升力特性是电动多旋翼植保无人机性能测试的重要参数之一。为了实现对电动多旋翼植保无人机升力特性的性能检测,针对不同型号、不同规格的电动多旋翼植保无人机在评价过程中存在无统一的评价指标问题,该文提出了一种半系留式电动多旋翼...升力特性是电动多旋翼植保无人机性能测试的重要参数之一。为了实现对电动多旋翼植保无人机升力特性的性能检测,针对不同型号、不同规格的电动多旋翼植保无人机在评价过程中存在无统一的评价指标问题,该文提出了一种半系留式电动多旋翼植保无人机升力特性的测试与评价方法,包括性能检测平台、升力特性测试方法及指标、升力特性的评价方法。为了验证方法的可行性,对3种不同机型(分别为四旋翼机型Ⅰ、六旋翼机型Ⅱ、八旋翼机型Ⅲ)进行了升力特性指标的性能测试试验。试验结果表明:3种机型在功率载荷、重量效率、热效比等方面有较大差异,功率载荷最好的机型Ⅲ比最差的机型Ⅰ大7.6 m N/W,重量效率最好的机型Ⅰ比最差的机型Ⅱ大0.33,热效比最好的机型Ⅲ比最差的机型Ⅱ大10.5 N/℃,反映出3种机型在设计过程中整个动力系统效率、机型整体结构和材料选择上的差异,从而在整机作业性能上表现出差异。在上述指标测试的基础上,结合无人机动力系统数学模型,提出了运用功率载荷、重量效率和热效比进行电动多旋翼植保无人机升力特性综合评价的评分方法,对上述3种机型进行综合评分的结果为:机型Ⅲ>机型Ⅰ>机型Ⅱ,该结果表明所提出的评价方法能有效对不同类型电动多旋翼植保无人机的升力特性进行综合评判。该文所给出的测试与评价方法,不仅能用于电动多旋翼植保无人机性能的评测,还能为机型性能的进一步改进提供参考。展开更多
Nanoporous silicon is a promising anode material for high energy density batteries due to its high cycling stability and high tap density compared to other nanostructured anode materials.However,the high cost of synth...Nanoporous silicon is a promising anode material for high energy density batteries due to its high cycling stability and high tap density compared to other nanostructured anode materials.However,the high cost of synthesis and low yield of nanoporous silicon limit its practical application.Here,we develop a scalable,low-cost top-down process of controlled oxidation of Mg2Si in the air,followed by HCl removal of MgO to generate nanoporous silicon without the use of HF.By controlling the synthesis conditions,the oxygen content,grain size and yield of the porous silicon are simultaneously optimized from commercial standpoints.In situ environmental transmission electron microscopy reveals the reaction mechanism;the Mg2Si microparticle reacts with O2 to form MgO and Si,while preventing SiO2 formation.Owing to the low oxygen content and microscale secondary structure,the nanoporous silicon delivers a higher initial reversible capacity and initial Coulombic efficiency compared to commercial Si nanoparticles(3,033 mAh/g vs.2,418 mAh/g,84.3%vs.73.1%).Synthesis is highly scalable,and a yield of 90.4%is achieved for the porous Si nanostructure with the capability to make an excess of 10 g per batch.Our synthetic nanoporous silicon is promising for practical applications in next generation lithium-ion batteries.展开更多
Lithium-sulfur （Li-S） batteries with intrinsic merits in high theoretical energy density are the most promising candidate as the next-generation power sources. The strategy to achieve a high utilization of active ma...Lithium-sulfur （Li-S） batteries with intrinsic merits in high theoretical energy density are the most promising candidate as the next-generation power sources. The strategy to achieve a high utilization of active materials with high energy efficiency is strongly requested for practical applications with less energy loss during repeated cycling. In this contribution, a metal/nanocarbon layer current collector is proposed to enhance the redox reactions of polysulfides in a working Li-S cell. Such a concept is demon- strated by coating graphene-carbon nanotube hybrids （GNHs） on routine aluminum （AI） foil current collectors. The interracial conductivity and adhesion between the current collector and active material are significantly enhanced. Such novel cell configuration with metal/nanocarbon layer current collectors affords abundant Li ions for rapid redox reactions with small overpotential. Consequently, the Li-S cells with nanostructured current collectors exhibit an initial discharge capacity of 1,113 mAh g-1 at 0.5 C, which is -300 mAh g-1 higher than those without a GNH coating layer. The capacity retention is 73% for cells with GNH after 300 cycles. A reduced voltage hysteresis and a high energy efficiency of ca. 90% are therefore achieved. Moreover, the AI/GNH layer current collectors are easily implanted into current cell assembly process for energy storage devices based on complex multi-electron redox reactions （e.g., Li-S batteries, Li-O2 batteries, fuel cells, and flow batteries）.展开更多
b The discharge performance of Mg-Al-Pb-La anode was investigated by electrochemical techniques and compared withthat of Mg-Al-Pb alloy. The results indicate that the Mg-Al-Pb-La anode provides enhanced corrosion resi...b The discharge performance of Mg-Al-Pb-La anode was investigated by electrochemical techniques and compared withthat of Mg-Al-Pb alloy. The results indicate that the Mg-Al-Pb-La anode provides enhanced corrosion resistance at open circlepotential, and exhibits better discharge activity than the Mg-Al-Pb alloy. The utilization efficiency of Mg-Al-Pb-La anode ishigher than that of commercial Mg-Al-Zn （AZ） and Mg-Al-Mn （AM） alloys. A single Mg-air battery with Mg-Al-Pb-La alloy asthe anode and air as the cathode has an average discharge potential of 1.295 V and a discharge capacity of 1370 mA·h/g duringdischarge at 10 mA/cm2, which is higher than that of batteries using Mg-Li anodes. The enhancement in discharge performance ofthe Mg-Al-Pb-La anode is caused by its modified microstructure, which reduces the self-corrosion and accelerates the spalling ofoxidation products during battery discharge. Furthermore, the dissolution mechanism of Mg-Al-Pb-La anode during the dischargeprocess was analyzed.展开更多
文摘升力特性是电动多旋翼植保无人机性能测试的重要参数之一。为了实现对电动多旋翼植保无人机升力特性的性能检测,针对不同型号、不同规格的电动多旋翼植保无人机在评价过程中存在无统一的评价指标问题,该文提出了一种半系留式电动多旋翼植保无人机升力特性的测试与评价方法,包括性能检测平台、升力特性测试方法及指标、升力特性的评价方法。为了验证方法的可行性,对3种不同机型(分别为四旋翼机型Ⅰ、六旋翼机型Ⅱ、八旋翼机型Ⅲ)进行了升力特性指标的性能测试试验。试验结果表明:3种机型在功率载荷、重量效率、热效比等方面有较大差异,功率载荷最好的机型Ⅲ比最差的机型Ⅰ大7.6 m N/W,重量效率最好的机型Ⅰ比最差的机型Ⅱ大0.33,热效比最好的机型Ⅲ比最差的机型Ⅱ大10.5 N/℃,反映出3种机型在设计过程中整个动力系统效率、机型整体结构和材料选择上的差异,从而在整机作业性能上表现出差异。在上述指标测试的基础上,结合无人机动力系统数学模型,提出了运用功率载荷、重量效率和热效比进行电动多旋翼植保无人机升力特性综合评价的评分方法,对上述3种机型进行综合评分的结果为:机型Ⅲ>机型Ⅰ>机型Ⅱ,该结果表明所提出的评价方法能有效对不同类型电动多旋翼植保无人机的升力特性进行综合评判。该文所给出的测试与评价方法,不仅能用于电动多旋翼植保无人机性能的评测,还能为机型性能的进一步改进提供参考。
基金This work was supported by Samsung SDI.Part of this work was performed at the Stanford Nano Shared Facilities(SNSF)Stanford Nanofabrication Facility(SNF).
文摘Nanoporous silicon is a promising anode material for high energy density batteries due to its high cycling stability and high tap density compared to other nanostructured anode materials.However,the high cost of synthesis and low yield of nanoporous silicon limit its practical application.Here,we develop a scalable,low-cost top-down process of controlled oxidation of Mg2Si in the air,followed by HCl removal of MgO to generate nanoporous silicon without the use of HF.By controlling the synthesis conditions,the oxygen content,grain size and yield of the porous silicon are simultaneously optimized from commercial standpoints.In situ environmental transmission electron microscopy reveals the reaction mechanism;the Mg2Si microparticle reacts with O2 to form MgO and Si,while preventing SiO2 formation.Owing to the low oxygen content and microscale secondary structure,the nanoporous silicon delivers a higher initial reversible capacity and initial Coulombic efficiency compared to commercial Si nanoparticles(3,033 mAh/g vs.2,418 mAh/g,84.3%vs.73.1%).Synthesis is highly scalable,and a yield of 90.4%is achieved for the porous Si nanostructure with the capability to make an excess of 10 g per batch.Our synthetic nanoporous silicon is promising for practical applications in next generation lithium-ion batteries.
基金supported by National Key Research and Development Program of China (2016YFA0202500, 2015CB932500)the National Natural Science Foundation of China (21776019, 21422604)
文摘Lithium-sulfur （Li-S） batteries with intrinsic merits in high theoretical energy density are the most promising candidate as the next-generation power sources. The strategy to achieve a high utilization of active materials with high energy efficiency is strongly requested for practical applications with less energy loss during repeated cycling. In this contribution, a metal/nanocarbon layer current collector is proposed to enhance the redox reactions of polysulfides in a working Li-S cell. Such a concept is demon- strated by coating graphene-carbon nanotube hybrids （GNHs） on routine aluminum （AI） foil current collectors. The interracial conductivity and adhesion between the current collector and active material are significantly enhanced. Such novel cell configuration with metal/nanocarbon layer current collectors affords abundant Li ions for rapid redox reactions with small overpotential. Consequently, the Li-S cells with nanostructured current collectors exhibit an initial discharge capacity of 1,113 mAh g-1 at 0.5 C, which is -300 mAh g-1 higher than those without a GNH coating layer. The capacity retention is 73% for cells with GNH after 300 cycles. A reduced voltage hysteresis and a high energy efficiency of ca. 90% are therefore achieved. Moreover, the AI/GNH layer current collectors are easily implanted into current cell assembly process for energy storage devices based on complex multi-electron redox reactions （e.g., Li-S batteries, Li-O2 batteries, fuel cells, and flow batteries）.
基金Project(2015JC3004)supported by the Science and Technology Plan of Hunan Province,ChinaProject(2016JJ2147)supported by the Natural Science Foundation of Hunan Province,ChinaProject(51401243)supported by the National Natural Science Foundation of China
文摘b The discharge performance of Mg-Al-Pb-La anode was investigated by electrochemical techniques and compared withthat of Mg-Al-Pb alloy. The results indicate that the Mg-Al-Pb-La anode provides enhanced corrosion resistance at open circlepotential, and exhibits better discharge activity than the Mg-Al-Pb alloy. The utilization efficiency of Mg-Al-Pb-La anode ishigher than that of commercial Mg-Al-Zn （AZ） and Mg-Al-Mn （AM） alloys. A single Mg-air battery with Mg-Al-Pb-La alloy asthe anode and air as the cathode has an average discharge potential of 1.295 V and a discharge capacity of 1370 mA·h/g duringdischarge at 10 mA/cm2, which is higher than that of batteries using Mg-Li anodes. The enhancement in discharge performance ofthe Mg-Al-Pb-La anode is caused by its modified microstructure, which reduces the self-corrosion and accelerates the spalling ofoxidation products during battery discharge. Furthermore, the dissolution mechanism of Mg-Al-Pb-La anode during the dischargeprocess was analyzed.
