Gangtie Lei

Efficient near-infrared-emitting cationic iridium complexes based on highly conjugated cyclometalated benzo[g]phthalazine derivatives

Two near-infrared- (NIR-) emitting cationic iridium(III) complexes, [Ir(dpbpa)2(Bphen)]+PF6− (1) and [Ir(dtbpa)2(Bphen)]+PF6− (2), were rationally designed and synthesized, where dpbpa, dtbpa, and Bphen represent 1,4-diphenylbenzo[g]-phthalazine, 1,4-di(thiophen-2-yl)benzo[g]phthalazine and 4,7-dipheny-1,10-phenanthroline, respectively. By using highly conjugated cyclometalated benzo[g]phthalazine ligands, these two complexes exhibited a significantly large red shift in wavelength to the truly NIR region with maximum peaks at 715 nm for 1 and 775 nm for 2. Complex 1 exhibited unexpectedly improved quantum efficiency up to 6.1% in the solid films. Based on these solution-processable phosphors, NIR organic-light-emitting devices (OLEDs) have been fabricated and demonstrated negligible efficiency roll-off with nearly constant external quantum efficiency around 0.5% over a wide range of current density of 1–100 mA cm−2. Density functional theory calculations were performed to discover that the newly cyclometalated benzo[g]phthalazine ligands have several areas of superiority over the previous benzo[g]quinoline ligands in views of stronger Ir–N bonds, smaller chelate congestion, higher electron-accepting ability, thus improving the overall phosphorescence of the corresponding iridium complexes in the NIR region.

A capsule-type gelled polymer electrolyte for rechargeable lithium batteries

A trilayer fibrous membrane was integrated by cross-linked PMMA (CL-PMMA) to form a blended fibrous membrane. Owing to encapsulation of the CL-PMMA component, the resultant gelled polymer electrolyte shows high thermal stability, good electrolyte retention and high ionic conductivity, which is suitable for rechargeable lithium batteries.

Hybrid LiV3O8/carbon encapsulated Li1.2Mn0.54Co0.13Ni0.13O2 with improved electrochemical properties for lithium ion batteries

A low coulombic efficiency in the first cycle and poor rate capability limit the practical application of a lithium rich manganese-based solid solution (LMSS) in lithium ion batteries. To resolve these problems, a core–shell type of Li1.2Mn0.54Co0.13Ni0.13O2@LiV3O8/C (LMSSVC) composite material was prepared using a sol–gel process, in which NH4VO3-derived V2O5 chemically leached lithium from the LMSS and formed the LiV3O8 during high temperature annealing. The effect of the hybrid LiV3O8/C layer on the electrochemical properties of the LMSS is investigated using cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge–discharge measurements. The as-prepared LiV3O8 nanoparticles are embedded within the carbon matrix uniformly, which becomes an outer shell to encapsulate the LMSS nanoparticles. Because of the Li-host nature of LiV3O8 and the electronic conductivity of carbon, the LMSSVC can deliver a capacity of 269 mA h g−1 at a 0.1C rate in the first cycle over the voltage range of 2.0–4.8 V together with a coulombic efficiency of 94%, and retain 94% of the initial capacity after 50 cycles. It can deliver capacities of 258, 245, 229, 207 and 176 mA h g−1 at the rates of 0.2C, 0.5C, 1C, 2C and 5C, respectively. The results indicate that surface coating of the hybrid LiV3O8/C layer can improve not only the initial coulombic efficiency but also the rate capability of the LMSS material.

Embedding of Mg-doped V2O5 nanoparticles in a carbon matrix to improve their electrochemical properties for high-energy rechargeable lithium batteries

Hierarchical Mg-doped V2O5@carbon (HVC) spheres were fabricated using poly(methacrylic acid) (PMAA) microgel as a microreactor. The monodisperse micron-sized spheres are formed from 200 nm particles, in which primary V2O5 nanoparticles are embedded uniformly in a carbon matrix to form a mulberry-like morphology. The effect of the Mg-doping level on the electrochemical properties of the as-prepared HVC spheres was studied. Benefitting from the unique morphology and chemical pre-insertion of Mg2+ ions, the Mg0.10V2O5@C sample exhibited an excellent rate capability and stable cyclability when operated over the potential range of 1.5–4.0 V (vs. Li+/Li). The results suggest that these porous HVC spheres hold promise for use as high-energy-density cathode materials for rechargeable lithium batteries.