A high-performance hybrid supercapacitor with Li4Ti5O12-C nano-composite prepared by in situ and ex situ carbon modification

In this work, we report on the synthesis of in situ and ex situ carbon-modified Li₄Ti₅O₁₂-C (LTO-C) nano-composite and its application in a hybrid supercapacitor constructed using activated carbon (AC) and LTO-C nano-composite as positive and negative electrodes, respectively. The hybrid capacitors are characterized by galvanostatic charge–discharge, cycle life testing, and electrochemical impedance spectroscopy. The results reveal that the AC/LTO-C hybrid capacitors exhibit high rate capability and long cycle life. In the potential range of 1.5–3.0 V, the AC/LTO-C hybrid system can deliver a specific capacitance of 83 F?g^?1 based on the total mass of AC and LTO-C electrodes at a current density of 60 mA g^?1 (2 C rate). At a higher discharge rate of 980 mA g^?1 (32 C), the capacity is 68 F?g^?1, about 82?% of that at 2 C rate. After 9,000 deep cycles at 32 C, the hybrid capacitor still maintains 84?% of its initial capacitance. The specific energy of such hybrid system is 20 Wh kg^?1, which is at least twice that of an AC/AC system. Combining the high energy density with power capability, the AC/LTO-C hybrid supercapacitor has demonstrated high performance for applications needing high power output.     

High-performance thin-film Li4Ti5O12 electrodes fabricated by using ink-jet printing technique and their electrochemical properties

Li₄Ti₅O₁₂ thin-film anode with high discharge capacity and excellent cycle stability for rechargeable lithium ion batteries was prepared successfully by using ink-jet printing technique. The prepared Li₄Ti₅O₁₂ thin film were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, cyclic voltammograms, and galvanostatic charge–discharge measurements. It was found that the average thickness of 10-layer Li₄Ti₅O₁₂ film was about 1.7~1.8 μm and the active material Li₄Ti₅O₁₂ in the thin film was nano-sized about 50–300 nm. It was also found that the prepared Li₄Ti₅O₁₂ thin film exhibited a high discharge capacity of about 174 mAh/g and the discharge capacity in the 300th cycle retained 88% of the largest discharge capacity at a current density of 10.4 μA/cm² in the potential range of 1.0–2.0 V.     

Boosting the electrochemical performance of Li4Ti5O12 through nitrogen‐doped carbon coating

The poor electronic conductivity restricts the wide applications of Li₄Ti₅O₁₂ as anode materials in Li‐ion batteries. We report a facile approach to fabricate nitrogen‐doped carbon‐coated Li₄Ti₅O₁₂ through carbonizing pyrrole and pyridine at different temperatures. Comparative experiments demonstrated that the carbon content plays a key role in governing the cycling performance and rate capability of Li₄Ti₅O₁₂. The composites with higher carbon content exhibited superior cycling performance, and the composite prepared at 600 °C using pyridine as the carbon source gave the best cycling and rate performance.     

Li4Ti5Ol2的合成及对Li+的离子交换动力学

用溶胶-凝胶法合成出Li4Ti5Ol2, 对其进行了酸改性, 制得锂离子筛IE-H. 测定了IE-H对Li+、Na+的饱和交换容量和pH滴定曲线等离子交换性能, 并对其进行了X射线衍射分析, 同时采用中断接触法判断该离子交换反应的控制机理, 用缩核模型描述离子筛IE-H交换Li+的动力学. 结果表明, 合成出的Li4Ti5Ol2和锂离子筛IE-H均为尖晶石结构; 用不同浓度HNO3溶液处理Li4Ti5Ol2时, Li+的抽出率为19.6%-81.5%, Ti4+的抽出率在4.2%以下; 锂离子筛IE-H 对Li+的饱和交换容量较高, 达到5.95 mmol·g-1, 离子筛IE-H交换Li+的控制步骤是颗粒扩散控制(PDC), 得到了25 ℃, Li+浓度为20.0 mmol·L-1和5.0 mmol·L-1时锂离子筛交换Li+的动力学方程和颗粒扩散系数.     

Nitridation-driven conductive Li4Ti5O12 for lithium ion batteries

To modify oxide structure and introduce a thin conductive film on Li4Ti5O12, thermal nitridation was adopted for the first time. NH3 decomposes surface Li4Ti5O12 to conductive TiN at high temperature, and surprisingly, it also modifies the surface structure in a way to accommodate the single phase Li insertion and extraction. The electrochemically induced Li4+deltaTi5O12 with a TiN coating layer shows great electrochemical properties at high current densities.     

Sb2O3掺杂Li4Ti5O12的电化学性能

采用Sb2O3掺杂改性Li4Ti5O12.用恒流充放电、循环伏安和交流阻抗技术对样品的电化学性能进行了测试.结果显示,当Ti:Sb＝4：1时,首次放电容量高达595.84mAhog-1,首次的库仑效率为45.7％,存在不可逆容量损失.提出了可能的反应机理,并用该机理解释了影响容量衰减的因素.经过20次充放电循环后,容量保持在249.57 mAhog-1.电化学阻抗谱表明,Sb的掺杂使得电化学反应阻抗减小了.     

Study of capacitive properties for LT-Li4Mn5O12 in hybrid supercapacitor

Spinel Li₄Mn₅O₁₂ nanoparticles have been prepared by a very simple sol–gel method. Various initial conditions were studied in order to find the optimal conditions for the synthesis of pure Li₄Mn₅O₁₂. X-ray diffraction results showed that spinel Li₄Mn₅O₁₂ was obtained at a low temperature of 300 °C without any miscellaneous phase. Scanning electron microscope analyses indicated that the prepared Li₄Mn₅O₁₂ powders had a uniform morphology with average particle size of about 50 and 100 nm. The prepared sample was firstly used as a cathode material in an asymmetric Li₄Mn₅O₁₂/AC supercapacitor in aqueous electrolyte. The capacitive properties of the hybrid supercapacitor were tested by cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge–discharge tests. The results showed that Li₄Mn₅O₁₂ annealed at 450 °C for 4 h exhibited the best electrochemical capacitive performance within the potential range of 0–1.4 V in 1 M Li₂SO₄ solution. A maximum specific capacitance of 43 F g⁻¹ based on the total active material weight of the two electrodes was obtained for the Li₄Mn₅O₁₂/AC supercapacitor at a current density of 100 mA g⁻¹. The capacitor showed excellent cycling performance and structure stability via 1,000 cycles.     

In situ neutron diffraction study of Li insertion in Li4Ti5O12

Developing an efficient in situ electrochemical cell for neutron diffraction of electrode materials for Li-ion batteries remains a major technical challenge. We recently published the results of the first experiment carried out with such a cell developed by our group. In order to improve the quality of data we optimized the preparation of the electrode, introduced a gradient in the carbon content, and controlled the porosity. Li₄Ti₅O₁₂ was used as a model material to demonstrate the advantages of the new approach. 10 diffractograms were recorded in situ during the first electrochemical cycle and then refined to obtain the evolution of unit cell parameters, oxygen position, and of the quantitative ratio between Li₄Ti₅O₁₂ and Li₇Ti₅O₁₂.     

煅烧温度对Li4Ti5O12的电化学性能的影响

用溶胶-凝胶法制备了尖晶石型锂钛复合氧化物L i4Ti5O12,并研究了煅烧温度对其电化学性能的影响。结果表明,在800℃煅烧12 h得L i4Ti5O12,晶型良好,粒度较均匀。并且表现出良好的电化学性能,循环10次后比容量仍保持在160 mAh.g-1左右。     

Graphitized carbon and graphene modified Fe2O3/Li4Ti5O12 as anode material for lithium ion batteries

Graphitized carbon (GC) and graphene (GE) modified Fe₂O₃/Li₄Ti₅O₁₂ (LTO) composites have been synthesized via a solid‐state reaction, respectively. The structure, morphology and electrochemical performance of the materials have also been characterized with X‐ray diffraction (XRD), scanning electron microscope (SEM) with an energy dispersive spectroscopy (EDS) system, X‐ray photoelectron spectrometer (XPS), Fourier transform infrared spectroscopy (FTIR) and electrochemical measurements. The discharge capacities of Fe₂O₃/LTO, GC/Fe₂O₃/LTO and GE/Fe₂O₃/LTO are 100.2 mAh g^?1, 207.5 mAh g^?1 and 238.9 mAh g^?1 after 100 cycles at the current density of 176 mA g^?1. The cyclic stability and rate capability are in the order of GE/Fe₂O₃/LTO > GC/Fe₂O₃/LTO > Fe₂O₃/LTO because of the synergistic effect between GC (GE) and Fe₂O₃/LTO. Copyright © 2016 John Wiley & Sons, Ltd.     

Neutron diffraction study of Li4Ti5O12 at low temperatures

The crystal structure of the “zero-strain” positive electrode material Li₄Ti₅O₁₂ was characterized by neutron powder diffraction in the temperature range 3.4 K–300 K. No phase transition was detected, and the thermal evolution of lattice parameters has been evaluated by the 2nd order Grüneisen approximation using the Debye formalism for internal energy and intrinsic anharmonicity contributions. A relatively high Debye temperature θ_D = 689 ± 71 K was determined. The thermal behavior of cation-anion bond lengths in octahedral and tetrahedral environments is discussed. The lithium diffusion pathway in Li₄Ti₅O₁₂ was discussed on the basis of bond-valence modeling.     

Preparation and electrochemical performance of monodisperse Li4Ti5O12 hollow spheres

Monodisperse Li₄Ti₅O₁₂ hollow spheres were prepared by using carbon spheres as templates. Scanning electron microscopy images show hollow spheres that have an average outer diameter of 1.0 μm and an average wall thickness of 60 nm. Compared with Li₄Ti₅O₁₂ solids, the hollow spherical Li₄Ti₅O₁₂ exhibit an excellent rate capability and capacity retention and can be charged/discharged at 10 C (1.7 A g⁻¹) with a specific capacity of 100 mA h g⁻¹, and after 200 charge and discharge cycles at 2 C, their specific capacity remain very stable at 150 mA h g⁻¹. It is believed that the hollow structure has a relatively large contact surface between Li₄Ti₅O₁₂ and liquid electrolyte, resulting in a better electrochemical performance at high charge/discharge rate.     

A strategy for scalable synthesis of Li4Ti5O12/reduced graphene oxide toward high rate lithium-ion batteries

Li₄Ti₅O₁₂/reduced graphene oxide (RGO) composites were prepared via a simple strategy. The as-prepared composites present Li₄Ti₅O₁₂ nanoparticles uniformly immobilized on the RGO sheets. The Li₄Ti₅O₁₂/RGO composites possess excellent electrochemical properties with good cycle stability and high specific capacities of 154 mAh g^− 1 (at 10C) and 149 mAh g^− 1 (at 20C), much higher than the results found in other literatures. The superior electrochemical performance of the Li₄Ti₅O₁₂/RGO composites is attributed to its unique hybrid structure of conductive graphene network with the uniformly dispersed Li₄Ti₅O₁₂ nanoparticles.     

Cycling behaviour of Li/Li4Ti5O12 cells studied by electrochemical impedance spectroscopy

We studied the behaviour of Li/Li(4)Ti(5)O(12) cells by electrochemical impedance spectroscopy to gain insight into the changes at the electrode/electrolyte interfaces during extensive cycling. A simple equivalent-circuit model is able to describe the impedance of the complete battery as a function of both state-of-charge and state-of-degradation. The formation of the solid-electrolyte interface and dendrite growth at the Li metal electrode have a strong influence on the impedance measurements although the battery performance is not significantly affected.     

反应气氛对Li4Ti5O12/C复合材料性能的影响研究

以葡萄糖为碳源,采用固相法制备了Li4Ti5O12/C复合材料。探讨了不同反应气氛（N2/O2）对材料物理性质及电化学性能的影响,并通过XRD、BET、电导率、电性能等测试手段对其进行表征。结果表明：氮气气氛中烧结的样品粒度、比表面积、电导率均比空气中烧结样品大。氮气中烧结样品的倍率性能优于空气中 烧结样品,在以0.1C倍率充放电时,首次放电比容量为166.8mAh/g。两样品1C时,经过50次循环容量保持率差别不大。     

反应气氛对Li4Ti5O12/C复合材料性能的影响

以葡萄糖为碳源,采用固相法制备了Li4Ti5O12/C复合材料. 探讨了不同反应气氛(N2/O2)对材料物理性质及电化学性能的影响,并通过XRD、SEM、BET、电导率、电性能等测试手段对其进行了表征. 结果表明,N2气气氛中烧结的样品粒度、比表面积、电导率均比空气中烧结样品大. N2气中烧结样品的倍率性能优于空气中烧结样品,在以0.1 C倍率充放电时,首次放电比容量为166.8 mA·h/g. 2种样品在1 C时,经过50次循环容量保持率差别不大.     

Kinetic analysis of one-step solid-state reaction for Li4Ti5O12/C

The kinetics of one-step solid-state reaction of Li(4)Ti(5)O(12)/C in a dynamic nitrogen atmosphere was first studied by means of thermogravimetric-differential thermal analysis technique at five different heating rates. According to the double equal-double steps method, the Li(4)Ti(5)O(12)/C solid-state reaction mechanism could be properly described as the Jander equation, which was a three-dimensional diffusion with spherical symmetry, and the reaction mechanism functions were listed as follows: f(α) = (3)/(2)(1 - α)(2/3)[1 - (1 - α)(1/3)](-1), G(α) = [1 - (1 - α)(1/3)](2). In FWO method, average activation energy, frequency factor, and reaction order were 284.40 kJ mol(-1), 2.51 × 10(18) min(-1), and 1.01, respectively. However, the corresponding values in FRL method were 271.70 kJ mol(-1), 1.00 × 10(17) min(-1), and 0.96, respectively. Moreover, the values of enthalpy of activation, Gibbs free energy of activation, and entropy of activation at the peak temperature were 272.06 kJ mol(-1), 240.16 kJ mol(-1), and 44.24 J mol(-1) K(-1), respectively.     

Solution-Based,Anion-Doping of Li4Ti5O12 Nanoflowers for Lithium-Ion Battery Applications

Solution-based, anionic doping represents a convenient strategy with which to improve upon the conductivity of candidate anode materials such as Li₄Ti₅O₁₂ (LTO). As such, novel synthetic hydrothermally-inspired protocols have primarily been devised herein, aimed at the large-scale production of unique halogen-doped, micron-scale, three-dimensional, hierarchical LTO flower-like motifs. Although fluorine (F) doping has been explored, the use of chlorine (Cl) dopants is the primary focus here. Several experimental variables, such as dopant amount, lithium hydroxide concentration, and titanium butoxide purity, were probed and perfected. Furthermore, the Cl doping process did not damage the intrinsic LTO morphology. The analysis, based on interpreting a compilation of SEM, XRD, XPS, and TEM-EDS results, was used to determine an optimized dopant concentration of Cl. Electrochemical tests demonstrated an increased capacity via cycling of 12 % for a Cl-doped sample as compared with pristine LTO. Moreover, the Cl-doped LTO sample described in this study exhibited the highest discharge capacity yet reported at an observed rate of 2C for this material at 143mAh g⁻¹. Overall, these data suggest that the Cl dopant likely enhances not only the ion transport capabilities, but also the overall electrical conductivity of our as-prepared structures. To help explain these favorable findings, theoretical DFT calculations were used to postulate that the electronic conductivity and Li diffusion were likely improved by the presence of increased Ti³⁺ ion concentration coupled with widening of the Li migration channel.     

A study on structure-performance relationship of overcharged 18650-size Li4Ti5O12/LiMn2O4 battery

The electrochemical properties and thermal generation behavior of 18650 Li₄Ti₅O₁₂/LiMn₂O₄ batteries were tested before and after overcharge. The experimental results showed that after overcharge, the specific capacity decreased obviously. The higher the current density was, the more obvious the capacity decreased. For instance, the overcharged battery had almost no capacity when the current density increased to 5C. At the same time, the overcharged battery presented a much more apparent thermal runaway trend compared to the normal battery. After measuring the electrochemical impedance spectroscopy of the batteries and characterizing the crystal structure/nanostructure of the electrode materials, these phenomena could be attributed to the following two reasons: (1) the decomposition of the electrolyte arisen from the overcharge process resulted in increased internal resistance; (2) the thermal runaway due to the increased internal resistance resulted in the damage to crystal structure/nanostructure and aggregation of the electrode materials, thus leading to the secondary decrease in capacity.     

不同形貌结构Li4Ti5O12负极材料的最新进展

由于电子和信息行业的需要, 过去十年锂离子电池得以快速发展. 目前, 锂离子电池仍呈现需求量增长的趋势, 对锂离子电池的安全性要求也越来越高. 因此促使寻找一种比碳/石墨材料更安全, 循环性能更理想的锂离子电池负极材料以满足电动汽车等新兴行业的需求. 尖晶石型Li₄Ti₅O₁₂作为“零应变材料”具有优异的循环稳定性、价格便宜、容易制备、较高的平台电压和良好的安全性, 已成为锂离子动力电池负极材料的研究热点, 被认为是目前最具应用前景的锂离子电池负极材料. 由于形貌选择对于Li₄Ti₅O₁₂材料的电化学性能有着至关重要的影响, 本文综述了球形、多孔(中空)结构、纳微结构、核壳结构等不同形貌Li₄Ti₅O₁₂的合成及其性能研究的最新进展; 总结了各种形貌的优点, 已解决和待解决的问题, 常用合成方法以及各自的适应领域; 并对Li₄Ti₅O₁₂材料的发展趋势进行了展望.