MnO nanoparticles anchored on graphene nanosheets via in situ carbothermal reduction as high-performance anode materials for lithium-ion batteries Danfeng Qiu, Luyao Ma, Mingbo Zheng n , Zixia Lin, Bin Zhao, Zhe Wen, Zibo Hu, Lin Pu, Yi Shi Nanjing National Laboratory of Microstructures, School of Electronic Science and Engineering, Nanjing University, Nanjing 210093, China article info Article history: Received 5 May 2012 Accepted 11 June 2012 Available online 18 June 2012 Keywords: MnO Graphene Nanoparticles Nanocomposites Energy storage and conversion Lithium-ion battery abstract A MnO nanoparticle/graphene composite was prepared via in situ carbothermal reduction of Mn 3 O 4 on the surface of graphene nanosheets. The formed MnO nanoparticles with diameters ranging from 20 nm to 250 nm integrated tightly with the graphene nanosheets. As anode material for lithium-ion batteries, the nanocomposite showed a high specific capacity of approximately 700 mA h g 1 at 100 mA g 1 , excellent cyclic stability, and good rate capability. During the charge-discharge process, graphene nanosheets served as a three-dimensional conductive network for MnO nanoparticles. Furthermore, the detachment and agglomeration of MnO nanoparticles were effectively prevented due to the tight combination of MnO nanoparticles and graphene. & 2012 Elsevier B.V. All rights reserved. Introduction Transition metal oxides have long been considered as anode materials for lithium-ion batteries (LIBs) because of their high capacities [1]. However, the large volume change of metal oxides during the Li insertion/extraction process causes mechanical degradation and results in the rapid loss of capacity. Moreover, the low conductivity of metal oxides further hastens the degrada- tion process. To solve these problems, carbonaceous materials with high electrical conductivity and good stability can be used as matrices for metal oxides [2–5]. Among various metal oxides, manganese monoxide (MnO) is extremely attractive because of its relatively low electrochemical motivation force (1.032 V vs. Li/Li þ ), small overpotential, low cost, and environmental benig- nity [6–8]. Recently, MnO/carbon composite materials, such as coaxial MnO/carbon nanotubes [9], MnO/carbon core–shell nanorods [10], and MnO cubic particles/carbon composite [11], have been reported as anode materials for LIBs. The results showed that the combination of MnO and carbon could improve the electrochemical performance. Graphene is an excellent matrix on which to anchor LIB active materials due to its superior electrical conductivity, excellent mechanical flexibility, and good chemical stability [12,13]. Recently, Zhang et al. reported the synthesis of nitrogen-doped MnO/graphene hybrid material for LIBs via a hydrothermal method followed by ammonia annealing at 800 1C [14]. In the present work, MnO nanoparticle/graphene composite was pro- duced via in situ carbothermal reduction of Mn 3 O 4 on the surface of graphene nanosheets (GNS). The MnO/GNS nanocomposite showed high performance as an anode material for LIBs. Experimental GNS was fabricated via the thermal exfoliation method described in our previous work [15]. Briefly, graphite oxide was thermally exfoliated at 300 1C for 3 min in air, and subsequently treated at 900 1C for 3 h in Ar. In a typical synthesis of MnO/GNS nanocomposite, 1.51 g of Mn(NO 3 ) 2 aqueous solution (50 wt%) was mixed with 20 mL of enthanol. 100 mg of GNS was added into the solution and then ultrasonically treated for 10 min. The suspension solution was mixed using a magnetic stirrer in a ventilation cabinet; the ethanol in the solution evaporated continuously. Lastly, dried Mn(NO 3 ) 2 /GNS composite was col- lected and treated at 700 1C for 5 h in Ar. The final MnO content in MnO/GNS was about 75% by weight. In the control experiments, simplex Mn 3 O 4 sample was prepared by heating Mn(NO 3 ) 2 at 700 1C for 5 h in Ar, whereas Mn 3 O 4 /GNS nanocomposite was obtained by heating Mn(NO 3 ) 2 /GNS at 500 1C for 5h in Ar. The obtained samples were investigated via X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/matlet Materials Letters 0167-577X/$ - see front matter & 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.matlet.2012.06.045 n Corresponding author. Tel.: þ86 25 83621220; fax: þ86 25 83621220. E-mail address: zhengmingbo@nju.edu.cn (M. Zheng). Materials Letters 84 (2012) 9–12