Synthesis of Tricyclic (λ5)-Phosphoranes; unusual N-demethylation/N-alkylation reactions during the oxidative addition of hexafluoroacetone and tetrachloro-ortho-benzoquinone to benzodiaza-λ3-phosphorinones. Single crystal X-ray diffraction studies of various products

The reaction of methylisatoic acid anhydride 1 with benzylamines led to the N-benzyl-N′-methylanthranilamide derivatives 2 – 4 . Their reaction with phosphorus trichloride furnished the 2-chloro-1-halobenzyl/benzyl-3-methyl-4(1 H)-1,3,2-benzodiazaphosphorin-4-ones 5 – 7 which, upon reaction with bis-(2-chloroethyl)ammonium chloride/triethylamine, were converted into the P-bis-(2-chloroethyl)amino-1-halobenzyl/benzyl-3-methyl-4(1 H)-1,3,2-benzodiazaphosphorin-4-ones 8 – 10 and 12 . With 2-chloroethylammonium chloride/triethyl-amine the P? NHCH₂CH₂Cl-substituted compound 11 was obtained from the P^IIICl-species 6 . The reaction of 8 – 10 and 12 with hexafluoroacetone (HFA) took an unusual course: apart from the oxidative addition of HFA and formation of the perfluoropinacolyl ring system, one of the two CH₂CH₂Cl groups was found to alkylate the CH₃N atom with formation of a five-membered (diazaphospholane) ring in the tricyclic phosphoranes 13 – 16 . The reaction of 11 with HFA also produced a spirophosphorane 17 which involved a λ⁵-oxazaphosphetidine ring system. In the reaction of 8, 10 and 12 with tetrachloro-o-benzoquinone, an oxidative addition reaction with concomitant N-alkylation and formation of the tricyclic phosphoranes 18 – 20 was found to take place. Single crystal X-ray structure determinations are described for the phosphoranes 13, 14 and 16 , and for the precursor compound 9 . The following features are common to the isostructural compounds 13 and 16 and the diethyl ether hemisolvate of 14 : the (λ⁵)-spiro phosphorus atom lies out of the plane of the other atoms of the rings to which it is common, and the dioxaphospholane rings display a twist conformation. In the λ³P-compound 9 the phosphorus atom also lies out of the plane of the other ring atoms.     

Ortho-Alkoxy-benzamide Directed Formation of a Single Crystalline Hydrogen-bonded Crosslinked Organic Framework and Its Boron Trifluoride Uptake and Catalysis

Boron trifluoride (BF₃) is a highly corrosive gas widely used in industry. Confining BF₃ in porous materials ensures safe and convenient handling and prevents its degradation. Hence, it is highly desired to develop porous materials with high adsorption capacity, high stability, and resistance to BF₃ corrosion. Herein, we designed and synthesized a Lewis basic single-crystalline hydrogen-bond crosslinked organic framework (H_COF-50) for BF₃ storage and its application in catalysis. Specifically, we introduced self-complementary ortho-alkoxy-benzamide hydrogen-bonding moieties to direct the formation of highly organized hydrogen-bonded networks, which were subsequently photo-crosslinked to generate H_COFs. The H_COF-50 features Lewis basic thioether linkages and electron-rich pore surfaces for BF₃ uptake. As a result, H_COF-50 shows a record-high 14.2 mmol/g BF₃ uptake capacity. The BF₃ uptake in H_COF-50 is reversible, leading to the slow release of BF₃. We leveraged this property to reduce the undesirable chain transfer and termination in the cationic polymerization of vinyl ethers. Polymers with higher molecular weights and lower polydispersity were generated compared to those synthesized using BF₃ ⋅ Et₂O. The elucidation of the structure–property relationship, as provided by the single-crystal X-ray structures, combined with the high BF₃ uptake capacity and controlled sorption, highlights the molecular understanding of framework-guest interactions in addressing contemporary challenges.     

Electrochemical Investigations of Mn and Al Co‐doped Li2FeSiO4/C Cathodes for Li‐Ion Battery

Few studies on orthosilicate cathodes co‐doped with two cations have been reported until now. Here, we report the synthesis of Mn and Al co‐doped Li₂Fe_0.8?xMn_0.2Al_xSiO₄ (x = 0.05 and 0.1) by a solid‐state reaction route and characterized by X‐ray diffraction (XRD), particle size analysis, scanning electron microscopy (SEM), galvanostatic charge/discharge tests, and capacity intermittent titration technique (CITT), as compared to the single‐doped Li₂Fe_0.8Mn_0.2SiO₄. Though the co‐doping leads to a slight decreased capacity owing to the increased impurity and Al³⁺ inertia, a better cycling performance is obtained as expected. Especially when x is 0.05, the modified sample (Li₂Fe_0.75Mn_0.2Al_0.05SiO₄) shows an initial discharge capacity of 159.3 mAh/g and high capacity retention of 78% after 50 charge/discharge cycles. The present work indicates that a synergistic effect of Mn and Al co‐substitution at the Fe site could partly make up the disadvantage of single Mn doping, and might provide an effective guide for the dopant incorporation to Li₂FeSiO₄ systems.     

锂镍钴复合氧化物锂离子电池正极材料的研究

本文报道了以碱式碳酸镍、碱式碳酸钴和碳酸锂为原料 ,柠檬酸为络合剂的新溶胶凝胶法制备复合锂镍钴氧化物锂离子电池正极材料 .氧气流中制备的LiNi0 .8Co0 .2 O2 具有高的循环容量 (～ 190mAhg 1)     

TiO2 coating of LiNi1/3Co1/3Mn1/3O2 cathode materials for Li-ion batteries

TiO₂-coated LiNi_1/3Co_1/3Mn_1/3O₂ materials were prepared by the hydrolyzation of Ti(OBu)₄. The impact of TiO₂ coating on the structure and electrochemical properties of LiNi_1/3Co_1/3Mn_1/3O₂ was investigated using X-ray diffraction, scanning electron microscope, and charge–discharge tests. The results indicated that TiO₂ coating did not affect the lattice of LiNi_1/3Co_1/3Mn_1/3O₂, but exhibited obvious effects on its discharge capacity and cycling stability. As coated TiO₂ increased from 0.0 to 2.0 mol%, the initial capacity of samples decreased slightly, but the cycling stability over 2.5∼4.3 V increased remarkably. The capacity retention reached 99.5% at the 50th cycle at a coating amount of 2.0 mol%.     

Two-step process and fatigue in Li<Subscript><Emphasis Type="BoldItalic">x</Emphasis></Subscript>CrMnO<Subscript>4</Subscript> as positive electrode material for lithium ion batteries

The electrochemical behavior and structural changes of the positive electrode material LiCrMnO₄ are studied for different end-of-charge voltages. A potentiostatic intermittent titration technique (PITT) experiment performed up to 5.2 V shows three oxidative peaks. Cells charged to 4.88 V, which corresponds to the minimum between the second and the third oxidative peak, show 89% of capacity retention for the 60th cycle. Compared to that only 23% of capacity are preserved in the 60th cycle when the cell is charged to 5.2 V. The structural analysis by Rietveld refinement shows that for the former case, the amount of structural defects is low and their formation is reversible, while the defect amount is significantly higher for the latter case and the defect formation is only partially reversible. Paper presented at the 11th EuroConference on the Science and Technology of Ionics, Batz-sur-Mer, Sept. 9–15, 2007     

Application of electrospinning for the fabrication of proton-exchange membrane fuel cell electrodes

Electrospun materials have been gaining great interest in the energy sector. Their tunability and robustness make them highly attractive, particularly for proton-exchange membrane fuel cell (PEMFC) electrodes. Conventional PEMFC electrodes, prepared by either spraying, painting, or slot-die coating, have not yet met the needs of large-scale PEMFC use. Electrospinning of fibrous materials has already shown great promise as an alternative methodology for electrode fabrication. Electrospinning has been used in fuel cell electrodes through two primary means: (1) segmented carbon or inorganic fibers to serve as precious metal catalyst support, and (2) high aspect ratio polymer/particle fibers to serve directly as the electrode. The use of electrospun fibrous electrodes has led to improved PEMFC durability and increased power output at low catalyst loadings, both of which are of paramount importance to large-scale commercialization of PEMFC electric vehicles.     

Prussian blue analogues as aqueous Zn-ion batteries electrodes: Current challenges and future perspectives

The urgency of integrating renewable energy sources in the power grid has pushed the development of aqueous metal-ion batteries because of their low cost, nontoxicity, high safety, and environmentally friendliness. Among the variety of aqueous metal-ion batteries that are currently under development, aqueous Zn-ion batteries (A-ZIBs) have recently gained a great attention because of their high specific energy and high reversibility in aqueous solutions, together with the low cost and high abundancy of the zinc. In this article, the authors intend to present an overview of the Prussian blue analogue materials, which are among the most promising materials for positive electrodes in A-ZIBs because of their easier synthesis route, reversible ion-insertion, high safety, and low toxicity, highlighting their strength points and open challenges.     

Evaluation and Improvement of the Stability of Poly(ethylene oxide)-based Solid-state Batteries with High-Voltage Cathodes

Solid-state batteries (SSBs) with high-voltage cathode active materials (CAMs) such as LiNi_1−x−yCo_xMn_yO₂ (NCM) and poly(ethylene oxide) (PEO) suffer from “noisy voltage” related cell failure. Moreover, reports on their long-term cycling performance with high-voltage CAMs are not consistent. In this work, we verified that the penetration of lithium dendrites through the solid polymer electrolyte (SPE) indeed causes such “noisy voltage cell failure”. This problem can be overcome by a simple modification of the SPE using higher molecular weight PEO, resulting in an improved cycling stability compared to lower molecular weight PEO. Furthermore, X-ray photoelectron spectroscopy analysis confirms the formation of oxidative degradation products after cycling with NCM, for what Fourier transform infrared spectroscopy is not suitable as an analytical technique due to its limited surface sensitivity. Overall, our results help to critically evaluate and improve the stability of PEO-based SSBs.     

Quantifying Degradation Parameters of Single-Crystalline Ni-Rich Cathodes in Lithium-Ion Batteries

Single-crystal LiNi_xCo_yMn_zO₂ (SC-NCM, x+y+z=1) cathodes are renowned for their high structural stability and reduced accumulation of adverse side products during long-term cycling. While advances have been made using SC-NCM cathode materials, careful studies of cathode degradation mechanisms are scarce. Herein, we employed quasi single-crystalline LiNi_0.65Co_0.15Mn_0.20O₂ (SC-NCM65) to test the relationship between cycling performance and material degradation for different charge cutoff potentials. The Li/SC-NCM65 cells showed >77 % capacity retention below 4.6 V vs. Li⁺/Li after 400 cycles and revealed a significant decay to 56 % for 4.7 V cutoff. We demonstrate that the SC-NCM65 degradation is due to accumulation of rock-salt (NiO) species at the particle surface rather than intragranular cracking or side reactions with the electrolyte. The NiO-type layer formation is also responsible for the strongly increased impedance and transition-metal dissolution. Notably, the capacity loss is found to have a linear relationship with the thickness of the rock-salt surface layer. Density functional theory and COMSOL Multiphysics modeling analysis further indicate that the charge-transfer kinetics is decisive, as the lower lithium diffusivity of the NiO phase hinders charge transport from the surface to the bulk.