Facile preparation and electrochemical properties of cubic-phase Li4Mn5O12 nanowires

Single crystalline Li4Mn5O12 nanowires with cubic phase were prepared in a large scale by a simple molten salt route without using any surfactant as template; the nanowires exhibited high storage capacity and coulombic efficiency as cathode materials for lithium-ion batteries.     

Li4Mn5O12Cathode for Both 3 V and 4 V Lithium-ion Batteries

Spinel Li₄Mn₅O₁₂ has been of economical and academic interest as cathode material for 3 V lithium-ion batteries(LIBs) since the 1990s. Recent studies also demonstrate that the increase of upper cut-off voltage to 5.0 V can significantly promote the specific capacity and the average operating voltage thus enabling its possibility to be used in 4 V LIBs. It is cost-effective and environmentally benign, shows structural stability without suffering from Jahn-Teller distortion due to the tetravalent oxidation state of Mn ion. However, the undesirable decomposition reactions during high-temperature calcination result in the difficulty of fabricating stoichiometric Li₄Mn₅O₁₂ compounds. Meanwhile, the high capacity led by the enlarged voltage window is combined with fast capacity fading due to the poor reversibility of oxygen redox. In this review, the understanding of the relationship between structure and stochiometric chemistry of Li₄Mn₅O₁₂ is discussed and the ways to improving its electrochemical performance are summarized. Our focus is its recent developments of being used as high voltage cathode or "additive" for layered cathodes. At last, we also provide our perspectives on this material regarding to the target of enabling its application in 4 V LIBs.     

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.     

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.     

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.     

Structure refinement of the spinel-related phases Li2Mn2O4 and Li0.2Mn2O4

The crystal structures of the lithium-rich and lithium-deficient spinel phases Li₂[Mn₂]O₄ and Li_0.2[Mn₂]O₄ have been determined by neutron-diffraction techniques. Structure refinements confirm earlier reports that the [Mn₂]O₄ framework of the Li[Mn₂]O₄ spinel remains intact during both lithium insertion and extraction, but demonstrate unequivocally that in Li₂[Mn₂]O₄ the Li⁺ ions reside in face-shared tetrahedra and octahedra of the cubic-close-packed oxygen-anion array; in Li_0.2[Mn₂]O₄ the Li⁺ ions are located randomly on only the tetrahedral sites of the spinel structure.     

Synthesis and electrochemical performance of nanoporous Li4Ti5O12 anode material for lithium-ion batteries

Nanoporous Li₄Ti₅O₁₂ (N-LTO) was prepared by sol–gel method using monodisperse polystyrene spheres as a template and followed by calcination process. The as-prepared N-LTO has a spinel structure, large special surface area, and nanoporous structure with the pore average diameter of about 100?nm and wall thickness of 50?nm. Electrochemical experiments show that N-LTO exhibits a high initial discharge capacity of 189?mAh?g^?1 at 0.1?C rate cycled between 0.5 and 3.0?V and excellent capacity retention of 170?mAh?g^?1 after 100?cycles. EIS and CV analysis show that N-LTO has a higher mobility for Li⁺ diffusion and a higher exchange current density, indicating an improved electrochemical performance. It is believed that the nanoporous structure has a larger electrode/electrolyte contact area, resulting in better electrochemical properties at high charge/discharge rates.     

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.     

(Li0.91Mn0.09)Mn2O4

Lithium manganese oxide crystals with composition (Li_0.91Mn_0.09)Mn₂O₄ were synthesized by a flux method. The crystals have a structure closely related to that of the cubic spinel LiMn₂O₄, but 9% of the lithium ions in the tetrahedral 4a site are substituted by Mn²⁺ ions. This substitution lowers the average Mn oxidation state below 3.5+, resulting in a Jahn–Teller distortion of the MnO₆ octahedron.     

Synthesis of MgCo2O4-coated Li4Ti5O12 composite anodes using co-precipitation method for lithium-ion batteries

Journal of Solid State Electrochemistry - In the present work, we report synthesis of MgCo2O4 (MCO)/Li4Ti5O12 (LTO) composites for Li-ion battery anodes by a co-precipitation method. The objective...     

Improvement of overcharge performance using Li4Ti5O12 as negative electrode for LiFePO4 power battery

Liquid state soft packed LiFePO₄ cathode lithium ion cells with capacity of 2 Ah were fabricated using graphite or Li₄Ti₅O₁₂ as negative electrodes to investigate the 3 C/10 V overcharge characteristics at room temperature. The LiFePO₄/Li₄Ti₅O₁₂ cell remained safe after the 3 C/10 V overcharge test while the LiFePO₄/graphite cell went to thermal runaway. Temperature and voltage variations during overcharge were recorded and analyzed. The cells after overcharge were disassembled to check the changes of the separated cell components. The results showed that the Li₄Ti₅O₁₂ as anode active material for LiFePO₄ cell showed obvious safety advantage compared with the graphite anode. The lithium ionic diffusion models of Li₄Ti₅O₁₂ anode and graphite anode were built respectively with the help of morphology characterizations performed by scanning electron microscopy. It was found that the different particle shapes and lithium ionic diffusion modes caused different lithium ionic conductivities during overcharge process.     

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.     

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.     

Structure and electrochemical performance of Li4Ti5O12-coated LiMn1.4Ni0.4Cr0.2O4 spinel as 5 V materials

LiMn_1.4Cr_0.2Ni_0.4O₄ and a series of Li₄Ti₅O₁₂/LiMn_1.4Cr_0.2Ni_0.4O₄ composites were prepared by a solution method. XRD reveals that the LTO-coated LiMn_1.4Cr_0.2Ni_0.4O₄ samples have better crystallinity than that of pure LiMn_1.4Cr_0.2Ni_0.4O₄. SEM and EDX show that the surface of LiMn_1.4Cr_0.2Ni_0.4O₄ was successfully coated with Li₄Ti₅O₁₂ particles after the surface modification treatment. Galvanostatic charge–discharge testing indicates 4 wt.% LTO-coated LiMn_1.4Cr_0.2Ni_0.4O₄ has the highest electrochemical performance among three samples, implying that surface modification is beneficial to the reversible intercalation and de-intercalation of Li⁺.     

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.     

Influence of preparation method on the performance of Mn–Ce–O catalysts

Mn–Ce–O catalysts were prepared by the sol–gel method with different citric acid amounts in preparation. The catalysts were characterized by using BET, XRD, TPR, XPS and their catalytic activities in methane combustion were also investigated. Results showed that the surface area, Mn⁴⁺ and O_latt are responsible for the high catalytic activity of Mn–Ce–O catalysts.     

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.     

Study on the capacitance performance of Sn4+-doped V2O5

Sn⁴⁺-doped V₂O₅ cathode materials were prepared by a sol–gel method. The results showed that the modified cathode material was a mixture of V⁴⁺ and V⁵⁺. It was a kind of typical mesopore material with pores of 2–4 nm diameter. Symmetrical curves were obtained by cyclic voltammetry (CV) tests performed at different scanning rates and voltage ranges. In particular, the CV curve showed more obvious rectangle property and better redox properties when the scanning rate was 5 mV s^?1. At the current density of 200 mA g^?1, the maximum specific energy, specific power, and coulomb efficiency of the material were 27.25 mA h?g^?1, 494.87 W?kg^?1, and 97%, respectively. It was indicated that small amounts of Sn⁴⁺ doping would improve the surface morphology and electronic conductivity of V₂O₅. The Sn⁴⁺-doped V₂O₅ showed good capacitance characteristics.     

晶态Li_4Ti_5O_(12)负极材料的制备及其与电解液的兼容性研究

本文以醋酸锂和钛酸丁酯为原料,以冰醋酸为抑制剂,采用溶胶-凝胶法制备了晶态Li4Ti5O12负极材料。与自制的3种电解液和实验室常用的电解液分别组装成锂/钛酸锂半电池。采用恒流充放电测试、循环伏安法(CV)及交流阻抗法(EIS)对其电化学性能进行研究。研究结果发现:在以环状碳酸酯类(EC、PC)和线性碳酸酯类(MEC)为溶剂、以六氟磷酸锂(LiPF6)为电解质的电解液中添加双乙二酸硼酸锂(LiBOB),有利于提高半电池的性能,首次放电比电容达到了198mA.h.g-1,且放电比电容经多次充放电后衰减得较小。而在电解液中加入碳酸亚乙烯酯(VC),半电池的性能有所下降。Li4Ti5O12对电解液表现出较明显的兼容性。