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Table of Content

    30 April 2021, Volume 27 Issue 2
    Impact of River Impounding on Material Cycling and Its Ecological Significance in Southwest China
    Rapid determination of TOC, TN and BSi content in reservoir sediments based FTIR
    MEI Lin, FAN Xinyi, YUE Yihong, LIU Liu, CHU Yongsheng, WANG Fushun
    2021, 27(2):  227-235.  doi:10.12066/j.issn.1007-2861.2290
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    Fourier transform infrared spectroscopy (FTIR) was used to analyse sediments from Yantan (YT) Reservoir in Southwest China, and a rapid analysis method for sediment total organic carbon (TOC), total nitrogen (TN) and biogenic silica (BSi) content based on FTIR was investigated. The FTIR prediction models of TOC/TN/BSi contents were established by partial least squares regression (PLSR) method, respectively. The prediction accuracy of this model was verified based on the measured data. This method can effectively extract geochemical information from reservoir sediments and can be applied to the study of high-resolution paleoenvironmental changes. The method requires small sample size and simple pretreatment process to rapidly and economically determine the content of various sediments components, which is of great advantage in determining a large number of sediment samples.

    Distribution characteristics, influencing factors and sources of heavy metals in karst deep-water reservoirs: a case study of Longtan Reservoir
    GUAN Tianhao, LI Xiaodong, WANG Yiyao, YANG Mengdi, CUI Gaoyang, DING Shiyuan, ZHANG Xuecheng
    2021, 27(2):  236-249.  doi:10.12066/j.issn.1007-2861.2289
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    In order to reveal the influencing factors and sources of the temporal and spatial variation of dissolved heavy metals in karst deep-water reservoirs, this paper selected Longtan Reservoir in Pearl River basin as the research object, and analysed the dissolved heavy metals in stratified water, surface water of tributaries flowing into the reservoir area and discharged water in July 2019 and January 2020, as well as the hydrochemical parameters of the reservoir area in April, July, October 2019 and January 2020. Through Piper diagram of main ions, Pearson correlation analysis among the different kinds of heavy metals, cluster analysis and canonical correlation analysis (CCA) between environmental factors and dissolved heavy metals, the results showed that the weathering of carbonate rocks in the basin was an important external source of dissolved heavy metals in Longtan Reservoir. The change in relative water column stability (RWCS) caused by the seasonal thermal stratification of reservoir water body was the main factor affecting the spatial and temporal distribution of dissolved heavy metals in the study area. Higher RWCS usually promoted the release of Cr and Cu, whereas lower RWCS promoted the release of Fe and As. This study provided a theoretical basis for exploring the relationship between hydrodynamic conditions and dissolved heavy metals, and had important guiding significance for scientific utilization and protection of water resources in karst deep-water reservoirs.

    Spatial and seasonal variability of particulate organic carbon in the Wujiang River
    ZHANG Jinhua, HUANG Jiaqi, LIN Xin, WANG Fushun, MA Jing
    2021, 27(2):  250-259.  doi:10.12066/j.issn.1007-2861.2145
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    Surface water samples were collected from seven cascade reservoirs across the mainstream Wujiang River and Hongfeng Reservoir on the tributary of Maotiao River, to measure the concentration of total suspended matter (TSM). Samples were analysed for elemental and stable carbon isotopic ($\delta ^{13}$C) composition and lignin phenols to investigate the variability in the spatial and seasonal distribution of particulate organic carbon (POC). The TSM in surface water varied greatly across the seasons. It was higher in the spring and summer than in autumn and winter. POC and lignin content ($\Sigma $8 and $\Lambda $8, respectively) in surface water showed high variability that were greatly influenced by season. POC in upstream waters was higher than in downstream waters in the autumn and winter, reflecting dam interception. $\Sigma $8 and $\Lambda $8 in the TSM samples exhibited a significant linear relationship, stronger in autumn and winter than in spring and summer. The $\delta ^{13}$C of TSM was significantly negative. This was potentially due to the more depleted $\delta ^{13}$C of terrestrial plant debris and freshwater plankton, that was likely to exist in surface water. Angiosperms were the dominant vegetation species reflected by lignin. There was a high diversity in the plant sources of terrestrial organic matter in surface particulate matter samples. The extent of degradation of TSM samples was relatively low, and aggravated degradation was observed in July and October, likely related to vigorous microbial activity.

    Impact of dam construction on land-use change at the catchment and landscape scale: a case study of Hongjiadu Reservoir
    FU Junjie, WANG Wei, LI Wei, SUN Junyao
    2021, 27(2):  260-270.  doi:10.12066/j.issn.1007-2861.2291
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    Land-use change is closely related to the human disturbance. Dam construction alters the land-use of a reservoir's surroundings, ultimately affecting the transport of matters from terrestrial ecosystem to the ocean through inland waters. Taking the Hongjiadu Reservoir in Wujiang River as an example, a land-use transfer matrix was applied to discuss the dam-induced change in land-use in the Hongjiadu Reservoir catchment at both the catchment scale and landscape scale. Results showed as follows. From a time scale perspective, land-use change mainly occurred in the second stage after reservoir impoundment. In the first stage, the overall change of Hongjiadu Reservoir catchment was that the cropland area decreased by 91.33 km$^{2}$, while the forest, grassland, water and urban areas increased by 26.54, 8.84, 55.51 and 0.45 km$^{2}$, respectively. In the second stage, the cropland, forest and grassland areas decreased by 230.98, 30.17 and 42.88 km$^{2}$, respectively, while water and urban areas increased by 9.07 and 295.46 km$^{2}$, respectively. At the spatial scale, the land-use change was mainly concentrated in the vicinity of Hongjiadu Reservoir, in the decrease of cropland areas and the increase of grassland areas. The land-use type changed the most within the 0-1 km buffer zone at the reservoir's landscape scale, mainly manifested as water becoming grassland and urban becoming cropland. Different land-use types were inundated to form the reservoir area after the construction of Hongjiadu dam, which with the greatest impact on the land-use change within the 0-1 km buffer zone of the reservoir.

    Characteristics of lignin in sediment cores from cascade reservoirs downstream of the Wujiang River and[1mm] source analysis of organic carbon
    HUANG Jiaqi, LIN Xin, WANG Fushun, MA Jing
    2021, 27(2):  271-279.  doi:10.12066/j.issn.1007-2861.2280
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    The terrestrial organic carbon (OC) in sediment cores from two large deep-water reservoirs (Silin and Pengshui) located in the lower reaches of the Wujiang River in the karst landscape of Southwest China were analysed and quantified using lignin biomarker technology. Qualitative analysis and quantitative calculations of terrestrial-derived organic carbon in sediment cores using the lignin biomarker technique showed that the lignin content index $\Sigma 8$ ranged from 0.55 to 2.97 mg/10 g dw (dry weight) and $\Lambda 8$ ranged from 0.38 to 1.42 mg/100 mg OC. The lignin in the sediment cores was derived mainly from the herbaceous tissues of angiosperms, and had been degraded via demethylation, demethoxylation, and oxidative degradation of the side chains by white rot and brown rot bacteria. The end-member model showed that the contribution of exogenous organic carbon to the sediment cores was slightly greater than that of endogenous organic carbon, with soil organic carbon contributing the most. The influence of river cascade damming on sedimentary organic carbon was manifested in the interception of exogenous organic carbon and the accmulation of endogenous organic carbon, and there was obvious spatial heterogeneity in the distribution of both types of organic carbon.

    Research Articles
    Effects of boron content on microstructure and mechanical properties of FeCoNiCrAl$_{\bf 0.1}$B$_{ x }$ high-entropy alloy
    XIE Yaxi, CHEN Yexin, MA Xingxing
    2021, 27(2):  280-288.  doi:10.12066/j.issn.1007-2861.2161
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    The effects of boron content on the microstructure and mechanical properties of FeCoNiCrAl$_{0.1}$B$_{x }(x = 0{\sim}$0.1) high-entropy alloy were investigated in this study. The results suggested that the FeCoNiCrAl$_{0.1}$B$_{x}$ high-entropy alloy consisted of single face-centered cubic (FCC) $\gamma $ phases when $x\le 0.03$, whereas it consisted of FCC $\gamma $ phase, trace of ordered FCC phase, and boride when $x\ge 0.05$. With the addition of boron atoms in the alloy, the grain size of the alloy refined, tensile strength of the alloy increased, and elongation of the alloy decreased with an increase in the boron content. The fractographs of the FeCoNiCrAl$_{0.1}$B$_{x}$ high-entropy alloy exhibited all transgranular fracture patterns during tensile testing in vacuum.

    Quasi-twisted codes achieving the Gilbert-Varshamov bound
    LU Xiaohua, WANG Yongchao, DING Yang
    2021, 27(2):  289-297.  doi:10.12066/j.issn.1007-2861.2129
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    Quasi-twisted codes are regarded as a generalisation of cyclic codes. The Gilbert-Varshamov bound is an important criterion for measuring the quality of quasi-twisted codes. A class of randomized one-generator quasi-twisted codes was presented. Furthermore, it was proved that, using the properties of irreducible polynomials, random one-generator quasi-twisted codes asymptotically achieved the Gilbert-Varshamov bound with high probability and identified a one-generator module of a polynomial quotient ring.

    First-principles calculation of the rectification characteristic of single-molecule diodes
    YUAN Ying, LI Weiju, CHEN Jingzhe
    2021, 27(2):  298-306.  doi:10.12066/j.issn.1007-2861.2148
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    In the field of molecular electronics, structural design of a molecule is necessary to achieve different functionalities. The rectification behaviour of single-molecule diodes is one of the most attractive device features. The electron transport of symmetric and asymmetric single molecular junctions was studied, which correspond to tetraphenyl and dipyrimidiny-diphenyl monomolecular junctions, respectively. Both of them were covalently bonded to two gold electrodes. Asymmetric diblock molecules exhibited significant rectifying behaviour compared to their homologous symmetric blocks, and the electrons flow from diphenyl to dipyrimidinyl. The first-principles method was used, including density functional theory (DFT) and the non-equilibrium Green's function (NEGF) method, to study the electronic structure and quantum transport of single-molecule junctions. The asymmetry in the $I$-$V$ could be explained by the localisation of the electron density at one end of the asymmetric molecule, leading to a nonequilibrium effect under bias voltage. Theoretical results agreed qualitatively with the experimental works reported in the literature. Moreover, upon investigating different contacting ends, it was found that the scanning tunneling microscope (STM)-tip setup in the experiment would cancel the rectification effect to some extent; meanwhile, the STM-tip results also confirmed the previous theoretical prediction.

    Numerical simulation of the supersonic flow/jet flow and their interaction at different flight altitudes
    DENG Fang, HAN Guilai, LIU Meikuan, DING Jue, WENG Peifen, JIANG Zonglin
    2021, 27(2):  307-324.  doi:10.12066/j.issn.1007-2861.2147
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    The two-dimensional Navier-Stokes equations were solved using high-precision schemes, and the basic structure of the flow field in the supersonic flow and jet flow at different flight altitudes was studied. The three-order Runge-Kutta scheme was adopted in the time-marching scheme. The five-order weighted essentially non-oscillatory (WENO) and the six-order central difference schemes were used to discretize the convection term and viscous term, respectively. The parallel computation was performed using MPI non-blocking communication. The basic structural characteristics of backward-facing step flow and jet flow under backward-facing steps at different flight altitudes were studied. Furthermore, by combining the two flows, the flow field structure of the interaction between the supersonic flow and jet flow was studied. The supersonic flow above the backward-facing step was changed to simulate the environment of different flight altitudes, and the environment affected structures such as vortices, shear layers, and shock waves in the flow field. It was observed that after the interaction between the supersonic flow and jet flow, a recirculation zone was generated near the back step, and the presence of supersonic flow affected the structures of the jet flow.

    Progressive damage analysis of the bearing capacity of L-type carbon fibre reinforced composite connectors
    DU Yapeng, HU Xiaoyu, CHU Haijian
    2021, 27(2):  325-335.  doi:10.12066/j.issn.1007-2861.2126
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    The failure modes and bearing capacities of L-type carbon fibre reinforced composite connectors (CFRCC) were studied through experimental testing and computational simulation. The results demonstrated the following. ① Delamination at the corner and matrix damage around bolt holes were the dominant failure modes of L-type CFRCC under tensile loading. ② Comparing the different combinations of two strength failure criteria and two material degradation criteria revealed that the combination of mixed strength failure criteria and the Camanho-Mathews stiffness degradation criteria was more suitable for analysing the progressive damage to the connectors. ③ The predictions from the finite element simulation were in good agreement with the experimental results, and the relative error of the bearing capacity was 9.4%. The strategy of "design-test-simulation-prediction-validation" and the results obtained in this study may provide reliable guidance for the design of L-type CFRCC.

    Numerical simulation of particle flow during a drawing test of a ribbed geomembrane and sandy soil interface under different temperatures
    GAO Junli, XU Hongfei, YUAN Chuan, CAO Wei
    2021, 27(2):  336-346.  doi:10.12066/j.issn.1007-2861.2128
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    The features of a ribbed geomembrane and sandy soil interface in a landfill liner system were studied by comparing the results of an indoor experiment and a two-dimensional particle flow code (PFC$^{\rm 2D})$ simulation using the discrete element method. An interface drawing test of the ribbed geomembrane and sandy soil interface was conducted under different combinations of ribbed heights and temperatures. Then, the macroscopic stress-strain curves of the ribbed geomembrane and sandy soil interface, the changing rule of the displacement field of microscopic particles, and the stress field were investigated. The results showed that the tensile stress of the ribbed geomembrane and sandy soil interface was superior to that of the smooth geomembrane ($h =0$ mm) and sandy soil interface. The drawing stress limit of the interface increased with the increase in rib height, and decreased with the increase in temperature. In addition, the friction coefficient of the interface decreased with the increase in temperature. Simulation of the microscopic aspects (particle displacement and internal contact force) also corresponded with the results of the ribbed geomembrane and sandy soil interface drawing experiment. The soil particle displacement near the ribbed geomembrane and sandy soil interface was larger, and the overall particles moved to the top left. The sandy soil at the top after the rib had downward movement owing to the normal stress. With an increase in temperature or decrease in rib height, the displacement of sand particles near the ribbed geomembrane and sandy soil interface increased, and the interface stability between the ribbed geomembrane and sandy soil became negligible. The contact forces on the left side of the drawing model and near the ribbed geomembrane were larger, and gradually decreased to the upper and lower sides. With an increase in rib height or a decrease in temperature, the contact force around the interface between the ribbed geomembrane and sandy soil increased. The entire process of drawing the ribbed geomembrane and sandy soil interface from macroscopic to microscopic was described.

    Seismic test and finite element analysis of bolted joints connecting concrete-filled square steel tubular column and H-type steel beam
    CHEN Jingyuan, YANG Feng, DING Xinbiao, WANG Peicheng
    2021, 27(2):  347-359.  doi:10.12066/j.issn.1007-2861.2130
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    Three concrete-filled square steel tubular column and H-type steel beam for two-sided all-bolted connections were fabricated according to the specifications of two countries, China and America. Repeated low cyclic loading tests were conducted on different loading systems. The results showed that the hysteretic loop curves and skeleton curves of the welded joint had obvious characteristics because of the relative slip in the clapboard flange, and the hysteretic loop curve in the horizontal section showed a pinch shrink shape. The test results indicated that the loading system controlled by the displacement angle was more complete and better than the loading system controlled by "two stages" owing to the existence of the slip section in tests on all the bolted joints. At the same time, using the finite element software, ABAQUS, for repeated low cyclic loads on the steel beam and concrete-filled steel tube, the stress performance of the bolt connection node was calculated and analysed. These results verified the accuracy of the test results. Further, the stiffness degradation, ductility performance, and overall strength degradation coefficient of the seismic performance of the nodes were analysed. In addition, because of the existence of the relative slip in the plate flange, a revised evaluation of these indicators was proposed.

    An improved genetic algorithm based mixed-model U-shaped assembly line balancing problem of type-Ⅱ
    PENG Yunfang, LIANG Yuzhen, XIA Beixin
    2021, 27(2):  360-368.  doi:10.12066/j.issn.1007-2861.2165
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    To solve the type-Ⅱ balancing problem of a mixed-model U-shaped assembly line to minimise the cycle time, a mathematical model was established and an improved genetic algorithm was designed. In the decoding process of the genetic algorithm, three search techniques were used to assign tasks to workstations, and workstation times under these search techniques were compared. The optimal assignment was selected according to the expected cycle time. The task assignment result determined whether to update the value of the expected cycle time automatically. The performance of the proposed improved genetic algorithm was proved by a set of benchmark instances. Finally, a practical balancing problem was analysed and effectively solved by the proposed method.

    Design and application of Co-Mn metal-organic-frameworks derived bimetallic sulfides as anode for lithium-ion batteries
    CHEN Hengqiao, LÜ Liping, WU Minghong
    2021, 27(2):  369-378.  doi:10.12066/j.issn.1007-2861.2157
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    The facile synthesis of a Co-Mn metal-organic-framework (MOF) with a porous structure is reported. The prepared bimetallic MOF was then vulcanized to obtain a porous CoS$_{2}$/MnS bimetallic composite. By comparing single metal MnS and CoS$_{2}$ materials prepared by the same method, it was observed that the CoS$_{2}$/MnS bimetal composite exhibited a petal-like porous sheet structure and a smaller particle size than that of single metal composites. When used as an electrode material in lithium-ion batteries, the CoS$_{2}$/MnS composite exhibited the best lithium storage performance among contemporary composites. It was believed that the porous petal-like structure provided a short transport pathway for lithium-ions. The synergistic combination of the two metal sulfides also effectively inhibited the rapid capacity decay caused by volume changes during cycling. In addition, the carbon skeleton derived from the MOF organic ligands further played a positive role in the enhancement of the electronic conductivity of the material.

    Preparation of lactic acid by catalytic conversion of glucose by dual-metal ions
    LI Hangwei, YANG Xiang, LUO Xiaofei, GUO Xiaoya, KONG Lingzhao-
    2021, 27(2):  379-388.  doi:10.12066/j.issn.1007-2861.2152
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    Different dual-metal ions were selected as catalysts to prepare lactic acid (LA) by hydrothermal conversion of glucose under alkaline conditions, and Sn$^{2+}$ and Cu$^{2+}$ were found to have a certain synergistic effect. The effects of reaction temperature, time, alkali addition amount, and metal ion ratio on lactic acid yield were studied to optimise the experimental conditions. The optimum process conditions were as follows: 0.025 g glucose, 2 mmol sodium hydroxide, $n$(Sn$^{2+})$:$n$(Cu$^{2+})$=0.25:0.75 (1 mmol total), 20 mL water, reaction temperature 200 ${^\circ}$C, and reaction time 3 h. Under optimal conditions, the yields of lactic acid, formic acid (FA), and acetic acid (AA) were 64.1%, 20.3% and 11%, respectively. Several model compounds were selected as intermediate products for the hydrothermal transformation experiments. According to the experimental results, the conversion mechanism of the hydrothermal conversion of glucose was investigated. Important intermediates detected in the conversion process were fructose, 1,3-dihydroxyacetone and pyruvaldehyde. There was a synergistic effect between the two metal ions, as Cu$^{2+}$ inhibited the decomposition of lactic acid, and Sn$^{2+}$ increased the conversion efficiency of pyruvaldehyde to lactic acid, finally increasing the yield of lactic acid.

    Physicochemical characterization of ambient particulate matter emitted from solid fuel combustion in high lung cancer incidence areas in Xuanwei, Yunnan
    XIAO Kai, PENG Jiaxian, XIE Tingting, ZENG Junyang, YAO Chuanhe, MYAT Sandar Win, LÜ Senlin, WANG Qingyao, YONEMOCHI Shinich
    2021, 27(2):  389-399.  doi:10.12066/j.issn.1007-2861.2156
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    Samples of atmospheric particulate matter from solid fuel (coal and wood) combustion were collected in the high lung cancer incidence area of Xuanwei, Yunnan, and 796 particles emitted by combustion were analysed by scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDX). According to the microscopic characteristics and chemical element compositions of the particles, the particles were divided into four categories, namely mineral particles, fly ash, soot aggregates, and unidentified particles. The $P$(X) method was used to further classify the mineral particles into eight different types, namely Si-rich, S-rich, Ca-rich, Fe-rich, Ti-rich, Al-rich, Na-rich, and others. The percentages of Si-rich, Ca-rich, Fe-rich, and S-rich particles in coal-fired particulate matter and combustion biomass particles accounted for 44.47%, 20.49%, 8.85%, 1.22% and 55.91%, 17.27%, 6.36%, 2.27%, respectively. The chemical analysis results showed that the mass concentrations of the crustal elements Al, Fe, Ca, and Mg in the particles were relatively high, and the mass concentrations of heavy metal elements were relatively low. There was a positive correlation ($R^{2}=0.63$) between the results of the chemical analysis of particulate matter emitted from coal combustion and the results of single particle analysis.

    Preparation and electrochemical properties as anode materials for lithium-ion batteries of MnO@CoMn$_{\textbf{2}}$O$_{\textbf{4}}$/N-C nanowire composites
    CHENG Erbo, WANG Shangdai, HUANG Shoushuang, CHEN Dayong, HU Zhangjun, CHEN Zhiwen
    2021, 27(2):  400-410.  doi:10.12066/j.issn.1007-2861.2155
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    Transition metal oxides have a higher theoretical capacity as anode materials for lithium-ion batteries (LIBs). However, they often suffer from poor capacity retention owing to their low electrical conductivity and large volume variations during the charge/discharge process. Carbon coating is an effective way to enhance the electrical conductivity of metal oxides. The synergistic effects of the two components can also effectively improve the electrochemical performance of the material. In this study, MnO$_{2}$@ZIF-67 organic-inorganic hybrid nanostructures were prepared using MnO$_{2}$ nanowires as a template. N-doped carbon-coated MnO@CoMn$_{2}$O$_{4}$ nanowire composites (MnO@CoMn$_{2}$O$_{4}$@N-C) were synthesised by annealing. The organic ligand of ZIF-67 underwent carbonisation during high-temperature calcination to produce N-doped carbon, which improved the electrical conductivity. When MnO@CoMn$_{2}$O$_{4}$/N-C nanowire composites were used as the anode material for LIBs, a discharge capacity of 1 594.6 mA$\cdot$h/g was achieved in the first cycle, with a retention capacity of 925.8 mA$\cdot$h/g even after 100 cycles at current density of 0.1 A/g and a reversible capacity of 837.6 mA$\cdot$h/g at 0.5 A/g. It also had an excellent rate cycling performance. The outstanding electrochemical performance was attributed to the unique structure as well as the coating effect of N-doped carbon.