The effects of irradiation and high temperature on chemical states in Li2TiO3

In the future D-T fusion reactor, tritium will be bred mainly by the reaction of ⁶Li (n, α) T, as well as ⁷Li (n, n’ α) T in tritium breeding materials. Solid breeding materials will experience harsh conditions under both irradiations by energetic particles (neutron, tritium, helium and self-particles) and high temperature. The interactions of irradiations and high temperature on lithium ceramics will influence tritium breeding ratio (TBR). The changes of chemical states and its effects on release behavior of hydrogen isotopes in deuterium-irradiated Li₂TiO₃ and deuterium-exposed Li₂TiO₃ at high temperature have been investigated. The peak of O-1s shifted to higher binding energy by both irradiation and deuterium exposure, indicating that O-D bonds formed. The amount of O-D bonds enhanced as increase of irradiation fluence and exposure temperature. The main deuterium atoms were trapped by defects for irradiated samples. Annihilation of E-centers was thought to trigger the release of hydrogen isotopes. O-D bonds were the main deuterium trapping sites in deuterium-exposed Li₂TiO₃. Deuterium recovered by detrapping O-D bonds would require higher temperature. Both deuterium-irradiation and deuterium-exposure at high temperature could result in the change of chemical states in Li₂TiO₃. The changes in chemical states had effects on deuterium release. It illustrates that tritium breeding materials in fusion reactor will be modified by both irradiation and high temperature and could result in lower tritium recovery.     

Fabrication and electrochemical properties of three-dimensional net architectures of anatase TiO2 and spinel Li4Ti5O12 nanofibers

As a new type of electrodes engineering method with three-dimensional (3D) architecture for 3D rechargeable lithium ion batteries, an electrospinning has been successfully employed to prepare 3D net architectures of anatase TiO₂ and spinel Li₄Ti₅O₁₂ nanofibers. Scanning electron microscopy, X-ray diffraction, cyclic voltammetry and the discharge/charge measurements were used to characterize their structures and electrochemical properties. Our results demonstrated that 3D architectures stacked from a cross-bar array of electrospun anatase TiO₂ nanofibers could be accomplished but were destroyed after the insertion of Li ion. Significantly, spinel Li₄Ti₅O₁₂ could be selected as one of promise candidates for the realization of 3D batteries considering its structure stability of 3D spinel Li₄Ti₅O₁₂ nanofibers associated with well cyclability.     

Influence of oxygen and water related surface defects on the dye sensitized TiO2 solar cell

Oxygen- and water-related surface defects on porous TiO₂ (anatase) can be well controlled by the oxygen and water partial pressures and therefore such defects are of technological relevance for dye sensitized TiO₂ solar cells. We investigated the action of oxygen and water-related surface defects in situ by impedance spectroscopy, photoconductivity, photoluminescence, and optical transmission as well as by characterizing solar cells which were prepared under respective conditions. Oxygen loss from the TiO₂ surface leads to electrical doping by Ti³⁺/oxygen donor states. Such defects create recombination paths for injected electrons back into the electrolyte. Pre-treatment of porous TiO₂ by chemisorption of water increases the open circuit voltage of the solar cells without altering the short circuit current. Water-related surface defects decrease the saturation current of the diode, probably by raising the barrier height at the TiO₂/electrolyte interface.     

Thermal properties of Li4/3Ti5/3O4/LiMn2O4 cell

The thermal properties of Li_4/3Ti_5/3O₄ and Li_1+xMn₂O₄ electrodes were investigated by isothermal micro-calorimetry (IMC). The 150-mAh g⁻¹ capacity of a Li/Li_4/3Ti_5/3O₄ half cell was obtained through the voltage plateau that occurs at 1.55 V during the phase transition from spinel to rock salt. Extra capacity below 1.0 V was attributed to the generation of a new phase. The small and constant entropy change of Li_4/3Ti_5/3O₄ during the spinel/rock-salt phase transition indicated its good thermal stability. Accelerated rate calorimetry confirmed that Li_4/3Ti_5/3O₄ has better thermal characteristics than graphite. The IMC results for a Li/Li_1+xMn₂O₄ half cell indicated less heat variation due to the suppression of the order/disorder change by lithium doping. The heat profiles of the Li_4/3Ti_5/3O₄/Li_1+xMn₂O₄ full cell indicated less heat generation compared with a mesocarbon-microbead graphite/Li_1+xMn₂O₄ cell.     

Advanced electrochemical performance of Li4Ti4.95V0.05O12 as a reversible anode material down to 0 V

Li₄Ti_4.95V_0.05O₁₂ and Li₄Ti₅O₁₂ powders were successfully prepared by a solid-state method. XRD reveals that both samples have high phase purity. Raman spectroscopy indicates that the Ti–O vibration have a blue shift. SEM shows that Li₄Ti_4.95V_0.05O₁₂ has a slightly smaller particle size and a more regular morphological structure with narrow size distribution than those of Li₄Ti₅O₁₂. Galvanostatic charge–discharge testing indicates both samples have nearly equal initial capacities at different discharge voltage ranges (0–2 and 0.5–2 V), but Li₄Ti_4.95V_0.05O₁₂ has a higher cycling performance than that of Li₄Ti₅O₁₂. CV suggests that Li₄Ti_4.95V_0.05O₁₂ has lower electrode polarization and high lithium ion diffusivity in solid-state body of sample, implying that the vanadium doping is beneficial to the reversible intercalation and de-intercalation of Li⁺. The novel Li₄Ti_4.95V_0.05O₁₂ materials may find promising applications in lithium ion batteries and electrochemical cells due to the excellent electrochemical performace and simple synthesis route.     

Self-doped Ti@TiO2 visible light photocatalyst: Influence of synthetic parameters on the H2 production activity

Self-doped TiO₂ shows visible light photocatalytic activity, while pristine TiO₂ is only UV responsive. Ti³⁺ has been demonstrated to be responsible for this improvement. We systematically studied various experimental parameters, such as the amount of reducing agent imidazole, types of imidazoles and Ti sources, and determined effects of these parameters on the combustion process and final materials. The phase composition, Ti³⁺ concentration, light absorption, surface area, and crystallinity of the product are significantly affected by the amount of imidazoles. Through comparing different imidazoles, we found that only flammable/combustible imidazoles are able to convert Ti⁴⁺ into Ti³⁺. This result is very helpful in understanding the mechanism and reactions in combustion process. Titanium precursors also have a great influence in production of Ti³⁺ doped TiO₂ materials. Titanium alkoxides allow the successful synthesis of blue partially reduced TiO₂, while TiCl₄ only lead to white pristine TiO₂.     

Synthesis, structure and electrochemical Li insertion behaviour of Li2Ti6O13 with the Na2Ti6O13 tunnel-structure

Li₂Ti₆O₁₃ has been prepared from Na₂Ti₆O₁₃ by Li ion exchange in molten LiNO₃ at 325 °C. Chemical analysis and powder X-ray diffraction study of the reaction product respectively indicate that total Na/Li exchange takes place and the Ti-O framework of the Na₂Ti₆O₁₃ parent structure is kept under those experimental conditions. Therefore, Li₂Ti₆O₁₃ has been obtained with the mentioned parent structure. An important change is that particle size is decreased significantly which is favoring lithium insertion. Electrochemical study shows that Li₂Ti₆O₁₃ inserts ca. 5 Li per formula unit in the voltage range 1.5-1.0 V vs. Li⁺/Li, yielding a specific discharge capacity of 250 mAh g⁻¹ under equilibrium conditions. Insertion occurs at an average equilibrium voltage of 1.5 V which is observed for oxides and titanates where Ti(IV)/Ti(III) is the active redox couple. However, a capacity loss of ca. 30% is observed due to a phase transformation occurring during the first discharge. After the first redox cycle a high reversible capacity is obtained (ca. 160 mAh g⁻¹ at C/12) and retained upon cycling. Taking into consideration these results, we propose Li₂Ti₆O₁₃ as an interesting material to be further investigated as the anode of lithium ion batteries.     

Effects of dopant on the electrochemical performance of Li4Ti5O12 as electrode material for lithium ion batteries

The effects of dopant on the electrochemical properties of spinel-type Li_3.95M_0.15Ti_4.9O₁₂ (M = Al, Ga, Co) and Li_3.9Mg_0.1Al_0.15Ti_4.85O₁₂ were systematically investigated. Charge–discharge cycling were performed at a constant current density of 0.15 mA cm⁻² between the cut-off voltages of 2.3 and 0.5 V, the experimental results showed that Al³⁺ dopant greatly improved the reversible capacity and cycling stability over the pristine Li₄Ti₅O₁₂. The substitution of the Ga³⁺ slightly increased the capacity of the Li₄Ti₅O₁₂, but did not essentially alleviate the degradation of cycling stability. Dopants such as Co³⁺ and Mg²⁺ to some extent worsened the electrochemical performance of the Li₄Ti₅O₁₂.     

Visible-light-driven TiO2 catalysts doped with low-concentration nitrogen species

Visible-light-driven nitrogen-doped TiO₂ was synthesized using a novel nitrogen-ion donor of hydrazine hydrate. Low-concentration (0.2 at%) nitrogen species and Ti³⁺ were detected in the TiO₂-based photocatalyst by X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR) spectroscopy. The trace amount of Ti–N would contribute to the minor band-gap narrowing of about 0.02 eV. Those nitrogen-containing species, especially the NO₂²⁻ species, form surface states, which make the catalysts possible to degrade 4-chlorophenol (4-CP) under visible irradiation (λ>400 nm). Moreover, Ti³⁺ species induce oxygen vacancy states between the valence and the conduction bands, which would also contribute to the visible response. The photocatalytic activity of the nitrogen-doped TiO₂ catalyst was thought to be the synergistic effect of nitrogen and Ti³⁺ species. The catalysts showed higher photocatalytic activity for degradation of 4-CP than pure TiO₂ under not only visible but also UV irradiation. The visible response and the higher UV activity of the nitrogen-doped TiO₂ make it possible to utilize solar energy efficiently to execute photocatalysis processes.     

Electrical conductivity and charge compensation in Ta doped Li4Ti5O12

Ta doping in Li₄Ti₅O₁₂ (Li₄Ti_4.95Ta_0.05O₁₂) as function of different heat-treat atmospheres (oxidizing/reducing) was investigated and compared to Li₄Ti₅O₁₂ to determine its effect on ionic/electronic conductivity and the charge compensating defects. Under oxidizing conditions Li₄Ti_4.95Ta_0.05O₁₂ was primarily an ionic conductor where the extra charge of Ta was compensated by Ti vacancies. Under reducing conditions Li₄Ti_4.95Ta_0.05O₁₂ was primarily an electronic conductor where the extra charge of Ta was compensated by an electron. The charge compensating defects were confirmed by sintering data.     

Basic molten salt process—A new route for synthesis of nanocrystalline Li4Ti5O12-TiO2 anode material for Li-ion batteries using eutectic mixture of LiNO3-LiOH-Li2O2

A nanocrystalline Li₄Ti₅O₁₂-TiO₂ duplex phase has been synthesized by a simple basic molten salt process (BMSP) using an eutectic mixture of LiNO₃-LiOH-Li₂O₂ at 400-500 °C. The microstructure and morphology of the Li₄Ti₅O₁₂-TiO₂ product are characterized by means of X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM). The sample prepared by heat-treating at 300 °C for 3 h (S-1) reveals dense agglomerates of ultra-fine nanocrystalline Li₄Ti₅O₁₂; with heat treatment at 400 °C for 3 h (S-2), there is a duplex crystallite size (fine < 10 nm, and coarse > 20 nm) of Li₄Ti₅O₁₂-TiO₂; at 500 °C for 3 h (S-3), a much coarser and less-dense distribution of lithium titanate (crystallite size ∼15-30 nm) is observed. According to the results of electrochemical testing, the S-2 sample shows initial discharge capacities of 193 mAh g⁻¹ at 0.2 C, 168 mAh g⁻¹ at 0.5 C, 146 mAh g⁻¹ at 1 C, 135 mAh g⁻¹ at 2 C, and 117 mAh g⁻¹ at 5 C. After 100 cycles, the discharge capacity is 138 mAh g⁻¹ at 1 C with a capacity retention of 95%. The S-2 sample yields the best electrochemical performance in terms of charge-discharge capacity and rate capability compared with other samples. Its superior electrochemical performance can be mainly attributed to the duplex crystallite structure, composed of fine (<10 nm) and coarse (>20) nm nanoparticles, where lithium ions can be stored within the grain boundary interfaces between the spinel Li₄Ti₅O₁₂ and the anatase TiO₂.     

Hot-pressed Li0.33La0.57TiO3

The electrical and mechanical properties of hot-pressed versus sintered Li_0.33La_0.57TiO₃ at temperature of 1050 °C were investigated. It was observed that hot-pressed Li_0.33La_0.57TiO₃ exhibited a higher total Li-ion conductivity (∼20×) and hardness (∼11×) compared to sintered Li_0.33La_0.57TiO₃ as a result of its higher density. Hot-pressed Li_0.33La_0.57TiO₃ had a similar relative density and total Li-ion conductivity when compared to Li_0.33La_0.57TiO₃ sintered at 1250 °C, where significant Li₂O loss occurs. These results suggest that hot-pressing can be used as a consolidation method to reduce Li₂O loss to obtain dense Li_0.33La_0.57TiO₃.     

Electrochemical performance of all-solid-state lithium secondary batteries improved by the coating of Li2O-TiO2 films on LiCoO2 electrode

All-solid-state lithium secondary batteries using LiCoO₂ particles coated with amorphous Li₂O-TiO₂ films as an active material and Li₂S-P₂S₅ glass-ceramics as a solid electrolyte were fabricated; the electrochemical performance of the batteries was investigated. The interfacial resistance between LiCoO₂ and solid electrolyte was decreased by the coating of Li₂O-TiO₂ films on LiCoO₂ particles. The rate capability of the batteries using the LiCoO₂ coated with Li₂Ti₂O₅ (Li₂O·2TiO₂) film was improved because of the decrease of the interfacial resistance of the batteries. The cycle performance of the all-solid-state batteries under a high cutoff voltage of 4.6 V vs. Li was highly improved by using LiCoO₂ coated with Li₂Ti₂O₅ film. The oxide coatings are effective in suppressing the resistance increase between LiCoO₂ and the solid electrolyte during cycling. The battery with the LiCoO₂ coated with Li₂Ti₂O₅ film showed a large initial discharge capacity of 130 mAh/g and good capacity retention without resistance increase after 50 cycles at the current density of 0.13 mA/cm².     

Hydrogen storage behaviour of Li3N doped with Li2O and Na2O

Mixtures of Li₂O/Li₃N and Na₂O/Li₃N have been investigated for hydrogen storage. When Li₃N is doped with ca. 5 mol% Li₂O and annealed, both binary compounds exist as separate phases as evident from powder X-ray diffraction. Li₂O acts as a spectator in the hydrogen storage reactions and there is no evidence of enhanced Li⁺ or H⁺ mobility. Na₂O (5 mol%) interacts more strongly with Li₃N, leading to the generation of an unidentified phase, which also appears to play no part in the hydrogen storage reactions of the composite system. We conclude that addition of these levels of Li₂O or Na₂O to Li₃N followed by annealing does not improve the hydrogen storage properties of Li₃N.     

Influence of conductive additives and surface fluorination on the charge/discharge behavior of lithium titanate (Li4/3Ti5/3O4)

Effect of conductive additives and surface modification with NF₃ and ClF₃ on the charge/discharge behavior of Li_4/3Ti_5/3O₄ (≈4.6 μm) was investigated using vapor grown carbon fiber (VGCF) and acetylene black (AB). VGCF and mixtures of VGCF and AB increased charge capacities of original Li_4/3Ti_5/3O₄ and those fluorinated with NF₃ by improving the electric contact between Li_4/3Ti_5/3O₄ particles and nickel current collector. Surface fluorination increased meso-pore with diameter of 2 nm and surface area of Li_4/3Ti_5/3O₄, which led to the increase in first charge capacities of Li_4/3Ti_5/3O₄ samples fluorinated by NF₃ at high current densities of 300 and 600 mA g⁻¹. The result shows that NF₃ is the better fluorinating agent for Li_4/3Ti_5/3O₄ than ClF₃.     

High-density spherical Li4Ti5O12/C anode material with good rate capability for lithium ion batteries

Li₄Ti₅O₁₂ is a very promising anode material for lithium secondary batteries. To improve the material's rate capability and pile density is considered as the important researching direction. One effective way is to prepare powders composed of spherical particles containing carbon black. A novel technique has been developed to prepare spherical Li₄Ti₅O₁₂/C composite. The spherical precursor containing carbon black is prepared via an “outer gel” method, using TiOCl₂, C and NH₃ as the raw material. Spherical Li₄Ti₅O₁₂/C powders are synthesized by sintering the mixture of spherical precursor and Li₂CO₃ in N₂. The investigation of TG/DSC, SEM, XRD, Brunauer–Emmett–Teller (BET) testing, laser particle size analysis, tap-density testing and the determination of the electrochemical properties show that the Li₄Ti₅O₁₂/C composite prepared by this method are spherical, has high tap-density and excellent rate capability. It is observed that the tap-density of spherical Li₄Ti₅O₁₂/C powders (the mass content of C is 4.8%) is as high as 1.71 g cm⁻³, which is remarkably higher than the non-spherical Li₄Ti₅O₁₂. Between 1.0 and 3.0 V versus Li, the initial discharge specific capacity of the sample is as high as 144.2 mAh g⁻¹, which is still 128.8 mAh g⁻¹ after 50 cycles at a current density of 1.6 mA cm⁻².     

Enhanced charge transfer for efficient photocatalytic H2 evolution over UiO-66-NH2 with annealed Ti3C2Tx MXenes

The annealed Ti₃C₂T_x MXenes retained original layered morphology and gave rise to the formation of TiO₂ is anticipated to achieve improved photocatalytic hydrogen evolution performance as a noble-metal-free co-catalyst. In this work, a novel Ti₃C₂/TiO₂/UiO-66-NH₂ hybrid was rationally designed for the first time by simply introducing annealed Ti₃C₂T_x MXenes over water-stable Zr-MOFs (UiO-66-NH₂) precursors via a facile hydrothermal process. As expected, the rationally designed Ti₃C₂/TiO₂/UiO-66-NH₂ displayed significantly improvement in photocatalytic H₂ performance (1980 μmol·h⁻¹·g⁻¹) than pristine UiO-66-NH₂ under simulated sunlight irradiation. The excellent photocatalytic HER activity can be attributed to the formation of multi-interfaces in Ti₃C₂/TiO₂/UiO-66-NH₂, including Ti₃C₂/TiO₂/UiO-66-NH₂, Ti₃C₂/TiO₂ and Ti₃C₂/UiO-66-NH₂ interfaces, which constructed multiple pathways at the interfaces with Schottky junctions to accelerate the separation and transfer of charge carriers and endowed the accumulation of photo-generated electrons on the surface of Ti₃C₂. This work expanded the possibility of porous MOFs for the development of efficient photocatalytic water splitting using annealed MXenes.     

High-rate performance of all-solid-state lithium secondary batteries using Li4Ti5O12 electrode

The all-solid-state Li–In/Li₄Ti₅O₁₂ cell using the 80Li₂S·20P₂S₅ (mol%) solid electrolyte was assembled to investigate rate performances. It was difficult to obtain the stable performance at the charge current density of 3.8 mA cm⁻² in the all-solid-state cell. In order to improve the rate performance, the pulverized Li₄Ti₅O₁₂ particles were applied to the all-solid-state cell, which retained the reversible capacity of about 90 mAh g⁻¹ at 3.8 mA cm⁻². The 70Li₂S·27P₂S₅·3P₂O₅ glass–ceramic, which exhibits the higher lithium ion conductivity than the 80Li₂S·20P₂S₅ solid electrolyte, was also used. The Li–In/70Li₂S·27P₂S₅·3P₂O₅ glass–ceramic/pulverized Li₄Ti₅O₁₂ cell was charged at a current density higher than 3.8 mA cm⁻² and showed the reversible capacity of about 30 mAh g⁻¹ even at 10 mA cm⁻² at room temperature.     

Li4Ti5O12/Sn composite anodes for lithium-ion batteries: Synthesis and electrochemical performance

Li₄Ti₅O₁₂/tin phase composites are successfully prepared by cellulose-assisted combustion synthesis of Li₄Ti₅O₁₂ matrix and precipitation of the tin phase. The effect of firing temperature on the particulate morphologies, particle size, specific surface area and electrochemical performance of Li₄Ti₅O₁₂/tin oxide composites is systematically investigated by SEM, XRD, TG, BET and charge-discharge characterizations. The grain growth of tin phase is suppressed by forming composite with Li₄Ti₅O₁₂ at a calcination of 500 °C, due to the steric effect of Li₄Ti₅O₁₂ and chemical interaction between Li₄Ti₅O₁₂ and tin oxide. The experimental results indicate that Li₄Ti₅O₁₂/tin phase composite fired at 500 °C has the best electrochemical performance. A capacity of 224 mAh g⁻¹ is maintained after 50 cycles at 100 mA g⁻¹ current density, which is still higher than 195 mAh g⁻¹ for the pure Li₄Ti₅O₁₂ after the same charge/discharge cycles. It suggests Li₄Ti₅O₁₂/tin phase composite may be a potential anode of lithium-ion batteries through optimizing the synthesis process.     

Hydrogen adsorption properties of Ag decorated TiO2 nanomaterials

In this work, we present the synthesis of Ag doped TiO₂ materials. The products are characterized by powder X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, nitrogen adsorption, and hydrogen adsorption. The Ag/TiO₂ materials exhibit 3.65 times higher in hydrogen adsorption capability compared with the non-doped TiO₂ materials thank to the existence of Ti³⁺ species, which are Kubas-type hydrogen adsorption centers, and the Ag nanoparticles which provide spillover effects. We believe that this is the first time that both Kubas-type adsorption and spillover are exploited in the design of novel hydrogen storage materials.