【作者】 常靓；

【导师】 麦立强；

【作者基本信息】 武汉理工大学 ， 材料学， 2012， 硕士

【摘要】 锂离子电池具有比能量大、工作电压高、循环寿命长、可快速充放电、无记忆效应等优点,在便携电子设备市场占据了主导地位且有大规模应用于电动汽车领域和大规模储能系统的潜力。电极材料是制约锂离子电池发展的关键,设计构筑新型的电极材料使其具有高的能量密度,长的循环寿命,低的成本是锂离子电池发展的一大挑战。过渡金属氧化物的储锂机理是基于电化学转换反应。由于转换反应过程中大的体积变化和副反应的发生导致了电极材料的退化和失效,大大影响了电极材料的使用寿命。因此,为了获得长寿命、高容量的负极材料,本文通过构筑新型的纳米结构这一策略对电极材料进行优化。本文以锰氧化物为研究对象,构筑了具有介孔结构的锰氧化物和碳包覆的锰氧化物,并测试了它们的电化学性能。通过性能对比研究,探索材料结构与电化学性能之间的内在规律。主要研究成果如下：采用水热法和热分解法相结合,通过控制形貌的转变制得了孔结构可控的Mn203微球。500℃、700℃和900℃得到的样品分别为介孔Mn203微球、多孔Mn203微球和无孔Mn203微球。将它们作为锂离子电池的负极材料进行电化学性能测试,结果发现,介孔Mn203微球具有最高的放电比容量、最高的容量保持率和超长的循环寿命。在200mA/g的电流密度下,200次循环后仍具有524mAh/g的可逆容量；在1000mA/g的电流密度下可以实现1000次的可逆循环,可逆容量为125mAh/g。优异的电化学性能主要归因于高的比表面积和丰富的表面缺陷有效地增大了电解液和活性材料的接触面积,缩短了锂离子扩散距离,使更多的活性物质参与了反应,从而有效的提高了比容量；与此同时孔结构的存在,有效的缓冲了锂离子嵌入脱出引起的体积变化,提高了电极材料的结构稳定性,从而提高了电极材料的循环寿命。本文采用了碳包覆的方法,来进一步提高锰氧化物在大电流密度下的电化学性能。Mn203和葡萄糖反应制得的Mn3O4@C纳米材料具有最高的可逆容量,相比于介孔Mn203微球虽然缺少了一个电化学反应,但其1000次循环后的比容量仍然提高了15%,可逆比容量达142mAh/g。这主要归因于碳包覆可以有效地增加电极的电导率,提高材料的表面化学活性,保护电极材料不与电解液直接接触,最终可以有效的提高电池的循环寿命。更多还原

【Abstract】 Lithium ion batteries have dominated the portable electronic markets and have potential applications in electric vehicles and stationary energy storage system due to their advantages of high capacity, high operation voltage, long cycling life, fast charge/discharge ability and no memory effect. Electrode materials are the key limitation in the progress of lithium ion batteries. The challenge is to construct novel electrode materials of lithium ion batteries to meet the requirements of high energy density, long cycling life and low cost. The lithium storage mechanism of transition metal oxides is based on conversion reaction. During electrochemical reaction process, the degradation of electrode materials take negative influence on the life of electrode materials due to the large volume change and occurance of side reactions. Therefore, electrode materials are optimized by constructing novel nanostructure to obtain anode materials with long cycling life and high capacity.Herein, manganese oxides are investigated by constructing meosporous structure and carbon-coating structure. By investigating and comparing the electrochemical performance, internal principles between structures and electrochemical properties are further studied. The main conclusions are as follows.Mn2O3microspheres with controlled pore size were successfully synthesized by morphology-conserved transformation. As-prepared samples annealed at500,700, and900℃are mesoporous Mn2O3microspheres, porous Mn2O3microspheres and non-porous Mn2O3microspheres, respectively. As anodes for lithium ion batteries, mesoporous Mn2O3microspheres annealed at500℃show the highest discharge capacity, the minor capacity fading per cycle and ultralong cycling life. At current density of200mA/g, it can deliver reversible capacity of524mAh/g after200cycles. Meanwhile, it can realize1000cycles stable charge/discharge process with125mAh/g reversible capacity at current density of1000mA/g. The remarkable electrochemical performance can be attributed to the relatively high surface area and abundant surface active sites of mesoporous structure, which can improve the contact area between electrolyte and active materials, shorten Li ion diffusion distance and make more active materials to take part into the reaction, leading to improve capacity of electrode materials. Meanwhile, the existence of pore structure can accomodate the volume change caused by Li ion insertion/extraction, leading to keep the integrated structure of electrode materials and enhance the cycling life.Carbon coating stategy was utilized to further improve the electrochemical performance of manganese oxides at high current density. Mn3O4@C nanomateials synthesized by the reaction between Mn2O3and glucose have the highest reversible capacity. Although Mn3O4electrode materials are short of an electrochemical reaction compared with Mn2O3, its reversible capacity still improves15%after1000th cycle. The reversible capacity can reach142mAh/g. It is attributed to carbon coating, which can effectively increase the electrode conductivity, improve the surface chemisty of the active material, and protect the electrode from direct contact with electrolyte, leading to enhanced cycle life of batteries.更多还原