Preparation Of Robust Electrode Composites For Rechargeable Batteries And Their Electrochemical Energy-storage Properties

Lithium-sulfur batteries have attracted extensive attention due to their high theoretical energy density,but there are a series of challenges in lithium-sulfur batteries,such as low conductivity of sulfur,volume expansion and"shuttle effect",which have always hindered the development of lithium-sulfur batteries.Similarly,as a potential anode material for lithium ion batteries,transition metal oxides have some shortcomings such as particle agglomeration and electrode collapse.Regarding to the rapid development of various electronic devices and vehicles,it is urgent to develop high-performance electrode materials.This thesis aims at obtaining high-capacity and high-stability energy-storage materials,and alleviating the volume change of electrodes.The preparation methods and performance of electrode composites are investigated.Some new ideas and technical foundation for the development of high-performance batteries have been proved.The main research contents and innovations are as follows:?1?A porous sulfur particle was prepared through a sacrificially templated method.Then,on the surface of the sulfur,polypyrrole?PPy?was coated,forming a novel porous S@PPy composite.Lithium-sulfur battery based on the S@PPy cathode exhibits a capacity of 900 mAh g^-1 at a rate of 0.12 C after cycling for 100 times,along with a Coulombic efficiency as high as 99.9%.During three rounds of rate-performance tests,the capacity retention rate at the same current density is about97%.A density functional theory model was also set up,which well confirmed that PPy had a good adsorption effect on polysulfides,and thus improving the stability of electrode structure.?2?A special spiral SiO₂ nanowire was synthesized as the host,then the SiO₂@C@polyaniline?PANI?@S composite was prepared by a facile chemical method.The special spring-like structure accommodates the volume expansion effectively,where carbon increases the surface roughness of SiO₂,which is beneficial to the formation of burr-like PANI.On the other hand,PANI is able to enhance the conductivity of the sulfur cathode;while the burr-like structure provides a larger specific surface area for the sulfur loading.We find that the SiO₂@C@PANI@S composite delivers a capacity of 940 mAh g^-1 after 100 cycles at a rate of 0.1 C.?3?Furthermore,the spiral SiO₂ was used as the substrate to prepare some composites such as SiO₂@Fe₂O₃ and SiO₂@Co₃O₄ by a facile hydrothermal route.The spiral structure can effectively alleviate the particle agglomeration and volume change of transition metal oxides during charge and discharge,thereby improving the cycle performance of the constructed batteries.The SiO₂@Fe₂O₃ composite presents a stable capacity of 770 mAh g^-1 cycling at 0.1 C for 580 times,along with a Coulombic efficiency higher than 99%;and the capacity of the SiO₂@Co₃O₄ composite stabilizes at 670 mAh g^-1 when cycling at 0.1 C for 380 cycles,along with a Coulombic efficiency as high as 99.9%.In conclusion,the investigations mentioned above would be able to provide some new ideas and pathways for addressing the structure-change issues of electrode materials,and thus exhibiting a good potential for applications.In addition,the fabricated high-performance electrode composites and their preparing methods enable the construction of some emerging batteries.