Electrostatic spray deposition of spinel Li4Ti5O12 thin films for rechargeable lithium batteries

Spinel Li₄Ti₅O₁₂ thin films are important for the fabrication of rechargeable lithium microbatteries. Porous thin films of Li₄Ti₅O₁₂ were prepared by electrostatic spray deposition (ESD) technique with lithium acetate and titanium butoxide as the precursors. The structures of these films were analyzed by scanning electron microscopy and X-ray diffraction. Coin-type cells with a liquid electrolyte were made with the Li₄Ti₅O₁₂ films against metallic lithium. Their electrochemical performance was investigated by means of galvanostatic cell cycling, cyclic voltammetry and Ac impedance spectroscopy. It was found that pure spinel phase of Li₄Ti₅O₁₂ was obtained. After annealing at the optimal temperature of 700 °C, the films can deliver a reversible specific capacity of about 150 mAh/g with excellent capacity retention after 70 cycles. Their electrochemical characteristics were quite comparable with those of the Li₄Ti₅O₁₂ laminate electrodes containing carbon black additive.     

Recent development and application of Li4Ti5O12 as anode material of lithium ion battery

Lithium-ion batteries with both high power and high energy density are one of the promising power sources for electric devices, especially for electric vehicles (EV) and other portable electric devices. One of the challenges is to improve the safety and electrochemical performance of lithium ion batteries anode materials. Li₄Ti₅O₁₂ has been accepted as a novel anode material of power lithium ion battery instead of carbon because it can release lithium ions repeatedly for recharging and quickly for high current. However, Li₄Ti₅O₁₂ has an insulating character due to the electronic structure characterized by empty Ti 3d-states, and this might result in the insufficient applications of LTO at high current discharge rate before any materials modifications. This review focuses first on the present status of Li₄Ti₅O₁₂ including the synthesized method, doping, surface modification, application and theoretical calculation, then on its near future development.     

Synthesis of spinel lithium titanate anodes incorporated with rutile titania nanocrystallites by spray drying followed by calcination

Lithium insertion into spinel Li₄Ti₅O₁₂ incorporated with rutile TiO₂ was investigated in order to clarify the redox mechanism responsible for the first plateau at 1.5 V vs. Li/Li⁺. Spherical Li₄Ti₅O₁₂ powders with an average diameter of 2-3 μm can be achieved by spray drying followed by sintering process. The Li/Ti molar ratio in the precursor is selected as the factor for preparing spinel Li₄Ti₅O₁₂ powders with different concentrations of rutile TiO₂. The specific capacity from the first plateau at 1.5 V contributes to the major portion in the overall capacity. The rutile TiO₂ in spinel Li₄Ti₅O₁₂ anodes tends to improve the specific capacity at the first plateau. This can be attributed to two possible reasons: (i) rutile TiO₂ provides an additional number of sites (i.e., oxygen octahedral vacancy in rutile TiO₂) for the Li insertion, and (ii) less amount of residual Li oxides results in high electronic conductivity. The Li₄Ti₅O₁₂ anodes display high rate capability with low irreversible capacity, indicating good reversibility of insertion/de-insertion of Li ions. The results presented in this work show unambiguously that the presence of rutile TiO₂ in spinel Li₄Ti₅O₁₂ has a positive effect on the performance promotion of Li₄Ti₅O₁₂ anodes.     

糠醇辅助的聚合凝胶法制备纳米Li4Ti5O12负极材料

以硝酸锂、钛酸正丁酯和糠醇为反应物,采用糠醇聚合凝胶法制备了纳米Li₄Ti₅O₁₂粉体．利用XRD、SEM和BET比表面测试对产物进行了表征,并研究了纳米Li₄Ti₅O₁₂粉体作为锂离子电池负极材料的电化学性能．在700℃或更高温度烧结时产物为纯相的尖晶石型．通过柠檬酸、聚乙烯吡咯烷酮、十六烷基三甲基溴化铵(CTAB)表面活性剂的加入能够减少产物颗粒的团聚程度,增大粉体的比表面积,提高其电化学性能．加入0.5 g CTAB、700℃烧结12 h的Li₄Ti₅O₁₂粉体展示出最高的比容量和最佳的循环性能,10 C下充电比容量高达156.7 mAh/g．     

Synthesis and electrochemical properties of Li4Ti5O12/C composite by the PVB rheological phase method

Spinel Li₄Ti₅O₁₂/C powders were synthesized successfully by a simple rheological phase method using polyvinylbutyral (PVB) as both template and carbon source. The structure and morphology characteristics of the composite were investigated by X-ray diffraction (XRD), field emission scanning electron microscopy and transmission electron microscopy. The XRD results showed that the composite had a good crystallinity. Its average particle size was about 2.1 μm with a narrow size distribution as a result of homogeneous mixing of the precursors. The in situ carbon coating produced by decomposition of PVB played an important role in improving electrical conductivity, thereby enhancing the rate capacity of Li₄Ti₅O₁₂ as anode material in Li-ion batteries. The Li₄Ti₅O₁₂/C composite, synthesized at 800 °C for 15 h under argon, containing 0.98 wt% of carbon, exhibited better electrochemical properties in comparison with the pristine Li₄Ti₅O₁₂, which could be attributed to the enhanced electrical conductive network of the carbon coating on the particle surface.     

Significant effect of electron transfer between current collector and active material on high rate performance of Li4Ti5O12

The rate and cycling performances of the electrode materials are affected by many factors in a practical complicated electrode process. Learning about the limiting step in a practical electrochemical reaction is very important to effectively improve the electrochemical performances of the electrode materials. Li₄Ti₅O₁₂, as a zero-strain material, has been considered as a promising anode material for long life Li-ion batteries. In this study, our results show that the Li₄Ti₅O₁₂ pasted on Cu or graphite felt current collector exhibits unexpectedly higher rate performance than on Al current collector. For Li₄Ti₅O₁₂, the electron transfer between current collector and active material is the critical factor that affects its rate and cycling performances.     

Characteristics of spherical-shaped Li4Ti5O12 anode powders prepared by spray pyrolysis

Spherical-shaped Li₄Ti₅O₁₂ anode powders with a mean size of 1.5 μm were prepared by spray pyrolysis. The precursor powders obtained by spray pyrolysis had no peaks of crystal structure of Li₄Ti₅O₁₂. The powders post-treated at temperatures of 800 and 900 °C had the single phase of spinel Li₄Ti₅O₁₂. The powders post-treated at a temperature of 1000 °C had main peaks of the Li₄Ti₅O₁₂ phase and small impurity peaks of Li₂Ti₃O₇. The spherical shape of the precursor powders was maintained after post-treatment at temperatures below 800 °C. The Brunauer-Emmett-Teller (BET) surface areas of the Li₄Ti₅O₁₂ anode powders post-treated at temperatures of 700, 800 and 900 °C were 4.9, 1.6 and 1.5 m²/g, respectively. The initial discharge capacities of Li₄Ti₅O₁₂ powders were changed from 108 to 175 mAh/g when the post-treatment temperatures were changed from 700 to 1000 °C. The maximum initial discharge capacity of the Li₄Ti₅O₁₂ powders was obtained at a post-treatment temperature of 800 °C, which had good cycle properties below current densities of 0.7 C.     

Structure and physical properties of Li4Ti5O12 synthesized at deoxidization atmosphere

Powders of spinel Li₄Ti₅O₁₂ (LTO) were successfully synthesized at reducing conditions by solid-state method. The structure and physical properties of Li₄Ti₅O₁₂ were examined by X-ray diffraction (XRD), Raman spectroscopy, scanning electronic microscopy (SEM), and differential capacitance, respectively. XRD shows that both samples are single-phase spinel compounds. LTO synthesized in Ar/H₂(8% mol) has a larger lattice parameter than that in Ar. SEM indicates that all of the prepared powders have the uniform, nearly cubic structure morphology with narrow size distribution in the range of 200–300 nm. Raman spectra indicate that the Raman bands corresponding to the Ti–O vibration has a blue shift from 674 to 680 cm⁻¹ due to the few H₂ in the synthesized condition, indicating that there is very few oxygen vacancies in the Li₄Ti₅O₁₂ synthesized under Ar/H₂ (8% mol). The dQ/dV vs. voltage plots reveals the redox potentials for the synthesized Li₄Ti₅O₁₂-negative electrode materials.     

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.     

Structural and electrochemical study on Li(Li1/3Ti5/3)O4 anode material for lithium ion batteries

Chemical and electrochemical studies have shown that various titanium oxides can incorporate lithium in different ratios. Other compounds with a spinel-type structure and corresponding to the spinel oxides LiTi₂O₄ and Li₄Ti₅O₁₂ have been evaluated in rechargeable lithium cells with promising features. The spinel Li[Li_1/3Ti_5/3]O₄ [1–5] compound is a very appealing electrode material for lithium ion batteries. The lithium insertion-deinsertion process occurs with a minimal variation of the cubic unit cell and this assures high stability which may reflect into long cyclability. In addition, the diffusion coefficient of lithium is of the order of 10⁻⁸ cm²s⁻¹ [5] and this suggests fast kinetics which may reflect in high power capabilities. In this work we report a study on the kinetics and the structural properties of the Li[Li_1/3Ti_5/3]O₄ intercalation electrode carried out by: cyclic voltammetry, galvanostatic cycling and in-situ X-ray diffraction. The electrochemical characterization shows that the Li[Li_1/3Ti_5/3]O₄ electrode cycles around 1.56 V vs. Li with a capacity of the order of 130 mAhg⁻¹ which approaches the maximum value of 175 mAhg⁻¹ corresponding to the insertion of 1 equivalent per formula unit. The delivered capacity remains constant for hundred cycles confirming the stability of the host structure upon the repeated Li insertion-deinsertion process. This high structural stability has been confirmed by in situ Energy Dispersion X-ray analysis. Paper presented at the 7th Euroconference on Ionics, Calcatoggio, Corsica, France, Oct. 1–7, 2000.     

Advanced electrochemical performances of Li4Ti5O12/Ag prepared by a facile synthesis route

Spinel Li₄Ti₅O₁₂ coated by highly dispersed nanosized Ag particles was synthesized via a facile and effective ultrasonic-assisted method in this paper. X-ray diffraction (XRD) results indicated that Ag was not doped into the lattice of spinel Li₄Ti₅O₁₂. The as-synthesized Li₄Ti₅O₁₂/Ag exhibited enhanced electronic conductivity and excellent electrochemical performances. Its electronic conductivity was increased about four times compared to that of the pristine Li₄Ti₅O₁₂. Even at 10 C rate, the as-synthesized Li₄Ti₅O₁₂/Ag could keep 86.5 % of the reversible capacity at 1 C rate and its reversible capacity was higher than 140 mAhg^?1 whereas those were 75.3 % and 118 mAhg^?1 for the pristine Li₄Ti₅O₁₂.     

Research progress on the low-temperature electrochemical performance of Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript> anode material

Li₄Ti₅O₁₂ is regarded as the ideal anode material for its stable structure, high charge/discharge platform, and safety performance. But low ionic and electronic conductivity of the Li₄Ti₅O₁₂ anode material under the condition of low temperature greatly limit its application in practical production. In this paper, some modified methods for improving the low-temperature electrochemical performance of Li₄Ti₅O₁₂ anode material were summarized. Meanwhile, we explored its influence mechanisms at low temperature, one is, with the subtle changes of lattice parameters and oxygen atom fraction coordinates of Li₄Ti₅O₁₂ at low temperature, the changes of the bond length influence the structural stability of Li₄Ti₅O₁₂ and the diffusion path of lithium ions; the other reason is that the charge transfer resistance increases obviously and the lithium ion diffusion coefficient reduces under low temperature. Finally, the research directions for improving the low-temperature electrochemical performance were proposed.     

Preparation and characteristics of Li4Ti5O12 with various dopants as anode electrode for hybrid supercapacitor

Spinel-Li₄Ti₅O₁₂ is successfully synthesized by a solid phase synthesis. The Li₄Ti₅O₁₂ powders with various dopants (Al³⁺, Cr³⁺, Mg²⁺) synthesized at 800 °C are in accordance with the Li₄Ti₅O₁₂ cubic spinel phase structure. The dopants are inserted into the lattice structure of Li₄Ti₅O₁₂ without causing any changes in structural characteristics. In order to study the effect on various dopants, the hybrid supercapacitor is prepared by using un-doped Li₄Ti₅O₁₂ and doped Li₄Ti₅O₁₂ in this work. The electrochemical performance of the hybrid supercapacitor is characterized by impedance spectroscopy and cycle performance. The results show Cr³⁺ and Mg²⁺ dopants enhance the conductivity of Li₄Ti₅O₁₂. Also, Al³⁺ substitution improves the reversible capacity and cycling stability of Li₄Ti₅O₁₂. It is found that effect of dopant on the electrochemical performance of Li₄Ti₅O₁₂ as electrode material for hybrid supercapacitor where the EDLC and the Li ion secondary battery coexist in one cell system.     

A new composite material Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript>–SnO<Subscript>2</Subscript> for lithium-ion batteries

A new Li₄Ti₅O₁₂–SnO₂ composite anode material for lithium-ion batteries has been prepared by loading SnO₂ on Li₄Ti₅O₁₂ to obtain composite material with improved electrochemical performance relative to Li₄Ti₅O₁₂ and SnO₂. The composite material was characterized by X-ray diffraction and scanning electron microscopy. The results indicated that SnO₂ particles have encapsulated on the surface of the Li₄Ti₅O₁₂ uniformly and tightly. Electrochemical results indicated that the Li₄Ti₅O₁₂–SnO₂ composite material increases the reversible capacity of Li₄Ti₅O₁₂ and has good cycling reliability. At a current rate of 0.5 mA/cm², the material delivered a discharge capacity of 236 mAh/g after 16 cycles. It suggests the existence of synergistic interaction between Li₄Ti₅O₁₂ and SnO₂ and that the capacity of the composite is not a simple weighted sum of the capacities of the individual components. In the composite material, SnO₂ can act as a bridge between the spinel particles to reduce the interparticle resistance and as a good material for the Li intercalation/deintercalation. Thus, electrochemical performance of the Li₄Ti₅O₁₂ spinel can be improved by the surface modification with SnO₂, and the stability of Li₄Ti₅O₁₂ also serves to buffer the internal stress caused by the volume changes in lithium insertion and extraction reactions.     

Synthesis and electrochemical performances of Li4Ti4.95Al0.05O12/C as anode material for lithium-ion batteries

Spinel compounds Li₄Ti_5−xAl_xO₁₂/C (x=0, 0.05) were synthesized via solid state reaction in an Ar atmosphere, and the electrochemical properties were investigated by means of electronic conductivity, cyclic voltammetry, and charge-discharge tests at different discharge voltage ranges (0-2.5 V and 1-2.5 V). The results indicated that Al³⁺ doping of the compound did not affect the spinel structure but considerably improved the initial capacity and cycling performance, implying the spinel structure of Li₄Ti₅O₁₂ was more stable when Ti⁴⁺ was substituted by Al³⁺, and Al³⁺ doping was beneficial to the reversible intercalation and deintercalation of Li⁺. Al³⁺ doping improved the reversible capacity and cycling performance effectively especially when it was discharged to 0 V.     

Electrical and electrochemical properties of molten salt-synthesized Li4Ti5−xSnxO12 (x=0.0, 0.05 and 0.1) as anodes for Li-ion batteries

Submicron-sized polyhedral Li₄Ti_5−xSn_xO₁₂ (x=0.0, 0.05, and 0.1) materials were successfully prepared by a single-step molten salt method. The structural, morphological, transport and electrochemical properties of the Li₄Ti_5−xSn_xO₁₂ were studied. X-ray diffraction patterns showed the formation of a cubic structure with a lattice constant of 8.31 Å, and the addition of dopants follows Vegard's law. Furthermore, FT-IR spectra revealed symmetric stretching vibrations of octahedral groups of MO₆ lattice in Li₄Ti₅O₁₂. The formation of polyhedral submicron Li₄Ti_5−xSn_xO₁₂ particles was inferred from FE-SEM images, and a particle size reduction was observed for Sn-doped Li₄Ti₅O₁₂. The chemical composition of Ti, O and Sn was verified by EDAX. The DC electrical conductivity was found to increase with increasing temperature, and a maximum conductivity of 8.96×10⁻⁶ S cm⁻¹ was observed at 200 °C for Li₄Ti₅O₁₂. The galvanostatic charge–discharge behavior indicates that the Sn-doped Li₄Ti₅O₁₂ could be used as an anode for Li-ion batteries due to its enhanced electrochemical properties.     

Crystal structure of Li5B7O12.5Cl at 296 and 425 K

The structure of the boracite-type Li₅B₇O_12.5Cl has been determined at two different temparatures. It has a cubic symmetry with a cell parameter of 12.136(3) Å and space group F23. The rigid B₇O₁₂ three-dimensional framework is similar to that of other boracites. Changes in the coordination of the B(2), B(3) and Li(1) arise from the insertion of the additional O(3) atom and the ordering of Li(2). On the basis of the results relative to the temperature factors and electron density of the Li(1) atom at different temperatures a transport mechanism is proposed.     

Structure,ionic conduction,and phase transformations in lithium titanate Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript>

The spinel structure of lithium titanate Li₄Ti₅O₁₂ is refined by the Rietveld full-profile analysis with the use of x-ray and neutron powder diffraction data. The distribution and coordinates of atoms are determined. The Li₄Ti₅O₁₂ compound is studied at high temperatures by differential scanning calorimetry and Raman spectroscopy. The electrical conductivity is measured in the high-temperature range. It is shown that the Li₄Ti₅O₁₂ compound with a spinel structure undergoes two successive order-disorder phase transitions due to different distributions of lithium atoms and cation vacancies (□, V) in a defect structure of the NaCl type: (Li)_8a[Li_0.33Ti_1.67]_16dO₄ → [Li□]_16c[Li_1.33Ti_1.67]_16dO₄ → [Li_1.33□_0.67]_16c[Ti_1.67□_0.33]_16dO₄. The low-temperature diffusion of lithium predominantly occurs either through the mechanism ... → Li(8a) → V(16c) → V(8a) → ... in the spinel phase or through the mechanism ... → Li(16c) → V(8a) → V(16c) → ... in an intermediate phase. In the high-temperature phase, the lithium cations also migrate over 48f vacancies: ... Li(16c) → V(8a, 48f) → V(16c) → ....     

Identification of the Li sites in the Li ion conductor, Li6SrLa2Nb2O12, through neutron powder diffraction studies

In this paper a neutron powder diffraction structural study of the Li ion conducting garnet-related system, Li₆SrLa₂Nb₂O₁₂, is reported. The results show that this phase is cubic, space group Ia-3d, and contains Li in two partially occupied crystallographic sites. The first site, Li1, corresponds to the ideal tetrahedral site in the garnet framework and possesses an occupancy of 0.59(1). The second site, Li2, is significantly more distorted and possesses an occupancy of 0.352(3). Compared to the related Li₅La₃Nb₂O₁₂ system, the Li2 site occupancy is greatly increased, while the Li1 site occupancy is reduced. Despite these large differences in site occupancies, the reported conductivities for Li₅La₃Nb₂O₁₂ and Li₆SrLa₂Nb₂O₁₂ are similar, showing the complexities of these new garnet Li ion conductors.     

Synthesis and electrochemical performance of hole-rich Li4Ti5O12 anode material for lithium-ion secondary batteries

Hole-rich Li₄Ti₅O₁₂ composites are synthesized by spray drying using carbon nanotubes as additives in precursor solution, subsequently followed calcinated at high temperature in air. The structure, morphology, and texture of the as-prepared composites are characterized with XRD, Raman, BET and SEM techniques. The electrochemical properties of the as-prepared composites are investigated systematically by charge/discharge testing, cyclic voltammograms and AC impedance spectroscopy, respectively. In comparison with the pristine Li₄Ti₅O₁₂, the hole-rich Li₄Ti₅O₁₂ induced by carbon nanotubes exhibits superior electrochemical performance, especially at high rates. The obtained excellent electrochemical performances of should be attributed to the hole-rich structure of the materials, which offers more connection-area with the electrolyte, shorter diffusion-path length as well faster migration rate for both Li ions and electrons during the charge/discharge process.