Optical,surface, and microstructural properties of Li4Ti5O12 thin films coated by RF magnetron sputtering

Li₄Ti₅O₁₂ thin films were deposited on glass substrates by the RF magnetron sputtering method in an argon gas atmosphere at different powers. Some properties of the coated Li₄Ti₅O₁₂ films were examined using some techniques. Structural characteristics of the produced Li₄Ti₅O₁₂ films were investigated by X-ray diffraction. The Li₄Ti₅O₁₂ phases were identified as (311) and (222). The surface morphology of the produced Li₄Ti₅O₁₂ films was investigated using an atomic force microscope. The transmittance and the absorbance were measured using a UV–vis spectrophotometer. The transmittance values were around 88% and 90%. The absorbance values were approximately 0.053 and 0.048. The film thickness values were 140 and 50?nm. The transparency values of the produced films were high. The optical band gap values of the produced LTO films were calculated as ～3.8?eV. The refractive index and the reflectance spectra values of samples were determined using interferometer measurements. The refractive index values were 1.51 and 1.44 at 550?nm, respectively.     

Controlled Ag-driven superior rate-capability of Li4Ti5O12 anodes for lithium rechargeable batteries

The morphology and electronic structure of a Li₄Ti₅O₁₂ anode are known to determine its electrical and electrochemical properties in lithium rechargeable batteries. Ag-Li₄Ti₅O₁₂ nanofibers have been rationally designed and synthesized by an electrospinning technique to meet the requirements of one-dimensional (1D) morphology and superior electrical conductivity. Herein, we have found that the 1D Ag-Li₄Ti₅O₁₂ nanofibers show enhanced specific capacity, rate capability, and cycling stability compared to bare Li₄Ti₅O₁₂ nanofibers, due to the Ag nanoparticles (<5 nm), which are mainly distributed at interfaces between Li₄Ti₅O₁₂ primary particles. This structural morphology gives rise to 20% higher rate capability than bare Li₄Ti₅O₁₂ nanofibers by facilitating the charge transfer kinetics. Our findings provide an effective way to improve the electrochemical performance of Li₄Ti₅O₁₂ anodes for lithium rechargeable batteries.      

Ti3+ Self‐Doped Li4Ti5O12 Anchored on N‐Doped Carbon Nanofiber Arrays for Ultrafast Lithium‐Ion Storage

Omnibearing acceleration of charge/ion transfer in Li₄Ti₅O₁₂ (LTO) electrodes is of great significance to achieve advanced high‐rate anodes in lithium‐ion batteries. Here, a synergistic combination of hydrogenated LTO nanoparticles (H‐LTO) and N‐doped carbon fibers (NCFs) prepared by an electrodeposition‐atomic layer deposition method is reported. Binder‐free conductive NCFs skeletons are used as strong support for H‐LTO, in which Ti³⁺ is self‐doped along with oxygen vacancies in LTO lattice to realize enhanced intrinsic conductivity. Positive advantages including large surface area, boosted conductivity, and structural stability are obtained in the designed H‐LTO@NCF electrode, which is demonstrated with preeminent high‐rate capability (128 mAh g^?1 at 50 C) and long cycling life up to 10 000 cycles. The full battery assembled by H‐LTO@NCFs anode and LiFePO₄ cathode also exhibits outstanding electrochemical performance revealing an encouraging application prospect. This work further demonstrates the effectiveness of self‐doping of metal ions on reinforcing the high‐rate charge/discharge capability of batteries.     

Polygonal multi-polymorphed Li4Ti5O12@rutile TiO2 as anodes in lithium-ion batteries

Li₄Ti₅O₁₂ (LTO) has attracted considerable attention in lithium-ion battery (LIB) applications because of its favorable characteristics as an anode material. Despite its promise, the widespread use of LTO is still limited primarily due to its intrinsically poor electric and ionic conductivities and high surface reactivity. To address these issues, we designed polygonal nanoarchitectures composed of various Li–Ti oxide crystal polymorphs by a facile synthesis route. Depending on the pH condition, this synthesis approach yields multi-polymorphed Li–Ti oxides where the interior is dominantly composed of a Li-rich phase and the exterior is a Li-deficient (or Li-free) phase. As one of these variations, a polygonal LTO-rutile TiO₂ structure is formed. The rutile TiO₂ on the surface of this LTO composite significantly improves the kinetics of Li⁺ insertion/extraction because the channel along the c-axis in TiO₂ provides a Li⁺ highway due to the significantly low energy barrier for Li⁺ diffusion. Moreover, the presence of rutile TiO₂, which is less reactive with a carbonate-based electrolyte, ensures long-term stability by suppressing the undesirable interfacial reaction on LTO.

     

Characterizations and electrochemical performance of pure and metal-doped Li4Ti5O12 for anode materials of lithium-ion batteries

Pure and metal (Cu, Al, Sn, and V)-doped Li₄Ti₅O₁₂ powders are prepared with solid-state reaction method. The effects of dopants on the physical and electrochemical properties are characterized by using TGA, XRD, and SEM. Compared with pure Li₄Ti₅O₁₂, metal-doped Li₄Ti₅O₁₂ powders show structural stability and enhanced lithium ion diffusivity brought by doped metal ions. Voltage characteristics and initial charge–discharge characteristics according to the C rates in pure and metal-doped Li₄Ti₅O₁₂ electrode materials are studied. Pure Li₄Ti₅O₁₂ powder shows a relatively good discharge capacity of 164 mAh/g at a rate 0.2C, and some of metal-doped Li₄Ti₅O₁₂ powders show higher discharge capacities. Metal-doped Li₄Ti₅O₁₂ powders are promising candidates as anode materials for lithium-ion batteries.     

Lithium intercalation and deintercalation processes in Li4Ti5O12 and LiFePO4

We have studied the kinetics of electrochemical lithium intercalation and deintercalation processes at different currents in lithium iron phosphate and lithium titanate based composite materials containing fine carbon particles. The results demonstrate that lithium intercalation and deintercalation processes in the electrode materials are characterized by an overvoltage: 4 and 2 mV, respectively, for a cell with a lithium titanate based electrode and 4 and 24 mV for a lithium iron phosphate based cell. Li₄Ti₅O₁₂ solubility in Li₇Ti₅O₁₂ is 1.1% (the limit of the solid solution at Li_4.03Ti₅O₁₂), and Li₇Ti₅O₁₂ solubility in Li₄Ti₅O₁₂ is 2.5% (the limit of the solid solution at Li_6.93Ti₅O₁₂). The conductivity of the phosphate and titanate solid solutions involved in the lithium intercalation and deintercalation processes has been determined.     

Preparation and characterization of Ruthenium doped Li4Ti5O12 anode material for the enhancement of rate capability and cyclic stability

Li₄Ti₅O₁₂ and Ru-doped Li₄Ti₅O₁₂ with the formulation of Li₄Ti_4.99Ru_0.01O₁₂ were prepared by a modified solid-state method. The structure and electrochemical properties of the as-prepared powders were systematically investigated. Li₄Ti_4.99Ru_0.01O₁₂ exhibited an excellent rate capability with a discharge capacity of 146 mAhg^? 1 at 1 C, 126 mAhg^? 1 at 5 C, 119 mAhg^? 1 at 10 C and even 107 mAhg^? 1 at 20 C. Electrochemical impedance spectra (EIS) reveal that the Li₄Ti_4.99Ru_0.01O₁₂ exhibited the improved electronic conductivity and higher lithium-ion diffusivity than that of Li₄Ti₅O₁₂. The novel Li₄Ti_4.99Ru_0.01O₁₂ material stands as a promising potentially high rate anode material for the lithium ion batteries.     

Electrochemically active flame-made nanosized spinels: LiMn2O4, Li4Ti5O12 and LiFe5O8

Electrochemically active LiMn₂O₄, Li₄Ti₅O₁₂, and LiFe₅O₈ particles with spinel structure (normal, mixed and mixed inverse) were made at production rates of 10–20 g h⁻¹ by flame spray pyrolysis (FSP), a scalable, one-step, dry process. These materials were characterized by X-ray diffraction and nitrogen adsorption, and had a primary crystallite size in the range of 8–30 nm and exhibited high temperature stability. Electrochemical properties, as measured by slow cyclic voltammetry, are reported for LiMn₂O₄ and Li₄Ti₅O₁₂ as potential cathode and anode materials, respectively, in secondary lithium-ion batteries. LiFe₅O₈ nanoparticles were made also by FSP containing the electrochemically active β-phase as shown by the corresponding cyclic voltammogram and specific charge–discharge spectra.     

Li4Ti5O12/Li3SbO4/C composite anode for high rate lithium-ion batteries

Nanocrystalline Li₄Ti₅O₁₂/Li₃SbO₄/C composite-prepared by mechanical ball-milling of Li₄Ti₅O₁₂ (synthesized by aqueous combustion), Li₃SbO₄ (synthesized by solid state method) and activated carbon, has been investigated as anode in lithium-ion coin cells and compared to pristine Li₄Ti₅O₁₂. Galvanostatic charge–discharge measurements in the potential window of 0.05–2.0 V show three plateau regions corresponding to Li insertion/extraction in the composite: a large flat plateau at ~ 1.52/1.59 V, followed by a second plateau at ~ 0.75/1.1 V and a sloppy tail at ~ 0.4/0.6 V. While the plateaus at ~ 0.4/0.6 V and ~ 1.52/1.59 V correspond to Li₄Ti₅O₁₂, the other one at ~ 0.75/1.1 V corresponds to Li₃SbO₄. At a high rate of ~ 15 C, the capacity for Li₄Ti₅O₁₂/Li₃SbO₄/C composite is found to be 105 mAhg^?1 retaining ~ 78% of its initial capacity compared to only 58 mAhg^?1 (~ 27% of the initial capacity) at 14 C for pristine Li₄Ti₅O₁₂ up to 100 cycles. Thus, such composite material might find application in lithium-ion batteries requiring high rate of charge and discharge.     

Pine‐Needle‐Like Cu–Co Skeleton Composited with Li4Ti5O12 Forming Core–Branch Arrays for High‐Rate Lithium Ion Storage

High‐performance of lithium‐ion batteries (LIBs) rely largely on the scrupulous design of nanoarchitectures and smart hybridization of bespoke active materials. In this work, the pine‐needle‐like Cu–Co skeleton is reported to support highly active Li₄Ti₅O₁₂ (LTO) forming Cu–Co/LTO core–branch arrays via a united hydrothermal‐atomic layer deposition (ALD) method. ALD‐formed LTO layer is uniformly anchored on the pine‐needle‐like heterostructured Cu–Co backbone, which consists of branched Co nanowires (diameters in 20 nm) and Cu nanowires (250–300 nm) core. The designed Cu–Co/LTO core–branch arrays show combined advantages of large porosity, high electrical conductivity, and good adhesion. Due to the unique positive features, the Cu–Co/LTO electrodes are demonstrated with enhanced electrochemical performance including excellent high‐rate capacity (155 mAh g^?1 at 20 C) and noticeable long‐term cycles (144 mAh g^?1 at 20 C after 3000 cycles). Additionally, the full cell assembled with activated carbon positive electrode and Cu–Co/LTO negative electrode exhibits high power/energy densities (41.6 Wh kg^?1 at 7.5 kW kg^?1). The design protocol combining binder‐free characteristics and array configuration opens a new door for construction of advanced electrodes for application in high‐rate electrochemical energy storage.     

Effect of freeze-drying and self-ignition process on the microstructural and electrochemical properties of Li4Ti5O12

Crystalline Li₄Ti₅O₁₂ is synthesized by a method involving the freeze-drying and self-ignition of a gel prepared from titanium isopropoxide, lithium nitrate and hydroxypropylmethylcellulose (HPMC). This synthesis route yields crystalline Li₄Ti₅O₁₂ particles after calcination at 800 °C for 2 h. In an alternative route, addition of ammonium nitrate shifts the self-ignition mode from wave-like propagation to simultaneous. Powders with different microstructures are thereby obtained. Electrochemical characterization shows that the best results for Li⁺ intercalation/desintercalation are obtained for the powder prepared without ammonium nitrate addition. These results highlight the necessity for a control of the self-ignition mode to obtain adequate properties.     

Focus on Spinel Li4Ti5O12 as Insertion Type Anode for High‐Performance Na‐Ion Batteries

Sodium‐ion batteries (SIBs) toward large‐scale energy storage applications has fascinated researchers in recent years owing to the low cost, environmental friendliness, and inestimable abundance. The similar chemical and electrochemical properties of sodium and lithium make sodium an easy substitute for lithium in lithium‐ion batteries. However, the main issues of limited cycle life, low energy density, and poor power density hamper the commercialization process. In the last few years, the development of electrode materials for SIBs has been dedicated to improving sodium storage capacities, high energy density, and long cycle life. The insertion type spinel Li₄Ti₅O₁₂ (LTO) possesses “zero‐strain” behavior that offers the best cycle life performance among all reported oxide‐based anodes, displaying a capacity of 155 mAh g^?1 via a three‐phase separation mechanism, and competing for future topmost high energy anode for SIBs. Recent reports offer improvement of overall electrode performance through carbon coating, doping, composites with metal oxides, and surface modification techniques, etc. Further, LTO anode with its structure and properties for SIBs is described and effective methods to improve the LTO performance are discussed in both half‐cell and practical configuration, i.e., full‐cell, along with future perspectives and solutions to promote its use.     

Preparation and photocatalytic activity of alkali titanate nano materials A2TinO2n+1 (A = Li, Na and K)

Photocatalysts nano A₂Ti_nO_2n+1 (A = Li, Na, K) were prepared successfully by novel hydrothermal synthesis process. Powders were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), ultraviolet-visible (UV-vis) absorption spectra and field-emission scanning electron microscope (FE-SEM) measurements. These results showed that the compositions of lithium, sodium and potassium titanates were Li₂TiO₃, Na₂Ti₃O₇ and K₂Ti₈O₁₇, respectively. The nano crystals of Li₂TiO₃ were self-assembled as snowflakes while that of Na₂Ti₃O₇ and K₂Ti₈O₁₇ were nanorods. Photocatalytic properties of alkali titanates were also investigated. The results indicated that alkali titanates as prepared have higher photocatalytic activities compared with P25 TiO₂ in the degradation of chloroform under UV light irradiation. A combination of K₂Ti₈O₁₇ and NiO produces a photocatalyst effective for the degradation of chloroform in aqueous solution. The framework of the tunnel structure was suitable for accommodating cocatalysts such as NiO to induce a strong interaction between the active species and cocatalysts. Na₂Ti₃O₇ has high photocatalytic activity under visible-light irradiation due to its strong absorption in the visible light region. The photocatalytic properties of Li₂TiO₃ are inferior to that of Na₂Ti₃O₇ and K₂Ti₈O₁₇ due to its mono-perovskite structure.     

Low temperature sintering of Li1.1Nb0.58Ti0.5O3-xBi2O3 dielectric with adjustable temperature coefficient

Ceramics of Li_1.1Nb_0.58Ti_0.5O₃-xBi₂O₃ with low sintering temperature have been prepared by the solid-solution reaction method using B₂O₃ (2 wt% added) as sintering aid. For all compounds, the sintering temperature achieves 900 °C. Microstructure and dielectric properties of Li_1.1Nb_0.58Ti_0.5O₃-2 wt% B₂O₃-xBi₂O₃ (LNT-B-xBi) ceramics have been investigated. The X-ray diffraction patterns indicate for higher Bi₂O₃ content (x = 0.1 mol%) that the material is composed by two phases identified as M-phase and Bi₄Ti₃O₁₂. The Li_1.1Nb_0.58Ti_0.5O₃ + 0.15 mol% Bi₂O₃ composition sintered at 900 °C with B₂O₃ addition exhibits attractive dielectric properties (ε _r = 59.68, tan δ = 1.2×10^?4 and a temperature coefficient of the relative permittivity near zero) at 1 MHz. It is also shown that the introduction of Bi₂O₃ can tune the temperature coefficient of the relative permittivity. All dielectric properties lead this system compatible to manufacture sliver based electrodes multilayer dielectric devices.     

Electrode characteristics of Li2Ti3O7-ramsdellite processed by mechanical grinding

The effect of mechanical grinding on the electrochemical properties of Li₂Ti₃O₇ regarding lithium insertion is studied. X-ray diffraction experiments of milling compounds showed a progressively amorphization of the crystalline material due to both crystalline size decreasing and internal strain increasing. These structural modifications are reflected in the electrochemical behavior of Li₂Ti₃O₇, when it is used as the positive electrode in lithium cells. As a function of milling time a higher specific capacity is obtained during the first discharge of the cell, but when charging an increasing in the irreversible capacity is observed. The most promising Li₂Ti₃O₇ based electrode has been achieved, under our experimental conditions, for 13 hours milling that produces a compound with crystallite size of approximately 20 nm.     

Interface compounds formed during the diffusion bonding of Al2O3 to Ti

The interfacial reaction products of Ti/Al₂O₃ joints obtained in the context of real diffusion bonding technology were investigated by means of X-ray diffraction analysis, X-ray photoelectron spectroscopy, and transmission electron microscopy. Some Ti reacted with Al₂O₃ giving titanium oxides, but the main mass transport occurred into the bulk Ti due to Al₂O₃ dissolution. The formation of a Ti[Al, O] solid solution followed by a order/disorder reaction yielded Ti₃Al. Further Al enrichment at the interface could lead to the formation of TiAl, which was not observed in the present work due to either the short residence time at the bonding temperatures or to its lower oxygen solubility. For joints obtained at 800°C and shear test fractured it was ascertained that the crack always propagated within the Ti₃Al layer.     

EPR and mixed electronic-ionic conductivity studies of pure and manganese doped layered Potassium–Lithium tetra titanates (K1.9Li0.1Ti4O9)

Lithium (5%) mixed layered K₂Ti₄O₉ and its 0.01, 0.02, 0.05, 0.1 and 1.0 molar percentage MnO₂, doped derivatives have been prepared and characterized through electrical conductivity studies in the temperature range 373–900 K and room temperature EPR investigation. Three distinct regions have been identified in the Log(σT) versus 1000/T plots. The lowest temperature region is attributed to electronic hopping conduction (except for K_1.9Li_0.1Ti₄O₉ (PLT) in which interlayer lithium ionic conduction is proposed) involving loose electrons from Ti₄O₉²⁻ groups. The intermediate region to associated interlayer ionic conduction through dilated interlayer space and the highest temperature region to unassociated interlayer ionic conduction. The room temperature EPR investigations reveal that at a lower percentage of doping the substitution of manganese ions occur as Mn⁴⁺ at Ti⁴⁺ sites, whereas for higher percentage of doping Mn²⁺ ions predominantly occupy the two different interlayer alkali sites. The dilation of interlayer space has further been proposed to occur due to manganese ions substitution at octahedral Ti⁴⁺ sites. In both these cases the charge compensation mechanism should operate to maintain the overall charge neutrality of the lattice.     

Electronic structure of Li2O2 {0001} surfaces

The surface properties of the Li₂O₂ discharge phase are expected to impact strongly the capacity, rate capability, and rechargeability of Li-oxygen batteries. Prior calculations have suggested that the presence of half-metallic surface states in Li₂O₂ may mitigate electrical passivation resulting from the growth of Li₂O₂, which is a bulk insulator. Here we revisit the electronic structure of bulk Li₂O₂ and the dominant Li₂O₂ {0001} surface by comparing results obtained with the PBE GGA functional, the HSE06 hybrid functional, and quasiparticle GW methods. Our results suggest that the bulk band gap lies between the value predicted by the G₀W₀ method, 5.15 eV, and the value predicted by the self-consistent quasiparticle GW (scGW) approximation, 6.37 eV. The PBE, HSE06, and scGW methods agree that the most stable surface, an oxygen-rich {0001} termination, is indeed half-metallic. This result supports the notion that the electronic structure of surfaces may play an important role in understanding performance limitations in Li-oxygen batteries.     

First-principles investigation of magnetic coupling mechanism in A-site-ordered perovskite CaFe3Ti4O12

We have investigated the electronic and magnetic properties of A-site-ordered perovskite CaFe₃Ti₄O₁₂ using first-principles calculations. Our calculated results indicate that CaFe₃Ti₄O₁₂ is mechanically stable and it is an antiferromagnetic insulator. Similar to its isostructural perovskite CaCu₃Ti₄O₁₂, the primary magnetic coupling mechanism in CaFe₃Ti₄O₁₂ is ascribed to the Fe–O–Ti–O–Fe superexchange interaction. From this fact we can clearly see that the empty 3d orbitals play an important role to realize the superexchange interaction. Moreover, comparing CaFe₃Ti₄O₁₂ and CaCu₃Ti₄O₁₂ in some details, we find that Fe (Cu)–O bond distance is one of the important parameters to determine the antiferromagnetic strength within this superexchange interaction.     

Bending impact on the performance of a flexible Li4Ti5O12-based all-solid-state thin-film battery

The growing demand of flexible electronic devices is increasing the requirements of their power sources. The effect of bending in thin-film batteries is still not well understood. Here, we successfully developed a high active area flexible all-solid-state battery as a model system that consists of thin-film layers of Li₄Ti₅O₁₂, LiPON, and Lithium deposited on a novel flexible ceramic substrate. A systematic study on the bending state and performance of the battery is presented. The battery withstands bending radii of at least 14 mm achieving 70% of the theoretical capacity. Here, we reveal that convex bending has a positive effect on battery capacity showing an average increase of 5.5%, whereas concave bending decreases the capacity by 4% in contrast with recent studies. We show that the change in capacity upon bending may well be associated to the Li-ion diffusion kinetic change through the electrode when different external forces are applied. Finally, an encapsulation scheme is presented allowing sufficient bending of the device and operation for at least 500 cycles in air. The results are meant to improve the understanding of the phenomena present in thin-film batteries while undergoing bending rather than showing improvements in battery performance and lifetime.