Microchannel Reactor Synthesis Of MnC₂O₄ Microtubes And Metal Ion Doped MnO As Anode Materials For Lithium Ion Batteries

MnC2O4 and MnO are high-capacity and low-cost anode materials for lithium-ion batteries,but lower electronic conductivity and poor rate performance limits their application.Several strategies have been adopted to overcome the low conductivity of MnC2O4 and MnO including reducing particle size,doping with guest ion and combining it with the conductive network.Therefore,T-type microchannel reactor was used to prepare MnC2O4 using Mn(CH3COO)2·4H2O and C2H2O4·2H2O as raw materials.Unlike traditional precipitation,the supersaturation can distribute homogeneously by molecular diffusion before nucleation in T-type microchannel reactor.Therefore,crystal nucleation and growth occur under the condition of the supersaturation homogeneous distribution so that uniform and fine manganese oxalate primary particles are generated.Manganese oxalate primary particles are are assembled into microtubules by a rapid assembly process induced by hydrodynamic force.When heated under vacuum condition,tubular MnC2O4·2H2O(C2/c monoclinic? phase)transforms into tubular MnC2O4(Pmna orthorhombic structure),where the removal of crystallized water molecules is accompanied by a transformation of the crystal structure.Owing to the unique microtube structure composed of nanoparticles,as-synthesized MnC2O4 microtubes exhibit a high reversible capacity of 925 mAh·g-1 after 100 cycles at 1 A·g-1.Even cycled at 5 A·g-1,the prepared microtubes still deliver a capacity of 721 mAh·g-1 with a capacity retention of 97.0%after 100 cycles,exhibiting good electrochemical performance.MnO can be obtained by pyrolysis of MnC2O4·2H2O at 450 ? for 6 h under nitrogen atmosphere.Metal ion doping MnO can be get by adding metal ion manganese acetate solution.Metal ion M2+(M= Zn,Mg,Cu,Co and Ni)is introduced into the crystal lattice to solid solution Mn1-xMxO.When the amount of the doped metal ion increases,the activation energy values of the diffusion in the SEI membrane(W),the interfacial electrochemical reaction(?G)and the Li+diffusion in the solid material(Ea)first decrease and then increase.Mn0.85Zn0.15O,Mn0.95Mg0.05O,Mn0.90Cu0.100,Mn0.95Co0.05O and Mn0.90Ni0.10O have lower values of W,?G and Ea,indicating that these samples should have good performances.The specific capacity of Mn0.85Zn0.18O,Mn0.95Mg0.05O,Mn0.90Cu0.100,Mn0.95Co0.05O and Mn0.90Ni0.10o is 380,488,504,263 and 312 mAh·g-1 after 200 cycles at 5 C rate,which are much higher than that of MnO(267 mAh·g-1).These results demonstrate that metal ion doping synergistically improve the electrochemical performance of MnO.