One-step Solvothermal Method Synthesis Graphene/MnCo₃ Composites And Electrochemical Performance For Lithium-ion Batteries

The development of energy storage equipment that has high energy efficiency, environmental protection and low cost encountered huge challenge,because of excessive energy consumption, increase demand of portable electronic devices and serious environmental pollution. Lithium ion battery exhibit great performance such as high specific capacity, long cycle life, high power density, low self-discharge, recharge quickly and environment friendly.Lithium ion batteries was consist of cathode electrode, anode electrode,electrolyte, diaphragm and the stainless steel shell.The cathode and anode electrode materials were most important factor in performance of lithium-ion battery such as specific capacity, cycle life and safety.Manganese carbonate has extremely application prospect due to the high specific capacity, abundant in nature, Price is cheap and convenient preparation.But lack of stability, poor cycle number, low electrical conductivity, poor performance weaken their electrochemical properties and limits its practical application as electrode material.There is a kind of new research tendency that manganese carbonate forms acomposite with conductive material not only improve electrical conductivity but also alleviate capacity attenuation caused by contraction and expansion of manganese carbonate crystals, thus increase the capacity retention ratio.A large amount of active material combine with Manganese carbonate and graphene that has high specific capacity, long cycle life, cycling stability.Such as MnCO₃/large-area graphene composites, MnCO₃@rGO composites,monodispersed MnCO₃/graphene nanosheet composites, porous manganese carbonate single crystal materials, graphene-wrapped mesoporous MnCO₃ single crystal composites.But these preparation methods dose not suitable for large-scale industrial production on account of low efficiency, high cost and may lead to environment pollution.They developed a solvothermal method to synthesize a nano-size, high purity, uniform dispersion, higher crystallinity composite electrode materials due to high temperature and high pressure environment produced by autoclave. When preparation of active materials at high temperature circumstance the method avoid the irreversible reunion.In this paper, a modified program to fabrication GO and a facial method to synthesis MnCO₃/graphene nanoparticle composites by one-step solvothermal process,and related electrochemical properties were tested and analyze. The main contents are as follows:1.Modified hummers method to prepared graphene. When the reaction time was extend in low temperature and medium temperature, the thickness of graphene is about 0.01 nm and graphene were entirely stripped. Electrochemicaltests indicated that the products showed a specific capacity up to 900 mA h/g when the low temperature reaction time is 25 min, the reaction time increased to160 min in medium temperature, 15 min for high temperature. GO has the highest yield when KMnO4, H2SO4, Na NO₃ additive amount was 3 g, 30 mL,0.5 g, respectively. The electrochemical test indicated that restore graphite oxide shows high specific capacity?1140 mA h/g? and stable cycle performance?after60 cycles, capacity retention ratio was more than 80%?.2.Graphene/MnCO₃ composite materials was synthesized by one-step solvothermal method without any poisonous reductant. Using the graphite oxide synthesized above, ethanol, KMnO4 aqueous solution in the case of 180?,18 h.As shown in SEM figure, MnCO₃ nanoparticles uniform attached on the layered graphene when reaction condition were KMmO4 0.2 g, 190?, 18 h. The electrochemical measurements indicated that the composites shows an initial discharge is 1700 mA h/g, 700 mA h/g after 80 cycles, capacity retention ratio keep 39% and excellent performance.