| Nowadays,the concept of clean and environmentally friendly energy has been deeply rooted in people's mind,which leads to the increasing demand for long-endurance electric vehicles and various green electronic products.However,although lithium-ion battery?LIB?has been well developed in the last decades,it's difficult for LIB to meet the ever increasing demands of the electric vehicles because of its theoretical capacity limitation and high cost.In comparison,Lithium-sulfur?Li-S?battery has a higher theoretical capacity(1675 mAh g-1),high abundance and low cost of sulfur,making it a promising system for next-generation energy storage application.However,the“shuttle effect”in Li-S battery system is the most prominent challenge hampering its further development and application in energy storage industry.The most direct research method to solve the“shuttle effect”is the development of sulfur cathode host materials.Many researchers have carried out a lot of researches on various sulfur host materials.Compared with traditional carbon materials,metal-organic framework?MOF?derived carbon?MDC?materials are considered to be efficient sulfur hosts to confine the polysulfides because of their unique porous structure and heteroatom doping.In this thesis,a simple and efficient modification method of low-pressure chemical vapor deposition?LPCVD?was used to perform in-situ recoordination on the surface of ZIF-8 derived carbon?ZDC?,so as to obtain a core-shell structure with a dual combination of ZDC and ZIF-8.Through phase and morphology characterizations,we tested and analyzed the components of the host material in detail.In addition,we analyzed the electrochemical performance advantages of the composite structure for the battery under various electrochemical tests.The main research results of this thesis are as follows:Instead of the removing the metal oxide residuals in MDC in the literature,the uniformly dispersed ZnO nanoparticles in ZDC are directly used as the metal sources,which can in situ recoordinate with 2-methylimidazole to in-situ prepare a new ZIF-8coating layer by LPCVD.This green and environmentally friendly surface modification method not only avoids the acidic waste solution caused by strong acid cleaning,but also the high cost disadvantage caused by expensive atomic layer deposition?ALD?or physical vapor deposition?PVD?method.Herein,the composite consisting of ZIF-8coating layer and ZDC?ZIF-8@ZDC?can be employed as a high-efficiency sulfur host for Li-S batteries with dual protection mechanism.When used as sulfur host material,ZIF-8@ZDC possesses not only the unique inner porous structure and high electrical conductivity of pyrolytic carbon,but also the extra protection from ZIF-8 layer with both physical confinement and chemisorption to polysulfides.The cathode displays a high initial capacity of 1410 mAh g-1,desirable cycling stability over 300 cycles and good rate capability.Even the electrode has a higher areal sulfur loading of 6.9 mg cm-2,it shows a capacity of 962 mAh g-1(the corresponding areal capacity is 6.6 mAh cm-2)after 100 cycles at the current density of2.3 mA cm-2.Additionally,the DFT calculation results prove that ZIF-8 can effectively confine the Li2Sn/S8 in this core-shell structure to mitigate the“shuttle effect”,which contributes to the good stability and long cycle life of the Li-S battery. |
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