Improving the Electrochemical Performance of the Li4Ti5O12 Electrode in a Rechargeable Magnesium Battery by Lithium–Magnesium Co‐Intercalation

Rechargeable magnesium batteries have attracted recent research attention because of abundant raw materials and their relatively low‐price and high‐safety characteristics. However, the sluggish kinetics of the intercalated Mg²⁺ ions in the electrode materials originates from the high polarizing ability of the Mg²⁺ ion and hinders its electrochemical properties. Here we report a facile approach to improve the electrochemical energy storage capability of the Li₄Ti₅O₁₂ electrode in a Mg battery system by the synergy between Mg²⁺ and Li⁺ ions. By tuning the hybrid electrolyte of Mg²⁺ and Li⁺ ions, both the reversible capacity and the kinetic properties of large Li₄Ti₅O₁₂ nanoparticles attain remarkable improvement.     

锂离子电池负极材料Li_(4-x)K_xTi_5O_(12)结构和电化学性能

采用固相反应的方法制备了尖晶石型Li4Ti5O12和K掺杂Li4-xKxTi5O12(x=0.02,0.04,0.06)。通过XRD、SEM、BET等对制备材料进行了分析。结果表明,K掺杂没有影响立方尖晶石型Li4Ti5O12的合成,同时也没有改变Li4Ti5O12的电化学反应过程。K掺杂Li4-xKxTi5O12具有比Li4Ti5O12小的颗粒粒径和比Li4Ti5O12大的比表面积、孔容积。适量的K掺杂能够明显改善Li4Ti5O12的电化学性能,尤其是倍率性能,但是过多的K掺杂却不利于材料电化学性能的提高。研究表明,Li3.96K0.04Ti5O12体现了相对较好的倍率性能和循环稳定性。0.5C下,首次放电比容量为161mAh·g-1,3.0和5.0C下,容量保持分别为138和121mAh·g-1。3.0C下,200次循环后容量保持为137mAh·g-1。     

Li4Ti5O12 Anode: Structural Design from Material to Electrode and the Construction of Energy Storage Devices

Spinel Li₄Ti₅O₁₂, known as a zero‐strain material, is capable to be a competent anode material for promising applications in state‐of‐art electrochemical energy storage devices (EESDs). Compared with commercial graphite, spinel Li₄Ti₅O₁₂ offers a high operating potential of ∼1.55 V vs Li/Li⁺, negligible volume expansion during Li⁺ intercalation process and excellent thermal stability, leading to high safety and favorable cyclability. Despite the merits of Li₄Ti₅O₁₂ been presented, there still remains the issue of Li₄Ti₅O₁₂ suffering from poor electronic conductivity, manifesting disadvantageous rate performance. Typically, a material modification process of Li₄Ti₅O₁₂ will be proposed to overcome such an issue. However, the previous reports have made few investigations and achievements to analyze the subsequent processes after a material modification process. In this review, we attempt to put considerable interest in complete device design and assembly process with its material structure design (or modification process), electrode structure design and device construction design. Moreover, we have systematically concluded a series of representative design schemes, which can be divided into three major categories involving: (1) nanostructures design, conductive material coating process and doping process on material level; (2) self‐supporting or flexible electrode structure design on electrode level; (3) rational assembling of lithium ion full cell or lithium ion capacitor on device level. We believe that these rational designs can give an advanced performance for Li₄Ti₅O₁₂‐based energy storage device and deliver a deep inspiration.     

Li4Ti5O12/CMK-3复合材料的制备及其作为锂离子电池负极材料的性能

将LiNO₃和Ti(OC₄H₉)₄填填充在有序介孔碳CMK-3 孔道中, 然后烧结合成了Li₄Ti₅O₁₂/CMK-3复合材料. 利用扫描电子显微镜(SEM)、透射电子显微镜(TEM)和X射线衍射(XRD)对其结构和微观形貌进行了表征. 利用差热-热重分析(TG-DTA)测试复合材料中Li₄Ti₅O₁₂的含量. 利用充放电测试、循环伏安和电化学阻抗技术考察了复合材料作为锂离子电池负极材料的性能. 发现Li₄Ti₅O₁₂分布在CMK-3孔道中及其周围, 复合材料的高倍率充放电性能显著优于商品Li₄Ti₅O₁₂, 复合材料中Li₄Ti₅O₁₂的比容量明显高于除去CMK-3的样品(在1C倍率时比容量为117.8 mAh·g^-1), 其0.5C、1C和5C倍率的放电比容量分别为160、143 和131 mAh·g^-1, 库仑效率接近100%, 5C倍率时循环100次的容量损失率只有0.62%. 本研究结果表明CMK-3明显提高了Li₄Ti₅O₁₂的高倍率充放电性能, 可能是CMK-3特殊的孔道结构和良好的导电性减小了Li₄Ti₅O₁₂的粒径并提高了其电导率.     

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.     

Effect of Nb-doping on electrochemical stability of Li4Ti5O12 discharged to 0?V

Li₄Ti_4.95Nb_0.05O₁₂ is synthesized by a citric acid-assistant sol–gel method. X-ray diffraction (XRD) reveals that highly crystalline Li₄Ti_4.95Nb_0.05O₁₂ without any impurity is obtained. The electrochemical performances of the Li₄Ti_4.95Nb_0.05O₁₂ and the Li₄Ti₅O₁₂ in the range from 0 to 2.5 V are investigated. The Li₄Ti_4.95Nb_0.05O₁₂ presents a higher specific capacity and better cycling stability than the Li₄Ti₅O₁₂ due to the improved conductivity. The Li₄Ti_4.95Nb_0.05O₁₂ exhibits a capacity as high as 231.2 mAh g⁻¹ after 100 cycles, which is much higher than the Li₄Ti₅O₁₂ (111.1 mAh g⁻¹). The effect of Nb-doping on electrochemical performance of Li₄Ti₅O₁₂ discharged to 0 V has also been discussed.     

Synthesis and electrochemical performances of Li4Ti4.95Zr0.05O12/C as anode material for lithium-ion batteries

Spinel Li₄Ti_5 − x Zr _x O₁₂/C (x = 0, 0.05) were prepared by a solution method. The structure and morphology of the as-prepared samples were characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The electrochemical performances including charge–discharge (0–2.5 V and 1–2.5 V), cyclic voltammetry, and ac impedance were also investigated. The results revealed that the Li₄Ti_4.95Zr_0.05O₁₂/C had a relatively smaller particle size and more regular morphology than that of Li₄Ti₅O₁₂/C. Zr⁴⁺ doping enhanced the ability of lithium-ion diffusion in the electrode. It delivered a discharge capacity 289.03 mAh g⁻¹ after 50 cycles for the Zr⁴⁺-doped Li₄Ti₅O₁₂/C while it decreased to 264.03 mAh g⁻¹ for the Li₄Ti₅O₁₂/C at the 0.2C discharge to 0 V. Zr⁴⁺ doping did not change the electrochemical process, instead enhanced the electronic conductivity and ionic conductivity. The reversible capacity and cycling performance were effectively improved especially when it was discharged to 0 V.     

Electrochemical behavior and stability of Li4Ti5O12 in a broad voltage window

Electrochemical behavior and stability of spinel Li₄Ti₅O₁₂ are investigated in a broad voltage window (0.0–5.0 V vs. Li/Li⁺). The voltage profile of the Li₄Ti₅O₁₂ electrode shows a plateau region at 1.55 V and two sloped regions below 1.55 V when the electrode is cycled between 0.0 and 2.0 V. It is found that Li₄Ti₅O₁₂ maintains high lithium storage characteristic with the increase of the current density. Moreover, Li₄Ti₅O₁₂ shows excellent rate performance in 0.0–2.0 V and good cyclic performances in 0.0–4.0 and 1.0–5.0 V. Besides, the crystal structure is kept when it is cycled between 0.0 and 5.0 V.     

Sol–gel preparation and electrochemical properties of La-doped Li4Ti5O12 anode material for lithium-ion battery

A sol–gel method using Ti(OC₄H₉)₄, LiCH₃COO·2H₂O, and La(NO₃)₃·6H₂O as starting materials and ethyl acetoacetate as chelating agent to prepare pure and lanthanum (La)-doped Li₄Ti₅O₁₂ is reported. The structure and morphology of the active materials characterized by powder X-ray diffraction and scanning electron microscopy analysis indicate that doping with a certain amount of La³⁺ does not affect the structure of Li₄Ti₅O₁₂, but can restrain the agglomeration of the particles during heat treatment. The electrochemical properties measured by cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge–discharge cycling tests show that La-doped Li₄Ti₅O₁₂ presents a much improved electrochemical performance due to a decrease in charge transfer resistance. At current densities of 1 and 5 C, the La-doped Li₄Ti₅O₁₂ exhibits excellent reversible capacities of 156.16 and 150.79 mAh?g^?1, respectively. The excellent rate capability and good cycling performance make La-doped Li₄Ti₅O₁₂ a promising anode material for lithium-ion batteries in energy storage systems.     

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.     

Li4Ti5O12/(Ag+C)电极材料的固相合成及电化学性能

以Li₂CO₃,TiO₂为原料,葡萄糖为碳源,采用固相煅烧工艺合成了亚微米级的Li₄Ti₅O₁₂/C复合负极材料。并将之与AgNO₃复合,采用固相方法制备出了Ag表面修饰的Li₄Ti₅O₁₂/(Ag+C)复合材料。采用XRD、SEM和TEM测试方法对材料的微结构进行了表征。结果表明,C的存在对Ag单质在Li₄Ti₅O₁₂/C颗粒表面的大量形成起到了积极的促进作用,从而很大程度地提高了Li₄Ti₅O₁₂/C的电导率,因此有效地改善了其电化学性能。在1C倍率下,Li₄Ti₅O₁₂/(Ag+C)复合材料的首次放电容量达到了164 mAh·g^-1。     

The role of Li2MO2 structures (M=metal ion) in the electrochemistry of (x)LiMn0.5Ni0.5O2·(1−x)Li2TiO3 electrodes for lithium-ion batteries

The electrochemical reactions of lithium with layered composite electrodes (x)LiMn_0.5Ni_0.5O₂·(1−x)Li₂TiO₃ were investigated at low voltages. The metal oxide 0.95LiMn_0.5Ni_0.5O₂·0.05Li₂TiO₃ (x=0.95) which can also be represented in layered notation as Li(Mn_0.46Ni_0.46Ti_0.05Li_0.02)O₂, can react with one equivalent of lithium during an initial discharge from 3.2 to 1.4 V vs. Li⁰. The electrochemical reaction, which corresponds to a theoretical capacity of 286 mAh/g, is hypothesized to form Li₂(Mn_0.46Ni_0.46Ti_0.05Li_0.02)O₂ that is isostructural with Li₂MnO₂ and Li₂NiO₂. Similar low-voltage electrochemical behavior is also observed with unsubstituted, standard LiMn_0.5Ni_0.5O₂ electrodes (x=1). In situ X-ray absorption spectroscopy (XAS) data of Li(Mn_0.46Ni_0.46Ti_0.05Li_0.02)O₂ electrodes indicate that the low-voltage (<1.8 V) reaction is associated primarily with the reduction of Mn⁴⁺ to Mn²⁺. Symmetric rocking-chair cells with the configuration Li(Mn_0.46Ni_0.46Ti_0.05Li_0.02)O₂/Li(Mn_0.46Ni_0.46Ti_0.05Li_0.02)O₂ were tested. These electrodes provide a rechargeable capacity in excess of 300 mAh/g when charged and discharged over a 3.3 to −3.3 V range and show an insignificant capacity loss on the initial cycle. These findings have implications for combating the capacity-loss effects at graphite, metal–alloy, or intermetallic negative electrodes against lithium metal-oxide positive electrodes of conventional lithium-ion cells.     

Li4Ti5O12/(Cu+C)复合材料的制备及电化学性能

以Li₄Ti₅O₁₂,Cu(CH₃COO)₂·H₂O和C₆H₁₂O₆为前驱体,化学沉积与热分解结合合成锂离子电池负极材料Li₄Ti₅O₁₂/(Cu+C)。采用X-射线衍射(XRD)、扫描电子显微镜(SEM)、恒流充放电、循环伏安和电化学阻抗方法表征样品的结构、形貌和电化学性能。结果表明,Li₄Ti₅O₁₂表面包覆的Cu与C提高了Li₄Ti₅O₁₂电极材料的导电率,其循环性能和倍率性能得到有效地改善。在0.5C、1C和3C倍率下,经过50次充放电循环,放电比容量分别为168.2、160、140.6 mAh·g^-1,其容量保持率分别为88.7%、84.4%、71.2%。电化学阻抗测试表明,表面包覆的Cu与C使其电荷转移阻抗大幅度减少。     

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.     

Doping-induced memory effect in Li-ion batteries: the case of Al-doped Li4Ti5O12

In Li-ion batteries (LIBs), a memory effect has been revealed in two-phase electrode materials such as olivine LiFePO₄ and anatase TiO₂, which complicates the two-phase transition and influences the estimation of the state of charge. Practical electrode materials are usually optimized by the element doping strategy, however, its impact on the memory effect has not been reported yet. Here we firstly present the doping-induced memory effect in LIBs. Pristine Li₄Ti₅O₁₂ is free from the memory effect, while a distinct memory effect could be induced by Al-doping. After being discharged to a lower cutoff potential, Al-doped Li₄Ti₅O₁₂ exhibits poorer electrochemical kinetics, delivering a larger overpotential during the charging process. This dependence of the overpotential on the discharging cutoff leads to the memory effect in Al-doped Li₄Ti₅O₁₂. Our discovery emphasizes the impact of element doping on the memory effect of electrode materials, and thus has implications for battery design.     

Sulfone-based electrolytes for high-voltage Li-ion batteries

Sulfone-based electrolytes have been investigated as electrolytes for lithium-ion cells using high-voltage positive electrodes, such as LiMn₂O₄ and LiNi_0.5Mn_1.5O₄ spinels, and Li₄Ti₅O₁₂ spinel as negative electrode. In the presence of imide salt (LiTFSI) and ethyl methyl sulfone or tetramethyl sulfone (TMS) electrolytes, the Li₄Ti₅O₁₂/LiMn₂O₄ cell exhibited a specific capacity of 80 mAh g^?1 with an excellent capacity retention after 100 cycles. In a cell with high-voltage LiNi_0.5Mn_1.5O₄ positive electrode and 1 M LiPF₆ in TMS as electrolyte, the capacity reached 110 mAh g^?1 at the C/12 rate. When TMS was blended with ethyl methyl carbonate, the Li₄Ti₅O₁₂/LiNi_0.5Mn_1.5O₄ cell delivered an initial capacity of 80 mAh g^?1 and cycled fairly well for 1000 cycles under 2C rate. The exceptional electrochemical stability of the sulfone electrolytes and their compatibility with the Li₄Ti₅O₁₂ safer and stable anode were the main reason behind the outstanding electrochemical performance observed with high-potential spinel cathode materials. These electrolytes could be promising alternative electrolytes for high-energy density battery applications such as plug-in hybrid and electric vehicles that require a long cycle life.     

Ab initio Studies on Li4+xTi5O12 Compounds as Anode Materials for Lithium‐Ion Batteries

The structural and electronic properties of Li_4+xTi₅O₁₂ compounds (with 0≤x≤6)—to be used as anode materials for lithium‐ion batteries—are studied by means of first principles calculations. The results suggest that Li₄Ti₅O₁₂ can be lithiated to the state Li_8.5Ti₅O₁₂, which provides a theoretical capacity that is about 1.5 times higher than that of the compound lithiated to Li₇Ti₅O₁₂. Further insertion of lithium species into the Li_8.5Ti₅O₁₂ lattice results in a clear structural distortion. The small lattice expansion observed upon lithium insertion (about 0.4 % for the lithiated material Li_8.5Ti₅O₁₂) and the retained [Li₁Ti₅]^16dO₁₂ framework indicate that the insertion/extraction process is reversible. Furthermore, the predicted intercalation potentials are 1.48 and 0.05 V (vs Li/Li⁺) for the Li₄Ti₅O₁₂/Li₇Ti₅O₁₂ and Li₇Ti₅O₁₂/Li_8.5Ti₅O₁₂ composition ranges, respectively. Electronic‐structure analysis shows that the lithiated states Li_4+xTi₅O₁₂ are metallic, which is indicative of good electronic‐conduction properties.     

Li ion diffusion in Li4Ti5O12 thin film electrode prepared by PVP sol-gel method

Li₄Ti₅O₁₂ thin films for rechargeable lithium batteries were prepared by a sol-gel method with poly(vinylpyrrolidone). Interfacial properties of lithium insertion into Li₄Ti₅O₁₂ thin film were examined by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and potentiostatic intermittent titration technique (PITT). Redox peaks in CV were very sharp even at a fast scan rate of 50 mV s⁻¹, indicating that Li₄Ti₅O₁₂ thin film had a fast electrochemical response, and that an apparent chemical diffusion coefficient of Li⁺ ion was estimated to be 6.8×10⁻¹¹ cm² s⁻¹ from a dependence of peak current on sweep rates. From EIS, it can be seen that Li⁺ ions become more mobile at 1.55 V vs. Li/Li⁺, corresponding to a two-phase region, and the chemical diffusion coefficients of Li⁺ ion ranged from 10⁻¹⁰ to 10⁻¹² cm² s⁻¹ at various potentials. The chemical diffusion coefficients of Li⁺ ion in Li₄Ti₅O₁₂ were also estimated from PITT. They were in a range of 10⁻¹¹-10⁻¹² cm² s⁻¹.     

Electrospun Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript>/Li<Subscript>2</Subscript>TiO<Subscript>3</Subscript> composite nanofibers for enhanced high-rate lithium ion batteries

Li₄Ti₅O₁₂/Li₂TiO₃ composite nanofibers with the mean diameter of ca. 60 nm have been synthesized via facile electrospinning. When the molar ratio of Li to Ti is 4.8:5, the Li₄Ti₅O₁₂/Li₂TiO₃ composite nanofibers exhibit initial discharge capacity of 216.07 mAh g^?1 at 0.1 C, rate capability of 151 mAh g^?1 after being cycled at 20 C, and cycling stability of 122.93 mAh g^?1 after 1000 cycles at 20 C. Compared with pure Li₄Ti₅O₁₂ nanofibers and Li₂TiO₃ nanofibers, Li₄Ti₅O₁₂/Li₂TiO₃ composite nanofibers show better performance when used as anode materials for lithium ion batteries. The enhanced electrochemical performances are explained by the incorporation of appropriate Li₂TiO₃ which could strengthen the structure stability of the hosted materials and has fast Li⁺-conductor characteristics, and the nanostructure of nanofibers which could offer high specific area between the active materials and electrolyte and shorten diffusion paths for ionic transport and electronic conduction. Our new findings provide an effective synthetic way to produce high-performance Li₄Ti₅O₁₂ anodes for lithium rechargeable batteries.     

Synthesis and electrochemical properties of spinel Li4Ti5O12−x Cl x anode materials for lithium-ion batteries

Li₄Ti₅O_12−x Cl _x (0 ≤ x ≤ 0.3) compounds were synthesized successfully via high temperature solid-state reaction. X-ray diffraction and scanning electron microscopy were used to characterize their structure and morphology. Cyclic voltammetry, electrochemical impedance spectroscopy, and charge/discharge cycling performance tests were used to characterize their electrochemical properties. The results showed that the Li₄Ti₅O_12−x Cl _x (0 ≤ x ≤ 0.3) compounds were well-crystallized pure spinel phase and that the grain sizes of the samples were about 3–8 μm. The Li₄Ti₅O_11.8Cl_0.2 sample presented the best discharge capacity among all the samples and showed better reversibility and higher cyclic stability compared with pristine Li₄Ti₅O₁₂. When the discharge rate was 0.5 C, the Li₄Ti₅O_11.8Cl_0.2 sample presented the superior discharge capacity of 148.7 mAh g⁻¹, while that of the pristine Li₄Ti₅O₁₂ was 129.8 mAh g⁻¹; when the discharge rate was 2 C, the Li₄Ti₅O_11.8Cl_0.2 sample presented the discharge capacity of 120.7 mAh g⁻¹, while that of the pristine Li₄Ti₅O₁₂ was only 89.8 mAh g⁻¹.