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.     

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.     

Improvement electrochemical performance of Li1.5Ni0.25Mn0.75O2.5 with Li4Ti5O12 coating

Layered cathode Li_1.5Ni_0.25Mn_0.75O_2.5 has been synthesized and coated by Li₄Ti₅O₁₂. The pristine and coated Li_1.5Ni_0.25Mn_0.75O_2.5 powders are characterized by X-ray diffraction (XRD), indicating the materials remained the layered structure before and after coating. The coated Li₄Ti₅O₁₂ has been detected by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (DEX). The electrochemical performance, especially rate performance of Li_1.5Ni_0.25Mn_0.75O_2.5 electrode, is improved effectively after Li₄Ti₅O₁₂ coating. The first discharge capacity, coulombic efficiency, and capacity retention of Li₄Ti₅O₁₂-coated Li_1.5Ni_0.25Mn_0.75O_2.5 electrode are 244 mA h g^?1, 81.5 %, and 98.3 % after 50 cycles, respectively. The Li₄Ti₅O₁₂-coated Li_1.5Ni_0.25Mn_0.75O_2.5 electrode exhibits 108 mA h g^?1 at 10 °C rate. Electrochemical impedance spectroscopy (EIS) results show that the charge transfer resistance (R _ct) of Li_1.5Ni_0.25Mn_0.75O_2.5 electrode decreases after coating, which is due to the existence of Li₄Ti₅O₁₂ with high lithium ion diffusion coefficient and suppression of the solid electrolyte interfacial (SEI) layer development and is responsible for the excellent rate capability and cyclic performance.     

Li4Mn5O12 prepared using l-lysine as additive and its electrochemical performance

l-Lysine was employed as additive to prepare face-centered cubic spinel Li₄Mn₅O₁₂. During the process, l-lysine played important roles such as complexing agent as well as combusting agent and adjusting the pH values of solution. The physical characteristics of Li₄Mn₅O₁₂ were characterized by X-ray diffraction and scanning electron microscopy. The electrochemical capacitance performance of Li₄Mn₅O₁₂ electrode was characterized by cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance spectroscopy. These analyses indicated that Li₄Mn₅O₁₂ was able to deliver 168 F?g^?1 within the potential range of 0–1.4 V at a scan rate of 5 mV?s^?1 in 1 mol?L^?1 Li₂SO₄. Nine hundred cycles later, the capacitance faded to 165 F?g^?1 with cutting down by 0.003 F?g^?1 per cycling period and also can remain 98.2 % of original value, displaying a good cycling performance.     

Surface nitridation induced high electrochemical performance of Li4Ti5O12 using urea as a nitrogen source

Surface nitridation of the Li₄Ti₅O₁₂ particles was carried out by thermal treatment with urea as the nitrogen source in a controllable manner. The titanium nitride (TiN) was formed in the well-dispersed zones on the surface of the Li₄Ti₅O₁₂ particles, depending on the coverage of the nitride. The surface TiN formed led to a great improvement of the conductivity of the oxide. The extent of the surface nitridation exhibited a large effect on electrochemical behaviors of the Li₄Ti₅O₁₂ particles, with the Li₄Ti₅O₁₂/TiN composite (prepared using 6 % urea) providing the best initial capacity and rate capability. Thus, the electrochemical performance of the Li₄Ti₅O₁₂ particles can be achieved by optimizing surface nitridation of the oxide. The chemically inert TiN occupied the surface sites of the Li₄Ti₅O₁₂ particles which may have prevented the electrolyte from decomposition and stabilized the surface structure of the Li₄Ti₅O₁₂ particles, endowing the oxide with excellent cycleability     

Synthesis and characterization of Li4Ti5O12/graphene composite as anode material with enhanced electrochemical performance

The use of graphene as a conductive additive to enhance the rate capability and cycle stability of Li₄Ti₅O₁₂ electrode material has been demonstrated. Li₄Ti₅O₁₂ and its composite with graphene (1.86 wt%) are prepared by ball milling and simple chemical method, respectively. Among the as-synthesized composites, Li₄Ti₅O₁₂ particles uniformly clung to the graphene sheets. When used as an electrode material for lithium ion battery, the composite presents excellent rate performance and high cyclic stability. It is found that the composite displayed high-rate capacity of 118.7 mAh?g^?1 at 20 C. Furthermore, the composite exhibits good cycle stability, retaining over 96 % of its initial capacity after 50 cycles at 10 C. The excellent electrochemical performance is attributed to a decrease in the charge-transfer resistance.     

Solid-state synthesis of graphite carbon-coated Li4Ti5O12 anode for lithium ion batteries

Graphites are widely used for their high electrical conductivity and good thermal and chemical stability. In this work, graphitic carbon-coated lithium titanium (Li₄Ti₅O₁₂/GC) was successfully synthesized by a simple one-step solid-state reaction process with the assistance of sucrose without elevating sintering temperature. The lattice fringe of 0.208 nm clearly seen from the high-resolution transmission electron microscopy (HRTEM) images was assigned to graphite (010). The average grain size of the as-prepared Li₄Ti₅O₁₂/GC was about 100–200 nm, 1 order smaller than that of pure Li₄Ti₅O₁₂ prepared similarly. The rate performance and cycle ability were significantly improved by the hybrid conducting network formed by graphitic carbon on the grains and amorphous carbon between them. The specific capacity retention rate was 66.7 % when discharged at a rate of 12C compared with the capacity obtained at 0.5C. After 300 cycles, the capacity retention was more than 90 % at a high rate of 15C.     

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.     

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.     

High-rate Li4Ti5O12/C composites as anode for lithium-ion batteries

The Li₄Ti₅O₁₂/C composites were synthesized by a simple solid-state reaction at 800 °C for 12 h by using Super P® conductive carbon black as carbon source. X-ray diffraction analysis shows that the Li₄Ti₅O₁₂ with 0, 5, 7.5, and 10 wt% carbon shows similar patterns with cubic spinel structure. Scanning electron microscope shows that Li₄Ti₅O₁₂ aggregated seriously, but the aggregation was inhibited by the addition of Super P® carbon. The results indicate that the addition of 5 wt% carbon during sintering and a further 5 wt% carbon during slurry preparation shows the best rate capability of 110 mAh/g when the cells were charge/discharged at 10 C rate. The comparison of the charge–discharge curves shows that the higher rate improvement should further decrease the particle size of LTO or improve the conductivity of LTO itself.     

磁控溅射法制备的CaCu3Ti4O12薄膜

采用溅射方法成功地制备了CaCu3Ti4O12薄膜,用原子力显微镜、x射线衍射(XRD)仪和LCR分析仪对样品进行形貌、物相结构和介电性质的研究.XRD表明,薄膜比块体的晶格常数小但晶格畸变较大;LCR测量结果显示,在相同温度下薄膜比块体的相对介电常数低,薄膜相对介电常数由低到高转变时对应的温度较高且激活能较大.分析表明:薄膜的相对介电常数较低是样品中晶相含量较低、缺陷较多使内部阻挡层电容大量减小、致密度不高引起的;薄膜中激活能的增大由膜和基底间晶格的不匹配造成膜中的内应力增大、微结构、缺陷和畴等因素决定;介电常数在低频时的急剧增大,意味着存在界面极化,它与界面的缺陷、悬挂键有关.     

Kinetic performance of Li4Ti5O12 anode material synthesized by the solid-state method

Li₄Ti₅O₁₂ anode was successfully synthesized by solid-state method. X-ray diffraction and scanning electron micrographs show that Li₄Ti₅O₁₂ prepared by solid-state method has a purity phase with a uniform particle size in the range of 0.5?C1???m. Cyclic voltammogram reveals that there is a big irreversible capacity for the first cycle. Li₄Ti₅O₁₂ shows a stable cycling stability at 1?C rate. After 152 cycles, the discharge capacity is 213?mAh?g^?1, which keeps 93% of it at the second cycle. Electrochemical impedance spectroscopy shows that the resistance of charge-transfer of Li₄Ti₅O₁₂ electrode decreased with increasing the storage temperatures, and the lithium diffusion coefficient is increased with increasing the storage temperatures, revealing that the kinetics of Li⁺ and electron transfer into the electrodes were much faster at high temperature than that at low temperature. The apparent activation energy of the charge transfer and lithium diffusion can be calculated to be 33.1 and 27.3?kJ?mol^?1, respectively.     

Dielectric properties of Bi4Ti3O12–SrBi4Ti4O15 intergrowth ceramics synthesized by a modified oxalate route

In this study, Bi₄Ti₃O₁₂–SrBi₄Ti₄O₁₅ (BIT–SBTi) intergrowth ferroelectric ceramics was synthesized by a modified oxalate route. The phase formation behaviour, structure, morphology and electrical properties of the intergrowth ceramics were also investigated. The phase formation takes place through intermediate phases like SrBi₂O₄ and Bi₁₂TiO₂₀. The precursor mostly changes to Bi₄Ti₃O₁₂ at 600°C and to BIT–SBTi intergrowth at 800°C. Rietveld analysis of the X-ray diffraction pattern showed that the structure of the intergrowth compound was orthorhombic with lattice parameters a = 5.4408(3), b = 5.4505(1) and c = 74.0851(4) Å. The intergrowth ferroelectrics showed a phase transition at 610°C and a frequency-stable permittivity and dielectric loss behaviour. The intergrowth ferroelectrics also showed a larger 2P_r than their constituents BIT and SBTi.     

A single-crystal study of the electrochemically Li-ion intercalated spinel-type Li4Ti5O12

Single crystals of Li_4 + xTi₅O₁₂ were prepared by means of electrochemical Li-ion intercalation technique using parent Li₄Ti₅O₁₂ single crystals. The obtained Li_4 + xTi₅O₁₂ (x = 1.35) crystallizes in the cubic spinel-related type structure, space group Fd3?m, and lattice parameters of a = 8.346(2) Å and V = 581.3(5) Å³ and Z = 8. The Li-ion intercalated sites were successfully determined to be both the 8a and 16c sites by using the difference Fourier synthesis map. The structure was determined by single-crystal X-ray structure analysis and refined to the conventional value of R = 3.7% for 132 independent observed reflections. The chemical composition has been determined to be Li_5.35Ti₅O₁₂ from the result of site-population refinements. In addition, theoretical electron density distributions and total energy were calculated for three postulated compounds of “Li_4.5Ti_4.5O₁₂” and “Li_4.5 + xTi_4.5O₁₂” with x = 1.5 and 3.0.     

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.     

ZnFe2O4的固相法和水热法制备及其电化学性能研究

本文用固相反应法和水热法制备了ZnFe₂O₄材料,X射线衍射(X-ray diffraction, XRD)表明制备出来的ZnFe₂O₄为尖晶石结构,表面形貌测试 (scanning electron microscopy, SEM) 显示两种方法制备的材料的平均粒径分别为500 nm和200 nm.比表面积测试结果表明,两种方法制备的样品的比表面积分别为136.7 m² g^{-1关键词： 2O₄')" href="#">ZnFe₂O₄ 尖晶石结构 电化学性能 锂离子电池}     

Performance of solid-state hybrid supercapacitor with LiFePO4/AC composite cathode and Li4Ti5O12 as anode

We report the studies on quasi-solid battery-supercapacitor (BatCap) systems fabricated using sol–gel-prepared LiFePO₄ and its composites (LACs) with activated charcoal (AC) as hybrid cathode and Li₄Ti₅O₁₂ powder as anode separator by flexible gel polymer electrolyte (GPE) film. The GPE film comprises 1.0 M lithium trifluoromethane sulfonate (LiTf) solution in ethylene carbonate (EC)–propylene carbonate (PC) mixture, immobilized poly(vinylidene fluoride-co-hexafluoro-propylene) (PVdF-HFP), which is of high ionic conductivity (∼3.8 × 10⁻³ S cm⁻¹ at 25 °C) and electrochemical stability window (∼3 V). The effect of the addition of AC in composite electrode LACs has been analyzed using various techniques such as X-ray diffraction, porosity analysis, and electrochemical methods. The interfaces of composite LACs and GPE film not only offer high rate performance but also show high specific energy (>27.8 Wh kg⁻¹) as compared to the symmetric supercapacitors and pristine lithium iron phosphate (LiFePO₄)-based lithium ion batteries. The full BatCap systems have been characterized by cyclic voltammetry and galvanostatic charge–discharge tests. The BatCap systems with composite electrodes (LACs) offer better cyclic performance as compared to that of pristine LiFePO₄-based BatCap or LIB LiFePO₄/Li₄Ti₅O₁₂.

     

简化共沉淀法制备CaCu3Ti4O12陶瓷及其介电性能研究

具有巨介电常数的CaCu₃Ti₄O₁₂陶瓷是一种理想的高储能密度电容器材料.本文以草酸为沉淀剂、以乙酸铵为调节pH值的定量缓冲剂,获得制备CaCu₃Ti₄O₁₂陶瓷的简化共沉淀法.确定了pH=30为制备前驱粉料的最佳反应条件.通过显微分析和介电性能测量,发现在1040℃—1100℃范围内,随着烧结温度的提高,陶瓷的品粒尺寸增大,非线性系数上升,电位梯度和介电损耗下降,1100℃烧结的试样tanδ最低达到0.04.认为CaCu₃Ti₄O₁₂陶瓷介电损耗包含直流电导分量、低频松弛损耗和高频松弛损耗.低频松弛活化能为0.51 eV.,对应于晶界处的Maxwell-Wagner松弛极化;高频松弛过程活化能为0.10 eV,对应晶粒内部的氧空位缺陷.烧结温度的升高导致晶界电阻下降.