锂硫电池正极材料研究进展
郑智慧, 谷峰, 赵晓琳, 王有伟, 高彦峰, 刘建军
电动汽车行业的迅速发展,逐步提高了对二次电池容量的要求,因此急需发展新型高容量锂电池。锂硫电池具有高理论比容量(1675mAh/g)和高理论比能量(2600Wh/kg),使其能够实现锂离子电池3~5倍的能量密度。但是,正极长链多硫化物溶解引起的容量衰减快、循环寿命短等因素限制了锂硫电池的实用化进程。本文针对正极聚硫锂溶解问题,从正极材料表面包覆、表面吸附、表面催化的角度对近年来提高锂硫电池循环性能的正极材料研究思路和研究进展进行综述,最后对提高锂硫电池性能的发展趋势提出展望。
关键词: 锂硫电池, 正极材料, 表面包覆, 表面吸附, 表面催化
Improved Hole Injection Property of Solution-Processed MoO3 with
Dan DONG, Zhiyuan MIN, Jun LIU, Gufeng HE
【物理化学学报】doi: 10.3866/PKU.WHXB201803222
The hole injection layer (HIL) plays a significant role in determining the performances of organic light-emitting diodes (OLEDs), especially when hole transport materials with deep highest occupied molecular orbital levels (HOMOs) are employed. Intensive efforts have been devoted to exploring novel hole injection materials with good solution-processing abilities in recent years. In this study, the solution-processed molybdenum trioxide (s-MoO3) is prepared via an ultra-facile method. Three different s-MoO3 layers prepared by three different methods, viz. layers annealed at 150 ℃ (s-MoO3 (150)), layers annealed at 150 ℃ and then processed in UV-ozone for 15 min (s-MoO3 (150, UVO)), and layers processed in UV-ozone for 15 min without annealing (s-MoO3 (UVO)), are obtained to investigate their influences on hole injection. The device with the s-MoO3 (150) layer has the lowest current density and the largest driving voltage, showing poor hole injection ability. In contrast, with the s-MoO3 (150, UVO) layer as HIL, the OLED produces a greatly enhanced current and sharply reduced driving voltage, comparable to the device using vacuum-evaporated MoO3. Similar results are obtained for the device with the s-MoO3 (UVO) film, suggesting that high-temperature annealing is not essential for the s-MoO3 film with UV-ozone treatment. Hole injection efficiencies of MoO3 films are quantitatively characterized by analyzing the space-charge-limited current of hole-only devices; the hole injection efficiencies of s-MoO3 (150, UVO) and s-MoO3 (UVO)-based devices are ~0.1, far exceeding that of the s-MoO3 (150)-based device (10−5). XPS analysis is performed to detect the impact of the above treatments on the surface electronic properties of the s-MoO3 films. A typical characteristic of Mo5+ species is obtained for the s-MoO3 (150) film and a high-binding-energy shoulder appears in the O 1s peak of the s-MoO3 (150) film, indicating the existence of oxygen vacancies and oxygen adsorbed at the surface of s-MoO3 (150) film. When UV-ozone treatment is applied to this s-MoO3 (150) film, it produces a decrease of Mo5+ state and elimination of oxygen-rich adsorbates, resulting in MoO3 stoichiometry similar to that of the vacuum-evaporated MoO3 film. Consequently, a maximum current efficiency of 48.3 cd∙A−1 is realized with the optimized UV-ozone treated s-MoO3 HIL. It This UV-ozone treated s-MoO3 should have widespread applications in low-cost solution-processed OLEDs as an excellent hole injection layer.
关键词: Hole injection property, Solution process, Organic light-emitting diode, Stoichiometry, UV-ozone treatment

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