For the state-of-the-art quantum dot light-emitting diodes, while the ZnO nanoparticle layers can provide effective electron injections into quantum dots layers, the hole transporting materials usually cannot guarantee sufficient hole injection owing to the deep valence band of quantum dots. Developing proper hole transporting materials to match energy levels with quantum dots remains a great challenge to further improve the device efficiency and operation lifetime. Here we demonstrate high-performance quantum dot light-emitting diodes with much extended operation lifetime using quantum dots with tailored energy band structures that are favorable for hole injections. These devices show a T95 operation lifetime of more than 2300 h with an initial brightness of 1000 cd m-2, and an equivalent T50 lifetime at 100 cd m-2 of more than 2,200,000 h, which meets the industrial requirement for display applications.
Extensins are one subfamily of the cell wall hydroxyproline-rich glycoproteins, containing characteristic SerHyp4 glycosylation motifs and intermolecular cross-linking motifs such as the TyrXaaTyr sequence. Extensins are believed to form a cross-linked network in the plant cell wall through the tyrosine-derivatives isodityrosine, pulcherosine, and di-isodityrosine. Overexpression of three synthetic genes encoding different elastin-arabinogalactan protein-extensin hybrids in tobacco suspension cultured cells yielded novel cross-linking glycoproteins that shared features of the extensins, arabinogalactan proteins and elastin. The cell wall properties of the three transgenic cell lines were all changed, but in different ways. One transgenic cell line showed decreased cellulose crystallinity and increased wall xyloglucan content; the second transgenic cell line contained dramatically increased hydration capacity and notably increased cell wall biomass, increased di-isodityrosine, and increased protein content; the third transgenic cell line displayed wall phenotypes similar to wild type cells, except changed xyloglucan epitope extractability. These data indicate that overexpression of modified extensins may be a route to engineer plants for bioenergy and biomaterial production.
Ni-rich layered oxides (LiNixMnyCozO2, x ≥ 0.6, x + y + z = 1) are promising positive electrode materials for high energy density lithium-ion batteries thanks to their high specific capacity. However, large-scale application of Ni-rich layered oxides is hindered by its poor structural and interfacial stability, especially during cycling at a high cutoff potential (i.e., ≥ 4.3 V, versus Li+/Li). Herein, we demonstrate that lithium difluoro(oxalato)borate (LiDFOB) as a film-forming additive plays a dual role on the electrode|electrolyte interphase formation in a LiNi0.83Mn0.05Co0.12O2||graphite cell, meaning that it can not only be reduced on the graphite negative electrode but also oxidized on the nickel-rich oxide LiNi0.83Mn0.05Co0.12O2 positive electrode cycled at a high cutoff potential (4.4 V, versus Li+/Li) prior to typical carbonate-based electrolyte constituents. As a result, the addition of 1.5 wt % LiDFOB greatly reduces the polarization and improves the cycling stability of the LiNi0.83Mn0.05Co0.12O2||graphite cell, which shows a high discharge capacity of 198 mA h g–1, and more than 83.1% of the initial capacity was retained after 200 cycles at C/3 (the capacity retention obtained at the same cycling condition is only 59.9% for the cell without LiDFOB additive). Furthermore, the employ of LiDFOB additive also significantly suppresses the self-discharge of the LiNi0.83Mn0.05Co0.12O2||Li cell during high-temperature and long-term room-temperature storage at 4.4 V. These electrochemical performance enhancements could be attributed to the participation of LiDFOB in forming a stable and Li+ transfer favorable protective layer that is rich in inorganic boron, fluorine, and carbonate compounds on both the surface of the LiNi0.83Mn0.05Co0.12O2 positive electrode and the graphite negative electrode, thus suppressing the electrolyte decomposition on the positive electrode and negative electrode surfaces and decreasing the dissolution of transition-metal ions from the positive electrode bulk.
Solid polymer electrolytes play a vital role in improving the safety of lithium batteries. However, low ionic conductivity and poor mechanical property limit their further applications. Herein, we fabricated a composite solid electrolyte (CSE) based on a polymer (polyvinylidene fluoride-hexafluoro propylene, PVDF-HFP) and an inorganic filler of porous graphitic carbon nitride (PGCN) nanosheets with a high specific surface area. The porous structure facilitated good distribution of PGCN in the PVDF-HFP matrix and offered abundant PVDF-HFP/PGCN interfaces, which might be beneficial for the Li+ transport. The CSE showed high ionic conductivity (2.3 × 10–4 S/cm at 30 °C), excellent cycling performance, and outstanding physical and chemical properties. Moreover, the correlation of the ionic conductivities of the CSEs and the specific surface of the PGCN fillers was discussed, and the results revealed that the ionic conductivity of the CSE was increased with the increase in the specific surface of PGCN, indirectly demonstrating that the transport of the Li+ was mainly conducted on the interfaces between the polymer and the inorganic fillers.
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