【作者】 杨洋；

【导师】 文衍宣；

【作者基本信息】 广西大学 ， 化学工艺， 2019， 硕士

【摘要】 MnC2O4和MnO是两种高容量的廉价锂离子电池负极材料,但它们的电导率低,导致倍率性能差,从而制约了它们的实际应用。目前主要通过合成纳米尺度材料、离子掺杂和与导电材料形成复合物来提高电导率。本文以醋酸锰和草酸为原料,采用T型微通道反应器强化共沉淀法制备MnC2O4。与传统的沉淀反应器相比,微通道反应器具有良好的微观混合性能,在成核之前形成了均匀的过饱和度分布,得到均匀的MnC2O4·2H2O纳米粒子。MnC2O4·2H2O纳米粒子在高速流体-颗粒相互作用的诱导下组装成微管结构。MnC2O4·2H2O微管真空脱水后得到MnC2O4微管,晶体结构也从单斜α相(C2/c)转变为Pmna正交相结构。独特的一维管状结构使得MnC2O4微管表现出较好的电化学性能,1 A·g-1电流密度下经过100次充放电后,仍有925 mAh·g-1的高可逆容量,5 A·g-1的大电流下放电比容量为721 mAh·g-1,循环100次后容量保持率为97.0%。MnC2O4热解后得到MnO,在原料醋酸锰溶液中引入其它金属离子制备金属离子掺杂的氧化锰。XRD和XPS的结果表明掺杂的金属离子M2+(M=Zn、Mg、Cu、Co、Ni)进入了晶格形成了固溶体Mn1-xMxO。随着掺杂量(x)的增加,SEI膜扩散活化能W、界面电化学反应活化能AG以及锂离子固相扩散活化能Ea先减小后增加。Mn0.85Zn0.15O、Mn0.95Mg0.05O、Mn0.90Cu0.10O、Mno.95Coo.05O、Mn0.90Ni0.10O具有较低的SEI膜扩散活化能、界面电化学反应活化能以及固相扩散活化能,在3.775 A·g-1电流下循环200次后放电比容量分别为380、488、504、263和312 mAh·g-1,远高于MnO(267 mAh·g-1)的容量,说明离子掺杂能更好地提高MnO的电化学性能。更多还原

【Abstract】 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 monoclinicα 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(ΔG)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,ΔG 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.更多还原