Shuang-Yuan Yang

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.

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.

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.

Effect of temperature on lithium-ion intercalation kinetics of LiMn1.5Ni0.5O4-positive-electrode material

LiMn1.5Ni0.5O4 is synthesized by a sol–gel method and the intercalation kinetics as positive electrode for lithium-ion batteries is investigated by EIS. LiMn1.5Ni0.5O4 particles prepared via sol–gel process possess spinel phase with Fd-3m space group. The charge-transfer resistance, the exchange-current density and the solid-phase diffusion are found as a function of temperature. The apparent activation energy of the exchange current, the charge transfer, and the lithium diffusion in solid phase are also determined, respectively. This result indicates that the effect of the temperature on the cell capacity and the current dependence of the capacity results mainly from the enhancement of the lithium diffusion at elevated temperatures. It can be concluded that LiMn1.5Ni0.5O4 cell has a bad rate cycling performance at elevated temperatures before any modification due to the high diffusion apparent activation energy. The relevant theoretical elucidations thus provide us some useful insights into the design of novel LiMn1.5Ni0.5O4-based positive-electrode materials.