Wet-chemistry synthesis of Li4Ti5O12 as anode materials rendering high-rate Li-ion storage

Compared with traditional anode materials, spinel-structured Li₄Ti₅O₁₂ (LTO) with “zero-strain” characteristic offers better cycling stability. In this work, by a wet-chemistry synthesis method, LTO anode materials have been successfully synthesized by using CH₃COOLi·2H₂O and C₁₆H₃₆O₄Ti as raw materials. The results show that sintering conditions significantly affect purity, uniformity of particle sizes, and electrochemical properties of as-prepared LTO materials. The optimized LTO product calcined at 650°C for 20 hours demonstrates small particle sizes and excellent electrochemical performances. It delivers an initial discharge capacity of 242.3 mAh g⁻¹ and remains at 117.4 mAh g⁻¹ over 500 cycles at the current density of 60 mA g⁻¹ in the voltage range of 1.0 to 3.0 V. When current density is increased to 1200 mA g⁻¹, its discharge capacity reaches 115.6 mAh g⁻¹ at the first cycle and remains at 64.6 mAh g⁻¹ after 2500 cycles. The excellent electrochemical performances of LTO can be attributed to the introduction of rutile TiO₂ phase and small particle sizes, which increases electrical conductivity and electrode kinetics of LTO. Therefore, as-synthesized LTO in this study can be regarded as a promising anode candidate material for lithium-ion batteries.     

Insight into effects of graphene and zinc oxide in Li4Ti5O12 as anode materials for Li-ion full-cell battery

Programmable design of nanocomposites of Li₄Ti₅O₁₂ (LTO) conducted through hydrothermal route in the presence of ethylenediamine as basic and capping agent. In this work, effect of ZnO and Graphene on the Li₄Ti₅O₁₂ based nanocomposites as anode materials investigated for Li-Ion battery performances. The full cells battery assembled with LTO based nanocomposites on Cu foil as the anode electrode and commercial LMO (LiMn₂O₄) on aluminum foil as cathode electrode. X-Ray diffraction (XRD), Energy-dispersive X-ray spectroscopy (EDS), Fourier-transform infrared spectroscopy (FT-IR), along with Field Emission Scanning Electron Microscopy (FE-SEM) and Transmission electron microscopy (TEM) images was applied for study the composition and structure of as-prepared samples. The electrochemical lithium storage capacity of prepared nanocomposites was compared with pristine LTO via chronopotentiometry charge-discharge techniques at 1.5–4.0 V and current rate of 100 mA/g. As a result, the electrode which is provided by LTO/TiO₂/ZnO and LTO/TiO₂/graphene nanocomposites provided 765 and 670 mAh/g discharge capacity compared with pristine LTO/TiO₂ (550 mAh/g) after 15 cycles. Based on the obtained results, fabricated nanocomposites can be promising compounds to improve the electrochemical performance of lithium storage.     

Synthesis and characterization of spinel Li4Ti5O12 anode material by oxalic acid-assisted sol–gel method

Anode material Li₄Ti₅O₁₂ for lithium-ion batteries has been prepared by a novel sol–gel method with oxalic acid as a chelating agent and Li₂CO₃ and tetrabutyl titanate [Ti(OC₄H₉)₄] as starting materials. Various initial conditions were studied in order to find the optimal conditions for the synthesis of Li₄Ti₅O₁₂. Oxalic acid used in this method functioned as a fuel, decomposed the metal complexes at low temperature and yielded the free impurity Li₄Ti₅O₁₂ compounds. Thermal analyses (TG–DTA) and XRD data show that powders grown with a spinel structure (Fd3m space group) have been obtained at 800 °C for 16 h. SEM analyses indicated that the prepared Li₄Ti₅O₁₂ powders had a uniform cubic morphology with average particle size of 200 nm. The influence of synthesis conditions on the electrochemical properties was investigated and discussed. The discharge capacity of Li₄Ti₅O₁₂ synthesized with an oxalic acid to titanium ratio R = 1.0 was 171 mAh g⁻¹ in the first cycle and 150 mAh g⁻¹ after 35 cycles under an optimal synthesis condition at 800 °C for 20 h. The very flat discharge and charge curves indicated that the electrochemical reaction based on Ti⁴⁺/Ti³⁺redox couple was a typical two-phase reaction.     

Low temperature performance of nanophase Li4Ti5O12

The low temperature electrochemical performances of 700 and 350 nm Li₄Ti₅O₁₂ were compared. At high rate, room temperature and at low rate and low temperature (0, −10, −20 and −30 °C), the 350 nm Li₄Ti₅O₁₂ showed higher capacity than the 700 nm Li₄Ti₅O₁₂. This difference is proposed to result from the shorter diffusion lengths and higher number of lithium insertion sites in the 350 nm Li₄Ti₅O₁₂ compared to the 700 nm Li₄Ti₅O₁₂. However, at high rate and low temperature, a transition in performance was observed, that is, the 700 nm material had higher capacity. At high rate and low temperature, it is proposed that interparticle contact resistance becomes rate limiting owing to the temperature dependence of this property and this accounts for the different behavior at low temperature and high rate.     

Preparation and characterization of high-density spherical Li4Ti5O12 anode material for lithium secondary batteries

Li₄Ti₅O₁₂ is a very promising anode material for lithium secondary batteries. A novel technique has been developed to prepare Li₄Ti₅O₁₂. The spherical precursor is prepared via an “inner gel” method by TiCl₄ as the raw material. Spherical Li₄Ti₅O₁₂ powders are synthesized by sintering the mixture of spherical precursor and Li₂CO₃. The investigation of XRD, SEM and the determination of the electrochemical properties show that the Li₄Ti₅O₁₂ powders prepared by this method are spherical, and have high tap-density and excellent electrochemical performance. It is tested that the tap-density of the product is as high as 1.64 g cm⁻³, which is remarkably higher than the non spherical Li₄Ti₅O₁₂. Between 1.0 and 3.0 V versus Li, a reversible capacity is as high as 161 mAh g⁻¹ at a current density of 0.08 mA cm⁻².     

Synthesis of lithium insertion material Li4Ti5O12 from rutile TiO2 via surface activation

The synthesis of spinel-type lithium titanate, Li₄Ti₅O₁₂, a promising anode material of secondary lithium-ion battery, from “inert” rutile TiO₂, is investigated. On the purpose of increasing the reactivity of rutile TiO₂, it is treated by concentrated HNO₃. By applying such activated rutile TiO₂ as the titanium source in combination with the cellulose-assisted combustion synthesis, phase-pure Li₄Ti₅O₁₂ is successfully synthesized at 800 °C, at least 150 °C lower than that based on solid-state reaction. The resulted oxide shows a reversible discharge capacity of ～175 mAh g^?1 at 1 C rate, near the theoretical value. The resulted oxide also shows promising high rate performance with a discharge capacity of ～100 mAh g^?1 at 10 C rate and high cycling stability.     

Preparation and research for Li4Ti5O12/AC-based hybrid supercapacitors

尖晶石型Li4Ti5O12因其长循环寿命、高功率以及宽工作温度特性,现已成为新一代超级电容器的重点发展方向。本工作分别选用商品化活性炭、钛酸锂为正、负电极材料,通过“Z型”叠片方式组装成容量达30000 F、内阻值小于0.5 mΩ的混合型超级电容器。考察了不同导电剂添加量、不同正负电极平衡比、单体高低温与安全性能测试情况。结果表明,导电剂含量为8%（质量分数）、正负电极质量比为2.23～2.82时,混合型超级电容器具有30000 F以上的容量和稳定的循环寿命,同时单体内阻能够恒定在0.5 mΩ以下。此外,该混合型超级电容器具有良好的高低温与安全性能,是一种具有广阔应用前景的储能器件。     

Recent research progress of Li4Ti5O12 as anode materials for lithium-ion batteries

锂离子电池凭借诸多优势广泛应用于便携式电子产品（3C）领域,在电动汽车及可穿戴设备方面具有巨大应用前景,是未来最具潜力的储能电池之一。作为一种锂离子电池负极材料,尖晶石型Li₄Ti₅O₁₂相比石墨负极具有较高嵌锂电位,且"零应变材料"的特性决定Li₄Ti₅O₁₂材料具有较好的循环稳定性及热稳定性,从而备受关注。本文简要介绍了钛酸锂（Li₄Ti₅O₁₂）的结构和性能,详细阐明了Li₄Ti₅O₁₂的嵌锂机制、制备及改性方法,总结了相应制备及改性方法对Li₄Ti₅O₁₂材料的充放电特性、循环性能等电化学性能的影响,针对Li₄Ti₅O₁₂的胀气产生原因、机制和胀气解决方法进行简单阐述,并对纯电动乘用车的应用前景提出了几点建议。     

The degradation analysis of lithium-ion storage battery with Li4Ti5O12 anode

钛酸锂作为储能电池负极材料,在长循环和安全性上有突出的表现。通过对室温1C和2C倍率下循环的三元+钴酸锂/钛酸锂储能电池拆解,结合SEM、FTIR、XRD和EIS等分析手段,发现造成容量衰减和阻抗增大的原因出现在正极,由于正极与电解液发生反应,在表面生成界面膜,并且循环过程中界面膜不稳定,进一步消耗活性锂离子导致。另外,对这款电池的产气分析发现,所产生气体的主要成分为CO2和C2H6,原因可能是在制备电池过程中严格控制水分以及在电解液添加剂方面做了改进。     

Electrochemical performance of Li4Ti5O12/carbon nanotubes/graphene composite as an anode material in lithium-ion batteries

A three-dimensional Li₄Ti₅O₁₂/carbon nanotubes/graphene composite (LTO-CNT-G) was prepared by ball-milling method, followed by microwave heating. The as-prepared LTO-CNT-G composite as anode material in lithium-ion battery exhibited superior rate capability and cycle performance under relative high current density compared with that of Li₄Ti₅O₁₂/CNTs (LTO-CNT) and Li₄Ti₅O₁₂/graphene (LTO-G) composites. Graphene nanosheets and CNTs were used to construct 3D conducting networks, leading to faster electron transfer and lower resistance during the lithium ion reversible reaction, which significantly enhanced the electrochemical activity of LTO-CNT-G composite. The synergistic effect of graphene and CNTs can greatly improve the rate capability and cycling stability of Li₄Ti₅O₁₂-based anodes. The LTO-CNT-G composite exhibited a high initial discharge capacity of 172 mAh g^?1 at 0.2 C and 132 mAh g^?1 at 20 C, as well as an excellent cycling stability. The electrochemical impedance spectroscopy demonstrated that the LTO-CNT-G composite has the smallest charge-transfer resistance compared with the LTO-CNT and LTO-G composites, indicating that the fast electron transfer from the electrolyte to the LTO-CNT-G active materials during the lithium ion intercalation/deintercalation owing to the three-dimensional networks of graphene and CNTs.     

Li4Ti5O12/poly(methyl)thiophene asymmetric hybrid electrochemical device

Electrochemically prepared poly(methyl)thiophene is characterized by cyclic voltammetry and galvanometry with an activated carbon counter-electrode. It is then used as a cathode in a laminated plastic asymmetric hybrid electrochemical device with a nano-structured Li₄Ti₅O₁₂ anode. This device displays the specific power of a supercapacitor, with a higher specific energy of 10 Wh/kg, and better cycle-life than a Li-ion battery. The matching ratio of the active materials was found to strongly influence cycle-life.     

Effect of conductive additives on electrochemical performance of Li4Ti5O12 in hybrid capacitor

将添加不同导电剂的钛酸锂负极与活性炭正极组装成混合电容器,研究了不同导电剂对混合电容器性能的影响。利用扫描电子显微镜表征了钛酸锂负极的表面形貌,采用LAND测试仪、电化学工作站对混合电容器的电化学性能进行测试分析,最终确定最佳的导电剂类型。实验表明,以super-P/VGCF为导电剂的混合电容器具有最佳的电化学特性,在0.1 A/g条件下,电容器的比容量达到45.4 F/g,在2 A/g时容量保持率为91.5%;在0.5 A/g条件下,经过10000次循环后,容量保持率为93.2%。     

Electrochemical performance of VOMoO4 as negative electrode material for Li ion batteries

Polycrystalline samples of VOMoO₄ are prepared by a solid-state reaction method and their electrochemical properties are examined in the voltage window 0.005–3 V versus lithium. The reaction mechanism of a VOMoO₄ electrode for Li insertion/extraction is followed by ex situ X-ray diffraction analysis. During initial discharge, a large capacity (1280 mAh g⁻¹) is observed and corresponds to the reaction of ∼10.3 Li. The ex situ XRD patterns indicate the formation of the crystalline phase Li₄MoO₅ during the initial stages of discharge, which transforms irreversibly to amorphous phases on further discharge to 0.005 V. On cycling, the reversible capacity is due to the extraction/insertion of lithium from the amorphous phases. A discharge capacity of 320 mAh g⁻¹ is obtained after 80 cycles when cycling is performed at a current density of 120 mA g⁻¹.     

Mn3O4 nanoparticles on activated carbonitride by soft chemical method for symmetric coin cell supercapacitors

Trimanganese tetraoxide (Mn₃O₄) is limited in supercapacitor application due to its poor electrical conductivity and cycle stability. An effective strategy for improving its electrochemical performance is to be combined with good conductive materials, such as carbon materials. A facile method was developed to prepare a Mn₃O₄/activated carbonitride composite (MONC) as electrode material for supercapacitor. Mn₃O₄ particles with small size were homogeneously grown on the surface of activated carbonitride (NC). Notably, the addition of NC not only improves the electrical conductivity of Mn₃O₄ but also serves as a supporting matrix to maintain the stability of the composite. Electrochemical characterization results show that the specific capacitance of the composite can reach 180 F/g at a current density of 0.5 A/g, which is two times higher than that of Mn₃O₄ at the same current density. After 2000 cycles, the specific capacitance of MONC can be maintained at 80.2% of the initial specific capacitance. The symmetric coin cell (SCC) assembled by MONC as positive and negative electrodes shows large voltage window, excellent cycle stability, and superior energy/power densities. This work will be one of important references for the application of other transition metal oxides in energy storage devices.     

Structural studies of Li4/3Me5/3O4 (Me = Ti,Mn) electrode materials: local structure and electrochemical aspects

Raman scattering spectroscopy have been applied to the study of local structure of Li_4/3Me_5/3O₄ (Me = Ti, Mn) spinel oxides used as electrode materials for rechargeable lithium batteries and hybrid supercapacitors. We report the analysis of their vibrational spectra using both the classical factor group analysis and a local environment model. Electrochemical performance was carried out using a lithium cell with solvent-free solid-polymer. Raman spectra of Li_4/3+xMe_5/3O₄ spinels are compared and analyzed on the basis of structural modifications of their lattices upon lithium insertion.     

Electrochemical behaviors of wax-coated Li powder/Li4Ti5O12 cells

The wax-coated Li powder specimen was effectively synthesized using the drop emulsion technique (DET). The wax layer on the powder was verified by SEM, Focused Ion Beam (FIB), EDX and XPS. The porosity of a sintered wax-coated Li electrode was measured by linear sweep voltammetry (LSV) and compared with that of a bare, i.e., un-coated Li electrode. The electrochemical behavior of the wax-coated Li powder anode cell was examined by the impedance analysis and cyclic testing methods. The cyclic behavior of the wax-coated Li powder anode with the Li₄Ti₅O₁₂ (LTO) cathode cell was examined at a constant current density of 0.35 mA cm⁻² with the cut-off voltages of 1.2–2.0 V at 25 °C. Over 90% of the initial capacity of the cell remained even after the 300th cycle. The wax-coated Li powder was confirmed to be a stable anode material.     

Improvement of 12 V overcharge behavior of LiCoO2 cathode material by LiNi0.8Co0.1Mn0.1O2 addition in a Li-ion cell

The 12 V overcharge instability of the LiCoO₂ cathode material was improved by the physical blending it with LiNi_0.8Co_0.1Mn_0.1O₂. Even though a Li-ion cell containing a LiCoO₂ cathode did not exhibit thermal runaway at 12 V at the 1 C overcharging rate, it showed thermal runaway at the 2 C overcharging rate, and the cell surface temperature reached more than 400 °C. However, the LiCoO₂ cell containing 40, 50, and 60 wt.% LiNi_0.8Co_0.1Mn_0.1O₂ did not exhibit thermal runaway at the 2 C overcharging rate. In conclusion, 60 wt.% LiNi_0.8Co_0.1Mn_0.1O₂ in the LiCoO₂ cathode showed the lowest cell surface temperature of <90 °C even at a 3 C overcharging rate.     

Effects of drying control chemical additive on properties of Li4Ti5O12 negative powders prepared by spray pyrolysis

High-density Li₄Ti₅O₁₂ powders comprising spherical particles are prepared by spray pyrolysis from a solution containing dimethylacetamide (drying control chemical additive) and citric acid and ethylene glycol (organic additives). The prepared powders have high discharge capacities and good cycle properties. The optimum concentration of dimethylacetamide is 0.5 M. The addition of dimethylacetamide to the polymeric spray solutions containing citric acid and ethylene glycol helps in the effective control of the morphology of the Li₄Ti₅O₁₂ powders. At a constant current density of 0.17 mA g⁻¹, the initial discharge capacities of the powders obtained from the spray solution with and without the organic additives are 171 and 167 mAh g⁻¹, respectively.     

Structural and chemical analyses of the new ternary La5MgNi24 phase synthesized by Spark Plasma Sintering and used as negative electrode material for Ni-MH batteries

In the present work, starting from the nominal composition La_0.85Mg_0.15Ni_3.8, samples have been synthesized by SPS (Spark Plasma Sintering) technique at different temperature from 810 °C to 900 °C. The crystallographic structures as well as the phase compositions have been studied by X-ray diffraction (XRD) and Electron-Probe Micro Analysis (EPMA). A new ternary La₅MgNi₂₄ phase with stacking structure (space group R-3m) has been identified and its structure determined by XRD analysis. This (1:4) phase forms at higher temperature than the (5:19) and (2:7) ones. In the present work, the phases (2:7); (5:19); (1:4) and (1:5) coexist for all samples. The substitution of La by Mg only occurs in the layer corresponding to the Laves phase for all the stacking structure phases. The substitution rate (La/Mg ratio in the Laves layer) is equal to half and does not change with the SPS temperature treatment. The hydrogen storage capacity and the electrochemical capacity are not too much influenced by the SPS temperature. In contrast, the cycling stability shows better resistance to corrosion for the samples containing larger amount of (5:19) phase.     

Improvement of cathode performance of LiMn2O4 as a cathode active material for Li ion battery by step-by-step supersonic-wave treatments

As a novel partial substitution and surface modification process, we focused on a step-by-step (double-step) supersonic-wave treatment in a Zn-containing aqueous solution without any heat-treatments, and performed the treatment on LiMn₂O₄ powder. From XRD measurements, it was demonstrated that the lattice constant of LiMn₂O₄ decreased slightly by the treatments, indicating a partial substitution of Zn for Mn. It was also suggested by SEM–EDX and XPS that Zn was well dispersed in/on the samples and their surfaces were modified by Zn compounds. Such a partial substitution and surface modification was supported by crystal structure analysis based on the Rietveld method using neutron diffraction. Cycle performance of LiMn₂O₄ was significantly improved by the step-by-step supersonic-wave treatments. In the processes, it was especially effective for the improvement to apply lower and higher frequencies at the first and second steps, respectively, keeping the power higher. The cathode property improvement was considered due to the partial substitution and the surface coating caused by the step-by-step supersonic-wave treatments. From the investigation on the cathodes and electrolytes after the cycle tests, it was suggested that the crystal structure of LiMn₂O₄ was stabilized by the treatments.