多金属氧酸盐功能化金属有机框架材料的制备、吸附催化性能及在锂硫电池中的应用

Study on Preparation，Adsorption and Catalytic Performance of Polyoxometal-Functionalized Metal-Organic Frame Materials and Their Application in Lithium-Sulfur Battery

摘要:

锂硫电池因优异的理论比容量（1 675 mAh?g^-1）和能量密度（ 2 600 Wh?kg^-1），以及活性物质硫储量丰富、环境友好和低成本等优点，有望成为下一代储能电池。然而，在锂硫电池充放电过程中，可溶性多硫化锂极易溶解于电解液，导致氧化还原反应缓慢，且在溶度差作用下扩散到负极参与副反应，从而不可逆地降低了活性材料的含量，进而使锂硫电池出现放电容量低、容量衰减较快等问题。金属有机框架材料是一类以金属或金属团簇为中心、有机配体为连接单元，在共价键的作用下自组装形成的多孔晶体材料，具有较大的比表面积、高孔隙率和高度有序的孔结构及结构可调性等优点，且可被有效人为设计功能化特性。因此，设计了一种具有孔道缺陷的多金属氧酸盐功能化金属有机框架材料（Fe-NENU-5），用作高性能锂硫电池正极的硫载体。Fe-NENU-5的孔道缺陷，一方面可提供载硫与多硫化锂反应的空间，另一方面可使得缺陷孔道内的多金属氧酸盐能够有效吸附和催化转化多硫化锂，从而极大抑制了多硫化锂的穿梭效应，提高了活性物质的利用率。Fe-NENU-5/S正极所构建的锂硫电池在倍率性能和循环稳定性方面远优于NENU-5/S的锂硫电池，在电流密度1 C下循环500次后的放电比容量仍有617 mAh?g^-1。此外，在高载量4.7 mg·cm^-2下，锂硫电池放电容量可达3.1 mAh·cm^-2。本研究为满足日益增长的能源储能需求，解决锂硫电池放电容量差及循环寿命低的问题提供了理论依据。

Abstract:

In order to meet the growing demand for energy storage， lithium-sulfur batteries are expected to become the next generation of energy storage batteries due to their excellent theoretical specific capacity （1 675 mAh?g^-1） and energy density （2 600 Wh?kg^-1）， as well as rich reserves of active sulfur， environmental friendliness and low cost. However， in the charge and discharge process of lithium-sulfur batteries， soluble polysulfide lithium is easily dissolved in the electrolyte， resulting in a slow redox reaction， and diffuses to the negative electrode under the action of poor solubility to participate in side reactions， thus irreversibly reducing the content of active materials， and then low discharge capacity， capacity decay and other problems. Metal-organic frame materials are a kind of porous crystal materials with metal or metal clusters as the center， organic ligands as the connecting units， and self-assembly under the action of covalent bonds. Due to the advantages of large specific surface area， high porosity， highly ordered pore structure and structural tunability， metal-organic frame materials can be effectively designed with functional porous materials. Therefore， a polyoxometal-functionalized metal-organic framework material （named Fe-NENU-5） with pore defects was designed in this report to be used as a sulfur carrier for the positive electrode of high-performance lithium-sulfur batteries. On the one hand， the flaw design of Fe-NENU-5 provides the space to carry sulfur and react with lithium polysulfide， and on the other hand， the polyoxometrate in the flaw channel can effectively adsorb and catalyze the transformation of lithium polysulfide， which greatly inhibits the shuttle effect of lithium polysulfide， thus improving the utilization rate of active substances. The lithium-sulfur battery constructed by Fe-NENU-5/S positive electrode is much better than the lithium-sulfur battery of NENU-5/S in terms of rate performance and cycle stability， and the specific discharge capacity is still 617 mAh?g^-1 after 500 cycles at 1 C. In addition， the discharge capacity of the lithium-sulfur battery can reach 3.1 mAh·cm^-2 at a high load of 4.7 mg·cm^-2.