Yan-Rong Zhu

Rapid Charge–Discharge Property of Li4Ti5O12–TiO2 Nanosheet and Nanotube Composites as Anode Material for Power Lithium-Ion Batteries

Well-defined Li4Ti5O12-TiO2 nanosheet and nanotube composites have been synthesized by a solvothermal process. The combination of in situ generated rutile-TiO2 in Li4Ti5O12 nanosheets or nanotubes is favorable for reducing the electrode polarization, and Li4Ti5O12-TiO2 nanocomposites show faster lithium insertion/extraction kinetics than that of pristine Li4Ti5O12 during cycling. Li4Ti5O12-TiO2 electrodes also display lower charge-transfer resistance and higher lithium diffusion coefficients than pristine Li4Ti5O12. Therefore, Li4Ti5O12-TiO2 electrodes display lower charge-transfer resistance and higher lithium diffusion coefficients. This reveals that the in situ TiO2 modification improves the electronic conductivity and electrochemical activity of the electrode in the local environment, resulting in its relatively higher capacity at high charge-discharge rate. Li4Ti5O12-TiO2 nanocomposite with a Li/Ti ratio of 3.8:5 exhibits the lowest charge-transfer resistance and the highest lithium diffusion coefficient among all samples, and it shows a much improved rate capability and specific capacity in comparison with pristine Li4Ti5O12 when charging and discharging at a 10 C rate. The improved high-rate capability, cycling stability, and fast charge-discharge performance of Li4Ti5O12-TiO2 nanocomposites can be ascribed to the improvement of electrochemical reversibility, lithium ion diffusion, and conductivity by in situ TiO2 modification.

Recent developments in the doping and surface modification of LiFePO4 as cathode material for power lithium ion battery

Lithium ion batteries have become attractive for portable devices due to their higher energy density compared to other systems. With a growing interest to develop rechargeable batteries for electric vehicles, lithium iron phosphate (LiFePO4) is considered to replace the currently used LiCoO2 cathodes in lithium ion cells. LiFePO4 is a technically important cathode material for new-generation power lithium ion battery applications because of its abundance in raw materials, environmental friendliness, perfect cycling performance, and safety characteristics. However, the commercial use of LiFePO4 cathode material has been hindered to date by their low electronic conductivity. This review highlights the recent progress in improving and understanding the electrochemical performance like the rate ability and cycling performance of LiFePO4 cathode. This review sums up some important researches related to LiFePO4 cathode material, including doping and coating on surface. Doping elements with coating conductive film is an effective way to improve its rate ability.

Li5Cr7Ti6O25 as a novel negative electrode material for lithium-ion batteries

Novel submicron Li5Cr7Ti6O25, which exhibits excellent rate capability, high cycling stability and fast charge-discharge performance is constructed using a facile sol-gel method. The insights obtained from this study will benefit the design of new negative electrode materials for lithium-ion batteries.

Understanding the Thermal and Mechanical Stabilities of Olivine-Type LiMPO4 (M = Fe, Mn) as Cathode Materials for Rechargeable Lithium Batteries from First Principles

To elucidate the microscopic origin of the difference behaviors, first-principles calculations were performed to investigate the thermal and mechanical stabilities of LixFePO4 and LixMnPO4. The calculated free energies suggested that LiFePO4 and LiMnPO4 are thermal stable with respect to relevant oxides both in their pristine and fully delithiated states. According to the calculations, it can be identified that the shear deformations are more easier to occur with respect to the volume compressions in LixFePO4 and LixMnPO4, and this phenomenon is related to M-O(I) and M-O(II) bonds. Typically for MnPO4, Li(+) extraction from the host structures further weakens the Mn-O(I) bonds by about 33%, and it thus becomes very brittle. The shear anisotropy (AG) of MnPO4 is abnormally large and has already reached 19.05 %, which is about 6 times as large as that of FePO4. Therefore, shear deformations and dislocations occur easily in MnPO4. Moreover, as the Mn-O(I) bonds in MnPO4 are mainly spread within the {101} and {1̅01} crystal planes, the relevant slip systems thus allow the recombination of bonds at the interfaces, leading to the experimentally observed phase transformation. It can be concluded that mechanical reason will play an important role for the poor cycling performance of MnPO4.

Enhanced fast charge–discharge performance of Li4Ti5O12 as anode materials for lithium-ion batteries by Ce and CeO2 modification using a facile method

A facile solid-state method to improve the fast charge–discharge and kinetic performance of Li4Ti5O12 in lithium-ion batteries by Ce and CeO2 in situ modification is presented in this work. XRD shows that the Ce doping and CeO2 modification do not change the spinel structure of Li4Ti5O12. Little Ce doping (Ti/Ce = 4.9:0.1 and Ti/Ce = 4.85:0.15) reduces the lattice parameter of doped Li4Ti5O12, but more Ce4+ doping (Ti/Ce = 4.8:0.2) increases the lattice parameter due to the large ionic radius of Ce4+. Raman spectra reveal that CeO2 is not completely incorporated into the host structure and leads to the formation of a uniform coating on the surface of Li4Ti5O12. The doping of Ce4+ and the combination with in situ generated CeO2 in Li4Ti5O12 are favorable for reducing the electrode polarization and charge-transfer resistance and improve the lithium insertion/extraction kinetics of Li4Ti5O12, resulting in its relatively higher capacity at a high charge–discharge rate. The Ce-doped Li4Ti5O12–CeO2 composites show a much improved rate capability and cycling stability compared with pristine Li4Ti5O12 at a 10 C charge–discharge rate in a broad voltage window (0–2.5 V). The introduction of Ce and CeO2 enhances not only the electric conductivity of Li4Ti5O12, but also the lithium ion diffusivity in Li4Ti5O12, resulting in a significantly improved high-rate capability, cycling stability, and fast charge–discharge performance of Li4Ti5O12.

Enhanced electrochemical performanceof Li-rich low-Co Li 1.2 Mn 0.56 Ni 0.16 Co 0.08− x Al x O 2 (0≤ x ≤0.08) as cathode materials

Layered Li1.2Mn0.56Ni0.16Co0.08−xAlxO2 (0 ≤ x ≤ 0.08) cathode materials were successfully synthesized by a sol-gel method. X-ray diffraction and the refinement data indicate that all materials have typical α-NaFeO2 structure with R-3m space group, and the a-axis has almost no change, but there is a slight decrease in the c lattice parameter as well as the cell volume. Scanning electron microscopy and high resolution transmission electron microscopy prove that all the samples have uniform particle size of about 200–300 nm and smooth surface. The energy-dispersive X-ray spectroscopy mapping shows that aluminum has been homogeneously doped in the Li1.2Mn0.56Ni0.16Co0.08O2 cathode material. The cyclic voltammetry and electrochemical impedance spectroscopy reveal that appropriate Al-doping contributes to the reversible lithium-ion insertion and extraction, and then reduces the electrochemical polarization and charge transfer resistance. Li1.2Mn0.56Ni0.16Co0.08−xAlxO2 (x = 0.05) shows the lowest charge transfer resistance and the highest lithium-ion diffusion coefficient among all the samples. The Li-rich electrodes with low-level Al doping shows a much higher discharge capacity than the pristine one, especially the Li1.2Mn0.56Ni0.16Co0.08−xAlxO2 (x = 0.05) sample, which exhibits greater rate capacity and better fast charge-discharge performance than the other samples. Li1.2Mn0.56Ni0.16Co0.08−xAlxO2 (x = 0.05) also exhibits higher discharge capacity than the pristine one at each cycle at 55°C. These results clearly indicate that the high rate capacity together with a good high rate cycling performance and high-temperature performance of the low-Co Li1.2Mn0.56Ni0.16Co0.08−xAlxO2 (x=0.05) is a promising alternative to next-generation lithium-ion batteries.摘要本文采用溶胶凝胶法成功合成了层状Li1.2Mn0.56Ni0.16Co0.08−xAlxO2 (0≤x≤0.08)正极材料. XRD及其精细结果表明, 所有的材料均具有 典型的α-NaFeO2结构, 属于R-3m空间群. Al掺杂后的材料晶胞参数a值几乎不变, 但是c值和晶胞体积略微减小. SEM和HRTEM证明了所有 样品均具有200–300 nm的均一粒径和光滑的表面. EDS谱图说明Al已经成功地进入了Li1.2Mn0.56Ni0.16Co0.08O2正极材料的晶格. CV和EIS说 明适量的Al掺杂有利于锂离子的可逆脱嵌, 减小了材料的电化学极化和电荷转移电阻. 在所有样品中, Li1.2Mn0.56Ni0.16Co0.08−xAlxO2 (x=0.05) 展示了最小的电荷转移电阻和最高的锂离子扩散系数. 电化学性能测试表明, 少量Al掺杂的富锂电极具有比纯样更高的放电容量, 特 别是Li1.2Mn0.56Ni0.16Co0.08−xAlxO2 (x=0.05)样品具有比其他样品更高的倍率容量和更好的快速充放电性能. 55°C时, Li1.2Mn0.56Ni0.16Co0.08−xAlxO2 (x=0.05)展示了比纯样更高的放电容量. 高的倍率容量、好的高倍率循环稳定性以及优秀的高温性能使得低钴Li1.2Mn0.56Ni0.16Co0.08−xAlxO2 (x=0.05)材料成为下一代锂离子电池颇具前景的选择.

Hollow and hierarchical Na2Li2Ti6O14 microspheres with high electrochemical performance as anode material for lithium-ion battery

Relying on a solvent thermal method, spherical Na2Li2Ti6O14 was synthesized. All samples prepared by this method are hollow and hierarchical structures with the size of about 2–3 μm, which are assembled by many primary nanoparticles (~300 nm). Particle morphology analysis shows that with the increase of temperature, the porosity increases and the hollow structure becomes more obvious. Na2Li2Ti6O14 obtained at 800°C exhibits the best electrochemical performance among all samples. Charge-discharge results show that Na2Li2Ti6O14 prepared at 800°C can delivers a reversible capacity of 220.1, 181.7, 161.6, 144.2, 118.1 and 97.2 mA h g−1 at 50, 140, 280, 560, 1400, 2800 mA g−1. However, Na2Li2Ti6O14-bulk only delivers a reversible capacity of 187, 125.3, 108.3, 88.7, 69.2 and 54.8 mA h g−1 at the same current densities. The high electrochemical performances of the as-prepared materials can be attributed to the distinctive hollow and hierarchical spheres, which could effectively reduce the diffusion distance of Li ions, increase the contact area between electrodes and electrolyte, and buffer the volume changes during Li ion intercalation/deintercalation processes.摘要本文采用溶剂热法合成了球形Na2Li2Ti6O14材料. 所有溶剂热法制备得到的材料均具有中空的分级结构, 并且均由粒径约为300 nm的 初级粒子通过组装形成, 微球的直径大约为2−3 μm. 粒子的形貌分析表明, 随着合成温度的增加, 孔隙率逐渐增加且中空结构更加明显. 在 所有材料中, 800°C合成的Na2Li2Ti6O14具有最好的电化学性能. 充放电测试表明, 在电流密度为50、140、280、560、1400、2800 mA g−1时, 800°C合成的Na2Li2Ti6O14样品的可逆容量分别为220.1、181.7、161.6、144.2、118.1、97.2 mA h g−1. 但是在相同电流密度条件下, 块状的 Na2Li2Ti6O14的可逆容量分别为187、125.3、108.3、88.7、69.2、54.8 mA h g−1. 中空分级结构微球可以有效地减小锂离子的扩散距离、增 加电极与电解液的接触面积、以及缓冲锂离子嵌脱过程中的体积变化, 从而使其具有较高的电化学性能.

Robust Strategy for Crafting Li5Cr7Ti6O25@CeO2 Composites as High-Performance Anode Material for Lithium-Ion Battery

A facile strategy was developed to prepare Li5Cr7Ti6O25@CeO2 composites as a high-performance anode material. X-ray diffraction (XRD) and Rietveld refinement results show that the CeO2 coating does not alter the structure of Li5Cr7Ti6O25 but increases the lattice parameter. Scanning electron microscopy (SEM) indicates that all samples have similar morphologies with a homogeneous particle distribution in the range of 100-500 nm. Energy-dispersive spectroscopy (EDS) mapping and high-resolution transmission electron microscopy (HRTEM) prove that CeO2 layer successfully formed a coating layer on a surface of Li5Cr7Ti6O25 particles and supplied a good conductive connection between the Li5Cr7Ti6O25 particles. The electrochemical characterization reveals that Li5Cr7Ti6O25@CeO2 (3 wt %) electrode shows the highest reversibility of the insertion and deinsertion behavior of Li ion, the smallest electrochemical polarization, the best lithium-ion mobility among all electrodes, and a better electrochemical activity than the pristine one. Therefore, Li5Cr7Ti6O25@CeO2 (3 wt %) electrode indicates the highest delithiation and lithiation capacities at each rate. At 5 C charge-discharge rate, the pristine Li5Cr7Ti6O25 only delivers an initial delithiation capacity of ∼94.7 mAh g-1, and the delithiation capacity merely achieves 87.4 mAh g-1 even after 100 cycles. However, Li5Cr7Ti6O25@CeO2 (3 wt %) delivers an initial delithiation capacity of 107.5 mAh·g-1, and the delithiation capacity also reaches 100.5 mAh g-1 even after 100 cycles. The cerium dioxide modification is a direct and efficient approach to improve the delithiation and lithiation capacities and cycle property of Li5Cr7Ti6O25 at large current densities.

Thermodynamic stability and transport properties of tavorite LiFeSO4F as a cathode material for lithium-ion batteries

First principles computation methods play an important role in developing and optimizing new energy storage and conversion materials. The thermodynamic stability, transport properties of the carriers and the lithium diffusion mechanisms of LiFeSO4F compounds are calculated by using the first principles computation. According to the calculated formation enthalpies and electronic properties, it can be concluded that both LiFeSO4F and delithiated FeSO4F have high thermodynamic stability during cycling. Band structure analysis reveals that the conduction and valence bands that are mainly composed of Fe3d states are rather localized, leading to large band gaps and effective masses of the carriers. LiFeSO4F and FeSO4F thus exhibit poor electronic conductivities. To improve the electronic conductance of the materials, introduction of delocalized states in the band gap region via doping or nano-crystallization of the electrode material is still necessary. Further investigations on lithium diffusion dynamics suggest that suitable amounts of lithium vacancies at the 2i sites are particularly crucial. Under high lithium concentration conditions, these vacancies are very helpful to initiate the transfer of lithium into the empty positions by eliminating the Li–Li repulsions and then activate the diffusion of lithium through the channels. While under low lithium concentration conditions, they can act as intermediate sites effectively for several high-speed diffusion channels. As the calculated activation energies for the possible diffusion paths (0.185–0.563 eV) are very small, LiFeSO4F and FeSO4F thus show excellent ionic conductance.

Improved electrochemical performance of Ag-modified Li4Ti5O12 anode material in a broad voltage window

AbstractLi4Ti5O12/Ag composites were synthesized by a solid-state method. The effect of Ag modification on the physical and electrochemical properties is discussed by the characterizations of X-ray diffraction, scanning electron microscopy, cyclic voltammetry, electrochemical impedance spectroscopy, cycling and rate tests. The lattice parameter of Li4Ti5O12 with a low Ag content is almost not changed, but the lattice parameter becomes larger due to the high content of Ag. Li4Ti5O12/Ag material has a uniform particle size which is about 1