【作者】 朱立才；

【导师】 袁中直； 李伟善；

【作者基本信息】 华南师范大学 ， 物理化学， 2005， 硕士

【摘要】 为了了解化学组成对电解二氧化锰（EMD）电化学行为的影响及其在碱性水溶液介质中的放电过程,化学分析了三种商品EMD的组成,它们的组成分别为Mn³⁺_0.054O²⁺_1.677（OH）^-_0.322,X射线衍射表明它们晶型都是γ-MnO₂;通过循环伏安、恒流放电、电位—时间关系、现场紫外—可见吸收光谱、红外光谱等实验研究了其在9mol·L^-1 KOH溶液中的电化学行为。结果为:当EMD中结合水含量（阳离子空位数）增加时,样品开路电压、放电容量增大,第1电子还原的峰电位正移;放电过程中溶出的Mn（Ⅲ）在470nm处有紫外—可见吸收峰,部分还原EMD产生渐变的红外吸收。结果表明了EMD中阳离子空位可能通过晶格内OH“桥”的作用降低质子在晶格中的扩散活化能,提高质子扩散速率及电极电位,从而改善其电化学活性;EMD的第1电子放电过程中质子先嵌入EMD的[1×2]隧道还原斜方锰矿,而后接着还原其[1×1]隧道的软锰矿。 为了寻找二次锂离子电池和碱性电池的新型正极材料,本论文利用“化学沉淀、离子交换和水热晶化三步法”合成了[3×3]隧道MnO₂材料—Todorokite。Mg-Todorokite在1mol·L^-1 LiPF₆溶液中的首次放电容量为286mAh·g^-1,第二次循环的放电容量锐减到103mAh·g^-1。Ni-Todorokite在1mol·L^-1 LiPF₆溶液中首次放电容量为124mAh·g^-1,第二次放电容量为104mAh·g^-1,此后基本保持稳定。Ni-Todorokite样品的循环性能要比Mg-Todorokite样品好。9mol·L^-1 KOH溶液中,Mg-Todorokite和Ni-Todorokite的首次放电容量分别为232mAh·g^-1和244mAh·g^-1。 利用恒沸回流法合成了[2×2]隧道MnO₂材料—Cryptomelane和无定型二氧化锰,Cryptomelane呈纳米针状外形,无定型二氧化锰为纳米颗粒。样品Cryptomelane在1mol·L^-1 LiPF₆溶液中的首次放电容量为196mAh·g^-1,第二次放电容量仅为92mAh·g^-1,循环性仍有待改善。无定型二氧化锰的首次放电容量为208mAh·g^-1,第五次循环的放电容量为首次的80.6%,即167.6mAh·g^-1。结更多还原

【Abstract】 Three electrolytic manganese dioxide （EMD） samples were characterized by XRD and chemical analyses. Their electrochemical performances were studied by cyclic voltametry, constant-current discharge, and choronopotentiometry. It is found that three samples have the same structure, γ-MnO₂, but their combined water contents are different. The chemical compositions of three samples can be formulated as A: Mn_0.881⁴⁺Mn_0.044³⁺O_1.655^2-（OH）₍0.345_<sup>-, B: Mn_0.880⁴⁺ Mn_0.048³⁺O_1.666^2-（OH）^0.334- and C: Mn_0.879⁴⁺Mn_0.054³⁺O_1.677^2-（OH）_0.322^-. The electrochemical performances are influenced by the combined water contents, which are related to the number of cation-vacancy in the samples. The open circuit potential, discharge capacity and peak potential of one electron reduction increase with the increase of the combined water contents in the samples.EMD were inserted with H by chemical methods in a nonaqueous environment. Compounds with compositions varying from the staring material to fully H-inserted material were prepared and investigated by FTIR spectroscopy. Slow-scan cyclic voltammery was used to investigate the voltammetric behavior of EMD. The concentrations of soluble Mn（III） species, during the reduction of electrolytic manganese dioxide in alkaline solution, have been monitored in situ by UV-visible spectroscopy. The concentration of Mn（III） ion in solution changes with discharge time. The first electron discharge process of EMD can be described by three different steps: （1） the reduction of Mn⁴⁺ ions on the surface of EMD particles and the structural defect regions within the EMD, （2） the reduction of Mn⁴⁺ ions in ramsdellite, （3） the reduction of Mn⁴⁺ ions in pyrolusite.Microporous todorokite-type manganese oxides had been synthesized by a route inwhich the key Na-birnessite precursor was prepared by oxidation of Mn（0H）2 with K2S2O8 in aqueous NaOH. The foreign metal cations, such as Mg2+ and Ni2+, were used in a subsequent ion-exchange reaction that converted Na-birnessite into a related layered material, buserite. Hydrothermal treatment of the buserite ultimately yielded Mg-todorokite or Ni-todorokite. In lmol-L"1 LiPF6 solution, it was found that the initial capacity of Mg-todorokite was 286 mAh-g"1 and the second discharge only had a capacity of 103 mAhg1. On the other hand, the initial capacity of Ni-todorokite was 124 mAh-g"1, and a capacity of 104 mAh g’1 was still found in the second cycle. Therefore, Ni-todorokite was better than Mg-todorokite in the performance of reversiblility.Cryptomelane and amorphous manganese dioxide were prepared by using reflux methods after the oxidation of Mn2+ by KMnO4. Cryptomelane was attained by using water as solvent, while yielded amorphous manganese dioxide was yielded by using ethanol as solvent. The initial capacity of Cryptomelane was 196 mAhg"1, but it had a poor rechargeability. The amorphous manganese dioxide yielded superior electrochemical cycling stability. It was found that the initial capacity of amorphous manganese dioxide was 208 mAh-g"1, and it still had a capacity of 167.6 mAh-g"1 after four charge/discharge cycles.更多还原