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.     

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．     

Spinel lithium titanate (Li4Ti5O12) as novel anode material for room-temperature sodium-ion battery

This is the first time that a novel anode material, spinel Li₄Ti₅O₁₂ which is well known as a “zero-strain” anode material for lithium storage, has been introduced for sodium-ion battery. The Li₄Ti₅O₁₂ shows an average Na storage voltage of about 1.0 V and a reversible capacity of about 145 mAh/g, thereby making it a promising anode for sodium-ion battery. E_x-situ X-ray diffraction (XRD) is used to investigate the structure change in the Na insertion/deinsertion process. Based on this, a possible Na storage mechanism is proposed.     

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.     

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.     

The effect of additional doping with Nb, Al or Cu on ferromagnetism and conductivity in V-doped TiO2 powders

Rutile Ti_0.94V_0.06O₂ and Ti_0.93V_0.06M_0.01O₂ (M=Nb, Al, and Cu) polycrystalline powders are synthesized by the standard solid-state reaction method. The room-temperature saturation magnetization and resistivity of Ti_0.94V_0.06O₂ powders are 2.5×10⁻³ emu/g (≈0.60×10⁻³μ_B/V) and above 10⁷ Ω cm, respectively. The ferromagnetism weakens remarkably, and the conductivity enhances after additional doping with Nb or Al in V-doped rutile TiO₂ powders. The room-temperature magnetization and resistivity of Ti_0.93V_0.06Cu_0.01O₂ powders are 2.1×10⁻³ emu/g and 1.26×10⁶ Ω cm, respectively. Based on analysis for chemical valence of dopants by the x-ray photoelectron spectroscopy spectra, and using the bound magnetic polaron model, the microscopic mechanisms of ferromagnetism in V-doped rutile TiO₂ powders with or without additional dopants are discussed in detail.     

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.     

Effects of high-energy milling on the solid-state synthesis of pure nano-sized Li4Ti5O12 for high power lithium battery applications

Li₄Ti₅O₁₂ was synthesized from Li₂CO₃ and anatase TiO₂ using different degree of milling to test the hypothesis that finer starting materials can result in a smaller Li₄Ti₅O₁₂ particle size and better high-rate discharging capacities. The degree of milling was controlled using three different ZrO₂ media sizes for 3 hours of high-energy milling, whereas 5 mm balls were used for 24 hours ball milling. High-energy milling produced significantly finer starting materials and Li₄Ti₅O₁₂ particles compared to those produced by ball milling. Among the three different balls used in high-energy milling, the 0.10 mm media showed the most favorable results. Pure Li₄Ti₅O₁₂ with a mean particle size of 146 and 175 nm were synthesized by an economic solid-state reaction combined with high-energy milling using 0.05 and 0.10 mm beads, respectively. These pure nano-sized Li₄Ti₅O₁₂ exhibited a much higher specific capacity and superior rate capability than those of coarse rutile TiO₂-contained Li₄Ti₅O₁₂ particles.     

Electrochemical properties of stacked-nanoflake Li4Ti5O12 spinel synthesized by a polymer-pyrolysis method

Stacked-nanoflake Li₄Ti₅O₁₂ spinel was synthesized via the pyrolysis of a Li–Ti copolymeric precursor formed by in situ polymerization of LiOH and [Ti(OC₄H₉)₄] and acrylic acid. XRD and SEM characterization shows that the powders calcined at 700 °C for 3 h was well-crystallized particles with submicron diameter. Charge–discharge measurement showed the Li₄Ti₅O₁₂ electrode had displayed excellent rate capability and delivered reversible capacity of 171, 158, 148, 138 and 99 mAh g⁻¹ at rates of 0.1C, 0.5C, 1C, 2C and 4C, respectively. The test electrode also showed excellent cyclability as the capacity retains 96.1% after 60 cycles between 0.5 and 2.5 V.     

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.     

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.     

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.     

Preparation and electrochemical properties of Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript>/Ti<Subscript>4</Subscript>O<Subscript>7</Subscript> composite for lithium-ion batteries

In order to improve the rate capability of Li₄Ti₅O₁₂, Ti₄O₇ powder was successfully fabricated by improved hydrogen reduction method, then a dual-phase composite Li₄Ti₅O₁₂/Ti₄O₇ has been synthesized as anode material for lithium-ion batteries. It is found that the Li₄Ti₅O₁₂/Ti₄O₇ composite shows higher reversible capacity and better rate capability compared to Li₄Ti₅O₁₂. According to the charge-discharge tests, the Li₄Ti₅O₁₂/Ti₄O₇ composite exhibits excellent rate capability of 172.3 mAh g^?1 at 0.2 C, which is close to the theoretical value of the spinel Li₄Ti₅O₁₂. More impressively, the reversible capacity of Li₄Ti₅O₁₂/Ti₄O₇ composite is 103.1 mAh g^?1 at the current density of 20 C after 100th cycles, and it maintains 84.8% of the initial discharge capacity, whereas that of the bare spinel Li₄Ti₅O₁₂ is only 22.3 mAh g^?1 with a capacity retention of 31.1%. The results indicate that Li₄Ti₅O₁₂/Ti₄O₇ composite could be a promising anode material with relative high capacity and good rate capability for lithium-ion batteries.     

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.     

Preparation of TiO2-coated LiMn2O4 by carrier transfer method

The TiO₂-coated LiMn₂O₄ has been prepared by a carrier transfer method and investigated. This novel synthetic method involved the transfer of TiO₂ into the surface of LiMn₂O₄ with Vulcan XC-72 active carbon powders as a dispersant. The X-ray diffraction shows that spinel structure of materials does not change after the coating of TiO₂. The electrochemical performance tests show that the initial discharge capacity of TiO₂-modified LiMn₂O₄ is 111.5 mA h g⁻¹, which is better than that of pristine LiMn₂O₄ (103.8 mA h g⁻¹). The cyclic performance is significantly improved after surface modification. The TiO₂-modified LiMn₂O₄ by a carrier transfer method exhibits better discharge capability and lower resistance.     

Li4Ti2.5Cr2.5O12 as anode material for lithium battery

Chromium-substituted Li₄Ti₅O₁₂ has been investigated as a negative electrode for future lithium batteries. It has been synthesized by a solid-state method followed by quenching leading to a micron-sized material. The minimum formation temperature of Li₄Ti_2.5Cr_2.5O₁₂ was found to be around 600 °C using thermogravimetric and differential thermal analysis. X-ray diffraction, scanning electron microscopy, cyclic voltammetry (CV), impedance spectroscopy, and charge–discharge cycling were used to evaluate the synthesized Li₄Ti_2.5Cr_2.5O₁₂. The particle size of the powder was around 2–4 μm. CV studies reveal a shift in the deintercalation potential by about 40 mV, i.e., from 1.54 V for Li₄Ti₅O₁₂ to 1.5 V for Li₄Ti_2.5Cr_2.5O₁₂. High-rate cyclability was exhibited by Li₄Ti_2.5Cr_2.5O₁₂ (up to 5  C) compared to the parent compound. The conduction mechanism of the compound was examined in terms of the dielectric constant and dissipation factor. The relaxation time has been evaluated and was found to be 0.07 ms. The mobility was found to be 5.133 × 10⁻⁶ cm² V⁻¹ s⁻¹.     

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.     

Atomic force microscopy study of surface morphology change in spinel LiMn2O4: Possibility of direct observation of Jahn-Teller instability

Surface morphology in 3.5 × 3.5 μm² area of spinel LiMn₂O₄, which is a typical cathode material for Li ion secondary batteries, is studied using an atomic force microscopy (AFM) with a conductive probe. Negative bias voltage is applied to the probe to attract Li⁺ ions toward LiMn₂O₄ surface during the AFM observation. Before applying the voltage (0 V), the whole LiMn₂O₄ surface is covered with scale-shaped grains. Under the negative voltage of 5.5 V, electric current abruptly increases, indicating Li⁺ ionic conduction. Simultaneously, part of the scale-shaped grains expand and flatten. Jahn-Teller phase transition, which is induced by the repulsive interaction between the Mn-e_g and O-2p electrons in Li accumulated layer, is proposed as a possible origin of these results.     

Preparation of binder-free thin film Li4Ti5O12 anode with an adjustable thickness through anodic TiO2 nanotubes

Binder-free thickness-controllable Li₄Ti₅O₁₂ for application in lithium ion batteries was fabricated by the reaction of Li₂CO₃ and anodic nanotubular TiO₂ at 800 °C. As the concentration of Li₂CO₃ increased, the thickness of Li₄Ti₅O₁₂ film increased, leading to increase in discharge capacity. The Li₄Ti₅O₁₂ film prepared at the optimized concentration of Li₂CO₃ of 3.8 × 10^?6 mol displayed the maximum capacity of 104 μA h cm^?2 at the first cycle, which corresponds to 103 mA h g^?1. We found that excess Li₂CO₃ led to creation of LiTiO₂ phases in the Li₄Ti₅O₁₂ film, which reduced the discharge capacity. For comparison, a Li₄Ti₅O₁₂ film was prepared by the reaction of Li₂CO₃ on a non-anodized Ti foil. In this case, discharge capacity was dramatically reduced due to the formation of Li₂TiO₃ phases in Li₄Ti₅O₁₂, which was confirmed by TEM and XRD analysis.     

Li4Ti5O12/Ag composite as electrode materials for lithium-ion battery

The Li₄Ti₅O₁₂/Ag composites were prepared by thermal decomposition of AgNO₃ added to Li₄Ti₅O₁₂ powders. The influence of the Ag contents and the mixing media on the particle size, morphology and electrochemical performance of Li₄Ti₅O₁₂/Ag composites were investigated. The highest discharge capacity of the Li₄Ti₅O₁₂/Ag composite reached at the 5 wt.% of Ag content. Compared with alcohol medium, distilled water as mixing medium presented the Li₄Ti₅O₁₂/Ag composite with higher specific capacity and better cycling performance, leading to a reversible capacity after 50 cycles of 184.2 mAh/g with a capacity degradation of 3.31% compared to the second cycle at 2 C rate.