Effect of Heat-treatment Temperature on the Electrochemical Performances of the Li_2MnSiO_4/C Composite Prepared through Polyol Process

The Li2MnSiO4/C composite was synthesized through a polyol process following by heat-treatment at intermediate temperatures.The precursors were precipitated from Si(OC2H5)4,LiAc·2H2O and Mn(Ac)2·4H2O in ethylene glycol by refluxing at 196℃ for 16h,the dried powders were milled,pressed and heat-treated at 500℃,600℃ and 700℃ for 10h.The obtained samples were characterized by X-ray diffraction,automatic elemental analyzer,field emission scanning electron microscope(FESEM),energy dispersive spectroscope(EDS),and high resolution transmission electron microscope(HRTEM).As a result of the Rietveld refinement,two possible Li2MnSiO4 forms crystallizing in Pmn21 and P121/n1 space groups,respectively,are considered as the major phases,and Li2SiO3 is identified as the impurity phase.According to the FESEM observation,the mean particle size increases from 5-20nm to 20-40nm as the heat-treatment temperature increasing from 500℃ to 700℃.Carbon is homogenously distributed on the prepared Li2MnSiO4/C composites.The HRTEM examination confirms that the Li2MnSiO4 particles are surrounded by a very thin amorphous carbon layer.The electrochemical experiments reveal that the Li2MnSiO4/C composite heat-treated at 600℃ for 10h has the higher electrochemical performance with an initial discharge capacity of 132.4mAh/g and a capacity retention ratio of 80% at the tenth cycle.