Preparation and electrochemical performance of Li4Ti5O12/carbon/carbon nano-tubes for lithium ion battery

A Li₄Ti₅O₁₂/carbon/carbon nano-tubes (Li₄Ti₅O₁₂/C/CNTs) composite was synthesized by using a solid-state method. For comparison, a Li₄Ti₅O₁₂/carbon (Li₄Ti₅O₁₂/C) composite and a pristine Li₄Ti₅O₁₂ were also synthesized in the present study. The microstructure and morphology of the prepared samples are characterized by XRD and SEM. Electrochemical properties of the samples are evaluated by using galvanostatic discharge/charge tests and AC impedance spectroscopy. The results reveal that the Li₄Ti₅O₁₂/C/CNTs composite exhibits the best rate capability and cycling stability among the samples of Li₄Ti₅O₁₂, Li₄Ti₅O₁₂/C and Li₄Ti₅O₁₂/C/CNTs. At the charge-discharge rate of 0.5 C, 5.0 C and 10.0 C, its discharge capacities were 163 mAh/g, 148 mAh/g and 143 mAh/g, respectively. After 100 cycles at 5.0 C, it remained at 146 mAh/g.     

Preparation and characterization of novel spinel Li4Ti5O12−xBrx anode materials

Br-doped Li₄Ti₅O₁₂ in the form of Li₄Ti₅O_12−xBr_x (0 ≤ x ≤ 0.3) compounds were successfully synthesized via solid state reaction. The structure and electrochemical properties of the spinel Li₄Ti₅O_12−xBr_x (0 ≤ x ≤ 0.3) materials were investigated. The Li₄Ti₅O_12−xBr_x (x = 0.2) presents the best discharge capacity among all the samples, and shows better reversibility and higher cyclic stability compared with pristine Li₄Ti₅O₁₂, especially at high current rates. When the discharge rate was 0.5 C, the Li₄Ti₅O_12−xBr_x (x = 0.2) sample presented the excellent discharge capacity of 172 mAh g⁻¹, which was very close to its theoretical capacity (175 mAh g⁻¹), while that of the pristine Li₄Ti₅O₁₂ was 123.2 mAh g⁻¹ only.     

High-rate characteristics of novel anode Li4Ti5O12/polyacene materials for Li-ion secondary batteries

In recent years, spinel lithium titanate (Li₄Ti₅O₁₂) as a superior anode material for energy storage battery has attracted a great deal of attention because of the excellent Li-ion insertion and extraction reversibility. However, the high-rate characteristics of this material should be improved if it is used as an active material in large batteries. One effective way to achieve this is to prepare electrode materials coated with carbon. A Li₄Ti₅O₁₂/polyacene (PAS) composite were first prepared via an in situ carbonization of phenol-formaldehyde (PF) resin route to form carbon-based composite. The SEM showed that the Li₄Ti₅O₁₂ particles in the composite were more rounded and smaller than the pristine one. The PAS was uniformly dispersed between the Li₄Ti₅O₁₂ particles, which improved the electrical contact between the corresponding Li₄Ti₅O₁₂ particles, and hence the electronic conductivity of composite material. The electronic conductivity of Li₄Ti₅O₁₂/PAS composite is 10⁻¹ S cm⁻¹, which is much higher than 10⁻⁹ S cm⁻¹ of the pristine Li₄Ti₅O₁₂. High specific capacity, especially better high-rate performance was achieved with this Li₄Ti₅O₁₂/PAS electrode material. The initial specific capacity of the sample is 144 mAh/g at 3 C, and it is still 126.2 mAh/g after 200 cycles. By increasing the current density, the sample still maintains excellent cycle performance.     

The preparation and characterization of Li4Ti5O12/carbon nano-tubes for lithium ion battery

Li₄Ti₅O₁₂/carbon nano-tubes (CNTs) composite was prepared by sol-gel method while Ti(OC₄H₉)₄, LiCH₃COO·2H₂O and the n-heptane containing CNTs were used as raw materials. The characters of Li₄Ti₅O₁₂/CNTs composite were determined by XRD, SEM, and TG methods. Its electrochemical properties were measured by charge-discharge cycling and impedance tests. It was found that the prepared Li₄Ti₅O₁₂/CNTs presented an excellent rate capability and capacity retention. At the charge-discharge rate of 5C and 10C, its discharge capacities were 145 and 135 mAh g⁻¹, respectively. After 500 cycles at 5C, the discharge capacity retained as 142 mAh g⁻¹. It even could be cycled at the rate of 20C. The excellent electrochemical performance of Li₄Ti₅O₁₂/CNTs electrode could be attributed to the improvement of electronic conductivity by adding conducting CNTs and the nano-size of Li₄Ti₅O₁₂ particles in the Li₄Ti₅O₁₂/CNTs composite.     

Structural and electrochemical characteristics of Li4−xAlxTi5O12 as anode material for lithium-ion batteries

Al-doped Li₄Ti₅O₁₂ in the form of Li_4−xAl_xTi₅O₁₂ (x = 0, 0.05, 0.1 and 0.2) was synthesized via solid state reaction in an Ar-flowing atmosphere. Al-doping does not change the phase composition and particle morphology, but easily results in the lattice distortion and thus the poor crystallinity of Li₄Ti₅O₁₂. Al-doping decreases the specific capacity of Li₄Ti₅O₁₂, while improves remarkably its cycling stability at high charge/discharge rate. The substitution of Al for Li site can enhance the electronic conductivity of Li₄Ti₅O₁₂ via the generation of mixing Ti⁴⁺/Ti³⁺, whereas impede the Li-ion diffusion in the lattice. Excessive Al causes large electrode polarization due to the lower Li-ion conductivity, and thus leads to low specific capacity at high current densities. Li_3.9Al_0.1Ti₅O₁₂ exhibits a relatively high specific capacity and an excellent cycling stability.     

Preparation of micro-dot electrodes of LiCoO2 and Li4Ti5O12 for lithium micro-batteries

Fabrications of micro-dot electrodes of LiCoO₂ and Li₄Ti₅O₁₂ on Au substrates were demonstrated using a sol-gel process combined with a micro-injection technology. A typical size of prepared dots was about 100 μm in diameter, and the dot population on the substrate was 2400 dots cm⁻². The prepared LiCoO₂ and Li₄Ti₅O₁₂ micro-dot electrodes were characterized with scanning electron microscopy, X-ray diffraction, micro-Raman spectroscopy, and cyclic voltammetry. The prepared LiCoO₂ and Li₄Ti₅O₁₂ micro-dot electrodes were evaluated in an organic electrolyte as cathode and anode for lithium micro-battery, respectively. The LiCoO₂ micro-dot electrode exhibited reversible electrochemical behavior in a potential range from 3.8 to 4.2 V versus Li/Li⁺, and the Li₄Ti₅O₁₂ micro-dot electrode showed sharp redox peaks at 1.5 V.     

Microstructure effect on the electrochemical property of Li4Ti5O12 as an anode material for lithium-ion batteries

Porous (P-) and dense (D-) lithium titanate (Li₄Ti₅O₁₂) powders as an anode material for lithium-ion batteries have been synthesized by spray drying followed by solid-state calcination. Electrochemical testing results showed that the discharge capacities of P-Li₄Ti₅O₁₂ are 144 mAh/g, 128 mAh/g and 73 mAh/g at the discharging rate of 2C, 5C and 20C, respectively (cut-off voltages: 0.5-2.5 V). The corresponding values for D-Li₄Ti₅O₁₂ are 108 mAh/g, 25 mAh/g and 17 mAh/g. The higher capacity of the P-Li₄Ti₅O₁₂ at high charge/discharge rates was attributed to the shorter transport path of Li ions and higher electronic conductivity in the P-Li₄Ti₅O₁₂ as a result of its smaller primary particle size and higher surface area compared with those of the D-Li₄Ti₅O₁₂.     

Hydrothermal synthesis of Li4Ti5O12 microsphere with high capacity as anode material for lithium ion batteries

Lithium titanate (Li₄Ti₅O₁₂) microsphere has been successfully synthesized by a hydrothermal method. X-ray diffraction (XRD) and scanning electron microscope (SEM) are used to characterize the structure and morphology of the prepared Li₄Ti₅O₁₂ crystallites. The results show that the as-synthesized powders exhibit outstanding rate capacities and excellent cycling performance. The first discharge capacity at 0.1 C is 172.5 mAh g⁻¹, which is close to the theoretical capacity of 175 mAh/g. After 50 cycles, the efficiency of the synthesized Li₄Ti₅O₁₂ still retains up to 92.8% at 0.1 C and 95.2% at 0.5 C of its initial value, which present a promising applications as anode materials for lithium ion batteries in hybrid and plug-in hybrid electric vehicles.     

All-solid-state lithium battery with a three-dimensionally ordered Li1.5Al0.5Ti1.5(PO4)3 electrode

To fabricate all-solid-state Li batteries using three-dimensionally ordered macroporous Li_1.5Al_0.5Ti_1.5(PO₄)₃ (3DOM LATP) electrodes, the compatibilities of two anode materials (Li₄Mn₅O₁₂ and Li₄Ti₅O₁₂) with a LATP solid electrolyte were tested. Pure Li₄Ti₅O₁₂ with high crystallinity was not obtained because of the formation of a TiO₂ impurity phase. Li₄Mn₅O₁₂ with high crystallinity was produced without an impurity phase, suggesting that Li₄Mn₅O₁₂ is a better anode material for the LATP system. A Li₄Mn₅O₁₂/3DOM LATP composite anode was fabricated by the colloidal crystal templating method and a sol-gel process. Reversible Li insertion into the fabricated Li₄Mn₅O₁₂/3DOM LATP anode was observed, and its discharge capacity was measured to be 27 mA h g⁻¹. An all-solid-state battery composed of LiMn₂O₄/3DOM LATP cathode, Li₄Mn₅O₁₂/3DOM LATP anode, and a polymer electrolyte was fabricated and shown to operate successfully. It had a potential plateau that corresponds to the potential difference expected from the intrinsic redox potentials of LiMn₂O₄ and Li₄Mn₅O₁₂. The discharge capacity of the all-solid-state battery was 480 μA h cm⁻².     

Effect of particle dispersion on high rate performance of nano-sized Li4Ti5O12 anode

Nano-sized Li₄Ti₅O₁₂ powders with high dispersivity were fabricated by a sol-gel process using P123 as surfactant, which exhibited much better high rate performance towards Li⁺ insertion/extraction as compared to the densely aggregated Li₄Ti₅O₁₂ particles although the primary grain sizes of both samples were almost the same. The Li₄Ti₅O₁₂ electrode prepared from the well-dispersed nanopowders can preserve 88.6% of the capacity at 0.1 A g⁻¹ when being cycled at 1 A g⁻¹, which is obviously higher than that of the densely aggregated sample, in which only 30% capacity can be retained. By improving the dispersivity, the specific surface area of the Li₄Ti₅O₁₂ nanoparticles, hence the electrode-electrolyte contact area was increased; meanwhile, more homogeneous mixing of the active materials with carbon black was achieved. All these factors might have resulted in the better high rate performance.     

Preparation and cycling performance of Aland F co-substituted compounds Li4AlxTi5−xFyO12−y

Li₄Al_xTi_5−xF_yO_12−y compounds were prepared by a solid-state reaction method. Phase analyses demonstrated that both Al³⁺ and F⁻ ions entered the structure of spinel-type Li₄Ti₅O₁₂. Charge-discharge cycling results at a constant current density of 0.15 mA cm⁻² between the cut-off voltages of 2.5 and 0.5 V showed that the Al³⁺ and F⁻ substitutions improved the first total discharge capacity of Li₄Ti₅O₁₂. However, Al³⁺ substitution greatly increased the reversible capacity and cycling stability of Li₄Ti₅O₁₂ while F⁻ substitution decreased its reversible capacity and cycling stability slightly. The electrochemical performance of the Al³⁺-F⁻-co-substituted specimen was better than the F⁻-substituted one but worse than the Al³⁺-substituted one.     

Improving the electrochemical performance of Li4Ti5O12/Ag composite by an electroless deposition method

Nano-sized silver particle (<20 nm) was highly dispersed on the surface of Li₄Ti₅O₁₂ particles by an electroless deposition method. The Ag additive played a positive role in improving the electrical contact between Li₄Ti₅O₁₂ particles and the current collector and therefore improved the high rate capacity of Li₄Ti₅O₁₂, but it did not take part in the electrochemical reactions with Li⁺ in Li₄Ti₅O₁₂/Ag composite during the cycling. The experimental results showed that the smaller the silver particles and the more homogeneous dispersion of silver particles in the Li₄Ti₅O₁₂ matrix, the better the cycling performance we obtained.     

Synthesis of spinel Li4Ti5O12 anode material by a modified rheological phase reaction

Using lithium acetate dihydrate and tetra-n-butyl titanate as the raw materials, spinel Li₄Ti₅O₁₂ was successfully synthesized by a modified rheological phase method. Thermogravimetric analysis and differential scanning calorimetry (TG–DSC) of the thermal decomposition process of the precursor and X-ray diffraction (XRD) data indicate the crystallization of lithium titanates has occurred at 580 °C, and main phase Li₄Ti₅O₁₂ has obtained at 600 °C. Laser granulometer and scanning electron microscope (SEM) have been employed to estimate the particle size distribution, morphology and microstructure of the products. It reveals the prepared Li₄Ti₅O₁₂ powder had a small particle size (about 140 nm) and narrow size distribution (d_0.1 = 0.07, d_0.5 = 0.139, d_0.9 = 2.813 μm). Galvanostatic charge and discharge tests were carried out to characterize the electrochemical performances of Li₄Ti₅O₁₂. The result indicates that the Li₄Ti₅O₁₂ electrode material obtained from the precursor that had been experienced heat treatment at 110 °C exhibited discharge capacities of 161.6, 156.5 and 112.3 mAh g⁻¹ after 50 cycles at current rates 1, 2.5 and 10 C, respectively, demonstrating excellent high rate performance, due to the pure and well crystallized Li₄Ti₅O₁₂ with ultrafine particles and narrow size distribution.     

Effects of the starting materials and mechanochemical activation on the properties of solid-state reacted Li4Ti5O12 for lithium ion batteries

Li₄Ti₅O₁₂ was synthesized by a solid-state reaction between Li₂CO₃ and TiO₂ for applications in lithium ion batteries. The effects of the TiO₂ phase and mechanochemical activation on the Li₄Ti₅O₁₂ particles as well as the corresponding electrochemical properties were investigated. Rutile TiO₂ was more desirable in acquiring high purity Li₄Ti₅O₁₂ than anatase due to the anatase to rutile phase transformation, which was found to be more rigid in the solid-state reaction than the intact rutile phase. Mechanochemical activation of the starting materials was effective in decreasing the reaction temperature and particle size as well as increasing the Li₄Ti₅O₁₂ content. The specific capacity depended significantly on the Li₄Ti₅O₁₂ content, whereas the rate capability improved with decreasing particle size due to the enhanced contact area and reduced diffusion path. Overall, a 200 nm-sized Li₄Ti₅O₁₂ powder with a specific capacity of 165 mAh/g could be synthesized by optimizing the milling method and starting materials.     

Niobium doped lithium titanate as a high rate anode material for Li-ion batteries

Niobium doped lithium titanate with the composition of Li₄Ti_4.95Nb_0.05O₁₂ has been prepared by a sol-gel method. X-ray diffraction (XRD) and scanning electron microscope (SEM) are employed to characterize the structure and morphology of Li₄Ti_4.95Nb_0.05O₁₂. The Li₄Ti_4.95Nb_0.05O₁₂ electrode presents a higher specific capacity and better cycling performance than the Li₄Ti₅O₁₂ electrode prepared by the similar process. The Li₄Ti_4.95Nb_0.05O₁₂ exhibits an excellent rate capability with a reversible capacity of 135 mAh g⁻¹ at 10 C, 127 mAh g⁻¹ at 20 C and even 80 mAh g⁻¹ at 40 C. Electrical resistance measurement and electrochemical impedance spectra (EIS) reveal that the Li₄Ti_4.95Nb_0.05O₁₂ exhibits a higher electronic conductivity and faster lithium-ion diffusivity than the Li₄Ti₅O₁₂, which indicates that niobium doped lithium titanate (Li₄Ti_4.95Nb_0.05O₁₂) is promising as a high rate anode for the lithium-ion batteries.     

Synthesis of sawtooth-like Li4Ti5O12 nanosheets as anode materials for Li-ion batteries

Hierarchical layered hydrous lithium titanate and Li₄Ti₅O₁₂ microspheres assembled by nanosheets have been successfully synthesized via a hydrothermal process and subsequent thermal treatment. The electrochemical properties of the two samples have been investigated by galvanostatic methods. The former, with the obvious layered structure and a large surface area, delivers a reversible capacity of 180 mA h g⁻¹ after 200 cycles at 200 mA g⁻¹. As for Li₄Ti₅O₁₂, with the intriguing and unique sawtooth-like morphology, it presents exceptional high rate performance and excellent cycling stability. Up to 132 mA h g⁻¹ is obtained after 200 cycles at 10,000 mA g⁻¹ (57 C), proving itself promising for high-rate applications.     

Effects of carbon source and carbon content on electrochemical performances of Li4Ti5O12/C prepared by one-step solid-state reaction

Li₄Ti₅O₁₂/C composites were synthesized by one-step solid-state reaction method using four commonly used organic compounds or organic polymers as carbon source, i.e., polyacrylate acid (PAA), citric acid (CA), maleic acid (MA) and polyvinyl alcohol (PVA). The physical characteristics of Li₄Ti₅O₁₂/C composites were investigated by X-ray diffraction, electron microscopy, Raman spectroscopy, particle size distribution and thermogravimetry-derivative thermogravimetry techniques. Their electrochemical properties were characterized by cyclic voltammograms, electrochemical impedance spectra, constant current charge–discharge and rate charge–discharge. These analyses indicated that the carbon source and carbon content have a great effect on the physical and electrochemical performances of Li₄Ti₅O₁₂/C composites. An ideal carbon source and appropriate carbon content effectively improved the electrical contact between the Li₄Ti₅O₁₂ particles, which enhanced the discharge capacity and rate capability of Li₄Ti₅O₁₂/C composites. PAA was the best carbon source for the synthesis of Li₄Ti₅O₁₂/C composites. When the carbon content was 3.49 wt.% (LiOH·H₂O/PAA molar ratio of 1), as-prepared Li₄Ti₅O₁₂/C showed the maximum discharge capacity. At 0.2 C, initial capacity of the optimized sample was 168.6 mAh g⁻¹ with capacity loss of 2.8% after 50 cycles. At 8 and 10 C, it showed discharge capacities of 143.5 and 132.7 mAh g⁻¹, with capacity loss of 8.7 and 9.9% after 50 cycles, respectively.     

Densification, microstructural evolution and microwave dielectric properties of fluxed sintered 12R-Ba(Ti0.5Mn0.5)O3 ceramics

Doped hexagonal BaTiO₃ (h-BaTiO₃) ceramics have recently been identified as potential candidates for use in microwave dielectric resonators. However, similar to other common microwave ceramics, doped h-BaTiO₃ ceramics require a sintering temperature higher than 1400 °C. In this study, the effects of Bi₂O₃ and Li₂CO₃ on the densification, microstructural evolution and microwave properties of hexagonal 12R-Ba(Ti_0.5Mn_0.5)O₃ ceramics were examined. Results indicate that Bi₂O₃ and Li₂CO₃ are able to effectively reduce the sintering temperature of 12R-Ba(Ti₀₅Mn_0.5)O₃ ceramics through liquid phase sintering while retaining the hexagonal structure and the microwave dielectric properties. The best results were obtained for the 12R-Ba(Ti_0.5Mn_0.5)O₃ with the additions of 5 wt% Bi₂O₃ sintered at 1200 °C (?_r: 36.0, Qf_r: 6779 GHz, and τ_f: 25.3 ppm/°C), and 5 wt% Li₂CO₃ sintered at 1200 °C (?_r: 28.1, Qf_r: 5304 GHz, and τ_f: 35.3 ppm/°C).     

Spray-drying synthesized lithium-excess Li4+xTi5−xO12−δ and its electrochemical property as negative electrode material for Li-ion batteries

Li₄Ti₅O₁₂ (Fd-3m space group) materials were synthesized by controlling the lithium and titanium ratios (Li/Ti) in the range of 0.800-0.900 by using a spray-drying method, followed by calcination at several temperatures between 700 and 900 °C for large-scale production. Chemical and structure studies of the final products were done by X-ray diffraction (XRD), neutron diffraction (ND), X-ray photon electron spectroscopy (XPS), scanning electron microscopy (SEM) and inductively coupled plasma mass spectrometry (ICP-MS). The optimum synthesis condition was examined in relation to the electrochemical characteristics including charge-discharge cycling and ac impedance spectroscopy. It was found that when the spray-drying precursors at the Li/Ti ratio of 0.860 were calcined at 700-900 °C for 12 h in air, a pure Li_4+xTi_5−xO_12−δ (x = 0.06-0.08) phase with a lithium-excess composition was obtained. Based on the structural studies, it was found that the excess lithium is located at the lithium and titanium layer of the 16d site in the spinel structure (Fd-3m). These pure Li_4+xTi_5−xO_12−δ (x = 0.06-0.08) phase materials showed a higher discharge capacity of ∼164 mAh g⁻¹ at 1.55 V (vs. Li/Li⁺), between the cut-off voltage of 1.2-3.0, with an excellent cyclability and superior rate performance in comparison with the Li₄Ti₅O₁₂ phase containing impurity phases.     

All solid-state lithium polymer secondary batteries using spinel Li4/3Ti5/3O4 as an active material

Present paper describes electrochemical performance of the all solid-state lithium polymer battery (LBP) using spinel-type Li_4/3Ti_5/3O₄ which has been known as the potential candidate of anode materials.The assembled LPB with Li|solid polymer electrolyte(SPE)|Li_4/3Ti_5/3O₄ construction showed stable charge-discharge cycles more than 300 times at 1 C condition. On the other hand, strong charge-discharge rate dependence for the specific capacity and initial capacity loss was indicated. Such a poor rate performance stemmed from low diffusivity of Li⁺ ion in the by-products produced by the decomposition of SPE components at the SPE|Li_4/3Ti_5/3O₄ interface.