into a Li[NixLi(1/3−2x/3)Mn(2/3−x/3)]O2 cathode

Li[Ni_xLi_(1/3−2x/3)Mn_(2/3−x/3)]O₂ (X=0.17, 0.25, 0.33, 0.5) compounds are prepared by a simple combustion method. The Rietvelt analysis shows that these compounds could be classified as having the α-NaFeO₂ structure. The initial charge-discharge and irreversible capacity increases with the decrease of x in Li[Ni_xLi_(1/3−2x/3)Mn_(2/3−x/3)]O₂. Indeed, Li[Ni_0.50Mn_0.50]O₂ compound shows relatively low initial discharge capacity of 200 mAh/g and large capacity loss during cycling, with Li[Ni_0.17Li_0.22Mn_0.61]O₂ and Li[Ni_0.25Li_0.17Mn₀.₅₈]O₂ compounds exhibit high initial discharge capacity over 245 mAh/g and stable cycle performance in the voltage range of 4.8 -2.0 V. On the other hand, XANES analysis shows that the oxidation state of Ni ion reversibly changes between Ni²⁺ and about Ni³⁺, while the oxidation state of Mn ion sustains Mn⁴⁺ during charge-discharge process. This result does not agree with the previously reported ‘electrochemistry model’ of Li[Ni_xLi_(1/3−2x/3)Mn_(2/3−x/3)]O₂, in which Ni ion changes between Ni²⁺ and NI⁴⁺. Based on these results, we modified oxidation-state change of Mn and Ni ion during charge-discharge process.     

Structure,ionic conduction,and phase transformations in lithium titanate Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript>

The spinel structure of lithium titanate Li₄Ti₅O₁₂ is refined by the Rietveld full-profile analysis with the use of x-ray and neutron powder diffraction data. The distribution and coordinates of atoms are determined. The Li₄Ti₅O₁₂ compound is studied at high temperatures by differential scanning calorimetry and Raman spectroscopy. The electrical conductivity is measured in the high-temperature range. It is shown that the Li₄Ti₅O₁₂ compound with a spinel structure undergoes two successive order-disorder phase transitions due to different distributions of lithium atoms and cation vacancies (□, V) in a defect structure of the NaCl type: (Li)_8a[Li_0.33Ti_1.67]_16dO₄ → [Li□]_16c[Li_1.33Ti_1.67]_16dO₄ → [Li_1.33□_0.67]_16c[Ti_1.67□_0.33]_16dO₄. The low-temperature diffusion of lithium predominantly occurs either through the mechanism ... → Li(8a) → V(16c) → V(8a) → ... in the spinel phase or through the mechanism ... → Li(16c) → V(8a) → V(16c) → ... in an intermediate phase. In the high-temperature phase, the lithium cations also migrate over 48f vacancies: ... Li(16c) → V(8a, 48f) → V(16c) → ....     

Crystal structure analysis of novel complex hydrides formed by the combination of LiBH4 and LiNH2

Combination of LiBH₄ and LiNH₂ by ball milling forms the series of novel complex hydrides Li₂BNH₆, Li₃BN₂H₈ and Li₄BN₃H₁₀, depending on the combination ratios. The crystal structure of Li₄BN₃H₁₀ analyzed by synchrotron X-raydiffraction measurements is determined to be a cubic system (space group: I2₁3) with the lattice constant of a=10.673(2)Å. It should be emphasized that Li₄BN₃H₁₀ is an ionic crystal which is composed of a lithium cation Li⁺ and two different kinds of the complex anion [BH₄]^- and [NH₂]^-. These anions are located in the vertex and face-center of the cubic sub-lattice, and the lithium cation Li⁺ in the interstitial site between the anions, respectively. The other series of complex hydrides, Li₂BNH₆ and Li₃BN₂H₈, are also predicted to possess similar structures composed of a lithium cation Li⁺ and two different kinds of the complex anion [BH₄]^- and [NH₂]^-.     

Electrochemical properties of Li[CnF2n+1BF3] as electrolyte salts for lithium-ion cells

The fundamental electrochemical properties of lithium perfluoroalkyltrifluoroborates Li[C_nF_2n+1BF₃] (n = 1∼4) were evaluated as electrolyte salts for lithium-ion battery in comparison with LiBF₄ and LiPF₆. Li[C_nF_2n+1BF₃] showed higher electrolytic conductivities than LiBF₄ in aprotic solvents. In these series, the conductivities decreased with the perfluoroalkyl group being longer, and Li[C₂F₅BF₃] exhibited a comparable conductivity to LiPF₆. The relationship between the conductivity and the anion size showed that the anion with a moderate size is in favor of obtaining high conductivities. The limiting oxidation potentials determined by linear sweep voltammetry demonstrated that Li[C_nF_2n+1BF₃] were less resistant against oxidation than LiBF₄. The HOMO energies and ionization energies of [C_nF_2n+1BF₃]⁻ calculated by ab initio molecular orbital (MO) theory and density functional theory (DFT) supported this observation, however, there was no accuracy to explain the effect of the chain length of perfluoroalkyl groups on the limiting oxidation potentials. The cell performances of a LiC₆/Li_0.5CoO₂ cell using Li[C₂F₅BF₃] were comparable to those using LiPF₆ at room temperature, however, it deteriorated at elevated temperature due to the reaction on the cathode.     

Electrical properties of LiBSe ternary system

Amorphous products were obtained in the LiBSe ternary system by quenching melts of Li₂Se, B and Se mixture prepared at 100°C in sealed silica tubes. The vitreous region was slightly lower selenium composition than that of the Li₂SeB₂Se₃ tie-line. The amorphous products were lithium ionic conductors and most of them showed contributions to their total conductivity. The amorphous product of composition Li₂₅B₃₆Se₃₉ has the least electronic contribution to its total conductivity of 6.0 × 10⁻⁶ S/cm at room temperature. A new crystalline compound and crystalline LiBH₄ were also obtained in LiBSe ternary. Both of them were lithium ionic conductors having conductivities of about 1 × 10⁻⁶ S/cm at room temperature.     

Crystalline-structure-dependent green and red upconversion emissions of Er-Yb-Li codoped TiO2

Crystalline structures and infrared-to-visible upconversion luminescence spectra have been investigated in 1 mol% Er³⁺, 10 mol% Yb³⁺ and 0-20 mol% Li⁺ codoped TiO₂ [1Er10Yb(0-20)Li:TiO₂] nanocrystals. The crystalline structures of 1Er10Yb(0-20)Li:TiO₂ were divided into three parts by the addition of Yb³⁺ and Li⁺. Both green and red upconversion emissions were observed from the ²H_11/2/⁴S_3/2 → ⁴I_15/2 and ⁴F_9/2 → ⁴I_15/2 transitions of Er³⁺ in Er³⁺-Yb³⁺-Li⁺ codoped TiO₂, respectively. The green and red upconversion emissions of 1Er:TiO₂ were enhanced significantly by Yb³⁺ and Li⁺ codoping, in which the intensities of green and red emissions and the intensity ratio of green to red emissions (I_green/I_red) were highly dependent on the crystalline structures. The significant enhanced upconversion emissions resulted from the energy migration between Er³⁺ and Yb³⁺ as well as the distortion of crystal field symmetry of Er³⁺ caused by the dissolving of Li⁺ at lower Li⁺ codoping concentration and the phase transformation at higher Li⁺ concentration. It is concluded that codoping with ions of smaller ionic radius like Li⁺ can efficiently improve the upconversion emissions of Er³⁺ or other rare-earth ions doped luminsecence materials.     

Ab initio calculations of endo-and exohedral C60 fullerene complexes with Li+ ion and the endohedral C60 fullerene complex with Li2 dimer

The results of ab initio Hartree-Fock calculations of endo-and exohedral C₆₀ fullerene complexes with the Li⁺ ion and Li₂ dimer are presented. The coordination of the Li⁺ ion and the Li₂ dimer in the endohedral complexes and the coordination of Li⁺ ion in the exohedral complex of C₆₀ fullerene are determined by the geometry optimization using the 3–21G basis set. In the endohedral Li⁺C₆₀ complex, the Li⁺ ion is displaced from the center of the C₆₀ cage to the centers of carbon hexa-and pentagons by 0.12 nm. In the Li₂ dimer encapsulated inside the C₆₀ cage, the distance between the lithium atoms is 0.02 nm longer than that in the free molecule. The calculated total and partial one-electron densities of states of C₆₀ fullerene are in good agreement with the experimental photoelectron and X-ray emission spectra. Analysis of one-electron density of states of the endohedral Li⁺@C₆₀ complex indicates an ionic bonding between the Li atoms and the C₆₀ fullerene. In the Li⁺C₆₀ and Li⁺@C₆₀ complexes, there is a strong electrostatic interaction between the Li⁺ ion and the fullerene.     

Effect of allied and alien ions on the EPR spectrum of Mn-containing lithium-manganese spinel oxides

Electron paramagnetic resonance spectroscopy was used for studying the effect of allied and alien ions on the EPR spectrum of Mn⁴⁺-containing lithium-manganese spinel oxides. Manganese spinel oxides with paramagnetic Mn⁴⁺ and diamagnetic substituents in the 16d spinel sites were studied: Li[Mg_0.5Mn_1.5]O₄, Li[Mg_0.5−xCo_2xMn_1.5−x]O₄, 0<x≤0.5, and Li[Li_1/3Mn_5/3]O₄. Ni²⁺-ions with integer-spin-ground state (S=1) were selected as alien ions: Li[Mg_0.5−xNi_xMn_1.5]O₄ (0≤x≤0.5), Li[Li_(1−2x)/3Ni_xMn_(5−x)/3]O₄ (0≤x≤0.5), and Li[Ni_0.5Mn_1.5−yTi_y]O₄ (0≤y≤1.0). It was shown that in Ni-substituted oxides the low temperature EPR response comes from magnetically correlated Ni-Mn spins, while at high registration temperature Mn⁴⁺ ions give rise to the EPR profile. Analysis of the EPR line width allows differentiating between the contributions of the density of paramagnetic species and the strength of the exchange interactions in magnetically concentrated systems. The density of allied and alien paramagnetic species has no effect on the EPR line width in cases when the strengths of antiferro- and ferromagnetic interactions on an atomic site are close. On the contrary, when antiferro- or ferromagnetic interactions on an atomic site are dominant, the EPR line width increases with the density of paramagnetic species.     

Ionic diffusion and structural changes in lithium compounds

⁷Li NMR measurements have been performed to study milling effects on ionic diffusion in lithium cobalt oxide, LiCoO₂ and piezoelectric compound, LiNbO₃ prepared by mechanical milling method. The milling process gives quite different effects on NMR spectra of these compounds. Both ⁷Li MAS and static NMR spectra of the milled LiCoO₂ show the line broadening with increasing milling time. ⁵⁹Co static spectra also show specific changes in the line shape with increasing milling time. These results would be attributed to the change in an electronic state of Co 3d orbitals because of charge compensation associated with oxygen vacancies and/or defects. ⁷Li static NMR spectrum of milled LiNbO₃ shows complicated line shape with increasing milling time. It is explained by superposition of two spectra arising from mobile Li⁺ ions and non-mobile ones settled on the fixed site. It is shown that the ratio of mobile Li⁺ ions increases up to a maximum of 9.4% with increasing milling time. Milling effects on the Li⁺ ionic diffusion in LiCoO₂ and LiNbO₃ are discussed in connection with changes in local structure.     

Investigation of interaction between lithium and tantalum under a silicon film coating by electron-stimulated desorption technique

The electron-stimulated desorption of Li⁺ ions from lithium layers adsorbed on the tantalum surface coated with a silicon film has been investigated. The measurements are performed using a static magnetic mass spectrometer equipped with an electric field-retarding energy analyzer. The threshold of the electron-stimulated desorption of lithium ions is close to the ionization energy of the Li 1s level. The secondary thresholds are observed at energies of about 130 and 150 eV. The threshold at an energy of 130 eV is approximately 30 eV higher than the ionization energy of the Si 2p level and can be associated with the double ionization. The threshold at 150 eV can be caused by the ionization of the Si 2s level. It is demonstrated that the yield of Li⁺ ions does not correlate with the silicon amount in near-the-surface region of the tantalum ribbon and drastically increases at high annealing temperatures. The dependence of the current of Li⁺ desorption on the lithium concentration upon annealing of the tantalum ribbon at T>1800 K exhibits two maxima. The ions desorbed by electrons with energies higher than 130 and 150 eV make the largest contribution to the current of lithium ions after the annealing. The yield of lithium ions upon ionization of the Li 1s level at an energy of 55 eV is considerably lesser, but it is observed at higher concentrations of deposited lithium. The results obtained can be interpreted in the framework of the Auger-stimulated desorption model with allowance made for relaxation of the local surface field.     

Effects of Al doping for Li[Li0.09Mn0.65*0.91Ni0.35*0.91]O2 cathode material

Li-rich Mn-based Li[Li_0.09Mn_{0.65*(0.91???x)} Ni_{0.35*(0.91???x)} Al _x ]O₂ cathode materials have been prepared by traditional solid-state reaction. The lattice parameters a, c, and V have decreased, but c/a increased with the increase of Al doping. All the samples show analogy morphology of a quasi-spherical shape. Li[Li_0.09Mn_0.591Ni_0.319]O₂ sample shows a higher initial discharge capacity of 239.4 mAh?g^?1 at 20 mA?g^?1, while Li[Li_0.09Mn_0.582Ni_0.314Al_0.015]O₂ sample presents a higher discharge capacity of 170.1 mAh?g^?1 and ratio of 72.0 % with 200 vs. 20 mA?g^?1. The solid electrolyte interface resistance (R _SEI) and charge transfer process resistance (R _ct ) values are relatively smaller for Al-doped samples than those of non-doped samples. Almost no reduction is observed after 24-time cycles in different discharge rates for the samples prepared.     

NMR study of Li+-ion diffusion in the solid solution Li3+x(P1−x,Six)O4> with the γII-Li3PO4 structure

Diffusive motion of a Li⁺ ion in the solid solution of Li₃+x(P₁?x, Si_x)O₄ (0?x?0.4) with the γ_II-Li₃PO₄ structure was studied by the measurement of the ⁷Li spin-lattice relaxation time. The observed motion was a local motion instead of a long-range one. In comparison with the previous study on the solid solution of Li₄?x(P_x, Si₁?x)O₄ with the Li₄SiO₄ structure, it is noticeable that the activation energy is low and almost independent of the composition and that the attempt frequency is smaller in this phase. These characteristics were attributed to the availability of a large interstitial void in the γ_II-Li₃PO₄ structure. The low values of activation energy for the Li⁺ ionic conduction may be explained on the same basis.     

Clustering and polymerization of Li15C60

The structural and electronic properties of lithium intercalated fullerides (of which Li₁₅C₆₀ is the most representative) are still puzzling and unclear. Above 520 K, x-ray/neutron diffraction shows an fcc phase in which the 15 Li atoms clusterize in the octahedral interstices. However, at lower temperatures, a change in the crystalline symmetry and also in the electronic properties takes place as observed from ¹³C, ⁷Li/⁶Li NMR and x-ray diffraction measurements. X-ray diffraction data suggest the presence of two different stable structures: a tetragonal monomeric and an orthorhombic polymerised phase. Detailed ¹³C magic angle spinning NMR experiments in the latter phase indicate sp ³ bondings among the carbon atoms, whereas the relative (sp ²/sp ³) intensities, together with x-ray data, suggest the C₆₀ polymerization to be a [2+2] cycloaddition. Multiple quantum NMR experiments on ⁷Li confirm the presence of lithium clusters, as observed by x-ray diffraction in the high temperature phase, also at lower temperatures. However, the inferred cluster size is significantly smaller than that suggested by the stoichiometry. The distortion in the low-T structure of L₁₅C₆₀ is supposed to induce the migration of Li atoms from octahedral to tetrahedral voids, thus accounting for the lower number of Li atoms in the clusters. Further evidence of this scenario is obtained also from preliminary measurements of line shapes and T ₁ relaxation times, which exhibit a multiexponential recovery with very different constants that are hardly compatible with a single family of Li atom sites.     

Theoretical study of cisplatin adsorption on silica

The adsorption of cisplatin and its complexes, cis-[PtCl(NH₃)₂]⁺ and cis-[Pt(NH₃)₂]²⁺, on a SiO₂(1 1 1) hydrated surface has been studied by the Atom Superposition and Electron Delocalization method. The adiabatic energy curves for the adsorption of the drug and its products on the delivery system were considered. The electronic structure and bonding analysis were also performed. The molecule-surface interactions are formed at expenses of the OH surface bonds. The more important interactions are the Cl-H bond for cis-[PtCl₂(NH₃)₂] and cis-[PtCl(NH₃)₂]⁺ adsorptions, and the Pt-O interaction for cis-[Pt(NH₃)₂]²⁺ adsorption. The Cl p orbitals and Pt s, p y d orbitals of the molecule and its complexes, and the s H orbital and, the s and p orbitals of the O atoms of the hydrated surface are the main contribution to the surface bonds.     

Secondary-Phase Formation in Spinel-Type LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript>-Cathode Materials for Lithium-Ion Batteries: Quantifying Trace Amounts of Li<Subscript>2</Subscript>MnO<Subscript>3</Subscript> by Electron Paramagnetic Resonance Spectroscopy

Spinel-type lithium manganese oxides are considered as promising cathode materials for lithium-ion batteries. Trace amounts of Li₂MnO₃ usually occur as a secondary phase in lithium-manganese spinels in the common high-temperature, solid-state synthesis, affecting the overall Li–Mn stoichiometry in the spinel phase and thereby the electrochemical performance. However, the formation of Li₂MnO₃ lower than 1 wt.% can hardly be quantified by the conventional analytical techniques. In this work, we synthesized lithium-manganese spinels with different Li/Mn molar ratios and demonstrate that electron paramagnetic resonance (EPR) enables quantifying trace amounts of Li₂MnO₃ below 10^?2 wt.% in the synthesized products. The results reveal that the formation of Li₂MnO₃ secondary phase is favored by lithium excess in the synthesis. Based on the quantitative evaluation of the EPR data, precise determining Li–Mn stoichiometry in the spinel phase in Li_1+xMn_2?xO₄ materials can be assessed. Accordingly, it is possible to estimate the amount of lithium on 16d-sites in the Li-rich manganese spinels.