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