Coating of Al2O3 on layered Li(Mn1/3Ni1/3Co1/3)O2 using CO2 as green precipitant and their improved electrochemical performance for lithium ion batteries

Li(Mn_1/3Ni_1/3Co_1/3)O₂ cathode materials were fabricated by a hydroxide precursor method. Al₂O₃ was coated on the surface of the Li(Mn_1/3Ni_1/3Co_1/3)O₂ through a simple and effective one-step electrostatic self-assembly method. In the coating process, a NHCO₃-H₂CO₃ buffer was formed spontaneously when CO₂ was introduced into the NaAlO₂ solution. Compared with bare Li(Mn_1/3M_1/3Co_1/3)O₂, the surface-modified samples exhibited better cycling performance, rate capability and rate capability retention. The Al₂O₃-coated Li(Mn_1/3Ni_1/3Co_1/3)O₂ electrodes delivered a discharge capacity of about 115 mAh·g^?1 at 2 A·g^?1, but only 84 mAh·g^?1 for the bare one. The capacity retention of the Al₂O₃-coated Li(Mn_1/3Ni_1/3Co_1/3)O₂ was 90.7% after 50 cycles, about 30% higher than that of the pristine one.     

Electrochemical kinetics and cycling performance of nano Li[Li0.23Co0.3Mn0.47]O2 cathode material for lithium ion batteries

Li[Li_0.23Co_0.3Mn_0.47]O₂ cathode material was prepared by a sol–gel method. The material had a primary particle size of about 100 nm, covered by a 30 Å of Li₂CO₃ layer. The material showed promising electrochemical performance when cycled up to 3C rate. The electrochemical kinetics of the first charge was much slower than that of the second charge, due to the complex electrochemical process which involved not only Li⁺ diffusion but also release of oxygen. By taking account of this, the material was pre-charged very slowly (C/50) in the first cycle. This led to excellent electrochemical performance in the following cycles. For instance, the 1C-rate capacity increased to 168 mA h g⁻¹ after 50 cycles, comparing with the 145 mA h g⁻¹ obtained without pre-charging.     

Li1.2Mn0.54Ni0.13Co0.13O2正极材料的Ga2O3包覆改性及电化学性能

首先采用共沉淀方法制备富锂锰基正极材料Li_1.2Mn_0.54Ni_0.13Co_0.13O₂原始样品(P-LRMO),然后通过简单的湿化学法以及低温煅烧方法对其进行不同含量Ga₂O₃原位包覆。透射电子显微镜(TEM)以及X射线光电子能谱(XPS)结果表明在P-LRMO表面成功合成了Ga₂O₃包覆层。电化学测试结果表明：含有3%Ga₂O₃的改性材料G3-LRMO具有最优的电化学性能,其在0.1C倍率(电流密度为25 mA·g^-1)下首圈充放电比容量可以达到270.1 mAh·g^-1,在5C倍率下容量仍能保持127.4 mAh·g^-1,优于未改性材料的90.7 mAh·g^-1,表现出优异的倍率性能。G3-LRMO在1C倍率下循环200圈后仍有190.7 mAh·g^-1的容量,容量保持率由未改性前的72.9%提升至85.6%,证明Ga₂O₃包覆改性能有效提升富锂锰基材料的循环稳定性。并且,G3-LRMO在1C倍率下循环100圈后,电荷转移阻抗(R_ct)为107.7 Ω,远低于未改性材料的251.5 Ω,表明Ga₂O₃包覆层能提高材料的电子传输速率。     

A simple and effective strategy to synthesize Al2O3-coated LiNi0.8Co0.2O2 cathode materials for lithium ion battery

A facile method has been developed to synthesize Al₂O₃-coated LiNi_0.8Co_0.2O₂ cathode materials. The sample was characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and energy dispersive analysis of X-rays (EDAX). Electrochemical tests show that the cycling stability of LiNi_0.8Co_0.2O₂ at room temperature is effectively improved by Al₂O₃ coating. The differential scanning calorimetry (DSC) and high temperature (60 °C) cycling tests indicate that Al₂O₃ coating can also improve the thermal stability of LiNi_0.8Co_0.2O₂, which is attributed to that the coating layer can protect the LiNi_0.8Co_0.2O₂ particles from reacting with the electrolyte.     

Impacts of fluorine on the electrochemical properties of Li[Ni0.5Mn0.5]O2 and Li[Li0.2Ni0.15Co0.1Mn0.55]O2

The impact of the fluorine substitution on the electrochemical properties of layered lithium nickel manganese positive electrode materials for lithium ion batteries is summarized. The addition of a controlled amount of fluorine to the oxygen lattice can effectively improve the capacity retention as well as reduce the impedance of the positive electrode materials. The fluorination of the nickel and manganese based layered oxide cathode material has also led to significant improvement in cycle life and power capability of the battery.     

Li1.2Mn0.54Ni0.13Co0.13O2正极材料的Ga2O3包覆改性及电化学性能

首先采用共沉淀方法制备富锂锰基正极材料 Li_1.2Mn_0.54Ni_0.13Co_0.13O₂原始样品(P-LRMO), 然后通过简单的湿化学法以及低温煅烧方法对其进行不同含量 Ga₂O₃原位包覆。透射电子显微镜(TEM)以及 X射线光电子能谱(XPS)结果表明在 P-LRMO表面成功合成了 Ga₂O₃包覆层。电化学测试结果表明:含有 3 %Ga₂O₃的改性材料 G3-LRMO具有最优的电化学性能, 其在 0.1C倍率(电流密度为 25 mA·g^-1)下首圈充放电比容量可以达到 270.1 mAh·g^-1, 在 5C倍率下容量仍能保持 127.4 mAh·g^-1, 优于未改性材料的 90.7 mAh·g^-1, 表现出优异的倍率性能。G3-LRMO在 1C倍率下循环 200圈后仍有 190.7 mAh·g^-1的容量, 容量保持率由未改性前的 72.9 %提升至 85.6 %, 证明 Ga₂O₃包覆改性能有效提升富锂锰基材料的循环稳定性。并且, G3-LRMO在 1C倍率下循环 100圈后, 电荷转移阻抗(R_ct)为 107.7 Ω, 远低于未改性材料的 251.5 Ω, 表明 Ga₂O₃包覆层能提高材料的电子传输速率。     

CO2 fixation by hydrogenation over coprecipitated Co/Al2O3

CO₂ fixation by hydrogenation over coprecipitated 36 wt.% Co/Al₂O₃ has been studied under a range of reaction conditions to clarify the effects of reaction variables and to determine the kinetics and mechanism of the reaction. A comparison of the results with those reported for CO hydrogenation on the same catalyst indicates that, although product distributions of CO₂ and CO hydrogenation differ, the kinetics and mechanism are similar.     

Li[Ni1/3Mn1/3Co1/3]O2掺杂Mo研究

采用高温固相合成法制备了Li[Ni_(1－x)/3Mn_(1－x)/3Co_(1－x)/3Mo_x]O₂ (x＝0, 0.005, 0.01, 0.02). 对它们进行了XRD, SEM, 循环伏安及充放电容量测试, 结果发现, 掺杂x＝0.01 Mo的样品具有较高的嵌锂容量和良好的循环稳定性, 在20 mA/g放电电流密度和2.3～4.6 V的电压范围内具有211.6 mAh/g的首次放电比容量, 循环50周后放电比容量仍能达到185.9 mAh/g, 容量损失为12.1%.     

Preparation of Mn2O3 and Mn3O4 nanofibers via an electrospinning technique

Thin PVA/manganese acetate composite fibers were prepared by using sol-gel processing and electrospinning technique. After calcinations of the above precursor fibers, Mn₂O₃ and Mn₃O₄ nanofibers with a diameter of 50-200 nm could be successfully obtained. The fibers were characterized by TG-DTA, Scanning electron microscopy, FT-IR, WAXD, respectively. The results showed that the crystalline phase and morphology of nanofibers were largely influenced by the calcination temperature.     

Enhanced electrochemical performance and mechanism study of AgLi1/3Sn2/3O2 for lithium storage

AgLi_1/3Sn_2/3O₂ with delafossite structure is prepared by treating Li₂SnO₃ with molten AgNO₃ and it exhibits improved electrochemical performance compared to Li₂SnO₃.     

Origin of the irreversible plateau (4.5 V) of Li[Li0.182Ni0.182Co0.091Mn0.545]O2 layered material

Layered LiNi_0.4Co_0.2Mn_0.4O₂, Li[Li_0.182Ni_0.182Co_0.091Mn_0.545]O₂, Li[Li_1/3Mn_2/3]O₂ powder materials were prepared by rheological phase method. XRD characterization shows that these samples all have analogous structure to LiCoO₂. Li[Li_0.182Ni_0.182Co_0.091Mn_0.545]O₂ can be considered to be the solid solution of LiNi_0.4Co_0.2Mn_0.4O₂ and Li[Li_1/3Mn_2/3]O₂. Detailed information from XRD, ex situ XPS measurement and electrochemical analysis of these three materials reveals the origin of the irreversible plateau (4.5 V) of Li[Li_0.182Ni_0.182Co_0.091Mn_0.545]O₂ electrode. The irreversible oxidation reaction occurred in the first charging above 4.5 V is ascribed to the contribution of Li[Li_1/3Mn_2/3]O₂ component, which maybe extract Li⁺ from the transition layer in Li[Li_1/3Mn_2/3]O₂ or Li[Li_0.182Ni_0.182Co_0.091Mn_0.545]O₂ through oxygen release. This step also activates Mn⁴⁺ of Li[Li_1/3Mn_2/3]O₂ or Li[Li_0.182Ni_0.182Co_0.091Mn_0.545]O₂, it can be reversibly reduced/oxidized between Mn⁴⁺ and Mn³⁺ in the subsequent cycles.     

Sulfuration of Pt/Al2O3, Pt?Re/Al2O3 and Pt?Ir/Al2O3 catalysts

Three reforming catalysts Pt/Al₂O₃, Pt–Ir/Al₂O₃ and Pt–Re/Al₂O₃ have been sulfurated by H₂S and tested by their activities in benzene hydrogenation. By treatment at 500°C under hydrogen flow only a part of the initial activity of the non-sulfurated catalyst is retained. So only a part of the adsorbed sulfur is easily removed in these conditions. The remaining sulfur for each of the catalysts (Pt/Al₂O₃, Pt–Ir/Al₂O₃ and Pt–Re/Al₂O₃) gives the same atomic ratio of 0.5 sulfur atom per accessible metallic atom.

---

Pt/Al₂O₃, Pt–Ir/Al₂O₃ Pt–Pe/Al₂O₃ . 500°C H₂ . . ., . (Pt/Al₂O₃, Pt–Ir/Al₂O₃ Pt–Pe/Al₂O₃) 0,5.

     

The effect of Li and La on NiO/Al2O3 catalyst for CH4/O2 to syngas reaction

The thermal stability and an 80 h life test over nickel-based catalysts for CH₄/O₂ to syngas reaction were investigated by flow-reactor, XPS, XRD and AAS analysis. The results indicate that the introduction of Li and La not only stabilized the support γ-Al₂O₃ phase, but also suppressed the sintering and loss of nickel, and in addition, enhanced the ability to suppress the carbon-deposition over NiO/Al₂O₃ during the high-temperature reaction.     

TPR studies on steam reforming of 2-propanol on Rh/Al2O3, Ru/Al2O3 and Pd/Al2O3

Reaction pathways for steam reforming of 2-propanol (isopropyl alcohol, IPA) on Rh/Al₂O₃, Ru/Al₂O₃ and Pd/Al₂O₃ have been studied by temperature-programmed reactions (TPRs) of IPA and acetone in the presence of steam. The results of TPRs suggest that that of IPA on Rh/Al₂O₃ and Ru/Al₂O₃ proceeds via acetone, while the steam reforming of IPA on Pd/Al₂O₃ takes place via propene from acetone. This revised version was published online in August 2006 with corrections to the Cover Date.     

High-pressure synthesis of solid solutions between trigonal LiNiO2 and monoclinic Li[Li1/3Ni2/3]O2

High-pressure synthesis in an oxygen-rich atmosphere yields solid solutions between LiNiO₂ and Li₂NiO₃ over the whole concentration range. Structural characterization of the high-pressure oxides was performed using powder XRD, SEM analysis, IR spectroscopy, EPR spectroscopy at 9.23 and 115 GHz and magnetic susceptibility measurements. The crystal structure of Li[Li_xNi_1−x]O₂ ,, changes from trigonal R-3m to monoclinic C2/m at Li-to-Ni ratio of 2 (or ). The incorporation of Li into NiO₂-layers causes a decrease in the mean Li-O and Ni_1-xLi_x-O bond distance. Li and Ni ions in the mixed Ni_1-xLi_xO₂-layers display a tendency to order at a short length scale in such a way that mimics the Li_1/3Ni_2/3-arrangment of the end Li[Li_1/3Ni_2/3]O₂ composition. The charge distribution in these oxides proceeds via Ni³⁺ and Ni⁴⁺ ions.     

Sulfurization of Pt/Al2O3?Cl catalysts. IV. Adsorption sites of H2S on Al2O3, Al2O3?Cl and Pt/Al2O3?Cl

Chemisorption of H₂S on Al₂O₃, Al₂O₃–Cl and Pt/Al₂O₃–Cl has been studied by gravimetry and IR spectroscopy. The influence of the amount of Cl on the H₂S adsorption equilibrium value and the nature of the adsorption sites at low and high coverages are discussed.

---

H₂S Al₂O₃, Al₂O₃–Cl Pt/Al₂O₃–Cl . Cl H₂S, .

     

Skeletal isomerization of 1-butene on ZrO2/Al2O3 treated with sulfate ion

The catalytic activity for skeletal isomerization of 1-butene on ZrO₂ supported on Al₂O₃ and doped with sulfate ion has been found to be higher than on pure ZrO₂/Al₂O₃, Al₂O₃ containing sulfate ion and a commercial SiO₂–Al₂O₃ of H_o<–13.7. Sulfate ion was capable of transforming ZrO₂/Al₂O₃ into a solid superacid.

---

1- ZrO₂, Al₂O₃ , , ZrO₂, , Al₂O₃, , SiO₂–Al₂O₃ H_o < –13,7. ZrO₂/Al₂O₃ .

     

MgO/Al2O3吸附剂对CO2动态吸附性能的研究

以γ- Al₂O₃为载体,采用等体积浸渍法制取MgO/Al₂O₃吸附剂,利用BET、XRD等表征手段对吸附剂进行表征;并通过固定床测量穿透曲线的方法研究其对CO2动态吸附性能的影响,考察了MgO负载量、吸附温度、气体流量等因素对吸附剂吸附CO₂性能的影响,同时还通过多次吸脱附实验考察MgO/Al₂O₃吸附剂的稳定性和再生能力。结果表明,MgO负载量为10%的吸附剂,吸附温度在50℃左右,流量为45mL/min动态吸附量最大;经数次循环后材料的结构性质和吸附性能未见明显变化,可再生性能比较优异,是一种潜在的可工业化应用的CO₂吸附剂。     

层状Li(Ni1/3Co1/3Mn1/3)O2正极材料的合成与电化学性能研究

采用共沉淀-喷雾造粒法制备前驱体, 于750 ℃在空气中煅烧20 h合成出层状Li(Ni_1/3Co_1/3Mn_1/3)O₂正极材料, 并用XRD, SEM, 粒度分析和电性能测试考察了所得材料结构、形貌及电化学性能. 本层状Li(Ni_1/3Co_1/3Mn_1/3)O₂正极材料具有α-NaFeO₂结构, 六方晶系, R3m空间群, 其晶胞参数为a＝0.2865 nm, c＝1.4238 nm. 当材料分别在2.8～4.2, 2.8～4.5 V间进行充放电时, 其首次放电容量分别为173.5和185.4 mAh•g^－1, 首次充放电效率分别为90%和83.8%, 40次循环后容量保持率分别为96%和84%.