Experimental results indicated that the Mn3O4−Fe2O3 composite successfully synthesized at below 300ºC with a highly crystalline structure. The imaging results revealed that the morphology of composite consist of a very small clusters and a very tiny particles in a range between 100 and 1000 nm, respectively. These tiny particles were confirmed due to the existence of manganese, iron and oxygen elements. Electrochemical testing, including constant current charge-discharge was carried out. The composite contained 15% of activated carbon delivered much better electrochemical performance compared to the other two samples of 20 and 10%, respectively. The discharge capacity of 15% of activated carbon sample was calculated to be 657 mAh g-1 , which is higher than the sample of 20% (421 mAh g-1) and 10% (55 mAh g-1) after 100 cycles. The excellent electrochemical performance of sample 15% might be due to sufficiency of activated carbon in composite which provide a good contact between particles, increase electronic conductivity and accelerate the reaction of ions in chemical reduction and oxidation processes.

Keywords: Molten Salts Method, Mn3O4, Fe2O3, Composite, Anode, Lithium-ion battery

1.0 Introduction Rechargeable lithium-ion batteries have long been considered as an attractive power source due to high energy density, low maintenance, no memory effect, no scheduled cycling needed, less self-discharge rate and a little harm when disposed, making lithium-ion well suited for modern fuel gauge applications (Chen, Yang, Fang, Zhang, & Hirano, 2013; Fu et al., 2005; Megahed & Scrosati, 1994; Min-min, Deng-jun, & Kai-yu, 2011; Takehara & Kanamura, 1993; Wang et al., 2004; Yang et al., 2012; Zhang, Song, Chen, Zhou, & Zhang, 2012). To ensure the lithium-ion battery is relevant to the current and future demands, research and development on battery electrodes needs to remain continue to ascertain that the electrodes maintain their good capacity retention, high rate capability, and safe operation over many charge-discharge cycles (Fan et al., 2004; Ji & Zhang, 2009b; Poizot, Laruelle, Grugeon, Dupont, & Tarascon, 2000; Rai, Anh, Gim, et al., 2013). In battery field, Cr, Mn, Fe, Co, Ni and Cu are the transition metal oxide compounds which are received increasing attention because of their promising electrochemical properties, such as a double theoretical capacity than carbon and safety advantage for evading the development of harmful Li dendrites (Cheng, Tao, Liang, & Chen, 2008; Fan et al., 2004; Poizot et al., 2000; Rai, Anh, Park, & Kim, 2013; Wu & Chiang, 2006), making them fascinating anode materials for LIBs. Nonetheless, the intensive researches have revealed that anodes based on pure transition metal oxides suffer serious capacity loss caused by the huge volume changes and aggregation during lithium insertion/ extraction processes resulting polarization, and slow diffusion of lithium ions and electrons in the active materials (Cheng et al., 2008; Fan et al., 2004; Lee et al., 2008; Yan et al., 2003; X. J. Zhu et al., 2009; X. Zhu, Zhu, Murali, Stoller, & Ruoff, 2011). Integration two or more compounds of transition metal oxides are anticipated to outwit these problems because the resultant composites merge the advantages of both transition metal oxides fillers, which have large Li storage capacity, low discharge potential and good interface affinity between composite particles (Cheng et al., 2008; Fan et al., 2004; Hassan, Guo, Du, Wexler, & Liu, 2009; Poizot et al., 2000). Furthermore, these transition metal oxides have highly-developed internal surface area, and large pore volume, which facilitate easy access of lithium-ions to the whole interior places of anodes, reduce lithiumion disperse distance, and amplify severely the pace of electron transport (Bruce, Scrosati, & Tarascon, 2008; Ji & Zhang, 2009a). As a result, these composites can be promising candidates as anodes in LIBs. In this study, we report on the preparation of manganese-iron oxides (Mn3O4−Fe2O3) composite from commercial MnCl2•2H2O and FeCl2•3H2O as structuring agents via a relatively simple and inexpensive molten salts technique (Hassan, Guo, Chen, & Liu, 2010; Hassan, Rahman, Guo, Chen, & Liu, 2010; Liu et al., 2010), and then coated with different amount of activated carbon. The as-prepared composite evidently improved electrochemical performance in terms of their high reversible capacities, excellent cycling performance, and good rate capability.

2.0 Material and methods

2.1 Materials Mn3O4-Fe2O3 composite was prepared from starting materials of lithium nitrate (LiNO3, 99%), lithium hydroxide monohydrate (LiOH•H2O, 99%), hydrogen peroxide (H2O2, 32%), manganese chloride (MnCl2•2H2O, 98%) and iron chloride (FeCl3•6H2O, 99%). All chemicals were purchased from Sigma Aldrich Chemical Reagent Company and used without further purification.

2.2 Sample preparation The starting precursors were weighted as follow: 1.7229 g (100 mmol) of LiNO3, 0.2118 g (20 mmol) of LiOH•H2O, 0.4047 g (10 mmol) of MnCl2•2H2O and 0.6756 g (10 mmol) of FeCl3.6H2O. All precursors were mixed together and hand grinded in an agate mortar until it literally homogeneous. An amount of 1.42 European International Journal of Science and Technology Vol. 3 No. 9 December, 2014 63 g (50 mmol) of H2O2 was dropped cautiously under a fume hood and stirred for a few minutes. The mixture was transferred in a beaker and dried at 100°C for 24h in a vacuum oven and further heated at 300°C for 3h in a muffle furnace. The beaker was cooled down naturally before the heated sample was collected and washed for several times with distilled water and acetone using a centrifuge to remove any possible residual reactants and impurities. The product was dried in vacuum oven at 100°C for 12h, giving the final asprepared sample.

2.3. Characterization techniques Thermogravimetric analysis (TGA) was carried out with Mettler Toledo TGA/SDTA851e and recorded under air at a heating rate of 10°C min-1. X-ray diffraction (XRD) patterns of the as-prepared products were recorded on a MiniFlex II diffractometer equipped with an X’celerator using CuKα radiation (λ) 0.1542 nm, operated at 40 kV and 40 mA in the 2θ range between 20° and 80°. Scanning electron microscopy (SEM) observations and energy dispersive spectroscopy (EDS) measurements were carried out on a JSM 6360LA SEM. For the morphology observations, powder samples were pasted on studs and run for the gold coating to avoid the discharge problem, and then observed on a the same JSM 6360LA SEM at an acceleration voltage of 20 kV.

2.4 Electrochemical measurements The as-synthesized material was used to prepare the electrode by mixing together Mn3O4−Fe2O3 composite, polyvinylidene fluoride (PVDF) binder, and activated carbon (AC) in 3 different weight ratios of 80:10:10 (sample A), 75:10:15 (sample B) and 70:10:20 (sample C), respectively. All the compounds were grinded together in an agate mortar. N-methylpyrrolidone (NMP) was dropped into the agate mortar to form a viscously slurry. The slurry was pasted onto Cu foils and dried in vacuum at 100 °C for 12 hours to remove the NMP solvent. The electrode was then pressed using a hydraulic pressure to enhance the contact between the copper foil, active materials, and conductive carbon. Cells were assembled in an argon-filled glove box (H2O, O2 < 0.1 ppm, Mbraun, Unilab, USA). The electrolyte was 1M LiPF6 in a mixture of ethylene carbonate (EC) and dimethyl carbonate (DEC) (1:1 by volume, provided by MERCK KgaA, Germany), and microporous polypropylene film was used as a separator. Lithium metal foil was used as a counter electrode. The cells were galvanostatically discharged and charged using a Neware battery cycler at current density of 93 mA g-1 in the voltage range of 0.01- 3.0 V vs Li/Li+ .

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