【作者】 李妍；

【导师】 曹丽云；

【作者基本信息】 陕西科技大学 ， 材料物理与化学， 2018， 硕士

【摘要】 氧化钼（MoO_x）是一种过渡金属氧化物,具有远远高于石墨的理论容量（838-1117 mAh/g）,有望替代石墨电极成为新一代的锂离子电池负极材料。但是,由于氧化钼电极在循环过程中的体积变化较大,从而导致容量快速衰减,阻碍了其在商业化中的使用。因此,提升氧化钼电极的循环稳定性成为当前研究的一个热点。本论文以提升氧化钼电极的电化学性能为目的,以钨酸钠、钼酸钠和葡萄糖分别为钨源、钼源和碳源,通过不同的工艺合成了具有不同化学计量比的氧化钨/氧化钼复合材料,并探讨了其组成、结构以及电化学性能之间的关系。（1）由于材料的结构对其性能有着较大的影响,因此设计具有特殊结构的材料可以达到提高其性能的目的。本论文通过一步水热法成功地合成了超小WO₂纳米颗粒修饰的碳包覆的MoO₃纳米棒（MoO₃/WO₂@C）三维自组装球状结构。对MoO₃/WO₂@C电极的电化学性能进行评估发现,该电级材料具有优异的循环稳定性,其在0.05 C的电流密度下循环100次的容量稳定在905 mAh/g。结果表明,该材料优异的电化学性能主要来源于这种独特的三维自组装结构。其中,碳包覆层不仅缓解了复合材料的体积变化,还阻止了纳米粒子的聚集。此外,表面附着的超小二氧化钨纳米颗粒增加了复合材料的导电性,促进了锂离子的传输。而三维自组装纳米结构使得锂离子的传输距离变短,加快了锂离子的嵌入和脱出,从而提高了材料的电化学性能。（2）将Mo O₃/WO₂@C纳米复合材料在空气条件下热处理得到了三元氧化物W_0.4Mo_0.6O₃固溶体材料。对W_0.4Mo_0.6O₃电极的电化学性能进行评估发现,该电级材料具有较好的循环稳定性,其在0.05 C的电流密度下循环100次的容量稳定在650 mAh/g。结果表明,三元氧化物通过协同作用的方式有效地提高了材料的电化学性能。（3）将Mo O₃/WO₂@C纳米复合材料在保护气氛下热处理得到了MoO₂/WO_2.83/C纳米复合材料。对MoO₂/WO_2.83/C电极的电化学性能进行评估发现,该电级材料展现出良好的循环稳定性,其在0.05 C的电流密度下循环100次的容量稳定在830 mAh/g。结果表明,引入氧缺陷浓度较高的WO_2.83可以提高材料的导电性,加快锂离子在材料中的传输,而复合碳可以缓解循环过程中复合材料的体积变化以及机械应力,从而提高材料的电化学性能。更多还原

【Abstract】 Molybdenum oxide（MoO_x）,as one of the transition-metal oxides,has the theoretical specific capacity（838-1117 mAh/g）much higher than that of graphite,and is expected to replace graphite as a new generation anode material for lithium ion batteries（LIBs）.However,the capacity of MoO_x tends to decay rapidly due to the large volume change during the cycle,which hinders its commercial production and practical application.Therefore,to enhance the cycle stability of MoO_x electrodes becomes a hot topic in current research.This dissertation aims to improve the electrochemical performance of MoO_x electrodes.The WO_x/Mo O_x composites were synthesized by different preparation processes,in which sodium tungstate dihydrate and sodium molybdate dihydrate served as tungsten and molybdate sources,respectively,and D-glucose acted as a source of carbon.The relationship among their composition,structure and properties of the as-obtained composites was investigated.（1）Elaborate design of high-performance anode materials is of vital significance for lithium-ion batteries,because the structure of materials has a great influence on its performance.In this dissertation,carbon-coated MoO₃nanorods decorated with WO₂ nanoparticles（MoO₃/WO₂@C）,a novel structured nanohybrid in which MoO₃ nanorods are encapsulated by the amorphous carbon layer and decorated with ultrasmall WO₂ nanoparticles,have been successfully synthesized via a facile one-step hydrothermal method.When evaluated as the anode materials for LIBs,the MoO₃/WO₂@C eletrodes demonstrated superior cycling stability,which delivered a high reversible capacity of 815 mAh/g after100 cycles at 0.05 C.Results show that the excellent electrochemical performance of the MoO₃/WO₂@C nanocomposites can be ascribed to the unique 3D self-assembled structure.MoO₃ nanorods coated by carbon not only alleviates the volume expansion but prevents the aggregation of MoO₃ nanorods during cycling.The decoration of ultrasmall WO₂ nanoparticles can further increase the conductivity of nanocomposites and facilitates the redistribution of lithium ion.The unique nanoarchitecture shortens the distance of Li⁺diffusion and enhances the electrochemical performance.（2）The ternary oxide W_0.4Mo_0.6O₃ solid solution materials were synthesized by heat treatment of MoO₃/WO₂@C nanocomposites under under air conditions.When evaluated as the anode materials for LIBs,the W_0.4Mo_0.6O₃ eletrodes showed excellent cycling stability,which exhibited a high reversible capacity of650 mAh/g after 100 cycles at 0.05 C.Results show that ternary oxides can improve the electrochemical performance of anode materials by a synergistic effect.（3）The MoO₂/WO_2.83/C nanocomposites were obtained by heat treatment of MoO₃/WO₂@C nanocomposites under protective atmosphere.When evaluated as the anode materials for LIBs,the MoO₂/WO_2.83/C eletrodes exhibited excellent cycling stability,which delivered a high reversible capacity of 830mAh/g after 100 cycles at 0.05 C.Results show that the introduction of WO_2.83with a high concentration of oxygen defects can improve the conductivity of nanocomposites and accelerate the transmission of Li⁺,and compositing with carbon can buffer the volume expansion and alleviate mechanical stress,thereby enhancing the electrochemical performance of anode materials.更多还原