Ting-Feng Yi

Recent advances of Li4Ti5O12 as a promising next generation anode material for high power lithium-ion batteries

Lithium-ion batteries are considered as one of the most promising power sources for energy storage system for a wide variety of applications such as electric vehicles (EVs) or hybrid electric vehicles (HEVs). The anode material often plays an important role in the determination of the safety and cycling life of lithium-ion batteries. Among all anode materials, spinel Li4Ti5O12 has been considered as one the most promising anode candidates for the next-generation large-scale power lithium-ion batteries used for HEVs or EVs because it has a high potential of around 1.55 V (vs. Li/Li+) during charge and discharge, excellent cycle life due to the negligible volume change, and high thermal stability and safety. In this review, we present an overview of the breakthroughs in the past decade in the synthesis and modification of both the chemistry and morphology of Li4Ti5O12. An insight into the future research and further development of Li4Ti5O12 composites is also discussed.

Advanced electrochemical properties of Mo-doped Li4Ti5O12 anode material for power lithium ion battery

Mo6+-doped Li4Ti5−xMoxO12 (0 ≤ x ≤ 0.2) samples have been synthesized via a simple solid-state reaction. The products were characterized by X-ray diffraction (XRD), Raman spectroscopy (RS), scanning electronic microscope (SEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge-discharge testing. Li4Ti5−xMoxO12 (x = 0, 0.05) shows the pure phase structure, but several impurity peak can be detected when x ≥ 0.1. Mo-doping did not change the electrochemical reaction process and basic spinel structure of Li4Ti5O12. The particle size of the Li4Ti5−xMoxO12 (0≤ x ≤ 0.2) sample was about 2–3 μm and Li4Ti5O12 has less agglomeration. Electrochemical results show that the Mo6+-doped Li4Ti5O12 samples display a larger diffusion coefficient of lithium ions, lower charge transfer resistance, higher rate capability and excellent reversibility. The Li4Ti5−xMoxO12 (x = 0.1, 0.15) sample maintained considerable capacities until 6 C rates, whereas pristine Li4Ti5O12 shows a severe capacity decline at high rates. After 100 cycles, the specific reversible capacities of Li4Ti5O12 and Li4Ti4.9Mo0.1O12 are 195.8 and 210.8 mAh g−1, respectively. The superior cycling performance and wide discharge voltage range, as well as simple synthesis route and low synthesis cost of the Mo-doped Li4Ti5O12 are expected to show a potential commercial application.

Structure and Electrochemical Performance of Niobium-Substituted Spinel Lithium Titanium Oxide Synthesized by Solid-State Method

Niobium-substituted Li 4 Ti 5―x Nb x O 12 electrodes (0 ≤ x ≤ 0.25) have been synthesized by a solid-state method. The structure and electrochemical performance of these as prepared powders have been characterized by differential thermal analysis (DTA) and thermogravimetery (TG), X-ray diffraction (XRD), Raman spectroscopy (RS), scanning electron microscopy (SEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and the galvanostatic charge―discharge test. The XRD and RS results show that the Nb 5+ can partially replace Ti 4+ and Li + in the spinel and there are very few oxygen vacancies in the Li 4 Ti 4.95 Nb 0.05 O 12 with a higher electronic conductivity. The Nb-doped lithium titanium oxide samples show smaller particle size and more regular morphology structure, and Li 4 Ti 4.95 Nb 0.05 O 12 has the highest initial discharge capacity and cycling performance among all the samples cycled between 0.0 and 2.0 V. CV implies that the niobium doping is beneficial to the reversible intercalation and deintercalation of Li + . EIS indicates that Li 4 Ti 4.95 Nb 0.05 O 12 has a smaller charge transfer resistance corresponding to a much higher conductivity than that of Li 4 Ti 5 O 12 corresponding to the extraction of Li + ions. The superior cycling performance and wide discharge voltage range, as well as simple synthesis route and low synthesis cost of the Li 4 Ti 4.95 Nb 0.05 O 12 are expected to show a potential commercial application.

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.

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.

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.

Electrochemical intercalation kinetics of lithium ions for spinel LiNi0.5Mn1.5O4 cathode material

The crystal structure and electrochemical intercalation kinetics of spinel LiNi0.5Mn1.5O4 such as the resistance of a solid electrolyte interphase (SEI) film, charge transfer resistance (Rct), surface layer capacitance, exchange current density (i0), and chemical diffusion coefficient are evaluated by Fourier transform infrared (FT-IR) and electrochemical impedance spectroscopy (EIS), respectively. FT-IR shows that LiNi0.5Mn1.5O4 thus obtained has a cubic spinel structure, which can be indexed in a space group of Fd3m with a disordering distribution of Ni. EIS indicates that Rs is almost a constant at different states of charge. The thickness of SEI film increases with increasing of the cell voltage. Rct values evidently decreases when lithium ions deintercalated from the cathode in the voltage range from OCV to 4.6 V, and Rct value increases with increasing potential of deintercalation over 4.7 V. i0 varies between 0.2 and 1.6 mA cm−2, and the solid phase diffusion coefficient of Li+ changed depending on the electrode potential in the range of 10−11–10−9 cm2 s−1.

Effect of Sodium-Site Doping on Enhancing the Lithium Storage Performance of Sodium Lithium Titanate.

Via Li(+), Cu(2+), Y(3+), Ce(4+), and Nb(5+) dopings, a series of Na-site-substituted Na1.9M0.1Li2Ti6O14 are prepared and evaluated as lithium storage host materials. Structural and electrochemical analyses suggest that Na-site substitution by high-valent metal ions can effectively enhance the ionic and electronic conductivities of Na2Li2Ti6O14. As a result, Cu(2+)-, Y(3+)-, Ce(4+)-, and Nb(5+)-doped samples reveal better electrochemical performance than bare Na2Li2Ti6O14, especially for Na1.9Nb0.1Li2Ti6O14, which can deliver the highest reversible charge capacity of 259.4 mAh g(-1) at 100 mA g(-1) among all samples. Even when cycled at higher rates, Na1.9Nb0.1Li2Ti6O14 still can maintain excellent lithium storage capability with the reversible charge capacities of 242.9 mAh g(-1) at 700 mA g(-1), 216.4 mAh g(-1) at 900 mA g(-1), and 190.5 mAh g(-1) at 1100 mA g(-1). In addition, ex situ and in situ observations demonstrate that the zero-strain characteristic should also be responsible for the outstanding lithium storage capability of Na1.9Nb0.1Li2Ti6O14. All of this evidence indicates that Na1.9Nb0.1Li2Ti6O14 is a high-performance anode material for rechargeable lithium ion batteries.