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971.
972.
采用水基流变相辅助的固相法,以异质碳蔗糖和石墨为碳源,合成了LiMn0.8Fe0.2PO4/C复合材料,研究了不同石墨加入方式对所制复合材料电化学性能的影响,并对所制备的LiMn0.8Fe0.2PO4/C复合材料进行了X射线衍射(XRD)、N2吸附-脱附测试、扫描电子显微镜(SEM)、透射电子显微镜(TEM)等表征。结果表明,不同石墨包覆工艺对材料结构和电化学性能具有显著影响。前驱体煅烧后再加入石墨获得的样品纯度高,形貌呈均一的椭圆形,在0.1C下的放电比容量为149 mAh·g-1,达到其理论比容量的87%;在5C下最大的放电比容量为133 mAh·g-1;在2C倍率下经过300次循环后比容量维持在127 mAh·g-1,衰减率仅为1.9%,表现出了优良的循环稳定性。 相似文献
973.
采用高温固相法在1 050℃下烧结,制备了LiCoO2低浓度梯度改性样品,分别为LiF掺杂包覆(LCOLF、LCO@LF)和MgF2掺杂包覆(LCOMF、LCO@MF)。通过光电子能谱、透射电子显微镜和电化学技术等表征方法,对比分析材料形貌及电化学性能。结果表明,体相掺杂复合电极中,LCOLF热重测试显示出最优热稳定性,LCOMF晶体中(003)和(104)晶面间距收缩;45℃下1C倍率循环70圈后,LCOLF和LCOMF比容量分别为141.45和166.98 mAh·g-1,循环性能优于LiCoO2。表面包覆复合电极中,LCO@LF和LCO@MF晶粒表面光洁且晶格氧键价都向更高结合能方向增强;LCO@MF构建了坚实且紧密的包覆层,循环70圈后,放电比容量和容量保持率分别为183 mAh·g-1和91.26%(LCO@LF分别为154.38 mAh·g-1和77.54%),循环性能显著优于体相掺杂。 相似文献
974.
975.
宽禁带半导体SiC功率器件发展现状及展望 总被引:7,自引:0,他引:7
碳化硅(SiC)是第三代半导体材料的典型代表,也是目前晶体生长技术和器件制造水平最成熟、应用最广泛的宽禁带半导体材料之一,是高温、高频、抗辐照、大功率应用场合下极为理想的半导体材料.文章结合美国国防先进研究计划局DARPA的高功率电子器件应用宽禁带技术HPE项目的发展,介绍了SiC功率器件的最新进展及其面临的挑战和发展前景.同时对我国宽禁带半导体SiC器件的研究现状及未来的发展方向做了概述与展望. 相似文献
976.
Tianyong Liu Qian Dang Xunhui Zhou Jin Li Zhen Ge Hang Che Prof. Shaobin Tang Prof. Yi Luo Prof. Jun Jiang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(23):6945-6953
Developing the low-cost and efficient single-atom catalysts (SACs) for nitrogen reduction reaction (NRR) is of great importance while remains as a great challenge. The catalytic activity, selectivity and durability are all fundamentally related to the elaborate coordination environment of SACs. Using first-principles calculations, we investigated the SACs with single transition metal (TM) atom supported on defective boron carbide nitride nanotubes (BCNTs) as NRR electrocatalysts. Our results suggest that boron-vacancy defects on BCNTs can strongly immobilize TM atoms with large enough binding energy and high thermal/structural stability. Importantly, the synergistic effect of boron nitride (BN) and carbon domains comes up with the modifications of the charge polarization of single-TM-atom active site and the electronic properties of material, which has been proven to be the essential key to promote N2 adsorption, activation, and reduction. Specifically, six SACs (namely V, Mn, Fe, Mo, Ru, and W atoms embedded into defective BCNTs) can be used as promising candidates for NRR electrocatalysts as their NRR activity is higher than the state-of-the art Ru(0001) catalyst. In particular, single Mo atom supported on defective BCNTs with large tube diameter possesses the highest NRR activity while suppressing the competitive hydrogen evolution reaction, with a low limiting potential of −0.62 V via associative distal path. This work suggests new opportunities for driving NH3 production by carbon-based single-atom electrocatalysts under ambient conditions. 相似文献
977.
《Mendeleev Communications》2021,31(5):715-717
Nanoporous silicon carbide with a specific surface area of up to 186.45 m2 g−1 has been efficiently synthesized from waste rice husk using a magnesiothermic reduction at 950 °C as a key step. Throughout the entire process, the recovery rates of silicon, potassium and phosphorus from rice husk can reach 88.46, 91.5 and 65.5%, respectively. Turning rice husk waste into a real treasure, this promising method for producing porous SiC protects the environment and brings economic benefits. 相似文献
978.
Studying the vibrational behavior of feed drive systems is important for enhancing the structural performance of computer numerical control (CNC) machines. The preload on the screw and nut position have a great influence on the vibration characteristics of the feed drive as two very important operational conditions. Rotational acceleration of the screw also affects the performance of the CNC feed drive when machining small parts. This paper investigates the influence of preload and nut position on the vibration characteristics of the feed drive system of a CNC metal cutting machine in order to be able to eliminate an observed resonance occurred at high rotational speeds of the screw, corresponding to high feed rates. Additionally, rational structural parameters of the feed drive system are selected in order to increase the rotational acceleration for improving the performance of the CNC machine. Experiments and analyses showed that by selecting specific parameters of feed drive system and simultaneously applying a certain value of preload, a 97% increase in rotational acceleration and 30% time reduction considering the vibration resistance at high rotational speeds can be achieved. 相似文献
979.
构建表面无机-有机复合包覆层,用于改善高镍层状(NCM811)正极材料结构和界面不稳定问题。复合包覆层由纳米偏铝酸锂(LiAlO2,LAO)和环化聚丙烯腈(cPAN)构成。该复合包覆层中LAO是一种典型的锂离子导体,可提供Li+迁移通道;PAN环化后,可产生离域的π键,形成具有电子导电性的cPAN。材料表面复合包覆层的结构及成分研究表明,该复合包覆层均匀分布在 NCM811 材料表面。半电池测试结果表明,在 2.7~4.3 V(vs Li/Li+)电压范围内,在 180 mA·g-1电流密度下,改性后的NCM811材料循环150周后容量保持率为84.8%。而同样条件下,原始NCM811材料容量保持率为65.5%。该复合包覆层可有效提升NCM811结构和界面稳定性,减少电解液分解,降低界面阻抗。 相似文献
980.
Thi Anh Le Ngoc Quang Tran Yeseul Hong Prof. Hyoyoung Lee 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(4):1037-1043
The exploration of the rational design and synthesis of unique and robust architectured electrodes for the high capacitance, rate capability, and stability of supercapacitors is crucial to the future of energy storage technology. Herein, an in situ synthesis of multilayered titanium carbide MXene tightly caging within a 3 D conducting tangled polypyrrole (PPy) nanowire (NW) network is proposed as an effective strategy to prevent the aggregation of MXene, profoundly enhancing the electrochemical performance of the supercapacitor. Owing to the beneficial effects of an ideal 3 D interconnected porous structure and high electrical conductivity, the obtained electrode exhibits fast charge and ion transport kinetics as well as full usage of active material. As expected, the 3 D Ti3C2Tx@PPY NW exhibits a specific capacitance five times higher than that of pristine MXene (610 F g−1), a good rate capability up to a current density of 25 A g−1, and excellent stability with 100 % retention after 14 000 cycles at 4 A g−1, outperforming the known state-of-the-art MXene-based supercapacitor. Our work provides a facile method for enhancing the performance of MXene-based energy storage devices. 相似文献