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.     

Structural characterization for the chemically Li ion extracted LiyCoO2, LiyCo0.95Ga0.05O2, and LiyCo0.9Ga0.1O2 compounds

Chemical Li ion extraction processes have been carried out for pristine LiCoO₂, LiCo_0.95Ga_0.05O₂, and LiCo_0.9Ga_0.1O₂ compounds by swirling them in 0.35 M H₂SO₄ solution. It is confirmed from XRD patterns that the compounds maintain the two-dimensional framework with pristine-type structure even after the acid treatment up to 12 h. The Ga-substituted compounds keep Li ions for longer time on the acid treatment rather than the LiCoO₂. The average oxidation state of Co ions increases with the Li⁺ ion extraction time up to 3.45+. The local structure refinements for the chemically Li⁺ ion extracted compounds have been investigated by Co K-edge X-ray absorption spectroscopy. The extraction causes the increase of Debye-Waller (DW) factor or static disorder around the Co ion. The DW factor of the Co-Co bond pair less increases with the extraction time for the Li_yCo_0.95Ga_0.05O₂, and Li_yCo_0.9Ga_0.1O₂ compounds than that for the LiCoO₂. The Ga-substituted compounds are more stable against acid treatments than the LiCoO₂, since more basic Ga³⁺ ion retards the structural distortion of the CoO₆ octahedra against the Li ion extraction.     

The ionic conductivity of Li6BaLa2M2O12 with coexisting Nb and Ta on the M sites

In a view to balancing cost and lithium ion conductivity, Li₆BaLa₂Nb _x Ta_2???x O₁₂ (x?=?0–2) was prepared by solid-state reaction, and its corresponding AC impedances were tested at temperatures ranging from 20 to 250 °C in air. Li₆BaLa₂Ta₂O₁₂ exhibits the highest conductivity, 8.77?×?10^?6?S/cm, and the second highest is Li₆BaLa₂Nb₂O₁₂ with 6.69?×?10^?6?S/cm. Partial replacement of Ta with Nb cannot bestow the advantages of cost saving or the enhancement of lithium ion conductivity. X-ray diffraction patterns revealed a gradual change as an increasing amount of Nb replaces Ta in Li₆BaLa₂Nb _x Ta_2???x O₁₂ (x?=?0–2), and it is thought that the trending of Nb and Ta to rest on the crystallographic planes is different.     

Electronic energy calculation in three models of (La,Li)Ti2O6 ionic conductor with vacancies

The electronic energy calculation using the linear-muffin-tin-orbital method is performed to study the property of Li ion diffusion in La_{4/3 − y}Li_3yTi₂O₆ (y = 0.21) with vacancies. The total electronic energy of three models, LiTi₂O₆, LaLiTi₂O₆, and La₂LiTi₄O₁₂ shows the stable position of Li ions strongly dependent on each model, suggesting that the stable position and the activation energy change with the existence of vacancy.     

Emission features of Ho ion in Nb2O5, Ta2O5 and La2O3 mixed Li2O-ZrO2-SiO2 glasses

Li₂O-ZrO₂-SiO₂: Ho³⁺ glasses mixed with three interesting d-block elemental oxides, viz., Nb₂O₅, Ta₂O₅ and La₂O₃, were prepared. Optical absorption and photoluminescence spectra of these glasses have been recorded at room temperature. The luminescence spectra of Nb₂O₅ and Ta₂O₅ mixed Li₂O-ZrO₂-SiO₂ glasses (free of Ho³⁺ ions) have also exhibited broad emission band in the blue region. This band is attributed to radiative recombination of self-trapped excitons (STEs) localized on substitutionally positioned octahedral Ta⁵⁺ and Nb⁵⁺ ions in the glass network. The Judd-Ofelt theory was successfully applied to characterize Ho³⁺ spectra of all the three glasses. From this theory various radiative properties, like transition probability A, branching ratio β_r and the radiative lifetime τ_r, for ⁵S₂ emission levels in the spectra of these glasses have been evaluated. The radiative lifetime for ⁵S₂ level of Ho³⁺ ions has also been measured and quantum efficiencies were estimated. Among the three glasses studied the La₂O₃ mixed glass exhibited the highest quantum efficiency. The reasons for such higher value have been discussed based on the relationship between the structural modifications taking place around the Ho³⁺ ions.     

Calculation of chemical bonds and diffusion path of Li ion in (LaLi)Ti2O6 by DV-Xα cluster method

The chemical bonds and lithium diffusion of La_4/3−y Li_3y Ti₂O₆ (y = 0.21) were investigated by using the DV-Xα cluster method. The cluster model used is the formula La₈Li₂Ti₂O₁₁. A Li ion was moved on the ab plane at z = 1/2. The Na ion was moved along the x axis in the cluster model La₈Na₂Ti₂O₁₁ for comparison. The total bond overlap population (BOP) between the moving Li ion and the other ions was calculated on the ab plane at z = 1/2. The total BOP of the Li ion along the x axis increased near the oxygen ion site, whereas the BOP of the Na ion decreased. The decrease in total BOP indicates the decrease in covalent interaction between the Na and the other ions. The change of the net charge of the Li ion was almost the same as that of the Na ion. This suggests that the smaller change of covalent interaction in the mobile Li ion determines the diffusion path of Li ion.     

Ionic conduction and chemical bonds of Li ion in La4/3−yLi3yTi2O6

The electronic state of La_4/3−yLi_3yTi₂O₆ (y=0.21) was studied by the DV-Xα cluster method. Four model clusters were used to calculate the density of state (DOS), the bond overlap population (BOP) and the net charge (NC). A Li ion in the model cluster was moved from 1b site to another 1b site along the x axis, and the BOP and the NC calculated were discussed. Furthermore, we calculated the potential energy with the movement of the Li ion along the x axis. Paper presented at the Patras Conference on Solid State Ionics - Transport Properties, Patras, Greece, Sept. 14 – 18, 2004.     

Dielectric properties and temperature stability of BaTiO3 co-doped La2O3 and Tm2O3

The influence of La₂O₃ and Tm₂O₃ co-doping on the dielectric properties and the temperature stability of BaTiO₃ was investigated. BaTiO₃ ceramics were prepared with the compositional formula of (Ba_1−xLa_x)(Ti_1-x/4−yTm_y)O₃. La₂O₃ and Tm₂O₃ co-doping in BaTiO₃ mainly had effects on an increase in the dielectric constant and the temperature stability, respectively. The increase of La₂O₃ concentration and the decrease of Tm₂O₃ concentration in BaTiO₃ resulted in a decrease of lattice parameter and tetragonality because La³⁺ ion substituting for Ba site is smaller than Ba²⁺ ion and Tm³⁺ ion substituting for Ti site is larger than Ti⁴⁺ ion. With the increase of La₂O₃ and the decrease of Tm₂O₃, the dielectric constant of BaTiO₃ was enhanced in spite of the reduction of tetragonality. P-E hysteresis measurements revealed that this phenomenon was based on the improvement of remanent polarization with the increase of La₂O₃ concentration. The introduction of excess Tm₂O₃ in BaTiO₃ suppressed the grain growth and BaTiO₃ ceramics showed higher temperature stability due to the stable tetragonal structure and the small grain size with the increase of Tm₂O₃ concentration.     

Synthesis and structure refinement of layered perovskites Ba5−xLaxNb4−xTixO15 (x=0, 1, 2, 3 and 4) solid solutions

Ba_5−xLa_xNb_4−xTi_xO₁₅ solid solutions were prepared by solid state reaction method. Structural analysis for the stoichiometric phases was performed for x=0, 1, 2 and 3 by Rietveld analysis of neutron powder diffraction data. The x=0, 1 and 2 members could be refined in the space group P-3m1 (stacking sequence chhcc, polytypoid 5 H). There is a decrease in cell volume as x increases. La³⁺ occupies preferentially the A2 site (Wyckoff site 2d) and Ti⁴⁺ the B2 site (Wyckoff site 2c). As x increases there is an increase of the global instability index (GII) (which is a measure of the extent to which the BVS rule is violated over the whole structure) indicating the presence of intrinsic strains large enough to cause instability at room temperature. This strain is responsible for a structural change for the member with x=3, which could be refined in the space group P-3c1 (stacking sequence (chhcc)₂, polytypoid 2×5H=10H). This change in space group is associated with a cooperative rotation of (Nb/Ti)O₆ octahedra around the c-axis, necessary to accommodate the smaller La³⁺ ion in the cuboctahedral cavity.     

Solid solutions Li1+xV3O8 as cathodes for high rate secondary Li batteries

Following a preliminary investigation, Li/Li_1+xV₃O₈ cells have been examined. Using samples of low x content, up to 3 eq Li⁺ could be accepted both chemically and electrochemically by one mole of active material. Li⁺ is accomodated in the tetrahedral sites existing between the (V₃O₈)^(1+x)- layers. Li⁺ jumping from site to site is fast and permits high rate capabilities: at 10 mA/cm², 1.1 eq Li⁺ per mole could still be inserted. The structure does not show irreversible alterations upon extended lithiation, allowing long cycle lives to be achieved. Kinetic constraints limit the recovery of the full capacity of the first discharge at medium-high rates, but the second-discharge capacity declines slowly with cycle number.     

Li ion conduction in Li2ZrO3, Li4ZrO4, and LiScO2

The results of ac and dc conductivity measurements on Li₂ZrO₃, Li₄ZrO₄, and LiScO₂ show that these phases are Li ion conductors. Even though the Li ion conductivity in these phases is quite low, 3.3×10^?5, 3.0×10^?4, and 4.2×10^?7 S m^?1 at 573 K, respectively, they are of special interest since they are among the small group of ternary oxides which may be thermodynamically stable against Li. Mechanisms are proposed for the decomposition of these phases at the anode due to Li loss during dc polarization. In addition the electrical conductivity of ternary oxide phases which are, or may be, thermodynamically stable against Li are summarized.     

Ferroelectric properties of Bi3.25−x/3La0.75Ti3−xNbxO12 films prepared by pulsed laser deposition

Bi₄Ti₃O₁₂ (BiT), Bi_3.25La_0.75Ti₃O₁₂ (BLT), Bi_4−x/3Ti_3−xNb_xO₁₂ (BTN) and Bi_3.25−x/3La_0.75Ti_3−xNb_xO₁₂ (BLTN) thin films have been prepared by pulsed laser deposition. BTN and BLTN films exhibit a maximum in the remanent polarization P_r at a Nb content x=0.018. At this Nb content, the BLTN film has a P_r value (25 μC/cm²) that is much higher than that of BiT and a coercive field similar to that of BiT. The polarization of this BLTN film is fatigue-free up to 10⁹ switching cycles. The high fatigue resistance is mainly due to the substitution of Bi³⁺ ions by La³⁺ ions at the A site and the enhanced P_r arises largely from the replacement of Ti⁴⁺ ions by Nb⁵⁺ ions at the B site. The mechanisms behind the effects of the substitution at the two sites are discussed.     

Dielectric properties of the Li0.07Na0.93Ta0.1Nb0.9O3 and Li0.07Na0.93Ta0.111Nb0.889O3 solid solutions

Dielectric properties of perovskite ferroelectric solid solutions Li_0.07Na_0.93Ta_0.1Nb_0.9O₃ and Li_0.07Na_0.93Ta_0.111Nb_0.889O₃ are studied over the 290?C700 K range of temperature within the frequency range of 25?C10⁶ Hz. A decrease of the Curie temperature (??75 K) compared with Li_0.07Na_0.93Ta_0.1Nb_0.9O₃ synthesized from mechanical mixture of pentoxides Ta₂O₅ and Nb₂O₅ is observed in Li_0.07Na_0.93Ta_0.111Nb_0.889O₃ synthesized from co-precipitated pentoxide Ta_2y Nb_{2(1 ? y)}O₅.     

Challenges regarding thin film deposition of garnet electrolytes for all-solid-state lithium batteries with high energy density

In this work, we studied the deposition of garnet electrolyte thin films in order to realize an all-solid-state battery with high energy density. Therefore, in a first step we investigated the stability of the garnet Li₅La₃Ta₂O₁₂ with the spinel LiCoMnO₄ in order to determine the temperature window for a successful thin film deposition on high-voltage spinels. A mixture of both materials showed a thermal stability up to 600 °C, so that all-solid-state batteries could be realized when the electrolyte is applied at a low deposition temperature. The second part of the work was the thin film deposition of Li₅La₃Ta₂O₁₂ by a sputter deposition process. When a stoichiometric Li₅La₃Ta₂O₁₂ sputter target was used, the surface of the target showed a depletion of lithium after several depositions, which leads to decreasing Li content in the thin films. In order to compensate the lithium loss we enriched the target with LiOH?H₂O. Depositions carried out with the lithium rich target showed the garnet structure on glass substrates after deposition at 500 °C. The garnet structure was observed on Au-coated EN 1.4767 substrates already at a substrate temperature of 400 °C, which is 300 K lower than comparable depositions of Li₇La₃Zr₂O₁₂. These results show that the combination of thin garnet-structured electrolytes and high-voltage spinels is possible.     

Effects of Li/Ti ratios on the electrochemical properties of Li4Ti5O12 examined by time-resolved X-ray diffraction

Li₄Ti₅O₁₂ for anodic active material of lithium ion batteries is synthesized using different Li/Ti ratios of 3.5/5.0, 4.0/5.0 and 4.5/5.0 by a solid-state reaction between Li₂CO₃ and anatase TiO₂ at 850?°C. All samples contain a small amount of transformed rutile TiO₂ in the final Li₄Ti₅O₁₂, where the amount of rutile TiO₂ decreases with the increase in Li/Ti ratio. A stoichiometric Li₄Ti₅O₁₂ with Li/Ti = 4.0/5.0 shows a slightly larger particle size and higher charge capacity than those of Li-deficient and Li-excessive particles, while the discharging rate capability is shown to mainly depend on particle size regardless of Li/Ti ratio. According to the time-resolved X-ray diffraction patterns using a synchrotron source, however, no significant difference is found in spite of the difference in Li/Ti ratio, indicating the structural stability of Li₄Ti₅O₁₂ during the Li insertion and extraction process.     

Li2O-Nb2O-SiO2系统非晶态离子导体的结构与电学性能

本文采用红外吸收光谱法、X射线散射法和EXAFS方法研究了LiO-Nb₂O-SiO₂系统非晶态离子导体的结构,认为Nb⁵⁺在非晶结构网络中主要是以[NbO₆]形式存在。非晶结构随Nb₂O₅含量的多少而变化。低Nb₂O₅含量时,[NbO₆]相互间以边相连,并与[SiO₄]组成多元环后,形成非晶网络结构。高Nb₂O₅含量时,非晶网络结构主要是以角顶相连的[NbO₆]所组成。根据电导测试结果,讨论了结构与电学性能的关系,认为Li₂O含量在0.45左右,Nb₂O₅,含量在0.3左右组成的非晶材料有最高的电导率。 关键词：     

The solid solutions of Li2Mn4O8-Li1Fe5O8

A solid solution of (1 ?x)(Li₂Mn₄O₈)x(Li₁Fe₅O₈) for 0<x<1 has been investigated by Mössbauer spectroscopy at room temperature and at 80 K. The saturated magnetic moment has been measured forx>0.6. The results are explained by a change of site preference of the Li ion from the tetragonal (A) site atx=0 to the octahedral [B] site atx=1.     

石墨/Li（Ni1/3Co1/3Mn1/3）O2电池充放电过程中电极材料的XRD研究

利用XRD系统地研究了石墨/Li（Ni_1/3Co_1/3Mn_1/3）O₂ 18650型锂离子电池充放电过程中正负极活性材料的晶体结构和微结构的变化.已观测到,由于Li原子的脱嵌,使得LiMO₂点阵参数a缩小,c增大,微应变增大,衍射强度比I₁₀₄/I₁₀₁和I₀₁₂/I₁₀₁降低;此外,由于Li原子的嵌入,2H-石墨的点阵参数a和c,以及微应变ε和堆垛无序度P都增加.同时,讨论了活性材料Li（Ni_1/3Co_1/3Mn_1/3）O₂和石墨在电池充放电过程中的嵌脱锂的物理机理.在充电时,正极Li（Ni_1/3Co_1/3Mn_1/3）O₂中处于（000）位的Li原子优先脱离晶体点阵,继后才是位于（2/3 1/3 1/3）和（1/3 2/3 2/3）位的Li原子离开点阵.锂嵌入石墨,优先进入碳原子六方网格面间的间隙位置,当负极的堆垛无序度达到一定值后,3R相逐渐析出.当电池满充或过充时,在六方石墨中形成LiC₁₂和LiC₆相.放电时,与上述过程相反,但并非是完全可逆的. 关键词： 锂离子电池 微结构 X射线衍射 嵌脱锂物理机理     

Low- and infralow-frequency dielectric properties of the Pb(Mg1/3Nb2/3)O3 + 2 wt % Li2O ceramics

A dielectric response of the Pb(Mg_1/3Nb_2/3)O₃ ferroelectric ceramics with impurity of 2 wt % Li has been studied. The phase transition has been found to exhibit a relaxor character, as is the case in PMN without Li. However, unlike pure PMN, the dielectric response dispersion in PMN + 2 wt % Li₂O has been described by the Cole-Cole equation at temperatures below the temperature of the low-frequency maximum of the permittivity. An analysis of the dispersion parameters in a wide temperature range has demonstrated that it can be due to the relaxation of domain walls in PMN + 2 wt % Li₂O that appear most likely because of the existence of anomalously coarse grains in PMN + 2 wt % Li₂O.     

Experimental and theoretical studies on dynamic properties of Li ions in LixMn2O4

In order to study the dynamic properties of Li_xMn₂O₄, potential relaxation techniques (PRT) is used to measure the chemical diffusion coefficient of Li_xMn₂O₄. Results are presented for x ranges from x=0.1 to 0.9. They show that the chemical diffusion coefficient at the two-phase coexistent stage near x=0.3 and 0.7 is higher than at the single-phase stage during the insertion and extraction process. Monte Carlo (MC) simulations are also used to simulate the ionic conductivity σ of Li ions in Li_xMn₂O₄ and its dependence as a function of lithium concentration x. The results show an M shaped curve in the plot of ionic conductivity σ versus x when the simulation temperature is 293 K, which confirms the experimental PRT results. The voltage profiles of Li_xMn₂O₄/Li cells were also simulated with different boundary conditions.