碳纳米材料ppt课件.ppt

1、MnO/C coreshell nanorods as high capacity anode materials for lithium-ion batteries,Journal of Power Sources,1,Four parts,1. Introduction 2. Experiment 3. Results and discussion 4. Conclusions,2,Introduction,transition metal oxides have attracted great attention as anode materials for lithium ion ba

2、tteries, due to 1 their high theoretical capacity 2 safety 3 low cost 4 natural abundance,3,Some obstacle 1 poor cycling performance (large volume expansion due to the generation of Li2O) 2 poor electronic conductivity (electrode materials with designed nanostructure can improve it),4,MnO shows rela

3、tively low electromotive force电动势 (emf) value (1.032V vs. Li+/Li) and high density (5.43gcm3) . However, this kind of material has seldom been reported as an anode material nanocrystalline MnO thin film, and MnO powder as anode has shown low overpotential超电势 and good cycling performance,5,In this pa

4、per The prepared MnO/C coreshell nanorods much higher specific capacity than that of MnO microparticles and MnO2 nanowires as anode material of lithium ion battery.,返回,6,Experiment,合成部分 MnO/C coreshell nanorods were synthesized by the reduction of carbon precursor coated MnO2 nanowires. The MnO2 nan

5、owires were synthesized by a typical hydrothermal reaction,7,Experiment,表征 X-ray diffraction Field emission scanning electron microscopy (FESEM ） transmission electron microscopy(TEM) SAED,8,Experiment,电化学实验部分 performing using 2032 coin-type cells assembled in an argon-filled glove box slurry :activ

6、e materials (70wt%), acetylene black乙炔黑 (20wt%), and polyvinylidene fluoride 聚偏二氟乙烯(PVDF 10wt%) in N-methyl-2-pyrrolidone 氮甲基二吡咯烷酮(NMP). The slurry was spread onto the Cu foil with a doctor blade刮墨刀片 and dried at 120C overnight under vacuum,9,Experiment,electrode area is 1cm2 loading of active mater

7、ial is 1.01.2mgcm2 electrolyte :a solution of 1M LiPF6 in ethylene carbonate 碳酸亚乙酯(EC) and dimethyl carbonate 碳酸二甲酯(DMC) with a weight ratio of 1:1,10,Experiment,Pure lithium foil was used as counter and reference electrode Cyclic voltammetry循环伏安法 (CV) Chargedischarge testing was performed in the ra

8、nge of 0.013.0V specific capacity,返回,11,Results and discussion,1 、 MnO2 nanowires were synthesized by hydrothermal reaction. The crystal structure of the as-prepared MnO2 nanowires was confirmed by XRD (Fig. 1) All the diffraction peaks can be indexed to the body-centered tetragonal -MnO2 phase,12,R

9、esults and discussion,2、 MnO/C coreshell nanorods were obtained through sintering the carbon precursor coated MnO2 nanowires in flowing Ar containing 5vol.% H2. As shown in Fig. 1 the crystal structure of MnO/C coreshell nanorods can be indexed to the face-centered cubic phase of MnO low intensity d

10、iffraction peak in the range of 2030 is likely associated with the presence of amorphous carbon无定形碳(originated from the decomposition of the copolymer surfactant).,13,Results and discussion,14,Results and discussion,FESEM: nanowire structure with diameters ranging from 2050 nm and There is no signif

11、icant change in diameter,15,Results and discussion,TEM,16,The nanorods show polycrystalline feature and are agglomerated into bundles with a length extending to a few hundred nanometers. The fracturing of the nanowire structure into nanorods may be caused by the reduction from MnO2 to MnO. An indivi

12、dual nanorod consists of nanoparticles with diameters from 20 nm to 30 nm.,Results and discussion,17,Results and discussion,All the diffraction rings can be indexed to the face-centered cubic Fm-3m crystal structure.,18,Results and discussion,HRTEM,19,Results and discussion,In the region A:the surfa

13、ce of the MnO crystal, and the lattice can be clearly resolved with a d-spacing of 0.255nm for the (111) planes. in the region B :carbon layer, which presents numerous black spots, indicating that the surface of the nanorod is covered with a thin layer of amorphous carbon. On the edge of the nanorod

14、, a thin carbon layer with a thickness of 12nm is clearly visible.,20,Results and discussion,cyclic voltammetry (CV),21,Results and discussion,22,Results and discussion,23,Results and discussion,Cycling performance,24,Results and discussion,This nanorod electrode exhibited higher capacity than that

15、of MnO2 nanowire electrode after 40 cycles. The good electrochemical performance is a result of the combined advantages of the nanorod structure and the porous carbon coating layer.,25,Results and discussion,Nanosize materials with large surface area can provide more active sites for Li+ intercalati

16、on/de-intercalation and shorten the diffusion length for lithium ions in the solid phase. The nanoporous carbon coating layer with mesopores can form a mixed conducting 3D network that facilitates the migration of both the Li+ and the e, so that they reach each surface of the MnO nanorods .,返回,26,Co

17、nclusions,1、Using block copolymer F127 as the carbon source, MnO/C coreshell nanorods were successfully prepared from MnO2 nanowires by calcination in a gas ow of 5 vol.% H2 in Ar. 2、The XRD pattern shows that the product has a face-centered cubic phase structure. FESEM and TEM images show that a thin carbon layer was coated on the surfaces of the MnO nanorods.,27,Conclusions,3、The MnO/C coreshell nanorod electrodes delivered a higher specic discharge capacity than MnO2 nanowires after 40 cycle