Structural and Electrochemical Study of Vanadium‐Doped TiO2 Ramsdellite with Superior Lithium Storage Properties for Lithium‐Ion Batteries

Titanium‐oxide‐based materials are considered attractive and safe alternatives to carbonaceous anodes in Li‐ion batteries. In particular, the ramsdellite form TiO₂(R) is known for its superior lithium‐storage ability as the bulk material when compared with other titanates. In this work, we prepared V‐doped lithium titanate ramsdellites with the formula Li_0.5Ti_1?xV_xO₂ (0≤x≤0.5) by a conventional solid‐state reaction. The lithium‐free Ti_1?xV_xO₂ compounds, in which the ramsdellite framework remains virtually unaltered, are easily obtained by a simple aqueous oxidation/ion‐extraction process. Neutron powder diffraction is used to locate the Li channel site in Li_0.5Ti_1?xV_xO₂ compounds and to follow the lithium extraction by difference‐Fourier maps. Previously delithiated Ti_1?xV_xO₂ ramsdellites are able to insert up to 0.8 Li⁺ per transition‐metal atom. The initial gravimetric capacities of 270 mAh g^?1 with good cycle stability under constant current discharge conditions are among the highest reported for bulk TiO₂‐related intercalation compounds for the threshold of one e^? per formula unit.     

Lithium Intercalation into Titanium Dioxide Films from a Propylene Carbonate Solution

Intercalation of lithium from an LiClO₄ propylene carbonate solution into thin-film TiO₂ (rutile) electrodes produced by thermal oxidation of a titanium substrate are studied using cyclic voltammetry and impedance measurements at 0.01 to 10⁵ Hz. An equivalent circuit adequately modeling the impedance spectra of TiO₂- and Li _x TiO₂ electrodes throughout the frequency range studied is proposed. The electrochemical characteristics of film electrodes, the reversibility of intercalation-deintercalation process, the effect of surface passivation on the lithium transfer rate, and the dependence of electric, kinetic, and diffusion parameters on the electrode potential (composition) are discussed. The diffusion coefficient of lithium in Li _x TiO₂ is 10^–12 cm²/s, as estimated by the impedance method.     

Layered xLiMO2·(1−x)Li2M′O3 electrodes for lithium batteries: a study of 0.95LiMn0.5Ni0.5O2·0.05Li2TiO3

The electrochemical properties of 0.95LiMn_0.5Ni_0.5O₂·0.05Li₂TiO₃ have been investigated as part of a study of xLiMO₂·(1−x)Li₂M^′O₃ electrode systems for lithium batteries in which M=Co, Ni, Mn and M^′=Ti, Zr, Mn. The data indicate that the electrochemically inactive Li₂TiO₃ component contributes to the stabilization of LiMn_0.5Ni_0.5O₂ electrodes, which improves the coulombic efficiency of Li/xLiMn_0.5Ni_0.5O₂·(1−x)Li₂TiO₃ cells for x<1. The 0.95LiMn_0.5Ni_0.5O₂·0.05Li₂TiO₃ electrodes provide a rechargeable capacity of approximately 175 mAh/g at 50 °C when cycled between 4.6 and 2.5 V; there is no indication of spinel formation during electrochemical cycling.     

Activation of Bulk Li2S as Cathode Material for Lithium-Sulfur Batteries through Organochalcogenide-Based Redox Mediation Chemistry

Lithium sulfide (Li₂S) is considered as a promising cathode material for sulfur-based batteries. However, its activation remains to be one of the key challenges against its commercialization. The extraction of Li⁺ from bulk Li₂S has a high activation energy (E_a) barrier, which is fundamentally responsible for the initial large overpotential. Herein, a systematic investigation of accelerated bulk Li₂S oxidation reaction kinetics was studied by using organochalcogenide-based redox mediators, in which phenyl ditelluride (PDTe) can significantly reduce the E_a of Li₂S and lower the initial charge potential. Simultaneously, it can alleviate the polysulfides shuttling effect by covalently anchoring the soluble polysulfides and converting them into insoluble lithium phenyl tellusulfides (PhTe-S_xLi, x>1). This alters the redox pathway and accelerates the reaction kinetics of Li₂S cathode. Consequently, the Li||Li₂S-PDTe cell shows excellent rate capability and enhanced cycling stability. The Si||Li₂S-PDTe full cell delivers a considerable capacity of 953.5 mAh g⁻¹ at 0.2 C.     

Study on Lithium Insertion in Lepidocrocite and ,λ-MnO2 Type TiO2： A First-Principles Prediction

TiO2 is a latent anode material for rechargeable lithium batteries. Our simulation models, basing lepidocrocite and 2-MnO2 type TiO2 were investigated by density functional theory （DFT）. The key issues are focused on the lithium insertion sites, electronic structures, and the conducting paths of Li＋ ions. Our calculated data indicate the calculated voltage of 2-MnO2 type TiO2 is higher than that of lepidocrocite type TiO2. The Li＋ ion migration energy barrier of lepidocroeite type YiO2 along the [1 0 0] direction （0.45 eV） is lower than that of along the [110] direction （0.57 eV）. The energy barriers of 2-MnO2 type TiO2 to move a Li＋ ion among the adjacent embedded sites （16c or 8a sites） is 0.68 eV.     

Electrospun Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript>/Li<Subscript>2</Subscript>TiO<Subscript>3</Subscript> composite nanofibers for enhanced high-rate lithium ion batteries

Li₄Ti₅O₁₂/Li₂TiO₃ composite nanofibers with the mean diameter of ca. 60 nm have been synthesized via facile electrospinning. When the molar ratio of Li to Ti is 4.8:5, the Li₄Ti₅O₁₂/Li₂TiO₃ composite nanofibers exhibit initial discharge capacity of 216.07 mAh g^?1 at 0.1 C, rate capability of 151 mAh g^?1 after being cycled at 20 C, and cycling stability of 122.93 mAh g^?1 after 1000 cycles at 20 C. Compared with pure Li₄Ti₅O₁₂ nanofibers and Li₂TiO₃ nanofibers, Li₄Ti₅O₁₂/Li₂TiO₃ composite nanofibers show better performance when used as anode materials for lithium ion batteries. The enhanced electrochemical performances are explained by the incorporation of appropriate Li₂TiO₃ which could strengthen the structure stability of the hosted materials and has fast Li⁺-conductor characteristics, and the nanostructure of nanofibers which could offer high specific area between the active materials and electrolyte and shorten diffusion paths for ionic transport and electronic conduction. Our new findings provide an effective synthetic way to produce high-performance Li₄Ti₅O₁₂ anodes for lithium rechargeable batteries.     

锂参与合成MOF-5用于CO2/CH4混合气体分离

利用溶剂热法合成了不同锂含量的MOF-5(xLi-MOF-5, x=0, 1, 3, 5).在MOF-5结晶过程中,锂离子被合并入其骨架结构中.实验表明,合并入骨架的锂能够改变MOF-5的结构和表面化学性质.不同的xLi-MOF-5能够不同程度降低骨架相互穿插的程度从而导致其吸附分离能力的大幅改变.其中,3Li-MOF-5具有最高的二氧化碳捕获能力(5.47 mmol·g^-1),对40% CO₂/60% CH₄混合气体具有最优吸附选择性.     

锂参与合成MOF-5用于CO_2/CH_4混合气体分离

利用溶剂热法合成了不同锂含量的MOF-5(x Li-MOF-5,x=0,1,3,5)。在MOF-5结晶过程中,锂离子被合并入其骨架结构中。实验表明,合并入骨架的锂能够改变MOF-5的结构和表面化学性质。不同的x Li-MOF-5能够不同程度降低骨架相互穿插的程度从而导致其吸附分离能力的大幅改变。其中,3Li-MOF-5具有最高的二氧化碳捕获能力(5.47 mmol·g-1),对40%CO2/60%CH4混合气体具有最优吸附选择性。     

Preparation and characterization of lithium ion-conducting glass-ceramics in the Li1 + xCrxGe2 − x(PO4)3 system

Li₂O–Cr₂O₃–GeO₂–P₂O₅ based glasses were synthesized by a conventional melt-quenching method and successfully converted into glass-ceramics through heat treatment. Experimental results of DTA, XRD, ac impedance techniques and FESEM indicated that Li_1.4Cr_0.4Ge_1.6(PO₄)₃ glass-ceramics treated at 900 °C for 12 h in the Li_1 + xCr_xGe_2 − x(PO₄)₃ (x = 0–0.8) system exhibited the best glass stability against crystallization and the highest ambient conductivity value of 6.81 × 10⁻⁴ S/cm with an activation energy as low as 26.9 kJ/mol. In addition, the Li_1.4Cr_0.4Ge_1.6(PO₄)₃ glass-ceramics displayed good chemical stability against lithium metal at room temperature. The good thermal and chemical stability, excellent conducting property, easy preparation and low cost make it promising to be used as solid-state electrolytes for all-solid-state lithium batteries.     

Fe_2O_3/TiO_2纳米管阵列的制备及其光催化性能

在钛基体上采用阳极氧化法制备了TiO2纳米管阵列,采用化学浴方法在TiO2纳米管阵列上修饰了Fe2O3纳米颗粒。利用扫描电镜、X射线衍射和紫外可见漫反射光谱等手段对材料进行了表征,同时测试了材料的光电化学性能及其光催化降解亚甲基蓝染料废水的性能。结果表明,Fe2O3纳米颗粒的修饰将TiO2纳米管阵列的光响应拓宽至可见光区域,提高了光电流,Fe2O3/TiO2纳米管阵列的光电流是未修饰的TiO2纳米管阵列的9倍。而在光催化反应中,亚甲基蓝最高降解率可达80%,比未修饰的TiO2纳米管阵列高出30%。     

Fe2O3/TiO2纳米管阵列的制备及其光催化性能

在钛基体上采用阳极氧化法制备了TiO₂纳米管阵列,采用化学浴方法在TiO₂纳米管阵列上修饰了Fe₂O₃纳米颗粒.利用扫描电镜、X射线衍射和紫外可见漫反射光谱等手段对材料进行了表征,同时测试了材料的光电化学性能及其光催化降解亚甲基蓝染料废水的性能.结果表明,Fe₂O₃纳米颗粒的修饰将TiO₂纳米管阵列的光响应拓宽至可见光区域,提高了光电流,Fe₂O₃/TiO₂纳米管阵列的光电流是未修饰的TiO₂纳米管阵列的9倍.而在光催化反应中,亚甲基蓝最高降解率可达80%,比未修饰的TiO₂纳米管阵列高出30%.     

Electrical conductivity studies in the system Li<Subscript>2</Subscript>TiO<Subscript>3</Subscript>-Li<Subscript>1.33</Subscript>Ti<Subscript>1.67</Subscript>O<Subscript>4</Subscript>

Electrical conductivity in the monoclinic Li₂TiO₃, cubic Li_1.33Ti_1.67O₄, and in their mixture has been studied by impedance spectroscopy in the temperature range 20–730 °C. Li₂TiO₃ shows low lithium ion conductivity, σ₃₀₀≈10^–6 S/cm at 300 °C, whereas Li_1.33Ti_1.67O₄ has 3×10^–8 at 20 °C and 3×10^–4 S/cm at 300 °C. Structural properties are used to discuss the observed conductivity features. The conductivity dependences on temperature in the coordinates of 1000/T versus log_e(σT) are not linear, as the conductivity mechanism changes. Extrinsic and intrinsic conductivity regions are observed. The change in the conductivity mechanism in Li₂TiO₃ at around 500–600 °C is observed and considered as an effect of the first-order phase transition, not reported before. Formation of solid solutions of Li_{2– x} Ti_{1+ x} O₃ above 900 °C significantly increases the conductivity. Irradiation by high-energy (5 MeV) electrons causes defects and the conductivity in Li₂TiO₃ increases exponentially. A dose of 144 MGy yields an increase in conductivity of about 100 times at room temperature. Electronic Publication     

Preparation and characterization of nanotube Li-Ti-O by molten salt method

Nanotube Li-Ti-O compound with high surface (198.6 m²·g⁻¹) was prepared by a method involving the treatment of nanotube Na₂Ti₂O₅·H₂O in molten LiNO₃ and characterization by means of transmission electron microscopy (TEM), energy-dispersive spectra (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and thermogravimetry-differential thermal analysis (TG/DTG). Results show that the nanotube Li-Ti-O compound prepared by this method involves two crystal phases: spinel Li₂Ti₂O₄ and anatase Li_xTiO₂ (x < 0.1). Li⁺ exhibits different Li1s binding energy in the two crystal phases. In ambient air, the Li-Ti-O compound adsorbs water easily, and the chemically adsorbed water is difficult to remove below 400°C. Translated from Chinese Journal of Inorganic Chemistry, 2006, 22(12): 2135–2139 [译自: 无机化学学报]     

Determination of diffusion coefficient of lithium in LiMyMn2 ? yO4 spinels using galvanostatic intermittent titration technique

The galvanostatic intermittent titration technique is used to study lithium transport in the LiM _y Mn_{2 − y} O₄ compounds with a spinel structure intended for application as cathodic materials in lithium-ion and lithium-polymer batteries. Equilibrium intercalation isotherms of the Li _x Mn₂O₄ and Li _x Mn_1.95Cr_0.05O₄ compounds and also their diffusion characteristics are determined at 25°C as dependent on lithium content x, 0 < x < 1. The diffusion coefficient of lithium varies in a complex way in the range of 10⁻¹⁰ to 10⁻¹² cm²/s under variation of the electrode composition.     

Intercalation processes influence the structure and electrophysical properties of lithium-conducting compounds having defect perovskite structure

The structural features and electrophysical properties of lithium-conducting compounds having defect perovskite structure based on Li_0.5La_0.5Nb₂O₆ and Li_0.5La_0.5TiO₃ were studied using X-ray diffraction and synchrotron analyses, potentiometry, and complex impedance spectroscopy. Intercalated lithium was found to differently influence ion conductance in titanium- and niobium-containing materials. This difference was found to arise from the structural features of the materials. The systems studied have high chemical diffusion coefficients of lithium (D _Li⁺ = 1 × 10⁻⁶ cm²/s for Li_0.5La_0.5Nb₂O₆ and D _Li⁺ = 3.3 × 10⁻⁷ cm²/s for Li_0.5La_0.5TiO₃).     

Kinetics of Anodic Dissolution of Lithium out of Li x C6 Electrodes in Nonaqueous Lithium Perchlorate Solutions

Kinetics of processes occurring during anodic dissolution of Li _x C₆ electrodes formed in structures of carbonized fiber and cloth (CC) in solutions of lithium perchlorate in a mixture of propylene carbonate and dimethoxyethane is studied. It is shown that the Li _x C₆ (CC) electrodes have an approximately three times greater intercalation capacity, which is caused by specific features of the structure of CC. Values of the initial concentration of lithium defects in the structure of a surface layer of the CC matrix and the diffusion coefficients for lithium in the temperature range 293–323 K are calculated.     

Thermal properties and stability of lithium titanophosphate glasses

DTA was used to study thermal properties and thermal stability of (50-x)Li₂O-xTiO₂-50P₂O₅ (x=0–10 mol%) and 45Li₂Ot-yTiO₂-(55-y)P₂O₅ (y=5–20 mol%) glasses. The addition of TiO₂ to lithium phosphate glasses results in a non-linear increase of glass transition temperature. All prepared glasses crystallize under heating within the temperature range of 400–540°C. The lowest tendency towards crystallization have the glasses with x=7.5 and y=10 mol% TiO₂. X-ray diffraction analysis showed that major compounds formed by annealing of the glasses were LiPO₃, Li₄ P₂O₇, TiP₂O₇ and NASICON-type LiTi₂(PO₄)₃. DTA results also indicated that the maximum of nucleation rate for 45Li₂O-5TiO₂-50P₂O₅ glass is close to the glass transition temperature.     

Lithium electrochemistry of NiSe2: A new kind of storage energy material

NiSe₂ thin film has been successfully fabricated by reactive pulsed laser deposition and was investigated for its electrochemistry with lithium for the first time. The reversible discharge capacities of NiSe₂/Li cells cycled between 1.0 V and 3.0 V were found in the range of 314.9–467.5 mA h g⁻¹ during the first 200 cycles. By using ex situ X-ray diffraction, transmission electron microscopy, and selected-area electron diffraction measurements, the intermediates of β-NiSe, and Ni₃Se₂ were identified during the reversible conversions of NiSe₂ into metal nickel and Li₂Se. Both cation (nickel) and anion (selenium) in NiSe₂ provide the redox active centers in its electrochemical reaction with lithium, indicating one of the features of its lithium electrochemistry. The high reversible capacity and good cycle ability of NiSe₂ electrode made it become a promising cathode material for future rechargeable lithium batteries.     

Photocatalytic Activity and Characterization of the Sol-Gel Derived Pb-Doped TiO2 Thin Films

Photocatalytically active Pb-doped TiO₂ thin films were prepared on a soda-lime glass substrate by sol-gel dip-coating technique using TiO₂ sols containing lead(II) nitrate. The thin films were characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), UV-VIS spectroscopy and X-ray diffraction (XRD). A shift of the UV-VIS absorption towards longer wavelengths was observed, which indicated a decrease in the band-gap of TiO₂ upon Pb doping. XRD results showed both pure and Pb-doped TiO₂ thin films were polycrystalline, anatase type, and oriented predominantly to the (101) plane. A slight shift in the d-spacing for the Pb-doped film indicated the incorporation of Pb into the TiO₂ lattice to form Pb _x Ti_1–x O₂ solid solution. AFM results showed Pb-doped TiO₂ thin films were composed of larger TiO₂ particles and had rougher surface, compared with un-doped TiO₂ thin films. XPS results showed that except for the enrichment of Pb near the surface, Pb exists in the forms of Pb _x Ti_1–x O₂ and PbO. Dimethyl-2,2-dichlorovinyl phosphate (DDVP) was efficiently degraded in the presence of the Pb-doped TiO₂ thin films by exposing the insecticide solution to sunlight. The mechanism of photocatalytic activity enhancement of the Pb-doped TiO₂ thin films was discussed.