The effects of Ni and Li doping on the performance of lithium manganese oxide material for lithium secondary batteries

Layered Li_0.7[M_1/6Mn_5/6]O₂ (M=Li, Ni) was synthesized using a sol-gel method. P2-Na_0.7[M_1/6Mn_5/6]O₂ precursor was first synthesized by a sol-gel method, and then O2-Li_0.7[M_1/6Mn_5/6]O₂ was prepared by an ion exchange of Li for Na in P2-Na_0.7[M_1/6Mn_5/6]O₂ precursor. From charge/discharge curves, it was seen that Li_0.7[Li_1/6Mn_5/6]O₂ has two plateaus similar to those observed from a spinel structure, but Li_0.7[Ni_1/6Mn_5/6]O₂ holds a single plateau as observed from a typical layered structure. It was considered that Li_0.7[Li_1/6Mn_5/6]O₂ undergoes a phase transformation from layered to spinel structure during the charge/discharge cycle, but Li_0.7[Ni_1/6Mn_5/6]O₂ maintains O2-layered structure after the cycles. Li_0.7[Ni_1/6Mn_5/6]O₂ was higher in discharge capacity and retention rate than Li_0.7[Li_1/6Mn_5/6]O₂.     

Fractionation and enrichment of CLA isomers by selective esterification with Candida rugosa lipase

A commercial product of CLA contains almost equal amounts of cis-9,trans-11 (c9,t11)-CLA and trans-10,cis-12 (t10,c12)-CLA. We attempted to enrich the two isomers by a two-step selective esterification using Candida rugosa lipase that acted on c9,t11-CLA more strongly than on t10,c12-CLA. An FFA mixture containing CLA isomers was esterified with an equimolar amount of lauryl alcohol in a mixture of 20% water and the lipase. When the esterification of total FA reached 50%, two isomers were fractionated in a good yield: t10,c12-CLA was enriched in FFA, and c9,t11-CLA was recovered in lauryl esters. The FFA were esterified again to enrich t10,c12-CLA. At 27.3% esterification of total FA, the t10,c12-CLA content in FFA increased to 64.8 wt% with 89.3% recovery: The ratio of the content of t10,c12-CLA to that of two isomers was 95.9%. Lauryl esters obtained by the single esterification were employed for enrichment of c9,t11-CLA. After the esters were hydrolyzed, the resulting FFA were esterified again with lauryl alcohol. At 62.0% esterification of total FA, the c9,t11-CLA content in lauryl esters increased to 73.3 wt% with 79.4% recovery: The ratio of the content of c9,t11-CLA to that of two isomers was 95.6%. In a 600-g-scale purification, molecular distillation was effective in separating the reaction mixture into lauryl alcohol, FFA, and lauryl ester fractions.     

均相玻璃态高分子中溶剂扩散系数的数学模型

以自由体积理论为基础 ,提出改良的玻璃态高分子中溶剂扩散系数的数学模型 .模型推导过程中考虑了溶剂可塑化效应对高分子凝聚态的影响 ,并以明确的物理概念计算玻璃态聚合物的自由体积 .对橡胶态适用的自由体积参数在此模型中保持有效 ,所引入的表达溶剂可塑化效应的唯一参数 β可以通过计算玻璃化温度来确定 .所以 ,本模型中无可调节参数存在 ,具有完全可预测性 .以芳香族溶剂苯、甲苯、乙苯在玻璃态聚苯乙烯和聚甲基丙烯酸甲酯中的扩散系数为例对模型进行验证 ,理论计算结果和实验值取得良好一致     

Effect of oxygen flow rate on the structural and electrochemical properties of lithium nickel oxides synthesized by the sol–gel method

The structural and electrochemical properties of LiNiO₂ powders were investigated as a function of the oxygen flow rate employed in the preparation of lithium nickel oxide. It was found that oxygen played an important role in the synthesis of highly crystallized LiNiO₂(R3¯m). In the crystallization process of LiNiO₂, a deficiency of oxygen in the calcination reactor induced the formation of impurities and cubic rock-salt structure (Fm3m) in LiNiO₂ powders. For LiNiO₂ prepared at higher oxygen flow rates, the electrode delivered high discharge capacities with relatively good retention rates. But very low electrode capacity was obtained from LiNiO₂ prepared at lower oxygen flow rates.     

Electrophoretic Deposition Behavior of Aqueous Nanosized Zinc Oxide Suspensions

The rheological behavior and electrophoretic deposition (EPD) of ZnO nanopowder (nano-ZnO) in aqueous media have been described. A cationic polyelectrolyte (polyethylenimine, PEI) was used to disperse and modify the surfaces of the ZnO nanoparticles. The rheological properties of the ZnO aqueous suspension were investigated by measuring the viscosity versus the pH and amount of dispersant. The EPD processing was conducted via cathodic electrodeposition, using stable suspensions with low viscosity, and the depositional behavior was investigated. Bubble-free nano-ZnO deposits with uniform microstructures were successfully obtained, which was an indication of good sintering behavior.     

Phase Transformation and Texture in Hot-Forged or Annealed Liquid-Phase-Sintered Silicon Carbide Ceramics

Starting from three powder mixtures of 80 vol% SiC (100α, 50α/50β, 100β) and 20 vol% YAG, liquid-phase-sintered silicon carbide ceramics were prepared by hot pressing at 1800°C for 1 h under 25 MPa, and then by hot forging or annealing at 1900°C for 4 h under an applied stress of 25 MPa in argon. The phase transformation and texture development in the as-hot-pressed, hot-forged, and annealed SiC ceramics were investigated via X-ray diffraction (XRD) and the pole figure measurements. The 6H → 4H polytypic transformation was observed in samples consisting of both α- and β-SiC phases when subjected to compressive deformation but absent in the case of annealing, suggesting the deformation-enhanced solubility of aluminum in SiC. Deformation was also found to enhance the 3C → 4H transformation in the sample containing entirely β-phase, which is due to the accelerated solution-precipitation process assisted by grain boundary sliding. The current study showed that the β- →α-phase transformation had little effect on texture development in SiC. Hot forging generally produced the strongest texture, with the calculated maximum of 2.2 times random in samples started with pure α-SiC phase. The mechanism for texture development was explained based on the microstructural observations.     

Preparation and Luminescence Spectra of Calcium- and Rare-Earth (R = Eu, Tb, and Pr)-Codoped α-SiAlON Ceramics

Rare-earth-doped oxynitride or nitride compounds have been reported to be luminescent and may then serve as new phosphors with good thermal and chemical stabilities. In this work, we report the photoluminescence (PL) spectra of europium-, terbium-, and praseodymium-doped Ca-α-SiAlON ceramics. The highly dense ceramics were prepared by hot pressing at 1750°C for 1 h under 20 MPa in a nitrogen atmosphere. Europium-doped Ca-α-SiAlON displayed a single broad emission band peaking at λ= 550–590 nm depending on the europium concentration. The emission bands in the spectra of europium-doped Ca-α-SiAlONs were assigned to the allowed transition of Eu²⁺ from the lowest crystal field component of 4 f ⁶5 d to ⁸S_7/2 (4 f ⁷) ground-state level. The emission spectra of terbium- and praseodymium-doped Ca-α-SiAlON ceramics both consisted of several sharp lines, which were attributed to the ⁵D₄→⁷F _j ( j = 3, 4, 5, 6) transitions of Tb³⁺ and ³P₀→³H _j ( j = 3, 4, 5) transitions of Pr³⁺, respectively. In particular, the terbium-doped α-SiAlON ceramics showed a strong green emission among these phosphors.     

Transformation of Lower Alkanes into Aromatic Hydrocarbons over ZSM-5 Zeolites

Much attention has been paid to the transformation of lower alkanes such as propane and butanes into aromatic hydrocarbons from both industrial and academic points of view. The aromatic hydrocarbons can be utilized as a booster for high octane number gasoline and are fundamental raw chemicals in petroleum chemistry. The activation of lower alkanes is an intriguing subject. In early work, Csicsery [1-5] described dehydrocyclodimerization of lower alkanes over bifunctional catalysts such as platinum on alumina and Cr₂O₃ on alumina.     

Nucleation Effects of Nucleobases on the Crystallization Kinetics of Poly(L‐lactide)

The effects of nucleobases, especially uracil, on the nonisothermal and isothermal crystallization, melting behavior, spherulite morphology, and crystalline structure of bio‐based and biodegradable PLLA are studied. The melt‐ and cold‐crystallization rates of PLLA increase with increasing uracil loading. The melting behavior of nonisothermally melt‐ and cold‐crystallized PLLAs depends on the uracil content. The isothermal crystallization kinetics is analyzed based on an Avrami model. The incorporation of uracil changes the t_1/2/T_c profile of PLLA due to the more distinct heterogeneous nucleation effects at small supercooling. The crystalline structure of PLLA is not affected by uracil presence. The nucleation density increases and the spherulite size decreases by uracil incorporation.

     

Modification of Rheological Properties Under Elongational Flow by Addition of Polymeric Fine Fibers

A new technique to provide melt elasticity using flexible fine fibers prepared from a polymer with high melting point is demonstrated. A polymer composite of poly(propylene) with a small amount of fine fibers of poly(butylene terephthalate) shows marked strain‐hardening behavior in elongational viscosity, i.e., a rapid increase in the transient elongational viscosity with time or strain. The blend also shows prominent normal stress difference at steady shear. These elastic properties have not been observed for polymer composites with rigid fibers and can be applicable to the modification of rheological properties and thus the improvement of processability.